Cardiovascular System Flashcards
Describe the general nature and functions of blood, specify the main components of blood and
describe the importance of each.
Blood is a type of connective tissue containing cells and cell fragments in a liquid matrix. The volume of blood in a normal adult is about 7-8% of the body weight, which works out to about an average of ~ 6 litres.
Blood has three general functions:
* Transport of gases, nutrients, processed molecules (e.g. Vitamin D), regulatory molecules (hormones) and waste materials through the body.
* Regulation of pH, temperature and osmosis (i.e. fluid and ion balance)
* Protection, blood can clot preventing excessive loss from the cardiovascular system. It also
contains white blood cells and various defensive proteins eg. Antibodies.
Blood consists of three main components - cells, plasma, and platelets.
Cells-These include red blood cells (erythrocytes) and white blood cells (leukocytes). Red blood cells are by far the most numerous (~5 million/μl) while white blood cells are only around 8000/μl.
There are a number of different types of white blood cells (neutrophils, lymphocytes, monocytes, eosinophils & basophils) and all have varying functions in the body’s defence mechanisms.
Plasma-the acellular fluid component of blood. It is a pale yellow colloidal fluid.
The functions of plasma are to:
1) Carry the cells of blood in circulation
2) Transport nutrients to tissues and carry away waste materials
3) Maintain the acid-base balance of the blood.
4) Effect intercellular communication through transport of hormones
5) Defence functions through clotting and transport of antibodies
Platelets (also called thrombocytes) are disc-shaped membrane-bound fragments derived from large resident bone marrow cells called megakaryocytes. They contain no haemoglobin, no nuclei and are the smallest formed element in the blood. They play an essential role in blood clotting.
Describe the production of the formed elements of blood.
The various components of blood are shown in Figure 1. The cellular components of blood are red blood cells (erythrocytes) and white blood cells (leucocytes). Note that the erythrocytes are far more numerous than leucocytes and are smaller than leucocytes. All blood cells begin development in the red bone marrow.
Leucocytes are of two basic types, granulocytes and agranulocytes. Figure 1 illustrates the three types of granulocytes: neutrophils, eosinophils and basophils. Each type has granules in the cytoplasm and each has a complex lobed nucleus.
The other major group of leucocytes are the agranulocytes. Figure 1 illustrates the two types of agranulocytes: lymphocytes and monocytes. Agranulocytes have a clear cytoplasm without granules present. Lymphocytes have very little cytoplasm and have a large circular nucleus which fills up most of the cell. Monocytes are relatively large cells and have a nucleus which fills up almost 2/3 of the cell. The shape of the nucleus is more variable in monocytes than in lymphocytes.
Platelets, also known as thrombocytes, are cell fragments produced when megakaryocytes undergo a fragmentation process to produce many small, granular fragments surrounded by membranes. Platelets are not true cells, have no nuclei, and cannot reproduce. They have a fairly short lifetime, degenerating after about 10 days, so they have to be produced continuously. Platelets are essential for the blood clotting process.
Describe the major factors that stimulate the body to produce more erythrocytes.
- Low oxygen supply stimulates production of more erythrocytes
- Hormone erythropoietin from kidney stimulates red bone marrow to produce more erythrocytes
Specify the types of leucocytes (white blood cells), their origins and relative quantities in normal blood.
Neutrophil(60-70%), Lymphocyte(20-25%), Monocyte(3-8%), Eosinophil(2-4%), Basophil(0.5-1%)
Describe the procedure, what information is provided by, and the normal range for the following tests: hemoglobin (Hb), hematocrit (Hct).
The hemoglobin test is used to determine if there is anemia due to a lack of hemoglobin. Anemia is a condition where there is less than the normal amount of erythrocytes or hemoglobin in the blood. This most often results in pallor and fatigue. In this test a fixed volume of blood is hemolysed and the colour of the hemolysed blood is compared to a set of standards. Normal hemoglobin values are indicated in Table 2.
