The Circulatory System: Blood Chapter 18

• Functions and properties of blood

• Plasma

• Blood cell production

• Erythrocytes

• Leukocytes

• Blood Types

• Hemostasis

Functions and Properties of Blood

• Functions in respiration, nutrition, waste elimination,

thermoregulation, immune defense, water balance,

electrolyte and pH balance

• Adults have 4-6 L of blood composed of:

– plasma, a clear extracellular fluid

– formed elements = blood cells and platelets

• Properties of blood:

– viscosity = resistance to flow

– osmolarity = concentration of dissolved particles

Hematocrit

• Centrifuge separates formed elements from plasma

• Hematocrit is the percent of total volume that is cells

– Normal hematocrit values Female: 37-48% Male: 45-53%

Plasma and Plasma Proteins

• Plasma is a mixture of proteins, enzymes, nutrients, wastes, hormones, and gases – if allowed to clot, the liquid that remains is called serum

• 3 major categories of plasma proteins: – albumins are the most abundant plasma protein

• contributes to viscosity and osmolarity and influences blood pressure, flow and fluid balance

– fibrinogen is precursor of fibrin threads that help form blood clots

– globulins (antibodies) provide immune system defenses • alpha, beta and gamma globulins

• Albumens and fibrinogen plasma proteins are formed by the liver

• Globulins are antibodies produced by white blood cells called plasma cells

Blood to which no

anticoagulant has been

added will clot. Blood cells

get caught in the clot leave

serum behind.

Blood to which an

anticoagulant has been

added will not clot. Blood

cells will settle to the bottom

of the tube leaving plasma at

the top of the tube.

Plasma and Serum

Non-protein Components of Plasma

• Nitrogenous compounds

– amino acids from dietary protein or tissue breakdown

– nitrogenous wastes (urea and ammonia) are toxic end

products of catabolism that are normally removed from

the blood by the kidneys

• Nutrients (glucose, vitamins, fats, minerals)

• Dissolved gases like O2 and CO2 are transported in

plasma

• Many electrolytes (Na+, Cl+, K+, HCO3-, Ca+2, and

others)

– sodium makes up 90% of plasma cations accounting for

more of the blood’s osmolarity than any other solute

Formed Elements of Blood

• Formed Elements = Erythrocytes, Platelets, Leukocytes (neutrophil, eosinophil, basophil, monocyte, lymphocyte)

• Non-formed Elements = Plasma

erythrocyte

neutrophil eosinophil

basophil

lymphocyte

monocyte

platelets

Blood Cell Production

(Hematopoiesis/Hemopoiesis) • The following hematopoietic tissues produce blood cells:

– yolk sac of vertebrate embryos produce stem cells that colonize fetal bone marrow, liver, spleen lymph nodes and thymus

– liver stops producing blood cells at birth and the thymus stops at about age 10, but the other tissues continue to produce WBCs

– bone marrow contains stem cells that produce RBCs, WBCs and platelets

• Stem cells multiply continually and are pluripotent (capable of differentiating into multiple cell lines)

• Red bone marrow is active; yellow bone marrow is inactive and fatty

• Stem cells are stimulated by hormones including erythropoietin (EPO) from the kidney and the liver

amniotic sac

placenta

yolk sac

Stem Cells of

Hematopoiesis

Erythrocytes (RBCs) • Biconcave Disc-shaped cells

– 7.5 M diameter, 2.0 m thick at rim

– Flexible center allows folding so cells can pass through narrow capillaries

– More surface area than a simple disk facilitates diffusion rate of gasses in and out of the cell

• Major function of RBCs is gas transport – Loses nucleus and most organelles during

maturation resulting in increased surface area/volume ratio

– 33% of cytoplasm is hemoglobin (Hb)

– O2 delivery to tissues and CO2 transport back to lungs

– contains the enzyme, carbonic anhydrase (CA) that produces carbonic acid from CO2 and water which plays an important role in gas transport and pH balance

• RBC count normal values – men 4.6-6.2 million RBCs/L

– women 4.2-5.4 million RBCs/L

Erythrocytes on the tip of a Needle

Flexible center of

erythrocytes allows

folding so cells can

pass through narrow

capillaries.

Capillaries are formed

by cells called

Endothelial Cells

Erythrocyte Production

• Erythropoiesis from stem cells in bone marrow produces 2.5 million RBCs/second.

• In response to erythropoietin (EPO), some stem cells develop into proerythroblasts which multiply and develop into erythroblasts.

