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AEHBY Semester 1 Exam Cheatsheet

26/03/2026

Chapter 1: Science Inquiry Skills

Experimental Design & Variables

  • Hypothesis: A testable statement predicting an outcome. Example: “Dietary iodine consumption affects blood pressure” or “Increased temperature increases enzyme reaction rate.”
  • Variables:
    • Independent (IV): What you deliberately change in the experiment.
    • Dependent (DV): What you measure as the outcome.
    • Controlled: Kept identical to ensure a fair test (e.g., temperature, pH, equipment, light exposure, time duration).
  • Placebo: An inactive, fake treatment used as a control (e.g., a sugar pill) to account for psychological effects. Important in pharmaceutical and behavioral experiments.
  • Reliability: How consistent the results are when repeated. Increased by repeating the experiment multiple times or increasing the number of trials and sample size.
  • Validity: Whether the experiment accurately tests the hypothesis. Ensured by controlling all other variables and ensuring the test measures what it claims to measure.

Data Representation & Errors

  • Sources of Data:
    • Primary: Direct, firsthand data collected from your own experiment or observation.
    • Secondary: Interpretations or summaries of data from other sources like books, documentaries, podcasts, or published research.
  • Density Ratio (Surface Area to Volume Ratio - SA:V): The smaller the cell, the larger the SA:V ratio, allowing faster transport of materials relative to cell volume. This is critical for understanding cell efficiency.
  • Types of Errors:
    • Systematic Errors: Consistent faults in equipment or experimental design (e.g., faulty thermometer, calibration errors, or biased technique). These push results consistently in one direction.
    • Random Errors: Unpredictable human or environmental variations (e.g., slight changes in temperature, inconsistent timing, or observer errors). These cause results to scatter around the true value.
  • Graphs (when to use each):
    • Line Graph: Continuous data showing trends over time; must have titles, axis labels with units, and connected points.
    • Histogram: Frequency distributions of continuous data (e.g., heights in age ranges, temperature ranges).
    • Bar Graph: Discrete, categorical data with separate bars (no connecting line).
    • Pie Chart: Proportions or percentages of a whole.

Chapter 2: Cells Make Up The Human Body

Cell Theory & Structure

  • Cell Theory (Three Main Principles):

    1. All living things are made of cells.
    2. Cells are the basic structural and functional unit of life.
    3. All cells come from pre-existing cells (cell division).

  • Cellular Components and Organization:

    • Cytoplasm: The jelly-like material AND all organelles inside the cell membrane. Everything inside the cell except the nucleus.
    • Cytosol: Only the liquid part of the cytoplasm (without organelles).
    • Inclusions: Chemical substances stored in the cytosol for later use (e.g., melanin pigment in skin cells, glycogen in liver cells).

  • The Nucleus Structure and Function:

    • Nuclear membrane (Envelope): A double layer that controls what enters and exits the nucleus.
    • Nuclear pores: Allow large molecules like RNA to exit the nucleus.
    • Nucleoplasm: The jelly-like substance inside the nucleus.
    • Nucleolus: The dark-staining region that synthesizes and assembles ribosomes.
    • Chromatin: Made of DNA and histone proteins; loosely coiled during interphase. Condenses into visible chromosomes during cell division.

  • Cell Organelles - Structure and Function:

    • Ribosomes: Sites of protein synthesis. Can be free in cytosol or attached to ER (forming rough ER).
    • Rough Endoplasmic Reticulum (RER): Has ribosomes attached; synthesizes, modifies, and transports proteins.
    • Smooth Endoplasmic Reticulum (SER): Lacks ribosomes; primarily synthesizes lipids and stores calcium ions.
    • Golgi Apparatus (Golgi Body): Modifies, packages, and sorts proteins into vesicles for transport to their destinations.
    • Lysosomes: Membrane-bound sacs containing digestive enzymes (hydrolytic enzymes) that break down waste materials, damaged organelles, and cellular debris. Lack of functional lysosomes = Sandhoff disease (lysosomal storage disease).
    • Mitochondria (Powerhouse of the cell): Double membrane organelle where aerobic respiration occurs; primary site of ATP production.
    • Cytoskeleton: Network of protein filaments (microtubules and microfilaments) providing cell shape, maintaining structure, and enabling organelle and vesicle movement.
    • Cilia and Flagella: Hair-like (cilia) or whip-like (flagella) extensions from the cell surface that enable movement of the cell or movement of fluid past the cell.

The Fluid Mosaic Model

  • Phospholipid Bilayer Structure - Why it’s a Bilayer (IN DETAIL):

    • Phospholipids have a hydrophilic (water-loving) “head” containing phosphate groups and a hydrophobic (water-hating) lipid “tail.”
    • In aqueous environments, phospholipids naturally arrange with heads facing outward (toward the watery cytosol and extracellular fluid) and tails facing inward (away from water).
    • This dual arrangement creates a bilayer as the most thermodynamically stable configuration.
    • The hydrophobic interior prevents polar water molecules from passing through easily, creating a selective barrier.

  • Components of the Cell Membrane:

    • Phospholipids: Form the basic bilayer structure.
    • Cholesterol: Maintains membrane fluidity by reducing phospholipid movement at higher temperatures while preventing excessive fluidity at lower temperatures. Also stabilizes the membrane.
    • Integral Proteins: Span the entire membrane; function as channels, receptors, or carriers for substances.
    • Peripheral Proteins: Located on the inner or outer surface; often involved in support and signaling.

  • What is NOT in the Cell Membrane:

    • Nucleic acids (DNA, RNA)
    • Cytosol (the liquid component is inside the cell, not part of the membrane)

Cell Transport (Movement of Substances Across the Membrane)

  • Passive Transport Processes (No ATP Energy Required - High to Low Concentration):

    • Simple Diffusion: Small or lipid-soluble molecules (O₂, CO₂, steroids, alcohol) pass directly through the phospholipid bilayer without protein assistance. Movement is down the concentration gradient.
    • Facilitated Diffusion: Larger or polar molecules (water via aquaporins, glucose, amino acids) use protein channels or carrier proteins to cross the membrane. Movement is down the concentration gradient; no ATP needed.
    • Osmosis: The diffusion of water molecules across a semi-permeable membrane from an area of higher water potential (lower solute concentration) to lower water potential (higher solute concentration).

