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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