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Samenvatting Physiology - Endocrine System
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Summary of the lecture of the course Physiology, from the study Biology at the University of Groningen, about the endocrine system. Images included.
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Physiology notesAdrenals = cap on the kidneys. Important in stress response/hormones.
Activated in the hypothalamus and the pituitary gland (connected).
Adrenals secrete steroid hormones.
Pituitary = receives input from neurons in hypothalamus, these neurons
secrete stimulating releasing/inhibiting hormones. These hormones
stimulate the pituitary (only anterior pituitary!)
- Produces ACTH stimulates adrenal cortex.
Adrenals
Adrenal cortex surrounds the adrenal medulla. Capsule surrounds the
adrenal.
Medulla produces catecholamines (adrenalin) and is stimulated by the
sympathetic NS.
Cortex (stimulated hormonally):
1. Zona glomerulosa: mineralocorticoids
2. Zona fasciculata: glucocorticoids (cortisol)
3. Zona reticularis: sex hormones
Adrenal cortex
Basis of all steroid hormones = cholesterol
Hormones produced depends on the specific enzymes absent/present.
- Steroid hormones are not ‘stored’ in cells, because they are
lipophilic (diffuse through cell membranes). Cannot be contained in a
vesicle. ‘Slow hormones’
- 21-hydroxylase (enzyme) is sometimes not sufficiently produced in
patients (not enough cortisol (stress) and aldosterone (salt retention
in kidneys)).
- Congenital adrenal hyperplasia: adrenogenital syndrome (high
level of testosterone). Because there is not enough 21-hydroxylase
more progesterone turns into testosterone etc.
- CRH (corticotrope releasing hormone/factor) is produced in the
hypothalamus. Released in the blood of the pituitary.
stimulates release of ACTH (adrenocorticotropic
hormone) circulates through whole body
adrenal gland stimulates release of cortisol.
- Cortisol influences the brain stem and immune
system (with high levels)
- POMC in the anterior pituitary is cleaved into
fractions, of which ACTH.
Cortisol
- Origin = adrenal cortex
- Chemical nature = steroid
- Made from cholesterol
- Transported on corticosteroid-binding globulin
(made in liver)
- Stress enhances release
- CRH (hypothalamus ACTH (anterior pituitary)
cortisol (adrenal cortex)
, - Necessary for glucagon and catecholamines (hormones)
- Necessary as a preparation for activity (synthesizes neurons for
noradrenalin). + sensitizes the receptors in the hypothalamus for
noradrenalin.
Circadian rhythm
ACTH
- Activates cyclic AMP activates all kind of enzymes in adrenal
cortex
- Stimulates synthesis and release cortisol
Effects cortisol on metabolism:
Mobilisation of energy
o Liver: gluconeogenesis glucose
o Fat: lipolysis FFA
o Muscle: glycogenolysis to release amino acids
With hypoglycemia (low blood sugars) cortisol is needed for the action of
glucagon (antagonist of insulin)
Cortisol has a hormone that stimulates lung riping of the foetus: facilitate
maturation.
Cortisol helps us to remember certain stressful moments.
Hypercortisolemia (extremely high levels of cortisol):
Types of hypercortisolemia
1. Primary: problem with adrenal cortex (low CRH and low ACTH)
2. Secondary: problem with pituitary (low CRH and high ACTH)
3. Tertiary: problem with hypothalamus (high CRH and high ACTH)
4. Iatrogenic: caused by medication
Chronic elevated cortisol: inhibition of cortisol
Acute, short-lasting elevated cortisol: preparation immune response
Cushing’s syndrome/disease: chronically high cortisol levels
- Local fat disposition (abdominal, facial, between shoulders)
- Breakdown muscle and connective tissue (striae)
Addison’s disease: autoimmune disorder where your adrenal cortex cells
are broken down and attacked by your own body.
- Fatigue, weight loss, hyperpigmentation (failing feedback to alpha-
MSH)
- Low blood pressure
- Low blood sugar (hypoglycemia)
- Depression
Cortisol/corticosterone effect structure of neurons and their excitability.
Play a role in emotional events and memory.
- Membrane and cytosolic receptors
Adrenal medulla
Tyrosine dihydroxyphenylalanine
dopamine norepinephrine epinephrine
Membrane receptors of adrenalin: 1, 2, 3
and 1, 2
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