  • Active Transport Processes (Requires ATP Energy - Low to High Concentration):

    • Active Transport: Carrier proteins use ATP energy to pump specific ions and molecules against their concentration gradient (e.g., Na⁺/K⁺ pump moving sodium out and potassium in).
    • Endocytosis (Vesicular Transport - Active): The cell membrane engulfs material and brings it into the cell.
      • Phagocytosis: Engulfing solid particles (like pathogens or cellular debris).
      • Pinocytosis: Engulfing liquid droplets.
    • Exocytosis (Vesicular Transport - Active): Vesicles fuse with the cell membrane to release contents outside the cell (e.g., mucus secretion, enzyme release, waste removal).

  • Examples of Substance Transport:

    • Oxygen and carbon dioxide: Simple diffusion
    • Glucose in intestinal cells: Active transport (against gradient)
    • Water: Osmosis
    • Proteins and hormones: Exocytosis

Tissues (Organization of Cells)

  • Organizational Hierarchy: Cells → Tissues → Organs → Organ Systems

  • Tissue Types (In Depth):

    • Epithelial Tissue:

      • Lines surfaces and covers organs; provides protection and absorption.
      • Examples: Skin (stratified squamous), intestinal lining (simple columnar), ciliated respiratory tract (pseudostratified ciliated columnar).
      • Functions: Protection, absorption, secretion, and sensory reception.

    • Connective Tissue:

      • Cells separated by a large non-cellular matrix (extracellular material).
      • Types:
        • Bone: Hard, mineralized matrix containing osteocytes; provides support and protection.
        • Cartilage: Flexible matrix with chondrocytes; reduces friction at joints.
        • Blood: Liquid plasma matrix with RBCs, WBCs, and platelets; transports materials.
        • Adipose (Fat): Stores energy in the form of triglycerides.
        • Loose Connective Tissue: Wraps organs and fills spaces between tissues.
        • Dense Connective Tissue: Tendons (muscle to bone) and ligaments (bone to bone); provides strength.

    • Muscular Tissue:

      • Skeletal: Striated, voluntary, attached to bones for movement.
      • Smooth: Non-striated, involuntary, found in hollow organs and blood vessels.
      • Cardiac: Striated, involuntary, found only in the heart.

    • Nervous Tissue:

      • Neurons conduct electrical impulses to transmit information throughout the body.
      • Glial cells provide support and insulation.

Chapter 3: Metabolism

  • Metabolism Definition: All chemical reactions occurring in a cell that are necessary for life. Includes:

    • Catabolic Reactions: Breakdown of large molecules into smaller units, releasing energy (e.g., cellular respiration breaking down glucose).
    • Anabolic Reactions: Building of large molecules from smaller units, requiring energy (e.g., protein synthesis from amino acids).
    • Key Concept: If you consume excess nutrients, an abundance of catabolic reactions breaks them down into subunits, which are then stored via anabolic reactions as fat (triglycerides) or glycogen.

  • Nutrients & Organic Compounds (Macromolecules):

    • Carbohydrates (Polysaccharides): Primary energy source; broken down to glucose for ATP production.
    • Lipids: Energy storage; 9 kcal/gram (more than twice carbs). Used for membrane structure and signaling.
    • Proteins: Structural components, enzymes, hormones, antibodies; can be broken down for energy when other fuels are scarce.
    • Nucleic Acids: DNA and RNA; carry genetic instructions and regulate protein synthesis.

  • Vitamins & Minerals - Functions (IN DETAIL):

    • Vitamins: Act as co-enzymes or co-factors for enzyme function.
      • Fat-soluble (A, D, E, K): Stored in body fat; can accumulate to toxic levels.
      • Water-soluble (B complex, C): Easily excreted; require regular dietary intake.
    • Minerals: Act as co-factors for enzyme activity.
      • Iron: Component of haemoglobin for oxygen transport.
      • Calcium: Bone structure, muscle contraction, nerve transmission.
      • Iodine: Thyroid hormone synthesis.
      • Sodium (Salt): Regulates the chemical composition and osmotic pressure of body fluids; maintains blood pH and nerve/muscle function.

Enzymes

  • Enzyme Function: Enzymes are biological catalysts that lower activation energy, speeding up chemical reactions without being consumed. Many different enzymes exist because protein shapes are infinitely variable based on the sequence and arrangement of amino acids.

  • Enzyme Models:

    • Lock and Key Model: The active site is fixed and complementary (perfectly fitted) to a specific substrate. The substrate fits into the active site like a key into a lock. Once the reaction completes, the product is released.
    • Induced Fit Model: The active site is flexible and molds to fit the substrate, wrapping around it to optimize catalysis. This explains why some enzymes have higher specificity and are more efficient.

  • Factors Affecting Enzyme Activity:

    • Temperature: Increases reaction rate as molecules move faster and collisions increase. Too high = enzyme denaturation (unfolding of protein structure) and loss of activity.
    • pH: Each enzyme has an optimal pH. Extreme pH causes denaturation.
    • Substrate Concentration: Increases reaction rate until enzyme saturation (when all enzyme active sites are occupied; further substrate addition has no effect).

Cellular Respiration

  • Anaerobic Respiration (Glycolysis - Occurs in the Cytosol):

    • Glucose → 2 Pyruvate (or lactic acid during intense exercise) + ATP (2 net ATP produced) + NADH
    • Occurs with or without oxygen; primary source of ATP in anaerobic conditions.
    • Lactic acid buildup causes muscle fatigue.

  • Aerobic Respiration (Requires Oxygen - Occurs Mainly in Mitochondria):

    • Krebs Cycle (Citric Acid Cycle) - Occurs in Mitochondrial Matrix:

      • Pyruvate → Acetyl CoA → CO₂ (released) + NADH + FADH₂ + GTP/ATP (2 ATP equivalent)
      • Electrons captured in carrier molecules (NADH, FADH₂) for the next stage.