• Erythroblasts multiply, synthesize hemoglobin and develop into normoblasts.

• Normoblasts synthesize more hemoglobin, discard their nucleus and develop into reticulocytes.

• Reticulocytes have a reticulated pattern of nuclear debris and a well-developed network of endoplasmic reticulum that was used for hemoglobin synthesis.

– a few reticulocytes enter the bloodstream before they fully mature into erythrocytes and can be 0.5% to 1.5% of the circulating RBCs

• Development from a stem cell to a RBC takes 3-5 days and involves:

– reduction in cell size, increase in cell number, synthesis of hemoglobin, loss of nucleus

– blood loss speeds up the process increasing reticulocyte count in circulating blood which is called a “shift to the left”

Erythrocyte Homeostasis

• Negative feedback control – kidney and liver hypoxia

– EPO production

– bone marrow stimulation

– RBC count in 3-4 days

• Causes of Hypoxia – low levels of atmospheric O2

• high elevation or altitude

– increase in exercise • Endurance-trained athletes

have RBC counts as high as 6.5 million/ l (normal range is 4-6 million)

– inhaling carbon monoxide

– hemorrhage

Nutritional Needs for Erythropoiesis • Iron is key nutrient for erythropoiesis

– Iron is lost daily through urine, feces, and bleeding

– on average, men lose 0.9 mg/day and women lose 1.7 mg/day

– low absorption rate requires consumption of 5-20 mg/day

– dietary iron comes in 2 forms: ferric (Fe+3) and ferrous (Fe+2)

• stomach acid converts Fe+3 to absorbable Fe+2

• gastroferritin from stomach binds Fe+2 and transports it to the intestines

• absorbed into blood & binds to transferrin to travel to bone marrow and liver

• liver binds surplus iron to apoferritin to create ferritin for storage

• erythrocytes use iron to make hemoglobin

• muscle uses iron to make myoglobin which stores O2

• all cells use iron to make cytochromes in mitochondria

• Other nutritional requirements include B12, Folic Acid, Vitamin C and Copper (Cu is used as a cofactor for enzymes)

Iron Absorption, Transport & Storage

Hemoglobin

• Normal, adult hemoglobin (HbA) consists of 4 protein chains called globins (2 alpha chains and 2 beta chains).

• Each globin has a heme group which binds oxygen to ferrous ion (Fe+2).

• Each Hb molecule can carry four O2 molecules. • Fetal hemoglobin (HbF) has gamma instead of beta chains

– HbF has a higher affinity for O2 than HbA enabling the fetus to extract O2 from the mother’s bloodstream

Erythrocytes and Hemoglobin

• RBC count and hemoglobin concentration determine the amount of oxygen the blood can carry.

• Hemoglobin concentration of whole blood:

– men 13-18g/dL

– women 12-16g/dL (dL = deciliter = 100ml)

• Why are values are lower in women?

– androgens that stimulate RBC production are lower in women

– women may have periodic menstrual loss of blood

Erythrocyte Disorders

• Polycythemia is an excess of RBCs

– primary polycythemia is due to cancer of

erythropoietic cell line in the red bone marrow

• RBC count as high as 11 million/L (normal range is 4-6

million /L)

• hematocrit of 80%

– secondary polycythemia can result from

dehydration, high altitude, or physical conditioning

• RBC count of 8 million/L

• Dangers of polycythemia

– increased blood viscosity can lead to embolism,

stroke or heart failure

Anemia = Deficiency of RBCs or Hb

• Types of anemia

– iron-deficiency anemia

– hemorrhagic anemias from loss of blood

– hemolytic anemias from RBC destruction

• Effects of anemia

– tissue hypoxia and resulting necrosis

– low blood osmolarity and resulting tissue edema

– low blood viscosity and resulting increased heart

rate

Sickle-Cell

Disease

Sickle-Cell Disease • Sickle-Cell is a hereditary defect in Hemoglobin (HbS)

– Recessive allele modifies hemoglobin structure

• Caused by a single amino acid substitution (valine is inserted in the

protein where a glutamic acid should be)

• homozygous for HbS have sickle-cell disease

• heterozygous for HbS have sickle-cell trait but rarely have symptoms

• Most common in African Americans and people from Mediterranean

region

– Implications of sickle-cell disease:

• HbS turns to gel (polymerizes) at low oxygen concentrations causing

cell elongation and inflexible sickle shape that is prone to lysis

• Sickle cells are sticky and agglutinate, blocking vessels, causing

intense pain, kidney and heart failure, paralysis, and stroke

• chronic hypoxia activates hematopoietic tissue producing more

deformed cells

– HbS gene persists despite its harmful effects to the homozygous

individual because it protects from malaria

• HbS indigestible by malaria parasites

The ABO Group

• Your ABO blood type is determined by presence or absence of antigens (agglutinogens) A and/or B on RBCs

blood type A has A antigens

blood type B has B antigens

blood type AB has both A and B antigens

blood type O has neither antigen

• Frequency of blood types varies among populations, but in the USA, O is the most common and AB is the rarest.

