Endocrine Organs

21Jan08

ENDOCRINE ORGANS

GENERAL CHARACTERISTICS:

þ ENDOCRINE SYSTEM <ES> provides intercellular communications thru the release of hormones.

þ hormones à secretory products of endocrine cells n organs.

þ EO à X excretory duct!

þ hormones à circulatory system à target cells <have receptors!>

þ microcirculatory bed of EO àFENESTRATED SINUSOIDAL CAPILLARIES.

þ ES à interrelated with NS <both act simultaneously on target cells n some neuron cells secrete hormones>

þ HYPOTHALAMUS :


à coordinates most of the endocrine functions of the body.


à one of controller in the centers of ANS.

þ organs of ES à gonads, liver, kidney, lung, heart, gastrointestinal system, etc.

HYPOPHYSIS

þ or PITUITARY GLAND à the master gland!

þ pear-shaped endocrine gland.

þ 0.5g in normal males n 1.5g in multi porous women <who gave birth at least 2x!>

þ short stalk or INFUNDIBULUM à
attaches hypophysis to HYPOTHALAMUS.

þ surrounded by CT capsule.

þ staining: [CT – blue] n [nucleus-pink]

þ has 2 MAIN FUNCTIONAL COMPONENTS:

adenohypophysis

neurohypophysis

þ ADENOHYPOPHYSIS à formed by GLANDULAR EPITHELIAL TISSUE. Derived from an invagination of the ectoderm of the embryonic oral cavity towards the brain à RATHKE’S POUCH

þ NEUROHYPOPHYSIS àconsist of neural secretory tissue. Derived from the down growth of NEUROEPIDERM of the flow of the third ventricle of the developing brain.

ADENOHYPOPHYSIS

þ hormones à
produced within adenohypophysis!

þ consist of 3 derivatives of Rathke’s pouch:

pars distalis
à anterior part of adenohypophysis. It comprises the bulb of the adenohypophysis n arises from a thickened anterior wall of the pouch.


pars intermedia
à thin remnant of the posterior wall of the pouch at the border with the pars neurosa.

pars tuberalis à develops from the lateral wall of the pouch near the infundibulum <basis of infundibulum!>

PARS DISTALIS

F the anterior lobe of hypophysis consist of cords of glandular cells that are irregularly arranged among large amount of sinusoids.

F the cells can be recognized n classified on the basis of staining prop. N also under structural n histophysiological featues.

F using mixtures of acidic n basic dyes, 3 types of acells are identified:

basophiles

acidophiles

chromophiles <leave almost colorless after staining>

[ BASOPHILES]

F according to their hormones à divided into:

ADRENOCORTICOTROPES <ACTH cells>

GONADOTROPES < FSH n LH cells>

THYROTROPES <TSH cells>

F
ADRENOCORTICOTROPES
à
produces hormone named ACTH. F: maintain the structures n stimulates the secretion of glucocorticoids n gonaded corticoids of adrenal cortex.

F
GONADOTROPES
à
stimulate the sex glands. F: produces luteinizing <LH> n follicle-stimulated hormones <FSH>.


þ
LH
à stimulates the secretion f sex hormones

in male n female.


þ
FSH
à stimulate the development of oocytes n

sperm cells.

F
THYROTROPES
à produces thyrostimulated hormones <TSH>.

[ACIDOPHILES]

F divided into SOMATOTROPES N LACTOTROPES <MAMMATROPES>.

F
SOMATOTROPES
à produce somatotropic, named as growth hormone <GH>

F GH à stimulates kidney n liver to produce hormone somatomeidin which stimulate the growth of long bones.

F
LACTOTROPES
à produce prolactin hormone <PR>. It could be also named LACTOGENIC HORMONE <LGH>.

F PR hormone promotes the development n milk secretion of mammary gland.

[CHROMOPHORES]

F some of chromophores are probably stem cells, that give rise to the secretory cells. Another one are actually transient forms of secretory cells.

PARS INTERMEDIA

þ characterized by no. of follicle-shaped cavities named PSEUDOFOLLICLES.

þ produces MELANOCYTES STIMULATED HORMONE <MSH> n ENDORPHINES <group of similar hormone>

þ MSH stimulates the pigmentation of the skin n mucosa.

þ ENDORPHINES à morphine related compounds.

Pars tuberalis

F highly vascular region containing GONADOTROPES.

NEUROHYPOPHYSIS

<HORMONES PRODUCED IN HYPOTHALAMUS !>

F the embryonic infundibulum gives rise to the neurohypophysis.

F contains PARS NERVOSA N INFUNDIBULUM.

F F of INFUNDIBULUM: conducting of neurosecretory nerve fibers n blood vessels btw the hypothalamus n hypophysis.

F
pars nervosa
à posterior lobe of hypophysis, contains the neurosecretory nerve fibes whose cell bodies lie in the supraoptic n PARAventricular nuclei of the hypothalamus.

F the nerve endings with the neurosecretory granules lie in close proximity to the fenestrated capillaries.

