Topic 11

How is it possible that when a heart is transplanted from one individual to another it can still beat on its own?

-A very important control mechanism called the pacemaker, alternately known as the sinoatrial (SA) node. -SA node is located at the top of the right atrium. -The SA node sends out electrical impulses that tell the heart to beat at a rate between 60 to 100 bpm.

Peripheral Vascular Disease (PDV)

A condition caused by a narrowing of the arteries in the legs, resulting in a lack of blood flow to the thighs, calf muscles, and feet. Symptoms generally include: Pain Fatigue in the lower extremities Burning sensation in the calf muscle. The disease strikes both men and women, African-American's are at a greater risk. Smoking greatly increases a person's risk. Exercise lowers the risk and lessens the symptoms. Medications to dilate arteries and prevent clots help control the disorder. In severe cases, surgery or the placement of a stent to open the narrowed artery may be required.

Heart Failure

A condition in which the heart cannot adequately pump blood to meet the oxygen needs of the body, or the heart muscle becomes stiff and has difficulty filling with blood. Heart failure can occur in either ventricle, most commonly occurs in both. When the heart's pumping ability diminishes, fluid backs up in the lungs, liver, arms, legs, and GI tract. Other symptoms include: Shortness of breath Cough Edema (excess fluid) in the ankles Weight gain Frequent urination (particularly at night) Several different drugs are used to treat heart failure, often with very good outcomes. The most common cause of heart failure is coronary artery disease, but it can also be caused by infection that weakens the heart muscle, called cardiomyopathy. Heart failure usually happens gradually, but can develop quickly after a heart attack has damaged the heart muscle. Heart transplants are usually performed on individuals with end-stage heart failure and on children with congenital heart defects (although transplantation into a child is rare).

Arterial Supply of the Brain and the Circle of Willis

A continuous supply of blood to the brain is crucial. The brain is supplied by two pairs of arteries, the carotid arteries (left and right) and the vertebral arteries (left and right). Once inside the cranium, the left and right carotid arteries, divide into anterior and middle cerebral arteries, which supply most of the cerebrum.

Electrocardiogram (ECG or EKG)

A record of overall spread of electrical activity through heart . Impulses can be detected on the body surface and recorded. Illustrates what is happening electrically in the conduction system and mechanically in the atria and ventricles when they depolarize (contract) and repolarize (relax). Wave = upwards or downwards deflection Segment = flat portion between waves Interval = often a wave plus a segment An ECG is a piece of graph paper containing a record of the electrical events in the heart. The placement of electrodes on the body surface affects the size and shape of the waves. This example shows a normal ECG and a summary of electrical and mechanical events.

Cardiac Circulation

Although the heart chambers are bathed with blood almost continuously, the blood contained in the heart does not nourish the myocardium. The blood supply that oxygenates and nourishes the heart is provided by the right and left coronary arteries. The coronary arteries branch from the base of the aorta and encircle the heart at the junction of the atria and ventricles. The myocardium is drained by several cardiac veins, which empty into an enlarged vessel on the backside of the heart called the coronary sinus. The coronary sinus, in turn, empties into the right atrium. When the heart beats at a very rapid rate, the myocardium may receive an inadequate blood supply because the relaxation periods (when the blood is able to flow to the heart tissue) are shortened. Situations in which the myocardium is deprived of oxygen often result in crushing chest pain called angina pectoris. This pain warning should never be ignored. If angina is prolonged, the ischemic heart cells may die, forming an infarct. The resulting myocardial infarction is commonly called a "heart attack" or "coronary."

Cardiac Output

An important measurement because it can have an effect on blood pressure, cardiovascular fitness level, and body temperature. Cardiac output (Q) is the amount of blood pumped from the heart per minute. Units of measurement is liters per minutes (L/min). The number of units is determined by multiplying the heart rate (HR) and the stroke volume (SV). Stroke volume is the amount of blood pumped from the heart per beat, and the units are milliliters per beat (ml/beat). SV X HR = Q (ml/beat) (beats/min) (cardiac output) The average HR and SV for a male are ~ 72bpm and 70 mL/beat , which means the cardiac output is 5, 040 Liters/min.

