Blood

THE BLOOD

Overview

• Blood
• Composition and functions
• Red blood cells:
• -Characteristics & functions, formation and destruction
• White blood cells:
• -Characteristics, functions, formation
• Platelets :
• -Haemostasis, fibrinolysis

Blood groups and transfusion problems

Blood Composition

• Blood
• Is an opaque, red liquid
• Consisting of several types of cells suspended in a complex, amber fluid
• Plasma
• Composed of
• Cells
• Plasma, liquid in which the cells are suspended
• The cells (formed elements) include
• Erythrocytes (RBCs)
• Leukocytes (WBCs)

Platelets (cell fragments)

The branch of science concerned with the study of blood, blood-forming tissues, and the disorders associated with them is called Hematology.

Cells of the body are serviced by 2 fluids

• blood
• composed of plasma and a variety of cells
• transports nutrients and wastes
• interstitial fluid

bathes the cells of the body

Nutrients and oxygen diffuse from the blood into the interstitial fluid and then into the cells Wastes move in the reverse direction.

Blood

• Its pH is 7.4 (7.35-7.45)
• 99% of the cells are RBC which are the O2 carrying cells of blood
• Blood is thicker (more viscous) than water and flows more slowly than water
• Average blood volume = 8% of body weight

= 5.6L (70*0.08)

• On the average
• 60% of blood vol = plasma ( 3 liters)
• 40% of blood vol = RBC (2 liters)

Values vary considerably in different people depending on sex and other factors

The haematocrit

• Defined as the % of total blood that is erythocytes
• It is determined by centrifuging a sample of blood in a haematocrit tube
• Erythrocytes are forced to the bottom
• Plasma remains at the top
• Leucocyte and platelets form a thin layer in between
• Blood

Plasma = 55%

• Leukocytes and platelets (buffy coat)

RBC = 45% (Hct = 45%)

Components of Blood

• Hematocrit
• 55% plasma
• 45% cells
• 99% RBCs

< 1% WBCs and platelets

Blood Plasma

• Non-cellular part of blood
• 0ver 90% water
• 7% plasma proteins
• created in liver
• confined to bloodstream
• albumin
• maintain blood osmotic pressure
• globulins (immunoglobulins)
• antibodies bind to foreignsubstances called antigens
• form antigen-antibody complexes
• fibrinogen
• for clotting
• 2% other substances

electrolytes, nutrients, hormones, gases, waste products

Plasma Constituents

• Constituent
• Functions
• 1
• Water =92% of plasma wt
• Medium for carrying all other constituents
• 2
• Electrolytes (inorganic) Total < 1% plasma wt
• Keep water in ECF, act as buffers, for blood clotting, for excitability of cells
• 3
• Proteins 7% of plasma wt.= 7.3 g/100 ml
• Albumin,
• globulin, fibrinogen
• Provide non penetrating solute of plasma,
• Act as buffers, transport protein,clotting factors, enzymes, antibodies

Blood

Plasma Constituents

• Constituent
• Functions
• 4
• Gases

CO2, O2

• CO2 is waste product, O2, for oxidative metabolism,
• 5
• Nutrients
• Glucose, amino acids, lipids and cholesterol, vitamins, trace elements
• Nutrition

Blood

Plasma Constituents

• Constituent
• Functions
• 6
• Waste products: urea, creatinine, uric acid, bilirubin
• 7
• Individual hormnes
• Metabolic, Control system

Blood

Formed Elements of Blood

• Red blood cells ( erythrocytes )
• White blood cells ( leukocytes )
• Granular leukocytes
• neutrophils, eosinophils, basophils
• Agranular leukocytes
• lymphocytes = T cells, B cells, and natural killer cells
• monocytes

Platelets (special cell fragments)

Erythrocytes (RBC)

• Blood
• Erythrocytes
• Functions of RBC
• To transport Haemoglobin
• Hb carries O2
• Hb carries O2 form lungs to tissue
• In lower animals Hb circulates as free protein in plasma
• In human being when it is free
• 3% leaks from capillaries

