Copyright 2009, John Wiley & Sons, Inc. Chapter 13 The Cardiovascular System: Blood.

Copyright 2009, John Wiley & Sons, Inc.

Chapter 13The Cardiovascular System: Blood


Introduction The cardiovascular system consists of three interrelated

components: blood, the heart, and blood vessels. Blood transports various substances, helps regulate several life

processes, and affords protection against disease. Blood is a connective tissue composed of a liquid portion called

plasma and a cellular portion consisting of various cells and cell fragments.

Interstitial fluid is the watery fluid that bathes body cells and is constantly renewed by the blood.

Blood transports oxygen into the lungs. Blood also transports water and nutrients into the gastrointestinal tract. Carbon dioxide and other wastes from the body cells into the interstitial fluid and then into the blood.

Blood then transports the wastes to various organs—the lungs, kidneys, skin, and digestive system—for elimination from the body.


Functions of Blood

1 . Transportation: Blood transports oxygen from the lungs to the cells of the body and carbon dioxide from the body cells to the lungs for exhalation.

2. Regulation: Circulating blood helps maintain homeostasis in

all body fluids. (regulate pH, adjust body temperature, and blood osmotic pressure mainly through interactions of dissolved ions and proteins).

3. Protection: Against excessive blood loss and disease.


Physical Charateristics of Blood Blood is denser and more viscous (thicker) than water, which is part of

the reason it flows more slowly than water.

The temperature of blood is about 380C (100.40F), which is slightly higher

than normal body temperature,

Blood is slightly alkaline pH ranging from 7.35 to 7.45.

The color of blood varies. When saturated with oxygen it is bright red;

when unoxygenated, the blood is dark red to purple.

Blood constitutes about 8% of the total body weight.

The blood volume is 5–6 liters (1.5 gal) in an average-sized adult male

and 4–5 liters (1.2 gal) in an average sized adult female.


Components of Blood (Fig. 13.1)


Blood Plasma Plasma is about 91.5% water and 8.5% solutes, most of which

(7% by weight) are proteins. Some of the proteins in plasma are also found elsewhere in the

body, but those confined to blood are called plasma proteins. Hepatocytes (liver cells) synthesize most of the plasma proteins,

which include the albumins (54% of plasma proteins), globulins (38%), and fibrinogen (7%).

Certain blood cells develop into cells that produce gamma globulins, an important type of globulin, also called antibodies or immunoglobulins.

Other solutes in plasma include electrolytes, nutrients, regulatory substances such as enzymes and hormones, gases, and waste products such as urea, uric acid, creatinine, ammonia, and bilirubin.


Formed Elements The formed elements of the blood include red blood cells

(RBC s ), white blood cells (WBCs), and platelets . Although RBCs and WBCs are living cells, platelets are cell

fragments. There are several distinct types of WBCs— neutrophils,

lymphocytes, monocytes, eosinophils, and basophils—each having a unique microscopic appearance.

The percentage of total blood volume occupied by RBCs is called the hematocrit . The normal range of hematocrit for adult females is

about 38–46% (average542); for adult males it is about 40–54% The hormone testosterone, which is present in much higher

concentration in males than in females, stimulates synthesis of a hormone called erythropoietin the kidneys. This hormone, which stimulates production of RBCs, contributes to higher hematocrits in males.


Formed Elements (Fig. 13.2)


Red Blood CellsRed blood cells (RBCs) or erythrocytes; contain the oxygen

carrying protein hemoglobin, which is a pigment that gives whole blood its red color.

An adult male has about 5.4 million red blood cells per microliter (mL) of blood, and a healthy adult female has about 4.8 million.

To maintain normal numbers of RBCs, new mature cells enter the circulation at a rate of at least 2 million per second,

a pace that balances the equally high rate of RBC destruction.

RBC Anatomy - are biconcave discs with a diameter of 7– 8mm. RBCs lack a nucleus and other organelles and can neither

reproduce nor carry on extensive metabolic activities. The cytosol of RBCs contains hemoglobin molecules


Red Blood Cells (Fig. 13.3)


RBC Function Each RBC contains about 280 million hemoglobin molecules; each

hemoglobin molecule can carry up to four oxygen molecules. A hemoglobin molecule consists of a protein called globin, four

polypeptide chains (two alpha and two beta chains), plus four nonprotein pigments called hemes .

At the center of each heme ring is an iron ion (Fe2+) that can combine reversibly with one oxygen molecule.

Hemoglobin releases oxygen, which diffuses first into the interstitial fluid and then into cells.

Hemoglobin also transports about 13% of the total carbon dioxide, a waste product of metabolism.

Hemoglobin also plays a role in regulation of blood flow and blood pressure. The gaseous hormone nitric oxide (NO), produced by the endothelial cells that line blood vessels, binds to hemoglobin. The released NO causes vasodilation, improves blood flow and enhances oxygen delivery to cells near the site of NO release.


Shapes of Red Blood Cells(Fig. 13.4)


RCB Life Cycle Red blood cells live only about 120 days Ruptured red blood cells are removed from circulation and

destroyed by fixed phagocytic macrophages in the spleen and liver, and the breakdown products are recycled.

