the cardiovascular system - biology...

Biology 12 – Unit 3A

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The Circulatory System

The circulatory system is responsible for many functions within our body:

o Transport of hormones, nutrients, vitamins, minerals, gases, and wastes to and from tissues

o It helps us fight disease

o It maintains homeostasis by stabilizing body temperature and pH

The circulatory system is composed of 2 subsystems:

1) The cardiovascular system distributes blood and its constituents

2) The lymphatic system distributes lymph

The Cardiovascular System The Heart

The heart is a powerful organ that weighs approximately 250 – 300 grams and is about the size of a clenched fist

Located in the thoracic cavity

a two-layered sac called the pericardium surrounds the heart

The layers of the pericardium are separated by fluid that reduces friction as the heart beats.

Throughout history physicians, as well as citizens, of many cultures developed their own beliefs concerning the nature of the heart and the circulatory system. The Greeks believed that the heart was the seat of the spirit; the Egyptians believed the heart was the center of the emotions and the intellect, and the Chinese believed the heart was the center for happiness. Although the heart is linked to emotions and virtues, when it is stripped of its romantic cloak, the heart is no more than a transport system pump that uses blood to transport oxygen, nutrients, wastes, and many other substances through miles of blood vessels that reach virtually every organ and crevice in the body. Essentially, the circulatory system provides the transport system that keeps blood continuously circulating to fulfill our homeostatic needs.

Did You Know?

The average human heart beats 72 times per minute, approx 100,000 times per day and 2.5 billion times during a lifetime (~ 66 years).

In a single day, the heart circulates the body's blood supply about 1,000 times.

During our lifetime the heart circulates 20,000 L of blood through 96,000 km of vessels.

To the Canadian taxpayer, the heart is worth $21 billion, the amount spent treating heart related illnesses each year.


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Internal Anatomy of the Heart


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The heart is divided into 4 chambers:

o Atria are the upper chambers of the heart

left atrium - collects oxygen rich blood returning from the lungs via the pulmonary veins

right atrium – collects oxygen poor blood returning from the body via the superior (anterior) and inferior (posterior) vena cava

o Ventricles (lower chambers) have thick specialized muscular walls for pumping blood out to the lungs and the rest of the body

left ventricle – pumps oxygen rich blood out the aorta to the body

right ventricle- pumps oxygen poor blood out the pulmonary arteries to the lungs

o The ventricles make-up most of the volume of the heart

A muscular wall called the septum, divides the heart into its right and left sides

Heart Valves

1) Tricuspid Valve (Atrioventricular Valve) – as the right ventricle contracts, the tricuspid valve closes to prevent backflow into the right atrium.

2) Mitral Valve (Bicuspid Valve / Atrioventricular Valve) – as the left ventricle contracts, the mitral valve prevents backflow into the left atrium.

3) Pulmonary Semilunar Valve – prevents backflow from the pulmonary artery into the right ventricle.

4) Aortic Semilunar Valve – prevents backflow from the aorta from going into the left ventricle.

Strong fibrous strings called chordae tendinae prevent the A/V valves from inverting


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External Anatomy of the Heart

Major Blood Vessels Directly Associated With the Heart

1) Superior Vena Cava

A large vein that returns oxygen-poor blood from the upper half of the body to the right atrium.

2) Inferior Vena Cava

A large vein that returns oxygen-poor blood from the lower half of the body to the right atrium.

3) 4 pulmonary veins (2 on the left, 2 on the right)

Carry oxygen rich blood from the lungs into the left atrium.

** They are the only veins in the adult human body that carry oxygen rich blood.

4) Pulmonary Arteries

The right ventricle pumps oxygen poor blood into the pulmonary trunk which branches off to form the left and right pulmonary arteries.

The pulmonary arteries carry oxygen-poor blood to the lungs where gas exchange occurs.

