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ENDOCRINE SYSTEM

FUNCTION:

1. integrates & coordinates physiologic functions of the body

2. serves these functions in conjunction with the nervous system

MECHANISM OF ACTION:

1. secrete chemical agents called hormones

o blood stream ---> distant target organs

2. organs have specific surface receptors which bind the hormone & induce an intracellular response

3. use of feedback mechanism o gland (A) secretes hormone (A) & acts on target organ --> target organ

secretes hormone (B)

when hormone (B) reaches its optimum level, it acts on endocrine gland (A) secreting the hormone (A). Endocrine gland (A) will now cease to secrete hormone (A) until such time that hormone (B) goes down to low levels

ENDOCRINE: HYPOPHYSIS

LOCATION:

1. at the base of the brain

2. occupies the deep recess of the sphenoid bone, the sella turcica

SUBDIVISIONS: a. neurohypophysis (posterior lobe) b. adenohypophysis

A. Neurohypophysis: o develops as a downward growth from the diencephalon

divisions: 1. median eminence - a downward extension of the hypothalamus 2. infundibular stem 3. infundibular process - forms the neural lobe of the hypophysis

B. Adenohypophysis: o originates as a dorsal evagination from the roof of the embryonic pharynx

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divisions: 1. pars distalis (anterior lobe) 2. pars tuberalis (pars infundibularis)

o envelops the infundibular stem & median eminence of the neurohypophysis (infundibular stem + pars tuberalis = infundibular or pituitary stalk

3. pars intermedia o a rudiment in the human adultendocrine: hypophysis

C. Blood vessels & nerves: HYPOPHYSEOPORTAL SYSTEM

o neurohormones (releasing factors): o produced by neurons in median eminence, o carried to adenohypophysis thru the system, o effecting secretory activity of cells in the gland

ENDOCRINE: HYPOPHYSIS - ADENOHYPOPHYSIS

o vasculature of the pituitary gland the anterior pituitary receives the majority of its blood supply not from the arteries but from

the portal system the portal system forms a vital link between the hypothalamus & the pituitary gland

A. Pars distalis: histology o composed of irregular cords or clusters of glandular cells o scanty stroma

cells: classification (before) a. Chromophilic cells 1. Acidophilic cells – stain red/pink with eosin 2. Basophilic cells – stain blue with Mallory’s trichrome stain b. Chromophobes

B. Cytologic smear of anterior lobe: A. Acidophiles B. basophils C. Chromophobes

anterior lobe:

HE stain: o chromophobic o adicophilic o basophilic

PAS-orange G stains o acidophils orange o basophils blue o chromophobes gray or lacking staining

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Cell classification (current) - refers to the cell types of the anterior pituitary that identify the target organs stimulated by the hormone produced

a. Thyrotrophs – cells secreting thyroid stimulating hormone b. Gonadotrophs – cells secreting gonadotrophic hormones c. Corticotrophs – cells secreting adrenocorticotrophic hormones

Acidophils

o most numerous in the posterolateral portion of the anterior lobe o relatively small rounded cells with developed golgi complex o granules are larger

Type of cells a. Somatotrophs

o most abundant cell type in the anterior lobe o secrete growth hormone (somatotropin) o secretion stimulated by growth-hormone-releasing hormone (GHRH) by the

hypothalamus o secretion suppressed by another hormone, somatostatin o secretion has generalized effect on cells throughout the body o growth effect is mediated by protein called somatomedins, which is synthesized

by the liver in response to growth hormone

Adenohypophysis: o stained for GH showing SOMATOTROPHS medium-sized ovoid cells with abundant cytoplasm,

comprising 50% of anterior lobe cells presence of numerous secretory granules give

strong staining reaction

b. mammotrophs (lactotrophs) o distributed singly in the anterior lobe o small cells with ovoid or polygonal shape o with large dense granules o secrete hormone prolactin which promotes mammary gland development during pregnancy o stimulated by suckling

Adenohypophysis stained for prolactin: LACTOTROPHS (MAMMOTROPHS)

comprise about 15-20% of anterior lobe cells Majority are sparsely granulated angular cells showing paranuclear staining

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Basophils cell types:

a. Thyrotrophs o located in the anterimedial portion of anterior lobe o makes up 15% of the cells o deeply situated in the cords of parenchymal cells and usually in contact with sinusoids

secrete thyroid-stimulating hormone (TSH), also called thyrotropin, which acts by

binding to specific receptors of thyroid follicles, stimulating the secretion of thyroid hormone, thyroxine and triiodothyronine

Stimulated by thyrotrophin-releasing hormone secreted by the hypothalamus Anterior pituitary stained for THYROTROPHS:

medium-sized angulated cells with elongated processes comprise about 5% of anterior lobe secretory cells

b. Corticotrophs o round or ovoid cells, widely distributed in the anteromedial region of the hypothalamus o secrete adrenocorticotrophin (ACTH), also called corticotrophin, which acts on receptors of

cells of adrenal cortex to produce hormone cortisol o secretion stimulated by corticotrophin-releasing hormone (CRH) produced in the hypothalamus

