NTA Level 4 • Semester 1 • PST04103

Composition and Functions of Blood

Human Anatomy and Physiology • Source Session/Topic 17

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Session 17: Composition and Functions of Blood

Total Session Time: 120 minutes

Prerequisites

• None

Learning Tasks

By the end of this session, students are expected to be able to:

• List the Components of Blood

• Describe Functions of Blood

• Describe Blood Plasma

• Describe Erythrocytes, Leucocytes and Platelets

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board, chalk and whiteboard markers

• Overhead Projector and Transparencies or Slide Projector/LCD and

Computer

SESSION OVERVIEW

| | | | |

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Components of Blood (10 minutes)

|Activity: Brainstorming (5 minutes) |

|Ask students to brainstorm on the following question: |

| |

|What are the components of blood? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• Blood is the specialized bodily fluid that delivers necessary

substances to the body's cells such as nutrients, oxygen and

transports waste products away from those same cells

• Blood accounts for 7% of the human body weight

• By volume the red blood cells constitute about 45% of whole blood, the

plasma constitutes about 55%

• The average adult has a blood volume of roughly 5 litres, composed of:

o Plasma

o Formed elements

• These formed elements of the blood are

o Erythrocytes (red blood cells)

o Adult humans have roughly 2–3 × 1013 red blood cells

o Leukocytes (white blood cells) and 4,000–11,000 white blood cells

o Thrombocytes (platelets). 150,000–400,000 platelets in each microliter

• Women have about 4 to 5 million erythrocytes per microliter (cubic

millimeter) of blood and men about 5 to 6 million; people living at

high altitudes with low oxygen tension will have more

STEP 3: Functions of Blood (10minutes)

|Activity: Buzzing (5 minutes) |

|ASK students to pair up and buzz on the following question for 2 |

|minutes |

| |

|What are the functions of blood? |

| |

|ALLOW few pairs to respond and let other pairs to add on points not |

|mentioned |

| |

|WRITE their response on the flip chart/board |

| |

|CLARIFY and SUMMARIZE by using the content below |

Functions of blood

• Supply of oxygen to tissues (bound to haemoglobin which is carried in

red cells) bound to plasma proteins (e.g. blood lipids)

• Removal of waste such as carbon dioxide, urea and lactic acid

• Immunological functions, including circulation of white cells, and

detection of foreign material by antibodies

• Coagulation, which is one part of the body's self-repair mechanism

• Messenger functions, including the transport of hormones and the

signalling of tissue damage

• Regulation of body pH (the normal pH of blood is in the range of 7.35

– 7.45)

• Regulation of core body temperature

STEP 4: Blood Plasma and Platelets (15minutes)

Blood Plasma

• Is the fluid portion of the blood,

• The plasma, is a remarkable solution containing an immense number of

ions, inorganic molecules, and organic molecules that are in transit

to various parts of the body or aid in the transport of other

substances

• The normal plasma volume is about 5% of body weight, or roughly 3500

mL in a 70kg man

• Plasma clots on standing, remain fluid only if an anticoagulant is

added

• If whole blood is allowed to clot and the clot is removed, the

remaining fluid is called serum

• Serum has essentially the same composition as plasma except that its

fibrinogen an clotting factors II, V, and VIII have been removed and

it has higher serotonin content because of the breakdown of platelets

during clotting

• The plasma consist of protein; albumin, globulin, and fibrinogen

fractions

• The capillary walls are relatively impermeable to the proteins plasma,

and the proteins are therefore exerting an osmotic force of about 25

mm Hg across the capillary wall (oncotic pressure) that pulls water

into the blood

Blood Platelets

• Platelets or thrombocytes are minute fragment of cells consisting of a

small amount of cytoplasm surrounded by a plasma membrane

• Platelets are roughly disk-shaped and an average about 3μm in

diameter.

• They play an important role in controlling blood loss by forming

platelets plugs which seal holes in small vessels

• The life expectancy of platelets is about 5 – 9 days

• Platelets arise in a unique manner by the shedding of thousands of

cytoplasmic fragments from the tips of processes of megakaryocytes in

the bone marrow

• The first detectable cell of this line is the highly basophilic

megakaryoblast, followed by a promegakaryocyte stage, in which

synthesis of granules begins

• Finally, the fully differentiated megakaryocyte, a giant cell with a

large, dense, polyploid, multilobed nucleus, appears

STEP 5: Production and Functions of Red Blood Cell (35 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is the red blood cell? |

|What are the functions of Red blood cells? |

| |

|ALLOW few students to respond |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

Red Blood Cells

• Red blood cells (Erythrocytes) are the most common type of blood cell

• The cells are filled with haemoglobin, a biomolecule that can bind to

oxygen

• They take up oxygen in the lungs and release it while squeezing

through the body's capillaries.

• The blood's red colour is due to the colour of haemoglobin.