    • Oxidative Phosphorylation (Electron Transport Chain) - Occurs on Inner Mitochondrial Membrane:

      • Electrons from NADH and FADH₂ pass through the electron transport chain.
      • Oxygen acts as the final electron acceptor, forming water.
      • Energy released pumps protons across the membrane, creating a gradient.
      • ATP synthase uses this gradient to produce up to 34 ATP per glucose molecule.

  • Complete Equation:

    • C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~30-32 ATP (net per glucose)

Chapter 4: Respiratory System

Anatomy & Function

  • Primary Function: Supply oxygen to cells for aerobic respiration and remove carbon dioxide (waste product) from the body.

  • Pathway of Air (IN DETAIL):

    • Nasal cavity (warms, filters, humidifies air)
    • Pharynx (choana) (throat; passageway for air and food)
    • Epiglottis (flap of cartilage that blocks food from entering the trachea during swallowing)
    • Larynx (voice box; contains vocal cords)
    • Trachea (windpipe; lined with ciliated epithelium; C-shaped cartilage rings prevent collapse but allow food passage behind it)
    • Primary Bronchi (branch into left and right)
    • Bronchioles (smaller branches with smooth muscle but no cartilage; can constrict during asthma)
    • Alveoli (tiny air sacs where gas exchange occurs)

  • Pleural Membrane: Double membrane that connects the lungs to the chest wall. The outer layer lines the chest cavity; the inner layer covers the lungs. Creates a sealed space where pressure changes drive breathing.

  • Mucus & Cilia - Airway Protection:

    • Goblet cells in the respiratory epithelium release mucus via exocytosis to trap particles and pathogens.
    • Cilia beat upward in coordinated waves to clear debris and move mucus toward the pharynx for swallowing (mucociliary clearance).

Mechanics of Breathing & Gas Exchange

  • Inhalation (Inspiration) - Filling the Lungs:

    • Diaphragm contracts and moves downward into the abdominal cavity.
    • Intercostal muscles (external intercostals) contract, lifting the ribs upward and outward.
    • Thoracic cavity volume increases.
    • Intrapulmonary pressure (pressure inside lungs) decreases below atmospheric pressure.
    • Air rushes into the lungs down the pressure gradient.

  • Exhalation (Expiration) - Emptying the Lungs:

    • Diaphragm relaxes and moves upward.
    • Intercostal muscles (internal intercostals) relax, lowering the ribs inward.
    • Thoracic cavity volume decreases.
    • Intrapulmonary pressure increases above atmospheric pressure.
    • Air is forced out of the lungs.

  • Gas Exchange in the Alveoli:

    • Alveoli have massive surface area (200+ m² in adult lungs) for exchange.
    • Alveolar walls are one cell thick, minimizing diffusion distance.
    • Dense capillary network allows close contact with blood.
    • Oxygen diffuses from the alveolus into the blood along the concentration gradient.
    • CO₂ diffuses from the blood into the alveolus along the concentration gradient.

Respiratory Diseases

  • Asthma: Smooth muscle constricts the bronchioles (bronchoconstriction), causes airway inflammation, and triggers excess mucus production. Results in wheezing, difficulty breathing, and chest tightness during attacks.

  • Acute Bronchitis: Short-term infection (usually viral) causing inflammation of the bronchi. Presents with productive cough (phlegm), chest discomfort, and fatigue.

  • COPD (Chronic Obstructive Pulmonary Disease):

    • Chronic Bronchitis: Long-term inflammation and mucus production in the bronchi; results in persistent productive cough.
    • Emphysema: Alveolar walls break down, drastically reducing surface area for gas exchange. Loss of elastic recoil makes exhalation difficult. Results in dyspnea (shortness of breath) and permanent airflow limitation.

Chapter 5: Circulatory & Lymphatic Systems

Blood Structure & Composition

  • Plasma (Liquid Matrix): Transports dissolved gases (oxygen, CO₂), nutrients (glucose, amino acids), hormones, antibodies, blood clotting factors, and wastes. Makes up ~55% of blood.

  • Erythrocytes (Red Blood Cells - RBCs): (~45% of blood)

    • Biconcave disc shape (increases surface area to volume ratio for efficient oxygen loading/unloading).
    • No nucleus (mature mammalian RBCs; allows more space for haemoglobin).
    • Packed with haemoglobin protein for oxygen transport.
    • Lifespan: ~120 days; old cells removed by the spleen.

  • Leucocytes (White Blood Cells - WBCs): (<1% of blood)

    • Large, nucleated cells.
    • Defend against disease pathogens and foreign material.
    • Types: Neutrophils, lymphocytes (B and T cells), monocytes, eosinophils, basophils.

  • Thrombocytes (Platelets): (<1% of blood)

    • Cell fragments from megakaryocytes in bone marrow.
    • Essential for blood clotting; form platelet plugs at damaged vessels.

Gas Transport & Blood Clotting

  • Oxygen Transport in Blood:

    • 98% binds to haemoglobin forming oxyhaemoglobin (within RBCs).
    • 2% dissolved in plasma (minimal contribution but important at high altitudes or low oxygen conditions).
    • Haemoglobin has 4 iron-containing heme groups; each can bind one O₂ molecule.

  • Carbon Dioxide Transport in Blood (IN DETAIL):

    • 70% travels as bicarbonate ions (HCO₃⁻) in plasma: CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻ (carbonic acid acts as a buffer).
    • 20% binds to haemoglobin forming carbaminohaemoglobin (different binding site than oxygen; increases blood acidity).
    • 10% dissolved in plasma and RBC cytosol.
    • CO₂ increases H⁺ ion concentration, lowering blood pH (acidemia).

