Unit Overview: In this section you will learn about how the heart works and the certain jobs every thing has. Like, for example, how blood leaves the heart into the arteries oxygenated and comes back deoxygenated in veins. Also you will learn that tachycardia is a heart rate above one hundred beats per minute and bradycardia is a heart rate below sixty beats per minute. In this section you will also read about blood pressure and how important it is.


1. Structure of the Heart & Cardiac Cycle

Structure of the Heart:
The heart contains 4 chambers: two atria (receive blood from venous system), and two ventricles (pump blood into the arterial system). The right ventricle pumps blood to the lungs, where it becomes oxygenated. The left ventricle pumps the oxygenated blood to the entire body.
The right atrium and right ventricle are separated from the left atrium and left ventricle by a muscular wall called a septum. The septum is what prevents blood from mixing between the two sides of the heart. Fibrous skeleton, a layer of dense connective tissue, is between the atria and ventricles.

Pulmonary and Systemic Circulations

Blood with partially depleted oxygen content and increased carbon dioxide content returns to the right atrium. Then this blood enters the right ventricle where it is pumped into the pulmonary trunk and pulmonary arteries.
Part of the vascular system that includes the pulmonary arteries and pulmonary veins is part of pulmonary circulation. The blood returning to the left atrium by pulmonary veins is enriched in oxygen and depleted partially of carbon dioxide. It transports blood from the right ventricle through the lungs and back to the left atrium. When the path of blood completes one circuit, it has complete pulmonary circulation.
The systemic circulation carries oxygenated blood from the left ventricle to the tissue cells and that carries blood without oxygen to the right atrium.

Atrioventricular and Semilunar Valves
Embedded within the fibrous skeleton are one-way atrioventricular valves (AV). The tricuspid valve, which has three flaps, is an AV valve located between the right atrium and right ventricle. The biscuspid valve, which has two flaps, is an AV valve that is between the left atrium and the left ventricle. The bicuspid valve is also known as the mitral valve.


13.10.jpgCardiac Cycle:
Pressure changes in both atria and ventricles as they go through the cardiac cycle are responsible for the flow of blood through the heart chambers and out into the arteries. The repeating pattern of contracting and relaxing of the heart is referred to as the cardiac cycle. When the heart is in the phase of contracting, it is called systole. When the heart is in the phase of relaxing, it is called diastole. If these terms are used without any reference to specific chambers, they refer to contraction and relaxation of the ventricles.


Pressure Changes During the Cardiac Cycle

When the heart is in diastole, these events in the cardiac cycle occur: The ventricles contract, the intraventricular pressure rises, and the AV valves snap shut and produce the first sound of the heart. When the pressure becomes greater in the left ventricle than in the aorta, the semilunar valves open and begin ejection. As the pressure in the ventricles falls below the pressure that is in the arteries, the back pressure will cause the semilunar valves to snap shut and produce the second sound that the heart makes. This part of the cycle lasts until the ventricle pressure falls below the pressure in the atria. Once this happens, the AV valves open and a phase of rapid filling of the ventricle occurs. Atrial systole delivers the final amount of blood into the ventricles immediately.

2. Blood Vessels are one of the most important items in your body keeping you alive. They allows blood flow and other essentials from your heart throughout the body to the cells keeping them alive and then back to the heart. As the blood leaves the heart it goes through vessels the start to get smaller in width. The order is arteries followed by arterioles then capillaries. The arteries and veins have three layers surrounding them. From the outside going in the layers are the tunica externa, tunica media, and tunica interna. There are some differences that help distinguish the difference between arteries and veins. For one at cross sections, arteries look more rounded while veins look like they have collapsed. Veins also contain valves and have a thicker smooth muscle layer. On the other hand, arteries have more muscle in their diameter. In larger arteries such as the aorta, there are some things called elastic arteries that help expand the arteries when a persons blood pressure rises, but they are like elasticity, so when a persons blood pressure goes back down, it has the ability to go back to its resting position. There is also muscular arteries, but they don't change in diameter when blood pressure rises. Since they don't have much elastic to them they are the ones that cause the most resistance to a persons blood flow throughout their arterial system.



