Expt 26 2. How does one develop Rh antibodies? When Rh-positive red blood cells from the fetus enter the blood of an Rh-negative woman through a tear in the placenta, the mother is sensitized to the Rh antigen and produces anti-Rh antibodies before or during delivery. 3. What is HDN? Explain how HDN is acquired. During a subsequent pregnancy of an Rh-negative mother with an Rh-positive fetus, the Rh-positive red blood cells once again cross the maternal circulation where it can stimulate the mother to produce antibodies against the Rh antigen in a rapid antibody production due to initial Rh sensitization. The anti-Rh antibodies from the mother cross the placenta, causing agglutination and hemolysis of fetal red blood cells, and hemolytic disease of the newborn (HDN) develops. Expt 27 1. What causes the absence of intravascular clotting? Clots are dissolved by a process called fibrinolysis where an inactive plasma protein called plasminogen is converted to its active form, plasmin. Thrombin, other clotting factors activated during clot formation, and tissue plasminogen activator (t-PA) released from surrounding tissues can stimulate the conversion of plasminogen to plasmin, which will slowly break down the fibrin in a blood clot. 2. What is the importance of determining clotting time? The time taken for blood to clot mainly reflects the time required for the generation of thrombin. If the plasma concentration of prothrombin or of some of the other factors is low (or if the factor is absent or functionally inactive), clotting time will be prolonged.Clotting time is done in 2 main ways: prothrombin time (PT) or partial thromboplastin time (pTT). This is important to determine if the patient doesn’t have any clotting disorders such as hemophilia or liver disease, to monitor anticoagulant therapy such as warfarin or heparin, or to check whether the patient may need transfusions of blood products after having a large hemorrhage. 3. Discuss the mechanism of hemostasis. After inactive clotting factors are activated by exposure to connective tissue or by chemicals from tissues, these clotting factors form prothrombinase which converts prothrombin to thrombin, which further convers fibrinogen to fibrin and forming the clot. The formation of this clot is controlled to prevent spread from the point of initiation throughout the blood vessels. Anticoagulants prevent clotting factors from forming clots under normal conditions. For example, antithrombin and heparin inactivate thrombin. Without thrombin, fibrinogen is not convrted to fibrin, and no clot forms. At an injury site, however, the activation of clotting factors is very rapid. Enough clotting factors are activated that the anticoagulants can no longer prevent a clot from forming. Away from the injury site, there are enough anticoagulants to prevent clot formation from spreading. Expt 28 1. Can there be prolonged bleeding time with normal clotting time or vice versa? Explain your answer. There can b a prlonged bleeding time with normal clotting time or a shortened bleeding time with abnormal clotting time. This is because bleeding time depends upon the depth of the wound and the degree of hyperemia in the body part influenced by tissue fluids, the elasticity of the surrounding tissues, and the chemical effects of the destroyed platelets, and not exactly pertaining ot the ablity of the blood to clot (which is measured by the clotting time). 2. Enumerate the advantages and disadvantages of using the earlobe as puncture site for determining bleeding time. Advantages of skin puncture using the earlobe: 1. It is less painful due to lesser nerve endings. 2. There is more free flow of blood due to thinner skin 3. There is less tissue juice contamination of blood due to lesser tissue and muscles in the earlobe 4. It is ideal when searching for abnormal cells Disadvantages of skin puncture using the earlobe:
1. Poor reproducibility and unreliable test results due to variability of earlobe thickness and variability of puncture depth 2. Outdated and rarely used site for puncture as new methods use the forearm for an improved sensitivity and reproducibility Use of the earlobe to determine bleeding time was developed by Dr. William W. Duke in 1910. It was replaced by the Ivy Bleeding Time with the following advantages: "Surgical" incision more closely approximated patient's hemostatic response to surgery Large surface area of template (longer incision) minimized skin displacement Depth of incision was controlled Clotting Time In order for blood to clot, the enzyme thrombin must be generated from the plasma precursor prothrombin. Thrombin then converts soluble fibrinogen into insoluble fibrin. Generation of thrombin involves the sequential activation of a number of other plasma clotting factor, this process is also being assisted by Ca++ and by factors released by platelets and damaged tissues . The time taken for blood to clot mainly reflects the time required for the generation of thrombin in this manner. If the plasma concentration of prothrombin or of some of the other factors is low (or if the factor is absent, or functionally inactive), clotting time will be prolonged. The expected range for clotting time is 4-10 mins. Bleeding Time This test measures the time taken for blood vessel constriction and platelet plug formation to occur. No clot is allowed to form, so that the arrest of bleeding depends exclusively on blood vessel constriction and platelet action. Expt 29 Expt 29 1. What are the signs of hyperemia?
