(Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland pdf - Endocrinology and Reproduction

toward the central lumen of the seminiferous tubule. The Sertoli

In the first stage of spermatogenesis, the spermatogonia migrate among

remainder of life but decreasing markedly in old age.

the result of stimulation by anterior pituitary gonadotropic hormones, begin-

through definite stages of development to form sperm, as shown in Figure

division, beginning at puberty, and continually proliferate and differentiate

). The spermatogonia begin to undergo mitotic

of one is shown in Figure 80–2

primordial germ cells

During formation of the embryo, the

Spermatogenesis

(Cowper’s glands) located near the origin of the urethra.

is the last connecting link from the testis to the exterior. The

Finally, the

, too, empty from the

internal urethra. Prostatic ducts

static end of the ampulla, and the contents from both the ampulla and the seminal

, one located on each side of the prostate, empty into the pro-

Two

, which enlarges into the

, another coiled tube about 6 meters long. The epididymis leads into the

half meter long, in which the sperm are formed. The sperm then empty into the

seminiferous tubules,

gives a more detailed structure of the testis and epididymis. The testis

Figure 80–1

shows the various portions of the male reproductive system, and

Figure 80–1

Male Sexual Organs

lar metabolism, growth, and other functions of the body.

sex hormones on the accessory sexual organs, cellu-

by the various hormones. Associated with these

sperm; (2) performance of the male sexual act; and

matogenesis, which means simply the formation of

divided into three major subdivisions: (1) sper-

The reproductive functions of the male can be

996

Reproductive and Hormonal

Functions of the Male (and

Function of the Pineal Gland)

(3) regulation of male reproductive functions

reproductive functions are the effects of the male

Physiologic Anatomy of the

is composed of up to 900 coiled

each averaging more than one

epididymis
vas deferens

ampulla of the vas deferens immediately before

the vas enters the body of the prostate gland.

seminal vesicles

vesicles pass into an ejaculatory duct leading through the body of the prostate gland
and then emptying into the
prostate gland into the ejaculatory duct and from there into the prostatic urethra.

urethra

urethra is supplied with mucus derived from a large number of minute urethral
glands located along its entire extent and even more so from bilateral bulbourethral
glands

migrate into the

testes and become immature germ cells called spermatogonia which lie in two
or three layers of the inner surfaces of the seminiferous tubules (a cross section

80–2B.

Steps of Spermatogenesis

Spermatogenesis occurs in the seminiferous tubules during active sexual life as

ning at an average age of 13 years and continuing throughout most of the

Sertoli cells

80–4, each spermatozoon is composed of a

and elongate into spermatozoa. As shown in Figure

epithelioid cells, but soon they begin to differentiate

formed, they still have the usual characteristics of

When the spermatids are first

Chapter 82.

fertilizes the ovum. This is discussed further in

. The sex of the eventual offspring is

, and the female X chro-

the male Y chromosome goes to one spermatid that

. During meiotic division,

male chromosome

some, the

, and one Y chromo-

female chromosome

This pair is composed of one X chromosome, which is

tion that determines the sex of each eventual offspring.

In each spermatogonium, one of the

matogonia to spermatozoa, takes about 74 days.

The entire period of spermatogenesis, from sper-

oocyte provided by the mother.

the father, while the other half are derived from the

to the second spermatid. This also divides the chro-

chromosomes) of the spermatocyte are divided, so that

the spermatid stage, the 46 chromosomes (23 pairs of

During the change from the spermatocyte stage to

spermatozoa

another few days, these too divide to form

. After

Each of these, in turn, undergoes meiotic

(Figure

nia all the way to the central lumen of the tubule.

cells are very large, with overflowing cytoplasmic

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

997

envelopes that surround the developing spermatogo-

Meiosis.

Spermatogonia that cross the barrier into the

Sertoli cell layer become progressively modified and
enlarged to form large primary spermatocytes
80–3).
division to form two secondary spermatocytes

spermatids

that are eventually modified to become
(sperm).

23 chromosomes go to one spermatid and the other 23

mosomal genes so that only one half of the genetic
characteristics of the eventual fetus are provided by

Sex Chromosomes.

23 pairs of chromosomes carries the genetic informa-

called the

then becomes a male sperm
mosome goes to another spermatid that becomes a
female sperm
determined by which of these two types of sperm

Formation of Sperm.

head and a

Prepuce

Glans

penis

Seminiferous

tubules

Testis

Scrotum

Head of

epididymis

Erectile

tissue

Prostate

gland

Urinary
bladder

Ampulla

Seminal
vesicle

Ejaculatory
duct

Bulbourethral
gland

Vas deferens

Efferent
ductules

Body of
epididymis

Rete testis

Tail of epididymis

Epididymis

Seminiferous
tubules

Testicular artery

Physiology. Philadelphia: Saunders College Publishing, 1985.)

testis to the epididymis. (Redrawn from Guyton AC: Anatomy and

Internal structure of the testis and relation of the

DW: Textbook of Histology, 10th ed. Philadelphia: WB Saunders

Male reproduction system. (Modified from Bloom V, Fawcett

Figure 80–1

Co, 1975.) B,

Seminiferous
tubules

Interstitial cells

Secondary
spermatocyte

Spermatozoa

Primary
spermatocyte

Spermatogonium

Sertoli cell

Spermatids

opment of sperm from spermatogonia.

Cross section of a seminiferous tubule.

Figure 80–2

B, Stages in the devel-

in the interstitium of the testis, is essential for

, secreted by the

Testosterone

mones play essential roles in spermatogenesis. Some

later, but at this point, let us note that several hor-

We shall discuss the role of hormones in reproduction

Spermatogenesis

Hormonal Factors That Stimulate

of 1 to 4 mm/min. This allows them to move through

tubules that make up the axoneme. The energy for this

movement) provides motility for the sperm. This

axoneme; and (3) a collection of mitochondria sur-

Chapter 2; (2) a thin cell membrane covering the

of 11 microtubules, collectively called the

major components: (1) a central skeleton constructed

, has three

The tail of the sperm, called the

(which can digest proteins). These enzymes play

found in lysosomes of the typical cell, including

This contains a number of enzymes similar to those

that is formed mainly from the Golgi apparatus.

layer around its surface. On the outside of the anterior

cell with only a thin cytoplasmic and cell membrane

. The head comprises the condensed nucleus of the

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Unit XIV

Endocrinology and Reproduction

tail

two thirds of the head is a thick cap called the acro-
some

hyaluronidase (which can digest proteoglycan fila-
ments of tissues) and powerful proteolytic enzymes

important roles in allowing the sperm to enter the
ovum and fertilize it.

flagellum

axoneme—

the structure of this is similar to that of cilia found
on the surfaces of other types of cells described in

rounding the axoneme in the proximal portion of the
tail (called the body of the tail).

Back-and-forth movement of the tail (flagellar

movement results from a rhythmical longitudinal
sliding motion between the anterior and posterior

process is supplied in the form of adenosine triphos-
phate that is synthesized by the mitochondria in the
body of the tail.

Normal sperm move in a fluid medium at a velocity

the female genital tract in quest of the ovum.

of these are as follows:
1.

Leydig cells located

Primordial germ cell

Enters

testis

Spermatogonia

Primary

spermatocyte

Secondary

spermatocytes

Meiotic division II

Differentiation

Meiotic division I

Spermatids

Mature

sperm

Spermatogonia
proliferate by mitotic
cell division inside
testis

Birth

Puberty

25 days

12-14

years

9 days

19 days

21 days

spermatozoa.

spermatocytes produce spermatids, which differentiate to form

cytes. After completion of meiotic division II, the secondary

through meiotic division I to become secondary spermato-

begin meiosis to become primary spermatocytes and continue

after birth), the spermatogonia proliferate rapidly by mitosis. Some

they become spermatogonia. At puberty (usually 12 to14 years

development the primordial germ cells migrate to the testis where

Cell divisions during spermatogenesis. During embryonic

Figure 80–3

Acrosome

Surface membrane

Vacuole
Anterior head cap

Posterior head cap

Neck

Body

Mitochondria

Chief piece of tail

End piece of tail

Structure of the human spermatozoon.

