Lec.1.Blood,2018.pptx

The Cardiovascular System: The Blood
Lec.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Blood Physiology
 The cardiovascular system consists of three interrelated components:
 Blood,
 The heart
 Blood vessels
 Blood is a highly differentiated, complex living tissue that pulsates
through the arteries to every part of the body, interacts with
individual cells via an extensive capillary network, and returns to the
heart through the venous system.
 Many of the functions of blood are undertaken in the capillaries,
allowing the efficient diffusion and transport across the monolayer
of endothelial cells that form the thin capillary walls.

Physical Characteristics of Blood
 Blood is denser and more viscous (thicker) than water and slightly
sticky.
 The temperature of blood is 38°C (100.4°F), about 1°C higher than
oral or rectal body temperature
 pH ranging from 7.35 to 7.45.
 The color of blood varies with its O+2 content. When saturated with
oxygen, it is bright red. When unsaturated with O+2, it is dark red.
 Blood constitutes about 20% of extracellular fluid, amounting to 8%
of the total body mass.
 The blood volume is 5 to 6 liters in adult male and 4 to 5 liters in
adult female.
 The gender difference in volume is due to differences in body size.

The general Functions of blood
Blood has three general functions:
• Transportation
 Blood transports O+2 from the lungs to the cells of the body and
carbon dioxide from the body cells to the lungs for exhalation.
 It carries nutrients from the gastrointestinal tract to body cells and
 hormones from endocrine glands to other body cells.
 Blood also transports heat and waste products to various organs for
elimination from the body.
• Regulation
 Circulating blood helps maintain homeostasis of all body fluids.
 Blood helps regulate pH through the use of buffers.

 It helps adjust body temperature through the heat absorbing and
coolant properties of the water in blood plasma and its variable rate
of flow through the skin, where excess heat can be lost from the
blood to the environment.
 Protection
 Blood can clot, which protects against its excessive loss from the
cardiovascular system after an injury.
 its white blood cells protect against disease by carrying on
phagocytosis.
 Several types of blood proteins, including antibodies, interferons, and
complement, help protect against disease in a variety of ways.

Whole blood has two components:
1. The yellow upper layer is plasma, the liquid portion of blood,
which accounts for about 55% of the total volume of whole blood.
2. The lower layer consists of the formed elements normally constitute
about 45% of the total volume of whole blood.
 If a sample of blood is centrifuged (spun)
in a small glass tube, the cells
(which are more dense) sink to the bottom
of the tube
 while the plasma (which is less dense)
forms a layer on top.
Composition of blood
Components of blood

 The plasma is a complex solution and suspension of chemical
substances.
 It consists of about 90% water, 1% inorganic substances, 6-8%
proteins, with the remainder glucose, amino acids, lipids,
nitrogenous wastes of metabolism (e.g. urea),
 gases, enzymes, hormones and other substances.
 The water of plasma serves in transport functions and
 the inorganic substances act as buffers and osmotically active
particles and ensure proper excitability of cells.
The plasma

 The plasma proteins are so named because they usually remain in
the plasma, and maintain oncotic pressure which helps to keep the
blood volume constant.
 The three major types of plasma proteins are
 Albumins (54% of plasma proteins),
 globulins (38%)
 fibrinogen (7%).
 Most plasma proteins are made in the liver.
 An exception is the antibodies or immunoglobulin produced by B-
lymphocytes, which function in immunity.
 The primary sign of plasma protein deficiency is development of
edema because water filtered from blood vessels and is not
osmotically return to the capillaries.
The plasma proteins

 The percentage of total blood volume occupied by RBCs is called
the hematocrit.
 A hematocrit of 40 indicates that 40% of the volume of blood is
composed of RBCs.
 The normal range of hematocrit for adult females is 38–46%
(average 42); for adult males, it is 40–54% (average 47).
 The hormone testosterone, present in much higher conce. in males
than in females, stimulates synthesis of erythropoietin (EPO), the
hormone that in turn stimulates production of RBCs.
 Thus, testosterone contributes to higher hematocrits in males.
 A significant drop in hematocrit indicates anemia.
Hematocrit

