Histology Flashcards
Name the 3 layers of an artery
lumen
- tunica intima
- tunica media
- tunica adventitia
What is the term used to describe the recoil effect of arteries during diastole - what is the benefit?
Elasticity: they act as an auxiliary pump, give back the elastic energy to propel blood into arterioles (high resistance)
List the 3 types of arteries, which has the narrowest shape?
- elastic arteries
- muscular arteries
- arterioles: the narrowest!
What is the role of elastic arteries
They are the conducting arteries, widest and act as pressure reservoirs that can stretch and recoil to push blood through
What to muscular arteries do? How big are they?
Medium diameter, distribute blood to arterioles
Why are the walls of elastic arteries stained yellow?
Abundant elastin
What are vaso vasorum and where can they be found?
Vessels supplying other arteries, they can be found in the tunica adventitia of arteries
Name features of an elastic artery’s
a) intima
b) media
c) adventitia
a) Intima: endothelial cells with long axes oriented parallel to the artery, narrow subendothelial CT and discontinuous internal elastic lamina
b) media: 40-70 layers of fenestrated elastic membranes, between lamellae is smooth muscle cells and collagen, thin layer of external elastic lamina may be present
adventitia: thin layers of fibroelastic CT, vaso vasorum
Why is dissection of the aorta a medical emergency?
Blood has created a false lumen by diverting down the media, this narrows blood flow in the actual lumen
(part of differential for chest pain)
Name characteristics of muscular artery’s…
a) Intima
b) Media
c) Adventitia
a) Intima: thick internal elastic membrane
b) 40 layers of smooth muscle cells, connected by gap junctions for coordinated contraction, prominent external elastic lamina
c) Adventitia: Same as elastic + lymphatic vessels and nerve fibres
How/What stimulates vasoconstriction for muscular arteries?
Sympathetic nerve fibres:
- NA released and diffuse through fenestrations to travel from external elastic lamina – internal
- Some smooth muscle cells depolarised
- Depolarisation propagated to all cells of tunica media via gap junctions
What is it meant by an end artery?
What happens if it’s occluded?
Name 3 examples
A terminal artery supplying all/most blood to a body part, if occluded an independent tissue will receive insufficient perfusion
Renal, splenic, coronary
Name the term used to describe the flow pattern as you move a doppler ultrasound closer to arterioles:
Explain it.
Triphasic flow:
- systole: high velocity of blood flow
- early diastole: negative flow as when blood hits arterioles the high peripheral resistance causes some reverse flow
- late diastole: stabilized, low velocity. elastic recoil pushes blood into muscular arteries
What is ABI, and what could make it higher?
Ankle-brachial index, stenosis in a leg artery
Why do arterioles have such a high resistance?
Their vessels are less than 0.1 mm, when smooth muscle cells contract the lumen significantly narrows
Name characteristics for an arteriole’s…
a) Intima
b) Media
c) Adventitia
a) Intima: layer of endothelial cells, thin layer of subendothelial CT, thin internal elastic lamina
b) Media: 1-3 layers of media, but in small arterioles, media will be a single smooth muscle cell that encircles the endothelial cells, NO external elastic lamina
c) Adventitia: Scant, layers of fibroblasts
What is a precapillary sphincter, what does it do and what does it feed into?
A single smooth muscle cell that contracts or dilates to control blood flow into capillaries, feeds into the metarterioles which branch into capillaries
What is vasomotor tone?
What happens if it increases and decreases
The degree of tension of the smooth muscle surrounding the vessels
Increases: more contraction = higher flow resistance and vasoconstriction
Decreases: less contraction = lower flow resistance vasodilation
If sympathetic controls vasoconstriction, what controls vasodilation? (Trick)
What determines their effect?
Name 3
Vasodilator metabolites: metabolites produced in the tissues that feedback onto the arteriole
Their effect is determined by the rate they’re produced and the rate bloodflow washes them away
K+, H+, adenosine
What is reactive hyeraemia?
Why does it occur and how does it go back to normal?
Reactive hyperemia is the transient increase in blood flow to an organ following a brief period of ischemia.
Why? Metabolites continue to be produced in the tissues despite blood supply being cut off, these vasodilator metabolites stimulate huge vasodilation in the smooth muscle cells, lowering the resistance and increasing blood flow. Eventually, the increased blood flow washes away these metabolites and smooth muscle can constrict again
How do vasodilator metabolites play a role in autoregulation?
What 3 basic conclusions can you make from this?
If supply pressure lowers, blood flow to tissues lower, this increases the conc of metabolites (produced by the tissue) in the arteriole, which vasodilates the vessel (lowering resistance) and increases blood supply
- Therefore, tissues receive the perfusion they need to match their metabolism.
- Basic Rule: As long as BP remains in certain limits tissues will be able to get the blood they need
- TPR is inversely proportional to the body’s need for blood flow
Name 2 characteristics of capillaries that aid their function
- Minimal distance/diffusion pathway for gases: single layer of endothelium and BM, one RBC fills the lumen
- Blood velocity is lowest: time for gas/nutrient exchange
Name the 3 types of capillaries, what differentiates them? List some organs that have each
They are differentiated by the nature of their endothelial layer:
1. Continuous: most common, continuous endothelial layer with pores: nervous, muscle, CTs, exocrine glands and lungs
- Fenestrated: windows allowing larger molecules to pass through; parts of the gut, endocrine glands and renal glomerulus
- Sinusoidal/discontinuous: large breaks in capillaries allow movement of cells: large diameter, slower blood flow
Liver, spleen, Bone Marrow
Describe the histological appearance of…
A) small-medium sized veins:
b) most large veins AND an exception
a) thin tunica intima and media (2-3 layers of sm muscle cells), well-developed adventitia
b) Large veins: thicker tunica intima, thin media, well-developed adventitia
Exception: superficial veins: well defined muscular wall (media) likely to resist distension in gravity
What are venue comitantes and what is unique about the way they propel blood?
Paired veins running parallel to an artery, they use the pulsations of the artery to propel blood to the heart
What’s the term used to describe the pressure in great veins leading to the heart, why is it important?
Central Venous Pressure: a major factor in determining the amount of blood that gets back to the heart
What’s the formula for arterial pressure?
Arterial pressure = CO X TPR
What characterizes a biphasic and monophasic waveform and what could cause each?
Biphasic: Mild stenosis, decreased systole and small negative
Monophasic: Tight stenosis means the wall have become much stiffer; systole is decreased and there is no negative flow as there’s no regurgitation and recoil
How does an endothelial nucleus appear in a transverse vs longitudinal section?
Transverse: circular
Longitudinal: elongated
What determines the pressure in veins?
The volume of blood and the balance between blood flow coming in via the body and out into the heart
