Introduction to Anatomy & Physiology

Definitions and Scope

• Anatomy studies the structure of body parts and their relationships to one another.

• Physiology concerns the function of the body, that is, how body parts work and carry out their life-sustaining activities.

Levels of Structural Organization

Hierarchy of Organization

• Chemical Level: Atoms combine to form molecules, which are the building blocks of all matter.

• Cellular Level: Cells are made up of molecules and are the basic units of life.

• Tissue Level: Tissues consist of groups of similar cells that have a common function. Examples: Blood, muscle, nerves.

• Organ Level: Organs are made up of different types of tissues working together to perform specific functions.

• Organ System Level: Organ systems consist of different organs that work closely together.

• Organismal Level: The human organism is made up of many organ systems functioning together to sustain life.

Necessary Life Functions

Basic Functions Required for Life

• Maintaining Boundaries: Separation between internal and external environments must exist. Examples: Plasma membranes separate cells; skin separates the organism from the environment.

• Movement: Muscular system allows movement of body parts via skeletal muscles and movement of substances via cardiac muscle (blood) and smooth muscle (digestion, urination).

• Responsiveness: Ability to sense and respond to stimuli. Examples: Withdrawal reflex prevents injury; control of breathing rate adapts to activity.

• Digestion: Breakdown of ingested foodstuffs, followed by absorption of simple molecules into the blood.

• Metabolism: All chemical reactions that occur in body cells. Includes: Catabolism (breakdown of molecules) and anabolism (synthesis of molecules).

• Excretion: Removal of wastes from metabolism and digestion. Examples: Urea (from protein breakdown), carbon dioxide (from metabolism), feces (unabsorbed foods).

• Reproduction: At the cellular level, reproduction involves division of cells for growth or repair. At the organismal level, it is the production of offspring.

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

Organ Systems Overview

The Eleven Organ Systems of the Human Body

• Integumentary System: Forms the external body covering, protects deeper tissues, synthesizes vitamin D, and houses cutaneous receptors and glands.

• Skeletal System: Protects and supports body organs, provides a framework for muscles, forms blood cells, and stores minerals.

• Muscular System: Allows manipulation of the environment, locomotion, facial expression, maintains posture, and produces heat.

• Nervous System: Fast-acting control system that responds to internal and external changes by activating muscles and glands.

• Endocrine System: Glands secrete hormones that regulate growth, reproduction, and metabolism.

• Cardiovascular System: Blood vessels transport blood carrying oxygen, carbon dioxide, nutrients, and wastes; the heart pumps blood.

• Lymphatic System/Immune System: Returns leaked fluids to blood, disposes of debris, houses white blood cells, and mounts immune responses.

• Respiratory System: Keeps blood supplied with oxygen and removes carbon dioxide; gas exchange occurs in the lungs.

• Digestive System: Breaks down food into absorbable units and eliminates indigestible food as feces.

• Urinary System: Eliminates nitrogenous wastes, regulates water, electrolyte, and acid-base balance.

• Reproductive System: Male: Produces sperm and male sex hormones; delivers sperm to female tract. Female: Produces eggs and female sex hormones; supports fertilization and fetal development; mammary glands produce milk.

Survival Needs

Essential Factors for Human Survival

• Nutrients: Chemicals for energy and cell building (e.g., carbohydrates, proteins, fats, vitamins, minerals).

• Oxygen: Essential for energy release (ATP production) from foods.

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

• Normal Body Temperature: Necessary for proper metabolic reactions.

• Appropriate Atmospheric Pressure: Required for adequate breathing and gas exchange in the lungs.

Homeostasis

Definition and Importance

• Homeostasis: The maintenance of a relatively stable internal environment despite continuous outside changes.

• Homeostatic Imbalance: Disturbance of homeostasis increases risk of disease; associated with aging and may allow destructive positive feedback mechanisms to take over.

• Homeostasis is a ceaseless process of activities in response to stresses in an attempt to maintain equilibrium.

Homeostatic Control Mechanisms

• Homeostatic control mechanisms are generally self-regulating and serve to maintain the homeostatic steady state.

• All mechanisms involve at least three components working together:

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

  • Control Center: Determines the set point at which the variable is maintained, receives input from receptor, and determines appropriate response.

  • Effector: Provides the means to respond to the stimulus (either reducing or enhancing the stimulus).

Feedback Mechanisms

• Negative Feedback: The output shuts off the original effect of the stimulus or reduces its intensity. Example: Regulation of body temperature (thermostat analogy), blood glucose by insulin.

• Positive Feedback: The response enhances the original stimulus so that the response is accelerated. Examples: Blood clotting, labor contractions, orgasm. Note: Positive feedback is rare in the body.

Comparison Table: Negative vs. Positive Feedback

Example: Homeostatic Regulation of Body Temperature

• Stimulus: Increased body temperature (e.g., exercise, hot environment).

• Receptor: Thermoreceptors in skin and brain detect change.

• Control Center: Hypothalamus receives input and initiates response.

• Effector: Sweat glands increase secretion, blood vessels dilate to dissipate heat.

• Result: Body temperature decreases toward set point.

Additional info: Homeostatic mechanisms are crucial for survival; failure leads to disease or death. The concept of homeostasis underpins all physiological processes studied in Anatomy & Physiology.