Chapter 1

Homeostasis

  • Definition: The dynamic process by which the internal environment of the body is maintained within physiological limits despite external change.
    • Involves constant monitoring and adjustment of variables such as temperature, pH, fluid balance, and glucose concentration.
    • Significance: Essential for survival; failure results in disease or death.
  • Key Components
    • Variable (factor being regulated; e.g.
      temperature, blood glucose).
    • Receptor (sensor that detects change).
    • Control center (often the CNS or an endocrine gland; interprets input and sets the set-point).
    • Effector (muscle or gland that carries out corrective action).
  • Example: Regulation of body temperature through sweating (cooling) and shivering (heating) to keep core temperature ≈ 37 ∘C37\,^{\circ}\text{C}.

Feedback Mechanisms: Negative vs. Positive

  • Negative Feedback
    • Output reverses the original stimulus.
    • Most common type (≈ >95\% of feedback loops).
    • Example: Blood glucose regulation—elevated glucose triggers insulin release; insulin lowers glucose.
  • Positive Feedback
    • Output amplifies the stimulus until an event outside the loop stops it.
    • Less common; usually involved in processes that must be completed rapidly.
    • Example: Oxytocin-mediated uterine contractions during labor, or platelet plug formation during hemostasis.
  • Comparative Table
    • Stability: Negative (promotes); Positive (drives rapid change).
    • Risk: Positive feedback can be chaotic if unregulated (e.g., cytokine storm).

Hierarchy of Organization in Biology

  1. Chemical (atoms & molecules)
  2. Cellular (organelles → cells)
  3. Tissue (similar cells performing a function)
  4. Organ (2+ tissue types → discrete structure; e.g., heart)
  5. Organ system (related organs; e.g., cardiovascular)
  6. Organismal (the human body as a whole)
  • Connection: Dysfunction at a lower level typically propagates upward (e.g., mitochondrial defect → cellular energy crisis → organ failure).

Serous Membranes and Body Cavities

  • Serous Membrane = double-layered membrane producing lubricating serous fluid; reduces friction.
    • Parietal layer: lines cavity wall.
    • Visceral layer: covers organs.
  • Major Cavities & Corresponding Serosae
    • Pleural (lungs) → parietal & visceral pleura.
    • Pericardial (heart) → parietal & visceral pericardium.
    • Peritoneal (abdominopelvic) → parietal & visceral peritoneum.
  • Clinical Note: Inflammation (e.g., peritonitis) increases friction → pain & organ dysfunction.

Basic Terminology of Anatomy

  • Anatomy: Study of structure.
  • Physiology: Study of function.
  • Pathology: Study of disease.

Orientation and Directional Terms

  • Superior (cranial) vs. Inferior (caudal)
  • Anterior (ventral) vs. Posterior (dorsal)
  • Medial vs. Lateral
  • Proximal vs. Distal (limb reference)
  • Superficial vs. Deep
  • Example Usage: The heart is medial to the lungs and deep to the sternum.

Regional Terms

  • Axial: Head, neck, trunk.
    • Cephalic: Frontal, orbital, nasal, oral, mental.
    • Thoracic: Sternal, axillary, mammary.
    • Abdominal: Umbilical.
    • Pelvic: Inguinal (groin).
  • Appendicular: Limbs.
    • Upper limb: Brachial, antecubital, carpal, digital.
    • Lower limb: Femoral, patellar, crural, tarsal.

Body Planes and Sections

  • Sagittal Plane
    • Midsagittal (median): Divides body into equal right and left halves.
    • Parasagittal: Unequal halves.
  • Frontal (coronal) Plane: Anterior vs. posterior portions.
  • Transverse (horizontal) Plane: Superior vs. inferior portions (aka cross-section).
  • Oblique Section: Cuts at angles other than 90∘90^{\circ}.
  • Imaging Correlation: CT and MRI often use transverse and coronal planes.

Atomic Structure

  • Atom: Smallest unit