Chapter 17 – Blood

Functions of blood

• Transportation/distribution – Oxygen, carbon dioxide, nutrients, waste

products, hormones • Regulation/homeostasis – Body temperature, pH, fluid volume

• Protection – Clotting – Fights infection

Blood

• Classified as connective tissue – Large extracellular matrix (plasma) approx 55%– Formed elements approx 45%

• Color – Due to hemoglobin in red blood cells

• Bright red = oxygen-rich; dark brick red = oxygen-poor

• pH– Slightly alkaline 7.35 – 7.45

• Volume – Approx 8% of body weight – Males – 5-6 L– Females – 4-5 L

Whole blood composition

Formed elements

• Are created in red bone marrow (hematopoiesis or hemopoiesis) from stem cells

• Erythrocytes (red blood cells)• Leukocytes (white blood cells)– Only type that are true cells

• Thrombocytes (platelets)

Erythrocyte structure

• Biconcave discs – Allows for

rapid gas diffusion

• Anucleate and no organelles

• Packed with hemoglobin

Hemoglobin structure • 4 polypeptide chains

(2 alpha and 2 beta chains)

• Each chain has an associated heme group

• Each heme group has a central iron atom – Serves as the binding

site for oxygen molecule

Gas exchange

• In lungs – Oxygen diffuses from air sacs in lungs into blood and

binds with iron in hemoglobin • Oxyhemoglobin – bright red

• In body tissues – Oxygen detaches from iron to diffuse out of bloodstream

• Deoxyhemoglobin – dark red

• Hemoglobin also carries about 20% of carbon dioxide – Carbaminohemoglobin

• CO2 binds to amino acids of globin chains

Erythrocyte production • Red bone marrow

– Large capillaries (blood sinusoids)– Cells

• Immature blood cells • Marcophages – consume debris/foreign cells

• Hemocytoblast – Ability to become any bloodcell type – Once ‘committed’ it can not change pathway

• Pathway – Color of cell changes from blue to pink as

hemoglobin accumulates – Reticulocytes

• Speckled appearance due to clumped ribosomes • In circulation approx 2 days before forming mature

RBC• 1 – 2% of RBC count; indicates rate of RBC production

Regulation of RBC production

• Erythropoietin (EPO)– Hormone produced by (mainly) kidneys and liver – Stimulates RBC production in response to low

blood oxygen levels • Also in response to testosterone

– Commerically available for kidney failure patients• EPO increases hematocrit (measure of % of RBCs in

whole blood)• Has been abused by athletes

Blood Typing

• Antigens or agglutinogens– Glycoproteins on the surface of RBCs that serve as

identification• Antibodies or agglutinins – Will attack foreign antigens – Causes agglutination, or clumping

• Small vessels can become blocked • Leads to cell destruction

– Free hemoglobin in kidneys can result in acute renal failure

• ABO and Rh can cause severe reactions if mismatched during a blood transfusion

ABO blood types

Rh factor • + has the Rh antigen; - does not • Rh – individuals do not have preformed antibodies

against the Rh factor– Must have an exposure to the antigen in order to form

antibodies against it • Rh- woman – Risk of erythroblastosis fetalis – Given Rogam during pregnancy

Erythroblastosis fetalis

Leukocytes • Involved with immunity• Diapedesis – WBCs can leave bloodstream and enter

the lymphatic system and loose connective tissue – Amoeboid movement

• Types – Granulocytes – cytoplasm contains obvious granules

• Neutrophil • Eosinophil • Basophil

– Angranulocytes – cytoplasm does not contain granules• Monocyte • Lymphocyte

Granulocytes • Neutrophil

– Nucleus is multilobed• Also called polymorphonuclear

leukocytes (PMNs)

– Phagocytize bacteria

• Eosinophil – Fight parasites that are too

large for phagocytosis • Release enzymes that digest

parasite

• Basophil – Histamine – allergic reactions

• Vasodilator; attracts other WBCs

– Heparin – antocoagulant

Agranulocytes • Monocytes

– Enters tissues to become macrophages

– Fight viral infections, chronic infections, bacterial-infected cells

• Lymphocytes – Most are located within the

lymphatic system – T cells

• Destroy infected cells and tumor cells

– B cells• Plasma cells produce antibodies • Fight ‘free’ infectious agents

(haven’t entered a cell yet)

Leukocyte production • Relative amount of WBCS– “Never Let Mom Eat

Beans”

• Lifespan = less than 10 days

• Stem cell lines– Hemocytoblast

differentiates into either:• Lymphoid stem cell line

– Develops into lymphocytes • Myeloid stem cell line

– Develops into all formed elements of blood except lymphocytes

Thrombocyte (platelet) production

• Stimulated by thrombopoietin (produced by kidneys)

• Megakaryocyte is formed by mitosis without cytokinesis

• Megakaryocyte presses against sinusoid wall and extends cytoplasmic branches through walls into bloodstream – Break off to form platelets

Hemostasis • Hemostasis – stopping of bleeding • 3 stages – Vascular

• Vascular spasm • Endothelial damage exposes underlying collagen • Smooth muscle contraction; endothelium becomes sticky

– Platelet • Platelets adhere to endothelium and each other to form a plug

– Coagulation• Clotting cascade ultimately forms fibers

• Clot retraction – Platelets contract – brings damaged regions closer together

for repair

Fibrinolysis

• Clot dissolution • Plasminogen converts to plasmin – Plasminogen trapped in clot• Slow conversion

– Digests fibrin strands

Abnormal values • Red blood cells

– Anemia - low • Iron insufficiency, blood loss, kidney disease, bone marrow disorder

– Polycythemia – elevated • Bone marrow disorder, dehydration

• White blood cells – Leukopenia – low

• Bone marrow disorder

– Leukocytosis – elevated• Infection, inflammation, bone marrow disorder

• Platelets – Thrombocytopenia – low

• Excessive destruction or inadequate production

– Thrombocytosis – elevated • Infection, inflammation, cancer