** The pulmonary arteries are the only arteries in the body that carry oxygen poor blood.

5) Aorta

The left ventricle ejects oxygenated blood into the aorta, the largest artery in the body.

The aorta delivers oxygen rich blood to all parts of the body.


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The Systemic & Pulmonary Circuits

The heart is actually 2 side-by-side pumps and is often called a double pump

The right side of the heart is the pulmonary circuit pump

o Vessels in the pulmonary circuit carry blood to and from the lungs for gas exchange.

The left side of the heart is the systemic circuit pump

o Vessels in the systemic circuit carry blood to and from all body tissues and organs.

There is NO MIXING of blood between the right and left sides of the heart in adults


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Passage of Blood through the Heart

The Cardiac Cycle

The chambers of the heart alternatively contract and relax in a rhythmic cycle.

When the heart contracts (systole), the heart pumps blood from the L & R ventricles into the arteries that serve the systemic and pulmonary circuits.

During the period of relaxation (diastole), the L & R atria fill with blood and send it to the ventricles

One complete sequence of filling and pumping blood is called a cardiac cycle, or heartbeat.

In healthy adults, the heart beats about 70 times per minute and each beat lasts about 0.85 seconds.


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When the heart beats, the familiar “lub-dub” sound can be heard.

“Lub” is heard when the tricuspid and mitral valves close (atrioventricular valves) and cause vibrations.

“Dub” is a shorter and sharper sound heard when the aortic and pulmonary semilunar valves close due to backpressure in the arteries.

Control of the Heartbeat

The heartbeat is controlled both intrinsically and extrinsically

Intrinsic Control - the heartbeat is regulated by an electrical conduction system embedded in the muscle tissue of the heart

Extrinsic control – there is a cardiac control center in the brain that regulates our heartbeat by way of the autonomic nervous system

Homeostatic Imbalance

Abnormal heart sounds are called heart murmurs. Blood flows silently as long as the flow is smooth and uninterrupted. However, if it runs into obstructions, blood flow becomes turbulent and generates heart murmurs that can be heard with a stethoscope. Some heart murmurs result when one of the atrioventricular valves is leaky and lets blood backflow into an atrium during ventricular contraction, others occur because valve openings are too narrow. Heart murmurs are also fairly common in young children and the elderly, but they usually result because their heart walls are thin and vibrate as blood rushes through the heart.


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Intrinsic Control – The Heart’s Electrical Conduction System

The intrinsic conduction system of the heart consists of:

1) Sinoatrial Node (SA Node)

2) Atrioventricular Node (AV Node)

3) Bundle of His (right and left bundle branches)

4) Purkinje Fibers

The SA (sinoatrial) Node is the pacemaker for the heart

The SA Node’s job is to send an electrical impulse that spreads through the muscular walls of both atria every 0.85 seconds (70 times per minute)

This impulse causes both atria to simultaneously contract and also stimulates the AV Node

The AV Node sends the signal along the right and left bundle branches of the Bundle of His

The impulse ends at the Purkinje fibers, where it stimulates the walls of the ventricles to simultaneously contract from the bottom up.

Artificial Pacemakers

If the SA node fails to work properly, the heart will still beat thanks to impulses generated by the AV node, however the impulses are sent much slower, one every 1-1.5 seconds

In fact, thanks to the AV node the heart will continue to beat, even outside the body, as long as its cells are alive

Artificial pacemakers are implanted into people who have a faulty SA node that results in a heartbeat that is too fast, too slow, or irregular


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Extrinsic Control

The medulla oblongata, a portion of the brain capable of controlling the heart rate by sending signals to the heart via the autonomic nervous system

o When our body is in a resting state (low activity) a signal is sent to the heart that decreases activity in the SA and AV nodes

o When we are active or stressed a signal is sent to the heart that increases activity in the SA and AV nodes

Adrenaline and Heart Rate

On top of each kidney there is an adrenal gland which also maintain extrinsic control over our heart by secreting hormones

During exercise or in times of stress the adrenal glands release 2 hormones into the bloodstream that stimulate the heart and cause it to beat faster and stronger.

