Week 2 - Neuroendocrinology

Question 1

Neuroendocrinology

Answer 1

the interaction between the nervous system and the endocrine system - the two major homeostatic systems involved in control and regulation of bodily functions.

Question 2

What is the role of the Nervous system?

Answer 2

uses neurotransmitters to relay messages from one nerve to another or from a nerve to a tissue.

Question 3

What is the role of the endocrine glands?

Answer 3

endocrine glands releases hormones into blood to circulate to tissues.

Question 4

Hormones

Answer 4

chemical messengers secreted from endocrine glands that signal changes in other organs and tissues throughout the body.

They only affect tissues that contain specific hormone receptors.

Question 5

3 classes of hormones

Answer 5

1) Amino acid derivatives (thyroxine, epinephrine and norepinephrine)
2) Peptide/protein (insulin, glucagon, ADH and ACTN)
3) Steroids (glucocorticoids, aldosterone)

Question 6

What is plasma concentration determined by?

Answer 6

1. Rate of secretion of hormone from endocrine gland
2. Rate of metabolism or excretion of hormone
3. Quantity of transport proteins
4. Changes in plasma volume

Question 7

What is the magnitude of the effect of a hormone dependent on?

Answer 7

1) Concentration of the hormone
2) Number of target receptors on the cell
3) Affinity of the receptor for the hormone

Question 8

What is the difference between downregulation and upregulation in receptors?

Answer 8

Downregulation - decrease in receptor number in response to high concentration of hormone

Upregulation - increase in receptor number in response to low concentration of hormone

Question 9

What is an example of downregulation?

Answer 9

an individual with high bp could be treated with beta-blocker drug which reduces binding of adrenaline to the cell.

Question 10

What are the 3 mechanisms of hormone action?

Answer 10

1) Activation of genes to alter protein synthesis (steroid hormones: cortisol, testosterone)

2) Activating ‘second messengers’ in the cell via G protein (cyclic AMP)

3) Altering membrane transport (insulin via tyrosine kinase)

Question 11

Hypothalamus

Answer 11

controls secretion of hormones from pituitary glands (anterior and posterior)

Question 12

Antidiuretic hormone (ADH)
1) Site of release
2) Stimulus for release
3) Predominant action

Answer 12

1) Secreted from posterior pituitary gland

2) Release is stimulated by high plasma osmolality and low plasma volume (due to sweat loss without water replacement)

3) Reduces water loss from the body to maintain plasma volume - favours the reabsorption of water from kidney tubules to the capillaries

Question 13

How does exercise influence plasma ADH concentrations?

Answer 13

Exercise >60% of V02 max increases plasma ADH due to increase in plasma osmolality and decrease in plasma volume.

Question 14

Aldosterone (mineralocorticoid)
1) Site of release
2) Stimulus for release
3) Predominant action

Answer 14

1) Secreted from the adrenal cortex

2) Release stimulated by an increased plasma K+ concentration (causes negative feedback loop), decrease plasma volume and bp when extracellular Na+ is lost, Angiotensin II, ACTH.

3) Control of Na+ reabsorption and K+ secretion (Na+/H20 balance) + regulation of blood volume and blood pressure

Question 15

How does exercise influence renin, angiotensin II and aldosterone?

Answer 15

all 3 hormones increased during exercise, the effect takes >45mins (steroid hormones) so major effect is post exercise

Question 16

Name the 2 hormones responsible for control of plasma volume.

Answer 16

1) Aldosterone
2) Antidiuretic hormone (ADH)

Question 17

What are the 4 processes that maintain blood glucose during exercise?

Answer 17

1) Mobilisation of glucose from liver glycogen stores
2) Mobilisation of FFA from adipose tissue (spares blood glucose)
3) Gluconeogenesis from amino acids, lactic acid, and glycerol
4) Blocking the entry of glucose into cells (forces use of FFA as a fuel)

Question 18

Two types of “acting” hormones

Answer 18

1) Permissive or slow-acting (Thyroid, cortisol, growth hormone): allow other hormones to exert their full effect.

2) Fast-acting (Epinephrine, norepinephrine, insulin and glucagon)

Question 19

Growth hormone
- Why is it essential for growth of all tissues?
- How does it change during exercise?
- What is its secretion stimulated by and when is its secretion at its peak?

Answer 19

Increases amino acid uptake, cartilage growth and protein synthesis in muscle and long bone growth.

Increase in plasma GH with an increase in exercise intensity.

Its secretion is stimulated by ghrelin and secretion it as its peak during sleep.

Question 20

What are the 3 ways which growth hormone spares plasma glucose?

Answer 20

1. Reduces the use of plasma glucose
2. Increases gluconeogenesis (in liver)
3. Mobilize fatty acids from adipose tissue

Question 21

Cortisol
- Where is it derived from?
- Where is it secreted from?
- What is it stimulated by?
- What is its role?
- Influence of exercise intensity on cortisol.

