Chapter 14

Chapter 14 The Cardiovascular System: Blood

Copyright 2010, John Wiley & Sons, Inc.

Functions 

 

Transportation: water, gases, nutrients, hormones, enzymes, electrolytes, wastes, heat Regulation: pH, temperature, water balance Protection: blood clotting, defense: phagocytic cells, interferons, complement

Copyright 2010, John Wiley & Sons, Inc.

Composition 

A connective tissue with components readily seen when blood is centrifuged: 



Plasma(~55%): soluble materials (mostly water); lighter so at top of tube Formed elements (~45%): cells (heavier so at bottom of tube) 

Mostly red blood cells (RBCs) Percent of blood occupied by RBCs = hematocrit (Hct)  Normal hematocrit value: 42-47%  Females: 38 to 46%; males: 40 to 54% 



Buffy coat: site of white blood cells (WBCs), platelets

Copyright 2010, John Wiley & Sons, Inc.

Composition

Copyright 2010, John Wiley & Sons, Inc.

Composition

Copyright 2010, John Wiley & Sons, Inc.

Plasma: Liquid Portion of Blood  

Water: 91.5% Plasma proteins: 7%   



Albumin (54%): function in osmosis; carriers Globulins (38%): serve as antibodies Fibrinogen (7%): important in clotting

Other: 1.5% 

Electrolytes, nutrients, gases, hormones, vitamins, waste products

Copyright 2010, John Wiley & Sons, Inc.

Formed Elements I. Red Blood Cells (RBCs) II. White blood cells (WBCs) A. Granular leukocytes 1. Neutrophils 2. Eosinophils 3. Basophils

B. Agranular leukocytes 1. Lymphocytes and natural killer (NK) cells 2. Monocytes

III Platelets

Copyright 2010, John Wiley & Sons, Inc.

Formation of Blood Cells  

Called hemopoiesis or hematopoiesis Occurs throughout life 



In response to specific hormones, stem cells undergo a series of changes to form blood cells

Pluripotent stem cells in red marrow 



Lymphoid stem cells  lymphocytes (in lymphatic tissues) Myeloid stem cells  all other WBCs, all RBCs, and platelets (in red bone marrow)

Copyright 2010, John Wiley & Sons, Inc.

Formation of Blood Cells

Copyright 2010, John Wiley & Sons, Inc.

Formation of Blood Cells

Copyright 2010, John Wiley & Sons, Inc.

Erythrocytes (RBCs) 

Hemoglobin (red pigment) 



RBC count: about 5 million/µl 



Carries 98.5% of O2 and 23% of CO2 Male: 5.4 million cells/µl; female: 4.8 million/µl

Structure of mature RBC  

No nucleus/DNA so RBCs live only 3 to 4 mos Lack of nucleus causes biconcave disc shape with extensive plasma membrane  

Provides for maximal gas exchange Is flexible for passing through capillaries

Copyright 2010, John Wiley & Sons, Inc.

RBC Recycling  

Cleared by macrophages (liver and spleen) Recycled components  

Globin  amino acids recycled to form proteins Heme broken down into: 

Fe Carried in blood by transferrin (“protein escort” of Fe)  Recycled in bone marrow for forming synthesis of new hemoglobin; proteins and vitamin B12 required also 



Non-Fe portion of heme biliverdin  bilirubin Bilirubin to liver  bile  helps absorb fats  Intestinal bacteria convert bilirubin into other chemicals that exit in feces (stercobilin) or urine (urobilin) 

Copyright 2010, John Wiley & Sons, Inc.