F the granules contain either OXYTOXINS or VASOPRESSINS. Those nerve fibers produce hormones into blood.

F OXYTOXINS à INDUCE UTERINE SMOOTH MUSCLE CONTRACTION + CONTRACTION OF MYOEPITHELIAL CELLS OF MAMMARY GLANDS .

F VASOPRESSINS <ANTIDIURETIC HORMONE> à

increase the reabsorption of water from the urine by kidney

increase blood pressure by promoting the contraction of smooth muscle n small arteries.

F neurohypophysis also contain pituicyes n some amount of fibroblast n mass cells/ typical CT.

F pituicytes à the only cell type that is specific to the neurohypophysis. It has some amount of branched processes.

F light astroglia à often have processes that terminate in the perivascular space / pericapillaries. These cells resemble astrocytes n play the supporting n tropic role for the neurosecretory elements.

BLOOD SUPPLY N HYPOTHALAMUS-HYPOPHYSIS RELATIONS

Î the supply is derived by 2 sets of vessels:

superior hypophysial arteries

inferior hypophysial arteries

Î the superior arteries supply the infundibulum stem n pars tuberalis. They give rise to the primary capillary plexus. These capillaries drain into hypophysial portal vein that give rise to the secondary capillary plexus in the pars distalis.

Superior hypophysial arteries à primary capillary plexus à hypophysial portal vein à secondary capillary plexus.

Î inferior arteries serve mostly the pars nervosa.

N/B: most of the anterior lobe of the hypophysis has no direct arterial supply.

Î specific neuro secretory cells of hypothalamus send their axons to the hypophysial infundibulum.

Î Their terminal product – hypophysial trophic hormone called regulating factor which enter hypophysial portal system, therefore the anterior lobe receives the blood from a primary capillary plexus where hypothalamic nerves release their neuro-endocrine secretion.

Î different regulating factors may act on the adenohypophysial cells à promote or inhibit their activity.

Î so hypothalamic regulating factors are divided into releasing n inhibitory factors.

Î most of the blood of hypophysis drains into systemic circulation. However some of the blood can flow the pars distalis to the pars nervosa and the blood from pars nervosacan flow toward the hypothalamus.

Î this short pathway provides feedback directly to the brain w/o making the full circuit of the systemic circulation.

Î the hormones of the adenohypophysis can be transported to the neurosecretory cells of the hypothalamus to regulate the secretion of hypothalamic regulating factor.

-pineal body/gland-

N in adult – small, tail-shaped projection of diencephalons, about 5-8mm height n 3-5mm in diameter.

N weight à 100-200mg, covered by pia mater.

N the parenchyma is separated by thin CT into the small lobules.

N the lobules consist of pineolocytes n interstitsial cells.

N pineolocytes àmost common parenchymal cells of the gland.

N they are arranged in clumps of cord.

N cytoplasm à
þ well dev. typical organelles n secretory inclusions.

N pineolocytes form processes à associated with blood capillaries to release the neurosecretions.

N interstitsial cells àare glial cells. They comprise about 5% of all cells in the gland. They have staining n other structural features that closely resemble astrocytes n are reminiscent of pituicytes of neurohypophysis.

F: supporting n trophic role for secretory cells.

N pineal gland à presence of calcified concretion called BRAIN RAND.

N concretion à consist of Ca2+ phosphate n carbonate. F: unknown!

N concretion à recognizable in childhood n ­ in no. with age.

N because they are opaque to x-rays, they serve as convenient mark in radiographic n computed tomography <CT > scanning studies.

N pineal gland à neuroendocrine gland but its function is not so clear!

N function of pinealocytes à produce MELATONINI

N MELATONIN

à regulate reproductive function by INHIBITING THE STEROIDOGENIC ACTIVITY IN THE GONADS!

à melanin metabolism

N in human, pineal activity is indicated by changes in plasma level of melatonin , rises during darkness n falls during light.

N clinically, tumors that destroy the pineal gland are associated with precautious puberty.

N it is related to some daily, seasonal n aging activities.

Extract of pineal gland contains nearly 40 neurotransmitters n neuroendocrine regulatory peptide à SEROTONIN, SOMATOSTATIN, THYROTROPHIN RELEASING FACTORS, etc.

THYROID

F 2 lobes connected by thin band of CT/ thyroid tissue called ISTHMUS.

F
þ CT capsule surrounding the gland which sends trabecules into the parenchyma to form irregular lobules.

F lobules à secretory follicles – constitute functional unit of the the gland.

F follicle à sphere-shaped formation.

F thyroid gland produces 3 hormones:

thyroxin / tetraiodothyronine <T4>

triiodothyronine <T3>

calcitonin à lowers blood Ca2+ level

F I n ii à regulate cell n tissue metabolism

F follicle à spherical structure lined by SIMPLE CUBOIDAL EPITHELIUM.

F its lumen is filled by gell-like mass à
colloids.

