Body Structures and Systems

Cells

The building blocks of life, starting as a single cell that duplicates exponentially over time.

Plasma membrane

A selectively permeable membrane made of phospholipids and proteins surrounding the entire cell.

Cytoplasm

Gel-like fluid filling the inside of the cell, comprised primarily of water, electrolytes, metabolic waste products, and nutrients.

Nucleus

Control center of the cell that regulates cell activity and contains genetic material in the form of DNA.

Nuclear membrane

Double-layered, porous membrane surrounding the nucleus that protects it and allows in only specific materials.

Nucleolus

Dark, dense body within the nucleus without an enclosing membrane, typically containing one to four in most cells.

Mitochondria

Elongated, rod-shaped bodies filled with fluid that convert nutrients into energy for use by the cell/body and create adenosine triphosphate (ATP).

Ribosomes

Small granules of RNA found in the nucleolus or cytoplasm that are responsible for protein synthesis for both internal and external use.

Endoplasmic reticulum

Complex connection of membranous fluid-filled, flat sacs and tubular channels that transports materials throughout the cell.

Rough endoplasmic reticulum (RER)

Supports the synthesis and transport of proteins.

Smooth endoplasmic reticulum (SER)

Supports the synthesis of some lipid molecules, including steroids.

Golgi apparatus

Four to six flat membranous sacs connected to the endoplasmic reticulum that package and release materials secreted by the cell.

Lysosomes

Sacs surrounded by membranes created by the Golgi apparatus that digest waste materials including damaged materials and old cell components.

Cytoskeleton

Comprised of protein microfilaments and microtubules that maintain the shape and structure of the cell.

Centrioles

Pair of rod-shaped bodies made of microtubules found near the nucleus that participate in cell reproduction through the distribution of DNA to new cells.

Cilia

Short, hair-like microtubules projecting from the cell membrane that aid in the movement of substances along the surface of the cell.

Flagella

Long, hair-like microtubules projecting from the cell membrane that move the cell itself through a whip-like motion.

Planes of the Body

Three main planes that describe sections of the body and are frequently used with various radiographic studies.

Sagittal plane

Divides the body into left and right sides.

Midsagittal

Refers to an equal division of left and right sides, running along the midline of the body.

Transverse plane

Divides the body into upper and lower sections, not necessarily equally.

Frontal plane

Also called coronal plane, divides the body into anterior and posterior sections.

Cranial cavity

Within the skull; houses the meninges (brain).

Spinal cavity

Traveling down the midline of the back and formed by the vertebrae, this contains the spinal cord.

Thoracic cavity

Within the chest; houses the lungs, heart, and major vessels.

Abdominal cavity

Within the abdomen; houses several major organs such as the stomach, liver, gallbladder, and intestines.

Pelvic cavity

Inferior to the abdominal cavity; houses the bladder and reproductive organs.

Integumentary System

The following make up the integumentary system.

Skin

Responsible for protection, temperature regulation, sensation, excretion, and vitamin D production.

Epidermis layer

Outermost layer of epithelial tissue, covers the external surface of the body.

Dermis layer

Thick layer beneath the dermis that contains arteries, veins, nerves.

Subcutaneous layer

Loose, connective tissue composed of adipose tissue and lipocytes.

Hair follicles

Generate hair.

Sebaceous (oil) glands

Produce sebum to keep skin and hair soft and prevent bacteria from growing on the skin.

Fingernails and toenails

Protect the ends of fingers and toes.

Sudoriferous (sweat) glands

Produce sweat to aid in cooling the body.

Axial skeleton

The adult axial skeleton has 80 bones, including the skull, vertebrae, and ribs.

Appendicular skeleton

The adult appendicular skeleton has 126 bones, including arms, legs, and pelvic girdle.

Ligament

The ligaments attach bone to bone for joint stability.

Tendons

The tendons join muscles to bones that help in moving extremities.

Connective Tissue/Cartilage

This tissue maintains, protects, and gives form to other tissues and organs.

Musculoskeletal system

The systems of bones and muscles referenced as one.

Long bones

Bones that have epiphysis, diaphysis, and medullary cavity containing yellow bone marrow.

Articular cartilage

Covers the ends of long bones to allow joint movement without causing friction.

Examples of long bones

Femur, humerus, tibia, fibula, ulna, radius.

Short bones

Typically small and round bones found in the wrists and ankles.

Examples of short bones

Carpals, tarsals.

Flat bones

Bones with a majority of surface area that is flat or slightly curved.

Examples of flat bones

Skull, ribs.

Irregular bones

Bones with an unusual shape that is typically related to their function.

