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🧬 UNIT I — INTRODUCTION TO PHYSIOLOGY

TOPIC 1: Functional Organization of the Human Body & Control of the Internal Environment

TOPIC 2: The Cell and Its Functions

TOPIC 3: Genetic Control of Protein Synthesis, Cell Function & Cell Reproduction

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STAGE 1: BIG PICTURE

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Why Does Physiology Exist?

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Its Role in Homeostasis

"La fixite du milieu interieur est la condition de la vie libre." ("The constancy of the internal environment is the condition of free life.")

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Connection to Other Systems

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Real-Life Importance

• Why do you sweat in summer? - Temperature homeostasis
• Why do you breathe faster after running? - CO2/O2 homeostasis
• Why does a diabetic become comatose? - Glucose homeostasis fails
• Why does kidney failure cause death? - Electrolyte/fluid homeostasis collapses

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STAGE 2: BASIC FOUNDATION

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Key Definitions

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Body Fluid Compartments (The Internal Ocean)

Total Body Water (42 L in 70 kg man)
        │
        ├── Intracellular Fluid (ICF) = 28 L (40% body wt)
        │       └── Inside cells
        │
        └── Extracellular Fluid (ECF) = 14 L (20% body wt)
                ├── Interstitial Fluid = 11 L (15% body wt)
                └── Plasma = 3 L (5% body wt)

Clinical Pearl: A 70 kg adult male has ~42 L total body water. Women and obese individuals have proportionally less (fat has low water content).

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The Extracellular Fluid - The Internal Environment

Exam Trap: The values in the table are for venous blood (pO2 = 40 mmHg, pCO2 = 45 mmHg). Arterial: pO2 = 95 mmHg, pCO2 = 40 mmHg.

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STAGE 3: CORE PHYSIOLOGY

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CONTROL SYSTEMS OF THE BODY

Components of Every Control System

STIMULUS (Disturbance from set point)
        ↓
RECEPTOR (Sensor - detects change)
        ↓
AFFERENT PATHWAY (Signal to control center)
        ↓
CONTROL CENTER (Integrator - brain, hypothalamus, etc.)
        ↓
EFFERENT PATHWAY (Signal to effector)
        ↓
EFFECTOR (Organ that makes correction)
        ↓
RESPONSE (Restores set point)
        ↓
FEEDBACK (Loops back to receptor)

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Negative Feedback - The Body's Stabilizer

CO2 rises in blood
        ↓
Chemoreceptors in medulla detect rise
        ↓
Medullary respiratory center activated
        ↓
Breathing rate & depth increase
        ↓
More CO2 exhaled
        ↓
CO2 returns to normal (45 mmHg)
        ↓ (negative feedback loop closes)

BP rises (e.g., stress)
        ↓
Baroreceptors in carotid sinus/aortic arch detect stretch
        ↓
Signal to brainstem (nucleus tractus solitarius)
        ↓
↓ Sympathetic, ↑ Parasympathetic outflow
        ↓
↓ Heart rate + ↓ Peripheral resistance
        ↓
BP falls back toward normal (~100 mmHg)

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The Gain of a Control System

Gain = -Correction / Error that remains

• Without baroreceptors: Blood transfusion raises BP from 100 → 175 mmHg (75 mmHg rise)
• With baroreceptors: Same transfusion raises BP by only 25 mmHg
• Correction = 75 - 25 = 50 mmHg
• Gain = -50/25 = -2

Higher gain = more powerful correction. The body's arterial pressure control system has a gain of about -2 (moderate). Kidney's long-term pressure control has an infinite gain (perfect long-term regulation).

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Positive Feedback - The Body's Amplifier

Memory trick: Negative feedback = NURSE (stabilizing). Positive feedback = BOMB (amplifying). The body uses the NURSE most of the time, but occasionally uses the BOMB for a purpose.

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Feedforward Control

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TOPIC 2: THE CELL AND ITS FUNCTIONS

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STAGE 2: BASIC FOUNDATION - The Cell

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The Cell - The Basic Unit of Life

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Structure of the Generalized Cell

