Cardio lecture 1

Question 1

Circulatory system consists of two circuits: systemic and pulmonary circulation. Describe the flow of blood through the heart.

Answer 1

Pulmonary circulation: supplies lungs with deoxygenated blood via pulmonary arteries. Blood receives oxygen from lungs also where CO2 is removed, then returns to left side of heart via pulmonary vein.

Left side of heart pumps oxygenated blood into aorta and around the body. Deoxygenated blood returned to right side of the heart via vena cava.

Question 2

What are the vessels of the heart?

Answer 2

Arteries -> arterioles -> capillaries -> venules -> veins

Question 3

Each vessel is specialized for their different roles. What is the role of arteries?

Answer 3

Arteries – carry blood away from the heart. They are thick walled and elastic.

Question 4

You can feel the stretching of vessel wall with each heart contraction when taking a pulse. The relaxation of arteries between each beat, causes stored blood to _____________

Answer 4

continue to flow between heart beats.

Question 5

Which vessel allows for the exchange of gasses and electrolytes?

Answer 5

Capillaries – Highly branching, thin walled vessels.

Maximize the SA over which gas and electrolyte exchange takes place between blood and tissues. (one cell thick)

Question 6

Arterioles – branch from arteries. What is their function?

Answer 6

Constrict and dilate to control blood flow to a specific tissue.

Question 7

Where does the blood then flow to from the capillaries via venules?

Answer 7

To thin walled, highly compliant veins.

The pressure in the systems is significantly lower at this point.

Question 8

How does the blood flow back to the heart? venous return

Answer 8

Veins have valves that prevent backflow of blood.

The intermittent contraction of skeletal muscles (e.g. muscles in legs)

Increase / decrease in thoracic pressure as we breathe

Diaphragm compresses abdominal veins with each breath

Increase in blood in the veins as we get close to the heart.

More blood has returned from tissues via the venules.

Question 9

Describe the left and right side of the heart

Answer 9

LHS: larger and stronger to pump oxygenated blood around systemic circulation

RHS: receives deoxygenated blood from body and pumps it towards the lungs for oxygenation.

2 atria – receive blood from systemic circulation or lungs

2 ventricles – pumping function

Question 10

What is the purpose of heart valves?

Answer 10

Valves: stop backflow of blood backwards.
Exist between atria and ventricles, and also ventricles and arteries.

-4 valves: atrioventricular and pulmonary, aortic valves.
-Open in one direction

Question 11

How do papillary muscles influence valves?

Answer 11

*Papillary muscles contract to prevent valves opening in wrong direction.

Question 12

List the different valves of the heart and their function.

Answer 12

Atrioventricular valves: sit between atria and ventricle:
-Tricuspid valve: between right atrium and right ventricle

• Mitral valve: between left atrium and left ventricle

Pulmonary and aortic valves:
- Pulmonary valve: sits between the pulmonary artery and right ventricle
- Aortic valve: sits between the aorta and left ventricle

Question 13

During Diastole (heart relaxation), AV valves are _____, aortic/pulmonary valves are _____. The blood flows from the ____into the _____.

Answer 13

AV valves are open

Aortic / pulmonary valves are closed

Blood flows from atria to ventricles.

Question 14

Describe what happens during systole (heart contraction).

Answer 14

Heart contraction – systole (atria contract, pushing last bits of blood into the ventricles from the atria. Resulting in a higher pressure in ventricles than atria = closing tricuspid and mitral valves.

Papillary muscles contract to prevent valves from closing too far and opening in the other direction.

The atria refill with blood from vena cava and pulmonary vein = causing ventricles to contract = further increasing the ventricular pressure; and pushes aortic and pulmonary valves open.

Once pressure in arteries increases enough due to blood flow into them and pressure being higher than ventricles – this pushes aortic and pulmonary valves closed again causing ventricles to relax. The pressure in ventricles becomes lower than atrial pressure = pushing atrioventricular valves open again and diastole occurs.

Question 15

What is The Frank Starling Mechanism

Answer 15

The heart adapts so that it always pumps the blood that is returned to it via the venous side onwards.

The greater the heart is stretched, the stronger it contracts.

This is due to intrinsic properties of cardiac muscle cells and overlap of myosin and actin (protein molecules in muscles involved in muscle contraction).

Question 16

Electrical activity spreads between muscle cells to control contraction and relaxation of the heart muscle to cause diastole and systole.
What is the hearts electrical conducting system?

