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Chapter 19 Blood Introduction How does blood contribute to homeostasis? It contains most of the immune cells, but by itself doesn’t do anything--it is a transport medium. Arteris = Oxygenated blood that is going to the tissues Veins = Deoxygenated blood that is going back to the heart Functional components of the CV System Digestive System: Nutrients are absorbed across the wall of the small intestine Kidneys: Part of the circulatory path. Blood is filtered here! Lungs: Where oxygenation occurs. Blood picks up oxygen here, and drops off CO 2 Functions of Blood All the functions of blood contribute to homeostasis. Distribution: Nutrients (oxygen, glucose, fatty acids, vitamins, minerals, etc…) Wastes to kidneys for excretion CO 2 to lungs for excretion Chemical messengers to target cells (Hormones) Enzymes (Ex: Renin-AngII-Aldosterone pathway) Regulation: Temperature (thermoregulation ). This is done via redistribution and shunting of blood flow depending on body needs pH of body fluids : blood contains buffers…albumin is the main one Volume of body fluids : maintaining blood volume, thus ECF volume and BP. If blood vessel is at the right volume, the ICF and ECF are good, too. Composition of body fluids: fluid/solute exchanges are continuous between the ICF/ECF fluid compartments Protection via: Hemostasis prevents blood loss to maintain ECF volume. This is done via blood clotting. The blood carries clotting proteins (fibrinogen becomes fibrin when clotting is necessary). Leukocytes are the primary cellular component of the immune system. Basically, all the blood cells except erythrocytes and platelets are part of the immune system. Composition of Whole Blood Blood is a fluid connective tissue (matrix + cells) The matrix of blood is plasma (matrix is ground substance + fibers) Ground substance = serum Fibers = fibrinogen Exchanges are made at the capillaries! pH of blood is 7.35 to 7. Fibrinogen is a fibrous protein that is dissolved in the plasma unless converted into fibrin during clotting.
The watery portion of whole blood is the plasma. The cellular portion is the hematocrit (WBC, RBC, platelets). The major components of blood can be seen in a tube after centrifuge: o Plasma makes up 55% of blood o Buffy coat accounts for less than 0.1% and includes leukocytes and platelets o Erythrocytes account for about 45% Hematocrit refers to the percentage of blood that consists of formed elements. RBCs make up 99.9% of the formed elements, WBCs and platelets account for 0.1%). Men have a higher hematocrit due to more lean body mass, at about 46%. Women have a hematocrit of about 42%. Characteristics of blood o The amount of blood you have is equal to about 7% of body weight in kilograms. o Blood is not neutral. It is slightly alkaline at 7.4pH. Note that though this is alkaline, it is NORMAL for the body, so anything above 7.4 is considered basic (causing alkilosis) and anything below 7.4 is considered acidic (acidosis). o At a normal hematocrit of 40%, blood is 3-4x more viscous than water. The more cells you have the higher the viscocity of the blood. If hematocrit rises to 60%, then the relative viscocity increases to 8x that of water….sludgy!! This is why blood doping is sooo dangerous! The higher the hematocrit, the more viscous the blood gets, and the harder the heart has to work to pump the thicker blood. You can have heart failure and blood vessels can get clogged, causing tissue death. o Note that plasma has a relative viscocity of about 1.8. Plasma Plasma is made up of about 92% water, and 8% solutes (both protein and non-protein). Most of the major proteins of plasma are produced in the liver (except for hormones and gamma globulins). The major proteins are: o Albumin: Most abundant protein in plasma (2/3 or 60%) Carrier protein for lipophilic substances Acts as a buffer to maintain pH Contributes to osmotic pressure b/c it affects exchange between blood and interstitial fluid. o Globulins: Next most abundant (1/3 or 35%) Alpha and Beta globulins act as transport proteins Gamma globulins are antibodies… made by B-lymphocytes Not produced in liver! o Clttng Protns: Fibrinogen makes up 4% of plasma proteins o Enzymes/Hs: Make up less than 1% of plasma proteins
