SPECIALIZED CELLS OF THE HUMAN BODY

Specialized Cells are needed because:

1. Surface area of Cells limits the growth potential of any single cell.2.As organisms increase in size, there is a need for special- ized transport functions.3. Specialized cells enable an organism to adapt to different environments and have different capabilities.

Organs of the body are composedof four types of tissue:

Epithelial Tissue protects all internal and external surfaces with one or more layers of cells.

Connective Tissue is the most widely distributed throughout the body.It supports and connects other tissues. There are a few cells imbedded in a thick, non-living matrix.

Muscle Tissue has the ability to contract and thereby produce move-ment.

Nervous Tissue can transmit messages throughout the body, providinginformation about the environment and controlling bodyfunctions.

In an average healthy person, approximately 45 percent of the blood volume is cells, among them red cells (the majority), white cells, and platelets. A clear, yellowish fluid called plasma makes up the rest of blood. Plasma, 95 percent of which is water, also contains nutrients such

as glucose, fats, proteins, and the amino acids needed for protein synthesis, vitamins, and minerals. The level of salt in plasma is about equal to that of sea water. The test tube on the right has been centrifuged to separate plasma and packed cells by density.

BLOOD CELLS

Erythrocytes, or red blood cells, are the primary carriers of oxygen to the cells and tissues of the body. The biconcave shape of the erythrocyte is an adaptation for maximizing the surface area across which oxygen is exchanged for carbon dioxide. Its shape and flexible plasma membrane allow the erythrocyte to penetrate the smallest of capillaries.

A mutation in the gene responsible for producing hemoglobin in the blood causes a disease known as sickle-cell anemia. In this disease the structure of the oxygen-carrying protein in the human bloodstream is severely altered. The mutation changes the structure of red blood cells to a slender sickle shape.

Scanning electron micrograph of a normal T lymphocyte. Lymphocytes are specialized white blood cells whose function is to identify and destroy invading organisms such as bacteria and viruses. Some T lymphocytes directly destroy invading organisms, whereas other T lymphocytes regulate the immune system by directing immune responses.

Thrombocytes, or platelets, are the smallest cellular component of blood. They circulate inactivated, about 250,000 per cubic mm of blood, until they come into contact with a damaged blood vessel. At this point, the platelets form a clump, adhering to each other and to the blood vessel wall. They secrete chemicals that alter a blood-borne protein,

fibrinogen, so that it forms a mesh of fibers at the damage site. A clot forms when platelets and red and white blood cells become trapped in the fibers. Blood clotting begins within seconds of injury. The same process can produce unwelcome clots in undamaged blood vessels.

MUSCLE CELLSHuman smooth muscle, also referred to as visceral or involuntary muscle,

is composed of slender, spindle-shaped cells. Controlled by the autonomic

nervous system, smooth

muscle cells help form

the structure of the skin,

blood vessels, and

internal organs.

Cardiac muscle is a unique muscle tissue found only in the heart. Requiring a constant supply of oxygen, cardiac muscle will quickly die if obstructions occur in the arteries leading to the heart. Heart attacks occur from the damage caused by insufficient blood supply to cardiac muscle.

This photomicrograph shows a number of multipolar nerve cells. The central cell body is clearly visible in each of the cells, as are the dendrites. The dendrites are short extensions of the nerve cell body that function in the reception of stimuli.

NERVE

CELLS

CELLS THAT AID THE CIRCULATORY SYSTEM

White spots are fat cells, dark spots are blood manufacturing cells found in marrow.

This shows a capillary in between muscle fibers (the large pink objects). In the capillary, three red blood cells can be seen.

This picture shows a capillary in the very center, surrounded by a single layer of muscle cells.

STRUCTURAL SYSTEM

Cartilage Cells with fibers

In the middle of this picture is bone. On the left are marrow cells, on the right are muscle cells which attach to the bone.

SKIN CELLS

Cross section of thick skin, showing different kinds of skin cells and a sweat gland.

How is thick skin different from thin skin?

Why are they different?

Thin skin cross-section showing different kinds of skin cells and a sweat gland.

This shows the very outer layer of skin cells, with their melanin, which gives skin its color and protection from the sun.

ORGAN CELLSSpleen cross-section. The white areas are where arterial blood flows through.the dark spots are lymph type cells.

CELLS IN THE RESPIRATORY TRACT

This shows the different cells in the trachea (breathing passages). In the upper left is the airway. The dark, solid, layer next to it is mucus. Underneath that layer are the specialized cells that exchange gasses... oxygen and carbon dioxide. There is a layer,

outlined in pink, of cartilage tissue which supports the exchanging cells.

This shows the trachea again at higher magnification. The bottom third or so is the supporting cartilige. Above it is a blood vessel with red blood cells in it, which transport oxygen and carbon dioxide to and from the lungs. Above the vessel is a layer of cells which go up and down. These are the specialized skin cells which do the exchanging. They are covered by mucus.

This is an even closer look at the surface of the trachea. Little foreign objects (dust, tobacco smoke....) are caught in the mucus and will be moved out of the way by special cells called cilia that look like little hairs. If they can’t move it enough, you might cough.

DIGESTIVE TRACT CELLSHere we see cells from the colon, that aid in the digestion of food.

This picture shows cells at the junction of the esophagus (to the left) with the upper part of the stomach (right). Why are they different? What different conditions do they encounter? What different jobs must they perform?

Here we see stomach cells with a thin layer of muscle cells to support them.

This picture shows villi (at the top) that are within the duodenum (intestinal tract).

MUSCLE CELLS

These are smooth muscle fibers (from involuntary muscles).

More smooth muscle fiber cells, with their nuclei visible.

These are smooth muscle fibers that are wrinkled, along with their nuclei that have also “wrinkled” because they have contracted. Muscles contract to do their work.

These are muscle fibers from skeletal muscles (under voluntary control). See how different they are from involuntary muscle fibers. There are dark spots at the edge of the cells because that is where the nucleii are. The lines going across are striations within the muscle fiber cells.

Here are muscle fibers from the heart, a third kind of muscle tissue.

There are capillaries running horizontally that contain red blood cells.