Figure 80–4

act, is composed of the fluid and sperm from the vas

Semen, which is ejaculated during the male sexual

ejaculation, and thus enhances the motility and fertil-

rises to about 6.0 to 6.5. Consequently, it is probable

acidic (pH of 3.5 to 4.0). Sperm do not become opti-

fertility. Also, the vaginal secretions of the female are

the sperm and, consequently, helps to inhibit sperm

successful fertilization of the ovum, because the fluid

the bulk of the semen. A slightly alkaline characteris-

thin, milky fluid of the prostate gland adds further to

enzyme, and a profibrinolysin. During emission, the

tains calcium, citrate ion, phosphate ion, a clotting

The prostate gland secretes a thin, milky fluid that con-

Function of the Prostate Gland

and (2) by possibly causing backward, reverse peri-

two ways: (1) by reacting with the female cervical

semen, and the fructose and other substances in the

sperm. This adds greatly to the bulk of the ejaculated

During the process of emission and ejaculation, each

, and other nutrient substances, as well

Each seminal vesicle is a tortuous, loculated tube lined

Function of the Seminal Vesicles

genital tract is only 1 to 2 days.

life expectancy of ejaculated sperm in the female

the suppressed state in the genital ducts of the testes,

shortened. Although sperm can live for many weeks in

lism, causing the life of the sperm to be considerably

creasing temperature, but so does the rate of metabo-

The activity of sperm increases markedly with in-

acidic medium. A strong acidic medium can cause

lated semen, but it is greatly depressed in a mildly

and slightly alkaline medium, as exists in the ejacu-

fluid medium at velocities of 1 to 4 mm/min. The

The normal motile, fertile

estrogens), enzymes, and special nutrients that are

fluid that is ejaculated along with the sperm. This fluid

. The Sertoli cells and the

they also become capable of fertilizing the ovum, a

After ejaculation, the sperm become motile, and

longer than a few days.

sexual activity and ejaculations, storage may be no

tions of the ducts. Conversely, with a high level of

this time, they are kept in a deeply suppressed inactive

maintaining their fertility, for at least a month. During

are stored in the vas deferens. They can remain stored,

tity of these can be stored in the epididymis, but most

form up to 120 million sperm each day. A small quan-

The two testes of the human adult

, even though several

in the epididymis for some 18 to 24 hours, they deve-

ize an ovum. However, after the sperm have been

the epididymis are nonmotile, and they cannot fertil-

. Sperm removed from the

require several days to pass through the 6-meter-long

After formation in the seminiferous tubules, the sperm

Maturation of Sperm in the Epididymis

infertility.

is severely deficient or absent, thus causing

absence, as in pituitary dwarfs, spermatogenesis

division of the spermatogonia themselves; in its

background metabolic functions of the testes.

Growth hormone

for spermiogenesis.

stimulating hormone, are probably also essential

, formed from testosterone by the

spermiogenesis) will not occur.

; without this stimulation, the conversion

anterior pituitary gland, stimulates the

, also secreted by the

Follicle-stimulating hormone

secrete testosterone.

pituitary gland, stimulates the Leydig cells to

, secreted by the anterior

cells, which is the first stage in forming sperm.

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

999

growth and division of the testicular germinal

2. Luteinizing hormone

Sertoli

cells
of the spermatids to sperm (the process of

4. Estrogens

Sertoli cells when they are stimulated by follicle-

(as well as most of the other

body hormones) is necessary for controlling

Growth hormone specifically promotes early

tubule of the epididymis
seminiferous tubules and from the early portions of

lop the capability of motility
inhibitory proteins in the epididymal fluid still prevent
final motility until after ejaculation.

Storage of Sperm.

state by multiple inhibitory substances in the secre-

process called maturation
epithelium of the epididymis secrete a special nutrient

contains hormones (including both testosterone and

essential for sperm maturation.

Physiology of the Mature Sperm.

sperm are capable of flagellated movement though the

activity of sperm is greatly enhanced in a neutral

rapid death of sperm.

with a secretory epithelium that secretes a mucoid
material containing an abundance of fructose,
citric acid
as large quantities of prostaglandins and fibrinogen.

seminal vesicle empties its contents into the ejacula-
tory duct shortly after the vas deferens empties the

seminal fluid are of considerable nutrient value for
the ejaculated sperm until one of the sperm fertilizes
the ovum.

Prostaglandins are believed to aid fertilization in

mucus to make it more receptive to sperm movement

staltic contractions in the uterus and fallopian tubes to
move the ejaculated sperm toward the ovaries (a few
sperm reach the upper ends of the fallopian tubes
within 5 minutes).

capsule of the prostate gland contracts simultaneously
with the contractions of the vas deferens so that the

tic of the prostatic fluid may be quite important for

of the vas deferens is relatively acidic owing to the
presence of citric acid and metabolic end products of

mally motile until the pH of the surrounding fluids

that the slightly alkaline prostatic fluid helps to neu-
tralize the acidity of the other seminal fluids during

ity of the sperm.

Semen

through the oocyte membrane and cause multiple

pellucida of the ovum, calcium ions diffuse inward

oocyte? The reason is not entirely known, but within

sperm as there are, why does only one enter the

With as many

; then the embryo begins to develop, as

and genes from mother and father. This is the process

genome, containing equal numbers of chromosomes

and the oocyte combine to form a completely new cell

At the same time, the genetic material of the sperm

the oocyte fuse with each other to form a single cell.

minutes, the cell membranes of the sperm head and of

lucida to the inside of the ovum. Within another 30

minutes, these enzymes open a penetrating pathway

and all the acrosomal enzymes are released. Within

cida. Then, rapidly, the entire acrosome dissolves,

ovum, the anterior membrane of the sperm itself binds

When the sperm reaches the zona pellucida of the

to be released. It is believed that the hyaluronidase

achieve this, the stored enzymes in the acrosome begin

. To

zona pellucida

covering of the ovum itself, the

cell layers, and then it must penetrate though the thick

fertilize the ovum, it must dissolute these granulosa

tiple layers of granulosa cells. Before a sperm can

licle into the fallopian tube, it still carries with it mul-

When the ovum is expelled from the ovarian fol-

ovarian granulosa cells together. The proteolytic

Acrosome Enzymes, the “Acrosome Reaction,”

capacitation. Without these, the sperm cannot make its

Thus, multiple changes occur during the process of

pellucida of the ovum itself.

granulosa cell mass surrounding the ovum, and

covers the leading edge of the acrosome, making

undulating motion. In addition, the calcium ions

the activity of the flagellum, giving it a powerful

more permeable to calcium ions, so that calcium

3. The membrane of the sperm also becomes much

acrosome) becomes much weaker.

cholesterol over the next few hours. In so doing,

cholesterol vesicles upward into the uterine cavity,

of its enzymes. After ejaculation, the sperm

cellular membrane covering the sperm acrosome,

This cholesterol is continually added to the

male genital ducts, they are continually exposed

2. While the spermatozoa remain in the fluid of the

activity in the male genital ducts.

1. The uterine and fallopian tube fluids wash away

requires from 1 to 10 hours. Some changes that are

. This normally

capacitation of the spermatozoa

processes of fertilization. These collective changes are

with the fluids of the female genital tract, multiple

in fertilizing the ovum. However, on coming in contact

in the semen, they are unable to perform their duties

duct epithelia. Therefore, when they are first expelled

they leave the epididymis, their activity is held in check

Although spermatozoa are said to be “mature” when

“Capacitation” of the Spermatozoa—Making It

been preserved for years.

