Week 6: The Circulatory System Flashcards
What are the 3 major types of blood vessels?
- Arteries and arterioles
- These carry blood away from the heart
- These are the thickest
- Blood within the systemic circuit in arteries and arterioles is oxygenated
- Blood within the pulmonary circuit within arteries and arterioles is deoxygenated (pulmonary trunk into pulmonary arteries carries deoxygenated blood to the lungs) - Capillaries
- Is the site of exchange with tissues (structurally therefore they are the thinnest vessels)
- Where oxygen, nutrients etc. is dropped off
- Where waste like carbon dioxide is picked up - Veins and Venules
- These carry blood towards the heart
- These are thinner than arteries
- Deoxygenated blood in the systemic circulation
- Oxygenated blood in the pulmonary circulation (pulmonary veins carry oxygenated blood into the left atrium)
What are the 3 layers of blood vessels?
Tunica externa or tunica adventitia - primarily made up of connective tissue
Tunica Media - primarily made up of smooth muscle
Tunica interna or tunica intima
What are the 2 types of arteries?
- Elastic artery
Have thick walls and a wide lumen. Made up of a lot of elastin so that they can withstand the pressure of ejection from the ventricles
- Muscular arteries
Have thickest tunica media, are vasoactive (can vasoconstict and vasodilate) –> these are good at prevention of bleeding out as they can vasoconstrict unlike veins
There is elastic artery then musclar artery then ____ then capillary
arteriole
Are arterioles vasoactive and if not or they are, why so?
- These are also vasoactive and have a protective mechanism that restricts blood pressure and flow for the capillary beds (stopping friction and pressure damage)
What are the 3 things that can initiate contraction of smooth muscle?
- membrane potential –> have resting membrane potential of around -40mV. Have a voltage threshold for voltage L type gated calcium channels. A depolarisation will trigger influx of calcium and therefore a contraction.
- Chemicals –> faciliated by a ligand gated potassium channel or through g protein coupled receptor which leads to inhibition or influx of calcium.
- Mechanical forces –> myogenic mechanism –> myogenic stretch receptors, an increase in arterial pressure will open these receptors and cause an influx of calcium. These are mechanically gated ion channels.
What are the 3 types of capillaries?
- Continuous capillaries - Are made up of endothelium cells which butt up together with tight junctions between them
- Fenestrated capillaries -These types of capillaries have numerous pores known as fenestrations
- Sinusoids
- These are the leaky capillaries, which are usually fenestrated
What are the 3 things which regulate blood flow?
- Vasomotor nervous control (opens and closes supply)
- local chemical factors
- Activity in skeletal muscle produces more potassium, more carbon dioxide causing vasodilation to match the supply with demand - Vascular shunts
- Are metarterioles and thoroughfare channels which bypass capillaries not in use
- In doing, this shunts blood to places which need it
- This is controlled by precapillary sphincters (which is smooth muscle wrapped around like a bracelet, when contraction occurs it prevents blood flowing through the capillary directing it towards the vascular shunt)
How many ‘tunics’ (layers) do veins contain?
3
How do veins return their blood supply to the heart in areas which compete against gravity (such as returning blood from lower limb to heart)?
Use skeletal muscle pump. Will have valves which prevents backflow of blood. When gastrocnemius contracts will squeeze and push blood in vein up.
What is an anastomoses?
A connection between two peripheral vessels without an intervening capillary bed
this is so there are multiple passages for blood flow
What are the mechanisms that faciliate filtration (movement of substances through capillarymembrane) (x4)
If lipid soluble can diffuse straight through
Intracellular clefts allow passage of water soluble substances
Fenestrations
Vesicles
Describe the movement of fluid for the starling force plasma colloid osmotic pressure
reabsorption of fluid into capillaries (from proteins)
Describe the movement of fluid for the starling force interstitial fluid pressure
Basically just interstitial hydrostatic pressure –> NOTE: this can either favour filtration or reabsorption
Describe the gradient of forces at the arterial end and why its like this?
Favour delivery (pushing out of capillary) at arterial end to delivery nutrients to tissues
Describe the gradient of forces at the venousand why its like this?
Favour reabsorption which ensures there is no fluid build-up and dexoygenated substances that do no provide any benefit
What happens to the fluid in the arterial end that is not filtered (not delivered to tissue)
the lymphatic vessels reabsorbed most of the left over fluid
Whats the significance of having 1 sheet of elastin in walls of arteries in comparison to have lots?
Lots of elastin will allow these vessels to cope under increased pressure and blood volume. This increase will also creates a form of stored energy which recoils the blood along the length of the vessel allowing it to travel further.
1 sheet of elastin will make the artery much easy to tear and decrease the compliance
Do alpha 1 adrenergic receptors cause vasoconstriction or vasodilation?
Vasoconstriction from ACh neurotransmitter
Do beta 1 adrenergic receptors cause vasoconstriction or vasodilation
vasodilation from ACh neurotransmitter
What features of the capillary beds ensures that the appropriate material transverses the vessel wall?
fenestrations and intercelluluar clefts and vesicles
What important function is served by having hydrostatic/blood pressure lower in the venule than in the interstitium?
Pressure needs to be lower in venules than in capillary so you have blood flowing into those vessels (from high to low pressure)
What factor influences the ability of blood to return to the heart via the veins?
Skeletal muscle pump
