Blood Vessels and Hemodynamics Flashcards
List the way blood is transported from and to the heart (in order)
arteries»_space; arterioles»_space; capillaries»_space; venules»_space; veins
Arteries carry blood _____ the heart and veins carry blood ____ the heart
arteries = away from
veins = towards
What is the function of capillaries?
- Transport blood with nutrients and oxygen to cells in organs and systems
- transport blood with waste and CO2 to collection/expulsion sites
- Perform the exchange of gases between blood and interstitial fluid
What is the difference in structure between veins and arteries?
- veins don’t have elastic membranes like arteries
- veins have valves unlike arteries
What is a capillary’s structure like?
- basement membrane
- endothelial cells
What does the tunica intima consist of in arteries?
- endothelium
- subendothelial layer
- internal elastic membrane
what does the tunica intima consist of in veins?
- endothelium
- subendothelial layer
what does the tunica media consist of in arteries?
- smooth muscle and elastic fibres
- external elastic membrane
what does the tunica media consist of in veins?
- smooth muscle and elastic fibres
what does the tunica externa consist of in arteries?
- collagen fibers
- vasa vasorum
what does the tunica externa consist of in veins?
- collagen fibers
- vasa vasorum
What are the 3 types of arteries and how are they unique?
- elastic, conducting, arteries: thick walls, large diameters of >1cm, a lot of elastic fibers
- muscular, distributing, arteries: more smooth muscle rather than elastin, medium size of 0.3mm-1cm, distant from elastic arteries
- arterioles (aka. resistance vessels): 10 micrometres - 0.3 mm, tunica media of mostly smooth muscle which is only 1 layer in smaller arterioles
what are the differences in function in the 3 different arteries?
- elastic arteries: smooth pressure fluctuations and recoil to help maintain blood pressure or flow
- muscular arteries: deliver blood to specific organs
- arterioles: determine which capillary beds flushed min by min, create resistance to blood flow through the alteration of diameter
What are the characteristics of capillaries?
- microscopic
- thin tunica intima as walls
- 1mm long, and 8-10 micrometre diameter of the luman
- contain pericytes
What is a pericyte?
- stabilize capillary walls
- control permeability of the capillary’s membrane
What are the 3 types of capillaries?
continuous, fenestrated and sinusoidal
What differentiates the 3 types of capillaries?
Continuous capillaries: least permeable, most common
In muscles and the skin: they have endothelial cells linked by tight junctions => uninterrupted lining
In the CNS: they contain intercellular clefts that allow for limited fluid and small solute passage
Fenestrated capillaries: Endothelial cells with pores or fenestrations meaning they have higher permeability
small intestine, endocrine organs and
kidneys
Sinusoidal capillaries: modified and leaky, they have large and irregular lumens which are usually porous or fenestrated, a few tight junctions and large intercellular clefts for proteins and RBCs to pass through
Define microcirculation
Flow of blood through arterioles to venules through a capillary bed
How is flow through a capillary bed regulated?
By the diameter of the arteriole
What is a terminal arteriole?
It’s a branch of an arteriole that further divides into 10-20 smaller “exchange vessels” or true capillaries for gas exchange, forming a capillary bed
What are further features (additional to true capillaries, terminal arterioles, arterioles and veins) that belong to capillary beds?
Precapillary sphincters, metarterioles (kind of like a main branch of the arteriole past the terminus of division). thoroughfare channels (main branch of a venule)
What is a venule?
- Formed in areas where capillary beds unite
- post capillary venules have only endothelium and pericytes, whereas some larger ones have sparse tunica media and thin tunica externa
What is a vein?
- Where venules converge
- they have a tunica externa, media, and intima, but with thinner walls and larger lumens than arteries
- they have a lesser amount of muscle in the tunica media and minimal elastin
- the tunica externa is its thickest layer
What is the capacitance vessel or blood reservoir?
When up to 65% of blood is located in the veins at any one time
What is the difference in the lumen of arteries vs veins?