100°C, sperm have

semen can be stored for several weeks, and when

body temperature. At lowered temperatures, however,

genital ducts, once they are ejaculated in the semen,

become highly motile.

As the coagulum dissolves, the sperm simultaneously

bile, possibly because of the viscosity of the coagulum.

after ejaculation, the sperm remain relatively immo-

from the prostatic profibrinolysin. In the early minutes

lies. The coagulum then dissolves during the next 15 to

Also, a clotting enzyme from the prostatic fluid causes

mucous glands gives the semen a mucoid consistency.

appearance, and fluid from the seminal vesicles and

semen. The prostatic fluid gives the semen a milky

The average pH of the combined semen is about 7.5,

fluid, which is the last to be ejaculated and serves

glands. Thus, the bulk of the semen is seminal vesicle

from the mucous glands, especially the bulbourethral

prostate gland (about 30 per cent), and small amounts

seminal vesicles (almost 60 per cent), fluid from the

deferens (about 10 per cent of the total), fluid from the

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Unit XIV

Endocrinology and Reproduction

to wash the sperm through the ejaculatory duct and
urethra.

the alkaline prostatic fluid having more than neutral-
ized the mild acidity of the other portions of the

the fibrinogen of the seminal vesicle fluid to form a
weak fibrin coagulum that holds the semen in the
deeper regions of the vagina where the uterine cervix

30 minutes because of lysis by fibrinolysin formed

Although sperm can live for many weeks in the male

their maximal life span is only 24 to 48 hours at

frozen at temperatures below

Possible for Them to Penetrate the Ovum

by multiple inhibitory factors secreted by the genital

changes occur that activate the sperm for the final

called

believed to occur are the following:

the various inhibitory factors that suppress sperm

to many floating vesicles from the seminiferous
tubules containing large amounts of cholesterol.

toughening this membrane and preventing release

deposited in the vagina swim away from the

and they gradually lose much of their other excess

the membrane at the head of the sperm (the

now enters the sperm in abundance and changes

whiplash motion in contrast to its previously weak

cause changes in the cellular membrane that

it possible for the acrosome to release its enzymes
rapidly and easily as the sperm penetrates the

even more so as it attempts to penetrate the zona

way to the interior of the ovum to cause fertilization.

and Penetration of the Ovum

Stored in the acrosome of the sperm are large quanti-
ties of hyaluronidase

and proteolytic enzymes.

Hyaluronidase depolymerizes the hyaluronic acid
polymers in the intercellular cement that hold the

enzymes digest proteins in the structural elements of
tissue cells that still adhere to the ovum.

among these enzymes is especially important in open-
ing pathways between the granulosa cells so that the
sperm can reach the ovum.

specifically with receptor proteins in the zona pellu-

for passage of the sperm head through the zona pel-

of fertilization
discussed in Chapter 82.

Why Does Only One Sperm Enter the Oocyte?

a few minutes after the first sperm penetrates the zona

on the glans stimulates the sensory end-organs, and the

. The slippery massaging action of intercourse

The glans contains an especially sensitive sensory end-

The most important source of sensory nerve signals

of the Male Sexual Act

the person is likely to be infertile, even though the

sperm are morphologically abnormal or are nonmotile,

or relatively nonmotile. Whenever the majority of the

not understood, they are either entirely nonmotile

sperm appear to be structurally normal, but for reasons

mal tails, as shown in Figure 80–5. At other times, the

having two heads, abnormally shaped heads, or abnor-

half the sperm are found to be abnormal physically,

infertile. When this occurs, sometimes as many as one

Effect of Sperm Morphology and Motility on Fertility.

ovum, for reasons not understood, the ejaculate usually

20 million, the person is likely to be infertile. Thus, even

present in the several milliliters of each ejaculate. When

males this can vary from 35 million to 200 million. This

of about 120 million sperm, although even in “normal”

milliliters, and in each milliliter of semen is an average

The usual quantity of

Effect of Sperm Count on Fertility.

enough testosterone. The surgical operation for cryp-

not most, instances of cryptorchidism are caused by

into the scrotum from the abdomen. Therefore, many, if

Testosterone secretion by the fetal testes themselves

testes.

Nevertheless, for this reason, operations to relocate the

quently, to cause sterility, although this is not certain.

this degeneration of the tubular epithelium and, conse-

interstitial structures of the testis. It has been claimed

epithelium becomes degenerate, leaving only the

nal cavity is incapable of forming sperm. The tubular

inguinal canal, or elsewhere along the route of descent.

so that one or both testes remain in the abdomen, in the

ally this descent does not occur or occurs incompletely,

through the inguinal canals into the scrotum. Occasion-

before birth of the baby, the testes normally descend

the abdomen. However, at about 3 weeks to 1 month

fetus, the testes are derived from the genital ridges in

of birth of a fetus. During development of the male

Cryptorchidism

weather.

cooling), without

Thus, the scrotum theoretically acts as a cooling mech-

testes close to the body to maintain this 2° differential.

the musculature of the scrotum to contract, pulling the

nal temperature. On cold days, scrotal reflexes cause

body, although usually only about 2°C below the inter-

ferous tubules besides the spermatogonia. It has often

Effect of Temperature on Spermatogenesis.

another cause of sterility, usually temporary, is

in the genital ducts or other abnormalities. Finally,

some affected males. Also, some male infants are born

by a number of diseases. For instance, bilateral orchitis

The seminiferous tubular epithelium can be destroyed

does more than one sperm enter the oocyte during

already begun to bind to fall off. Thus, almost never

sperm, and they even cause any sperm that have

the oocyte into the perivitelline space. These granules

cortical granules to be released by exocytosis from

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

1001

contain substances that permeate all portions of the
zona pellucida and prevent binding of additional

fertilization.

Abnormal Spermatogenesis and
Male Fertility

of the testes resulting from mumps causes sterility in

with degenerate tubular epithelia as a result of strictures

excessive

temperature of the testes.

Increasing the

temperature of the testes can prevent spermatogenesis
by causing degeneration of most cells of the semini-

been stated that the reason the testes are located in
the dangling scrotum is to maintain the temperature
of these glands below the internal temperature of the

anism for the testes (but a controlled
which spermatogenesis might be deficient during hot

Cryptorchidism means failure of a testis to descend
from the abdomen into the scrotum at or near the time

A testis that remains throughout life in the abdomi-

that even the few degrees’ higher temperature in the
abdomen than in the scrotum is sufficient to cause

cryptorchid testes from the abdominal cavity into the
scrotum before the beginning of adult sexual life are
frequently performed on boys who have undescended

is the normal stimulus that causes the testes to descend

abnormally formed testes that are unable to secrete

torchidism in these patients is unlikely to be successful.

semen ejaculated during each coitus averages about 3.5

means an average total of 400 million sperm are usually

the number of sperm in each milliliter falls below about

though only a single sperm is necessary to fertilize the

must contain a tremendous number of sperm for only
one sperm to fertilize the ovum.

Occa-

sionally a man has a normal number of sperm but is still

remainder of the sperm appear to be normal.

Male Sexual Act

Neuronal Stimulus for Performance

for initiating the male sexual act is the glans penis.

organ system that transmits into the central nervous
system that special modality of sensation called sexual
sensation

Abnormal infertile sperm, compared with a normal sperm on the

Figure 80–5

right.

