Endocrine pdf - رجاء علي محسن

Histology 2016-2017
Department of Anatomy &Histology:

Dr.Rajaa Ali

*************************************************************

Endocrine System I:

 The

endocrine system

produces various secretions called

hormones

[Gr.

hormaein, to set in motion] that release for delivery to the bloodstream for

transport to target cells and organs, serve as effectors to regulate the activities of

various cells, tissues, and organs in the body.

 Its functions are essential in maintaining homeostasis and coordinating body

growth and development and are similar to that of the nervous system: Both

communicate information to peripheral cells and organs.

 These two systems are functionally interrelated. But endocrine system produces

a slower and more prolonged response than the nervous system.

 Both systems may act simultaneously on the same target cells and tissues.



The endocrine system including the discrete

endocrine Glands (pituitary

gland & hypothalamus, thyroid gl., adrenal gl. ,pineal gl. ,parathyroid gl.)

as well as

individual cells

within the gonads, liver, pancreas, kidney, and

gastrointestinal system.

Pituitary Gland(Hypophisis):

The

pituitary gland

and the

hypothalamus

, the portion of the brain to which the

pituitary gland is attached, are morphologically and functionally linked in the

endocrine and neuroendocrine control of other endocrine glands.

Gross Structure and Development

The pituitary gland is composed of glandular epithelial tissue and neural

(secretory) tissue.

The

pituitary gland

[Lat. Pituta , phlegm—reflecting its nasopharyngeal

origin] is a pea-sized, compound endocrine gland .

It is centrally located at the base of the brain, where it lies in a depression

of the sphenoid bone called the

sella turcica

A short stalk, the

infundibulum

, and a vascular network connect the

pituitary gland to the hypothalamus.

The pituitary gland has two functional components (Fig. 1,2):

Fig. (1) : development of pituitary gland

•

Anterior lobe (adenohypophysis)

, the glandular epithelial tissue.

•

Posterior lobe (neurohypophysis)

, the neural secretory tissue .

These two portions are of different embryologic origin.

The anterior lobe of the pituitary gland is derived from an evagination of the

ectoderm of the oropharynx

toward the brain

(Rathke’s pouch)

The posterior lobe of the pituitary gland is derived from a downgrowth (the

future infundibulum) of

neuroectoderm of the floor of the third ventricle

(the

diencephalon) of the developing brain (Fig. 1) .

The

anterior lobe of the pituitary gland

consists of three derivatives of

Rathke’s pouch:



Pars distalis

, which comprises the bulk of the anterior lobe of the

pituitary gland and arises from the thickened anterior wall of the pouch .



Pars intermedia

, a thin remnant of the posterior wall of the pouch that

abuts the pars distalis.



Pars tuberalis

, which develops from the thickened lateral walls of the

pouch and forms a collar or sheath around the infundibulum.

The

posterior lobe of the pituitary gland

consists of the following:

Pars nervosa

, which contains neurosecretory axons and their

endings.

Infundibulum

, which is continuous with the:

 median eminence

and contains the neurosecretory axons forming the

hypothalamohypophyseal tracts .

Blood Supply & the Hypothalamo-Hypophyseal Portal System:

The blood supply derives from two groups of vessels coming off the internal

carotid artery .

The pituitary blood supply is derived from two sets of vessels:

•

Superior hypophyseal arteries

supply the pars tuberalis , median eminence, and

infundibulum.

•

Inferior hypophyseal arteries

primarily supply the pars nervosa. These vessels arise

solely from the internal carotid arteries.

An important functional observation is that most of the anterior lobe of the pituitary

gland has no direct arterial supply.

The hypothalamohypophyseal portal system provides the crucial link between the

hypothalamus and the pituitary gland.

The arteries that supply the pars tuberalis , median eminence, and infundibulum give

rise to fenestrated capillaries (the primary capillary plexus). These capillaries drain

into portal veins, called the

hypophyseal portal veins

, which run along the pars

tuberalis and give rise to a second fenestrated sinusoidal capillary network (the

secondary capillary plexus).

Nerve Supply

 The nerves that enter the infundibulum and pars nervosa from the hypothalamic

nuclei are components of the posterior lobe of the pituitary gland .

 The nerves that enter the anterior lobe of the pituitary gland are postsynaptic

fibers of the autonomic nervous system and have vasomotor function.