liver and bone marrow at the organ level. The AAs and Fe is recycled and put back into the bone marrow for the construction of new RBCs. Transferrin is the plasma protein that transports Fe in circulation. A small amount of Hb is lost from hemolysis and is not recycled…it is lost in the urine. When you have too much Hb in the urine it is Hemoglobuinuria (red/brown urine color). When you have RBCs in the urine it’s Hematuria. This may be a sign of kidney damage. The Heme Group does not go to the bone marrow for recycling…it is converted to bilirubin in the macrophage and is transported to the liver and incorporated into bile. Some goes to the digestive sytem to be secreted in the feces, and some goes out in the blood stream to the kidney and out in the urine. Macrophages do not always get the RBCs before they die. About 10% of them undergo hemolysis in the blood plasma and get lost through the kidneys and aren’t recycled. When you do a urinalysis you will see some Hb. If outside the normal range, then there is a problem. Hemotopoiesis is the formation of blood cells in the red bone marrow. The blood cell stem cell is the hemocytoblast…it produces RBCs, WBCs and platelets. The hemocytoblast is the most “pluripotent” stem cell. The “commited cell” is the one in the pathway that is now committed to making a specific type of cell. For the RBC that is the proerythroblast. Red Blood Cell Formation = Erythropoiesis All RBCs are produced in the red bone marrow from the proerythroblast, which is the committed cell. The pathway is: Hemocytoblast to Myeloid stem cell to Proerythroblast to Reticulocyte to Erythrocyte If you have an abnormal accumulation of bilirubin then you have jaundice!
The RBC enters the blood stream as a reticulocyte (immature RBC). It then ejects the nucleus to become an erythrocyte…this takes about a day. Hormonal regulation of erythropoiesis Erythropoiesis is controlled by negative feedback. It goes like this: EPO (released by the kidney in response to low oxygen delivery to the kidney cells) stimulates the red bone marrow, which leads to enhanced erythropoiesis to increase the RBC count. This increases the oxygen-carrying ability of blood, which eventually puts the brakes on the feedback loop. The goal of the loop is to maintain a level hematocrit, or to adjust it if necessary due to altitude. Erythropoiesis requires AAs, Fe and B Vitamins. If you don’t have enough B12, then you have pernicious anemia. RBC Disorders Anemia: Anemia is caused by any lack of Fe, AA or B12. This leads to insufficient oxygen carrying capacity, so it is important to note that anemia is not always based on a low RBC count. It can have several causes! Anemia caused by deficient numbers of RBCs o Hemorrhage causes hemorrhagic anemia o Premature cell deal causes hemolytic anemia o Dysfunctional red bone marrow causes aplastic anemia Anemia caused by deficient Hb content o Iron deficiency causes Iron-deficiency anemia o Vit-B12 deficiency causes Pernicious anemia o This is caused by a lack of intrinsic factor, which is produced by the stomach o Athlete’s anemia is caused by acute high BV, which dilutes RBCs relative to the normal hematocrit volume, it is low because BV is high. Anemia caused by abnormal Hb (usually genetic) o Sickle-cell anemia is caused by a small genetic defect (an incorrect AA). With this disease, the Hb becomes rod-like and spiky, which leads to the RBC “sickling” and becoming crescent-shaped. Causes for the kidney cells to be low on oxygen are: altitude, anemia, pulmonary disease.
Type O Blood: Has no antigens on the surface Has A & B antibodies in the plasma Only concerned with the antigens coming in! Note that if you take out the plasma, you take out the antibodies…which can be important if doing a large transfusion of more than 1 liter…in this case the number of donor antibodies would not be diluted and ineffective…they could cause problems. When blood typing, it is based on which antigens are present! In addition to the A, B antigens, a third antigen is added to determine the Rh-Factor. Recall that Rh antibodies are not preformed. If you are Rh-, then you might someday form Rh antibodies. You can do this by being pregnant with an Rh+ baby because the antigens can get across the barrier…causes problems with subsequent Rh+ baby. If you are Rh+ then you will never form antibodies to Rh-Factor…and can receive blood that is either Rh+ or Rh–. Can receive A, O Can receive B, O^ Can receive Can receive O AB, A, B, O Universal Recipient Universal Donor Give to A, AB Give to Give to AB A, B, AB, O Give to B, AB