Lecture 6 Flashcards
Does aortic and arterial pressure rise or fall in diastole/early systole?
Falls.
What name refers to the minimum pressure?
Diastolic pressure. (DP)
Does the pressure rise or fall when the aortic valve opens?
Rise.
What name refers to the maximum pressure?
Systolic pressure. (SP)
How do you measure systolic blood pressure?
Place cuff above elbow, and pump up to the point you can’t hear sounds any more using stethoscope on lower arm.
How do you measure diastolic blood pressure?
Release pressure in cuff, until you can’t hear pulse any more in lower arm.
Normal blood pressure?
120/80 mm Hg.
Hypertension levels?
140-159/90-99 mm Hg.
Severe hypertension levels?
> 159/>99 mm Hg.
What 4 main causes increase the risk of hypertension?
Obesity, high cholesterol, smoking, genetic disposition.
What is atherosclerosis, and which condition does it relate to?
Build up of fatty deposits in walls of arteries, causing narrowing of the lumen.
Relates to hypertension.
Why does blood pressure tend to rise with age?
Reduced elasticity of the arterial system.
Is heart muscle neurogenic or myogenic, and why?
Myogenic.
Signals to contract arise from the heart itself.
What word can be used to describe the heart’s ability to regulate its beat?
Autorhythmicity.
What two types of cells make up the heart, and how do they differ?
Myocardial cells (contractile muscle). Pacemaker cells (not contractile, generate electrical impulses).
The pacemaker cells are concentrated in two regions of the myocardium. Where are these and what are they called?
Sinoatrial node (SA node), upper right atrium. Atrioventricular node (AV node), near tricuspid valve.
What do conduction fibres do?
Spread electrical signals from SAN and AVN throughout the heart muscle.
What is the interatrial pathway?
… is it quick or slow?
SA node -> right atrium -> left atrium.
What is the internodal pathway?
SA node -> AV node.
Is AV node transmission quick or slow?
Slow - 0.1s.
In the interatrial pathway, do the right and left atria contract simultaneously?
Yes.
Is there a steady membrane potential in pacemaker potentials?
No, because action potential triggered, before membrane slowly depolarises, and another action potential is initiated.
Which ions are required to generate pacemaker potentials?
… Is the concentration of these ions particularly different to other cells?
Na+, K+, Ca2+.
Similar concentration to other cells.
What is the slow depolarisation due to?
The funny channels controlling movement of K+ and Na+.
What is the cardiac action potential mainly due to?
Ca2+.
What happens during slow depolarisation?
K+ channels close.
Funny channels open.
Slower efflux of K+.
Influx of Na+.
What happens just before cardiac threshold?
Ca2+ channels open.
Slow influx of Ca2+.
What happens at the threshold?
Rapid Ca2+ influx.
What happens at repolarisation?
Ca2+ influx decreases.
K+ efflux increases.
On average, how often does the cardiac cycle occur over a lifetime?
100,000 times/day.
36.4 X 10^6 times/year.
3000 X 10^6 times/lifetime.
What type of ion channels are the calcium channels that open before rapid depolarisation?
T-type voltage gated calcium channels.
What type of ion channels are the calcium channels that open after rapid depolarisation?
L-type voltage gated calcium channels.
What is cardiac output, and what is it determined by?
Volume of blood pumped out of each ventricle in one minute.
Determined by:
- Heart rate (HR) (bpm)
- Stroke volume (SV) (cm3)
What is the formula for Cardiac Output?
CO = HR * SV
Average HR and SV?
Average HR = 72bpm.
Average SV = 70cm3.
What is the average cardiac output (approximately?
~5 litres/minute.
What neurotransmitter does the vagus nerve (parasympathetic) use? And what does it connect?
Acetylcholine.
Connects medulla oblongata to SA and AV nodes.
What neurotransmitter does the sympathetic cardiac nerve use? And what does it connect?
Noradrenaline.
Medulla oblongata to spinal cord, to sympathetic trunk, to SA, AV nodes and ventricular myocardium.
What 3 effects does sympathetic input have on the heart?
Increases action potential frequency at SA node (heart rate increases).
Decreases delay at AV node (ventricular contraction starts sooner).
Increases contractile force of cardiac muscle.
What effect does parasympathetic have in relation to the sympathetic system?
The opposite effect.
What hormone enhances sympathetic input?
Adrenaline.
What 3 factors is stroke volume affected by?
- Ventricular contractility.
- End-diastolic volume (EDV).
- Afterload.
What effect does sympathetic input and adrenaline have on ventricular contractility?
Gives increased force.
What affects the degree of stretching of cardiac muscle?
The volume of blood in the heart at the end of diastole.
What is afterload?
The back-pressure in the arteries.
What is Starling’s Law of the Heart?
When the rate at which blood flows into the heart from the veins changes, the heart automatically adjusts its output to match the inflow.
If an increase in end-diastolic volume occurs, what happens to the force of ventricular contraction, and why?
Force of ventricular contraction rises, producing increase in stroke volume and cardiac output.
Does the stretching of muscle fibres increase or decrease contraction force?
Increase.
