Processes of the heart

When do the AV valves open and close?

• Open: when pressure is higher in atria compared to ventricles

• Close: when pressure is higher in ventricles than atria

When do semilunar valves open and close?

• Open: when the pressure is higher in the ventricle compared to the arteries

• Close: when the pressure is higher in the arteries compared to the ventricles

role of septum

• separates oxygenated and deoxygenated blood

• maintains high conc. of O2 in oxygenated blood

  • to maintain conc. gradient to therefore enable diffusion at respiring cells

some babies are born with a hole between the right and left ventricles. suggest why these babies are unable to get enough oxygen to their tissues

mixing of oxygenated and deoxygenated blood
- therefore lower volume of oxygenated blood leaves the left ventricle and flows into the aorta

role of tendons

prevents inversion of valves due to high pressure

2 ways in which blood moves in one direction as it passes through the heart

1. blood moves down a pressure gradient

   • blood moves from high to low pressure

   2. valves stop backflow of blood

structure of arteries

1. thick walls: enabling it to carry blood at high pressures

2. elastic tissue: smooths out blood flow and maintains pressure

3. muscles in wall: to control blood flow

4. smooth endothelium: to reduce friction

contrast the structure of arterioles and arteries

• Arterioles have thicker muscle layer than arteries, which contract to control the flow of blood

• Arterioles elastic layer is relatively thinner than the elastic layers in arteries, because blood pressure is lower

why is an arteriole described as an organ?

made up of different tissues/made up of more than one tissue

how do the muscle fibres in arterioles reduce blood flow to the capillaries?

the muscle contracts

• so the arterioles narrows/constricts

• vasoconstriction

structure of aorta

1. elastic tissue: to allow stretching/recoil to maintain pressure

   • elastic tissue stretches when ventricles contract

2. muscles: contraction/vasoconstriction

3. thick walls: to withstand pressure

4. smooth endothelium: to reduce friction

5. SLV: to prevent back flow of blood

suggest why the rise and fall in blood pressure in the aorta is greater than in the small arteries

1. aorta is directly linked to the heart, therefore the pressure is higher in the aorta than in the small arteries

2. aorta has elastic tissue, so it can stretch/recoil

describe the difference in the thickness of aorta wall during each time in cardiac cycle

1. during systole: aorta wall stretches bc ventricles contract
2. during diastole: aorta walls recoil bc ventricles relax

this helps maintain smooth blood flow

explain how the highest blood pressure is produced in the left ventricle

left ventricle has thicker, muscular walls

• therefore stronger contractions

structure of veins

1. thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards

2. less muscular and elastic tissue bc they don’t have to control blood flow

3. smooth endothelium to reduce friction

explain the difference in thickness between pulmonary artery and pulmonary vein

pulmonary artery contains muscle and elastic fibres

• b/c pulmonary arteries handle high pressures and smooth out blood flow

structure of capillaries

1. permeable capillary membrane

2. thin, one-cell thick walls: short diffusion distance/pathway

3. small diameter: short diffusion distance

4. flattened endothelial cells: short diffusion distance

5. numerous and highly branched: provides large SA

6. narrow lumen: reduces blood flow rate to give more time for diffusion

advantage of capillaries being narrow

short distance b/w blood and the outside of the capillary

• therefore fast diffusion

why is the blood flow in capillaries slow?

so that theres more time for diffusion

what factor limits the internal diameter of the lumen of a capillary?

width/diameter of blood cell

how can the widening of blood vessels reduce blood pressure

widening of blood vessels causes larger lumen, which reduces the blood pressure in blood vessels

• therefore less friction/resistance in the blood vessels

suggest why pulse can be used to measure heart rate

pulse is caused by the pressure from one contraction/beat of the heart

role of heart in formation of tissue fluid

1. contraction of ventricles produces high hydrostatic pressure

2. this forces water and some dissolved substances out of the capillaries

how tissue fluid is formed and returned to circulatory system

• high blood/hydrostatic pressure at arterial end of capillary which forces water out

• large proteins remain

• water potential in capillary becomes lower/negative due to these proteins

  • water potential now lower than hydrostatic pressure

• so water enters venous end of capillary by osmosis

• water moves out at the arteriole end and back in at the venule end

• lymph system collects any excess tissue fluid which returns to blood/circulatory system

how does high blood pressure lead to an accumulation of tissue fluid

1. high blood pressure = high hydrostatic pressure

2. increases outward pressure from arterial end of capillary

3. more fluid forced out of capillary due to high pressure

4. so more tissue fluid formed

5. less return of fluid into capillary (due to high pressure)

Explain why a lack of protein in the blood causes a build up of tissue fluid.

water potential in the capillary is higher

- therefore less water removed by osmosis

suggest how an increase in volume of blood entering the heart reduces angina

1. large amount of blood leaves the heart

2. therefore more blood/oxygen flow to the heart muscle via coronary arteries

explain how blood in a vein in the leg is returned to the heart

1. muscles surrounding the vein contracts and press on the walls of the vein, squeezing blood along the veins

2. valves prevent backflow

3. contraction of heart pumpls blood through arteries into vein (systole)

4. the recoil of heart muscle after contraction/ during diastole draws the blood from the veins into the atria

5. veins have wide lumens therefore theres little resistance

how to calculate something with eyepiece graticule

1. measure using eyepiece graticule

2. calibrate eyepiece graticule against stage micrometer

3. take a number of measurements to calculate a mean