Week One Readings

1.1 Overview of Anatomy and Physiology

• Anatomy = body structure (what it is; how parts relate); traditionally driven by dissection; today also uses living-body imaging.

• Physiology = body function (how it works); grounded in chemistry/physics; investigated with controlled experiments.

• Specializations and methods:

  • Gross (macroscopic) anatomy vs. microscopic anatomy (cytology = cells; histology = tissues).

  • Regional anatomy (all structures in an area) vs. systemic anatomy (one body system across the body).

  • Neurophysiology and other functional subfields operate from organ down to molecular levels.

1.2 Structural Organization of the Human Body

• Levels of organization (increasing complexity):
  \text{subatomic particles} \rightarrow \text{atoms} \rightarrow \text{molecules} \rightarrow \text{organelles} \rightarrow \text{cells} \rightarrow \text{tissues} \rightarrow \text{organs} \rightarrow \text{organ systems} \rightarrow \text{organism} \rightarrow \text{biosphere}.

• Cells are the smallest independently functioning unit; membranes keep intracellular vs. extracellular environments distinct; organelles carry out specialized tasks.

• Tissues = coordinated groups of similar (or closely related) cells; organs = anatomically distinct structures composed of ≥2 tissues; organ systems = organs working together for major body functions.

• Eleven organ systems (each organ may contribute to multiple systems): Integumentary, Skeletal, Muscular, Nervous, Endocrine, Cardiovascular, Lymphatic, Respiratory, Digestive, Urinary, Reproductive (male/female).

• Usage note on “female/male” in the text: refers to biological sex for typical XX/XY anatomy; gender identity is distinct.

1.3 Functions of Human Life

• Defining life functions: organization, metabolism, responsiveness, movement, development (including growth & differentiation), and reproduction.

• Compartmentalization & barriers: Skin and internal membranes isolate, protect, and maintain proper internal fluid composition; vessels keep blood in a closed system; connective tissues ensheathe nerves/muscles.

• Metabolism:

  • Anabolism builds complex molecules from simpler ones (requires energy).

  • Catabolism breaks complex molecules down (releases energy).

  • ATP (adenosine triphosphate) stores/transfers usable energy; made and used continuously.

• Responsiveness & movement: Respond to external and internal changes (e.g., sweating with heat); movement spans whole-body locomotion and internal motions (blood flow, peristalsis, cellular motility).

• Development, growth, reproduction:

  • Development includes differentiation (cells specialize), growth, and repair.

  • Growth by increasing cell number, some increase in cell size, and non-cellular matrix (e.g., bone mineral).

  • Reproduction perpetuates the species through male/female reproductive systems.

1.4 Requirements for Human Life

• Oxygen: \approx 20\% of air; essential for ATP-producing reactions; brain cells are especially sensitive (damage within minutes without oxygen).

• Nutrients:

  • Water (most critical; \approx 70\% of adult body mass): solvent, transport medium, reaction medium, thermoregulation, lubrication, cushioning.

  • Energy-yielding macronutrients (carbohydrates, lipids) and proteins (primarily amino acid supply for building).

  • Micronutrients (vitamins, minerals): needed in smaller amounts for reactions, signalling, structure (e.g., Ca^{2+}). Some are stored; many water-soluble vitamins must be regularly consumed.

• Narrow temperature range: Chemistry of life runs near 37^{\circ}\text{C} (98.6^{\circ}\text{F}). Heat stress → sweating/evaporation; cold stress → shivering, vasoconstriction, metabolic heat production; extremes denature enzymes and destabilize physiology.

• Narrow pressure range: Atmospheric pressure keeps gases dissolved and enables gas exchange; deviations (high altitude/space; diving) impair gas exchange and can cause decompression sickness (gas bubbles in tissues). Adequate fluid pressures (e.g., blood pressure) are likewise critical.

1.5 Homeostasis

• Definition: steady internal conditions maintained by continuous monitoring and adjustment. Each parameter has a set point and normal range.

• Negative feedback (default stabilizer): Reverses deviations back toward set point. Three core parts:

  • Sensor (receptor) detects change

  • Control center compares to range

  • Effector executes corrective action

  • Examples:

  • Thermoregulation: heat-loss center triggers vasodilation, sweating, deeper respiration; heat-gain center triggers vasoconstriction, shivering, endocrine responses.

