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Lecture 56

Physiology 3120 Lecture Notes - Lecture 56: Zona Fasciculata, Zona Glomerulosa, Zona Reticularis

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Tom Stavraky

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Lecture 56 Adrenal Physiology
Functional anatomy
- Can deal with short term stress and chronic stress (cold, hypoglycemia, fear)
-  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
- 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
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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
- Steroidogenic enzymes are cytochrome p450se.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
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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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