Introduction to the Endocrine System

Question 1

What is the function of the endocrine system?

Answer 1

Regulation of multiple organs to meet growth and reproduction demands; major role in homeostasis

Question 2

What are the major endocrine glands?

Answer 2

Hypothalamus, anterior/posterior pituitary, thyroid, parathyroid, adrenal cortex/medulla, gonads, endocrine pancreas, and placenta

Question 3

Name some endocrine cells that synthesize hormones within organs whose primary function is not endocrine

Answer 3

Adipose, heart, liver, kidney, GI tract

Question 4

What are some hormones modified by peripheral conversion?

Answer 4

Angiotensin II, vitamin D

Question 5

Describe protein/peptide hormones

Answer 5

Stored in secretory vesicles until needed; water soluble

Question 6

Describe steroid hormones

Answer 6

Synthesized from cholesterol; lipid soluble; not stored

Question 7

Where are amine hormones derived from?

Answer 7

Tyrosine

Question 8

Describe the synthesis of protein/peptide hormones

Answer 8

1) Most are synthesized as non-functional preprohormone
2) Modified in ER to prohormone
3) Packed into vesicles
4) Proteolytic enzymes cleave to form functional hormone
5) Protein/peptide hormones stored in secretory vesicles
6) Endocrine cell stimulus causes release of hormone

Question 9

What causes endocrine cell stimulation and the subsequent release of hormone?

Answer 9

Increased intracellular calcium; increased cAMP and PKA activation

Question 10

What are some examples of steroid hormones?

Answer 10

Cortisol, aldosterone, estradiol, estriol, progesterone, testosterone, and 1, 25-dihydroxycholecalciferol

Question 11

What are steroid hormones derived from? How do they become steroids?

Answer 11

Derived from cholesterol; modifications via addition or removal of side chains, hydroxylation, or aromatization of steroid nucleus

Question 12

What are steroid hormones synthesized and secreted by?

Answer 12

Adrenal cortex, gonads, corpus luteum, placenta

Question 13

What are the 2 groups of amine hormones? How are they synthesized and how do they work?

Answer 13

Catecholamines: synthesized in cytosol and secretory granules; act through cell-membrane associated receptors

Thyroid: synthesized by thyroid gland and stored as thyroglobulin in follicles with the gland; cross cell membrane and act through nuclear receptors

Question 14

What is the neural mechanism for regulating hormone secretion? Give an example

Answer 14

Neuronal input to an endocrine cell increases or decreases hormonal secretion; example is sympathetic preganglionic innervation of the adrenal medulla; when stimulated causes the release of catecholamines into the circulation

Question 15

What is the positive endocrine feedback mechanism?

Answer 15

Some feature of hormone action causes additional secretion of the hormone; uncommon in biologic systems; when it occurs, leads to an explosive event (ovulation, labor contractions)

Question 16

What is the negative endocrine feedback mechanism?

Answer 16

Predominant mode of feedback loop among endocrine glands; some feature of hormone action inhibits further secretion of the hormone; confer stability by keeping a physiological parameter (blood glucose level) within a normal range

Question 17

What is the long-loop feedback?

Answer 17

Hormone released from 3rd tier (peripheral endocrine gland) feeds back all the way to the 1st (hypothalamus) and 2nd (pituitary) tier

Question 18

What is the short-loop feedback?

Answer 18

Hormone secreted from the 2nd tier feeds back to the 1st tier

Question 19

What is the ultra short-loop feedback?

Answer 19

Gland inhibits its own secretion

Question 20

What are the major inputs to the hypothalamus for hormone secretion and how do they function?

Answer 20

Suprachiasmatic nucleus: impose a circadian rhythm on the secretion of hypothalamic releasing hormones and endocrine axes

Pineal Gland: releases melatonin which feedbacks to the SCN information about day-night

Question 21

How can the responsiveness of a tissue to hormones be changed?

Answer 21

Changing the # of receptors or changing the affinity of the receptors for the hormone

Question 22

Describe up-regulation

Answer 22

Increase the # of receptors or sensitivity of target tissue when hormone levels are low; increase the synthesis of new receptors, decrease the degradation of existing receptors, activating receptors

Question 23

Describe down-regulation

Answer 23

Reduce receptor numbers or sensitivity of target tissue when hormone levels are high (chronic); decrease in receptor synthesis, increase degradation of existing receptors, inactivating/desensitizing receptors

Question 24

What are the 2 categories of tyrosine kinases? Describe them

Answer 24

RTK’s: intrinsic tyrosine kinase activity; when activated, tyrosine kinase phosphorylates downstream proteins

Tyrosine Kinase-Associated Receptors: associate non-covalently to proteins that have kinase activity; when activated, kinase phosphorylates downstream proteins