Hypertension

Another word for high blood pressure. It occurs when the force of blood against the arterial wall remains elevated for an extended period of time. In many cases, doctors are unable to determine the cause. Individuals with a BP reading greater than 140/90 mmHg on three separate occasions are considered to have high BP. Many people don't know they have high blood pressure because there are often no symptoms, thus it is called the silent killer. CDC estimates one in five US adults has high BP and doesn't know it. Approximately one-third of the people in the US have high BP, and the risk of developing it increases with age. When energy intake exceeds the body's energy needs, the excess energy is stored for future use, in the form of triglycerides or glycogen. Because the body's glycogen storage capacity is limited, chromic energy excess leads to fat formation and obesity. In turn, obesity increases the risk of hypertension, stroke, and coronary artery disease. Risk factors for developing hypertension: family history, obesity, smoking, & physical inactivity.

Taking Vital Signs

Blood pressure is measured at the brachial artery using a stethoscope and a sphygmomanometer (blood pressure cuff). Inflating the cuff causes the brachial artery to collapse. As the cuff is deflated, the brachial artery gradually reopens, and you can hear the pulse, which creates a tapping sound. When the artery is completely open, the tapping sound disappears. The systolic BP is the pressure in the brachial artery when the left ventricle contracts. The diastolic BP is the pressure in the brachial artery when the left ventricle is relaxed and filling with blood.

Blood Flow through the Heart

Deoxygenated blood enters the right atrium from both the superior and inferior vena cava. The blood collects in the right atrium. The collecting blood increases in pressure against the tricuspid (AV) valve, causing the valve to open. At this stage, with the tricuspid valve open, the right ventricle fills passively. Then, the right atrium contracts, forcing the remaining blood into the ventricle. Now the right ventricle contract, and pressure increases in the chamber. This causes the tricuspid valve to close and the pulmonary valve to open, forcing blood into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it becomes oxygenated in the capillary network of lungs. Oxygenated blood returns to the left atrium via the pulmonary veins. Blood collects in the left atrium, causing pressure to increase in the chamber, thereby forcing the mitral (AV) valve to open. At this stage the left ventricle is filling passively. Atrial contraction forces the remaining blood into the left ventricle The ventricle contracts, and the pressure increases in the chamber. The increased pressure in the chamber causes the mitral valve to close and the aortic valve to open. The blood is forced into the aorta. Oxygenated blood begins its journey of supplying oxygen to all parts of the body.

Pulmonary circulation:

Deoxygenated blood enters the right atrium from the IVC & SVC. Deoxygenated blood flows through the tricuspid valve into the right ventricle. The right ventricle contracts and deoxygenated blood is ejected through the pulmonary valve into the pulmonary artery. The pulmonary artery splits into two smaller arteries, which carry the deoxygenated blood to the lungs. The two smaller pulmonary arteries branch into arterioles that merge with the capillary network into the lungs. The blood becomes oxygenated in the lungs and then flows through the venules, which merge with four pulmonary veins that carry the oxygenated blood back to the heart. The pulmonary veins empty oxygenated blood into the left atrium. Oxygenated blood flows through the mitral (AV) valve into the left ventricle The left ventricle contracts and ejects oxygenated blood through the aorta to the rest of the body

Walls of the Heart

Enclosed by a fluid-filled, doubled membraned sac called the pericardium. The fibrous outer wall of the sac anchors the heart to the surrounding structures, such as the sternum, diaphragm, and lungs. The inner wall of the sac is divided into two layers, which are separated by a fluid filled cavity that allows the heart to beat in a frictionless environment.

