HUMAN BIOLOGY

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What is your “Blood IQ”? To find out how much you know about blood and public blood

supplies, visit http://www.nhlbi.nih.gov, the website of the National Heart, Lung, and Blood Institute,

and take the Blood IQ test. The website offers information about blood, blood donation, and even

current research on blood substitutes and other topics.

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toxins can poison the blood

Some bacteria release toxins into the blood, a condition

called septicemia. An example is Staphylococcus aureus

or “Staph A” pictured in Section 1.8. It lives harmlessly in

some people but in others it produces enzymes that destroy

red blood cells and prevent blood clotting. Some strains

are now highly resistant to antibiotics. One of these, MRSA

(for methicillin-resistant staph A), is common in health care

facilities, including hospitals (Figure 8.12). In some cases

MRSA simply colonizes the infected person’s body and

periodically causes an abscess to develop on the skin. In the

worst cases, however, the infection causes death.

Metabolic poisons in the body cause toxemia. For

example, the kidneys normally remove many toxic wastes

from blood. In someone whose kidneys don’t function well

due to disease or some other cause, the buildup of certain

wastes prevents the normal replacement of red blood cells.

It also prevents platelets from functioning. Thus anemia

develops and the person’s blood doesn’t clot properly.

summary

section 8.1 Blood consists of watery

plasma, red and white blood cells, and cell

fragments called platelets. In addition to

blood cells and platelets, plasma transports

proteins, simple sugars, amino acids, mineral

ions, vitamins, hormones, and oxygen and

carbon dioxide gases that are dissolved in

plasma water.

Stem cells in bone marrow give rise to red blood cells

(erythrocytes), white blood cells (leukocytes), and platelets.

Red blood cells carry oxygen and some carbon dioxide.

White blood cells are involved in body defenses and debris

removal. One subgroup (granulocytes) includes neutrophils,

basophils, and eosinophils. Another group (agranulocytes)

includes lymphocytes and monocytes, which develop into

macrophages that scavenge debris and cleanse tissues of

foreign material. Lymphocytes destroy specific microbes and

other agents of disease. Platelets produce substances that

initiate blood clotting.

section 8.2 Red blood cells contain

hemoglobin, an iron-containing protein

that binds reversibly with oxygen, forming

oxyhemoglobin. Hemoglobin in red blood

cells also carries some carbon dioxide to the

lungs to be exhaled.

section 8.3 Red blood cells live for

about 120 days. A cell count measures the

number of them in a microliter of blood.

Macrophages remove dead or damaged

red blood cells while stem cells provide

replacements.

sections 8.4, 8.5 Blood type is deter-

mined by proteins on the surface of red blood

cells. The four main human blood types are

A, B, AB, and O. Agglutination is a defense

response activated when a person’s blood

mixes with an incompatible type. Rh blood

typing determines the presence or absence of

Rh factors ( 1 or 2 ) on red blood cells.

section 8.7 Mechanisms of hemostasis

slow or stop bleeding. These events include

spasms that constrict blood vessels, the

formation of platelet plugs, and blood

clotting.

reVieW Questions

1. What is blood plasma, and what is its function?


2. What are the cellular components of blood? Where do the
   various kinds come from?

Figure 8.12 A microbiologist examines a lab culture of

MRSA bacteria.

Science Source

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