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-4

-Ensherah Mokheemer

- Rama Nada

-

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We will continue talking about hemoglobin oxygen dissociation curve:

As you all know the figure below is called the hemoglobin oxygen

dissociation curve, and from this curve we notice the following:

1-when PO2 is 100 mm Hg in the lungs, the hemoglobin does not

become 100% saturated, only 97.2% of it will be saturated.

2- At tissue level when PO2 is 40 mmHg not the whole oxygen is

released just 25% is released, 75% remains bound to hemoglobin (that’s

mean not the whole oxygen is released at the tissue level).

3-The value of PO2, when 50% of hemoglobin is saturated, is 26 mm Hg.

Remember that the PO2 at which half of the hemoglobin is saturated is

called P50 and it equals 26 mm Hg.

**The previous curve is the normal curve that we find in all normal

people despite their hemoglobin concentration, it represents the

dissociation of hemoglobin, the release of oxygen at tissue level, and the

P50, please note that it has nothing to do with hemoglobin

concentration.

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**When we plot oxygen content against PO2 depending on the

hemoglobin concentration, we get different curves. As shown in the

figure below.

This figure shows the oxygen

content in the blood at

different hemoglobin

concentration: at

7g/dl,10g/dl and 14g/dl.

Important notes:

-The oxygen content

(quantity of oxygen) carried

in the blood depends on:

1- The partial pressure of

oxygen (PO2), The higher the

PO2, the higher the content

of oxygen in the blood.

2-The concentration of

hemoglobin. The higher the

hemoglobin concentration,

the higher the content of

oxygen in blood.

-The percentage of

hemoglobin saturation with

oxygen is dependent on

PO2 and it is INDEPENDENT

of hemoglobin concentration.

-Thus, if oxygen content was plotted against PO2, the level of the curve

will be dependent on hemoglobin concentration of the sample of blood,

and so, the curve will not be the same for all people as it depends on the

hemoglobin concentration variations. (second figure) But when the

percentage saturation of hemoglobin is plotted against PO2, the level of

the curve will always be the same, whatever the hemoglobin

concentration is. Therefore, the plot will always be the same for all

people, males and females. (first figure)

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Remember the structure of hemoglobin, it contains 4 subunits, 2 alphas

and 2 betas, each subunit contains a heme group, so it is a total of 4

heme groups for the whole hemoglobin molecule, each heme group

binds to 1 oxygen molecule and therefore the hemoglobin binds to 4

oxygen molecules (8 atoms). These 4 heme molecules, however, do not

bind oxygen all at the same time. Consequently, the binding of oxygen

molecules occurs one by one (this is called cooperativity). The binding of

the first oxygen molecule facilitates the binding of the second, the

binding of the second facilitates the binding of the third and so on.

In this figure there are 2

curves one is normal

and the other is shifted

to the right.

Let’s go through them in

details:

- First, how to know

whether it’s normal or

shifted? by the value of

p50 which is 26 mm Hg,

so the normal curve must

have the value of PO2

equal to 26 mm Hg when the hemoglobin saturation is 50%.

- Shifting the curve to the right is associated with these changes:

1) The affinity of hemoglobin toward

oxygen decreases, and this means that the body needs

oxygen.

2) P50 increases (here, it is slightly

more than 30 mm Hg. The normal

value= 26 mm Hg)

3) Oxygen release from hemoglobin

increases (due to decreased affinity

for oxygen).

4) This means that the body needs

more oxygen (as during exercise or hemorrhagic loss ...Etc.)

- You might be asking yourself what caused this shifting to the right

here are some factors which caused the shifting to the right:

Normal

Shifted to the right

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1) increase partial pressure of CO2 (pCO2)

2) decrease pH (high acidity)

3) increase temperature

4) increase the concentration of 2,3-BPG (physiologic or

pathologic)

In this figure we also notice 2 curves one is normal and the other is

shifted to the left:

- Also, in this case we

depend on the value of

P50 to differentiate

between the normal

curve and the one shifted

to the left. The normal

curve has p50 equals 26

mm Hg, as for the curve

shifted to the left the P50

is less than 26 mm Hg.

- Shifting the curve to the

lift is associated with

these changes:

1) The affinity of hemoglobin toward oxygen increases.

2) P50 decreases (here it is less than 16 mm Hg instead of 26 mm

Hg)

3) Oxygen release decreases because the hemoglobin doesn’t

release the oxygen easily

4) Shifting to the left means that the body doesn’t need

too much oxygen or there is abnormality such as the increase

in fetal hemoglobin concentration (in physiological or

pathological conditions).

