Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
31 General, Organic, and Biochemistry, 7e Bettelheim, Brown, and March © 2003 Thomson Learning, Inc. All rights reserved 31-1 31 Chapter 31 Body Fluids © 2003 Thomson Learning, Inc. All rights reserved 31-2 31 Body Fluids • Body fluids serve as a medium for carrying nutrients to and waste products from cells, and for carrying the chemical communicators that coordinate activities among cells • extacellular fluids: all body fluids not inside cells; collectively, they make up about 25% of a person’s body weight • interstitial fluid: the extracellular fluid that surrounds most cells and fills the space between them; makes up about 17% of body weight • blood plasma: the fluid that flows through arteries and veins; makes up about 5% of body weight © 2003 Thomson Learning, Inc. All rights reserved 31-3 31 Body Fluids • other body fluids occurring in lesser amounts are urine, lymph, cerebrospinal fluid, aqueous humor, and synovial fluid • Blood can exchange substances with other body fluids © 2003 Thomson Learning, Inc. All rights reserved 31-4 31 Body Fluids • there is only limited exchange, however, between blood and cerebrospinal fluid because of the blood-brain barrier • the blood-brain barrier is permeable to water, oxygen, carbon dioxide, glucose, alcohols, and most anesthetics • it is impermeable or only slightly permeable to electrolytes such as Na+, K+, and Cl-; also to many higher-molecular weight compounds © 2003 Thomson Learning, Inc. All rights reserved 31-5 31 Functions of Blood • Blood • caries O2 from the lungs to tissues • carries CO2 from tissues to the lungs • carries nutrients from the digestive system to tissues • carries waste products from tissues to the excretory organs • by means of its buffers, maintains the pH of the body (with the help of the kidneys) • maintains a constant temperature • carries hormones from the endocrine glands to their target locations • carries infection-fighting leukocytes and antibodies © 2003 Thomson Learning, Inc. All rights reserved 31-6 31 Composition of Blood • The three main cellular elements in blood are: 1. Erythrocytes • are very specialized cells whose main function is to carry O2 to cells and CO2 away from them • are formed in bone marrow • have a half-life of about 32 days • are removed by the liver and spleen and destroyed 2. Leukocytes (white blood cells) • are formed in the bone marrow • most of the different leukocytes destroy invading bacteria or other foreign substances by phagocytosis © 2003 Thomson Learning, Inc. All rights reserved 31-7 31 Composition of Blood 3. Platelets or thrombocytes • are formed in the bone marrow and spleen • control bleeding when there is a cut or injury • Plasma • the fluid remaining after all cellular elements have been removed from whole blood by centrifugation • is 92% water • the dissolved solids are mainly proteins (7%) • the remaining 1% contains glucose, lipids, enzymes, vitamins, hormones, and waste products such as urea and CO2 © 2003 Thomson Learning, Inc. All rights reserved 31-8 31 Composition of Blood • if plasma is allowed to stand, it forms a clot, a gel-like substance • serum: the clear liquid that can be extracted from blood plasma • serum contains all the components of plasma but lacks fibrinogen that makes blood clot © 2003 Thomson Learning, Inc. All rights reserved 31-9 31 Blood as a Carrier of O2 • The oxygen carriers in blood are hemoglobin (Hb) molecules, which are located in erythrocytes • the active sites are the hemes; at the center of each heme is an Fe2+ ion • because each Hb contains four hemes, it can carry four O2 • the ability of Hb to carry O2 depends on how much oxygen is in the environment • as shown by an oxygen dissociation curve, each heme has a cooperative effect on the other hemes © 2003 Thomson Learning, Inc. All rights reserved 31-10 31 Blood as a Carrier of O2 • an oxygen dissociation curve © 2003 Thomson Learning, Inc. All rights reserved 31-11 31 Blood as a Carrier of O2 • the oxygen-carrying capacity of Hb is also affected by its environment • a slight change in pH of the environment, for example, changes Hb’s oxygen-binding capacity • Bohr effect: the relationship between the oxygencarrying capacity of Hb and the levels of H+ and CO2 • when muscle contracts, both H+ and CO2 are produced • as pH decreases, more oxygen is released for an active muscle than for a muscle at rest • similarly, active muscle produces CO2 which accumulates and further enhances the release of O2 © 2003 Thomson Learning, Inc. All rights reserved 31-12 31 Transport of CO2 in Blood • CO2 also binds to Hb • as O2 is released from HbO2, CO2 becomes bound to the terminal NH2 group of each polypeptide chain of Hb • the product formed is called