appendicular skeleton
The division of the skeletal system consisting of the bones of the paired appendages, including the pelvic and pectoral girdles to which they are attached.
axial skeleton
The division of the skeletal system that forms the central column, including the skull, vertebral column, and rib cage.
bone
A connective tissue that provides support and structure to the body and that often is the site of fat storage and blood cell production.
cardiac muscle
The type of striated muscle tissue that forms the muscles of the heart.
A fluid transport system of the body, consisting of the heart, all the blood vessels in the body, the blood that flows through these vessels, and the bone marrow tissue in which red blood cells are formed.
A connective tissue that serves as padding in most joints, forms the human larynx (voicebox) and trachea (windpipe), and links each rib to the breastbone.
Dense bone that forms the outer portion of bones, structured as a set of parallel osteons and their associated nerves and blood vessels.
connective tissue
A tissue, active in the support and protection of other tissues, whose cells are surrounded by a material that they have secreted. In humans, one of the four principal types of tissue.
dermis
In certain animals, the thick layer of the skin—composed mostly of connective tissue—that underlies, nourishes, and supports the epidermis.
The organ system that transports food into the body, secretes digestive enzymes that help break down food to allow it to be absorbed by the body, and excretes waste products. This system consists of the esophagus, stomach, and large and small intestines p
The organ system that sends signals throughout the body through use of the chemical messengers called hormones.
The outermost layer of skin in animals or the outermost cell layer in plants.
A tissue that covers surfaces exposed to an external environment. In humans, skin is an epithelial tissue, as is the lining of the digestive tract.
A gland that secretes its materials through ducts (tubes). For example, sweat glands conduct perspiration through ducts to the skin.
In skeletal muscle, a single elongated muscle cell, containing hundreds of long, thin myofibrils that run the length of the cell. In nutrition, one of the three principal classes of dietary carbohydrate, defined as a complex carbohydrate that is indigesti
An organ or group of cells that secretes one or more substances.
The maintenance of a relatively stable internal environment in living things.
A substance that, when released in one part of an organism, goes on to prompt physiological activity in another part of the organism. Both plants and animals have hormones.
The collection of cells and proteins that, in mammals, function together to kill or neutralize invading microorganisms.
The organ system that protects the body from the external environment and assists in regulation of body temperature. This system consists of the skin and associated structures, such as glands, hair, and nails.
A flexible, water-resistant protein, abundant in the outer layers of skin, that also makes up hair and fingernails.
In anatomy, a connective tissue that links one bone to another.
In humans, the transport network that collects interstitial fluid, transports it as lymph through lymphatic vessels, checks the fluid for infection, and delivers the fluid to blood vessels.
A single skeletal muscle cell; called a fiber because of its extreme length relative to most cells.
Tissue that has the ability to contract. In humans, one of the four principal types of tissue.
The organ system composed of all the skeletal muscles of the body, which is to say all muscles that are under voluntary control.
A system of control in which the product of a process reduces the activity that led to the product.
A bundle of axons in the peripheral nervous system that transmits information to or from the central nervous system.
A tissue specialized for the rapid conduction of electrical impulses. In humans, one of the four principal tissue types.
The organ system composed of all the skeletal muscles of the body, which is to say all muscles that are under voluntary control.
A system of control in which the product of a process reduces the activity that led to the product.
A bundle of axons in the peripheral nervous system that transmits information to or from the central nervous system.
A tissue specialized for the rapid conduction of electrical impulses. In humans, one of the four principal tissue types.
The organ system that monitors an animal’s internal and external environment, integrates the sensory information received, and coordinates the animal’s responses. This system consists of all the body’s neurons, plus the supporting neuroglia cells, plus th
A highly organized unit within an organism, performing one or more functions, that is formed of several kinds of tissue. Kidneys, heart, lungs, and liver are all familiar examples of organs in humans.
A group of interrelated organs and tissues that serve a particular set of functions in the body. For example, the digestive system consists of mouth, stomach, and intestines and functions in digesting food and eliminating waste.
An immature bone cell that secretes organic material that becomes bone matrix, thus producing new bone.
A type of bone cell that dissolves bone matrix, thus liberating the minerals stored in it.
Mature bone cell that maintains the structure and density of bone by continually recycling calcium compounds around itself.
The study of the physical functioning of animals and plants.
The blood cells, also known as erythrocytes, that transport oxygen to and carry carbon dioxide from every part of the body.
A tissue, found in cavities of bones in the human body, within which all of the adult body’s blood cells are produced.
In humans, the organ system that develops gametes and delivers them to a location where they can fuse with other gametes to produce a new individual.
The functional unit of a striated muscle that contracts when thin filaments slide past thick filaments. The sarcomeres shorten, thus contracting the whole muscle.
A type of gland in the skin that produces a waxy, oily secretion (sebum) that lubricates the hair shaft and inhibits bacterial growth in the surrounding area.
In humans, muscle that is attached to bone, that is under conscious control, and that microscopically has a striped or “striated” appearance owing to the parallel orientation of the long, fibrous units that make it up.
The human organ system that forms an internal supporting framework for the body and protects delicate tissues and organs. This system consists of all the bones and cartilages in the body and the connective tissues and ligaments that connect the bones at t
In humans, an organ consisting of two tissue layers, an outer epidermis and inner dermis, and covering the outside of the body. The skin protects the body and receives signals from the environment.
In humans, muscle that is not under voluntary control and that lacks a striated appearance. Smooth muscle is responsible for contractions of the uterus, digestive tract, blood vessels, and passageways of the lungs.
Type of bone that is porous and less dense than compact bone. Spongy bone fills the expanded ends of long bones.
An organ that performs digestion and that serves as a temporary, expandable storage site for food.
In humans, a type of duct-containing (exocrine) gland that produces perspiration.
The connective tissue that attaches a skeletal muscle to a bone.
An organized assemblage of similar cells that serves a common function. Nervous, epithelial, and muscle tissue are some familiar examples.
A flexible column of bones extending from the anterior to posterior end of an animal. Also known as a backbone, the vertebral column distinguishes vertebrates from other chordates.
In human beings, a tissue largely made up of energy-storing fat cells found in the marrow cavity of long bones.