Hepatic Portal Circulation

Hepatic portal circulation plays a vital role in maintaining proper carbohydrate, fat, and protein levels in the blood. The hepatic portal circulation does something unusual. Whereas the arteries supplies blood to different parts of the body, the veins of the hepatic portal circulation supply the blood to the liver.

Heart Attack

If an artery becomes completely blocked, a myocardial infarction, or heart attack, occurs. This can happen suddenly when a piece of arterial plaque ruptures and occludes (closes) the artery. Basically, blood flow to the heart is reduced. The first two phases of a heart attack are ischemia and injury to the heart tissue. These phases are reversible with proper intervention; but there is only a 20-60 minute window before death of cardiac tissue occurs, which is irreversible

Fetal Circulation

Most blood enters the fetus through the ductus venosus vein, bypassing the liver and going directly to the right atrium by way of the IVC. Blood bypasses the right ventricle and is shunted (diverted) to the left atrium because of an opening in the septal wall, between the atria, called the foramen ovale. A small amount of blood does go to the right ventricle, but it is drained through the ductus arteriosus, a vessel that connects the pulmonary artery to the aorta. Once the blood is pumped from the left ventricle, the oxygenated blood flows through the infant's body. Deoxygenated blood returns to the placenta via the umbilical arteries. Shortly after birth, the foramen ovale, ductus arteriosus and venosus close.

The Conduction System (Pathway of an impulse generated by SA node)

Once the SA node fires, the electrical impulse is carried to the left atrium via Bachmann's bundle. The impulse also goes to the AV node via three internodal pathways. The AV node (only point of electrical contact between chambers) is a very dense network of fibers, which causes the electrical impulse to get "tied up", or delayed there for approximately a tenth of a second. This delay ensures atrial contraction precedes ventricular contraction to allow complete ventricular filling Once the electrical impulse leaves the AV node it is carried through conducting fibers called the AV bundle (bundle of His) in the interventricular septum. The AV bundle/bundle of His then divides, and the electrical impulse travels down the left and right bundle branches to millions Purkinje fibers in both ventricles. When the Purkinje fibers receive the impulse, they stimulate the ventricles to contract. Cells in the ventricles are activated by cell-to-cell spread of impulse through intercalated disks that connect cardiac muscle cells.

Symptoms of Cardiovascular Disease

People with cardiac symptoms should take an aspirin (works as a blood thinner) and call 911 within 5 minutes of onset of the symptoms. Symptoms are early warnings, giving the person a chance to survive. Others are not so lucky: n approximately 1/3 of all heart attacks, the first symptom is death. It was long thought, mistakenly, that heart disease was primarily a problem for men.

Taking Vital Signs pt2

Place the BP cuff around the arm (about two fingertips above the fold in the elbow), with the arrow on the cuff pointed toward the brachial artery Place the head of the stethoscope over the brachial artery. Squeeze the bulb of the cuff repeatedly, while listening for a "tapping" sound. Continue to pump up the cuff 30 mmHg more after the "tapping" sound stops. This would be ~150mmHG for someone with a normal blood pressure of 120/80 mmHG Open the release valve so that the cuff deflates at the rate of about 2 mmHG/second. The first "tap" that you hear is the systolic blood pressure. The last muffled sound that you hear is the diastolic blood pressure. The systolib BP is the pressure in the brachial aretey when the left ventricle contracts. The diastolic BP is the pressure in the brachial artery when the left ventricle is relaxed and filling with blood.

Premature atrial contractions (PACs)- a condition in which an irritable piece of atrial heart tissue fires before the SA node. This causes contraction to occur too early in the rhythm. Usually PACs are harmless. Caffeine ingestion, other stimulates, and stress can increase their likelihood.

Premature atrial contractions (PACs)- a condition in which an irritable piece of atrial heart tissue fires before the SA node. This causes contraction to occur too early in the rhythm. Usually PACs are harmless. Caffeine ingestion, other stimulates, and stress can increase their likelihood.