The hematocrit test is used to determine if there is anemia due to a lack of red blood cells, or polycythaemia because of overproduction of blood cells. Refer to this weeks lab for further explanation and procedure for this test. The normal range for the hematocrit (also called packed cell volume (PCV)) is 42-54% for men and 38- 46% for women.
A differential count is used in the diagnosis of an infection or disease on the basis of an increase or decrease in numbers of specific types of white blood cells
In adults, an increase in leucocytes is described as leucocytosis (i.e. > 10,000 WBCs/μl) while a decrease is called leucopenia (i.e. < 5,000 WBCs/μl). The normal ranges for the different types of leucocytes and some causes of leucocytosis and leucopenia are indicated in Table 1.
Describe the structure and function of platelets.
Platelets, also known as thrombocytes, are cell fragments produced when megakaryocytes undergo a fragmentation process to produce many small, granular fragments surrounded by membranes. Platelets are not true cells, have no nuclei, and cannot reproduce. They have a fairly short lifetime, degenerating after about 10 days, so they have to be produced continuously. Platelets are essential for the blood clotting process.
Specify the two main components of blood that give blood its viscosity, and describe the importance of each to the blood.
There are two major components of blood that affect its viscosity: These are the number of red blood cells and the amount of albumins. An increase in either of
these two components will increase the viscosity of the blood.
Define hemostasis and describe the mechanisms involved in achieving hemostasis: vascular spasm, platelet plug formation, blood clotting.
Hemostasis is the reduction and stoppage of blood loss from a damaged blood vessel. There are three mechanisms involved in achieving hemostasis:
a) vascular spasm
The first response of a damaged artery is contraction of circularly arranged smooth muscle within the wall of the blood vessel. The resulting constriction (reduction in diameter) of the blood vessel can greatly reduce blood loss for about 30 minutes, until longer lasting mechanisms have taken over.
b) platelet plug formation
Under normal circumstances, platelets do not adhere to each other or to the endothelial lining of blood vessels. However, platelets do adhere tightly to collagen fibers of connective tissue that are exposed when the lining of a blood vessel is ruptured. Once platelets adhere to collagen fibers they become activated, which causes them to swell, extend pointed projections, and become sticky. Activated platelets also release a variety of chemicals that stimulate vascular spasms, activate other platelets, and assist with the formation of a blood clot. By sticking to each other and to any exposed collagen, the activated platelets form a platelet plug which reduces blood loss
c) bloodclotting
Blood clotting, or coagulation, is a complex sequence of events (chemical reactions) that results in the conversion of blood from a liquid to a gel. This change in consistency of the blood is due to the formation of a network of fibers consisting of fibrin protein, and it involves more than a dozen chemicals called clotting factors. Most of these clotting factors are plasma proteins made by the liver and released into the blood in inactive forms. Other clotting factors include calcium ions (Ca2+), phospholipids associated with platelets, and a mixture of lipoproteins and phospholipids released from damaged tissues. Blood clotting is divided into three major stages: (i) the formation prothrombinase, also known as prothrombin activator, (ii) the formation of thrombin and (iii) the formation of fibrin
There are two main clotting pathways: the extrinsic and the intrinsic pathways. The extrinsic occurs when there is tissue damage and bleeding from the blood vessel. The intrinsic pathway is stimulated by activated platelets when there is damage to the inner lining of the blood vessel . The extrinsic pathway is very fast and can result in a clot within about 15 seconds. In contrast, the intrinsic pathway is slower and usually requires several minutes. Both pathways usually work together and lead to the formation of prothrombinase.
Explain the disorders: thrombus, embolus, and hemophilia
A thrombus is a blood clot that forms within an uninjured blood vessel. The formation of such abnormal clots can be initiated by platelets that have been activated by the endothelial linings of blood vessels that have been roughened by inflammation or atherosclerosis (a progressive disease causing formation of lesions on the walls of arteries).
An embolus is a mass of any substance that is flowing freely within blood vessels. Examples of such floating masses are dislodged fragments of blood clots (usually a thrombus), bubbles of air, and globules of fat.
If either a thrombus or an embolus blocks blood flow to a tissue, the result is death of that tissue. This is the basis of most heart attacks and strokes.
