Answer:
Epithelial tissue is the covering or lining tissue that forms the outer layer of the body surface and lines internal organs and cavities. It is classified based on the number of cell layers and the shape of cells.
Based on number of cell layers:
1. Simple Epithelium: This type consists of a single layer of cells resting on a basement membrane. All cells are in direct contact with the basement membrane.
- Simple Squamous Epithelium: Cells are flat and scale-like. Found in the walls of blood capillaries (endothelium) and alveoli of lungs. Functions in diffusion and filtration.
- Simple Cuboidal Epithelium: Cells are cube-shaped with a central nucleus. Found in kidney tubules, thyroid gland, and salivary gland ducts. Functions in absorption and secretion.
- Simple Columnar Epithelium: Cells are tall and column-like with nuclei near the base. Found in the lining of the stomach, intestine, and gallbladder. Functions in secretion and absorption.
- Ciliated Columnar Epithelium: Columnar cells bearing cilia on their free surface. Found in the trachea, bronchi, and fallopian tubes. Cilia move mucus and trapped particles.
- Pseudostratified Epithelium: Appears layered but is actually a single layer of cells at different heights. Found in the trachea. Functions in secretion and movement of mucus.
2. Stratified (Compound) Epithelium: Consists of multiple layers of cells. Only the innermost layer touches the basement membrane.
- Stratified Squamous Epithelium: Multiple layers where the outer cells are flat. Found in skin (epidermis), mouth, and oesophagus. Provides protection against mechanical and chemical injury.
- Stratified Cuboidal Epithelium: Two or more layers of cube-shaped cells. Found in sweat glands and ovarian follicles.
- Stratified Columnar Epithelium: Multiple layers with columnar cells on the surface. Found in male urethra and larynx.
Based on function:
Glandular Epithelium: Specialised for secretion. Forms glands of the body. Unicellular glands (goblet cells) secrete mucus. Multicellular glands form organs like the pancreas and salivary glands.
Functions of Epithelial Tissue:
- Protection from mechanical injury, pathogens, and chemicals
- Absorption of nutrients in the intestine
- Secretion of enzymes, hormones, and mucus
- Excretion of waste products
- Sensory reception (neuroepithelium)
Answer:
Connective tissue is the most abundant and widely distributed tissue in the body. Unlike epithelial tissue, connective tissue cells are widely scattered in a matrix (ground substance) and fibres.
Components of Connective Tissue: 1. Cells — fibroblasts, chondroblasts, osteoblasts, adipocytes, macrophages 2. Matrix (Ground Substance) — intercellular material that can be fluid, semi-solid, or solid 3. Fibres — collagen fibres (white, strong), elastic fibres (yellow, stretchable), reticular fibres (fine network)
Classification of Connective Tissue:
A. Loose Connective Tissue
- Cells and fibres are loosely arranged in a semi-fluid matrix
- Areolar Tissue: Found under the skin, around organs and blood vessels. Supports and connects organs. Contains fibroblasts, macrophages, and mast cells. Acts as a packing material between organs.
- Adipose Tissue: Cells (adipocytes) contain large fat droplets. Found beneath the skin (hypodermis), around kidneys and heart. Functions in energy storage, insulation, and padding.
- Reticular Tissue: Forms a delicate network (stroma) in lymph nodes, spleen, and bone marrow. Supports blood cells.
B. Dense Connective Tissue
- Cells and fibres are densely packed
- Dense Regular Connective Tissue: Collagen fibres run parallel. Found in tendons (connecting muscle to bone) and ligaments (connecting bone to bone). Extremely strong and resistant to stretching in one direction.
- Dense Irregular Connective Tissue: Fibres run in all directions. Found in the dermis of skin and joint capsules. Resists forces from multiple directions.
C. Specialised Connective Tissue
Cartilage (Hyaline, Fibrocartilage, Elastic):
- Semi-rigid, flexible tissue
- Matrix (chondrin) secreted by chondrocytes
- Hyaline Cartilage: Found in trachea rings, articular surfaces of joints, nose tip. Provides smooth surface for joint movement.
- Fibrocartilage: Found in intervertebral discs and knee menisci. Withstands great pressure.
- Elastic Cartilage: Found in pinna (outer ear) and epiglottis. Very flexible.
Bone:
- Rigid due to calcified matrix (ossein + calcium phosphate)
- Bone cells = osteocytes located in lacunae
- Compact Bone: Dense, few spaces. Found in shaft of long bones. Haversian systems (osteons) present.
- Spongy Bone: Lighter, has spaces filled with red bone marrow. Found at ends of long bones.
- Functions: support, protection, movement (with muscles), mineral storage (calcium and phosphorus), blood cell formation (haematopoiesis).
