Mass transport in humans

Question 1

What is mass flow? (1)

Answer 1

Bulk movement of liquids (and gases) due to a pressure difference

Question 2

Why are two pumps (left and right) needed instead of one? (3)

Answer 2

To maintain blood pressure around the body
When blood passes through narrow capillaries of the lungs, pressure drops sharply and therefore would not be flowing strongly enough to continue around the whole body
Therefore, it is returned to the heart to increase pressure

Question 3

Why is the left ventricle thicker than the right? (2)

Answer 3

The left ventricle must pump blood throughout the entire body so requires more pressure and the right only has to go to the lungs.

Question 4

What is pressure? (1)

Answer 4

The amount of force acting on the surface

Question 5

Why is there a change in pressure in the heart chambers? (2)

Answer 5

Because of both the changes in the volume of blood within the chambers and the contractions of the heart muscle

Question 6

What is systole? (1)

Answer 6

Contraction of heart muscle

Question 7

What is diastole? (1)

Answer 7

Relaxation of heart muscle

Question 8

What is the purpose of the valves in the heart? (2)

Answer 8

Prevent backflow of blood and maintain high blood pressure

Question 9

Explain the role of each valve found within the heart (2)

Answer 9

Left atrioventricular valve - prevents backflow from ventricle to atrium
Semilunar valve - prevent backflow from artery to ventricle

Question 10

What is cardiac output defined as? (2)

Answer 10

Volume of blood pumped out of the left ventricle per minute

Question 11

What is the equation for cardiac output? (1)

Answer 11

CO = SV x HR

Question 12

Describe and explain the structure of arteries (4)

Answer 12

Endothelial layer is only one cell thick which reduces friction and gives a smooth flow
Elastic tissue stretches as pressure increases and recoils to even out pressure and flow
Smooth muscle layer - muscle contracts which reduces diameter of lumen which changes flow and pressure
Outer layer has fibrous proteins and is thick so it can withstand high blood pressure

Question 13

What is the function of arterioles? (1)

Answer 13

Connect artery to the capillaries

Question 14

Describe and explain the structure of arteriole? (3)

Answer 14

Vessel diameter is smaller than artery so there is greater friction
Thinner elastic layer
Thicker muscle layer - contract to constrict vessel

Question 15

Describe and explain the structure of capillaries (4)

Answer 15

Wall only has endothelial layer (thin wall) - short diffusion pathway
Numerous and branched which increases surface area for diffusion and exchange of substances
Narrow diameter which creates greater friction and ensures red blood cells stay in contact with the wall - decreasing the diffusion distance
Fenestration - allow rapid formation of tissue fluid and allow white blood cells to leave the capillaries and destroy infections in tissues.

Question 16

What is the function of veins (1)

Answer 16

Transport deoxygenated blood from the body back to the heart

Question 17

Describe and explain the structure of veins (3)

Answer 17

Thin elastic and muscle layer - no need for (stretching) vasoconstriction as all the blood is going back to the heart or recoiling as pressure is low
Wide lumen - maximise volume of blood carried to the heart
Have valves which only allow the blood to pass through in one direction to ensure that the blood goes back to the heart

Question 18

What is the function of capillaries? (2)

Answer 18

Involved in exchange of materials between blood and tissue cells

Question 19

Describe how tissue fluid is formed and how it is returned to the circulatory system. (6)

Answer 19

Formation:
High blood/hydrostatic pressure
Forces water/fluid out
Large proteins remain in capillary
Return:
Lower water potential in capillary/blood
Due to plasma proteins
Water enters capillary
By osmosis
Excess fluid drains into lymphatic capillaries - now called lymph

Question 20

Describe the role of the hydrostatic pressure of blood and of osmosis in the formation and reabsorption of tissue fluid (5)

Answer 20

High hydrostatic pressure at arteriole and
tissue fluid is forced out
large plasma proteins remain in the blood, this lowers the water potential of the blood
Water moves back into the blood by osmosis down a water potential gradient
Excess water is drained by lymph vessels

Question 21

High blood pressure leads to an accumulation of tissue fluid. Explain how (3)

Answer 21

High blood pressure creates high hydrostatic pressure
Increases outward pressure from arteriole end of capillary
So more tissue fluid formed

Question 22

How does blood keep travelling back to the heart? (5)

Answer 22

Muscles around veins contract and squeeze blood through valves
Valves in veins prevent backflow so always travels towards the heart
Veins have a wide lumen which creates little resistance to blood travelling
Systole pumps blood through arteries to veins
Heart during diastole has less pressure than veins so draws blood from veins into atrium

Question 23

Explain the role of the heart in the formation of tissue fluid (2)

Answer 23

Contraction of ventricles produces high hydrostatic pressure
Forces water out of capillaries

Question 24

What is one of the functions of the liver? (2)

Answer 24

Process absorbed food molecules and adjust their concentrations in the blood

Question 25

What are the blood vessels associated with the liver? (3)

Answer 25

Hepatic artery
Hepatic vein
Hepatic portal vein

Question 26

How do the blood vessels in the liver work? (3)

Answer 26

Hepatic artery takes blood from the aorta to the liver
Hepatic vein takes blood from the liver to the vena cava
Hepatic portal vein takes blood from the intestines to the liver (contains absorbed food molecules)

Question 27

What is the function of the kidney? (1)

Answer 27

Important for excretion of nitrogenous waste and for osmoregulation

Question 28

What are the blood vessels associated with the kidney and what do they do? (2)

Answer 28

Renal artery and vein take blood to and from the kidney

Question 29

Pressure changes in the arteries (3)

Answer 29

Flow is fast and pressure is high and fluctuating pulsar due to the contraction of the left ventricle

Question 30

Pressure changes in the capillaries (5)

Answer 30

Increased cross-sectional area causes increased friction which reduces blood pressure and flow changes from pulsar to smooth and speed of flow decreases

Question 31

Pressure changes in the veins (3)

Answer 31

Pressure is low and flow is slow and non-pulsar