Blood Vessels Flashcards
What type of organ does a blood vessel qualify as?
tubular organ
What is the only exception regarding blood vessels qualifying as ‘tubular organs’?
typical names describing all layers are NOT used!
What does the blood vessel wall layer composition depend on?
the size of the vessel
What are the three principal layers the arterial wall?
tunica interna (intima)
tunica media
tunica externa
State all layers present in the arterial wall (from lumen to outside)
- endothelium
- tunica interna (intima)
- internal elastic membrane
- tunica media (+elastic fibers)
- external elastic membrane
- tunica externa
What is the name(s) of the vessel wall layer adjacent to the lumen? What is it comprised of?
Tunica Interna (Tunica Intima):
- endothelium (simple squamous epithelium)
- subendothelium (fibrous connective tissue)
- internal elastic membrane (elastic fibers)
What is endothelium?
simple squamous epithelium which lines blood vessels and lymphatics.
What is subendothelium?
fibrous connective tissue
What is the internal elastic membrane?
A condensation of elastic fibers in the deep region of the tunica interna of blood vessels.
State the names of the 3 principal arterial wall layers, and what they would be called in a typical tubular organ.
Tunica Interna (Intima) = Tunica Mucosa
Tunica Media = Tunica Muscularis
Tunica Externa = Tunica Adventitia
What is another name for “Tunica Interna”?
Tunica Intima
Why do blood vessels have specific wall names?
In order for its users to know that one is talking strictly about blood vessels (not any other tubular organ).
What helps resist the high arterial blood pressure?
The internal elastic membrane positioned in the tunica interna of arteries. (condensation of elastic fibers in the deep region of the tunica interna)
What is the function of the elastic membranes of arteries?
Elastic membranes guarantee elastic properties for the entire structure, resisting changes in shape, and ensuring that the structure returns to its original shape afetr stretching.
What is a significant difference in the composition of veins in comparison to arteries?
Veins lack: Elastic Membranes!
- no high pressure= no high resistance needed
- no condensation of elastic fibers
What is the composition of tunica media?
mixture of:
- smooth muscle (major)
- connective tissue (minor)
What is the location of tunica media?
between:
- tunica interna
- tunica externa
What is present in some vessels as an outer layer of tunica media? What is it? Name?
External Elastic Membrane:
- condensation of elastic fibers
What is the third, outermost layer, of blood vessels? What does this layer usually blend into?
Tunica Externa:
- tissue layer usually blends into the surroundng connective tissue
What is tunica externa composed of?
connective tissue proper: loose connective tissue
same as tunica adventitia
In what pattern are smooth muscle cells arranged in tunica media?
How does this compare to that of other tubular organs?
circular pattern
(all cells go in the circular pattern, there is no longitudinal layer!)
NOT TYPICAL IN TUBULAR ORGANS! usually: inner circular, outer longit.
What are the different types of arteries?
- elastic arteries
- muscular arteries
What is the major difference between elastic and muscular arteries?
TUNICA MEDIA!
State the specificity of tunica media and tunica interna of elastic arteries.
- high proportion of elastic membranes
very few in tunica interna, however still more than in muscular arteries
State the specificity of tunica media of muscular arteries.
- low proportion of elastic membranes
In what pattern is the elastic membrane of tunica media arranged in vessles?
circular pattern (sheets):
- same as muscle cells
State the composition of tunica media in elastic arteries.
mixture of:
- smooth muscle (minor)
- connective tissue (minor)
- elastic membrane (major)
elastic membranes take up most of teh proportions (little smooth muscle)
What is the function of the tunica externa of blood vessels?
connects blood vessels with other surrounding organs (usually muscles)
What structure may be present in the tunica externa of blood vessles?
vasa vasorum (blood vessel in a blood vessel)
What is the function of vasa vasorum?
guarantee energy and oxygen to the walls of large arteries (eg. aorta)
What is another name used to refer to elastic arteries?
large arteries
In short, state the structure of tunica media of elastic arteries.
Large amounts of elastic fibers scattered among smooth muscle cells.
In short, state the structure of tunica media of muscular arteries.
- smooth muscle
- internal elastic membrane
- lacks elastic fibers in the tunica media
What is another name used to refer to muscular arteries?
medium arteries
How to tell an elastic artery from a muscular artery?
Look at the composition of the tunica media.
- if there are a lot of squiggles = lot of elastic fibers = elastic artery (large artery)
- if there are little squiggles = majority smooth muscle = muscular artery (medium artery)
What is the name of the structures that develop from arteries?
arterioles
What is the wall of arterioles composed of? How does it compare to arteries?
- tunica interna: thinner
- tunica media: smooth muscle (1 or 2 layers)
- tunica externa: thinner
What is the tunica media of arterioles composed of?
1 to 2 smooth muscle layers
What is the same in arteries and arterioles?
tunica interna (intima)
What is the greatest difference between the structure of arteries and arterioles?
tunica media!
- arteries: many smooth muscle cell layers
- arterioles: 2 to 6 smooth muscle cell layers
Are all arterioles uniform in size?
NO:
- arterioles closer to arteries are thicker, larger in size,
- arterioles closer to capillaries are thinner, smaller in size (decreased number of muscle cells in their walls).
What blood vessels are of highest concentration in the organism?
capillaries
What are the different types of capillaries?
- continuous capillary
- fenestrated capillary
- sinusoidal (discontinuous) capillary
What are continuous capillaries? Specific attributes?
- no interruptions/pores in the endothelium
- tight junctions between cells
most common capillaries
What is the most common type of capillary?
Where are they present?
continuous capillary
skin, internal organs, organism
What are fenestrated capillaries? Specific attributes?
Where are they present?
