blood lecture 2

8/2/2019 Blood Lecture 2

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Blood PhysiologyBlood Physiology

Blood Physiology Lecture 2

Dr. A-M Zagrean


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Blood Physiology Syllabus

Lecture 1

Functions of the blood. Composition and physicochemical properties

blood. The hematocrit. Blood volume. Hematopoiesis

Lecture 2

. . .

Therapeutic uses of blood. Transfusions.

Lecture 3

Physiology of Immune System. Function of specific defense.

Lymphocytes. Function of nonspecific (cellular) defense. Leukocytes.

Lecture 4

Function of maintaining the fluid coagulant balance. Hemostasis.

Fibrinol sis.

References: Guyton, Borone, Berne & Levy, Rhoades & Bell, Sircar


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Red Blood Cells (RBC) Erythropoiesis: PSC pronormoblast (1) progressively smaller normoblasts*

nucleus is squeezed out of the cell & ingested by macrophage RBC are terminally differentiated (never divide).

spends 12 days in the marrow, circulates 12 days in

peripheral blood (0.51%), mature mainly in the spleen*Obs: Nucleated cells (normoblasts) appear in the blood in case of extramedullary

RBC precursors (up to reticulocytes) manufacture hemoglobin until it accounts forsome 90% of the dry weight of the cell (34 g/dl of cell fluid metabolic limit of cell

orm ng mec an sm

RBCs have a lifespan of120 days and then are ingested by phagocytic cells in the

liver and s leen:

~ 3 millions RBCs die & are scavenged by the liver/second

~200 billion new RBCs are made /day to replace the dead ones.

break up in the bloodstream =hemolysis, but the majority are engulfed by

macrop ages o t e reticu o en ot e ia system RES . the iron from hemoglobin is reclaimed for reuse.

the remainder of the heme portion of the molecule is degraded into bile pigmentsand excreted b the liver


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Erythropoiesis


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RBCs

ce s a ac nuc eus an mem ranous organe es

- no mitochondria, no aerobic metabolism;

- no ribosomes, RNA and protein synthesis, no renew of

enzymes or membrane components

loss of plasma membrane flexibility with age simple membranous bag filled with Hb and enzymes

normal flexible membrane

shapes (round, slightly oval, parachute-like in the capillaries

, ,

Obs: poikilocytosis refers to an excessive variation in RBC shape

biconcave shape that modify with osmotic changes, large

sur ace- o-vo ume ra o o max m ze as gaseous exc ange

sizes: 7.8 / 2.5 / 1 m

Obs: anisocytosis refers to excessive variation in RBC size.

volume: 80 - 95 m3 surface: 135 m2


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Red blood cells are seen as biconcave disks


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Biconcave shape vs. Membrane flexibility


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Red cell metabolism

l col sis is the rimar source of ATP:

90% of glycolysis occurs through Embden Meyerhof pathway, with theparticularity that the phosphoglycerate kinase step is bypassed to produce 2,3DPG that influences the O2 affinity of Hb

g yco ysis generates NADH+H+, important to re uce met emog o in continuous yformed by Hb autooxidation) and to keep it


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Red Blood Cells (RBC)

RBC are most abundant of all the cells of the bloodRBC count - 2 years < 4,000,000 / mm3

- men: , , , mm ;

- women: 4,700,000 300,000 / mm3- changes - physiological: pregnancy, high altitude

- pathological : anemia, polycytemia

Ht > 52 (M), 47 (F)-

Hematocrit 40 45 %

emog o n g oo

up to 34 g/dl of cell fluid (metabolic limit of cell Hb-forming mechanism)

1 g pure Hb combine with 1.39 ml O214 16 g/dl blood combine with 19 21 ml O2


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The oxygen carrying capacity (OCC)

= maximum amount of oxygen that can be carried in adeciliter (100 mL) of blood, including both oxygen bound

.

1 g Hb can combine with and transport 1.34 mL oxygen.

2 .

dissolved / 100 mL of blood

ox en carr in ca acit in 100 mL of blood can be

calculated as follows:


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F n i n f RB

-RBCs transport Hb, which carries O2 , CO2 if free Hb in the plasma:

1. 3% Hb would leak through the capillary membrane with each pass2. plasma viscosity would markedly increase

. oo osmo c pressure wou ncrease

-RBCs contain large quantities of carbonic anhydrase (CA):

HCO3-

- -


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Blood tests

Blood is drawn from a vein veni uncture , usuallfrom the inside of the elbow or the back of the hand.