Into tissue spaces; glomerular filtrate

Erythrocytes

• Blood
• Hence for Hb to remain in blood stream
• It must exist inside the RBC
• Other functions of RBC include;
• Buffer function
• Contain carbonic Anhydrase which catalyze
• H2o + Co2 H2co3 Hco3- + H+
• -Thus transport CO2 from tissues to lungs in the form of HCO3-
• Hb is an excellent acid/base buffer

-Thus RBC are responsible for most buffering capacity of the blood

Erythrocytes

• Blood
• Shape and size of RBC
• Biconcave discs
• Diameter = 7.8 µm
• Thickness at the thickest point = 2.5 µm
• average volume = 90 – 95 µ3
• The shape of the RBC can change remarkably
• It is a bag which can be deformed
• To any shape; This allows it to pass through capillaries without problem
• Normal RBC
• Has great excess cell membrane for quantity inside

Hence deformation does not stretch the membrane to cause it to rapture

Concentration of RBC in Blood

• Blood
• In normal men average number of RBC
• Is 5,200,000 (+/- 300,000) per cubic ml
• In women average number of RBC

Is 4,700,000 (+/- 300,000)

• Quantity of Hb in RBC
• When Hb formation is deficient in bone marrow

% Of Hb in RBC may fall and volume of RBC may decrease

Concentration of RBC in Blood

• Blood

When Haematocrit = 40 – 45%

• Quantity of Hb in each cell is normal
• Whole blood of men contain 16 gm Hb/dl
• Whole blood of women contain 14 gm Hb/dl
• Each gram of pure Hb
• Combine with 1.39 ml of O2
• Hence in normal man total amount carried
• Is = 1.39 * 16 = 21 ml of O2 per dl of blood
• In normal woman
• Is = 1.39 * 14 = 19 ml of O2 per dl of blood

RBC have the ability to conc HB up to 34 g/dl

Erythropoeisis

• Blood
• Sites of RBC production include
• York sack
• During early weeks of embryonic life
• Liver, spleen, lymph nodes
• Middle trimester
• Bone marrow
• Last trimester, after birth
• Bone marrow of all bones
• Up to 5 yrs
• Bone marrow of membranous bones

> 20yrs

Substances Required for Synthesis of RBC

• Blood
• The production of RBC requires the usual things for normal production of any cell
• Amino acids, lipids, carbohydrates
• Iron,

Vitamin B12, folic acid

Genesis of RBC

• Blood

Pluripotential Haemopoetic stem cell (PHSC) Derived from blood islands in the embryonic yolk sac whose cells colonize liver, spleen & bone marrow All cells in circulating blood are derived from these stem cells.

• Pluripotent stem cells
• replenish themselves as they differentiate into either myeloid or lymphoid stem cells

Myeloid stem cell line of development continues:

progenitor cells(colony-forming units) no longer can divide and are specialized to form specific cell types example: CFU-E develops eventually into only red blood cells next generation is blast cells

• have recognizable histological characteristics
• develop within several divisions into mature cell types

Lymphoid stem cell line of development pre-B cells & prothymocytes finish their develop into B & T lymphocytes in the lymphatic tissue after leaving the red marrow

Genesis of RBC

• Blood
• PHSC
• Produce committed stem cells which produce colonies of specific types of blood cells
• Colony forming unit – erythrocytes (CFU -E)
• Colony forming unit – granulocytes & Monocytes(CFU-GM)
• Colony forming unit – megakaryocytes (CFU-M)
• Lymphoid stem cell (LSC)
• Also PHSC differentiates into other PHSC

Maintain line of stem cell

Myeloid stem cells give rise to RBCs, platelets, and all WBCs except for lymphocytes.

Lymphoid stem cells give rise to lymphocytes.

Myeloid stem cells differentiate into progenitor cells or precursor cells (blast cells) which will develop into the actual formed elements of blood.