Capillaries are the narrowest blood vessels in a persons body. They are composed of only one layer, either simple squamous epithelium or edothelium. When your arterioles vasoconstrict making it harder for blood flow through them but it makes very hard for the blood flow to make into the capillaries. There three different types of capillaries and depending on the organ is where you will find them. The three are: continuous, fenestrated, and discontinuous. Continuous are found in muscles, lungs, adipose tissue, and in the CNS. Continuous capillaries are very closely packed together. Fenestrated capillaries are found in the kidneys, intestines, and the endocrine glands. These capillaries consist of large intercellular pores. To make sure specific molecules don't get through the pores are covered by a layer of mucoprotein, it also serves as a basement membrane. The discontinous capillaries are found in the bone marrow, liver, and spleen. Capillaries can grow with the help of lots of oxygen and by a vascular endothelial growth factor. Capillary growth can also be caused by adenosine that also helps with vasodialation, which in turn increases blood flow.


Most of a persons total blood volume is found in their venous system. Veins are able to expand as they receive extra amounts of blood. The pressure though veins are 2 mmHg, while its 100 mmHg in arteries. Since the pressure though the veins are so low it takes the help of contracting skeletal muscles in a massaging action that the veins are around. This provides a one way flow of blood to the heart. This is ensured by the pressece of venous valves. These venous valves prevent the blood flow from going away from the heart. The massaging action is usually known and described as the skeletal muscle pump. When a person is bedridden or standing still, the pumps are less active causing the veins to bulge from extra amounts of blood. When a person is more active there is less blood in the veins.

3. Atherosclerosis & Cardiac Arrhythmias , and Lymphaitc System



Atherosclerosis of arteries can reduce blood flow to the heart and brain, causing up to 50% of all mortality in the United States, Europe, and Japan. This is caused by plaques (atheromas) build up. Which can lead to a thrombus forming in the area. Leading to a potential heart attack or stroke.

Atherosclerosis starts with an injury to the endothelium, the movement of monocytes and lymphocytes into the tunica interna, and the conversion of monocytes into macrophages that engulf lipids. Smooth muscle cells then proliferate and secrete extracellular matrix which then becomes Plaques.


Atherosclerosis can be caused by smoking, hypertension, and high blood cholesterol, among other risk factors; low-density lipoproteins (LDL), which carry cholesterol into the artery wall, and is oxidized by the endothelium making it a major contributor to atherosclerosis.

Lipids, including cholesterol, are carried in the blood attached to LDLs and HDLs (high-density lipoproteins)

LDLs and HDLs are produced in the liver and taken into cells by receptor-mediated endocytosis.

Oxidized LDLs (the electrons are striped from the lipid) can injure endothelial cells facilitating the formation of plaque. As stated above arteries have receptors for LDL.... But they don't have any for HDL.

HDL are good cholesterol because they can't be absorbed into the body.
LDL are bad cholesterol because they can be.

When you have high cholesterol this means you have to much LDL in your system. You just read that is can cause plaque build up in your arteries and can lead to heart attack or stoke. To reduce your cholesterol you need to reduce your LDLs and increase your HDLs. One way to do this is by increasing the amount of antioxidants you eat and decreasing the amount of fatty (saturated fat) foods you eat. Medication can also help such as Statins or " Lipator".

Ischemic Heart Disease
Occlusion of blood flow in the coronary arteries by atherosclerosis may produce ischemia of the heart muscle and angina pectoris, which may lead to myocardial infarction (heart attack). Ischemia occurs when blood supply to tissue is deficient which can lead to tissue death. Causing increased lactic acid from the anaerobic metabolism. Angina Pectoris is chest pain. Myocardial Ischemia can also be mistaken as shoulder pain as well.

Myocardial infraction can lead to the death of parts of the heart muscle which can't be replaced. When diagnosed a person has high levels of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) and the presence of plasma toponin T and I from the damaged muscle. Dead cells are replaced by noncontractile scar tissue which prevents the heart from pumping as strong as it used to.

Cardiac Arrhythmias

The ECG can be used to detect abnormal cardiac rates, abnormal conduction between the atria and ventricles, and other abnormal patterns of electrical conduction in the heart.