A needle is inserted into the vein, and the blood is

- .

may vary depending on the specific test.


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The mean cell (orcorpuscular) volume (MCV) is the index most often used. It

Erythrocyte indices

Normocytic - normal size cells; microcytic cells with a low MCV, macrocytic

cells with a high MCV. These size categories are used to classify anemias.

average hemoglobin content of each red blood cell.

va ues usua y r se or a as e s ncrease or ecrease . e s

often related to the MCHC as RBC count is usually related to the hematocrit.

The mean cell (orcorpuscular) hemoglobin concentration (MCHC) provides an

.is calculated as follows:

High MCHC values do not occur in erythrocyte disorders, because normally the Hbconcentration is close to the saturation point in red cells (here discuss hyperchromia)


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RBC count

.count using a red blood cell diluting

pipette (note the [red] crystal in the

dilated portion of the pipette).

.drawn and mixed with the blood

sample. This fluid functions to lyse

the WBCs in the blood sample.


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WBC

RB

C

cells

counting

chamber


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HemoglobinIn adult humans the Hb molecule (HbA) consists of four globular polypeptides:

- two alpha () chains of 141 amino acids- two beta () chains of 146 amino acids

For HbA2 (2.5% in adult): 2 alpha and 2 delta chains

For fetal Hb (HbF): 2 alpha and 2 gamma chains

Each of these is attached to a prosthetic group heme, with one atom ofiron atits center. One molecule of O2 can bind to each heme (reversible reaction,

.

When Hb is saturated with O2 it has a bright red color; as it loses oxygen it

becomes bluish (cyanosis).


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Heme group is a C-H-N porphyrin ring with an iron atom (Fe) in the center(70% of the iron in the body)


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Synthesis of Hemoglobin Hb molecule

From Guyton, 2006


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Iron

4-5 g, from which 65% in Hb, 4% myoglobin, 1% other heme compounds,0.1% combined with transferrin (blood carrier protein)

15-30% stored as ferritin mainly in the reticuloendothelial system and liver

Absorbtion in the small intestine (slow rate, few mg/day) iron bindloosely to apotransferrin (b-globulin in the bile) transferrin rec on the

intestinal epithelial cells absorbtion of transferrin by pinocytosis

plasma transferrin (1/3 saturated) released in the plasma transport to

the tissues in the cells cytoplasm iron combine mainly with apoferritin (aa pro e n o orm err n = s orage ron

When more iron than apoferritin, then an insoluble storage form =

hemosiderinTransferrin binds strongly with receptors on erythroblasts endocytosis

deliver of the iron directly to the mitochondria where heme is

Daily loss of iron: 0.6 1.3 mg/day


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At Sea Level the Partial Pressure of O2 is High Enough to

ve ear y a ura on o As the partial pressure of oxygen in

t e a veo i increases t e emog o in

in the red cells passing through thelungs rises until the hemoglobin is

at 100% saturation each Hb carries 4

O2 molecules . 2

A plot of % saturation vs pO2

gives an

Sshaped curve = "hemoglobin

dissociation curve"


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Iron Profile

Name Reference Ran e Reference SI Descri tion

Iron 50170 g/dL 930 mol/L Amount of iron bound to

transferrin in bloodFerritin 150200 ng/mL 15200 g/L Storage form of excess iron

Total Iron

Binding Capacity

(TIBC)

252479 g/dL 4586 mol/L Amount of iron needed to bind

to all transferrin

Transferrin 200380 mg/dL 23.8 g/L Transferrin which is not bound

to iron

Transferrin 20%50% 0.20.5 Percenta e of transferrin withSaturation

(Iron/TIBC)

iron bound to it


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Fetuses Live in a Low Oxygen Environment and

equ re a pec a emog o n

The developing fetus cannot breathe and must get all of its blood from

the placenta

Fetal blood has a very low pO2, about 30 mm Hg, equivalent to living at

" , ,

To extract more oxygen from the mother's blood fetuses make a special

hemoglobin (HbF 2 alpha and 2 gamma chains ) which has a very higha n y or oxygen:

HbF exhibits a low affinity for 2,3DPG (2,32,3diphosfoglycerate,diphosfoglycerate, lowers

affinity of Hb for O2

, by binding to deoxyhemoglobin)).. The positive histidine

residues of HbA subunits that are essential for forming the 2,3DPG binding

pocket are replaced by serine residues in HbF subunits.

