Endocrine

Question 0

Neuroendocrine system

Answer 0

Dispersed cells in brain (neuroendocrine)

Release neurohormones via neurosecretion (long distance vs neurotransmitters)

Question 1

General features of endocrine system

Answer 1

Ductless glands - release hormones into interstitial space - very vascular
Glands either dedicated, secondary fx, or dispersed cells (ex neuroendocrine cells in brain)
Receptors determine specificity
Can also include paracrine (interstitial) and autocrine (same cell), especially in dev’t (ex PDA) and inflammation
Vs nervous - long term modulation, act on all cells (vs muscles and glands)

Question 2

Types of hormones

Answer 2

Proteins - insulin, growth hormone, PTH
Small peptides - ex vasopressin
Steroids - adrenal cortical, ovarian, testicular
Amino acid/arachidonic derivatives - catecholamines, thyroid, prostaglandin, prostacycline, leukotriene

Question 3

Mechanism of action for hormones

Answer 3

Hormone = long distance vs paracrine and autocrine
Receptor -> specificity (different effects in different cells)
Water soluble -> transmembrane receptor/primary messenger -> secondary messenger
- also generally need transport proteins in plasma
Lipid soluble (ie steroid) -> diffuse across membrane -> nuclear receptor

Question 4

Regulation of hormone response

Answer 4

In response to chronic hormone levels
Up-regulation: low levels -> more receptors -> more sensitive
Down-regulation: high levels -> fewer receptors -> less sensitive

Question 5

Primary endocrine glands

Answer 5

Thyroid
Parathyroid
Adrenal
Pituitary
Pineal

Question 6

Organs with secondary hormone secretion

Answer 6

Stomach, liver, small intestine, pancreas, kidneys
Hypothalamus
Thymus
Skin
Heart
Placenta
Ovaries, testes

Question 7

General organization of hypothalamus/pituitary

Answer 7

Hypothalamus = superior
Pituitary = hypophysis = inferior
- pituitary is split into two lobes
- posterior = neurohypophysis (from diencephalon)
- anterior = adenohypophysis (from mouth/Rathke’s pouch)
Connected by hypothalamo-hypophyseal tract of axons within infundibulum

Question 8

Function of posterior pituitary

Answer 8

aka neuropituitary
Only releases hormones produced in hypothalamus
Supraoptic + paraventricular nuclei -> ADH, oxytocin -> hypothalamo-hypophyseal tract -> stored in axons terminals as Herring bodies/neurosecretory granules -> released with AP
“Pituicytes” = glial cells around unmyelinated nerve fibers
ADH - high osmolality -> ADH -> water resorption -> low osmolality
oxytocin - positive feedback from suckling or contractions

Question 9

Function of anterior pituitary

Answer 9

aka adenohypophysis
Makes hormones under control of hypothalamus
Higher brain centers -> hypothalamus -> 2 inhibiting/4 releasing hormones -> median eminence axon terminals -> hypothalamo-hypophyseal portal system -> anterior pituitary capillaries
Wide variety of cell types and hormones produced - chromophils (acidophils/basophils) and chromophobes (no hormones, progenitor or senescent)

Question 10

Segments of anterior pituitary

Answer 10

Pars distalis - all of secretory cells, largest
Pars tuberalis - around infundibulum
Pars intermedia - vestigial, remains of Rathke’s pouch

Question 11

Hormones of anterior pituitary

Answer 11

Trophic hormones - act on other endocrine glands - direct feedback
- all released by basophils!
- CRH -> corticotropes -> ACTH = adrenocorticotrophic hormone
- TRH -> thyrotropes -> TSH
- GnRH -> gonadotropes -> FSH, LH
Non-trophic hormones - act directly on tissue - metabolic feedback via effects
- released by acidophils
- GHRH -> somatotropes -> growth hormone -> adipose, IGF -> bone, muscle
- mammotropes -> prolactin (suckling reduces inhibition -> inc production)

Hypothalamic inhibition:
Somatostatin -> inhibits GH and TSH
PIH = dopamine -> inhibits PL

Question 12

Feedback to anterior pituitary

Answer 12

Almost all systems are negative feedback (high levels -> decreased production)

Exception: oxytocin during childbirth -> positive feedback -> amplifying response

Question 13

Regulation of thyroid

Answer 13

Hypothalamus -> TRH ->
Anterior pituitary -> TSH ->
Thyroid -> T3, T4
T3 -> negative feedback to hypothalamus and anterior pituitary

Question 14

Histology of thyroid gland

Answer 14

Large follicles filled with colloid
Follicular cells - change shape with activity!
- squamous if inactive -> columnar if active
C cells - outside of follicle
Also capillaries within CT capsule - very vascular

