Module 5 Section 2

Question 1

Describe the cardiac valves and how they achieve their purpose.

Answer 1

Atria = receive blood that’s returning to the heart and transfer it to the ventricles.

Ventricles = pump blood out of the heart.

Arteries = take blood Away from the heart.

Veins = return blood to the heart

When the pressure is great enough, the valves open to let blood flow through but when the pressure decreases, the valves shut to stop blood from flowing backwards.

• Valve is open: when the pressure is greater behind the valve
• Valve is closed: when the pressure is greater in front of the valve

Atrioventricular (AV) valves

• Located b/w the atria & ventricles
• When the pressure inside the atria > ventricles, these valves open and blood goes from atria -> ventricles
• Both valves are connected to the papillary muscles of the ventricular walls via chordae tendineae to prevent them from everting.
• Right AV valve = tricuspid valve b/c it has 3 cusps/leaflets; b/w the RA and RV
• Left AV valve = bicuspid or mitral valve; b/w LA and LV

Question 2

Describe the unique properties of cardiac muscle cells in relation to their function. Explain how cardiac muscle cells communicate w/ each other.

Answer 2

A single cardiac cell muscle doesn’t run the length of the heart since they are smaller than skeletal muscles.

Cardiac muscle cells are connected end-to-end to form a branching network of cardiac fibres. These connections are at specialized structures called intercalated discs.

Intercalated discs

• Composed of 2 types of membrane junctions: desmosomes and gap junctions
• Desmosomes = mechanically hold the cells together
• Gap junctions = allow the cells to communicate & spread action potentials from cell-to-cell, permitting each wave of excitation to spread very quickly through the atria and ventricles. This allows the chamber to contract in a wave-like motion which allows blood to be efficiently pushed out of the chamber

Question 3

Describe the cardiac cycle.

Answer 3

Deoxygenated blood from body to superior/inferior vena cava -> RA -> tricuspid valve -> RV -> pulmonary valve -> pulmonary artery -> blood vessels of the lungs -> lungs -> oxygenated blood returns to the pulmonary veins -> LA -> mitral valve -> LV -> aortic valve -> aorta -> rest of body except for lungs

Question 4

Describe the flow of blood through the body.

Answer 4

1) Oxygen rich blood is pumped from the left ventricle into the very large artery called the aorta.
2) The oxygen-rich blood is then delivered to the various tissues and organs.
3) At the level of the tissues and organs, O2 and other nutrients are removed from the blood while CO2 and other waste products are added to the blood.
4) The blood is now oxygen-poor. It circulates in the veins and eventually returns to the RA via 2 large veins called the venae cavae.
5) The blood is then pumped into the RV and then pumped again out through the pulmonary artery, taking the blood to the lungs.
6) In the lungs, the CO2 is removed and O2 is again added to the blood.
7) The now oxygen-rich blood flows through the pulmonary vein into the LA where it’s pumped into the LV to start the circuit again.

Question 5

What are some of the key features of cardiac muscles?

Answer 5

1) Is striated w/ thick and thin filaments organized into sarcomeres
2) Contains troponin and tropomyosin as the primary site where Ca activates cross bridge activity
3) Has T-tubules and a well defined SR
4) Contain lots of mitochondria
5) Has a well defined length-tension relationship
6) Ca comes from both the ECF and the SR
7) Is interconnected by gap junctions to allow spread of excitation
8) Is innervated by the ANS to modify rate and strength of contraction
9) Action potentials last longer in cardiac muscle than any other muscle type
10) Cardiac muscle fibres are joined in a branching network.

Question 6

How do you think the muscle fibres of the heart are arranged in order to create the necessary pressure to pump blood throughout the body?

Answer 6

The muscle fibres of the heart are arranged in a spiral fashion around its circumfrence. B/c of this, when the muscle fibres contract they cause a squeezing or wringing of the heart that generates pressure in the chambers.