Introduction to Anatomy & Physiology

Definition and Scope

Anatomy and physiology are foundational sciences in understanding the structure and function of the human body. Anatomy describes the physical structures, their composition, location, and associated features. Physiology focuses on the functions of these anatomical structures, both individually and in cooperation with other systems.

• Anatomy: Includes gross (macroscopic) anatomy and microscopic anatomy.

• Physiology: Includes cell, organ, systemic, and pathological physiology.

• Scientific Method: Used by physicians to diagnose by forming and testing hypotheses based on signs and symptoms.

Levels of Organization

Hierarchical Structure of the Human Body

The human body is organized into a hierarchy of structural levels, each building upon the previous. Understanding these levels is essential for grasping how the body functions as a whole.

• Chemical Level: Atoms and molecules form the basis of all matter.

• Cellular Level: Cells are the smallest living units, composed of molecules.

• Tissue Level: Groups of similar cells working together to perform specific functions.

• Organ Level: Organs consist of two or more types of tissues working together.

• Organ System Level: Organ systems are groups of organs that interact to perform complex functions.

• Organism Level: The complete living individual.

Example: The heart is composed of cardiac muscle tissue (tissue level), which consists of heart muscle cells (cellular level), built from protein molecules (chemical level).

The Organ Systems

Overview and Functions

Humans possess 11 major organ systems, each with distinct organs and functions. These systems work together to maintain health and homeostasis.

• Integumentary System: Skin, hair, nails; protects against environmental hazards, regulates temperature, provides sensory information.

• Skeletal System: Bones, cartilages, ligaments, bone marrow; supports and protects tissues, stores minerals, forms blood cells.

• Muscular System: Skeletal muscles, tendons; provides movement, support, generates heat.

• Nervous System: Brain, spinal cord, nerves, sense organs; directs responses, coordinates activities, interprets sensory information.

• Endocrine System: Glands (pituitary, thyroid, adrenal), pancreas, gonads; directs long-term changes, adjusts metabolism, controls development.

• Cardiovascular System: Heart, blood, blood vessels; distributes blood, nutrients, waste, oxygen, carbon dioxide, heat.

• Lymphatic System: Spleen, thymus, lymphatic vessels, nodes, tonsils; defends against infection, returns tissue fluids.

• Respiratory System: Nasal cavities, sinuses, larynx, trachea, bronchi, lungs, alveoli; delivers air, provides oxygen, removes carbon dioxide, produces sounds.

• Digestive System: Teeth, tongue, pharynx, esophagus, stomach, intestines, liver, gallbladder, pancreas; processes food, absorbs nutrients and water, stores energy.

• Urinary System: Kidneys, ureters, bladder, urethra; excretes waste, regulates water and ions, stores urine.

• Reproductive Systems: Male (testes, ducts, glands, penis, scrotum) and Female (ovaries, tubes, uterus, vagina, labia, clitoris, mammary glands); produce sex cells and hormones, support embryo, nourish infant.

Anatomical Terminology

Surface Anatomy and Landmarks

Surface anatomy involves identifying structures on or near the body surface. Anatomical position is the standard reference: standing, hands at sides, palms forward.

• Supine: Lying face up.

• Prone: Lying face down.

Anatomical Regions and Directions

The abdominopelvic region is divided into quadrants and regions for clinical reference. Directional terms describe locations relative to the body.

• Quadrants: RUQ, RLQ, LUQ, LLQ.

• Regions: Hypochondriac, epigastric, lumbar, umbilical, inguinal, hypogastric.

• Directional Terms: Superior, inferior, anterior (ventral), posterior (dorsal), medial, lateral, proximal, distal, superficial, deep.

Sectional Anatomy and Planes

Sectional anatomy uses slices (sections) to visualize internal structures. Sectional planes include frontal (coronal), sagittal (midsagittal, parasagittal), and transverse (horizontal).

• Frontal (Coronal) Plane: Divides body into anterior and posterior.

• Sagittal Plane: Divides body into left and right; midsagittal is at midline, parasagittal is offset.

• Transverse Plane: Divides body into superior and inferior.

Body Cavities

Functions and Structure

Body cavities protect internal organs and allow changes in size and shape. The ventral body cavity is divided by the diaphragm into thoracic and abdominopelvic cavities.

• Serous Membranes: Parietal layer lines cavity, visceral layer covers organ.

• Thoracic Cavity: Contains pleural (lungs) and pericardial (heart) cavities, separated by mediastinum.

• Abdominopelvic Cavity: Contains peritoneal cavity, abdominal cavity (digestive organs, retroperitoneal space), and pelvic cavity (reproductive organs, rectum, bladder).

Homeostasis

Definition and Regulation

Homeostasis is the maintenance of a stable internal environment. All body systems contribute to keeping variables within normal ranges.

• Autoregulation: Automatic response by cells, tissues, or organs.

• Extrinsic Regulation: Controlled by nervous and endocrine systems.

• Regulatory Mechanism: Involves receptor (detects stimulus), control center (processes signal), and effector (carries out instructions).

Negative and Positive Feedback

Feedback Mechanisms

Feedback mechanisms regulate homeostasis. Negative feedback negates the stimulus, restoring balance. Positive feedback amplifies the stimulus, moving the body away from homeostasis to quickly resolve a process.

• Negative Feedback Example: Body temperature regulation.

• Positive Feedback Example: Blood clotting.

Systems Integration and Equilibrium

Physiological systems work together to maintain dynamic equilibrium. Failure to maintain homeostasis results in disease.

Summary Table: Major Organ Systems