  • Blood Clotting (Coagulation and Clot Retraction):

    • Vasoconstriction: Damaged blood vessel walls constrict to slow blood flow.
    • Platelet Plug Formation: Platelets aggregate and adhere to damaged endothelium, forming a temporary plug.
    • Cascade Coagulation: Clotting factors are activated in sequence; converts fibrinogen (soluble protein) into fibrin (insoluble strands).
    • Fibrin Threads: Form a mesh that traps RBCs and platelets, creating a solid thrombus (clot).
    • Clot Retraction: Platelets contract, pulling the clot edges together to seal the wound more effectively.

The Heart Structure & Blood Flow

  • Outer Heart Anatomy:

    • Cardiac Muscle: Specialized muscle tissue forming the myocardium (thick muscular wall).
    • Pericardium: Double-walled protective sac surrounding the heart; contains pericardial fluid for friction reduction.
    • Septum: Wall dividing the left and right sides of the heart; prevents mixing of oxygenated and deoxygenated blood.

  • Complete Blood Flow Sequence (IN DETAIL): Superior/Inferior Vena Cava (from head and body) → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve → Pulmonary Artery → Lungs (oxygenation) → Pulmonary Vein → Left Atrium → Bicuspid (Mitral) Valve → Left Ventricle → Aortic Valve → Aorta → Arteries → Arterioles → Capillaries (gas/nutrient exchange) → Venules → Veins → Vena Cava

  • Blood Vessel Characteristics:

    • Arteries: Thick, elastic muscular walls for high-pressure; carry blood away from heart. NO valves (except pulmonary and aortic). Endothelium (single-cell-thick inner layer) with basement membrane.
    • Capillaries: Single-cell-thick endothelial cells allowing diffusion of small molecules; site of gas and nutrient exchange; extremely narrow (RBCs squeeze through single file).
    • Veins: Thin walls, low pressure. HAVE valves (semi-lunar) to prevent backflow. Collect blood and return to heart. Endothelium-lined.

Cardiac Cycle & Blood Pressure

  • Systole (Ventricular Contraction): Ventricles contract, forcing blood into arteries.

    • Atrioventricular valves (tricuspid and bicuspid) snap shut.
    • Sound: ‘Lub’ (first heart sound).

  • Diastole (Ventricular Relaxation): Heart chambers relax and fill with blood from veins and atria.

    • Semilunar valves (aortic and pulmonary) snap shut, preventing backflow.
    • Sound: ‘Dub’ (second heart sound).

  • Cardiac Output Formula: Cardiac Output (CO) = Stroke Volume (mL of blood per beat) × Heart Rate (beats/minute)

    • Normal: ~5L/minute at rest.
    • Decreases during a heart attack due to dead or damaged myocardial tissue losing contractility.

  • Blood Pressure & Osmosis (Hypertension - High Blood Pressure):

    • High salt intake increases blood Na⁺ concentration, creating a hypertonic blood plasma.
    • Water leaves cells via osmosis moving into the blood to dilute excess salt.
    • Increased blood volume increases blood pressure.
    • Sustained high blood pressure can rupture capillaries, causing stroke or kidney damage.

Blood Groups & Transfusions

  • ABO Blood Group System:

    • Type A: A antigens on RBCs; Anti-B antibodies in plasma.
    • Type B: B antigens on RBCs; Anti-A antibodies in plasma.
    • Type AB: Both A and B antigens; No anti-A or anti-B antibodies (universal recipient).
    • Type O: No A or B antigens; Anti-A and Anti-B antibodies (universal donor).

  • Rh Blood Group System:

    • Rh Positive (+): Has Rh antigen on RBCs.
    • Rh Negative (-): Lacks Rh antigen; can develop anti-Rh antibodies if exposed to Rh+ blood.

  • Agglutination (Fatal Incompatibility): When incompatible blood types mix, antibodies bind to antigens causing RBCs to clump (agglutinate) and hemolyze, leading to hemolytic transfusion reaction (fever, chest pain, organ failure, death).

  • Blood Transfusions - Types and Applications:

    • Whole Blood: For acute hemorrhage/severe blood loss; contains all components.
    • Red Cell Concentrates: For anemia; boosts oxygen-carrying capacity.
    • **Platelet Concentrates:**For leukemia, thrombocytopenia, or severe bleeding disorders.
    • Cryoprecipitate: For hemophilia (clotting factor deficiency); contains fibrinogen and clotting factors.
    • Immunoglobulins: For immune deficiencies; contains antibodies for passive immunity.
    • Autologous Transfusion: Patient’s own blood donated in advance for elective surgery; safest option (no incompatibility risk).

Lymphatic System

  • Functions:

    • Returns excess tissue fluid (lymph) back to the circulatory system, maintaining fluid balance.
    • Defends against disease through lymphocytes and removal of pathogens.

  • Structure of the Lymphatic System:

    • Lymph Capillaries: Highly permeable, blind-ended vessels at tissue level; collect tissue fluid.
    • Lymph Vessels: Have valves to prevent backflow; drain lymph toward lymph nodes.

  • Lymph Nodes:

    • Contain afferent vessels (lymph entering) and efferent vessels (lymph leaving).
    • House lymphocytes and macrophages that filter and trap debris, pathogens, and abnormal cells.
    • Sites of immune response (antigen presentation and lymphocyte activation).

  • Lymph Circulation:

    • Driven entirely by skeletal muscle contraction during movement; not pumped by the heart.
    • Promotes fluid return to the circulatory system.
    • Lack of activity causes fluid accumulation = lymphedema (swelling).

Chapter 6: Digestive System

Types of Digestion

  • Mechanical Digestion: Physical breakdown of food without enzymatic action.

    • Mastication (chewing) in the mouth.
    • Stomach churning and muscular contractions.
    • Bile emulsification of fats (breaks large fat droplets into smaller ones).

  • Chemical Digestion (IN DETAIL):

    • Carbohydrate Breakdown:

      • Amylase (from salivary glands and pancreas) breaks polysaccharides (starch, glycogen) into disaccharides (maltose, sucrose, lactose).
      • Specific disaccharidases (brush border enzymes on small intestine) then break disaccharides:
        • Maltase: Maltose → 2 Glucose
        • Sucrase: Sucrose → Glucose + Fructose
        • Lactase: Lactose → Glucose + Galactose
      • Result: Monosaccharides (glucose, fructose, galactose) absorbed into blood.