THE CELL
│
├── NUCLEUS
│     ├── Nuclear membrane (double-layered with pores)
│     ├── Nucleolus (rRNA synthesis)
│     ├── Chromatin (DNA + histone proteins)
│     └── Nuclear sap (nucleoplasm)
│
├── CELL MEMBRANE (Plasma Membrane)
│     ├── Lipid bilayer (phospholipids)
│     ├── Integral proteins (channels, pumps, receptors)
│     ├── Peripheral proteins (enzymes, structural)
│     └── Glycocalyx (carbohydrate coat on outer surface)
│
└── CYTOPLASM
      ├── Cytosol (gel-like fluid)
      ├── Endoplasmic Reticulum (ER)
      │     ├── Rough ER (ribosomes - protein synthesis)
      │     └── Smooth ER (lipid synthesis, detox, Ca2+ storage)
      ├── Golgi Apparatus (processing, packaging, secretion)
      ├── Mitochondria (ATP production)
      ├── Lysosomes (intracellular digestion)
      ├── Peroxisomes (oxidative reactions, H2O2)
      ├── Ribosomes (protein synthesis)
      ├── Cytoskeleton (actin, microtubules, intermediate filaments)
      └── Centrioles (cell division)

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STAGE 3: CORE PHYSIOLOGY - Cell Organelles

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THE CELL MEMBRANE

Fluid Mosaic Model (Singer & Nicolson, 1972)