1) Norepinephrine (aka NE, or noradrenaline)

2) Epinephrine (aka adrenaline)

Blood Vessels

There are several types of blood vessels that carry blood to and from all parts of the body:

1. Arteries

2. Arterioles

3. Capillaries

4. Venules

5. Veins

Did You Know?

All the blood vessels in the body joined end to end would stretch 96,000 km or two and a half times around the Earth.


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Arteries & Arterioles

Arteries are defined as vessels that carry blood away from the heart

The walls of arteries have 3 main layers: tunica adventitia, tunica media, tunica intima

The middle layer (tunica media) is the thickest and consists of strong elastic smooth muscle that can resist the pressure exerted by blood as it is forced from the ventricles

The muscular walls of arteries help the heart pump blood; when the heart beats, arteries expand as they fill with blood

When the heart relaxes, arteries contract, exerting a force that is strong enough to push the blood through the vessels

Arterioles branch off of the arteries, have the same three layers, but are smaller in diameter


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Major Arteries and Veins of the Body

Veins & Venules

Veins are defined as vessels that carry blood toward the heart

In systemic circulation veins always carry oxygen-poor blood

Venules are small veins that drain blood from capillary beds

As blood travels back to the heart from the tissues, venules converge to form veins

All blood returns to either the superior or inferior vena cava to be returned to the right atrium


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Veins differ from arteries in a few ways:

1) They experience low blood pressure therefore they have thin tunica media

2) As a result, veins have a larger internal diameter than arteries and at any given time about 70% of our blood supply is in veins

3) Veins require contractions of skeletal muscles to help squeeze blood along them because of the low blood pressure they experience

4) Valves are found in veins within the extremities

o When skeletal muscles contract, they compress the weak walls of veins and “squeeze” blood along,

o the valves prevent backflow once the contraction is over

Homeostatic Imbalance - Varicose Veins

Varicose veins develop when the valves of veins become weak and ineffective due to the backward pressure of blood. They are mostly superficial veins, in the anal region (hemorrhoids), and lower legs.

Causes of varicose veins include: genetic predisposition (women > men), obesity, pregnancy, prolonged standing, sitting with legs crossed. People who have varicose veins may have health related illnesses

because of them. i.e. ulcers, inflammation, etc. Treatment includes surgery to remove them or support

stockings that help with venous return.


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A Schematic Overview of Major Blood Vessels

Capillaries

Are tiny vessels only wide enough to allow one blood cell through them at a time that connect arterioles to venuoles

The walls of capillaries are extremely thin and as a result capillaries are often called “leaky vessels”

Although capillaries are small, they form vast capillary networks and have a HUGE surface area


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In tissues, capillaries function to:

1) Drop off oxygen & nutrients

2) Pick up carbon dioxide & metabolic wastes

Our body has the ability to open or close certain capillary beds depending on our needs for exchange.

Capillary Exchange

Two forces primarily control movement of fluid though the thin capillary walls:

1) Blood Pressure

The force exerted on the walls of blood vessels as the heart pumps blood

2) Osmotic Pressure

Pressure created by the presence of salts and plasma proteins in blood

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter21/animation__fluid_exchange_across_the_walls_of_capillaries.html




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1) Arterial End of the Capillary

Blood pressure is higher than the osmotic pressure of blood

This causes water to leave the capillary and enter tissues

2) Midpoint

Midway along a capillary blood pressure and osmotic pressure are approximately equal so there is no NET movement of water in or out of the capillary

Here, solutes diffuse in or out according to their concentration gradients

OUT - Nutrients, glucose, amino acids, oxygen

IN – Carbon dioxide and other metabolic wastes

3) Venous End of the Capillary

Blood pressure is lower than the osmotic pressure of blood

This causes water to enter the capillary and leave the tissues

Blood cells and most proteins dissolved in the blood are too large to pass through the walls of capillaries

Approximately 90% of the fluid that leaves a capillary at the arterial end, reenters at the venous end

This excess tissue fluid is collected by lymph capillaries that lie near capillary beds and is called lymph


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Total Cross-Sectional Area of Blood Vessels

Blood pressure decreases as the TOTAL cross-sectional area of blood vessels increases.

