Human Physiology Revision Notes for Biology NEET

Human Physiology is a fundamental chapter in NEET Biology, as it explores how various systems in our body function together to maintain life. Understanding the organs, mechanisms, and regulations within systems like respiration, circulation, excretion, movement, nervous, and endocrine ensures strong conceptual clarity and aids in quick problem-solving during exams. Effective revision of this chapter requires concise points, data, and well-organized content to remember key details and differentiate normal functions from associated disorders.

Breathing and Respiration Respiratory organs vary across animal groups. Fish possess gills, insects have tracheal systems, and mammals, birds, and reptiles use lungs. The human respiratory system consists of nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli, all of which filter, warm, and transport air to facilitate gas exchange. The lungs are spongy and highly vascular, maximizing oxygen absorption.

Mechanism of Breathing and its Regulation Breathing involves two phases: inspiration (inhalation) and expiration (exhalation). During inspiration, diaphragm and external intercostal muscles contract, increasing thoracic volume and reducing the pressure to draw air in. Expiration is typically passive and occurs when these muscles relax. Breathing rate and rhythm are regulated by the respiratory center in the medulla oblongata and pons in the brain. Chemoreceptors in the carotid body and aortic body detect CO2 and O2 levels, influencing the breathing rate.

Exchange and Transport of Gases Within alveoli, oxygen diffuses into blood while carbon dioxide diffuses out due to concentration gradients. Oxygen mostly binds to hemoglobin to form oxyhemoglobin, while carbon dioxide is transported as bicarbonate ions (majorly), dissolved in plasma, or bound to hemoglobin. The Bohr effect and Haldane effect explain how gas binding is affected by blood conditions, ensuring efficient exchange during different physiological states.

Respiratory Volumes Some important terms are:

• Tidal Volume (TV): Air taken in or out during normal breath (~500 ml in adults)
• Vital Capacity (VC): Max air expelled after maximum inhalation (~4000-4600 ml)
• Residual Volume (RV): Air left in lungs after maximal expiration (~1100-1200 ml)

Respiratory Disorders Asthma is marked by narrowing of bronchioles, causing breathing difficulty. Emphysema involves damage to alveolar walls, resulting in decreased surface area for gas exchange (often due to smoking). Occupational disorders such as silicosis and asbestosis are caused by inhalation of dust in certain professions, leading to chronic lung problems.

Body Fluids and Circulation Blood is composed of plasma (fluid part), red blood cells (RBCs), white blood cells (WBCs), and platelets. Plasma transports nutrients, hormones, and waste. RBCs carry oxygen, while WBCs defend against infection and platelets help in clotting. Blood groups (A, B, AB, O) depend on antigen type; Rh factor is also significant, especially during pregnancy. Blood coagulation (clotting) involves cascade of factors culminating in conversion of fibrinogen to fibrin, sealing wounds to prevent blood loss.

Lymph and its Function Lymph is a colorless fluid derived from blood plasma, lacking RBCs but containing WBCs. It circulates via lymphatic vessels, draining into venous blood. Lymph transports digested fats, returns protein and fluid from tissues to blood, and contributes in immune defense.

Human Circulatory System The human heart is a muscular, four-chambered organ with two atria and two ventricles. Deoxygenated blood returns via veins to the right atrium, moves to right ventricle, and is pumped into pulmonary artery to lungs. Oxygenated blood comes from lungs via pulmonary veins to left atrium, enters left ventricle, and is sent throughout the body by the aorta. Blood vessels include arteries, veins, and capillaries, each with specific structures and roles.

Cardiac Cycle and Double Circulation The cardiac cycle is the sequence of events during a heartbeat (average: 0.8 seconds). It consists of atrial systole, ventricular systole, and joint diastole. Cardiac output is the amount of blood pumped by each ventricle per minute (about 5 liters in adults). Double circulation means blood passes through the heart twice in one complete cycle: once for oxygenation in the lungs and once for distribution to body tissues.

Regulation and Disorders of Circulation Cardiac activity is regulated by the nervous system and hormones like adrenaline. Electrocardiogram (ECG) records the electrical activity of the heart, helping diagnose disorders. Common issues include:

• Hypertension: Chronic high blood pressure
• Coronary artery disease: Blockage in arteries supplying the heart
• Angina pectoris: Chest pain due to inadequate oxygen supply to heart muscles
• Heart failure: Inability of heart to pump sufficient blood

Excretory Products and Their Elimination Excretion is how the body removes waste. Animals exhibit different modes: ammonotelism (ammonia excretion, aquatic animals), ureotelism (urea excretion, mammals), and uricotelism (uric acid excretion, birds, reptiles). Humans are ureotelic.