The filling of the internal urethra with semen

the semen. The process to this point is

fluid also into the urethra, forcing the sperm forward.

the internal urethra. Then, contractions of the muscu-

, the forerunner of

leave the cord at T-12 to L-2 and pass to the genital

becomes extremely intense, the reflex centers of the

of the male sexual act. When the sexual stimulus

Nerves.

sensations.

because unlubricated intercourse causes grating,

lubrication, the male sexual act is seldom successful

organs rather than by the male. Without satisfactory

the lubrication during coitus. However, most of the

the bulbourethral glands to secrete mucus. This mucus

to promoting erection, cause the urethral glands and

stimulation, the parasympathetic impulses, in addition

hard and elongated. This is the phenomenon of

surrounded by strong fibrous coats; therefore, high

bodies, especially the two corpora cavernosa, are

venous outflow is partially occluded. Also, the erectile

soids, which are normally relatively empty of blood

This erectile tissue consists of large cavernous sinu-

shaft of the penis, shown in Figure 80–6.

of the penis, as well as relaxes the trabecular mesh-

choline. The nitric oxide especially relaxes the arteries

nitric oxide

fibers, are believed to release

nerve fibers, in contrast to most other parasympathetic

the pelvic nerves to the penis. These parasympathetic

degree of stimulation, whether psychic or physical.

Penile Erection—Role of the Parasympathetic Nerves.

Stages of the Male Sexual Act

or actual sexual stimulation from the sex organs, but

and lumbar spinal cord, and these mechanisms can be

the lumbar region. The male sexual act results from

it, brain function is probably not necessary for its per-

stages of sexual life, especially during the teens.

culminating in ejaculation. Indeed,

person to perform the sexual act. Simply thinking

urethral mucosa, inducing inflammation and vascular

and some “aphrodisiac” drugs, such as cantharidin,

sometimes cause almost continual sexual desire,

is filling of the sexual organs with secretions. Mild

deferens. Indeed, one of the causes of “sexual drive”

bladder, prostate, seminal vesicles, testes, and vas

internal structures, such as in areas of the urethra,

sensation. Sexual sensations can even originate in

lium, the scrotum, and perineal structures in general

sexual act. For instance, stimulation of the anal epithe-

of the spinal cord, and finally up the cord to undefined

sexual signals in turn pass through the pudendal nerve,

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Unit XIV

Endocrinology and Reproduction

then through the sacral plexus into the sacral portion

areas of the brain.

Impulses may also enter the spinal cord from

areas adjacent to the penis to aid in stimulating the

can send signals into the cord that add to the sexual

infection and inflammation of these sexual organs

increase sexual desire by irritating the bladder and

congestion.

Psychic Element of Male Sexual Stimulation.

Appropriate

psychic stimuli can greatly enhance the ability of a

sexual thoughts or even dreaming that the act of inter-
course is being performed can initiate the male act,

nocturnal emissions

during dreams occur in many males during some

Integration of the Male Sexual Act in the Spinal Cord.

Although psychic factors usually play an important
part in the male sexual act and can initiate or inhibit

formance because appropriate genital stimulation can
cause ejaculation in some animals and occasionally in
humans after their spinal cords have been cut above

inherent reflex mechanisms integrated in the sacral

initiated by either psychic stimulation from the brain

usually it is a combination of both.

Penile

erection is the first effect of male sexual stimulation,
and the degree of erection is proportional to the

Erection is caused by parasympathetic impulses that
pass from the sacral portion of the spinal cord through

and/or

vasoactive intestinal peptide in addition to acetyl-

work of smooth muscle fibers in the erectile tissue of
the corpora cavernosa and corpus spongiosum in the

but become dilated tremendously when arterial
blood flows rapidly into them under pressure while the

pressure within the sinusoids causes ballooning of the
erectile tissue to such an extent that the penis becomes

erection.

Lubrication, a Parasympathetic Function.

During sexual

flows through the urethra during intercourse to aid in

lubrication of coitus is provided by the female sexual

painful sensations that inhibit rather than excite sexual

Emission and Ejaculation—Function of the Sympathetic

Emission and ejaculation are the culmination

spinal cord begin to emit sympathetic impulses that

organs through the hypogastric and pelvic sympathetic
nerve plexuses to initiate emission
ejaculation.

Emission begins with contraction of the vas defer-

ens and the ampulla to cause expulsion of sperm into

lar coat of the prostate gland followed by contraction
of the seminal vesicles expel prostatic and seminal

All these fluids mix in the internal urethra with mucus
already secreted by the bulbourethral glands to form

emission.

elicits sensory signals that are transmitted through the
pudendal nerves to the sacral regions of the cord,
giving the feeling of sudden fullness in the internal

Deep penile

fascia

Corpus

cavernosum

Corpus
spongiosum

Central artery

Urethra

Erectile tissue of the penis.

Figure 80–6

chapter.

not. The intracellular functions are discussed later in the

dependent on this conversion, whereas other actions are

italia of the male fetus. Some actions of testosterone are

, especially in certain target organs such

for 30 minutes to several hours. By that time, the

After secretion by the testes,

Metabolism of Testosterone.

and in the adrenals, the androgens can be synthesized

dihydrotestosterone.

compounds, as shown by the formulas in Figure 80–8 for

Chemistry of the Androgens.

minute quantities of androgens, but they are not

The normal ovary also produces

of androgens in women; one such tumor is the

Rarely, embryonic rest cells in the ovary can deve-

teristics to occur even in the female. These effects

androgen-producing cells occurs, the quantity of

lary hair. But when an adrenal tumor of the adrenal

acteristics, except for causing growth of pubic and axil-

secrete at least five androgens, although the total mas-

body besides the testes. For instance, the adrenal glands

culinizing effects, including testosterone itself; it also

“androgen” means any steroid hormone that has mas-

The term

Secretion of Androgens Elsewhere in the Body.

often continue to produce testosterone.

heat, the Leydig cells, which are less easily destroyed,

secreted. Finally, when the germinal epithelium of the

cells of Leydig, great quantities of testosterone are

thermore, when tumors develop from the interstitial

testes secrete large quantities of testosterone. Fur-

male any time after puberty; at both these times the

terone, but they

the mass of the adult testes, as shown in Figure 80–7.

, which lie in the interstices between the semi-

Testosterone is formed by the

drotestosterone in the target tissues.

see, much, if not most, of the testosterone is eventually

significant testicular hormone, although as we shall

. Testosterone is so much more abun-

and

hormones, which are collectively called

The testes secrete several male sex

in the Testes.

Secretion of Testosterone by the Interstitial Cells of Leydig

Sex Hormones

Testosterone and Other Male

1 to 2 minutes and erection ceases, a process called

. At its termination, the male

This entire period of emission and ejaculation is

slightly into the cervix of the uterus.

pelvis and penis, which also help propel the semen into

. At the same time, rhythmical contractions

the urethra to the exterior. This final process is called

ducts and urethra, which “ejaculate” the semen from

cause rhythmical, wavelike increases in pressure in

of the penile erectile tissue. These effects together

genital organs. Also, these sensory signals further

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

1003

excite rhythmical contraction of the internal genital
organs and cause contraction of the ischiocavernosus
and bulbocavernosus muscles that compress the bases

both the erectile tissue of the penis and the genital

ejaculation
of the pelvic muscles and even of some of the muscles
of the body trunk cause thrusting movements of the

the deepest recesses of the vagina and perhaps even

called the male orgasm
sexual excitement disappears almost entirely within

resolution.

Secretion, Metabolism, and Chemistry
of the Male Sex Hormone

androgens,

including

testosterone,

dihydrotestosterone

androstenedione
dant than the others that one can consider it to be the

converted into the more active hormone dihy-

interstitial cells of

Leydig
niferous tubules and constitute about 20 per cent of

Leydig cells are almost nonexistent in the testes during
childhood when the testes secrete almost no testos-

are numerous in the newborn male

infant for the first few months of life and in the adult

testes is destroyed by x-ray treatment or excessive

includes male sex hormones produced elsewhere in the

culinizing activity of all these is normally so slight (less

than 5 per cent of the total in the adult male) that even
in women they do not cause significant masculine char-

androgenic hormones may then become great enough
to cause all the usual male secondary sexual charac-

are described in connection with the adrenogenital
syndrome in Chapter 77.

lop into a tumor that produces excessive quantities

arrhenoblastoma.

significant.

