BP104T Unit 1 – Cellular Structure, Homeostasis & Cellular Injury
Unit 1 provides the structural and physiological basis of the human body. It covers cell ultrastructure, the Singer-Nicolson fluid mosaic membrane model, passive and active transport mechanisms (Na+/K+ ATPase), classification and histology of the four primary tissue types (Epithelial, Connective, Muscular, Nervous), and homeostatic feedback mechanisms.
📋 Prescribed Syllabus Topics
📖 Detailed Lecture Notes & Solved Examples
11. Cell Ultrastructure & The Fluid Mosaic Plasma Membrane Model
Dedicated Webpage➔The cell is the basic structural, functional, and biological unit of all living organisms. The plasma membrane envelops the cytoplasm, isolating the intracellular fluid (ICF) from extracellular fluid (ECF). In 1972, S.J. Singer and G.L. Nicolson proposed the Fluid Mosaic Model, describing the plasma membrane as an amphipathic phospholipid bilayer (hydrophilic polar phosphate heads oriented outward and hydrophobic non-polar fatty acid tails oriented inward) with interspersed integral transmembrane proteins, peripheral proteins, cholesterol molecules (which buffer membrane fluidity), and surface glycolipids/glycoproteins (glycocalyx for cell-cell recognition).Cell hamare shareer ki sabse chhoti living unit hai. Plasma membrane phospholipid ki do layers (Bilayer) se bani hoti hai jisme bahar ki taraf paani se judne wale (Hydrophilic) heads aur andar tel jaise (Hydrophobic) tails hote hain. Smooth ER me dawaiyon ka metabolism (CYP450 enzymes) hota hai aur Mitochondria ATP banata hai.
▶Cellular Organelles and Their Pharmacological Significance
Key cellular structures targeted by pharmaceutical agents.
| Organelle | Structural Feature | Core Physiological Function | Clinical / Pharmacological Connection |
|---|---|---|---|
| Plasma Membrane | Phospholipid bilayer + proteins | Selective permeability & cell signaling | Site of drug receptors (GPCRs, Ion channels) |
| Smooth ER | Tubular network without ribosomes | Lipid synthesis & drug detoxification | Houses CYP450 enzymes responsible for Phase I drug metabolism |
| Mitochondria | Double membrane with inner cristae | Aerobic cellular respiration & ATP production | Targeted by biguanides (Metformin inhibits complex I) |
| Ribosomes | 80S (60S + 40S subunits in humans) | Translation of mRNA into peptide chains | Bacterial 70S ribosomes targeted by antibiotics (Tetracyclines, Macrolides) |
- •Phospholipid Bilayer: Amphipathic with outer hydrophilic glycerol-phosphate heads and inner hydrophobic fatty acyl chains.
- •Cholesterol: Intercalates between phospholipids to prevent crystallization at low temperatures and excessive fluidity at high temperatures.
- •Selective Permeability: Highly permeable to small non-polar lipid-soluble molecules ($O_2, CO_2$, steroid hormones); impermeable to large polar molecules (glucose, ions) without carrier proteins.
22. Membrane Transport: Passive vs. Active Mechanisms
Dedicated Webpage➔Molecules move across the plasma membrane through either passive transport (requiring no metabolic energy, moving down a concentration or electrochemical gradient) or active transport (requiring metabolic ATP hydrolysis, moving solutes uphill against their electrochemical gradient).Passive transport me particles bina energy ke high se low concentration ki taraf jate hain (Diffusion). Active transport me ATP ki energy kharch karke Na+/K+ ATPase pump 3 Sodium (Na+) bahar phekta hai aur 2 Potassium (K+) andar lata hai. Heart failure me di jaane wali Digoxin isi Na+/K+ pump ko block karke heart ki pumping badhati hai.
▶The Primary Active Sodium-Potassium Pump (Na+/K+ ATPase)
Physiological mechanism and clinical cardiac glycoside inhibition.
- •Simple Diffusion: Movement of lipophilic solutes directly across the lipid bilayer down concentration gradient (Fick's First Law: $J = -D \frac{dC}{dx}$).
- •Facilitated Diffusion: Passive carrier- or channel-mediated transport down concentration gradient without ATP (e.g. GLUT-4 glucose transporters).
- •Primary Active Transport: Solute is pumped against gradient via direct ATP hydrolysis ($Na^+/K^+$ ATPase, $Ca^{2+}$ ATPase, $H^+/K^+$ gastric pump).
