Introduction to the Endocrine System Hormones, Receptors and Signalling

Question 1

What kinds of glands are in the endocrine system?

Answer 1

Ductless

Question 2

How do glands communicate with each other over a distance?

Answer 2

Secretion of hormone into the blood stream and bulk transport to a target site

Question 3

What is an example of an integrated functional system?

Answer 3

Hypothalamus releases CRF that stimulates the anterior pituatru to release ACTH that causes the adrenal cortex to synthesise and release cortisol

Question 4

How is specificity of signalling achieved?

Answer 4

Chemically distinct hormones
Specific receptors for each hormone
Distinct distribution of receptors across target cells

Question 5

What are the major endocrine organs?

Answer 5

Pineal gland
Hypothalamus
Pituatry gland
Thyroid gland
Parathyroid gland
Thymus
Adrenal glands
Pancreas
Ovary
Testis

Question 6

What are the 4 chemical natures of hormones?

Answer 6

Modified Amino acids
Steroids
Peptides
Proteins

Question 7

What are some examples of modified amino acids?

Answer 7

Adrenaline

Thyroid hormone

Question 8

What are some examples of steroids?

Answer 8

Cortisol
Progesterone
Testosterone

Question 9

What are some examples of peptides?

Answer 9

Anrenocorticotrophic hormone (ACTH)
Anti-diuretic hormone (ADH)
Oxytocin

Question 10

What is an example of a protein?

Answer 10

Insulin

Question 11

What are all steroid hormones derived from?

Answer 11

Cholesterol

Question 12

What is autocrine signalling?

Answer 12

Cell produces signalling molecule that is released into to ECF, these molecules act on the cell itself
(Self-signalling)

Question 13

What is Paracrine signalling?

Answer 13

Cell signals to its close neighbors

Question 14

What is endocrine signalling?

Answer 14

The signalling molecule enters the circulation and signals via molecules transported by the blood to target distant cells

Question 15

What levels of hormones can affect organ function?

Answer 15

Can be very low concentrations

utilises signals which act at an extremely low concentration

Question 16

If the signal is very scarce, what must be increased?

Answer 16

Receptor Affinity

Hormone Potency

Question 17

What are some examples of where insulin can act?

Answer 17

Skeletal Muscle
Adipose tissue
Hepatocytes

Question 18

How is a biological response brought about?

Answer 18

Hormone binds to its cognate receptor which is expressed in a tissue selective manner

Question 19

What triggers a biological response?

Answer 19

Activated receptor engaging in a preferred signal transduction cascade that differs between individual receptors but typically causes amplification of the original signal

Question 20

Is the speed of onset and duration of a hormone variable?

Answer 20

Yes very

seconds to days

Question 21

How is hormone action terminated?

Answer 21

Enzyme mediated metaboloic inactivation in the liver or site of action

Question 22

What is a complementary action of a group of hormones?

Answer 22

Regulates many complex physiological functions on both short and long term scales

Question 23

What is an example of a complementary action of a group of hormones?

Answer 23

Adrenaline, cortisol and glucagon contribute to the response of the body to short term intense exercise enhancing physical performance and preventing potential hypoglycaemia

Question 24

How does an antagonistic action occur?

Answer 24

The balance of opposing influences

Question 25

What 2 hormones have opposing actions that regulates plasma glucose levels?

Answer 25

Insulin | Glucagon

Question 26

How are amines made, stores and released?

Answer 26

Pre-synthesised Stored in vesicles Released in response to stimuli by Ca2+ dependent exocytosis

Question 27

Are amines hydrophilic or hydrophobic?

Answer 27

Hydrophillic

Question 28

How are peptides and proteins made, stores and released?

Answer 28

Presynthesised from longer precursors Stored invesicles Released in response to stimuli by Ca2+ dependent exocytosis

Question 29

Are peptides hydrophillic or hydrophobic?

Answer 29

Hydrophyllic

Question 30

How are steroids made, stores and released?

