Ch. 18 Blood PDF

Chapter 18 Blood Blood Composition Blood: a fluid connective tissue composed of – Plasma 90% water 8% plasma proteins 2% other solutes (electrolytes, nutrients, hormones/enzymes, gases and wastes) – Formed elements Erythrocytes (red blood cells, or RBCs) Leukocytes (white blood cells, or WBCs) Throm...

Chapter 18 Blood Blood Composition Blood: a fluid connective tissue composed of – Plasma 90% water 8% plasma proteins 2% other solutes (electrolytes, nutrients, hormones/enzymes, gases and wastes) – Formed elements Erythrocytes (red blood cells, or RBCs) Leukocytes (white blood cells, or WBCs) Thrombocytes (platelets) Whole Blood Physical Characteristics and Volume Sticky, opaque fluid Color scarlet to dark red pH 7.35–7.45 38C ~8% of body weight Average volume: 5–6 L for males, and 4–5 L for females (more for males due to testosterone stimulates RBC production) Functions of Blood 1. Transportation - Distribution of O2 and nutrients (proteins, glucose, etc.) to body cells Metabolic wastes to the lungs and kidneys for elimination Hormones from endocrine organs to target organs Functions of Blood 2. Regulation of – Body temperature by absorbing and distributing heat (always 1 degree warmer than rest of the body because it absorbs heat) – Normal pH – Adequate fluid volume in the circulatory system Functions of Blood 3. Protection against – Infection Antibodies Complement proteins WBCs defend against foreign invaders – Blood loss Plasma proteins and platelets initiate clot formation Blood Plasma 90% water 8% Plasma proteins are mostly produced by the liver – Remain in the blood and not taken into cells – 60% albumin – substance carrier but can act as a buffer, major contributor of osmotic pressure – 36% globulins – 4% fibrinogen Blood Plasma Last 2% of plasma – Wastes - lactic acid, urea, creatinine – Nutrients—glucose, amino acids – Electrolytes—Na+, K+, Ca2+, Cl–, HCO3– – Respiratory gases—O2 and CO2 – Hormones – enzymes Formed Elements in Blood WBCs - are the only complete cells in blood RBCs - have no nuclei or organelles Platelets - are cell fragments Most formed elements survive in the bloodstream for only a few days Most blood cells originate in red bone marrow Erythrocytes Biconcave discs, anucleate, essentially no organelles Are the major factor contributing to blood viscosity Filled with hemoglobin (Hb) for gas transport Spectrin: a membrane protein that provides flexibility for RBC to change shape as necessary Red Blood Cells Erythrocytes Structural characteristics contribute to gas transport – Biconcave shape provides huge surface area relative to volume which aides in gas transport – >97% of cell is hemoglobin (not counting water) – No mitochondria; ATP production is anaerobic; no O2 is used in generation of ATP A superb example of complementary of structure and function! Erythrocyte Function RBCs are dedicated to respiratory gas transport Hemoglobin protein (Hb)structure: – Globin: 4 protein chains each containing a heme group Each heme group has an iron atom in the middle Heme group a has red pigment Each iron atom can bind to one O2 molecule Each Hb molecule can transport four O2 Each RBC contains 250 million Hb molecules Hemoglobin Hemoglobin (Hb) O2 loading in the lungs – Produces oxyhemoglobin (ruby red) O2 unloading in the tissues – Produces deoxyhemoglobin or reduced hemoglobin (dark red) CO2 loading in the tissues – Produces carbaminohemoglobin (carries 20% of CO2 in the blood) – Binds to the amino acid portion of the globin Hematopoiesis Hematopoiesis (hemopoiesis): blood cell formation – Occurs in red bone marrow of axial skeleton, girdles and proximal epiphyses of humerus and femur On average, the marrow turns out an ounce of new blood containing 100 billion new cells each and every day Erythropoiesis Erythropoiesis: red blood cell production The number of circulating erythrocytes remains constant and reflects a balance between RBC production and destruction Balance between RBC production and destruction depends on – Hormonal controls – Adequate supplies of iron, amino acids, and B vitamins Too few RBCs leads to tissue hypoxia Too many RBCs increases blood viscosity Hormonal Control of Erythropoiesis Erythropoietin (EPO) – Direct stimulus for erythropoiesis – Released by the kidneys in response to hypoxia Causes of hypoxia – Hemorrhage or increased RBC destruction reduces RBC numbers – Insufficient hemoglobin (e.g., iron deficiency) – Reduced availability of O2 (e.g., high altitudes) Hormonal Control of Erythropoiesis Effects of EPO – More rapid maturation of committed bone marrow cells – Increased circulating reticulocyte count in 1– 2 days Testosterone also enhances EPO production, resulting in higher RBC counts in males Development of Red Blood Cells Erythrocytes Life span: 100–120 days Old RBCs become fragile, and Hb begins to degenerate Macrophages engulf dying RBCs in the spleen Fate and Destruction of Erythrocytes Heme and globin are separated – Iron is salvaged for reuse – Heme is degraded to the yellow pigment bilirubin – Liver secretes bilirubin (in bile) into the intestines – Globin is metabolized into amino acids Breakdown of Hemoglobin Leukocytes Make up