Introduction to Anatomy and Physiology: The Human Organism

CHAPTER 1 - THE HUMAN ORGANISM

I. Anatomy

Anatomy is the study of the structure and form of living organisms. The term comes from the Greek words 'ana' (up) and 'tome' (a cutting), reflecting the practice of dissection to study body structures.

• Microanatomy: Study of structures too small to be seen without a microscope.

  • Cytology: Study of cells (kytos = hollow).

  • Histology: Study of tissues (histo = web).

• Gross Anatomy: Study of structures visible to the naked eye.

  • Systemic Anatomy: Study of body systems (e.g., cardiovascular, skeletal).

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

II. Physiology

Physiology is the study of the functions and vital processes of living organisms. The term comes from the Greek 'physis' (nature) and 'logos' (study of).

• Focuses on how body parts work and carry out life-sustaining activities.

III. Levels of Organization in the Human Body

The human body is organized into six hierarchical levels, each building on the previous one:

1. Chemical Level: Atoms and molecules; 92 elements make up all matter. Electron interactions lead to chemical reactions.

2. Cellular Level: Cells are the basic units of life (75-100 trillion in the human body). Organelles are functional subunits within cells.

3. Tissue Level: Groups of similar cells performing a common function. Four basic tissue types: epithelial, connective, muscle, and nervous.

4. Organ Level: Structures composed of two or more tissue types working together (e.g., heart, liver).

5. Organ System Level: Groups of organs performing related functions. There are 11 major organ systems (see table below).

6. Organism Level: A single, complete living thing (can be unicellular or multicellular).

Organ System	Main Function(s)
Nervous	Control, coordination, response to stimuli
Integumentary	Protection, temperature regulation, sensation
Cardiovascular	Transport of nutrients, gases, wastes
Lymphatic	Immunity, fluid balance
Muscular	Movement, heat production
Urinary	Waste elimination, water balance
Respiratory	Gas exchange
Digestive	Breakdown and absorption of nutrients
Endocrine	Hormone production, regulation of body processes
Reproductive	Production of offspring
Skeletal	Support, protection, blood cell production

IV. Characteristics of Life

All living organisms share six fundamental characteristics:

• Organization: Ordered structure and relationships among parts.

• Metabolism: All chemical reactions in the body, including energy production and use.

• Responsiveness: Ability to sense and respond to changes in the environment.

• Growth: Increase in size and/or number of cells.

• Development: Changes in form and function during an organism's life.

• Reproduction: Formation of new cells or organisms.

Biomedical Research

• Uses models (e.g., animals, bacteria) to study human biology and disease.

• Research on other organisms (e.g., bacteria, cats) provides insights applicable to humans.

V. Homeostasis

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

• Disruption of homeostasis leads to disease (non-health state).

• The body acts to restore homeostasis; not all deviations 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 reversing deviations (e.g., regulation of blood pressure, temperature, respiration, blood sugar). Usually beneficial.

• Positive Feedback: Increases deviation from homeostasis. Often harmful, but sometimes beneficial (e.g., uterine contractions during childbirth).

VI. Terminology & Body Plan

Understanding anatomical terminology and body organization is essential for clear communication in anatomy and physiology.

Directional Terms

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

• Directional terms are used regardless of the body's actual position.

• Prone: Lying face down.

• Supine: Lying face up.

Body Regions

• Axial/Central: Head and trunk.

• Appendicular: Limbs/extremities.

  • Arm: Shoulder to elbow.

  • Forearm: Elbow to wrist.

  • Thigh: Hip to knee.

  • Leg: Knee to ankle.

• Abdomen: Divided into four quadrants or nine regions for clinical reference.

Body Planes

• Midsagittal (Median) Plane: Divides body into equal left and right halves.

• Parasagittal Plane: Divides body into unequal left and right portions.

• Horizontal (Transverse) Plane: Divides body into superior (upper) and inferior (lower) parts.

• Frontal (Coronal) Plane: Divides body into anterior (front) and posterior (back) parts.

• 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: Contains cranial and spinal cavities.

• Ventral (Trunk) Cavities:

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

  • Abdominal Cavity: Contains digestive viscera.

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

Serous Membranes

• Line body cavities and secrete lubricating fluid.

• Parietal: Lines cavity wall.

• Visceral: Covers organs.

• Named by location:

  • Pleura: Lungs.

  • Pericardium: Heart.

  • Peritoneum: Abdominal/pelvic organs.

• Example: Parietal pericardium lines the pericardial cavity wall; visceral pericardium covers the heart.

Mesenteries and Retroperitoneal Organs

• Mesenteries: Folds of peritoneum that anchor organs to the posterior body wall and provide a pathway for blood vessels and nerves.

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

VII. Anatomical Imaging

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

• Examples include X-ray, CT scan, MRI, ultrasound, PET scan, and DSA.

Additional info: The six major imaging techniques typically include: X-ray, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasound, Positron Emission Tomography (PET), and Digital Subtraction Angiography (DSA).