Lecture 14 - Microcirculation and Edema Flashcards
How are substances moved between the blood and interstitial fluid?
They cross capillary walls by:
- Diffusion
- Transcytosis
- Bulk flow
Bulk flow
A large number of molecules, ions, or particles that are dissolved in fluid move from an area of high pressure to an area of low pressure through gaps between endothelial cells
What is bulk flow important for?
The regulation of the relative volumes of the blood and interstitial fluid
Transcytosis
Large, lipid-insoluble molecules cross the membrane in vesicles (ex. insulin uses this method).
Not efficient, only used for a few molecules that cannot cross any other way.
What factors affect a molecule’s ability to cross the lipid membrane?
- Lipid solubility (the more lipid-soluble a molecule is will cause it to be more permeable)
- The size and shape of the molecule (large, irregular shaped molecules will not pass as easily)
What provides the driving force for diffusion?
Concentration gradients
Facilitated diffusion
The movement of molecules from high to low concentrations with the use of transporter proteins (small water soluble molecules use this method)
Which direction will oxygen and nutrients diffuse?
From the blood into the cell
Which direction will carbon dioxide and metabolic waste diffuse?
From body cells to the blood
Is bulk flow passive or active?
Passive
Is diffusion passive or active?
Passive
Is facilitated diffusion passive or active?
Passive
Is transcytosis passive or active?
Active
Types of capillaries
- Continuous (no holes)
- Fenestrated (small holes)
- Sinusoid (large holes)
Which type of capillary is in the brain?
Continuous
Where are fenestrated capillaries found?
- Intestines
- Kidneys
Where are continuous capillaries found?
- Muscle
- Skin
- Fat
What is the most common type of capillary?
Continuous
Where are sinusoid capillaries found?
- Bone marrow
- Lymph nodes
- Spleen
What can pass through sinusoid capillaries?
Entire blood cells.
What can pass through continuous capillaries?
Small molecules like gases, water, ions, glucose, and some hormones.
What can pass through fenestrated capillaries?
Larger molecules.
Hydrostatic pressure
Pressure exerted by a fluid.
What are the factors that impact hydrostatic pressure?
- Density of the fluid
- Acceleration due to gravity
- Depth below the surface of the fluid
What is the hydrostatic pressure gradient?
The difference in pressure between two fluids (ex. capillary blood pressure and interstitial fluid pressure)
Osmotic pressure gradient
The gradient is generated due to the capillary wall being a semipermeable membrane
Osmotic pressure
Concentration difference in non-permeable solutes between two areas separated by a semi-permeable membrane.
The tendency of solvent molecules is to move from an area of lower solute concentration to a higher solute concentration.
What factors affect osmotic pressure?
- Concentration of solute particles
- Ideal gas constant
- Absolute temperature
Filtration
Bulk flow from capillaries to interstitial fluid.
Reabsorption
Bulk flow from the interstitial fluid to capillaries.
What is the driving force for bulk flow?
Pressure gradient
List the capillary types from least leaky to most leaky
- Continuous
- Fenestrated
- Sinusoid
Features of continuous capillaries
Endothelial cells are separated by intercellular clefts which limits movement, no holes within cells.
Features of fenestrated capillaries
Endothelial cells contain small holes (fenestrations)
Features of sinusoid capillaries
Incomplete basement membrane, large intercellular clefts and pores, allows the most movement.
Blood hydrostatic pressure (BHP)
Pressure of blood against the capillary walls - generated by pumping action of heart.
Which direction does the BHP force fluids?
Typically out of the capillary walls into the interstitial fluid.
How does BHP change within vessels?
It decreases over the capillary bed - it is higher on the arterial end and lower on the venule end.
Blood osmotic pressure (BOP)
Pressure created by nondiffusible plasma proteins too large to cross capillary walls.
Which direction does BOP force fluid?
Into the capillary
What is the gradient between the hydrostatic pressure in the capillary and interstitial fluid?
Movement of fluid is directed out of the capillary into the interstitial fluid.
Blood hydrostatic pressure is higher than interstitial hydrostatic pressure.
What is the gradient between the osmotic pressure in the capillary and interstitial fluid?
Movement of fluid is directed out of the interstitial fluid into the capillary.
Blood osmotic pressure is higher than interstitial osmotic pressure.
What drives filtration?
Blood hydrostatic pressure
What drives reabsorption?