    • Protein Breakdown:

      • Pepsin (stomach, acidic pH): Proteins → Smaller polypeptides
      • Trypsin (pancreas, small intestine): Polypeptides → Shorter chains
      • Peptidases (small intestine brush border): Dipeptides and tripeptides → Individual amino acids (absorbed).

    • Lipid (Fat) Breakdown:

      • Lipases (from tongue, stomach, pancreas): Triglycerides → Fatty acids + Glycerol

    • Nucleic Acid Breakdown:

      • Nucleases: DNA/RNA → Nucleotides

  • Elimination vs. Excretion:

    • Elimination: Removal of unabsorbed materials (feces) from the digestive system; not metabolic waste.
    • Excretion: Removal of metabolic wastes (urea, uric acid) via kidneys and other organs.

The Alimentary Canal & Digestive Juices

  • Mouth:

    • Mechanical digestion (mastication).
    • Salivary amylase begins starch digestion.
    • Tongue facilitates mixing and swallowing.

  • Stomach:

    • Three layers of smooth muscle (oblique, circular, longitudinal) allow powerful churning action.
    • Converts food into chyme (semi-liquid partially digested food).
    • Secretes gastric juice:
      • Hydrochloric acid (HCl): Denatures proteins, kills pathogens.
      • Pepsin: Protease enzyme for initial protein breakdown.
      • Mucus: Protects stomach lining from acid.
    • Pyloric sphincter controls release of chyme into duodenum.

  • Pancreatic Juice (Enters Duodenum of Small Intestine):

    • Highly alkaline pH 8-9 (bicarbonate buffer) neutralizes stomach acid.
    • Protects small intestine lining from acid damage.
    • Contains: Trypsin, amylase, lipases, nucleases.

  • Bile (Made in Liver, Stored in Gallbladder):

    • Emulsifies fats (increases surface area for lipase action).
    • Helps absorb fat-soluble vitamins (A, D, E, K).
    • Contains cholesterol and bile pigments (breakdown products of hemoglobin).

  • Intestinal (Succus Entericus):

    • Secreted by intestinal glands (crypts of Lieberkühn).
    • Contains: Maltase, sucrase, lactase, peptidases, nucleotidases.
    • Nearly neutral pH suitable for brush border enzyme function.

Absorption (IN DETAIL)

  • Massive Surface Area Creation:

    • Length of small intestine (~6-7 meters).
    • Circular folds (plicae circulares): Permanent folds in mucosa.
    • Villi: Finger-like projections of mucosa (0.5-1 mm tall).
    • Microvilli: Microscopic projections on epithelial cells (0.001 mm); formed from cell membrane.
    • Total surface area: ~200-400 m² (equivalent to a tennis court!)

  • Nutrient Absorption Mechanisms:

    • Simple Sugars (Glucose, Galactose): Absorbed via active transport (requires ATP; against concentration gradient). Some also via facilitated diffusion.
    • Amino Acids: Absorbed via active transport (selective carriers for different amino acids).
    • Fatty Acids and Glycerol: Absorbed via simple diffusion. Reform into triglycerides within intestinal cells. Packaged into chylomicrons for lymphatic transport (in lacteals).

  • Blood Capillaries: Absorb simple sugars and amino acids directly; transport to liver via hepatic portal vein.

  • Lacteals (Lymphatic Capillaries): Absorb fat-soluble materials; transport through lymph eventually reaching bloodstream.

Digestive Disorders

  • Constipation: Slow movement through colon → excessive water absorption → hard, infrequent stools. Causes: Low fiber, dehydration, lack of exercise.

  • Diarrhea: Rapid movement through colon → inadequate water absorption → loose, frequent stools. Causes: Infections (viral/bacterial), food intolerance, inflammatory bowel disease.

    • Common in lactose intolerance: Lactose cannot be digested (lactase deficiency) → lactic acid accumulation → osmotic diarrhea.

  • Celiac Disease: Autoimmune/immune-mediated reaction to gluten (protein in wheat, barley, rye). Damages intestinal villi → malabsorption of nutrients. Symptoms: Diarrhea, abdominal pain, fatigue, anemia.

  • Bowel Cancer (Colorectal Cancer): Malignancy developing in the large intestine/colon. Linked to: High red/processed meat consumption, low fiber, genetics, chronic inflammation (IBD). Can obstruct bowel or metastasize.

Chapter 7: Excretory System

Organs That Process and Remove Waste

The excretory system consists of: Kidneys, ureters, urinary bladder, urethra, and supportive organs (liver, skin, lungs).

The Liver & Skin

  • Liver Functions:

    • Processes nutrients from the digestive system.
    • Produces bile for fat digestion/absorption.
    • Detoxifies harmful substances (alcohol, drugs).
    • Produces clotting factors.
    • Stores vitamins and minerals.

  • Deamination (Protein Breakdown) - IN DETAIL:

    • Excess amino acids cannot be stored; liver breaks them down.
    • Removal of the amino group (-NH₂) requires oxygen.
    • Amino group produces toxic ammonia (NH₃).
    • Ammonia is immediately converted to less toxic urea (CO(NH₂)₂) in the urea cycle.
    • Urea is excreted by kidneys dissolved in urine.
    • The remaining carbohydrate skeleton is used for energy (via Krebs cycle) or converted to glucose/glycogen.

  • Skin (Sweat Excretion):

    • Excretes small amounts of: Water, salts (NaCl, KCl), and trace urea.
    • Primary function: Thermoregulation; minor excretory role.

The Kidneys & Nephron System

  • Kidney Structure (Three Main Regions):

    • Renal Cortex (Outer Layer):

      • Contains renal corpuscles (sites of ultrafiltration).
      • Contains portions of proximal and distal convoluted tubules (PCT and DCT).

    • Renal Medulla (Middle Layer):

      • Contains 8-12 renal pyramids (triangular structures).
      • Pyramids contain loops of Henle and collecting ducts.

