Introduction to Human Anatomy & Physiology

Overview

This study guide introduces the foundational concepts of human anatomy and physiology, focusing on definitions, organization, life functions, requirements for survival, homeostasis, and regulatory mechanisms. These principles are essential for understanding the structure and function of the human body in health and disease.

What is Anatomy?

Definition and Branches

• Anatomy is the study of body parts and their relationship to one another.

• Gross anatomy: Study of large, visible structures.

• Regional anatomy: Examines all structures in a particular area of the body.

• Systemic anatomy: Focuses on just one system (e.g., cardiovascular, nervous, muscular).

• Microscopic anatomy: Deals with structures too small to be seen by the naked eye.

• Cytology: Study of cells.

• Histology: Study of tissues.

• Developmental anatomy: Studies anatomical and physiological development before birth.

Clinical Application: Anatomical terminology is essential for describing, palpating, and auscultating body structures.

What is Physiology?

Definition and Scope

• Physiology is the study of the function of body parts and how they work to carry out life-sustaining activities.

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

• Examines cellular and molecular levels of the body.

• The body's abilities depend on chemical reactions within individual cells.

• Understanding physiology requires knowledge of basic physical principles (e.g., electrical currents, pressure, movement) and chemical principles.

Complementarity of Structure and Function

Principle of Complementarity

• Anatomy and physiology are inseparable: Function always reflects structure.

• What a structure can do depends on its specific form.

• This is known as the principle of complementarity of structure and function.

• Example: The shape of incisors (structure) enables them to cut food (function).

Levels of Structural Organization

Hierarchy of Organization

• The body is highly organized, from the smallest chemical level to the organism level:

• Chemical level: Atoms, molecules, and organelles.

• Cellular level: Single cell.

• Tissue level: Groups of similar cells.

• Organ level: Contains two or more types of tissues.

• Organ system level: Organs that work closely together.

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

Necessary Life Functions

Major Life Functions

Survival Needs

Essential Requirements

Homeostasis

Definition and Importance

• Homeostasis is the maintenance of relatively stable internal conditions despite changes in the environment.

• Dynamic state of equilibrium, always readjusting as needed.

• Maintained by contributions of all organ systems.

• Variables (e.g., blood sugar, body temperature, blood volume) must be monitored and regulated.

• Nervous and endocrine systems play major roles in maintaining homeostasis.

Homeostatic Controls: Negative Feedback

Mechanism and Examples

• Negative feedback reduces or shuts off the original stimulus, causing changes in the opposite direction of the initial change.

• Most common feedback mechanism in the body.

• Examples:

  • Regulation of body temperature (nervous system mechanism).

  • Regulation of blood glucose by insulin (endocrine system mechanism).

  • When blood glucose increases, the pancreas (control center) secretes insulin, causing body cells (effectors) to absorb more glucose, lowering blood glucose levels.

Homeostatic Controls: Positive Feedback

Mechanism and Examples

• Positive feedback enhances or exaggerates the original stimulus.

• May exhibit a cascade or amplifying effect; feedback causes variable to continue in the same direction as the initial change.

• Usually controls infrequent events that do not require continuous adjustment.

• Examples:

  • Enhancement of labor contractions by oxytocin.

  • Platelet plug formation and blood clotting.

Disturbance of Homeostasis

Consequences

• Disturbance increases risk of disease.

• Contributes to changes associated with aging.

• If negative feedback mechanisms are overwhelmed, destructive positive feedback mechanisms may take over.

Anatomical Position and Directional Terms

Standard Reference and Terminology

• Anatomical position: Standing upright, head and eyes forward, upper limbs at sides, palms facing forward, thumbs pointing away from body, lower limbs parallel, feet flat and facing forward.

• Directional terms describe one body structure in relation to another, always based on standard anatomical position.

• Common directional terms:

  • Supine

  • Ventral

  • Dorsal

  • Superficial

  • Deep

  • Unilateral

  • Bilateral

  • Ipsilateral

  • Contralateral

Body Planes and Sections

Major Planes

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

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

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

Body Cavities

Major Internal Cavities

• Thoracic cavity: Contains pleural cavities (lungs), mediastinum (esophagus, trachea), pericardial cavity (heart).

• Abdominopelvic cavity: Contains abdominal cavity (stomach, intestines, pancreas) and pelvic cavity (urinary bladder, reproductive organs).

Membranes

Serous Membranes

• Serosa (serous membrane): Thin, double-layered membrane covering surfaces in ventral body cavity.

• Parietal serosa: Lines internal body cavity walls.

• Visceral serosa: Covers internal organs.

• Double layers are separated by serous fluid, which is secreted by both layers and reduces friction.

References

• OpenStax Anatomy and Physiology 2e

• Marieb Human Anatomy & Physiology