• In humans, red blood cells develop in the bone marrow, take the form

of flexible biconcave disks, lack a cell nucleus, subcellular

organelles and the ability to synthesize protein,

• It takes about 7 days for erythrocytes to mature and live a total of

about 120 days

• Erythropoiesis is the process by which red blood cells (erythrocytes)

are produced

o In human adults, this usually occurs within the bone marrow

o In the early foetus, erythropoiesis takes place in the mesodermal cells

of the yolk sac.

o By the third or fourth month, erythropoiesis moves to the spleen and

liver

o In humans with certain diseases, erythropoiesis also occurs outside the

bone marrow, within the spleen or liver

o This is termed extramedullary erythropoiesis

• The tibia and femur cease to be important sites of haematopoiesis by

about age 25; the vertebrae, sternum, pelvis and ribs, and cranium

bones continue to produce red blood cells throughout life.

• Erythrocytes and granulocytes belong to the myeloid lineage.

• The earliest identifiable erythroid stem cells are capable of rapid

bursts of cell division to form numerous daughter cells.

• In the process of red blood cell maturation, a cell undergoes a series

of differentiations.

• The following stages of development all occur within the bone marrow.

o Pluripotent haematopoietic stem cell is cells which are capable of giving

rise to all

blood cell types.

o The first readily identifiable cell of the erythroid series is the

proerythroblast, a large cell with a large euchromatic nucleus and

moderately basophilic cytoplasm

o It also responds to erythropoietin

o The proerythroblast contains small amounts of ferritin and bears some of

the protein spectrin on its plasma membrane

o Proerythroblasts proliferate to produce smaller basophilic erythroblasts,

rich in ribosomes, in which haemoglobin-RNA synthesis begins

o The cytoplasm becomes partially, and then uniformly, eosinophilic (the

polychromatic erythroblast and orthochromatic erythroblast respectively).

o The nucleus becomes intensely pyknotic and is finally extruded from the

cell, leaving an anucleate reticulocyte, which enters a sinusoid

o Its reticular staining pattern, visible using special stains, results

from residual cytoplasmic RNA which is lost within 24 hours of entering

the peripheral blood circulation

o Reticulocyte numbers in peripheral blood are therefore a good indicator

of the rate of red cell production

o The whole process of erythropoiesis takes 5-9 days

• After these stages, the cell is released from the bone marrow, and

ultimately becomes an ‘erythrocyte’ or matures red blood cell

circulating in the peripheral blood

Regulation of Erythropoiesis

• Erythropoietin is a glycoprotein (protein-sugar conjugate) that serves

as the primary regulator of red blood cells (erythrocytes).

• It stimulates bone marrow stem cells to differentiate into red blood

cells and controls haemoglobin synthesis and red blood cell

concentration.

• Erythropoietin production is stimulated by reduced oxygen content in

arterial blood in the kidneys.

• Circulating erythropoietin binds to receptors on the surface of

erythroid progenitor cells that in turn mature into red blood cells.

• In infants, erythropoietin is produced mostly in the liver, but the

kidneys become the primary site of erythropoietin synthesis shortly

after

Functions of Red Blood Cells

• Red blood cells are highly specialized for their oxygen transport

function.

• Because mature RBCs have no nucleus, all their internal space is

available for oxygen transport.

• Because RBCs lack mitochondria and generate ATP anaerobically (without

oxygen), they do not use up any of the oxygen they transport

• Even the shape of an RBC facilitates its function. A biconcave disc

has a much greater surface area for the diffusion of gas molecules

into and out of the RBC than would, say, a sphere or a cube

• Each RBC contains about 280 million haemoglobin molecules

• A haemoglobin molecule consists of a protein called globin, composed

of four polypeptide chains (two alpha and two betachains); a ring like

non protein pigment called a heme is bound to each of the four chains

• At the center of eachheme ring is an iron ion (Fe2_) that can combine

reversibly with one oxygen molecule, allowing each haemoglobin

molecule to bind four oxygen molecules.

• Each oxygen molecule picked up from the lungs is bound to an iron ion

• As blood flows through tissue capillaries, the iron–oxygen reaction

reverses.

• Haemoglobin releases oxygen, which diffuses first into the

interstitial fluid and then into cells.

• Haemoglobin also transports about 23% of the total carbon dioxide, a

waste product of metabolism.

• Blood flowing through tissue capillaries picks up carbon dioxide, some

of which combines with amino acids in the globin part of haemoglobin.

• As blood flows through the lungs, the carbon dioxide is released from

haemoglobin and then exhaled.

• In addition to its key role in transporting oxygen and carbon dioxide,

haemoglobin also plays a role in the regulation of blood flow and

blood pressure.

• The gaseous hormone nitric oxide (NO), produced by the endothelial

cells that line blood vessels, binds to haemoglobin.

• Under some circumstances, haemoglobin releases NO. The released NO

causes vasodilation, an increase in blood vessel diameter that occurs

when the smooth muscle in the vessel wall relaxes.

• Vasodilation improves blood flow and enhances oxygen delivery to cells

near the site of NO release.

STEP 6 : Production and Functions of White Blood Cells (35minutes)

|Activity: Small Group Discussion ( 20 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following questions |

|What are the white blood cells? |

|What are the functions of white blood cells? |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW each groups to present for 5 minutes |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• White blood cells, or leukocytes, are cells of the immune system

defending the body against both infectious disease and foreign

materials

• Five different and diverse types of leukocytes exist, but they are all

produced and derived from a multipotent cell in the bone marrow known

as a hematopoietic stem cell

• Leukocytes are found throughout the body, including the blood and

lymphatic system.

