Tissues

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Tissues — Quick Facts

Key Definitions:

• Tissue: A group of similar cells that perform a common function
• Histology: The study of tissues
• Epithelium: Tissue that lines surfaces and cavities
• Connective Tissue: Tissue that connects, supports, and protects
• Muscle Tissue: Tissue that contracts and produces movement
• Nervous Tissue: Tissue that transmits nerve impulses

Four Primary Tissue Types:

Tissue Type	Function	Location
Epithelial	Covering/lining	Skin, gut lining, glands
Connective	Support/connection	Bone, blood, cartilage
Muscular	Movement	Skeletal muscles, heart
Nervous	Signalling	Brain, spinal cord, nerves

⚡ Exam Tips for MDCAT:

• Remember: Blood is a connective tissue (it connects different parts of the body via transport)
• Areolar tissue is the “universal packing material” — found everywhere
• Simple epithelium has one layer, stratified has multiple layers
• Glands are always epithelial tissue — remember this for gland classification questions

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🟡 Standard — Regular Study (2d–2mo)

For students who want genuine understanding.

Tissues — Study Guide

Epithelial Tissue:

Classification by Shape:

• Squamous: Flat, scale-like cells — walls of capillaries, alveoli
• Cuboidal: Cube-shaped cells — kidney tubules, thyroid glands
• Columnar: Tall, pillar-like cells — gut lining, respiratory tract
• Transitional: Variable shape — urinary bladder, ureter

Classification by Layers:

• Simple: One layer — absorption, diffusion, secretion
• Stratified: Multiple layers — protection
• Pseudostratified: Appears layered but isn’t — respiratory tract (has cilia)

Specialisations:

• Cilia: Hair-like projections for moving substances (e.g., mucus in trachea)
• Microvilli: Tiny finger-like projections for absorption (e.g., intestinal villi)
• Keratin: Protein layer on skin (stratified squamous — waterproofing)

Connective Tissue:

Types:

1. Areolar (Loose): Most widespread CT — “universal packing material”

   • fibroblasts + collagen + elastic fibres
   • Found: under skin, around blood vessels

2. Adipose: Fat-storing tissue

   • Adipocytes with large lipid droplets
   • Found: subcutaneous layer, around organs

3. Dense (Fibrous): Packed collagen fibres

   • Regular: tendons (muscle → bone), ligaments (bone → bone)
   • Irregular: dermis of skin, periosteum

4. Cartilage:

   • Hyaline: Most common — fetal skeleton, nose, trachea rings
   • Elastic: External ear, epiglottis (yellow elastic cartilage)
   • Fibrocartilage: Intervertebral discs, meniscus

5. Bone (Osseous Tissue):

   • Hard, mineralised matrix (calcium phosphate + collagen)
   • Haversian system (osteons) with central canal
   • Two types: Compact (outer) and Spongy (inner, with red marrow)

6. Blood:

   • Liquid connective tissue
   • RBCs (O$_2$ transport), WBCs (immunity), Platelets (clotting), Plasma

Muscle Tissue:

Type	Appearance	Location	Function
Skeletal (Striated)	Long cylindrical, multinucleated, striated	Attached to skeleton	Voluntary movement
Cardiac (Striated)	Branched, single nucleus, intercalated discs	Heart wall	Involuntary pumping
Smooth (Non-striated)	Spindle-shaped, single nucleus	Gut, blood vessels, uterus	Involuntary (peristalsis)

Nervous Tissue:

• Neurons: Cell body (soma), dendrites (receive), axon (conduct away)
• Neuroglia: Supporting cells — astrocytes, oligodendrocytes, microglia
• Synapse: Junction between two neurons (neurotransmitter release)

Common Student Mistakes:

• Thinking blood is not a connective tissue — it is, because it connects body parts via transport
• Confusing smooth muscle (involuntary) with skeletal muscle (voluntary)
• Not remembering that cartilage lacks blood supply (explains slow healing)

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🔴 Extended — Deep Study (3mo+)

Comprehensive theory for thorough preparation.

Tissues — Comprehensive Notes

Epithelial Tissue — Glandular Epithelium:

Exocrine Glands: Secrete onto epithelial surface via ducts

• Structure: Acinar (sac-like) or Tubular
• Modes of secretion:
  • Merocrine: No cell damage (e.g., sweat glands, pancreas)
  • Apocrine: Apex pinches off (e.g., mammary glands, milk production)
  • Holocrine: Whole cell disintegrates (e.g., sebaceous glands, oil)

Endocrine Glands: Secrete hormones directly into bloodstream (no ducts)

• Examples: Pituitary, thyroid, adrenal, pancreas (both exo and endocrine)

Connective Tissue Matrix:

The extracellular matrix determines tissue properties:

• Protein fibres: Collagen (strength), Elastin (elasticity), Reticulin (fine network)
• Ground substance: Gel-like material — glycoproteins (fibronectin, laminin), proteoglycans
• Cells: Fibroblasts (produce fibres), Macrophages (phagocytosis), Mast cells (histamine), Plasma cells (antibodies)

Bone Tissue — Detailed Structure:

Compact Bone:

• Osteons (Haversian systems): Cylindrical units
• Central Haversian canal: blood vessels + nerves
• Lamellae: Concentric mineralised layers
• Lacunae: Spaces containing osteocytes
• Canaliculi: Tiny channels connecting lacunae
• Volkmann’s canals: Perforating canals connecting Haversian canals

Spongy Bone:

• Trabeculae: Needle-like bony spicules
• Red marrow between trabeculae (blood cell production)
• No osteons — diffuses from surface

Bone Formation:

• Intramembranous ossification: Flat bones (skull, clavicle)
• Endochondral ossification: Long bones (limbs) — cartilage model first
• Epiphyseal plate: Growth plate in developing bone
• Ossification centres: Primary (diaphysis, ~8 weeks fetal) and Secondary (epiphysis, ~puberty)

Muscle Contraction Mechanism:

The sliding filament theory:

1. Nerve impulse arrives at neuromuscular junction
2. Acetylcholine released → depolarisation of muscle cell membrane
3. Calcium released from sarcoplasmic reticulum
4. Troponin changes shape → tropomyosin moves → active sites on actin exposed
5. Myosin head binds to actin → power stroke
6. ATP hydrolysis re-cocks myosin head
7. Contraction continues until Ca$^{2+}$ removed

Muscle Energy:

• Immediate: ATP + Creatine phosphate (first 10 seconds)
• Short-term: Glycolysis (anaerobic, 30-60 seconds)
• Long-term: Aerobic respiration (citric acid cycle + oxidative phosphorylation)

Nervous Tissue — Synapse:

Types of Synapses:

• Chemical Synapse: NT released from presynaptic knob — e.g., acetylcholine, dopamine, serotonin
• Electrical Synapse: Gap junctions — direct ionic connection (rare in humans)

Reflex Arc: Receptor → Sensory neuron → CNS → Motor neuron → Effector (muscle/gland)

Membranes of the Body:

• Serous membranes: Line body cavities — pleura (lungs), pericardium (heart), peritoneum (gut)
• Mucous membranes: Line passages — respiratory, digestive, urinary tracts
• Synovial membranes: Line joint cavities
• Cutaneous membrane: Skin

⚡ MDCAT High-Yield Patterns:

• Gland classification (exocrine vs. endocrine) and modes of secretion are frequently tested
• Cartilage types are commonly asked in comparative questions
• The sliding filament theory is a must-know for muscle questions
• Bone ossification and growth plate location are favourite NEET/MDCAT questions

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