L68 Endocrinology Basics

Question 1

What are characteristics of classical endocrine glands

Answer 1

Ductless
Secrete into bloodstream/EC space
entire organ dedicated primariy to endocrine function

Question 2

What are non classical endocrine organs and what do they secrete?

Answer 2

Brain/Hypothalamus: releasing hormones
Kidney: Renin, Vitamin D, EPO
Heart: ANP, BNP
Liver: IGF-1
GI: Stomach: Serotonin, Ghrelin
Adipose: Leptin

Question 3

What are the 3 mechanisms of hormone action?

Answer 3

Endocrine: secrete into blood to act on downstream target tissues
Paracrine: secrete into interstitial space and act on nearby cells
Autocrine: secrete into interstitial space and act back on same cell

Question 4

What type of signaling is neurotransmitter transmission?

Answer 4

Paracrine

Question 5

How do hormone binding proteins affect hormone half lives?

Answer 5

They increase it by binding hormones in blodo to facilitate transport

Question 6

Which hormones use hormone binding proteins?

Answer 6

Steroid hormones (lipophilic)
IGF-1, GF, T4/T3

Question 7

What hormones do SHBG (sex hormone binding globulin) bind?

Answer 7

Estrogen and TEstosterone

Question 8

What hormones do CBG (Corticotrophin binding protein) bind?

Answer 8

Cortisol/Corticosterone

Question 9

What hormones do TBG ad TTR (Thyroid Binding Globulin and Transthyretin) bind?

Answer 9

Thyroid hormones

Question 10

Which hormones are considered bioavailable?

Answer 10

Free/Unbound and Albumiin bound hormones

Question 11

Which hormones are considered free?

Answer 11

Unbound/free

Question 12

What role does albumin play in hormone transport in blood?

Answer 12

Binds nonspecifically to lipophilic hormones in blood

Question 13

How is hormone delivered to atarget cell?

Answer 13

1. Steroid hormone released at membrane -> cross lipid bilayer-> intracellular target
2. Hormone/Protein complex binds to MEGALIN -> Form endocytic vesicle-> hormone dissociates and is released from vesicle

Question 14

What is required for hormones to elicit their effects?

Answer 14

Receptors

Question 15

What is the difference between specificity and affinity?

Answer 15

specificity: ability to distinguish between similar substances (Ki: ability to displace ligand at 50% of max activity=> smaller ki->higher specificity)
Affinity: binding affinity (Kd: ligand concentration that takes up 50% of binding sites; smaller number-> higher affinity)

Question 16

What are lipophobic receptor characteristics?

Answer 16

Bind to cells urface receptors
Use 2nd messenger signaling pathways
Rapid internalization/degradation

Question 17

What are xamples of lipophobic receptors?

Answer 17

GPCR: protein hormones
Receptor linked Kinases: EPO, GH, Prolactin
Receptor Kinases: Insulin, ANP

Question 18

What are lipophilic receptor characteristics?

Answer 18

Bind to intracellular receptors
Bound to large chaperone proteins in cytoplasm
Slow biological response
Repress/Activate Transcription
Example: Thyroid hormone receptor

Question 19

How does the thyroid hormone receptor work?

Answer 19

Thyroid hormone binds to nuclear receptors
Nuclear receptors not bound to ligand repress transcription-> binding of thyroid hormone allows activation of gene transcription4

NOTE: Thyroid hormones are NOT steroid hormones!

Question 20

Describe how Steroid hormones and receptors work in a cell

Answer 20

Steroid hormones freely enter cells -> bind to intracellular receptors that are associated with chaperone proteins -> chaperones dissociate with hormone binding -> hormone/receptor complex translocate to nucleus-> act as transcription factor for genes

Question 21

What factors affect hormone bioavailability?

Answer 21

Hormone transport
Target tissues: receptors, chaperone proteins
Hormone Synthesis/Release
Regulatory Mechanisms