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Blood
blood liquid connective tissue consist of plasma and formed elements(red blood
cells,white blood cells and platelets)
Plasma is the liquid medium for carrying various substances in the blood.. About
91% of plasma is water The remaining 9% of plasma consists of various salts (ions)
and organic molecules.
Salts are dissolved in plasma As mentioned previously, salts and plasma proteins
maintain the osmotic pressure of blood. Salts also function as buffers that help
maintain blood pH. Small organic molecules such as glucose and amino acids are
nutrient in the cells; urea is a nitrogenous waste product on its way to the kidneys for
excretion.
The most abundant organic molecules in blood are called the plasma proteins. The
liver produces the majority of the plasma proteins. The plasma proteins have many
functions that help maintain homeostasis.1- Like salts, they are able to take up and
release hydrogen ions. Therefore, they help keep blood pH around 7.4.
2- Plasma proteins are too large to pass through capillary walls. They remain in the
blood, establishing an osmotic gradient between blood and tissue fl uid. This osmotic
pressure is a force that prevents excessive loss of plasma from the capillaries into
tissue fl uid.
Three major types of plasma proteins are the albumins, globulins, and fi brinogen.
Albumins are the most abundant plasma proteins and contribute most to plasma’s
osmotic pressure. They also combine with and help transport other organic molecules.
The globulins are of three types called alpha, beta, and gamma globulins. Alpha and
beta globulins also combine with and help transport substances in the blood such as
hormones, cholesterol, and iron. Gamma globulins are also known as antibodies and
are produced by white blood cells called lymphocytes, not by the liver. Gamma
globulins are important in fi ghting disease- causing pathogens .Fibrinogen is an
inactive plasma protein. Once activated, fi brinogen forms a blood clot
Formed elements
Red Blood Cells
Red blood cells are an excellent example of structure suiting function. They have no
nucleus; their biconcave shape comes about because they lose their nucleus during
maturation
. The biconcave shape of RBCs gives them a greater surface area for the of the
internal space of RBCs is used for transport of oxygen, RBCs also lack most
organelles including mitochondria. RBCs anaerobically produce ATP, and they do not
consume any of the oxygen they transport
Red Blood Cells Carry Oxygen
Red blood cells are highly specialized for oxygen (O2) transport. RBCs contain
hemoglobin (Hb), a pigment that makes red blood cells and blood red. The globin
portion of hemoglobin is a protein that contains four highly folded polypeptide chains.
The heme part of hemoglobin is an iron-containing group in the center of each
polypeptide chain . Each hemoglobin molecule can transport four molecules of O2 ,
and each RBC contains about 280 million hemoglobin molecules.
. When oxygen binds to heme in the lungs, hemoglobin assumes a slightly different
shape and is called oxyhemoglobin.
In the tissues, heme gives up this oxygen, and hemoglobin resumes its former shape,
called deoxyhemoglobin The released oxygen diffuses out of the blood into tissue
fl uid and then into cells
Red Blood Cells Help Transport Carbon Dioxide
After blood picks up carbon dioxide (CO2) in the tissues,about 7% is dissolved in
plasma., hemoglobin directly transports about 25% of CO2, combining it with the
globin protein. Hemoglobin-carrying CO2 is termed carbaminohemoglo bin The
remaining CO2 (about 68%) is transported as the bicarbonate ion (HCO3 –) in the
plasma. Consider this equation CO2 + H2O H2CO3
H+ + HCO3
When Carbon dioxide moves into RBCs, combining with cellular water to form
carbonic acid. An enzyme found inside RBCs, called carbonic anhydrase, speeds the
reaction. Carbonic acid quickly separates, or dissociates, to form hydrogen ions (H+)
and bicarbonate ions (HCO3 –). The bicarbonate ions diffuse out of the RBCs to be
carried in the plasma. The H+ from this equation binds to globin, the protein portion
of hemoglobin. Thus, hemoglobin assists plasma proteins and salts in keeping the
blood pH constant.
. When blood reaches the lungs, the reaction is reversed Hydrogen ions and
bicarbonate ions reunite to re-form carbonic acid. The carbonic anhydrase enzyme
also speeds this reverse reaction. Carbon dioxide diffuses out of the blood and into the
airways of the lungs, to be exhaled from the body.
