Homeostasis, Cell Structure, Membranes, Blood, and Immunity: ANP Study Guide

Homeostasis

Introduction to Anatomy and Physiology

• Anatomy is the study of the structure and location of body parts.

• Physiology is the study of the functions of body parts and how they work together.

• The two disciplines are interrelated: understanding structure helps explain function, and vice versa.

• Example: The structure of the heart (anatomy) enables it to pump blood (physiology).

Levels of Organization

• Living organisms are organized hierarchically:

• Atom → Molecule → Macromolecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

• Example: Muscle tissue is made of muscle cells, which contain mitochondria (organelles).

Structure-Function Relationship

• The shape and structure of a body part determines its function.

• Example: The flat, thin shape of red blood cells allows them to move easily through capillaries.

Concept of Homeostasis

• Homeostasis is the maintenance of a stable internal environment.

• Regulated variables include body temperature, blood glucose, and pH.

• Set points are the normal target values for these variables.

• Control systems monitor changes and restore balance when deviations occur.

Feedback Loops

• Components of a feedback loop:

  • Stimulus: Change in the regulated variable.

  • Sensor (Receptor): Detects the change.

  • Integrating Center: Compares the change to the set point.

  • Effector: Carries out the response to restore balance.

  • Response: The action that returns the variable to the set point.

• Example: Body temperature rises (stimulus), thermoreceptors detect the change (sensor), hypothalamus compares to set point (integrating center), sweat glands are activated (effector), sweating cools the body (response).

Control Mechanisms in Homeostasis

• Intrinsic (Local) Control: Regulation within an organ or tissue.

• Extrinsic Control: Regulation by the nervous or endocrine system, affecting the body more broadly.

• Negative Feedback: Reverses a change to maintain stability (e.g., temperature regulation).

• Positive Feedback: Amplifies a change for a specific outcome (e.g., blood clotting).

Cell Structure

Cellular Components and Functions

• Cell Wall: Supports and protects (mainly in plants, bacteria).

• Glycocalyx: Traps water, aids in protection and cell recognition.

• Capsule: Helps evade the immune system (bacteria).

• Appendages: Pili and flagella for attachment and movement.

• Extracellular Matrix (animal): Gel-like carbohydrate network for support and signaling.

• Nucleus: Contains DNA, controls cell activities.

• Plasma Membrane: Regulates entry/exit of substances, cell signaling.

• Cytosol: Fluid inside the cell, outside organelles.

• Cytoskeleton: Network of protein filaments for structure and movement.

• Microtubules: Cell division, intracellular transport.

• Centrosomes: Organize microtubules, important in cell division.

• Flagella: Movement.

• Intermediate Filaments: Cell rigidity, structural support.

• Actin Filaments: Cell movement, shape changes.

• Endomembrane System: Includes nucleus, ER, Golgi, lysosomes, plasma membrane, vacuoles; transports materials via vesicles.

• Rough ER: Protein synthesis and sorting.

• Smooth ER: Lipid modification, calcium storage, carbohydrate metabolism.

• Golgi Apparatus: Protein processing, sorting, secretion.

• Lysosomes: Contain acid hydrolases for digestion and recycling.

• Vacuoles: Storage, structure, and waste disposal (varies by cell type).

• Peroxisomes: Break down molecules by removing hydrogen or adding oxygen.

• Mitochondria: ATP production, metabolism.

• Chloroplasts: Photosynthesis (plants, algae).

ATP Production

• Aerobic Respiration:

  • Glycolysis (cytosol): 2 ATP

  • Krebs Cycle (mitochondria): 2 ATP

  • Oxidative Phosphorylation (inner mitochondrial membrane): 26–28 ATP

• Anaerobic Respiration:

  • Glycolysis (cytosol): 2 ATP

• Total ATP (aerobic): About 30–32 ATP per glucose molecule

Clinical Application of Cell Structure

• Dysfunction in organelles leads to specific symptoms:

  • Mitochondrial disease: Low energy, fatigue (less ATP).

  • Abundant rough ER and Golgi: Indicates protein production/secretion function.

Membranes

Structure and Components

• Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails inward; forms selective barrier.

• Proteins: Channels, carriers, receptors.

• Carbohydrates: Cell recognition.

Membrane Transport

• Passive Transport: No ATP required; moves substances down concentration gradient.

  • Simple Diffusion: Small, nonpolar molecules move directly through membrane.

  • Facilitated Diffusion: Uses channel or carrier proteins for larger or charged molecules.

• Active Transport: Requires ATP; moves substances against concentration gradient.

  • Primary Active Transport: Direct use of ATP (e.g., sodium-potassium pump).

  • Secondary Active Transport: Uses energy from another molecule's gradient.

Penetrating vs. Non-Penetrating Solutes

• Penetrating Solutes: Small, little/no charge; can cross membrane.

• Non-Penetrating Solutes: Larger, charged; cannot cross membrane.

Osmolarity and Tonicity

• Osmolarity: Total concentration of solute particles in a solution.

• Tonicity: Effect of a solution on cell volume (depends on non-penetrating solutes).

• Direction of Water Movement: Water moves toward higher concentration of non-penetrating solutes.

Carrier-Mediated Transport

• Specificity: Each carrier binds only one molecule.

• Saturation: Transport maximum when all carriers are occupied.

• Competition: Similar molecules compete for the same carrier.

• Reversibility: Direction depends on gradient.

• Can be passive or active.

Types of Active Transport

• Primary: Direct ATP use (e.g., sodium-potassium pump).

