Vascular System Flashcards
Where is the tunica intima? What does it contain?
- located closes to the lumen of the cell
- contains a single layer of squamous epithelial cells (endothelium)
- can have a subendothelial layer (in large vessels)
- interal elastic lamina (tube of elastic running up and down the vessel)
What are the three layers of vessels? what does each layer (Generally) contain?
- Tunica intima (closest to the lumen): contains endothelium, subendothelium, internal elastic lamina
- Tunica media: contains smooth muscles, fibroelastic CT, elastic lamellae… thus contains elastic fibers, type I/III collagen, CIRCUMFERENTIALLY. Also contains an external elastic lamina
- Tunica adventitia: contains colllagenous CT, fibroblasts, elastic fibers, smooth muscle (elastic fibers, type I/III collagen, arranged LONGITUDNIALLY)
Also contains vaso vasorum, nervi vascularis
what is the subendothelial layer of the tunica intima composed of?
loose CT
ONLY FOUND IN LARGER VESSELS
Tunica Media: what does it contain
Depending on the vessel type/size:
either smooth muscle or elastic lamellae (sheets) arranges CIRCUMFERENTIALLY
-also an external elastic membrane in some vessels
Explain the course of the pulmonary and systemic circulation
pulmonary: deoxygenated blood goes through the pulmonary arteries (from heart) and into the lungs, where it gets oxygenated and leaves (back to the heart) via the pulmonary veins
systemic: oxygenated blood leaves the heart via the aorta, goes through arteries/arterioles/capillaries becomes deoxygenated and travels via /venules/veins/IVC or SVC back into the heat
what does the smooth muscle in the tunica media produce?
the extracellular molecules: type I and III collagen, elastic fibers
Tunica Adventitia: what does it contain?
longitudinally arranged type I collagen and elastic fibers, type III collagen, smooth muscle cells, and fibroblasts
-can contain blood vessels (in large vessels)= vaso vasorum, lymphatic vessels, and nerves = nervi vascularis
what are nervi vascularis and what is their function
nerves found in the tunica adventia of a blood vessel (a large vessel).
control the contraction of smooth muscle in the vessel walls
Vascular endothelium
-simple squamous epithelium with the long axis of the cell aligned in the direction of flow
-rest on the basal lamina
-first barrier between the blood and surrounding tissue
(part of the tunica intima)
what is the function of the vascular endothelium?
- control the 2-way traffic between blood and the vessel (into/out of blood/vessel) MAINTAIN SELECTIVE PERMEABILITY
- MAINTAIN THROMBOGENIC SURFACE, INDUCE CLOTTING, DISSOLVE CLOTS, via secretion
- REGULATE LEUKOCYTE MIGRATION
- REGULATE VASCULAR RESISTANCE (vasodilation/constriction)
how do endothelial cells regulate the thrombosis functions of blood vessels?
secretion of
- Antithrombogenic agents: thrombomodulin, prostacyclin, NITRIC OXIDE.. MAINTAINS NONTHROMBO SURFACE
- prothrombogenic agents: von Williebrand factor (tissue thromboplastin, factor III) INDUCE CLOTTING
- Thrombolytic agents: tissue plasminogen activator (TPA) DISSOLVES CLOTS
what are the antithrombotic agents?
nitric oxide, thrombomodulin, prostacyclin
what is a prothrombotic agent?
von Williebrand factor, thrombin
induce blood clotting
What is the function of an artery? What are the 3 types of arteries?
conduct blood away from the heart and distribute it throughout the body.
- elastic arteries
- muscular arteries
- arterioles
what is elastic lamellae
concentric tubular fenestrated elastic sheets
what is the internal elastic lamellae? what division of a vessel is it a part of?
part of the tunica intima
its the first elastic lamellae
what is the external elastic lamellae? what tunic is it a part of
part of the tunica media.
it is the last elastic lamellae in a vessel
what marks the border of the tunica media?
the internal and external elastic lamina
what is the function of the fenestrae in lamellae? what are fenestrae?
they are little holes that function in the diffusion of substances within the vessel wall.
the ______ of lamellae in the tunica intima increases with age and hypertension
total number/thickness
what is the function of elastic arteries?
conducting vessels: they are the first vessels to receive blood from the heart and transport blood from the heart to the muscular arteries.
what are some examples of elastic arteries?
aorta, common carotid, subclavian, pulmonary trunk
describe the tunica intima of muscular arteries
prominent internal elastic lamina!
