chapter 19: the blood Flashcards
All cells need
nutrients and get rid of waste products
Body must maintain
homeostasis
Body fluids help in
connecting cells
– Intracellular fluid: cytoplasm
– Extracellular fluid: interstitial fluid, blood plasma, lymph, CSF
Two major networks help in connecting cells:
– Cardiovascular system: Heart, blood vessels, blood
– Lymphatic system: Lymphatic tissues/organs, lymphatic vessels, lymph
function of blood
- Transportation : gases, nutrients, hormones, vitamins, wastes
- Regulation : temperature, pH, water, minerals, nutrients
- Protection : against diseases, loss of body fluids
characteristics of blood
thicker than water ( it has a greater viscosity)
constitutes 8% of body weight
in a human adult, there are 4-6 liters of blood
pH = 7.5- 7.45
blood is composed of a fluid portion called PLASMA and solid formed elements, called FORMED ELEMENTS. These formed elements are RED BLOOD CELLS, WHITE BLOOD CELLS AND PLATELETS
PLASMA
- fluid portion of blood which consists 91% water and the rest, are solutes- electrolytes and proteins (albumin accounts for 58% of plasma proteins and it is important in the movement of water between the tissues and the blood), blood clotting proteins, wastes, nutrients and respiratory gases). Since plasma is the fluid portion of blood, it’s increase or decrease will be central in the volume of blood. Homeostatic mechanisms attempt to maintain blood at volume within a narrow limit -water intake through the digestive system closely matches water loss through the kidneys, lungs, digestive tract and skin.
- Plasma composes 55% of whole blood
- Plasma is a straw colored, clear liquid
FORMED ELEMENTS
cells and cell fragments. composes approximately 45% of whole blood
Red blood cells (RBCs) = erythrocytes
White blood cells (WBCs) = leukocytes
Platelets = thrombocytes
Hematocrit
measurement of % of RBCs in blood
females 39-45%
males 41-47%
Hemopoiesis
Blood cells are formed by a process called HEMOPOIESIS. In adults, hemopoiesis mostly
occurs in red bone marrow in the proximal humerus, femurs, the flat bones of the skull, sternum and ribs and the vertebrae and the pelvis (os coxae). Within the red bone marrow there are undifferentiated cells (stem cells) called HEMOCYTOBLASTS, which will give rise to RBCs, WBCs and Platelets.
It’s interesting to note that in children, hemopoiesis occurs in MOST bones. As a person gets
older, yellow bone marrow replaces red bone marrow.
Red blood cells ( RBCs)
- Compose more than 95% of formed elements.
- 4 days is required for the formation of a single RBC.
3.–RBCs–are biconcave discs that will not have nuclei when they are mature and circulating.
This absence of a nucleus: gives more room for them to hold HEMOGLOBIN = an oxygen carrying pigment.
Hemoglobin
Hemoglobin is made up of the protein GLOBIN bound to the red HEME pigment. The globin consists of 4 polypeptide chains each bound to a heme group. Each heme group contains an atom of iron in the center which bonds to oxygen. Each hemoglobin molecule can carry 4 oxygens. In each RBC there are 280 million hemoglobin molecules and therefore 1 billion molecules of oxygen
Remember that Vit B12 is necessary for red blood cell production and that this B12 comes from
the dietj absorbed into the circulation from the small intestine in the presence of Intrinsic Factor
(from stomach)
Structure and Function of RBCs
There is a close relationship between structure and function of RBCs.
a. The biconcave shape will result in increase surface area for gas diffusion AND gives the
cell more flexibility to fit through the small vessels.
b. Lack of a nucleus will allow for hemoglobin to fit in - therefore, more O2 can be carried.
Since there is no nucleus, no repair can occur, and about 120 days in males and 110 in
females, the RBC becomes fragile and either breaks or is phagocytized by the liver, spleen and
red bone marrow.
Production of RBCs
The process of RBC production is ERYTHROPOIESIS (erythropoiesis is a type of hemopoiesis).
Erythropoiesis occurs in steps within the red bone marrow.
The production of RBCs begins as all formed elements do, as hemocytoblasts. Some will divide
and differentiate into preerythroblasts which have nuclei, so hemoglobin can be synthesized.
Eventually, this developing cell ejects its nucleus, becoming a reticulocyte. The cell will now
have the biconcave shape due to the loss of the nucleus, allowing for more room for the
hemoglobin and therefore oxygen. These reticulocytes pass into the blood from the red bone
marrow. Under normal conditions, they develop into mature RBCs within 1-2 days after their
release into the blood.
Normally, 2.5 million RBC’s are produced/second. To maintain homeostasis, 2.5 million must be destroyed per second. The total amount of RBC’s circulating in 25 trillion in an adult.
Reticulocyte Count: The rate of erythropoiesis is measured by a reticulocyte count, hi health, older RBCs are replaced by new reticulocytes. It then will take 1-2 days for these reticulocytes to mature into fully functioning RBCs. Reticulocytes account for 0.5-1.5% of all RBCs in the blood sample
Erythropoiesis
is a type of hemopoiesis
Reticulocyte Count
The rate of erythropoiesis is measured by a reticulocyte count, In health, older RBCs are replaced by new reticulocytes. It then will take 1-2 days for these reticulocytes to mature into fully functioning RBCs. Reticulocytes account for 0.5-1.5% of all RBCs in the blood sample.
Homeostasis and RBCs - erythropoietin.
The number of RBCs that are circulating must be kept constant. The body maintains this level by
ERYTHROPOIETIN, a hormone that controls erythropoiesis.
erythropoietin
Hormone that is released by the kidneys that will stimulate the red bone marrow to increase the production of RBC. The direct stimulus is HYPOXIA (lack of adequate O2 to the tissues.) This hypoxic state can be caused by different situations like a decrease in RBCs (hemorrhage) or a respiratory illness (pneumonia or emphysema).
Renal failure patients may lack erythropoeitin and therefore suffer a low hct, often one half the
normal level. RECOMBINANT ERYTHROPOIETIN can be given.
RBC LIFE SPAN
RBCs can only live for 110 - 120 days due to the lack of the nucleus and therefore their inability to produce new proteins. When they are removed from circulation and destroyed, the breakdown products are recycled.
Macrophages (type of WBC that is a phagocyte) located in the SPLEEN, LIVER and RED BONE MARROW take up the ruptured RBCs. The lysosomes within these macrophages digest the hemoglobin , reducing it to globin, iron and bilirubin
Hemoglobin from ruptured RBC’s is broken down into:
GLOBIN: This is a protein which will eventually be broken into AMINO ACIDS and used by cells in protein synthesis.
IRON: This is released, taken to red bone marrow and recycled into hemoglobin as new RBC’s are formed.
BILIRUBIN: This is the breakdown product of heme caused by degradation of RBC’s in the liver, where it becomes part of the bile and thus gives bile it’s yellow color. Bilirubin is released into the plasma, where it binds to ALBUMIN and transported to liver. It eventually become part of BILE, a product of the liver.
This bile will be stored in the GALLBLADDER, eventually released into the small intestine become part of the chime and give the feces their characteristic color. Some of the bile will be absorbed from the intestine into the blood, modified by the kidney and excreted into urine, giving the urine its characteristic color
JAUDICE
is the yellow color that is seen in the skin and sclerae of the eyes. It iscaused by a buildup of bilirubin in the circulation and within the interstitial spaces.