SN7
SHORT NOTE
5M
Define apoptosis. Differentiate it from necrosis and describe its pathways.
Definition
Apoptosis = programmed, energy-dependent cell death by which the body eliminates unwanted, aged or damaged cells without inflammation.
Apoptosis VS Necrosis
| Feature | Apoptosis | Necrosis |
|---|---|---|
| Nature | Physiological or pathological | Always pathological |
| Cells involved | Single cells | Groups of cells |
| Cell size | Shrinks | Swells |
| Membrane | Intact; blebs form | Ruptures |
| Nucleus | Fragments; internucleosomal DNA cleavage (ladder pattern) | Pyknosis, karyorrhexis, karyolysis; random cleavage (smear) |
| ATP | Required | Not required |
| Inflammation | Absent | Present |
| Fate | Phagocytosed by neighbours | Enzymatic digestion |
Pathways
A. Intrinsic (mitochondrial) pathway
Cell injury / withdrawal of growth factor → ↓ Bcl-2, ↑ Bax and Bak → ↑ mitochondrial permeability → Cytochrome c released → Apaf-1 + caspase-9 (apoptosome) → Caspase-3
B. Extrinsic (death receptor) pathway
Fas ligand / TNF → Fas or TNF receptor → FADD adaptor → Caspase-8 → Caspase-3
- Both converge on caspase-3 — the executioner caspase
Physiological Roles
- Embryogenesis — interdigital web removal, Müllerian duct regression
- Involution — thymus, endometrium in menstruation, post-lactational breast
- Deletion of self-reactive lymphocytes
- Turnover of intestinal crypt cells
Applied Aspects
- ↓ Apoptosis → cancer — p53 mutation (the "guardian of the genome"); bcl-2 overexpression in follicular lymphoma
- ↓ Apoptosis → autoimmunity — failure to delete self-reactive clones
- ↑ Apoptosis — neurodegeneration (Alzheimer, Parkinson), CD4 loss in AIDS, ischaemia–reperfusion injury
All questions in General Physiology & Body Fluids
- Q1Describe the structure of the cell membrane. Classify the mechanisms of transport across it and describe passive transport in detail. ★
- Q2Define active transport. Classify it and describe the sodium–potassium pump with its functions. Add a note on secondary active transport. ★
- Q3Enumerate the body fluid compartments with their volumes and ionic composition. Describe the methods used to measure them. ★
- Q4Define resting membrane potential. Describe its ionic basis and the factors responsible for it. Add a note on the Nernst equation. ★
- Q5Define homeostasis. Describe the components of a control system and explain negative and positive feedback with examples. ★
- SN1Define osmosis and osmotic pressure. Explain tonicity with examples. ★
- SN2Write a short note on the Gibbs–Donnan equilibrium.
- SN3Define oedema. Describe the Starling forces and enumerate the mechanisms by which oedema is produced. ★
- SN4Classify cell junctions and describe their functions.
- SN5Write a short note on facilitated diffusion. ★
- SN6Enumerate the second messenger systems and describe the cyclic AMP pathway. ★
- SN7Define apoptosis. Differentiate it from necrosis and describe its pathways.