Section 13: The Circulatory System

The circulatory system carries oxygen, nutrients, hormones and enzymes to the cells of the body and carries carbon dioxide and other wastes away from the cells to the excretory organs (kidneys, lungs, and skin). It takes one minute for blood to make a complete circulation in the body. Humans have approximately 5-7 liters of blood in their system. The circulatory system also aids in the coagulation process, assists in defending the body against disease, and plays an important role in the regulation of body temperature. A thorough knowledge of this system is especially important to the phlebotomist, who must access it to collect blood specimens for analysis.

The heart and circulation

Watch this video. (He talks fast so feel free to pause it to read the notes posted on the video).

The heart tissue is made up of three layers:

Endocardium- The endothelial layer lining of the heart
Myocardium- The muscular middle layer, responsible for contracting the heart.
Epicardium- The fibrous outer layer. Coronary arteries (supply blood to the heart) are found in this layer.

The heart has four chambers. Upper chambers are called atriums and the lower chambers are called ventricles. The heart is divided into two sides, right and left. Each atrium contracts and pushes blood through a valve into the ventricle below it. Then the ventricles push blood through a valve out of the heart. There are two circulations occurring. Pulmonary circulation: The right side of the heart receives deoxygenated blood from the veins of the body and pumps it to the lungs to receive oxygen. Systemic Circulation: The left side of the heart receives oxygenated blood from the lungs and pumps it out of the heart to the rest of the body through arteries.

The step by step:

Deoxygenated blood enters the RIGHT ATRIUM through the SUPERIOR VENA CAVA.
The right atrium contracts and pushes the blood through the TRICUSPID VALVE into the relaxed RIGHT VENTRICLE.
The right ventricle contracts and pushes blood through the PULMONARY VALVE into the PULMONARY ARTERY which carries the blood to the lungs to receive oxygen (this occurs at the capillary level at the alveoli of the lungs).
Blood travels from the lungs to the heart through the PULMONARY VEIN and enters the LEFT ATRIUM.
The left atrium contracts and pumps the blood through the MITRAL VALVE into the relaxed LEFT VENTRICLE.
The left ventricle contracts and pushes the blood up through the AORTIC VALVE into the AORTA which branches out and carries the oxygenated blood to the body through the arteries.

NOTE: Both right and left atriums are pumping simultaneously, as well as right and left ventricles. Atriums, ventricles, atriums, ventricles... etc. Both ventricles contracting are called Systole.

Blood Pressure:

A normal blood pressure is 120/80. The 120 or the top number is the Systolic Blood Pressure or the peak pressure when the ventricle contracts. The 80 or the bottom number is the Diastolic Blood Pressure which is the pressure in the arteries when the ventricles are resting.

Heart Sounds:

Lub= Tricuspid and Mitral Valves closing

Dub= Pulmonary and Aortic valves closing

The Blood Vessels

Blood vessels in the human body:

Arteries- Main branches from the heart to arterioles
Arterioles- Smaller branches from the arteries to body tissue
Capillaries- Exchanging nutrients for waste
Venules- Smaller Branches from body tissue to veins
Veins- Main branches from venules to heart
- Veins contain one-way valves that direct the flow of blood traveling against gravity back to the heart to prevent backflow.

Blood Vessel Layers (not capillaries):

Tunica Adventitia- outer connective tissue
Tunica Media- middle, smooth, muscular layer
Tunica Intima- inner endothelial layer

Capillaries:

Composed of only one single endothelial cell layer
Connects the arterioles and venules
Exchanges oxygen, carbon dioxide, nutrients, and waste between blood and tissue cells
Capillary blood is a mixture of arterial and venous blood.

Components of whole Blood

Whole blood consists of 55% plasma (liquid) and 45% formed elements (cells). Plasma is a pale yellow fluid that carries nutrients, lipids, glucose, sodium, magnesium, calcium, potassium, oxygen, carbon dioxide, nitrogen, antibodies, vitamins, and hormones through the blood vessels to the body. The other formed elements or cells of whole blood are thrombocytes (platelets), erythrocytes (red blood cells), and leukocytes (white blood cells).

Thrombocytes

Also known as platelets
Small, irregularly shaped packets of cytoplasm
Formed in the bone marrow
Aids in hemostasis (a process to prevent and stop bleeding)
Help repair blood vessels after injury
Essential for blood coagulation

Erythrocytes

Also called Red Blood Cells (RBC)
Contains hemoglobin (oxygen carrying protein)
Contain antigens that determine blood type
Lifespan of a RBC is 120 days
Produced continuously in the marrow of certain bones
Enters the bloodstream as a reticulocyte and matures into a erythrocyte in one to two days
4.2-6.2 million RBCs per microliter of blood
Anemia is the condition where a person lacks enough RBCs to carry adequate amounts of oxygen to the body's tissue.
After a whole blood donation it takes 6-8 weeks for the body to regenerate the lost RBCs.