 In polycythemia the percentage of RBCs is abnormally high, and
the hematocrit may be 65% or higher.
 The formed elements
 Blood cells include erythrocytes (red blood cells),
 leukocytes (white blood cells),
 blood thrombocytes (platelets)
 RBCs and WBCs are whole cells

Regulation of Blood Cell Production
 The process of blood cell generation, hematopoiesis, occurs in
healthy adults only in the bone marrow.
 Extramedullary hematopoiesis (e.g., the generation of blood cells in
the spleen) is observed only in some disease states, such as leukemia.
 Hematopoietic cells are also found in the blood of adults, but in
extremely low numbers.
 Large numbers of hematopoietic cells can be recovered from
aspirates of the iliac crest, sternum, pelvic bones, long bones, and
ribs of adults.
 Within the bones, hematopoietic cells germinate in extravascular
sinuses, called marrow stroma. stromal cells, are differentiating cells found in
abundance within bone marrow. The most common stromal cells
include fibroblasts and pericytes.

 All blood cells are production begins with the proliferation of
pluripotent hematopoietic stem cells (uncommitted) in red bone
marrow,
 A single population of bone marrow cells, which are undifferentiated
cells
 capable to produce two further types of stem cells, which have the
capacity to develop into several types of cells.
 These stem cells are called myeloid stem cells and lymphoid stem
cells.
 Myeloid stem cells give rise to red blood cells, platelets, monocytes,
neutrophils, eosinophils, and basophils.

 Lymphoid stem cells begin their development in red bone marrow
but complete it in lymphatic tissues; they give rise to lymphocytes.
 During hemopoiesis, some of the myeloid stem cells differentiate
into progenitor cells.
 Other myeloid stem cells and the lymphoid stem cells develop
directly into precursor cells.
 Progenitor cells are no longer capable of reproducing themselves
and are committed to giving rise to more specific elements of blood.
 Some progenitor cells are known as colony-forming units (CFUs).
 Following the CFU designation is an abbreviation that indicates the
mature elements in blood that they will produce:

 CFU-E ultimately produces erythrocytes;
 CFU-Meg produces megakaryocytes, the source of platelets;
 CFU-GM ultimately produces granulocytes (specifically,
neutrophils) and monocytes.
 In the next generation, the cells are called precursor cells, also
known as blasts.
 Over several cell divisions they develop into the actual formed
elements of blood.
 For example, monoblasts develop into monocytes,
 Eosinophilic myeloblasts develop into eosinophils.
 Several hormones called hemopoietic growth factors regulate the
differentiation and proliferation of particular progenitor cells.

 Erythropoietin increases the number of RBCs precursors and
produced primarily by cells in the kidneys that lie between the kidney
tubules (peritubular interstitial cells).
 Thrombopoietin is a hormone produced by the liver that stimulates
the formation of platelets from megakaryocytes.
 Several different cytokines regulate development of different blood
cell types.
 Two important families of cytokines that stimulate white blood cell
formation are:
 Colony-stimulating factors (CSFs) and
 Interleukins.

The Erythrocyte
 Mature erythrocyte is disc biconcave,
 Non nucleated and flexible.
 Disc averaging 7.8-8 µm in diameter, 2 µm thick at their edges and
1 µm thick at their center.
 The shape disc biconcave provides the maximum surface area to
give the greatest possible surface for diffusion of gasses.
 The erythrocyte maintains its shape by virtue of its complex
membrane skeleton, which consists of an insoluble mesh of fibrous
proteins attached to the inside of the plasma membrane.
 This structural arrangement allows the erythrocyte great flexibility
as the cell twists and turns through small, curved vessels.