Structure and Function of the Pituitary Gland

Anterior Lobe of the Pituitary Gland (Adenohypophysis)

 The anterior lobe of the pituitary gland regulates other endocrine glands .
 Most of the

anterior lobe of the pituitary gland

has the typical organization of

endocrine tissue.

 The cells are organized in clumps and cords separated by fenestrated sinusoidal

capillaries of relatively large diameter.

 These cells respond to signals from the hypothalamus and synthesize and secrete

a number of pituitary hormones

 Four hormones of the anterior lobe—

adrenocorticotropic hormone (ACTH),

thyroidstimulating (thyrotropic) hormone (TSH, thyrotropin), follicle-

stimulating hormone (FSH)

, and

luteinizing hormone (LH)

—are called

tropic hormones

because they regulate the activity of cells in other endocrine

glands throughout the body.

 The two remaining hormones of the anterior lobe,

growth hormone (GH)

and

prolactin (PRL)

, are not considered tropic because they act directly on target

organs that are not endocrine.

Pars Distalis .

The cells within the

pars distalis

vary in size, shape, and staining properties.

The cells are arranged in cords and nests with interweaving capillaries.

Histologists identified three types of cells according to their staining reaction,

namely,

basophils (10%)

acidophils (40%)

, and

chromophobes (50%)

fig.(2)

Five functional cell types are identified in the pars distalis on the basis of

immunocytochemical reactions (Table).

In addition to the five types of hormone-producing cells, anterior lobe of the

pituitary gland contains folliculostellate cells .

Folliculo-stellate cells

present in the anterior lobe of the pituitary gland are

characterized by a starlike appearance with their cytoplasmic processes encircling

hormone-producing cells. They have the ability to make cell clusters or small follicles,

and they do not produce hormones. It transmits signals from the pars tuberalis to pars

distalis. These signals may regulate hormone release throughout the anterior lobe of

the pituitary gland.

Pars Intermedia.

The

pars intermedia

surrounds a series of small cystic cavities that

represent the residual lumen of Rathke’s pouch

fig.(2)

. The parenchymal cells of the

pars intermedia surround colloid-filled follicles. The cells lining these follicles appear

to be derived either from folliculo-stellate cells or various hormone-secreting cells,

pars intermedia have vesicles larger than those found in the pars distalis.. The pars

intermedia contains

basophils

and

chromophobes

(Fig. 2). Frequently, the basophils

and cystic cavities extend into the pars nervosa.

fig.(2):Gross & microhistological sections of pituitary gland

Pars Tuberalis.

The

pars tuberalis

is an extension of the anterior lobe along the stalklike

infundibulum

fig.(2)

It is a highly vascular region containing veins of the hypothalamohypophyseal

system. The parenchymal cells are arranged in small clusters or cords in

association with the blood vessels.

Nests of squamous cells and small follicles lined with cuboidal cells are

scattered in this region. These cells often show immunoreactivity for ACTH,

FSH, and LH.

Posterior Lobe of the Pituitary Gland

(Neurohypophysis)

The posterior lobe of the pituitary gland is an extension of the central

nervous system (CNS) that stores and releases secretory products from the

hypothalamus , consists of the

pars nervosa

, the

infundibulum& median

eminance

that connects it to the hypothalamus

fig.(2).

The pars nervosa, contains the unmyelinated axons and their nerve endings of

approximately 100,000

neurosecretory neurons

whose cell bodies lie in the

supraoptic nuclei

and

paraventricular nuclei

of the hypothalamus.

The axons form the

hypothalamohypophyseal

tract and are unique in two

respects:

First, they do not terminate on other neurons or target cells but end in close proximity

to the fenestrated capillary network of the pars nervosa.

Second, they contain secretory vesicles in all parts of the cells, i.e., the cell body,

axon, and axon terminal.



The posterior lobe of the pituitary gland is not an endocrine gland. Rather, it

is a storage site for neurosecretions of the neurons of the supraoptic and

paraventricular nuclei of the hypothalamus.

The nonmyelinated axons convey neurosecretory products to the pars

nervosa.

Other neurons from the hypothalamic nuclei also release their secretory

products into the fenestrated capillary network of the infundibulum, the

first capillary bed of the hypothalamohypophyseal portal system .

