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Chapter 19

Nursing HAP201 Chapter Notes - Chapter 19: Bone Marrow, Natural Killer Cell, Progenitor Cell


Department
Nursing
Course Code
Nursing HAP201
Professor
Judith Card
Chapter
19

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HAP201/Week Three/Chapter 19: Functions and Properties of Blood
LO 19.1: Describe the functions of blood
Blood: this is a liquid connective tissue that consists of cells surrounded by a liquid extracellular matrix. This matrix is called
blood plasma and suspends various cells and cell fragments
Interstitial fluid: the fluid that bathes body cells and is constantly renewed by the blood.
Blood is able to transport oxygen form the lungs and nutrients from the blood into the GI tract, which diffuse from the blood
into the interstitial fluid and then into body cells. Carbon dioxide and other wastes move in the reverse direction. These wastes
are transported by the blood to various organs, such as the lungs, kidneys, and the skin, for elimination from the body
Functions of Blood
It has three general functions
o Transportation: it transports oxygen 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 GI tract to body cells and hormones from endocrine glands to other body
cells. It also transports heat/waste products to various organs for elimination from the body
o Regulation: circulating blood helps maintain homeostasis of all body fluids. It helps regulate pH through the use of
buffers (chemicals that convert strong acids/bases into weak ones). It also helps adjust temperature through its heat-
absorbing and coolant properties of the water in blood plasma and its variable rate of through the skin, where excess heat
can be lost from the blood to the environment.
o Protection: after an injury, blood clots to protect against its excessive loss form the CVS after an injury. WBC protect
against disease by carrying on phagocytosis.
LO 19.2: Describe the components of whole blood
Whole blood has two components
o Blood plasma: a watery liquid extracellular matrix that contains dissolved substances
o Formed elements: cells and cell fragments
If a sample of blood is centrifuged (spun), the cells (which are denser) will sink to the bottom of the tube, while the plasma will
form a layer at the top (it is less dense)
Blood is 45% formed elements and 55% blood plasma.
Platelets are less dense than RBC but denser than blood plasma, thus forming a thin buffy coat layer between the RBC and
plasma in centrifuged blood
Blood Plasma
This is the liquid that remains when formed elements are removed from blood.
It is 91.5% water and 8.5% solutes, most of which are proteins. Some of these proteins are formed elsewhere in the body, but
those confined to blood are called plasma proteins
These plasma proteins are synthesized by hepatocytes, and include albumins, globulins, and fibrinogen.
Certain blood cells develop into cells that produce gamma globulins. These plasma proteins are called antibodies, since they are
produced during certain immune responses. An antibody specifically binds to the antigen that stimulated its production and thus
disables the invading antigen
Other solutes in plasma include electrolytes, nutrients, regulatory substances (enzymes and hormones), gases, and waste
products (e.g. urea, uric acid, creatinine, ammonia and bilirubin)
Formed Elements
The formed elements of blood include three principle components:
o Red blood cells: also called erythrocytes, these cells transport oxygen from the lungs to body cells and deliver carbon
dioxide from body cells to the lungs
o White blood cells: also called leukocytes, these cells protect the body from invading pathogens and other foreign
substances. There are several types of WBC (pg. 664) and each type contributes in its own way to the body’s defense
mechanisms
o Platelets: these are fragments of cells that do not have a nucleus. They release chemicals that promote blood clotting when
blood vessels are damaged. They are the functional equivalent of thrombocytes, nucleated cells found in lower vertebrates
that prevent blood loss by clotting blood.
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Hematocrit: the percentage of total blood volume occupied by RBCs. A hematocrit of 40 indicates that 40% of the blood
volume is composed of RBCs.
o In adult females, the normal range of hematocrit is 38-46% and in adult males, it is 40-54%.
o Testosterone contributes to higher hematocrits in males because the hormone stimulates synthesis of erythropoietin (EPO),
the hormone that in turn stimulates production of RBC
o In females, lower values during reproductive years may be due to excessive blood loss in menstruation
o A large drop in hematocrit indicates anemia, a lower-than-normal RBC count.
LO 19.3: Discuss the term hemopoiesis and where this process takes place
Most formed elements of blood last only a few hours, days or weeks and must be replaced continually.
Negative feedback regulates RBC count and platelets circulation, in order for their numbers to remain steady.
Hemopoiesis: the process the formed elements are developed by. It first occurs before birth, in the yolk sac of the embryo. Later
on, it occurs in the liver, spleen, thymus and lymph nodes of the fetus. In the last three months before birth, red bone marrow
becomes the primary site of this process; it will continue as the source of blood cells after birth and throughout life.
Red bone marrow: this is a highly vascularized connective tissue located in the spaces between trabeculae of spongy bone
tissue. About 1% of red bone cells are called pluripotent stem cells or hemocytoblasts and are derived from mesenchyme.
These cells have the capacity to develop into many different types of cells.
Stem cells in RBM produce themselves, proliferate and differentiate into cells that produce blood cells, macrophages, reticular
cells, mast cells, and adipocytes. Some also form osteoblasts, chondroblasts, and muscle cells. They may be used as a source of
bone, cartilage, and muscular tissue for tissue and organ replacement.
Blood from nutrient and metaphyseal arteries enters a bone and passes into the capillaries, called sinuses, that surround RBM
cells and fibres. After blood cells form, they enter the sinuses and other blood vessels and leave the bone through nutrient and
periosteal veins.
In order to form blood cells, pluripotent stem cells in RBM produce two further types of stem cells; which have the capacity to
