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Human Body Systems and Homeostasis

Organization of Human Body​

1. Levels of Organization​

Cells → Tissues → Organs → Systems → Organism

Tissues:

  • Epithelial: Covering and lining (skin, digestive tract)
  • Connective: Support and structure (bones, cartilage, fat)
  • Muscular: Movement (skeletal, cardiac, smooth)
  • Nervous: Communication (nerves, brain)

2. Organ Systems​

11 Major Systems:

  • Digestive, Circulatory, Respiratory, Nervous, Endocrine, Integumentary, Skeletal, Muscular, Lymphatic, Urinary, Reproductive

Digestive System (पाचन तंत्र)​

1. Structure and Function​

Feeding → Digestion → Absorption → Egestion

Mouth (मुँह):

  • Mechanical digestion (chewing)
  • Chemical digestion (saliva with amylase)
  • Breaks down starch to maltose
  • Formation of bolus

Esophagus (ग्रसनी):

  • Peristalsis (muscular waves)
  • Pushes food to stomach
  • No digestion

Stomach (आमाश्य):

  • Churning (mechanical digestion)
  • Pepsin (protease enzyme) breaks protein to peptides
  • Gastric juice (HCl) environment
  • 1-4 hours retention
  • Produces chyme (semi-liquid)

Small Intestine (छोटी आंत):

  • Duodenum: Receives food and digestive juices
  • Jejunum and ileum: Absorption
  • Pancreatic enzymes (amylase, protease, lipase)
  • Bile from liver (breaks fat)
  • Brush border (villi for absorption)
  • Most digestion and absorption occurs
  • Trypsin: Protein → Peptides
  • Lipase: Fat → Fatty acids and glycerol
  • Disaccharidase: Disaccharides → Monosaccharides

Large Intestine (बड़ी आंत/कोलन):

  • Water reabsorption
  • Mineral absorption
  • Bacterial fermentation
  • Forms feces
  • 12-24 hours transit

Rectum and Anus:

  • Storage of feces
  • Defecation

2. Enzyme Action​

Enzymes Involved:

  • Amylase: Carbohydrate digestion
  • Protease: Protein digestion (pepsin, trypsin)
  • Lipase: Fat digestion
  • Disaccharidase: Simple sugar digestion

Optimal Conditions:

  • pH (varies by enzyme)
  • Temperature (37°C for human)
  • Enzyme concentration (more = faster)
  • Substrate concentration

3. Absorption​

Small Intestine Wall:

  • Villi (finger-like projections)
  • Microvilli on epithelial cells
  • Increased surface area (all 100-fold)
  • Large capillary network

Selective Absorption:

  • Glucose and amino acids → Active transport (energy needed)
  • Fatty acids → Diffusion into lacteal
  • Water → Osmosis

Circulatory System (संचार तंत्र)​

1. Components​

Heart:

  • Muscular pump
  • Four chambers (two atria, two ventricles)
  • Septum separates left/right
  • Unidirectional valves
  • Cardiac cycle (contraction and relaxation)

Blood Vessels:

  • Arteries: Thick wall, carries blood from heart, high pressure
  • Veins: Thin wall, carries blood to heart, low pressure, has valves
  • Capillaries: Single epithelial cell, exchange substances

Blood:

  • Plasma (55%): Water, proteins, minerals, glucose
  • Red blood cells (44%): Oxygen transport, hemoglobin
  • White blood cells (1%): Immune defense
  • Platelets: Blood clotting

2. Cardiac Cycle​

Atrial Systole:

  • Atria contract
  • Push blood to ventricles
  • Atrioventricular valves open

Ventricular Systole:

  • Ventricles contract
  • Push blood to arteries
  • Semilunar valves open
  • Atria relax

Diastole:

  • Both relax
  • Blood fills chambers
  • Chambers relax

Heart Rate: ~70 beats/minute (variable)

3. Blood Pressure​

Systolic/Diastolic:

  • Systolic: Maximum (ventricular contraction) ~120 mmHg
  • Diastolic: Minimum (relaxation) ~80 mmHg
  • Generally 120/80 normal

Regulation:

  • Nervous system (sympathetic/parasympathetic)
  • Hormones (adrenaline, ADH)
  • Physical activity (increases)
  • Stress (increases)

Respiratory System (श्वसन तंत्र)​

1. Structure​

Upper Respiratory:

  • Nose/mouth (warm, moisten, filter air)
  • Pharynx (throat)
  • Larynx (voice box)
  • Trachea (windpipe)

Lower Respiratory:

  • Bronchi (branch into lungs)
  • Bronchioles (smaller branches)
  • Alveoli (肺泡): Tiny air sacs for gas exchange
    • ~300 million per lung
    • Single cell wall
    • Large surface area
    • Surrounded by capillaries

Muscles:

  • Diaphragm: Primary breathing muscle
  • Intercostal muscles: Between ribs
  • Assist ventilation