Recall: Arteries Arterioles Capillaries Venules Veins

Because there are millions of capillaries within our tissues, they have the highest TOTAL cross-sectional area of all the vessels.

By the time blood reaches veins, blood pressure is not affected much by the heart.

Because blood encounters so much resistance as it passes through the millions of tiny capillaries, the pumping action of the heart is not strong enough to have an effect on the movement of blood through veins.

This is why venous return depends on skeletal muscle contractions and the pressure changes created from inhalation and exhalation.

Blood Velocity

Blood flows through the vessels of the circulatory system at an uneven speed.

E.g. Blood travels 1000 x faster in the aorta than in capillaries.

The TOTAL cross-sectional area of blood vessels is what determines the velocity of the blood travelling through them.

As the TOTAL cross-sectional area of blood vessels increases, blood velocity decreases.

Therefore: Blood velocity decreases as blood moves through arteries arterioles capillaries and picks up again as blood leaves capillaries venules veins.


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Lymphatic System

The lymphatic system is closely associated to the cardiovascular system

Functions:

1) Lymphatic vessels take up excess interstitial fluid that is lost during capillary exchange (4L per day) fluid from tissues and return it to the bloodstream

2) Provides our immune defenses, by producing lymphocytes (WBCs) that help the body fight bacterial and viral invaders

3) Filters foreign substances and cell debris from the blood and destroys them

4) Lacteals in intestinal villi absorb fats from the digestive tract and transport them to the bloodstream

The fluid that escapes from capillaries during capillary exchange enters the lymphatic system by diffusing into tiny lymph capillaries that are intermingled among capillaries of the cardiovascular system.

Once inside the lymphatic system, the fluid is called lymph

Lymph vessels, like veins, have valves that prevent the backflow of fluid toward the capillaries and depend on movement of skeletal muscles to squeeze fluid along

Along lymph vessels there are specialized swellings called lymph nodes

Lymph nodes are an important player in our immune defense system; they are filled with lymphocytes (WBCs) specialized for defense against bacterial and viral invaders.


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Lymphatic organs include:

1) Red Bone Marrow

production site of lymphocytes

2) Thymus

Immature T cells made in bone marrow travel in the bloodstream to the thymus where they mature (95% of T cells stay in the thymus)

3) Spleen

Main function is to cleanse the blood

4) Tonsils (lymph nodes)

The tonsils contain a high concentration of lymphocytes and are believed to be involved in helping fight off pharyngeal and upper respiratory tract infections.

Pathway of lymph through the lymphatic system:

1) Lymph Capillaries

2) Lymph vessels

3) Lymph nodes

4) Lymphatic ducts

Thoracic Duct - returns lymph collected from the body below the thorax and the left side of the body into the LEFT subclavian vein.

Right Lymphatic Duct - returns lymph from the right arm, and the right side of the head and neck into the RIGHT subclavian vein.

5) Subclavian Veins


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Fetal Circulation

There are 4 main differences between the circulatory system of a fetus and an adult

The main condition that influences these differences is that the fetus receives oxygenated blood from

the maternal blood via the placenta and does not use its' own pulmonary circuit to obtain oxygen until

birth 1. Umbilical vein and arteries

housed in the umbilical cord which attaches the placenta to the umbilicus (future belly

button) of the fetus

The umbilical vein carries oxygenated blood with maternal nutrients from the

placenta to the fetus The umbilical arteries carry deoxygenated blood with fetal waste from the fetus to

the placenta.

