Chapter 1: The Human Body – An Orientation (Anatomy & Physiology Study Notes)

The Human Body: An Orientation

Introduction to Anatomy and Physiology

Anatomy and physiology are foundational sciences that provide a framework for understanding the structure and function of the human body. Mastery of these subjects is essential for careers in health and biological sciences.

• Anatomy: The study of the structure of body parts and their relationships to one another.

• Physiology: The study of the function of the body; how body parts work and carry out life-sustaining activities.

• Form determines function: The structure of a body part dictates its function, a concept known as the principle of complementarity.

Reference Standards in Anatomy

For consistency, anatomical and physiological reference values are based on standard individuals:

• Reference male: Healthy, young male weighing about 155 lb (70 kg).

• Reference female: Healthy, young female weighing about 125 lb (57 kg).

Anatomical Variability

While most anatomical structures match textbook descriptions, some variability exists:

• Nerves or blood vessels may be positioned differently.

• Small muscles may be absent in some individuals.

• Extreme anatomical variations are rare and usually incompatible with life.

Sex and Gender in Anatomy

• Sex: Biological attributes based on chromosomes, gene expression, and hormone action; reflected in reproductive anatomy and physiology (male or female).

• Gender: Psychosocial construct including behaviors, expressions, and identities (e.g., man, woman, transgender, non-binary).

Divisions of Anatomy

Gross (Macroscopic) Anatomy

• Regional anatomy: Study of all structures in a specific area of the body.

• System anatomy: Study of one body system at a time (e.g., cardiovascular, nervous).

• Surface anatomy: Study of internal structures as they relate to the overlying skin (e.g., visible muscles, veins).

Microscopic Anatomy

• Cytology: Study of cells.

• Histology: Study of tissues.

Developmental Anatomy

• Traces structural changes throughout the lifespan.

• Embryology: Study of developmental changes before birth.

Essential Tools and Techniques in Anatomy

• Observation, manipulation, palpation (feeling organs), and auscultation (listening with a stethoscope).

• Medical imaging technologies: X-ray, MRI, CT, ultrasound.

Divisions of Physiology

• Based on organ systems (e.g., renal physiology, neurophysiology, cardiovascular physiology).

• Often focuses on cellular and molecular events, such as chemical reactions in cells.

• Requires understanding of basic chemical and physical principles (e.g., electrical currents, pressure, levers).

Levels of Structural Organization

The human body is organized into hierarchical levels:

• Chemical level: Atoms and molecules.

• Cellular level: Cells and their organelles.

• Tissue level: Groups of similar cells.

• Organ level: Two or more tissue types forming organs.

• Organ system level: Organs working together.

• Organismal level: All organ systems combined to form the whole organism.

Organ Systems of the Human Body

The body has 11 major organ systems, each with specific functions:

• Integumentary

• Skeletal

• Muscular

• Nervous

• Endocrine

• Cardiovascular

• Lymphatic

• Respiratory

• Digestive

• Urinary

• Reproductive

Requirements for Life

Living organisms must perform certain vital functions and require specific substances and conditions to survive.

Necessary Life Functions

• Maintaining boundaries: Separation between internal and external environments (e.g., plasma membranes, skin).

• Movement: Of body parts (skeletal muscle), substances (cardiac muscle, blood), and cells (white blood cells).

• Responsiveness: Ability to sense and respond to stimuli (e.g., withdrawal reflex, breathing rate adjustment).

• Digestion: Breakdown of food and absorption into blood.

• Metabolism: All chemical reactions in the body, including catabolism (breakdown) and anabolism (synthesis). $\text{Metabolism} = \text{Catabolism} + \text{Anabolism}$

• Excretion: Removal of wastes (e.g., urea, CO2, feces).

• Reproduction: Cellular division for growth/repair; production of offspring.

• Growth: Increase in size of a body part or organism.

Survival Needs

• Nutrients: Carbohydrates (energy), proteins (cell building), fats (energy storage), vitamins and minerals (chemical reactions, structure).

