The Circulatory System

Question 1

What is the composition of blood?

Answer 1

Plasma: the liquid part, making up approximately 55% of the blood volume.

Formed Elements: the non-liquid part, making up 45% of the blood volume and consisting of erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets).

Question 2

What is plasma?

Answer 2

A mixture of water with dissolved substances such as sugar and salts. Plasma transports the components of the blood, including nutrients, wastes, hormones, proteins and antibodies, throughout the body.

Question 3

What are erythrocytes?

Answer 3

One of the formed elements of the blood containing haemoglobin-

• Account for 40-45% of the volume of blood, (haematocrit).
• Biconcave shape.
• Do not contain a nucleus which increases their flexibility and, hence, their ability to move blood through blood vessels.
• Life span of 120 days on average.
• Function is the transport oxygen from the lungs to the cells throughout the body.

Question 4

What is the haematocrit?

Answer 4

The ratio of red blood cells to the total volume of blood.

Question 5

What are leucocytes?

Answer 5

One of the blood cells; it contains a nucleus, but no haemoglobin. They play an important role in protecting the body from infection. They make up 1% of the blood and are larger than erythrocytes.

Question 6

Neutrophils.

Answer 6

Contain enzymes to digest pathogens.

Question 7

Monocytes.

Answer 7

Form other cells, including macrophages that engulf pathogens and aged or damaged cells by phagocytosis.

Question 8

Lymphocytes

Answer 8

Are involved in the immune repose.

Question 9

Basophils.

Answer 9

Are responsible for allergic reactions, producing heparin and histamine to defend the body against parasites and bacteria.

Question 10

Eosinophils.

Answer 10

Also lead to inflammatory responses; they respond to larger parasites such as worms.

Question 11

What are thrombocytes?

Answer 11

One of the formed elements of blood; a fragment of cytoplasm enclosed in a membrane but lacking a nucleus; also called a platelet. When a blood vessel is injured, the platelets adhere to the lining and form a scaffold for the coagulation of blood to form a clot.

Question 12

How is oxygen carried in the blood (percentages)?

Answer 12

3% of oxygen is carried in the blood plasma.

97% is carried in combination with haemoglobin molecules, only found in red blood cells.

Question 13

How is oxygen transported in the blood?

Answer 13

Oxygen combines with haemoglobin when the oxygen concentration is relatively high. This occurs in the capillaries in the lungs, where oxygen diffuses from the air in the alveoli. Oxyhaemoglobin breaks down to haemoglobin and oxygen when the concentration of oxygen is relatively low. As the cells of the body are continually using oxygen, tissue fluids around the cells have a relatively low oxygen concentration. Therefore, when the red blood cells flow through the capillaries between the body cells, they give up their oxygen, which diffuses into the tissue fluid and then into the cells.

Question 14

Why are red blood cells well suited to their function of oxygen transport?

Answer 14

• Contain haemoglobin, which is able to combine with oxygen.
• Have no nucleus, so there is more room for haemoglobin molecules.
• Are shaped like biconcave discs- the biconcave centre increases the surface area for oxygen exchange and the thicker edges give a large volume that allows room for the haemoglobin molecules.

Question 15

How is carbon dioxide carried in the blood (percentages)?

Answer 15

Approximately 7-8% is dissolved in the plasma and carried in solution.

Another 22% or so combines with the globin part of the haemoglobin molecule to form a compound called carbaminohaemoglobin.

The remainder, about 70%, is carried in the plasma as bicarbonate ions, HCO3-.

Question 16

How is carbon dioxide transported in the blood?

Answer 16

As the blood is flowing through the capillaries between the body cells, carbon dioxide diffuses into the plasma due to the difference in carbon dioxide concentration. Some carbon dioxide dissolves in the plasma, some combines with haemoglobin, but most reacts with water to form carbonic acids (H2CO3). Carbonic acid then ionises into hydrogen ions and bicarbonate ions.