Arrhythmias are abnormal heart rhythms.


Bradycardia- is a heart rate below 60 BPM

Tachycardia- is a heart rate above 100 BPM.


Flutter- are contraction rates can be 200-300 BPM

Fibrillation- is a contraction of myocardial cells is uncoordinated and pumping ineffectivly

- Ventricular fibrillation is life-threatening

AV node (atrioventricular node) block occurs when the node is damaged. If damaged it can affect signals getting to the node and pumping blood.

There are 3 degrees of AV node block:


First-degree AV node block is when conduction through AV node is less then 0.2 sec which causes a long P-R interval.

Second-degree AV node block is when only 1 out of every 2-4 atrial active post. can pass to the ventricles which causes P waves with no QRS.

Third-degree AV node block is when no artial activity passes to the ventricles.
-Ventricles are driven slowly by the His bundle or Purkinjes bundle.

Lymphatic System

There are 3 basic functions:
  • Transports interstitial fluid or lymph back to the blood.
  • Transports absorbed fat from the small intestine to the blood.
  • And helps provide immunological defenses against pathogens.

Lymphatic capillaries are closed-ended but highly permeable and forms vast networks in the intercellular spaces.

They drain excess tissue fluid into lymph ducts or nodes.

Lymph passes through lymph nodes and is returned by way of the lymph ducts to the venous blood.

The lymph nodes filter lymph before returning into the Rt. and Lt. subclavian veins through the thoracic duct or right lymphatic duct.

Nodes make lymphocytes and contain phagocytic cells that remove pathogens. They are also made in the tonsils, spleen, and thymus.

4. Cardiac Output & Blood Volume
The volume of blood that is pumped per minute by each ventricle is the cardiac output. The product of the average resting cardiac rate and the average stroke volume (volume of blood pumped per beat by the left and right ventricle) gives an average cardiac output per minute. With the absence of neuronal influences, the SA node will drive the heart at rate of its spontaneous activity. Sympathetic and parasympathetic nerve fibers are continuously active to a greater or lesser degree. Norepinephrin and epinephrine open the HCN channels of the pacemaker cells. This induces a faster rate of diastolic depolarization and causes action potentials to be produced rapidly. This results in a faster cardiac rate.


The stroke volume is regulated by three different variables: the end-diastolic volume (EDV), the total peripheral resistance, and the contractility. The EDV is the volume of blood in both ventricles before they begin to contract. The total peripheral resistance is the frictional or impedance to blood flow in the arteries. The contractility is the strength of ventricular contraction. The stroke volume is directly proportional to the preload and to contractility. Preload is a workload imposed on the ventricles prior to contraction. Afterload is the total peripheral resistance that is presents impedance to the ejection of blood from the ventricle. The greater the peripheral resistance, the lower the stroke volume will be.
The Frank-Starling law of the heart is a statement that describes the relationship between end diastolic volume, contraction strength, and stroke volume. A contraction of greater strength is produced by a greater amount of blood in a ventricle before contraction which results in a greater stretch of the myocardium.


The venous return is the return of blood to the heart through veins. The rate at which the atria and ventricles are filled with venous blood depends on the total blood volume and the pressure in the veins. It is venous pressure that serves as the driving force for the return of blood to the heart. Veins have a thinner, less muscular wall that arteries, which means they have a higher compliance. Compliance means that a given amount of pressure will cause more expansion in veins than arteries, so the veins can hold more blood. Because of this, veins are called capacitance vessels.


Blood volume is influenced by the kidneys because urine is derived from blood plasma and the hormones ADH and aldosterone act on the kidneys to help regulate the blood volume. It constitutes a small fraction of the total body fluid. About two-thirds of the total body water is contained within cells in the intracellular compartment. The remaining one-third is in the extracellular compartment. The total volume of intracellular and extracellular fluid is usually maintained constant by a balance between water loss and water gain.
The distribution of extracellular fluid between the plasma and interstitial compartments is in a state of dynamic equilibrium. Filtration is the result from blood pressure within capillaries. This hydrostatic pressure is equal to about 37 mmHg at the arteriolar end and drops to about 17 mmHg at the venual end of the capillaries. The net filtration is equal to the hydrostatic pressure in the capillaries minus the hydrostatic pressure of tissue fluid that is outside the capillaries. This opposes filtration. The colloid osmotic pressure of the plasma, osmotic pressure exerted by plasma proteins, is much greater than the colloid osmotic pressure of interstitial fluid. Oncotic pressure is the difference between these to osmotic pressures. Depending on the magnitude of the net filtration, the fluid will move out of or into the capillary. It varies from the arteriolar to the venular end of the capillary and on the oncotic pressure. Starling forces are the opposing forces that affect the distribution of fluid across the capillary


