Anatomical Basis of Homeostasis II: Endocrine glands

Question 1

List characteristics of peptide/protein hormone cell

Answer 1

• Lots of RER
• Golgi
• Secretory vesicles – vary in size

Question 2

List characteristics of Steroid-secreting cells

Answer 2

Lots of smooth ER
Abundant mitochondria
Lipid droplets

Question 3

What is function of pituitary gland?

Answer 3

Major interface between brain and the endocrine system.

Question 4

Describe anatomy of pit gland

Answer 4

• rounded body, about 1 cm dia.
• connected to floor of III ventricle by the infundibulum (pituitary stalk), just posterior to the optic chiasma
• lies in a depression in the body of the sphenoid bone = pituitary (hypophyseal) fossa - also called the sella turcica

Question 5

What is the pit fossa lined and covered over by?

Answer 5

• dura

- covered over by a sheet of dura (diaphragma sellae), pierced by the pituitary stalk

Question 6

Name the 2 parts of the pit gland

Answer 6

1. Adenohypophysis (Anterior pituitary)

2. Neurohypophysis (Posterior pituitary)

Question 7

Name parts of ant. pit

Answer 7

• pars distalis
• pars tuberalis
• pars intermedia

Question 8

Name parts of pos. pit

Answer 8

• pars nervosa

- infundibulum (neural stalk)

Question 9

Where does the ant. pit dev from?

Answer 9

• an upgrowth of ectoderm/ endoderm from the embryonic oral cavity (remnant of Rathke’s Pouch).

Question 10

Where does post. pit dev from?

Answer 10

• downgrowth from floor of the diencephalon in brain.

Question 11

What does post. pit consist of?

Answer 11

• axons of modified neurones, supported by a population of glial-like cells = pituicytes.
• Cell bodies of these neurones lie in the supraoptic and paraventricular nuclei of the hypothalamus - Hormones syn in nuclei travel down axons

Question 12

List functions of ADH/vasopressin

Answer 12

• increases water retention in kidney.

- raises blood pressure by contracting vascular smooth muscle cells (at high concentrations).

Question 13

List functions of oxytocin

Answer 13

• contraction of smooth muscle cells, esp. of uterus during childbirth; and myoepithelial cells of mammary gland during lactation.
• bonding both socially and sexually

Question 14

What types of hormones are ADH and oxytocin and how many aa?

Answer 14

• peptides

- 9

Question 15

Where are ADH + oxytocin made and how are they released?

Answer 15

• made in cell bodies of neurones (in hypothalamus) initially as a larger protein, subsequently cleaved to yield the hormone and a binding protein (neurophysin).
• transported down axons to terminals
• released from terminals into fenestrated capillaries on stimulation of the cell bodies in the hypothalamus
  – fenestrations allow plasma in blood to come into contact with cells lying underneath capillary endo.

Question 16

What are Herring bodies?

Answer 16

• accumulations of hormone within the axons

– secretory granules containing hormone

Question 17

What is in the pars distalis region?

Answer 17

Cords of cuboidal/polygonal epithelial secretory cells clustered around large, fenestrated sinusoids.

Question 18

What are the cells in the pars distalis region trad classed into and how do they stain?

Answer 18

• Acidophils (stain pink/orange with H & E)
• Basophils (stain blue with H & E)
• Chromophobes (stain poorly)

Question 19

List 2 types of acidophils and hormones they secrete

Answer 19

• Somatotrophs - Growth Hormone

- Mammotrophs - Prolactin

Question 20

List 3 types of basophils and hormones they secrete

Answer 20

Thyrotrophs - Thyroid Stim. Hormone (TSH)
Corticotrophs - Adrenocorticotrophic hormone (ACTH)
Gonadotrophs - Follicle Stim. Hormone (FSH), Luteinizing hormone (LH)

Question 21

What is function of chromophobes?

