Human Anatomy and Physiology: Biological Systems and Homeostasis

Biological Organization of the Human Body

The hierarchy of life follows this progression: Atom → Molecule → Cell → Tissue → Organ → Organ System → Organism (Wingspan = Height).

Body Symmetry and Structure

• Radial: Symmetry around a central axis.
• Bilateral: Divided equally across a plane.
• Asymmetrical: Inability to be divided.

Humans exhibit bilateral symmetry and are proportionate.

Functional Principles

Function follows form. For example, the Cell Membrane acts as a Plasma Membrane, while the Cutaneous Membrane acts as skin.

Life Processes and Homeostasis

Essential life functions include:

• Maintenance of Boundaries: Separating internal from external (Integumentary).
• Movement: Muscular and Skeletal systems.
• Responsiveness: Nervous and Endocrine systems.
• Digestion: Digestive and Circulatory systems.
• Metabolism: Digestive, Respiratory, and Integumentary systems.
• Excretion: Urinary, Respiratory, Digestive, and Integumentary systems.
• Reproduction: Reproductive and Endocrine systems.
• Growth: Skeletal, Muscular, Endocrine, Digestive, Respiratory, and Circulatory systems.

Basic Survival Needs: Nutrients, Oxygen, Water, Normal Body Temperature (Cold = slow/stop; Hot = break/speed), and Atmospheric Pressure. Homeostasis represents internal stability.

Homeostatic Control Mechanisms

The body maintains stability through specific control mechanisms:

• Receptor: Monitors and responds to stimuli.
• Control Center: Determines the set point for variable maintenance.
• Effector: Provides the means to respond to stimuli.

Feedback Loops: Stimulus (change) → Afferent Neuron (signals to Control Center) → Efferent Neuron (signals to Effector). Most feedback mechanisms are negative (opposing the original stimulus to maintain homeostasis), while positive feedback moves toward a disturbance, away from homeostasis, leading to homeostatic imbalance.

Anatomical Terminology

Anatomical Position: Body erect, feet together, palms anterior, thumbs lateral.

• Superior: Toward the head.
• Inferior: Away from the head.
• Anterior/Ventral: Toward the front.
• Posterior/Dorsal: Toward the back.
• Medial: Toward the midline.
• Lateral: Away from the midline.
• Intermediate: Between medial and lateral.
• Proximal: Close to the origin of a body part.
• Distal: Farther from the origin.
• Superficial: Toward the body surface.
• Deep: Away from the body surface.

Major Human Organ Systems

• Digestive: Absorbs nutrients and removes undigestible food (feces). Includes mouth, esophagus, stomach, small/large intestine, rectum, anus, pancreas, liver, and gallbladder.
• Circulatory: Transports materials throughout the body. Includes heart, veins, arteries, capillaries, and red blood cells.
• Nervous: Gathers, interprets, and responds to information to maintain homeostasis. Includes brain, spinal cord, and nerves.
• Endocrine: Regulates body activities with hormones (slow but long-lasting). Includes hypothalamus, pituitary, thyroid, thymus, adrenal, pancreas, ovaries, and testes.
• Immune: Fights foreign invaders. Includes white blood cells, T-cells, B-cells, antibodies, macrophages, and skin.
• Integumentary: First line of defense, regulates body temperature, removes excretory waste, protects against UV rays, and produces Vitamin D. Includes epidermis, sweat glands, sebaceous (oil) glands, hair follicles, blood vessels, and nerves.