Microcirculation + Oedema Flashcards
describe the 3 types of capillaries with reference to their structure, distribution + function
continuous= are least leaky (most common) found in skin, skeletal muscle, heart, lungs, BBB.
structure; continuous basement membrane, sealed endothelium and tight junctions. Have intracellular clefts (only BBB dont have these clefts)
fenestrated= These are medium leaky. Fenestra means ‘windows’ aka holes/pores; these fenestrations allow free movement of solutes e.g. glucose, HCO3-. structure: small circular pores/fenestrations in endothelial cells - intercellular clefts much wider than continuous
These are found in organs that need to filter or absorb e.g. in kidneys {glomerulus is a fenstrated capillary}, gut{to absorb nutrients}, pancreas (+other exocrine glands)
.
discontinuous/sinusoid= structure: widest capillary;these are most leaky; basement membrane is not continuous– wide spaces between endothelial cells. These capillaries allow for the movement of cells + large molecules. Found in spleen,liver,bone marrow.
n.b. capillaries have NO SMOOTH MUSCLE
n.b. all capillaries are composed of. a:
basement membrane= underlies endothelial cells providing structural support + part of filtration system
endothelial cells (ECs)= single layer ECs held together by tight junctions
what percentage of total body water (which makes up 60% of the body) is
*intracellular fluid
*extracellular fluid
-interstitial fluid
-blood plasma
*intracellular fluid= 66%found inside cells of every kind of tissue e.g. blood cells, bone cells, muscle cells, adipose cells
*extracellular fluid= 33%
-interstitial fluid=25% includes fluid between cells, lymph, GI fluids, spinal column fluid, fluid in eyes,tears, synovial fluid)
-blood plasma8%
what does microcirculation consist of + what’s its function
microcirculation = network of the smallest blood vessels; arterioles, capillaries, venules
n.b. certain organs will have arteriovenous anastomoses to enable decreased blood flow
function of microcirculation:
*delivering nutrients
*removal of waste products
*gas exchange
*cellular communication
*fluid balance between vascular and cellular compartments
*immunity {getting immune cells to infected site}
microcirculation plays huge role in blood pressure:
CAPACITANCE= arterioles + venules; major resistance vessels that determine TPR{total peripheral resistance} aka SVR {systemic vascular resistance}
define vascular capacitance
vascular capacitance The measure of a BLOOD VESSEL’’s ability to increase the volume of BLOOD it holds without a large increase in BLOOD PRESSURE. The vascular capacitance is equal to the change in volume divided by the change in pressure
what is the equation linking cardiac output, stroke volume and heart rate
cardiac output= stroke volume x heart rate
what are some examples of large proteins that can pass through sinusoid/discontinuous capillaries?
- Albumin - most abundant protein in the blood plasma, plays critical role in maintaining blood volume and pressure
- Globulins - Including antibodies (immunoglobulins) + other globulins involved in transport, clotting, and other functions
- Fibrinogen - large protein involved in blood clotting that can be converted into fibrin
- Lipoproteins - complexes of lipids and proteins that transport cholesterol and triglycerides in the blood.
- Hormones - Some larger peptide hormones may also pass through, especially in the sinusoidal capillaries of endocrine glands where hormones are released into the circulation
- Cells - WBCs/RBCs can pass through the open spaces in sinusoidal capillaries
E.g. In the liver, Kupffer cells (type of macrophage) reside within the sinusoids, able to capture and digest bacteria, old RBCs, and other debris
what are caveolae= mechanism by which molecules move between blood and tissues through capillaries.
caveolae, which are a special type of endothelial cell membrane indentation, are small invaginations of the plasma membrane inside of pits lined with lipid binding proteins; caveolae not same as vesicle since they only have specific places in cell membrane where they occur - vesicles can appear in any part of cells. Both caveolae and vesicles move large molecules.
