Chapter 3 — Tissue Level of Organisation
Key Concepts Quick Recap
| Tissue Type | Key Feature | Function |
|---|
| Epithelial | Cells closely packed; no intercellular space; avascular | Protection, secretion, absorption, filtration |
| Connective | Cells sparse in matrix (fibres + ground substance) | Support, binding, insulation, defence, transport |
| Muscular | Contractile proteins (actin + myosin) | Movement, locomotion, circulation |
| Nervous | Neurons with axon/dendrites | Impulse conduction, coordination |
Epithelial Tissue Types
| Type | Structure | Location |
|---|
| Simple squamous | Single layer, flat cells | Bowman's capsule, alveoli, blood vessels (endothelium) |
| Simple cuboidal | Single layer, cube-shaped | Kidney tubules, thyroid follicles |
| Simple columnar | Single layer, tall cells | Stomach, intestine lining |
| Pseudostratified | Single layer appears stratified | Trachea (with cilia), nasal cavity |
| Stratified squamous | Multiple layers, flat cells | Skin (keratinised), oesophagus (non-keratinised) |
| Transitional | Multiple layers; stretches | Urinary bladder, ureter |
I. Choose the Best Answer (MCQs)
1. The tissue that lines the alveoli of the lungs is: (a) Simple cuboidal (b) Stratified squamous (c) Simple squamous (d) Simple columnar
Answer(c) Simple squamous Alveolar walls are lined by simple squamous epithelium (extremely thin) — allows rapid diffusion of O₂ and CO₂ between alveoli and capillaries. The thin single-cell layer minimises diffusion distance.
2. Cardiac muscle differs from skeletal muscle in having: (a) No striations (b) Intercalated discs (c) Many nuclei (d) Conscious control
Answer(b) Intercalated discs Cardiac muscle is striated (like skeletal) but involuntary. Unique features: intercalated discs (gap junctions + desmosomes between cells) that allow rapid ionic communication → coordinated contraction. Cardiac cells are branched; one nucleus per cell.
3. Mast cells are found in which tissue? (a) Epithelial (b) Nervous (c) Muscular (d) Connective
Answer(d) Connective Mast cells are found in loose connective tissue (areolar tissue). They contain histamine and heparin granules — released during allergic reactions and inflammation. Other cells in connective tissue: fibroblasts (synthesise fibres), macrophages (phagocytes), plasma cells (produce antibodies).
4. The Schwann cells are associated with: (a) Muscle fibres (b) Nerve fibres (c) Connective tissue (d) Epithelial cells
Answer(b) Nerve fibres Schwann cells (peripheral nervous system) wrap around nerve axons to form the myelin sheath. Myelin insulates the axon and speeds up nerve impulse conduction. In the CNS, oligodendrocytes perform this function.
5. Which type of muscle is found in the wall of the urinary bladder? (a) Skeletal muscle (b) Cardiac muscle (c) Smooth muscle (d) Striated muscle
Answer(c) Smooth muscle Smooth (visceral) muscle is found in walls of hollow organs — intestine, urinary bladder, uterus, blood vessel walls. It is non-striated, uninucleate, spindle-shaped, and involuntary. Contracts slowly and sustainedly.
6. Tendons connect: (a) Bone to bone (b) Muscle to bone (c) Cartilage to cartilage (d) Muscle to muscle
Answer(b) Muscle to bone
- Tendons (dense regular connective tissue, collagen fibres): connect MUSCLE to BONE.
- Ligaments (dense elastic connective tissue): connect BONE to BONE.
7. The myelin sheath of nerve fibres is formed by: (a) Neurons (b) Astrocytes (c) Schwann cells (d) Microglia
Answer(c) Schwann cells Schwann cells (neurilemma cells) in the peripheral nervous system wrap multiple times around the axon, depositing lipid-protein myelin layers. The gaps between Schwann cells = Nodes of Ranvier. Nerve impulse jumps between nodes (saltatory conduction) → faster transmission.
