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Tri B > Structure and Function of Heart > Flashcards

Structure and Function of Heart Flashcards

1
Q

Discuss the Structure of the Heart.

A
  • Heart divided into left and right with and upper (atria) and lower (ventricle) chamber on each side.
  • Composed of cardiac muscle
  • Innervated by ANS
  • About 12cm long
  • Has its own blood supply (Coronary arteries)
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2
Q

Discuss the main valves of the heart.

A

Atrial ventricular valves - On the right this is the Tricuspid valve and on the left is the Mitral valve.
Semilunar Valves - These sit at exit from both ventricles preventing back flow. Aortic semilunar valve and pulmonary semilunar valve.

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3
Q

Describe the flow of blood in the bodies circulation.

A

-Blood returns to heart via Vena Cava
-Enter right atrium
-Enters right ventricle
-Pulmonary artery and circulation
-Returns via pulmonary veins to left atrium
-Left ventricle
-Exits via Aorta into circulation
RTN

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4
Q

Discuss cardiac muscle cell structure and function.

A
  • Cells are SHORT and BRANCHED or Z SHAPED.
  • Joined at INTERCALATED DISCS which contain GAP JUNCTIONS allowing for action potential spread.
  • MANY MITROCHONDRIA for AEROBIC metabolism.
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5
Q

Discuss the hearts own blood supply.

A

The heart is permeated by coronary arteries. Most areas of heart have multiple to ensure sufficient oxygenation.

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6
Q

Discuss autonomic innervation of the heart.

A

The heart receives input from both the sympathetic and parasympathetic nervous system, both of which affect heart rate

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7
Q

What is cardiac contractility?

A

The strength of any given cardiac contraction which is governed by the sympathetic nervous system.

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8
Q

Where are action potentials that trigger heart contractions generated?

A

Sino Atrial Node

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9
Q

What is special about the cells of the SA node?

A

Their membrane potential is constantly changing allowing for AP’s to be rhythmically produced

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10
Q

Discuss the pathway of an AP generated by the SA node.

The heart conducting system.

A

THE HEART CONDUCTING SYSTEM

  • AP generated by the SA node
  • Spread horizontally causing atrial contraction
  • Spread down to AtrioVentricular node
  • Spread down to Bundle of His
  • Split into right and left bundle branches
  • Enter purkinje fibres of right and left ventricle
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11
Q

What does the P wave represent?

A

Atrial depolarisation

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12
Q

What does the QRS complex represent?

A

Depolarisation of ventricles

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13
Q

What does the T wave represent?

A

Repolarisation of the ventricles

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14
Q

When do the atria re-polarise?

A

At the same time as the QRS depolarisation - hence it is hidden on the ecg

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15
Q

Do both sympathetic and parasympathetic systems connect to the sino atrial node?

A

Yes - allowing for the ANS to control heart rate by governing the frequency of action potentials.

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16
Q

Do both sympathetic and parasympathetic systems connect to the heart ventricles?

A

No - Only the sympathetic system connects to the ventricle to increase heart contractility

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17
Q

What causes the heart to contract?

A

Action potentials which come from the SA node which is the ‘cardiac pacemaker’

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18
Q

In ECG terms what is one cardiac cycle?

A

P wave to P wave

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19
Q

Discuss the mechanical events of the cardiac cycle?

A

Diastole - blood fills atria
AV valves open and blood flows into ventricles
Atria contract moving any blood still in atria into ventricles
Ventricles contract, AV valve closes so no blood returns to atria. Pressure in ventricles increases during contraction.
When pressure is high enough the semi lunar valves open and blood will exit the ventricles
-Semi lunar valves shut preventing back flow
-Diastole
-Cycle repeats

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20
Q

What is isovolumetric contraction?

A

Ventricle contracts but blood volume remains the same

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21
Q

What determines the length of the cardiac cycle?

A

Heart Rate

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22
Q

What is a normal at rest heart rate?

A

70 bpm

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23
Q

How long is a normal cardiac cycle?

A

0.8 seconds

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24
Q

How much of a cardiac cycle is taken up by ventricular systole and diastole?

A
  1. 3 seconds

0. 5 seconds

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25
Q

How much of the cardiac cycle is taken up by atrial systole and atrial diastole?

A

Atrial systole = 0.1 sec

Atrial Diastole = 0.7 sec

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26
Q

What factors determine how much blood is pumped by the heart?

A

Heart Rate

Stroke Volume

27
Q

What is stroke volume?

A

The volume of blood ejected by one ventricle each time it contracts?

28
Q

How do you calculate cardiac output?

A

Stroke volume (litres/beat) x Heart Rate (bpm)

29
Q

Discuss the distribution of cardiac output?

A

The proportion of cardiac output that an organ receives is not fixed but can be altered to meet demand. Reduce it in one area while increasing it in others.

30
Q

During exercise how much of cardiac output is routed to muscles?

31
Q

Cardiac output to the skin increases during exercise, why?

A

Temperature regulation

32
Q

Does cardiac output to the brain change during exercise?