All androgens are steroid

testosterone and

Both in the testes

either from cholesterol or directly from acetyl coen-
zyme A.

about 97 per cent of the testosterone becomes either
loosely bound with plasma albumin or more tightly
bound with a beta globulin called sex hormone–binding
globulin and circulates in the blood in these states

testosterone either is transferred to the tissues or is
degraded into inactive products that are subsequently
excreted.

Much of the testosterone that becomes fixed to

the tissues is converted within the tissue cells to dihy-
drotestosterone
as the prostate gland in the adult and the external gen-

Interstitial cells
of Leydig

Germinal
epithelium

Blood vessel

Fibroblasts

located in the interstices between the seminiferous tubules.

Interstitial cells of Leydig, the cells that secrete testosterone,

Figure 80–7

the top of the head; a man who does not have func-

Testosterone decreases the growth of hair on

the body to become more prolific.

back. It also causes the hair on most other portions of

(5) less often on other regions of the body, such as the

and above, (3) on the face, (4) usually on the chest, and

growth of hair (1) over the pubis, (2) upward along the

Testosterone causes

Effect on the Distribution of Body Hair.

follows.

themselves, distinguish the male from the female as

sexual characteristics, in addition to the sexual organs

puberty and ending at maturity. These secondary

characteristics of the male to develop, beginning at

addition, testosterone causes the secondary sexual

enlarge about eightfold before the age of 20 years. In

secretion cause the penis, scrotum, and testes to

After puberty, the increasing amounts of testosterone

of Adult Primary and Secondary

Effect of Testosterone on Development

during fetal life.

testosterone, indicating again that testosterone is an

descend. Thus, the stimulus for descent of the testes is

to produce testosterone, can also cause the testes to

stimulate the Leydig cells of the newborn child’s testes

Administration of gonadotropic hormones, which

pass.

testes, the administration of testosterone usually

ing reasonable quantities of testosterone. If a male

The

Effect of Testosterone to Cause Descent of the Testes.

the formation of female genital organs.

male genital ducts, while at the same time suppressing

formation of the prostate gland, seminal vesicles, and

formation of a clitoris and a vagina. Also, it causes

opment of the male body characteristics, including

Thus, testosterone secreted first by the genital ridges

development of female sexual organs.

sexual organs even though the fetus is female. Also,

gens. Injection of large quantities of male sex hormone

ing genital ridge to secrete testosterone, whereas the

Indeed, one of the major functional differences

testes at about the seventh week of embryonic life.

Testosterone begins to be elaborated by the male fetal

Functions of Testosterone During

shown in Figure 80–9, dwindling rapidly beyond age 50

lasts throughout most of the remainder of life, as

to 13 years. Then testosterone production increases

birth; thereafter, essentially no testosterone is

during fetal life, the testes are stimulated by chorionic

guishing characteristics of the masculine body. Even

In general, testosterone is responsible for the distin-

Functions of Testosterone

the liver, probably accounting for as much as 80 per cent

androstanediol in other tissues of the body, especially

testosterone to estradiol. (2) Much larger amounts

important role in spermiogenesis. This estrogen is

gens in the male is unclear, but the following are known:

recovered from a man’s urine. The exact source of estro-

female), and a reasonable quantity of estrogens can be

terone, small amounts of estrogens are formed in the

the liver bile or into the urine through the kidneys.

larly). These are excreted either into the gut by way of

either glucuronides or sulfates (glucuronides, particu-

verted, mainly by the liver, into

The testosterone

Degradation and Excretion of Testosterone.

1004

Unit XIV

Endocrinology and Reproduction

that does not become fixed to the tissues is rapidly con-

androsterone and dehy-

droepiandrosterone and simultaneously conjugated as

Production of Estrogen in the Male.

In addition to testos-

male (about one fifth the amount in the nonpregnant

(1) the concentration of estrogens in the fluid of the
seminiferous tubules is quite high and probably plays an

believed to be formed by the Sertoli cells by converting

of estrogens are formed from testosterone and

of the total male estrogen production.

gonadotropin from the placenta to produce moderate
quantities of testosterone throughout the entire period
of fetal development and for 10 or more weeks after

produced during childhood until about the ages of 10

rapidly under the stimulus of anterior pituitary
gonadotropic hormones at the onset of puberty and

to become 20 to 50 per cent of the peak value by age
80.

Fetal Development

between the female and the male sex chromosome is
that the male chromosome causes the newly develop-

female chromosome causes this ridge to secrete estro-

into pregnant animals causes development of male

removal of the testes in the early male fetus causes

and later by the fetal testes is responsible for the devel-

the formation of a penis and a scrotum rather than

testes usually descend into the scrotum during the last
2 to 3 months of gestation when the testes begin secret-

child is born with undescended but otherwise normal

causes the testes to descend in the usual manner if the
inguinal canals are large enough to allow the testes to

important hormone for male sexual development

Sexual Characteristics

linea alba of the abdomen sometimes to the umbilicus

Baldness.

Testosterone

Dihydrotestosterone

Testosterone and dihydrotestosterone.

Figure 80–8

causing a spurt in total body height. However, the

child, the rate of bone growth increases markedly,

When great quantities of testosterone (or any other

to treat osteoporosis.

size and strength of bones, it is often used in older men

is similar to that of the female.

testosterone, the male pelvis develops into a pelvis that

of the entire pelvis for load-bearing. In the absence of

the female pelvis, and (4) greatly increase the strength

narrow the pelvic outlet, (2) lengthen it, (3) cause a

Testosterone has a specific effect on the pelvis to (1)

of bone matrix and causes calcium retention. The

salts. Thus, testosterone increases the total quantity

injection of testosterone), the bones grow considerably

Testosterone Increases Bone Matrix and Causes Calcium Reten-

vigor, but with questionable results.

as a “youth hormone” to improve muscle strength and

in relation to sports physiology. Testosterone or syn-

effects of excess androgens, as we discuss in Chapter 84

improve their muscular performance. This practice is to

other androgens have on the body musculature,

bolic function of testosterone.

to deposition of proteins in the skin, and the changes

body as well. Many of the changes in the skin are due

muscle mass over that in the female. This is associated

puberty, averaging about a 50 per cent increase in

Testosterone Increases Protein Formation and Muscle Devel-

it to overcome the acne.

several years of testosterone secretion, the skin nor-

becoming introduced to increased testosterone. After

. Therefore, acne is one of the most common

sebaceous glands of the face, because this can result

some or perhaps all the body’s sebaceous glands.

Testosterone also increases the rate of secretion by

increases the ruggedness of the subcutaneous tissues.

Testosterone increases

Testosterone Increases Thickness of the Skin and Can Con-

masculine voice.

voice, but this gradually changes into the typical adult

effects cause at first a relatively discordant, “cracking”

laryngeal mucosa and enlargement of the larynx. The

Testosterone secreted by the testes

Effect on the Voice.

. A woman who has the appropriate

development of baldness and, second, superimposed

genetic background

result of two factors: first, a

tional testes does not become bald. However, many

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

1005

virile men never become bald because baldness is a

for the

on this genetic background, large quantities of andro-
genic hormones
genetic background and who develops a long-
sustained androgenic tumor becomes bald in the same
manner as does a man.

or injected into the body causes hypertrophy of the

tribute to Development of Acne.

the thickness of the skin over the entire body and

Especially important is excessive secretion by the

in acne
features of male adolescence when the body is first

mally adapts to the testosterone in a way that allows

opment.