Adenohypophysis stained for ACTH: CORTICOTROPHS

Comprise about 15-20% of anterior lobe cells mainly located in the mucoid wedge ovoid-polyhedral with clustering of cells, a characteristic feature

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c. Gonadotrophs o round cells, situated close to sinusoids o secrete follicle-stimulating hormone (FSH) and luteinizing

hormone (LH) o rising levels of FSH stimulates development of follicles in

ovary (also plays in the initiation of spermatogenesis) o midcycle surge of LH production triggers ovulation

Anterior pituitary stained for FSH: GONADOTROPHS (FSH & LH) > paucity of strongly staining cells because comprises only 10% of secretory cells

Chromophobes > small cells in the interior of the cords of pars distalis > have less cytoplasm > acutally partially degranulated acidophils or basophils

C. pars intermedia: histology o no longer identifiable as distinct layer in human adults o secrete melanocyte stimulating hormone (MSH) o MSH act on the melanocytes of the skin

D. Pars tuberalis: histology o most highly vascularized subdivision of the hypophysis o epithelial cells arranged in cords occupy the interstices between longitudinally oriented blood

vessels o no specific hormone identified o no function known

ENDOCRINE: NEUROPHYPOHYSIS

1. NEURAL LOBE o contains pituicytes o Herring bodies present –

aggregations of deeply staining material of varying sizes found in dilatations of the axons throughout the neural lobe

o hypothalamohypophyseal tract – unmyelinated axons of neurons in the supraoptic nucleus & paraventricular nucleus of

the hypothalamus

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2. PITUITARY GLAND: POSTERIOR LOBE fibrillary texture results from large number of pituicytes, glial cells indigenous to posterior lobe axonal fibers emanating from hypothalamic nuclei

stained positively with glial fibrillary acid protein (GFAP)

3. HORMONES: a. Oxytocin (OT)

acts on the myometrium of pregnant uterus

stimulates contraction of the uterine smooth muscle b. Antidiuretic hormone (ADH)

acts on collecting ducts of the kidneys by increasing the permeability of the apical plasma membrane to water

also involved in the control of blood pressure ENDOCRINE: THYROID location: below the larynx in the anterior neck parts: two lateral lobes & a middle isthmus (a pyramidal lobe may be present, an extension of isthmus) function: under the control of the hypophyseal hormone, thyroid-stimulating hormone hormone: essential in normal growth & development

stored extracellularly in lumen of follicles with colloid

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histology: thyrocytes are cuboidal or squamous or columnar, depending on glandular activity, arranged in follicles with colloid in the lumen

types of cells: a. principal cells

> secrete thyroxin and triiodothyronine

b. Parafollicular cells

occur singly or in groups between bases of principal cells

secrete calcitonin which suppresses bone resorption when blood calcium level is high

C-cells stained with anti-calcitonin antibody

location of cells in interfollicular areas

also acts on kidneys to increase secretion of calcium in urine

size 2-3 x larger than principal cells

pale cytoplasm, round or ovoid nucleus, indented on one side

Disturbances:

1. Cretinism > deficiency in thyroid hormone during infancy leading to mental retardation & stunted growth

2. Myxedema > deficiency in adults giving sallow puffy appearance of the face, dry & sparse hair, lethargy and slow

cerebration 3. Grave’s disease

> weight loss, nervousness, fatigue & rapid heart rate > results from prolonges stimulation of hormone production ENDOCRINE: PARATHYROID Origin:third and fourth branchial pouches of the embryo Function:

Produces hormones which act of the kidneys, intestine and bones to maintain the necessary concentration of calcium

Maintains the concentration of calcium ions in the body fluids within the narrow limits of 8.5 to 10.5 mg/100 ml.

gross: four small rounded or ovoid bodies adhering to the posterior surface of the thyroid gland enclosed with thin capsule from which trabeculae extend inward

histology:

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Parenchyma consists of anastomosing cords and clusters of epithelial cells supproted bya delicate network of reticular fibers

shows only sheets of chief cells with no fat cells

Types of cells:

a. chief cells 5-8 um in diameter, pale, eosinophilic cytoplasm produces hormone preproparathyroid hormone,

synthesized in ribosomes into proparathyroid hormone and in the Golgi complex into parathyroid hormone

hormone present in the cell surface for subsequent exocytosis

mixture of chief cells and oxyphilic cells oxyphilic cells show eosinophilic cytoplasm stain shows abundance of chromogranin in the chief cells

oxyphil cells are free of chromogranin granules (right lower corner)

b. Oxyphil cells

6-10 um in diameter, stain more deeply eosin

relatively few in number and arranged singly or in small groups

c. Transitional cells

features in between chief and oxyphil cells

nucleus more deeply staining and smaller Pathology: primary hyperparathyroidism

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signs & symptoms:

high blood calcium level

low blood phosphate

rarefaction of the bones

tendency to develop kidney stones

deposition of calcium in other tissues

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ENDOCRINE: ADRENALS function: > maintain the constancy of the internal environment of the organism gross: > flat, triangular, paired organs with light yellow cortex and thin gray medulla > origin and parts:

a. cortex – 80-90% of the gland – mesoderm b. medulla - 10-20% of the gland – neural crest

