Lymphatics, Fluid Compartments, Local Blood Flow Flashcards
What percentage of total body weight is intracellular and extracellular fluid?
ICF = 40% ECF = 20%
What is generally considered an isotonic solution?
A solution that is around 280 osmolality
Less than 280 hypotonic
Greater than 280 hypertonic
What factors affect of fluid movement?
Net driving force
- capillary pressure vs interstitial fluid pressure
- plasma colloid osmotic pressure vs interstitial fluid colloid osmotic pressure
Capillary filtration constant
Surface area
Hydrostatic forces are higher at the arteriolar or venule end?
Arteriolar
Tends to force fluids outwards through capillary membranes
Interstitial fluid hydrostatic pressure is _________. Why?
Negative
Due to the pumping action of the lymphatic
*usually an outward force for fluid movement. Helps pull fluid out of capillary beds
What generates about 70% of the oncotic pressure and tends to cause inward movement of fluid?
Plasma colloid osmotic pressure
Aka: plasma oncotic pressure
*albumin is the most abundant plasma protein
The is caused by the small amount of plasma proteins that leak into the interstitial space?
Interstitial fluid osmotic pressure
Aka: interstitial fluid oncotic pressure
*tends to cause outward movement of fluid
What is the Gibbs-Donnan Effect?
Albumin exerts a greater osmotic force than can be account for solely on the basis of the number of molecules dissolved in the plasma
- Albumin has a negative charge: attracts sodium ions
- Albumin binds a small number of chloride ions: attractors sodium ions
This is the sum of the hydrostatic and osmotic forces favors the new movement of water from the capillary to the interstitial space
Filtration
Happens on the arteriole side
This is the sum of the hydrostatic and osmotic forces factor the net movement of water from the interstitial space to the the capillary
Reabsorption
Happens on the venous side
Pressure in the capillary is _______ with a net driving force of ________ causing fluid to move________of the capillary
High
13-15mmHg
Out
What is the net inward force on the venous side of the capillary bed?
7
What happens to the capillary pressures when a pt is dehydrated?
- decreased capillary hydrostatic pressure
- increased oncotic pressure (on venule end)
*now the pressure gradient is smaller
- beginning of capillary pressure gradient decreases
- end of capillary, want to bring fluid back in at a greater lever
What is the lymphatic system?
- Close-ended network of highly permeable lymph capillaries
- lacking in tight junctions
- fine filament anchors to connective tissue
- muscular contraction: has ability to “pump” creating negative interstitial environment
- drains back at the thoracic duct
*up to 10% of fluid filtered out of capillaries is picked up by lymphatic system
Plasma filtrate is returned to the circulation by? What is returned to the circulation?
By
- tissue pressure
- intermittent skeletal muscle activity
- lymphatic vessel contraction
- system of one-way valves
Returns
- protein (albumin)
- bacteria
- fat
- excess fluid
What are some causes of edema?
Lymphatic obstruction
Change in capillary permeability
Reduction in plasma protein
Increased capillary hydrostatic pressure
*someone at risk for decreased plasma oncotic pressure—> hypoproteinemia during malnutrition
How much of a 70kg adult male is fluid?
60% or 42L
2/3 of that is intracellular
1/3 is extracellular
-80% ECF is interstitial fluid
-20% ECF is plasma
55% for females
Isotonic solution
- it neither shrinks nor swell cells
- 0.9% NS
- 5% dextrose
*will increase volume everywhere
Hypotonic solution
Solution has a lower osmolality (<282 mOsm/L)
- water will diffuse in the cell, causing it to swell
- solution with NaCl < 0.9% are hypotonic
- 0.45% NS
- D5W
Hypertonic solution
Solution that’s hyperosmolar
- Water will flow out to the cell into the extracellular fluid concentrating the intracellular fluid and diluting the extracellular fluid
- NaCl > 0.9% are hypertonic
How do you know if you should give NS or LR to a pt?
If its a renal pt, or a pt with hyperkalemia give NS bc LR has potassium in it.
What is the most commonly used colloid?
5% albumin
- contains plasma protein fractions obtained from human plasma
- used for volume expansion
- moderate protein replacement
- some j-witnesses don’t want albumin
- considered a blood transfusion product and requires all the same nursing precautions used when administering blood products
Describe the components of dual control regarding regulation of peripheral blood flow?
Extrinsic
- primary by the nervous system
- humorally also
Intrinsic (locally by the tissues)
-controlled by the conditions in the immediate vicinity of the blood vessels
Name pharmacologic stimuli that cause contraction of vascular smooth muscle
Catecholamines -epinephrine -norepinephrine -dopamine Endothelin Serotonin Angiotensin II Vasopressin
Name pharmacologic stimuli that cause relaxation of vascular smooth muscle
Histamine Adenosine Nitric Oxine (NO) Carbon Dioxide Potassium Hydrogen ion Prostaglandins Acetylcholine Bradykinin
What is the main factor in acute control of local blood flow?