One of the most important male characteris-

tics is development of increasing musculature after

with increased protein in the nonmuscle parts of the

in the voice also result partly from this protein ana-

Because of the great effect that testosterone and

synthetic androgens are widely used by athletes to

be severely deprecated because of prolonged harmful

thetic androgens are also occasionally used in old age

tion.

After the great increase in circulating testos-

terone that occurs at puberty (or after prolonged

thicker and deposit considerable additional calcium

increase in bone matrix is believed to result from the
general protein anabolic function of testosterone plus
deposition of calcium salts in response to the increased
protein.

funnel-like shape instead of the broad ovoid shape of

Because of the ability of testosterone to increase the

androgen) are secreted abnormally in the still-growing

Trimester

Year

Fetal

Neonatal

Pubertal

Adult

1st 2nd 3rd

2.5

5.0

100

gestation

Birth

Old age

Plasma testosterone (nmol/L)

(ng/ml)

Sperm production (% of maximal)

Metabolic Control and Disease,

Griffin JF, Wilson JD: The testis. In:

different ages. (Modified from

sperm production (blue line) at

concentrations (red line) and

average plasma testosterone

sexual function as reflected by

The different stages of male

Figure 80–9

Bondy PK, Rosenberg LE [eds]:

8th ed. Philadelphia: WB Saun-
ders Co, 1980.)

gonadotropes,

secreted by the same cells, called

Both of the gonadotropic hormones, LH and FSH, are

Gonadotropic Hormones: LH and FSH

releasing hormone.

LH secretion, GnRH is also widely known as

to longer-term changes in GnRH. Because of the

fluctuation of GnRH secretion; instead, it changes

pulsatile release of GnRH. Conversely, FSH secretion

is also cyclical, with LH following fairly faithfully the

The secretion of LH by the anterior pituitary gland

the quantity of GnRH released with each cycle.

the frequency of these cycles of secretion and (2) by

hormone’s stimulus is determined in two ways: (1) by

time once every 1 to 3 hours. The intensity of this

stimulates the release of the two gonadotropins, LH

Then the GnRH is transported to the anterior

hypothalamus, where they release GnRH into the

. The endings of these neurons

Secretion of LH and FSH

GnRH and Its Effect in Increasing the

FSH mainly stimulates spermatogenesis.

lus for the secretion of testosterone by the testes, and

. In turn, LH is the primary stimu-

hypothalamus (see Figure 80–10). This hormone in

and Anterior Pituitary Gland

by Hormones from the Hypothalamus

Control of Male Sexual Functions

actions of testosterone, however, has yet to be

proteins. The physiological role of these nongenomic

steroidal hormones, may also exert some rapid, non-

Recent studies suggest that testosterone, like other

primary and secondary male sexual characteristics.

specifically affecting those proteins in “target” organs

virtually everywhere in the body, although more

Testosterone stimulates production of proteins

prostatic cells.

lar protein. After several days, the quantity of DNA

cells; this is followed by progressive increase in cellu-

centration of RNA begins to increase in the prostatic

RNA polymerase has become activated and the con-

induces DNA-RNA transcription. Within 30 minutes,

cell nucleus, where it binds with a nuclear protein and

“receptor protein.” This combination migrates to the

, and this in turn binds with a cytoplasmic

-reductase, to

is most often converted, under the influence of the

cells within a few minutes after secretion. Then it

terone. In this gland, testosterone enters the prostatic

gland, one of the organs that is most affected by testos-

cells. This has been studied extensively in the prostate

of Action of Testosterone

eralocorticoids. Nevertheless, after puberty, the blood

kidneys. Testosterone also has such an effect, but only

Chapter 77, many steroid hormones can increase the

Effect on Electrolyte and Water Balance.

millimeter than the average woman. This difference

blood increases 15 to 20 per cent. Also, the average

testosterone are injected into a castrated adult, the

When normal quantities of

cells.

anabolism, the increased quantity of proteins—the

This increased rate of metabolism is possibly an

the value that it would be were the testes not active.

metabolic rate by as much as 15 per cent. Also, even

Testosterone Increases Basal Metabolism.

which occurs in males castrated before puberty.

men, the final adult height is slightly less than that

testosterone not been secreted at all. Even in normal

age. Therefore, despite the rapidity of growth, this

1006

Unit XIV

Endocrinology and Reproduction

testosterone also causes the epiphyses of the long
bones to unite with the shafts of the bones at an early

early uniting of the epiphyses prevents the person
from growing as tall as he would have grown had

Injection of

large quantities of testosterone can increase the basal

the usual quantity of testosterone secreted by the
testes during adolescence and early adult life increases
the rate of metabolism some 5 to 10 per cent above

indirect result of the effect of testosterone on protein

enzymes especially—increasing the activities of all

Effect on Red Blood Cells.

number of red blood cells per cubic millimeter of

man has about 700,000 more red blood cells per cubic

may be due partly to the increased metabolic rate that
occurs after testosterone administration rather than
to a direct effect of testosterone on red blood cell
production.

As pointed out in

reabsorption of sodium in the distal tubules of the

to a minor degree in comparison with the adrenal min-

and extracellular fluid volumes of the male in relation
to body weight increase as much as 5 to 10 per cent.

Basic Intracellular Mechanism

Most of the effects of testosterone result basically
from increased rate of protein formation in the target

intracellular enzyme 5

dihydrotestos-

terone

in the prostate gland has also increased and there
has been a simultaneous increase in the number of

or tissues responsible for the development of both

genomic effects that do not require synthesis of new

determined.

A major share of the control of sexual functions in
both the male and the female begins with secretion
of gonadotropin-releasing hormone (GnRH) by the

turn stimulates the anterior pituitary gland to secrete
two other hormones called gonadotropic hormones:
(1) luteinizing hormone (LH) and (2) follicle-stimulat-
ing hormone (FSH)

GnRH is a 10-amino acid peptide secreted by neurons
whose cell bodies are located in the arcuate nuclei of
the hypothalamus
terminate mainly in the median eminence of the

hypothalamic-hypophysial portal vascular system.

pituitary gland in the hypophysial portal blood and

and FSH.

GnRH is secreted intermittently a few minutes at a

increases and decreases only slightly with each

more slowly over a period of many hours in response

much closer relation between GnRH secretion and

LH-

in the

It has been isolated from cultured Sertoli cells. Its

Inhibin is a glycoprotein, like both LH and FSH,

This hormone has a strong direct effect on the ante-

(see Figure 80–10).

pituitary secretion of FSH diminishes.The cause of this

versely, when spermatogenesis proceeds too rapidly,

the anterior pituitary gland increases markedly. Con-

tubules fail to produce sperm, secretion of FSH by

When the seminiferous

Negative Feedback Control of Seminiferous Tubule Activity—

terone are necessary.

Thus, to initiate spermatogenesis, both FSH and testos-

also has a strong tropic effect on spermatogenesis.

substances. Simultaneously, testosterone (and dihy-

Sertoli cells in the seminiferous tubules. This causes

and Testosterone

Regulation of Spermatogenesis by FSH

amounts of GnRH, with a corresponding increase in

the desired operating level. Conversely, too little

gland, reduces the testosterone secretion back toward

great, this automatic negative feedback effect, operat-

Thus, whenever secretion of testosterone becomes too

reduces the secretion of testosterone by the testes.

by the anterior pituitary, and the decrease in LH

the secretion of GnRH. This in turn causes a corre-

anterior pituitary secretion of LH (see Figure 80–10).

The testosterone secreted by the testes in

Testosterone—Negative Feedback Control of Testosterone

Inhibition of Anterior Pituitary Secretion of LH and FSH by

ing Leydig cells.

until after the age of about 10 years. However, either

Mature Leydig cells are normally found in a child’s

available.

from the anterior pituitary gland. Furthermore, the

the testes, but only when they are stimulated by LH

Testos-

Testosterone—Regulation of Its Production by LH.

enzyme systems in the respective target cells.

