Human Body - Endocrine, Circulatory and Nervous Systems

• (a) Thyroid Gland: Secretes Thyroxine.
Function: Regulates the Basal Metabolic Rate (BMR), carbohydrate/protein metabolism, and physical/mental development.
• (b) Beta Cells of Pancreas: Secretes Insulin.
Function: Lowers blood glucose levels by promoting cellular glucose uptake and converting excess glucose into glycogen in the liver.
• (c) Adrenal Medulla: Secretes Adrenaline.
Function: Prepares the body for emergency stress ("Fight or Flight") by elevating heart rate, blood pressure, and blood glucose.
• (d) Pituitary Gland: Secretes Growth Hormone (GH).
Function: Stimulates normal longitudinal bone growth and body tissue development during childhood.

• Diabetes Mellitus: A chronic metabolic disorder characterized by abnormally high levels of glucose in the bloodstream (Hyperglycemia).
• Cause: Hyposecretion (deficiency) of Insulin by the beta cells of the Islets of Langerhans in the pancreas.
• Common Symptoms:
1. Glycosuria: Excretion of glucose in urine.
2. Polyuria: Frequent, excessive urination.
3. Polydipsia: Intense, unquenchable thirst.
4. Rapid unexplained weight loss and fatigue.
• Management: Controlled carbohydrate diet, regular physical exercise, oral hypoglycemic drugs, and periodic subcutaneous insulin injections.

• The Right Ventricle pumps deoxygenated blood only over a very short distance to the nearby lungs through the pulmonary artery under low pressure.
• The Left Ventricle must pump oxygenated blood through the systemic aorta to all distant organs and extremities of the body (from the brain to the tips of the toes).
• To generate the powerful, high systolic pressure ($120\text{ mm Hg}$) required to overcome systemic vascular resistance, the left ventricle is built with a muscular wall approximately three times thicker than that of the right ventricle.

• Double Circulation: A circulatory system in which blood flows through the human heart TWICE during one complete circuit through the body.
• Two Constituent Pathways:
1. Pulmonary Circulation: Deoxygenated blood pumped from the Right Ventricle travels via the pulmonary artery to the lungs for oxygenation, and oxygenated blood returns via pulmonary veins to the Left Atrium.
2. Systemic Circulation: Oxygenated blood pumped from the Left Ventricle is distributed via the aorta to all body tissues, and deoxygenated blood returns via the vena cava into the Right Atrium.
• This ensures that oxygenated and deoxygenated blood never mix.

1. When a blood vessel is damaged, disintegrating blood platelets and damaged tissue cells release an enzyme called Thromboplastin (Thrombokinase).
   2. In the presence of Calcium ions ($\text{Ca}^{2+}$) and vitamin K, thromboplastin converts inactive plasma protein Prothrombin into active enzyme Thrombin.
   3. Thrombin then catalytically converts soluble plasma protein Fibrinogen into insoluble, sticky, thread-like Fibrin polymers.
   4. The fibrin threads form a dense microscopic meshwork over the wound, trapping red and white blood cells to form a solid, dark red Clot (Thrombus) that seals the vessel and arrests bleeding.

• Reflex Action: A rapid, automatic, involuntary motor response to a sensory stimulus, controlled directly at the level of the Spinal Cord without conscious intervention by the brain.
• Reflex Arc Pathway:
1. Receptor: Thermoreceptors in the fingertip skin detect intense heat.
2. Sensory Neuron: Transmits the electrical nerve impulse along the sensory nerve fiber to the spinal cord.
3. Association (Relay) Neuron: Inside the grey matter of the spinal cord, passes the impulse directly to a motor neuron.
4. Motor Neuron: Carries the command impulse from the spinal cord to the arm muscle.
5. Effector: The biceps muscle contracts immediately, snatching the hand away in a fraction of a second before pain is consciously registered in the brain!

1. Direction of Blood Flow: Arteries carry blood away from the heart; Veins carry blood toward the heart.
   2. Wall Thickness & Lumen: Arteries have thick, muscular, elastic walls and a narrow lumen; Veins have thin, less elastic walls and a wide lumen.
   3. Internal Valves: Arteries have no internal valves (blood surges under high pressure); Veins have semilunar flap valves that prevent the backflow of slow-moving blood under low pressure.

• Simple Goitre: A conspicuous non-cancerous enlargement and swelling of the Thyroid Gland in the front of the neck.
• Cause: Dietary deficiency of Iodine.
• Why Iodised Salt?
The thyroid gland requires mineral iodine as an essential chemical ingredient to synthesize the hormone Thyroxine.
In mountainous regions, glacier runoff washes iodine out of soil and drinking water.
Consuming iodised salt ensures a steady supply of iodine, allowing the thyroid to synthesize adequate thyroxine and preventing thyroid gland swelling.