Chapter 8.2

Question 1

Coronary arteries

Answer 1

-The heart is a muscle and so requires its own blood supply for aerobic respiration -The heart receives blood through arteries on its surface, called coronary arteries -It’s important that these arteries remain clear of plaques, as this could lead to angina or a heart attack (myocardial infarction)

Question 2

Valves in the heart:

Answer 2

-Open when the pressure of blood behind them is greater than the pressure in front of them -Close when the pressure of blood in front of them is greater than the pressure behind them

Question 3

Valves are important for

Answer 3

keeping blood flowing forward in the right direction and stopping it flowing backwards. They are also important for maintaining the correct pressure in the chambers of the heart

Question 4

The right atrium and right ventricle are separated by the

Answer 4

atrioventricular valve, which is otherwise known as the tricuspid valve

Question 5

The right ventricle and the pulmonary artery are separated by the

Answer 5

pulmonary valve

Question 6

The left atrium and left ventricle are separated by the

Answer 6

mitral valve, which is otherwise known as the bicuspid valve

Question 7

The left ventricle and aorta are separated by the

Answer 7

aortic valve

Question 8

There are two blood vessels bringing blood to the heart

Answer 8

the vena cava and pulmonary vein

Question 9

There are two blood vessels taking blood away from the heart

Answer 9

the pulmonary artery and aorta

Question 10

The heart is divided into four chambers.

Answer 10

The two top chambers are atria and the bottom two chambers are ventricles

Question 11

The left and right sides of the heart are separated by a wall of

Answer 11

muscular tissue, called the septum. The portion of the septum which separates the left and right atria is called the interatrial septum, while the portion of the septum which separates the left and right ventricles is called the interventricular septum -The septum is very important for ensuring blood doesn’t mix between the left and right sides of the heart

Question 12

pericardium

Answer 12

a tough and fibrous sac It protects the heart in the chest cavity

Question 13

right ventricle

Answer 13

-The blood pumped out from the right ventricle travels to the lungs -The right ventricle generates less pressure from the contraction of its thinner walls, as blood only has to reach the lungs

Question 14

Left ventricle

Answer 14

-blood leaving the left ventricle has to travel to the rest of the body to deliver oxygen for respiration. -To reach the rest of the body, the blood leaving the left ventricle must be under high pressure -This is generated by the contraction of the muscular walls of the left ventricle

Question 15

The Walls of the Heart

Answer 15

-The muscular walls of the atria are thinner than those of the ventricles -When the atria contract, the thin muscular walls do not generate much pressure, but enough to force blood down into the ventricles, through the atrioventricular valves -In contrast, the walls of the ventricles are thicker and more muscular -Following contraction of the atria, the ventricles contract and squeeze blood inwards, increasing its pressure and pushing it out of the heart through right and left semilunar valves

Question 16

The Cardiac Cycle

Answer 16

-The contraction of the heart is called systole, while the relaxation of the heart is called diastole -Atrial systole is the period when the atria are contracting and ventricular systole is when the ventricles are contracting -Atrial systole happens around 0.13 seconds after ventricular systole -During ventricular systole, blood is forced out of the pulmonary artery (to the lungs) and aorta (to the rest of the body)

Question 17

Pressure changes

Answer 17

During systole and diastole, heart valves open and close as a result of pressure changes Valves are an important mechanism to stop blood flowing backwards

Question 18

During diastole

Answer 18

-the heart is relaxing –The atrioventricular valves open and the semilunar valves are closed

Question 19

During systole

Answer 19

• the heart contracts and pushes blood out of the heart –During this time, the atrioventricular valves are closed and the semilunar valves are open

Question 20

-One systole and diastole

Answer 20

makes a heartbeat and lasts around 0.8 seconds in humans.

Question 21

Stages in the cardiac cycle

Answer 21

Question 22

The Annulus fibrosus

Answer 22

is a region of non-conducting tissue which prevents the depolarisation spreading straight to the ventricles -Instead, the depolarisation is carried to the atrioventricular node (AVN) -This is a region of conducting tissue between atria and ventricles

Question 23

Control of the basic heartbeat is

Answer 23

myogenic, which means the heart will beat without any external stimulus -This intrinsic rhythm means the heart beats at around 60 times per minute

Question 24

The sinoatrial node (SAN)

Answer 24

is a group of cells in the wall of the right atrium. The SAN initiates a wave of depolarisation that causes the atria to contract -After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His

Question 25

bundle of His

Answer 25

The bundle of His is a collection of conducting tissue in the septum (middle) of the heart. The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them

Question 26

The Purkyne fibres spread around the

Answer 26

ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart -This makes the ventricles contract and blood is forced out of the pulmonary artery and aorta

Question 27

The Sinoatrial node sends out a wave of

Answer 27

excitation and this spreads across both atria, causing atrial systole. Non-conducting tissue called the Annulus fibrosus prevents the excitation from spreading to the ventricles and so this ensures that atria and ventricles don’t contract at the same time. The Atrioventricular node then sends the wave of excitation to the ventricles after a short delay of around 0.1 – 0.2 seconds, ensuring that the atria have time to empty their blood into the ventricles. The Purkyne fibres conduct the excitation down the septum of the heart and to the apex, before the excitation is carried upwards in the walls of the ventricles. This means that during ventricular systole, the blood contracts from its base and blood is pushed upwards and outwards.

Question 28

heart structure

Answer 28