Hydrostratic pressure (Pc)
within capillaries; forces fluid/dissolved substances through capillary pores into interstitial space (trying to force fluid outward)
Osmotic pressure (np)
caused by plasma proteins (colloid osmotic pressure), causes fluid movement by osmosis from interstitial spaces into the blood (trying to force water inward); opposes filtration
Hydrostatic pressure (Pif)
within interstitial fluid; forces fluid/dissolved substances through capillary wall back into circulation (trying to force fluid inward)
Osmotic pressure (nif)
caused by tissue proteins (colloid osmotic pressure), causes fluid movement by osmosis from capillary into interstitial space (trying to force fluid outward); promotes filtration
Osmotic vs hydrostatic
Osmotic pressure moves fluid toward the pressure, hydrostatic pressure moves fluid away from the presssure
Ex. hydrostatic pressure in capillaries forces fluid from capillaries to interstitial space
Equation for NFP (net filtration pressure)
(Pc+nif)-(Pif-np)
(hydrostatic pressure in capillaries + osmotic pressure in interstitial fluid) - (hydrostatic pressure in interstitial fluid + osmotic pressure in capillaries)
Equation for filtration rate
Kf x NFP
- where Kf is filtration coefficient and NFP is net filtration pressure
- negative value represents reabsorption
- positive value represents filtration
Filtration coefficient (Kf)
Product of surface area times hydraulic conductivity of the membrane
Starling equilibrium
The amount of fluid filtered outward from the arterial end of capillaries equals almost exactly the amount of fluid returned back to circulation
Whole body capillary filtration coefficient
Average net imbalance of forces at capillary membranes causes net fluid filtration in the entire body (expressed as each millimeter of mercury imbalance)
Example: filtration coefficient of an average tissue is about 0.01 mL/min/mmHg/100g (varies more than
Affect of increasing mean capillary pressure on lymphatics
When mean capillary pressure rises above 17 mmHg, net filtration pressure increases almost 70 times higher; this requires a 70 times than normal flow of fluid into the lymph which is impossible, thus the result is EDEMA
Affect of increased interstitial fluid pressure on lymph flow
Directly proportional; any factor that increase interstitial fluid pressure also increases lymph flow (if lymph vessels are functioning normally)
Factors that increase interstitial fluid pressure/ lymph flow
1. Elevated capillary hydrostatic pressure
2. Decreased plasma colloid osmotic pressure
3. Increased interstitial fluid colloid osmotic pressure
4. Increased permeability of capillaries
Lymph pump
When larger lymph vessel becomes stretched with fluid, smooth muscle in the wall of the vessel automatically contracts; degree of pump activity depends on smooth muscle filaments and external compression
Exercise _____ lymph flow
increases
Edema
Large increase in interstitial fluid volume
Causes of edema
1. Increased capillary hydrostatic pressure (Pc)
2. Decreased plasma oncotic pressure (nif)
3. Increased interstitial oncotic pressure (np)
4. Increased capillary permeability (Kf)
5. Reduced lymphatic flow (obstruction)
Examples of increased capillary hydrostatic pressure
(increased venous pressure)
1. Standing posture
2. Venous obstruction
3. Hypervolemia (liquid portion of plasma is too high)
4. Cardiac failure
Examples of reduced plasma oncotic pressure
(hypoproteinemia)
1. Liver diseases (decreased albumin production)
2. Nephrotic syndrome (decreased albumin; excreted)
3. Malnutrition
4. Protein losing enteropathy
Examples of increased interstitial oncotic pressure
(accumulation of metabolites)
1. Edema in exercising muscles
Examples of increased capillary permeability
(substance P histamine kinin)
1. Anaphalaxis
Examples of reduced lymphatic flow
(lymphatic obstruction)
1. Radial mastectomy
2. Filariasis (secondary to nematodes; mosquito vector)
Intrinsic control of blood flow
Local control
Ex. autoregulation, active hyperemia, reactive hyperemia
Extrinsic control of blood flow
Neuronal or hormonal control
Myogenic hypothesis
(explains autoregulation but no hyperemia); stretching o f vascular smooth muscle results in it's contraction (vasoconstriction) which increases arteriole resistance and maintains flow in the face of increased pressure (Q=deltaP/R)
Metabolic hypothesis
(explains local blood flow control); the delivery of oygen to tissue can be matched to oxygen consumption of the tissue by altering the resistance of arterioles which in turn alters blood flow (greater the level of metabolic activity, the greater the prod
Vasodilator molecules
CO2, H+, K+, lactate and adenosine
Which vasodilator metabolites is coronary circulation most sensitive to?
P(O2) and adenosine
Which vasodilator metabolites is cerebral circulation most sensitive to?
P(CO2)
Sympathetic innervation of skin and skeletal muscle
high density
Sympathetic innervation of coronary, pulmonary, and cerebral vessels
low density
Vasoactive substances
Histamine, bradykinin, serotonin, and prostaglandin
Effects of histamine and bradykinin
Released in response to trauma; causes simultaneous dilation of arterioles and constriction of venules -- result is increased pressure, increased filtration out of capillaries and thus tissue edema
Effects of serotonin
Released in response to blood vessel damage; causes local vasoconstriction, decreased blood flow and decreased blood loss (implicated in patho. of vascular spasm in migraines)
Prostaglandins (vasodilators)
Prostacyclins, prostaglandin E
Prostaglandins (vasoconstrictors)
Troboxane A2, prostoglandin F
Effects of Angiotension II and Vasopressin
Act via V1 receptors; potent vasoconstrictors (leading to increased TPR)
Effects of atrial natriuretic peptide (ANP)
Vasodilator; response to an increase in arterial pressure
Aldosterone
Central role in the regulation of blood pressure by increasing reabsorption of ions and water in the kidney to cause conservation of sodium, secretion of potassium, increase in water retention, and increase in blood pressure and blood volume
Anti-diuretic hormone
Prevents the production of dilute urine; two major functions are to retain water and constrict blood vessels
Angiotensin
Causes vasoconstriction and subsequent increase in blood pressure (also stimulates the release of aldosterone)
1. Angiotensin I is formed by the action of renin and is inactive (precursor for angiotensin II)
2. Angiotensin II increases blood pressure by s
Orthostatic hypertension
Decrease in arterial pressure that occurs when a person moves from a supine to a standing position