ADRENAL GLANDS – Physiology Lecture Slideshow

Learning Objectives

At the end of the lecture all the students should be able

to:

• Explain the location of adrenal gland, its functional anatomy and importance.
• Elucidate the mechanism of synthesis of the adrenal hormones.
• Know the different hormones secreted from adrenal cortex and medulla.
• Elucidate the general features regarding the ACTH

Adrenal Glands

• Divided into two parts; each with separate functions
• Adrenal Cortex
• Adrenal Medulla

Zona Glomerulosa

• Outermost zone – just below the adrenal capsule
• Secretes mineralocorticoids.
• Mineralocorticoids are termed as they are involved in regulation of electrolytes in ECF.
• The naturally synthesized mineralocorticoid of most importance is aldosterone.
• The other is deoxycorticosterone.

Mineralocorticoids

• Aldosterone
• Deoxycorticosterone
• Corticosterone
• 9α- Fluorocortisol
• Cortisol
• Cortisone

Zona Fasciculata

• Middle zone – between the glomerulosa and reticularis
• Primary secretion is glucocorticoids.
• Glucocorticoids, as the term implies, are involved the increasing of blood glucose levels. However they have additional effects in protein and fat metabolism.
• The naturally synthesized glucocorticoid of most importance is cortisol.

Zona Reticularis

• Innermost zone – between the fasciculata and medulla
• Primary secretion is androgens.
• Androgenic hormones exhibit approximately the same effects as the male sex hormone – testosterone.

Overlap in the secretions of androgens and glucocorticoids exist between the fasciculata and reticularis.

Glucocorticoids

• Cortisol
• Corticosterone
• Cortisone
• Prednisolone
• Methylprednisolone
• Dexamethasone

Synthetic pathway

• LDL
• Via endocytosis
• ACTH
• Cholesterol desmolase as rate limiting enzyme

ACTH: corticotropin

• Cell: Corticotropes
• Type: peptide 39 aa
• Receptor: cell surface
• Mechanism of Action: cAMP
• CRF?

Transport

• Transcortin
• Cortisol binding globulin
• Albumin
• 90-95% cortisol
• 60% aldosterone

Metabolism

• In liver
• Conjugated to glucuronic acid and sulphates
• Excretion via feces and urine

Regulation of glucocorticoids

• Circadian Rhthem
• Highest level at 6 A.M.
• About 75 % of cortisol are produced at 4-10 AM
• These changes are parallel to changes in ACTH and CRH
• Changes in sleep wake cycles as in shift worker results in daily changes in rhythm of cortisol secretion

EPINEPHRINE & NOR-EPINEPHRINE

Catecholamines

1. Dopamine
   – Biosynthetic precursor of noradrenaline and adrenaline
   – Acts as a neurotransmitter in the central nervous system
2. Noradrenaline (norepinephrine)
   – Neurotransmitter of sympathetic nerves (Autonomic
   Nervous System)
3. Adrenaline (epinephrine)
   – Produced primarily in the adrenal medulla
   – Only catecholamine whose action is strictly hormonal

Regulation of Adrenal Medullary Secretion

Catecholamine receptors