Cardiovascular System - Venous and Lymphatics Flashcards
Describe vein structure in relation to function.
Veins have thin walls with smooth muscle and a large radius. Facilitates passage of blood from the body back to the heart.
Valves also present which are folds of tunica intimate that create flaps and prevent the back flow of blood when it tries to flow in the reverse direction.
Veins have a storage function for blood also.
Describe the pressure gradient in the cardiovascular tree
High at heart decreases in pattern of
Arteries -> arterioles -> capillaries -> venules -> veins -> vena cava.
As the distance blood travels from left ventricle increases, blood pressure decreases.
Velocity of flow is inversely proportional to the cross-sectional area.
What is venous return?
= volume of blood returning from systemic veins to the heart.
Determined by the pressure gradient and venous resistance.
What are the factors that facilitate venous return?
Venous tone - degree of constriction or dilation in the veins, regulated by sympathetic nervous system activity
Venous valves - one-way valves that prevent the backflow of blood and promote unidirectional flow towards the heart
Respiratory pump - during inhalation, the decrease in intra-thoracic pressure expands the thoracic cavity, leading to a decrease in pressure in the thoracic veins. This creates a pressure gradient favoring blood flow towards the heart
Muscular pump - when muscles contract, they compress nearby veins, pushing blood towards the heart against gravity
Blood volume - an increase in blood volume increases venous return by increasing the filling pressure of the veins
What is venous compliance.
Venous compliance refers to the ability of veins to accommodate changes in blood volume with minimal changes in pressure.
The compliance of a vessel is determined by its elasticity, or the ability to stretch and recoil in response to changes in pressure.
Allows veins to act as capacitance vessels, capable of storing large volumes of blood.
What factors influence venous compliance?
Smooth muscle tone - Constriction of smooth muscle decreases compliance, while relaxation increases compliance.
Venous pressure - Increased pressure tends to stretch the venous wall, while decreased pressure allows the vein to recoil.
Sympathetic nervous system activity - increased sympathetic activity leads to veno-constriction and reduced compliance, vice versa for decreased
Endothelial factors - release various substances that can influence vascular tone and compliance
Explain the function of veins as capacitance vessels
Veins function as capacitance vessels due to their high compliance, which allows them to act as reservoirs for storing a significant portion of the body’s blood volume.
Crucial for maintaining cardiovascular homeostasis and ensuring efficient blood flow throughout the body.
Can adapt to changes in blood volume and flow, helping to optimise cardiac function and tissue perfusion in various physiological conditions
Describe the functions of the lymphatic system.
Fat absorption
Defence against disease
Fluid balance - collects and returns interstitial fluid to blood
Explain how veins differ from arteries
Veins transport deoxygenated blood towards the heart but arteries transport oxygenated blood away from heart.
Arteries have pustule blood flow but veins have smooth blood flow.
Arteries have small lumen but veins have large lumen.
More elastic tissue in arteries than veins.
Valves present in veins and not arteries.
Blood transported under high pressure in arteries but low pressure in veins.
Describe the regulation of venous tone.
Venous tone is the degree of constriction or relaxation in vein walls, determining their capacity to hold blood.
It is crucial for controlling blood pressure, maintaining adequate venous return to the heart, and regulating cardiovascular function.
Factors influencing venous tone include the sympathetic nervous system, hormones like vasopressin and angiotensin II, endothelial factors like nitric oxide and prostacyclin, and local metabolic factors like adenosine, potassium, and hydrogen ions.
Mechanical factors like changes in intravascular pressure can also influence venous tone
Describe the normal distribution of blood volume at rest.
Systemic circulation - largest reservoir
Pulmonary circulation
Heart
Microcirculation
What factors contribute to venous tone?
Sympathetic nervous system
Local factors
Hormonal factors
Mechanical factors