- Factors that causes shifting to the left:

1) decrease partial pressure of CO2

2) increase pH (low acidity)

3) decrease temperature

4) decrease concentration of 2,3-BPG

Note: shifting the curve to the right or to the lift isn’t associated only

with pathological conditions, it may occur at normal conditions

(physiologically).

Norma

Shifted to the

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Note from the previous lecture:

*what the different between oxygenation and oxidation?

Oxidation: binding of oxygen and not releasing it “irreversible”.

Oxygenation: binding of oxygen and releasing it (that's what happens in

case of hemoglobin), “reversible”.

- There are two types of

hemoglobin presented in this

figure the fetal hemoglobin

and the adult hemoglobin, as

shown in the figure the fetal

hemoglobin is to the left of the

adult hemoglobin which

indicates that the fetal

hemoglobin has higher affinity

for oxygen. So, foetal

haemoglobin doesn’t release

oxygen easily unless the pO2 is

low. The importance of this

difference in the affinity comes

when the mother’s blood enters the placenta, it transfers oxygen to

the blood of the foetus (because foetal Hb has higher affinity toward

oxygen than adult Hb).

- As you can see, the dissociation curve of myoglobin (muscle

hemoglobin) is far to the left of that for adult hemoglobin and has a

hyperbolic shape. Thus,

hemoglobin transfers oxygen

readily to myoglobin as

myoglobin has higher affinity

toward oxygen than

haemoglobin. Myoglobin

stores this oxygen until the

oxygen pressure drops as in

exercise (low P50). Then

myoglobin releases oxygen to

be used in cellular respiration.

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**Myoglobin in muscle doesn't release oxygen easily unless its pO2 is

very low (sometimes 6 or below 6).

The effect of 2,3- Bisphosphoglycerate (DPG) on oxygen dissociation

- As we took in

biochemistry

2,3-DPG reduces

the affinity of

hemoglobin

toward oxygen

and we also said

that in people

who live in high

altitude, the

concentration of

2,3- DPG increases in response to chronic hypoxia. The formation of

extra DPG by red blood cells, as occurs in high altitudes, shifts the

dissociation curve to the right. This means that in high altitudes oxygen

is released more easily, and this makes sense as in high altitudes

(hypoxia) we need higher oxygen supply.

- At Higher ph→ the curve is

shifted to left.

- At Lower ph→ the curve

shifted to right.

- At Higher temperature→ the curve shifted to the right. - At Lower temperature→ the

curve shifted to the left.

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Factors that regulate erythropoiesis 1) Oxygen supply

2) Vitamins

3) Iron

4) Proteins

5) Trace element (copper, cobalt)

6) Healthy bone marrow

7) Liver

8) Hormones (androgen, erythropoietin, thyroid hormones, growth hormones, and steroid hormones)

Blood parameters (erythrocytes)

By now, you know some of these blood parameters including:

1) RBC or ERCS (RBC count): for men is 4.7 to 5.5 mcL, the normal RBC range for women who aren’t pregnant is 4.2 to 5 mcL. { mcL: Million cell per liter}

2) HCT (haematocrit): 45% of blood, less in females almost 40%

3) Haemoglobin concentration: in males: 16g, in females: 14g (~15g/100ml).

4) MCV (Mean Corpuscular Volume): 80-90 micron cubic or pg* {pg: pictogram (1 g = 10^12 pg)}.

This figure represents the oxygen

dissociation curve of different kind of

mammalians and you can notice the

following:

The elephant curve is shifted to the left

(compared to human curve) meaning

it’s Hb has higher affinity (lower oxygen

need).

As for the cat and the mouse curves

they are shifted to the right (compared

to human curve) meaning that their Hb

has lower affinity (higher oxygen need).

The reason of this difference in affinity

is that the demand of oxygen in each

mammalian differs according to its

activity.

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By using these parameters, we can find out new blood parameters and we should be familiar with all these blood parameters to know the different types of anaemias.

1. MCH {The mean corpuscular (cell) hemoglobin}

MCH= weight of haemoglobin in 1 µL of blood

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑅𝐵𝐶 𝑖𝑛 1 µ𝐿 𝑜𝑓 𝑏𝑙𝑜𝑜𝑑

= 𝐇𝐞𝐦𝐨𝐠𝐥𝐨𝐛𝐢𝐧 𝐗 𝟏𝟎

𝐑𝐁𝐂 𝐜𝐨𝐮𝐧𝐭 𝐢𝐧 𝐦𝐢𝐥𝐥𝐢𝐨𝐧

- MCH indicates the average (mean) weight of hemoglobin in the red

blood cell, but without taking the volume of the RBC into consideration

(the amount of haemoglobin in one RBC).

