6.2

Question 1

Layers of arteries
(Outermost to innermost)

Answer 1

• tunica externa: tough layer of connective tissue
• tunica media: muscle layer (smooth muscle) and elastic fibres made of protein elastin
• tunica intima: endothelium layer forming the lining of the artery

Question 2

Structure of capillaries (walls)

Answer 2

• walls of capillaries consist of a single layer of epithelial cells created by a filter like protein gel (lamina) with pores
• walls of capillaries allow it to be semi-permeable
• basement membrane is semi-permeable to many substances
• one cell thick, allows for diffusion
• low pressure, blood travels slowly so there is more opportunity for exchange

Question 3

Veins structure

Answer 3

• large lumen, low bp
• walls are thinner and less elastic compared to arteries
• contain valves which move blood through during low bp
• contain skeletal muscles which squeeze vein and pushes blood in one direction

Question 4

William Harvey determined that:

Answer 4

• blood flow is unidirectional (valves prevent backflow)
• blood is recycled as flow rate of blood is too high to be consumed

Question 5

Pulmonary circulation means:

Answer 5

To/from the lungs

Question 6

Systemic circulation means:

Answer 6

To/from the body (other than the heart)

Question 7

Parts of the heart

Answer 7

• atrium: receives blood from body/lungs
• ventricle: receives blood from the atrium, pumps it out of the heart through arteries
• AV (atrioventricular) valve: btwn atria and ventricles
• semi-lunar valve: btwn ventricles and atria
• pulmonary artery: carries unoxygenated blood from the heart to the lungs
• pulmonary vein: carries oxygenated blood from the lungs back to the heart
• coronary arteries: arteries which wrap around the heart to supply oxygenated blood to the heart muscle
• vena cava (superior and inferior) carries blood from the body to the heart

Question 8

SA node

Answer 8

• located near the right atrium
• known as the pacemaker
• initiates the heartbeat
• made of a group of specialized muscle cells
• myogenic: initiates own contractions w/o neurons

Question 9

Steps of a cardiac cycle

Answer 9

• SA node initiates a heartbeat, sends a signal
• this results in atria systole
• blood travels through the AV valve to the ventricles
• SA node signal sent to the AV node
• AV node sends a signal delayed by 0.1s through the bundle of his to the purkinje fibres
• ventricles undergo systole, AV valves snap shut, blood leaves the ventricles, enter atrium or leaves the heart
• semilunar valves close
• ventricles relax, AV valves open and blood fills the ventricles
• all four chambers are in diastole
• when atria filled and ventricles are 70% filled, cycle is complete

Question 10

What controls heart rate?

Answer 10

Heart rate is controlled by
- the automatic nervous system: 2 nerves originating from the cardiovascular centre in the medulla —> send signals to the SA node
- cardiovascular centre in the medulla receives input from the receptors, monitor BP, blood pH [CO2] and [O2]
- adrenaline: when in bloodstream causes rapid inc. in heart rate in prep. for physical activity or flight-or-fight response: adrenaline produced by adrenal glands, controlled by the brain