14.0, 15.0 ENDOCRINE SYSTEM

Endocrine I: Hypothalamus, pituitary and pineal

Upon completion of this lecture, students will be able to:

a)Define and use properly the following words:Endocrine organ, Ductless glands , Highly vascular, Hypophysis cerebri (pituitary), Adenohypophysis, pars distalis, pars tuberalis, pars intermedia, Neurohypophysis, pars nervosa (neural lobe) infundibulum, infundibular stalk, median eminence, Adenohypophysis, Pars distalis, Chromophobe, Acidophil, somatotropes (alpha), lactotopes (epsilon), Basophil, thyrotropes (beta), gonadotropes (delta), corticotropes, Pars tuberalis, Pars intermedia, Melanotropes, Hypothalmo-adenohypophysial system, Neuroendocrine cells, Hypophysial portal system, Neurohypophysis, Pituicytes, Axons unmyelinated, Herring bodies, Hypothalamic nuclei, Supraoptic, Paraventricular, Neurophysins, Epiphysis cerebri (pineal), Pinealocytes, Astrocytes, Corpora arenacea.

b)Describe and associate basic structure/function for the following: all structures listed above.

c)Identify by microscopy: Acidophil, Adenohypophysis, Basophil, Chromophobe, Corpora arenacea, Corticotropes, Ductless glands, Herring bodies, hypophysial portal system, Infundibular stalk, infundibulum, Median eminence, Neural lobe, Neurohypohysis, pars distalis, pars intermedia, pars nervosa, pars tuberalis, Pituitary.

Endocrine II: Thyroid, parathyroid, adrenal

Upon completion of this lecture, students will be able to:

a)Define and use properly the following words:Thyroid gland, Colloid, Follicular lining cells (chief cells), Parafollicular cells (C cells), Transport iodine, Thyroglobulin, Calcitonin, Parathyroid gland, Principal cells (chief cells), Oxyphil cell, Parathyroid hormone, Suprarenal gland (adrenal gland), Capsule, Stroma, Adrenal Cortex , Zona glomerulosa or Zona arcuata, Zona fasiculata, Zona reticularis, Mineralocorticoids, Glucocorticoids, Androgen, Estrogen , Adrenal medulla, Chromaffin cells, Ganglion cells.

b)Describe and associate basic structure/function for the following: all structures listed above.

c)Identify by microscopy: Adrenal cortex, Adrenal gland (suprarenal), Adrenal medulla, capsule, Chief cells, chromaffin cells, Colloid, Cords, cortex, follicle, Follicular lining cells (chief cells), Ganglion cells, Medulla, Medullary endocrine cells (chromaffin cells), Oxyphil cell, Parafollicular cell (C-cells), Parathyroid gland, Polyhedral, Principal cells (chief cells), Thyroid, Zona fasiculata, zona fasiculata, zona glomerulosa, Zona arcuata, zona intermedia, Zona reticularis.

Endocrine System

I. General characteristics of endocrine organs

  1. Ductless glands
  2. formed by invagination of epithelium which separates and sinks below the surface
  3. an exocrine glands maintains connection with the surface through a duct system
  1. Highly vascular
  2. secretions are released into and transported by the vascular system
  1. Distinct organ, part of an organ, or a single cell
  2. ex. hypophysis cerebri (pituitary) or pancreatic islets
  1. Cell arrangement
  2. single cell
  3. cluster
  4. cord
  5. follicle
  1. Produce and sometimes store hormones

