Lecture 9 - ACTH and Glucocorticoids- the regulators of stress responses Flashcards
HPA axis: what is it, what do each of the parts release, and what do these secreted hormones do?
Hippocampus - pituitary gland - adrenal gland
The hippocampus releases corticotrophin-releasing hormone (CRH) which activates the pituitary gland
Pituitary gland - releases adrenocorticotrophic hormone which activates the adrenal gland
Adrenal gland - releases cortisol which affects the body
Glucocorticoids: what is an example of a difference between humans and rats/mice?
- Cortisol in humans
- Corticosterone in rats and mice
Hypothalamus and pituitary locations
Hypothalamus sits behind the eye with the pituitary gland just below it, connected by the infundibulum, a stalk of nerves and blood vessels connecting the posterior parts
The pituitary gland sits just below the optic chiasm and just above the sphenoid sinus
Infundibulum
Pituitary stalk
Hormones produced by the adrenal gland: where are they produced, what are the types, and what are examples of them?
Cortex:
* Glucocorticoids - cortisol
* Mineralocorticoids - aldosterone
* Sex steroids - testosterone/oestrogen
Medulla:
* Epinephrine
* Norepinephrine
Glucocorticoid effects: liver, adipose tissue, muscle, immune system, bone, brain, cardiovascular system, kidney, skin, and fetus
- Liver - Increases blood glucose - stimulates gluconeogenesis and glycogenolysis
- Adipose tissue - increase lipolysis
which go to the liver - Muscle - decreases protein synthesis and increases protein metabolism
- Immune system - anti-inflammatory and immunosuppressive effects
- Bone - decrease osteoblasts and stimulate bone resorption
- Brain - affect memory and sleep patterns and mood
- CV system - increase blood pressure and cardiac output
- Kidney - increase water diuresis and glomerular filtration rate, minor effect on sodium retention and potassium
excretion - Skin - inhibit keratinocyte proliferation and
differentiation and reduce sebum production - Fetus - required for organ maturation particularly the lung
Glucocorticoids: what are their effects on the liver?
Liver - Increases blood glucose - stimulates gluconeogenesis and glycogenolysis
Glucocorticoids: what are their effects on the adipose tissue?
Adipose tissue - increase lipolysis
which go to the liver
Glucocorticoids: what are their effects on the muscles?
Muscle - decreases protein synthesis and increases protein metabolism
Glucocorticoids: what are their effects on the immune system?
Immune system - anti-inflammatory and immunosuppressive effects
Glucocorticoids: what are their effects on the bones?
Bone - decrease osteoblasts (inhibiting bone formation) and stimulate bone resorption
Glucocorticoids: what are their effects on the brain?
Brain - affect memory and sleep patterns and mood
Glucocorticoids: what are their effects on the cardiovascular system?
CV system - increase blood pressure and cardiac output
Glucocorticoids: what are their effects on the kidneys?
Kidney - increase water diuresis and glomerular filtration rate, minor effect on sodium retention and potassium
excretion
Glucocorticoids: what are their effects on the skin?
Skin - inhibit keratinocyte proliferation and
differentiation and reduce sebum production
Glucocorticoids: what are their effects on the fetus?
Fetus - required for organ maturation particularly the lung
Glucocorticoids: how do they affect insulin?
They result in glucose production from the liver - initially suppressing insulin to raise blood glucose levels
Once blood glucose levels have been raised, this acts back on the pancreas, causing insulin secretion which causes the recruitment and storing of glucose in tissues such as muscles, supplying them with the glucose they need for the stressful situation they are in
Is the immunosuppressive nature of glucocorticoids always bad?
No, it is only bad when it is uncontrolled
Stopping inflammation is important in not having excessive inflammation and damage to tissues and the body
Gluconeogenesis
Producing glucose from non-carbohydrate sources (proteins etc)
Glycogenolysis
Breaking down glycogen into glucose
Lipolysis
Metabolic process that breaks down fat stores into energy-rich fatty acids and glycerol
Water diuresis
Increased urine flow caused by decreased reabsorption of solute-free water in the collecting ducts
Mechanisms controlling the HPA axis
- Circadian - ACTH/cortisol vary on time
- Pulsatile -
- Stress - promotes CRH release
Circadian rhythm: what is it, how is it different to a diurnal rhythm, and how can it be related to the HPA axis?
The natural 24-hour cycle of physical, mental, and behavioural changes that occur in the body
Diurnal rhythm - 24-hour cycle synchronized to and dependent on an external cue
Circadian rhythm - 24-hour cycle based on internal, cyclic events (synchronised to but not dependent on an external cue)
Diurnal Rhythm - ACTH and cortisol levels are highest at ~06.00 and lowest at ~00:00