- Normal range for the MCH = 28-32 pg. - An MCH lower than 28 pg is found in microcytic anemia, and in hypochromic, normocytic red blood cells. - An MCH greater than 32 pg is found in macrocytic anemia and in some cases of spherocytosis in which hyperchromia occurs. - MCH within the normal range is found in normal cell.

2. MCHC {The mean corpuscular hemoglobin concentration}

MCHC= 𝐡𝐞𝐦𝐨𝐠𝐥𝐨𝐛𝐢𝐧 𝐢𝐧 𝐠/𝐝𝐥

𝐇𝐞𝐦𝐚𝐭𝐨𝐜𝐫𝐢𝐭 /𝐝𝐥 *100%= [Hb/HCT] *100%

MCHC is an expression of the average concentration of hemoglobin in

the red blood cells. It gives the ratio of the weight of hemoglobin to the

volume of the red blood cell. (We relate hemoglobin weight to MCV).

- MCHC is the scientific indicator (discussed in page 11)

- Normal value of MCHC = 32-36% of MCV (the normal content of

haemoglobin concentration).

- An MCHC below 32% indicates hypochromia.

- An MCHC above 36% indicates hyperchromia.

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- Red blood cells with normal MCHC are termed normochromic.

- Always correlate with the MCH and MCHC to know if the hemoglobin

concentration in the RBCs is normal or not.

3. MCV {Mean corpuscular volume}

MCV = 𝐯𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐑𝐁𝐂𝐬 𝐢𝐧 𝐟𝐥/𝛍𝐥 𝐨𝐟 𝐛𝐥𝐨𝐨𝐝

𝐑𝐁𝐂𝐬/𝛍𝐥 𝐨𝐟 𝐛𝐥𝐨𝐨𝐝 =

𝐇𝐞𝐦𝐚𝐭𝐨𝐜𝐫𝐢𝐭 𝐗 𝟏𝟎

𝐑𝐁𝐂 𝐜𝐨𝐮𝐧𝐭 𝐢𝐧 𝐦𝐢𝐥𝐥𝐢𝐨𝐧

The normal value of MCV is around 80-90 μm3 (or femtoliter)

(normocytic)

- Below 80 is considered microcytic like in iron deficiency anemia,

sideroblastic anemia and thalassemia.

- If above ~97: macrocytic anemia (vitamin B12 deficiency and folic acid

deficiency anemia [pernicious anemia]).

NOTE** these parameters are also called red cell indices.

Note: We can't just use MCH to determine whether the cells are

hypochromic, normochromic, or hyperchromic. We also look at MCHC.

The doctor said that it is like the relation between a person's height and

weight. We don't look at the weight without the height to determine

whether the person is normal, under or over weighted. And here in RBCs

we use MCHC because it's the relation between hemoglobin weight and

cell volume. To make it simpler, some cells have lower weight of

hemoglobin and lower volume, so the MCHC will be normal.

Red blood cell (RBC) indices are part of the complete blood count (CBC) test. They are used to help diagnose the cause of anemia, a condition in which there are too few red blood cells.

The indices include:

Average red blood cell size (MCV)

Hemoglobin amount per red blood cell (MCH)

The amount of hemoglobin relative to the size of the cell (hemoglobin

concentration) per red blood cell (MCHC)

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When the MCH is lower than normal but MCHC so normal, we say these

cells are normochromic. When talking about MCHC it must be exactly

from 32-36% to be normal (not less than 32 or more than 36). (we

usually neglect MCH value and only look at MCHC to determine if it is

normochromic or not, that is because MCH indicates the hemoglobin

amount per one red blood cell, so it is not that scientifically important).

Examples:

MCV 92 65 67 150

MCH 31 22 20 38

MCHC 34 33 30 33

Description of cells

Normocytic normochromic

Microcytic normochromic

Microcytic hypochromic

Macrocytic Normochromic

Important notes on the table above:

MCV normal range is 80-90 but it does not have to be exactly 90 we

consider it normal from 80-97.

MCH is not scientifically considered so we ignore it is value.

MCHC is scientifically considered in describing hemoglobin

concentration and its range Must be between 32-36 %.

MCV is used to describe the size (normocytic, microcytic, macrocytic) of

the cell whereas MCHC is used to describe the concentration of

haemoglobin (normochromic, hypochromic, hyperchromic).

Anemia (erythrocytopenia)

- Anemia is name given for a group of disorders that develops when

your blood lacks enough healthy red blood cells or hemoglobin.