Examples of irregular bones

Vertebrae, pelvis.

Sesamoid bones

Small, round bones found in joints that are held in place by tendons.

Example of sesamoid bone

Patella.

Red bone marrow

Responsible for producing new blood cells, a process known as hematopoiesis.

Skeletal muscle

Responsible for body movement; also called voluntary muscle or striated muscle.

Smooth muscle

Found within the walls of hollow organs and blood vessels; also called involuntary muscle.

Cardiac muscle

Found only in the heart; cross-fibered to allow the heart to contract from the top and bottom.

Tendons

Ends of skeletal muscles that attach the muscle to a bone.

Lymph nodes

Small, glandular structures that produce and store lymphocytes.

Lymph nodules

Masses of lymphoid tissue comprised of macrophages and lymphocytes, not encapsulated like lymph nodes.

Thymus

Responsible for the production and maturation of T-cells, located posterior to the sternum.

Spleen

Largest lymphoid organ, located in the upper-left quadrant of the abdomen, home to macrophages that filter the blood.

Interstitial fluid

Tissue fluid found between cells, called lymph once collected and filtered.

Antigen

Foreign substance within the body

Antibody

Protein the body creates in response to specific antigens

Immunoglobulins

Antibodies

B-cells

Type of lymphocyte that can recognize antigens and responds by turning into plasma cells; these plasma cells then create antibodies against specific antigens

T-cells

Type of lymphocyte that can recognize antigens and attaches to them to attack the invading cells directly

Monocytes

Engulf and destroy pathogens that have been coagulated with antibodies

Heart

Located within the central part of the chest (mediastinum) and functions as a pump to move blood throughout the body

Artery/Arteriole

Thick-walled vessels that carry blood away from the heart. They propel blood with each contraction of the heart and are associated with various pulse points on the body. Smaller branches are arterioles.

Vein/Venule

Vessels that carry blood toward the heart. They are thinner-walled than arteries and contain valves to prevent backflow. Smaller branches are venules.

Capillary

The smallest blood vessels, which connect arterioles to venules. They aid in the exchange of oxygen and nutrients between blood and body cells.

Endocardium

Innermost layer of cells that lines the atria, ventricles, and heart valves

Myocardium

Muscular layer of the heart

Pericardium

Outermost layer of the heart; a membrane that surrounds the heart and secretes pericardial fluid

Epicardium

Outermost layer of the heart

Right atrium

Receives deoxygenated blood from the superior and inferior vena cava

Left atrium

Receives oxygenated blood from the pulmonary veins (the only veins in the body that carry oxygenated blood)

Right ventricle

Receives blood from the right atrium and sends deoxygenated blood through the pulmonary valve to the pulmonary artery and then to the lungs, where gas exchange occurs

Left ventricle

Receives blood from the left atrium and sends the oxygenated blood through the aortic valve to the aorta, which then branches off into smaller arteries that carry the blood to the body

Tricuspid valve

Located between the right atrium and right ventricle; prevents backflow of blood into the atria when the ventricles contract

Bicuspid (mitral) valve

Located between the left atrium and left ventricle; prevents backflow of blood into the atria when the ventricles contract

Systemic circulation

Consists of arteries, arterioles, capillaries, venules, and veins in the body as a whole

Pulmonary circulation

Consists of arteries, arterioles, capillaries, venules, and veins going to, within, and coming from the lungs

Electrical conduction system

Keeps the cardiac muscle contracting and blood flowing

Electrocardiogram (EKG)

A test that maps and analyzes the electrical impulses of the heart to detect heart issues.

Sinoatrial (SA) node

The pacemaker of the heart that generates electrical impulses.

Atrioventricular node

Also called the gatekeeper, it receives impulses from the SA node.

Bundle of His

A collection of heart muscle cells that transmit impulses from the atrioventricular node.

Purkinje fibers

Fibers that cause the ventricles to contract and pump blood.

Cardiac cycle

The entire process of electrical impulse generation and heart contraction.

Kidneys

Organs responsible for removing waste from the blood and producing urine.

Ureters

Long tubes that carry urine from the kidneys to the urinary bladder.

Urinary bladder

A small muscular sac responsible for storing urine.

Urethra

A tube that carries urine from the urinary bladder to the outside of the body.

Urinary meatus

The opening at the end of the urethra where urine exits the body.

Urinary system

The system primarily responsible for filtering blood to remove waste products and forming urine.

Gastrointestinal system

Also known as the gastrointestinal tract, it is responsible for digestion and nutrient absorption.

Mouth (oral cavity)

The part of the gastrointestinal system responsible for initiating digestion.