Erythropoiesis: Production of RBCs,starts in the red bone marrow with a precursor cell called a proerythroblast .

The proerythroblast divides producing cells that begin to synthesize hemoglobin.

Ultimately, the cell ejects its nucleus and becomes a reticulocyte. Reticulocytes, which are composed of about 34% hemoglobin and

retain some mitochondria, ribosomes, and endoplasmic reticulum, pass from red bone marrow

Reticulocytes usually develop into erythrocytes, or mature red blood cells, within 1–2 days after their release from red bone marrow.


Blood Group System More than 100 kinds of genetically determined antigens have been

detected on the surface of red blood cells; at least 14 are currently recognized.

The ABO blood grouping system is based on two antigens, symbolized as A and B.

Individuals whose erythrocytes manufacture only antigen A are said to have blood type A.

Those who manufacture only antigen B are type B. Individuals who manufacture both A and B are type AB. Those who manufacture neither are type O.

The Rh blood grouping system is so named because it was first worked out using the blood of the Rhesus monkey.

Individuals whose erythrocytes have the Rh antigens (D antigens) are designated Rh1. Those who lack Rh antigens are designated Rh2.


WBC Anatomy and Types

White blood cells, or leukocytes, have a nucleus and do not contain hemoglobin

WBCs are classified as either granular or agranular, depending on whether they contain conspicuous cytoplasmic vesicles (originally called granules) that are made visible by staining when viewed through a light microscope.

Granular leukocytes include neutrophils, eosinophils, and basophils; Agranular leukocytes include lymphocytes and monocytes. Monocytes and granular leukocytes develop from myeloid stem

cells. Lymphocytes develop from lymphoid stem cells.


Granular Leukocytes Eosinophil: The large, uniform-sized granules within an eosinophil

are eosinophilic they stain red-orange with acidic dyes. Most often has two or three lobes connected by either a thin strand or a thick strand of nuclear material.

Basophil: The round, variable-sized granules of a basophil are basophilic —they stain blue-purple with basic dyes The granules commonly obscure the nucleus, which has two lobes.

Neutrophil : The granules of a neutrophil are smaller, evenly distributed, and pale lilac in color. Because the granules do not strongly attract either the acidic (red) or basic (blue) stain, these WBCs are neutrophilic. The nucleus has two to five lobes, connected by very thin strands of nuclear material.

Because older neutrophils have several differently shaped nuclear lobes, they are called polymorphonuclear leukocytes (PMNs), or “polys.”


Agranular Leukocytes Lymphocyte are classified by cell diameter as large

lymphocytes(10–14 mm) or small lymphocytes (6–9 mm). Monocyte – found in blood, migrate from the blood into the tissues,

where they enlarge and differentiate into macrophages. Fixed macrophages - reside in a particular tissue. Wandering macrophages, which roam the tissues and gather at

sites of infection or inflammation. White blood cells and other nucleated body cells have proteins,

called major histocompatibility (MHC) antigens, protruding from their plasma membranes into the extracellular fluid. These cell identity markers are unique for each person (except identical twins). Although RBCs possess blood group antigens, they lack the MHC antigen.


Structure of White Blood Cells (Fig. 13.5)


WBC Functions The general function of white blood cells is to combat them by

phagocytosis or immune responses. To accomplish these tasks, many WBCs leave the bloodstream and collect at points of pathogen invasion or inflammation.

Once granular leukocytes and monocytes leave the bloodstream to fight injury or infection, they never return to it.

Lymphocytes, on the other hand, continually recirculate—from blood to interstitial spaces of tissues to lymphatic fluid and back to blood.

WBCs are able to cross capillary walls by a process termed emigration.

During emigration, WBCs roll along the endothelium that forms capillary walls, stick to it, and then squeeze between endothelial cells. The precise signals that stimulate emigration through a particular blood vessel vary for the different types of WBCs.


Platelets Hemopoietic stem cells also differentiate into cells that produce

platelets. Under the influence of the hormone thrombopoietin, myeloid stem cells develop into megakaryocyte that develop into precursor cells called megakaryoblasts

Megakaryoblasts transform into megakaryocytes, huge cells that splinter into 2000–3000 fragments. Each fragment, enclosed by a piece of the cell membrane, is a platelet (thrombocyte).

Platelets break off from the megakaryocytes in red bone marrow and then enter the blood circulation.

Between 150,000 and 400,000 platelets are present in each mL of blood.


Platelets Platelets help stop blood loss from damaged blood vessels by

coming together to form a platelet plug that fills the gap in the blood vessel wall.

Platelets can initiate a series of chemical reactions that culminates in the formation of a network of insoluble protein threads called fibrin.

A blood clot consists of fibrin threads, platelets, and any blood cells trapped in the fibrin.

The blood clot not only provides a seal in the damaged area of a blood vessel to prevent blood loss, but also pulls the edges of the damaged vessel together to help heal the damage.

Platelets have a short life span, normally just 5–9 days. Aged and dead platelets are removed from the circulation by fixed

macrophages in the spleen and liver.


Blood Clot (Fig. 13.6)

Copyright 2009, John Wiley & Sons, Inc. Chapter 13 The Cardiovascular System: Blood.

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