II. Hypophysis cerebri (Pituitary)

  1. Organization
  2. Adenohypophysis
  3. pars distalis
  4. pars tuberalis
  5. pars intermedia
  6. derived from oral ectoderm
  1. Neurohypophysis
  2. pars nervosa (neural lobe) infundibulum
  3. infundibular stalk
  4. median eminence
  5. derived from neural ectoderm
  1. Adenohypophysis
  2. Pars distalis
  3. Chromophobe
  4. 50%
  5. does not stain well
  6. not secretory
  1. Acidophil
  2. 40%
  3. somatotropes (alpha) - somatotropin
  4. lactotopes (epsilon) - prolactin > mammary gland, crop
  1. Basophil
  2. 10%
  3. thyrotropes (beta) - thyrotropin > thyroid follicles
  4. gonadotropes (delta) - LH and FSH > testes and ovaries
  5. corticotropes - ACTH, beta-lipotropin
  1. Pars tuberalis
  2. function uncertain
  3. weakly basophilic cuboidal cells
  1. Pars intermedia
  2. melanotropes- melanocyte stim. hormone & ACTH
  3. target: skin and adrenal
  1. Hypothalmo-adenohypophysial system
  2. neuroendocrine cells of the hypothalamus
  3. factors from these cells stimulate or inhibit the release of pituitary hormones
  4. hypophysial portal system
  5. rostral hypophyseal aa. forms capillary bed in upper pit. stalk (median eminence) and hypothalamus
  6. pick up releasing factors from hypothalamic neurons and carry to pars distalis through portal venules
  7. form second capillary bed in pars distalis where factors are released
  8. caudal hypophyseal a. - single capillary bed in pars nervosa; not a portal system
  1. Neurohypophysis

-- ventral evagination of nervous tissue of the hypothalamus

  1. Regions
  2. Median eminence
  3. Infundibular stalk
  4. Neural lobe (Pars nervosa)
  5. Cells and cell processes
  6. Pituicytes
  7. modified astrocytes; form framework among axons and capillaries
  8. Axons
  9. unmyelinated
  10. contain neurosecretory granules (Herring bodies)
  11. storage form of the hormone secretions of the neuron in the hypothalamic nuclei
  12. Hypothalamohypophyseal tract
  13. hypothalamic nuclei - where neuron cell bodies are located
  14. Supraoptic
  15. vasopressin (ADH)
  16. target: kidney
  17. Paraventricular
  18. oxytocin
  19. target: repro organs, milk let down, stimulate myometrium
  20. Neurophysins
  21. carrier proteins that transport hormones
  22. axons which extend into the neural lobe
  23. release stored hormones into endocrine capillaries

III. Epiphysis cerebri (Pineal)

-- light sensitive organ responsible for the production of melatonin and serotonin

-- role in sexual maturation, circadian rhythms, thermoregulation

A.Capsule

1.is pia mater

B.Pinealocytes

1.large cells with round open nucleus

C.Astrocytes

1.interdigitated between pinealocytes and vessels

D.Corpora arenacea

1.intercellular Ca deposits

2.associated with increasing age but not decreased glandular function

IV. Thyroid

  1. Structure
  2. Capsule
  3. dense irregular ct
  4. Parenchymal arrangement
  5. cells arranged in follicles
  6. hollow sphere of variable size
  7. surrounded by dense capillary network
  8. Colloid
  9. gel-like material in center of follicle
  10. storage product of follicular epithelium
  11. acidophilic
  12. vacuolation at the periphery indicates active follicle
  13. Cells
  14. Follicular lining cells (chief cells)
  15. vary from squamous to columnar
  16. acidophilic with a basal nucleus and microvilli
  1. Parafollicular cells (light cells, C cells)
  2. outside follicular epithelium; do not reach lumen
  3. pale staining
  4. secrete calcitonin
  1. Synthesis and storage of thyroid hormone
  2. collect and transport iodine
  3. uptake of circulating iodide
  4. iodide concentrated and oxidized to iodine
  1. synthesize thyroglobulin
  2. polypeptides synthesized and glycosylated to form thyroglobulin
  3. thyroglobulin transported into the colloid
  1. tyrosine residues of thyroglobulin iodinated in colloid
  2. stored thyroglobulin contains mono- and di-iodotyrosine which are the building blocks of T 3 and T4
  1. Mobilization of thyroid hormone
  2. Regulation
  3. regulated by TSH
  1. Changes in the morphology of the follicle
  2. lg. apical pseudopods form> increased intracellular colloid droplets and phagolysosomes
  3. colloid becomes foamy at edge
  1. Secretion of T 3 (triiodothyronine) and T 4 (tetraiodothyronine, thyroxine)
  2. Thyroglobulin phagocytosed
  3. Secondary lysosome formed
  4. T 3 and T 4 released across cell membrane
  1. Effects of thyroid hormone
  2. involves energy metabolism, growth and differentiation
  1. Calcitonin
  2. Secretion
  3. parafollicular cells produce
  4. released in response to high blood Ca; causes blood Ca decrease
  1. Action
  2. inhibits osteoclasts and stimulates osteoblasts
  3. inhibits Ca absorption from gut

