Microcirculation Flashcards
Define: Microcirculaltion
where exchange of oxygen and nutrients occurs in the tissues
arterioles and capillaries
What happens if things aren’t working properly in the microcirculation?
it can cause excess fluid in the tissue space → edema
What role do the lymphatic channels play in microcirculation?
They pick up excess fluid and protein from the interstitial space and bring it back to the vasculature
What are the parts of microcirculation?
Arterioles
Capillaries
Lymphatic system
What controls microcirculation?
sympathetic nervous system
What type of muscle do arterioles have alot of?
smooth muscle
What innervates the arterioles?
sympathetic nerves
Define: Precapillary Sphincters
smooth muscle that regulates blood flow through capillaries (constrict and dilate)
open and close based on metabolic activity
What are the two types of blood flow?
Nutrient blood flow
Nonnutrient blood flow
Define: Nutrient Blood Flow
blood that flows through capillaries
provides nutrients to tissues
Define: Nonnutrient blood flow
blood doesn’t flow through capillaries
blood goes from arterioles to venule through AV shunt
What is the purpose of nonnutrient blood flow?
primarily present in the skin for temperature regulation
goes to venule near surface of the skin that disapates heat
What type of flow do vessels 20 microns in diameter or larger experience?
laminar flow
What type of flow do vessels less than 20 microns in diameter experience?
turbulent flow with cells in a somewhat single file line
What factors influence vessel diameter?
O2
Circulating E and NE
Tissue metabolites
BP
Sympathetic nerves
Endothelial cells
What factors constrict vessel diameter?
O2
Circulating E and NE
BP
Sympathetic nerves
Endothelial cells → endothelin
what factors relax vessel diameter?
Tissue metabolites
Endothelial cells → Nitric Oxide
What happens to vessel diameter when you increase BP?
local vessel constriction
How do different endothelial cells effect fluid movement?
they pose dif limitations
tight junction → little fluid can move across the membrane → Blood brain barrier
Discontinuous endothelium → gaps in endothelium allow fluid to move freely → intestines
What are the two types of transport seen in cells?
flow-limited transport
diffusion limited transport
Define: Flow-limited transport
some substances are able to leave the capillary and enter ISF but some cannot
the amount of a substance allowed to leave the capillary is determined by concentration gradient in the capillary
What establishes the concentration gradient of a capillary?
the amount of flow carrying a substance to a capillary
increase flow bringing substances to the capillary → increase concentration gradient → more diffuse to cell
When is diffusion most efficient?
when you have the largest surface area, high concentration, and short distance
What is diffusion dependent on?
large cross sectional area and high concentration
Define: Diffusion limited transport
Large ISF → greater diffusion distance → fewer substances permeate cell
What can cause an increase in the ISF?
edema
What factors help control amount of fluid across capillary membrane?
Pc, Pi, πp, πi, k
Fluid movement = k[(Pc + πi) - (Pi + πp)]
Define: Pc (capillary hydrostatic pressure )
pressure inside capillary
Define: Pi (interstitial fluid hydrostatic pressure)
pressure in interstitial space
normally negative
Define: πp (plasma protein oncotic pressure)
proteins retained in capillary pull fluid back into venous end
Define: πi (interstitial fluid oncotic pressure)
caused by proteins in the interstitial fluid
Define: filtration
occurs when the algebraic sum is positive
from capillary to interstitial space
Define: reabsorption
occurs when the value is negative
movement of fluid from interstitial space to capillary
What factors make up primary filtration?
Pc and πi
What factors make up primary reabsorption?
Pi and πp
What would happen to the Pc (capillary hydrostatic pressure) if you increase resistance by constricting artery going into the capillary?
Pc would decrease
velocity flow would increase
volume flow would decrease
What would happen to the Pc (capillary hydrostatic pressure) if you increase resistance by constricting the veins going into the capillary?
Pc would increase
increase venous constriction or pressure → increase Pc
What happens to pressure as fluid flows from the arterial end of the capillary to the venous end of the capilary?
Pressure gradually drops as you move from arterial to venous side of capillary
Pc gradually decreases
no net gain or loss of fluid
If the flow of movement is equal to 14 on the arterial side and -1 on the venous side; is the capillary mostly filtering or reabsorbing?
filtering
If the flow of movement is equal to 14 on the arterial side and -1 on the venous side; what is the next effect across the capillary?
mostly filtering
pushing more fluid into the interstitial space than being reabsorbed by the veins
If the flow of movement through a capillary is primarily being filtered out, what would happen if the lymphatic channels are not taking up the extra fluid?
the capillary would promote edema
Which side of the capillary mainly works in filtration?
arterial
Which side of the capillary mainly works in reabsorption?
venous
