FORMED ELEMENTS OF BLOOD (cont.)

Functions of plateletsImportant role in hemostasis and blood coagulation; secondary role in defending against bacterial attacks

Hemostasis: refers to stoppage of blood flow; however, if injury is extensive, the blood-clotting mechanism is activated to assist

FORMED ELEMENTS OF BLOOD (cont.)

Platelet plug formation One to five seconds after injury to vessel wall,

platelets adhere to damaged endothelial lining and to each other, forming a platelet plug

Temporary platelet plug is an important step in hemostasis

Normal platelets (positive charge) adhere to damaged capillary wall and underlying collagen fibers, both of which have a negative charge

“Sticky platelets” form physical plug and secrete several chemicals involved in the coagulation process

Formation and life span of platelets (7 to 10 days): formed in red bone marrow, lungs, and spleen by fragmentation of megakaryocytes

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19-6 Platelets

• Platelet Counts

• 150,000 to 500,000 per microliter

• Thrombocytopenia

• Abnormally low platelet count

• Thrombocytosis

• Abnormally high platelet count

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19-5 White Blood Cells - nomenclature• WBC Disorders

• Leukopenia

• Abnormally low WBC count

• Leukocytosis

• Abnormally high WBC count

• Leukemia

• A malignancy of the bone marrow, often with an

extremely high WBC count, (and the WBC’s are

cancerous- it is not just the # which is abnormal)

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19-1 Physical Characteristics of Blood

• Important Functions of Blood

• Transportation of dissolved substances

• Regulation of pH and ions

• Restriction of fluid losses at injury sites

• Defense against toxins and pathogens

• Stabilization of body temperature

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19-1 Physical Characteristics of Blood

• Three Types of Formed Elements

1. Red blood cells (RBCs) or erythrocytes

• Transport oxygen

2. White blood cells (WBCs) or leukocytes

• Part of the immune system

3. Platelets

• Cell fragments involved in clotting

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19-1 Physical Characteristics of Blood

• Three General Characteristics of Blood

1.38C (100.4F) is normal temperature (10 higher than body)

2. High viscosity

3. Slightly alkaline pH (7.35–7.45)

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19-4 Blood Typing

• Surface Antigens

• Are cell surface proteins that identify cells to immune

system

• Normal cells are ignored and foreign cells attacked

• Blood Types• Are genetically determined

• By presence or absence of RBC surface antigens A, B, Rh (or D)

BLOOD TYPES: BLOOD GROUPS The ABO system Every person’s blood belongs to one

of four ABO blood groups Named for antigens on RBC

membranesType A: antigen A on RBCsType B: antigen B on RBCsType AB: both antigens A and B on RBCs; known as universal recipient

Type O: neither antigen A nor B on RBCs; known as universal donor

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Figure 19-7a Blood Types and Cross-Reactions

Type A Type B

Type A blood has RBCs withsurface antigen A only.

Type B blood has RBCs withsurface antigen B only.

Surfaceantigen A

Surfaceantigen B

If you have Type A blood, yourplasma contains anti-Bantibodies, which will attackType B surface antigens.

If you have Type B blood, yourplasma contains anti-Aantibodies, which will attackType A surface antigens.

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Figure 19-7a Blood Types and Cross-Reactions

Type AB

Type O

Type AB blood has RBCswith both A and B surfaceantigens.

Type O blood has RBCslacking both A and B surface antigens.

If you have Type AB blood,your plasma has neitheranti-A nor anti-B antibodies.

If you have Type O blood, yourplasma contains both anti-Aand anti-B antibodies.

So, A person with Type A blood will carry anti B antibodies

A person with Type B blood will carry anti A antibodies

A person with Type AB blood will carry NEITHER anti A NOR anti B

antibodies !!!

A person with Type O blood will carry BOTH anti A AND anti B

antibodies

Agglutination - it means ‘clumping’

A donor

A recipient

B recipient

A donor

BLOOD TYPES The Rh system Rh: the RHESUS ANTIGEN the Rh antigen is either present or absent on the

RBCs Rh-negative: RBCs have no Rh antigen

present Anti-Rh antibodies are not normally present

in blood; even on Rh negative blood BUT, anti-Rh antibodies can appear in Rh-negative blood if it has come in contact

with Rh-positive RBCs, such as when an Rh- mother gives birth to an Rh + baby.

Usually it only becomes a problem in a future pregnancy with another Rh positive

baby.

