Hormones & Receptors

Question 1

Paracrin effectors act on?

Answer 1

Neighboring cells, released in ECF.

Question 2

Autocrine effectors act on?

Answer 2

the cell releasing the effecto

Question 3

What is a hormone?

Answer 3

A chemical produced by certain cells, released into blood stream in minute amounts and acts on distant targets.

Question 4

General methods of classifying hormones

Answer 4

Chemical

Functional

Question 5

Types of hormones

Answer 5

1. Tyrosine derivatives
2. Cholesterol derivative
3. Proteins/peptides

Question 6

Describe protein/peptide synthesis

Answer 6

1. Pre-prohormone is synthesized on ribosome
2. Taken into RER and presequence is cleaved.
3. Prohormone taken to golig for processing and put in vesicles
4. Exocytosis in a Ca++ dependent manner in reponse o stimuli

Question 7

Transport of peptide/protein hormones in blood

Answer 7

Most are free form excet for GH, IGF, and PRL. Short half life

Question 8

Properties of steroid hormones

Answer 8

• lipophilic, cross membrane easily
• Immedate release following synthsis
• Require a protein carrier
• longer half life due to carriers.

Question 9

What is the active hormone: free hormone or atached to carrier

Answer 9

Free hormone, only 1–5% is free in blood and the rest acts like a resevoir. Free hormones are responsble for regulating secretion via feedback mechanisms.

Question 10

Ways to measure [Hormone] in blood:

Answer 10

1. Bioassay: tests for function on exogenous systems.

2. Immunoassay: tests for protein levels using radio immunoassays or ELIZA.

Question 11

Types of peptide/protein hormone receptors

Answer 11

1. G-protein coupled (EPI & NE)
2. Cytokine receptors, aka JAK/STAT (GH & PRL)
3. Ectodermal Growth Factor (EGF) receptors (insulin & IGF)

Question 12

Explain G-proteins

Answer 12

Hormone receptors are associtaed with a G protein that couples it to enzymes such as adenylate cyclase (cAMP) or phospholipase C (DAG & IP3).
-Has 3 subunits (alpha, beta, gamma)
-Alpha has inherent GTPase activity.
Alpha can be inhibitory or stimulatory

Question 13

JAK/STAT receptors: hormones

Answer 13

GH and PRL

Question 14

JAK/STAT mechanism

Answer 14

Activation of these receptors results in coupling and activation of a tyrosine kinase (Janus kinase or JAK), which then causes the phosphorylation of a group of proteins called signal transducers and activators of transcription (STATs).

Question 15

Insulin & IGF receptors

Answer 15

EGF receptors are a large family of protein tyrosine kinase receptors. In this case the receptors themselves are tyrosine kinases that can be activated upon hormone binding

Question 16

Steroid hormone signaling

Answer 16

Receptors are cytoplasmic or nuclear, forming a complex and migrating to nucleus to bind to Hormone Responsive Elements (HREs) and acting as transcription factors.

Question 17

How is hormone secretion regulated?

Answer 17

Feedback loops

Question 18

Classes of feedback loops

Answer 18

1. Hormone level is the regulated variable (usually -ve feedback)
2. Plasma concentration of a metabolite or a mineral acts as the regulated variable
   Feedback loops can be direct or indirect.

Question 19

T or F: +ve feedback loops are common

Answer 19

False, very rare (ex: oxytocin secretion during birth)

Question 20

Termination of +ve feedback loop

Answer 20

The only way a positive feedback loop can be terminated is by the exhaustion of the hormone or by an explosive event such as ovulation

Question 21

Patterns of hormone secetion

Answer 21

• Hormone secretion often occurs in a pulsatile fashion.

- levels of many hormones are regulated by diurnal variation showing characteristics of circadian rhythms.