Frequency of ABO Blood Groups

Population O A B AB Cherokee, NC, USA 95% 4% 2% 0%

Pawnee, OK, USA 58% 40% 3% 0%

African-American, USA 51% 25% 19% 4%

Caucasian, USA 46% 42% 9% 4%

Eskimo, USA 47% 45% 6% 2%

Nikappu, Japan 31% 38% 22% 9%

Bengali, India 30% 26% 36% 7%

Agglutinins against the ABO Group

Antibodies (agglutinins) against the A and B antigens appear 2-8 months after birth and reach a maximum concentration at 10 about years.

– you do not normally produce antibodies that would react against your own antigens (agglutinogens).

– each antibody can attach to several antigens at the same time causing agglutination (clumping) of red blood cells.

ABO Blood Types • RBC antigens

called agglutinogens A & B

– inherited combinations of

proteins, glycoproteins and

glycolipids on red blood cell

membranes

• Plasma antibodies

called agglutinins anti-A & B

– agglutinins are gamma

globulins in blood plasma

that recognize (stick to)

foreign agglutinogens on

RBCs

– responsible for RBC

agglutination in mismatched

blood transfusions

ABO Blood Types

Agglutination of Erythrocytes

ABO

Blood

Typing

Mismatched Transfusion Reaction

• Agglutinated RBCs block blood vessels and RBCs can rupture

– free Hb can block kidney tubules and cause death

• Universal

donors and recipients

– AB called universal recipient since it lacks both antibody A and B; O called universal donor

– problem is donor’s plasma may have antibodies against recipient’s red blood cells

– solution is giving packed cells with minimum plasma

The Rh Group • Rh or D agglutinogens were discovered in the Rhesus monkey

in 1940, and then a similar system was found in humans.

The Rh Group • Blood type is Rh+ if type D agglutinogens are present on RBCs

• Anti-D agglutinins are not normally present in blood and only

form in Rh- individuals who are exposed to Rh+ blood:

– Rh- person gets a blood transfusion of Rh+ blood

– Rh- woman carrying an Rh+ fetus

• no problems result with either the first transfusion or the

first pregnancy

– Hemolytic Disease of the Newborn (HDN or

erythroblastosis fetalis) occurs if mother has formed

anti-D antibodies and is pregnant with 2nd Rh+ child

– RhoGAMTM can be given to a pregnant woman with a fetal

Rh incompatibility

• RhoGAM binds to fetal agglutinogens that get into in the

mother’s blood so her immune system will not mount an

attack against the fetus during pregnancy

Hemolytic Disease of Newborn

• In the first pregnancy, some fetal Rh+ blood crosses into the mother and she slowly develops anti-D agglutinins

• In second pregnancy, the mother’s antibodies can cross into the fetus and hemolyze the fetal blood causing severe anemia in the baby.

• Hemolyzed RBCs release hemoglobin which is converted to bilirubin.

• High bilirubin is toxic to the mother and child and can cause brain damage.

• Treat with transfusion or UV phototherapy to degrade bilirubin.

There is a dominant allele for the D antigen. The genetic pairs that can

exist in humans are as follows:

Genetic makeup Blood type

+ + Rh positive

+ - Rh positive

- - Rh negative

Parents' Possible allele Possible Rh

Rh types combinations in the children

Both + + + & + + + + positive

Both + + + & + - + + or + - positive

Both + + - & + - + + or + - or - - positive or negative

Both - - - & - - - - negative

One + & One - + + & - - + - positive

One + & One - + - & - - + - or - - positive or negative

Frequency of Rh Blood Groups

Population + - Cree, Quebec 98% 2%

African-American, USA 85% 15%

Caucasian, USA 85% 15%

Eskimo, USA 100% 0%

Bengali, India 95% 5%

Leukocytes (WBCs)

