BLOOD

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OVERVIEW OF BLOOD CIRCULATION

Circulates continuously

Gas exchange occurs across capillary walls

O2 rich blood leaves lungs and is pumped systemically via the heart

CO2 rich blook enters heart and is pumped into lungs to be oxygenated

COMPOSITION OF BLOOD

Fluid tissue

Liquid plasma and formed elements

Hematocrit – the percentage of RBCs out of the total blood volume

PHYSICAL CHARACTERISTICS AND VOLUME Blood is a sticky, opaque, metallic taste

Color varies from scarlet to dark red

The pH of blood is 7.35–7.45

Temperature is 38C

Blood accounts for approximately 8% of body weight

Average volume: 5–6 L for males, and 4–5 L for females

FUNCTIONS AND DISTRIBUTION OF BLOOD

Protects against fluid loss

Provides immunity

Regulates pH

Maintains osmotic pressure

BLOOD PLASMA Blood plasma contains over 100 solutes, including:

Proteins: albumin, transferrin, globulins, complement and clotting proteins

Waste products: lactic acid, urea, creatinine

Nutrients – glucose, carbohydrates, amino acids

Electrolytes – sodium, potassium, calcium, chloride, bicarbonate

Respiratory gases – oxygen and carbon dioxide

FORMED ELEMENTS

Erythrocytes, leukocytes, and platelets Life span is variable

Stem cell renewal or division

ERYTHROCYTES (RBCS)

Biconcave discs

Anucleate

Essentially no organelles

Spectrin allows flexibility

Hemoglobin (97%)

Anerobic ATP generation

STRUCTURE OF HEMOGLOBIN

Figure 17.4

PRODUCTION OF ERYTHROCYTES

Hematopoiesis –born of blood

Stem cells in the red bone

Maintain constant level

ERYTHROPOIESIS REGULATION Indirectly through thyroxine, androgens, GH

Vitamin B12

Erythropoietin (EPO)

release by the kidneys

triggered by hypoxia

Increases division of erythroblasts and maturation rate

Oxygen carrying ability of the blood

Homeostasis: Normal blood oxygen levels

IncreasesO2-carryingability of blood

Erythropoietinstimulates redbone marrow

Reduces O2 levelsin blood

Kidney (and liver to a smallerextent) releases erythropoietin

Enhancederythropoiesisincreases RBC count

Stimulus: Hypoxia due todecreased RBC count,decreased amount of hemoglobin, or decreased availability of O2

Start

Imbalance

Imbalance

ERYTHROPOIETIN MECHANISM

Figure 17.6

FATE AND DESTRUCTION OF ERYTHROCYTES The life span =100–120 days

Dying RBCs are engulfed by macrophages

Iron returned to blood bound by transferrin

Heme is degraded into bilirubin, bile, feces

Globin metabolized or excreted

Hemoglobin

Aminoacids

Globin

Raw materials aremade available inblood for erythrocytesynthesis.

Iron is bound to transferrin and released to blood from liver as needed for erythropoiesis

Food nutrients,including aminoacids, Fe, B12,and folic acidare absorbedfrom intestineand enter blood

Heme

Circulation

Iron storedas ferritin,hemosiderin

Bilirubin

Bilirubin is picked up fromblood by liver, secreted intointestine in bile, metabolizedto stercobilin by bacteriaand excreted in feces

Erythropoietin levelsrise in blood.

Erythropoietin and necessaryraw materials in blood promoteerythropoiesis in red bone marrow.

New erythrocytesenter bloodstream;function about120 days.

Low O2 levels in blood stimulatekidneys to produce erythropoietin.

Aged and damaged redblood cells are engulfed bymacrophages of liver, spleen,and bone marrow; the hemoglobinis broken down.

1

2

3

4

5

6

Figure 17.7

ERYTHROCYTE RECYCLING

ERYTHROCYTE DISORDERS Anemia – blood has abnormally low oxygen-

carrying capacity

It is a symptom rather than a disease itself

Blood oxygen levels cannot support normal metabolism

ERYTHROCYTE DISORDERS

Hemorrahgic anemia

Hemolytic anemia

Aplastic anemia

Iron-deficiency anemia

Pernicious anemia

Thalassemias

Sickel-cell anemia

Polycythemia

LEUKOCYTES (WBCS)

Leukocytes, the only blood components that are complete cells:

Are less numerous than RBCs

Make up 1% of the total blood volume

Capable of diapedesis and margination

PERCENTAGES OF LEUKOCYTES

Figure 17.9

SUMMARY OF FORMED ELEMENTS

Table 17.2.1

(a) (b) (c) (d) (e)

Hemocytoblast

Myeloid stem cell Lymphoid stem cell

Myeloblast MyeloblastMyeloblast Lymphoblast

Stem cells

Committedcells

Promyelocyte PromyelocytePromyelocyte Promonocyte Prolymphocyte

Eosinophilicmyelocyte

Neutrophilicmyelocyte

Basophilicmyelocyte

Eosinophilicband cells

Neutrophilicband cells

Basophilicband cells

Develop-mentalpathway

Eosinophils NeutrophilsBasophils

Granular leukocytes

Plasma cells

Some become

Monocytes Lymphocytes

Macrophages (tissues)

Agranular leukocytes

Some become

Figure 17.11

LEUKOCYTES DISORDERS

Leukocytosis

Leukemia refers to cancerous conditions involving WBCs

Myelocytic leukemia

Lymphocytic leukemia

Acute leukemia

Chronic leukemia

PLATELETS Fragments of megakaryocytes

Platelets are part of the clotting

HEMOSTASIS

A series of reactions for stoppage of bleeding

Three phases occur in rapid sequence

Vascular spasms

Platelet plug formation

Coagulation (blood clotting)

DETAILED EVENTS OF COAGULATION

Figure 17.13b

CLOT RETRACTION AND REPAIR Clot retraction – stabilization of the clot by squeezing

serum from the fibrin strands

Repair

Platelet-derived growth factor (PDGF) stimulates rebuilding of blood vessel wall

Fibroblasts form a connective tissue patch

Endothelial cells multiply , restoring the lining

FACTORS PREVENTING UNDESIRABLE CLOTTING

Endothelial lining of blood vessels

Platelet adhesion is prevented by:

Heparin and PGI2 secreted by endothelial cells

Vitamin E quinone, a potent anticoagulant

Aspirin

Wafarin (coumadin)

HEMOSTASIS DISORDERS

Thrombus

Embolus

Thrombocytopenia

Hemophilias

Hemophilia A, B, C

HUMAN BLOOD TYPING

Humans have 30 varieties of naturally occurring RBC antigens

The antigens of the ABO and Rh blood groups cause vigorous transfusion reactions when they are improperly transfused

Other blood groups (M, N, Dufy, Kell, and Lewis) are mainly used for legalities

ABO BLOOD GROUPS

Table 17.4