 In addition to structural proteins of the membrane, several functional
proteins are found in the cytoplasm of erythrocytes.
 These include haemoglobin,
 Antioxidant enzymes, and
 Glycolytic systems to provide cellular energy (ATP).
 The plasma membrane possesses ion pumps that maintain a high
level of intracellular K+ and a low level of intracellular Ca+2 and Na+.
 RBCs does not contain nucleus, to consume small amounts of O2,
glucose and ATP, and
 Produce small quantities of CO2.
 Because mature RBCs have no nucleus, all their internal space is
available for O2 transport.

 Because RBCs lack mitochondria and generate ATP anaerobically, they
do not use up any of the O2 they transport.
 A healthy adult male has about 5.4 million RBCs per microliter of
blood,
 A healthy adult female has about 4.8 million.
 To maintain normal numbers of RBCs, new mature cells must enter
the circulation at the astonishing rate of at least 2 million per second,
a pace that balances the equally high rate of RBC destruction.
 The red, oxygen-transporting protein of erythrocytes consists of
 A globin (or protein) portion and
 Four heme groups, the iron-carrying portion.

Hemoglobin
 This complex protein possesses four polypeptide chains: two α -globin
molecules of 141 amino acids each and two molecules of another type
of globin chain (β, γ, Δ, £), each containing 146 amino acid residues.
 Four types of hemoglobin molecules can be found in human
erythrocytes:
 embryonic, fetal, and two different types found in adults (HbA,
HbA2).
 Each hemoglobin molecule is designated by its polypeptide
composition.
 For example, the most prevalent adult hemoglobin, HbA, consists of
two α chains and two β chains.
 Its formula is given as α2β2.

RBC shape and Structure of hemoglobin A. Each molecule of hemoglobin
possesses four polypeptide chains, each containing iron bound to its heme group

 HbA2, which makes up about 1.5 to 3% of total haemoglobin in an
adult, has the subunit formula (α2Δ2).
 Fetal haemoglobin (α2γ2) is the major hemoglobin component
during intrauterine life.
 Its levels in circulating blood cells decrease rapidly during infancy
and reach a conce. of 0.5% in adults.
 Embryonic hemoglobin is found earlier in development. It consists
of (α2£2), the production of £ chains ceases at about the third month
of fetal development.
 Sickle-cell anemia, for example, results from the presence of sickle-
cell haemoglobin (HbS), which differs from normal adult HbA
because of the substitution of a single amino acid in each of the two
β chains.

 In normal people, the percentage of Hb in RBCs is always near the
maximum value.
 The heme portion of Hb is synthesized in mitochondria and the
protein part (globin) is synthesized in ribosomes.
 However, when Hb formation is deficient in the bone marrow,
 The percentage of Hb in these cells may lower below normal value
 The volume of RBCs decrease because of diminished Hb to fill the
cell.
 When the hematocrit value or packed cell volume (is the volume of
red cells expressed as percentage of total volume of blood-
normally=40-45%), and The quantity of Hb in each cells are normal,
Quantity of Hemoglobin in RBCs

 The whole blood of men contains about 16gm Hb/(dl) of blood
 In women contain about 14gm Hb/(dl) of blood. and
 Each gram of pure Hb is able to combine with about 1.39
milliliters of oxygen.
 Each RBC contains about 280 million hemoglobin molecules.

Regulation of RBCs production
 Tissue oxygenation consider as the basic regular of RBCs
production so that, any condition that causes decrease in the quantity
of O+2 transported to the tissue ordinarily increases the rate of RBCs
production. such as:
 Low blood volume, anemia, low Hb,
 Poor blood flow-cardiac failure,
 Pulmonary disease
 Hemorrhage
 Thus when a person becomes extremely anemic as a result of
hemorrhage or other conditions, the bone marrow immediately
begins to produce large quantities of RBCs.

