Microcirculation and capillary filtration

what os the microcirculation,

• what its made out of

• its function structure

• made out of terminal arterioles capilaries and post capillary venules

• function is to transfer of gases, water, nutrients, waste materials, and other substances between blood and body tissues

• structure is a 3d mesh of tubes

• e.g in the head   

  

explain the denisity of the organisation of the microcirculation

density of microcirculation will vary depending on function and demands of that tissue

What do the terminal arterioles do?

 -control blood flow through into capilary beds
- are the gates of microcirculation
- aren't innervated by the ANS unlike arteries and arterioles tone ( constriction and dialtion) is controlled by local factors e.g o2,co2, metabolites

How do the smooth muscle cells and endothelial cells line the arterioles?

- smooth muscle cells line it perpindicular so they can restrict blood flow if needs be
- endothelial cells line parelel the direction of flow

What is vasomotion?

• the rhythmic constriction and relaxation of terminal arterioles that helps maintain blood flow through capillaries.

•  At rest, this causes uneven (heterogeneous) blood flow. 

• During exercise, arterioles relax more uniformly (decreased tone), leading to smoother, faster blood flow through capillaries for efficient gas and nutrient exchange.

What is the structure capillaries & post-capillary venules in the microcirculation?

• do not contain smooth muscle

• aren't innervated

• continuous capillaries can be surrounded by pericytes which can constrict and reduce diameter of capillaries

• 500-1000 micrometres long & 4-8 microns wide

What is the function capillaries & post-capillary venules in the microcirculation?

• function: where substances are exchnaged 

what do pericytes do

like smooth muscle they constrict and reduce te diameter of th elumen of capillaries

What are the 3 types of capillaries and their differnece in permeability to water?

Where are continuous capillaries located

in lungs, skeletal muscle, myocardium, skin, connective tissue, and fat

What is the structure of a continuous capillary and what deos it allow

• continous thin layer of endothlial cells surrounded by basment membranes 

• it allows for effecient gas exchnage as short diffusion distance

Where are fenestrated capillaries located

kidneys, intestinal mucosa, joints

Describe the structure of a fenestrated capillary and why this is important .

- the endothelium is perforated by small fenestrae (holes)(50-60nm wide)

- bridged by a fenestrae diaphragm which is a thin layer of glycoproteins

- this allows water and solutes to pass through but not proteins

- important for fluid transfer

Where is discontinuous (sinusoidal) capillary located

liver, bone marrow, spleen (i.e. clearance, cell transport)

Describe the discontinuous capillary and what is it important for

- they have large gaps (>100 nm) between endothelial cells- cells can travel across endothelium

- no diaphragm

- basal lamina  (thin layer below capilary wall)  is interrupted 

- important for cell movement

How do lipophilicmolecules (e.g. O2, CO2) cross the capillary wall

• via transcellular route

• diffuse directly through the endotherlial cell membrane 

How do gases move across plasma membrane

can move across the plasma membrane

• Very fast, involves diffusion (i.e flows down conc. gradient.)

How do small lipophobicmolecules (e.g. H20, ions) cross the capillary wall

They move by diffusion through intercellular clefts or fenestrations (pores) in the endothelium.

How do small solutes move across plasma membrane?

Small solutes (e.g. salts, glucose, amino acids) move through intercellular junctions or fenestrae by diffusion or filtration, following concentration and water gradients.

How does water move across plasma membrane?

about 90% via intercellular junctions, about 10% via water channels in the plasmalemma

• Fast, involving filtration (moves from high pressure to low pressure)

How do large lipophobic molecules (e.g. proteins) cross the capillary wall

either by vesicular transport, through trans-endothelial channels, or via wide intercellular gaps that open during acute inflammation.

How do proteins move across plasma membrane

Formed by vesicular fusion, this transport is very slow and occurs by convection (movement with water flow).

What are the relative permeabilities of the capillaries towards substances?

What is fluid filtration dependent on

• Fluid filtration is dependent on 2 pressure gradients:

  • Hydrostatic pressure gradien

  • Osmotic pressure gradient (oncotic or colloid osmotic pressure)

What is Starling's equation?

• says that net movement of fluid (Jv) is dependant on the hydrostatic and oncotic pressure

• Jv- net movement of fluid 

• sigma- reflection coefficient whihc masures how permiable the capillary wall is to proteins

• Pc-Pi hydrostatic pressure 

• Pi c - Pi i osmotic pressure

• c is inside capilary 

• i is outside

Filtration is dynamic and varies locally. True or Fals

true, it changes along th elength of the capillary from the arteriolar to venous side

What is the function of lymphatic capillaries in the microcirculation?

• absorb fluid & protein, return these to the blood

• take up & transport microorganisms to lymph glands

simple summary of what the lymphatic system function is

excess plasma  tissue fluid being returned to the blood stream to mainrain fluid balance

What does a lymphatic capillary consist of?

- continuous, overlapping endothelium with interrupted basal lamina & anchoring filaments including elastin

- also have a high oncotic pressure so they can draw out fluid from interstitium

Describe an adaptation of lymphatic capillaries

are slightly larger and blunted at the tips, allowing unidirectional flow

What is the movement of lymph driven by?

compression and one-way valves

what is oedema and how does it occur

• swelling beacsue of the build up of excess fluid in tissues

• when too much fluid leaves the capillaries or the lymphatic drainage can’t keep up.

What are the 3 reasons for oedema developing?

1. increased capillary hydrostatic pressure gradient

2. decreased oncoticpressure gradient

3. the lymphatic system is blocked

example oedema in dentistry

• inflamation of gums