Overview of Anatomy and Physiology

Definitions 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’s structural machinery. Anatomy can be divided into:

• Gross (macroscopic) anatomy: Study of large body structures visible to the naked eye.

• Microscopic anatomy: Study of structures too small to be seen with the naked eye, including cytology (cells) and histology (tissues).

• Developmental anatomy: Study of structural changes throughout life, including embryology (development before birth).

Physiology

Physiology focuses on the functions of the body, often at the cellular or molecular level. Examples include:

• Neurophysiology: Study of nervous system function.

• Cardiovascular physiology: Study of heart and blood vessel function.

Principle of Complementarity

The principle of complementarity states that function always reflects structure; what a structure can do depends on its specific form.

Levels of Structural Organization

Hierarchy of Organization

The human body is organized into six levels, from simplest to most complex:

• 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 closely.

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

Organ Systems of the Human Body

Major Organ Systems

The body is composed of several organ systems, each with specific functions and representative organs:

• Integumentary system: Skin, hair, nails; protects the body.

• Skeletal system: Bones, joints; supports and protects organs.

• Muscular system: Skeletal muscles; allows movement.

• Nervous system: Brain, spinal cord, nerves; fast-acting control system.

• Cardiovascular system: Heart, blood vessels; transports blood.

• Lymphatic system: Lymph nodes, lymphatic vessels; immunity.

• Respiratory system: Lungs, airways; gas exchange.

• Digestive system: Stomach, intestines; breaks down food.

• Urinary system: Kidneys, bladder; eliminates waste.

• Endocrine system: Glands; hormone production.

• Reproductive system: Ovaries/testes; produces offspring.

Necessary Life Functions

Basic Functions Required for Life

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

• Movement: Locomotion, movement of substances, contractility.

• Responsiveness: Ability to sense and respond to stimuli.

• Digestion: Breakdown of ingested foodstuffs.

• Metabolism: All chemical reactions in the body.

• Excretion: Removal of wastes.

• Reproduction: Cellular (cell division) and organismal (offspring).

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

Survival Needs

Essential Requirements for Human Life

• Nutrients: Chemicals for energy and cell building.

• Oxygen: Required for metabolic reactions.

• Water: Most abundant chemical in the body.

• Normal body temperature: Necessary for chemical reactions.

• Atmospheric pressure: Required for proper breathing and gas exchange.

Homeostasis

Definition and Importance

Homeostasis is the ability to maintain a relatively stable internal environment despite changes in the external environment. It depends on chemical, thermal, and neural factors.

Homeostatic Control Mechanisms

Homeostatic regulation involves three main components:

• Receptor: Monitors changes (stimuli).

• Control center: Determines the set point and processes information.

• Effector: Responds to the control center to influence the stimulus.

Disturbance of homeostasis can lead to disease.

Negative Feedback

In negative feedback, the response reduces or shuts off the original stimulus. Most homeostatic mechanisms are negative feedback (e.g., body temperature regulation, ADH control of water balance).

Positive Feedback

In positive feedback, the response enhances or exaggerates the original stimulus. Examples include blood clotting and oxytocin intensifying labor contractions.

Anatomical Terminology

Anatomical Position

The anatomical position is the standard reference point for describing body parts and positions: body erect, palms facing forward, thumbs pointing away from the body.

Directional Terms

Directional terms are used to describe the location of body parts relative to each other:

• Superior/Inferior: Above/below

• Anterior/Posterior: Front/back

• Dorsal/Ventral: Back/belly

• Medial/Lateral/Intermediate: Toward midline/away from midline/between

• Proximal/Distal: Closer to/farther from the origin of a body part

• Superficial/Deep: Toward/away from the body surface

Body Planes

Body planes are imaginary lines used to divide the body:

• Sagittal plane: Divides body into right and left parts

• Midsagittal (median) plane: Lies on the midline

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

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

• Oblique section: Cuts made diagonally

Body Cavities and Membranes

Major Body Cavities

• Dorsal body cavity: Protects the nervous system; includes cranial and vertebral cavities.

• Ventral body cavity: Houses internal organs (viscera); includes thoracic and abdominopelvic cavities.

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

• Abdominopelvic cavity: Contains abdominal (digestive organs) and pelvic (bladder, reproductive organs, rectum) cavities.

Ventral Body Cavity Membranes

Serous membranes line body cavities and cover organs:

• Parietal serosa: Lines internal body walls

• Visceral serosa: Covers internal organs

• Serous fluid: Separates the serosae, reducing friction

Other Body Cavities

• Oral and digestive cavities: Mouth and digestive organs

• Nasal cavity: Within and posterior to the nose

• Orbital cavity: Eyes

• Middle ear cavity: Contains ossicles for hearing

• Synovial cavities: Joint cavities

Abdominopelvic Regions and Quadrants

Regions

The abdominopelvic cavity is divided into nine regions for anatomical study:

• Right/Left hypochondriac

• Epigastric

• Right/Left lumbar

• Umbilical

• Right/Left iliac (inguinal)

• Hypogastric (pubic)

Quadrants

Clinically, the abdominopelvic cavity is divided into four quadrants:

• Right upper quadrant (RUQ)

• Left upper quadrant (LUQ)

• Right lower quadrant (RLQ)

• Left lower quadrant (LLQ)

Additional info:

• Situs inversus is a condition where the major visceral organs are reversed or mirrored from their normal positions.

• Practice questions in the notes help reinforce understanding of directional terms and anatomical positions.