Abstract:

This video provides a rapid revision summary of General Physiology, concentrating on high-yield, crisp points for exam preparation. The lecture covers four main topics: the composition and structure of the cell membrane, the components and functions of the cytoskeleton, the mechanisms of transport across the cell membrane (active and passive), and the distribution and shifts of total body fluids. Key clinical correlations are highlighted, including membrane protein defects (Hereditary Spherocytosis, Duchenne Muscular Dystrophy, PNH), lipid markers (Annexin V for apoptosis), and the analysis of fluid shifts in pathological conditions like Adrenal Insufficiency, SIADH, and shock using the Darrow-Yannet diagram.

Rapid Revision of General Physiology

• 0:47 Cell Membrane Composition: The cell membrane is primarily composed of Proteins (55%) and Lipids (45%), with Carbohydrates (3-5%). The protein-to-lipid ratio is typically 1:1.
  • Key Detail: Proteins are maximally present in the Inner Mitochondrial Membrane and Pre-synaptic membrane. Lipids are maximally present in the Schwann Cell Membrane (80% lipids) for myelination.
• 0:58:56 Membrane Lipids: Phospholipids are the maximum lipids, but Triglycerides are absent.
  • Key Takeaway: Cholesterol acts as a fluidity buffer. Phosphatidylcholine (Lecithin) is the major lipid in lung surfactant.
• 0:19:53 Phosphatidylserine (PS): PS is normally internalized but externalized in apoptotic cells, serving as an "eat me" signal.
  • Key Detail: Annexin V binds to externalized PS, making it a marker for apoptosis.
• 0:21:51 Cardiolipin and APLA: Cardiolipin is primarily found in the mitochondrial membrane. Anti-Cardiolipin antibodies are associated with Antiphospholipid Antibody Syndrome (APLA) and Syphilis, often causing recurrent second-trimester abortions.
• 0:07:27 Membrane Proteins: Proteins are classified as Integral (Transmembrane), Peripheral, and Lipid-anchored.
  • Key Detail: Integral proteins include channels, pumps (Na/K ATPase), and G-protein coupled receptors.
• 0:11:17 Peripheral Proteins (Clinical Correlates):
  • Ankyrin/Spectrin: Maintain RBC shape. Defects cause Hereditary Spherocytosis (Ankyrin defect) or Elliptocytosis (Spectrin defect).
  • Dystrophin: Deficiency causes Becker's Muscular Dystrophy; complete absence causes Duchenne Muscular Dystrophy (DMD) (characterized by calf pseudo-hypertrophy and Gower's sign). DMD commonly results in respiratory failure.
• 0:16:15 Lipid-Anchored Proteins (GPI): GPI absence causes Paroxysmal Nocturnal Hemoglobinuria (PNH).
• 0:27:00 Cytoskeleton Components: Consists of Microtubules (Tubulin, 25nm), Microfilaments (Actin/Myosin), and Intermediate Filaments (IFs). Microtubules and microfilaments are Dynamic; IFs are Static and cell-specific.
• 0:33:42 Molecular Motors (Transport):
  • Kinesin: Moves cargo towards the positive end (Anterograde transport).
  • Dynein: Moves cargo towards the negative end (Retrograde transport). (Mnemonic: Dr. = Dynein Retrograde).
• 0:37:04 Microtubule Inhibitors: Used in cancer treatment (Vincristine, Vinblastine) and acute gout (Colchicine).
• 0:39:11 Intermediate Filaments (Markers): Used in pathology to identify tumor origin: Keratin (Carcinomas/Epithelial), Desmin (Rhabdomyosarcomas/Muscle), GFAP (Astrocytes), Vimentin (Fibroblasts/Connective Tissue).
• 0:42:44 Membrane Transport: Divided into Active (needs ATP, against gradient) and Passive (no ATP, down gradient).
  • Primary Active Transport: Direct ATP use (e.g., ATPases/Pumps).
  • Secondary Active Transport: Indirect ATP use (e.g., Co-transporters, Exchangers, SGLTs).
  • Passive Transport: Simple Diffusion (Gases, O2/CO2) vs. Facilitated Diffusion (Carrier protein involved, e.g., GLUTs/Glucose Transporters).
• 0:55:24 Vesicular Transport: Endocytosis (Clathrin, Caveolin) and Exocytosis (SNARE proteins). Requires Calcium.
• 0:58:06 Total Body Water (TBW): Males (60% of weight), Females (50%). TBW decreases with age.
• 1:03:57 Fluid Compartments (Adult Male): Intracellular Fluid (ICF) is 40% of body weight (2/3 of TBW). Extracellular Fluid (ECF) is 20% of body weight (1/3 of TBW).
  • Key Detail: Plasma is 5% of body weight (1/4 of ECF).
• 1:06:00 Fluid Measurement: Blood Volume = Plasma / (1 - Hematocrit).
  • Indicators: Total Body Water (Deuterium Oxide), ECF (Inulin, Mannitol), Plasma (Evans Blue Dye, Radio-labeled Albumin). ICF is calculated (TBW - ECF).
• 1:14:45 Fluid Shifts (Darrow-Yannet Diagram): Analysis of ECF/ICF volume and tonicity (osmolarity).
  • Isosmotic Changes (Tonicity constant): Diarrhea (ECF contraction); Isotonic Saline Infusion (ECF expansion).
  • Hyperosmotic Changes (Tonicity raised): Sweating (Both ECF/ICF contraction); Hypertonic Saline Infusion (ECF expansion, ICF contraction).
  • Hypo-osmotic Changes (Tonicity decreased): Adrenal Insufficiency (ECF contraction, ICF expansion); SIADH (Both ECF/ICF expansion – pure volume expansion).