Histology: Endocrine System

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endocrine glands

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-ductless
-parenchymatous cells usually large epithelial in close contact with dense networks of capillaries
- secrete products (hormones) directly into intercellular or perivascular CT spaces whereby they reach the circulatory system
-hormones regulate fx of specific tissues or organs: target organs

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parts of hypophysis/ pituitary gland

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1. adenohypophysis
2. neurohypophysis

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adenohypophysis

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1. pars distalis
2. pars intermedia
3. pars tuberalis

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acidophils of pars distalis of adenohypophysis

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1. somatotrophs: production of somatotrophin or growth hormone
2. lactotrophs or prolactin cells: induces the secretion of mammary gland (lactogenic activity)

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basophils of pars distalis (of adenohypophysis)

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1. thyrotrophs: TSH, induces thyroid gland to release thyroxine
2. gonadotrophins: FSH and LH
3. corticotrophs: adrenocorticotropic hormone (ACTH), acts on adrenal cortex

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chromophobes

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- most chromophobic cells considered to be temporarily resting degranulated chromophils

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pars intermedia of adenohypophysis

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-closely associated with the neurohypophysis
-completely separated from pars distalis by the hypophyseal cleft
- melanotropes

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melanotropes

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- of pars intermedia of adenohypophysis
- most abundant cells
- may surround colloid- filled follicles
- produce melanocyte- stimulating hormone (MSH)

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pars tuberalis of adenohypophysis

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- clusters of epithelial cells often forming small follicles
- cells morphological characteristics of peptide- secreting cells that are subject to seasonal variation
-believed to play a role in seasonal repro of some animals
- few gonadotrophs and thyrotrophs are present

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supraoptic and paraventricular nuclei of Hypothalamo-Neurohyposphyseal system

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- make up hypothalamic component
- characterized by large neuronal bodies containing neurosecretory granules which produce:
1. oxytocin
2. vasopressin/ antidiuretic hormone

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axons of the Hypothalamo-Neurohypophyseal tract

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-transport oxytocin and ADH to the neurohypophysis

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Herring bodies of Hypothalamo-Neurohypophyseal system

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-enlarged axon terminals of the neural lobe that store and release neurosecretory granules in the perivascular space of sinusoidal capillaries

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pituicytes of Neurohypophysis

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modified astrocytes which from an extensive network around axons and capillaries
- microglial cells also present in neurohypophysis

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Thyroid capsule

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- dense irregular CT
-trabecula extend into the parenchyma, dividing it into lobules

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thyroid lobules

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1. thyroid follicles: filled with gel like substance (colloid), lined by follicular cells
2. parafollicular cells
3. dense networks of sinusoidal capillaries

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thyroid stimulated

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- cuboidal or low columnar
- colloid dissolved, may be at luminal surface
- golgi on apical surface
- secretes thyroid hormone

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thyroid resting

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- low cuboidal
- colloid appears very dense

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parafollicular cells of thyroid

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- usually single cells in basal lamina of follicle
- dogs: sometimes groups outside follicles
- light cytoplasm
- abundant golgi
- vesicles: secrete calcitonin which lowers B Ca by supressing bone resorption

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parathyroid gland gen

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- dense irregular CT capsule
- parenchyma: clusters of cords, highly vascular
- parathormone: maintains Ca and P B levels

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Cells of parathyroid gland

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1. light: principle, inactive
2. dark: principle, active
3. oxyphillic: horses and ruminants, few, large, light, unknown fx
4. transitional: structural b/w principal and oxyphillic

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adrenal gland

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- thin CT capsule
- parenchyma: outer cortex, inner medulla

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zones of adrenal cortex

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1. glomerulosa
2. fasciculata
3. reticularis

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zona glomerulosa of adrenal cortex

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- steroid secreting: produce mineralcorticoids (aldosterone) which maintains Ca and K in ECF
1. ruminant: irregular clusters of cords of cells
2. horse, carnivore, pig: zona arcuata, cells arranged in arcs

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zona fasciculata of adrenal cortex

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- radially arranged cords
- cuboidal or columnar
- large number of lipid droplets

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zona reticularis of adrenal cortex

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-irregular network of anastamosing cords
- cells similar to zona fasiculata

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zona fasiculata and reticularis of adrenal cortex

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- involved in producing glucocorticoids: protein, fat and carb metabolism

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adrenal medulla

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- irregular cords and clusters separated by dense networks of sinusoidal capillaries
- chromaffin cells sometimes with PS ganglionic cells among them

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chromaffin cells of adrenal medula

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1. stronger chromaffin reaction: secretes NorEpi
2. less affinity to chromium salt: secrete epinephrine

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pancreatic islets

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- irregular anastamosing cords of 5 cell types:
1. A
2. B
3. C
4. D
5. small granulated

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A cells of pancreatic islets

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- 4-30%
- secretory granules insoluble in -OH
- secrete glucagon: increases B sugar
- nucleus indented or lobulated
- Mason's T and Gomori's A-F: brilliant red

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B cells of pancreatic islets

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- secretory granules soluble in -OH
- produce insulin: reduces B sugar
- Mallory's T: orange
- Gomori's A-F: deep purple

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C cells of pancreatic islets

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-immature precursor cells to other islet cells
- nongranulated or sparsely granulated

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D cells of pancreatic islets

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- rare
- produce somatostatin: inhibits secretion of insulin and glucagon

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small granulated cells of pancreatic islets

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- heterogeneous
- precursors to a variety of cells which produce gastro-entero-pancreatic hormones that inhibit intestinal motility and bile secretion