- It is either characterised by low RBCs or low hemoglobin.

- The problem is either increased blood loss or decreased blood production

or high RBCs destruction (rupture).

- There are many types of anemia (erythrocytopenia), we will classify

anemia into types depending on the etiology:

increased blood loss could be caused by:

1. Acute or chronic haemorrhage

2. Haemolysis: which can be caused by:

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- Corpuscular: The problem is either in the cell itself or its

membrane. Like a deficiency of some enzymes such as G6PD

(Glucose-6-phosphate dehydrogenase) or pyruvate kinase.

- Extra corpuscular: The problem is outside the cells, in the

plasma for example: which include blood group

incompatibility, venoms, drugs, few penicillin, toxins and

infections like malaria.

Decreased blood production: 1. Nutritional: Inadequate dietary intake of some

essential substances for erythropoiesis such as

deficiency in vitamin B12, folic acid, pyridoxine

(vitamin B6), ascorbic acid or proteins.

2. Problem in the bone marrow (bone marrow failure),

as the bone marrow is the place where erythropoiesis

takes place.

Effects of anemia on the body

1. Decrease in the viscosity of the blood because of the low

number of RBCs. Blood viscosity depends mainly on the blood

concentration of RBCs then on the plasma proteins (mainly

fibrinogen). “The main factor affecting blood viscosity is RBCs

concentration”. So, what happens is that when the RBCs

number becomes low> the viscosity of the blood decreases >

and therefore the resistance to blood flow to the peripheral

blood vessels decrease “the blood flow increase”> more than

normal amounts of blood flow through the tissues and return

to the heart> increasing cardiac output.

Moreover, Hypoxia leads to vasodilatation of peripheral tissue

blood vessels>> causing further increase in the amount of

blood returned to the heart and increasing the cardiac output.

2. The heart beats also increase.

So, the effect of anaemia on heart is to increase the cardiac output &

increase the heart beats.

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Polycythaemia (erythrocytosis)

polycythaemia is defined as an increase in the number of the RBCs in the

circulation.

Classification of polycythemia or erythrocytosis:” During this course we will

use these terms interchangeably”

1. Relative erythrocytosis:

Results from dehydration, in which the plasma volume decreases so the

total volume of blood decreases, while the RBCs number is still the same

>>>as a result the RBCs concentration increases RELATIVELY “relative to

the volume of the blood”. This case usually occurs during fasting.

2. True erythrocytosis:

It is further divided into:

EXTRA note mentioned by the doctor: Polycythemia is sometimes called

erythrocytosis, but the terms are not synonymous:

Polycythemia: is an abnormal condition that occurs when excess red blood cells are

produced as a result of an abnormality of the bone marrow.

Erythrocytosis:” aKa secondary polycythemia “:it is normal condition which is caused

by either natural or artificial increases in the production of erythropoietin, hence an

increased production of erythrocytes.

You may be wondering why I wrote normal condition even though the number of RBCs

is above normal !! Erythrocytosis as mentioned above is an increase in the RBCs as a

result of increase in the production of erythropoietin but what cause the increase in

the production of erythropoietin?

Either natural causes like high altitude, chronic hypoxia, Neoplasms - Renal-cell

carcinoma (remember erythropoietin is released from the kidney), Or artificial causes

like some kinds of drugs people who abuses steroids, or people on testosterone

replacement or people who take erythropoietin.

So, in erythrocytosis the factory which produces RBCs (Bone marrow) is normal, the

problem is elsewhere but affected the production of RBCs indirectly by increasing

the production of erythropoietin, Erythrocytosis resolves when the underlying cause is

treated.

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a) With Increase erythropoietin: physiological due to: 1. high altitude or

2. drugs. Some drugs cause an increase in the level of erythropoietin

some of these drugs are (Cobalt, androgens) *{from the extra note this is

called erythrocytosis}.

b) With low or normal erythropoietin: for example, cancer *{This is

called polycythaemia and the problem is in the bone marrow}.

Effects of polycythaemia on the circulation: The viscosity increases as a result of increased RBCs >> this leads to an

increase in the resistance to blood flow in peripheral blood vessels >>

as a result the blood flow will decrease becoming very sluggish>> the

pumping workload on the heart increases (the heart pumps hardly).

When the viscosity is high, the venous return relatively decreases but

the blood volume is high, due to increased number of RBCs (From 7 to 8

litres) So, whatever the amount of return is, it will be very high (because

of increased volume), This causes an increase in the load on the heart.

So, in both cases, anemia and polycythaemia, the heart work is

increased, and this may lead to heart failure.

Best of luck 😊

Sorry for any mistake.