    • Renal Pelvis (Innermost):

      • Collects urine from collecting ducts.
      • Funnels urine to the ureter.

    • Functional Unit: The nephron (microscopic filtration and reabsorption unit). Each kidney contains ~1 million nephrons.

  • Nephron Structure (IN DETAIL):

    • Renal Corpuscle (Glomerulus + Bowman’s Capsule):

      • Glomerulus: Capillary network where ultrafiltration occurs.
      • Bowman’s Capsule: Cup-shaped structure surrounding glomerulus.
      • Filtration membrane: Endothelium (fenestrated), basement membrane, and podocytes (specialized cells with filtration slits).

    • Renal Tubule:

      • Proximal Convoluted Tubule (PCT): Reabsorption of useful substances.
      • Loop of Henle: Concentration of urine (descending limb permeable to water; ascending limb impermeable to water but permeable to sodium).
      • Distal Convoluted Tubule (DCT): Fine-tuning of urine composition via tubular secretion.
      • Collecting Duct: Final concentration under antidiuretic hormone (ADH) regulation; empties into renal pelvis.

  • Urine Production - Three Stages (IN DETAIL):

    1. Glomerular Filtration:

    • The afferent arteriole is narrower than the efferent arteriole, creating high hydrostatic pressure within the glomerulus.
    • Pressure forces small molecules through the filtration membrane into Bowman’s capsule.
    • Small substances filtered: Water, glucose, amino acids, urea, uric acid, ions (Na⁺, K⁺, Cl⁻), ammonia.
    • Large substances retained in blood: Large proteins (albumin, globulins), blood cells, platelets.
    • Result: Glomerular filtrate formed (~180 L/day in both kidneys).

    2. Reabsorption (IN DETAIL):

    • Proximal Convoluted Tubule (PCT):

      • Glucose: 100% actively reabsorbed (carrier-mediated; energy-dependent).
      • Amino acids: 100% actively reabsorbed.
      • Sodium (Na⁺): Actively reabsorbed.
      • Water: Passively reabsorbed by osmosis following sodium reabsorption.
      • Some ions and water returned to peritubular capillaries.

    • Loop of Henle (Countercurrent Multiplier System):

      • Descending Limb: Permeable to water; water exits passively (osmosis) → urine concentrates.
      • Ascending Limb: Impermeable to water; sodium actively reabsorbed → medullary interstitium becomes hypertonic.
      • Creates a concentration gradient allowing maximum water recovery later.

    • Distal Convoluted Tubule (DCT) and Collecting Duct:

      • Fine-tuning under hormonal control (ADH, aldosterone).
      • Sodium reabsorbed; water follows passively.
      • Amount controlled by ADH (increases water reabsorption when blood is dehydrated).

    3. Tubular Secretion:

    • Active and passive movement of substances from peritubular capillaries into the tubular fluid (mainly in DCT).
    • Substances secreted: Potassium (K⁺), hydrogen ions (H⁺), creatinine, ammonia, some drugs.
    • Purposes: Control blood pH (H⁺ secretion increases or decreases to buffer pH changes from CO₂). Regulate electrolyte balance (extra K⁺ is secreted).

  • Urine Composition (Normal):

    • Water (95%), Urea (nitrogen waste), Uric Acid (from nucleic acid breakdown), Ions (Na⁺, K⁺, Cl⁻).
    • Notably ABSENT: Glucose (normally reabsorbed), Blood cells (not filtered), Large proteins (not filtered).
    • Detection of glucose or blood in urine indicates kidney disease or metabolic disorder.

Kidney Disorders & Dialysis

  • Kidney Stones (Renal Calculi): Hardened crystal deposits formed from concentrated urine minerals (calcium oxalate, uric acid). Causes: Dehydration, high dietary salt/protein, genetic factors. Symptoms: Severe flank pain, blood in urine.

  • Kidney Failure (Renal Failure): Loss or severe reduction in kidney filtration ability.

    • Acute: Sudden loss (often reversible) due to shock, sepsis, or toxins.
    • Chronic: Progressive loss (irreversible) due to diabetes, hypertension, glomerulonephritis.
    • Results in: Uremia (toxic buildup of urea and other wastes), hyperkalemia (dangerous potassium levels), anemia, bone disease.

  • Kidney Dialysis - Artificial Filtration:

    • Hemodialysis:

      • Blood is pumped from the patient’s artery through a dialyzer (artificial kidney).
      • Inside: Semipermeable membrane separates blood from dialysis fluid.
      • Small waste molecules (urea, creatinine, K⁺) diffuse from blood into dialysate; glucose and other useful substances are retained.
      • Cleaned blood is returned to the patient’s vein.
      • Frequency: 3-4 times per week, 3-5 hours per session.

    • Peritoneal Dialysis:

      • Dialysis fluid is pumped into the abdominal cavity through a catheter.
      • The patient’s own peritoneum (membrane lining the abdominal cavity) acts as the semipermeable membrane.
      • Waste diffuses from blood into the dialysate across the peritoneal membrane.
      • After several hours, the used dialysate is drained out and fresh fluid is reintroduced.
      • Advantages: Can be done at home; allows more frequent dialysis (CAPD - continuous ambulatory peritoneal dialysis).

Chapter 8: Musculoskeletal System

Types of Muscle Tissue (Structure, Function, Location)

  • Skeletal Muscle:

    • Appearance: Striated (striped pattern from organized sarcomeres).
    • Control: Voluntary (under conscious control).
    • Location: Attached to bones via tendons; also in face, tongue, pharynx.
    • Function: Movement of body parts; maintains posture; generates heat.

  • Smooth Muscle:

    • Appearance: Non-striated (uniform appearance); spindle-shaped cells.
    • Control: Involuntary (automatic; regulated by autonomic nervous system).
    • Location: Hollow organs (GI tract, blood vessels, bladder, uterus, bronchi).
    • Function: Peristalsis (wave-like contractions in digestive tract); vasoconstriction/vasodilation; sphincter control.