  • Blood glucose: high glucose → pancreatic β-cells secrete insulin → uptake/storage; falling glucose reduces insulin.

• Positive feedback (goal-directed amplifier): Intensifies change until a natural end point, then stops.

  • Examples:

  • Childbirth: stretch receptors → hypothalamus/pituitary oxytocin → stronger uterine contractions → more stretch, until birth.

  • Blood clotting: cascade accelerates locally to seal a vessel.

1.6 Anatomical Terminology

• Anatomical position: Body upright, feet slightly apart, palms forward, thumbs outward; all directional terms assume this reference.

• Directional terms (paired, relative):

  • Superior (cranial) / Inferior (caudal) — toward head / toward feet.

  • Anterior (ventral) / Posterior (dorsal) — front / back (in humans, ventral ≈ anterior; dorsal ≈ posterior).

  • Medial / Lateral — toward / away from midline.

  • Proximal / Distal — closer to / farther from point of limb attachment.

  • Superficial / Deep — near surface / farther from surface.

1.7 Medical Imaging

• Purpose: Visualize internal anatomy (structure, some function) in living patients—critical for diagnosis and guidance without invasive exploration.

• X-ray (radiography): High-energy radiation absorbed differently by tissues; bones show well; limited soft-tissue contrast; ionizing.

• CT (computed tomography): Rotating X-ray tube + computer reconstruction → cross sectional “slices” and 3-D views; better soft-tissue detail than plain films; ionizing.

• MRI: Magnetic fields + radio waves; excellent soft-tissue contrast (e.g., neural, ligamentous); no ionizing radiation; contraindications with some implants. Variants include fMRI for blood-oxygen-level dependent changes (functional mapping).

• PET: Radioactive tracers map metabolic activity (e.g., glucose uptake in oncology/neurology); functional emphasis; often fused with CT/MRI.

• Ultrasound (sonography): High-frequency sound echoes; safe (no ionizing radiation), real-time motion (e.g., fetal, cardiac), but lower resolution for air/ossified regions.

• Angiography & contrast studies: Contrast agents visualize vessels and lumens; DSA enhances vessel images by subtracting background structures.

2. Variation Among Human Cells

• Individual vs. collective behavior:

  • Some cells, like red blood cells, operate independently—detached from their neighbors—and circulate freely to deliver O_{2} throughout the body.

  • Others, such as epithelial cells lining the respiratory tract, are physically attached, creating continuous protective surfaces.

  • Notably, those epithelial cells have cilia—tiny hair-like projections that sweep debris and pathogens upward, helping keep airways clean.

• Capacity for division:

  • Skin cells and bone cells continually divide, renewing tissues and repairing damage.

  • Nerve cells (neurons) generally cannot divide, meaning neural injuries (like spinal cord damage) often result in permanent loss.

• Secretion roles:

  • Certain cells specialize in producing and releasing substances—for example, pancreatic cells secrete the hormone insulin, while some epithelial cells generate mucus to trap airborne particles.

3. Genetic Identity & Cellular Specialization

• All cells within a human share the same genetic information, yet they differ substantially in form and function. This diversity arises through differential gene expression—where only certain genes are activated in different cell types.

4. Examples of Specialized Cell Types

• Bone cell subtypes (4 distinct types):

  • Osteogenic cells – undifferentiated stem-like cells capable of developing into osteoblasts.

  • Osteoblasts – immature cells that synthesize new bone matrix; they mature into osteocytes.

  • Osteocytes – star-shaped, mature bone cells; the most abundant in bone tissue.

  • Osteoclasts – large, multinucleated cells that resorb (break down) bone as part of bone remodeling.

• White blood cell (leukocyte) subtypes (5 distinct forms):

  • Monocytes (~5%) – engulf and destroy pathogens via phagocytosis.

  • Eosinophils (~2%) – target larger parasites and play roles in allergy responses.

  • Basophils (under 1%) – release histamines, initiating inflammation.

  • Lymphocytes (~30%) – include B cells (produce antibodies) and T cells (destroy virus-infected or cancerous cells).

  • Neutrophils (~62%) – the most abundant; specialize in phagocytizing bacteria and fungi.

