Cardiac - Microcirculation Flashcards
What pathways can blood take through the microcirculation?
Arterioles - capillaries - venules
Arterioles - Metaarterioles - Capillaries - Venules
Arterioles - Metaarterioles - Venules
What is the structure of capillaries?
They contain no connective tissue or smooth muscle
They consist of a thin tube of endothelial cells with their wall eing only one cell thick
What type of innervation do the arterioles, metaarterioles, precapillary sphincter, and venules all receive?
Sympathetic
Do the capillaries receive sympathetic innervation?
No
Where is capillary density generally high?
Metabolically active tissue (heart)
Where is capillary density usually low?
Tissues with low metablic activity
What is blood flow like in capillaries?
Turbulent
How does blood flow through the capillaries?
RBCs tendn to flow in a single fle formation and are usually folded to fit through the capillary lumen.
Blouses of plasma turbulently flow between RBCs
Why is the turbulent mixing of flow as plasma moves through capillaries important?
It helps expose all the pladma to the endothelial surface/exchange area
How is flow in the microcirculation regulated and controlled?
By active modulatin of anatomical components
Balance between constrictor influences and metabolic vasodilators
Vessel radius has a major influence on flow
What are the major mechanisms that modify vessel radius?
Metabolic activity
Activity of autonomic nerves
Ciculating vasoactive agents (NE, Angiotensin II, etc.)
Endothelium derived vasoconstrictors and dilators
What is the primary regulators of capillary flow? Why?
Precapillary vessels because they have the most vascular smooth muscle
What regulates capillary flow?
Vascular smooth muscle and sympathetic innervation in the arterioles, metarterioles,or precapillary sphincters and their exposure to tissue metabolites
Vascular smooth muscles in enules effect vascular capacitance more and has little effect on vascuale flow
Arterioles are most sensitive to..
neural stimuli
Precapillary sphincters are most sensitive to…
Tissue metabolites (H+, CO2, adenosine, etc.)
Under normal circumstancs, the degree of vasoconstriction in the microcirculatory vasculature is determined by…
The algebraic sum of the effects of constrictor neural stimuli and vasodilatory metabolites
Increasing the neural activity in sympathetic efferents results in…
constriction
Dilation of vasomotor tone occurs by…
passievly reducing sympathetic efferent activity
What mediates active vasodilation?
Sympathetic Cholinergic fibers
What effect does increased metabolic activity have on precapillary vessels and over all capillary perfusion?
There is an increase in the number of precapillary vessels that are open, resulting n increased capillary perfusion
By products of metabolism are all local….
Vasodilators
Oxygen, BP, circulating catecholamines, and sympathetic nerves are all vaso…
vasoconstrictor stimuli
What are the types of exchange vessels?
Capillaries
Portions of terminal arterioles
Venules not encircled with smooth muscle
Why does most exchange occur across the capillaries?
There are more capillaries than other exchange vessels
Capillaries have the greatest surface to volume ratio
The velocity of flow is slowest there
Plasma is continually mixed as blood flows through the capillaries, enhacing the possibilities for exchang
What are the four main types of exchange vessel endotheium?
Continuous endothelium
Fenestrated Endothelium
Discontinuous Endotelium
Tight junction Endothelium
Where is continuous endothelium found?
Skin
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Lungs
Where is fenestrated endothelium found?
GI mucosa, renal glomerulus, peritubular capillaries
Where is discontinuous endothelium found?
Liver and bone marrow sinusoids, spleen
Where is tight junction endothelium found?
CNS and retina
How does exchange of substances across the vascular endothelium occur?
Simple Diffusion
Bulk Flow - Ultrafiltration
Vesicular Transport
The interstitial fluid functions as he…
exchange compartment
What three factors are involved when considering the movement of substances at the capillary level?
Transport across the capillary wall
Transport across tissue cell membrane
Diffusion distance
The rate of diffusion for most substances is determined by..
Interstitial Fluid concentration
Diffusion of solutes can be limited by…
Interaction between solute molecules
Pore configuration
Charge (diffusing molecule vs. endothelial cell)
The rate of diffusion depends on…
Blood-interstitial fluid concentration gradient
Membrane characteristics relative to the substance in question
Molecular characteristics of the substance (size, charge, lipid solubility)
Ultrafiltration aids the diffusion process by…
keeping tissue fluids in a constant state of motion (filtration and reabsorption)
The direction and magnitude of the movement of water across the capillary wall by filtration nis determined by…
The algebraic sum of the hydrostatic and osmotic forces existing scross the membrane
Capillary hydrostatic pressure is determined by…
Arterial pressure
Venous Pressure
Precapillary resistance
Postcapillary resistance
The hydrostatic driving force of filtration is ___ the capillary hydrostatic pressure
greater than
The permeability of the endothelium to proteins is very low, therefore…
proteins are largely retained within the vasular space
___ is the largest contributor to plasma colloid osmotic pressure
Albumin
The Starling Hypothesis relates…
Capillary Hydrostatic Pressure
Interstitial fluid hydrostatic pressure
Plasma Protein oncotic pressure
Interstitial fluid oncotic pressure
In order to predict the direction of fluid movement along the capillary
What is the equation of fluid movement?
FM = k[(Pc+ piI) - (Pi + Pip)]
Filtration occurs when the algrebraic sum is…
positive
Reabsorption occurs when the algebraic sum is…
negative
The determinant of capillary filtration/reabsorption that is most variable is the….
precapiullary resistance
When is there no net movement of fluid in the capillary?
whenh FM = 0
When a capillary is at its equillbrium point, filtration noccurs on the __ side and reabsorption occurs on the ___ side of this point
Arterial
Venous
If the dynamic center is located on the arteruial side of the capillary, the whole capillary is…
absorbing
If the dynamic center is on the venous side, the entire capillary is…
filtrating
What is the importance of the lymphatic system to the microcirculation?
The lymphatic system recovers the plasma protein that leaks from the vascular space and into the interstitial space and returns the excess fluid to the circulatory system via the lymph ducts
Where does edema formation occur?
In a variety of pathological states where the blance of capillary filtration and lymphatic drainage is disturbed
What are some causes of edema?
Venous congestion
hypoproteinemia (hypoalbuminemia)
Arteriolar Vasodilation
Disorganization of interstitial matrix
Increased endothelial permeability to proteins
Lymphatic obstruction
Immobilization of dependent limbs
Venous congestion results in…
increased capillary hydrostatic pressure
Arteriolar vasodilation results in…
increased capillary hydrostatic pressure
Disorganization of interstitial matrix ___ interstitial tissue compliance and ___ interstitial fluid pressure
Increases
Decreases
The ___ and ___ are most susceptible to the detrimental effects of tissue edema
Brain
Lungs
What effect does edema have in the brain?
Edema inside the closed skull results in increased pressure on critical neural and vascular regions
What effect does edema have on the lungs?
Accumulation of interstitial fluid and or alveolar edema widens the distance between alveolar gas and blood in the pulmonary capillaries and may impair O2 and CO2 diffusion