, which in turn activates specific

. They exert their

secretion from the hypothalamus, the gonadotropes in

anterior pituitary gland. In the absence of GnRH

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

1007

the pituitary gland secrete almost no LH or FSH.

LH and FSH are glycoproteins

effects on their target tissues in the testes mainly by
activating the cyclic adenosine monophosphate second
messenger system

terone is secreted by the interstitial cells of Leydig in

quantity of testosterone secreted increases approxi-
mately in direct proportion to the amount of LH

testes for a few weeks after birth but then disappear

injection of purified LH into a child at any age or
secretion of LH at puberty causes testicular interstitial
cells that look like fibroblasts to evolve into function-

Secretion.

response to LH has the reciprocal effect of inhibiting

Most of this inhibition probably results from a direct
effect of testosterone on the hypothalamus to decrease

sponding decrease in secretion of both LH and FSH

ing through the hypothalamus and anterior pituitary

testosterone allows the hypothalamus to secrete large

anterior pituitary LH and FSH secretion and conse-
quent increase in testicular testosterone secretion.

FSH binds with specific FSH receptors attached to the

these cells to grow and secrete various spermatogenic

drotestosterone) diffusing into the seminiferous
tubules from the Leydig cells in the interstitial spaces

Role of the Hormone Inhibin.

negative feedback effect on the anterior pituitary is
believed to be secretion by the Sertoli cells of still
another hormone called inhibin

rior pituitary gland to inhibit the secretion of FSH and
possibly a slight effect on the hypothalamus to inhibit
secretion of GnRH.

having a molecular weight between 10,000 and 30,000.

potent inhibitory feedback effect on the anterior pitu-

Spermatogenesis

Virilizing effects

Sertoli
cell

Leydig cell

FSH

Testis

Behavorial

effects

CNS

Hypothalamus

GnRH

Anterior
pituitary

Testosterone

Inhibin

follicle-stimulating hormone.

gonadotropin-releasing hormone; LH, luteinizing hormone; FSH,

feedbacks inhibitory effects are shown by

axis in males. Stimulatory effects are shown by

Feedback regulation of the hypothalamic-pituitary-testicular

Figure 80–10

and negative

. GnRH,

decreased but not lost, provided sexual activities have

Also in a castrated adult male, sexual desires are

and loss of the musculature of the virile male.

line hair production, loss of the thick masculine bones,

quality only slightly. Conversely, there is loss of mascu-

childlike state, and the voice regresses from the bass

The sexual organs regress slightly in size but not to a

a child and others remain of adult masculine character.

When a man is castrated after puberty, some of his

does not occur.

is no loss of hair on the head, and the normal adult

than those of a normal man. The voice is childlike, there

epiphyses are slow to unite, although the bones are

throughout life. The height of an adult eunuch is slightly

When a boy loses his testes before puberty, a state of

sexual organs is suppressed, and instead, male organs

in the presence of testosterone, formation of female

female sexual organs if there are no sex hormones. But

tic of the fetus, whether male or female, is to form

The reason for this is that the basic genetic characteris-

develop in the fetus. Instead, female organs are formed.

during fetal life, none of the male sexual characteristics

When the testes of a male fetus are nonfunctional

Hypogonadism in the Male

and the bones partially heal. This treatment does not

removal of the testes, by estrogen therapy, or by both;

can be inhibited by administration of estrogens.

testosterone cannot be formed. Prostatic cancer usually

prostate gland does occur, the cancerous cells are

2 to 3 per cent of all male deaths. Once cancer of the

and is a common cause of death, accounting for about

tissue itself.

obstruction. This hypertrophy is caused not by testos-

production of testosterone by the testes.

some men it begins to involute, along with decreased

this size up to the age of about 50 years. At that time, in

stimulus of testosterone. This gland reaches an almost

The prostate gland remains relatively small throughout

Prostate Gland and

Sexual Function

Abnormalities of Male

symptoms in the female.

tration of testosterone, synthetic androgens, or even

female. These symptoms can be abrogated by adminis-

with symptoms of hot flashes, suffocation, and psychic

macteric.

testosterone secretion, as shown in Figure 80–9. The

tions was 68, although the variation was great. This

functions in their late 40s or 50s, and one study showed

men, however, begin to exhibit slowly decreasing sexual

spermatogenesis usually continues until death. Most

itary gland for the remainder of life, and at least some

After puberty,

childhood inhibition, and adult sexual life begins.

reasons still not understood, at the time of puberty, the

effect on hypothalamic secretion of GnRH. Yet, for

for this is that, during childhood, the slightest secretion

. One of the reasons

childhood the hypothalamus simply does not secrete

mystery. But it has now been determined that

Puberty and Regulation of Its Onset

nancy in greater detail in Chapter 82.

earlier. We discuss hCG and its functions during preg-

formation of the male sexual organs, as pointed out

testosterone. This testosterone is critical for promoting

During pregnancy, if the fetus is a male, hCG from

organs as LH.

it circulates both in the mother and in the fetus. This

is secreted by the placenta, and

gonadotropin (hCG)

human chorionic

During pregnancy, the hormone

Testosterone Secretion by the Fetal Testes

the Placenta During Pregnancy Stimulates

Human Chorionic Gonadotropin Secreted by

in a rough truck is said to inhibit the bull’s fertility—

and the female. For instance, transporting a prize bull

limbic system of the brain into the hypothalamus, can

Many psychic factors, feeding especially from the

Secretion and Sexual Activity

Psychic Factors That Affect Gonadotropin

mechanism for control of spermatogenesis, operating

1008

Unit XIV

Endocrinology and Reproduction

itary gland provides an important negative feedback

simultaneously with and in parallel to the negative
feedback mechanism for control of testosterone
secretion.

affect the rate of secretion of GnRH by the hypothal-
amus and therefore can also affect most other aspects
of sexual and reproductive functions in both the male

and the human male is hardly different.

hormone has almost the same effects on the sexual

the placenta causes the testes of the fetus to secrete

Initiation of the onset of puberty has long been a

during

significant amounts of GnRH

of any sex steroid hormones exerts a strong inhibitory

secretion of hypothalamic GnRH breaks through the

Male Adult Sexual Life and Male Climacteric.

gonadotropic hormones are produced by the male pitu-

that the average age for terminating intersexual rela-

decline in sexual function is related to decrease in

decrease in male sexual function is called the male cli-

Occasionally the male climacteric is associated

disorders similar to the menopausal symptoms of the

estrogens that are used for treatment of menopausal

Its Abnormalities

childhood and begins to grow at puberty under the

stationary size by the age of 20 years and remains at

A benign prostatic fibroadenoma frequently develops

in the prostate in many older men and can cause urinary

terone but instead by abnormal overgrowth of prostate

Cancer of the prostate gland is a different problem

usually stimulated to more rapid growth by testosterone
and are inhibited by removal of both testes so that

Even some patients who have prostatic cancer that has
already metastasized to almost all the bones of the body
can be successfully treated for a few months to years by

after this therapy the metastases usually diminish in size

stop the cancer but does slow it and sometimes greatly
diminishes the severe bone pain.

are induced.

eunuchism ensues in which he continues to have infan-
tile sex organs and other infantile sexual characteristics

greater than that of a normal man because the bone

quite thin and the muscles are considerably weaker

masculine hair distribution on the face and elsewhere

male secondary sexual characteristics revert to those of

several other, similar substances. Either melatonin or

Second, the pineal gland secretes

vation. The nervous pathway involves the passage of

each day activates the pineal gland, whereas

For instance, in the hamster, greater than 13 hours of

light or “time pattern” of light seen by the eyes each day.

