The Circulatory System Part II- BLOOD AND VESSELS

THE CIRCULATORY SYSTEM PART II- BLOOD AND VESSELS

The Link to the Lymphatic System

The hearts pumping action keeps pressure on vessels and blood in the circulatory system.  That pressure leads to some water and dissolved proteins being forced out of the tiny capillary vessels, where it becomes part of the interstitial fluid- the fluid that surrounds each cell.  A network of vessels called the Lymphatic system pick up excess fluid and solutes and returns it to the circulatory system. Lymph nodes are small bean shaped structures in the lymphatic system that have lymphocytes ( white blood cells) in them. They help to filter the fluid and to fight infections. You can see your tonsils are part of that system....unless yours were removed!

                                                                                                                                                                              1. diagram from https://www.healthdirect.gov.au/lymph-nodes

CHARACTERISTICS OF BLOOD

Blood is a connective tissue, formed in the bone marrow.  The majority the blood cells are made in the pelvic bones, the breast bone, and vertebral bones. It has several jobs.  It carries the chemical messengers called hormones and carries away waste. It stabilizes your internal pH, and is a highway for blood cells that fight infections to get to the site of the infection.  It helps to stabilize body temperature by carrying heat to the skin, where it can be dissipated. 

A. Blood Volume and Composition

Blood volume depends on a persons size and on the amount of water and solutes a person has in their system.  Average blood volume for an adult is 4-5 quarts, and it is made up of four components:

B. Plasma- The liquid portion of your blood. Mostly made up of water with plasma proteins in it. Important nutrients, gasses, and wastes dissolve in plasma including:  ions, glucose, lipids, amino acids, vitamins, and hormones. 

2. Photo: https://www.sciencefacts.net/types-of-blood-cells.html

C. Red Blood Cells (RBC's)- These are also called Erythrocytes.  They are the principal means of delivering oxygen to the body. They are shaped like biconcave discs. When oxygen dissolves into the blood in the lungs, it binds to to the protein Hemoglobin- an iron containing pigment that gives red blood cells their color.  RBC's are made by stem cells in the bone marrow. Mature red blood cells have no nucleus.  They function for about 120 days. Phagocytes (a type of cell within the body that disposes of old cells and bacteria) engulf and dispose of old cells.  New cells continually replace the old.  CELL COUNT- the number of cells of a given type in a microliter of blood.  Males average 5.4 million cells and females average 4.8 million cells. 

D. White Blood Cells- The job of these cells is house keeping and defense. They engulf foreign bodies, bacteria and viruses and squeeze out of your capillaries into the tissues.  Puss is dead white blood cells that were fighting an infection or surrounding a foreign object. They live only one to three days. 

There are 5 types of white blood cells:

Neutrophils- search and destroy

eosinophils- promote inflammation

basophils- respond to allergens

monocytes- search and destroy

lymphocytes- B lymphocytes make antibodies.  T lymphocytes kill tumor cells and help control the immune system. 

E. Platelets- these come from giant cells called megakaryocytes- which shed fragments of cytoplasm enclosed in a bit of membrane. Those fragments are platelets.  They last 5 to 9 days and hundreds of thousands are always in circulation in the blood.  They release substances that initiate blood clotting. 

THE CIRCULATION

3. photo: https://www.worldinvisible.com/apologet/humbody/bloodcir.htm

OUR VASCULATURE ( our arteries and veins)

Our arteries leave our heart, those arteries lead to arterioles which are smaller than arteries.  Those arterioles lead to capillaries which lead to venules which are larger, and then to veins which are larger again.  Capillaries can be so small that blood cells must travel single file through them. 

BLOOD PRESSURE

Blood Pressure- is the fluid pressure generated by heart contractions.  It does not stay the same throughout the systemic or pulmonary circuit.  Its high on the aorta and the big arteries but drops along the circuit heading away from the heart.  Why and how does it drop?  As blood flows through different kinds of blood vessels, energy in the form of pressure is lost as it overcomes resistance.  The lowest pressure is in the capillaries and the highest pressure is in arteries.  Arteries smooth out the pulsations in the blood pressure from the heart beating. Arteries have elastic walls that bulge with the pressure surge from the heart beat, then recoil and force the blood onward. There is very little resistance to blood flow in an artery.  