In the alveoli, the carbon dioxide dissolved in the plasma diffuses out of the blood into the air in the alveolus. The carbaminohaemoglobin breaks down, and the carbon dioxide molecules released also diffuse into the alveolus. Hydrogen ions and bicarbonate ions recombine to form carbonic acid, which then breaks down under enzyme action into water and carbon dioxide. This carbon dioxide also diffuses into the alveolus.

Question 17

Explain how nutrients and wastes are transported in the blood.

Answer 17

Nutrients and wastes are dissolved and transported in the blood plasma.

Nutrients (the essential elements and molecules that are obtained from the food we eat) include:

• Inorganic nutrients (transported as ions)- sodium ions, calcium ions, potassium ion, chloride ions and iodide ions.
• Organic: glucose, vitamins, amino acids, fatty acids and glycerol.

Metabolic wastes are substances produced by the cells that cannot be used and that would be harmful if allowed to accumulate.
Organic wastes that are transported in solution in blood plasma- urea, creatinine and uric acid.

Question 18

Blood clotting minimises blood loss from broken vessels and prevents the entry of micro-organisms. List the steps of blood clotting.

Answer 18

1- Vasoconstriction.
2- Platelet plug.
3- Coagulation.

Question 19

Explain vasoconstriction.

Answer 19

The muscles in the walls of the small arteries that have been injured or broken constrict immediately to reduce blood flow and therefore, blood loss.

Question 20

Explain the platelet plug.

Answer 20

Damage to internal walls of blood vessels create a rough surface to which platelets ‘stick’.

Sticking platelets attract others so a ‘plug’ is built at the injury site to prevent blood loss.

The platelets release substances that act as vasoconstrictors, which enhance and prolong the constriction of the damages vessels.

Question 21

Explain coagulation.

Answer 21

For more serious injuries. Coagulation is the process of blood becoming gel-like, forming a blood clot.

This process involves a large number of clotting factors, that are present in blood plasma. The complex series of reactions results in the formation of threads and an insoluble protein called fibrin. The fibrin forms a mesh that traps blood cells, platelets, and plasma. This is the blood clot. The treads stick to the damaged blood vessel and hold the clot in position.

Question 22

Explain clot retraction.

Answer 22

Clot retraction is the contraction of the fibrous threads of a blood clot. As this occurs, a fluid known as serum is squeezed out. The clot then dries, forming a scar over the wound that prevents the entry of infecting microorganisms.

Question 23

What is the heart?

Answer 23

The pump that pushes blood around the body, located between the two lungs in the mediastinum, behind and slightly left of the sternum.

Question 24

What is the name of the membrane which encloses the heart.

Answer 24

The pericardium is the membrane that encloses the heart. It holds the heart in place, but also allows the heart to move as it beats and prevents in from stretching.

Question 25

What is the wall of the heart made up of?

Answer 25

Cardiac muscle.

Question 26

What is the name of the wall that separates the left and right sides of the heart?

Answer 26

The septum.

Question 27

Where does the blood come from that goes into each side of the heart?

Answer 27

The right side of the heart collects blood from the body and pumps it to the lungs. The left side of the heart receives blood from the lungs and pumps it to the rest of the body.

Question 28

List the four chambers of the heart.

Answer 28

The right atrium receives blood from the body and passes it to the right ventricle. The right ventricle pumps blood to the lungs. The left atrium receives blood from the lungs and passes it to the left ventricle. The left ventricle pumps blood to the body.

Question 29

What is the purpose of valves in the heart?

Answer 29

They ensure that blood can only flow in one direction, preventing the back flow of blood.

Question 30

What are the atrioventricular valves?

Answer 30

Valves that ensure the blood flows through the heart in one direction only. Location: Between the atria and the ventricles. Structure: Flaps of thin tissue with the edges held by tendons (chordae tendineae), that attach to the heart on papillary muscles. Function: When the ventricles contract, the blood catches behind the flaps and they billow out like a parachute, sealing off the opening between the atria and the ventricles. Blood must then leave the heart through the arteries and not flow back into the atria.

