Circulation of blood around the body Flashcards
Structure and function of the aorta
Expands during contraction phase of cardiac cycle and contracts elastically between contractions - allow continuous flow (like a balloon)
- reduces pressure fluctuations between beats
- helps propel blood into the aorta and prevent back-flow
Structure and function of arteries and arterioles
- Adjust their diameter (therefore resistance to blood flow) so change the amount of blood flowing through them
- called resistance vessels because they control blood flow to specific tissues.
What is the structure of arteries and arterioles?
Tunica adventitia
• connective tissue (OUTERMOST)
• external elastic lamina
Tunica media
• smooth muscle
Tunica intima
•internal elastic lamina
•endothelium (INNERMOST)
What structure allows arteries and arterioles to withstand high pressure?
- Many collagen and elastin fibers in the tunica adventitia
* this strengthens the vessel wall
What allows the aorta to expand and recoil?
Elastin
What allows the artery/arterioles to adjust diameter?
- Smooth muscle in the tunica media contracts • causes vasoconstriction (narrowing of artery diameter)
- Endothelial cells in tunica intima produce factors that cause vasodilation or vasoconstriction
What is the function of veins?
Drains blood from capillary beds under very low pressure (not sufficient to propel blood to the heart)
Smooth muscle contracts to help blood return to the heart under low pressure
• thin smooth muscle layer, but large volume in veins and a small contraction pushes a lot of blood towards the heart
Why are venules and veins called capacitance vessels?
Because of their ability to stretch and store blood
Describe the structure of a vein
Outermost:
Tunica Adventitia
• loose connective tissue
Tunica media (smooth muscle)
Tunica intima
• internal elastic lamina
• endothelium
Valve - innermost
How are veins expandable?
They have little muscle or less collagen in the adventitia
Outline the main structural difference between arteries and veins
Arteries
• more elastin
• more smooth muscle
• more fibrous collagen in tunica adventitia
Veins
• less elastin
• less smooth muscles and valves
• less collagen
What factors influence venous return?
venous return - returning blood to the heart
• Gravity affects venous return
• larger veins have some smooth muscle which contracts to assist venous return
• skeletal muscles contract in surrounding muscles
• valves in veins prevent back-flow
What is Deep Vein Thrombosis (DVT) and what causes it?
Formation of a blood clot (“thrombus”) in a deep vein
• in a person sitting upright, gravity causes blood to accumulate in the veins of the lower body
• decreased flow rate of blood due to immobility can lead to venous thrombosis
Venous return in aviators and astronauts
- invention of anti-gravity suit
* prevented blood pooling in the lower part of the body during acceleration which deprives the brain of blood
What do capillaries do?
- Receives high pressure blood from arterioles
* allow exchange of materials and interstitial fluid
What materials are exchanged by capillaries?
- Gas exchange: O2 delivered to tissues and CO2 removed
- Nutrient delivery: glucose, ions, water etc to tissue
- waste removal: Metabolites removed from tissue
- production of tissue fluid: extracellular/interstitial fluid
1-3 rely on diffusion
Brielfly describe the structures of capillaries, related to its function
- very narrow (5-10 microns)
- single layer of endothelial cells endothelium - improves diffusion and osmosis
- have tiny holes - allows water, some ions, solutes like glucose and very small proteins to leak out
Fenestrations
Small holes in capillaries which allow water, some ions, solutes like glucose and very small proteins to leak out
How is surface area of capillaries increased, and how does this affect the pressure?
- arterioles branch into extensive networks of capillaries - hugely increases the overall cross-sectional area (CSA)
- this reduces pressure and flow
- enough pressure remains for water and small solutes to be squeezed through capillaries and into interstitial spaces
Starling’s forces
Two opposing forces that maintain water balance in capillaries
How is blood volume maintained if fluid is continuously leaking out of the capillaries?
Starling’s forces
• Blood pressure (Hydrostatic) - tends to force water and small solutes out
• Osmotic pressure: Tends to draw water back into capillaries
What creates osmotic pressure in capillaries?
Large protein molecules that cannot leave the capillaries - causes water to be drawn back into capillaries
Describe the starling’s forces along a capillary. (Venular and arteriolar end)
Arteriolar end - carrying oxygenated blood
• higher blood pressure than osmotic pressure
• net driving force for fluid to leave capillary
Venular blood - carry deoxygenated blood back to the heart
• osmotic pressure higher than blood pressure
• net driving force for fluid to reenter the capillary
What changes in starling’s forces lead to oedema?
- Tissue fluid drains into the lymphatic system and is returned to the Cardiovascular system (CVS)
- An imbalance between blood pressure, osmotic pressure and lymphatic draining lead to oedema
Coronary Heart Disease (CHD)
Narrowing of the small blood vessels that supply the blood and oxygen to the heart
• can lead to heart attacks and strokes
What is atherosclerosis?
- Begins with damage smooth endothelial lining found in healthy arteries
- Inflammatory response occurs - deposits form (plaque)
- smooth muscle cells migrate towards the lumen and attract lipids so plaque becomes fatty
- Fibrous connective tissue produced causing ‘hardening’ of artery
Artery narrowed
What arteries provide blood supply to the heart?
Left and right coronary arteries
• branch off base of the aorta
• if they become blocked heart muscle can become damaged or stop beating (heart attack)
How does aspirin treat chronic heart disease?
• prevent the blood clots from forming in the arteries - reducing the risk of having a heart attack
What does the tunica adventitia consist of?
- connective tissue
* external elastic lamina
What does the tunica intima consist of?
- Internal elastic lamina, connective tissue
* endothelium
What does the tunica media consist of?
Smooth muscle
What best describe the differences in blood pressure along a capillary?
- Blood pressure is highest at the arterial end
* osmotic pressure remains constant throughout the capillary
What do the endothelial cells in the tunica intima do?
• They produce factors that cause vasodilation or vasoconstriction (widening or narrowing of artery diameter)
What is the name and function of the small openings at the base of the aorta?
Coronary arteries
• supply oxygen-rich blood to the entire heart muscle
What is the function of the septomarginal trabecula?
- right atrium
- string that prevents the ventricle from overstretching
- also acts as an electrical conductor pathway