2. Venous duct or ductus venosus

receives blood from the umbilical vein and directs it to the posterior/inferior vena cava

acts as a liver bypass and moves blood into the fetal systemic circulation

3. Oval opening or foramen ovale

An opening or hole between the right and left atria of the heart

allows blood to move from the right atrium to the left atrium, bypassing the lungs

4. Arterial duct or ductus arteriosus

a connection between the pulmonary artery and the aorta

acts to direct blood away from the lungs and into the systemic circulation


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Blood Pressure

http://blood-pressure.emedtv.com/high-blood-pressure-video/what-is-blood-pressure.html

Blood pressure is the measurable amount of force exerted on the walls of blood vessels as blood is pumped from the heart

Systemic blood pressure is greatest in the aorta and decreases as blood travels further from the heart into arterioles and capillaries

Blood pressure is minimal in venules and veins and so venous return depends on skeletal muscle contractions to move blood back to the heart.

A) Systolic Pressure

As the left ventricle contracts and blood is pumped into the aorta, its elastic walls stretch to accommodate the pressure exerted by the pumping action of the heart.

The pressure exerted on the walls of blood vessels as blood is pumped through them is referred to as systolic pressure.

B) Diastolic Pressure

Diastolic pressure is measured during ventricular diastole, when the ventricles are relaxing and filling with blood.

Measuring Blood Pressure

Clinicians use a sphygmomanometer, or blood pressure cuff to measure arterial blood pressure, usually in the brachial artery of the arm.

Normal blood pressure for an adult is 120/80 mmHg.

120 = systolic pressure

80 = diastolic pressure

Blood pressure readings are always recorded in millimeters of mercury (mmHg) as:

systolic pressure mmHg diastolic pressure mmHg

http://blood-pressure.emedtv.com/high-blood-pressure-video/what-is-blood-pressure.html


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Hypotension “Low Blood Pressure”

Hypotension, or low blood pressure, occurs when systolic pressure is below 100 mmHg.

In many cases, hypotension simply reflects individual variations and is no cause for concern.

In fact, low blood pressure is often associated with long life and an old age free of illness.

Causes include reduced arterial blood volume from:

Hemorrhage or blood loss Starvation Venous Pooling Being in a state of shock Dehydration Vomiting Diarrhea Excessive use of diuretics Excessive Vasodilatation

The cardinal symptom of low blood pressure is light headedness or dizziness.

Hypertension “High Blood Pressure - The Silent Killer”

When we have a fever, are emotionally upset or are physically exerting ourselves we experience temporary periods of hypertension that are relatively harmless.

Hypertension becomes a concern when a person’s blood pressure is chronically elevated above 140/90 mmHg.

Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure, arterial aneurysms and can cause kidney failure.

Even a moderate elevation of arterial blood pressure can significantly reduce life expectancy.

Homeostatic Imbalance

It is estimated that 30% of people over the age of 50 are hypertensive. What makes this condition so dangerous is that a person who suffers from this condition rarely has symptoms for the first 10-20 years. Over time, the heart becomes strained and arteries are damaged. Prolonged hypertension is the major cause of heart failure, vascular disease, renal failure, and stroke. Because the heart is forced to pump against greater resistance, it must work harder, and in time the myocardium enlarges. When it is strained for a prolonged period of time the walls of the heart weaken and become flabby. Hypertension also causes tears in small blood vessels and is an underlying cause of atherosclerosis, a condition where arteries become clogged with fatty plaque. As vessels become blocked, blood flow to tissues is reduced and complications appear in the brain, heart, kidneys, and eyes. Diet, obesity, age, race, heredity, stress and smoking are all factors which contribute to hypertension. Most cases of primary hypertension can be controlled by restricting fat, cholesterol and salt from the diet, increasing exercise, losing weight, managing stress and stopping smoking.


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Blood Pressure & Your Pulse

Pulse pressure is felt as a throbbing sensation in an artery during ventricular systole as the elastic artery expands.