OUTSIDE CELL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Glycocalyx (carbohydrate coat)
  | Glycoprotein | Glycolipid |
~~~~~~~~~Phospholipid Bilayer~~~~~~~~~~~
  |Integral Protein| |Channel| |Pump|
  | Peripheral Protein (on inner face) |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
INSIDE CELL

• Hydrophilic HEAD (loves water, faces ECF and ICF)
• Hydrophobic TAIL (hates water, faces interior of bilayer)
• This arrangement creates a selectively permeable barrier

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Functions of Cell Membrane Proteins

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The Glycocalyx - The Cell's Identity Card

1. Negative surface charge - repels other negatively charged objects (prevents unwanted cell-cell adhesion)
2. Cell-cell recognition - cells recognize "self vs. non-self"
3. Hormone receptors - insulin receptor is a glycoprotein
4. Immune reactions - ABO blood group antigens are glycoproteins on RBCs
5. Cell adhesion - mediates attachment to ECM and other cells

Clinical: ABO blood typing relies on glycocalyx antigens. Blood group A has A antigens, B has B antigens, AB has both, O has neither. Mismatched transfusion causes hemolysis because antibodies attack foreign glycocalyx antigens.

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CYTOPLASM AND ORGANELLES

Endoplasmic Reticulum (ER)

ROUGH ER                          SMOOTH ER
─────────────────                ─────────────────
Has RIBOSOMES on surface         NO ribosomes
Protein synthesis                Lipid synthesis
Protein folding & quality        Steroid hormone synthesis
  control                        Drug/toxin detoxification
Glycoprotein formation           Ca2+ storage (muscle cells)
Proteins go to Golgi             Glycogen metabolism

Clinical: Hepatic smooth ER contains cytochrome P450 enzymes for drug metabolism. Patients on enzyme inducers (e.g., rifampicin, phenytoin) have proliferated smooth ER - this is why their drug metabolism is faster (drug-drug interactions!).

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Golgi Apparatus

cis-Golgi face (receiving end)
    ↓ Receives vesicles from Rough ER
    ↓ Processes: glycosylation, phosphorylation, sulfation
trans-Golgi face (shipping end)
    ↓
    ├── Secretory vesicles → Exocytosis (secreted outside)
    ├── Lysosomes (intracellular digestion)
    └── Cell membrane components

Clinical: Kartagener syndrome - defect in dynein (motor protein for vesicular transport). Causes immotile cilia + situs inversus + bronchiectasis. Shows importance of intracellular trafficking!

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Mitochondria - The Powerhouse

• Double membrane (outer + inner)
• Inner membrane folded into cristae (increases surface area)
• Matrix (space inside inner membrane)
• Own DNA - circular, like bacteria (supports endosymbiotic theory)
• Own ribosomes (70S, like bacteria)

MITOCHONDRIAL FUNCTION
        ↓
Aerobic Respiration
        ↓
  Glucose → Pyruvate (Glycolysis, cytoplasm)
        ↓
  Pyruvate → Acetyl-CoA (Pyruvate dehydrogenase, matrix)
        ↓
  Acetyl-CoA → Krebs Cycle (matrix) → NADH, FADH2
        ↓
  NADH/FADH2 → Electron Transport Chain (inner membrane)
        ↓
  ETC + O2 → ATP (via ATP synthase) + H2O
        ↓
  NET: 36-38 ATP per glucose molecule

Clinical: Mitochondrial diseases (e.g., MELAS, MERRF, Leber's hereditary optic neuropathy) are maternally inherited because mitochondria in the zygote come from the egg (maternal), not sperm. Affects high-energy tissues: brain, muscle, retina.

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Lysosomes - The Recycling Plant

Autophagy:
  Old/damaged organelle → Surrounded by membrane → Autophagosome
        ↓ Fuses with lysosome → Autolysosome
        ↓ Contents digested → Amino acids/sugars recycled

Heterophagy:
  Endocytosed material (bacteria, foreign particles)
        ↓ Endosome fuses with lysosome
        ↓ Digestion
        ↓ Useful products released to cytosol
        ↓ Waste remains as residual body

Clinical - Lysosomal Storage Diseases: When lysosomal enzymes are deficient, substrates accumulate:

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Peroxisomes

• Small organelles containing oxidase enzymes and catalase
• Oxidize fatty acids (especially very long chain fatty acids - VLCFA)
• Detoxify H2O2: 2H2O2 → 2H2O + O2 (via catalase)

Clinical: Zellweger syndrome - absent peroxisomes → VLCFA accumulate → severe neurological dysfunction. Fatal in first year of life.

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TRANSPORT ACROSS CELL MEMBRANE

Types of Transport

TRANSPORT ACROSS MEMBRANE
        │
        ├── PASSIVE (no energy required)
        │       ├── Simple Diffusion
        │       │     (small, lipid-soluble molecules: O2, CO2, steroid hormones)
        │       ├── Osmosis
        │       │     (water through aquaporins)
        │       ├── Facilitated Diffusion
        │       │     (via protein channels/carriers: glucose via GLUT, ions via channels)
        │       └── Filtration (hydrostatic pressure)