Hemophilia is an inherited deficiency in the ability to form blood clots, resulting in excessive bleeding either spontaneously or after only mild trauma. There are actually a number of different types of hemophilia, each type due to a deficiency in the ability to make a specific clotting factor. The most common type of hemophilia, hemophilia A, is the result of a deficiency for factor VIII.
Describe how the process of blood clotting is regulated, particularly with respect to prevention of blood clotting when it is not required, rapid initiation and progression of blood clotting when damage occurs, localization of blood clotting to the damaged region, and the dissolution of blood clots (fibrinolysis).
Obviously the blood clotting process must be very carefully regulated. If blood clots too easily, it can result in a thrombus. Alternatively, if blood clots too slowly, excessive blood loss (hemorrhage) can occur. Whether or not clotting occurs depends on a balance between clotting factors and numerous substances that inhibit clotting (anticoagulants).
Examples of anticoagulants include:
1. antithrombin which blocks the action of several clotting factors including thrombin
2. heparin which increases the ability of antithrombin to block thrombin.
When blood clotting is not required, many of the clotting factors exist in an inactive form and a predominance of anticoagulants prevents clotting. However, when damage to blood vessels occurs, clotting factors are rapidly activated and amplified so that the balance shifts and clotting is initiated. To minimize blood loss, rapid progression of the clotting process is ensured by positive feedback involving thrombin. That is, once some thrombin is produced, it stimulates more production of itself. This is accomplished in two ways: (i) thrombin stimulates the production of more prothrombinase; and (ii) thrombin activates more platelets.
There are at least two reasons that, despite positive feedback, blood clotting is normally localized to the region of damage. First, if they contact rapidly moving blood, clotting factors that were released or activated at the site of damage are diluted, washed away, and inactivated by anticoagulants. Second, as the clot forms virtually all the activated thrombin becomes bound to fibrin, effectively confining the enzyme that would be required to make more fibrin and expand the clot.
Once a blood vessel has been permanently repaired by the growth of new tissue, the blood clot must be dissolved (i.e. undergo dissolution). Furthermore, despite all the regulation described above, many unnecessary clots start to form every day. These unnecessary clots must also be dissolved. The process of chemically breaking down fibrin threads to dissolve clots is called fibrinolysis and requires the enzyme plasmin. (This enzyme is the active form of plasminogen, an inactive plasma protein made by the liver and integrated into clots as they are formed.)
Describe how each of the following affects blood clotting: vitamin K, anticoagulant drugs, thrombolytic agents.
a) The liver requires vitamin K in order to make prothrombin and three other clotting factors. The clotting process is therefore very sensitive to levels of vitamin K in the blood. There are two sources for vitamin K: bacteria in our large intestine make some and our diet provides the rest. Vitamin K and other fat- soluble vitamins must be absorbed from the intestine in association with fat and other lipids. Several disorders that decrease the absorption of fats, as well as the prolonged use of antibiotics that kill intestinal bacteria, can thus lead to vitamin K deficiency and uncontrolled bleeding.
b) Anticoagulant drugs are substances that are used to delay or prevent undesirable blood clotting in patients at risk of heart attack or stroke. Three examples of anticoagulant drugs are:
(i) heparin which helps inactivate thrombin; (ii) warfarin (Coumadin or dicumarol) which interferes with the action of Vitamin K and (iii) aspirin which inhibits vasoconstriction and platelet aggregation
c) Thrombolytic agents are substances used in the treatment of patients that have suffered heart attacks or strokes to activate plasminogen into plasmin and dissolve blood clots. Two examples of thrombolytic agents are: (i) streptokinase which is an enzyme made by streptococcal bacteria and (ii) t-PA (tissue plasminogen activator, which converts inactive plasminogen into active plasmin) that has been made readily available through genetic engineering.