5. From Cells to Tissues

• Definition & coordination: Tissues are groups of connected cells working together to perform specific functions. Cells may be homogeneous or mixed types.

• The four primary human tissue types:

  • Epithelial tissue – lines internal and external surfaces (e.g., skin, digestive tract); performs protection, secretion (e.g., mucus, hormones), and absorption; cell shapes include squamous, cuboidal, columnar, arranged in layers such as simple, stratified, pseudostratified, transitional.

  • Connective tissue – supports and anchors organs; composed of cells embedded in an extracellular matrix (ECM) that may be liquid (blood), flexible (tendons/ligaments with collagen/elastin), or rigid (bone/cartilage).

  • Muscle tissue – made up of contractile cells categorized into:

  • Skeletal muscle (striated, voluntary, attached to bones)

  • Smooth muscle (non-striated, involuntary, found in organs like the gut and vessels)

  • Cardiac muscle (striated, involuntary, specialized for the heart).

  • Nervous tissue – comprises neurons (signal-transmitting cells) and glial cells (support cells); forms the basis for the central nervous system (brain, spinal cord) and peripheral nervous system (nerve networks).

6. Cells: Cell Membrane and Transport Mechanisms

• Cell membrane: separates inside from outside; semi-permeable – only certain substances can pass; some pass freely through the nonpolar section.

• Freely permeable substances: Small, nonpolar molecules: \text{O}2,\; \text{CO}2,\; \text{lipids},\; \text{alcohol}.

• Phospholipid bilayer: heads face outside + inside aqueous environment; hydrophilic (polar) heads, hydrophobic (nonpolar, saturated + unsaturated) tails = phospholipid bilayer.

• Fluidity: Enhanced by unsaturated fatty acids and cholesterol.

• Fluid Mosaic: bilayer made of phospholipids, proteins, cholesterol; phospholipids aren’t fixed in respect to each other, changing places.

• Glycocalyx:

  • Coating formed by carbohydrates from glycoproteins/lipids.

  • Functions: Cell recognition, adhesion, immune defense.

• Membrane proteins:

  • Integral proteins – embedded in the membrane.

  • Peripheral proteins – attached to the outside surface.

• Glycoproteins and Receptors: involved in chemical signaling.

• Diffusion: transfer of tiny nonpolar molecules down their concentration gradient (higher to lower), without protein channels.

  • Passive transport: movement of molecules with protein channels, with concentration gradient, with no energy use.

  • Simple diffusion: molecules move down their concentration gradient; Example: \text{O}2 into cells, \text{CO}2 out of cells.

  • Facilitated diffusion: movement with help of membrane channel or carrier proteins; Used for: glucose, ions like \text{Na}^+ and \text{K}^+.

• Osmosis: diffusion of water through a semipermeable membrane; water moves to higher solute concentration (lower water concentration).

• Tonicity:

  • Isotonic: equal solute concentration; no net water movement.

  • Hypertonic: more solutes outside → cell shrinks (water exits).

  • Hypotonic: fewer solutes outside → cell swells (water enters).

• Filtration: uses hydrostatic pressure to move fluid/solutes; example: in capillaries and kidneys.

• Active Transport: movement of molecules with protein channels against concentration; uses energy; both active transport and diffusion use transport channels allowing only certain molecules.

• Mitochondria: metabolism.

• Nucleus: genetic information.

• Vesicular Transport:

  • Endocytosis (into the cell):

  • Phagocytosis: Engulfs large particles (cell eating).

  • Pinocytosis: Engulfs fluid (cell drinking).

  • Receptor-mediated endocytosis: Selective; uses receptors (e.g., iron uptake via transferrin).

  • Exocytosis (out of the cell): Vesicles fuse with the membrane to release contents.

  • Used for: Enzymes (pancreas), Hormones (endocrine system), Neurotransmitters and immune chemicals.

• N.B. Terms to know:

  • Phospholipid bilayer structure: hydrophilic heads, hydrophobic tails.

  • Glycocalyx functions: cell recognition, adhesion, immune defense.

  • Distinction between integral and peripheral proteins.

  • Examples of transport types: diffusion, osmosis, filtration, active transport, vesicular transport (endocytosis/exocytosis).