NEET Biology Notes – Human Physiology Complete Guide

Human Physiology is one of the most important units in NEET Biology, contributing approximately 20-25% of questions. This comprehensive guide covers all chapters with key concepts, diagrams, and important points for quick revision.

Chapter 1: Digestion and Absorption

Human Digestive System

The human digestive system consists of the alimentary canal and associated digestive glands.

Alimentary Canal Components:

• Mouth: Contains teeth (32 in adults), tongue, and salivary glands
• Pharynx: Common passage for food and air
• Oesophagus: 25 cm long muscular tube, peristalsis occurs here
• Stomach: J-shaped organ, capacity 1-1.5 liters, pH 1.5-2.5
• Small Intestine: 6 meters long (Duodenum + Jejunum + Ileum)
• Large Intestine: 1.5 meters (Caecum + Colon + Rectum)

Important Enzymes:

Key Points for NEET:

• Dental formula for adult: 2123/2123
• HCl in stomach activates pepsinogen to pepsin
• Bile emulsifies fats (no enzyme action)
• Maximum absorption occurs in small intestine
• Villi and microvilli increase surface area for absorption

Chapter 2: Breathing and Exchange of Gases

Respiratory System

Respiratory Organs:

• Nostrils: Filter, warm, and moisten air
• Pharynx → Larynx → Trachea: Air passage
• Bronchi → Bronchioles → Alveoli: Site of gas exchange
• Lungs: Right lung (3 lobes), Left lung (2 lobes)

Lung Volumes and Capacities:

• Tidal Volume (TV): 500 mL – normal breathing
• Inspiratory Reserve Volume (IRV): 2500-3000 mL
• Expiratory Reserve Volume (ERV): 1000-1100 mL
• Residual Volume (RV): 1100-1200 mL
• Vital Capacity (VC): TV + IRV + ERV = 3500-4500 mL
• Total Lung Capacity (TLC): VC + RV = 5000-6000 mL

Transport of Gases:

• O₂ transported: 97% as Oxyhaemoglobin, 3% dissolved in plasma
• CO₂ transported: 70% as bicarbonates, 23% as carbaminohaemoglobin, 7% dissolved
• Bohr effect: Low pH and high CO₂ decrease O₂ affinity of Hb
• Haldane effect: High O₂ decreases CO₂ affinity of Hb

Chapter 3: Body Fluids and Circulation

Blood Composition

• Plasma (55%): Water (90-92%), Proteins (6-8%), others
• Formed elements (45%): RBCs, WBCs, Platelets
• RBC count: 5-5.5 million/mm³ (males), 4.5-5 million/mm³ (females)
• WBC count: 6000-8000/mm³
• Platelet count: 1.5-3.5 lakh/mm³

Blood Groups:

Human Heart

• 4-chambered: 2 atria + 2 ventricles
• Weight: 300g (males), 250g (females)
• Heart rate: 72 beats/min (average)
• Cardiac output: 5 liters/min
• SA Node: Pacemaker (70-75 impulses/min)
• AV Node: 40-60 impulses/min

Cardiac Cycle (0.8 sec):

• Atrial systole: 0.1 sec
• Ventricular systole: 0.3 sec
• Joint diastole: 0.4 sec

Chapter 4: Excretory Products and Their Elimination

Human Excretory System

Kidney Structure:

• Bean-shaped, 10-12 cm long, 5-7 cm wide
• Weight: 120-170 g
• Contains ~1 million nephrons per kidney
• Cortex (outer) and Medulla (inner)

Nephron – Functional Unit:

• Glomerulus: Tuft of capillaries, filtration occurs here
• Bowman’s Capsule: Cup-shaped structure surrounding glomerulus
• PCT: Maximum reabsorption (65-70%)
• Loop of Henle: Concentrates urine
• DCT: Selective reabsorption and secretion
• Collecting duct: Final concentration of urine

Important Values:

• GFR (Glomerular Filtration Rate): 125 mL/min or 180 L/day
• Urine output: 1.5 L/day
• 99% of filtrate is reabsorbed
• Normal urine pH: 6.0

Hormonal Regulation:

• ADH (Vasopressin): Increases water reabsorption
• Aldosterone: Increases Na+ reabsorption
• ANF: Causes vasodilation, decreases BP

Chapter 5: Locomotion and Movement

Types of Muscles

Skeletal System:

• Total bones in adult: 206
• Axial skeleton: 80 bones (skull, vertebral column, ribs, sternum)
• Appendicular skeleton: 126 bones (limbs, girdles)
• Smallest bone: Stapes (ear)
• Largest bone: Femur (thigh)

Sliding Filament Theory:

• Actin (thin) filaments slide over Myosin (thick) filaments
• H-zone and I-band decrease during contraction
• A-band remains constant
• Ca²+ is essential for muscle contraction

Chapter 6: Neural Control and Coordination

Nervous System Organization

• CNS: Brain + Spinal cord
• PNS: Cranial nerves (12 pairs) + Spinal nerves (31 pairs)
• ANS: Sympathetic + Parasympathetic

Human Brain:

• Weight: ~1.4 kg
• Contains ~100 billion neurons
• Cerebrum: Largest part, intelligence, memory, thinking
• Cerebellum: Balance and coordination
• Medulla: Vital functions (breathing, heartbeat)
• Hypothalamus: Body temperature, hunger, thirst regulation

Synapse:

• Junction between two neurons
• Neurotransmitters: Acetylcholine, Dopamine, Serotonin, GABA
• Synaptic cleft: 20-40 nm

Chapter 7: Chemical Coordination and Integration

Endocrine Glands and Hormones

Important Disorders:

• Diabetes mellitus: Insulin deficiency
• Goitre: Iodine deficiency, thyroid enlargement
• Cretinism: Hypothyroidism in children
• Gigantism: Excess GH in childhood
• Acromegaly: Excess GH in adults
• Dwarfism: GH deficiency in childhood
• Addison’s disease: Adrenal cortex hyposecretion
• Cushing’s syndrome: Excess cortisol

NEET Preparation Tips for Human Physiology

1. Focus on NCERT: 90% questions come directly from NCERT
2. Learn Diagrams: Practice drawing and labeling diagrams
3. Memorize Values: Normal values are frequently asked
4. Understand Mechanisms: Don’t just memorize, understand the processes
5. Practice MCQs: Solve previous year NEET questions
6. Make Tables: Compare similar structures/functions

Disclaimer: This content is for educational purposes. Always refer to the latest NCERT textbook and official NEET syllabus for accurate information.