Answer 21

• Derived from cholesterol
• Secreted from the adrenal cortex
• Stimulated by stress (via ACTH - adrenocorticotropic hormone) and exercise
• Increases the release of fatty acids from adipocytes and glucose from liver cells
• Increases proportional to increases in exercise intensity

Question 22

What are two considerations when measuring cortisol?

Answer 22

1) Diurnal variation: concentrations peak in the am (6am) and drop throughout the day
2) Emotional arousal

Question 23

Catecholamines
- Where is it secreted from?
- What receptors do they bind to?
- Slow-acting or fast-acting?
- Influence of exercise
- How does endurance training influence catecholamine at a fixed intensity exercise bout?
- What do trained individuals have a greater capacity to do? Why?

Answer 23

• Adrenal medulla: epinephrine (80%) and norepinephrine
• Adrenergic receptors
• Fast-acting
• Plasma E and NE increase during exercise which is related to increased HR and BP during exercise (sympathetic activation)
• Rapid decrease in catecholamine in response to a fixed intensity exercise about.
• Greater capacity to increase catecholamines (35%) compared to untrained individuals in response to supramaximal exercise - because regular stimulation of SNS increases capacity of response.

Question 24

How does high-intensity exercise influence plasma epinephrine? What is plasma epinephrine a powerful stimulator of?

Answer 24

High-intensity exercise results in greater increase in plasma epinephrine.
Plasma epinephrine is a powerful stimulator of glycogenolysis.

Question 25

Explain why the blocking of epinephrine doesn’t stop glycogenolysis (muscle glycogen breakdown).

Answer 25

Breakdown of muscle glycogen is under dual control.
1) Epinephrine is the extracellular way and this activates phosphorylase kinase which activates phosphorylase to breakdown glycogen.
2) The intracellular control involves calcium release from SR which bind to calmodulin (+ AMP release), in turn activating phosphorylase kinase which then activates phosphorylase to breakdown glycogen.

Question 26

Insulin
- Define its role.
- How does exercise change plasma insulin?

Answer 26

• promotes uptake and storage of glucose, amino acids, and fats (lower their levels in plasma)
• during moderate-intensity exercise, insulin levels drop (50%) to favour mobilization of glucose from the liver and FFA from adipose tissue

Question 27

Glucagon
- Describe its role.
- How does endurance training change plasma glucagon during exercise?

Answer 27

• promotes the mobilization of fatty acids and glucose + stimulates gluconeogenesis in the liver.
• Glucagon response is diminished to the point there is little to no increase during exercise.

Question 28

What does the ratio of glucagon to insulin determine?

Answer 28

the mobilization of FFA and glucose

Question 29

Where is insulin and glucagon released from?

Answer 29

Insulin from beta-cells in the pancreas
Glucagon from alpha-cells in the pancreas

Question 30

What is the effect of catecholamines on insulin and glucagon secretion?

Answer 30

Increased E/NE leads to increased glucagon secretion and decreased insulin secretion. This leads to increase liver glycogen breakdown which maintains blood glucose, and it increases lipolysis of TG which increased plasma FFA.

Question 31

Name the hormones that increase in plasma concentration, mobilise fat and CHO, and preserve blood glucose during exercise.

Answer 31

Epinephrine, Norepinephrine, Growth Hormone, Cortisol, Glucagon

Question 32

Explain why trained individuals can use more fat as a fuel whilst sparing the limited CHO stores?

Answer 32

1) Decreased lactate concentration at any fixed work rate, which reduces this inhibition to FFA mobilization from adipose tissue.
2) Increases in mitochondria which increases capacity for FFA oxidation.

Question 33

Difference between nervous control and hormonal control.

Answer 33

Nervous control
- Rapid response to reflex excitation.
- Rapid offset after stimulus removed.

Hormonal
- Response may take minutes to hours to reach maximum.
- After stimulus is removed, effects can last for minutes or even hours.

Question 34

Is aldosterone secretion controlled by hormonal feedback?

Answer 34

No
- Aldosterone secretion is regulated by the need to maintain a normal blood volume and blood pressure and a normal plasma K+ concentration.

Question 35

What is the difference between endocrine signaling and paracrine signaling?

Answer 35

Endocrine signaling allows control of cell function throughout the body. Hormones are secreted from endocrine cells and enter the blood to be carried to the target organs.

Paracrine signaling is important in regulating gastrointestinal secretions and motility. Neuroendocrine cells secrete peptides that diffuse locally and affect smooth muscle and secretory glands. Also vital in fetal development.

Question 36

Epinephrine role

Answer 36

increases release of fatty acids from adipocytes and release of glucose from the liver

Question 37

What are the 2 influences of thyroid hormones?

Answer 37

1) Influences the number of receptors on the surface of a cell for other hormones to interact with.
2) They influence the affinity of the receptor for the hormone.