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

Introduction to Anatomy and Physiology

Definition and Scope

Anatomy is the study of the structure of body parts and their relationships to one another, while physiology is the study of the function of the body—how body parts work to carry out life-sustaining activities. Understanding both is essential for a comprehensive knowledge of the human body.

• Anatomy: Focuses on form and structure.

• Physiology: Focuses on function and processes.

• Form determines function: The structure of a body part enables its function.

Reference Standards and Anatomical Variability

Reference Individuals

Textbook values are based on a reference male (70 kg) and a reference female (57 kg). However, anatomical variability exists among individuals.

• Over 90% of anatomical structures match textbook descriptions.

• Minor variations (e.g., nerves or blood vessels out of place) are common.

• Extreme variations are rare and usually incompatible with life.

Sex and Gender

• Sex: Biological attributes (chromosomes, gene expression, hormone action, reproductive anatomy).

• Gender: Psychosocial construct (behaviors, expressions, identities).

Studying Anatomy

Methods and Tools

Studying anatomy requires understanding terminology and using various techniques:

• Observation

• Manipulation

• Palpation: Feeling organs with hands

• Auscultation: Listening to organs with a stethoscope

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

Subdivisions of Anatomy and Physiology

Anatomy

• Gross (macroscopic) anatomy: Large structures visible to the naked eye

• Regional anatomy: All structures in a specific area

• System anatomy: One system at a time (e.g., cardiovascular)

• Surface anatomy: Internal structures as related to overlying skin

• Microscopic anatomy: Structures too small to see unaided (cytology—cells, histology—tissues)

• Developmental anatomy: Structural changes throughout life (embryology—before birth)

Physiology

• Subdivided by organ systems (e.g., renal, neurophysiology, cardiovascular physiology)

• Focuses on cellular and molecular events

• Requires understanding of chemistry and physics

Levels of Structural Organization

Hierarchy from Atoms to Organism

The human body is organized into a hierarchy of structural levels:

• Chemical level: Atoms combine to form molecules

• Cellular level: Cells are made up of molecules

• Tissue level: Tissues consist of similar types of cells

• Organ level: Organs are made up of different types of tissues

• Organ system level: Organ systems consist of different organs that work together

• Organismal level: The human organism is made up of many organ systems

The Body’s Organ Systems and Their Major Functions

Overview of the 11 Organ Systems

The human body is composed of 11 organ systems, each with specific functions essential for survival.

System	Main Functions
Integumentary	Protects body, synthesizes vitamin D, houses receptors and glands
Skeletal	Supports and protects organs, provides framework, forms blood cells, stores minerals
Muscular	Allows movement, maintains posture, produces heat
Nervous	Fast-acting control system, responds to stimuli
Endocrine	Secretes hormones for regulation of growth, reproduction, metabolism
Cardiovascular	Transports blood, nutrients, gases, wastes
Lymphatic/Immunity	Returns leaked fluid, disposes debris, houses immune cells
Respiratory	Supplies blood with oxygen, removes carbon dioxide
Digestive	Breaks down food, absorbs nutrients, eliminates waste
Urinary	Eliminates nitrogenous wastes, regulates water, electrolytes, acid-base balance
Reproductive	Produces offspring, sex hormones

Requirements for Life

Necessary Life Functions

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

• Movement: Of body parts, cells, and substances

• Responsiveness: Ability to sense and respond to stimuli

• Digestion: Breakdown and absorption of food

• Metabolism: All chemical reactions in the body (catabolism, anabolism, cellular respiration)

• Excretion: Removal of wastes

• Reproduction: Cellular and organismal levels

• Growth: Increase in size or number of cells

Survival Needs

• Nutrients: Carbohydrates, proteins, fats, vitamins, minerals

• Oxygen: Essential for energy production

• Water: Most abundant chemical in the body

• Normal body temperature: Necessary for metabolic reactions

• Appropriate atmospheric pressure: Required for breathing and gas exchange

Homeostasis

Definition and Importance

Homeostasis is the maintenance of relatively stable internal conditions despite continuous environmental changes. It is a dynamic equilibrium, maintained by all organ systems.

• Law of mass balance: Input equals output for substances in the body.

Homeostatic Control Mechanisms

• Receptor: Monitors environment, responds to stimuli

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

• Effector: Carries out response, reduces or enhances stimulus

Types of Feedback

• Negative feedback: Most common; reduces or shuts off original stimulus (e.g., body temperature, blood glucose regulation)

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

• Feedforward response: Anticipatory response before a change occurs (e.g., salivation before eating)

Homeostatic Imbalance

• Disturbance increases risk of disease and aging-related changes.

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

Additional info: Homeostasis is a central concept in physiology, underlying the regulation of all body systems and their integration for survival.