Reproductive system pdf - Dr. Abdullah

بسم ه الرحمن الرحيم

Reproductive system(male)

introduction

• The reproductive functions of the male can be

divided into three major subdivisions:

• (1)

spermatogenesis

, which means simply the

formation of sperm;

• (2) performance of the

male sexual act

; and

• (3)

regulation

of male reproductive functions by

the various

hormones

• Associated with these

reproductive functions

are

the effects of the male sex hormones on the

accessory sexual organs

cellular metabolism

growth

, and other functions of the body.

Spermatogenesis

• During formation of the embryo, the

primordial germ

cells 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 ( Figure ).

• The spermatogonia begin to undergo

mitotic

division

, beginning at

puberty

, & continually

proliferate & differentiate through definite
stages of development to form sperm(Figure ).

Internal structure of the testis and relation of the

testis to the epididymis

Cross section of a seminiferous tubule.

Stages in the development

of sperm from spermatogonia.

Sex Chromosomes

• In each

spermatogonium

, one of the

23 pairs

chromosomes carries the genetic information
that

determines the sex

of each eventual off

spring.

• This pair is composed of

one X chromosome

which is called the

female chromosome

, and

one

Y chromosome

, the

male chromosome

• During

meiotic division

, the male

Y chromosome

goes to one spermatid that then becomes a

male

sperm

, and the female

X chromosome

goes to

another spermatid that becomes

a female sperm

• The sex of the eventual offspring is determined by

which of these two types of sperm fertilizes the
ovum.

• At

puberty

(usually 12 to14 years after birth),

the spermatogonia proliferate rapidly by

mitosis

• Some begin meiosis to become

primary

spermatocytes

and continue through meiotic

division I to become

secondary

spermatocytes

• After completion of meiotic division II, the

secondary spermatocytes produce

spermatids

, which differentiate to form

spermatozoa.

Hormonal Factors That Stimulate

Spermatogenesis

• several hormones play essential roles in

spermatogenesis. Some of these are as
follows:

• 1.

Testosterone

, secreted by the Leydig cells

located in the interstitium of the testis, is
essential forgrowth and division of the
testicular germinalcells, which is the first stage
in forming sperm.

• 2.

Luteinizing hormone

, secreted by the

anterior pituitary gland, stimulates the

Leydig

cells

to secrete

testosterone

Hormonal Factors That Stimulate

Spermatogenesis

. Follicle-stimulating hormone

, also secreted by the

anterior pituitary gland, stimulates the

Sertoli cells

;

without this stimulation, the conversion of the
spermatids to sperm (the process of spermiogenesis)
will not occur.

Estrogens

, formed from testosterone by the Sertoli cells

when they are stimulated by follicles timulating
hormone, are probably also essential for
spermiogenesis.

Growth hormone

specifically promotes early division

of the spermatogonia themselves; in its absence, as in
pituitary dwarfs, spermatogenesis is severely deficient
or absent, thus causing

infertility

semen

• Semen, is composed of the

fluid and sperm

from the

vasdeferens

fluid from the

seminal vesicles

, fluid from the prostate gland , and

small amounts from the

mucous glands

, especially the

bulbourethral glands.

• Thus, the bulk of the semen is seminal vesicle fluid, which is the

last to be ejaculated and serves to wash the sperm through the
ejaculatory duct and urethra.

• The average

of the combined semen is about

7.5

, the alkaline

prostatic fluid having more than neutralized the mild acidity of the
other portions of the semen.

• The

prostatic

fluid gives the semen

a milky

appearance, and fluid

from the

seminal vesicles

and mucous glands gives the semen

mucoid

consistency

• Also,

a clotting enzyme

from the prostatic fluid causes 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 lies.

• The coagulum then dissolves during the next 15 to 30 minutes

because of lysis by fibrinolysin formed from the prostatic
profibrinolysin.

semen

• In the early minutes after ejaculation, the sperm

remain relatively immobile, possibly because of
the

viscosity of the coagulum

• As the coagulum dissolves, the sperm

simultaneously become highly motile.

• Although sperm can live for

many weeks

in the

male genital ducts, once they are ejaculated in
the semen, their

maximal life span

is only

24 to

48 hours

at body temperature.

• At lowered temperatures, however, semen can be

stored for

several weeks

, and when frozen at

temperatures below

-100°C

, sperm have been

preserved for years.

Secretion of Testosterone by the Interstitial Cells of

Leydig in the Testes

• The testes secrete several male sex hormones,

which are collectively called

androgens

, including

testosterone

dihydrotestosterone

, and

androstenedione

• Testosterone is so much

more abundant

than the

others that one can consider it to be the
significant testicular hormone, although ,much, if
not most, of the testosterone is eventually
converted into the more active hormone

dihydrotestosterone

in the target tissues.

• Testosterone is formed by the interstitial cells of

Leydig

, which lie in the interstices between the

seminiferous tubules

• Effect of Testosterone on Development of Adult

Primary and Secondary Sexual Characteristics

• Effect on the Distribution of Body Hair(Baldness)

• Effect on the Voice.

• Testosterone Increases Thickness of the Skin and Can

Contribute to Development of Acne.

• Testosterone Increases Protein Formation and Muscle

Development.

• Testosterone Increases Bone Matrix and Causes

Calcium Retention.

• Testosterone Increases Basal Metabolism

• Effect on Red Blood Cells.

• Effect on Electrolyte and Water Balance.

Function of the testesteron

Control of Male Sexual Functions by Hormones from the

Hypothalamus and Anterior Pituitary Gland

• 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

hypothalamus .

• This hormone in turn stimulates the

anterior pituitary

gland to secrete two other hormones called

gonadotropic hormones

(1) luteinizing hormone (LH) and

(2) follicle-stimulatinghormone (FSH).
• In turn,

is the primary stimulus for the secretion of

testosterone by the testes, and

FSH

mainly stimulates

spermatogenesis.

Thank you