The excessive accumulation of interstitial fluid is known as edema. It can be prevented by a proper balance between capillary filtration and osmotic uptake of water and by proper lymphatic drainage.


5. Vascular Resistance to Blood Flow

  • Determines how much blood flows through an organ or tissue through vasodialation- decreases resistance, increases blood flow or vasoconstriction- increases resistance, decreases blood flow. Each organ has a different resistance to blood flow.

The physical laws describing blood flow

According to Poiseuille's law, blood flow is directly related to the pressure difference between the two ends of a vessel and is inversely related to the resistance to blood flow through the vessel.

The picture shown the the left represents the systemic flow from and to the heart. Its shows the average pressure and driving force of blood flow.


Total Peripheral Resistance- is the sum of all vascular resistances with the systemic circulation. The Arteries supply tissues and organs in parallel circuits. Changes in resistance in these circuits determines the relative blood flow. Arterial blood doesn't usually flow from one organ to the next.

Extrinsic regulation of vascular resistance is provided mainly by the sympathetic nervous system, which stimulates vasoconstriction of arterioles in the viscera and skin.

Paracrine Regulation of Blood Flow

The endothelium produces many paracrine regulators that promote relaxation: Prostacyclin, Nitric Oxide (NO), and bradykinin. Nitric Oxide takes part in setting the resting "tone" of vessels. Levels are increased by Parasympathetic activity. Vasodilator drugs such as Viagra or nitroglycerin act through Nitric Oxide. Endothelin 1 is a vasoconstrictor also produced by endothelium.

Intrinsic Regulation of Blood Flow

Intrinsic control of vascular resistance allows organs to autoregulate their own blood flow rates. Myogenic regulation occurs when vessels constrict or dilate as a direct response to a rise or fall in blood pressure. Metabolic regulation occurs when vessels dilate in response to the local chemical environment within the organ.

Blood Pressure

Arterioles play a role in blood distribution and control of Blood Pressure. The blood flow to capillaries and blood pressure is controlled by the diameter of arterioles.


Capillary blood pressure is decreased because they are downstream of the high resistance arterioles and low because of the large total cross-sectional area.

Blood Pressure is controlled by your heart rate, stroke volume, and peripheral resistance. If any of these increase it can result in increasing the blood pressure.

Kidneys can play a role blood pressure by regulating the blood volume which would also regulate the stroke volume.

Baroreceptors in the aortic arch and carotid sinuses affect, via the sympathetic nervous system, the cardiac rate, and the total peripheral resistance.negative_feedback_control_of_blood_pressure_by_the_baroreceptor_reflex.jpg

The baroreceptor reflex causes pressure to be maintained when an upright posture is assumed.
This reflex can cause a lowered pressure when the carotid sinuses are massaged.


Other mechanisms that affect blood volume help to regulate blood pressure. One is the Atrial Stretch Receptors, they are activated by increased venous return and act to reduce blood pressure and in response slows the heart rate and inhibits ADH to be released and promotes the secretion of ANP.

Blood pressure is commonly measured indirectly by auscultation of the brachial artery when a pressure cuff is inflated and deflated.


The first sound of Korotkoff, caused by turbulent flow of blood through a constriction in the artery, occurs when the cuff pressure equals the systolic pressure. The last sound of Korotkoff is heard when the cuff pressure equals the diastolic blood pressure. The mean arterial pressure represents the driving force for blood flow through the arterial system.