• 4,500-10,000 white blood cells/mcl (cells per microliter)

• Granulocytes contain specific granules – eosinophils - pink-orange granules and bilobed nucleus

(2-4%)

– basophils - abundant, dark violet granules (<1%) • large U or S-shaped nucleus hidden by granules

– neutrophils - multilobed nucleus (60-70%) • Very lightly stained reddish to violet granules in cytoplasm

• Agranulocytes contain no noticeable granules – lymphocytes - round, uniform dark violet nucleus (25-

33%) • variable amounts of bluish cytoplasm (scanty to abundant)

– monocytes – indented nucleus (3-8%) • large cell with abundant cytoplasm

Granulocytes

• Neutrophils ( in bacterial infections)

– phagocytosis of bacteria

– releases antimicrobial chemicals

• Eosinophils ( in parasitic infections or

allergies)

– phagocytosis of antigen-antibody complexes,

allergens and inflammatory chemicals

– release enzymes that destroy parasites such

as worms

• Basophils ( in inflammation or infection)

– secrete histamine (vasodilator)

– secrete heparin (anticoagulant)

Agranulocytes

• Lymphocytes ( in diverse infections and immune responses)

– destroy cancer cells, foreign cells, virally infected cells

– coordinate actions of other immune cells

– secrete antibodies and provide immune memory

– two groups: T-lymphocytes and B-lymphocytes

• Monocytes ( in viral infections and inflammation)

– mature into macrophages that consume (phagocytosis) pathogens and debris

– “present” antigens to activate other immune cells

Abnormalities of Leukocyte Count

• Leukopenia = low WBC count (<5000/L)

– causes: radiation, poisons, infectious disease

• Leukocytosis = high WBC count (>10,000/L)

– causes: infection, allergy and disease

• Leukemia = cancer of hemopoietic tissue

– myeloid (granulocyte) or lymphoid (lymphocyte)

– effects: patient subject to opportunistic infection,

anemia and impaired clotting

Normal and Leukemia Blood Smears

Megakaryocytes and Platelets

• Megakaryocytes are bone marrow cells that

repeatedly replicate their DNA without dividing

– megakaryocytes are gigantic cells (100 m

diameter) with a huge nucleus

– megakaryocytes remain in the bone marrow

• Megakaryocytes release fragments that enter

the bloodstream as platelets

– platelets live for about 10 days

– some platelets are stored in the spleen and can be

released as needed

Megakaryocytes & Platelets

Science volume 317 21 September 2007 p. 1689

Platelets

• Platelets are small fragments of megakaryocytes

– platelets are only 2-4 m diameter

– platelets contain granules used in clot formation

– platelets have pseudopods used for phagocytosis and clot

retraction

• Normal Count: 130,000 to 400,000 platelets/L

• Functions

– secrete clotting factors, growth factors for endothelial

repair, and vasoconstrictors in broken vessels

– form temporary platelet plugs

– attract WBCs to sites of inflammation

– retract and eventually dissolve old blood clots

Hemostasis

1) Vascular Spasm: Vasoconstriction reduces bleeding

2) Platelet Plug Formation: platelets adhere to exposed collagen fibers

3) Blood Clotting: RBCs and more platelets become enmeshed in fibrin

threads

1) Vascular Spasm

• Prompt constriction of a broken blood vessel

• Triggers for a vascular spasm:

– some pain receptors directly innervate smooth

muscle surrounding the blood vessel

• lasts only a few minutes

– injury to smooth muscle

• longer-lasting constriction

– platelets release serotonin which is a chemical

vasoconstrictor

2) Platelet Plug Formation

• Normal endothelium is very smooth and is coated with prostacyclin (an ecosanoid that repels platelets)

• Broken vessel exposes rough surfaces of collagen

• Platelet plug formation: – platelet pseudopods stick to damaged vessel and other

platelets

– pseudopods contract and draw walls of vessel together forming a platelet plug

– platelets degranulate releasing a variety of substances • serotonin is a vasoconstrictor

• thromboxane, an eicosanoid that promotes aggregation and degranulation of platelets and vessel vasoconstriction

• Positive feedback cycle is active until break in vessel is sealed

3) Blood Clotting (Coagulation) • Clotting is the most effective defense against bleeding

– conversion of soluble plasma protein fibrinogen into insoluble fibrin threads that form the framework of a clot

• Clotting Factors are always present in the plasma and in tissues

– activating one factor will activate the next to form a reaction cascade

• Factors released by damaged blood vessel tissues cause the extrinsic cascade pathway to begin.

