Cardiovascular System: an Introduction

Chapter 19

Cardiovascular System: An Introduction

▪Cardiovascular system is composed of blood, the heart, and blood vessels.

▪The first body system to become fully functional in a developing embryo.

The Nature of Blood

▪Functions of Blood

▪Composition of Blood

▫Blood is a fluid connective tissue with a matrix called plasma

▫Formed elements are the blood cells and fragments that are suspended in the plasma. There are three types of formed elements; red blood cells, white blood cells, and platelets.

▫Plasma and formed elements constitute whole blood. Whole blood from any source in the body has the same physical characteristics:

-Blood temperature is roughly 38 degrees C.

-Blood is five times as viscous as water.

-Blood has a pH averaging 7.4 (7.35 to 7.45)

▫Adult males have about 5-6 L of blood, adult females have 4-5 L.

▫Blood is usually around 7% of body weight.

Plasma

▪Plasma makes up about 46-63 percent of the volume of whole blood, 92% of which is water

▪The primary differences between plasma and interstitial fluid involve

▪Plasma Proteins- 99% of blood proteins are made up of 3 classes:

▫Albumins- about 60% of the plasma proteins

▫Globulins- about 35% of the plasma proteins

▫Fibrinogen- about 4% of plasma proteins

▫The remaining 1% of plasma proteins include some hormones, concentrations rise and fall from day to day, or even from hour to hour.

▫The liver synthesis and releases more than 90% of the plasma proteins.

▫Antibodies are produced by plasma cells, plasma cells are derived from lymphocytes.

Red Blood Cells

▪RBC account for 99.9% of the formed elements.

▪RBC contain the pigment hemoglobin, which binds and transports oxygen and carbon dioxide.

▪Abundance of RBC’s

▫A single drop of whole blood contains approximately 260 million RBC’s

▫Hematocrit-

▪Structure of RBC’s

▫RBC have a biconcave disc cell shape with a thin central region, and a thicker outer margin.

▫This shape has three important effects on RBC function:

▫RBC lack nuclei and most of their organelles, cannot divide, and live for only about 120 days.

▪Hemoglobin (Hb)

▫Hb account for over 95% of intracellular proteins in RBC’s.

▫Hb is responsible for the cell’s ability to transport O2 and CO2

▫Hemoglobin structure- each Hb has a complex quaternary shape.

-Contains two alpha () and two beta () chains of polypeptides.

-Each chain contains a single molecule of heme, a pigment complex

-Each heme unit holds an iron ion so that it can bind to an oxygen

-Once bound to an oxygen, it forms oxyhymoglobin (HbO2).

-This bond is fairly weak, and when concentrations of oxygen change, oxygen leaves the heme unit, and carbon dioxide is picked up. Once bound to carbon dioxide, it forms carbaminohemoglobin

-Fetal hemoglobin binds to oxygen more readily, able to “steal” oxygen from the mother’s blood stream.

▫Hemoglobin Function

-Each RBC contains about 280 mil Hb molecules.

-The amount of oxygen bound to Hb depends on the oxygen content of the plasma.

▪RBC Formation and Turnover

▫A single round-trip from the heart, through the peripheral tissues, and back to the heart usually takes less than a minute, putting much mechanical stress on RBC’s

▫When a RBC is finished with it’s 120 day life span, it either ruptures or it gets engulfed by a phagocyte.

▫New RBC’s enter the blood stream at a comparable rate of exit

▫About 3 million new RBC’s enter the bloodstream each second!

▫Hemoglobin conservation and recycling

-Phagocytic cells of the liver, spleen, and bone marrow monitor the condition of the circulating RBC’s.

-Hb remains intact only under the conditions inside the RBC’s, when outside of the cell, the Hb breaks down and the alpha and beta chains are filtered by the kidneys and eliminated in the urine.

-Biliverdin-

-Bilirubin-

▫Iron

-Large quantities of free iron are toxic to the body, so it is bound to transport or storage proteins.

-Transferrin-

-Ferritin and hemosiderin-

▪RBC Production

▫Erythropoiesis- red blood cell formation, only occurs in red marrow in adults.

▫RBC’s begin as a hemocytoblast in bone marrow, this type of stem cell is the precursor to all formed elements.

▫After a few divisions of the hemocytoblasts, RBC proerythroblasts are formed.

▫Proerythroblasts are the first stage of RBC production, cell then moves through various erythroblast stages, then the cell spends some time as a reticulocyte, then finally a mature RBC.

