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Blood and the Cardiovascular System

Blood-componentsSystem functions

Common conditions

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Functions of Blood

• Transportation

• Regulation

• Protection

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Physical Characteristics

• Heavier, thicker and more viscous than water

• Adhesive qualities (stickiness)

• Temperature about 38º C

• Slightly alkaline pH 7.35 – 7.45

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Physical Characteristics

• Constitutes about 8% of body weight• Adult blood volume:

– 5-6 litres (male) – 4-5 litres (female)

• Volume and osmotic pressure are regulated by hormonal negative feedback systems

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Components of Blood• Whole blood composed of

two portions:– Plasma (55%)– Formed elements (45%)

• Red blood cells (RBC’s) make up 99% of the formed elements

• White cells and platelets make up the remaining 1%

Herlihy 2007 pg 265

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Blood Plasma (Plasma)

• Straw coloured fluid

• 91% water

• 8.5% solutes (mostly proteins)

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Break Down of Components

Other fluids and

tissues 92%

Body Weight

WholeBlood

8%

Blood Plasma

55%

Formed Elements

45%

Volume

Proteins 7%

Plasma weight

Water91%

Other solutes1.5%

Platelets25,000 – 400,000

Leucocytes5,000 – 10,000

Erythrocytes4.8 – 5.4 Million

(numberPer mm3)

Neutrophils 60 –70%

Lymphocytes20 – 25%

Monocytes3-8%

Eosinophils 2 –4%

Basophils 0.5 – 1.0%

(Leucocytes)

ElectrolytesNutrients

GasesRegulatorySubstances

VitaminsWaste products

Albumins 54%Globulins 38%Fibrinogen 7%All others 1%

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Formation of Blood Cells

• Process is known as hemopoiesis• Negative feedback systems monitor the amount of RBC’s in the system at any given time• Numbers of differing types of white cells varies in response to invading pathogens and antigens

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How stuff works

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Micrograph of Blood Cells

Tortora 1996 pg 558

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Erythrocytes (RBC’s)

• Make up more than 99% of the formed elements• Contain haemoglobin molecules• Biconcave disc • No nucleus or organelles

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Structure of a Molecule of Haemoglobin

Tortora 1996 Fig 19.3 p. 559

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Red Blood Cells

www.whyfiles.org/090doping_sport/3.html

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Origin and Development of Blood Cells

Herlihy 2007 pg 265

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Life Cycle of RBC’s

• Mature RBC develops 1-2 days after release (Erythrocyte)• Lives about 120 days in circulation• Cell membrane becomes fragile through wear and tear• Cells burst• Removed from circulation and destroyed by phagocytic macrophages in the spleen and liver

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Hemoglobin and Iron• Large protein

molecule• Globin – protein• Heme- iron containing

substance

Herlihy 2007 pg 266-267.

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Regulation of RBC production by erythropoietin

Herlihy 2007 pg 268

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Herlihy 2007 pg 269

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RBC Recycling

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Causes of Anemia

Herlihy 2007 pg 270

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WBC Physiology

• RBC’s outnumber WBC’s 700:1• Normal WBC count is about 5000 – 10,000 /mm3• Leucocytosis = increased number of WBC’s• Leukopenia = abnormally low count (below 5,000/mm3)

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Leukocytes (WBC’s)

• Contain a nucleus• Do not contain haemoglobin• Two major groups:

– Granulocytes– Agranulocytes

• Live for a few hours up to years -depending on the type of cell

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Naming of White Blood Cells

Herlihy 2007 pg 272.

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Neutrophils & Macrophages

– Chemicals released by microbes and inflamed tissues attract phagocytes (neutrophils & macrophages)– Phagocytes ingest bacteria and dispose of dead matter– Phenomenon known as chemotaxis

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Neutrophils

• Respond first:– Engulf the bacteria– Release – lysozyme and strong oxidants– Neutrophils contain defensins – proteins that exhibit antibiotic activity. These form spears that poke holes in microbe membranes

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White blood cells : Traveling, housekeeping &

eating

Herlihy 2007 pg 271

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Monocytes

• Take longer to arrive than neutrophils• Enlarge on arrival and differentiate into wandering macrophages• Destroy more microbes and clean up cellular debris

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Eosinophils

• Leave capillaries and enter tissue fluid• Release enzymes such as histaminase• Phagocytize antigen-antibody complexes• Effective against certain parasitic worms