Capillary

Single layer of epithelial cells; only layer is the tunica intima. Gas/nutrient and waste-product exchange between blood and tissues

Heart Attack Can stems cells help repair the heart?

Stem Cell Therapy using Cardiac Cells A possible and hopeful solution for patients with damaged heart tissue, as it can promote tissue regeneration in the heart. Thousands of patients have had stem cell therapy for heart disease by direct and/or indirect stem cell injections. Has been shown to clearly improve ventricular performance, survival rates and most importantly the quality of life with no side effects.

You now know that oxygen is supplied to the body by the arteries, which carry blood away from the heart. But how does the heart receive its oxygen supply?

The blood circulating through the chambers of the heart does NOT supply oxygen to the heart.

External Control of the Heart (The Cardiac Center)

The cardiac center is located in the medulla oblongata. It has sympathetic and parasympathetic branches (collectively referred to as the autonomic nervous system-ANS). The cardiac center is always making adjustments in heart rate (HR), contraction strength, and stroke volume. It gives the heart a "green light" (sympathetic stimulation) when it wants the heart rate (HR) to increase or a "red light" (parasympathetic stimulation) when the HR needs to slow down. Baroreceptors that are sensitive to pressure are located in the atrium of the heart, aortic arch, and carotid arteries. They constantly monitor blood pressure and send sensory information back to the cardiac center stimulating either the parasympathetic or the sympathetic braches. The parasympathetic branch is dominant while you are at rest, which is why your HR is low at rest. As necessary, acetylcholine is released to decrease HR. The cardiac center is also affected by emotions and physical activity affect the cardiac center. The sympathetic branch takes over during exercise or if you are emotionally stressed (fear, anxiety).

Cardiac Cycle

The cardiac cycle consists of two phases: contraction and relaxation. During one complete cardiac cycle, the four chambers of the heart undergo a period of relaxation, called diastole when the chambers are filling with blood. Each cycle also includes a period of contraction called systole, when the chambers are pumping blood out of the heart. Systole and diastole mean heart contraction and relaxation, respectively. Since most of the contraction is done by the ventricles, these terms always refer to the contraction and relaxation of the ventricles. In a healthy heart, when the atria contract, the ventricles are relaxed. When the ventricles contract, the atria are relaxed. During systole, atrioventricular valves are closed and semilunar valves are open. Number listed on top (ex. 120/80); represents the amount of pressure exerted on artery walls during actual contraction (pumping) In diastole, AV valves are open to allow ventricular filling and semilunar valves are closed to prevent backflow of blood to the heart from either systemic circulation or pulmonary circulation. Number listed on bottom (ex. 120/80); represents pressure in artery during relaxation of the heart One cardiac cycle is approximately 0.81 second in duration. In general, for an individual who has a resting heart rate (HR) of 72 to 82 bpm, approximately two-thirds of the cardiac cycle is spent in diastole, and one-third is spent in systole. This ratio is the basis for the formula mean arterial pressure (MAP). MAP= 2/3 Diastolic BP + 1/3 Systolic BP The MAP measures the overall pressure within the cardiovascular system, which determines blood flow to various organs. If this pressure falls below 60 mmHG (millimeters of mercury), the organs of the body will become damaged from lack of oxygen. A lower BP also means that the body will not receive the nutrient rich blood flow that it needs. During the cardiac cycle, the AV valves and the semilunar valves makes sounds when they close. Normal heart sounds are caused by the closing of heart valves. As valves snap shut, the walls of the chambers and major arteries vibrate The sounds are referred to as "lub-dup". The "lub" sound is produced when the AV valves close and the "dup" sound is produced when the semilunar valves close, If the valves don't close properly, there may be an additional sound called a heart murmur. In children, most murmurs are harmless and are caused by rapid growth spurts rather than a heart abnormality.