2. After differentiating active from passive hyperemia, what type of hyperemia is produced by 70% isopropyl alcohol? Explain.
Expt 30 1. Explain the importance of the capillary resistance test. The capillary resistance test is important in measuring the ability of the capillary walls to resist pressure which is needed to facilitate capillary exchange. It is through capillary exchange that nutrients diffuse across the capillary walls into the interstitial spaces, whereas waste products diffuse in the opposite direction. This happens as fluid at the arterial end from the capillaries flow out due to the higher osmotic pressure present in blood outside (water moves towards inside of capillaries pushing solutes outside), afterwhich 9/10 of its volume will reenter at the venous end due to osmosis (as water now moves towards the outside of capillaries pushing solutes inside). 2. Enumerate the conditions characterized by fragile capillaries Weak capillaries lead to small spots of bleeding in the skin and easy bruising. Bruises look like areas of blue to purple-colored skin that can turn yellow to dark brown over the course of a few days. Capillaritis is the name given to a harmless skin condition in which there are reddish-brown patches caused by leaky capillaries. It is also known as pigmented purpura. Purpura is a skin discoloration caused by bleeding (hemorrhage) under the skin. A small hemorrhage is called a petechia and a large one, as in a bruise, is called an ecchymosis. Purpura may result from trauma, from fragility of the blood vessels, or from clotting disorders. Fragility of the blood vessels usually is inherited, although it seldom is serious. In a more serious inherited form of the disorder, a condition known as telangiectasia, there are obvious abnormalities of the blood vessels in the lips, mouth, and fingers. Expt. 31 1. What are the functions of the following heart structures? a. Chordae tendineae The chordae tendineae are strong, fibrous strings attached to the leaflets (or cusps) of the heart on the ventricular side; i.e., the lower chamber. These strings originate from small mounds of muscle tissue, the papillary muscles, which project inward from the walls of the ventricle. When the cusps close, the chordae tendineae prevent them from swinging back into the atrium cavity (the upper chamber). When the ventricles of the heart contract in ventricular systole, the increased blood pressuresin both chambers push the AV valves to close simultaneously, preventing backflow of blood into the atria. Since the blood pressure in atria is much lower than that in the ventricles, the flaps attempt to evert to the low pressure regions. The chordae tendineae prevent the eversion, prolapse, by becoming tense thus pulling the flaps, holding them in closed position. [1] b. Tricuspid valve Prevent the back flow of blood into the right atrium c. Interventricular septum d. Bicuspid valve
Calculating the MAP MAP, or mean arterial pressure, is defined as the average pressure in a patient’s arteries during one cardiac cycle. It is considered a better indicator of perfusion to vital organs than systolic blood pressure (SBP). True MAP can only be determined by invasive monitoring and complex calculations; however it can also be calculated using a formula of the SBP and the diastolic blood pressure (DBP).
To calculate a mean arterial pressure, double the diastolic blood pressure and add the sum to the systolic blood pressure. Then divide by 3. For example, if a patient’s blood pressure is 83 mm Hg/50 mm Hg, his MAP would be 61 mm Hg. Here are the steps for this calculation: MAP = SBP + 2 (DBP) 3 MAP = 83 +2 (50) 3 MAP = 83 +100 3 MAP = 183 3 MAP = 61 mm HG Another way to calculate the MAP is to first calculate the pulse pressure (subtract the DBP from the SBP) and divide that by 3, then add the DBP: MAP = 1/3 (SBP – DBP) + DBP MAP = 1/3 (83-50) + 50 MAP = 1/3 (33) + 50 MAP = 11 + 50 MAP = 61 mm Hg There are several clinical situations in which it is especially important to monitor mean arterial pressure. In patients with sepsis, vasopressors are often titrated based on the MAP. In the guidelines of the Surviving Sepsis Campaign, it is recommended that mean arterial pressure (MAP) be maintained ≥ 65 mm Hg. Also, in patients with head injury or stroke, treatment may be dependent on the patient’s MAP.