• The number of leukocytes in the blood is often an indicator of disease

• There are normally between 4×109 and 11×109 white blood cells in a

litre of blood, making up approximately 1% of blood in a healthy adult

• In conditions such as leukaemia, the number of leukocytes is higher

than normal, and in leukopenia, this number is much lower

Types of White Blood Cells

• There are several different types of white blood cells

• They all have many things in common, but are all different

• One primary technique to classify them is to look for the presence of

granules, which allows the differentiation of cells into the

categories granulocytes and granulocytes

Granulocytes (Polymorphonuclear Leukocytes)

• Leukocytes characterised by the presence of differently staining

granules in their cytoplasm when viewed under light microscopy

• These granules are membrane-bound enzymes which primarily act in the

digestion of endocytosed particles

• There are three types of granulocytes: neutrophils, basophils, and

eosinophils, which are named according to their staining properties

Agranulocytes (Mononuclear Leucocytes)

• Leukocytes characterized by the apparent absence of granules in their

cytoplasm

• Although the name implies a lack of granules these cells do contain

non-specific azurophilic granules, which are lysosomes

• The cells include monocytes, macrophages and lymphocytes

Functions of White Blood Cells

Neutrophil

• Neutrophils defend against bacterial or fungal infection and other

very small inflammatory processes that are usually first responders to

microbial infection; their activity and death in large numbers forms

pus.

• Neutrophils are very active in phagocytosing bacteria and are present

in large amount in the pus of wounds.

• These cells are not able to renew their lysosomes used in digesting

microbes and die after having phagocytosed a few pathogens

Eosinophil

• Eosinophils primarily deal with parasitic infections and an increase

in them may indicate parasitic infection

• They are also the predominant inflammatory cells in allergic reactions

• The most important causes of eosinophilia include allergies such as

asthma, hay fever, and hives; and also parasitic infections

• Basophils are chiefly responsible for allergic and antigen response by

releasing the chemical histamine causing inflammation

Monocyte

• They have the kidney shaped nucleus and are typically agranulated

• They also possess abundant cytoplasm

• Monocytes share the ‘vacuum cleaner’ (phagocytosis) function of

neutrophils

• Are much longer lived as they have an additional role: they present

pieces of pathogens to T cells so that the pathogens may be recognized

again and killed, or so that an antibody response may be mounted

• Monocytes eventually leave the bloodstream to become tissue

macrophages which remove dead cell debris as well as attacking

microorganisms

• Neither of these can be dealt with effectively by the neutrophils

• Unlike neutrophils, monocytes are able to replace their lysosomal

contents and are thought to have a much longer active life

Macrophage

• Once monocytes move from the bloodstream out into the body tissues,

they undergo changes (differentiate) allowing phagocytosis and are

then known as macrophages

Lymphocyte

• Lymphocytes are much more common in the lymphatic system

• Lymphocytes are distinguished by having a deeply staining nucleus

which may be eccentric in location

• Are relatively small amount of cytoplasm

• The blood has three types of lymphocytes.

o B cells; which make antibodies that bind to pathogens to enable their

destruction

o T cells; these include CD4+ (helper) T cells co-ordinate the immune

response (they are what become defective in an HIV infection).

o CD8+ (cytotoxic) are able to kill virus-infected and tumour cells.

o T cells are crucial to the immune response because they possess a unique

'memory' system which allows them to remember past invaders and prevent

disease when a similar invader is encountered again.

o Natural Killer Cells (NK cells).

o Natural killer cells are able to kill cells of the body that are infected

by a virus or have become cancerous.

STEP 7:Key Points (5minutes)

• Blood is a specialized bodily fluid that delivers necessary substances

to the body's cells such as nutrients, oxygen and transports waste

products away from those same cells

• The fluid portion of the blood is called the plasma.

• White blood cells, or leukocytes, are cells of the immune system

defending the body against both infectious disease and foreign

materials.

• Platelets play an important role in controlling blood clotting.

STEP 8: Evaluation (5minutes)

• What are the components of blood?

• What are the functions of blood?

• What is blood plasma?

• What are the functions of leukocytes and erythrocytes?

References

Seeley, R. R., Stephens, T. D., &Tate, P. (2003). Anatomy and Physiology.

(5th ed.).Boston:

McGraw-Hill.

Standring, S. (2008). Grays’s Anatomy; the anatomical basis of clinical

practice.(40th ed.).

Elservier: Churchill Livingstone.

Thibodeau, G. A., & Patton, K. T. (1999). Anatomy & Physiology. Mosby:

Hoffman

Press, Inc.

Tortora, G.J & Derrickson, B (2009). Principles of Anatomy and Physiology

12th Edition,

USA, John Wiley & Sons Inc, USA

Waugh, A., & Grant, A. (2006). Ross and Willson Anatomy and physiology in

Health and

illness. China: Churchill Livingstone Elservier

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