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

This Matters

Importance of Anatomical Terminology

Learning and understanding anatomical terminology is essential for effective communication in the health sciences. Accurate use of terms ensures clarity among healthcare professionals and supports safe, precise patient care.

• Anatomical terminology provides a universal language for describing locations, relationships, and functions of body parts.

• Mastery of these terms is foundational for further study in anatomy and physiology.

Form and Function of Anatomy & Physiology

Definitions and Scope

Anatomy and physiology are closely related disciplines that together explain the structure and function of the human body.

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

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

• Example: Investigating how muscles shorten is physiology; exploring the location of the lungs is anatomy.

Structural Organization of the Human Body

Levels of Organization

The human body is organized into hierarchical levels, each building upon the previous to form the complete organism.

• Chemical level: Atoms combine to form molecules and organelles.

• Cellular level: Cells are the basic units of life, made up of molecules.

• Tissue level: Groups of similar cells form tissues, such as muscle or epithelial tissue.

• Organ level: Organs consist of two or more types of tissues working together (e.g., heart, liver).

• Organ system level: Organ systems are groups of organs that work closely together to perform major functions (e.g., cardiovascular system).

• Organismal level: All organ systems combine to make the whole organism.

Additional info: The levels of organization are foundational for understanding how complex functions arise from simple building blocks.

Survival Needs of the Human Body

Essential Factors for Life

Humans require several factors for survival, each of which must be present in appropriate amounts.

• Nutrients: Chemicals for energy and cell building.

  • Carbohydrates: Major source of energy.

  • Proteins: Needed for cell building and cell chemistry.

  • Fats: Long-term energy storage.

  • Minerals and vitamins: Involved in chemical reactions and structural purposes.

• Oxygen: Essential for the release of energy from foods; survival without oxygen is limited to a few minutes.

• Water: Most abundant chemical in the body; provides a watery environment for chemical reactions and is the fluid base for secretions and excretions.

• Normal body temperature: Must be maintained around 37°C; deviations affect rates of chemical reactions.

• Appropriate atmospheric pressure: Necessary for adequate breathing and gas exchange in the lungs.

Homeostasis

Maintaining Internal Stability

Homeostasis is the maintenance of relatively stable internal conditions despite continuous changes in the environment. It is a dynamic state of equilibrium, constantly readjusting as needed.

• All organ systems contribute to homeostasis.

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

Homeostatic Controls

The body uses complex control mechanisms to monitor and regulate internal variables.

• Variables: Factors that can change (e.g., blood sugar, body temperature, blood volume).

• Three main components:

  • Receptor (sensor): Monitors environment and responds to stimuli.

  • Control center: Determines set point, receives input from receptor, and determines appropriate response.

  • Effector: Receives output from control center and provides the means to respond.

Feedback Mechanisms

• Negative feedback: Most common; response reduces or shuts off original stimulus. Variable changes in the opposite direction of initial change.

  • Example: Regulation of body temperature and blood glucose by insulin.

  • Process: Receptors sense increased blood glucose; pancreas releases insulin; cells absorb glucose, lowering blood glucose levels; insulin release stops when normal levels are restored.

• Positive feedback: Rare; initial response enhances original stimulus, causing further responses in the same direction.

  • Examples: Labor contractions, blood clotting.

Homeostatic Imbalance

Disturbance of homeostasis increases risk of disease and contributes to aging. If negative feedback mechanisms are overwhelmed, destructive positive feedback may take over (e.g., heart failure).

Anatomical Terms

Anatomical Position and Directional Terms

Standard anatomical position is used as a reference for describing locations and relationships of body parts.

• Standard anatomical position: Body erect, feet slightly apart, palms facing forward, thumbs pointing away from body.

• Directional terms: Describe one body structure in relation to another; always based on standard anatomical position.

• Right and left refer to the body being viewed, not the observer.

Major Divisions of the Body

• Axial: Head, neck, and trunk.

• Appendicular: Limbs (arms and legs).

• Regional terms: Designate specific areas within these divisions.

Body Planes and Sections

Common Body Planes

Body planes are imaginary surfaces used to divide the body for anatomical study.

• Sagittal plane: Divides body vertically into right and left parts.

  • Midsagittal (median) plane: Cut made perfectly on midline.

  • Parasagittal plane: Cut off-centered, not on midline.

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

• Transverse (horizontal) plane: Divides body horizontally into superior (top) and inferior (bottom) parts; produces a cross section.

• Oblique section: Cut at an angle other than 90° to vertical plane.

Body Cavities

Major Body Cavities and Their Subdivisions

The body contains internal cavities that protect organs and provide compartmentalization.

Body Cavity	Subdivisions	Main Contents
Dorsal body cavity	Cranial cavity Vertebral cavity	Brain Spinal cord
Ventral body cavity	Thoracic cavity Abdominopelvic cavity	Heart, lungs Digestive organs, reproductive organs

Additional info: The diaphragm separates the thoracic and abdominopelvic cavities. The ventral cavity houses the internal organs collectively called viscera.