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Basophils

• Leave capillaries and enter tissues• Develop into mast cells• Can liberate heparin, histamine and serotonin• Are responsible for “allergic” reactions

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Cells of the Immune System

www.user.rcn.com/…/H/Hemotopoiesis2.gif

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Lymphocytes

• Three major types:– B cells – attack and destroy bacteria and inactivate their toxins– T cells – attack viruses, fungi, transplanted cells, cancer cells and some bacteria– Natural killer cells – attack many infectious microbes and certain spontaneously arising tumour cells

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Differential WBC Count

• Normal differential:– Neutrophils 60 - 70%– Lymphocytes 20 - 25%– Monocytes 3 - 8%– Eosinophils 2 - 4%– Basophils 0.5 – 1%

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Platelets

• Result from splintering of megakaryocytes in red bone marrow, into 2000-3000 fragments• Each fragment is enclosed by a piece of the cell membrane (thrombocyte)• Between 250,000 and 400,000 platelets are present in each mm3 of blood

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Platelets

library.thinkingquest.org/._../platelets.htm

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Homeostasis

• “Stoppage of bleeding”• Three basic mechanisms to reduce blood loss:

– Vascular spasm– Platelet plug formation– Blood clotting (coagulation)

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Hemostasis Steps

Herlihy 2007 pg 274

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Vasospasm

• Circularly arranged smooth muscle in the walls of the capillaries contract immediately• Able to reduce blood loss for several minutes to several hours• Spasm due to damage of the smooth muscle and from reflexes initiated by pain receptors.

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Platelet Response

www.gcarlson.com/cellular_plateletsrupture.htm

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Steps in Plug Formation

• Platelet adhesion

• Platelet release reaction

• Platelet aggregation

• Platelet plug

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Platelet Plug Formation

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Clotting (Coagulation)

• Blood remains in liquid form as long as it circulates within the vessels• Once out, it thickens to form a gel• Gel separates from serum• The remaining network of insoluble protein fibres (fibrin) form the clot

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Stages of Blood Clotting

Herlihy 2007 pg 275

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Stages of Clotting

Stage 1• Formation of prothrombinase

– Extrinsic pathway – external source– Intrinsic pathway – internal cause

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Stages 2

• Once prothrombinase is formed a common pathway follows• Stage 2:

– Prothrombinase + Ca++ activate prothrombin and convert it to thrombin

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Stage 3

• Stage 3:– Thrombin and Ca++ causes fibrinogen to loose fibrin threads– Factor XIII then strengthens and stabilizes the clot

• Positive feedback loops cause increased production of prothrombinase and promotes platelet aggregation

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Role of Vitamin K

• Required for synthesis of four clotting factors liver cells (Factors II, VII, IX and X)• Produced by bacteria in the large intestine• Fat soluble • Disorders that prevent absorption of fat from the intestine increase risk of bleeding

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Clot Retraction and Repair

• Fibrin threads gradually contract• Pull edges of damaged vessels towards each other• Relies on the presence of adequate numbers of platelets• Platelets in the clot release Factor XIII which strengthens and stabilizes the clot.

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Fibrinolysis

• Dissolving of clots• Fibrinolytic system stops clots from spreading throughout the system• Plasminogen plasmin• Thrombin• Tissue plasminogen activator (t-PA)

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Fibrinolysis

Herlihy 2007 pg 276

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Haemostatic Control Mechanisms

• Prostacyclin (PGI2)• Anticoagulants

– Antithrombin III (AT-III)– Protein C

• Alpha-2-macroglobulin • Alpha-1-antitrypsin

– Heparin– Warfarin– Aspirin

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Blood Groups

Herlihy 2007 pg 277

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References

• Herlihy B.( 2007) The Human Body in Health and Illness (3rd ed) Elsevier Canada. (264-277)• Tortora, GJ & Grabowski, SR (1996) Principles of Anatomy and Physiology (8th ed).. HarperCollins Publishers Inc. New York (553-570) • www.howstuffworks.com• www.us.novoseven.com/…/blood_coagulation.asp• www.kingsnake.com/toxinology/hemotoxinology.html• www.merck.com/mmhe/sec14/ch173/ch173a.html• www.gcarlson.com/cellular_plateletsrupture.htm• library.thinkingquest.org/._../platelets.htm• www.user.rcn.com/…/H/Hemotopoiesis2.gif• www.lrf.org.uk/_en/1/infdispatbmt.html• www.whyfiles.org/090doping_sport/3.html