Answer 16

1. Sinoatrial node (right atrium) – pacemaker of heart. Initiates heartbeat and determines HR. Spread throughout both atria and stimulate them to contract. * (ion permeability creates depolarisation that spreads across the atria towards AV node = causing atria to contract)
2. Atrioventricular node (right atrium near AV valve) – acts as an electrical gateway to the ventricles. Delays passage of electrical impulses to the ventricles to ensure the atria have fully ejected all the blood into ventricles before the ventricles contract. Receives signal from SA node and passes them to atrioventricular bundle (bundle of His).
3. Bundle of His. Divided into right and left bundle branches. They conduct impulses towards the apex of heart. Signals are then passed to the Purkinje fibres.
4. Purkinje fibres – The electrical impulse turns upward and spreads through the ventricular myocardium allowing ventricles to contract to pump blood out.

Question 17

What is the role of annulus fibrosis between SA node and AV node ?

Answer 17

The depolarisation can’t progress to ventricles without passing through the AV node due to non-conductive fibrous tissue known as annulus fibrosis. Allows atria to empty fully before ventricles contract.

Question 18

Electrical pathway essential for the _____ __________ of the heart.

Answer 18

coordinated contraction

Question 19

What is an electrocardiogram?

Answer 19

The flow of current around the heart can be measured using an ECG – an electrocardiogram.

Helps check rhythm of heart and electrical activity.

Electrodes placed onto skin that detects the direction and amount of current flowing through the heart.

Question 20

What is a12 lead ECG ?

Answer 20

provides 12 directional views of electricity across the heart. Can see rate of electrical activity and abnormalities in the direction of electrical flow or timing of conduction.

Question 21

Describe the waves on an ECG.

Answer 21

P wave: shows atrial activity in contraction.

QRS wave: (peak) shows ventricular depolarization and contraction.

T wave: repolarization of cells for next current and contraction.

Question 22

Normal heart rate is ___ bpm.

Answer 22

60- 100 bpm

Question 23

Fast HR (>100bpm) is known as ________.

Answer 23

Tachycardia

Question 24

Slow HR (<60bpm) is known as ________.

Answer 24

Bradycardia

Question 25

How is heart rate controlled?

Answer 25

Heart rate is set by sinoatrial node – keeps generating impulses due to ion permeability. The para and sympathetic nervous system also contributes

Question 26

Describe how the sympathetic NS is involved in controlling heart rate.

Answer 26

Sympathetic NS: fight or flight! Releases catecholamines - epinephrine and norepinephrine - to accelerate the heart rate.

Reduced parasympathetic inhibition of HR and increase in sympathetic stimulation.

Releases noradrenaline; which acts on beta adrenergic receptors which increases the rate of firing of SA node. It also increases rate at which impulses are transmitted through the heart and increases the force of contraction of the heart. The heart rate also increases in response to increased venous return keeping the system balanced. The HR slows down when there is a reduced sympathetic stimulation and increased parasympathetic inhibition.

Question 27

How does the parasympathetic NS affect HR?

Answer 27

Parasympathetic NS: relax - slows HR.

At rest, provides a baseline inhibition of the HR, preventing it from getting too fast. This is via the vagus nerve which imputs to SA node and AV node to slow HR.

Question 28

What is an escape rhythm?

Answer 28

If the SA node is slowed to a stop, the cells in the ventricles can also generate their own depolisations, but this occurs too slowly to be of any use. But in the absence of any stimulation from SA node, it can cause an escape rhythm (very slow – 15-40bpm).

Question 29

Cardiac output is constantly balanced by the circulatory system. What is cardiac output?

Answer 29

The volume of blood that the heart pumps around the body / unit time.

Needs to be constant as tissues need a baseline amount of O2 and nutrients.

This distribution may be altered depending on usage by different tissues.

Can increase during increased metabolism e.g. exercise, physiological stress e.g. medical emergencies.

Question 30

Cardiac output = ____________ X ___________

Answer 30

Cardiac output = Heart Rate X Stroke Volume
*Amount of blood pumped / heart beat times by how often the heart is beating.

Question 31

How is the amount of blood the tissues are receiving per unit time increased?

Answer 31

Either the HR needs to be increased or the stroke volume OR both.

However, the heart can only pump out as much blood as it’s receiving from the veins – the venous return.

The venous return depends on how much blood is being pumped out to the tissues in the first place. There are venous reservoirs which change the circulating volume in the body (changes how much blood is actively circulating around the tissues – not volume of blood*)

Question 32

When increasing cardiac output, venous return can be increased by _______________.

Answer 32

constricting blood vessels in the splanchnic circulation (e.g. spleen, GIT). The blood is squeezed into circulation so it is re-distributed elsewhere – where needed.

Question 33

How else is venous return increased?

Answer 33

Respiratory pump: changes in thoracic pressure caused by breathing and compressive action of diaphragm on abdominal vessels – all increase venous return by increasing respiratory rate. Which is why breathing and circulation are so closely linked (e.g. ABCDE in medical emergencies).

Question 34

What is blood pressure?

Answer 34

A crude measurement of the amount of force caused by the heart contractions to push blood around the body.

