Cell signalling and the endocrine system

Question 1

What are the 3 main types of hormone?

Answer 1

Peptide
Amine
Steroid

Question 2

What hormone is produced by the pineal gland?

Answer 2

Melatonin

Question 3

What glands produce peptide hormones?

Answer 3

Hypothalamus
Pituitary
Thyroid
Parathyroid
Pancreas

Question 4

What glands produce amine hormones?

Answer 4

Thyroid
Parathyroid
Adrenal

Question 5

What glands produce steroid hormones?

Answer 5

Ovaries
Testes
Adrenal

Question 6

What are amine hormones?

Answer 6

Pre-synthesised hormones that are stored in vesicles

Question 7

What stimulates release of amine hormones?

Answer 7

They are released in response to a stimuli by Ca2+ dependant exocytosis

Question 8

How are amine hormones transported?

Answer 8

Amines are hydrophilic and are transported mainly free in the plasma

Question 9

What are peptide hormones?

Answer 9

Peptides are pre-synthesised, usually from a longer precursor, and are stored in vesicles

Question 10

What stimulates release of peptides?

Answer 10

They are released in response to stimuli by Ca2+ dependant exocytosis

Question 11

How are peptide hormones transported?

Answer 11

Peptides are hydrophilic and are transported mainly free in the plasma

Question 12

What stimulates steroid hormones?

Answer 12

• Increased cellular uptake and availability of cholesterol
• Increased rate of conversion of cholesterol to pregnenolone (Rate limiting)

Question 13

How are steroid hormones transported?

Answer 13

Steroids are hydrophobic and are transported in plasma, mainly bound to plasma proteins

Only free steroid hormones are biologically active

Question 14

What are some examples of specific carrier proteins of hormones?

Answer 14

• Cortisol-binding globulin (CBG) - Binds cortisol and some adrenaline
• Thyroxine-binding globulin (TBG) - Binds T4 and some T3
• Sex steroid-binding globulin (SSBG) - Binds testosterone and oestradiol

Question 15

What are some examples of general carrier proteins of hormones?

Answer 15

• Albumin - Binds many steroids and thyroxine
• Transthyretin - Binds thyroxine and some steroids

Question 16

What is the function of carrier proteins?

Answer 16

These carrier proteins are a buffer and reservoir that helps to maintain a relatively constant concentration of free lipophilic hormone in the blood, meaning that free and bound hormones are kept in equilibrium

Surges in hormone secretion are buffered by binding to carriers

Free hormone removed from plasma by elimination is replaced by bound hormone dissociating from carrier proteins

Question 17

What form of hormone can pass capillary walls?

Answer 17

Free hormones

Question 18

What is the half-life of amine hormones?

Answer 18

A few seconds

Question 19

What is the half life of proteins and peptide hormones?

Answer 19

A few minutes

Question 20

What is the half-life of steroid and thyroid hormones?

Answer 20

Hours to days

Question 21

Why do steroids and thyroid hormones have much longer half-lives?

Answer 21

Protein binding suppresses elimination

Question 22

What are the 3 main types of hormone receptors?

Answer 22

• G-protein coupled receptors (GPCR)
• Receptor kinases
• Nuclear receptors

Question 23

What types of hormones stimulate G-protein coupled receptors?

Answer 23

Amines
Some proteins/peptides

Question 24

What are the 3 classes of nuclear receptors?

Answer 24

Class I
Class II
Hybrid

Question 25

What usually stimulates class I nuclear receptors?

Answer 25

Activated by many steroid hormones; in the absence of activating ligand, these are mainly located in the cytoplasm, bound to inhibitory heat shock proteins, and move to the nucleus when activated

Question 26

What usually stimulates class II nuclear receptors?

Answer 26

Activated mostly by lipids; constitutively present in the nucleus

Question 27

What usually stimulates hybrid ulcer receptors?

Answer 27

Activated by thyroid hormone (T3) and other substances (Similar in function to class 1)

Question 28

What effect does Gs protein have on a cell?

Answer 28

Stimulation of adenylyl cyclase

Question 29

What effects does Gi protein have on a cell?

Answer 29

Inhibition of adenylyl cyclase

Question 30

What is the function of adenylyl cyclase?

Answer 30

Conversion of ATP to cAMP
Increased cAMP increases PK Activity, which causes cellular effects through phosphorylation of ser/thr residues

Question 31

What effect does Gq have on a cell?

Answer 31

Stimulation of phospholipase C (PLC)

Question 32

What is the function of phospholipase C in a cell?

Answer 32

Conversion of PIP2 to IP3 and DAG release
IP3 causes Ca2+ release from the ER
DAG phosphorylates ser/thr residues

Question 33

What type of receptor does insulin bind to?

Answer 33

Receptor kinase

Question 34

How do receptor kinases work?

Answer 34

Unbound insulin binds to the receptor, causing autophosphorylation of intracellular tyrosine residues

This causes activation of multiple adaptor proteins, notably IRS1, which are also tyrosine phosphorylated

This increases Akt/PKB activity

Question 35

What are some metabolic effects of insulin binding?

Answer 35

• Recruitment of glucose transporters
• Increased glycogen formation
• Increased fat formation
• Changes in gene expression
• Decreased glycogenolysis
• Increased formation of protein