Blood

Chapter 11

Pgs 343-359

Overview

• Functions of Blood• Composition of Blood• Plasma

– Plasma proteins

• Formed Elements– Production of formed elements– Red blood cells– White blood cells– Platelets

Functions of Blood

• Transportation of dissolved gases, nutrients, hormones, and metabolic wastes

• Regulation of pH and electrolyte composition of ISF

• Restriction of fluid loss through damaged vessels and other injury sites

• Defense against toxins and pathogens• Stabilization of body temperature

Composition of Blood

• Plasma

• Formed elements– Red blood cells (RBC) or Erythrocytes– White blood cells (WBC) or Leukocytes– Platelets

• Both constitute whole blood– 5-6 L in men– 4-5 L in women

Plasma

• Electrolyte concentration similar to ISF

• Plasma proteins– Lg so cannot diffuse– 3 primary classes

• Albumins• Globulins• Fibrinogen

• Serum

Formed Elements: The Production

• Hemopoiesis – Embryonic blood cells– Stem cells

• Hemocytoblasts

Hemocytoblasts

Myeloid stem cells Lymphoid stem cells

Red Blood Cells (Erythrocytes)

• Accounts for 99.9% of formed elements• RBC count (#RBCs per microliter)

– Adult male: 5.4million/μl

• Hematocrit: % of whole blood occupied by cellular elements– Determined by centrifuge– Adult male: avgs 46%– Closely approx vol of erythrocytes

• Hematocrit values often reported as:– Volume of packed red cells (VPRC)– Packed cell volume (PCV)

Structure of RBCs

• Specialized to transport oxygen and carbon dioxide

• Shape has 2 important effects on function:– Lg SA:vol

• Increases rate of diffusion between cytoplasm and plasma

– Enables bending and flexing to fit through narrow capillaries

• Contains hemoglobin (Hb)

RBC Formation (Erythropoiesis)

• Occurs in red bone marrow (myeloid tissue)

• Erythroblasts– Very immature RBCs

• Actively synthesizing Hb• After 4 days differentiates

into:

• Reticulocyte– Enter circulation after 2

days in bone marrow– After 24 hrs in circ,

complete maturation and become:

• Erythrocyte!

Hemocytoblasts

Myeloid stem cells Lymphoid stem cells

Proerythroblast

Erythroblast

Reticulocyte

Erythrocyte

RBCs and Blood Types

• Blood type classification determined by presence or absence of specific surface antigens in RBC membrane– Surface antigens of RBC called agglutinogens– Genetically determined

• 3 important antigens:– A– B– Rh

RBCs and Blood Typing

• Type A: antigen A only (40% US pop)

• Type B: antigen B only (10%)

• Type AB: both A and B (4%)

• Type O: neither A nor B (46%)

• Rh factor: present in some, absent in others

White Blood Cells (Leukocytes)

• Divided into 2 groups:– Granulocytes

• Neutrophils• Eosinophils• Basophils

– Agranulocytes• Monocytes• Lymphocytes

• Microliter typically contains 6,000-9,000 WBCs

• Most located in connective tissue proper or in organs of lymphatic system

WBC Circulation and Movement

• Do not circulate for extended periods of time

• 4 characteristics of circulating WBCs:– Amoeboid movement– Diapedesis – Positive chemotaxis– Phagocytosis

WBCs: General Functions

• Nonspecific defense– Neutrophils– Eosinophils– Basophils– Monocytes

• Specific defense– Lymphocytes

Neutrophils

• 50-70% circulating WBCs

• Dense, twisted nucleus

• 1st to arrive to injury scene

• Active phagocytes– Specialize in attacking

and digesting bacteria

Eosinophils

• 2-4% circulating WBCs

• Similar in size to neutrophils

• Contain granules and 2-lobed nucleus

• Attracted to foreign compounds that have reacted with circulating antibodies

Basophils

• Less than 1% circulating WBCs

• Numerous granules• Migrate to injury site,

cross cap wall, and accum w/in damaged tissue– Discharge granules

into ISF• Contain heparin and

histamine

Monocytes

• 2-8% circulating WBCs

• Lg, oval (kidney) shaped nucleus

• Remain in circ only 24 hrs before entering tissue– Become a free

macrophage• Very aggressive

Lymphocytes

• 20-30% circulating WBCs• Lg nucleus w/ thin halo of

cytoplasm• Continuously migrating

from bloodstream tissues blood stream

• Protect but do not rely on phagocytosis

• Attack foreign and abnormal cells

Differential Count and Changes in WBC Profiles

• Differential count– Number of circulating WBCs obtained in a blood

sample– Values reported indicate the # of each type of cell

encountered in a sample of 100 WBCs• Leukopenia

– Too few WBCs• Leukocytosis

– Too many WBCs• Leukemia

– Extreme form of leukocytosis (WBC counts of 100,000/μl

White Blood Cell Formation

• Stem cells originate in red bone marrow

• All from myeloid stem cells except for lymphocytes

• Neutrophils, eosinophils, basophils complete dev in marrow

• Monocytes begin in marrow, enter circ, complete development when free macrophages

WBC Formation: Lymphocytes

• Lymphoid stem cells migrate from bone marrow to lymphoid tissues

• Process called lymphopoiesis• Hormones involved in regulation of WBC

populations– Colony-stimulating factors (CSFs) regulate

WBCs other than lymphocytes– Thymosins promote differentiation of T-cells

from lymphocytes

Platelets

• Components of formed elements– Cell fragments; not individual cells

• Derived from megakaryocytes– Shed packets of cytoplasm

• Platelets!

• Initiate clotting process and help close injured blood vessels

• Continuously replaced• Thrombocytopenia: abnormally low count• Thrombocytosis: abnormally high count

Hemocytoblasts

Myeloid Stem Cells Lymphoid Stem Cells

Erythrocytes Platelets Basophils Eosinophils Neutrophils Monocytes Lymphocytes

B cells

T cells

NK cells