Blood osmotic pressure
Direction and amount of fluid flow depends on
The difference between hydrostatic pressure and osmotic pressure.
Net filtration pressure
Considers all the forces acting on a capillary wall, and determines the direction of fluid transfer at any given point along the capillary. It is the force promoting filtration minus the force promoting reabsorption.
How is net filtration pressure calculated?
NFP = (forces promoting filtration) - (forces promoting reabsorption)
NFP = (BHP + IFOP) – (BOP + IFHP)
Can be simplified to NFP=BHP-BOP due to the IFHP and IFOP being small in normal conditions but NOT in diseased conditions
What factors promote filtration?
- Blood hydrostatic pressure
- Interstitial fluid osmotic pressure
(directs fluid out of the capillary)
What factors promote reabsorption?
- Blood osmotic pressure
- Interstitial fluid hydrostatic pressure
(drives fluid into capillary)
What movement occurs at the arterial end of the capillary?
Filtration
Fluid moves into interstitial fluid because hydrostatic pressure is higher than blood osmotic pressure
What movement occurs at the venous end of the capillary?
Reabsorption
Fluid moves out of interstitial fluid because hydrostatic pressure is less than blood osmotic pressure
How does blood osmotic pressure change in a capillary?
It stays constant.
How does blood hydrostatic pressure change in a capillary?
It decreases toward the venule end.
Under normal conditions, the volume of fluid reabsorbed is ______ the volume filtered.
Under normal conditions, the volume of fluid reabsorbed is almost as large as the volume filtered.
What is the net pressure at the arterial end of a capillary?
10 mmHg out of the capillary.
What is the net pressure at the venule end of a capillary?
- 9 mmHg. (reabsorption)
What happens to excess fluid in the interstitial space?
It enters lymphatic capillaries.
How much fluid enters lymphatic capillaries every day?
About 3L.
What percentage of fluid is reaborbed?
85%
What causes BHP to change in a capillary?
The movement of fluid out of the capillary causes BHP to decrease.
When is there no net movement in a capillary?
When the reabsorption forces and filtration forces are equal, causing NFP to be 0.
Occurs somewhere in the middle of a capillary.
What will cause BHP to change?
- Change in blood volume
- Constriction of blood vessels
- Age (less elasticity of vessels, plaques forming)
What causes BOP to change?
- Blood volume
- Solute concentration
How do changes to BHP and BOP affect filtration and reabsorption?
More BHP increases filtration.
More BHP decreases reabsorption.
More BOP decreases filtration.
More BOP increases reabsorption.
If the mitral valve is affected, the result is elevated blood pressure in the veins and capillaries of the ____ and, if the pressure is high enough, fluid in the ____.
If the mitral valve is affected, the result is elevated blood pressure in the veins and capillaries of the LUNGS and, if the pressure is high enough, fluid in the LUNGS.
Failure of the AV valve to close properly results in ____.
Failure of the valve to close properly results in turbulent blood flow. Blood is regurgitated into the atrium, leading to an increase in atrial blood volume and size. When regurgitation is severe, the atrial pressure may also increase.
If the tricuspid valve is affected, elevated blood pressure in the veins and capillaries of ____ occurs, and accumulation of fluid in the ____ may develop.
If the tricuspid valve is affected, elevated blood pressure in the veins and capillaries of THE BODY occurs, and accumulation of fluid in the ABDOMEN, LEGS, OR ANKLES may develop.
Further damage to the heart can occur due to the continued ____ into the ____ and also to the body’s attempts to compensate for the ____ blood flow.
Further damage to the heart can occur due to the continued HIGH-SPEED FLOW OF BLOOD into the ATRIUM and also to the body’s attempts to compensate for the DECREASED blood flow.
At the end stage of the heart disease, these compensatory mechanisms become ____.
At the end stage of the heart disease, these compensatory mechanisms become HARMFUL RATHER THAN BENEFICIAL.
Why do lymphatic vessels have more valves than veins?
Low pressure, no pump.
Do capillaries filter or reabsorb more fluid?
Filter
What is the function of fluid recycling?
- Ensure constant plasma and interstitial fluid communication
- Maintain blood volume levels
- Prevent interstitial fluid levels from rising out of control
- Accelerate distribution of nutrients, hormones, and dissolved gases through tissues
- Transport insoluble lipids and tissue proteins that cannot cross capillary walls
- Flush bacterial toxins and chemicals to immune system tissues
Lymph
Tissue fluid (interstitial fluid) that enters the lymphatic vessels
The lymphatic system is connected to which other system?
