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Chapter 19�The Cardiovascular System: The Blood

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About this Chapter

Composition of Blood
Various cell types, origin and roles
Red blood cells, hemoglobin, RBCs life cycle
How coagulation works

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Blood composing

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Components of Blood

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The Origin of Blood Cells

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process of blood cells formation is known as: hematopoiesis or hemopoiesis

In the embryo

hemopoiesis occurs in yolk sac, liver, spleen, thymus, lymph nodes & red bone marrow.

In adult

occurs only in red marrow of flat bones like sternum, ribs, skull & pelvis and ends of long bones

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Characteristics of Red Blood Cells

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Red blood cells are:

Erythrocytes
Biconcave discs
One-third hemoglobin or:

Oxyhemoglobin
Deoxyhemoglobin

Able to readily squeeze through capillaries
Lack nuclei and mitochondria – (Can they reproduce or metabolize?)

Top view

2.0 micrometers

7.5 micrometers

Sectional view

(a)

(b)

b: © Bill Longcore/Photo Researchers, Inc.

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Red Blood Cell Counts

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RBC counts is the number of RBCs in a cubic millimeter or microliter of blood
It may vary depending on age and health
Typical ranges include:

4,600,000 – 6,200,000 in males (Why so high?)
4,200,000 – 5,400,000 in adult females (Why so low?)
4,500,000 – 5,100,000 in children (Why more than women?)

RBC counts reflect blood’s oxygen carrying capacity

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Hematocrit

Percentage of total blood volume occupied by blood cells (RBCs).

female normal range

38 - 46% (average of 42%)

male normal range

40 - 54% (average of 46%)
Testosterone and erythropoietin (EPO)

Anemia

Drop in hematocrit value.

Polycythemia

too many RBCs (over 65%)
dehydration, tissue hypoxia, blood doping in athletes or the use of EPO

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Hemoglobin

Globin protein consisting of 4 polypeptide chains
One heme pigment attached to each polypeptide chain

each heme contains an iron ion (Fe+2) that can combine reversibly with one oxygen molecule

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Transport of O2, CO2 and Nitric Oxide

Each hemoglobin molecule can carry 4 oxygen molecules from lungs to tissue cells
Hemoglobin transports 23% of total CO2 waste from tissue cells to lungs for release

combines with amino acids in globin portion of Hb

Hemoglobin transports nitric oxide & helping in regulation of blood pressure and blood flow

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RBC Life Cycle

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Red Blood Cell Production �and Its Control

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Low blood oxygen causes the kidneys and the liver to release erythropoietin (EPO) which stimulates RBC production
This is a negative feedback mechanism

(What does this mean?)

Within a few days many new blood cells appear in the circulating blood

Low blood oxygen

Liver

Kidney

Erythropoietin

Red bone marrow

+

–

Bloodstream

Stimulation

Inhibition

Release into

bloodstream

Increased

oxygen-

carrying

capacity

Increased

number of

red blood

cells

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Types of White Blood Cells

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White blood cells:

Are leukocytes
Protect against disease
WBC hormones are interleukins and colony-stimulating factors which stimulate development
There are five types of WBCs in two categories:

Granulocytes

Neutrophils
Eosinophils
Basophils

Agranulocytes

Lymphocytes
Monocytes

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Neutrophils

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First to arrive at infections
Phagocytic (What is this?)
54% - 62% of leukocytes

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Eosinophils

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Defend against parasitic worm infestations
1% - 3% of leukocytes
Elevated in parasitic worm infections and allergic reactions

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Basophils

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Release histamine (What does this do?)
Release heparin (What does this do?)
Less than 1% of leukocytes

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Monocytes

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Largest of all blood cells
May leave bloodstream to become macrophages
3% - 9% of leukocytes
Phagocytize bacteria, dead cells, and other debris

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Lymphocytes

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T cells and B cells

Both important in immunity

B cells produce antibodies
25% - 33% of leukocytes

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White Blood Cell Counts

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Typically 5,000 – 10,000 per cubic millimeter of blood

Leukopenia:

Low WBC count (below 5,000)

Leukocytosis:

High WBC count (above 10,000)

Differential WBC count

Lists percentages of types of leukocytes
May change in particular diseases

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Emigration

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Emigration is the process by which WBCs leave the blood stream, in which WBCs roll along endothelium, stick to it & squeeze between cells.

Neutrophils & macrophages phagocytize bacteria & debris. Phagocytosis is stimulated by factors released from microbs like toxin and kinins such process is called chemotaxis

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Hemostasis

Sequence of responses that stops bleeding in a quick & localized fashion when blood vessels are damaged
Methods utilized to reduce bleeding:

vascular spasm
platelet plug formation
blood clotting (coagulation = formation of fibrin threads)

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1-Blood Vessel Spasm

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Blood vessel spasm

Triggered by pain receptors, platelet release, or serotonin
Smooth muscle in blood vessel contracts (What does this do?)

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2-Platelet Plug Formation

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Platelet Adhesion

Platelet Release Reaction

Platelet Aggregation

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3- Blood Clotting Pathways

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Role of Vitamin K in Clotting

Normal clotting requires adequate vitamin K

fat soluble vitamin absorbed if lipids absorption is normal.
absorption slowed if bile release is insufficient

Required for synthesis of 4 clotting factors by hepatocytes

factors II (prothrombin), VII, IX and X

Produced by bacteria in large intestine

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Fate of Blood Clots

Tissue Plasminogen Activators (t-PA), which convert Plasminogen (inactive) to Plasmin (active) are released from injured vessel walls.

once plasmin is formed it digests fibrin threads and inactivates fibrinogen, prothrombin and factors V and XII.

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Fibrinolysis is the system whereby the fibrin clot is dissolved as the vessel heals in order to restore normal blood flow.

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Intravascular Clotting

Thrombus

clot (thrombus) forming in an unbroken blood vessel

forms on rough inner lining of BV
if blood flows too slowly (stasis) allowing clotting factors to build up locally & cause coagulation

Embolus

clot, air bubble or fat from broken bone in the blood

pulmonary embolus is found in lungs

Low dose aspirin blocks synthesis of thromboxane A2 & reduces inappropriate clot formation

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Blood Groups and Blood Types

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Hemolytic Disease of Newborn

Rh negative mom and Rh+ fetus will have mixing of blood at birth
Mom's body creates Rh antibodies unless she receives a RhoGam shot soon after first delivery, miscarriage or abortion

RhoGam binds to loose fetal blood and removes it from body before she reacts

In 2nd child, hemolytic disease of the newborn may develop causing hemolysis of the fetal RBCs

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Universal Donors and Recipients

People with type AB blood called “universal recipients” since have no antibodies in plasma
People with type O blood cell called “universal donors” since have no antigens on their cells

theoretically can be given to anyone

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