Associated Vessels

The heart functions as a dual pump with each half of the heart beating together in unison during a single cardiac cycle. The right atrium receives deoxygenated blood from the venous system (system of veins) via the inferior vena cava and superior vena cava after the blood has made its trip around the body. The right ventricle then pumps the blood to the lungs. The left atrium receives the oxygenated blood from the lungs, and the left ventricle then pumps the blood through the aorta to the body. The two ventricles contract almost simultaneously-as the right ventricle pumps blood to the lungs, the left ventricle pumps blood to the body.

The Four Chambers of the Heart

The heart has 4 hollow chambers/cavities: Right and left atria and right and left ventricles. The superior atria are primarily receiving chambers-as a rule-they are not important in pumping activity. Blood flows into the atria under low pressure from the veins of the body and then continues to fill the ventricles. The inferior, thick-walled ventricles are the discharging chambers, or actual pumps of the heart. When ventricles contract, blood is propelled out of the heart and into circulation through outgoing arteries. An interatrial septum separates the right and left atria, and the two ventricles are divided by a much thicker interventricular septum. The septal walls prevent oxygen-rich blood from mixing with oxygen-poor blood.

The Heart Valves

The heart is outfitted with 4 valves which permit blood to flow in only one direction-from the atria through the ventricles and out the great arteries leaving the heart. The valves are made of sheets of tough connective tissue that act like flaps. The heart valves open and close passively because of pressure differences on either side of the valve. When pressure is greater behind the valve, the flaps are blown open and the blood flows through the valve. However, when pressure is greater in front of the valve, the flaps snap shut and blood flow is stopped. The opening/closing of the AV valves is dependent on pressure differences between the atria and ventricles. When the ventricles relax, atrial pressure exceeds ventricular pressure, the AV valves are pushed open and blood flows into the ventricles.

The Heart: Location and Size

The human heart is the hardest working organ in the human body. A normal adult heart beats 72-82 times per minute (bpm). Approximately the size of a person's fist, hollow, weighs less than 1 lb (~8-10 oz. in women and ~10-12 oz. in men). Located in the thoracic cavity deep to the sternum. It is centered in the chest and tilted slightly to the left. The heart is flanked on each side by the lungs and it sits on top of the diaphragm. The broad base of the heart is positioned closer to the neck, at the second rib. The large vessels emerge from the base of the heart. The pointed apex, or bottom of the heart, lies at approximately the fifth rib and points down toward the left hip. Below is a cross (transverse) section through the body at the level indicated in the diagram on the previous slide.

Systematic Circulation

The major arteries of the body. Notice the arteries branch into smaller and smaller vessels, eventually becoming arterioles. The arterioles will merge with capillaries, where tissue and blood exchange nutrients and waste materials. The journey back to the heart begins with blood draining into the venules, which merge to form veins. The major veins that drain from the head to the trunk, as well as the upper and lower limbs. Generally, the names of the veins are the same as their arterial counterpart (for example, renal artery and renal vein). The systemic circulatory journey ends when the blood from the lower veins enters the inferior vena cava and blood from the upper veins empties into the superior vena cava. Both inferior and superior venae cavae drain into the right atrium.

Cardiac Circulation

The oxygen-rich blood that nourishes the heart is supplied by the right and left coronary arteries that lie on the epicardial (outermost) surface of the heart. The right coronary artery has two main branches, which supply blood to the inferior and posterior walls of the heart. The left main coronary artery divides into two arteries (the left anterior descending branch and circumflex artery) that supply oxygen-rich blood to the anterior, lateral, and posterior walls of the heart. The coronary arteries arise from the base of the aorta and fill when the ventricles are relaxed. The coronary arteries are closed when the ventricles contract, so they are protected from the high pressure generated during contraction. Blood from coronary arteries empties into several cardiac veins, which drain into the coronary sinus, located on the posterior wall of the right atrium.