• Secondary: Uses stored energy from ion gradients.

• Symport: Substances move in same direction.

• Antiport: Substances move in opposite directions.

• Bulk Transport: Endocytosis and exocytosis.

Fick's Law of Diffusion

• Rate of diffusion increases with greater concentration gradient and surface area.

• Rate decreases with increased membrane thickness.

Fick's Law Equation:

$J = \frac{DA(C_1 - C_2)}{X}$

• Where J is the rate of diffusion, D is the diffusion coefficient, A is surface area, C_1 - C_2 is the concentration gradient, and X is membrane thickness.

Blood and Immunity

Blood Components

• Red Blood Cells (RBCs): Carry oxygen; lifespan ~120 days.

• White Blood Cells (WBCs): Immune defense; various lifespans.

• Platelets: Blood clotting.

• Plasma: Fluid portion; contains proteins, nutrients, hormones.

Plasma Proteins

Protein	Percentage	Function
Albumins	~60%	Osmotic pressure, carriers
Globulins	~30%	Carriers, clotting, enzymes, immune (gamma globulins)
Fibrinogen	~4%	Blood clotting

RBC and Hemoglobin Structure

• RBCs: Biconcave, flexible, no nucleus in mature cells.

• Hemoglobin: 4 polypeptide chains (2 alpha, 2 beta), each with a heme group containing iron.

• Oxygen binds to iron in heme group.

Erythropoiesis and RBC Life Cycle

• Produced in red bone marrow, released into bloodstream.

• Circulate ~120 days, then broken down in spleen; components recycled.

White Blood Cells (WBCs)

Type	Structure	Function	Abundance
Neutrophils	Small, multi-lobed nucleus	Phagocytosis, first responders	Most abundant
Macrophages	Large, mononuclear	Phagocytosis, inflammation	Less abundant
Basophils	Granular	Promote inflammation	Rare
Eosinophils	Bilobed nucleus	Reduce inflammation, combat parasites	Low

Hemostasis (Blood Clotting)

• Vasoconstriction: Vessel constricts to reduce blood flow.

• Platelet Plug Formation: Platelets adhere to exposed collagen, release chemicals (e.g., prothrombin).

• Coagulation: Thrombin activates fibrinogen to fibrin, forming a stable clot.

Coagulation Pathways

• Intrinsic Pathway: Triggered by collagen exposure; involves factors XII, XI, IX, VIII.

• Extrinsic Pathway: Triggered by tissue damage; involves factors III, VII.

• Common Pathway: Begins at factor X; prothrombin (II) → thrombin, fibrinogen (I) → fibrin.

Limiting Clot Formation

• Anticoagulants and vasodilation prevent excessive clotting.

Blood Groups

• ABO System: Based on presence of A and B antigens.

• Rh Factor: Presence (+) or absence (−) of D antigen.

• Important for safe blood transfusions.

Lymphoid Tissues and Immunity

• Lymphoid tissues: Lymph nodes, spleen, thymus, tonsils; function in immune defense.

• Innate (Non-Specific) Immunity: General defenses (e.g., barriers, phagocytes).

• Adaptive (Specific) Immunity: Targeted response (B and T cells, antibodies).

Types of Immune Defenses

• Phagocytosis: Macrophages, neutrophils, dendritic cells ingest pathogens.

• Physical Barriers: Skin, mucous membranes.

• Body Secretions: Tears, saliva contain antimicrobial substances.

• Normal Flora: Compete with pathogens.

• Inflammation: Vasodilation, increased WBCs, swelling, pain.

• Cytokines: Chemical messengers (e.g., pyrogens induce fever).

• Complement System: Protein cascade ending in membrane attack complex.

• Fever: Pyrogens reset hypothalamic set point.

• Natural Killer Cells: Induce apoptosis in abnormal cells.

• Humoral Immunity: B cells, antibody production.

• Cell-Mediated Immunity: T cells, direct cell attack.

Cardinal Signs of Inflammation

• Redness and Heat: Due to vasodilation.

• Swelling and Pain: Due to increased WBCs and fluid in tissues; pain if nerves are affected.

Immunity: Key Distinctions

Term	Description
Classical, Alternative, Lectin Pathways	Different ways to activate complement system
Complete Antigen	Can trigger immune response alone
Incomplete Antigen (Hapten)	Needs carrier to be immunogenic
MHC I vs. MHC II	MHC I: all nucleated cells; MHC II: antigen-presenting cells
B Cells vs. T Cells	B: produce antibodies; T: cell-mediated immunity
T Helper vs. T Cytotoxic	Helper: activate other cells; Cytotoxic: kill infected cells
Primary vs. Secondary Immune Response	Primary: first exposure, slower; Secondary: faster, stronger
Natural vs. Artificial Immunity	Natural: infection or maternal; Artificial: vaccination
Passive vs. Active Immunity	Passive: antibodies given; Active: own immune response

Classes of Antibodies

• IgG: Most abundant, crosses placenta.

• IgA: In secretions (tears, saliva).

• IgM: First produced in response.

• IgE: Allergic responses, parasites.

• IgD: B cell receptor.

Self vs. Non-Self Recognition

• Immune system distinguishes self from non-self via antigens and MHC molecules.

Functions of Antibodies

• Neutralize pathogens, opsonization (mark for phagocytosis), activate complement, agglutination.

Clinical Application: Understanding these concepts is essential for diagnosing and treating disorders related to homeostasis, cell function, blood, and immunity.