You can take your pulse by gently placing your fingers over a superficial artery – commonly the radial (wrist) or carotid (neck) arteries.

Factors That Affect Blood Pressure

Family history, age, and race are factors that affect our blood pressure which are not under our control.

Blood pressure is affected by:

1. Heart Rate – i.e. How fast the heart beats

2. Stroke Volume – Volume of blood pumped with each beat

3. Vasoconstriction & Vasodilatation

Depending on the needs of various body systems, the body can adjust blood pressure.

The hypothalamus has the ability to send signals which can dilate arterioles to lower blood pressure, or constrict (narrow) arterioles to raise blood pressure.

4. Lifestyle Factors

a) Stress

Stress stimulates the sympathetic nervous system as well as the release of adrenalin (short term).

Adrenalin causes vasoconstriction and the heart to beat faster. b) Smoking

Nicotine is a vasoconstrictor and stimulates the production of adrenalin which speeds up the heart.

c) Obesity

One extra pound = seven miles of blood capillaries.

The heart must increase the pressure to account for the longer distances required to supply the adipose tissue.

d) Salt

Causes fluid to be retained in the blood vessels and increases blood pressure.

e) Exercise

Lowers blood pressure at rest.

Some physiological factors also affect blood pressure.


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Blood

Blood has several important functions:

1) Transport

Delivers oxygen and nutrients (glucose, amino acids, fatty acids) to tissues.

Picks up carbon dioxide and other metabolic wastes from tissues.

Medium for hormone transport.

2) Helps Maintain Immunity

Circulates white blood cells to fight infection.

Antibodies detect foreign invaders.

3) Self-Repair

Contains platelets and plasma proteins that heal wounds.

4) Regulates Water Balance

5) Regulates pH

Normal blood pH of blood is 7.35 - 7.45.

Transports acidic or basic ions throughout the body to maintain homeostatic pH.

6) Regulates core body temperature

As blood travels through vessels heat is dispersed throughout the body.

Blood flow can be increased in superficial arteries and veins to help cool the body.

Blood flow can be restricted to deep vessels to preserve body heat.

Origin of Blood Cells

All blood cells originate in the bone marrow of the skull, ribs, vertebrae and the ends of long bones

Over 2 million new blood cells are produced every second!


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If you take a sample of blood and spin it in a centrifuge, it will separate into 3 distinct layers.

1) Top Layer - 55% Plasma

2) Middle Layer < 1% Buffy Coat

Leukocytes (WBCs)

Platelets

3) Bottom Layer - 45%

Erythrocytes (RBCs)

Plasma

~ 90% water

~ 7-8 % plasma proteins

Globulins (fight infection)

Albumin (for osmotic pressure)

Fibrinogen (for clotting)

Gases - oxygen, carbon dioxide

Nutrients - glucose, amino acids, fats

Salts – Ca2+, Na+, Zn+

Wastes - urea, creatine, uric acid and ammonia (removed by kidney)

Hormones

Vitamins

Formed Elements

The formed elements collectively account for ~ 45% of the total volume of blood.

Red Blood Cells (RBCs) – AKA erythrocytes

White Blood Cells (WBCs) – AKA leukocytes

Platelets

Erythrocytes “RBCs” (Red Blood Cells)

most abundant blood cell in blood - 4 - 6 million per mm3 of blood!

Lifespan: 120 days

They are anucleate cells shaped like a biconcave disc.

As RBCs move single file through capillaries they drop off oxygen and pick up carbon dioxide in the tissues.

RBCs contain hemoglobin, a respiratory pigment that makes them red


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Hemoglobin allows RBCs to carry up to 60 times more oxygen than they could alone.

Erythropoiesis – Formation of RBCs

When the body has an insufficient number of RBCs, or the RBCs do not contain enough hemoglobin, a person suffers from a condition called anemia.