Formation and Destruction of RBC’s Circulation for about 120 days

7

3 Reused for protein synthesis

Amino acids

Globin

4

6

5

Fe3+

Fe3+ Transferrin

2 Heme

Fe3+

Ferritin Transferrin Bilirubin

9 1 Red blood cell

Biliverdin

Bilirubin

11

10

death and phagocytosis

Small intestine

Kidney

13

12

Urobilin

Macrophage in spleen, liver, or red bone marrow

Bilirubin

Urobilinogen Stercobilin

Urine

Liver

+ Globin + Vitamin B12 + Erythopoietin

8 Erythropoiesis in red bone marrow

Bacteria

Key: in blood

Large 14 intestine

Feces

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in bile

RBC Synthesis: Erythropoiesis 



Develop from myeloid stem cells in red marrow Cells lose nucleus; are then released into bloodstream as reticulocytes 



These almost-mature RBCs develop into erythrocytes after 1-2 days in bloodstream High reticulocyte count (> normal range of 0.5% to 1.5% as more of these circulate in bloodstream) indicates high rate of RBC formation

Copyright 2010, John Wiley & Sons, Inc.

RBC Synthesis: Erythropoiesis 

Production and destruction: normally balanced 

 

Stimulus for erythropoiesis is low O2 delivery (hypoxia) in blood passing to kidneys  Kidneys release erythropoietin release (EPO)  Stimulates erythropoiesis in red marrow  increased O2 delivery in blood (negative feedback mechanism)

Copyright 2010, John Wiley & Sons, Inc.

RBC Synthesis: Erythropoiesis 

Signs of lower-than-normal RBC count  changes in skin, mucous membranes, and finger nail beds  

Cyanosis: bluish color Anemia: pale color

Copyright 2010, John Wiley & Sons, Inc.

Regulation of Erythropoiesis

Copyright 2010, John Wiley & Sons, Inc.

White Blood Cells (WBCs or Leukocytes) Appear white because lack hemoglobin Normal WBC count: 5,000-10,000/µl

  

WBC count usually increases in infection

Two major classes based on presence or absence of granules (vesicles) in them]





Granular: neutrophils, eosinophils, basophils 



Neutrophils usually make up 2/3 of all WBCs

Agranular: lymphocytes, monocytes

Major function: defense against

  

Infection and inflammation Antigen-antibody (allergic) reactions Copyright 2010, John Wiley & Sons, Inc.

White Blood Cell Functions 

Neutrophils: first responders to infection  



Monocytes  macrophages (“big eaters”) 



Phagocytosis Release bacteria-destroying enzyme lysozyme Known as wandering macrophages

Eosinophils   

Phagocytose antibody-antigen complexes Help suppress inflammation of allergic reactions Respond to parasitic infections

Copyright 2010, John Wiley & Sons, Inc.

White Blood Cell Functions Basophils

 



Intensify inflammatory responses and allergic reactions Release chemicals that dilate blood vessels: histamine and serotonin; also heparin (anticoagulant)

Copyright 2010, John Wiley & Sons, Inc.

White Blood Cell Functions Lymphocytes

 

Three types of lymphocytes   



T cells B cells Natural killer (NK) cells

Play major roles in immune responses 



B lymphocytes respond to foreign substances called antigens and differentiate into plasma cells that produce antibodies. Antibodies attach to and inactivate the antigens. T lymphocytes directly attack microbes.

Copyright 2010, John Wiley & Sons, Inc.

White Blood Cell Functions 

Major histocompatibility (MHC) antigens 



Proteins protruding from plasma membrane of WBCs (and most other body cells) Called “self-identity markers”  



Unique for each person (except for identical twins) An incompatible tissue or organ transplant is rejected due to difference in donor and recipient MHC antigens MHC antigens are used to “type tissues” to check for compatibility and reduce risk of rejection

Copyright 2010, John Wiley & Sons, Inc.

WBC Life Span 

  

WBCs: 5000-10,000 WBCs/µl blood RBCs outnumber WBCs about 700:1 Life span: typically a few hours to days Abnormal WBC counts 





Leukocytosis: high WBC count in response to infection, exercise, surgery Leukopenia: low WBC count

Differential WBC count: measures % of WBCs made up of each of the 5 types Copyright 2010, John Wiley & Sons, Inc.

Platelets 

 

Myeloid stem cells  megakaryocytes  2000–3000 fragments = platelets Normal count: 150,000-400,000/µl blood Functions  



Plug damaged blood vessels Promote blood clotting

Life span 5–9 days

Copyright 2010, John Wiley & Sons, Inc.