        │
        └── ACTIVE (energy required)
                ├── Primary Active Transport
                │     (uses ATP directly)
                │     Examples: Na+/K+ ATPase, Ca2+ pump, H+ pump
                ├── Secondary Active Transport
                │     (uses Na+ gradient created by primary active transport)
                │     Examples:
                │     - Cotransport (symport): Na-glucose transporter (SGLT)
                │     - Countertransport (antiport): Na+/H+ exchanger
                └── Vesicular Transport
                      ├── Endocytosis (pinocytosis + phagocytosis)
                      └── Exocytosis

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Na+/K+ ATPase Pump - THE Most Important Pump in the Body

1. Maintains the resting membrane potential (essential for all nerve/muscle function)
2. Maintains cell volume (prevents osmotic swelling)
3. Creates the Na+ gradient that drives secondary active transport
4. Uses 20-30% of the body's resting energy!

3 Na+ (inside cell) bind to pump
        ↓
ATP hydrolyzed → ADP + Pi → phosphorylates pump
        ↓
Pump changes shape → 3 Na+ expelled OUTSIDE
        ↓
2 K+ from outside bind
        ↓
Phosphate released → pump returns to original shape
        ↓
2 K+ released INSIDE
        ↓
Net: 3 Na+ out / 2 K+ in per cycle

• High Na+ outside (142 mmol/L ECF vs. 14 mmol/L ICF)
• High K+ inside (140 mmol/L ICF vs. 4.2 mmol/L ECF)
• Net negative charge inside (electrogenic - more positive charges pumped out than in)
• Resting membrane potential = -70 mV (inside negative)

Clinical: Digoxin (cardiac glycoside) inhibits Na+/K+ ATPase. This raises intracellular Na+, which slows the Na+/Ca2+ exchanger, raising intracellular Ca2+, which INCREASES cardiac contractility. This is how digoxin treats heart failure!

Toxicity: Digoxin toxicity causes hyperkalemia (K+ not pumped back in), arrhythmias, nausea, visual disturbances (yellow-green halos).

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Osmosis and Osmolality

• Normal plasma osmolality = 280-295 mOsm/kg
• Formula: Posm = 2[Na] + Glucose/18 + BUN/2.8

Clinical: IV fluid choice is critical. 0.9% normal saline is isotonic. 5% dextrose is iso-osmotic in the bag but rapidly metabolized to free water (hypotonic effect in vivo) - can cause hyponatremia/cerebral edema if given excessively.

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ENDOCYTOSIS AND EXOCYTOSIS

Pinocytosis ("Cell Drinking")

Macromolecule (protein) binds receptor at coated pit
        ↓
Clathrin-coated pit invaginates
        ↓
Membrane closes over particle
        ↓
Clathrin-coated vesicle forms inside cytoplasm
        ↓
Clathrin coat shed → Early endosome
        ↓
Recycled to membrane OR degraded in lysosome

Phagocytosis ("Cell Eating")

Bacterium coated with antibody (opsonization)
        ↓
Antibody binds Fc receptor on macrophage
        ↓
Pseudopodia extend around bacterium
        ↓
Membrane fuses → Phagosome forms
        ↓
Phagosome + Lysosome → Phagolysosome
        ↓
Lysosomal enzymes kill/digest bacterium
        ↓
Residual body expelled by exocytosis

Clinical: Chronic Granulomatous Disease (CGD) - NADPH oxidase deficiency. Macrophages can phagocytose bacteria but CANNOT kill them (no superoxide/H2O2 production). Result: recurrent infections with catalase-positive organisms (Staph aureus, Aspergillus, E. coli).

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CELL MOVEMENT: AMEBOID LOCOMOTION & CHEMOTAXIS

Actin monomers polymerize at leading edge
        ↓
Form filamentous network (F-actin)
        ↓
Network contracts with myosin (using ATP)
        ↓
Pseudopodium extends forward
        ↓
Membrane receptors attach to ECM at leading edge
        ↓
Cell body pulled forward
        ↓
Rear membrane recycled via endocytosis → sent to front via vesicles

• Neutrophils and macrophages (chemotaxis toward infection)
• Fibroblasts (wound healing)
• Cancer cells (metastasis!)
• Embryonic cells (migration during development)

• Positive chemotaxis: toward higher concentration (e.g., neutrophils moving toward bacterial products like fMLP)
• Negative chemotaxis: away from higher concentration (rare)

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CILIA

Clinical: Kartagener syndrome (Primary Ciliary Dyskinesia) - dynein arm defect → immotile cilia. Causes:

• Bronchiectasis (mucus not cleared)
• Chronic sinusitis
• Male infertility (immotile sperm)
• Situs inversus (50% - because leftward fluid flow during embryogenesis determines body laterality)

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TOPIC 3: GENETIC CONTROL OF PROTEIN SYNTHESIS

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STAGE 3: CORE PHYSIOLOGY - Molecular Biology

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THE BIG PICTURE

DNA (in nucleus)
    ↓ TRANSCRIPTION (DNA → mRNA)
mRNA (travels to cytoplasm through nuclear pores)
    ↓ TRANSLATION (mRNA → Protein)
PROTEIN (functional molecule)

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DNA STRUCTURE

1. Deoxyribose sugar
2. Phosphate group
