SP&RS 13 Flashcards
The heart as a pump
What are the stats for cardiovascular deaths in the UK?
> 1800,000 year-1 people die from CVD- 1 in 3 of all deaths
Coronary heart disease (CHD)- ~20% male and ~12% female deaths, a total of 82,000
Stroke >49,000 deaths
Heart attack- every 6 min
Are physiological disease more popular in men or women? Neurological diseases?
Physiological: men > women
Neurological: men < women
What is the role of the heart and circulation?
Deliver nutrients and remove waste.
-delivers oxygen and sugar to the respiring tissues
-removes carbon dioxide and the products of metabolism
-delivers hormones to their site of action
-central to homeostasis
What controls breathing rate?
Co2 (removal), not O2.
How much O2 and CO2 does the human heart pump?
5 litres.min-1
delivers ~250ml O2.min-1
removes ~200ml CO2.min-1
What are the stats of the human heart?
-Weighs between 200 to 425g
-It is slightly larger than the size of your fist
-It beats ~100,00/day, pumping ~7,000 (whole body holds ~5000l of blood) litres of blood/day
-Over 80 yrs of life, will beat 3 billion times
Entire life existence is bracketed by the beating of the heart.
What is the order in speed of heart beat? Why?
Mouse (450/min), man (70/min), elephant (28/min)
Mouse has high SA:vol ratio- lots of heat loss, more burning of oxygen to create glucose to generate heat.
Where does the heart sit in the body?
Centrally with the apex situated on the left side, at the level of the 5th intercostal space.
What is the role of heart valves?
Control blood flow.
What is the pressure like in the aorta and veins?
Aorta- high pressure system
Veins- low pressure system
What is the pressure like in the left and right side of the heart? Why?
The left side of the heart operates under significantly higher pressure.
Thinner wall on the right than left.
Deeper/larger volume of blood, therefore higher hydrostatic pressure.
deoxygenated blood is at a lower pressure than oxygenated blood
How much time does the heart spend in systole than diastole?
The heart spends twice as much time in diastole than systole.
Systole:
-actively contracting (ventricular)
-~70ml of blood from each ventricle (both sides have to be equal
-lasts around 300 ms
Diastole:
-relaxation permits filling of the heart
-lasts about 550 ms at 70 beats.min-1
-filling occurs prinipally during the first 100 - 200 ms
What is mean arterial pressure?
1/3 systole + 2/3 diastole
What does cardiac output depend on?
The number of beats and their volume.
Cardiac output = stroke volume x heart rate
E.g. heart rate: 70 beats.min-1 at rest
stroke volume: ~70 mL.beat-1
therefore, cardiac output: ~5 L.min-1
What is Starling’s law of the heart?
‘Energy of contraction is a function of the length of the cardiac muscle fibres’- due to an increased sensitivity of the contractile proteins to Ca2+.
The heart depends on stretching of cardiac muscles.
Output of two pumps in series (e.g. heart) must be equal.
Stroke volume is governed by filling and stretching of muscle.
How does Starling’s law of the heart work?
Increased blood volume = increased stretch of myocardium
Increased force to pump blood out
What is the conduction pathway of the heart from atria to ventricle?
-The heartbeat is myogenic, initiated within the heart itself.
-Sinoatrial node, pacemaker of the heart: specialised muscle cells.
-Travels through the atrial muscle to the atrioventricular node.
-Travels to ventricles through Purkinje fibres of the bundles of His and their branches.
-It then spreads throughout the myocardium.
What does the ionic pacemaker depend on?
Ionic pacemaker potential depends on Ca2+, not Na+.
Depolarisation is generated by a reduced K+ and increased Na+ permeability.
Depolarisation may also be produced by increased Ca2+ permeability.
Unlike an action potential, it does not require a trigger- it acts upon a ‘leak’.
How are myocytes structured?
They are branched muscle cells, with a single nucleus.
Cylindrical cells, often branched, with a single central nucleus.
~50-100 um in length, 5-20 um in diameter.
Striated appearance under microscope.
How are myocytes electrically coupled?
Through intercalated disks.
-Connected by tight junctions, coupled through connexins.
-Contraction activated by entry of Ca2+: principally from intracellular stores and extracellular fluid.
What do intercalated disks allow?
Allow continuous flow.
-Action potential propagate through the electrical connections.
-Current flow creates ECG
How was the first ECG recorded?
Using a bucket of salt and water, water is saturated.
No change in salt, water or metal wire. Conductance around the body will change every time the heart beats.
These are the fundamentals of ECG.
What can ECG scans be used for?
To diagnose cardiac disease.
How can systole, diastole and heart rate be calculated?
Systole = QT interval
Diastole = RR-QT
Heart rate = (n-1/change in T)*60
-n = number of r waves
- change in T = R-R interval