Answer 21

• either reserve cells/stem cells or resting cells that have lost their secretory granules
  – replace acidophils and basophils when they die

Question 22

Describe characteristics of somatoptrophs in EM

Answer 22

packed with granules of moderate size

Question 23

Describe characteristics of thyrotrophs in EM

Answer 23

have smaller granules mostly at the periphery of the cell

Question 24

Describe characteristics of Gonadotrophs in EM

Answer 24

larger cells, variable sized granules

Question 25

Describe characteristics of Corticotrophs in EM

Answer 25

- paler cytoplasm under e.m. | - sparse granules located at periphery.

Question 26

What is located in pars tuberalis?

Answer 26

Thin layer of cuboidal cells, mostly gonadotrophs.

Question 27

What is located in pars intermedia?

Answer 27

- Cells (basophilic) secrete Melanocyte stimulating hormone – increases skin pigmentation, but physiological role in man is uncertain.

Question 28

Describe reg of secretion of ant. pit

Answer 28

- regulated by neuroendocrine cells of the hypothalamus whose axons project to the median eminence. - discharge releasing hormone into capillaries of the pituitary portal vessels. - these in turn end in capillaries bathing the cells of the anterior pituitary – RH stim release of hormones from acidophils and basophils.

Question 29

What can happen as a result of trauma to the stalk?

Answer 29

loss of hormonal control of pit

Question 30

What hormones do the hypothalamic hormones stimulate release of?

Answer 30

- Thyrotropin releasing hormone (TRH) – stim release of thyroid hormone - Gonadotropin releasing hormone (GnRH) – LH + FSH release - Growth hormone releasing hormone (GRH) - GH - Corticotropin releasing hormone (CRH) - ACH

Question 31

What hormones do the hypothalamic hormones inhib release of?

Answer 31

- Somatostatin (blocks GH and TSH release) | - Dopamine (blocks prolactin release)

Question 32

Why is it a portal system?

Answer 32

- Need less releasing hormone – short distance between hypo and pit – no need for circ around body before it arrives at destination - More immediate response - Can use the same hormone again locally elsewhere for other purposes. e.g. somatostatin from Islets of Langerhans blocks release of insulin and glucagon

Question 33

Describe anatomy of thyroid

Answer 33

- 2 pear-shaped lateral lobes connected by a midline isthmus - intimately associated with the trachea - isthmus lies at level of 2nd-4th tracheal rings - isthmus may be joined to the hyoid bone by a fibrous cord, a remnant of the embryological thyroglossal duct

Question 34

Describe dev of thyroid

Answer 34

Arises from a diverticulum (outpouch) in floor of the primitive pharynx just caudal to the site of the future tongue – thyroglossal duct - opens at base of tongue as the foramen caecum - connection to pharynx eventually lost, isolating the gland

Question 35

Describe cells of the thyroid

Answer 35

- Thyroid epithelial cells are organized into follicles. - secrete thyroglobulin (large glycoprotein, mw 660Kd) - accumulates in the follicles as “colloid”

Question 36

Describe storage of iodine in thyroid

Answer 36

- oxidized to Iodine | - covalently attached to the tyrosines of thyroglobulin within the lumen of the follicle

Question 37

Describe how iodine is released from thyroid

Answer 37

- On stimulation by TSH (from the anterior pituitary) - follicular cells endocytose (Take up) the iodinated thyroglobulin - break it down in lysosomes - release the iodinated tyrosine derivatives as tetra- iodothyronine (thyroxine) (T4) or tri-iodothyronine (T3)

Question 38

Describe structure and location of Thyroid C cells/Parafollicular cells

Answer 38

- scattered cells found within the follicular epithelium or as clusters between the follicles. - larger, more rounded than the follicle cells

Question 39

Describe function of Thyroid C cells/Parafollicular cells

Answer 39

secrete calcitonin (inhibits Ca++ mobilization) = release Ca from bone

Question 40

What is the neural crest?

