Veins and the lymphatic system Flashcards
How do veins differ from arteries?
Larger diameter; lie closer to skin surface; have less elastic tissue; have less smooth muscle; have thinner walls; have valves; are more distensible
What veins do not have valves and why?
Brain veins due to gravity
What happens if you have leaky valves in your veins?
Blood moves in opposite direction of heart, accumulating in the extremities and causing varicose veins
How do veins act as a blood reservoir?
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
What is the typical pressure in the veins?
~10mmHg (is low and non-pulsalite)
Why might pressure in the veins of the foot be lower than that of the upper limb?
Veins are affected by hydrostatic pressure which opposes blood flowing towards heart
What is the driving pressure for venous return?
Difference between capillary pressure and central venous pressure
What is central venous pressure (CVP) determined by?
Blood volume and compliance
What does it mean if a vein is more compliant?
Can be stretched more easily and hold the volume
What is compliance of veins affected by?
Neural, hormonal, and endothelial factors
How does sympathetic stimulation affect compliance of the veins?
Reduces compliance (particularly in GI, renal, hepatic, and cutaneous circulations)
What hormones affect the compliance of the veins?
Catecholamines vasoconstrict, decreasing compliance
How does the endothelium affect the compliance of the veins?
Releases paracrine vasoconstrictors and vasodilators to operate in veins
How does the skeletal muscle pump work?
Muscle contraction compresses veins, emptying blood within towards the heart
During exercise, what impact does the skeletal muscle pump have on CVP?
Rhythmic muscular contractions ensure CVP is maintained or slightly increases
During exercise, how does the skeletal muscle pump affect diversion of blood?
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
How does damage to valves in the veins affect the skeletal muscle pump?
Makes it ineffective, leading to permanent venous distension (varicose veins)
How does the respiratory pump increase flow to the heart?
During inspiration, diaphragm and intercostals contract; intrathoracic pressure decreases, intrabdominal pressure increases; flow to heart increases
How does the respiratory pump decrease flow to the heart?
During expiration, diaphragm and intercostals relax; intrathoracic pressure increases, intrabdominal pressure decreases; flow to heart decreases
Why can coughing be “dangerous” for the heart?
During forced expiration, intrathoracic pressure rises dramatically to ~400mmHg, which can cause temporary stop of flow to the heart
How is the lymphatic system similar to the venous system?
Start with capillaries; vessels have valves; lymph composition similar to plasma but lower protein content
How does the lymphatic system differ to the venous system?
Has lymph nodes; lymph has lower protein content than plasma
What is the purpose of the lymphatic system?
Collects filtered fluid from interstitial space and returns it to circulating blood volume
What is oedema?
The accumulation of excess fluid in interstitial spaces; particular in subcutaneous, abdominal, and lung regions
What causes oedema?
Filtration > lymphatic drainage
How is filtration increased/ lymphatic draining decreased in oedema?
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)
