L30-31 - endocrine glands

Question 1

endocrine vs. exocrine transport of hormones

Answer 1

exocrine = ducts
endocrine = secrete into ECS --> bloodstream --> target organs (NO ducts)

Question 2

whats the difference between the 2 types of hypothalamic neurons?

Answer 2

1. make/release neurotransmitters

2. make/release neurosecretory hormones to regulate pituitary gland activity

Question 3

which organ plays a central role in the coordination of endocrine functions and the integration of endocrine and autonomic functions?

Answer 3

hypothalamus

Question 4

list the releasing and inhibiting hypothalamic neurosecretory hormones and their functions

Answer 4

1. GHRH - stimulates somatotropin relese
2. prolactin releasing hormone
3. prolactin inhibitory factor
4. corticotropin releasing hormone - stim. adenocorticotropin release
5. thyroid stimulating hormone releasing hormone - stim. TSH release
6. GnRH - stim. release of luteinizing hormone and FSH

Question 5

describe the path of hypothaamic neurosecretory hormones from hypothalamus to target organs

Answer 5

• synth in hypothalamus
• stored in axon terminals in median eminence
• released into primary capillary plexus in median eminence (fenestrated capillaries)
• drain into hypophyseal portal veins in infundibulum
• move into secondary capillary plexus in anterior pituitary (sinusoidal capillaries with fenestrations)
• enter anterior pituitary parenchyma where they influence secretory cells
• released into blood
• end in target organs

Question 6

tell me about supratropic and paraventricular nuclei

• what do they release?
• what do their axons form?
• where do the hormones go?

Answer 6

• found in hypothalamus
• have neurosecretory cell bodies that make and release ADH (vasopressin), oxytocin and neurophysin
• axons form the hypothalamichypophyseal tract which carries hormones to posterior pituitary
• ADH and oxytocin release from posterior pituitary to the capillaries

Question 7

what’s the difference between anterior and posterior pituitary?
and what are different names for each?

Answer 7

anterior = glandular
posterior = neural

anterior = adenohypophysis, pars distalis, pars anterior

posterior = neurohypophysis, pars nervosa, pars posterior

Question 8

describe the anterior pituitary tissue and categorize its 2 cell types

Answer 8

• glandular epithelium, reticular fibers, fenestrated sinusoidal capillaries, 2 cell types:

1. chromophils - dye affinity
   - acidophiles = somatotropes and lactotropes (more common)
   - basophiles = corticotropes, thyrotropes and gonadotropes
2. chromophobes - no dye affinity (may be degranulated chromophils)

Question 9

tell me about somatotropes’ actions

• stim
• inhibition
• action
• pathology

Answer 9

• stimulated by GHRH
• inhibited by somatostatin
• secrete GH which increases metabolic rates/long bone growth
• excess = gigantism in children and acromegaly in adults

Question 10

tell me about lactotropes’ actions

• stim
• inhibition
• action

Answer 10

• aka mammotropes
• stim by PRH
• inhibited by PIF
• produce prolactin which promotes mammary gland growth in pregnancy and lactation postpartum

Question 11

tell me about corticotropes’ actions

• stim
• action

Answer 11

• stim by CRH

- secretes ACTH to stimulate adrenal cortex

Question 12

tell me about thyrotropes’ actions

• stim
• action
• inhibition

Answer 12

• stim by TRH
• secretes TSH (thyrotropin)
• inhibited by T3 and T4 in the blood

Question 13

tell me about gonadotropes’ actions

• stim
• action

Answer 13

• stim by GnRH
• secretes FSH and LH
• male and female reproduction

Question 14

whats a pituitary adenoma?

Answer 14

common benign tumor of the anterior pituitary, may affect secretory activity or wear down surrounding tissue

Question 15

describe the parts of the posterior pituitary

Answer 15

1. infundibulum - continuous with median eminence of hypothalamus
2. pars nervosa - receives unmyelinated hypothalamohypophyseal tract terminals and acts as a storage for neurosecretions produced by neurons of the supraoptic and paraventricular nuclei of hypothalamus
   - contains herring bodies and pituicytes

Question 16

what hormones are found in the hypothalamohypophyseal tract ?

Answer 16

ADH and oxytocin

Question 17

what are herring bodies and where are they found? and what do they contain?

Answer 17

• accumulations of neurosecretory granules that release contents near fenestrated capillary plexus when stimulated
• found in pars nervosa of posterior pituitary
• contain either vasopressin (ADH) or oxytocin

Question 18

target and function of vasopressin?