-endothelium, CT (thin!)
what is the significance of the high elastic content in the wall of elastic arteries
- facilitates continuos and uniform movement of blood along the artery
- maintains blood pressure between heart contractions
- help “smooth out” blood pulses ejected from the heart
what is the distinguishing characteristic of elastic arteries?
LOTS OF WAVY SHEETS (Concentric lamellae) in the tunica media
describe the tunica intima of elastic arteries
endothelium, connective tissue, internal elastic lamina
describe the tunica media of elastic arteries
40-70 concetric elastic lamellae with smooth muscle cells between the lamellae
- includes the external elastic lamina
- the smooth muscle cells secrete type I and type III collagen, ground substance
describe the tunica adventitia of elastic arteries
longitudinally arranged collagen and elastic fibers
- vaso vasorum and nervi vascularis may be present
- about 1/2 the thickness of tunica media
describe the tunica media of muscular arteries
3-40 layers of CONCENTRICALLY arranged SMOOTH MUSCLE cells
- collagen fibers and some elastic material present (NOT IN SHEETS/LAMELLAE)
- external elastic lamina present
describe the tunica adventitia of muscular arteries
-relatively thick layer (around the same thickness as tunica media)
LONGITUDINALLY arranged collagen (most prominent), fibroblasts, and elastic fibers
-may have vaso vasorum or nervi vascularis in larger vessels
why are vaso vasorum and nervi vascularis only present in larger vessels?
Because the smaller vessels can get everything they need via diffusion from blood through tunics
what is an anti-thrombotic agent
dissolves clots
**TPA: tissue plasminogen activator (changes plasminogen to plasmin which dissolves clots).. its what they give stroke patients!
what are discontinuous capillaries?
larger of the capillaries;
- have irregular channels that conform to the shape of the structure in which they are located
- have wide gaps within and between the endothelial cells
- no diaphragms or membrane bridge the gap (like in fenestrae).. thus MASS MOVEMENT OF MOLECULES!
what are some examples of muscular arteries?
femoral, brachial, renal
what is the distinguishing characteristic of muscular arteries?
3-40 layers of smooth muscles
- usually a PROMINENT internal elastic lamina (in tunica intima)
- lack of concentric elastic lamellae
describe the tunica intima of arterioles
basically just endothelim, maybe a small subendothelial layer
internal elastic lamina may be present
describe the tunica media of arterioles
1-2 smooth muscle cell layers arranged CONCENTRICALLY
describe the tunica adventitia of arterioles
usually just blends with the surrounding tissue; thin ill0defined sheath of connective tissue
what is the function of arterioles?
vasoCONSTRICTION of blood vessels (HIGH RESISTANCE VESSELS) via contraction of smooth muscle
how does the structure of smooth muscle impact its function?
has smooth muscle that contracts and causes:
- regulate flow of blood to caps (direct blood where its needed)
- reduction in blood pressure to a lower level to protect the capillary thin walls
- provide major peripheral resistance to blood flow (direct effect on flow and systemic arterial pressue)
what is the distinguishing characteristic of arterioles?
tunica media that only has 1-2 layers of smooth muscles
what is a myoendothelial cell?
an opening in the basement membrane of the tunica intima (endothelial cells) that forms a gap junction with smooth muscle and the tunica media and allows endothelial cells to send processes through it.
- function: to maintain ionic coupling between endothelial cells and smooth muscle cells
- function: autoregulation of the size of the vessel lumen
In what type of vessel is “myoendothelial” cells especially prevalent?
arterioles .. makes sense because myoendothelial cells help autoregulate the size of the vessel lumen, and arterioles function in regulating blood flow throughout the body
What is a metarteriole? What is its function?
