Human Physiology

Human physiology is the branch of biology that deals with the functions and mechanisms of the human body. It includes various systems responsible for processes such as digestion, respiration, circulation, excretion, movement, neural control, and chemical coordination. This chapter provides an in-depth understanding of how the human body maintains homeostasis and performs vital functions.

Digestion and Absorption

1. Human Digestive System

• Consists of the alimentary canal and digestive glands.

• Major organs include mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.

2. Digestion of Food

• Begins in the mouth with salivary amylase breaking down starch.

• Pepsin in the stomach digests proteins.

• Pancreatic enzymes further break down carbohydrates, proteins, and fats.

3. Absorption of Nutrients

• Takes place in the small intestine (villi and microvilli).

• Water and electrolytes are absorbed in the large intestine.

4. Disorders of Digestive System

• Indigestion, constipation, diarrhea, jaundice, and peptic ulcers.

Breathing and Exchange of Gases

1. Human Respiratory System

• Includes nostrils, pharynx, larynx, trachea, bronchi, bronchioles, alveoli, and lungs.

• Alveoli are the sites for gaseous exchange.

2. Mechanism of Breathing

• Inhalation: Diaphragm contracts, thoracic cavity expands, air enters lungs.

• Exhalation: Diaphragm relaxes, thoracic cavity shrinks, air is expelled.

3. Transport of Gases

• Oxygen is transported by hemoglobin in red blood cells.

• Carbon dioxide is transported as bicarbonate ions in plasma.

4. Disorders of Respiratory System

• Asthma, emphysema, bronchitis, pneumonia, and lung cancer.

Body Fluids and Circulation

1. Composition of Blood

• Plasma: Fluid part containing proteins, electrolytes, and hormones.

• Blood Cells:

  • Red Blood Cells (RBCs): Carry oxygen.

  • White Blood Cells (WBCs): Fight infections.

  • Platelets: Help in blood clotting.

2. Human Circulatory System

• Heart: Four-chambered muscular organ.

• Blood Vessels: Arteries, veins, and capillaries transport blood.

3. Circulatory Pathways

• Pulmonary Circulation: Between the heart and lungs.

• Systemic Circulation: Between the heart and body tissues.

4. Disorders of Circulatory System

• Hypertension, atherosclerosis, heart attack, stroke, and anemia.

Excretory Products and Their Elimination

1. Human Excretory System

• Includes kidneys, ureters, urinary bladder, and urethra.

2. Urine Formation

• Involves glomerular filtration, tubular reabsorption, and tubular secretion.

3. Regulation of Kidney Function

• Controlled by antidiuretic hormone (ADH), aldosterone, and renin-angiotensin system.

4. Disorders of Excretory System

• Kidney stones, uremia, renal failure, and nephritis.

Locomotion and Movement

1. Types of Movement

• Amoeboid movement: WBC movement.

• Ciliary movement: Found in the respiratory tract.

• Muscular movement: Locomotion in humans.

2. Human Skeletal System

• Axial Skeleton: Skull, vertebral column, ribs, and sternum.

• Appendicular Skeleton: Limbs and girdles.

3. Muscular System

• Skeletal Muscles: Voluntary movements.

• Smooth Muscles: Involuntary control.

• Cardiac Muscles: Found in the heart.

4. Disorders of Musculoskeletal System

• Osteoporosis, arthritis, muscular dystrophy, and gout.

Neural Control and Coordination

1. Human Nervous System

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): Cranial and spinal nerves.

2. Structure of Neuron

• Dendrites, cell body, axon, and synapse.

3. Transmission of Nerve Impulses

• Involves electrical and chemical signals.

4. Human Brain

• Forebrain: Cerebrum, thalamus, and hypothalamus.

• Midbrain: Connects forebrain and hindbrain.

• Hindbrain: Pons, medulla, and cerebellum.

5. Reflex Action

• Involuntary and automatic response to stimuli.

6. Disorders of Nervous System

• Alzheimer’s disease, Parkinson’s disease, epilepsy, and paralysis.

Chemical Coordination and Integration

1. Human Endocrine System

• Consists of ductless glands that secrete hormones.

2. Major Endocrine Glands and Their Hormones

• Pituitary Gland: Secretes growth hormone, oxytocin, and ADH.

• Thyroid Gland: Produces thyroxine and calcitonin.

• Adrenal Glands: Secretes adrenaline and cortisol.

• Pancreas: Releases insulin and glucagon.

• Gonads (Testes & Ovaries): Produce testosterone, estrogen, and progesterone.

3. Mechanism of Hormone Action

• Protein Hormones: Act via cell membrane receptors.

• Steroid Hormones: Act via intracellular receptors.

4. Disorders of Endocrine System

• Diabetes mellitus, hyperthyroidism, hypothyroidism, and Addison’s disease.