A. adrenal cortex: zones 1. zona granulosa

thin layer just beneath the capsule made up of columnar epithelial cells forming closely packed arcades acidophilic cytoplasm, heterochromatic nuclei with one or two prominent nucleoli lipid droplets present in cytoplasm\

produces mineralocorticoid (aldosterone) which controls body fluid volume by increasing the reabsorption of sodium in kidneys

acts on the distal tubules of the kidneys increasing the excretion of potassium & their resorption of sodium

stimulated by hormone angiotensin-II secreted by the kidney adrenal glands: cortex layers

1. zona glomerulosa 2. zona fasciculata 3. zona reticularis

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1. zona glomerulosa:

narrow inconstant band of cortex situated immediately beneath the capsule

cells are well outlined; aggregates into small clusters

endocrine: adrenals

2. zona fasciculata made up of pale-staining polyhedral cells arranged in long columns

oriented radially in relation to the medulla columns are one or two cells thick, separated from one another by

capillaries acidophilic cytoplasm with vacuolated appearance, promient

nucleolus secretes glucocorticoid (cortisol), which affects

metabolism of carbohydrates, proteins and fat has anti-inflammatory effect controlled by adrenocorticotrophic hormone

(ACTH) secreted by the pituitary

located below zona glomerulosa

shows two-cell wide columns of cells with clear cytoplasm

cells are large with distinct cell membranes; nuclei vesicular

3. zona reticularis arranged in three-dimensional network of anastomosing cell cords smaller cells & stain more deeply because cytoplasm contain less lipid droplets produces androgens (dehydroepiandrosterone) cells show acidophilic granular cytoplasm with no distinct borders & pattern

b. adrenal medulla

composed of large epithelioid cells arranged in rounded clusters or short cords that are in intimate relation to capillaries & venules

cytoplasm filled with small brown granules

products are norepinephrine and epinephrine

secretion in response to stimulation by preganglionic fibers from the splancnic nerves

increaseHR & BP

mobilize glucose & fatty acids as energy sources in stressful emergency situations

cells called pheochromocytes are arranged in clusters

nuclear size and shape vary

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ENDOCRINE: PINEAL GLAND

= epihysis cerebri gross:

a small organ in the middle of the brain, projecting from the roof of the diencephalon histology: invested by the pia mater the parenchyma consists of pale-staining epithelioid cells called pinealocytes nucleus is spherical or indented on one side with basophilic cytoplasm

types of cells:

a. pinealocytes b. interstitial cells

- found among pinealocytes & in greater number is the stalk - comparable to the neuroglial cells of the brain pineal gland or epiphysis: shows richly glandular architecture

corpora aranacea “brain sand” = bodies consisting of calcium phosphates & carbonates in an organic matrix, deposited in concentric layers > increase in size as one ages pineal gland or epiphysis:

corpora aranacea or brain sand increases with age

pinealocytes have synaptic ribbons of dense rod or lamella, in addition to common organelles

melatonin is the principal hormone which is released as it is synthesized; an indolamine synthesized from tryptophan

histophysiology: its biosynthesic activity exhibits a diurnal rhythmycity related to the periods of light & darkness

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stimulation dependent on its innervation & is therefore a neuroendocrine transducer synthetic activity is inhibited by light and favored by darkness

ENDOCRINE: ISLETS OF LANGERHANS

endocrine tissue of the pancreas, scattered through out the gland, more numerous in the tail

demarcated from the surrounding acinar cells by thin reticular fibers types of cells:

a. alpha cells (a-cells) - located at the periphery - secrete glucagon, in response to a fall in blood glucose which acts on hepatocytes to increase degradation of glycogen to release glucose into the blood Islet cells:

> glucagon secreting cells are predominantly peripheral in the islet > may also be present outside the islet

b. beta cells (B-cells) - the predominant cells type located in the center, making up 70% of its mass - secrete insulin, in response to high blood glucose level, binds on cell membrane & facilitate entry of

glucose into the cell Islet cells > stained for insulin

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c. Delta cells (D-cells) - secrete somatostatin, which is stimulated by the postprandial increase in blood glucose, amino

acides & fatty acids; inhibits the release of both insulin & glucagon; distant effect is to decrease or slow down the uptaked of nutrients from the ingested food & make the products available for long periods of time

somatostatin cells are rare >may present markedly elongated shape

d. F cells (PP cells)

> widely scattered, very few in number > secrete pancreatic polypeptide whose action is still unknown All secretory granules are released by exocytosis into the extracellular space Islet cells: pancreatic polypeptide cells (PP) > medium sized cells, lightly eosinophilic cytoplasm

Pathology: diabetes mellitus - in adult, hyalinization of the islets of Langerhans