Unit 4: The circulatory and excretory systems                       1   2   3   4

2.1. The blood

Blood is a viscous, red and salad liquid which flows within blood vessels.

An adult human has about 5 litres of blood, although it depends on weight, height, age and sex.

a. Functions of blood

- Transportation: The blood carries many different substances around

   the body. These include:

- Nutrients (glucose, amino acids, vitamins, minerals and oxygen)

- Waste products (water, urea and carbon dioxide)

- Hormones

- Maintaining Homeostasis:

- Immunity and defence: White blood cells fight infection and platelets help

   to repair damage and clot the blood.

- Distribution of heat and force.

b. Composition of blood

Blood is a liquid tissue. It is formed by a liquid part called plasma in which are immersed the cellular components: blood cells.

-  Plasma (55 % blood volume). It is a yellowish liquid formed by

   water (90 %), immersed substances (proteins, lipids, glucose) and

   dissolved substances (ions and gases).

      - Blood cells (45 % blood volume). There are three types of cellular

     components:

- Red blood cells (erythrocytes).

   They are little and biconcave cells (disc-shape) without nucleus.

   They are very elastic and deformable.

   They are rich in a protein called haemoglobin. Haemoglobin contains iron and

   its function is to transport oxygen (It oxidises when blood pass through

   alveoli).

   A healthy person has about 5.10⁶ erythrocytes / mm³ of blood.

- White blood cells (leukocytes).

   They are true cells, with nucleus (with variable shape).

   They are the least numerous of cellular blood components

   (5000-9000 leukocytes / mm³ of blood).

   There are two groups of leukocytes, but all of them participate in defending

   of the organism:

- Granulocytes (with granules in the cytoplasm)

     - Neutrophils

     - Eosinophils

     - Basophiles.

- Agranulocytes (without granules in the cytoplasm)

  They are the most important ones.

     - Lymphocytes produce antibodies.

     - Monocytes (macrophages) digest microorganisms. 

- Platelets (thrombocytes)

   They are not true cells, but fragments of cells.

   There are between 150.000 and 300.000 thrombocytes / mm³ of blood.

   Their function is blood coagulation (clotting)

Video: What is blood (AmericasBlood.org)

2.1. Make a double entry chart which allows you to compare the

        characteristics of the cellular components of blood:

        cellular characteristics (shape, size, contain, etc), amount,  

        types (if there would be any) and function.

2.2. Are red blood cells true cells? Why?

2.3. People who live at high altitude have more erythrocytes. Why?

2.4. Listen and indicate what type of blood cell is described:

2.5. The following pictures represent the steps in the formation of a clot.

         Listen, identify each one and put them in the correct order.