▫Erythropoiesis is regulated by many factors:

-Presence and abundance of amino acids, iron, and vitamins.

-Many hormones (EPO, thyroxine, androgens, and GH)

▪Blood Types- figured by 3 surface antigens that are genetically determined.

▫Type A blood has A antigens

▫Type B blood has B antigens

▫Type AB blood has both A and B antigens

▫Type O blood has neither A or B antigens

▫Presence or absence of the Rh (or D) factor gives the blood types a (+) or (–)

▫Blood plasma has antibodies that attack the antigens on foreign RBC’s

-Type A blood has anti-B antibodies

-Type B blood has anti-A antibodies

-TypeAB blood has no anti-A or anti-B antibodies

-Type O blood has both anti-A and anti-B antibodies

-Rh – individual does not necessarily have anti-Rh antibodies.

▫Cross Reactions- when an antibody meets its specific surface antigen, the RBC agglutinate and may hemolyze.

▫Type O blood is usually referred to as a universal donor, due to the fact that it lacks both A and B surface antigens.

Blood Type / Antigens / Antibody / Donate To: / Receive From:
A
B
AB
O

**Look at donors antigens and recipients antibodies**

White Blood Cells

▪Unlike RBC’s, WBC’s have a nucleus and other organelles, but they lack Hb.

▪WBC’s help defend the body against invasion by pathogens, and they remove toxins, wastes, and abnormal or damaged cells.

▪WBC’s spend a short portion of their life span circulating, they can migrate through the loose and dense C.T. of the body.

▪Circulating WBC’s have four characteristics:

▪There are 5 types of WBC’s, divided into two classes; granular and agranular

▫Granular- appearance of stained granules under the microscope

-Neutrophils- 50-70% of circulating WBC’s

-Eosinophils- 2-4% of circulating WBC’s

-Basophils- less than 1% of circulating WBC’s

▫Agranular- few, if any, stained granules under the microscope.

-Monocytes- 2-8% of circulating WBC’s

-Lymphocytes- 20-30% of circulating WBC’s

▪The Differential Count and Changes in WBC Profiles

▫A differential count is conducted by examining a stained blood smear. Values are then reported for the number of each type of cell in a sample of 100 WBC’s.

-Leukopenia-

-Leukocytosis-

-Leukemia-

▪WBC Production

▫Begins with hemocytoblasts dividing into myeloid stem cells and lymphoid stem cells.

▫Myeloid stem cells give rise to progenitor cells, which give rise to all the formed elements except lymphocytes.

▫All WBC’s except monocytes complete their development in the bone marrow.

▫Regulation of WBC Production- several hormones are involved in the regulation of WBC’s (factors regulating lymphocytes is yet fully understood)

-Colony-Stimulating Factors (CSFs)

-M-CSF-

-G-CSF-

-GM-CSF-

-Multi-CSF

Platelets

▪Platelets are a major participant in a vascular clotting system that also includes plasma proteins and the cells and tissues of the blood vessels.

▪Platelets are continuously replaced, they circulate for 9-12 days before being removed by phagocytes.

▪Three main functions of platelets

▪Platelet Production- occurs in the bone marrow.

▫Megakaryocytes are enormous cells that “sluff” off packets of enzymes and proteins which enter the bloodstream as platelets.

▫A mature megakaryocyte produces about 4000 platelets before it is engulfed by a phagocyte.

▫The rate of megakaryocyte activity is stimulated by:

1. thrombopoietin

2. interleukin-6

3. multi-CSF

Hemostasis

▪Hemostasis is a process of the cessation of bleeding. Prevents the loss of blood through damaged vessels.

▪Hemostasis consists of three phases; vascular, platelet, and coagulation phase.

▫Vascular Phase

-Endothelial cells contract exposing the underlying basal lamina to the bloodstream

-Endothelial cells begin releasing chemical factors and local hormones

-Endothelial cell membranes become “sticky”

▫Platelet Phase

-Platelet adhesion- platelets attach to “sticky” epithelial cells and to each other. Forms the platelet plug.

-Platelets begin releasing ADP, thromboxane A2, serotonin, clotting factors, PDGF (platelet-derived growth factor), and calcium ions

-Platelet aggregation is controlled so as to not clog vessel.

▫Coagulation Phase

-Starts about 30 seconds or more after the vessel has been damaged.

-There is a complex pathway that controls the blood clotting of a damaged vessel, including many clotting factors.

-Use fig. 19-11 (3) to work through the extrinsic, intrinsic, and common pathways of the coagulation phase.