• Oxygen: Essential for energy release from food.

• Water: Most abundant chemical; environment for reactions.

• Normal body temperature: Required for proper reaction rates (37°C/98.6°F).

• Appropriate atmospheric pressure: Needed for breathing and gas exchange.

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes. It is a dynamic equilibrium maintained by all organ systems.

• Law of mass balance: The amount of a substance in the body remains constant if input equals output.

Homeostatic Control Mechanisms

• Receptor (sensor): Monitors environment and detects changes (stimuli).

• Control center: Determines set point, analyzes input, and determines response.

• Effector: Carries out the response to restore homeostasis.

Types of Feedback

• Negative feedback: Reduces or shuts off the original stimulus; most common mechanism (e.g., body temperature regulation, blood glucose control).

• Positive feedback: Enhances or exaggerates the original stimulus; usually controls infrequent events (e.g., labor contractions, blood clotting).

• Feedforward (anticipatory) response: Occurs in anticipation of a change (e.g., salivation before eating).

Homeostatic Imbalance

• Disturbance of homeostasis increases risk of disease and contributes to aging.

• If negative feedback is overwhelmed, positive feedback may cause harm (e.g., heart failure).

Anatomical Terminology

Standardized terms describe body positions, regions, and planes, ensuring clear communication among professionals.

Anatomical Position

• Body erect, feet slightly apart, palms facing forward, thumbs away from body.

Directional Terms

• Describe the location of one body part relative to another (e.g., anterior/posterior, medial/lateral, proximal/distal, superficial/deep).

• Always based on the standard anatomical position.

• Right and left refer to the subject's sides, not the observer's.

Major Body Divisions

• Axial: Head, neck, trunk.

• Appendicular: Limbs (arms and legs).

Body Planes and Sections

• Sagittal plane: Divides body into right and left parts. Midsagittal: Exactly in the midline. Parasagittal: Offset from the midline.

• Frontal (coronal) plane: Divides body into anterior (front) and posterior (back) parts.

• Transverse (horizontal) plane: Divides body into superior (top) and inferior (bottom) parts.

• Oblique section: Cuts at angles other than 90°; less common.

Body Cavities and Membranes

Major Body Cavities

• Dorsal body cavity: Protects nervous system; includes cranial (brain) and vertebral (spinal cord) cavities; covered by meninges.

• Ventral body cavity: Houses internal organs (viscera); includes thoracic and abdominopelvic cavities, separated by the diaphragm.

Thoracic Cavity

• Pleural cavities (lungs), mediastinum (other thoracic organs), pericardial cavity (heart).

Abdominopelvic Cavity

• Abdominal cavity (stomach, intestines, spleen, liver).

• Pelvic cavity (urinary bladder, reproductive organs, rectum).

Serous Membranes

• Thin, double-layered membranes lining ventral body cavities.

• Parietal serosa: Lines cavity walls.

• Visceral serosa: Covers organs.

• Serous fluid between layers reduces friction.

• Named for location: Pleura (lungs), Pericardium (heart), Peritoneum (abdominopelvic organs).

Abdominopelvic Regions and Quadrants

Used for anatomical and clinical reference.

Quadrants	Regions
Right Upper (RUQ)	Right hypochondriac
Left Upper (LUQ)	Epigastric
Right Lower (RLQ)	Right lumbar
Left Lower (LLQ)	Umbilical
	Left lumbar
	Right iliac (inguinal)
	Hypogastric (pubic)
	Left iliac (inguinal)
	Left hypochondriac

Other Body Cavities

• Open to environment: oral, nasal, orbital, middle ear cavities.

• Closed: synovial cavities (joints).

Clinical Relevance

• Precise anatomical terminology is critical to avoid medical errors (e.g., wrong-site surgery).

Examples and Applications

• Example: Regulation of body temperature by negative feedback.

• Example: Labor contractions enhanced by positive feedback.

• Example: Use of anatomical planes in medical imaging (MRI, CT scans).