Question 31

What are semilunar valves?

Answer 31

Vales preventing blood from flowing back into the ventricles. Location: At the start of the aorta and pulmonary vein.. Structure: each valve has three cusps. Function: When the blood flows into the artery, the cusps are pressed flat against the artery wall. When the blood tries to flow back into the ventricle, the cusps fill out and seal off the artery, ensuring blood only flows in one direction.

Question 32

What creates the 'lub-dub' sound of the heart?

Answer 32

It is the closing of the valves that gives the heartbeats their characteristic ‘lub-dub’ sound. The two sounds are due to the closing of the atrioventricular and then semilunar valve.

Question 33

What is the name of the atrioventricular valve located between the right atrium and the right ventricle?

Answer 33

The tricuspid valve.

Question 34

What is the name of the atrioventricular valve located between the left atrium and the left ventricle?

Answer 34

The mitral valve.

Question 35

What is the name of the semilunar valve located between the right ventricle and the pulmonary artery?

Answer 35

The pulmonary valve.

Question 36

What is the name of the semilunar valve located between the left ventricle and the aorta?

Answer 36

The aortic valve.

Question 37

What are arteries?

Answer 37

Blood vessels that carry blood away from the heart. Structure: The wall of an artery contains smooth muscle and elastic fibres. Have thick, muscular, elastic walls. Have no valves. Function: When the ventricles contract and push blood into the arteries, the arteries stretch to accommodate the extra blood. When the ventricles relax, the elastic artery walls recoil. This recoil keeps the blood moving and maintains blood pressure. The very large arteries that receive blood pumped by the ventricles divide into smaller arteries. These in turn divide into very small arteries known as arterioles.

Question 38

Define vasoconstriction:

Answer 38

The muscles of the artery wall contract, decreasing the diameter of blood vessels and restricting the flow of blood.

Question 39

Define vasodilation:

Answer 39

The muscles of the artery wall relax, increasing the diameter of the blood vessels and increasing blood flow.

Question 40

How are the cells of the body supplied with the energy they need during exercise?

Answer 40

As the body exercises, the muscle cells continually require energy. Cellular respiration in the muscle cells make this energy available but also produces large amounts of wastes, including CO2 and lactic acid. These wastes act as vasodilators, resulting in increased blood flow through the muscle tissues which ensures that the cells are adequately supplied with oxygen and nutrients for continued functioning.

Question 41

What are capillaries?

Answer 41

Microscopic blood vessels that link the arterioles and venues. Structure: Their walls have only one layer of cells, allowing substances to pass early between the blood and the surrounding cells. Function: They form a network to carry blood close to nearly every cell in the body. This enables cells to get their requirements from the blood and to pass their waste into the blood.

Question 42

What are veins?

Answer 42

Blood vessels that carry blood towards the heart. Structure: The capillaries join into small veins (venules), which then join to make larger veins. Have thin, relatively inelastic walls with little muscle. Often have valves. Have a constant relatively low blood pressure.

Question 43

Where do veins culminate?

Answer 43

1. The inferior and superior vena cava: bring blood from the body to the right atrium. Superior brings blood from above the heart and inferior brings blood from below. 2. Pulmonary veins: bring blood from the lungs to the left atrium. There are four pulmonary veins, two in each lung.

Question 44

What are the two ways the blood flow to the cells can be changed to cater for the changes in cell requirements?

Answer 44

1. By changing the output of blood from the heart. | 2. By changing the diameter of the blood vessels supplying the tissues.

Question 45

What is the cardiac cycle?

Answer 45

The cycle of events that occurs in one complete heart beat.

Question 46

Define systole.

Answer 46

The period when the heart muscles contract.

Question 47

Define diastole.

Answer 47

The period of relaxation of the heart (between contractions), during which it fills with blood.

Question 48

Explain the cardiac cycle.