G t p t i th bl d O t p t


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Gas transport in the blood - Oxygen transportTotal blood OTotal blood O22= O2 dissolved in plasma+OO22 bound to Hbbound to Hb (oxyHb)

2% 98%

x 5 L of blood

m 2 m 2 m 2

Cells metabolism depends on Hb transport of oxygen:

Hb + O2

HbO2

Oxygen consumption at rest ~ 250 mL O2 / min.

~ from available O


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H n x n r n r


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Hb saturation depends on:

PO2 = f(air composition, alveolar ventilation, gas exchange) number of potential O2binding sites available in RBC =

% saturation of Hb

relationship between PO2 and % saturation of Hb:

oxyhemoglobin dissociation curve (in vitro determination)

PO2

= 100 mmHg 98% HbO2

saturation

PO = 650 mmH 100% HbO saturation

PO2 > 60 mmHg > 90% HbO2 saturation

PO2 = 45 mmHg 75% HbO2 saturation (reservoir)

= .

If blood loss blood transfusion / saline infusion

Artificial O2 carriers / artificial RBC will eliminate the need toestablish blood type

O h l bi di i ti


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Oxyhemoglobin dissociation curve

Factors involved in O2-Hb binding

t (C)

Changes in PCO2 Changes in HbO2 dissociation curvepH


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Factors involved in O Hb bindin

t C

Changes in PCO2

pH

Shift to the right of HbO2

dissociation curve

lungs

more changes in the

steep part of the

curve, corres ondinFor PO2 = 40 mmHg,

more O is released

Bohr effectssues

to the tissues in theperiphery

from Hb, withdecrease in pH


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Acid Conditions Help Release O2 in the Tissues: Bohr

The increased unloading/releasing of O2 at low pH is known as

t e Bo r e ect

the low pH decreases Hb affinity for O2 and causes more

oxygen to come off in the tissues an effect important duringexercise:

Hemoglobin takes up H+ (acts like a buffer). Deoxygenation increases

affinit of some sites for H+

. Amino groups of Hb bind CO2: stabilizes salt bridges therefore lowers Hb

affinity for O2 .


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Bohr effect shift curve to the right by decrease pH

The left (black) curve is at pH 7.4, the middle (red) curve is at pH 7.1, and the

. . 2

at pH 7.4 than at pH 6.8.


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Effect of pH and PCO2

on H O2 ssoc at on curve


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Effect of temperature


2 32 3--DPG (DPG (2 32 3--diphosfoglycerate)diphosfoglycerate)


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2,32,3--DPG (DPG (2,32,3--diphosfoglycerate)diphosfoglycerate)

Intermediate of glycolysis pathway

Increased production in RBC in chronic hypoxia (anemia, high altitude)Lowers affinity of Hb for O2, by binding to deoxyhemoglobin

Binds 1:1 with Hb - binds with 3 positively charged groups

on each -chain

Shift HbO2 dissociation curve to the rightAfter oxygenation 2,3-DPG is extruded.

1 1 1 1

HbF binds 2,3-DPG less strongly than HbA (adult Hb).

2 2

O2 O222

Oxyhemoglobine Deoxyhemoglobine


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Effect of 2,3DPG


ib i h l O


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Factors contributing to the total O2 content


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Gas transport in the blood - CO2 transport

CO2 potential toxic waste: when increase (hypercapnia) ac os s epress on o , etc

Transport / removal of CO2 from the tissues in 3 ways:

sso ve n t e p asma venous oo

93% diffuses in RBC

70% converted to HCO transported to the lungs & act as a buffer for metabolic acids

the H+ concomitantly released is buffered by Hb Hb.H; if CO

2 H+ no Hb available for H+ buffering

respiratory acidosis

23% binds to Hb Hb.CO2 (carbaminoHb) formation of Hb.CO2 is favoured by the presence of CO2 and H

+

(decrease Hb affinity for O2)


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CO removal at the lun s:

