Adrenal Glands & Physiology of stress Flashcards
How many adrenal glands do we have?
What happens when one is removed?
2
The other gets bigger.
What 3 parts is the adrenal correct split into and what does each part make?
Zona glomerulosa - mineralcortocoids (aldosterone)
Zona fasciculata - glucacorticoids (cortisol)
Zona reticularis -
glucacorticoids and some androgens
What does the medulla secrete?
Adrenaline (80%)
Noradrenaline (20%)
Give small details on adrenal histology
Fasciulata - cords of cells
Reticularis also has cords but are smaller.
Glomerulosa cells form below the capsule and then migrate in and go from making aldosterone to making cortisol.
How aldosterone works:
• The mineralocorticoid (comes from cortex and is involved in salt balance) aldosterone is produced exclusively in the zona —-.
• It acts on the distal tubules and collecting ducts of the kidney to promote Na+ —- (to reabsorb it - without aldosterone, we lose sodium in urine and plasma osmolarity falls and we lose plasma volume aka water) and enhances K+ elimination in urine.
• Promotion of Na+ retention induces osmotic retention of —-, causing expansion of the ECF volume, which is important in the long-term regulation of blood pressure.
• Mineralocorticoids are essential for life. Without aldosterone, a person rapidly dies from circulatory shock because of the marked fall in —- —- caused by excessive loss of Na+.
Aldosterone secretion is stimulated by activation of the renin-angiotensin system in response to a reduction in —-and a fall in blood volume. This is —- of anterior pituitary control. When the kidney detects a fall in blood volume, renin is released which activates —- which activates aldosterone).
glomerulosa
retention
water
plasma volume
Na+
independant
angiotensin
How does cortisol work?
It plays an important catabolic role in carbohydrate, protein and fat metabolism to generate an increased pool of glucose, amino acids and fatty acids for use as needed - releases fuel to allow you to respond to stress.
Adrenal medulla:
- What is it part of?
- What is it composed of?
- How do the hormones get released?
- What hormones does it secrete?
- What are stored in vesicles here and why?
Part of the sympathetic nervous system.
• The adrenal medulla is composed of modified postganglionic sympathetic neurons (chromaffin cells).
• They have no axons, but the cells release their chemical transmitter directly into the circulation upon stimulation by the preganglionic nerves.
• The adrenal medulla secretes both noradrenaline (20%), and adrenaline (80%).
Catecholamines are stored in vesicles and released into the circulation by exocytosis in response to acute stress. This is a rapid action telling us adrenaline and noradrenaline have rapid effects.
What is stress and what can it be caused by?
- Stress refers to the generalised non-specific response of the body to any factor that overwhelms, or threatens to overwhelm, the body’s compensatory abilities to maintain homeostasis.
- The agent inducing the response is correctly called a stressor. • Thus stress refers to the state induced by the stressor.
Stressors
Physical: trauma, surgery, intense heat or cold.
Chemical: reduced O2 supply, acid-base imbalance
Physiological: heavy exercise, haemorrhagic shock, pain.
Psychological (emotional): anxiety, fear, sorrow.
Social: personal conflicts, change in lifestyle.
What are the 3 phases of stress?
1) Alarm (fight/flight, short term, adrenaline)
2) Resistance to stress (chronic, cortisol levels elevated)
3) Exhaustion (immune suppression, illness, death)
What is the role of the hypothalamus in phase one?
What endocrine responses are there?
The hypothalamus activates the sympathetic division of the Autonomic Nervous System (ANS), while generally inhibiting parasympathetic control of dually innervated organs.
Endocrine response:
1) Increases sympathetic activation (noradrenaline)
2) Adrenaline release from medulla
3) Increased circulating (nor)adrenaline
What affects do noradrenaline and adrenaline have on the body?
- increased glycogenolysis (liver, muscle), provide glucose (for skeletal muscle)
- increased lipolysis, provide glycerol and fatty acids
- increased cardiac output (more oxygen for muscle and quicker excretion of waste)
- divert blood flow from viscera to skeletal muscle
- increase ventilation (bronchodilation, respiration rate)
What happens in the hypothalamus after 2-3 mins of the stressor?
This activates the adrenal cortex and controlled by anterior pituitary which is controlled by the hypothalamus.
Neurones project to the hypothalamus (the medium eminence).
Neurons make small peptides, made in cell body and transported down. This enters the portal circulation and carries the peptide to the anterior pituitary.
The peptide is the corticotrophin releasing factor. This controls the release of ACTH from the anterior pituitary.
ACTH released from the anterior pituitary enters the venous drainage to be transported to the adrenals.
Explain the mechanism of cortisol secretion and hence ACTH synthesis and secretion
(negative feedback)
• Cortisol secretion is regulated by a negative-feedback system involving the hypothalamus and anterior pituitary.
• ACTH is synthesised in corticotroph cells in the anterior pituitary.
• ACTH secretion is controlled by the hypothalamic secretion of corticotropin-releasing hormone (CRH).
• ACTH stimulates both the growth and secretory output of the two inner layers of the adrenal cortex.
- The feedback loop is completed by cortisol’s inhibitory actions on CRH and ACTH secretion by the hypothalamus and anterior pituitary, respectively.
What are short term affects that cortisol has?
Catabolic effects: opposite those of insulin, maintains metabolic enzyme expression.
• stimulate protein breakdown in muscle, bone, liver, etc. • stimulate hepatic gluconeogenesis
• stimulate lipolysis to generate FA and glycerol
Clinically important because of protein catabolism associated with illness/surgery; insulin requirement in diabetes.
What long term affects does cortisol have?
Enhances cardiovascular reactivity to catecholamines
• allows vasoconstriction in response to (nor)adrenaline
Clinically important because chronic stress can cause hypertension; low/absent cortisol can cause hypotension