3. Nitrogenous base (one of 4)

• Purines (2-ring): Adenine (A) and Guanine (G)
• Pyrimidines (1-ring): Cytosine (C) and Thymine (T)

A = T (2 hydrogen bonds)
G ≡ C (3 hydrogen bonds)

• Two antiparallel strands wound around each other
• Sugar-phosphate backbone on outside
• Bases stacked in center, held by hydrogen bonds
• Right-handed helix, one complete turn every 10 base pairs (3.4 nm pitch)

• ~3 billion base pairs (haploid set)
• ~20,000-25,000 protein-coding genes
• But coding sequences (exons) = only ~1.5% of genome! Rest is regulatory, repetitive sequences, introns, etc.

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THE GENETIC CODE

• Triplet code: 3 bases = 1 codon
• 4 bases × 4 × 4 = 64 possible codons for only 20 amino acids
• Therefore: Degenerate (multiple codons can code for same amino acid)
• Non-overlapping (each base is read only once)
• Universal (same in nearly all organisms, from bacteria to humans - proves common ancestry!)
• Unambiguous (each codon codes for only ONE amino acid)

Clinical: Sickle cell disease - a single base mutation in codon 6 of the beta-globin gene. Normal: GAG (glutamic acid). Mutant: GTG (valine). One amino acid change → entire disease!

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TRANSCRIPTION - DNA → RNA

Step 1: INITIATION
Transcription factors bind to PROMOTER region of gene
        ↓
RNA polymerase II recruited to promoter
        ↓
DNA double helix unwinds at transcription start site

Step 2: ELONGATION
RNA polymerase moves along TEMPLATE strand (3'→5' direction)
        ↓
Reads template, synthesizes complementary RNA (5'→3' direction)
        ↓
RNA bases pair with DNA template:
    DNA A → RNA U
    DNA T → RNA A
    DNA G → RNA C
    DNA C → RNA G

Step 3: TERMINATION
RNA polymerase reaches termination sequence
        ↓
Transcript released
        ↓
DNA double helix reforms

Pre-mRNA (primary transcript)
        ↓ 5' Capping (7-methylguanosine cap)
        ↓ 3' Polyadenylation (poly-A tail added)
        ↓ Splicing (introns removed, exons joined)
        ↓
Mature mRNA
        ↓
Exported through nuclear pores to cytoplasm

• 5' cap: Protects mRNA from degradation, helps ribosome recognition
• 3' poly-A tail: Stabilizes mRNA, helps in nuclear export

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Types of RNA

Clinical: RNA interference (RNAi) is now a therapeutic tool. Patisiran (Onpattro) - first RNAi drug, targets transthyretin mRNA → treats hereditary transthyretin amyloidosis. Nobel Prize 2006 (Fire & Mello) for discovery of RNAi.

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TRANSLATION - mRNA → Protein

• Large subunit: 60S (eukaryotes); contains peptidyl transferase activity
• Small subunit: 40S (eukaryotes)
• Together: 80S ribosome

Step 1: INITIATION
mRNA binds to small (40S) ribosomal subunit
        ↓
Ribosome scans for AUG start codon (5'→3')
        ↓
Initiator tRNA (carrying Met) binds AUG in P-site
        ↓
Large (60S) subunit joins → 80S initiation complex

Step 2: ELONGATION (repeat cycle)
Aminoacyl-tRNA enters A-site (codon-anticodon matching)
        ↓
Peptide bond formed between growing chain and new AA
        (by peptidyl transferase - actually the rRNA!)
        ↓
Ribosome translocates 3 nucleotides in 3' direction
        (old P-site tRNA moves to E-site and exits)
        ↓
Next codon now in A-site → repeat

Step 3: TERMINATION
Stop codon (UAA, UAG, UGA) enters A-site
        ↓
No tRNA matches stop codon
        ↓
Release factor binds → peptide released
        ↓
Ribosome dissociates from mRNA

3' end: carries specific amino acid (aminoacyl-tRNA synthetase charges it)
Anticodon loop: 3-base sequence complementary to mRNA codon

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STAGE 4: MOLECULAR & CELLULAR PHYSIOLOGY

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Gene Regulation

1. TRANSCRIPTIONAL CONTROL (most important)
   ├── Promoters and enhancers
   ├── Transcription factors (activators/repressors)
   ├── Epigenetic modifications
   │     ├── Histone acetylation (opens chromatin → gene ON)
   │     ├── Histone methylation (can activate OR silence)
   │     └── DNA methylation (silences genes)
   └── Chromatin remodeling

2. POST-TRANSCRIPTIONAL CONTROL
   ├── Alternative splicing (same gene → different proteins)
   ├── mRNA stability (miRNA-mediated degradation)
   └── mRNA export regulation

3. TRANSLATIONAL CONTROL
   ├── Initiation factor regulation
   └── Iron-response element (ferritin mRNA)

4. POST-TRANSLATIONAL CONTROL
   ├── Protein folding (chaperones)
   ├── Glycosylation, phosphorylation
   ├── Proteolytic cleavage (inactive precursor → active)
   └── Protein degradation (ubiquitin-proteasome pathway)

Clinical - Alternative Splicing: The BRCA2 gene can be alternatively spliced. Some splice variants are associated with cancer susceptibility. Explains why different mutations in same gene can cause different severity of disease.

Clinical - Epigenetics: Identical twins have same DNA but can develop different diseases due to different epigenetic patterns (methylation, acetylation) acquired over life. Explains how environment influences gene expression without changing the DNA sequence.