U.S. Blood-type Distribution O+ 38 percent of population A+ 34 percent of population B+ 9 percent of population O- 7 percent of population *

Universal donor A- 6 percent of population AB+ 3 percent of population * Universal

recipient B- 2 percent of population AB- 1 percent of population

* refers to Packed RBC’s, not whole blood

So, let’s practice some ‘type and cross matches: BP, who has blood type B+, is involved in anauto accident and has been bleeding. BP’s

Hemoglobin (Hgb) is down to 7.4 and is dropping. The call goes out for blood donors. BP’s classmates respond, but of the following, who will make suitable donor/s:

A. AN : Type A – D. OP Type O+ G. ABN AB-B. ON: Type O- E. BP Type BP H. ABP

AB+C. BN: Type B- F. AP A+

AnswerB+ recipient: Possible donors:

B+ O+

B- O-

B- recipient: only poss. Donors B- O-

Months later OP, who has blood type O+and had donated blood for BP, is now severely anemic due to a hemolytic reaction to a new medication, and her Hemoglobin (Hgb) is 6.5. BP, now healthy again, and so grateful, insists on donating his blood for OP. Can his blood be used? Of the classmates below, who would be suitable donors?

A. AN : Type A – D. OP Type O+ G. ABN AB-B. ON: Type O- E. BP Type BP H. ABP AB+C. BN: Type B- F. BN Type B- I. AP

A+

AnswerO+ recipient: only possible donor s O+

O-

(because the O recipient will have ANTIBODIES to A and B

antigens, Which would agglutinate types A, B, and AB red blood

cells )

BLOOD PLASMA Plasma: liquid part of blood; clear, straw-

colored fluid; composed of 90% water and 10% solutes)

Solutes: most of the plasma solutes are PROTEINS, consisting of three main compounds Albumins: help maintain osmotic balance of

the blood Globulins: essential component of the

immunity mechanism Fibrinogen: key role in blood clotting (and other ‘clotting factors’)

Plasma proteins have an essential role in maintaining normal blood circulation

BLOOD CLOTTING: COAGULATION Mechanism of blood clotting: goal of coagulation is to stop bleeding and

prevent loss of vital body fluid in a swift and sure method

Classic theory of coagulation advanced 1905

Identified four components critical to coagulationProthrombinThrombinFibrinogenFibrin

BLOOD CLOTTING: COAGULATION Current explanation of coagulation

involves three stages Stage 1: production of thromboplastin

activator by either of the following: Chemicals released from damaged tissues

(extrinsic pathway) Chemicals present in the blood (intrinsic

pathway)

Stage 2: conversion of prothrombin to thrombin

Stage 3: conversion of fibrinogen to fibrin and production of fibrin clot

COMMONPATHWAY

THE BOTTOM LINE TO REMEMBER: (the common coaglation pathway)

Prothrombin (factor II), >>>>>> THROMBIN

which activates

fibrinogen ( factor I) Fibri

n Network, clot

BLOOD CLOTTING: COAGULATION (cont.) Conditions that oppose clotting

Clot formation in intact vessels is opposed Several factors oppose clotting

Perfectly smooth surface of the normal endothelial lining of blood vessels does not allow platelets to adhere

Antithrombins: substances in the blood that oppose or inactivate thrombin; prevent thrombin from converting fibrinogen to fibrin (e.g., heparin)

BLOOD CLOTTING: COAGULATION (cont.) Conditions that hasten clotting

Rough spot in the endothelium Abnormally slow blood flow

Clot dissolution Fibrinolysis: physiological mechanism that dissolves clots Fibrinolysin: enzyme in the blood that

catalyzes the hydrolysis of fibrin, causing it to dissolve

Additional factors are presumed to aid clot dissolution (e.g., substances that activate profibrinolysin)

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• Fibrinolysis

• Slow process of dissolving clot

• Thrombin and tissue plasminogen activator (t-PA)

• Activate plasminogen

• Plasminogen produces plasmin

• Which digests fibrin strands

THE BIG PICTURE: BLOOD AND THE WHOLE BODY

Blood plasma transports substances, including heat, around the body, linking all body tissues together Substances can be transported between almost any two

points in the body Blood tissue contains formed elements—blood cells

and platelets RBCs assist in the transport of oxygen and carbon dioxide WBCs assist in the defense mechanisms of the whole

body Platelets prevent loss of the fluid that constitutes the

internal environment No organ or system of the body can maintain proper

levels of nutrients, gases, or water without direct or indirect help from blood Other systems assist the blood

Blood is useless unless it continues to transport, defend, and maintain balance