D. Hildbrand

THE BLOOD

Blood is a fluid connective tissue made up of plasma and cellular formed elements. The ratio of cells to plasma can be measured to give a haematocrit value. This is achieved by centrifuging the blood to separate plasma from blood cells. At sea level the average haematocrit value is 46%, that is 46% of the blood volume is made up of red blood cells. If, however, we climb to a high altitude, after about 3 weeks the haematocrit will rise to an average of 59.9%. The number of red blood cells increases to make it easier to transport oxygen in the "thin" atmosphere at altitude.

The volume of blood in the body varies with our body weight and averages about 79 ml per kilogram of body weight (10%). Fat tissue, however, has less blood volume, so the volume of blood per unit of body weight declines as the proportion of body fat increases.

For females the total blood volume is about 4-5 litres as opposed to 5-6 litres in males. The blood makes up about 7% of the total body weight and weighs about 5 kg It circulates around the body about 1000 times each day. This is a great deal of work for the heart to do, but it is essential work carrying oxygen and nutrients to the cells and removing potentially lethal wastes.

Blood plasma

Plasma is the pale straw-coloured fluid that makes up about 60% of the total blood volume in males and 64% in females. It is about 90% water, containing dissolved salts similar to those found in sea water. Sea water is about 3.5% salt while blood plasma is a 0.85% salt solution.

The main function of the plasma is transportation and for this reason it contains more than salts. It contains sugars (such as glucose), lipids, amino acids, vitamins and hormones. These are mostly non-protein substances and make up only 1% of the plasma. Protein materials, that give its sticky feeling to blood, make up the remaining 7-8% of the plasma. There are about 70 or so proteins in the blood but the most common are albumin, globulins and fibrinogen. These proteins serve many functions including the formation of blood clots (fibrinogen).

Words given

to contain - enthalten; dissolved - gelöst; components - Bestandteile; sodium - Natrium; potassium - Kalium; lipids - Fette (Lipide);sticky - klebrig, zäh; blood clots - Blutgerinnung

Red blood cells (erythrocytes)

The majority of the cells within the plasma are the red blood cells or erythrocytes. They give the red colour to the blood and contain the iron-containing pigment haemoglobin that transports oxygen around the body. When blood is oxygenated it is a bright red colour compared with the darker red of the deoxygenated blood.

An erythrocyte can be seen under the high-power of a microscope to be a disc-shaped cell without a nucleus, 7-8 micrometers across and 1-2 micrometers thick. There are between 5-6 million per mm³ of blood in males and 4.3-5.5 million per mm³ in females.

Red blood cells are made in the red bone marrow at a rate of 2.5 million every second. They live for about four months and then they are destroyed in the liver or spleen where the haemoglobin is broken down and the iron is removed and stored. Most of the "leftovers" from red cell destruction in the liver are re-cycled for further use.. Red blood cells are the only cells in your body that do not contain a nucleus. It is lost as the cell matures and enters the circulation.

If a person is anaemic it means they do not have enough red blood cells and/or they do not have enough haemoglobin. In healthy males there is 14-I8 g of haemoglobin per 100 cm3 of blood compared with 12-16 g in the female.

Words given

oxygen - Sauerstoff; bone marrow - Knochenmark; liver - Leber; spleen - Milz; destruction - vb. to destroy; to mature - reifen

White blood cells (leucocytes)

In contrast to red blood cells white ones lack any pigment, they have nuclei and their shapes vary considerably. They are much larger than red cells (10-15 micrometers across) and the numbers are less: there are only between 7000 and 10,000 cells per mm3. When they are stained with a biological dye the different-shaped nuclei show up clearly and the white cells can be seen to be of two main types, the granulocytes and the lymphocytes.

The granulocytes are formed in the red bone marrow and only live for a few days whereas the lymphocytes are produced in the bone marrow as well as in the lymph nodes, tonsils, and spleen. These lymphocytes are found in large quantities in the lymphatic system where they also help to defend the body against infection. They may live for several years

White blood cells can move around rather like the amoeba. They can squeeze in between cells and into blood and lymph vessels where they attack invading foreign bodies or pathogens like bacteria or viruses.

Words given

to lack - not to have; to stain - anfärben; dye - Färbemittel; tonsils - Mandeln; spleen - Milz; to squeeze in - sich hineinzwängen ; blood vessels - Blutgefäße.

Blood platelets (thrombocytes)

Platelets are not complete cells, but fragments of certain very big red bone marrow cells. As a result they have no nuclei, they are smaller than red blood cells (2-3 micrometers across) and the numbers are less: there are between 200.000 and 300.000 cells per mm3. These platelets survive for about four days only.

They contain a protein that is involved in blood clotting. The other clotting agents are found in the blood plasma. In order for blood to clot there also needs to be vitamin K available. This is made by the bacteria that live in our guts. If we take a lot of antibiotics then our gut bacteria may be killed, thus making it more difficult to clot the blood. There would then be a danger of haemorrhage. A haemorrhage is an unimpeded flow of blood resulting from a damaged blood vessel.

Words given

fragments - Bruchstücke; blood clotting - Blutgerinnung (vb. to clot); agents - Faktoren; guts - Darm; haemorrhage - Blutung(en); unimpeded - that can't be stopped; blood vessel - Blutgefäß

Complete:

The blood cells (44 %)

[Lösung]

Complete:

Blood Plasma (56 %)

1. Components

2. Function

The blood cells (44 %)