6. Hypertension, Shock, and Congestive Heart Failure

Hypertension is a result of high blood pressure. There is about twenty percent out of all of the adults is the United States that have this. If a person recieves hypertension as a result to having a disease is known as Secondary hypertension. Any person that has a systolic blood pressure over 115 mmHg and a diastolic pressure over 75 mmHg is at risk for developing hypertension. If a person can keep their blood pressure under 120/80 mmHg, they can reduce their risk of getting heart failure, heart attacks, strokes, and kidney disease. If a renal artery is pinched is increases your heart rate. Some possible causes of secondary hypertension is kidney disease, renal artery disease, excess aldosterone, damage to vasomotor center, excess catecholamines, a complete heart block, increased intacranial pressure, and arteriosclerosis. A person with a high salt diet, which casues an increase in plasma osmolality, is associated with hypertension. Hypertension is known as the silent killer because when a person has high blood pressure the blood is repeatedly force though organs until it eventually causes vascular damage and though all of this the person has no symptoms until its too late. Hypertension is dangerous because the ventricles must work harder, which is known to causing a pathological growth inside the ventricle walls. This can lead to obesity and heart failure. A person can treat hypertension usually by changing their lifestyle: stop smoking, drinking less alcohol, lose weight, exercise more, eating foods rich in potassium. If you change your life style and it doesn't seem to be working you can try medications.

There are different kinds of shock. The main ones include: Circulartory, hypovolemic, and septic. Circulatory shock is when there is not enough blood or oxygen flow taken in by the tissues. Some early signs of shock from not enough blood through the tissues include: an increased diastolic pressure, decreased pulse pressure, increased osmolality, increased pH due to hyperventilation, and slight restlessness. Some late signs include decreased systolic pressure, decreased urine volume, cold and clammy skin. Shock could for reasons unknown cause death when signs become unreversable. Hypovolemic shock is a result of low blood volume, which can be cause by bleeding, lack of water, and burns. Septic shock is when a person has hypotension. Nitric oxide has been proven to help a person with septic shock. Some other causes of circulatory shock is anaphylactic shock which is a result of a person having their blood pressure drop very fast. This could be caused by a bee sting to a person who is allergic to bees. Neurogenic shock is also a result of having a persons blood pressure drop very fast. Cardiogenic shock is a result of cardiac failure. Cardiac failure can result from valve damage.

Congestive heart failure
Cardiac failure happens when the cardiac output cant pump out what is required for the body. This can be a cause of hypertension or heart disease. If there is failure to the left ventricle it could cause a person shortness in breath and fatigue. If there is failure to the right ventricle it could cause a person to have congestion and swelling in a persons systemic circulation.

Essential Questions:
-What are the three most important variables that affect blood pressure? Describe each variable and how it affects blood pressure.

They are the:
cardiac rate- Which is the continus movement of blood vessels contracting and relaxing.
stroke volume- Which is the total amount of blood that the heart lets go into the veins with each beat.
peripheral resistance- Which is the opposition between the pressure in the blood and how big the vein or artery is.

-Describe two reflexes that help maintain blood pressure within limits.

Baroreceptor Reflexes- A negative feedback system which buffers short-term changes in blood pressure. Increased pressure stretches blood vessels which activates pressoreceptors (baroreceptors) in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.

Artial Stretch Reflexes- The receptors are activated by increased venous return to the heart and respond by stimulating the reflex tachycardia, as a result of increased sympathetic nerve activity. They inhibit ADH release, resulting in the excretion of larger quantities of urine and a lowering of blood volume, and promote increased secretion of atrial natriuretic peptides (ANP) which lowers blood volume by increasing urine excretion.

How does this pertain to PTA?

This pertains to our feild because when we are working with a patient on exercise we do not want to over work their heart so its life threatening to them. We need to know how much we can push them with out straining the heart too much. Knowing this will be able to help us get them stronger while making sure they dont over do it so they dont end up regressing. We need to be able to know the signs of problems like hypertension, shock, and congestive heart failure so if anything like that comes up we can be ready to act right away to keep them safe. It is also important for us to know how blood pressure works because we take it all the time while working with patients to make sure it stays in the range that its suppose to be in and if its not in the right ranges we will be able to detect how severe it is or if its nothing to worry about.

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