The lumen of arteries is smaller and rounded (oval) than that of veins, which have larger, more square yet crescent-shaped lumens
What is the difference in thickness and lumen diameter between the 3 arteries, 2 veins, and capillaries?
Elastic arteries are the largest with a diameter of 1.5 cm whereas the comparable vein (a vein not a venule) is 5 mm. The thickest arteries are the muscular and elastic, both with 1 mm of thickness, whereas veins have 0.5 mm. The smallest artery and vein have respective diameters of 37 and 20 microm, with thicknesses of 6 and 1 microm. Capillaries are by far the smallest, averaging a lumen diameter of 9 microm and 0.5 microm in thickness
How is blood flow measured?
ml/min
What is cardiac output?
The amount of blood being pumped out by the ventricles per min
What is blood flow?
- Essentially the measure of cardiac output for the entirety of the vascular system
- it’s fairly constant at rest
- varies through individual organs
How is blood flow regulated?
Independently, through many tissues and organs
Define blood pressure
Force per unit area exerted on the wall of a blood vessel by blood within
How is blood pressure measured?
It’s measured as a systemic arterial BP in large arteries near the heart such as the aorta
What unit is used to measure blood pressure?
mmHg
What keeps blood pressure moving?
A pressure gradient from high to lower pressure areas (arteries have the highest, veins have the lower which is why they require valves to keep flood from flowing backwards)
What is flow and why does it occur?
Flow is whether or not blood is moving through the blood vessels, it’s proportional to the change in pressure
What is resistance?
Resistance is the major determinant of blood flow because a decrease in blood vessel radius, increases resistance to the 4th power
flow and resistance are ____ related
inversely
What is the formula for blood flow?
Blood flow = difference in blood pressure/peripheral resistance
What is the most effective and quick way to change resistance to flow?
A change in the diameter of an arteriole
What does resistance measure?
The total frictional forces that impede blood flow
What factors impact resistance?
- Viscosity
- Vessel length
- Vessel diameter
Define blood viscosity
The thickness of blood because of the elements and plasma proteins within
How does vessel length impact resistance?
The longer the vessel is, the more resistance is created
How does vessel diameter impact resistance?
Since fluid close to the vessel walls moves more slowly and is more resistant than fluid in the center, and smaller vessels have more against the walls in the center, there is a higher resistance.
Small the diameter, higher the resistance
Resistance varies ___ with radius^___
inversely with radius^4
What is the overall formula for blood flow?
F ∝ change in pressure / radius^4
How is arterial blood pressure measured in the body
You have to measure for the mean arterial pressure
What is pulse pressure and how is it measured?
The difference between systolic and diastolic pressure (SP-DP)
How do you calculate MAP?
Diastolic pressure + [(systolic pressure-diastolic pressure)/3]
When is systemic pressure highest?
In the aorta (the artery closes to/attached to the heart)
When does pulse pressure disappear and why?
It disappears in the arterioles because blood flow is steady at that point and beyond
What are the characteristics of capillary beds?
- low blood pressure of about 35 mmHg at entry and about half (~17mmHg) at the end
- since capillaries are so thin and fragile high pressures are not suited for them
- lower blood pressures allow for more exchange at the highly permeable capillaries
What are the characteristics of venous blood pressure?
- Steady and doesn’t change a lot, with a gradient only ~15mm Hg
What factors aid in venous return?
Muscular pump, respiratory pump, and sympathetic venoconstriction
What is autoregulation?
It is the intrinsic control or management of the smooth muscles of arterioles near specific organ’s tissues to ensure the ideal amount of blood is distributed for each specific organ’s function
What would happen if only intrinsic controls functioned and they dilated all arterioles simultaneously?
Blood pressure would drop, causing near-immediate brain failure
What works conversely to intrinsic controls to ensure that not all arterioles dilate at once?
Extrinsic controls
What are extrinsic controls and how do they work?
They use nerves in the sympathetic nervous system, as well as hormones of the neuroendocrine system as control mechanisms.
