3.5 The Circulatory System in Animals

Question 1

Why is a cirulatory system needed?

Answer 1

Diffusion distances too long

Question 2

What is the advantage of a double circulatory system?

Answer 2

No mixing of oxygenated and deoxygenated blood.

Question 3

Describe cardiac diastole.

Answer 3

• The ventricles and atria are both relaxed
• semi- lunar valves closed to stop reversed blood flow from arteries
• The atria continue to fill with blood
• Pressure in the atria rises above that in the ventricles, forcing the AV valves open
• Blood flows passively into the ventricles without need of atrial systole

Question 4

Describe atrial systole.

Answer 4

• The walls of the atria contract
• Atrial volume decreases and pressure increases
• forcing the atrioventricular valves openand blood is forced into the ventricles
• Ventricular muscle is relaxed

Question 5

Describe ventricular systole.

Answer 5

• The walls of the ventricles contract
• Ventricular volume decreases and pressure increases
• This forces the AV valves to close, preventing back flow of blood
• This forces the semilunar valves open so blood is forced into the arteries
• Relaxed atria begin to fill with blood again

Question 6

What are arteries?

Answer 6

Vessels that transport blood away from the heart (usually at high pressure).
- thick walls
- elastic fibres

Question 7

What are veins?

Answer 7

Vessels that transport blood to the heart (usually at low pressure).
- thin walls
- valves
- larger lumen

Question 8

What are arterioles?

Answer 8

Blood vessels that transport blood into capillaries.
- muscle cells

Question 9

What are capillaries?

Answer 9

Smallest blood vessel responsible for the exchange of substances (e.g, O2)
- thin walls
- leaky

Question 10

Describe the structure and function of capillaries.

Answer 10

• Small diameter (lumen): This forces the blood to travel slowly which provides more opportunity for diffusion to occur
• The wall of the capillary is made solely from a single layer of epithelial cells: have gaps so allow cells of the wall have pores which allow blood plasma to leak out and form tissue fluid

-Capillary wall is only one cell thick → blood slows down when it reaches capillaries allowing more time for diffusion

Question 11

What is tissue fluid?

Answer 11

As blood passes through capillaries, some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body.

Question 12

How is tissue fluid formed?

Answer 12

1. When blood is at the arteriole end of a capillary, the hydrostatic pressure is great enough to push small molecules and water out of the capillary
2. large molecules remain in the blood, creating a lower water potential in capillaries
   3.overall movement of water is out from the capillaries into the tissue fluid by osmosis via the lymphatic system
3. At the venule end of the capillary, low hydrostatic pressure due to less fluid is pushed out
4. so water begins to flow back into the capillary from the tissue fluid

Question 13

What blood vessels are attached to the heart

Answer 13

Vena cava → carries deoxygenated blood from the body to the right atrium (blood that ’s been used)
Pulmonary artery ‘s carries deoxygenated blood from the right ventricle to the lungs to become oxygenated
Pulmonary vein - carries oxygenated blood from the lungs to the left atrium.
Aorta → carries oxygenated blood from left ventricle to the rest of the body

Question 14

What blood vessels are attached to the lungs

Answer 14

Pulmonary artery
Pulmonary vein

Question 15

Outline how the double circulatory system works

Answer 15

1. Deoxygenated blood flows through the lungs at a lower pressure to prevent damage to the capillaries in the alveoli
2. Oxygenated blood from the lungs goes through the heart at a higher pressure to the rest of the blood to ensure the blood reaches all respiring cells

Question 16

Why is it important to have enough plasma in the blood?

Answer 16

• So blood can flow easily
• So enough blood cells to transport oxygen
  If not through plasma= viscosity → heart has to pump harder to push blood around body so increased blood pressure

Question 17

Similarity between veins and lymph vessels

Answer 17

Both have valves

Question 18

Property of the arteries

Answer 18

Muscle layer: Thicker than veins so can constrict and dilate to control volume of blood pumped out
Elastic layer: Thicker than veins to help maintain blood pressure, walls can stretch and recoil
Wall thickens: thicker walls than veins to prevent vessels bursting due to high pressure
NO VALVES

Question 19

Properties of the veins

Answer 19

Muscle layer: relatively thin so can’t control blood flow
Elastic layer: relatively thin so pressure is much lower
Wall thickness: thin as pressure is lower and has a low risk of bursting
Has valves

Question 20

What is forced out the capillaries into the lymph

Answer 20

Water molecules
Dissolved minerals and salt
Glucose
Small proteins
Amino acids
Fatty acids
Oxygen

Question 21

What remains in the capillary

Answer 21

Red blood cells
Large proteins
Platelets

Question 22

Properties of the heart structure

Answer 22

Myogenic → can contract and relax without nervous or hormonal stimulation
Never fatigues → as long as it has a supply of oxygen and glucose

Question 23

Features of the atria

Answer 23

• thinner muscular walls than the ventricles AS doesn’t need to contract as hard as only pumping to the ventricles

Question 24

Features of the ventricles

Answer 24

• thicker muscular walls to enable bigger contraction → creates high blood pressure to flow longer distances ( the lungs, around the body)

Question 25

Features of the left ventricle

Answer 25

- pumps blood to the body - needs higher pressure to ensure blood reaches all cells in the body so has a **thicker muscular wall** to enable large contractions of the muscle to create a higher pressure.

Question 26

Features of the right ventricle

Answer 26

- pumps blood to the lungs - needs lower pressure to prevent damage to capillaries in lungs and blood and for blood to flow slowly to allow time for gas exchange SO **thinner muscular wall** than left ventricle

Question 28

What is the function of valves

Answer 28

Make sure blood flows in one direction - Valves open when pressure is higher behind the valve and close when pressure is higher in front of the valve →this prevents backflow of blood

Question 30

What is the septum and why is it important

Answer 30

- cardiac muscle that runs down the middle and separates the deoxygenated blood and the oxygenated blood - IMPORTANCE: means oxygenated blood isn’t being diluted by the deoxygenated blood, mantaining the concentration gradient to enable discussion at respiring cells

Question 31

Cardiac output formula

Answer 31

Cardiac output = heart rate (bpm) x stroke volume ( volume of blood that leaves the heart each beat)

Question 32

What are semi lunar valves connected to

Answer 32

Aorta and pulmonary atery ( so the ventricles Leaving to pump blood out of heart)

Question 33

What are atrioventricular valves

Answer 33

Found between atria and ventricles Bicuspid valve → found on the left side (2 flaps) Tricuspid value → found on the right side (3 flaps)

Question 34

Pressure changes in the valves

Answer 34

Behind SV valve: SV valve opens when pressure is higher behind In front of SV valve: SV valve close when pressure is higher in the aorta than ventricles Behind AV valve: AV valve close when pressure is higher in ventricle than atria In front of AV valve: AV valves open when pressure in atria is higher then in ventricles