Arterioles are branches off of arteries, and they have the greatest resistance to blood flow. A wall of smooth muscle in the arteriole can narrow when the muscle contracts and expand when it relaxes. The nervous and endocrine system control when the muscle contracts or relaxes.  More blood is directed toward areas with great metabolic activity. 

Capillary beds are where diffusion of oxygen and CO2 and nutrients are exchanged with the interstitial fluid.   Capillaries have the thinnest walls, a single layer of epithelial cells. There is high resistance to flow here, but there are so many capillaries, that they can actually hold more blood than the arterioles, so they have less resistance to the flow of blood than arterioles.  Capillaries merge into little veins called venules, which merge into larger diameter veins. Veins are transport tubes leading back to the heart.  They have valves that prevent back flow and contain 50 to 60% of the blood volume. A vein has thin walls and can bulge a lot under pressure. They have smooth muscle walls that help contract so blood flows faster, and skeletal muscle presses against the veins, helping move the blood. 

Blood pressure is written as a fraction systolic over diastolic.  A mnemonic that can help you remember is "Sky over Dirt."  

Systolic/Diastolic        or Sky/Dirt

The systolic number comes from the pressure when the heart is contracting.  The diastolic comes from when the heart is relaxed. A good blood pressure is about 120/70.  If there is too much pressure a person may get an Aneurysm- a abnormal ballooning of a vessel wall, that can rupture, causing internal bleeding which can lead to death.   They often don't have symptoms, or hard to diagnose symptoms.  Sometimes they can be repaired surgically.  High Blood pressure and arteries that have become less elastic are risk factors for an aneurysm.

HEMOSTASIS

Small vessels are near the surface of our bodies and at risk for cuts and damage. Hemostasis- a process that repairs damaged vessels. 

The process of Hemostasis:

1. Spasm- the smooth muscle wall contracts- temporarily stopping or reducing the blood flow

2. Plug- Platelets clump together as a temporary plug in the vessel wall.  The platelets release substances to attract more platelets and prolong the spasm.

3. Blood Clot- Blood coagulates and turns to a gel.  The clot then retracts into a compact mass of fibrin and seals the damage completely.

BLOOD TYPING

Your body protects itself by putting a marker on every cell in your body that indicates it is YOUR cell.  These are called SELF-MARKERS and your white blood cell and antibodies do not attack the cells as if they were a foreign body.  If you receive a blood transfusion that has the wrong self marker on it you could have a transfusion reaction, in which your body attacks the cells, you feel very sick, and your kidneys could be damaged. The antibodies form clumps around the "foreign" cells in a process called agglutination, and they can clog small vessels. It is important in blood transfusions that you are given the correct blood type.  ABO BLOOD TYPING- analyzes which self-marker you carry on your blood cells. You can have one of four types of Self Markers

Rh Typing

This is the "+" or "-" in your blood type.  Its called Rh because it was identified first in Rhesus monkeys. If you have the Rh marker your cells are positive "+".  If you don't have the marker your cells are Rh negative "-".   If an Rh negative woman becomes pregnant by an Rh positive man, there is a chance the baby will be Rh +. During pregnancy there can be a little mixing of Mom and Babies blood. If that happens, Mom will produce antibodies against the Rh+ marker.  They can cause babies blood cells to swell and rupture, and the baby to die.  The risk of this increases with every pregnancy.  Women can be treated for this after their first pregnancy, and lower their chances of losing children. 

CARIODVASCULAR DISORDERS

Cardiovascular disorders are the leading cause of death in the United States. They kill more than a million people each year. The most common disorders are :

1. Hypertension- sustained high blood pressure

2. Atherosclerosis- thickening of the arterial walls and narrowing of the arteriole lumen. 

When these damage the arteries of the heart, a person can have a heart attack or a stroke. The symptoms of a heart attack are crushing pain, pain radiating into the left arm, shoulder or neck, sweating, nausea, dizziness, or loss of consciousness.  The symptoms of a stroke include numbness or weakness of the face, arm or leg, sudden confusion, inability to speak or understand speech, trouble seeing in one or both eyes, sudden trouble walking, dizziness,  or lack of coordination.  There is a mnemonic to remember the stroke symptoms called FAST:

F- Face

A-Arm

S-Speech

T-Time

Treatment for strokes is very good now.  If a person is in the care of EMT's or a Doctor within 15 minutes they can be given medicine that will reduce the impact of the stroke.  It is important to act quickly if you think someone is having a stroke.