There are neurosecretory vesicles in the nerve endings of the pars

nervosa, aggregate to form Herring bodies that contain either

oxytocin

antidiuretic hormone

(

ADH

; also called

vasopressin).



Oxytocin promotes contraction of smooth muscle of the uterus and

myoepithelial cells of the breast.

The pituicyte is the only cell specific to the posterior lobe of the

pituitary gland , Because of their many processes and relationships to the

blood, the pituicyte serves a supporting role similar to that of astrocytes in

the rest of the CNS.

Histology 2016-2017
Department of Anatomy &Histology:

Dr.Rajaa Ali

***********************************************************

Endocrine system part II

Hypothalamus:

The hypothalamus regulates pituitary gland activity.

The

hypothalamus

is located in the middle of the base of the brain, and it encapsulates

the ventral portion of the third ventricle.

It coordinates most endocrine functions of the body and serves as one of the major

controlling centers of the autonomic nervous system.

Some of the functions that it regulates include blood pressure, body temperature, fluid

and electrolyte balance, body weight, and appetite.

The hypothalamus produces numerous neurosecretory products. In addition to

oxytocin

and

ADH

, hypothalamic neurons secrete polypeptides that promote and inhibit the

secretion and release of hormones from the anterior lobe of the pituitary gland.

Pineal Gland:

The

pineal gland

(pineal body, epiphysis cerebri) is an endocrine or neuroendocrine

gland that regulates daily body rhythm.

It develops from neuroectoderm of the posterior portion of the roof of the diencephalon

and remains attached to the brain by a short stalk, it is located at the posterior wall of

the third ventricle near the center of the brain.

The pineal gland is a flattened, pine cone–shaped structure, hence its name.

The pineal gland contains two types of parenchymal cells:

Pinealocytes and interstitial (glial) cells.

Pinealocytes

are the chief cells of the pineal gland. They are arranged in clumps or cords

within lobules formed by connective tissue septa that extend into the gland from the pia

mater that covers its surface.

The

interstitial (glial) cells

constitute about 5% of the cells in the gland. They have

staining and ultrastructural features that closely resemble those of astrocytes. In addition

to the two cell types, the human pineal gland is characterized by the presence of calcified

concretions, called

corpora arenacea

brain sand

(Fig. 1).

The human pineal gland relates light intensity and duration to endocrine

activity.The pineal gland is a photosensitive organ and an important timekeeper and

regulator of the day/night cycle (circadian rhythm).

Fig.(1)

•

Photomicrograph of human pineal gland. This higher-magnification photo micrograph

shows the characteristic concretions called brain sand or corpora arenacea.

Thyroid Gland:

 The thyroid gland, located in the cervical region anterior to the larynx, consists of

two lobes united by an isthmus (fig.3).

 It originates in early embryonic life from the foregut endoderm near the base of the

future tongue.

 Its function is to synthesize the thyroid hormones: thynoxine (tetra-iodothyronin. or

T4)and tri-iodothyronine (T3), which are important for growth, for cell

differentiation, and for the control of the basal metabolic rate and oxygen

consumption in cells throughout the body.

 Thyroid hormones affect protein, lipid, and carbohydrate metabolism .
 The thyroid is composed of epithelial structures called thyroid follicles (fig.2)..

Each follicle consists of a simple epithelium and a central lumen filled with a

gelatinous substance called colloid .



Thyroid is the only endocrine gland in which a large quantity of secretory product is
stored . Moreover the accumulations is outside the cells, in the colloid of the follicles.

 The thyroid gland is covered by a fibrous capsule from which septa extend into the

parenchyma , dividing it into lobules and carrying blood vessels, nerves, and

lymphatics.

 Follicles are densely packed together, separated from one another only by sparse

reticular connective tissue (fig.2).

 Follicular cells range in shape from squamous to low columnar and the follicles are

quite variable in diameter (fig.2).

 The size and cellular features of thyroid follicles vary with their functional activity.

Active glands have more follicles of low columnar epithelium ; glands with mostly
squamous follicular cells are considered hypoactive.

 Follicular epithelium contains two types of cells: follicular and parafollicular

cells.

 The parenchyma of the thyroid gland is composed of epithelium containing two types

of cells:

Follicular cells (principal cells)

are responsible for production of the thyroid

hormones T4 and T3, exhibit a slightly basophilic basal cytoplasm.

