anatomy and sss

7/30/2019 Anatomy and sss

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I. ANATOMY AND PHYSIOLOGY

The Circulatory System

The Circulatory System is the main transportation and cooling system for the

body. The Red Blood Cells act like billions of little UPS trucks carrying all sorts of


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packages that are needed by all the cells in the body. Instead of UPS, I'll call them

RBC's. RBC's carry oxygen and nutrients to the cells. Every cell in the body requires

oxygen to remain alive. Besides RBC's, there are also White Blood Cells moving in the

circulatory system traffic. White Blood Cells are the paramedics, police and street

cleaners of the circulatory system. Anytime we have a cold, a cut, or an infection the

WBC's go to work.

The highway system of the Circulatory System consists off a lot of one way

streets. The superhighways of the circulatory system are the veins and arteries. Veins

are used to carry blood *to* the heart. Arteries carry blood *away* from the heart. Most

of the time, blood in the veins is blood where most of the oxygen and nutrients have

already been delivered to the cells. This blood is called deoxygenated and is very *dark*red. Most of the time blood in the arteries is loaded with oxygen and nutrients and the

color is very *bright* red. There is one artery that carries deoxygenated blood and there

are some veins that carry oxygenated blood. To get to the bottom of this little mystery

we need to talk about the Heart and Lungs.

The Heart

This is a subject that is near and dear to my heart. The heart is a two sided, four

chambered pump. It is made up mostly of muscle. Heart muscle is very special. Unlike

all the other muscles in the body, the heart muscle cannot afford to get tired. Imagine

what would happen if every 15 minutes or so the pump got tired and decided to take a

little nap! Not a pretty sight. So, heart muscle is always expanding and contracting,

usually at between 60 and 100 beats per minute.

The right side of the heart is the low pressure side. Its main job is to push the

RBC's, cargo bays mostly empty now, up to the lungs (loading docks and filling stations)

so that they can get recharged with oxygen. Blood enters the right heart through a

chamber called the Right Atrium. Atrium is another word for an 'entry room.' Since the

right atrium is located *above* the Right Ventricle, a combination of gravity and an easy

squeeze pushes the blood though the Tricuspid Valve into the right ventricle. The


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tricuspid valve is a valve made up of three 'leaflets' that allows blood to go from top to

bottom in the heart but closes to prevent the blood from backing up into the right atrium

when the right ventricle squeezes.

After the blood is in the right ventricle, the right ventricle begins its contraction to

push the blood out toward the lungs. Remember that this blood is deoxygenated. The

blood leaves the right ventricle and enters the *pulmonary artery.* This artery and its

two branches are the only arteries in the body to carry deoxygenated blood. Important:

Arteries carry blood *away* from the heart. There is nothing in the definition that says

blood has to be oxygenated.

When the blood leaves the pulmonary arteries it enters *capillaries* in the lungs.

Capillaries are very, very small blood vessels that act as the connectors between veins

and arteries. The capillaries in the lungs are very special because they are located

against the alveoli or air sacks. When blood in the capillaries goes past the air sacks,

the RBC's pick up oxygen. The alveoli are like the loading docks where trucks pick up

their load. Capillaries are so small, in some places, that only one RBC at a time can get

through.

When the blood has picked up its oxygen, it enters some blood vessels known asthe *cardiac veins.* This is fully oxygenated blood and it is now in veins. Remember:

Veins take blood to the heart. The cardiac veins empty into the *left atrium.* The left

side of the heart is the high pressure side, its job is to push the blood out to the body.

The left atrium sits on top of the *left ventricle* and is separated from it by the

*mitral valve*. The mitral valve is named this because it resembles, to some people, a

Bishop's Mitered Hat. This valve has the same function as the tricuspid valve, it

prevents blood from being pushed from the left ventricle back up to the left atrium.

The left ventricle is a very high pressure pump. Its main job is to produce enough

pressure to push the blood out of the heart and into the body's circulation. When the

blood leaves the left ventricle it enters the Aorta. There are valves located at the

opening of the Aorta that prevent the blood from backing up into the ventricle. As soon


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as the blood is in the aorta, there are arteries called *coronary arteries* that take some

of the blood and use it to nourish the heart muscle. Remember: the heart is like James

Brown, it's the hardest working muscle in the body (in case you don't know, James

Brown says he's the hardest working man in show business).

The Aorta and the Arterial System

The aorta leaves the heart and heads toward, what else, the head. We have to

keep our brains well nourished so we can make good grades in school. The arteries that

take the blood to the head are located on something called the *aortic arch.* After the

blood passes through the aortic arch it is then distributed to the rest of the body. The

*descending aorta* goes behind the heart and down the center of the body.

Sometimes, if you are lying flat on your back, you can look down toward your feet

and actually see your abdomen pulsate with each heart beat. This pulsation is really the

aorta throbbing with each heart beat. Do not be alarmed, this is normal.

From the aorta, blood is sent off to many other arteries and arterioles (very small

arteries) where it gives oxygen and nutrition to *every* cell in the body. At the end of the

arterioles are, guess what, capillaries. The blood gives up its cargo as it passes through

the capillaries and enters the venous system.