  • Cardiac Muscle:

    • Appearance: Striated; branched fibers.
    • Control: Involuntary (autonomous pacemaker; sinoatrial node).
    • Location: Heart wall (myocardium).
    • Function: Pump blood; continuous, rhythmic contractions.
    • Special Feature: Intercalated discs (connections between cells) allow electrical/mechanical coupling.

Deep Skeletal Muscle Anatomy

  • Nested Organizational Structure:

    • Whole Muscle: Surrounded by epimysium (tough outer connective tissue layer).
    • Fascicles (Bundles): Groups of muscle fibers bundled together; surrounded by perimysium (connective tissue).
    • Individual Muscle Fiber (Cell): The basic contractile unit; surrounded by endomysium (thin connective tissue).
      • Cell Membrane: Called sarcolemma (specialized plasma membrane).
      • Cytoplasm: Called sarcoplasm; contains organelles and contractile proteins.
      • Calcium-Storage Organelle: Sarcoplasmic reticulum (specialized smooth ER) stores Ca²⁺ ions.

  • Inside the Muscle Fiber:

    • Myofibrils: Long, cylindrical structures running the length of the fiber; contain sarcomeres (contractile units).
    • Myofilaments: Protein filaments within myofibrils.
      • Thick Filaments: Made of myosin protein (head and tail structure).
      • Thin Filaments: Made of actin protein; wrapped by tropomyosin; with troponin positioned at intervals.

The Sliding Filament Model (IN DETAIL - Contraction and Relaxation)

  • Sarcomere Structure (The Contractile Unit - Bounded by Z-lines):

    • Z-line (Z-disc): The boundaries/anchors of the sarcomere. Anchors thin filaments. When sarcomeres shorten, Z-lines move closer together.
    • I-band (Isotropic Band): Light-staining band; contains ONLY thin actin filaments. Shortens during contraction.
    • A-band (Anisotropic Band): Dark-staining band; contains thick myosin filaments (and overlapping thin filaments when contracted). Width stays constant; the zone of overlap increases.
    • H-zone (H-band): Central region of the A-band containing ONLY thick myosin filaments (no thin filaments). Shrinks during contraction.
    • M-line: Center of the H-zone; anchors thick filaments.

  • Contraction Mechanism (7 Steps - IN DETAIL):

    1. Nerve Impulse Arrives: Action potential travels along the sarcolemma and down T-tubules.

    2. Calcium Release: Depolarization triggers sarcoplasmic reticulum to release Ca²⁺ into sarcoplasm.

    3. Calcium Binds to Troponin: Ca²⁺ binds to troponin (regulatory protein on thin filaments).

    4. Tropomyosin Displaced: Troponin conformational change pulls tropomyosin away from the myosin-binding sites on actin.

    5. Cross-Bridge Formation: Myosin heads (already “cocked” with stored ATP energy) bind to exposed actin-binding sites, forming cross-bridges.

    6. Power Stroke: Myosin heads pivot, pulling thin filaments toward the center of the sarcomere.

      • The H-zone and I-band shrink.
      • Z-lines move closer together.
      • Sarcomere shortens.

    7. Detachment and Reactivation: New ATP binds to myosin heads, causing detachment from actin. Hydrolysis of ATP re-energizes (cocks) myosin heads for the next cycle.

  • Relaxation:

    • Nerve impulse stops.
    • Ca²⁺ actively pumped back into sarcoplasmic reticulum.
    • Tropomyosin returns to cover myosin-binding sites.
    • Cross-bridges cannot form.
    • Muscle relaxes; sarcomeres lengthen.

  • Muscle Pairs and Movement Terms:

    • Agonist (Prime Mover): The muscle that contracts to produce the main movement.
    • Antagonist: The muscle that opposes the agonist; relaxes when agonist contracts (e.g., biceps and triceps).
    • Synergist: Assists the agonist by stabilizing joints or providing similar movement.
    • Fixator (Stabilizer): Stabilizes the origin (attachment point) of the agonist so it can move effectively.

Bone & Cartilage

  • The Skeleton - Two Divisions:

    • Axial Skeleton: Skull, vertebral column (spine), sternum, ribs. Function: Protection (brain, spinal cord, heart, lungs) and support.
    • Appendicular Skeleton: Limbs (arms and legs), pelvic girdle, pectoral girdle (shoulder). Function: Movement and locomotion.

  • Long Bone Structure (Femur as Example):

    • Epiphyses (Ends): Enlarged regions at each end; contain spongy bone and red marrow for blood cell production.
    • Diaphysis (Shaft): Long central portion; mainly compact bone; contains yellow marrow (fat storage) in medullary cavity.
    • Periosteum: Tough fibrous outer membrane covering bone; contains blood vessels and nerves; attachment site for ligaments and tendons.

  • Bone as Specialized Connective Tissue:

    • Matrix is mineral (calcium and phosphate crystals) providing hardness and strength.
    • Cells (osteocytes) embedded in lacunae (small spaces) within the matrix.
    • Provides structural support, protection of organs, and mineral storage (calcium and phosphate).

  • Compact Bone (Dense Bone) - Microscopic Structure:

    • Organized into osteons (Haversian systems):
      • Central Canal (Haversian Canal): Tiny channel running longitudinally; contains blood vessels and nerves.
      • Lamellae: Concentric layers of mineralized matrix surrounding the central canal.
      • Lacunae: Small spaces within lamellae; contain osteocytes.
      • Canaliculi: Microscopic channels connecting lacunae; allow osteocytes to communicate and exchange nutrients.
    • Provides maximum strength with minimal weight.

  • Spongy Bone (Cancellous Bone):

    • Porous, irregular network of bony plates called trabeculae.
    • Spaces filled with red marrow (blood cell production).
    • Lighter than compact bone; does not compromise strength (due to architecture).
    • Found in epiphyses, vertebrae, pelvis, sternum.

  • Cartilage (Three Types):

    • Hyaline Cartilage:

      • Appearance: Smooth, glassy, bluish-white matrix.
      • Location: Joint surfaces (articular cartilage), nose, tracheal rings, larynx, ribs.
      • Function: Reduces friction between bones; provides flexibility; template for bone development.