develop into several types of cells, called myeloid stem cells and lymphoid stem cells.
o Myeloid stem cells: begin their development in RBM and give rise to RBC, platelets, monocytes, neutrophils, eosinophils,
basophils, and mast cells.
o Lymphoid stem cells: give rise to lymphocytes, begin their development in RDM but complete it in lymphatic tissues.
They give rise to natural killer (NK) cells
During hemopoiesis, some myeloid stem cells differentiate into progenitor cells, while others and lymphoid stem cells develop
directly into precursor cells. Progenitor cells are not capable of reproducing and are committed to giving rise to more specific
elements of blood. Some are known as colony-forming units (CFUs)
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. They have recognizable microscopic appearances
Several hormones called hemopoitetic growth factors regulate the differentiation and proliferation of particular progenitor
cells.
o Erythropoietin (EPO) increases the number of RBC precursors. It is primarily produced by cells in the kidneys. With
renal failure, EPO release slows and RBC production is inadequate. This leads to a decreased hematocrit, which leads to a
decreased ability to deliver oxygen to body tissues.
o Thrombopoietin (TPO) is produced by the liver that stimulates the formation of platelets from megakaryocytes.
o Cytokines are small glycoproteins that are produced by cells such as RBM cells, leukocytes, macrophages, fibroblasts, and
endothelial cells. They act as local hormones and stimulate proliferation of progenitor cells in RBM and regulate activities
of cells involved in non-specific defenses and immune responses.
LO 19.4: Explain red blood cell (erythrocyte) structure and function with reference to the composition of haemoglobin
Red blood cells contain hemoglobin, an oxygen-carrying protein/pigment that gives whole blood its red color.
RBC Anatomy
Mature RBC have a simple structure. Their plasma membrane is strong and flexible, allowing them to deform without rupturing
as they squeeze through narrow blood capillaries.
Certain glycolipids in the plasma membrane of RBCs are antigens that account for the various blood groups.
RBCs lack a nucleus and other organelles and can neither reproduce nor carry on extensive metabolic activities.
RBCs cytosol contain hemoglobin molecules which are synthesized before loss of the nucleus during RBC production.
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RBC Physiology
Since RBC have no nucleus, all of their internal space is available for oxygen transport.
They also lack mitochondria and generate ATP anaerobically, so they do not use up any of the oxygen they transport
Each RBC contains ~280 million hemoglobin molecules. This molecule consists of a protein called globin and a non-protein
pigment called a heme. Each oxygen molecule picked up from the lungs is bound to an iron ion. As blood glows through tissue
capillaries, the iron-oxygen reaction reverses. Hemoglobin releases oxygen, which diffuses first into the interstitial fluid and
then into cells.
Blood flowing through tissue capillaries picks up carbon dioxide, some of which combines with amino acids in the globin part
of hemoglobin. As blood flows through the lungs, the carbon dioxide is released from hemoglobin and then exhaled.
Hemoglobin also plays a role in the regulation of blood flow and blood pressure.
RBC Life Cycle
RBC only 120 days because of the wear and tear their plasma membranes undergo as they squeeze through blood capillaries
Without a nucleus and other organelles, RBC cannot synthesize new components to replace damaged ones.
Ruptured RBC are removed from circulation and destroyed by phagocytic macrophages in the spleen and liver, and the
breakdown products are recycled and used in numerous metabolic processes, including the formation of new RBCs.
The cycling occurs as follows:
o Macrophages in the spleen, liver, or RBM phagocytize ruptured and worn-out RBCs
o The globin and heme portions of hemoglobin are split apart
o Globin is broken down into amino acids, which can be reused to synthesize other proteins
o 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
o In muscle fibres, liver cells and macrophages of the spleen and liver, Fe3+ detaches from transferrin and attaches to an
iron-storage protein called ferritin
o The Fe3+ - transferrin complex is then carried to RBM, 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
o Erythropoiesis in RBM results in the production of RBC, which enter the circulation
o When iron is removed from heme, the non-iron portion of heme is converted to biliverdin, a green pigment, and the into
bilirubin, a yellow-orange pigment
o Bilirubin enters the blood and is transported to the liver
o Within the liver, bilirubin is released by liver cells into bile, which passes into the small intestines and then into the large
intestine
o In the large intestine, bacteria convert bilirubin into urobilinogen
o Some urobilinogen is eliminated in feces in the form of brown pigment called stercobilin, which gives feces its
characteristic color
LO 19.5: Describe erythropoiesis and the life cycle of erythrocytes, including the fate of hemoglobin components
Erythropoiesis is the production of RBCs that starts in the RBM with a precursor cell called a proerythoblast.
The proerythoblast divides several times, producing cells that begin to synthesize hemoglobin. A cell near the end of the
development sequence ejects its nucleus and becomes a reticulocyte. Loss of the nucleus causes the centre of the cell to ident,
producing the RBC’s distinctive shape. These cells retain some mitochondria, ribosomes, and endoplasmic reticulum.
Erythropoiesis and RBC destruction proceed roughly at the same pace.
o If the oxygen-carrying capacity of the blood falls because erythropoiesis is not keeping up with RBC destruction, a
negative feedback system steps up RBC production. The controlled condition is the amount of oxygen delivered to body
tissues.
Cellular oxygen deficiency, called hypoxia, may occur if too little oxygen enters the blood. Oxygen delivery may fall due to
high altitudes, anemia, or some disorders. Circulatory problems that reduce blood flow to tissues may also reduce oxygen
delivery.
o Whatever the cause, hypoxia stimulates the kidneys to step up the release of erythropoietin, which spends the development
of proerythoblasts into reticulocytes in the RBM.
As the number of circulating RBCs increases, more oxygen can be delivered to body tissues
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