Answer 40

- all NS pop of cells derived from it | - migrate to thyroid during development

Question 41

Describe anatomy of parathyroid glands

Answer 41

- 2 pairs of parathyroid glands, each about the size of a pea - Usually found on or embedded in the posterior border of the lateral lobes of the thyroid gland, but position is somewhat variable (esp. inferior parathyroids) - No functional significance in the association between thyroid and parathyroid glands

Question 42

Describe cells of parathyroid glands

Answer 42

- Densely-packed, small Chief (or principal; P) cells arranged in irregular cords around blood vessels (C). - secrete parathyroid hormone (parathormone) stimulates calcium mobilization. - There is a second, minor population of larger, eosinophilic oxyphil cells (O), of unknown function (lack secretory granules)

Question 43

Describe anatomy of adrenal glands

Answer 43

- Pyramidal (right) or crescent- shaped (left) bodies in contact with the upper poles of the kidneys Separated from kidneys by connective tissue but surrounded by the renal fascia.

Question 44

Describe development of adrenal glands

Answer 44

- 2 distinct parts with different embryonic origins: - Cortex - derived from the coelomic epithelium (mesothelium) lining the posterior abdominal wall - Medulla - derived from an adjacent sympathetic ganglion, which was itself derived from neural crest

Question 45

Describe cells of adrenal cortex

Answer 45

- Cells secrete steroids - have lots of smooth endoplasmic reticulum (SER) and lipid droplets (containing cholesterol) so appear pale and "frothy" in histological sections. - Cells are organized into 3 zones:- 1) Zona glomerulosa (G) 2) Zona fasciculata (F) 3) Zona reticularis (R)

Question 46

Describe cells of zona glom

Answer 46

- cells arranged in rounded clusters, surrounded by capillaries - secrete mineralocorticoids – mainly aldosterone (95%) - target : Kidney (Na+ retention by distal convoluted tubule) regulated by renin/anigiotensin system

Question 47

Describe cells of zona fasciculata

Answer 47

- cells arranged in straight cords, running radially - secrete glucocorticoids – mainly cortisol (95%) - regulate : general glucose, lipid and protein metabolism - secretion regulated by ACTH

Question 48

Describe cells of Zona reticularis

Answer 48

- cells arranged in irregular cords - secrete some glucocorticoids and small quantities of sex steroids (mostly weak androgens) - functionally insignificant (?)

Question 49

Describe structure of adrenal medulla

Answer 49

- modified sympathetic ganglion - large, polyhedral cells arranged in clumps or cords - resemble “axon-less” ganglion cells

Question 50

Describe islets of Langerhans

Answer 50

- Small, rounded clusters of cells, - 100-200 µm dia., - embedded within the exocrine pancreas - The cells are smaller and more-lightly stained than the exocrine cells, and arranged in irregular cords around capillaries.

Question 51

List cells of IOL and what they secrete

Answer 51

- A or alpha cells (~20%) secrete glucagon - B or beta cells (~70%) secrete insulin - D or delta cells (5-10%) secrete somatostatin - F or PP cells (1-2%) secrete pancreatic polypeptide - Other, minor cell types secrete vasoactive- intestinal peptide (VIP), substance P, motilin, serotonin, etc.

Question 52

Describe cells of Diffuse neuroendocrine system

Answer 52

- Scattered cells found especially in the gut and respiratory system - Secrete amines or peptides with hormone-like (promote homeostasis) or neurotransmitter activity (promote sm contraction) e.g. gastrin, CCK, secretin, enteroglucagon, serotonin etc - Often secrete locally (paracrine)

Question 53

What do cells of Diffuse neuroendocrine system have ability to do and how?

Answer 53

- Cells often have ability to take up and decarboxylate amines – Old name – APUD cells (amine precursor uptake and decarboxylation) - Possess synaptic vesicle-like structures or neurosecretory-type granules (dense core granules) – released by exocytosis in response to external stimuli - Derived from neural crest - Produce hormones in vesicles