Leukocytes

Also known as White Blood Cells (WBC)
Provide protection to the body against infection, they are a part of the body's immune system
There are 5 types of white blood cells (Neutrophils, Eosinophils, Basophils, Lymphocytes, Monocytes)
They are made in the bone marrow
An increase in white blood cells (Leukocytosis) is usually due to an infection or leukemia
Leukopenia (or a decrease in leukocytes) is seen with viral infections or during chemotherapy
A differential count (called a DIFF) will count the percentages of each type in the blood
Slight elevation of leukocytes means the body is fighting an infection
To determine what kind of infection the body is fighting (bacterial, viral, parasitic, intracellular) doctors can look at levels of specific white blood cells.

5 Types of White Blood Cells:

Neutrophils- Help protect your body from infections by killing bacteria, fungi and foreign debris by engulfing and digesting the invading germ (phagocytosis).
Eosinophils-Identify and destroy parasites, cancer cells and assist basophils with your allergic response.
Basophils-Produces an allergic response like coughing, sneezing or a runny nose by carrying and releasing histamine.
Lymphocytes-Consist of T cells, natural killer cells and B cells to protect against viral infections and produce proteins to help you fight infection (antibodies).
Monocytes-Defend against infection by cleaning up damaged cells. They are the largest white blood cell.

Serum VS PLASMA

When you spin a blood sample in a centrifuge you will notice that the different components of the blood will separate depending on density. Each tube is different and used for different tests, we will go over all of these in the last Module. But it is important to note here that some tubes contain anticoagulants. This is a substance that mixes with the blood and prevents it from clotting (which it naturally does). If you take blood in a tube with no additive (so it would be just whole blood), let it clot and then spin it down, you will see a yellowish liquid on top. This is SERUM. Serum does not contain clotting factors, or fibrinogen (because you let it clot). The fibrinogen is in the blood clot with the red blood cells.

If you take a tube of blood that does have anticoagulant added to it, the blood will not clot. When you spin it down you will see a yellowish liquid on top. This is PLASMA. It does contain the clotting factors or fibrinogen because the blood did not clot. This means that the red blood cells below are just that- RBCs.

Blood pH

A pH scale determines the acidity of a solution. It ranges from 0 (acid) to 14 (basic or alkaline). Seven is the middle and the neutral between the extremes. Greater than 7 is basic and less than 7 is acidic. Arterial blood usually ranges from 7.35-7.45pH. The lungs and kidneys are responsible for regulating the blood pH. Acidosis is the condition in which blood is acidic and alkalosis is the condition in which blood is basic. Changes in pH are due to:

Metabolic acidosis: This occurs due to reduced bicarbonate or increased acid levels.

Respiratory acidosis: This occurs when the body removes less carbon dioxide than usual.

Metabolic alkalosis: This occurs due to increased bicarbonate or reduced acid levels.

Respiratory alkalosis: This occurs when the body removes more carbon dioxide than usual.

BLOOD Typing

Watch this video:

Not all blood is the same. We each inherit a "blood type" from our parents (as explained in the video).

Blood type is determined by the presence or lack of antigens carried by our RBCs. Antigens are substances that produce an immune response with antibodies. (Remember, antibodies are part of our immune system that fight infections). Antibodies are plasma proteins that combine with antigens and inhibit or destroy it. Think of it like this. Antibodies flow through the body like soldiers and identifies all the cells they come in contact with. If the cell IDs as a foreign cell, they destroy it. If it IDs as a cell belonging to your body, they move on. If you ever have to have a blood transfusion, the blood type has to match. If it doesn't, those antibodies will ID the new blood as foreign and destroy it. This is fatal for the patient.

There are four groups of blood types:

A: RBC only has "A" antigen

B: RBC only has "B" antigen

AB: RBC contains both "A" and "B" antigens

O: RBC has no antigens

The other part of blood typing refers to either the presence or lack of the RH factor. RH+ (positive) means that the RBC contains the RH antigen. RH- (negative) means the RBC does not have it. When you combine the grouping with the RH factor, you have the option of the following blood types:

A+ B+ AB+ O+

A- B- AB- O-

Universal DONOR: O- (Can give to any blood type)

Universal RECEIVER: AB+ (Can receive all blood types)

RETURN TO THE GOOGLE CLASSROOM AND DO THE PRACTICE WORKSHEET.

For more information and references on the reading material found in Section 13: The Circulatory System, click the link below. Test questions will be based on the reading in the sections and not from more information found in external references and website links.

Reference Page

Once you have completed reading and studying Module 4, and have completed Section 12-13 Practice Worksheets

RETURN TO THE GOOGLE CLASSROOM

and complete the MODULE 4 QUIZ.

(You may wait to take this quiz until after we go over Module 4 in class).

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