They reduce blood flow and allow intrinsic controls to allocate it according to need, maintaining the constant MAP
What are the 2 classifications of intrinsic control mechanisms?
Metabolic and myogenic
What does metabolic mean in the context of intrinsic control mechanisms?
chemical
What does myogenic mean in the context of intrinsic control mechanisms?
physical
What is reactive hyperemia?
The dramatically increased blood flow into tissues that occurs when blood supply in the area has been blocked temporarily when there is an occlusion
Results from myogenic response and metabolic wastes accumulating during the occlusion
What is occlusion?
A blockage in a peripheral artery
What are some intrinsic vasodilators?
metabolic
+ ions (K+/H+), oxygen, carbon dioxide, prostaglandins, adonsine, nitric oxide
what are some extrinsic vasodilators?
sympathetic tone (neural)
atrial natrieuretic peptide (hormonal)
What are some intrinsic vasoconstrictors?
myogenic: stretching
metabolic: endothelins
what are some extrinsic vasoconstrictors?
sympathetic tone (neural)
epinephrine, norepinephrine, antidiuretic (hormonal)
What happens when there is a more long-term need for extra flood to one area?
Angiogenesis
define angiogenesis
The number of blood vessels in the region will increase and the vessels already there enlarge.
What is the state of blood flow in skeletal muscles?
- higher capillary density and blood flow in slow oxidative (red) fibers than fast glycolytic (white) fibers
- myogenic and neural mechanisms dominate
- bloodflow increases at a direct connection to metabolic activity within the muscle (active hyperemia)
Define hyperemia
an increase in blood flow
What is the state of blood flow to the brain?
- 750 mL/min at relative consistency
- brain death occurs immediately with ischemia
- increased CO2 = vasodilation
Define ischemia
Inadequate blood supply to organs or muscles
What is the state of blood flow to the skin?
- dependent on body temperature, can change drastically by up to 50x
- uses nerve endings in the skin to sense external changes in temperature to which it either brings hot blood to the surface to release heat or strongly constricts superficial skin vessels, redirecting blood to organs and only leaving whatever little amount of blood remains
Define a venous plexus
Network of intertwining vessels
Define an anastomosis
connections between areas in networks
What is the state of blood flow in the lungs?
- relatively short pathway through the pulmonary circuit
- arteries and arterioles are structurally different with thinner walls and larger lumens with less pressure being required to push blood forward (blood pressure in lungs = 24/10 rather than 120/80)
- low O2 levels = vasoconstriction
- high O2 levels = vasodilation
What is the state of blood flow in the heart?
- myoglobin which usually stores oxygen to satisfy cellular needs has a reduced ability to receive said O2 when the heart rate is abnormally fast
- usually 250 ml/min controlled by myogenic mechanisms, so blood flow is usually consistent despite variations in pressure
- vessels dilate during exercise because of the buildup of vasodilators like adenosine, increasing blood flow by 3-4x
Where is blood flow the slowest?
In the capillaries
Where is blood pressure the lowest?
in the venae cavae
How do you determine velocity of blood flow?
1/sum of all capillary cross-sectional areas
__ fluid enters the interstitial fluid than ___ to the blood
more fluid enters the interstitial fluid than returns to the blood
osmotic pressure in interstitial fluid ___ fluid ___ of the capillary
pulls fluid out
hydrostatic pressure in the capillary ___ fluid ___ of the capillary
pushes fluid out
Hydrostatic pressure in the capillary and osmotic pressure outside the capillary work together to ____
filter waste and debris from the blood towards the arterial end of the capillary bed
Do arteries expand during systole or diastole?
systole
Do arteries constrict/recoil during systole or diastole?
diastole
What does atherosclerosis do to the blood vessel?
Decreases the elasticity of arteries as it is a degenerative vascular disease
Rank the different types of capilleries from most to least permeable
- sinusoidal
- fenestrated
- continuous
What connects a select few arterioles and venules in capillary beds?
vascular shunts or metarteriole-thoroughfare channels