Answer 48

1. For a short period of time both atria and ventricles are in diastole. - The atria fills with blood. - The ventricles also receive blood as the valves between them are open. 2. Atria systol: forces the remaining blood into the ventricles. 3. Atria relax and refill while the ventricles contract in ventricular systole. 4. Ventricular systole forces blood into the arteries.

Question 49

Define heart rate.

Answer 49

The number of heartbeats per minute.

Question 50

Define stroke volume.

Answer 50

The volume of blood pumped from the left ventricle during one contraction.

Question 51

Define cardiac output.

Answer 51

The volume of blood pumped from one ventricle of the heart in one minute.

Question 52

What is cardiac output equal to?

Answer 52

Cardiac output (mL/ minute)= stroke volume (mL) x heart rate (beats/ minute).

Question 53

Define transfusion.

Answer 53

The transfer of blood, or of some of the components of blood, into the circulation of a person.

Question 54

Define ABO blood group system.

Answer 54

A method of classifying blood types according to the antigens on the surface of the red blood cells.

Question 55

Define Rh blood group system.

Answer 55

A method of classifying blood types according to the antigens on the surface of the red blood cells.

Question 56

Define antigens.

Answer 56

Any substance capable of causing the formation of antibodies when introduced to the tissue.

Question 57

Define antibodies.

Answer 57

A substance produced in response to a specific antigen; it combines with the antigen to neutralise it or destroy it.

Question 58

What are the two sugar antigens involved in the ABO classification?

Answer 58

Antigen A and antigen B. A person may have A, B, both, or neither. These correspond to the four blood groups of the ABO system: - Group A (antigen A). - Group B (antigen B). - Group AB (both antigens). - Group O (neither antigens).

Question 59

What is the name of the antibody that reacts against antigen A and the name of the antibody that reacts against antigen B?

Answer 59

Antigen A: anti-A. | Antigen B: anti-B.

Question 60

What are the antibodies that each blood group produces?

Answer 60

- A group A person can only produce anti-B. - A group B person can only produce anti-A - A group AB person cannot produce either. - A group O person can produce both.

Question 61

What are the Rh antigens?

Answer 61

Proteins occurring on the surface of the red blood cells.

Question 62

List the Rh groups.

Answer 62

A person with Rh antigens is said to be Rh positive; a person without these antigens in Rh negative. An individual without the Rh antigens is able to produce an anti-Rh antibody that reacts against those antigens. Rh-positive individuals cannot produce an anti-Rh antibody.

Question 63

Why is it important to match the blood groups of the donor and the recipient during transfusions?

Answer 63

The mixing of blood types that are incompatible can cause the erythrocytes to clump together, or agglutinate. Agglutinate: The clumping together of micro-organisms or of red blood cells. If the receiver’s blood contains, or is able to make, antibodies against the antigens on the donor’s red cells, the foreign cells will clump together and disintegrate.

Question 64

What is a whole blood transfusion.

Answer 64

Is blood as it is taken from the donor but with a chemical added to prevent clotting. Used mainly in cases of severe blood loss.

Question 65

What does a red cell concentrate transfusion involve?

Answer 65

Produced by spinning blood at very high speed in a centrifuge. The heavier cells sink to the bottom, leaving the lighter plasma on top. The concentrate may or may not have platelets and leucocytes removed. Used for patients suffering from heart disease or severe anaemia.

Question 66

What does a platelet concentrate transfusion involve?

Answer 66

Given to patients who have abnormal platelets or a reduced number of platelets.

Question 67

What does a plasma transfusion involve?

Answer 67

Plasma may be given to patients requiring extra clotting factors for control of severe bleeding, or patients with liver disease.

Question 68

What does a cryoprecipitate transfusion involve?

Answer 68

Obtained by freezing the plasma and thawing it slowly. When the plasms is thawed, the cryoprecipitate remains solid. It contains many of the substances necessary for blood clotting. Used to treat some forms of haemophilia but is most often used for severe bleeding.

Question 69

What does an immunoglobin transfusion involve?

