Physiology 3120 Lecture Notes - Lecture 56: Zona Fasciculata, Zona Glomerulosa, Zona Reticularis
15 May 2018
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Lecture 56 – Adrenal Physiology
Functional anatomy
- Can deal with short term stress and chronic stress (cold, hypoglycemia, fear)
CORTEX
- zones
- Address stress in a chronic matter
o Fear over a long period of time, hypoglycemia, cold temperatures = activate
hypothalamic adrenal axis = make cortisol to deal with long term stress
- Source of adrenal steroids
- Regulated by pituitary ACTH
- Zona glomerulosa - aldosterone (steroid hormone)
- Zona fasciculata – cortisol
- Zona reticularis – sex steroids
- CORTISOL: raises blood glucose which is sent to the brain to help in stressful situations
o Opposes actions of insulin and behaves similarly to glucagon
o Unlike glucagon, cortisol is released under situations of stress rather than rapidly
MEDULLA
- Composed of chromaffin cells (neuroendocrine cells that are innervated)
- Source of catecholamines for fight or flight situations in addition to CNS
- Secretion controlled by direct innervation; neuroendocrine response
- In dealing with short term stress, SYN is not enough and adrenal medulla helps
Adrenal steroidogenesis
- Steroid hormone production occurs in the adrenal cortex
- Precursor for steroid hormones is cholesterol
- Due to intracellular enzymes in the cortex, cholesterol can be converted to different
hormones depending on the activity of the enzymes
o
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o Produce corticoesterone (inactive cortisol)
o 11-deoxycortisol → cortisol (glucocorticoid that helps deal with stress)
o Androstenedione: reproductive precursor hormones → testosterone + estradiol
- Intracellular enzymes in the cortex play a larger role than the synthesis of cholesterol itself
o Interconversion and activity of intracellular enzymes matters more than the amount
of hormone that is produced
o Hormones can be converted on route to its receptor by the action of intracellular
enzymes
- Steroidogenic enzymes are cytochrome p450s—e.g. Cyp17
- All steroid hormones come from cholesterol precursor and interconversion of hormones
occurs due to CYP enzymes in the adrenal cortex
- Found in membranes of mitochondria and ER of adrenocortical cells
- Energy comes from electron transport
- Adrenal cortex is a factory for making steroid hormones
Major pathways for the synthesis of steroid hormones in adrenal cortex
- Glucocorticoids deal with the stress response
- Adrenal cortex makes precursors for reproductive sex hormones (estrogen and
testosterone)
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Hypothalamuc pituitary adrenal axis
- Systemic stress (long term – cold, hypoglycemia, fear) is sensed by higher parts of the brain,
hypothalamus releases CRH and via parvacellular cells, it acts on CRH receptors on anterior
pituitary which then releases ACTH (peptide hormone)
- ACTH enters blood and binds to ACTH receptors in the adrenal cortex
- This leads to an increase in cortisol production from adrenocortical cells
- When levels of cortisol are too high in circulation, there is a negative feedback loop to shut
down the production of CRH at the level of the hypothalamus and ACTH at the level of the
anterior pituitary
- Cortisol helps to raise blood glucose for the brain
o Promotes gluconeogenesis in liver and other organs
o Promote muscle metabolism (break down proteins into AA to be used by the liver to
make more glucose)
o Inhibit GLUT4 in muscle and adipose– opposes actions of insulin to kep circulating
levels of blood glucose high for the brain
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