Question 15

Production of thyroid hormones

Answer 15

Follicular cells make thyroglobulin (rich in tyrosine) ->
Iodinized (at tyrosine residues) and stored in follicle (weeks to months of supply) ->
Resorbed by follicular cell (via endocytosis) ->
Lysosome -> breaks down thyroglobulin -> free T3, T4 -> released

Question 16

Thyroid hormones

Answer 16

T3 - triiodothyronine
T4 - tetraiodothyronine

Both are joined tyrosine residues of thyroglobulin protein with iodinization of rings
Release 20:1 T4:T3, converted in kidneys/tissue
(T3 is 5x more active)

Question 17

Functions of thyroid hormones

Answer 17

Essentially same function (at this point...)
Regulate BMR
Regulate heat production
Regulate growth (body and tissue)
Dev't of nervous system (peds only)

Question 18

Production of calcitonin

Answer 18

Produced in C (extrafollicular) cells of thyroid
Decreases serum calcium levels
- bone deposition
- decreased resorption in kidneys

Question 19

Location of parathyroid glands

Answer 19

Usually 4 glands in posterior capsule of thyroid
Lots of variation - migrate from 3/4 pharyngeal pouches during dev’t (vs thyroid migrates from tongue)
Need to preserve (and blood supply) in thyroidectomy

Question 20

Function of PTH

Answer 20

Increases serum calcium

• > osteoblasts -> osteoclast-stimulating factor -> inc number and activity of osteoclasts -> bone resorption
• > increased kidney resorption (and PO4 excretion)
• > increased GI absorption

Question 21

Oxyphil cells

Answer 21

Large, acidophilic cells
Found in PTH glands of older people
Unclear fx/significance

Vs Chief cells - active

Question 22

Gross structure of adrenal glands

Answer 22

Different embryology, functions, etc

Cortex - superficial, split into three layers -
All layers steroid producing - smooth ER, lipid droplets, mitochondria
- zona glomerulosa -> aldosterone
- zona fasciculata -> cortisol - appears most foamy
- zona reticularis -> androgens
Medulla - deep - neural crest cells (ganglion without axons)

Question 23

Cortisol production and function

Answer 23

ACTH -> zona fasciculata -> cortisol
“Glucocorticoid”
Metabolic:
- catabolic in most tissues (lipids, protein, carbs -> ATP)
- anabolic in liver - gluconeogenesis, glycogenesis
- diurnal, energy throughout circadian rhythm
Anti-inflammatory/immunosupressive

Question 24

Aldosterone production and function

Answer 24

"Mineralocorticoid" Part of RAAS system of fluid regulation Angiotensin -> zona glomerulosa (cortex) -> aldosterone -> Kidney -> resorb Na and Cl -> water, HCO3 follow Can also be stimulated somewhat by ACTH, inhibited by ANP

Question 25

Adrenal medulla

Answer 25

Deep to cortex Derived from neural crest cells -> chromaffin cells/pheochromocytes Acts as a sympathetic ganglion: preganglionic fibers -> epi and NE released into bloodstream

Question 26

Production of catecholamines (epi and NE)

Answer 26

In adrenal cortex Two blood streams - direct and through cortex ("portal") -> high glucocorticoid levels -> required for methyl transferase activity -> NE to epinephrine (ie low cortisol levels -> more NE, high cortisol -> more epi) Usually 80% epi

Question 27

Islet of Langerhands anatomy

Answer 27

Lots of capillaries (vs exocrine cells around duct) Alpha cells (glucagon) around edges Beta cells (insulin) in middle Delta and F usually near surface but rare More found in tail

Question 28

Pancreatic islet secretions

Answer 28

Alpha cells (20%) -> glucagon -> glycogenolysis, lipolysis Beta cells (70%) -> insulin -> glucose to cells, inhibits lipolysis Delta cells (5%) -> somatostatin -> inhibits -> paracrine -> lower insulin and glucagon -> anterior pituitary -> lower GH, TSH -> stomach -> lower HCl F cells -> pancreatic peptide -> stomach chief cells -> inc enzymes -> less bile and pancreatic enzyme release -> lower motility of small intestine

Question 29

Pineal gland

Answer 29

Roof of diencephalon Produces melatonin -> regulates light-dark cycles (induces sleepiness, inhibited by light -> NE -> less melatonin) Corpora arenacea/"brain sand" is identifiable as midline on xray

Question 30

Control of hormone release

Answer 30

Humeral - direct response to blood stimuli - ex insulin, aldosteron, PTH Neural - ex adrenal medulla Hormonal/trophic - hypothalamus -> anterior pituitary