Artery compared to vein

Functions of Blood System

Transport: to and from tissue cells

• Nutrients to tissue cells: amino acids, glucose, vitamins, minerals in solution in the plasma; lipids as lipoproteins.
• Oxygen: by red blood corpuscles.
• Wastes: urea, uric acid and some CO₂ in solution in the plasma. Most CO₂ is carried in the red blood corpuscles.

Temperature Regulation: by altering the blood flow through the skin.

Immunity: protection against pathogens — blood clotting; phagocytes, lymphocytes and antibodies distributed in blood.

Communication: hormones distributed to all parts of the body in the blood.

Composition of Blood

Plasma: pale yellow sticky liquid; 55% of blood volume.

Components: water 92%, dissolved protein 8%, glucose, amino acids, vitamins, minerals, urea, uric acid, CO₂, hormones, antibodies.

Suspended Solids

Textbook Diagram: structure of suspended solids of blood.

Red Blood Cells

• Tiny biconcave disc-shaped cells.
• Do not have a nucleus.
• Do not have mitochondria.
• Their cytoplasm is rich in haemoglobin.
• O₂ binds to the iron in haemoglobin.
• Made in the bone marrow.
• Survive for about four months.
• Destroyed and recycled by the liver and spleen.

White Blood Cells (leucocytes)

• These are colourless cells and possess a nucleus.
• They function in defending the body against pathogens.
• Some ‘feed’ on pathogens by phagocytosis.
• Others produce antibodies, the specific defence proteins.
• Made by the bone marrow and lymphatic tissue.

Platelets

• These are tiny fragments of large bone marrow cells.
• They carry specialised blood clotting chemicals.
• The clotting chemicals are released where blood and lymph vessels are injured.
• A nucleus is not present in platelets.

Specialist White Blood Cells

Monocytes: largest white blood cells – engulf viruses, cancer cells, damaged and dead tissue cells.

T Lymphocytes (T cells) – made in the bone marrow, mature in the thymus.

• Helper T Cells: stimulate the multiplication of other lymphocytes.
• Killer T Cells: inject lethal chemicals into pathogenic cells.
• Suppressor T Cells: halt the immune response when the infection has been overcome.
• Memory T Cells: give immediate future protection against the same pathogen.

B Lymphocytes (B cells): specific antibody producing cells.

Blood Grouping

ABO Blood Grouping System

Four groups. The blood group depends on the presence or absence of antigen A and antigen on the surface of red blood cells.

• Group A: antigen A only.
• Group B: antigen B only.
• Group AB: antigen A and antigen B are both present.
• Group O: antigen A is not present and antigen is not present.

Rhesus Blood Grouping System

Two groups. The group depends on the presence or absence of the Rhesus-antigen.

• Rh-positive: the Rhesus-antigen is present.
• Rh-negative: the Rhesus-antigen is not present.

Blood Vessels

Textbook Diagrams: transverse sections of artery, vein and capillary.

Artery compared to vein

• The wall of the artery is thicker: thicker connective tissue layer, thicker mixed layer of muscle and elastic tissue.
• The lumen of the artery is much narrower.
• Arteries do not have valves along their length, veins do.
• Valves in the veins prevent the backflow of blood so the flow is in one correct direction towards the heart.
• Blood flows away from the heart in arteries; blood flows towards the heart in veins.
• Blood pressure in arteries is higher and so also the speed of blood flow.
• Pulse flow in an artery, steady flow in a vein.

Muscle tissue in not present in the capillaries

The muscle layer allows change in the diameter of vessels. This helps to regulate blood flow to and from the tissues in response to their requirement.

Capillaries

• The real work of the blood, exchange with tissue cells, is carried out at the capillaries.
• Capillaries are the microscopic links between arteries veins.
• The capillary wall is one cell thick and somewhat porous — ideal to allow materials to pass in and out.
• All tissue cells very close to a capillary so exchange is very efficient.
• Exchange at the capillaries is by diffusion, mass flow and active transport.
• Blood flow in capillaries is slow giving enough time for effective exchange.

Date: 2015-12-24; view: 625