RBCs Production
The RBC stem cells in the bone marrow divide and produce new cells that
differentiate into mature RBCs. As red blood cells mature, they lose their nucleus and
acquire hemoglobin. Because they lack a nucleus, RBCs are unable to replenish
important proteins and repair cellular damage. Therefore, red blood cells only live
about 120 days. When they age, red blood cells are phagocytized by white blood cells
(macrophages) in the liver and spleen It is estimated that about 2 million RBCs are
destroyed per second, and therefore, an equal number must be produced to keep the
red blood cell count in balance. When red blood cells are broken down, hemoglobin is
released The globin portion of hemoglobin is broken down into its component amino
acids, which are recycled by the body.
The majority of the iron is recovered and returned to the bone marrow for reuse,
although some is lost and must e replaced in the diet. The rest of the heme portion of
the molecule undergoes chemical degradation and is excreted by the liver and
kidneys. If the liver fails to excrete heme, it accumulates in tissues, causing a
condition called jaundice.In jaundice, the skin and whites of the eyes turn yellow.
. The kidneys release a hormone called erythropoietin that stimulate the production
of RBCs in bone marrow in process called erythropoiesis
Disorders Involving Red Blood Cells
When there is an insufficient number of red blood cells or the cells do not have
enough hemoglobin, the individual suffers from anemia and has a tired, run-down
feeling.
Iron, vitamin B12, and folic acid are necessary for the production of red blood cells.
Iron-defi ciency anemia is the most common form. It results from inadequate
intake of dietary iron, which causes insufficient hemoglobin synthesis. A lack of
vitamin B12 causes pernicious anemia, in which stem-cell activity is reduced due to
inadequate DNA production. As a consequence, fewer red blood cells are produced.
Folic-acid-defi ciency anemia also leads to a reduced number of RBCs, particularly
during pregnancy.Pregnant women should increase their intake of folic acid, because
a defi ciency can lead to birth defects in the newborn.
Hemolysis is the rupturing of red blood cells. In hemolytic anemia, the rate of red
blood cell destruction increases. Sickle-cell disease is a hereditary condition in which
the individual has sickle-shaped red blood cells that tend to rupture as they pass
through the narrow capillaries.. The problem arises because the protein in two of the
four chains making up hemoglobin is abnormal. The life expectancy of sickleshaped
red blood cells is about 90 days instead of 120 days
White blood cells (leukocytes)WBCs
WBCs differ from red blood cells in that they are usually larger, have a nucleus, lack
hemoglobin, and are translucent unless stained. White blood cells are not as numerous
as red blood cells. There are only 5,000– 11,000 per mm3 of blood. White blood cells
are derived from stem cells in the red bone marrow, where most types mature. There
are several types of white blood cells and the production of each type is regulated by a
protein called a colony-stimulating factor (CSF). In a person with normally
functioning bone marrow, the numbers of white blood cells can double within hours,
if needed. White blood cells are able to squeeze through pores in the capillary wall;
therefore, they are also found in tissue fl uid and lymph White blood cells fight
infection; thus, they are an importantpart of the immune system.
WBCs divided to:
A- Granular Leukocytes
The granular leukocytes include neutrophils, eosinophils and basophils
1- Neutrophils account for 50–70% of all white blood cell Therefore, they are the
most abundant of the white blood cells. They have a multilobed nucleus, so they are
called polymorphonuclear leukocytes, or “polys.” The granules of neutrophils are not
easily stained with acidic red dye, nor with basic purple dye. (This accounts for their
name, neutrophil. Neutrophils can be recognized by their numerous light-pink
granules. Neutrophils are usually fi rst responders to bacterial infection, and their
intense phagocytic activity is essential to overcoming an invasion by a pathogen.
2-Eosinophils have a bilobed nucleus. Their large, abundant for their
name,eosinophil.) Not much is known specifi cally about the function of eosinophils,
but they increase in number in the event of a parasitic worm infection or an allergic
reaction
3-Basophils have a U-shaped or lobed nucleus. Their granules take up the basic stain
and become a dark-blue color. (This accounts for their name, basophil.) In the
connective tissues, basophils (and similar cells called mast cells) release
histamine associated with allergic reactions. Histamine dilates blood vessels but
constricts the air tubes that lead to the lungs, which is what happens during an asthma
attack when someone has diffi culty breathing.
B-Agranular Leukocytes
The agranular leukocytes include the lymphocytes and the monocytes. Lymphocytes
and monocytes do not have granules and have nonlobular nuclei. They are sometimes
called the mononuclear leukocytes