The Venous System

The venous system carries the blood back to the heart. The blood flows from the

capillaries, to venules (very small veins), to veins. The two largest veins in the body are

the *superior* and *inferior* vena cavas. The superior vena cava carries the blood from

the upper part of the body to the heart. The inferior vena cava carries the blood from the

lower body to the heart. In medical terms, *superior* means above and *inferior* means

under. Many people believe that the blood in the veins is *blue*; it is not. Venous blood

is really dark red or maroon in color. Veins do have a bluish appearance and this may

be why people think venous blood is blue. Both the superior and inferior vena cava end


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in the right atrium. The superior vena cava enters from the top and the inferior vena

cava enters from the bottom.

Blood Function and Composition

Blood facts

Approximately 8% of an adult's body weight is made up ofblood.

Females have around 4-5 litres, while males have around 5-6 litres. This

difference is mainly due to the differences in body size between men and women.

Its mean temperature is 38 degrees Celcius.

It has a pH of 7.35-7.45; making it slightly basic (less than 7 is considered

acidic).

Whole blood is about 4.5-5.5 times as viscous as water, indicating that it is more

resistant to flow than water. This viscosity is vital to the function of blood because if

blood flows too easily or with too much resistance, it can strain the heart and lead to

severe cardiovascular problems.

Blood in the arteries is a brighter red than blood in the veins because of the

higher levels of oxygen found in the arteries.

An artificial substitute for human blood has not been found.

Functions of blood

Blood has three main functions:

> Transport

> Protection

> Regulation.
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Protection

Blood has several roles in inflammation:

Leukocytes, or white blood cells, destroy invading microorganisms and cancercells

Antibodies and other proteins destroy pathogenic substances

Platelet factors initiate blood clotting and help minimise blood loss

Regulation

Blood helps regulate:

pH by interacting with acids and bases Water balance by transferring water to and from tissues

Composition of blood

Blood is classified as a connective tissue and consists of two main components:

Plasma, which is a clearextracellularfluid

Formed elements, which are made up of the blood cells and platelets

The formed elements are so named because they are enclosed in a plasmamembrane and have a definite structure and shape. All formed elements are

cells except for the platelets, which tiny fragments of bone marrow cells.

Formed elements are:

Erythrocytes, also known as red blood cells (RBCs)

Leukocytes, also known as white blood cells (WBCs)

Platelets

Blood Function and Composition

White blood cells

Granulocytes
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Agranulocytes

Platelets

Vascular spasm Platelet plug formation

Coagulation

Production of blood

Haemopoiesis

Erythropoesis

Leukopoiesis Thrombopoiesis

Aging changes in the blood

Platelets

Platelets are small fragments of bone marrow cells and are therefore not really

classified as cells themselves.

Platelets have the following functions:

Secrete vasoconstrictors which constrict blood vessels, causing vascular spasms

in broken blood vessels

Form temporary platelet plugs to stop bleeding

Secrete procoagulants (clotting factors) to promote blood clotting

Dissolve blood clots when they are no longer needed

Digest and destroy bacteria

Secrete chemicals that attract neutrophils and monocytes to sites of inflammation

Secrete growth factors to maintain the linings of blood vessels

The first three functions listed above refer to important haemostatic mechanisms

in which platelets play a role in during bleeding: vascular spasms, platelet plug

formation and blood clotting (coagulation).
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Vascular spasm

This is a prompt constriction of the broken blood vessel and is the most

immediate protection against blood loss. Injury stimulates pain receptors. Some of these

receptors directly innervate nearby blood vessels and cause them to constrict. After a

few minutes, other mechanisms take over. Injury to the smooth muscle of the blood

vessel itself causes a longer-lasting vasoconstriction where platelets release a chemical

vasoconstrictor called serotonin. This maintains vascular spasm long enough for the

other haemostatic mechanisms to come into play.

Platelet plug formation

Under normal conditions, platelets do not usually adhere to the wall of

undamaged blood vessels, since the vessel lining tends to be smooth and coated with a

platelet repellent. When a vessel is broken, platelets put out long spiny extensions to

adhere to the vessel wall as well as to other platelets. These extensions then contract

and draw the walls of the vessel together. The mass of platelets formed is known as a

platelet plug, and can reduce or stop minor bleeding.

Coagulation

This is the last and most effective defence against bleeding. During bleeding,

it is important for the blood to clot quickly to minimise blood loss, but it is equally

important for blood not to clot in undamaged vessels. Coagulation is a very complex

process aimed at clotting the blood at appropriate amounts. The objective of

coagulation is to convert plasma protein fibrinogen into fibrin, which is a sticky protein

that adheres to the walls of a vessel. Blood cells and platelets become stuck to fibrin,

and the resulting mass helps to seal the break in the blood vessel. The forming of fibrin

is what makes coagulation so complicated, as it involved numerous chemicals reactions

and many coagulation factors.


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Production of blood

Thrombopoiesis

Thrombopoiesis refers to the production of platelets in the blood, becauseplatelets used to be called thrombocytes. This starts when a haemocytoblast develops

receptors for the hormone thrombopoietin which is produced by the liver and kidneys.

When these receptors are in place, the haemocytoblast becomes a committed cell

called a megakaryoblast. This replicates its DNA, producing a large cell called a

megakaryocyte, which breaks up into tiny fragments that enter the bloodstream. About

25-40% of the platelets are stored in the spleen and released as needed. The

remainder circulate freely in the blood are live for about 10 days.
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