Cardiovascular
In what direction is lymph transported?
One-way transport to the bloodstream.
How is lymph moved?
There is no pump in the lymphatic system so lymph is moved through the action of skeletal muscles and contraction of smooth muscle in vessel walls.
Describe the path of lymph through the lymphatic system.
- Lymphatic capillary
- Lymphatic vessel
- Lymph node
- Lymphatic vessel
- Lymphatic trunk
- Collecting duct
- Vein
What are the lymphatic organs?
- Thymus
- Lymph nodes
- Spleen
- Tonsils
Which are more permeable: lymphatic capillaries or blood capillaries?
Lymphatic capillaries are more permeable.
Describe lymphatic capillaries.
They are blind-ended. They are made of a single layer of overlapping endothelial cells.
Are lymphatic vessels or veins thinner?
Lymphatic vessels
How many layers are lymphatic vessels?
3
Do lymphatic vessels or veins have more valves?
Lymphatic vessels.
How are lymphatic vessels arranged?
In superficial and deep sets.
What structure is interposed between lymphatic vessels?
Lymph nodes - interposed at intervals between vessels.
Are lymph nodes located alone or in clusters?
Both, but typically in clusters.
What is the function of lymph nodes?
Act as filters, slowing down and cleaning the lymph before returning it to the blood.
What causes lymph nodes to swell?
Lymph nodes trap pathogen that has invaded the body and sometimes become swollen with the white blood cells that fight that pathogen.
What is the function of tonsils?
Filter pathogens and produce white blood cells.
Why are tonsils removed?
They may be removed if they become so large they cause an obstruction or if they are chronically inflamed.
What is the thymus?
A small gland in the lymphatic system that makes and trains special white blood cells called T-cells.
What do T cells do?
Destroy the body’s own cells that have been taken over by viruses or have become cancerous.
What is the function of the spleen?
- It acts as a filter for blood as part of the immune system.
- Old red blood cells are recycled in the spleen, and platelets and white blood cells are stored there.
- The spleen also helps fight certain kinds of bacteria.
Where are lymphatic cells located?
In the lymphatic system and cardiovascular system.
What do lymphatic cells do?
Elicit an immune response.
List the types of lymphatic cells.
- Macrophages.
- Epithelial cells.
- Dendritic cells.
- Lymphocytes.
What are lymphocytes?
A type of white blood cell that is part of the immune system.
What are the two main types of lymphocytes?
- B cells
- T cells
What do B cells do?
Produce antibodies that are used to attack invading bacteria, viruses, and toxins.
What is edema?
An abnormal increased volume of interstitial fluid in a tissue or organ, accompanied by swelling.
What changes to hydrostatic pressure would cause edema?
Increased hydrostatic pressure would increase blood pressure, leading to more fluid entering the interstitium.
What changes to osmotic pressure would cause edema?
Reduced blood osmotic pressure results in less fluid being pulled into the blood stream - leads to buildup of fluid in interstitium.
What can cause edema?
- Increase in capillary permeability
- Decrease in plasma protein concentration
- Increase in blood hydrostatic pressure
- Lymphatic obstruction
What can cause reduced blood osmotic pressure?
- Renal disease
- Hepatic disease
- Malnutrition
How does renal disease cause a decrease in blood osmotic pressure?
Albumin is lost across the glomerular membrane and is excreted through urine.
How does hepatic disease reduce blood osmotic pressure?
There is a decrease in albumin synthesis which decreases the concentration of plasma proteins in the blood.
How does malnutrition cause reduced blood osmotic pressure?
Leads to inadequate albumin synthesis.
What can cause lymphatic obstruction?
- Tumours
- Fibrosis
- Inflammation
- Surgery
- Congenital abnormality
What is “stocking up”?
Swelling of the limbs in horses due to long periods of inactivity - lack of skeletal muscle use leads to local edema as skeletal muscles normally help lymphatic circulation.
What is the treatment for “stocking up”?
Exercise
What type of edema will be caused by heart failure?
Generalized
What type of edema will be caused by left ventricular failure?
Pulmonary
What type of edema will be caused by renal disease?
Generalized
What type of edema will be caused by liver disease?
Generalized
