Introduction to Anatomy & Physiology: Levels of Organization, Organ Systems, and Regional Terms

Terms and Definitions

Introduction to Anatomy and Physiology

• Anatomy: The study of body structure and relationships among structures.

• Physiology: The study of body function.

Levels of Organization

Chemical Level

The chemical level is the simplest level of organization, involving atoms and molecules that form the basis of all matter.

• Atoms: Fundamental units of matter (e.g., carbon, hydrogen, oxygen).

• Molecules: Combinations of atoms (e.g., water, proteins, nucleic acids).

• Example: Hemoglobin is a protein molecule essential for oxygen transport in blood.

Cellular Level

Cells are the basic unit of all living things, surrounded by a plasma membrane that regulates entry and exit of substances.

• Phospholipid membrane: Forms the main structure of the plasma membrane.

• Example: Human cells such as muscle cells, nerve cells, and epithelial cells.

Tissue Level

Tissues are groups of similar cells that work together to perform a specific function.

• Epithelial tissue: Covers body surfaces and lines cavities.

• Connective tissue: Supports and binds other tissues.

• Muscle tissue: Responsible for movement.

• Nervous tissue: Transmits electrical impulses.

Organ Level

Organs are structures composed of two or more tissue types that perform specific functions.

• Example: The heart contains muscle, connective, and epithelial tissues.

• A single organ can be part of more than one organ system.

Organ System Level

Organ systems are groups of organs that work together to perform complex functions.

• Example: The cardiovascular system includes the heart and blood vessels.

Organismal Level

The organismal level represents the whole living individual, with all organ systems working together to maintain life.

Organ Systems Overview

Integumentary System

• Forms the external body covering and protects deeper tissues from injury.

• Synthesizes vitamin D and houses cutaneous receptors (pain, pressure, etc.), sweat, and oil glands.

• Components: Hair, skin, nails.

Skeletal System

• Protects and supports body organs, provides a framework for muscles.

• Blood cells are formed within bones; bones store minerals.

• Components: Bones, joints.

Muscular System

• Allows manipulation of the environment, locomotion, and facial expression.

• Maintains posture and produces heat.

• Component: Skeletal muscle.

Nervous System

• Fast-acting control system; responds to internal and external changes by activating muscles and glands.

• Components: Brain, spinal cord, nerves.

Endocrine System

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

• Components: Thyroid gland, thymus, adrenal gland, pancreas, ovaries, testes, pituitary gland, pineal gland.

Cardiovascular System

• Blood vessels transport blood, carrying oxygen, carbon dioxide, nutrients, wastes, etc.

• The heart pumps blood.

• Components: Heart, blood vessels.

Lymphatic System / Immunity

• Picks up fluid leaked from blood vessels and returns it to blood.

• Disposes of debris; houses white blood cells (lymphocytes) involved in immunity.

• Components: Red bone marrow, thymus, lymphatic vessels, thoracic duct, spleen, lymph nodes.

Respiratory System

• Keeps blood supplied with oxygen and removes carbon dioxide.

• Gaseous exchanges occur through the walls of air sacs in the lungs.

• Components: Nasal cavity, pharynx, larynx, bronchi, trachea, lungs.

Digestive System

• Breaks down food into absorbable units; indigestible foodstuffs are eliminated as feces.

• Components: Oral cavity, esophagus, liver, stomach, small intestine, large intestine, rectum, anus.

Urinary System

• Eliminates nitrogenous wastes; regulates water, electrolyte, and acid-base balance.

• Components: Kidney, ureter, urinary bladder, urethra.

Reproductive System

• Overall function is production of offspring.

• Testes produce sperm and male sex hormones; ducts and glands aid delivery of sperm.

• Ovaries produce eggs and female sex hormones; remaining structures serve as sites for fertilization and development of fetus.

• Male components: Prostate gland, penis, testes, scrotum, ductus deferens.

• Female components: Mammary glands, ovaries, uterus, vagina, uterine tube.

Anatomical Position and Regional Terms

Anatomical Position

The standard reference point: standing, feet flat on the ground, toes pointing forward, palms of hands facing forward.

Axial Region

Central axis of the body, including head, neck, and trunk.

• Cephalic region (head):

  • Frontal: Forehead area

  • Orbital: Eye socket

  • Nasal: Nose

  • Oral: Mouth

  • Mental: Chin

• Cervical region: Neck

• Trunk:

  • Thorax: Sternum, axillary (armpit), mammary (breast)

  • Abdomen: Abdominal and pelvic regions

  • Pelvis: Inguinal (groin)

Appendicular Region

Limbs attached to the axis.

• Upper limbs:

  • Brachial (arm): Between shoulder and elbow

  • Antebrachial (forearm): Between elbow and wrist

  • Acromial: Shoulder area

  • Antecubital: Front of elbow

  • Carpal: Wrist

• Manus (hand):

  • Pollex: Thumb

  • Palmar: Palm

  • Digital: Fingers

• Lower limbs:

  • Coxal: Hip

  • Femoral: Thigh

  • Patellar: Knee (front)

  • Crural: Leg (between knee and ankle)

  • Fibular/peroneal: Side of leg

• Pedal (foot):

  • Tarsal: Ankle

  • Metatarsal: Top of foot

  • Digital: Toes

  • Hallux: Big toe

Summary Table: Levels of Organization

Level	Description	Example
Chemical	Atoms and molecules	Hemoglobin, water
Cellular	Cells and their organelles	Muscle cell, neuron
Tissue	Groups of similar cells	Epithelial tissue
Organ	Two or more tissue types	Heart, liver
Organ System	Organs working together	Cardiovascular system
Organismal	Whole living individual	Human body

Additional info:

• Regional terms are essential for describing locations and relationships of body parts in clinical and anatomical contexts.

• Organ systems interact to maintain homeostasis, the stable internal environment necessary for survival.