Circulation and Blood Answer Key

Blood Vessels

1.(a) To carry blood from the heart and to maintain blood pressure.

(b) To return blood to the heart.

(c) To provide an area for exchange of materials between blood and the tissues. Also to provide a means of controlling blood flow to and from a given region of the body. The entire capillary bed provides the resistance necessary to maintain high arterial blood pressure.

2. (a) The thick and elastic walls of the arteries enables these blood vessels to withstand and distribute the high pulse pressure resulting from the blood pumped into them by the

ventricles of the heart during systole.

(b) With walls much thinner than those of the arteries and provided with valves to prevent back-flow, the veins carry blood at relatively low pressure towards the heart. The valves ensure a one-way flow towards the heart. The large lumen of the veins decreases surface area (and therefore resistance to blood flow).

(c) With walls only one cell thick, the capillaries provide an ideal "market place. for the exchange between the blood and the tissues of materials such as water, hormones, nutrients, gases, and waste products. Capillary sphincters also provide for regulation of blood flow to/from a given region as well as control of blood pressure.

3. Essentially they are one-way valves so constructed as to open with the flow of blood towards the heart; if blood tries to go "backwards" the valves will close.

4. Instructional information.

5. Instructional information.


1. The Pulmonary System: The so called "lesser circulation" carries blood from the heart to the lungs for oxygenation and oxygenated blood back to the heart.

The Systemic System: The so-called "greater circulation" carries oxygenated blood from the heart to the "body" and deoxygenated blood from the "body" back to the heart.

2. A portal system is a pathway involving the passage of blood directly from one organ or region to another organ or region by a vein which does not lead to the heart (rather than via an artery).

3. The aorta or the coronary artery



4. Left ventricle ---> aortic valve ---> aorta ---> mesenteric artery ---> intestines ---> hepatic portal vein ---> liver ---> hepatic vein ---> posterior vena cave ---> right atrium ---> tricuspid valve ---> right ventricle---> pulmonary valve ---> pulmonary trunk ---> pulmonary arteries ---> lungs ---> pulmonary veins ---> left atrium ---> mitral (bicuspid) valve ---> left ventricle

Fetal Circulation

1. Ductus venosus

(a) To carry oxygen-rich blood from the placenta via the umblilical vein and direct this blood into the embryonic inferior vena cave.

(b) Towards the embryonic heart.

(c) The embryonic inferior (posterior) vena cave.

(d) Blood with a high oxygen content.

Ductus arteriosus

(a) From the pulmonary artery into the aorta.

(b) The blood has a high oxygen content, but not as high as the ductus venosus.

Foramen ovale

(a) To divert oxygen-rich blood around and thus by-passing the non-functional embryonic lungs.

Umbilical arteries

(a) From right and left illiac arteries running to the placenta.

(b) Carries deoxygenated blood from the fetus to the placenta.

Umbilical vein

(a) From the placenta to the fetal inferior (posterior) vena cave through the ductus venosus.

(b) Carries oxygenated blood from the mother to the fetus.




10. (a) The foremen ovale closes due to increased pressure in the pulmonary circuit after the first breath as the lungs inflate; i.e., pressure in the right and left atrium equalizes.

(b) The ductus venosus closes as blood flow from the umbilical vein ceases.

(c) The ductus arteriosus closes as the resistance to blood in the lungs decreases.

(d) The umbilical veins and arteries close and atrophy as blood flow from the placenta ceases; form the navel.

(e) With the closure of the foremen ovale after birth, the blood flowing through the right side of the heart is now completely separated from blood flowing through the left side of the heart.

The Lymphatic System

1. i. Removal of excess fluid from the tissues for retum to the blood vascular system, thus preventing edema.

ii. In lymph nodes, to produce lymphocytes to assist in fighting infection.

iii. In the villi to absorb fats from the small intestine lacteals.

2. (a) To collect excess fluids (plasma) from the tissues.

(b) To conduct the excess fluid from the lymph capillaries and ultimately return it to the blood circulatory system.

(c) To absorb digested fatty acids from the small intestine.

(d) To produce Iymphocytes, a type of white blood cell which help to fight infection.

(e) To ensure a one-way flow of lymph (towards the thoracic duct).

3. Because, lymph veins, and the larger lymph vessels have valves, and lymph can therefore flow in only one direction.

4. Lymph capillaries in lacteals ---> Lymph veins ---> Lymph nodes --->

Thoracic duct ---> Left subclavian vein.

5. Lymph is mainly water in which you find plasma proteins, antibodies, dissolved gases and fatty nutrients.

6. The interstitial fluid in the tissues.

7. Close to all major joints, in the neck, as well as around the small and large intestines. They produce Iymphocytes, filter and trap bacteria and other debris.

8. Lymphatic tissue.

9. Special white blood cells, whcih may produce antibodies.

10. To recognize foreign (non-self) proteins (antigens) and to destroy them.

11. Tonsils, spleen, thymus gland.

12. (a) Cells/tissues are destroyed by bacterial/viral toxins or by physical destruction.

(b) Basophils release histamine which

(c) increases permeability of blood vessels

(d) including capillaries.

(e) Neutrophils and monocytes enter the inflammed area through pores in the capillary walls.

(f) Neutrophils engulf (=phagocytosis) bacteria/viruses.

(g) Macrophages "mop up" by scavenging and destroying dead tissue and debris.

Blood Components

1. (a) About 55% of total volume.

