1. Anatomy of the Adrenal Glands

Located atop each kidney, the adrenal glands are dual-layered organs. The outer 80-90% is the Adrenal Cortex, while the inner core is the Adrenal Medulla. The medulla is functionally a modified sympathetic ganglion of the autonomic nervous system.

2. Chemistry of Medullary Hormones

The medulla secretes Adrenaline (Epinephrine) (~80%) and Noradrenaline (Norepinephrine) (~20%). These are amine hormones derived from the amino acid Tyrosine and are collectively called Catecholamines.

3. The 3F Response: Fight, Flight, or Fright

In response to any stress or emergency, the sympathetic nervous system triggers the rapid release of catecholamines. This is a survival mechanism designed to optimize physical performance.

4. Major Physiological Effects

• Cardiac Effects: Catecholamines increase the rate of heartbeat, the strength of heart contraction, and the speed of nerve impulse conduction through the heart. This maximizes cardiac output.
• Respiratory Effects: They cause bronchodilation (relaxation of smooth muscles in airways), increasing the rate of respiration and oxygen intake.
• Ocular Effects: They cause contraction of the radial muscles of the iris, leading to Pupillary Dilation (Mydriasis). This allows more light to enter the eye for better situational awareness.
• Integumentary Effects: They stimulate the arrector pili muscles, causing piloerection (goosebumps) and increasing activity in sweat glands.
• Vascular Effects: They cause vasoconstriction in the skin and digestive organs but vasodilation in skeletal muscles and the brain, diverting blood where it is needed most.

5. Metabolic Effects (Hyperglycemic Action)

To provide instant energy, catecholamines are strongly hyperglycemic:

• Glycogenolysis: Stimulation of glycogen breakdown in the liver and skeletal muscles into glucose.
• Lipolysis: Breakdown of lipids into fatty acids for energy.
• Proteolysis: Breakdown of proteins into amino acids.

6. Adrenal Medulla vs. Adrenal Cortex

7. Clinical Significance

Pheochromocytoma: A tumor of the adrenal medulla that causes hypersecretion of adrenaline. Symptoms include high blood pressure, rapid heart rate, and excessive sweating. Adrenaline is also used clinically to treat Anaphylactic Shock and Cardiac Arrest.

8. Summary of Findings for NEET

For the exam, remember that medullary hormones "speed everything up." The only thing they "dilate" or "expand" is the pupil and the bronchioles. Everything else (heart rate, blood sugar, sweat) goes UP. Pupillary constriction is a parasympathetic response, which is the opposite of what adrenaline does.