Chapter 17 Blood Composition of Blood Introduction Blood

Chapter 17 Blood

Composition of Blood • Introduction – Blood – 8% of total body weight • 55% plasma • 45% formed elements (Table 17 -1) • Complex transport medium – Picks up food and oxygen, delivers to cells – Picks up waste, delivers to excretory organs – Hormones, enzymes, buffers • Keystone of body’s heat-regulating mechanism – Blood volume • 4 -6 liters in adults • Blood volume varies according to age, body type, sex, and method of measurement

Formed Elements of Blood • Red blood cells (erythrocytes) – No nucleus – Biconcave disks – Do not contain ribosomes, mitochondria, and other organelles typical of most body cells – Primary component is hemoglobin – Most numerous of the formed elements • 5, 500, 000 per mm 3 in men • 4, 800, 000 per mm 3 in women

Formed Elements of Blood • Function of RBCs – Transport of oxygen and carbon dioxide • Depends on hemoglobin and carbonic anhydrase – Joins carbon dioxide and water to form carbonic acid – Carbonic acid dissociates to form bicarbonate ions – Ions are transported in blood plasma until excreted – Bicarbonate ions also maintain blood p. H levels – Total surface area of RBCs is greater than a football field

Formed Elements of Blood • Red blood cells (erythrocytes) (cont. ) – Hemoglobin • Approximately 200 to 300 million molecules of hemoglobin per RBC • Made up of four globin chains, each attached to a heme molecule • Hemoglobin is able to unite with four oxygen molecules to form oxyhemoglobin to allow RBCs to transport oxygen where it is needed • A male has a greater amount of hemoglobin than a female – 12 -16 g of hemoglobin per 100 ml of blood • Anemia—a decrease in number or volume of functional RBCs in a given unit of whole blood

Formed Elements of Blood • Red blood cells (erythrocytes) (cont. ) – Erythropoiesis—entire process of RBC formation (Figure 17 -6) • Begins in the red bone marrow with hematopoietic stem cells – Several stages of development – Process takes ~4 days • 100 million RBCs are created and destroyed per minute in an adult • RBC production increases if oxygen deficiency occurs

Formed Elements of Blood • Red blood cells (erythrocytes) (cont. ) – Destruction of RBCs (Figure 17 -8) • Life span of a circulating RBC averages 105 to 120 days • Macrophage cells phagocytose the aged, abnormal, or fragmented RBCs…often in the lining of blood vessels of the liver and spleen • Hemoglobin is broken down and amino acids, iron, and bilirubin are released – Iron is returned to bone – Amino acids are used in protein synthesis – Bilirubin is transported to the liver and excreted as part of bile » Gives feces its characteristic color

Formed Elements of Blood • White blood cells (leukocytes, WBCs) – Granulocytes • Neutrophils – Approximately 65% of total WBCs – Highly mobile and very active phagocytic cells – Capable of diapedesis – Cytoplasmic granules contain lysosomes • Eosinophils – 2% to 5% of circulating WBCs – Numerous in lining of respiratory and digestive tracts – Weak phagocytes – Capable of ingesting inflammatory chemicals and proteins associated with antigenantibody reaction complexes – Provide protection against infections caused by parasitic worms and allergic reactions • Basophils – Only 0. 5% to 1% of circulating WBCs – Motile and capable of diapedesis – Cytoplasmic granules contain histamine and heparin

Formed Elements of Blood • White blood cells (cont. ) – Agranulocytes • Lymphocytes – – Smallest of the WBCs Second most numerous type of WBC Approximately 25% of circulating WBCs T lymphocytes and B lymphocytes have an important role in immunity » T lymphocytes directly attack an infected or cancerous cell » B lymphocytes produce antibodies against specific antigens • Monocytes – Largest type of leukocyte – Mobile and highly phagocytic cells

Formed Elements of Blood • White blood cells (cont. ) – WBC numbers • 5, 000 -9, 000 per mm 3 • Change with certain abnormal conditions – Formation of WBCs • Granular and agranular leukocytes mature from the undifferentiated hemopoietic stem cell • Neutrophils, eosinophils, basophils, and a few lymphocytes and monocytes originate in red bone marrow • Most lymphocytes and monocytes develop from hemopoietic stem cells in lymphatic tissue

Formed Elements of Blood • Platelets – Structure • Small, pale bodies that appear as irregular spindles or oval disks • Three important properties – Agglutination – Adhesiveness – Aggregation • 250, 000 per mm 3 of blood • 150, 000 to 400, 000 per mm 3 is normal – Functions of platelets • Hemostasis • Blood clotting/coagulation

Formed Elements of Blood • Platelets (cont. ) – Platelet plug formation • 1 to 5 seconds after injury to vessel wall, platelets adhere to damaged endothelial lining and to each other, forming a platelet plug • Temporary platelet plug is an important step in hemostasis • Normal platelets (positive charge) adhere to damaged capillary wall and underlying collagen fibers, which both have a negative charge • “Sticky platelets” form physical plug and secrete several chemicals involved in the coagulation process – Formed in red bone marrow, lungs, and spleen by fragmentation of megakaryocytes – Life span of 7 to 10 days