Heart Flashcards
Label the heart diagram
Valves
Prevent the backflow of blood. They open and close in response to blood pressure changes
Why does the heart have a thick muscular wall?
To pump blood outside of the heart
What does myogenic mean?
The contraction of cardiac muscle- it is generated in the muscle itself without being stimulated by a nerve. When a muscle cell contracts it stimulates adjacent cells to contract
Cardiac cycle
The sequence of events that repeats with every heartbeat
Systole
Phases of contraction
Diastole
Phases of relaxation
Heart rate
Frequency of the cardiac cycle
Describe the events of the cardiac cycle
-The sinoatrial node initiates the cycle by firing an electrical signal, which is propagates and stimulates contraction
- The signal first spreads throughout the walls of both atria causing them to contract
- Blood is pumped from atria to ventricles through the open atrioventricular valves. The semilunar valves are closed, so the ventricles fill with blood
- After a time delay the signal passes to the ventricles, which contract and the pressure inside them rises rapidly
- The increase in pressure first causes the AV valves to close
- It then causes the semilunar valves to open
- Blood is pumped out into the arteries
- Atria start to refill by receiving blood from veins
- Ventricles stop contracting, the pressure inside them drops rapidly and the semilunar valves close
- When ventricular pressure is below atrial pressure, AV valves open and blood starts filling the ventricles
- When atria are filled and ventricles are 70% filled the cycle has ended
- The SA node fires again, the atria contract and the new cycle begins
What is the sinoatrial node?
The SA node initiates the heartbeat. It is called the pacemaker because it sets the pace for the beating of the heart. It is in the wall of the right atrium. It initiates the heartbeat by contracting spontaneously and producing an electrical signal, which stimulates contraction. The signal first spreads to the walls of atria.
Describe the control of heart rate
-The contraction of the heart is myogenic
-The SA node initiates the heartbeat. It contracts and the signal spreads stimulating contraction
- The AV node delays the passing of the signal to the ventricles
- While the basal heart rate is determined within the heart by the SA node, it can regulated by external signals
- The rate can be increased or decreased
- Two nerves bring impulses to the SA node to alter heart rate (vagus nerve) The two nerves originate in the brain medulla
- The SA node also responds to the hormone epinephrine by increasing the heart rate
What does low pressure, low O2 concentration and low pH indicate?
That heart rate should increase
Coronary arteries
The arteries that supply the cardiac muscle with oxygen and nutrients
Coronary heart disease
The damage to the heart as a consequence of blockages in coronary arteries and reduced blood supply to the heart tissues
Atherosclerosis
The hardening of the arteries caused by the formation of fatty plagues on the inner lining of arteries
How do plagues form?
Due to high levels of trans unsaturated fatty acids and cholesterol in the blood. Minerals and other material also deposit in the plaque and harden the artery wall
How does CHD happen?
The lumen of arteries narrows. Blood flow to the heart is restricted. If atheromas rupture, blood clots form which might block the artery completely. The blood clot is called a thrombus and the condition is called thrombosis. Platelets play an important role in clot formation.
What is the result of coronary thrombosis?
An area of cardiac muscle does not receive oxygen
Fibrillation
The uncoordinated contraction of cardiac muscle
Factors that correlate with a greater incidence of thrombosis, CHD and hypertension
-genetic factors
-high cholesterol levels
-diet- high levels of trans fats
-obesity
-diabetes
-smoking
-lack of exercise
-hypertension
-high-salt diet [overconsumption of alcohol, coffee and stress]
-sex
-age
See the image in the notes. Describe the pressure changes.
- atria contract causing a small increase in pressure which pumps blood to the ventricles
- semilunar valves are closed so the pressure in the arteries gradually drops to its minimum as blood continues to flow along them but no more is pumped in
- ventricles contract with a rapid pressure builds up, which causes the atrioventricular valves to close. The semilunar valves remain closed.
- when the pressure in the ventricles is above the pressure in the arteries, the semilunar valves open and blood is pumped from ventricles to arteries
-pressure slowly rises in the atria as blood drains into them from veins - the ventricles stop contracting, the pressure inside them rapidly drops below the pressure in the arteries, causing the semilunar valves to close. The AV valves close.
Cardiac muscle cells
They have one nucleus
Adaptations of cardiac muscle
- Cardiac muscle cells are connected; the junction between two cardiac muscle cells is called intercalated discs. In the intercalated disc there are gap junctions, which form channels of connected cytoplasm between the cells. These channels allow rapid movement of ions and this rapid conduction of electrical signals from one cell to the next.
- Cardiac muscle cells are Y-shaped and joined end to end in a complex network of interconnected cells. This allows electrical signals to be propagated rapidly throughout the heart wall; the network of cells contracts as it it was one large cell.
- Cardiac muscle cells have many mitochondria to release lots of energy.
- They have myofibrils divided into sarcomeres.
How does the impulse spread to the ventricles?
- Action potentials are initiated at the SA node myogenically
- the impulse spreads rapidly in all directions through the walls of the atria leading to atrial contraction
- the signal cannot pass directly from the atria to the ventricles, Instead it reached the AV node
- There is a delay between the arrival and passing of the signal at the AV node
- This delay ensures that atria contract and empty blood into the ventricles before ventricles contract. Contraction of ventricles closes the AV valves, so early ventricular contraction would lead to too small blood volume entering the ventricles
- The AV bundle receives the signal from the AV node
- The bundle branches conduct the signal through the septum
- At the base of the heart the bundle branches connect to Purkinje fibres which conduct the signal even more rapidly to the ventricles causing coordinated contraction of the ventricles