Question 35

Blood pressure = ___________ X ______________

Answer 35

Blood Pressure = Cardiac Output X Total Peripheral Resistance

Question 36

What is total peripheral resistance?

Answer 36

Total peripheral resistance – the amount of force exerted on circulating blood by the vasculature of the body.

Can be due to diameter of blood vessels. Smaller blood vessels generate a higher peripheral resistance. Larger vessels generate less resistance.

Question 37

There is a minimum total peripheral resistance because _______________

Answer 37

there is also friction caused by blood cells against vessel walls.

Can increase total peripheral resistance by constricting arterioles and to a degree the veins.

Question 38

Blood pressure can be increased rapidly by:

Answer 38

increasing HR and stroke volume (Cardiac output)

By constricting arterioles to non essential peripheral tissues which increases total peripheral resistance

Slight constriction in veins to increase venous return

Question 39

Constriction of arterioles and veins are controlled by the sympathetic NS. How is this process triggered?
* short term BP control

Answer 39

This is triggered by pressure receptors in blood vessels e.g. baroreceptors – which detect reduction in stretch = less pressure in system.

This triggers sympathetic system. IF they detect increased stretch (high BP) = triggers parasympathetic nervous system to cause reduction in HR, dilation of arterioles and veins, and inhibition of the tonic sympathetic constriction of blood vessels so they are dilated = this occurs to maintain BP. All these factors are short term factors to balance BP.

IF they detect reduced stretch (low BP) = triggers sympathetic nervous system to cause increase in HR, constriction of arterioles and veins, increased stroke volume.

Question 40

Describe the Renin-Angiotensin System.
Long term BP control.

Answer 40

Controls BP through the blood flow to the kidneys and hormonal regulation.

Question 41

Renin-Angiotensin System:
Persistently low BP leads to __________

Answer 41

• Arteriole constriction (also includes flow to the kidneys)
• This reduces the amount of Na and water excretion that occurs through kidneys.
• Triggers kidneys to produce renin; this converts angiotensin to angiotensin 1; which travels in blood being converted to angiotensin-2 by angiotensin converting enzyme (ACE) this occurs in lungs.
• Angiotensin 2 travels back around the body, and triggers adrenal glands to release aldosterone (hormone).
• Aldosterone causes vasoconstriction & Na + water reabsorption = increases circulating volume = increasing BP.

Question 42

High BP: doesn’t mean all the tissues are receiving increased blood supply equally. So how do the tissues receive the blood they need?

Answer 42

There is local autoregulation at the tissues so that blood is sent to where it is required.

A tissue working very hard creates more vasodilating products e.g. CO2, and uses up O2 near the tissue; which is a vasoconstrictor. This leads to vasodilation = increased blood flow to tissue.

Question 43

What are the key factors of cardiopulmonary resuscitation? CPR

Answer 43

1. Compressions: 1/3 the depth of the chest.
2. Ventilations: roughly half the bag.
3. Ratio 30:2. Balances need for oxygenation and need for perfusion.
4. AED

Question 44

Cardiac arrest – heart pump stops (not necessarily the electrical activity in the heart. Might be dis-coordinated). What happens when we administer CPR?

Answer 44

Compressions in CPR - act as heart pump. Creates pressure in the chambers of the heart to push blood onwards.

When lifting off the chest, it gives heart time to refill. As positive pressure is created down towards the chest, this increases pressure within thorax, which also increases pressure in the head via neck. This causes a rise in intracranial pressure – which can compress vessels reducing brain perfusion.

*Recoil phase of CPR important (need to lift off the chest enough)– maintains cerebral perfusion and brain damage is prevented.

If compressions are performed too fast = the heart doesn’t have enough time to fill fully between each compression. Stroke volume is reduced.

Question 45

Why is the bag valve mask important in CPR?

Answer 45

Bag valve mask: ventilates pt. Breath – inflates lungs to allow O2 absorption and CO2 removal. Also opens blood vessels in lungs to get into blood. Pressure of lung inflation squeezes on pulmonary vein to return blood to LHS of heart = increased left ventricular stroke vol.

Too little ventilation – reduces O2 delivery and waste gas removal.

Too much ventilation = increases thoracic pressure too high = reduces venous return to right side of heart and reduces cerebral perfusion.

Question 46

When might reduced thoracic pressure help keep pts conscious?

Answer 46

e.g. coughing – can help keep pts conscious when they’re in certain arrhythmias – increases venous return and therefore Cardiac output.

Question 47

What is the purpose of an AED?

Answer 47

Automated external defibrillator- delivers shock to heart that stops ongoing abnormal electrical activity e.g. ventricular fibrillation – gives SA node to kick in and re-start the heart.

– * if shockable – depends on whether there is electrical activity going on in the heart which may be preventing normal heart rhythm.