Human Excretory System The human excretory system includes two kidneys, ureters, urinary bladder, and urethra. Nephron is the functional unit, consisting of Bowman's capsule, glomerulus, proximal and distal convoluted tubules, loop of Henle, and collecting duct. Urine formation happens through three steps: glomerular filtration, tubular reabsorption, and tubular secretion.

Osmoregulation and Kidney Function Regulation The kidneys regulate fluid balance and electrolytes (osmoregulation). Key mechanisms for regulation include:

• Renin-angiotensin system: Increases blood pressure and maintains sodium balance
• Atrial Natriuretic Factor: Decreases blood pressure by promoting sodium excretion
• ADH (antidiuretic hormone): Controls water reabsorption; its deficiency causes diabetes insipidus (excessive dilute urine)

Other organs like lungs, skin, and liver also eliminate wastes.

Excretory System Disorders and Management Uraemia refers to high urea in blood due to kidney dysfunction. Renal failure is when kidneys cannot filter wastes effectively. Renal calculi are kidney stones (crystalline deposits), while nephritis is inflammation of nephrons. Dialysis is a medical process for waste removal in cases of renal failure; artificial kidney is used for patients awaiting transplant.

Locomotion and Movement Movement occurs in various forms:

• Ciliary (cilia in protozoa and human respiratory tract)
• Flagellar (flagella in sperm, Euglena)
• Muscular (muscles in limbs, face etc.)

Skeletal muscles contain contractile proteins: actin and myosin. Muscle contraction follows the sliding filament theory, needing ATP and calcium ions. The contraction is initiated by nerve stimulation.

Skeletal System, Joints, and Disorders The human skeleton supports, protects, and provides shape to the body. Joints connect bones and enable movement; types include fibrous, cartilaginous, and synovial. Muscular and skeletal disorders include:

• Myasthenia gravis: Weakness due to improper nerve-muscle communication
• Tetany: Muscle spasms due to low calcium
• Muscular dystrophy: Progressive wasting of muscles
• Arthritis: Joint inflammation
• Osteoporosis: Decrease in bone density
• Gout: Joint pain due to uric acid crystal deposition

Neural Control and Coordination Neurons are specialized cells transmitting nerve impulses. Each neuron consists of a cell body, dendrites, and an axon. Proper conduction ensures efficient communication. Human nervous system has three main parts:

• Central nervous system (CNS): Brain and spinal cord
• Peripheral nervous system (PNS): Nerves outside CNS
• Visceral nervous system: Regulates internal organs

The nerve impulse is generated by changes in membrane potential and conducted via action potentials.

Chemical Coordination and Regulation Coordination is also achieved chemically using hormones secreted by endocrine glands. The main glands are pituitary, hypothalamus, pineal, thyroid, parathyroid, adrenal, pancreas, and gonads. Each gland produces specific hormones that regulate metabolism, growth, reproduction, and other vital processes.

Mechanism of Hormone Action and Disorders Hormones act as messengers, binding to receptor sites on target cells and triggering specific responses. Their deficiency or excess leads to disorders:

• Dwarfism: Low growth hormone
• Acromegaly: Excess growth hormone in adults
• Cretinism: Low thyroid hormone in infants
• Goiter: Enlarged thyroid, usually due to iodine deficiency
• Exophthalmic goiter: Excess thyroid hormone (Graves’ disease)
• Diabetes: Insulin deficiency
• Addison’s disease: Low adrenal cortex hormones

Understanding these diseases and their symptoms is important for NEET preparation.

NEET Biology Revision Notes – Human Physiology: Key Concepts and Disorders

Mastering NEET Biology Human Physiology topics is essential for scoring well in entrance exams. Well-structured revision notes help students quickly recall facts about the respiratory, circulatory, excretory, locomotor, nervous, and endocrine systems. These notes also provide concise summaries of associated disorders and regulatory mechanisms crucial for MCQs.

Students can boost their preparation by focusing on diagrams, processes, and data points provided here. Organized revision helps in understanding complex physiological processes and enables rapid last-minute review. Convenient, targeted notes strengthen foundation for both theoretical and application-based questions in NEET exams.