CHAPTER 1 - THE HUMAN ORGANISM

Anatomy: The Study of Structure

Anatomy is the branch of biology concerned with the study of the structure and form of living organisms. The term derives from Greek: ana (up) and tome (a cutting). Anatomy is divided into microanatomy and gross anatomy.

• Microanatomy focuses on structures visible only with a microscope.

  • Cytology: The study of cells (kytos = hollow).

  • Histology: The study of tissues (histo = web).

• Gross Anatomy examines structures visible to the naked eye.

  • Systemic Anatomy: Study by organ systems (e.g., cardiovascular system).

  • Regional Anatomy: Study by specific regions (e.g., head, arm).

Physiology: The Study of Function

Physiology explores the functions and vital processes of living organisms. The term comes from Greek physis (nature) and logos (study of). It explains how anatomical structures operate and interact.

Organizational Levels of the Human Body

The human body is organized into six hierarchical levels, each building upon the previous.

• Chemical Level: Atoms and molecules; 92 elements make up all matter. Electron interactions drive chemical reactions.

• Cellular Level: Cells are the basic unit of life; humans have 75-100 trillion cells. Organelles are subcellular functional units.

• Tissue Level: Groups of similar cells performing a common function. Four basic tissue types.

• Organ Level: Two or more tissues working together to perform specific functions.

• Organ System Level: Two or more organs performing a set of functions. There are 11 major systems, remembered by "NICLMURDERS":

  • Nervous

  • Integumentary

  • Cardiovascular

  • Lymphatic

  • Muscular

  • Urinary

  • Respiratory

  • Digestive

  • Endocrine

  • Reproductive

  • Skeletal

• Organism Level: A single living individual, either unicellular or multicellular.

Characteristics of Life

Living organisms share six fundamental characteristics:

• Organization: Ordered structure and arrangement.

• Metabolism: All chemical reactions in the body, including catabolism and anabolism.

• Responsiveness: Ability to sense and respond to stimuli.

• Growth: Increase in size and number of cells.

• Development: Changes in structure and function over time.

• Reproduction: Production of new cells or organisms.

Biomedical Research

Biomedical research uses models and other organisms (such as bacteria and cats) to study human biology and disease.

Homeostasis

Homeostasis is the maintenance of a stable internal environment within narrow limits. It is essential for health and survival.

• Disease: A disruption of homeostasis; the body acts to restore balance. Not all disruptions are harmful (e.g., increased blood pressure during exercise).

• Hypertension: Blood pressure too high.

• Hypotension: Blood pressure too low.

Feedback Mechanisms

• Negative Feedback: Restores homeostasis by counteracting deviations. Most physiological processes use negative feedback (e.g., blood pressure, temperature, respiration, blood sugar).

• Positive Feedback: Amplifies deviations from homeostasis. Usually harmful, but beneficial in specific cases (e.g., childbirth, uterine contractions).

Terminology & Body Plan

Understanding anatomical terminology is essential for describing locations and relationships in the body.

Directional Terms

• Standard Anatomic Position (SAP): Body standing upright, facing forward, arms at sides, palms forward.

• Prone: Lying face down.

• Supine: Lying face up.

• Directional terms are used regardless of body position.

Body Regions

• Axial/Central: Head and trunk.

• Appendicular: Limbs and extremities.

  • Arm: Shoulder to elbow.

  • Forearm: Elbow to wrist.

  • Thigh: Waist to knee.

  • Leg: Knee to ankle.

• Abdomen: Divided into 4 quadrants and 9 regions for clinical reference.

Body Planes

• Midsagittal/Median: Divides body into equal left and right halves.

• Parasagittal: Divides body into unequal left and right halves.

• Horizontal/Transverse: Divides body into superior (upper) and inferior (lower) portions.

• Frontal/Coronal: Divides body into anterior (front) and posterior (back) portions.

• Organ Sections:

  • Longitudinal: Along the long axis.

  • Transverse/Cross: Perpendicular to the long axis.

  • Oblique: Any angle other than longitudinal or transverse.

Body Cavities

• Dorsal Cavity: Includes cranial and spinal cavities.

• Trunk Cavities:

  • Thoracic: Surrounded by rib cage, separated from abdomen by diaphragm. Contains mediastinum (heart, esophagus, trachea, thymus).

  • Abdominal: Contains viscera (internal organs).

  • Pelvic: Contains bladder and internal reproductive organs; enclosed by pelvic basin.

• Serous Membranes: Line body cavities and secrete fluid.

  • Parietal: Lines cavity wall.

  • Visceral: Lines organ.

  • Pleura: Lungs.

  • Pericardium: Heart.

  • Peritoneum: Abdomen and pelvis.

  • Membranes are named by combining location and organ (e.g., parietal pericardium).

• Mesenteries: Part of peritoneum; anchor organs posteriorly and provide pathways for blood vessels and nerves.

• Retroperitoneal: Organs located behind the peritoneum (e.g., kidneys, adrenals, bladder, pancreas).

Anatomical Imaging

Noninvasive techniques for viewing internal structures. Six major imaging methods are commonly used (see textbook for details).

Example Table: Directional Terms (Inferred from Table 1.2)

Example: Negative Feedback Mechanism

• Blood glucose regulation: When blood sugar rises, the pancreas releases insulin to lower it; when it falls, glucagon is released to raise it.

Example: Positive Feedback Mechanism

• Childbirth: Uterine contractions intensify until delivery.

Additional info:

• Four basic tissue types: epithelial, connective, muscle, and nervous.

• Imaging techniques include X-ray, CT, MRI, ultrasound, PET, and DSA (digital subtraction angiography).