Lymphoid stem cells differentiate into pre-B and prothymocytes which develop into B-lymphocytes and T-lymphocytes, respectively.

This process of hemopoiesis (or hematopoiesis) is stimulated by several hematopoietic growth factors. These hematopoietic growth factors stimulate differentiation and proliferation of the various blood cells.

Hematopoiesis

Genesis of RBC

• Blood
• Growth and reproduction of different stem cells
• Controlled by multiple protein (growth inducers)
• interleukin 3
• Promote growth and reproduction of all different stem cells
• Differentiation inducers
• -Cause one stem cell to differentiate into one or two stages towards adult form
• The formation of growth inducers & differentiation inducers
• Controlled by other factors
• erythropoeitin in case of RBC
• In case of some WBC

Infectious diseases cause growth, differentiation and formation of specific types of WBC

Regulation of RBC Production

• Blood
• Total mass of RBC in circulation
• Regulated within narrow limits
• Tissue oxygenation provides the basic regulation of RBC production
• Conditions that decrease oxygen transport to tissue
• Anaemia, high altitude, low blood volume, poor blood flow, lung diseases

Increase rate of RBC production

Hemopoietic Growth Factors

• Regulate differentiation & proliferation
• Erythropoietin (EPO)
• produced by the kidneys increase RBC precursors
• Thrombopoietin (TPO)
• hormone from liver stimulates platelet formation
• Cytokines (colony-stimulating factors and interleukins) are local hormones of bone marrow
• produced by some marrow cells to stimulate proliferation in other marrow cells

colony-stimulating factor (CSF) & interleukin stimulate WBC production

Role of erythropoeitin

• Blood
• Erythropoetin is a glycoprotein MW 34,000
• During hypoxia
• Rate of production of erythropoeitin increases
• Erythropoeitin is produced mainly by the kidneys (90%)
• The remaining amount is produced in some other tissue (liver)
• Erythropoeitin stimulates
• Production of proerythroblasts from PHSC
• Rapid differentiation of erythroblastic stages to form mature erythroblast

Hence there is rapid production of RBC

Regulation of Erythropoiesis

• Blood
• O2 delivery to Kidney
• Erythopoietin prod by Kidney

Plasma Erythopoietin

• Production of RBC by Bone marrow
• Blood Haemoglobin conc
• Blood O2 carrying capacity

restoration of O2 delivery

Feedback Control of RBC Production

• Tissue hypoxia (cells not getting enough O2)
• high altitude since air has less O2
• anemia
• RBC production falls below RBC destruction
• circulatory problems
• Kidney response to hypoxia
• release erythropoietin

speeds up development of proerythroblasts into reticulocytes

Medical Uses of Growth Factors

Growth factors, available through recombinant DNA technology, hold great potential for use in patients who cannot normally form the blood cells.

Available through Recombinant DNA technology Recombinant erythropoietin (EPO) very effective in treating decreased RBC production of end-stage kidney disease other products given to stimulate WBC formation in cancer patients receiving chemotherapy which kills bone marrow granulocyte-macrophage colony-stimulating factor granulocyte colony stimulating factor Thrombopoietin helps prevent platelet depletion during chemotherapy

Formation of Haemoglobin

• The synthesis of HB
• Begins at the Proerythroblast stage
• Continue up to reticulocyte stage
• Stages of Hb synthesis
• 2 succinyl CoA combine with 2 glycine molecule to form a pyrole molecule
• Blood
• NH
• HC
• CH
• C
• A
• P

Pyrole molecule

Formation of haemoglobin

• 4 pyrole molecules combine to form protoporphyrin IX
• Blood
• N
• Protoporphyrin IX
• CH3
• COO- – (CH2 )

CH=CH2

(CH2 ) – COO-

Formation of haemoglobin

• Protoporphyrin combine with Fe++ to form Haeme
• Blood
• N
• Fe++
• Haeme
• CH3
• COO- – (CH2 )