- •Secondary Active Transport: Couples uphill movement of solute to the downhill electrochemical gradient of $Na^+$ (e.g. SGLT-2 sodium-glucose cotransporter in renal tubules).
33. Classification and Histology of the Four Primary Tissue Types
Dedicated Webpage➔A tissue is a group of morphologically similar cells and their extracellular matrix specialized to perform specific physiological functions. The human body is composed of four primary tissue categories: Epithelial Tissue (covers surfaces, lines cavities, forms glands), Connective Tissue (supports, binds, and protects organs), Muscular Tissue (generates mechanical force for locomotion and organ movement), and Nervous Tissue (detects stimuli, processes information, and conducts electrical action potentials).Hamare shareer me 4 tarah ke tissues hote hain: (1) Epithelial (skin aur organs ki covering), (2) Connective (haddi, khoon, cartilage jo shareer ko jodte hain), (3) Muscular (Skeletal voluntary, Cardiac dil ki muscle, Smooth involuntary), aur (4) Nervous (Neurons jo signal bhejne ka kaam karte hain).
▶Histological Classification of Epithelial Tissues
Anatomical distribution based on layers and cell morphology.
| Primary Tissue | Distinctive Histological Feature | Sub-Types / Examples | Primary Biological Function |
|---|---|---|---|
| Epithelial | Avascular, resting on basement membrane, tight junctions | Simple squamous, stratified columnar, urothelium | Physical barrier, secretion, absorption, sensory reception |
| Connective | Abundant extracellular matrix with collagen/elastin | Areolar, Adipose, Bone, Cartilage, Blood | Structural scaffolding, physical protection, metabolic transport |
| Muscular | Contractile proteins (actin & myosin) | Skeletal, Cardiac, Smooth muscle | Locomotion, pumping blood, peristaltic food propulsion |
| Nervous | Excitable membranes with axons and synapses | Neurons and Neuroglia (Astrocytes, Microglia) | Rapid electrochemical transmission, cognitive integration |
- •Connective Tissue: Composed of cells (Fibroblasts, Macrophages, Mast cells) embedded in extracellular ground substance and fibers (Collagen type I/II/III, Elastin, Reticular).
- •Muscular Tissue Types: Skeletal (striated, voluntary, multinucleated), Cardiac (striated, involuntary, intercalated discs with gap junctions), Smooth (non-striated, involuntary, spindle-shaped, found in blood vessels and GI tract).
- •Nervous Tissue: Consists of excitable Neurons (soma, dendrites, axon) and supporting Glial Cells (Astrocytes, Oligodendrocytes, Microglia, Schwann cells).
44. Homeostatic Regulation & Feedback Loops
Dedicated Webpage➔Homeostasis (coined by Walter Cannon, 1932) is the dynamic physiological state of equilibrium in the internal environment maintained by coordinated regulatory systems despite external environmental disturbances. A homeostatic control system consists of three functional components: (1) Receptor/Sensor (detects physiological deviations), (2) Control Center/Integrator (evaluates input against set-point, e.g. Hypothalamus), and (3) Effector (generates compensatory response). In Negative Feedback Loops, the effector response opposes or reverses the original stimulus (e.g., blood pressure, blood glucose, core temperature). In Positive Feedback Loops, the effector response amplifies or reinforces the initial stimulus until a definitive endpoint is achieved (e.g., blood clotting cascade, oxytocin release during parturition).Homeostasis ka matlab hai shareer ke internal temperature, BP aur blood sugar ko balanced set-point par maintain rakhna. Negative Feedback me galti ko ulta karke theek kiya jata hai (jaise BP girne par Baroreceptors heart rate badha kar BP normal karte hain). Positive Feedback me process ko aur tez badhaya jata hai (jaise delivery ke waqt Oxytocin release).
▶Arterial Baroreceptor Negative Feedback Loop for Blood Pressure
Physiological response to an acute drop in systemic arterial pressure.
- •Negative Feedback: Counteracts the deviation to restore standard physiological set-point (Prevents instability).
- •Positive Feedback: Amplifies the perturbation in a self-reinforcing cascade until a natural termination event occurs (e.g., Oxytocin during labor, LH surge before ovulation).
- •Failure of Homeostasis: Results in disease states (pathology) or cellular death.
- In 10-mark questions, describe the fluid mosaic model, draw the phospholipid bilayer, and explain the Na+/K+ ATPase pump mechanism.
- Contrast Negative Feedback vs Positive Feedback loops with 2 physiological examples each.