Parafollicular cells (C cells)

are located in the periphery of the follicular epithelium

and lie within the follicle basal lamina. These cells have no exposure to the follicle
lumen. They secrete

calcitonin

, pale staining and occur as solitary cells or small

clusters of cells.

Figure (2). Thyroid gland .( a): A low-power micrograph of thyroid gland shows the thin capsule(C

), from which septa( S) with the larger blood vessels ,lymphatics and nerves enter the gland
. ( b):T he lumen( L) of each follicle is filled with colloid. (c,d,e) parafollicular cells (C)
which secrete calcitonin , may be part of the follicular epithelium or present in singly or in
groups outside of follicles follicular cells (F).

Parathyroid Glands:

 The parathyroid glands are four small oval masses.
 They are located on the back of the thyroid gland (fig.3), one at each end of the

upper and lower poles, usually embedded in the larger glandʾs capsule.



The parathyroid glands are derived from the pharyngeal pouches: the superior

glands from the fourth pouch and the inferior glands from the third pouch.

 Each parathyroid gland is contained within a capsule which

sends septa into the gland, where they merge with reticular

fibers that support elongated cordlike clusters of secretory cells.

 With increasing age many secretory cells are replaced with

adipocytes,

Two

types

cells

are

present

parathyroid

glands: chief (or principal) cells and oxyphil cells (fig.4).

 The chief cells are small polygonal cells with round nuclei and

pale-staining

,slightly

acidophilic

cytoplasm

filled

with

irregularly shaped. These are secretory granules containing the

polypeptide parathyroid hormone (PTH).



Much smaller often clustered populations of oxyphil cells are sometime

present more commonly in older individuals (fig.4).

 These are much larger than the principal cells and are

characterized

acidophilic

cytoplasm

filled

with

abnormally

shaped mitochondria Some oxyphilc ells show low levels of

PTH

synthesis

,suggesting

these

cells

are

transitional

derivatives from chief cells.

 Parathyroid hormone targets osteoblasts.

Figure (3). Parathyroid glands

Figure (4). Parathyroid principal cells. (a): A small lobe of parathyroid gland surrounded by connective

tissue septa (s), shows mainly densely packed cords of small principal cells (P), also called
chief cells, oxyphil cells (O), ( b): The micrograph shows that principal cells are slightly
eosinophilic present in cords separated by capillaries( C)

Histology 2016-2017
Department of Anatomy &Histology:

Dr.Rajaa Ali

***********************************************************

Endocrine system part III

 The

adrenal (suprarenal) glands

secrete both steroid hormones and

catecholamines.

 They have a flattened triangular shape and are embedded in the perirenal fat at the

superior poles of the kidneys.

 The adrenal glands are covered with a thick connective tissue capsule from which

trabeculae extend into the parenchyma , carrying blood vessels and nerves.

 The secretory parenchymal tissue is organized into two distinct regions (Fig.1):



The

cortex

is the steroid-secreting portion. It lies beneath the capsule and

constitutes nearly 90% of the gland by weight.



The

medulla

is the catecholamine-secreting portion. It lies deep to the

cortex and forms the center of the gland.

Parenchymal cells of the cortex and medulla are of different embryologic origin.

 Embryologically, the cortical cells originate from

mesodermal mesenchyme

whereas the medulla originates from

neural crest

cells that migrate into the

developing gland .

 Although embryologically distinct, the two portions of the adrenal gland are

functionally related . The parenchymal cells of the adrenal cortex are controlled

in part by the anterior lobe of the pituitary gland and function in regulating

metabolism and maintaining normal electrolyte balance.

Blood Supply:

The

adrenal glands

are supplied with blood by the

superior, middle

, and

inferior suprarenal arteries

. These vessels branch before entering the capsule,

to produce many small arteries that penetrate the capsule. The vessels form a

system that consists of :



capsular capillaries

that supply the capsule.



fenestrated cortical sinusoidal capillaries

that supply the

cortex and then drain into the fenestrated modularly capillary

sinusoids.



medullary arterioles

that traverse the cortex, traveling within

the trabeculae , and bring arterial blood to the

medullary

capillary sinusoids

Lymphatic vessels

are present in the capsule and the connective tissue around the

larger blood vessels in the gland.

