Flashcards in CVS 2.1 - Histology Of CVS Deck (33):
What is the pathway of blood from the capillaries back to the heart?
- Post Capillary Venules
- Medium Veins
- Large Veins
OR LYMPHATIC SYSTEM
What effect does a low cross sectional area have on the rate of blood flow?
Causes a high rate of blood flow
What is the significance of capillaries having a high total cross sectional area?
Causes a slow rate of blood flow therefore ensuring efficient gas exchange
What happens during systole?
- Left ventricle contracts
- Blood pressure in aorta increases (to around 120mmHg)
- Walls of elastic aorta stretch
What happens during diastole?
- Aortic semilunar valve closes
- Aorta walls recoil
- Pressure is maintained and blood is moved towards smaller vessels
- Pressure drops to around 70-80mmHg
What are the three layers of blood vessels?
- Tunica intima (closest to lumen)
- Tunica media
- Tunica Adventitia
Describe the tunica intima of elastic conducting arteries
- Simple squamous epithelium
- Narrow subendothelium of connective tissue
Describe the tunica media of elastic conducting arteries
- Has 40-70 fenestrated elastic membranes
- Smooth muscle and collagen are between lamellae
Describe the tunica adventita of elastic conducting arteries
- Thin fibroelastic connective tissue
- Contains vasa vasorum, lymph vessels and nerve fibres
Describe the tunica intima of muscular arteries
Same as elastic arteries but with the addition of a thick internal elastic Lamina
Describe the tunica media of muscular arteries
- 40 Layers of smooth muscle cells
- Connected by gap junctions
What is the significance of gap junctions in the tunica media of muscular arteries?
There can be quick transmission of depolarisation therefore the cont ratio is coordinated
Describe the tunica Adventitia of muscular arteries
- Same as elastic but vasa vasorum isn't very prominent
- Has unmyelinated nerve endings that release noradrenaline
What is the significance of the unmyelinated nerve endings in the tunica Adventitia?
- Release noradrenaline
- Noradrenaline diffuses through fenestrations of the external elastic Lamina into external tunica media
- Depolarises smooth muscle cells
Describe the structure of an arteriole
- Same three layers
- Tunica media has one smooth muscle cell around all endothelial cells
- No elastic external Lamina
- Tunica adventita is scarce
What is an end artery and what is their significance?
- Terminal artery
- Supply blood to parts without significant collateral circulation e.g. Coronary artery, central artery to retina (absolute end artery)
How are end arteries formed?
Progressive branching without connections with other arteries
What is the function of metarterioles?
To supply blood to and control the rate of flow into the capillary bed
Describe the structure of metarterioles
- Smooth muscle layer is not continuous
- Muscle cells are spaced apart and cover endothelium of the capillary (precapillary sphincter)
What is the function of capillaries?
Gas and nutrient exchange
Describe the structure of the capillary wall
Single layer of endothelium + basement membrane
What are the three types of capillary?
Describe a Sinusoidal/discontinuous capillary. Where can they be found?
- Larger diameter so slower blood flow
- Gaps in walls so whole cells can move between blood and tissue
- Liver, spleen and bone marrow
Describe a post capillary venule
- Similar wall to capillaries
- More permeable than capillaries
- Fluid drains in due to the decrease in pressure, except for inflammatory responses
Describe a venule
- Tunica media begins to appear
- Smooth muscle begins to associate
Describe the structure of a vein
- Larger diameter, thinner wall
- More connective tissue
- Fewer elastic and muscle fibres
Describe the layers of small/medium veins
- Thin tunica intima
- Thin tunica media
- Well developed tunica adventitia
Describe the layers of large veins
- Thicker tunica intima
- Less prominent tunica media
- Well developed Adventitia
What are venae comitantes?
Deep paired veins that accompany arteries
Describe how venae comitantes function
- Artery pulses
- Causes venous return in adjacent veins
What is the pathway of blood from the heart to the capillaries?
- Large (elastic/conducting) arteries
- Medium (muscular/distributing) arteries
Describe continuous capillaries. Where can they be found?
- Cells are joined by tight junctions
- Most common (nervous, muscle and connective tissues etc)