Answer 30

Synthesised and secreted upon demand Stimuli increase: -Cellular uptake and availlibility of cholesterol -Rate of conversion of choolesterol to pregnenolone

Question 31

When is cortisol released?

Answer 31

Immediately after it is formed | No prestorage or packaging

Question 32

What must occur for a cell to produce a steroid hormone?

Answer 32

The cell must initiate synthesis and release the steroid immediately

Question 33

Are steroids hydrophobic or hydrophyllic?

Answer 33

Hydrophobic

Question 34

How are steroids transported in blood?

Answer 34

Bound to specific transport proteins

Question 35

What is the fraction of steroid that is unbound able to do?

Answer 35

Biologically active | Can cross the wall

Question 36

What are 3 steroids that must be carried by circulating carrier proteins?

Answer 36

Steroids Thyroxine Triiodothyronine

Question 37

What are some functions of carrier proteins?

Answer 37

Increase amount transported in blood Provide a reservoir of hormone Extends half life of the hormone in the circulation

Question 38

What are 3 important plasma carried proteins?

Answer 38

Cortisol-binding globulin (CBG) Thyroxine-binding globulin (TBG) Sex steroid-binding globuling (SSBG)

Question 39

What are 2 general carrier proteins?

Answer 39

Albumin | Transthyretin

Question 40

What do carrier proteins act as?

Answer 40

A buffer and reservoir that helps to maintain relatively constant concentrations of free lipophilic hormone in the blood - equillibrium between free and bound hormone

Question 41

What hormones can cross the capillary wall?

Answer 41

Only free hormone

Question 42

What are surges in hormone secretion buffered by?

Answer 42

Binding to carriers - free concentration does not rise abruptly

Question 43

How is free hormone removed from plasma?

Answer 43

By elimination

Question 44

What is the free hormone that is removed by plasma replaced with?

Answer 44

Bound hormone dissociating from carrier proteins

Question 45

What is the primary determinant of plasma concentration?

Answer 45

Rate of secretion

Question 46

Describe the pathway in which cortisol is released?

Answer 46

``` Hypothalamus Secretes corticotrophin releasing factor (CRF) Anterior pituitary Secretes ACTH Adrenal cortex Secretes cortisol ```

Question 47

What is diurnal circadian rhythm?

Answer 47

Secretion rate fluctuates (up and down) as a function of time entrained by external cues

Question 48

What important routes can elimination occur by?

Answer 48

Metabolism locally Metabolism by the liver Excretion by the kidney

Question 49

What is plasma concentration of a hormone equal to?

Answer 49

Rate of secretion - rate of elimination

Question 50

What are 3 types of Hormone receptors?

Answer 50

G coupled protein receptors Receptor kinases Nuclear receptors

Question 51

How are GPCR activated and where are they found?

Answer 51

Activater by amines and some proteins and peptides | Found on the cell surface

Question 52

What are receptor kinases activated by and where are they found?

Answer 52

Proteins and petides | Found on the cell surface

Question 53

Where are nuclear receptors found?

Answer 53

INtracellularly - In cytoplasm (class 1) - In nucleus

Question 54

What are the 3 classes of nuclear receptors?

Answer 54

Class 1 - activated by many steroid hormones, in the absense of activating ligand these are mainly located in the cytoplasm bound to heat shock proteins Class 2 - activated mostly by lipids, present in the nucleus Hybrid class - Activated by thyroid hormone and other substances

Question 55

What is constitutive activity?

Answer 55

Always active without any signals

Question 56

What kind of receptor is the insulin receptor?

Answer 56

Receptor kinases

Question 57

What subunits are present in the insulin receptors?

Answer 57

Alpha and Beta subunits

Question 58

What does the binding of insulin to the receptor cause?

Answer 58

Autophosphorylation of intracellular tyrosine residues Recruitment of multiple adapter proteins (IRS1) that are also tyrosine phosphorylated - binding of Insulin receptor substrate proteins which become phosphorylated -AKT/Protein Kinase B -Metabolic effects