Microcirculation Flashcards
What are the two types og substance exchange in Micorcirculation?
- diffusion
2. filtration/resorption (Starling forces)
What do the two types of material exchange in the microcirculation determine?
The rate of delivery of nutrients to the tissues and the rate of the metabolite transport from the tissues.
What happens if the precapillary sphincter is closed?
There is no filtration, but resorption is possible.
Morphology of the Microcirculation:
Arterioles (+- 20um) –> then metarterioles (rich in smooth muscle) –> precapillary sphincters –> Capillaries
- Capillaries are running into venules, then veins carry the blood back to the heart.
- Some shunts also exist between arterioles and venules (creating arteriovenous anastomosis)
How many % of the capillaries are open during rest?
5-10%
Microcirculatory bed gives also room for?
Dead-end lumph vessels, collecting surplus EC fluid into the circulation.
Materials needed for Exchange of substances during diffusion
- gas exchange
- water/ion exchange
- small substances
What are the types of Exchange of substances with diffusion?
- Flow limited (small substances)
- Diffusion limited (bigger molecules)
What are the factors influencing diffusion?
- Concentration gradient
- Permeability
- surface of the capillary
- time available for the diffusion
The extent of gas diffusion depends on?
Partial Pressure
- that drops towards the end of the capillary and toeards the distant cells.
What happens with higher O2 consumption of a tissue?
The faster the drop of the pO2 will be (partial pressure oxygen)
- This will lead to hypoxia
What does Hypoxia mean?
It results in the involvment of more (resting) capillaries.
This local autoregulation is a very important way of insuring an even distribution of gases, and nutrients, in a tissue.
Hypoxia happens when the O2 consumption of a tissue gets higher, which leads to faster drop of pO2.
What happens with the diffusion when there is higher need for O2 in the tissue?
Higher need for O2 in the tissue, faster the blood flow, so the average time spent in the capillary will be too short for optimal gas-exchange.
- that lack of O2 turns on regulatory mechanisms, mo more capillaries will be connected into the microcirculation, more sphincter will open, larger capillary space will be active.
What is Partial Pressure?
It is the individual pressure exerted independently by a particular gas within a mixture of gases.
What are the major forces (Starling forces) of the Exchange of Substances with Filtration/Reabsorption?
- Hydrostatic pressure difference (Ph)
- Permeability
- The oncotic pressure (Ponc)
- The pressure of the surrounding tissue (Pinterst)
What is the Effective Filtration Pressure?
It determines the direction of the substance movement
The Direction of plasma flow equation?
Peff = (Ph.capill - Ph.interst) - (Ponc.capill - Ponc-interstit) - Pinterst
Oncotic pressure is?
constant in the capillary
Hydrostatic pressure is?
- constantly dropping to the venous end of capillary
- Hydrostatic pressure is lower in the capillary than in the artery, and gradually decreases while the blood flows through the capillary.
What happens if the hydrostatic pressure is higher than the oncotic?
= Net filtration
What happens if the hydrostatic pressure is lowerthan the oncotic?
= net reabsorption
How do Osmotic pressure occur?
The wall of the capillary is permeable for water and impermeable for plasma proteins, hence the macromolecules generate osmotic pressure.
What is the Gibbson-Donnan effect?
The plasma proteins are negatively charged, therefore they try to keep cathions within the plasma –> so they increase the osmotic gradient between the plasma and the interstitial space.
What is the sucking force?
The combination of the osmotic force and the Gibbs-Donnan effects generate suckng force, which absorb H2O form ISF to the plasma
This is called Colloid Oncotic pressure
Oncotic pressure is proportional with?
The protein concentration of plasma and of the ISF
Describe the veins
- Function: reservoir
- Resistance is zero
- Distended by increased pressure
- Enlargement is limited by collagen fibers
What type of Venule types exist?
- Postcapillary venule (some pericytes)
- Collecting venule (continous pericyte layer)
- Muscular venule (contractile elements are present)
What are characteristics of the venous system?
- Capacitance system (reservoir)
- Redistribution:
- the vasomotor mechanism, sympathetic vasoconstrictor through alpha-receptors, may redistribute blood toward the resistance segment. - Distensibility is large
- but the collagen network sets the limit.
Function of the Venous circulation is determined by?
Structure of the wall of venous valves
Pressure and flow rate change with certain rhythm in the veins due to?
Due to the valves and change of tissure pressure (i.e muscle pump) and gravitation
The maintenance of venous blood flow is determined by?
By the work of the heart and gravitation and pressure.
Factors maintaining the venous blood pressure:
- “Vis a tergo” the work of the heart (force from behind)
- Gravitation
- Venous valves
- Skeletal muscle pump
- Changing pressure in chest and abdomen
- CVP
What is the Central Venous Pressure (CVP)?
- Pressure in the RA and in the hollow veins is normally 0mmHg. due to the cardiac cycle, positive pressure changes can be detected in the RA (= CVP)
