WEEK 3: Histology of Blood Vessels Flashcards
What do the walls of blood vessels surround
A central cavity known as the lumen
Can wall complexity vary in large blood vessels?
Yes, it varies with vessel size (diameter) and proximity to heart
What circuits do blood vessels form with the heart?
The systemic circuit and pulmonary circuit.
What is the primary function of arteries?
deliver blood from the tissues to the heart
What are the three types of artieries?
- Elastic (close to heart)
-Muscular
-Arterioles
What is the primary function of the vein?
Return blood to heart
What are the different types of veins?
- Venules
- Medium/large veins
Similarities between veins and arteries?
- Both have 3 layers (Tunica shit)
Which layer of wall is closest to the lumen
Tunica interna (thin layer)
Which wall layer is the thickest of the three layers?
Tunica media
What do the composition of these wall layers influence?
Blood flow & Blood pressure
What is the tunica interna made up of?
Endothelium
- Thin- Simple squamous epithelium
- Smooth
- Antithrombogenic
-Basement membrane
-Subendothelial connective tissue
-Internal elastic lamina - IEL
What is the tunica media made up of?
- variable quanitites of elastic tissue/smooth muscle
- smooth muscle has a concentric arrangement of fibres that participate in contraction and relaxation
- Elastic laminae
What is the tunica externa made up of?
- thickest in veins
made up of fibrous connective tissues
abundant collagen fibres
external elastic lamina (EEL)
can contain smooth muscle in veins
can contain a number of smaller blood vessels (vasa vasorum)
Can contain adipose tissue
What are elastic arteries responsible for?
They are conducting arteries and asssist with the propulsion in a forward direction of the blood as the heart beats. These vessels have a large diameter and a thick wall, and are located close to the heart
Why do elastic arteries have thick walls?
so it can withstand very high pressures exerted on it from the blood
Media has?
a high elastin content organised as numerous concentric elastic laminae sheets
What does laminae stretching during systole and recoiling during diastole do?
Reduce the amplitude of fluctuations in blood pressure hence propelling blood forwards
Why is there vasa vasorum in the adventitia?
To provide O2 and nutrients to outer wall regions.
What are muscular arteries?
Distributing arteries that have a role in directing blood flow to particular organs/regions of the body as metabolic requirements change
T or F: The tunica media has less smooth muscle than elastic/collagen fibres
F
What are arterioles?
They are resistance vessels
- smaller diameter, thinner less complex wall structure than arteries
- less than 5 mm diameter
What is the primary function of these vessels (arterioles)?
- by constricting/varying/relaxing, they can reduce blood pressure and enable flow through capillaries - hence allowing for microcirculation
Define microcirculation
the circulation of blood in the smallest blood vessels -> arterioles, capillaries & venules
It’s primary role is maintaining tissue health & regulating blood pressure
What is the function of venules?
collect blood from capillaries
What occurs to the tunica intima layer in venules?
It is reduced to an endothelium
What occurs to the tunica media in a venule
It becomes thinner - 1-2 layers of smooth muscle fibres/elastic fibres
What is the function of pericytes
They surround small venules and control blood flow through the microvasculature
Define microvasculature
the network consisting of the smallest blood vessels in the body (arterioles, capillaries and venules)
What are the role of medium sized veins?
They are blood reservoirs, due to high capacitance
what is a capacitance vessel?
One that is able to distend/stretch readily, even at low pressures
what differentiates a medium vein from an artery
The lumen in a medium vein is thin-walled, large and irregular compared to the lumen in an artery
what is the function of the thin folds of tunica intima valves
- prevent backflow of blood
what distinguishes the tunica media in a medium vein?
It consists of a low muscle content that makes it patchy and discontinuous, 2-3 cell layers only
what distinguishes the tunica adventitia in a medium vein?
- it is the broadest layer compared to the intima and media
- it consists of longitudinal collagen fibres and vasa vasorum
what is the primary function of the large vein ?
acts as a blood reservoir
what distinguishes the large vein from other veins?
- contains no valves and no IEL
- the intima is thinner than the same sized arteries
- a very prominent tunica adventitia
high collagen content - prevents overdistension - vasa vasorum is present
Artery VS vein
artery is part of a high pressure system VS vein is a low pressure system
artery = pressure reservoir VS vein is a blood reservoir
vessels in the artery are at full blood capacity whereas the vessels in the vein are at 30-70% blood capacity
no valves present in arteries VS valves present in veins
well defined circumferential muscle layer in the media of an artery VS reduced muscle in media, less compact and patchy distribution in vein.
Adventitia in artery is thinner whereas it is thicker in vein
vessels have small lumens and thick walls in artery whereas in veins vessels have larger lumens and thin walls
What is vasa vasorum?
small blood vessels that supply the walls of large blood vessels like arteries and veins
What are capillaries?
they are the smallest vessels and are the sites of exchange between blood and tissues
what are the 3 types of capillaries
continuous, fenestrated and sinusoidal/discontinuous
What is the wall structure of capillaries?
- reduced complexity
- consists of endothelium that could consist of fenestrations and tight junctions, as well as pinocytotic vesicles
-Basal lamina - external to endothelial cell - could consist of pericytes
In a blood vessel, the endothelial cell is always simple squamous : T or F
T
Why are endothelial cells thin (attenuated)
To maximise the exchange between blood and tissues
Endothelial cells breakdown lipoproteins to triglycerides and cholesterol: T or F
T
Why are there intercellular tight junctions between endothelial cells?
To restrict passage of materials between endothelial cells
What is a continuous capillary
- It is the most widespread type of capillary
- Tight junctions
- Many pinocytotic vesicles for exchange
- No gaps between endothelial cells
What is a fenestrated capillary
- characterised by interruptions in endothelium
- endothelial cell cytoplasm is pierced by pores = fenestrations
- extend through full thickness of wall
-allow for extensive exchange between blood & tissue - thin diaphragm
- diaphragm is thinner than the cell membrane
What is a sinusoidal/discontinous capillary?
allow for the maximum exchange of blood and tissues, with gaps in walls allow transport of whole cells between blood/tissues
What are some characteristics of a sinusoidal capillary
- numerous large fenestrations
-large diameter
-follow a tortuous/irregular pathway
-incomplete endothelial lining
-discontinous basal lamina
what is the functional implication of continuous capillaries
tight capillaries that allow for selective exchange of molecules - slower exchange
what is the functional implication of fenestrated capillaries - where you want a reasonable amount of exchange fairly rapidly
less selective, more rapid, but not to the same extent to sinusoidal capillaries - so not extremely leaky but in the middle of the continuum
What kind of exchange can occur in capillaries?
either selective exchange or more rapid exchange