CH=CH2

(CH2 ) – COO-

Formation of haemoglobin

• Each haeme molecule combine with a long polypeptide chain (Globin)

To form haemoglobin chain

There are different types of chains formed depending on amino acid composition of the polypeptide chain Blood

• N
• Fe++
• O2
• Poypeptide chain (Globin)
• CH3
• COO- – (CH2 )

CH=CH2

(CH2 ) – COO-

Haemoglobin chain ( or )

Formation of haemoglobin

• The different types of haemoglobin chains include
•  Chain contain 141 AA residues
•  Chain contain 146 AA residues
• 10 individual residues differ from the  Chain
•  Chain contain 146 AA residues
• 37 individual residues differ from  Chain
• Blood
• N
• Fe++
• O2
• Poypeptide chain (globin)
• CH3
• COO- – (CH2 )

CH=CH2

(CH2 ) – COO-

Haemoglobin Chain

Formation of haemoglobin

• 2 alpha chains combine with 2 beta chains to form Haemoglobin molecule (Hb-A)
• Each chain has MW =16,000
• Total MW of Hb
• = 64,000
• Blood

Haemoglobin Molecule (Hb-A)

 chain

Haemoglobin

• Blood
• The most common type of heamoglobin

Haemoglobin A (Hb A)

• Formed by a combination of 2 chains and 2  chains
• Others

Haemoglobin A2 (Hb A2)

• Formed by a combination of 2 chains and 2  chains
• Fetal haemoglobin (Hb F)

Formed by combination of 2 chains and 2  chains

Haemoglobin

• Blood
• Each chain has a haeme prosthetic group

Hence there are 4 iron atoms in each Hb molecule Each iron atom can combine with 1 molecule of oxygen: total of 4 oxygen molecules (8 oxygen atoms) O2 binds loosely with iron (Fe++)

• To form oxyhaemoglobin
• A reversible reaction
• At the lungs Hb binds with O2

At the tissue level HB release the O2

Haemoglobin

• Blood
• If the Fe++ is oxidized to Fe+++
• Then methaemoglobin is formed
• It is dark coloured and causes cyanosis if it is in large amount
• Oxidation of Hb to methaemoglobin
• Does occur to some extent in circulation but
• NADH – methaemoglobin reductase enyme system in RBC
• Converts methaemoglobin back to Hb
• Absence of this enzyme system

Causes methaemoglobinaemia

Haemoglobin

• Blood
• Hb can combine also with carbon monoxide
• To form carbon monoxyhaemoglobin (carboxyheamoglobin)
• The affinity of Hb for O2 is lower than that for CO
• CO displaces O2 from Hb

This lowers O2 carrying capacity of Hb

Iron Metabolism

• Blood
• Different forms into which body iron exist include

Haemoglobin 65%

Myoglobin 4%

• Various forms of Haeme compounds 1%
• Combined with Transferrin 0.1%

Stored in RES, liver (in form of ferritin) 15 – 30%

Transport of Iron

• Blood
• After absorption in GIT
• Iron is combined with  – globulin (apotransferrin)
• To form Transferrin
• This is transported in plasma
• Iron is loosely combined to the globulin
• Easily released to tissue cells
• Excess iron in blood
• Deposited in cells of the body ( Liver, RES, bone marrow )
• In the cell’s cytoplasm
• Iron combine with apoferritin to form ferritin
• Ferritin is a storage form of iron
• Small quantity of iron is stored as

Haemosiderrin

Transport of Iron

• Blood
• When the quantity of iron in plasma falls
• Iron is easily removed from Ferritin
• It is transported in plasma as Transferrin
• In bone marrow
• Transferrin binds strongly to receptors of cell membrane of erythroblasts
• Iron is transported directly to mitochondria for haeme synthesis
• When RBC are destroyed
• Hb released from RBC is ingested by macrophages
• Free iron is released and it is either
• Stored as ferritin or

Re-used again in the formation of new Hb

Absorption of Iron

• Blood
• Liver bile
• apotransferrin
• Transferrin
• Free Fe, Hb, myoglobin
• Transferrin