• Factors found only in the blood itself causes the intrinsic cascade pathway to begin (platelet degranulation).

• Both cascades normally occur together and lead to a fibrin clot.

Colorized scanning

electron micrograph of

a blood clot removed

from the coronary

artery of a patient with

acute myocardial

infarction showing he

fibrin meshwork

(brown) with trapped

red blood cells and a

cholesterol crystal

(yellow). Science Vol

335 February 10, 2012

Coagulation

Pathways

• Extrinsic Pathway

– Factors released by damaged tissues cause the extrinsic cascade pathway to begin which usually lasts about 15 seconds.

• Intrinsic Pathway

– Factors released by platelets start the intrinsic cascade pathway which usually lasts about 3-6 minutes.

• Calcium is required for both pathways.

Completion of Coagulation • Both the intrinsic and extrinsic pathways lead to production of

Factor X.

• Factor X produces key enzymes for activating Thrombin which converts soluble fibrinogen into an insoluble fibrin polymer.

• Thrombin also feeds back on the system to amplify its own production.

Coagulation Disorders

• Unwanted coagulations:

– Thrombosis = abnormal clotting in unbroken vessel

• most likely to occur in leg veins of inactive people

• clots can travel from veins to lungs producing a

pulmonary embolism

• death can occur from hypoxia

– Embolism: abnormal clot traveling in a blood vessel

• Infarction, or tissue death, may occur if clot blocks blood

supply to an organ

– Myocardial Infarction (MI)

– Stroke (brain clot or bleed)

– 650,000 Americans die annually of thromboembolisms

Clot Retraction and Dissolution

• Clot retraction occurs within 30 minutes – pseudopods of platelets pull on fibers of fibrin which

compacts the clot

• Platelet-derived growth factor is secreted by platelets and endothelial cells – the growth factor is a mitotic stimulant for fibroblasts and

smooth muscle that multiply and repair the damaged vessel

• Fibrinolysis or dissolution of a clot – Fibrin is broken down by the enzyme plasmin

– Plasmin is produced by the intrinsic enzyme kallikrein and the extrinsic enzyme TPA (tissue plasminogen activator)

Blood Clot Dissolution

Kallikrein in the plasma and TPA (tissue plasminogen activator) from

damaged tissues quickly convert inactive plasminogen into plasmin

Plasmin breaks down clots and promotes formation of more kallikrein

Positive

Feedback

TPA

Dissolving Clots • Streptokinase

– Enzyme made by the Streptococcus bacteria dissolves clots when administered intravenously.

– Relatively non-specific and digests many proteins.

• Tissue plasminogen activator (TPA)

– Specifically converts inactive plasminogen into the clot-dissolving enzyme plasmin

– Now produced by transgenic bacteria.

• Hementin

– Anticoagulant produced by the giant Amazon leech, Haementeria.

– Used to dissolve clots in cardiac patients.

– Now produced in transgenic bacteria.

Medicinal Leeches Removing Clots

from a postsurgical hematoma

Prevention of Clots

• Platelet Repulsion:

– platelets do not adhere to prostacyclin-coating that normally lines blood vessels

• Thrombin Dilution:

– thrombin is normally diluted by circulating blood

• heart slowing, as during shock, can result in clot formation

• slow venous return in legs due to prolonged sitting can also result in clot formation

• Anticoagulants

– heparin secreted by basophils and mast cells during inflammatory response interferes with formation of clotting factors (prothrombin activator)

• Drugs like coumadin

Hemophilia

• Genetic lack of clotting factors

– hemophilia A is missing factor VIII (83% of cases)

– hemophilia B is missing factor IX (15% of cases)

– hemophilia C is missing factor XI (rare)

• Symptoms:

– physical exertion can cause bleeding and

excruciating pain

• Treatments:

– transfusion of plasma or purified clotting factors

– factor VIII is now produced by transgenic bacteria

Normal Blood Values

Adults have 4-6 L of blood

Female Male

Hematocrit: 37-48% 45-53%

Hemoglobin: 12-16g/dL 13-18g/dL

RBC count: 4.2-5.4 million/L 4.6-6.2 million/L

WBC count: 4,500-10,000/L

neutrophils 60-70%

eosinophils 2-4%

basophils <1%

lymphocytes 25-33%

monocytes 3-8%

platelet count: 130,000 to 400,000/L