V.Parathyroid gland

-- external - cranial pole of thyroid; 3rd pharyngeal pouch

-- internal (not present in birds, pigs) - caudal pole of thyroid-embedded within; 4th pharyngeal pouch

  1. Structure
  2. Capsule
  3. dense irregular connective tissue
  4. Parenchymal arrangement
  5. cords or clusters of cells
  6. Cells
  7. Principal cells (chief cells)
  8. lt and dk cells are different physiol. state of same cell
  9. lt - inactive
  10. most common cell type
  11. large acidophlic cell with light cytoplasm;
  12. few organelles
  13. dk - active
  14. dark cytoplasm with many active organelles
  15. Oxyphil cell
  16. in ox, horse, man
  17. lg cells with pale acidophilic cytoplasm
  18. derived from chief cell
  19. function unknown
  1. Transitional cell - characteristics of both cell types
  1. Parathyroid hormone
  2. produced by principal cells
  3. increases blood calcium, absorption of ca from intestine, resorption from bones
  4. decreases Ca loss from urine

VI.Suprarenal gland (Adrenal gland)

  1. Structure
  2. Capsule
  3. dense fibrous ct.
  4. Stroma
  5. ct trabecula and fine stroma
  1. Blood supply
  2. capsular arteries branch to supply cortex and then empty into medulla
  3. medullary arterioles supply the medulla directly
  4. a fresh blood supply plus one rich in adrenocortisteroids to stimulate adrenaline production in the medulla
  1. Cortex
  2. Cellular arrangement
  3. parenchyma in cords
  4. Zones
  5. Zona glomerulosa or Zona arcuata - cuboidal to columnar cells arranged in glomeruli or curved cords
  6. Zona fasiculata - cuboidal cells with foamy cytoplasm; lg amount of lipids
  7. Zona reticularis - less foamy than fasiculata
  1. TEM
  2. prominent SER related to steroid synthesis
  1. Function of adrenal cortex
  2. Mineralocorticoids
  3. aldosterone-control Na retention in the kidney (DCT and CD)
  4. z. glomerulosa
  5. Glucocorticoid production
  6. cortisol and corticosterone-gluconeogenesis; release of fatty acids; anti-inflammatory
  7. z. fasciculata and some from z. reticularis
  8. Androgen and estrogen
  9. zona reticularis and some in zona fasiculata
  10. Regulation
  11. zona glomerulosa regulated by renin-angiotensin system
  12. zona fasiculata and zona reticularis by ACTH of pit. And CRH of hypothalamus
  1. Adrenal medulla
  2. Cells
  3. Medullary endocrine cells (chromaffin cells)
  4. modified postganglionic sympathetic neurons
  5. contain membrane-bounded granules
  6. produce epinephrine and norepinephrine
  1. Ganglion cells
  2. sympathetic ganglion
  3. randomly scattered; difficult to find
  4. synapse with glandular cells and control their secretion

VII. Endocrine pancreas

  1. Pancreatic islets (Islets of Langerhans)

---randomly scattered throughout the organ

---clusters of cells with extensive vascular supply

---connected by gap jcts. at EM level

  1. A cell (alpha)
  2. secrete glucagons
  3. elevates blood glucose
  4. dense granules with halo TEM
  1. B cell (beta)
  2. secrete insulin
  3. decreases blood glucose
  4. halos around less dense granule with TEM; granules may be crystalloid in man, dog, cat
  1. D cells (delta)
  2. produce somatostatin
  3. somatostatin release of somatotrophin by pituitary; inhibits release of insulin and glucagons
  1. Other cells of the pancreatic islets
  2. pancreatic polypeptide cells (F cells)
  3. releases pancreatic polypeptide hormone which inhibits exocrine secretions of the pancreas
  4. G cells
  5. releases gastrin which stimulates production of gastric acid by parietal cells in stomach

VIII. Amine Precursor Uptake Derivative (APUD) cells

---single endocrine cells scattered around the body

1