- small pores scattered throughout the endothelial cells (vessel wall)
- diaphragms (control passing molecules)
gastrointestnal tract (intestines), endocrine glands, kidneys
What is the most common location of fenestrated capillaries?
gastrointestinal tract
What is the function of fenestrated capillary ‘diaphragms’?
control of the size of molecules allowed to pass through pores
What is the general sructure of capillaries?
- endothelium (simple squamous epithelium)
- basement membrane
Do continuous capillaries have pores?
usually no, however pores can be formed during an immune response.
- signals cause endothelial cells to change, forming a gap
- immune system cells (lymphocytes, neutrophils) move from the circulatory system to the site of infection
pathological reaction
Why are capillaries fenestrated? What purpose?
- maximize efficiency of absorption (easier and faster)
What are discontinuous capillaries? Other name? Specific attributes?
Discontinuous capillaries = Sinusoid capillaries
- larger lumen (than fenestrated capillaries)
- large, open fenestrations (varying sizes, in endothelial cells)
- incomplete basement membrane
- phagocytic cells (outside endothelium or in the lumen)
What is usually present within the lumen or outside the endothelium of discontinuous capillaries?
phagocytic cells
What is the rate of blood flow through sinusouid capillaries?
very slow!
What structures have a high proportion of sinusoid capillaries?
- liver (cells exit blood circulation)
- bone marrow (cells enter blood circulation)
What is the difference between the gaps present in sinusoid and fenestrated capillaries?
fenestrated: pores WITHIN cells
sinusoud: gaps BETWEEN cells
Do sinusoid capillary cells have gaps?
NO! The gaps are only present between cells in sinusoid capillaries.
In sinusoid capillaries, what are the gaps between cells covered by?
NOTHING!! there is no basement mebrane in the places of gaps.
What do sinusoid gaps allow for?
easy and fast movement of substances (blood)
In what locations are blood vessels NOT present?
- dental enamel, dentin, cementum
- cornea, vitreous body (eyeball), lens
- most cartilage
- most epithelia
Why do epithelial tissues not contain blood vessels?
epithelial tissues are located on a basement membrane, and have loose connective tissue beneath it.
loose connective tissue is very high in blood vessel concentration (supplies nutrients to epithelial tissue through diffusion)
even stratified squamous epithelium doesn’t contain blood vessels
Why do dental structures regenerate very slowly, or not at all?
- no blood vessels
- very mineralized
- diffusion process cannot occur
Why do cartilaginous structures regenerate very slowly?
lack vascularization
How do venules compare with capillaries?
- similar structure
- larger in diameter
What are venules called as they increase in diameter?
pericytic venules or collecting venules
What forms the tunica externa of venules? Is it thick or thin?
thin tunica externa:
- fibrocytes
- collagen fibers
What happens to the composition of venules as they increase in diameter?
pericytes are gradually replaced by muscle cells (circularly arranged)
How are the muscle cells in the venule wall arranged?
circularly
What is a muscular venule?
When circulary arranged muscle cells form 1-2 complete layers.
How is the venule called when it has 1-2 layers thick circular muscle layer?
muscular venule
Where do pericytic venules get their name from? What are they?
They contain pericytes.
Pericytes are stem cells for smooth muscle cells.
What is a major difference in composition between capillaries and venules?
capillaries:
- endothelium
- basement membrane
- there are NO pericytes or smooth muscle cells
venules:
- form a new layer (tunica media) composed of smooth muscle cells
What are the two types of venules? Where are they usually situated?
pericytic venule- close to capillaries
muscular venule- close to veins
How to distinguish between a vein/venule and an artery/arteriole?
artery/arteriole:
- smaller lumen
- thicker walls
- elastic membrane (internal/external)
vein/venules:
- large lumen
- thin walls
- very thick tunica externa
Compare and contrast the three types of veins (small, medium and large veins).
Small Veins:
- smooth muscle (tunica media)
Medium Veins:
- more smooth muscle than small veins (in tunica media)
- tunica externa is well developed
Large Veins:
- circularly arranged smooth muscle (in tunica media)
- longitudinally arranged smooth muscle fibers (in tunica externa)
Why are veins collapsed in most histological slides?
- very large lumen
- very thin walls
- very thick tunica externa
–> difficult to keep open
How does the tunica externa of veins compare with that of arteries?
- much thicker
- lingitudinal smooth muscle fibers present!
What structures are veins characterized by (not present in arteries)? What is their function?
Valves which extend into the lumen and prevent the backflow of blood in a vessel.
How are valves formed? What from?
leaflets of the tunica interna, include:
- endothelium (cuboidal epithelial cells)
- thin connective tissue core
What veins do not have valves?
- vena cava
- hepatic portal vein
What type of epithelium makes up the endothelium of veins?
- cuboidal epithelium!
What histological feature makes veins an acception from the whole cardiovascular system?
Its endothelium is composed of cuboidal epithelial cells (instead of flat simple squamous epithelial cells).
Compare veins and arteries.
Arteries:
- small lumen
- simple squamous endothelium
- thicker tunica media
- small tunica externa
- has elastic membranes (internal/external)
Veins:
- large lumen
- cuboidal endothelium
- thinner tunica media
- large tunica externa (+longitudinal smooth muscle cells)
- absent elastic membranes!
elastic membranes are associated with resistance to high blood pressure
What is the function of the external elastic membrane? What is its other name? What tunica is it part of? What structures is it associated with?
external elastic membrane = external elastic lamina
- seperates tunica media from tunica externa
- part of tunica media
- associated only with arteries
What is the composition of tunica externa?
very similar to tunica adventitia
- only loose connective tissue
- exception: veins may have longitudinal smooth connective tissue
- could have vasa vasorum (vessels in vessels)
