Functions and Composition of Blood

• Blood helps maintain homeostasis in several ways:

1.Transport of gases, nutrients, waste products

2.Transport of processed molecules

3.Transport of regulatory molecules

4.Regulation of pH and osmosis

5.Maintenance of body temperature

6.Protects against foreign substances such as microorganisms and toxins

7.Blood clotting prevents fluid and cell loss and is part of tissue repair

Functions and Composition of Blood

• Blood is a connective tissue consisting of plasma and formed elements

• Blood is the body’s only fluid tissue

• It is composed of liquid plasma and formed elements

• Formed elements include: – Erythrocytes, or red blood cells (RBCs)

– Leukocytes, or white blood cells (WBCs)

– Platelets

• Hematocrit: the percentage of RBCs out of the total blood volume

Functions and Composition of

Blood

• Total blood

volume is

approximately

5 liters

Fig. 16.1

Functions and Composition of Blood

• Blood is a sticky, opaque fluid with a 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 (1.5 gallons) for males, and 4–5 L for females

Plasma

• Pale yellow fluid containing over 100 solutes

• Mostly water (91%)

• Contains proteins (7%)– Albumin (58% of the plasma proteins)

• Helps maintain osmotic pressure

– Globulins (38% of the plasma proteins)• Immunity: antibodies and complement

• Transport: bind to molecules such as hormones

• Clotting Factors

– Fibrinogen (4% of the plasma proteins)• Converted to fibrin during clot formation

• Other substances (2%)– Ions (electrolytes): sodium, potassium, calcium, chloride,

bicarbonate

– Nutrients: glucose, carbohydrates, amino acids

– Waste products: lactic acid, urea, creatinine

– Respiratory gases: oxygen and carbon dioxide

Plasma

Tab. 16.1

Formed Elements

• Erythrocytes or red blood cells (RBCs)– About 95% of formed elements

– RBCs have no nuclei or organelles

• Leukocytes or white blood cells (WBCs)– Most of the remaining 5% of formed elements

– Only WBCs are complete cells

– Five types of WBCs

• Platelets – Just cell fragments

• Most formed elements survive in the bloodstream for only a few days

Tab.

16.2

Production of Formed Elements

• Most blood cells do not divide but are renewed by stem cells (hemocytoblasts) in bone marrow

• Hematopoiesis: blood cell production– Occurs in different locations before and after birth

• Fetus

– Liver, thymus, spleen, lymph nodes, and red bone marrow

• After birth

– In the red bone marrow of the

» Axial skeleton and girdles

» Epiphyses of the humerus and femur

– Some white blood cells are produced in lymphatic tissues

• Hemocytoblasts give rise to all formed elements– Growth factors determine the type of formed element

derived from the stem cell

Fig. 16.2

Hematopoiesis

Red Blood Cells

• Biconcave discs, anucleate, essentially no organelles

• RBCs are dedicated to respiratory gas transport– Filled with hemoglobin (Hb), a protein that functions in gas

transport

• RBCs are an example of how structure fits function– Biconcave shape has a huge surface area relative to volume

• Structural characteristics contribute to its gas transport function

– Biconcave shape also allows RBCs to bend or fold around their thin center

• Gives erythrocytes their flexibility

• Allow them to change shape as necessary

Fig. 16.3

Red Blood Cells

• Hemoglobin (Hb)– Accounts for about a third of the cell’s volume

– Consists of• The protein globin, made up of two alpha and two beta

chains, each bound to a heme group

• Each heme group bears an atom of iron, which can bind to one oxygen molecule

• Heme molecules transport oxygen (Iron is required)

– Oxygen content determines blood color

» Oxygenated: bright red

» Deoxygenated: darker red

• Globin molecules transport carbon dioxide

• One RBC contains 250 million Hb groups thus it can carry 1 billion molecules of O2

Hemoglobin

Fig. 16.4

Red Blood Cells

• Transport of Oxygen and Carbon Dioxide

– Oxygen

• Transported bound to hemoglobin ~98.5%

• Dissolved in plasma ~1.5%

• Each Hb molecule binds four oxygen atoms in a

rapid and reversible process

– Carbon dioxide

• Dissolved in plasma ~7%

• Transported as bicarbonate(HCO3–) ~70%

• Chemically bound to hemoglobin ~23%

• Transport and Exchange of Carbon Dioxide

– Carbon dioxide diffuses into RBCs and combines with

water to form carbonic acid (H2CO3), which quickly

dissociates into hydrogen ions and bicarbonate ions

•

– In RBCs, carbonic anhydrase reversibly catalyzes the

conversion of carbon dioxide and water to carbonic

acid

CO2 + H2O H2CO3 H+ + HCO3–

Carbon

dioxideWater

Carbonic

acid

Hydrogen

ion

Bicarbonate

ion

Red Blood Cells

Red Blood Cells

• Erythropoiesis is the production of RBCs– A hemocytoblast is transformed into a

proerythroblast

– Proerythroblasts develop into early erythroblasts

– The developmental pathway consists of three phases

1. Ribosome synthesis in early erythroblasts

2. Hb accumulation in intermediate erythroblasts and late erythroblasts

3. Ejection of the nucleus from late erythroblasts and formation of reticulocytes

– Reticulocytes are released from the red bone marrow into the circulating blood, which contains ~1-3% reticulocytes