Tissue metabolic activity
Metabolic mechanism
Any intervention that results in an inadequate O2 (nutrient) supply for the metabolic requirements of the tissues results in the formation of vasodilator substance which increase blood flow to the tissues
This relaxes and increases flow to the capillary
Precapillary sphincter
What are some of the metabolic mechanisms?
Hypoxia - #1
Tissue metabolites and ions
- adenosine
- potassium ions
- CO2
- hydrogen ions
- lactic acid
- inorganic phosphates
What are examples of metabolic control of local blood flow?
Active hyperemia
Reaction hyperemia
What is active hyperemia?
Something causes body to use more O2 increases flow to that area
*AKA functional hyperemia
What is reactive hyperemia?
Transient increase in blood flow after blood flow to tissue has been stopped.
-tourniquet is an example. Return to flow, there is a buildup of metabolites in that limb. Causes vasodilation
-within limits, the peak blood flow and the duration of the reactive hyperemia are proportional to the duration of the occlusion
What is autoregulation
-intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure
- possible explanations for autoregulation
- myotonic mechanism
- metabolic mechanism
Myotonic mechanism of autoregulation
- When the lumen of a blood vessel is suddenly expanded, the smooth muscles respond by contracting in order to restore the vessel diameter and resistance. The converse is also true
- Vascular smooth muscle cells depolarize when stretched
- proposed mechanism is stretch of vascular smooth muscles causes activation of membrane calcium channels (causes contraction)
pressure stays up, but flow goes back down to normal range
Metabolic mechanism of autoregulation
When the pressure increase to a tissue, the flow increases, and excess oxygen and nutrients are provided to the tissues. These excess nutrient cause the blood vessels to constrict and the flow to return nearly to normal despite the increased pressure
Endothelial factors of local blood control
- endothelium is a source of substance that elicit contraction or relaxation of the vascular smooth muscle
- vasoactive substances released from endothelium.
- nitric oxide (NO)
- endothelium-derived relaxing factor - most important!!!
- prostacyclin
- endothelin
- endothelial-derived hyperpolarizing factor (EDHF)
- nitric oxide (NO)
This is the most powerful vasodilator of endothelium
Nitric Oxide
This is the most powerful vasoconstrictor of the endothelium
Endothelin
Nitric Oxide
- generated from amino acid L-arginine
- generated from NO synthase
- increased CMP concentration which produces relaxation by decreasing cytotoxic free calcium (by decreasing free calcium will allow for relaxation)
- very short half-life (6 seconds)
- due to rapid oxidation to nitrite and nitrate
- also due to binding by substance such as hemoglobin
- NO is a gas and must be lived by an inhaled delivery system
Nitric Oxide production is stimulated by:
Sheering forces acting on the endothelium Angiotensin II Acetylcholine Bradykinin Histamine Insulin Substance P
What are some important function of Nitric Oxide in the cardiovascular system?
Vasodilation
Inhibition of vasoconstrictor influences
Inhibition of platelet adhesion to the vascular endothelium
Inhibition of leukocyte adhesion to the vascular endothelium
Anti proliferation
Free radical scavenger
What are systemic effects of Nitric Oxide?
Pulmonary vasodilation
- decreased PVR
- decreased pulmonary artery pressure
- pulmonary decreases right ventricular afterload and improves right ventricular performance
Increased arterial oxygen tension
- inhaled nitric oxide is delivered ONLY to ventilated alveoli
- this improves V/Q relations by vasodilating capillaries and importing blood flow to areas participating in gas exchange
Prostacyclin
- Prostacyclin synthase in endothelial cells acts on cyclo-endoperoxide products to form prostacyclin
- prostacyclin
- strong vasodilator
- inhibits platelet adhesion to the vascular endothelium
- increases cAMP this mediates relaxation
Endothelin
- Synthesized by endothelium
- Potent vasoconstrictor
- Other actions
- increased aldosterone section
- increased cardiac inotropy and chronotropy
- decreased Reynaldo blood flow and GFR
- releases atrial natriuretc pepitde
- in failing heard, contributes to calcium overload and hypertrophy
Endothelin is implicated in the pathogenesis of:
- hypertension
- vasospasm
- heart failure
- pulmonary HTN
What happens when damage to the endothelium occurs?
Damage to endothelial cells will lead to:
- Decreased NO and prostacyclin production (2 vasodilators)
- increased endothelin production
This will lead to:
- vasoconstriction
- vasospasm
- thrombosis
What happens with long-term blood flow regulation?
- long-term regulation of blood flow is important when the metabolic demands of the tissue change.
- over a period of hours, days and weeks, a long-term type of blood flow regulation develops in addition to acute control.
This is a key mechanism for long-term local blood flow regulation by changing the amount of vascularity of the tissues
Angiogenesis - the generation of new blood vessels
What is collateral circulation?
- when an artery or a vein in blocked, a new vascular channel usually develops the blockage and allows at least partial resupply of blood to the affected tissue
- the first stage in this process is dilation of small vascular loops that already connect the vessel above the blockage to the vessel below. Metabolic factor mediation
- within minutes to days adequate flow restored
