BLOOD
Blood is a liquid tissue that consists of a liquid portion-the plasma-and solid components-red blood cells, white blood cells,
and platelets. The blood serves as a medium of transport for nutrients, respiratory gases, hormones, metabolic wastes,
and a few other materials. It also serves a protective function against disease, and it is involved in the regulation of body
temperature.
1. Why is blood classified as a tissue?
2. What are the parts of human blood?
3. What are the functions of blood?
RED BLOOD CELLS:
Red blood cells, or erythrocytes, are disk-shaped structures that are thinner in the idle than they are around the edges. A
mature human red blood cell has no nucleus. In babies and young children, blood cells are made within the bone marrow
(the soft tissue inside our bones) of lots of bones throughout the body. In adults, erythrocytes are formed in the red
marrow of the long bones. The main function of the red blood cells is the transport of oxygen from the lungs to the cells in
the body. To a lesser extent, they also carry CO2 from the body cells to the lungs. Red blood cells contain the respiratory
pigment hemoglobin, which greatly increases their oxygen-carrying capacity.
Anemia, one of the more common blood disorders, occurs when the level of healthy red blood cells (RBCs) in the body
becomes too low. This can lead to health problems because RBCs contain hemoglobin, which carries oxygen to the
body's tissues. Anemia can cause a variety of complications, including fatigue and stress on bodily organs. Anemia can
be caused by many things, but the three main bodily mechanisms that produce it are:
1. Excessive destruction of RBCs
2. Blood loss
3. Inadequate production of RBCs
Among many other causes, anemia can result from inherited disorders, nutritional problems (such as an iron or vitamin
deficiency), infections, some kinds of cancer, or exposure to a drug or toxin.
1. What are the functions of the red blood cells?
2. What is hemoglobin and what function does it serve?
3. Where are erythrocytes formed in children? Adults?
4. How long does the average red blood cell remain in the circulatory system?
5. How are worn-out red blood cells removed from circulation?
6. Can a mature red blood cell replicate itself? Explain.
7. What is anemia and what are some possible causes.
WHITE BLOOD CELLS:
White blood cells (also called leukocytes) are a key part of the body's system for defending itself against infection. They
can move in and out of the bloodstream to reach affected tissues. The blood contains far fewer WBCs than red cells,
although the body can increase production of WBCs to fight infection. There are several types of WBCs, and their life
spans vary from a few days to months. New cells are constantly being formed in the bone marrow.
Several different parts of blood are involved in fighting infection. White blood cells called granulocytes and lymphocytes
travel along the walls of blood vessels. They fight germs such as bacteria and viruses and may also attempt to destroy
cells that have become infected or have changed into cancer cells.
Certain types of WBCs produce antibodies, special proteins that recognize foreign materials and help the body destroy or
neutralize them. The white cell count (the number of cells in a given amount of blood) in someone with an infection often
is higher than usual because more WBCs are being produced or are entering the bloodstream to battle the infection. After
the body has been challenged by some infections, lymphocytes "remember" how to make the specific antibodies that will
quickly attack the same germ if it enters the body again.
1. Where are white blood cells produced?
2.
3. What are the functions of the white blood cells?
4. What happens to the number of white blood cells when the body has an infection?
PLATELETS
Platelets (also called thrombocytes) are tiny oval-shaped cells made in the bone marrow. They help in the clotting
process. When a blood vessel breaks, platelets rupture and release thromboplastin. Thromboplastin and calcium ions, in
the blood, changes prothrombin (inactive form of the enzyme) to thrombin (the active enzyme). The thrombin in turn,
reacts with the blood protein, fibrinogen, to form fibrin, which is an insoluble protein. Strands of fibrin form a meshwork
over the wound and trap blood cells. The clot dries out and a scab forms. Platelets survive only about 9 days in the
bloodstream and are constantly being replaced by new cells.
1. What is the function of blood platelets?
2. Where in the body are platelets formed?
3. What is the first step in the clotting process?
4. From what substance is a blood clot actually formed?
BLOOD TYPES:
There are four major types of blood. A, B, AB, and O. Blood ty0pe is determined by the presence or absence of a certain
protein called agglutinogens on the surface of red blood cells. Type A blood has A agglutinogens on the surface of the
red blood cells; type B blood has B agglutinogen; and type AB blood has both A and B agglutinogens. Type O has no
agglutinogens.
In plasma of people with types A, B, and O are proteins called agglutinins. Type A has a b agglutinin; type B has an a
agglutinin; and O has both agglutinins. Type AB blood has no agglutinins. The agglutinins react with agglutinogens of the
same blood type, causing the blood cells to clump together.
Blood type is of basic importance when it comes to transfusions. A person cannot be given blood of a type to which their
own blood has agglutinins. For example, if a person with type A blood (b agglutinins) is give B type blood, the clumping
reaction between the b agglutinins and the B agglutinogens could be fatal.
Fill in with the correct information:
Blood Type Agglutinogen Agglutinin
A
B
AB
O
Blood Type Can receive Can be given to
A
B
AB
O
1. What determines blood type?
2. Which blood type is a universal donor?
3. Which blood type is a universal recipient?