– Reticulocytes then become mature erythrocytes

Red Blood Cell Production

• Circulating erythrocytes: The number remains constant and reflects a balance between RBC production and destruction– Too few RBCs leads to tissue hypoxia

– Too many RBCs causes undesirable blood viscosity

• Erythropoiesis is hormonally controlled and depends on adequate supplies of iron, amino acids, and B vitamins (folate and B12)– Erythropoietin (EPO) release by the kidneys is triggered by

• Hypoxia due to decreased RBCs

• Decreased oxygen availability

• Increased tissue demand for oxygen

– Enhanced erythropoiesis increases the

• RBC count in circulating blood

• Oxygen carrying ability of the blood

Red Blood Cell Production

Fig. 16.5

Red Blood Cells

• The life span of an erythrocyte is 100–120 days

• Old RBCs become rigid and fragile, and their Hb begins to degenerate

• Dying RBCs are engulfed by macrophages located in the spleen or liver

• Heme and globin are separated and the iron is salvaged for reuse– Globin chains are broken down to individual amino acids and are

metabolized or used to build new proteins

– Iron released from heme is transported to the red bone marrow and is used to produce new hemoglobin

– Heme becomes bilirubin that is secreted in bile

• In the intestines bilirubin is converted by bacteria into other pigments

– Gives feces its brown color

– Gives urine its yellow color

Hemoglobin Breakdown

Fig. 16.6

White Blood Cells

• Only blood components that are complete cells

• Are less numerous than RBCs

• Make up 1% of the total blood volume

• Can leave capillaries via ameboid movement and move

through tissue spaces

• Two functions of WBCs

– Protect the body against invading microorganisms

– Remove dead cells and debris from tissues by phagocytosis

• Named according to their appearance in stained

preparations

– Granulocytes: contain large cytoplasmic granules

– Agranulocytes: very small granules that cannot be easily seen

with the light microscope

White Blood Cells

• Granulocytes: neutrophils, eosinophils,

and basophils

– Contain cytoplasmic granules that stain

specifically (acidic, basic, or both) with

Wright’s stain

– Are larger and usually shorter-lived than

RBCs

– Have lobed nuclei

– Are all phagocytic cells

White Blood Cells

• Neutrophils most common type of WBC

– Have two types of granules that:

• Take up both acidic and basic dyes

• Give the cytoplasm a lilac color

• Contain peroxidases, hydrolytic enzymes, and

defensins (antibiotic-like proteins)

• Neutrophils are our body’s bacteria slayers

• Pus is an accumulation of dead

neutrophils, cell debris and fluid at sites of

infections

White Blood Cells

• Basophils account for 0.5% of WBCs

– Have large, purplish-black (basophilic)

granules that contain

• Histamine: inflammatory chemical that acts as a

vasodilator and attracts other WBCs

(antihistamines counter this effect)

• Heparin: prevents the formation of clots

White Blood Cells

• Eosinophils account for 1–4% of WBCs

– Have red-staining, bilobed nuclei connected

via a broad band of nuclear material

– Have red to crimson (acidophilic) large,

coarse, lysosome-like granules

– Lessen the severity of allergies by reducing

inflammation

– Lead the body’s counterattack against

parasitic worms

White Blood Cells

• Agranulocytes: lymphocytes and

monocytes

– Lack visible cytoplasmic granules

– Are similar structurally, but are functionally

distinct and unrelated cell types

– Have spherical (lymphocytes) or kidney-

shaped (monocytes) nuclei

White Blood Cells

• Lymphocytes account for 25% or more of WBCs– Have large, dark-purple, circular nuclei with a thin rim

of blue cytoplasm

– Are found mostly enmeshed in lymphoid tissue (some circulate in the blood)

• There are two types of lymphocytes: T cells and B cells– B cells

• Stimulated by bacteria or toxins

• Give rise to plasma cells, which produce antibodies

– T cells • Protect against viruses and other intracellular

microorganisms

• Attack and destroy the cells that are infected

White Blood Cells

• Monocytes account for 4–8% of leukocytes

– They are the largest leukocytes

– They have an abundant pale-blue cytoplasm

– They have purple-staining, U- or kidney-shaped nuclei

– They leave the circulation, enter tissue, and differentiate into macrophages

• Are highly mobile and actively phagocytic

• Activate lymphocytes to mount an immune response

Tab. 16.2

Fig. 16.7

Identification of WBCs

Fig. 16.8

Platelets

• Fragments of megakaryocytes with a blue-staining outer region and a purple granular center

• Function in clotting by two mechanisms

1. Formation of platelet plugs, which seal holes in small vessels

2. Formation of clots, which help seal off larger wounds in the vessels

• Their granules contain ADP and thromboxanes

Preventing Blood Loss

• A series of reactions for stoppage of

bleeding

• Three phases occur in rapid sequence

– Vascular spasms: immediate

vasoconstriction in response to injury

• Thromboxanes and endothelin can cause vascular

spasms

– Platelet plug formation

– Coagulation (blood clotting)