Anemia causes a person to have low blood oxygen levels, and the kidneys respond by releasing the hormone erythropoietin.

Erythropoietin travels to the red bone marrow and stimulates an increase in the production of red blood cells (RBCs).

Damaged or old RBCs are destroyed primarily by the liver and the spleen.

The heme portion of hemoglobin is recycled and is excreted as bile pigments by the liver.


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Leukocytes “WBCs” (White Blood Cells)

Are significantly larger than RBCs and have a nucleus.

There are 4,000 -11,000 WBCs per mm3 of blood (few compared to RBCs and platelets)

They fight infection and are involved in immunity, the ability to fight disease.

There are a total of 5 different types of WBCs, and on the basis of structure, they can be divided into 2 main groups.

1. Granular Leukocytes

Account for 40-70% of all leukocytes.

Basophils

Responsible for allergic and antigen responses.

Release Histamine - causes inflammation by promoting blood flow to injured tissues (can be a problem for people with allergies!)

Eosinophils

Attack parasites and phagocytize allergens.

Neutrophils

Phagocytize bacteria and fungi that enter the blood stream.

2. Agranular Leukocytes

Lymphocytes

Responsible for specific immunity against virus-infected cells or tumor cells.

Monocytes

Become macrophages that phagocytize pathogens and clean up cellular debris.


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Thrombocytes - Platelets

Play a vital role in blood clotting

When a blood vessel is damaged, platelets experience chemical changes that make them “sticky.”

These sticky platelets form a plug in the wound of the vessel.

Insoluble protein fragments then join together to form long threads of fibrin.

These fibrin threads trap RBCs and wind around the platelet plug to form a framework for a blood clot.

As soon as the vessel is repaired, the clot is destroyed to restore flow through the vessel.


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Blood Typing

Antigen D – The Rhesus Factor

The attack breaks down the baby’s red blood cells and anemia develops in the unborn child.

In severe cases this hemolytic disease can cause illness, brain damage and even death.


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Cardiovascular Diseases

Cardiovascular disease or heart disease is the number one killer in Canada. It is also the most costly disease in Canada, putting a huge financial burden on our health care system.

Examples of cardiovascular diseases include:

1. Atherosclerosis

Is a disease that affects arterial blood vessels.

Fatty deposits and cholesterol form plaques that collect in the inner lining of

arteries.

These plaques restrict blood flow by decreasing the diameter of arteries and they can cause blood clots to form.

If these blood clots break off, they are carried in the bloodstream and can cause a

heart attack or stroke.

2. Heart Attacks (myocardial infarction or MI)

A heart attack or MI, occurs when a portion of the heart muscle dies due to a lack

of oxygen.

Blockages of coronary arteries are the cause of heart attacks.

If a coronary artery becomes partially blocked, a person may suffer from angina pectoris – a painful squeezing sensation in the chest.

Symptoms of heart attacks include chest pain, and pain that travels through the left arm.


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3. Stroke

Strokes often result when a small cranial arteriole bursts or is blocked by a blood clot (embolus).

Lack of oxygen causes the portion of the brain fed by the arteriole to die.

Paralysis or death can result from a stroke.

Symptoms include numbness in the hands or face, difficulty speaking, or temporary blindness in one eye.

4. Aneurysms

An aneurysm (or aneurism) is a localized, blood-filled dilation (balloon-like bulge) of a blood vessels caused by disease or weakening of the vessel wall.

Aneurysms most commonly occur in arteries at the base of the brain and in the aorta heart aortic aneurysm.

As the size of an aneurysm increases, there is an increased risk of rupture, which can result in severe hemorrhage or other complications including sudden death.

http://en.wikipedia.org/wiki/Artery

http://en.wikipedia.org/wiki/Aorta

http://en.wikipedia.org/wiki/Heart

http://en.wikipedia.org/wiki/Aortic_aneurysm

the cardiovascular system - biology...

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