Describe the anatomy of the human heart with respect to the following: location, size, and shape.
a) The heart is located in the thoracic cavity posterior to the sternum. In most people about 2/3 of the heart is left of the midline of the body, and 1/3 is to the right
b) Heart size is variable, but as a general rule of thumb, is about the size of a clenched fist.
c) The heart is a hollow, muscular organ for pumping blood. It is shaped like a blunt cone and is divided into four chambers. The upper two chambers are called the atria. They are relatively thin-walled because they only have to pump blood down into the ventricles. The lower two chambers are called the ventricles, and they are relatively thick-walled. The left ventricle has a thicker wall than the right ventricle because it pumps blood a longer distance and the left side of the heart has greater pressures. The ventricles are separated from each other by a partition called the septum
Define and describe the location of the following: pericardium, epicardium, myocardium, endocardium.
a) The pericardium consists of two major components: an outer fibrous layer composed of dense irregular connective tissue, the fibrous pericardium and a smooth inner parietal serous pericardium which together comprise the pericardial sack in which the heart beats. The epicardium (visceral serous pericardium) is the outer layer of the heart wall.
b)Between the epicardium and pericardium is the pericardial cavity which contains a thin film of serous fluid. The membranes are lubricated by the fluid so that they slide smoothly past one another to reduce friction as the heart beats.
c) Below the epicardium is the myocardium, which is the muscular tissue of the heart. The myocardium consists of cardiac muscle which is involuntary, and contains striated, branched cells.
d) The inner surface of the heart is lined by a layer called the endocardium. It is a layer of epithelial tissue on a layer of connective tissue.
XIV. Describe the anatomy and relationship to each other of the four chambers of the heart including the location and general makeup of all valves. (See Objective XV notes below)
XV. Describe the double circulation and blood flow through the heart and explain the role of the four valves in controlling the direction of blood flow.
The heart is effectively two separate pumps in one organ. Blood returns from the head and body to the right atrium. The right atrium contracts and sends blood to the right ventricle. Blood from the right ventricle is pumped out of the heart to the lungs. From the lungs the blood returns to the left atrium. This blood flow from the heart to the lungs and back to the heart again is called the pulmonary circulation. From the left atrium the blood goes into the left ventricle, and is then pumped out to the head and the rest of the body. This circulation from the heart to the head and body and back to the heart again is called the systemic circulation. Because blood travels through two loops-a pulmonary loop and a systemic loop- we call it double circulation.
The heart valves are flaps or cusps of fibrous connective tissue covered by endocardium. They function in the prevention of the back-flow of blood in the heart. There are four valves in all. Between the right atrium and right ventricle is the tricuspid valve which has three cusps or flaps. Between the left atrium and left ventricle is the bicuspid valve, (or mitral valve). The flaps of connective tissue are anchored to the walls of the heart by cords of connective tissue called chordae tendinae which arise from the ends of pillars of ventricular muscle called papillary muscles.
When the atria contract blood is pushed into the ventricles and opens the valves. When the ventricles contract, blood is pushed up against the undersides of the flaps and the pressure closes the valve, preventing blood from flowing back into the atrium. The chordae tendinae and the papillary muscles prevent the valves from opening into the atria and so prevent back-flow of blood.
The other two valves of the heart are called semilunar valves because they are shaped like crescent moons. They are located at the base of each of the two main arteries leaving the heart. One is at the opening between the left ventricle and the aorta and is called the aortic valve. The other is at the opening between the right ventricle and the pulmonary trunk and is called the pulmonary valve. They prevent the back-flow of blood from the pulmonary trunk and the aorta into the heart.
Briefly describe the major components of the coronary circulation and parts of the heart that they feed.
The heart consists primarily of muscle which is active in pumping blood to the lungs and throughout the body. Heart muscle requires a continuous delivery of nutrients and oxygen to the muscle tissue. Two major arteries (left and right coronary arteries) branch off of the aorta near where the aorta leaves the left atrium. The left coronary artery generally serves the left atrium and left ventricle, and the right coronary artery generally serves the right atrium and ventricle. These arteries branch in to smaller arteries that distribute blood to all the cardiac muscle tissue. As set of veins collect blood leaving the cardiac muscle tissue. The coronary veins generally run parallel to the coronary arteries. The coronary veins direct blood to a large vein called the coronary sinus and the coronary sinus empties into the right atrium.