- branches off arterioles
- gives rise to capillaries and provides a direct channel between arteriole and post capillary venule (connection between arteriole and venule that gives cap branches)
- function: to regulate flow through capillaries via precapillary sphincters
precapillary sphincters
rings of smooth muscle cells at the opening to capillaries
- function: to regulate flow to capillary bed (off of metarteriole)
- metarteriole connects arteriole to venule and it branches off to capillaries. before each capillary branch there are precapillary schpincters that help control blood: if the sphincter is open, then the blood goes to that specific capillary. If all of the sphincters are closed, then blood can be SHUNT straight from metarteriole to venule
Capillary: what are they?
terminal ramifications of arterioles. ANASTOSOME TO FORM CAPILLARY BEDS.
blood flow is controlled via precapillary sphincters
what types of tissue have more extensive capillary networks?
metabolically active tissue (skeletal muscle, liver, kidney, cardiac muscle)
… less metabolically active tissue like dense connective tissue have less extensive capillary system
what are the layers (tunics) found in capillaries?
ONLY tunica intima
describe the tunica intima in capillaries
endothelium and occasionally pericytes
what is the function of muscular arteries?
distributing vessels: distribute blood to all of body
what is the function of capillaries?
-EXCHANGE: of o2, co2,h20, salts, nutrients, metabolites: between blood and surrounding tissue
what controls the transport of molecules in capillaries?
-transport is regulated by the size and charge of the particular molecule and the nature of the capillary endothelium (ie: continuous, fenestrated, discontinuous)
what is a pericyte? where is found in the body? where is it found relative to the tissue that its found in the body?
- pericytes = multipotent cells that wrap around capillary walls
- differentiate into smooth muscle cells and other cells during vessel growth or post-injury
- have some contractile properties
- the basal lamina of a capillary splits to cover the pericyte as well
where are continous capillaries found?
muscle and connective tissue
modified continuous capillaries found in brain and spinal cord
what is the distinguishable characteristic of continuous capillaries?
endothelium with distinct, thin, cytoplasm that completely encloses the lumen…. a CONTINUOUS layer of endothelium that is surrounded by a continuous basal lamina
LOTS of endocytotic vesicles can be found because movement is done via transcytosis
what are the three types of capillaries?
- continuous capillaries
- fenestrated capillaries
- discontinuous capillaries
what does the endothelium look like in fenestrated capillaries?
flattened with transcellular openings (fenestrae)
how does transport occur in fenestrated capillaries?
via fenestrae (have a single membrane on top called "diaphragm") -in the thicker areas, no fenestrae are presents and instead endocytotic vesicles are responsible for transportation (of water/molecules)
where are fenestrated capillaries found?
prevalent in tissues where there is a lot of fluid tranport, transport of large molecules, or hormone productions…. organs of digestive system, kidney, uvea of eye, and endocrine glands
where are discontinuous capillaries found?
in areas of the body that want intimate contact with whatevers outside of the capillary/blood…. ie: bone marrow, liver, spleen, lymphoid organs
what types of capillaries may have pericytes present? what types of capillaries will never have pericytes present?
can have pericyte: fenestrated and continuos capillaries
will not have pericyte: discontinuous capillaries
what are the characteristic structure of discontinuous capillaries
- wide gaps within and between the endothelial cells
- partial or total absence of basal lamina
- no diaphragms or membrane bridge the gap (like in fenestrae).. thus MASS MOVEMENT OF MOLECULES!
What are the types of veins?
- post capillary venules
- muscular venules
- small, medium (4) and large (5) veins
what is the structure of postcapillary venules? ie: describe the layers of the vessel
tunica intima: endothelium cells and pericytes
tunica media: absent
tunica adventitia: absent
LOOK JUST LIKE LARGE CAPILLARIES
what is the function of post capillary venules?
