Veins and the lymphatic system

Question 1

How do veins differ from arteries?

Answer 1

Larger diameter; lie closer to skin surface; have less elastic tissue; have less smooth muscle; have thinner walls; have valves; are more distensible

Question 2

What veins do not have valves and why?

Answer 2

Brain veins due to gravity

Question 3

What happens if you have leaky valves in your veins?

Answer 3

Blood moves in opposite direction of heart, accumulating in the extremities and causing varicose veins

Question 4

How do veins act as a blood reservoir?

Answer 4

Veins contains >60% of the total blood volume of the body; increasing rigidity of veins displaces blood held as a reservoir towards heart, allowing SV and thus CO to increase

Question 5

What is the typical pressure in the veins?

Answer 5

~10mmHg (is low and non-pulsalite)

Question 6

Why might pressure in the veins of the foot be lower than that of the upper limb?

Answer 6

Veins are affected by hydrostatic pressure which opposes blood flowing towards heart

Question 7

What is the driving pressure for venous return?

Answer 7

Difference between capillary pressure and central venous pressure

Question 8

What is central venous pressure (CVP) determined by?

Answer 8

Blood volume and compliance

Question 9

What does it mean if a vein is more compliant?

Answer 9

Can be stretched more easily and hold the volume

Question 10

What is compliance of veins affected by?

Answer 10

Neural, hormonal, and endothelial factors

Question 11

How does sympathetic stimulation affect compliance of the veins?

Answer 11

Reduces compliance (particularly in GI, renal, hepatic, and cutaneous circulations)

Question 12

What hormones affect the compliance of the veins?

Answer 12

Catecholamines vasoconstrict, decreasing compliance

Question 13

How does the endothelium affect the compliance of the veins?

Answer 13

Releases paracrine vasoconstrictors and vasodilators to operate in veins

Question 14

How does the skeletal muscle pump work?

Answer 14

Muscle contraction compresses veins, emptying blood within towards the heart

Question 15

During exercise, what impact does the skeletal muscle pump have on CVP?

Answer 15

Rhythmic muscular contractions ensure CVP is maintained or slightly increases

Question 16

During exercise, how does the skeletal muscle pump affect diversion of blood?

Answer 16

Blood drains into empty veins from distal veins, decreasing pressure in distal veins; blood flow through exercising muscles increases as atriovenous pressure difference is larger

Question 17

How does damage to valves in the veins affect the skeletal muscle pump?

Answer 17

Makes it ineffective, leading to permanent venous distension (varicose veins)

Question 18

How does the respiratory pump increase flow to the heart?

Answer 18

During inspiration, diaphragm and intercostals contract; intrathoracic pressure decreases, intrabdominal pressure increases; flow to heart increases

Question 19

How does the respiratory pump decrease flow to the heart?

Answer 19

During expiration, diaphragm and intercostals relax; intrathoracic pressure increases, intrabdominal pressure decreases; flow to heart decreases

Question 20

Why can coughing be “dangerous” for the heart?

Answer 20

During forced expiration, intrathoracic pressure rises dramatically to ~400mmHg, which can cause temporary stop of flow to the heart

Question 21

How is the lymphatic system similar to the venous system?

Answer 21

Start with capillaries; vessels have valves; lymph composition similar to plasma but lower protein content

Question 22

How does the lymphatic system differ to the venous system?

Answer 22

Has lymph nodes; lymph has lower protein content than plasma

Question 23

What is the purpose of the lymphatic system?

Answer 23

Collects filtered fluid from interstitial space and returns it to circulating blood volume

Question 24

What is oedema?

Answer 24

The accumulation of excess fluid in interstitial spaces; particular in subcutaneous, abdominal, and lung regions

Question 25

What causes oedema?

Answer 25

Filtration > lymphatic drainage

Question 26

How is filtration increased/ lymphatic draining decreased in oedema?

Answer 26

Increased capillary hydrostatic pressure: posture, increase in venous pressure; reduced plasma osmotic pressure: poor nutrition, liver failure, leakage of proteins out of blood, lymphatic damage (e.g. surgical removal for cancer)