Blood Composition
Blood Composition
Objectives
· Explain how the properties of blood qualify it as a connective tissue
· Describe the various functions of blood
· Distinguish among the three major categories of formed elements
· Describe the shape, structure, and contents of an erythrocyte
· Know what hematocrit test determines, and what are the normal lab values
· Describe the differences between agranulocytes and granulocytes
· Visually differentiate each of the leukocytes on a normal blood smear
· Visually identify platelets, describe their function, and explain what coagulation tests are used to determine
The Cardiovascular System: An Introduction
The term “cardiovascular system” is broadly used to describe a body system that consists of tubular organs, called vessels, a fluid tissue, known as blood, and a muscular pump (the heart) that functions in driving the blood through those vessels. It is often more accurate to describe all of the above components as the circulatory system, reserving the term “cardiovascular” for the heart and vessels only.
Blood as Connective Tissue
[Section 18.1: An Overview of Blood]
What are the properties that are common to all connective tissues? (see Section 4.3 in your textbook for review)
Blood is considered to be a “liquid connective tissue.” Describe the components of blood that fit the description of a connective tissue.
Functions of Blood
[Section 18.1.1: Functions of Blood]
List the various things that are transported by the blood.
List the many ways in which the blood serves a defensive, immune function for the body.
What homeostatic mechanisms are regulated and maintained by the blood?
Blood Composition
[Section 18.1.2: Composition of Blood]
[Figure 18.2: Composition of Blood]
· Define hematocrit
· 55% = Plasma
o Proteins (for blood pressure, clotting, and immune functions)
o Water (92% of plasma)
o Electrolytes
o Hormones
o Nutrients
o Blood gases
o Waste
· 45% = Formed Elements
o Red Blood Cells
o Platelets
o White Blood Cells
Erythrocytes
[Section 18.3.1: Shape and Structure of Erythrocytes]
Primary function: transport respiratory gases to and from tissues
Lack a nucleus
Most abundant of all blood cells
Biconcave to increase surface area to allow for rapid gas exchange, allows for the cells to squeeze through vessels
Contains millions of Hemoglobin molecules: allow for binding of O2 and CO2
Hematocrit
[Figure 18.2: Composition of Blood]
· Determines the volume of packed elements (mainly RBCs) in a blood sample (reported as a percentage)
· Provides information about the oxygen-carrying capacity of blood. Low percentages mean less RBC’s carrying O2.
· Averages: males: ____%; females: ____%
Platelets
Produced by the fragmentation of cells in the bone marrow called megakaryocytes
Don’t survive long
Involved in coagulation: the process of clot formation
During coagulation, molecules (fibrin) join to form long threads that form a net to trap platelets and plug the wound
Coagulation
Also known as clotting
Happens when blood sits for 3-4 minutes outside of the body
Process of “closing” a wound:
· Person cuts themselves
· Enzymes activate circulating proteins
· Proteins convert fibrinogen to fibrin
· Fibrin joins together to form long threads that form a net that “traps” platelets
· These trapped platelets form a clot
A coagulation test determines how fast this occurs in your blood
· A clinical test used to detect bleeding disorders (missing clotting factors, low platelet counts, etc.)
· An unusual coagulation test can result from genetic disorders, or other underlying problems, such as cancer, vitamin deficiency, etc.
Leukocytes
[Section 18.4.2: Classification of Leukocytes]
[Figure 18.11: Granular Leukocytes]
Only formed elements with a nucleus
lacks hemoglobin
travel between endothelial cells of capillaries and tissues
most are phagocytes
There are two types of WBC- granular and agranular
Granulocytes
All have granules in cytoplasm, these granules are secretory
· Neutrophils are the most common granulocytes (70% of total WBC count)
o 1st to arrive at wound/infection site, release cytotoxins
o phagocytize bacteria
o release chemokines (attract other WBCs), and once activated
o live only a day or two
· Eosinophils (3% of total WBC count)
o phagocytize bacteria and microbes that the immune system has coated with antibodies (Abs)
o decrease inflammatory response at site of wound
· Basophil (<1% of WBCs)
o release histamines (cause vasodilation) and heparin (prevents clotting)
o Important in allergies
Agranulocytes
· Monocytes (20-30% of total WBC count)
o Wanderers, patrol body tissue for microbes and worn-out tissue cells, 2nd to arrive at wound site, phagocytize dead cells/debris that has accumulated at site of wound/infection
· Lymphocytes (2-8% of WBCs)
o smallest leukocyte, abundant in bloodstream, occur in lymph nodes and glands
o specialized lymphocytes:
§ T-cells: attach to and destroy infected or cancerous cells by releasing cytotoxic molecules and secreting antiviral/pro-inflammatory molecules
§ B-cells: manufacture antibodies that attach to foreign pathogens/cells and help destroy them
§ Natural Killer cells: can detect sick, cancerous, and infected cells and release cytotoxic molecules to destroy them