Preventing Blood Loss

• Platelet Plugs

– Platelets do not stick to each other or to blood vessels

– Upon damage to blood vessel endothelium platelets:

• With the help of von Willebrand factor (VWF) adhere to

collagen

• Are stimulated by and then release more thromboxane and

ADP, which attract still more platelets

• Stick to exposed collagen fibers and form a platelet plug

– The platelet plug is limited to the immediate area of

injury by prostacyclin

– Can seal up a small breaks in a blood vessels that

occur many times each day

Platelet Plug Formation

Fig. 16.9

Blood Clotting

• Blood clotting, or coagulation, is the formation of a clot (a network of protein fibers called fibrin)

• Blood clotting begins with the extrinsic or intrinsic pathway

– Both pathways end with the production of activated factor X

• Extrinsic pathway begins with the release of thromboplastin from damaged tissue

• Intrinsic pathway begins with the activation of factor XII

Blood Clotting

• Activated factor X, factor V, phospholipids, and Ca2+ form prothrombinase

• Prothrombin is converted to thrombin by prothrombinase

• Fibrinogen is converted to fibrin by thrombin– Insoluble fibrin strands form the structural basis of a clot

– Fibrin causes plasma to become a gel-like trap

– Fibrin in the presence of calcium ions activates factor XIII that:

• Cross-links fibrin

• Strengthens and stabilizes the clot

• Away from the site of injury anticoagulants in the blood, such as antithrombin and heparin, prevent clot formation

Fig.

16.10

Clot Retraction and Fibrinolysis

• Clot retraction: stabilization of the clot by squeezing serum from the fibrin strands

– Results from the contraction of platelets, which pull the edges of damaged tissue closer together

– Serum, which is plasma minus fibrinogen and some clotting factors, is squeezed out to the clot

• Thrombin and tissue plasminogen activator activate plasmin, which dissolves fibrin (fibrinolysis)

Fig.

16.11

Blood Grouping

• RBC membranes have glycoprotein antigens on their external surfaces

• These antigens are:

– Unique to the individual

– Recognized as foreign if transfused into another individual

– Promoters of agglutination and are referred to as agglutinogens

• Presence or absence of these antigens is used to classify blood groups

Blood Grouping

• Transfusion reactions occur when

mismatched blood is infused

• Antibodies can bind to the donor’s RBC

antigens, resulting in agglutination or

hemolysis of RBCs, leading to

– Diminished oxygen-carrying capacity

– Clumped cells that impede blood flow

– Ruptured RBCs that release free hemoglobin

into the bloodstream

ABO Blood Group

• The ABO blood groups consists of:

– Two antigens (A and B) on the surface of the RBCs

– Two antibodies in the plasma (anti-A and anti-B)

Blood type Antigens Present Antibodies Present

A B Anti-A Anti-B

AB + + – –

B – + + –

A + – – +

O – – + +

Fig.

16.12

Agglutination Reaction

Fig. 16.13

Rh Blood Group

• Rh-positive blood has certain Rh antigens (the D antigen), whereas Rh-negative blood does not

• Antibodies against the Rh antigen are produced when a Rh-negative person is exposed to Rh-positive blood

• The Rh blood group is responsible for hemolytic disease of the newborn, which can occur when the fetus is Rh-positive and the mother is Rh-negative

Fig. 16.14

Hemolytic

Disease

of the

Newborn

(HDN)

Diagnostic Blood Tests

• Laboratory examination of blood can assess an individual’s state of health

• Microscopic examination:

– Variations in size and shape of RBCs: prediction of anemia

– Type and number of WBCs: diagnostic of various diseases

• Chemical analysis can provide a comprehensive picture of one’s general health status in relation to normal values

Diagnostic Blood Tests

• Red blood cell count (million/mL)– Male 4.6-6.2 million/mL

– Female 4.2-5.4 million/mL

• Hemoglobin measurement (grams of hemoglobin per/mL of blood– Male 14-18 g/100mL

– Female 12-16 g/100mL

• Hematocrit measurement (percent volume of RBCs)– Male 40%-52%

– Female 38%-48%

• White blood cell count (WBCs/mL)– Male and Female 5000-

9000 WBCs/mL

• Differential white blood cell count (the percentage of each type of WBC)– Neutorphils – 60%-70%

– Lymphocytes – 20%-25%

– Monocytes – 3%-8%

– Eosinophils – 2%-4%

– Basophils – 0.5%-1%

The complete blood count consists of the following

Fig.

16.15

Diagnostic Blood Tests

• Clotting

– Platelet count and prothrombin time measure the

ability of the blood to clot

• Blood Chemistry

– The composition of materials dissolved or suspended

in plasma can be used to assess the functioning and

status of the body’s systems

• Glucose

• Urea

• Nitrogen

• Bilirubin

• Cholesterol