Endocrine I: Basic Concepts

Question 1

Is the physiological effect (action) of the hormone carried out by the hormone itself or the receptor?

Answer 1

receptor

Question 2

What is the most common endocrine pathology?

Answer 2

Type II Diabetes Mellitus

Question 3

Receptors are autoregulated by their ______.

Answer 3

ligand

up/downregulation depends on hormone levels

Question 4

What are some examples of receptors for lipophobic (protein, peptide) hormones?

Answer 4

• GPCRs: most protein hormones
• Receptor kinases: insulin, ANP
• Receptor-linked kinases: GH, prolactin, EPO

Question 5

What is the difference b/t receptor kinases and receptor-linked kinases?

Answer 5

receptor kinases have intrinsic catalytic activity in the intracellular domain once ligand binds; receptor-linked kinases recruit an activated enzyme to the intracellular domain upon ligand binding

Question 6

Are ion channels hormone receptors?

Answer 6

NO! Hormones cannot bind to ion channels!

Question 7

What are the non-classical endocrine organs?

Answer 7

• brain (esp. hypothalamus)
• kidney
• heart
• liver
• GI
• adipose tissue

Question 8

What are the classical endocrine organs?

Answer 8

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

Question 9

Hormones are biologically active when they are _____ and not ______.

Answer 9

free; bound

Question 10

Which hormones are transported in the blood by binding proteins?

Answer 10

• steroid hormones
• IGF I/II
• GH
• T3/T4

Question 11

Hormones can be cleared through…

Answer 11

• intracellular metabolism
• liver metabolism
• urinary/fecal excretion

Question 12

What are the highly specific vs. non-specific hormone transport proteins in the blood?

Answer 12

• highly specific: SHBG, CBG, TBG, TTR

- non-specific: albumin

Question 13

Describe bioactive vs. bioavailable vs. biounavailable hormones.

Answer 13

• bioactive: “free” hormones
• bioavailable: free or albumin-bound hormones
• biounavailable: hormones bound by highly specific binding proteins

Question 14

How are hormones metabolized in the liver?

Answer 14

• Phase I processes: hydroxylation or oxidation
• Phase II processes: glucuronidation, sulfation, or reduction with glutathione
• Metabolic byproducts are then excreted through the bile or by the kidney

Question 15

What are the 2 ways of deliver lipophilic hormones to their target cells?

Answer 15

1: steroid hormone rel. at mem. after being cleaved from binding prot., freely diffuses across lipid bilayer, finds IC targets
2: hormone/protein complex binds to megalin, forms endocytic vesicle, hormone dissociates and is released from vesicle

Question 16

What happens if a target cell does NOT have a hormone receptor, or if the receptor is defective?

Answer 16

NO hormone action in that cell!

Question 17

What determines the duration of hormone activity?

Answer 17

the receptor

Question 18

Hormones bind to receptors with high _________ and _________.

Answer 18

specificity; affinity

Question 19

What are some factors that affect hormone bioavailability?

Answer 19

• hormone transport (binding proteins, kinetics)
• target tissues (receptors, chaperones)
• hormone synthesis/release (enzymatic activity, processing)
• regulatory mechanisms (feedback, aging, circadian rhythms, pulsatility, metabolism)

Question 20

How are cell surface receptors vs. intracellular receptors degraded?

Answer 20

• cell surface: rapid internalization/dissociation after ligand binding
• intracellular: ubiquitination

Question 21

What are intracellular receptors often bound to?

Answer 21

large chaperone proteins in cytoplasm (like HSPs)

Question 22

What is unique about thyroid hormones?

Answer 22

They are NOT steroids, but they ARE transported across the membrane and DO bind nuclear steroid receptors. The receptor is always located in the nucleus and bound to DNA w/ repressive complexes when not bound to hormone.