Adrenal Glands

Adrenal Glands

1. Anatomy

   • Located on top of the kidneys and weigh about 5g
   • Yellow in colour due to their lipid content
   • Pyramidal shape
   • It is a very vascular organ
   • Arterial supply
     • Inferior phrenic artery (superior spurarenal artery)
     • Aorta (middle suprarenal artery)
     • Renal artery (inferior suprarenal artert)
   • Venous drainage
     • Inferior vena cava (right)
     • Renal vein (left)
     • There is only a single venous drainage to each gland so are prone to thrombosis.

2. Adrenal Cortex

   • Zona Glomerulosa
     • Secretes mineralocorticoids
       • Affect mineral homeostasis
       • Aldosterone
         • Renin-angiotensin-aldosterone pathway (RAAS cycle)
           • Renin-angiotensin-aldosterone Pathway (RAAS Cycle) - Flowchart
         • Regulates homeostasis of Na+ and K+
         • Helps adjust blood pressure and blood volume
         • Promotes excretion of H+ in the urine
   • Zona Fasiculata
     • Secretes glucocorticoids
       • Affect glucose homeostasis and metabolism
       • Cortisol
       • Corticosterone
       • Cortisone
       • Functions
         • Breakdown of proteins in muscle fibres
         • Glucose formation (gluconeogenesis) in the liver
         • Lipolysis in adipose tissue
         • Resistance to stress by making blood vessels more sensitive to hormones that cause vasoconstriction
         • Anti-inflammatory effects by inhibiting innate white blood cells
         • Depression of immune responses (good in organ transplants)
   • Zona Reticularis
     • Secretes androgens
       • Steroid hormones with masculinising effects
       • Dehydroepiandrosterone (DHEA)
         • Only really significant in women
         • Promotes labido
         • Converting into oestrogens by other body tissues
       • Controlled by ACTH

3. Adrenal Medula

   • Inner region of adrenal gland
   • Modified sympathetic ganglion of the ANS
     • Chromaffin cells (produce hormones) are innervated by sympathetic preganglionic neurons of the ANS, so hormones are released VERY quickly
   • Produces catecholamines
     • 80% Epinephrine (adrenaline)
     • 20% Norepinephrine (noradrenaline)
     • Intensify sympathetic responses that occur in other parts of the body
       • Increase heart rate and force of contraction, thus increasing blood pressure
       • Increase blood flow to the heart, liver, skeletal muscles and adipose tissue
       • Dilate airways to the lungs
       • Increase blood levels of glucose and fatty acids
     • "Fight or flight"