There are many other arteries that arise from the aorta:

The right and left coronary arteries branch from the ascending aorta and supply the heart with blood (coronary circulation). The brachiocephalic artery, left common carotid, and left subclavian arteries branch from the aortic arch and supply the head, neck and arms with blood. These arteries subdivide into many more arteries. Many arteries branch from the descending aorta, supplying blood to various organs including the liver, kidneys, stomach, and the rest of the lower body.

How does this process work?

The venous blood that drains from the stomach (gastric vein), spleen (splenic vein), pancreas, small intestine & colon (mesenteric veins) is nutrient rich and is delivered to the liver through the hepatic portal vein. This blood is rich with nutrient sources from carbs and fats. As the blood percolates through the liver, some of the nutrients are removed, stored, or repackaged for another use. The best example is the fate of glucose. After a meal, the blood that drains into the liver may be high in glucose. The liver, which plays a role in regulating blood glucose levels, stores glucose as glycogen until the body needs the glucose for energy. Let's suppose a person is exercising and their blood glucose level starts to drop. As this happens, the liver breaks down its stored glycogen and releases it into the bloodstream as glucose, thereby maintain blood glucose levels. Once blood has been filtered by the liver, it returns to the IVC through the hepatic veins.

Venule

Thin-walled vessels bundled together to form a vein Transports blood from capillary to vein

Arteriole

Thinner; three-walled vessel, mostly smooth muscle Transports blood from arteries to capillaries; sympathetic NS has a greater impact on arterioles; acts to direct blood flow in the body

Artery*

Three-layered vessel (intima, media, externa); thick, elastic, muscular walls Transports oxygen-rich blood away from the heart; influenced by the sympathetic NS (contraction/dilation)

Vein

Three-layered vessel (intima, media, externa); thin-walled vessel with one-way valves. Transports oxygen-poor blood back to the heart

Functions of the Cardiovascular System

Transportation of oxygen and other nutrients; Removal of CO2 and other waste products; Regulation of body temperature Vasoconstriction-decrease in the diameter of blood vessels, which decrease blood flow. Vasodilation-expansion in the diameter of blood vessels, which increases blood flow Maintenance of the body's acid-base balance; Transportation of hormones; and Assistance with immune function

Cardiac Arrhythmias

Usually the heart follow a sequence of events at regular intervals. Sometimes, however, a beat comes too soon, or the conduction system may not work properly, and an abnormal heartbeat occurs. This irregularity if called an arrhythmia. Generally, arrhythmias that originate in the atria or AV node are not a problem, but those that originate in the ventricle are more dangerous and can be life threatening. Ventricular arrhythmias can affect blood flow to the heart and the rest of the body whereas atria arrhythmias do not. Arrhythmias have many causes including damage to the heart muscle (such as from a heart attack); coronary artery disease; hypertension; smoking; excessive alcohol consumption; excessive caffeine ingestion; electrolyte imbalances, illicit drug use; dietary supplements that contain stimulants; stress; and medications. The ECG is the best too for detecting abnormal rhythms. Abnormalities in the shape of the wave and changes in their timing send signals that something may be wrong with the system. Example: waves may indicate a MI (present or past); MI is an area of heart tissue in which the cardiac cells have died; generally a result of ischemia (loss of circulation) resulting in dead tissue. Angina pectoris-Chest pain, resulting from ischemia of myocardium.

Valvular stenosis

Valvular stenosis -a narrowing of the heart valve due to stiff or fused valve cusps. Can occur in one or more valves, making the heart work very hard to pump blood through a smaller-than-normal valve opening. Mild cases of stenosis may be symptom free Moderate cases may need to restrict physical activity Severe cases may require surgery to replace the valve.

Heart murmurs

are caused by abnormal blood flow in heart; faulty valve --Abnormal heart sounds (whooshing or swishing) of the heart upon auscultation-the act of listening to internal sounds of the body using a stethoscope-that are caused by one of the heart valves not closing properly. Common in young children (which usually doesn't require treatment) Can be caused by congenital heart defects, which are present at birth, and valvular disease, as a result of aging, infection, or other disease.