-2

PCO2

equilibrium of CO2

HCO3

reaction favours

CO2 release and diffusion into the alveoli

H+ + HCO3 H2CO3 CO2 + H2O CO2 released

use of H+ favours its release from Hb.H

3 3

exchange with Cl (chloride shift)


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CO2 transport

+ + + -CA


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Anemia

re a on p asma c vo ume conc.

decrease RBC number and / or decrease Hb

Blood loss anemia haemorhagy (acute/chronic)

Aplastic anemia Megaloblastic anemia

Hemolytic anemia (hereditary spherocytosis, sickle cell anemia,

erythroblastosis fetalis)

Polycythemia

Secondary polycythemia (hypoxic conditions); physiologic

Polycythemia vera (erythremia) excess production of RBC


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Figure 9.5 Pathological changes in erythrocyte morphology. The

synopsis of erythrocyte abnormalities presents a variety ofossible deviations that are hel ful for dia nosis of anemias and

other diseases.

Pathological changes in erythrocyte morphology. The synopsis of erythrocyteabnormalities presents a variety of possible deviations that are helpful for diagnosis

of anemias and other diseases (from Rhoades & Bell, 2009).


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The ABO Blood Groups & The Rh System

Blood rou s are created b anti ens AGs resent on

the surface of red blood cells.

encoded by a number of different genes, but lack the MHC

proteins found on nucleated cells.

First discovered in 1900 and from then on, the most

im ortant in assurin safe blood transfusions.


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The ABO Blood Groups:

structure of ABO antigens

Ceramide glu gal galgnac fuc

galnac

H

Ceramide glu gal galgnac

fuc

Antigen

A

Ceramide glu gal galgnacgal

fuc

Antigen

B

O group: H substance with a terminal L-fucose

A group: Galnac = n-acetyl galactosamine

B group: Gal = D-galactose


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The ABO Blood Groups


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When RBC carrying one or both antigens are exposed to the

, .

People usually have antibodies against those red cell antigensthat they lack.

Human red blood cells before (left) and after (right) adding serum containing anti-

A antibodies. The agglutination reaction reveals the presence of the A antigen on

the surface of the cells.

Transfusion


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Transfusion

Transfused blood must not contain RBC that the recipient'santibodies can clump.

Although theoretically it is possible to transfuse group O

blood into any recipient, the antibodies in the donated plasma

can amage e rec p en s re ce s.

Thus all transfusions should be done with exactly-matched

.

Why do we have antibodies against red cell antigens that we

lack?Bacteria living in our intestine, and probably some foods, express epitopes

similar to those on A and B.

We s nthesize antibodies a ainst these if we dont have the corres ondin

epitopes (if our immune system sees them as "foreign" rather than "self).


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Rh antigens are transmembrane proteins with loops exposed at thesurface of RBCs.

discovered.

T ere are a num er o R antigens. Re ce s t at are R positiveexpress the one designated D. About 15% of the population haveno RhD antigens and thus are "Rh negative".


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The ma or im ortance of the Rh s stem for human health is toavoid the danger of RhD incompatibility between mother and

fetus.

During birth, there is often a leakage of the baby's RBC into the mother'scirculation. If the baby is Rh+ (having inherited the trait from its father)

and the mother Rh, these RBC will cause her to develop antibodies.

The antibodies, IgG class, do not cause any problems for that child, but

can cross the lacenta and attack the RBC of a subse uent Rh+ fetus

anemia and jaundice (erythroblastosis fetalis or hemolytic disease of thenewborn, may be so severe as to kill the fetus or even the newborn infant.It is an example of an antibodymediated cytotoxicity disorder).


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Why is an Rh incompatibility so dangerous when ABO

ncompa y s no

Most antiA or antiB antibodies = IgM that do not cross thep acenta.

Rh/type O mother carrying an Rh+/type A, B, or AB fetus is resistantto sensitization to the Rh antigen. Presumably her antiA and antiB

elicit antiRh antibodies in her.

Preventive measure to avoid Rh sensitization:Shortly after each birth of an Rh+ baby, the mother is given aninjection of antiRh antibodies. The preparation is called Rh immuneglobulin (RhIG) or Rhogam. These passively acquired antibodies

elicit an active immune response in her.


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The Rh- mother will produce anti-Rh antibodies.

,

retardation, and even death.

blood lecture 2

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