- collect blood from the capillaries
- help resorb blood filtrate that leaks out of capillaries
- LEUKOCYTE MIGRATION from vasculature to vissue (diapedesis)
- site of vasodilators
explain diapedesis
- when leukocytes squeeze between adjacent endothelial cells to exit the vessel and go from the blood into the connective tissue of the organ
- mediated by selectins on the endothelium and integrins on the leukocytes
- occurs mainly in the postcapillary venules
what regulates diapedisis?
integrins on leukocytes
selectins on endothelial cells
explain the vasoactive action of post-capillary venules
post-capillary venules are the site of action for vasodilators (ie: histamine).. increase the vessel permeability
how does histamine affect post-capillary venules?
release of histamine causes:
- increase in the permeability of endothelial cells (easier for diapedesis).. so tons of wbc leave the vessel and become active (leaky vessels)
- upregulation of P-SELECTIN on the endothelial cell surface – induces wbc adhesion and rolling (then more leave via diapedisis)
what is the distinguishing characteristic of post-capillary venules?
look like large capillaries
muscular venules (aka venules) structure (layers)
tunica intima: endothelium with CT
tunica media: 1-2 layers of concentrically arrange smooth muscle cells… usually accompany arterioles which are smaller and rounder than muscular venules
tunica adventitia: thin layer
what is the function of muscular venules (aka venules)
collect blood from postcapillary venules and deliver the blood to small veins
what is the distinguishing characteristic of muscular venules (aka venules)
usually they accompany arterioles in the tissue; the venules usually is the larger, thinner walled vessel
what is a neurovascular bundle?
venule/vein, artery/arteriole, and nerve
AVN
what are small, medium, and large veins? what distinguishes them?
where the blood from the venules goes next; distinguished by size of the lumen
describe the tunica intima of s/m/l veins
endothelium, CT, internal elastic lamina is sometimes present
describe the tunica media of S/M/L veins
less than 4 layers of concentrically arranged smooth muscle cells
-much thinner than a similarly sized artery which they usually accompany
describe the tunica adventitia of S/M/L veins
LONGITUDINALLY arranged smooth muscle cells, collagen fibers, and elastic fibers
- CT usually predominates over the smooth muscle of the t.media (especially when the vessel is larger)
- vaso vasorum, nervi vascularis may be present
- thickest layer in veins
what is the function of S/M/L veins?
return blood to the heart
what is the distinguishing characteristic of veins?
may accompany arteries in tissues; since blood returns to the heart at a lower pressure, the vein has a larger lumen and thinner, more collapsable wall than the artery.. arteries usually have more smooth muscle in the tunica media
what are valves? where are they found?
- found in veins larger than 2 mm in diameter
- folds of tunica intima tissue that project into the vessel lumen and are covered with endothelium
- especially numerous in the arms and legs
what is the function of valve?
to present backflow of blood, especially in veins that carry blood against gravity
what is an arteriovenous anastomoses?
“AV shunt”
direct arteriole to venule connection that bypass the capillary bed:
heart to artery to arteriole to anastomosis to venule to vein to heart
where are av shunts prevalent? why does this make sense?
in the skin; function in thermoregulation
what is blood flow in av shunts regulated by?
smooth muscle contraction
-when the anastomosis is open, blood passes directly from the arterial circulation to venous circulation
how are av shunts different from metarterioles?
av shunts are NOT associated with a capillary bed (unlike metarterioles). They totally bypass the bed, and shunt blood away from the arteriole before the blood reaches the capillaries. but metarterioles CAN acts as shunts (if all of the pre-capillary sphincters are closed)
what is a portal system/vessel?
carries blood directly from one capillary bed to another WITHOUT first returning to the heart
describe the arterial portal system. what is an example of an arterial portal system?
2 capillaries connected via an artery:
heart to artery to artiole to capillaries to artery (arteriole) to capillaries to venule to vein to heart
EX: kidney: renal cortex
what is a venous portal system? what is an example of one?
2 capillaries connected via a vein:
heart to artery to arteriole to to capillary to venule to capillary to vein to heart
EX: hepatic portal system (intestine/liver), hypothalamic-hypophyseal portal system (adenohypophysis aka pituitary gland)
what is the function of a portal system?
- second capillary recovers material that was lot in the first capillary via filtration (ie: kidney)
- second capillary serves as a filter for material picked up in the first capillary (hormonal control) ie: hepatic portal system
