The heart

Question 1

What do the papillary muscles do?

Answer 1

help mitral valve contract & helping to prevent leakage through the AV valves during systole

Question 2

What do contractions within the heart do?

Answer 2

causes the pressure inside the chamber to rise causing blood to flow

Question 3

What are the 3 main layers of the heart wall?

Answer 3

-Endocardium
-myocardium
-epicardium

Question 4

Describe the structure of the endocardium?

Answer 4

most inner lining-is an endothelial lining, so consists of tightly compact endothelial cells that are directly in contact with the blood at all times

Question 5

describe the structure of the myocardium?

Answer 5

muscle lining & thickest layer- made up of specialised cells called cardiomyocytes
-generates contraction and relaxation
-plays a role in scaffolding and structure of heart
-plays a role during conduction

Question 6

describe the structure of the epicardium?

Answer 6

outer layer- consists of mesothelial cells
-functions for protection & forms protective layer around organs in the body

Question 7

why does the heart have a fibrous cardiac skeleton?

Answer 7

Fibrous rings form around valves in heart made up from connective tissue
-they form structural support for the heart tissue and valve leaflets

Question 8

Why are the fibres in the myocardium multidirectional?

Answer 8

meaning there are longitudinal fibres from base to apex of the heart
-means the heart can beat in 3 different ways at the same time:
-Beats inwards (radially), longitudinally and circumferential

Question 9

Where does the blood supply come from in the cardiac system?

Answer 9

from coronary arteries
-are 2 main coronary arteries: right coronary artery & left main coronary artery
-Left main artery divides into 2 arteries: the circumflex and the anterior interventricular artery

Question 10

Why can the heart contract by itself?

Answer 10

has an electrical conduction system

Question 11

What is the electrical conduction system in the heart?

Answer 11

-a collection of nodes and specialised conduction cells that initiate and coordinate contraction of the heart muscles

Question 12

What does action potential mean?

Answer 12

change in voltage

Question 13

depolarise defintion?

Answer 13

when electrical voltage becomes more positive- causes cardiomyocyte (heart) contraction

Question 14

repolarise defintion?

Answer 14

when voltage becomes more negative- causes cardiomyocyte (heart) relaxation

Question 15

describe the steps within the cardiac system?

Answer 15

-depolarization at sinoatrial node (SA node)
-Causes depolarization of all tissue surrounding SA node
-Whilst thats happening specialised cells called Bachmann’s Bundle takes electrical charge from depolarization to the left atrium and does the same thing there (both atriums contract)
-As this happens it causes pressure in atria to rise forcing blood out of atria into ventricles
-Electrical charge then transmits to the atrioventricular node (AV node) where the AV node functions to deliberately delay the charge spreading down heart (only for short time)- this is so the atria’s have finished contracting before charge spreads, allowing for as much blood to flow to ventricles
-then allows charge to continue thru conduction pathway to the bundle of hiss
-The bundle of hiss carries electrical charge towards ventricles where it divides into right bundle branch and left bundle branch
-At end of both branches are purkinje fibres which spread to everywhere in myocardium, ensuring all of electrical charge is delivered to all aspects

Question 16

what happens if the av node stops working?

Answer 16

atria and ventricles contract at the same time

Question 17

What are the 2 branches that come off the left branch?

Answer 17

-anterior branch-wraps around front of heart
-posterior branch-wraps around back of heart

Question 18

What is the purpose of a p wave on an electrocardiogram?

Answer 18

tells us if the SA node is depolarizing (suggests the atrium is contracting)

Question 19

How does cardiac conduction happen?

Answer 19

-Cardiomyocytes have ability to generate action potential automatically without any input from nervous system
-Contraction starts at SA node as it has regular rhythm of 100bpm so has the fastest generation ability (is the pacemaker cell)
-Gap junctions between pacemaker cell and contractile cells allow electrical charge to move thru so if action potencial in 1 cell occurs it triggers an action potential in the next cell

Question 20

What are cardiac cells?

Answer 20

polarised cells- have an electrical voltage across the cell membrane
-when cells arent contracting the membrane voltage is negative on the inside

Question 21

How does the voltage of cardiac cells become postive?

Answer 21

-When cell isnt contracting (at rest) there is more potassium inside the cell and more sodium and calcium outside the cell
-Ions within cell can move in and out freely due to specific channels
-Depolarization and repolarization are a result of ions moving
-In order for cell to become positive (depolarize)-it requires influx of sodium
-Then have plateau phase
- Cell relaxes (repolarization) and becomes more negative by potassium leaking out of cell

Question 22

What are 5 stages of contraction/ pressure in the cardiac cycle?

Answer 22

• atrial systole
  -Isovolumetric contraction-
  -Ventricular ejection
  -Isovolumetric relaxation
  -ventricular filling

Question 23

what happens during atrial systole?

Answer 23

atrial start to squeeze and push blood into ventricles so ventricular volume and pressure increases.

Question 24

what happens during Isovolumetric contraction?

Answer 24

ventricles starting to contract but all 4 heart valves are still closed (no change in volume) as not enough pressure has been generated yet
-Pressure increases and becomes higher than pressure in aorta the aortic valve opens

Question 25

what happens during Ventricular ejection

Answer 25

occurs so blood is ejected into body or lungs from ventricles and blood flow decreases
-Pressure continues to rise as ventricles continue to contract
-Once as much blood as possible is ejected out, pressure starts to drop and continues to drop to below the pressure of the aorta and valve closes

Question 26

what happens during Isovolumetric relaxation

Answer 26

all 4 valves close and ventricles are repolarizing
-Once pressure in atria is higher, mitral and tricuspid valve open and blood flows back thru causing ventricular filling

Question 27

what is preload?

Answer 27

the initial stretching of the cardiac myocyte prior to contraction

Question 28

what is after load?

Answer 28

the load the heart must eject blood against

Question 29

what does the frank starling mechanism suggest?

Answer 29

-Suggests that stroke volume is autoregulated by ventricular filling
(more in, more out)
-As ventricle fills during diastole myocardium begins to stretch, so the greater the stretch the stronger the ventricular contraction
-Elastic recoil occurs, allowing a greater volume of blood to be ejected during systole

Question 30

why does preload and diastolic volume plateau during exercise

Answer 30

Because valves have less time between contractions
-and as heart rate increases, diastolic filling time decreases

Question 31

What are the cardiac responses to exercise?

Answer 31

-chronotropic
-inotropic
-dromotropic

Question 32

dromotropic meaning

Answer 32

increased electrical charge (action potentials that trigger depolarization/ repolarization occur at a faster rate)

Question 33

why does heart rate and contractility increase during exercise and what is the effect of this?

Answer 33

due to increased firing rate within sympathetic nerve activity
-this increases stroke volume and as a result increases cardiac output