33
Q

What two systems can alter heart rate?

A

ANS and Hormonal control

Adrenaline and Noradrenaline levels can increase heart rate

34
Q

What influences stroke volume?

A

Improved venous return = greater stroke volume
Improved filling/high end diastolic volume = stretched heart muscle which gives a better contraction
End Systolic volume being low = better stroke volume

35
Q

What happens to the heart during exercise?

A
  • Cardiac output increase.

- This is done via the ANS and increased venous return.

36
Q

What is the average resting heart rate, stroke volume and cardiac output?

A

HR - 70bpm
SV - 70ml
CO - 5 litres/min

37
Q

What is the average maximum exercise heart rate, stroke volume and cardiac output?

A

HR - 195bpm
SV - 113ml
CO -22 litres/min

38
Q

What changes more with exercise stroke volume or heart rate?

A

Heart Rate - therefore cardiac output is mainly increased via heart rate.

39
Q

What happens to blood pressure during exercise?

A

Both systolic and diastolic bp will increase

40
Q

How does an athletes heart compare to a couch potato?

A

Athlete at rest has lower heart rate and higher stroke volume. During exercise it takes longer for them to achieve maximum heart rate and stroke volume is larger

41
Q

What are intrinsic factors in blood distribution?

A

Local mechanisms within a particular tissue

42
Q

What are extrinsic factors in blood distribution?

A

ANS & hormones

43
Q

What force causes blood flow in the cardiovascular system?

A

A pressure gradient

44
Q

Is blood flow constant?

A

No, Pulsatile

45
Q

How do you calculate mean arterial blood pressure?

A

MBP = Diastolic + 1/3(Systolic-Diastolic)

46
Q

What are some factors affecting blood pressure?

A
  • Cardiac Output

- Total Peripheral Resistance (TPR)

47
Q

What is Total Peripheral Resistance?

A

The resistance that the circulatorary system offers to the flow of blood through it

48
Q

What factors determine total peripheral resistance?

A
  • Blood vessel length
  • Blood viscosity
  • blood vessel radius
50
Q

What type of blood vessel has the most influence on total peripheral resistance?

51
Q

How does exercise affect blood pressure?

A

During exercise cardiac output increases which increases bp.
However during exercise vasodilation reduces total peripheral resistance.
Therefore bp increase is limited during exercise

52
Q

What does the size of arterioles influence?

A

Total peripheral resistance

Blood flow to capillaries and hence to any particular tissue

53
Q

What determines the diameter of arterioles?

A
  1. Local or intrinsic control
    - accumulation of waste can trigger vaso dilation
  2. Extrinsic Control
    - increased sympathetic activity such as noradrenaline cause vasoconstriction
54
Q

Name some hormone effects on blood pressure.

A

Noradrenaline, Angiotensin II, ADH = Vasoconstriction

Adrenaline = Vasodilation in skeletal muscle

55
Q

What are blood pressure sensors called?

A

Baroreceptors

56
Q

Where are baroreceptors located?

A

Aortic Arch and Carotid Sinus

57
Q

How do baroreceptors work?

A

They are stretch receptors. They fire action potentials the higher blood pressure is and they fire less when blood pressure falls.

58
Q

Discuss the chain of events following a haemorrhage in terms of the heart and the circulatory system.

A 
Blood volume drops
Venous return drops
End diastolic volume drops
Stroke volume drops
Cardiac output drops
Arterial BP drops
59
Q

What compensatory mechanisms does the cardiovascular system put in place to counteract blood pressure drops?

A
  • Vasoconstriction of veins particularly in lower parts of body
  • Vasoconstriction of arterioles to rest and digest organs
  • Prioritise coronary arteries, brain and other vital organs
  • Tachycardia
  • Redistribution of extracellular fluid
60
Q

Discuss the redistribution of extracellular fluid.

A
  • Capillary pressure reduces
  • This promotes reabsorption of extracellular fluid from interstitial space
  • Boosts plasma volume
  • Increases bp towards normal
61
Q

What are some long term compensatory mechanisms in response to haemorrhage?

A
  • Increased water reabsorption in kidneys
  • Urine output goes down
  • Stimulation of erythropoiesis by erythropoietin
62
Q

If compensatory mechanisms are not sufficient to stabilise the circulatory system what occurs?

A

Circulatory shock
A failure to maintain adequate blood flow to tissues leading to tissue damage.

Eventually the coronary circulation will weaken and this will impair cardiac output decreasing bp further.
Brain blood flow weakens meaning less vasoconstriction
Hypoxia due to reduced blood perfusion = increased capillary permeability which leads to reduced blood volume which leads to a dropped blood pressure

63
Q

If blood pressure is not restored during circulatory shock what occurs?

A
  • Widespread tissue and organ damage
  • CNS is depressed
  • Death
64
Q

What can cause circulatory shock?

A

-Catastrophic Haemorrhage
-Severe burns (fluid loss)
-Heart Failure
-Widespread vasodilation due to:
+sepsis
+Anaphylaxis
+Neurogenic injury

Tri B (13 decks)

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