 At high altitudes, where the quantity of O+2 in the air is greatly
decreased and insufficient O+2 is transported to the tissues and RBCs
production is considerably increased.
 The principal factor that stimulates RBCs production and maturation
is a circulating hormone called erythropoietin and its formation in
response to hypoxia (cellular O+2 deficiency) and
 This hormone enhances RBCs production until hypoxia is relieved.
 In normal person, about 90% of all erythropoietin is formed in the
kidney and the remainder is formed mainly in the liver.
 So that, in kidney failure, the person becomes very anemic, because
10% of erythropoietin that is formed mainly in the liver is not
sufficient to cause formation of RBCs as needed in the body.

Fig.4.Action of erythropoietin.

 When RBCs are delivered from bone marrow to the circulation, they
normally circulate an average of about 120 day before being
destroyed.
 Because of the wear and tear their plasma membranes undergo as they
squeeze through blood capillaries.
 Without a nucleus and other organelles, RBCs cannot synthesize new
components to replace damaged ones.
 The plasma membrane becomes more fragile with age, and the cells
are more likely to burst, especially as they squeeze through narrow
channels in the spleen.
 Some of the senescent (old) red cells break up in the bloodstream, but
the majority is engulfed by macrophages by the monocyte-
macrophage system,
Destruction of RBCs

 The breakdown products are recycled and used in numerous
metabolic processes, including the formation of new red blood cells.
 The recycling occurs as follows:
● Macrophages in the spleen, liver, or red bone marrow phagocytize
ruptured and worn-out red blood cells.
● The globin and heme portions of hemoglobin are split apart.
● Globin is broken down into amino acids, which can be reused to
synthesize other.
● Iron is removed from the heme portion in the form of Fe3+, which
associates with the plasma protein transferrin, a transporter for Fe3+ in
the bloodstream.

● In muscle fibers, liver cells, and macrophages of the spleen and
liver, Fe3+ detaches from transferrin and attaches to an iron-storage
protein called ferritin.
● On release from a storage site or absorption from the
gastrointestinal tract, Fe3+ reattaches to transferrin.
● The Fe3+-transferrin complex is then carried to red bone marrow,
where RBC precursor cells take it up through receptor mediated
endocytosis for use in hemoglobin synthesis.
• Iron is needed for the heme portion of the hemoglobin molecule,
• and amino acids are needed for the globin portion.
• Vitamin B12 is also needed for the synthesis of hemoglobin.

● Erythropoiesis in red bone marrow results in the production of
RBCs, which enter the circulation.
● When iron is removed from heme, the non-iron portion of heme is
converted to biliverdin, a green pigment, and
● Then into bilirubin, a yellow orange pigment.
● Bilirubin enters the blood and is transported to the liver.
● Within the liver, bilirubin is released by liver cells into bile, which
passes into the small intestine and then into the large intestine.
● In the large intestine, bacteria convert bilirubin into urobilinogen.

● Some urobilinogen is absorbed back into the blood, converted to a
yellow pigment called urobilin, and excreted in urine.
● Most urobilinogen is eliminated in feces in the form of a brown
pigment called stercobilin, which gives feces its characteristic color.

Reactions of Hemoglobin
 Hemoglobin binds O+2 to form oxyhemoglobin, O+2 attaching to the
Fe2+ in the heme.
 The affinity of hemoglobin for O+2 is affected by:
 PH,
 Temperature
 The conce. in the red cells of 2,3-biphosphoglycerate (2,3-BPG).
 These factors decreasing the affinity of hemoglobin for O+2.
 When blood is exposed to various drugs and other oxidizing agents in
vitro or in vivo, the ferrous iron (Fe2+) molecule is converted to ferric
iron (Fe3+), forming methemoglobin.

 Methemoglobin is dark-colored, and when it is present in large
quantities in the circulation, it causes a dusky discoloration of the
skin resembling cyanosis.
 Carbon monoxide reacts with hemoglobin to form carbon
monoxyhemoglobin (carboxyhemoglobin).
 Heme is a part of the structure of myoglobin, an oxygen-binding
pigment found in red muscles.
 Neuroglobin, an oxygen-binding globin, is found in the brain.

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