8.5 The Heart Flashcards
Function of the heart
Pumps blood around the body
Which side of the heart has deoxygenated blood?
Right side
Which side of the heart has oxygenated blood?
Left side
What muscle makes up the heart?
Cardiac muscle
Why is cardiac muscle special?
It doesn’t get tired or fatigued like other muscles
It does require an impulse from the brain to contract/relax
What supplies the heart with blood?
Coronary artery - provides oxygenated blood
What is the heart surrounded by? Why?
Inelastic pericardial membrane - prevents the heart over distending with blood
What is the valve between the RA and RL called?
Tricuspid valve
What is the valve between the LA and LV called?
Bicuspid valve
Function of vena cava
Brings deoxygenated blood from other parts of the body
Superior vena cava - blood from the head and neck areas
Inferior vena cava - blood from other areas of the body
Function of aorta
Pumps oxygenated blood out at high pressure to the rest of the body
Function of pulmonary artery
Transports deoxygenated blood from the RV to the lungs
Function of pulmonary vein
Brings back oxygenated blood from the lungs to LA
Where are the semi lunar valves found?
At the opening to the pulmonary artery
What is the septum?
Muscle that separates the two sides of the heart - prevents oxygenated and deoxygenated blood from mixing
Function of tendinous cords
Hold the valves in place
Makes sure the valves are not turned inside out by the pressures exerted when the ventricle contracts
What is the fat covering the heart called?
Epicardial adipose tissue
Why does the LV have a thicker muscle wall than the RV?
Pumps blood out at high pressure, thick walls to withstand the pressure
Blood also has to travel a larger distance
Why is the muscle thicker on the left side of the heart than the right side?
Lungs are relatively close to the heart and much smaller than the rest of the body, so right side has to pump blood for a relatively shorter distance and there is only resistance from the pulmonary circulation
The left side has to pump blood to the whole body and overcome the resistance of the arterial system of the body
Journey of blood through heart
Deoxygenated blood enters the RA of the heart through the superior and inferior vena cava at a relatively low pressure
As blood flows in, oressure builds up in the RA and the tricuspid valve opens to let blood into the RV
When both RV and RA are full of blood, the RA contracts, forcing all blood into RV and tricuspid valve closes
RV contracts fully and pumps deoxygenated blood through the semi lunar valves into the pulmonary artery
At the same time, oxygenated blood enters the LA from the pulmonary vein
Pressure in the LA builds, causing the bicuspid valve to open between the LA and LV so ventricle fills with blood
When both LA and LV are full of blood, LA contracts, forcing all blood into LV
LV contracts, blood flows through semi lunar valves into the aorta, to be transported around the whole body
Cardiac cycle
Events in a single heartbeat - lasts 0.8s
Diastole
Heart relaxes
Atria and then ventricles fill with blood
Volume and pressure of blood in the heart build as the heart fills, but pressure in the arteries is at a minimum
Systole
Atria contract (atrial systole) followed by the ventricles (ventricular systole)
Pressure in heart increases dramatically, blood forced out of heart
At the end of systole, volume and pressure of blood in the heart are low and blood pressure in the arteries is at a maximum.
What are the sounds of heartbeat?
Made by blood pressure closing the heart valves
LUB DUB sound
Lub - blood forced against atrioventricular valves as ventricles contract
Dub - semi lunar valves closed in the aorta and pulmonary artery as ventricles relax
Myogenic
Has its own intrinsic rhythm
How the heart beats
Wave of electrical excitation begins in the pacemaker area (SAN) so that atria contract and initiate heartbeat
This electrical activity is picked up by the AVN and imposes a slight delay before stimulating bundle of His, which penetrate through the septum between the ventricles
Bundle of His splits into 2 branches and conducts wave of excitation to apex of heart
At the apex, Purkyne fibres spread out through the walls of the ventricles on both sides. The spread of excitation triggers contraction of ventricles, starting at the apex
Why does contraction start at the apex?
Allows more efficient emptying of the ventricles
What is the bundle of His made of?
Purkyne fibres
How does an ECG work?
Measures tiny electrical differences in the skin, which are as a result of electrical activity of the heart
Tachycardia
Very rapid heartbeat
When is tachycardia normal?
During exercise, with a fever, or when frightened/angry
Bradycardia
Heart rate slows down below 60 bpm
How can severe bradycardia be treated?
Using an artificial pacemaker
Ectopic heartbeat
Extra heartbeats out of the heart’s normal rhythm
Arrhythmia
Abnormal rhythm of the heart
Atrial fibrillation
Rapid electrical impulses are generated in the atria and contract very fast.
However, they do not contract properly and only some impulses are passed onto the ventricles. Therefore, the heart does not pump blood very efficiently.