*Caveolae; detach from plasma membrane and move through cytosol - the way they move is called transcytosis - transporting substances like lipids, albumin in liver)
water primarily moves via [_____ _____] through the intracellular clefts, however, you do not have intracellular clefts in the [____]
water primarily moves via bulk flow through the intracellular clefts, however, you do not have intracellular clefts in the brain
other continuous capillaries (muscles, skin) their main water transport is bulk flow
capillaries w greater permeability (fenestrated capillaries) can facilitate movement of large lipid insoluble molecules as well as water via bulk flow
explain the mechanism of bulk flow
Volumes of fluid move from an area of higher pressure in a capillary bed to an area of lower pressure in the tissues via filtration
so you are looking at hydrostatic pressure within capillary (Pc) and comparing it to the hydrostatic pressure in the interstitial fluid (Pi).
You also compare:
πc= oncotic pressure exerted by plasma proteins within capillary.
πi=oncotic pressure in interstitial fluid
so to work out net filtration of bulk flow we need to do
(Pc-Pi)-(πc-πi)
^basically its overall hydrostatic pressure- oncotic pressure (aka the starling forces)
n.b. if the value is +VE there will be net net filtration, if the value is -VE there will be net reabsorption
so in kidneys its net filtration, in gut its net reabsorption
define oncotic pressure
oncotic pressure= osmotic pressure exerted by proteins, aka colloidal osmotic pressure
how is net filtration pressure calculated?
net volume flow (Jv) is determined by a balance of the 2 forces and is described in Starlings equation:
Jv= Kf[(Pc-Pi)- σ(πc-πi)]
Jv= Transendothelial filtration rate
Kf= filtration coefficient {capillary permeability of water}
Pc= capillary hydrostatic pressure
Pi= interstitial hydrostatic pressure
σ (sigma)= reflection coefficient (capillary permeability of solutes)
πc= capillary oncotic pressure
πi= interstitial oncotic pressure
capillary hydrostatic pressure drives fluid out of vasculature
capillary oncotic pressure draws water in from tissues
what are the determinants of
*capillary hydrostatic pressure
*capillary oncotic pressure
*determinants of capillary hydrostatic pressure:
-arteriolar + venule pressures=> pressure gradient
-capillary resistance to flow
-water movement in + out of capillary
*determinants of capillary oncotic pressure:
-plasma proteins => esp. ALBUMIN
n.b. if theres a disease where albumin is low the fluid can leave the capillary causing oedema
explain the lympathic system + role of lymph capillaries
lympathic system
* If more fluid were filtered than reabsorbed then there is surplus of fluid in ISF - excess fluid taken up by lymphatic system and returned to circulation
* Lymphatic system absorb fluid then goes in 1 direction (valves)
So issues with lymphatics system would cause fluid leakage into ISF
What do lymphatic capillaries do? Lymph capillaries help keep the overall fluid balance in your body. Throughout your body, interstitial fluid (fluid found in the spaces around cells) leaks from blood capillaries into your tissues. Lymph capillaries pick up this fluid and help return it to your circulatory system
lymph capillaries:
* Specialised vessels made up of an endothelial with lotta intracellular gaps surrounded by permeable BM
* End as blind sacs within tissues
Also contain 1-way valves to ensure lymph travels away from tissues
what are the factors that cause oedema {build-up of fluid causing affected tissues to become swollen- usually caused by fluid leaking from blood stream}
*increased capillary hydrostatic pressure
*decreased plasma oncotic pressure
*increased capillary permeability
*lymphatic obstruction
can be caused by
*low albumin
*obstruction in venous system (deep vein thrombosis/thromboembolism)
*volume overload
*heart failure {as heart not able to pump out all the blood causing a back up of pressure; ppl w heart failure have oedema}
what is nephrotic syndrome and how does it cause oedema
nephrotic syndrome= causes low albumin as ur losing albumin through the kidney; increased oedema in tissues v prominent around the eyes, esp, in children loose connective tisue {in adults less elastic con.tissue around eyes}
in nephrotic syndrome there is an exaggerated peripheral capillary permeability to albumin. This would lead to increased interstitial oncotic pressure and fluid retention in the peripheral tissues