carbaminohemoglobin HbO2 + CO2 O Hb-C-O- + H+ + O2 Carb amin oh emoglob in • each heme can carry four CO2 • CO2 is also carried in red blood cells as H2CO3 CO2 + H2 O © 2003 Thomson Learning, Inc. All rights reserved carbonic anhydrase H2 CO3 31-13 31 Blood Cleansing - Kidneys • The kidney is a superfiltration machine © 2003 Thomson Learning, Inc. All rights reserved 31-14 31 Blood Cleansing Kidneys © 2003 Thomson Learning, Inc. All rights reserved 31-15 31 Urine • Urine • normal urine contains about 4% dissolved waste products • the pH of urine varies from 5.5 to 7.5 O H 2 N-C-NH2 • the main solute is urea • other organic solutes present include CH3 N NH O O H2 N-C-N-CH2 -C-ONH CH3 O Creatine Creatin ine O N H COO- Hip puric acid • urine also contains inorganic ions such as Na+, Ca2+, Mg2+, Cl-, PO43-, SO42-, and HCO3- © 2003 Thomson Learning, Inc. All rights reserved 31-16 31 Buffer Production -Kidney • Among the waste products in the blood are H+ • H+ is neutralized by the HCO3- ions that are part of the blood’s buffer system H+ + HCO3 H2 CO3 • when the blood reaches the lungs, H2CO3 is decomposed by carbonic anhydrase and CO2 is exhaled • the lost HCO3- ions are replaced by the kidneys • the cell-lining of the walls of the distal tubules reabsorb the CO2 that was lost in the glomeruli CO2 + H2 O © 2003 Thomson Learning, Inc. All rights reserved H2 CO3 HCO3 - + H+ 31-17 31 Buffer Production -Kidney • the H+ ions move into the urine where they are partially neutralized by a phosphate buffer • to compensate for the loss of positive ions, Na+ ions from the tubules enter the cells • as this happens, Na+ and HCO3- ions move from the cells into the capillaries • thus, H+ ions picked up at the tissues and temporarily neutralized in the blood by HCO3- are finally pumped out into the urine • at the same time, the HCO3- ions lost in the lungs are regained by the blood in the distal tubules © 2003 Thomson Learning, Inc. All rights reserved 31-18 31 Water and Salt Balance • The balance in the kidneys between filtration and reabsorption is under hormonal control • the production of urine is called diuresis • vasopressin promotes reabsorption of water • in the absence of vasopressin, only the proximal tubules reabsorb water, and too much water passes into the urine • in the presence of vasopressin, water is also reabsorbed in the distal tubules • thus, vasopressin causes blood to retain more water and produces a more concentrated urine • any agent that reduces the volume of urine is called an © 2003 Thomson Learning, Inc. antidiuretic All rights reserved 31-19 31 Water and Salt Balance • usually the vasopressin level is sufficient to maintain the proper level of H2O in tissues • in severe dehydration, the hormone aldosterone helps to maintain proper fluid levels • aldosterone controls the Na+ concentration in blood • in the presence of aldosterone, the reabsorption of Na+ increases • as the concentration of Na+ in the blood increases, the concentration of Cl- (necessary to maintain electrical neutrality) also increases • more H2O is also retained to solvate these ions • thus, increased aldosterone production allows the body to retain more H2O © 2003 Thomson Learning, Inc. All rights reserved 31-20 31 Blood Pressure • Blood pressure is maintained by • the total volume of blood • the pumping of the heart • the muscles that surround the blood vessels and provide the proper resistance to blood flow • Blood pressure is controlled by several very complex systems, some of them operating within seconds and some that take days to react to a change in blood pressure © 2003 Thomson Learning, Inc. All rights reserved 31-21 31 Blood Pressure • In the event of a hemorrhage, three different control systems begin to operate within seconds • baroreceptors in the neck detect the drop in pressure and send signals to the heart to pump harder and to the muscles surrounding the blood vessels to contract and thus restore pressure • chemical receptors on the cells detect less O2 delivery or CO2 accumulation and also send nerve signals • the central nervous system reacts to an O2 deficiency by a feedback mechanism © 2003 Thomson Learning, Inc. All rights reserved 31-22 31 Blood Pressure • Hormonal control • hormonal controls act somewhat more slowly and may take minutes or even days • the kidneys secrete an enzyme called renin • renin acts on an inactive blood protein called angiotensinogen, converting it to angiotensin • antiotensin is a potent vasoconstrictor • Long-term renal control • when blood pressure falls, the kidneys retain more water and salt, thus increasing blood volume and pressure © 2003 Thomson Learning, Inc. All rights reserved 31-23 31 Body Fluids End Chapter 31 © 2003 Thomson Learning, Inc. All rights reserved 31-24