2. Ventilation​

Inspiration (inhalation):

  • Diaphragm contracts (moves down)
  • Volume increases, pressure decreases
  • Air enters lungs

Expiration (exhalation):

  • Diaphragm relaxes (moves up)
  • Volume decreases, pressure increases
  • Air exits lungs
  • Usually passive

Breathing Rate: ~12-20 breaths/minute

3. Gas Exchange​

In Alveoli (external respiration):

  • O₂ diffuses into blood (hypoxic capillary)
  • CO₂ diffuses out (hypercarbia)
  • Concentration gradients drive

In Cells (internal respiration):

  • O₂ leaves capillaries for cells
  • CO₂ enters capillaries from cells
  • Supporting aerobic respiration

Transport:

  • O₂: Mostly bound to hemoglobin (small amount dissolved)
  • CO₂: Dissolved, as bicarbonate ion, bound to hemoglobin

Nervous System (तंत्रिका तंत्र)​

1. Organization​

Central Nervous System (CNS):

  • Brain
  • Spinal cord
  • Processing and control

Peripheral Nervous System (PNS):

  • Somatic: Voluntary movement, sensory
  • Autonomic: Involuntary, organs and glands
    • Sympathetic: "Fight or flight" (stress response)
    • Parasympathetic: "Rest and digest" (normal)

2. Neuron Structure​

Parts:

  • Cell body: Nucleus and cytoplasm
  • Dendrites: Receive signals
  • Axon: Sends signals
  • Axon terminal: Release neurotransmitters

Types:

  • Sensory (afferent): Receptors → CNS
  • Motor (efferent): CNS → Muscles/glands
  • Relay (interneuron): Within CNS

3. Nerve Impulse​

Action Potential:

  • Resting potential: -70 mV
  • Stimulus causes depolarization
  • Na⁺ influx (positive)
  • Reaching threshold triggers action potential
  • K⁺ efflux (repolarization)
  • Return to resting state

Synaptic Transmission:

  • Neurotransmitter released
  • Crosses synaptic cleft
  • Receptor on postsynaptic membrane
  • Excitatory (depolarization) or inhibitory (hyperpolarization)

4. Reflex Arc​

Fast automatic response:

  1. Sensory receptor (stimulus)
  2. Sensory neuron to spinal cord
  3. Relay neuron in spinal cord
  4. Motor neuron to muscle
  5. Muscle contracts (response)

No brain involvement needed for quick response.

Endocrine System (अंतःस्रावी तंत्र)​

1. Hormones (हार्मोन)​

Definition:

  • Chemical messengers
  • Released by glands
  • Travel via bloodstream
  • Slow but long-lasting effects

Major Glands:

  • Pituitary: Growth hormone, ADH, FSH, LH
  • Thyroid: Thyroxine (metabolism)
  • Pancreas: Insulin, glucagon (blood glucose)
  • Adrenal: Adrenaline (stress response), cortisol
  • Ovaries/Testes: Sex hormones (estrogen, testosterone)

2. Blood Glucose Regulation​

Normal Range: 80-120 mg/100cm³ blood

High Glucose (Hyperglycemia):

  • Pancreas releases insulin
  • Cells absorb glucose
  • Liver stores as glycogen
  • Blood glucose decreases

Low Glucose (Hypoglycemia):

  • Pancreas releases glucagon
  • Liver breaks glycogen to glucose
  • Blood glucose increases

Negative Feedback:

  • Response counteracts stimulus
  • Maintains homeostasis
  • Example: Blood glucose regulation

Homeostasis (होमोस्टेसिस)​

1. Definition​

Maintaining stable internal environment:

  • Temperature
  • pH
  • Water/salt balance
  • Blood glucose
  • Oxygen levels

2. Temperature Regulation​

Hypothalamus:

  • Temperature monitoring center
  • Sets normal at 37°C
  • Responds to temperature changes

If Too Hot:

  • Vasodilation (blood vessels widen)
  • More blood to skin (heat loss)
  • Sweating (evaporative cooling)
  • Reduced metabolic rate

If Too Cold:

  • Vasoconstriction (blood vessels narrow)
  • Less blood to skin (heat conservation)
  • Shivering (muscle heat production)
  • Increased metabolic rate

3. Negative Feedback Loops​

Control Mechanism:

  1. Deviation from normal detected
  2. Response initiated
  3. Response counteracts deviation
  4. Return to normal
  5. Response stops

Example: Temperature regulation cycling

Summary​

Human body systems:

  • Digestive: Break down food, absorb nutrients
  • Circulatory: Transport oxygen, nutrients, waste
  • Respiratory: Gas exchange with environment
  • Nervous: Communication and control
  • Endocrine: Hormone regulation
  • Homeostasis: Maintain stable internal environment

Integration of systems essential for survival and health.