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Cell Division - Mitosis vs. Meiosis

G1 phase (gap 1): cell grows, prepares for DNA synthesis
        ↓
S phase (synthesis): DNA replication (genome doubled)
        ↓
G2 phase (gap 2): cell continues growing, checks DNA
        ↓
M phase (mitosis): cell divides
        ↓
        ├── Prophase (chromosomes condense, spindle forms)
        ├── Metaphase (chromosomes align at metaphase plate)
        ├── Anaphase (sister chromatids pulled to poles by spindle fibers)
        ├── Telophase (nuclear envelopes reform)
        └── Cytokinesis (cytoplasm divides)

• G1/S checkpoint: Is DNA damaged? Is cell big enough?
• G2/M checkpoint: Is DNA replication complete? Any damage?
• Spindle assembly checkpoint: Are all chromosomes attached to spindle?

Clinical - Cancer: Cancer cells bypass cell cycle checkpoints:

• Tumor suppressor genes (e.g., p53, Rb) normally enforce checkpoints
• Oncogenes (e.g., RAS, MYC) normally promote cell division
• Mutation in p53 → can't stop cell with DNA damage → cancer → most common tumor suppressor mutation in human cancers

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STAGE 7: CLINICAL PHYSIOLOGY

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What Happens When Homeostasis Fails?

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STAGE 8: PATHOPHYSIOLOGY

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Case: Loss of Negative Feedback - Cushing's Disease

Normal:
Hypothalamus → CRH → Anterior Pituitary → ACTH → Adrenal Cortex → Cortisol
        ↑_____________NEGATIVE FEEDBACK____________________________↑

Pathology (Cushing's Disease - pituitary ACTH-secreting adenoma):
Pituitary adenoma secretes ACTH autonomously
        ↓ Cortisol rises and rises
        ↓ Negative feedback FAILS (adenoma is relatively resistant)
        ↓
Signs & Symptoms:
- Central obesity (cortisol increases lipogenesis centrally)
- Buffalo hump, moon face
- Hypertension (cortisol has mineralocorticoid effect)
- Hyperglycemia/diabetes (cortisol is anti-insulin)
- Muscle wasting, osteoporosis
- Purple striae (protein catabolism + skin thinning)
- Immunosuppression

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STAGE 9: PHARMACOLOGICAL CORRELATIONS

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STAGE 10: IMPORTANT GRAPHS

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Graph 1: Negative Feedback - The Classic Sine-like Correction

Parameter
(e.g., BP)  |
            |     /\   (without feedback - diverges)
            |    /  \  /\
175 ─────── |   /    \/  \___
            |  /
100 (norm)  |─────────────────────────────────  Target/set point
            |         \
            |          \_____  (with feedback - rapidly restored)
            |
            Time ──────────────────────────────▶

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Graph 2: Diffusion Rate vs. Concentration Gradient

Rate of
Diffusion  |                 /
           |               /
           |             /
           |           /
           |         /  (Linear relationship)
           |       /
           |     /
           |   /
           | /
           |/___________________________
                Concentration Gradient

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Graph 3: Osmotic Pressure vs. Concentration

Osmotic
Pressure   |                  /
           |                /
           |              /
           |            /
           |          /  (Linear: van't Hoff equation)
           |        /    π = nCRT
           |      /
           |    /
           |  /
           |/___________________________
               Solute Concentration

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STAGE 11: IMPORTANT TABLES

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Intracellular vs. Extracellular Fluid Composition

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Negative vs. Positive Feedback

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DNA vs. RNA

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STAGE 12: NUMERICAL VALUES

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Must-Know Numbers for MBBS/PG

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STAGE 13: VIVA PREPARATION

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Short Viva Questions

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Long Viva Questions

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STAGE 14: EXAM PREPARATION

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High-Yield PG Entrance Points

1. Homeostasis coined by Walter Cannon. Internal environment by Claude Bernard.
2. Most numerous cells = Red blood cells (~25 trillion).
3. Gain of arterial pressure control system = approximately -2 (baroreceptors).
4. Positive feedback examples = Action potential, parturition, LH surge, blood clotting.
5. Na+/K+ ATPase pumps 3 Na+ out / 2 K+ in. Net negative charge inside. Inhibited by digoxin.