(b) About 45% of total volume.

2. (a) Water

(b) Plasma proteins

(c) Dissolves gases: mainly oxygen and carbon dioxide

(d) Nutrients

(e) Salts

(f) Waste products

(g) Hormones, vitamins






Origin. Marrow of long bones

Shape: Biconcave disk shaped

Nucleus? Absent in mature cells

Life Span: approximately 120 days

Function: To carry dissolved gases: oxygen and carbon dioxide.


Origin: Marrow of long bones and Lyrnphoid tissue.

Shape: Various, often amoeboid

Nucleus? Present

Life Span: Variable

Function: Recognition of foreign proteins (antigens) and fighting infection.

PLATELETS Origin: Marrow of long bones

Shape: Variable

Nucleus? Absent

Life Span: Variable

Function: To assist in blood clotting.

Transport of Oxygen and Carbon Dioxide

1. Because red blood cells contain hemoglobin, a red pigment with a high affinity for dissolved oxygen. Also, their shape gives them a large surface area for exchange of gases.

2. Iron

3. To combine with dissolved oxygen in the lung alveoli.

4. (a) HbO2 is oxidized hemoglobin.

5. (a) Hemoglobin takes up oxygen in the lung alveoli capillaries assuming that the partial pressure of oxygen is lower in the capillaries than in the alveoli so diffusion of the oxygen can occur.

(b) The hemoglobin gives off the oxygen in the tissue capillaries assuming that the partial pressure of oxygen is lower in the tissues so that diffusion can occur.

6.(a) Oxyhemoglobin would be found in the lung alveolar capillaries, pulmonary vein, aorta, arteries, and arterioles.

(b) Reduced hemoglobin would be found in the venous tissue capillaries, venules, veins, and pulmonary artery.

7. (a) Most of the oxygen is transported from the lungs to the tissues as oxyhemoglobin in the red blood cells. A small amount of the oxygen is carried dissolved in the blood plasma.

b) Most of the carbon dioxide is carried from the tissues to the lungs as bicarbonate ions (HC03-) in the blood plasma; a small amount is carried as as carbaminohemoglohin in the red blood cells.

Capillary-tissue Fluid Exchange

1. At the arterial end of a capillary blood pressure is higher than osmotic pressure causing water to exit

2. At the arterial end of a capillary blood pressure is higher than osmotic pressure causing water to exit. The concentration of oxygen, amino acids, and glucose in the arteriole end of the capillary is higher than that of the tissue fluid causing them to leave by diffusion.

3. The concentration of carbon dioxide in the venous end of the capillary is lower than that of the tissue fluid causing it to enter the capillary by diffusion.

Blood Clotting

1. At the site of injury a damaged blood vessel will cause a gathering of platelets which will partially seal the leak. The injured blood vessel releases the enzyme thrombin activator which converts the plasma protein prothrombin into thrombin. In the presence of calcium, thrombin will convert the plasma protein fibrinogen into fibrin. Fibrin threads weave a seal around the gathered platelets, thus completely sealing the leak.

2. (a) Lack of vitamin K interferes with the production of prothrombin thus blocking the production of thrombin, thus slowing blood clotting.

(b) Lack of calcium interferes with the conversion of prothrombin to thrombin, thus slowing blood clotting.

Sample Exam Questions

1. (a) Most of the oxygen is transported from the lungs to the tissues as oxyhemoglobin in the red blood cells. A small amount of the oxygen is carried dissolved in the plasma.

(b) Most of the carbon dioxide is carried from the tissues to the lungs as biarbonate ions in the plasma; a small amount is carried as carbaminoirmoglobin in the red blood cells.

2. Infection causes the liberation of histamine which causes an increase in the permability of the capillaries. This, aided by vasodilation of nearby arterioles, causes increased blood flow to the site of injury which now becomes red and hot. Increased numbers of neutrophils and monocytes engulf and destroy the invaders..

3. Because carbon monoxide combines much more readily with hemoglobin than does oxygen, thus interfering with the uptake and transport of oxygen and often resulting in death by asphyxia.

4. The net and biconcave shape of the red blood cell membrane increases greatly the surface area across which diffusion (exchange) of oxygen and carbon dioxide occurs; this makes for more efficient and more rapid gas exchange in the lungs and the tissues.

5. The fetus has 4 circulatory features that are not present in adult circulation. (All of these features can be related to the fact that the fetus does not use its lungs for gas exchange since it recieves oxygen and nutrients from the mother's blood by way of the placenta):

i. Oval opening, or foramen ovale, an opening between the two atria.

ii. Arterial duct, or ductus arteriosis, a connection between the pulmonary artery and the aorta.

iii. Umbilical arteries and vein, umbilical arteries are vessels that travel to the placenta with deoxygenated blood to leave wastes. Umbilical vein vessel that travels from the placenta bringing oxygenated blood containing nutrients.

iv. Venous duct, or ductus venosus, a connection between the umbilical vein and the inferior vena cava which passes directly through the liver. The place where oxygenated blood from the mother enters the adult portion of the fetal circulatory system and mixes with the deoxygenated blood already there.

6. At the arterial end of a capillary, blood pressure is higher than osmotic pressure causing water to exit. Tissue fluid created by this process consists of all the components of plasma except the proteins because they are too large to leave the capillary. Because blood pressure is reduced at the venous end of the capillary, osmotic pressure tends to pull some water back in. Any excess tissue fluid not picked up enters the lymphatic capillaries.