Hemostasis: “Blood Standing Still” Sequence of events to avoid hemorrhage 1. Vascular spasm  

Response to damage Quick reduction of blood loss

2. Platelet plug formation 

Platelets become sticky when contact damaged vessel wall

3. Blood clotting (coagulation) 

Series of chemical reactions involving clotting factors   

Copyright 2010, John Wiley & Sons, Inc.

Blood Clotting (Coagulation) 

Extrinsic pathway 



Intrinsic Pathway 



Tissue factor(TF) from damaged cells 1  2  3 Materials “intrinsic” to blood  1  2  3

Common pathway: 3 major steps 1. Prothrombinase  2. Prothrombin  thrombin 3. Fibrinogen  fibrin  clot



Ca++ plays important role in many steps Copyright 2010, John Wiley & Sons, Inc.

Clot Retraction and Vessel Repair  

Clot plugs ruptured area Gradually contracts (retraction) 



Pulls sides of wound together

Repair  

Fibroblasts replace connective tissue Epithelial cells repair lining

Copyright 2010, John Wiley & Sons, Inc.

Hemostatic Control Mechanisms 

Fibrinolysis: breakdown of clots by plasmin  



Inappropriate (unneeded) clots 





Inactivated plasminogen  Activated (by tPA)  plasmin Clots can be triggered by roughness on vessel wall = thrombosis Loose (on-the-move) clot = embolism

Anticoagulants: decrease clot formation  

Heparin Warfarin (Coumadin) Copyright 2010, John Wiley & Sons, Inc.

(a) Extrinsic pathway

Stages of Clotting

Tissue trauma

(b) Intrinsic pathway Blood trauma Damaged endothelial cells expose collagen fibers

Tissue factor (TF)

Damaged platelets

Activated XII Activated platelets

Ca2+

Ca2+

+ Platelet phospholipids

Activated X Activated X V

1

Ca2+

Ca2+

V +

PROTHROMBINASE (c) Common pathway Ca2+ Prothrombin (II)

THROMBIN Ca2+

2

XIII

Fibrinogen (I)

Activated XIII

Loose fibrin threads

STRENGTHENED FIBRIN THREADS

3

Copyright 2010, John Wiley & Sons, Inc.

Blood Groups and Blood Types 



RBCs have antigens (agglutinogens) on their surfaces Each blood group consists of two or more different blood types  

There are > 24 blood groups Two examples:  



ABO group has types A, B, AB, O Rh group has type Rh positive (Rh+), Rh negative (Rh–)

Blood types in each person are determined by genetics Copyright 2010, John Wiley & Sons, Inc.

ABO Group 

Two types of antigens on RBCs: A or B    

Type A has only A antigen Type B has only B antigen Type AB has both A and B antigens Type O has neither A nor B antigen 



Most common types in US: type O and A

Typically blood has antibodies in plasma   

These can react with antigens Two types: anti-A antibody or anti-B antibody Blood lacks antibodies against own antigens  

Type A blood has anti-B antibodies (not anti-A) Type AB blood has neither anti-A nor anti-B antibodies Copyright 2010, John Wiley & Sons, Inc.

ABO Group

Copyright 2010, John Wiley & Sons, Inc.

Rh Blood Group  

Name Rh: antigen found in rhesus monkey Rh blood types  

 



If RBCs have Rh antigen: Rh+ If RBCs lack Rh antigen: Rh–

Rh+ blood type in 85-100% of U.S. population Normally neither Rh+ nor Rh– has anti-Rh antibodies Antibodies develop in Rh- persons after first exposure to Rh+ blood in transfusion (or pregnancy  hemolytic disease of newborn) Copyright 2010, John Wiley & Sons, Inc.

Transfusions 





If mismatched blood (“wrong blood type”) given, antibodies bind to antigens on RBCs  hemolyze RBCs Type AB called “universal recipients” because have no anti-A or anti-B antibodies so can receive any ABO type blood Type O called “universal donors” because have neither A nor B antigen on RBCs so can donate to any ABO type 

Misleading because of many other blood groups that must be matched Copyright 2010, John Wiley & Sons, Inc.

End of Chapter 14 

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