| Term | Definition |
|---|
| epidermis | in humans and some other animals, the outermost protective layer composed of an outer layer of dead cells and an inner layer of living cells |
| keratin | protein found in the exterior portion of the epidermis that helps protect living cells in the interior epidermis |
| melanin | pigment found in the cells of the interior layer of the epidermis; protects cells from radiation damage |
| dermis | inner, thicker portion of the skin that contains structures such as blood vessels, nerves, nerve endings, hair follicles, sweat glands and oil glands |
| ligaments | tough band of connective tissue that attaches one bone to another; joints are often held together and enclosed by ligaments |
| tendons | thick bands of connective tussue that attach muscles to bones |
| red marrow | marrow found in the humerous, femur, sternum, ribs, vertebrae, and pelvis that produces red blood cells, white blood cells. and cell fragments involved in blood clotting |
| yellow marrow | marrow composed of stored fats found in many bones |
| smooth muscle | type of involuntary muscle found in the walls of internal organs and blood vessels; most common function is to squeeze, exerting pressure inside the tube or organ it surrounds |
| cardiac muscle | type of involuntary muscle found only in the heart; composed of interconnected cardiac muscle fibers; adapted to generage and conduct electrical impulses for muscle contraction |
| skeletal muscle | type of voluntary muscle that is attached to and moves the bones of the skeleton |
| pharynx | in planarians, the tubelike, muscular organ that extends from the mouth; aids in feeding and digestion |
| esophagus | muscular tube that connects the mouth to the stomach; moves food by peristalsis |
| peristalsis | series of involuntary smooth muscle contractions along the walls of the digestive tract that move food through the digestive tract |
| pancreas | soft, flattened gland that secretes digestive enzymes and hormones; products help break down carbohydrates, proteins and fats |
| liver | large, complex organ of the digestive system that produces many chemicals for digestion, including bile |
| endocrine glands | series of ductless glands that make up the endocrine system; release chemicals directly into the bloodstream where they relay messages to other parts of the body |
| pituitary gland | main gland of the endocrine system that controls many other endocrine glands |
| neuron | basic unit of structure and function in the nervous system; conducts impulses throughout the nervous system; composed of dendrites, a cell body and an axon |
| dendrite | branch-like extension of a neuron; transports impulses toward the cell body |
| axon | a single cytoplasmic extension of a neuron; carries impulses away from a nerve cell |
| synapse | tiny space between one neuron's axon and another neuron's dendrites over which a nerve impulse must pass |
| cerebrum | largest part of the brain, composed of two hemispheres connected by bundles of nerves; controls conscious activities, intelligence, memory, language, skeletal muscle movements, and the senses |
| cerebellum | rear portion of the brain; controls balance, posture and coordination |
| trachea | tubelike passageway for air flow that connects with two bronchi tubes that lead into the lungs |
| alveoli | sacs in the lungs where oxygen diffuses into the blood and carbon dioxide diffuses into the air |
| aorta | largest blood vessel in the body; transports oxygen-rich blood from the left ventricle of the heart to the arteries |
| plasma | fluid portion of the blood that makes up about 55% of the total volume of the blood; contains red and white blood cells |
| red blood cells | round disk-shaped cells in the blood that carry oxygen to body cells; makes up 44% of the total volume of the blood |
| hemoglobin | iron-containing protein molecule in red blood cells that binds to oxygen and carries it from the lungs to the body's cells |
| white blood cells | large, nucleated blood cells that play a major role in protecting the body from foreign substances and microscopic organisms; make up only 1% of the total volume of blood |
| platelets | small cell fragments in the blood that help blood clot after an injury |
| arteries | large thick-walled muscular vessel that carries blood away from the heart |
| capillaries | microscopic blood vessels with walls only one cell thick that allow diffusion of gases and nutrients between the blood and surrounding tissues |
| veins | large blood vessels that carry blood toward the heart |
| atria | two upper chambers of the mammalian heart through which blood enters |
| ventricles | two lower chambers of the mammalian heart; receives blood from the atria and send it to the lungs and body |
| nephron | individual filtering unit of the kidneys |
| kidney | organs of the vertebrate urinary system; remove wastes, control sodium levels of the blood and regulate blood pH levels |
| urethra | tube through which urine is passed from the urinary bladder to the outside of the body |
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