Cells of the Adrenal Medulla:

Chromaffin cells located in the adrenal medulla are innervated by

presynaptic sympathetic neurons.

The central portion of the adrenal gland, the

medulla

, is composed of a

parenchyma of large, pale-staining epithelioid cells called

chromaffin cells

(medullary cells)

, connective tissue, numerous sinusoidal blood capillaries, and

nerves.

The chromaffin cells are, in effect, modified neurons (Fig.1).

Numerous myelinated, presynaptic sympathetic nerve fibers pass directly to the

chromaffin cells of the medulla . When nerve impulses carried by the sympathetic

fibers reach the catecholamine-secreting chromaffin cells, they release their

secretory products.

Therefore, chromaffin cells are considered the equivalent of postsynaptic neurons.

However, they lack axonal processes.

Ganglion cells

are also present in the medulla. Their axons extend peripherally to

the parenchyma of the adrenal cortex to modulate its secretory activity and

innervate blood vessels.

Chromaffin cells of the adrenal medulla have a secretory function, the

catecholamines epinephrine and norepinephrine secreted by the chromaffin cells

are produced by different cell types:



One population of cells contains only large

dense core vesicles

These cells secrete norepinephrine.



The other population of cells

contains vesicles

that are smaller, more

homogeneous, and less dense. These cells secrete epinephrine.



Glucocorticoids secreted in the cortex induce the conversion of norepinephrine

to epinephrine in chromaffin cells. The catecholamines, in concert with the

glucocorticoids, prepare the body for the “fight-or-flight” response.

Zonation of the Adrenal Cortex:

The

adrenal cortex

is divided into three zones on the basis of the arrangement of

its cells (Fig.1):

•

Zona glomerulosa

, the narrow outer zone that constitutes up to 15% of the

cortical volume.

•

Zona fasciculata

, the thick middle zone that constitutes nearly 80% of the

cortical volume.

•

Zona reticularis

, the inner zone that constitutes only 5% to 7% of the cortical

volume but is thicker than the glomerulosa because of its more central location

Zona Glomerulosa:

The cells of the

zona glomerulosa

are arranged in closely packed ovoid clusters

and curved columns that are continuous with the cellular cords in the zona fasciculate ,

are relatively small and columnar or pyramidal. Their spherical nuclei appear closely

packed and stain densely.

The zona glomerulosa secretes aldosterone, which functions in the control of

blood pressure.

The cells of the zona glomerulosa secrete

mineralocorticoids

, compounds that

function in the regulation of sodium and potassium homeostasis and water balance. The

principal secretion,

aldosterone

, acts on the distal tubules of the nephron in the kidney,

the gastric mucosa, and the salivary and sweat glands to stimulate resorption of sodium

at these sites, as well as to stimulate excretion of potassium by the kidney.

Zona Fasciculata:

The cells of the

zona fasciculata

are large and polyhedral. They are arranged in

long straight cords, one or two cells thick, that are separated by sinusoidal capillaries.

The cells of the zona fasciculata have a lightly staining spherical nucleus. The principal

secretion of the zona fasciculata is glucocorticoids that regulate glucose and fatty acid

metabolism.

Zona Reticularis:

The zona reticularis produces glucocorticoids and androgens. The cells of the

zona reticularis

are noticeably smaller than those of the zona fasciculata, and

their nuclei are more deeply stained. They are arranged in anastomosing cords

separated by fenestrated capillaries. The cells have relatively few lipid droplets.

The cells in this zone are small because they have less cytoplasm than the cells in

the zona fasciculata; thus the nuclei appear more closely packed. They exhibit

features of steroid- secreting cells.

The principal secretions of the zona reticularis are weak androgens. The

principal secretion of the cells in the zona reticularis consists of weak

androgens

mostly

dehydroepiandrosterone (DHEA)

. The cells also secrete some

glucocorticoids, in much smaller amounts than those of the zona fasciculata.

Fig.(4): Adrenal gland A, arteries ; AT, adipose tissue ; BV, blood vessels ; Cap, capsule ; Cort,
cortex ; Med, medulla; ZF, zona fasciculate ; ZG, zona glomerulosa ; ZR, zona reticularis ;
arrows, connective tissue trabeculae ; dashed line, corticomedullary boundary.