6. Resting membrane potential = -70 mV (inside negative).
7. Lysosomal storage diseases = enzyme deficiency → substrate accumulation.
8. Ribosome = 80S (eukaryote), 70S (prokaryote). Aminoglycosides target 30S; macrolides/chloramphenicol target 50S.
9. DNA bases: A=T (2H bonds), G≡C (3H bonds). RNA substitutes U for T.
10. Alternative splicing = one gene → multiple proteins. Explains protein diversity.
11. Mitochondrial DNA = maternal inheritance. Disease affects high-energy tissues.
12. Pinocytosis requires ATP + Ca2+. Involves clathrin-coated pits.
13. Chemotaxis = directed cell movement toward chemical gradient. Neutrophils toward fMLP, C5a.
14. Kartagener syndrome = dynein defect → immotile cilia → bronchiectasis + situs inversus + infertility.
15. CGD = NADPH oxidase deficiency → can phagocytose but not kill catalase-positive organisms.

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STAGE 15: MEMORY TOOLS

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Mnemonics

• Gaucher - Glucocerebrosidase
• Tay-Sachs - hexosaminidase A
• Pompe - acid maltase (Pumps glycogen)
• Niemann-Pick - sphingomyelinase

• 60% body weight = total water
• 40% = ICF
• 20% = ECF
• 15% = Interstitial fluid
• 5% = Plasma

• Action potential
• LH surge (ovulation)
• Birth (parturition/oxytocin)
• Aggregation of platelets (clotting)

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Analogies

• Lets 2 VIPs (K+) in
• Kicks out 3 troublemakers (Na+)
• Needs energy (ATP = money) to work

• Receives mail (proteins from ER)
• Sorts, stamps, packages
• Sends to correct addresses (secretion/lysosomes/membrane)

• Decides who gets in and who doesn't
• Lipid-soluble substances (fat = "cool kids") get in easily
• Ions and polar molecules need special permission (channels/carriers = "VIP list")

• Set point = 25°C
• Too hot → AC turns on → temperature drops → AC turns off (negative feedback)
• Too cold → heater turns on → temperature rises → heater turns off (negative feedback)

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STAGE 16: FLOWCHARTS & MIND MAPS

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MASTER MIND MAP: Unit I - Physiology Foundations

                    PHYSIOLOGY
                        │
        ┌───────────────┼───────────────┐
        │               │               │
   HOMEOSTASIS      THE CELL      GENETICS & PROTEIN
        │               │           SYNTHESIS
        │               │               │
   ┌────┴────┐    ┌─────┴──────┐   ┌───┴────┐
   │Control  │    │ Membrane   │   │  DNA   │
   │Systems  │    │ Organelles │   │Structure│
   │         │    │ Transport  │   │        │
   └────┬────┘    └─────┬──────┘   └───┬────┘
        │               │               │
   ┌────┴──────┐   ┌────┴────┐    ┌────┴────┐
   │Negative   │   │Passive  │    │Transcription│
   │Feedback   │   │Active   │    │Translation  │
   │Positive   │   │Vesicular│    │Regulation  │
   │Feedforward│   │Transport│    │Gene Control│
   └───────────┘   └─────────┘    └────────────┘

Flowchart: Protein Synthesis Summary

DNA (Gene)
        ↓ [RNA Polymerase II | Promoter binding]
Pre-mRNA (Nucleus)
        ↓ [5' Cap | Poly-A tail | Splicing of introns]
Mature mRNA
        ↓ [Nuclear pore export]
Cytoplasm → Ribosome (80S) binds at 5' cap
        ↓ [Scans to AUG start codon]
Initiation → tRNA(Met) binds P-site
        ↓ [Elongation: codon-anticodon matching | peptide bond formation | translocation]
Growing polypeptide
        ↓ [Until stop codon UAA/UAG/UGA]
Termination → Protein released
        ↓ [Chaperones assist folding]
Native protein
        ↓ [Post-translational modifications: glycosylation, phosphorylation, cleavage]
Functional protein → secretion/membrane/enzyme/structural role

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STAGE 17: COMMON MISTAKES

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• Osmolarity = mOsm per liter of solution
• Osmolality = mOsm per kg of solvent
• Clinically, we measure osmolality (serum). Normal = 285-295 mOsm/kg.

• The nuclear envelope is a DOUBLE membrane (outer + inner), with nuclear pores.

• Free ribosomes in cytosol are NOT membrane-bound. Only rough ER has ribosomes on a membrane.

• Mitosis: somatic cells, diploid → diploid, 2 daughter cells (same as parent)
• Meiosis: germ cells only, diploid → haploid, 4 daughter cells (genetically unique)

• NO! DNA = Thymine. RNA = Uracil. ("U" is in RNA, "T" is in DNA)

• NO! It pumps 3 Na+ OUT and 2 K+ IN. "Three Na OUT, Two K IN."

• NO! Simple diffusion is through the lipid bilayer directly (small, lipid-soluble molecules). Facilitated diffusion uses a carrier.

• Some positive feedback is essential physiology: action potential, parturition, ovulation (LH surge).

• High gain = GOOD (effective correction). Gain formula includes a negative sign: Gain = -(Correction/Error remaining). Don't get confused by the negative sign.

• 3 are STOP codons (UAA, UAG, UGA). Only 61 code for amino acids (+AUG = start codon AND codes for methionine).

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STAGE 18: RAPID REVISION

