hydrostatic pressure

Examples of hydrostatic pressure in the following topics:

• Capillary Dynamics

  • Hydrostatic and osmotic pressure are opposing factors that drive capillary dynamics.
  • Hydrostatic pressure is the force generated by the pressure of fluid within or outside of capillary on the capillary wall.
  • Movement from the bloodstream into the interstitium is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure.
  • Due to the pressure of the blood in the capillaries, blood hydrostatic pressure is greater than interstitial fluid hydrostatic pressure, promoting a net flow of fluid from the blood vessels into the interstitium.
  • Describe hydrostatic pressure and osmotic pressure, the factors of capillary dynamics

• Regulation of Glomerular Filtration Rate

  • GFR=Filtration Constant X (Hydrostatic Glomerulus Pressure–Hydrostatic Bowman's Capsule Pressure)–(Osmotic Glomerulus Pressure+Osmotic Bowman's Capsule Pressure)
  • Changes in either the hydrostatic or osmotic pressure in the glomerulus or Bowman's capsule will change GFR.
  • GFR is most sensitive to hydrostatic pressure changes within the glomerulus.
  • The Bowman's capsule space exerts hydrostatic pressure of its own that pushes against the glomerulus.
  • Increased Bowman's capsule hydrostatic pressure will decrease GFR, while decreased Bowman's capsule hydrostatic pressure will increase GFR.

• Movement of Fluid Among Compartments

  • Hydrostatic pressure is generated by the contractions of the heart during systole.
  • The osmotic pressure drives water back into the vessels.
  • At the arterial end of a vessel, the hydrostatic pressure is greater than the osmotic pressure, so the net movement favors water and other solutes being passed into the tissue fluid.
  • At the venous end, the osmotic pressure is greater, so the net movement favors substances being passed back into the capillary.
  • Oncotic pressure exerted by proteins in blood plasma tends to pull water into the circulatory system.

• Bulk Flow: Filtration and Reabsorption

  • Capillary fluid movement occurs as a result of diffusion (colloid osmotic pressure), transcytosis, and filtration.
  • The movement of materials across the capillary wall is dependent on pressure and is bidirectional depending on the net filtration pressure derived from the four Starling forces.
  • When moving from the bloodstream into the interstitium, bulk flow is termed filtration, which is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure.
  • When moving from the interstitium into the bloodstream, the process is termed reabsorption and is favored by blood oncotic pressure and interstitial fluid hydrostatic pressure.
  • Modern evidence shows that in most cases, venular blood pressure exceeds the opposing pressure, thus maintaining a positive outward force.

• Glomerular Filtration

  • The force of hydrostatic pressure in the glomerulus (the force of pressure exerted from the pressure of the blood vessel itself) is the driving force that pushes filtrate out of the capillaries and into the slits in the nephron.
  • Osmotic pressure (the pulling force exerted by the albumins) works against the greater force of hydrostatic pressure, and the difference between the two determines the effective pressure of the glomerulus that determines the force by which molecules are filtered.

• Edema

  • Cutaneous edema is referred to as pitting when, after pressure is applied to a small area, the indentation persists for some time after the release of the pressure.
  • Edema may also occur as a result of cardiac failure due to the rise in hydrostatic pressure.
  • A fall in osmotic pressure occurs in nephrotic syndrome and liver failure, and may cause edema.

• Distribution of Lymphatic Vessels

  • This fluid is mainly water from plasma that leaks into the intersitial space in the tissues due to pressure forces exerted by capillaries (hydrostatic pressure) or through osmotic forces from proteins (osmotic pressure).
  • When the pressure for interstitial fluid in the interstitial space becomes large enough it leaks into lymph capillaries, which are the site for lymph fluid collection.
  • Lymph vessels become larger, with better developed smooth muscle and valves to keep lymph moving forward despite the low pressure and adventia to support the lymph vessels.

• Lymphatic Vessel Structure

  • The endothelium is designed with junctions between cells that allow interstitial fluid to flow into the lumen when pressure becomes high enough (such as from blood capillary hydrostatic pressure), but does not normally allow lymph fluid to leak back out into the interstitial space.
  • The next layer is smooth muscles arranged in a circular fashion around the endothelium that alters the pressure inside the lumen (space) inside the vessel by contracting and relaxing.
  • As the pressure falls, the open valve then closes so that the lymph fluid cannot flow backwards.
  • Smooth muscle contractions only cause small changes in pressure and volume within the lumen of the lymph vessels, so the fluid would just move backwards when the pressure dropped.
  • Blood vessels also have valves, but only in low pressure venous circulation.

• Introduction to Blood Pressure

  • Blood pressure is the pressure that blood exerts on the wall of the blood vessels.
  • Systolic pressure is thus the pressure that your heart emits when blood is forced out of the heart and diastolic pressure is the pressure exerted when the heart is relaxed.
  • During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure.
  • A normal blood pressure should be around 120/80, with the systolic pressure expressed first.
  • Gravity affects blood pressure via hydrostatic forces (for example, during standing) Valves in veins, breathing, and pumping from contraction of skeletal muscles also influence venous blood pressure.

• Lymphatic Capillaries

  • These regulate the pressure of interstitial fluid by draining lymph from the tissues.
  • This fluid is essentially plasma that leaks out of cardiovascular capillaries into the tissues due to the forces of hydrostatic or oncotic pressure.
  • Lymph capillaries have a greater oncotic pressure (a pulling pressure exerted by proteins in solution) than blood plasma due to the greater concentration of plasma proteins in lymph.
  • This moves lymph further along the system despite the fall in pressure that occurs when moving from the higher-pressure capillaries to the lower-pressure collecting vessels.
  • Describe the location, structure, and role of lymphatic capillaries in maintaining the pressure of the interstitial fluid