Tissue – a group of similar cells organized into a functional unit; usually integrated with other
tissues to form part of an organ.
There are only four types of tissues:
They are sheets of densely packed, tightly connected epithelial cells that cover inner and
outer body surfaces.
They act as barriers and provide transport across those barriers.
They form the skin and line the hollow organs of the body, such as the gut.
Epithelial cells have many roles in the body:
-Secreting hormones, milk, mucus, digestive enzymes, or sweat.
-Some have cilia that move substances over surfaces or through tubes.
-They can provide information to the nervous system. (e.g., smell and taste receptors
are epithelial cells that detect specific chemicals.)
-They create boundaries between the inside and the outside of the body and between
-They line the blood vessels and make up various ducts and tubules.
-Important functions of epithelial cells are filtration and transportation.
-They control what molecules and ions can leave the blood to enter the internal
environment or the urine.
-They can selectively transport ions and molecules from one side of an epithelial
membrane to the other. (e.g., the absorption of nutrient molecules from the gut and
the secretion of acid into the stomach.)
The skin and the lining of the gut are examples of epithelial tissues that receive much
wear and tear.
Consist of elongated cells that can contract to generate forces and cause movement.
The most abundant tissues in the body, and when animals are active, muscles use most of
the energy produced in the body.
There are 3 types of muscle tissues:
1.Skeletal Muscle Tissue
-They mostly attach to bones.
-Responsible for locomotion and other body movements such as facial
expressions, shivering, and breathing.
-They are under both conscious and unconscious control.
2.Cardiac Muscle Tissue
-Makes up the heart.
-Responsible for the heart beat and the pumping of blood.
-They are not under conscious control, but are controlled by physiologically