First, the pineal gland is controlled by the amount of

following.

this effect is not entirely clear, but it seems to be the

summer, when survival is most likely. The mechanism of

spring at the time of year, usually springtime or early

sonal fertility are lost. To these animals, such seasonal

gland have been sectioned, the normal periods of sea-

function. In lower animals that bear their young at

But now, after years of dispute, it looks as though the

gists preoccupied with sexual delusions.

and reproduction, functions that still others said were

lower animals. Many physiologists have been content

per cent). It is known from comparative anatomy that

mood, and (6) increasing longevity (as much as 10 to 25

staving off infection, (4) promoting sleep, (5) enhancing

(1) being the seat of the soul, (2) enhancing sex, (3)

myriad functions have been ascribed to it, including its

For as long as the pineal gland has been known to exist,

Fertility in Some Animals

in Controlling Seasonal

of hCG with functions similar to those of LH. Also,

develops in the tumor, it may secrete large quantities

hormones, but if a significant quantity of placental tissue

These tumors often secrete few

and so forth, all found together in the same tumorous

tissues, such as placental tissue, hair, teeth, bone, skin,

any type of cell, many of these tumors contain multiple

tumors are tumors of the germinal epithelium. Because

adult male, small interstitial cell tumors are difficult

muscles, and other male sexual characteristics. In the

development of the male sexual organs, all skeletal

wise. Such interstitial cell tumors also cause excessive

bones but also cause early uniting of the epiphyses, so

dren, they cause rapid growth of the musculature and

testosterone. When such tumors develop in young chil-

in the testes, but when they do develop, they sometimes

Hypergonadism in the Male

Testicular Tumors and

hypothalamic eunuchism.

, or

adiposogenital syndrome, Fröhlich’s

patient with this condition is shown in Figure 80–11; the

Consequently, obesity occurs along with eunuchism. A

hypothalamus, causing the person to greatly overeat.

amounts of GnRH. This often is associated with a

the testosterone-driven psychic desire.

lation can take place, primarily because the semen-

before, although with less ease, but it is rare that ejacu-

been practiced previously. Erection can still occur as

Chapter 80

Reproductive and Hormonal Functions of the Male (and Function of the Pineal Gland)

1009

forming organs degenerate and there has been a loss of

Some instances of hypogonadism are caused by a

genetic inability of the hypothalamus to secrete normal

simultaneous abnormality of the feeding center of the

condition is called
syndrome

Interstitial Leydig cell tumors develop in rare instances

produce as much as 100 times the normal quantities of

that the eventual adult height actually is considerably
less than that which would have been achieved other-

to diagnose because masculine features are already
present.

Much more common than the interstitial Leydig cell

germinal cells are capable of differentiating into almost

mass called a teratoma.

estrogenic hormones are sometimes secreted by these
tumors and cause the condition called gynecomastia
(overgrowth of the breasts).

Pineal Gland—Its Function

the pineal gland is a vestigial remnant of what was a
third eye located high in the back of the head in some

with the idea that this gland is a nonfunctional remnant,
but others have claimed for many years that it plays
important roles in the control of sexual activities

nothing more than the fanciful imaginings of physiolo-

sex advocates have won and that the pineal gland does
indeed play a regulatory role in sexual and reproductive

certain seasons of the year and in which the pineal gland
has been removed or the nervous circuits to the pineal

fertility is important because it allows birth of the off-

darkness
less than that amount of darkness fails to activate it,
with a critical balance between activation and nonacti-

light signals from the eyes to the suprachiasmal nucleus
of the hypothalamus and then to the pineal gland,
activating pineal secretion.

melatonin and

one of the other substances is believed to pass either by

and childlike sexual organs. (Courtesy Dr. Leonard Posey.)

Adiposogenital syndrome in an adolescent male. Note the obesity

Figure 80–11

55:325, 2003.

peptides, and other pineal transmitters. Pharmacol Rev

regulation of melatonin synthesis by norepinephrine,

endocrine message in mammals: a review of the complex

Simonneaux V, Ribelayga C: Generation of the melatonin

Rev Med 54:153, 2003.

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struction and conservation of the adult skeleton. Endocr

Riggs BL, Khosla S, Melton LJ 3rd: Sex steroids and the con-

ing. N Engl J Med 350:482, 2004.

Rhoden EL, Morgentaler A: Risks of testosterone-

pressure. Hypertension 37:1199, 2001.

Reckelhoff JF: Gender differences in the regulation of blood

primates. Endocr Rev 22:764, 2001.

Plant TM, Marshall GR: The functional significance of FSH

Estrogen and spermatogenesis. Endocr Rev 22:289, 2001.

O’Donnell L, Robertson KM, Jones ME, Simpson ER:

Cancer 3:845, 2003.

prostate cancer: good, bad or questionable? Nat Rev

Nelson PS, Montgomery B: Unconventional therapy for

N Engl J Med 349:366, 2003.

Nelson WG, De Marzo AM, Isaacs WB: Prostate cancer.

cardiovascular disease. Endocr Rev 24:313, 2003.

Liu PY, Death AK, Handelsman DJ: Androgens and

Klinefelter’s syndrome. Lancet 364:273, 2004.

Lanfranco F, Kamischke A, Zitzmann M, Nieschlag E:

some, in the light of evolution. Nat Rev Genet 2:207, 2001.

Lahn BT, Pearson NM, Jegalian K: The human Y chromo-

investigation, and treatment. Endocr Rev 22:342, 2001.

tion and its disorders: physiology, pathophysiology, clinical

Kandeel FR, Koussa VK, Swerdloff RS: Male sexual func-

evolutionary marker comes of age. Nat Rev Genet 4:598,

Jobling MA, Tyler-Smith C: The human Y chromosome: an

tors: an overview. Endocr Rev 23:175, 2002.

Heinlein CA, Chang C: Androgen receptor (AR) coregula-

and alterations of spermatogenesis. Endocr Rev 22:226,

Foresta C, Moro E, Ferlin A: Y chromosome microdeletions

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logical and molecular aspects of prostate cancer. Lancet

DeMarzo AM, Nelson WG, Isaacs WB, Epstein JI: Patho-

de Kretser DM: Is spermatogenic damage associated with

Nat Rev Genet 3:790, 2002.

Cooke HJ, Saunders PT: Mouse models of male infertility.

development. Physiol Rev 82:825, 2002.

Cheng CY, Mruk DD: Cell junction dynamics in the testis:

J Neuroendocrinol 15:432, 2003.

in the regulation of human circadian rhythms and sleep.

Cajochen C, Krauchi K, Wirz-Justice A: Role of melatonin

Rev Genet 5:509, 2004.

events that underlie testis versus ovary development. Nat

Brennan J, Capel B: One tissue, two fates: molecular genetic

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Anderson RA, Baird DT: Male contraception. Endocr Rev

controlling sexual drive and reproduction in humans.

ciated with hypogonadal or hypergonadal function. So

gland to destroy it. Both types of tumors are often asso-

excessive quantities of pineal hormones, whereas others

the region of the pineal gland. Some of these secrete

question is unknown. However, tumors often occur in

control of reproduction in humans? The answer to this

time of activity.

become functional once more, ready for a full spring-

darkness. But after about 4 months of dysfunction,

even partly involuted. This is what presumably occurs

species of animals, and the gonads become inhibited and

Thus, in the presence of pineal gland secretion,

1010

Unit XIV

Endocrinology and Reproduction

way of the blood or through the fluid of the third
ventricle to the anterior pituitary gland to decrease
gonadotropic hormone secretion.

gonadotropic hormone secretion is suppressed in some

during the early winter months when there is increasing

gonadotropic hormone secretion breaks through the
inhibitory effect of the pineal gland and the gonads

But does the pineal gland have a similar function for

are tumors of surrounding tissue and press on the pineal

perhaps the pineal gland does play at least some role in

References

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2003.

in spermatogenesis and the control of its secretion in male

replacement therapy and recommendations for monitor-