8.5 The Heart

Explain atrial fibrillation

Abnormal irregular rhythm of the heart -Rapid impulses generated in in atria so contract very fast but don't contract properly.

What is blood pressure affected by?

- Vary as ventricles contract - Diameter of blood vessels

Explain the atrial pressure in the cardiac cycle.

Always relatively low because of the thin walls can't create much force. Highest when contracting but drops when atrioventricular valve closes and walls relax. Atria fills with blood leading to gradual increase in pressure until drop when left atrioventricular valve opens and blood moves into ventricle

Describe the role of the purkyne fibres with relation to the apex

At the apex, purkyne fibres spread through walls of ventricles. These conduct wave of excitation from apexof heart and triggers contraction of ventricles, starting at apex. - Allows efficient emptying of ventricles

Cardiac muscle is myogenic. What does this mean?

Cardiac muscle has its own intrinsic rhythm at 60 bpm. This prevents wasting resources maintaining heart rate Did you know? basic heart rate maintained by electrical excitation

Define systole. What does this mean?

Contraction of the heart - Pressure inside heart drastically increases and blood forced out to lungs and body. - Max, pressure in arteries

What type of muscle is the heart made from and why is it special?

Made from cardiac muscle which contracts and relaxes in a regular rhythm. The muscle does not get tired

Describe the process of blood flow in the right side of the heart

Deoxygenated blood in right atrium from vena cava at low pressure. Blood comes in the atria and pressure increases until atrioventricular valve opens. When atria and ventricle are filled , atria contract forcing all blood into ventricle and stretching walls. As ventricle contracts, tricuspid valves close to prevent backflow. Cords prevent valves turning inside out by pressure. Ventricle contracts fully, blood forced through semilunar valve to the pulmonary artery.

Describe the role of the AVN in the rhythm of the heartbeat

Electrical activity picked up in the atrioventricular node (AVN). - Imposes small delay before stimulating bundle of His which are conducting tissue made of purkyne fibres , which penetrate through septum between ventricles - delay makes sure atria have stopped contracting and have completely emptied before ventricles start.

What are ECGs? What are they used for?

Electrocardiograms record electrical activity of the heart - Tiny electrical differences in the (clean) skin which results as activity of the heart - Diagnose heart problems so they can be treated

Explain ectopic heart beat

Extra heartbeats out of normal rhythm - common but serious when frequent

Why may the heart beat faster?

Factors such as exercise, excitement and stress

What does the cardiac cycle describe?

It describes all of the events in a heartbeat (every 0.8s)

Explain the ventricular pressure of the cardiac cycle.

Low at first but gradually increases as ventricles fill with blood as atria contact. Left atrioventricular valve close and pressure dramatically rises as ventricular walls contract. As pressure rises above the aorta, blood is forced into aorta past semilunar valves Pressure falls as ventricles empty and walls relax

How is blood pressure measured?

Manual sphygmomanometer where cuff inflates until blood supplying to arm, is cut off. Stethoscope placed over vessels at elbow. Pressure of where blood sound first appears, is recorded Systolic blood pressure measured by height of mercury at this point Diastolic blood pressure measured when blood return to normal as pressure decreases

What is the role of coronary arteries?

They supply the cardiac muscle with oxygenated blood

Describe the process of blood flow in the left side of the heart

Oxygenated blood from the lungs enters pulmonary vein and into the left atrium. Atrium pressure increases so bicuspid valve opens. Left ventricle fills with blood. Atria contract so ventricle is full with all the blood. Left ventricle contacts as pressure increased. The bicuspid valves close. Blood forced through semilunar valves, to the aorta and out to the body

Describe the role of the bundle of His in the rhythm of the heart beat

Penetrate through septum between ventricles and splits into two branches and conducts wave of excitation to apex of heart.

Define diastole. What does this mean?

Relaxation of the heart - atria and then ventricles fill with blood. Volume and pressure of blood increases as heart fills - min. pressure in arteries

What type of blood is transported by the left and right side of the heart

Right side: deoxygenated blood (body to lungs) Left side: oxygenated blood (lungs to body) Blood from both sides do not mix because of the septum

Explain the ventricle volume of the cardiac cycle

Rise as atria contract and ventricles fill with blood. Suddenly drops as blood forced into aorta when semi-lunar valves open. Volume increases again as ventricles fill with blood.

Explain the aortic pressure in the cardiac cycle. (top dotted line)

Rises when ventricles contract as blood forces into aorta. Gradually falls but not below 12kPa due to recoil. Recoil produces temporary rise in pressure at start of relaxation phase (diastole)

What is the heart surrounded with and why?

Surrounded with inelastic pericardal membranes which prevent the heart from over-distending with blood

Why does the left side of the heart need thicker muscular walls?

The left side pumps blood a longer distance and has to overcome greater resistance. More pressure is needed and so thicker walls are required to create such force.

Describe the role of the SAN in the rhythm of the heartbeat

Wave of electrical excitation begin in sino-atrial node (SAN), causing atria to contract and initiate heartbeat - layer of non-conducting tissue prevents excitation passing directly to ventricles

Explain bradycardia

When heart rate slows down below 60 bpm - common in fit people as training makes heart beat more slowly and efficiently - If severe, can lead to an artificial pacemaker

Explain Tachycardia

When the heartbeat is very rapid, over 100 bpm - common if you have a fever , frightened, angry or when exercising - treated with medication or surgery

What causes a hole in the heart? How can it be repaired?

When the septum is has a hole in it. Repaired by surgery. did you know? development not complete until after birth

Label the heart diagram

a: superior vena cava b: inferior vena cava c: right atrium d: tricuspid valve (right atrioventricular valve) e: right ventricle f: semi-lunar valves g: left pulmonary artery h: right pulmonary artery i: pulmonary vein j: left atrium k: bicuspid valve (let atrioventricular valve) l: left ventricle m: semi-lunar valve n: aorta o: carotoid arteries p: septum q: thick muscular wall r: tendinous cords

What creates the lub-dub sound?

opening and closing of valves - Blood forced against atrioventricular valves as ventricles contract - Back-flow of blood closes the semi-lunar valves as ventricles relax