Plasma Transferrin

• Pinocytosis
• Receptor in the membrane

Intestinal Lumen

• Epithelial cells

Capillary

Daily Loss of Iron

• Blood
• Man excretes about 1 mg of iron per day
• Mainly through faeces
• During haemorrhages
• For women menstrual blood loss

Brings the total iron loss to about 2 mg per day

Destruction of RBC

• Blood
• RBC normally circulate for an average of 120 days before destruction
• Mature RBC
• Do not have nucleus, mitochondria or endoplasmic reticulum
• Have some cytoplasmic enzymes
• Capable of metabolizing glucose to form
• ATP
• NADPH
• NADPH serves the RBC
• Maintaining the pliability of the cell membrane
• Maintaining membrane transport of ions
• Keeping the iron in Hb in Fe++ rather than Fe+++ state
• As the cells become old
• Metabolic processes become progressively less active
• Membrane become fragile ruptures easily especially

During RBC passage through spleen

Destruction of RBC

• Blood
• When RBC membrane rapture
• Released Hb is phagocytosed by macrophages RES
• Hb is split into
• Globin and haeme
• Haeme ring is opened to give
• Free iron -Transported in blood by Transferrin
• Phorphyrin portion
• Phophyrin portion of the haeme
• Converted into biliverdin
• Biliverdin (green) converted to bilirubin (yellow)

bilirubin secreted by liver into bile converted to urobilinogen then stercobilin (brown pigment in feces) by bacteria of large intestine if reabsorbed from intestines into blood is converted to a yellow pigment, urobilin and excreted in urine

Recycling of Hemoglobin Components

Anaemia

• Blood
• Anaemia means deficiency of RBCs which can be due to
• Too rapid loss of RBCs
• Slow production of RBCs
• Types
• Blood loss anaemia -loss of RBCs due to bleeding (ulcer)
• Iron-deficiency -lack of absorption or loss of iron
• Pernicious Anaemia -lack of intrinsic factor for B12 absorption
• Aplastic anaemia- destruction of bone marrow (radiation/toxins
• Magaloblastic anaemia- folic and vitamin b 12 deficiency

Haemolytic anaemia -defects in cell membranes cause rupture

Blood Loss Anaema

• Blood
• After haemorrhage
• Body replaces plasma within 1 to 3 days
• This leaves low conc of RBC in plasma
• RBC can return to normal within 3 to 6 weeks
• In chronic blood loss
• An individual cannot absorb iron rapidly enough to cope with HB synthesis
• RBC are formed with little Hb
• They are pale (Hypochromia)
• They are small in size (Microcytosis)

Microcytic hypochromic anaemia

Aplastic anaemia

• Blood

Due to lack of function of bone marrow Exposure to gamma radiation, certain industrial chemicals, excessive X-rays, certain drugs

Megaloblastic anaemia

• Blood
• Due to lack or deficiency of vitamin B12, folic acid
• Required for DNA synthesis
• Deficiency of these leads to
• Slow reproduction of erythroblasts in bone marrow
• They become large with odd shapes
• Megaloblasts (have fragile membrane) easily rapture
• Development of anaemia

Megaloblastic anaemia

Haemolytic anaemia

Blood

In this condition normal number of RBC is being formed but have abnormalities which make their membrane fragile They rapture easily as they go through the capillaries Hence life span greatly reduced

• Anaemia develops
• Examples
• Hereditary spherocytosis
• RBC are small and have spherical shape
• They are easily ruptured as they pass through the spleen pulp

Haemolysis

Haemolytic anaemia

• Blood
• Sickle cell anaemia
• RBC contain abnormal type of HB known as Hb-s
•  Chain of Hb are abnormal
• Valine is substituted for glutamic acid at one point
• When it is exposed to low O2
• It precipitates into long crystal inside the RBC
• Which elongate the cell into a sickle shape
• Fragile membrane

Breakdown of RBC –(Haemolysis)