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20 KEY TAKEAWAYS

1. Physiology = science of how the body works. Homeostasis = stable internal environment.
2. Claude Bernard coined "internal environment"; Walter Cannon coined "homeostasis."
3. The internal environment = ECF (interstitial fluid + plasma).
4. Body water: 60-40-20-15-5 rule (% body weight).
5. Negative feedback is the body's primary stabilizing mechanism. Positive feedback amplifies.
6. Every control system: Receptor → Control center → Effector → Response → Feedback.
7. Gain = -(Correction/Error remaining). Higher gain = more effective control.
8. The body has ~35-40 trillion cells; RBCs are most numerous (~25 trillion).
9. Cell membrane = fluid mosaic model (Singer & Nicolson). Lipid bilayer + proteins.
10. Glycocalyx = outer carbohydrate coat. Functions: recognition, receptors, ABO antigens.
11. Na+/K+ ATPase: 3 Na+ out / 2 K+ in / uses 1 ATP. Inhibited by digoxin.
12. Resting membrane potential = -70 mV (inside negative). Na+ high outside, K+ high inside.
13. Mitochondria have own DNA (circular) and 70S ribosomes. Maternal inheritance.
14. Lysosomes = acid hydrolases active at pH 5. Deficiency → lysosomal storage diseases.
15. Central dogma: DNA → RNA (transcription) → Protein (translation).
16. DNA: A=T (2H bonds), G≡C (3H bonds). RNA replaces T with U, deoxyribose with ribose.
17. Genetic code: 64 codons, degenerate, universal, non-overlapping. 3 stop codons.
18. Ribosome: 80S (eukaryote), 70S (prokaryote). Many antibiotics target 70S subunits.
19. Ameboid locomotion uses actin-myosin + ATP. Used by WBCs, macrophages, cancer cells.
20. Every disease is ultimately a failure of homeostasis at some level.

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ONE-PAGE SUMMARY

UNIT I - PHYSIOLOGY FOUNDATIONS

HOMEOSTASIS
• Internal env = ECF (interstitial + plasma)
• Control: Receptor → Control center → Effector → Feedback
• Negative feedback (most systems) → STABILIZING
• Positive feedback (few) → AMPLIFYING (action potential, birth, clotting, LH surge)
• Gain = -(Correction/Error remaining)

BODY FLUIDS (70 kg): TBW=42L; ICF=28L; ECF=14L; ISF=11L; Plasma=3L
KEY ECF VALUES: Na+=142, K+=4.2, pH=7.4, Glucose=90 mg/dL, Osm=285-295 mOsm/kg

THE CELL
• Cell membrane = Fluid mosaic (phospholipid bilayer + proteins)
• Glycocalyx = outer carbohydrate coat (recognition, hormone receptors, ABO antigens)
• Organelles: ER (protein/lipid synthesis), Golgi (packaging), Mitochondria (ATP),
              Lysosomes (digestion), Peroxisomes (oxidation)
• Transport: Passive (diffusion, osmosis, facilitated) vs. Active (primary/secondary/vesicular)
• Na+/K+ ATPase: 3Na+ out / 2K+ in / ATP → creates RMP of -70mV

GENETICS & PROTEIN SYNTHESIS
• DNA: double helix, A=T, G≡C, deoxyribose, thymine
• RNA: single strand, A=U, G≡C, ribose, uracil
• Transcription: DNA → mRNA (RNA polymerase II, in nucleus)
• Translation: mRNA → Protein (ribosomes, in cytoplasm)
• Ribosome: 80S (eukaryote), 70S (prokaryote - antibiotic target)
• Genetic code: triplet, degenerate, universal. AUG=start; UAA/UAG/UGA=stop

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STAGE 19: CLINICAL CASES

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Case 1 (Basic)

1. What organelle is defective and why?
2. What enzyme is missing and what substrate accumulates?
3. Why are macrophages specifically affected?
4. What is the treatment principle?

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Case 2 (Intermediate)

1. Which cellular structure is defective?
2. Explain why bronchiectasis occurs using your knowledge of cell movement.
3. Why is the heart on the right side?
4. Why is the patient infertile?
5. What protein is defective?

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Case 3 (Advanced)

1. Which homeostatic control mechanism has failed?
2. Draw the normal HPA axis as a feedback control diagram.
3. Explain each clinical feature using physiology of cortisol.
4. Why does dexamethasone fail to suppress cortisol in this patient?
5. What is the gain of the feedback system and how is it altered?

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STAGE 20: ACTIVE RECALL - MCQs & Questions

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MCQs

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True/False Questions

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1. Functional Organization & Homeostasis - Why and how the body maintains stability
2. The Cell - Every organelle, transport mechanism, and cellular process
3. Genetic Control of Protein Synthesis - From DNA to functional protein, with clinical links

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• Try solving the 3 clinical cases (Stage 19) before looking at answers
• Re-attempt all MCQs without looking at the options
• When you are ready, tell me: "Teach me Unit II: Membrane Physiology, Nerve, and Muscle" and we will continue with the same depth and rigor.

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Status Report

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