Answer 69

are a group of proteins that act as antibodies. They are extracted from the blood and used for patients who are deficient in antibodies. Particular immunoglobins from certain donors are used to treat patients who have no immunity to a particular disease. For example, tetanus immunoglobulin may be used to treat tetanus.

Question 70

What does an autologous transfusion involve?

Answer 70

When the own patient’s blood is used. The blood is collected from the patients prior to an operation that may require a transfusion. Often used for elective surgery and the blood is collected about four weeks before the operation. Autologous transfusions eliminate the risk of transmission of disease and most possible side effects of the usual transfusions.

Question 71

What is the lymphatic system?

Answer 71

A system of vessels that drains excess fluid from the tissues.

Question 72

What are the functions of the lymphatic system?

Answer 72

To collect some of the fluid that escapes the blood capillaries and return it to the circulatory system. The lymphatic system is also an important part body’s internal defence against disease-causing organisms.

Question 73

What is the structure of the lymphatic system?

Answer 73

A network of lymph capillaries joined to larger lymph vessels. Lymph nodes, which are located along the length of some lymph vessels.

Question 74

Why does fluid tend to leak out at the arterial end of a blood capillary?

Answer 74

Due to the high pressure in the vessel.

Question 75

What happens to the fluid that leaks from the capillaries?

Answer 75

Some, but not all, of this fluid returns to the capillary at the venous end. The excess fluid in the tissues is returned to the blood by the lymphatic system. Fluid returned to the blood in this way is known as lymph.

Question 76

What is lymph?

Answer 76

Colourless fluid that circulates through the lymphatic vessels before returning to the blood.

Question 77

Explain the structure of lymph vessels.

Answer 77

- Blind-ended tubes in the spaces between the cells of most tissues. - Have smooth muscle, skeletal muscle, and valves. - Slightly larger and more permeable than blood capillaries. - Proteins and disease-causing organisms in the intercellular fluid can easily pass through the walls of the lymph capillaries into the lymph. - The network of lymph vessels joins to form two lymphatic ducts that empty the lymph into large veins in the upper chest.

Question 78

How is lymph moved through the lymphatic vessels?

Answer 78

Smooth muscle, skeletal muscle, and valves. The smooth muscle layer of the vessels is able to contract to push the lymph along the vessel. The skeletal muscles surrounding the vessels are also able to contract, providing additional force. - No central pump, so there is no force driving the direction of the flow of lymph. Therefore, the larger lymph vessels have valves that close when the pressure drops, preventing the backflow of lymph.

Question 79

What are lymph nodes?

Answer 79

An oval or bean-shaped structure found on the lymphatic vessels; it is involved in protection against infection. They occur at intervals along the lymphatic system.

Question 80

Structure of lymph nodes?

Answer 80

Each is surrounded by a capsule of connective tissue that extends into the node, forming a framework. - Within the framework are masses of lymphoid tissue, containing lymphocytes, macrophages, and plasma cells. - Spaces between the cells of the lymphoid tissue are criss-crossed by a network of fibres.

Question 81

How does lymph travel through the lymphatic system?

Answer 81

Lymph enters through vessels on the convex side of the node, filters through the spaces and passes out through vessels on the opposite side. The lymph passes through several nodes before entering the circulatory system.

Question 82

How does the lymphatic system defend against disease in the human body?

Answer 82

Lymph entering the lymph nodes contains cell debris, foreign particles and micro-organisms that have penetrated the body’s external defences. Some of these micro-organisms may be able to cause disease and must therefore be destroyed. Larger particles, such as bacteria are trapped in the meshwork of fibres as lymph flows through the spaces in the nodes. Macrophages destroy these particles. The macrophages ingest the particles by phagocytosis. Projections from the macrophage surround the particle and take it into the cell, where it is destroyed by enzymes.

Question 83

Why do lymph nodes swell during infection?

Answer 83

When infections occur, the formation of lymphocytes increases, causing the lymph nodes to become swollen and sore. For example, an infected finger may result in swelling and tenderness in the armpit, where there are a large number of lymph nodes.