Heart wall

Question 1

What is the pericardium?

Answer 1

Membrane enclosing the heart

Question 2

What are the layers of pericardium?

Answer 2

Fibrous pericardium = outer layer
Serous pericardium is made up of parietal and visceral pericardium = parietal directly behind fibrous and visceral surrounding the heart
Pericardial space in-between parietal and visceral pericardium

Question 3

What is myocardium?

Answer 3

The muscular tissue of the heart

Thickest layer

Question 4

What is endocardium?

Answer 4

The inner layer of endothelial cells

Question 5

What is the function of the pericardium?

Answer 5

It fixes the heart to the mediastinum.
Provides protection against infection and provides lubrication (allows the layers to slide over each other so the heart can move independently)

Question 6

What is the function of the myocardium?

Answer 6

Stimulates heart contraction and relaxation.
Provides scaffolding for the heart chambers
Contractions allow pumping of blood from the ventricles.
Relaxation allows atria to receive blood

Question 7

What is the function of endocardium?

Answer 7

Controls myocardial function.
Forms the blood heart barrier
Controls the ionic composition of the ECF of cardiomyocytes

Question 8

Are cardiomyocytes uni-nucleate?

Answer 8

Yes

However, sometimes adjacent cells can fuse and become multi-nucleate this is called syncytium

Question 9

What is excitation contraction coupling?

Answer 9

The process by which an excitation in the cardiomyocyte leads to contraction of the muscle

Question 10

What is the function of the T-tubules?

Answer 10

They propagate the AP (made in the SAN) into the cardiomyocyte and this allows excitation contraction coupling

Question 11

What is a sarcomere?

Answer 11

The smallest contractile unit

Question 12

What is the function fo the sarcoplasmic reticulum?

Answer 12

Absorbs and stores Ca2+ until depolarisation occurs in which it is released so cause a contraction

Question 13

What is the function of intercalated discs?

Answer 13

They connect adjacent cardiomyocytes and provide electrical coupling

Question 14

What type of junctions are intercalated discs?

Answer 14

Desmosomes and gap junctions

Question 15

What are gap junctions?

Answer 15

Intracellular channels that allow for direct chemical communication between adjacent cells. Without contact of ECF

Question 16

What are desmosomes?

Answer 16

Fasteners through plasma membranes of adjacent cells. made of intermediate filaments (keratin or desmin)

Question 17

Why do cardiomyocytes have a branched structure?

Answer 17

Allows for extra strength when contracting

Question 18

Why do cardiomycoytes have lots of myoglobin?

Answer 18

To store lots of oxygen fro aerobic respiration

Question 19

What are the 2 types of fibres in the heart?

Answer 19

Pacemaker cells and conduction fibres

Question 20

What is the most common protein found at a gap junction?

Answer 20

Connexin

Question 21

Out of these 3 proteins which one does not require the presence of a similar structure on the receiving cell?
Cnnexin
Innexin
Pannexin

Answer 21

Pannexin

Question 22

Where is the SA node located?

Answer 22

On the top wall of the right atria

Question 23

What is the function of the SAN?

Answer 23

Establishes the rhythm of the heart

Question 24

What does the Bachmann’s bundle do?

Answer 24

Conduction to the left atria

Question 25

What is the function of the AVN?

Answer 25

Delays the conduction of the impulses into the ventricles so the ventricles can fill completely before they contract

Question 26

How does the AVN propagate the signal around the ventricles?

Answer 26

Down the bundle of His (right and left) and onto the Purkinje fibres

Question 27

Why does the heart contract from he apex?

Answer 27

To ensure all the blood is pushed out the heart

Question 28

How is the mechanism of contraction initiated?

Answer 28

AP arrives at the sarcoplasmic reticulum
Neurotransmitters open Na+ channels and Na+ moves into the cell
Depolarisation down the T-tubule causes the opening of L-type Ca2+ channels so Ca2+ moves into the cell.
This causes Ca2+ to be released from the sarcoplasmic reticulum and start the contraction

Question 29

How is the mechanism of relaxation initiated?

Answer 29

Ca2+ taken back up by the sarcoplasmic reticulum.
This causes Ca2+ to be pumped out into ECF.
1 Ca2+ out is exchanged for 3 Na+ in using a Ca2+/Na+ exchanger.
3Na+ out exchanged for 2K+ in with Na+/K+ ATPase.
This opens K+ channels and K+ moves out

Question 30

What are 3 important roles of Ca2+?

Answer 30

Depolarisation and propagation of excitation
Initiation of cardiomyocyte contraction
Signal molecule and second messenger

Question 31

What is the function of SERCA?

Answer 31

It is a Ca2+ ATPase that transports Ca2+ from the cytosol into the sarcoplasmic reticulum

Question 32

What is the function of phospholamban?

Answer 32

In its unphosphorylated state it is an inhibitor of SERCA (so calcium cannot enter the SER)

Question 33

How is calcium taken up by the SER?

Answer 33

cAMP dependent protein kinase phosphorylated phospholamban and this activates SERCA.

Question 34

What is the effect of the phosphorylation of phsopholamban?

Answer 34

Decrease contractility and rate of muscle contraction. This decreases SV and HR

Question 35

What is the maximal stretch of the sarcomeres?

Answer 35

2.6 micrometres

Question 36

Are the thick fibres in the sarcomere composed of myosin or actin?

Answer 36

Myosin

Question 37

What are the phases of contraction?

Movement of filaments and ATP

Answer 37

In the resting state ATP is hydrolysed on the myosin head.
Ca2+ binds troponin, this causes a conformational shape change to tropomyosin and reviles the myosin binding site.
The myosin head binds.
A power stroke occurs and the sarcomere contract. ADP and Pi dissociate from the head.
New ATP binds to the head and causes dissociation of the head from the actin.
ATP hydrolyses and cause myosin head to move back into original position