Endocrine Overview

Question 1

what is a hormone?

Answer 1

a chemical substance that is secreted into the internal body fluids by one cell or a group of cells and has a physiological control effect on other cells of the body.

Question 2

what are the major endocrine glands?

Answer 2

• pituitary gland
• testes
• thyroid and parathyroid glands
• adrenal glands
• pancreas
• ovaries

Question 3

whats the function of the endocrine glands?

Answer 3

they secrete hormones which regulate various functions throughout the body

Question 4

how does feedback control work?

Answer 4

A sensor detects a regulated variable and responds by modulating its secretion of a hormone

This hormone, either acts on a target to modify another hormone or affect a second target.

Question 5

when does GH peak?

Answer 5

night

Question 6

when does cortisol peak?

Answer 6

morning

Question 7

describe the release of hormones?

Answer 7

pulsatile and episodic (Frequency and amplitude) can vary daily (e.g. cortisol) or monthly (estradiol) or remain fairly constant (Thyroid hormone)

Question 8

where is the clock with an intrinsic 24-25 hour cycle located?

Answer 8

in the suprachiasmatic nucleus (SCN) of the hypothalamus.

This free running clock is entrained by environmental light signals to the external 24-hour day.

Question 9

name this gland and the hormone that is both an agent and regulator of the SCN

Answer 9

pineal gland; melatonin

Question 10

what is the synergistic effect of hormones?

Answer 10

the effect of the two synergistic hormones is greater than that of either hormone alone (example is thyroid hormone and epinephrine on heart rate, since in addition to its direct effects of increasing heart rate, thyroid hormone increases the number of adrenergic receptors which can then respond to epinephrine).

Question 11

what is the permissive effect of hormones?

Answer 11

thyroid hormone presence is necessary for aldosterone to stimulate Na+/K+ pumps, although TH has no stimulatory effect on these pumps by itself.

Question 12

what is the antagonistic effect of hormones?

Answer 12

insulin vs. glucagon/epinephrine effects on glycogen synthesis

Question 13

what are examples of cell-to-cell communication?

Answer 13

Direct contact

Synaptic

Chemical 
Signaling
-Endocrine Signaling
-Paracrine Signaling
-Autocrine

Question 14

how are hormones are removed from the blood and tissues by 6 basic methods?

Answer 14

• Enzymatic catabolism in blood and extracellular fluids
• Endocytosis of hormone-receptor complex by target cell with subsequent intracellular enzymatic catabolism and return of “cleared” receptor to plasma membrane
• Liver enzymatic degradation and/or excretion in bile
• Liver re-synthesis (example: aromatization of testosterone into estrogen)
• Kidney excretion into urine
• Hormonal binding to target sites

Question 15

what are steroids?

Answer 15

Small lipid soluble molecules derived from cholesterol

Question 16

T/F, steroids are not stored, synthesized de novo on demand

Answer 16

T

Question 17

how do steroids circulate?

Answer 17

they circulate bound to globulins and other plasma proteins

Question 18

what do steroids bind too?

Answer 18

bind intracellular receptors (cytosolic & nuclear)

Question 19

describe the effects of steroids?

Answer 19

Effects are slow (hours), depend on gene transcription, protein synthesis, etc.

Question 20

what are the four main domains of the steroid hormone receptor?

Answer 20

• The ligand (hormone) binding domain
• The DNA binding domain
• The N-terminal portion (transactivation domain)
• The DNA binding domain contains two Zinc Fingers which contain 4 cysteine residues which complex with zinc

Question 21

how long are peptide/protein hormones?

Answer 21

3 to 200 amino acids long

Question 22

how are peptide/protein hormones released?

Answer 22

• synthesized and stored, released in bursts

- generally circulate unbound in plasma, but there are exceptions (IGFs)

Question 23

what do Peptide/Protein Hormones bind too?

Answer 23

extracellular receptors, and depend on 2nd messengers for signal transduction

Question 24

what are the effects of peptide/protein hormones?

Answer 24

effects are very rapid (minutes), and initial effects do not depend on new protein synthesis

Question 25

what are amino acid hormones synthesized from?

Answer 25

TYROSINE, they are also stored and secreted in bursts

Question 26

describe how thyroid hormone is bound and its half life?

Answer 26

Thyroid Hormone circulates >99%bound, very long half-life (days)

Question 27

what are the type of receptors that thyroid hormones bind too?

Answer 27

Binds to intracellular receptors (but plasma membrane transporter)

note that effects through gene transcription, slow

Question 28

how does epinephrine and norepinephrine bind?

Answer 28

binds to extracellular receptors

effects through 2nd messengers, very rapid

Question 29

how can we measure hormones?

Answer 29

Radioimmunassay

Question 30

three levels of endocrine control?

Answer 30

Tertiary - hypothalamic stimulation
Secondary - pituitary stimulation
Primary - endocrine gland stimulation

Question 31

what are the endocrine neoplasias?

Answer 31

type 1 and 2. Autosomal dominant, multifocal in a given endocrine organ.

Question 32

what is type 1 neoplasia?

Answer 32

parathyroid tumors, pituitary tumors, pancreatic tumors
D/t inactivation of MEN1 gene on 11q13 affecting

1. parathyroid (hyperplasia→ primary hyperparathyroidism)
2. Pancreas (functional tumors, leading cause of death in MEN1, insulinoma → hypoglycemia, gastrinoma → Zollinger-Ellison syndrome)
3. Pituitary - prolactinoma

Question 33

what is type 2 neoplasia?

Answer 33

mutations of RET proto oncogene

Type 2a: medullary thyroid carcinoma, pheochromocytoma, parathyroid hyperplasia → hyperparathyroidism

Type 2b: medullary thyroid carcinoma, pheochromocytoma, mucosal neuromas
→ DO NOT develop parathyroid hyperplasia
→ develop extra endocrine manifestations: marfanoid habitus