    • Elastic Cartilage:

      • Contains elastic fibers in addition to collagen; more flexible than hyaline.
      • Location: External ear (auricle), epiglottis.
      • Function: Maintains shape while being flexible.

    • Fibrocartilage:

      • Dense, tough matrix with significant collagen; combines properties of fibrous connective tissue and cartilage.
      • Location: Intervertebral discs (shock absorbers between vertebrae), knee menisci, pubic symphysis.
      • Function: Shock absorption; load-bearing; stability.

Synovial Joints & Movement

  • Joint Classification (3 Types):

    • Fibrous Joints (Fixed/Immovable): Bones held together by fibrous connective tissue; no joint cavity (e.g., skull sutures). Immobile.
    • Cartilaginous Joints (Slightly Movable): Bones united by cartilage; slight movement possible (e.g., intervertebral joints, pubic symphysis). Semi-mobile.
    • Synovial Joints (Freely Movable): Have a joint cavity filled with fluid; enclosed in capsule; highly mobile (e.g., knee, shoulder). Allow various movements.

  • Synovial Joint Examples (6 Types) with Movements:

    • Ball-and-Socket: Rounded head of one bone fits into cup-shaped cavity of another. Examples: Shoulder (glenohumeral), hip. Movements: flexion, extension, abduction, adduction, rotation, circumduction.
    • Hinge Joint: Convex surface of one bone fits into concave surface of another; movement in one plane. Examples: Knee (tibiofemoral), elbow. Movements: flexion, extension.
    • Pivot Joint: Pointed bone rotates within a ring of ligament/bone. Example: Atlantoaxial joint (neck rotation). Movement: Rotation.
    • Gliding (Plane) Joint: Flat surfaces of bones slide past each other. Examples: Intercarpal (wrist bones), intertarsal (ankle bones). Movement: Sliding/gliding.
    • Saddle Joint: Concave-to-convex fit; allows flexion, extension, abduction, adduction. Example: Thumb carpometacarpal joint. Movement: Flexion, extension, abduction, adduction, opposition.
    • Condyloid (Ellipsoid) Joint: Oval head fits into oval depression. Example: Wrist (radiocarpal). Movements: Flexion, extension, abduction, adduction, circumduction (but not full rotation).

  • Synovial Joint Structure (IN DETAIL):

    • Joint Capsule: Double-layered capsule that encloses the joint.
    • Articular Cartilage: Hyaline cartilage covering bone ends; reduces friction; allows smooth movement.
    • Synovial Membrane: Inner capsule layer; secretes synovial fluid.
    • Synovial Fluid: Thick gel that lubricates the joint; reduces friction and provides nutrition to cartilage (which is avascular).
    • Articular Discs (Menisci): Fibrocartilage pads that improve fit between bones and absorb shock (e.g., knee menisci).
    • Bursae: Fluid-filled sacs between tendons/ligaments and bone; reduce friction during movement. Inflammation = bursitis.
    • Ligaments: Strong fibrous bands connecting bone-to-bone; prevent excessive movement; provide stability.

  • Joint Movements (Terminology):

    • Flexion: Decrease the angle between bones; bending (e.g., bending elbow, bending knee).
    • Extension: Increase the angle between bones; straightening (e.g., straightening arm, straightening leg).
    • Abduction: Move away from the midline (body axis); e.g., raising arm laterally.
    • Adduction: Move toward the midline; e.g., lowering raised arm back to body.
    • Rotation: Turning around the bone’s long axis; e.g., rotating head to look left/right.
    • Circumduction: Combination of flexion, extension, abduction, and adduction; traces a circle with the limb tip; e.g., shoulder circles.

Musculoskeletal Aging Diseases

  • Osteoarthritis (“Wear and Tear” Arthritis):

    • Cause: Gradual degeneration of articular cartilage over time or from injury.
    • Pathology: Cartilage wears away, exposing the bone underneath. Bone becomes rough and irregular (develops osteophytes/bone spurs).
    • Symptoms: Crepitus (crackling/grinding sensation), bone spurs (bony outgrowths), pain (especially with movement or morning stiffness), reduced range of motion. Symptoms worsen with age and usage.
    • Common Locations: Knees, hips, lower back, neck, hands.
    • Management: Pain relief (NSAIDs), physical therapy, weight management, joint injections, ultimately joint replacement in severe cases.

  • Osteoporosis (Brittle Bone Disease):

    • Cause: Severe loss of bone density and mineral content; deterioration of bone structure.
    • Pathology: Bone becomes highly porous and brittle; prone to fractures from minor falls or even spontaneous fracture.
    • Risk Factors: Aging (especially postmenopausal women due to estrogen loss), sedentary lifestyle, inadequate calcium/vitamin D, smoking, alcohol abuse.
    • Prevention and Treatment:
      • Adequate calcium intake (1000-1200 mg/day).
      • Vitamin D supplementation (aids calcium absorption).
      • Weight-bearing exercise (stimulates osteoblasts to build bone).
      • Medications: Bisphosphonates (slow bone resorption), hormone replacement therapy (HRT), selective estrogen receptor modulators (SERMs).
    • Complications: Vertebral fractures (loss of height), hip fractures (immobility), increased mortality risk.

Study Tips for A-Grade Success

  1. Memorize Key Terms and Structures: Use diagrams, flashcards, and labeled diagrams (especially cardiac cycle, nephron, sarcomere, synovial joint).

  2. Understand Mechanisms, Not Just Facts: Know HOW processes work (e.g., sliding filament mechanism, glomerular filtration, blood clotting cascade). Examiners test deeper understanding.

  3. Link Concepts Across Chapters: Cell transport → Osmosis → Blood pressure. Glycolysis → Aerobic respiration →Energy. Digestion → Absorption → Blood transport.

  4. Practice Past Paper Questions: Use the marking guide to understand exactly what examiners expect. Full sentences, specific terminology, and mechanism explanations are crucial.

  5. Revise Systematically: Go through each chapter once, then focus extra time on areas where you feel weakest.

Good luck! You’ve got this!