II. Short Answer Questions
Q1. Describe the types and functions of connective tissue.
Answer
Connective tissue (CT) is characterised by widely separated cells in an extracellular matrix (fibres + ground substance).
Types:
Loose CT:
- Areolar tissue: Most widely distributed; fibres (collagen, elastin, reticular) loosely arranged; fibroblasts, mast cells, macrophages, plasma cells in matrix. Function: packing and support, inflammatory response.
- Adipose tissue: Adipocytes storing fat; insulation, energy storage, cushioning.
Dense CT:
- Dense regular: Collagen fibres parallel → tendons (muscle to bone), ligaments (bone to bone).
- Dense irregular: Collagen fibres randomly arranged → dermis of skin.
Specialised CT:
- Cartilage: Semi-rigid; chondrocytes in lacunae; no blood vessels (avascular). Types: hyaline (joint surfaces), fibrocartilage (intervertebral discs), elastic (earlobe).
- Bone: Rigid; osteocytes in lacunae; Haversian systems (osteons); highly vascularised.
- Blood: Plasma (matrix) + RBC, WBC, platelets (cells); transport O₂, hormones, immune cells.
- Lymph: Plasma + lymphocytes; immunity and fluid balance.
Q2. Compare skeletal, cardiac, and smooth muscle.
Answer
| Feature | Skeletal (Striated) | Cardiac | Smooth (Visceral) |
|---|
| Location | Attached to bones | Heart wall | Visceral organs (intestine, bladder) |
| Striations | Present | Present | Absent |
| Nucleus | Multiple (multinucleate) | Single, central | Single, central |
| Shape | Long, cylindrical fibres | Branched, cylindrical | Spindle-shaped |
| Control | Voluntary | Involuntary | Involuntary |
| Speed | Fast contraction | Rhythmic | Slow, sustained |
| Intercalated discs | Absent | Present | Absent |
| Fatigue | Yes (tires) | No (continuous) | No |
Q3. Draw a labelled diagram of a neuron and explain its parts.
Answer
A neuron (nerve cell) is the structural and functional unit of the nervous system.
Parts: 1. Cell body (Soma/Perikaryon): Contains nucleus, Nissl granules (rER — for protein synthesis), cytoplasm. Metabolic centre of the neuron. 2. Dendrites: Short, branched processes arising from cell body. Receive incoming signals → transmit toward cell body. 3. Axon: Single long process from the axon hillock. Transmits impulses AWAY from cell body. May be myelinated (faster) or unmyelinated. 4. Myelin sheath: Lipid-protein covering of axon (Schwann cells in PNS). Insulates and speeds conduction. 5. Nodes of Ranvier: Gaps in myelin sheath; site of saltatory conduction. 6. Axon terminals (boutons): Tips of axon; release neurotransmitters into synapse. 7. Synapse: Junction between two neurons; neurotransmitters carry signal across synaptic cleft.
Types of neurons:
- Multipolar (most neurons): many dendrites, one axon.
- Bipolar (retina): one dendrite, one axon.
- Unipolar (sensory neurons): single process that divides.
Common Mistakes
- Confusing tendons (muscle to bone) and ligaments (bone to bone).
- Saying cardiac muscle is voluntary — it is involuntary (but striated).
- Forgetting that Schwann cells = PNS myelin; oligodendrocytes = CNS myelin.
- Confusing smooth muscle location (visceral organs) with its involuntary nature.
Exam Checklist
- Four tissue types: epithelial, connective, muscular, nervous.
- Simple squamous epithelium: alveoli, Bowman's capsule.
- Three muscle types comparison table.
- Connective tissue cells: fibroblast (fibres), mast cell (histamine), macrophage (phagocyte).
- Neuron parts: cell body + dendrites + axon + myelin sheath + Nodes of Ranvier.
- Tendons (muscle-bone), Ligaments (bone-bone): dense regular CT.