Blood:
- Fluid connective tissue with plasma as the matrix
- Contains Red Blood Cells (RBCs), White Blood Cells (WBCs), and Platelets
- Functions: transport of O2, CO2, nutrients, hormones, and waste products
Lymph:
- Fluid connective tissue similar to blood plasma but lacks RBCs and proteins
- Returns interstitial fluid to the bloodstream
- Carries fats absorbed from the intestine
Answer:
Muscle tissue is specialised for contraction and produces movement. There are three types of muscle tissue: skeletal (striated/voluntary), smooth (non-striated/involuntary), and cardiac.
| Feature | Skeletal Muscle | Smooth Muscle | Cardiac Muscle |
|---|---|---|---|
| Location | Attached to bones | Walls of hollow organs (stomach, intestines, urinary bladder, blood vessels) | Only in the heart wall (myocardium) |
| Control | Voluntary (under conscious control) | Involuntary (not under conscious control) | Involuntary |
| Shape of cell | Long, cylindrical, unbranched fibres | Spindle-shaped, tapered at both ends | Cylindrical, branched fibres |
| Striations | Present (alternating light and dark bands) | Absent (no cross-striations) | Present (but less distinct than skeletal) |
| Nuclei | Multiple nuclei per cell, located at periphery | Single central nucleus | Single central nucleus |
| Intercalated discs | Absent | Absent | Present — connect adjacent cardiac cells and allow electrical impulses to spread rapidly |
| Speed of contraction | Fast and powerful | Slow and sustained | Rhythmic and continuous |
| Fatigue | Fatigues quickly | Resistant to fatigue | Does not fatigue (beats throughout life) |
| Cell length | Very long (up to 30 cm in some muscles) | Short (30–200 micrometres) | 85–100 micrometres |
Detailed Description:
Skeletal Muscle: Each fibre is a large multinucleate cell. The alternating dark (A-bands) and light (I-bands) bands are due to the arrangement of thick myosin and thin actin filaments. Z-lines bisect I-bands. The unit between two Z-lines is a sarcomere — the functional unit of contraction. Contraction follows the sliding filament theory: actin filaments slide over myosin filaments, shortening the sarcomere.
Smooth Muscle: No sarcomere organisation, hence no striations. Contraction is slow but can be sustained for long periods. Controlled by the autonomic nervous system and hormones. Important for peristalsis (movement of food in the digestive tract) and regulation of blood pressure (in blood vessel walls).
Cardiac Muscle: Has features of both skeletal (striated) and smooth (involuntary) muscle. The intercalated discs contain gap junctions that allow ions to pass freely, making cardiac muscle behave as a functional syncytium — the whole heart contracts as one unit. The sinoatrial (SA) node (pacemaker) initiates the heartbeat. Cardiac muscle has abundant mitochondria (25–30% of cell volume) and relies primarily on aerobic respiration.
Answer:
A neuron (nerve cell) is the structural and functional unit of the nervous system. It is specialised for receiving, processing, and transmitting electrical impulses.
Structure of a Neuron:
Types of Neurons Based on Structure:
Types of Neurons Based on Function:
Answer:
In complex multicellular organisms like humans, cells are organised into increasingly complex levels: cells → tissues → organs → organ systems → organism.
Organ Level Organisation:
An organ is a group of different tissues working together to perform a specific function. Organs have a definite shape and are made up of more than one type of tissue.
Example: Heart
- Cardiac muscle tissue (myocardium) — contracts to pump blood
- Epithelial tissue (endocardium) — lines the inner chambers
- Connective tissue — forms the protective pericardium
- Nervous tissue — conducts electrical impulses for rhythmic beating
Example: Stomach
- Epithelial tissue (mucosa) — secretes gastric juice
- Smooth muscle tissue — churns food (peristalsis)
- Connective tissue — provides support
- Nervous tissue — controls secretion and movement
Organ System Level Organisation:
An organ system is a group of organs that work together to perform a major physiological function of the body.
Major Organ Systems in Humans:
| Organ System | Main Organs | Main Function |
|---|---|---|
| Digestive System | Mouth, oesophagus, stomach, small intestine, large intestine, liver, pancreas | Digestion and absorption of food |
| Circulatory System | Heart, blood vessels, blood | Transport of nutrients, O2, CO2, hormones |
| Respiratory System | Nostrils, trachea, bronchi, lungs | Exchange of O2 and CO2 |
| Excretory System | Kidneys, ureters, urinary bladder, urethra | Removal of metabolic waste products |
| Nervous System | Brain, spinal cord, nerves | Control and coordination |
| Endocrine System | Pituitary, thyroid, adrenal, pancreas (endocrine part) | Chemical regulation through hormones |
| Skeletal System | Bones, cartilage, ligaments | Support, protection, movement |
| Muscular System | Skeletal muscles, tendons | Movement and posture |
| Reproductive System | Ovaries/testes, uterus, associated ducts | Reproduction |
| Immune System | Lymph nodes, spleen, bone marrow, thymus | Defence against pathogens |
| Integumentary System | Skin, hair, nails | Protection, temperature regulation |
Significance of Organ System Organisation:
1. Division of Labour: Different systems perform specific functions, allowing high efficiency. 2. Integration: All organ systems are interconnected and work in coordination for homeostasis. 3. Efficiency: Specialisation of tissues within organs allows each function to be performed optimally. 4. Adaptability: Complex organ systems allow organisms to respond to environmental changes.
The organisation from cell to organ system represents increasing structural complexity and functional specialisation, which is the hallmark of higher animals.
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