Answer 18

target: distal tubule ad collecting ducts of kidney, which resorb water
function: lower urine volume

Question 19

target and function of oxytocin

Answer 19

target: uterine myometrium and myoepithelial cells of mammary glands
function: stim. smooth muscle contraction of uterus (parturition) and mammay gland (lactation)

Question 20

what are pituicytes?

Answer 20

glia-like, supportive cells in the pars nervosa of the posterior pituitary
- supports axons and their terminals

Question 21

what is diabetic insipidus?

Answer 21

• caused by damage to hypothalamus or pars nervosa of posterior pituitary
• result = low ADH –> insufficient water resorption by kidney –> polyurea (excess urination) and dehydration

Question 22

describe the thyroid capsule.

• derivation
• tissue type
• function

Answer 22

• derived from deep cervical fascia
• dense irreg collagenous CT
• gives rise to trabeculae/septa and houses parathyroid glands posteriorly

Question 23

what’s the function of the thyroid gland?

and what does it’s secretions each do?

Answer 23

synthesizes T3, T4 and calcitonin

T3 and T4 regulate cell/tissue metabolism and heat production
calcitonin lowers blood calcium

Question 24

describe the thyroid follicle

• histology/parts
• storage of secretory product
• types of cells

Answer 24

• spherical, lumen in center contains colloid, thyroglobulin, T3 and T4
• surrounded by BL, reticular fibers which anchor follicles and fenestrated capillary plexus for hormone passage
• secretory product is stored extracellularly in lumen (other endocrine glands store in parenchyma of cells)
• 2 types of cells: follicular and parafollicular

Question 25

describe follicular cells... | - change in cell type with activity

Answer 25

- principle thyroid cells - surround lumen - simple squamous with low activity and cuboidal with normal activity - columnar indicates high activity

Question 26

describe parafollicular cells - derivation - placement in follicles - histology appearance - function/storage

Answer 26

- aka clear cells - derived from neural crest - wedged between follicles in BL - not exposed to colloid - near many capillaries - light staining, round nucleus - function = make calcitonin (thyrocalcitonin)

Question 27

function of calcitonin?

Answer 27

peptide hormone released by parafollicular cells when blood calcium is high function = LOWER blood calcium levels to NORMAL by 1. inhibiting bone breakdown by osteoclasts 2. promoting calcium deposition in bones (osteoid calcification)

Question 28

how is thyroid hormone synthesis controlled?

Answer 28

by TSH and iodide levels

Question 29

describe thyroid hormone synthesis

Answer 29

1. follicular cells make thyroglobulin (glycoprotein+tyrosine) and release it into follicular lumen 2. iodine (diet) reduced to iodide in GI --> blood --> absorbed by thyroid 3. iodide actively pumped into follicular cells via Na-iodide symporter then oxidized at the apical PM (by peroxidase) to form active iodine --> lumen 4. iodine attaches to tyrosine on thyroglobulin by peroxidase to form MIT and DIT

Question 30

describe thyroid hormone release

Answer 30

anterior pituitary basophils (thyrotropes) --> TSH --> blood --> thyroid --> binds basally located TSHR of follicular cells --> luminal filopodia form and endocytose colloid --> vesicles join with endosomes --> proteases release iodinated tyrosine residues --> T3 and T4 released from follicular cell basal PM --> blood/lymph capillaries

Question 31

what are the physiological effects of T3 and T4?

Answer 31

- INCREASES cholesterol and FA synthesis, cell metabolism, growth, mental activity, carb metabolism endocrine gland functions, HR, muscle fxn, respiration, appetite - DECREASES 3 things only: phospholipid and triacylglyceride levels and weight - pathologically high levels lead to muscle tremors, fatigue, impotence, abnml menstruation

Question 32

what happens with hyperthyroidism?

Answer 32

- toxic goiter or Graves' - autoAb (IgG) binds TSHR --> enhanced colloid uptake --> excessive thyroid hormone in circulation --> follicular lumen depleted of colloid --> enlarged thyroid/exopthalmos

Question 33

what is postmortem eye

Answer 33

fibrotic rectus muscle, loose CT accumulation behind eyeball - no widespread skeletal muscle fibrosis, mild cardiac muscle fibrosis

Question 34

what's the difference between tri/tetraiodinated tyrosine and tri-tetraiodothyronine

Answer 34

the first is attached to thryoglobulin the second is after cleavage

Question 35

where is T4 and T3 predominantly made?

Answer 35

T4 - thyroid ONLY | T3 mostly by kidney, liver and heart converting T4--> T3