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BLOOD

CARDIOVASCULAR SYSTEM

     By the time a human embryo is a only few mm in size, it needs energy & produces wastes faster than diffusion can remove.  A system to perform transport is needed and thus by the end of the 3rd week the heart beats while other organ systems have barely begun.  Fluid necessary in body since the differentiated cells of the body can't get their own food or move away from their wastes.  These specialized cells are also less able to protect themselves from temperature changes, pH changes, & toxic chemicals.  The cardiovascular system must help control the composition of the fluid which bathes the cells. Blood therefore serves three main functions:

--it transports oxygen, nutrients, heat, wastes, hormones, & enzymes

--it regulates pH with buffers; the water in blood resists temperature change

--it protects the body from blood loss & microbes

 

BLOOD

     Blood represents about 8%of the human body weight: this is 5-6 liters in average male and 4-5 liters in the average female.  When blood is centrifuged (spun) the components of blood are separated according to weight.   Blood is 55% plasma, 45% formed elements (blood cells).  The blood cells can be divided into red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

HEMATOCRIT

A) PLASMA

     Plasma is 91.5% water, 7% protein, 1.5% other (wastes, urea, hormones, creatine, ammonia). Most of the blood proteins are made in the liver.  Their roles include transport, fighting disease, controlling the movement of water, and clotting.

 

 

B) ERYTHROCYTES (red blood cells)

     Erythropoiesis (the process of making red blood cells) begins as proerythroblasts synthesize the protein hemoglobin.  At later stages, the nucleus is ejected from the cell and the cell becomes biconcave.  The flexible biconcave cells can squeeze through the endothelial cells lining the marrow and enter the blood.  Hemoglobin contains a protein portion (globin) and a non-protein heme group that binds oxygen.

HEMOGLOBIN

     There are 5.2 million red blood cells per ml of blood in a male, 4.8 million per ml in a female.  The amazing total of 25 trillion cells in an adult humans means that red blood cells compose about 1/3 the cells in the human body! More than  99% of blood cells are red blood cells.  One third of the weight of a red blood cell is hemoglobin which is made before the loss of the ribosomes and nucleus.  Each cell has about 280 million molecules of hemoglobin.

      As the saying goes, blood is thicker than water.  The proteins in blood plasma make plasma thicker than water alone; the cells increase blood’s viscosity even more.  Normally, rbcs compose 40% volume of the blood; this measure is called the  hematocrit. (Once blood is centrifuged, the ratio of the volume of rbcs to the total blood volume is used to determine the hematocrit.)   Hematocrits in men are higher than in women on average (due to the effects of testosterone and menstruation

     Hemoglobin is the respiratory pigment in vertebrate red blood cells.  The following images are of blood smears of a bony fish, frog, turtle, and human.  The human slide shows a reticulocyte, the precursor to circulating red blood cells which has not yet ejected its nucleus.

FISH BLOOD FROG BLOOD
TURTLE BLOOD RETICULOCYTE
Sickle Cell Anemia
sickle cell sickle cell

 

2) LEUKOCYTES (white blood cells)

     Most leukocytes are located in peripheral tissues rather than in the blood, only about 2% are actually in the blood.  They travel through blood looking for disturbances in your body's normal functioning. If they detect the appropriate signal, demonstrate both chemotaxis (the ability to move towards the signal) and emigration or diapedesis (they can fit between small spaces between cells and pass through capillary walls due to their ability to move in an amoeboid fashion).  Microbe toxins, colony stimulating factors, & kinins (produced by damaged tissues) may attract leukocytes (especially neutrophils & macrophages).

     Some leukocytes (neutrophils, macrophages, monocytes) phagocytize (engulf) microbes and may kill with chemicals such as lysozyme, defensins, & strong oxidants.  Eosinophils undergo the exocytosis of these chemicals onto parasites that are too large for phagocytosis.  Basophils facilitate the inflammatory response.  Most leukocytes live only a few days and during an infection they may only survive a few hours.  Because they are so short-lived, 75% of blood cells made by the bone marrow (perhaps 4-6 million per second are leukocytes.

  Neutrophil

neutrophil neutrophil
neutrophil
EOSINOPHIL
eosinophil eosinophil
eosinophil eosinophil

BASOPHIL

BASOPHIL

basophil
LYMPHOCYTE
LYMPHOCYTE LYMPHOCYTE
LYMPHOCYTE
MONOCYTE
MONOCYTE MONOCYTE
LEUKEMIA
LEUKEMIA LEUKEMIA
LEUKEMIA
LEUKEMIA
LEUKEMIA
PLATELETS
PLATELET PLATELET
PLATELET