F 2 basic cell types are present in the follicular epithelium:

i. principle/ follicular cells

ii. parafollicular cells/ clear cells/ C-cells

F FOLLICULAR CELLS à secrete T4 n T3 hormones <ion containing hormones>

F PARAFOLLICULAR à secrete calcitonin

F the follicles are surrounded by network of blood capillaries/ FENESTRATED blood capillaries.

N/B: FENESTRATED à for all endocrine glands!

F principle component of colloids à THYROGLOBULIN <X a hormone!!!>. it is an INACTIVE storage form of the thyroid hormones.

F ACTIVE THYROID HORMONES, T4 n T3 are produced by the FOLLICULAR CELLS from the colloid in response to THYROID-STIMULATED HORMONE <TSH> of HYPOPHYSIS.

-Parathyroid hormone-

] paired, small, ovoid formation, a few mm in d.

] located within the thyroid capsule.

] composed od densely packed cords of cells separated by thin CT interlayers containing blood capillaries.

] parenchyma of the glands include no. of fenestrated blood capillaries.

] the parenchymal cells are divided into 2 epithelial cells:

principle cells <most numerous>

oxyphilic cells

PRINCIPLE CELLS

à F: secretion of the parathyroid hormone <PTH>.

à PTH à essential for life. Functions in REGULATION OF BLOOD ION LEVELS OF Ca2+ N PHOSPHATE.

à small polygonal cells, d – 7-10 µm n centrally located nuclei, slightly acidophilic cytoplasm – þ typical organelles n well-developed trophic n secretory inclusions/

OXYPHILIC CELLS

à X secretory role

à more rounded n larger than principle cells n have distinctly acidophilic cytoplasm.

à are found singly or in clusters n increase in no with age with their cytoplasm containing some amount of typical organelles n trophic inclusions but a no of mito.

à normally, no secretory granules are present!

Adrenal <suprarenal> gland

F covered by thick CT capsule from which very thin interlayers with blood vessels n nerves extend into the parenchyma.

F the secretory parenchymal tissue is organized in cortex n medulla.

F embryologically the cortical cells originated from MESODERMAL MESENCHYME. The medullary cells originate from neural crest cells that migrate into the developing gland.

FEATURES OF BLOOD SUPPLY:

FThe ADRENAL ARTERIES form 2 capillary networks in its parenchyma.

F the 1st network consist of cortical capillaries that supply the cortex n then drain into the medullary capillaries. It contains the cortical hormones.

F the 2nd medullary capillary networks is formed from the medullary arterials independently, it contains the fresh arterial blood.

ZONATION OF ADRENAL CORTEX:

F 3 zones < depends on the arrangement of the parenchymal cells>:

i. zona glomerulosa

ii. zona fasciculate

iii. zona reticularis

i. ZONA GLOMERULOSA:

à outer zone consist of closely-packed, ovoid aggregates of epithelial cells <secretpry!>.

à the cells secrete MINERAL CORTICOIDS – compounds that regulate water electrolyte metabolism. Principle secretion à aldosteron : control of blood pressure in association with certain hormones of the kidney n lung.

ii. ZONA FASCICULATA

à thick, middle zone.

à it s cells are arranged in LONG, STRAIGHT CORDS, one or two cells thick.

à they are separated by SINUSOIDAL CAPILLARIES!

à principle secretion: glucocorticoids à regulate glucose n fatty acids metabolism.

à this zone is under feedback control of the HYPOTHALAMIC HYPOPHYSEAL SYSTEM.

iii. ZONA RETICULARIS

à deepest zone, THINNER THAN FASCICULATA layer.

à each cells are arranged in anastomising cords separated by FENESTRATED CAPILLARIES.

à they appear irregularly disposed within the zone.

à this zone produces glucocorticoids n androgens.

à this zone is also under feedback control of the hypothalamic hypopheseal system.

ADRENAL MEDULLA

Î central portion of adrenal gland.

Î consist of large epitheloid cells <epithelial-like cells or named CHROMOFFIN CELLS>, CT, SINUSOIDAL CAPILLARIES, BLOOD SINUSES N NERVES.

Î the cells are modified post ganglionic neuronal cells that have a SECRETORY FUNCTION.

Î the parenchymal cells of medulla include:

LIGHT CELLS à produce EPINEPHRINE n are called EPINEPHROCYTES

DARK CELLS à produce NOREPINEPHRINE n are called NOREPINEPHROCYTES

Î The GLUCOCORTICOIDS secreted in the cortex induce the conversion of NOREPINEPHRINE n APENEPHRINE in medullary cells. Thus, the distribution of light n dark cells within medulla is determined by its DUAL blood supply!

Î both hormones are released in the medulla. They establish conditions for max. their functions:

i. utilization of energy n thus max. physical effort.

ii. stimulate releasing of glucose into blood stream n

mobilization of free fatty acids from adipose

tissue.

iii. cause in blood pressure n blood circulation n

activity of the heart, lung n skeletal muscles.

Î the releasing of medullary hormones in stimulated by the PRE-GANGLIONIC SYMPATHETHIC AXONS that synapse with each medullary cells.




One Response to “Endocrine Organs”

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