osmotic pressure

Examples of osmotic pressure in the following topics:

• Introduction to Osmoregulation

  • Osmosis is the diffusion of water across a membrane in response to osmotic pressure caused by an imbalance of molecules on either side of the membrane.
  • Isotonic cells have an equal concentration of solutes inside and outside the cell; this equalizes the osmotic pressure on either side of the semi-permeable membrane.
  • When disease or injury damage the mechanisms that regulate osmotic pressure, toxic waste or water may accumulate, with potentially dire consequences.
  • Water movement due to osmotic pressure across membranes may change the volume of these fluid compartments.
  • Because blood plasma is one of the fluid components, osmotic pressure can directly influence blood pressure and other medical indicators.

• Osmoregulators and Osmoconformers

  • Persons lost at sea without any fresh water to drink are at risk of severe dehydration because the human body cannot adapt to drinking seawater, which is hypertonic (having higher osmotic pressure) in comparison to body fluids.
  • These fish are incapable of osmotic regulation in the alternate habitat.
  • In relatively hypotonic (low osmotic pressure) fresh water, their skin absorbs water (see [a] in ).
  • Sharks are "ureotelic" animals that secrete urea to maintain osmotic balance.
  • Salmon physiology responds to freshwater and seawater to maintain osmotic balance

• Kidney Structure

  • Kidneys regulate the osmotic pressure of a mammal's blood through extensive filtration and purification in a process known as osmoregulation.

• Transport of Electrolytes across Cell Membranes

  • Osmotic pressure is influenced by the concentration of solutes in a solution.
  • Because electrolytes dissociate into ions, adding relatively more solute molecules to a solution, they exert a greater osmotic pressure per unit mass than non-electrolytes such as glucose.
  • Explain the relationship between osmotic pressure and the transport of electrolytes across cell membranes

• Malpighian Tubules of Insects

  • They are lined with microvilli for reabsorption and maintenance of osmotic balance.
  • The secretion of ions alters the osmotic pressure, which draws water, electrolytes, and nitrogenous waste (uric acid) into the tubules.
  • Explain how insects use malpighian tubules to excrete wastes and maintain osmotic balance

• Plasma and Serum

  • Plasma consists of 90 percent water along with various substances required for maintaining the body's pH, osmotic load, and for protecting the body.
  • Other components in the serum include proteins, which assist with maintaining pH and osmotic balance while giving viscosity to the blood; antibodies, or specialized proteins that are important for defense against viruses and bacteria; lipids, including cholesterol, which are transported in the serum; and various other substances including nutrients, hormones, metabolic waste, and external substances, such as drugs, viruses, and bacteria.
  • Albumin, which constitutes about one-half of the blood serum protein, transports hormones and fatty acids, buffers pH, and maintains osmotic pressures.

• Concept of Osmolality and Milliequivalent

  • In order to calculate osmotic pressure, it is necessary to understand how solute concentrations are measured.
  • Osmolarity is related to osmolality, but is affected by changes in water content, as well as temperature and pressure.
  • In contrast, osmolality is unaffected by temperature and pressure.

• Osmoregulation

  • Tonicity is the ability of a solution to exert an osmotic pressure upon a membrane.
  • In nonwoody plants, turgor pressure supports the plant.
  • Plants lose turgor pressure in this condition and wilt .
  • Fish, however, must spend approximately five percent of their metabolic energy maintaining osmotic homeostasis.
  • This protein is too large to pass easily through plasma membranes and is a major factor in controlling the osmotic pressures applied to tissues.

• Kidney Function and Physiology

  • The process of glomerular filtration filters out most of the solutes due to the high blood pressure and specialized membranes in the afferent arteriole.
  • The blood pressure in the glomerulus is maintained independent of factors that affect systemic blood pressure.
  • Because Na+ is actively transported out of the tubule, water follows to even out the osmotic pressure.
  • This occurs due to the low blood pressure and high osmotic pressure in the peritubular capillaries.
  • The osmotic gradient increases as it moves deeper into the medulla.

• Other Hormonal Controls for Osmoregulation

  • Thus, via the RAAS, the kidneys control blood pressure and volume directly.
  • Mineralocorticoids are hormones synthesized by the adrenal cortex that affect osmotic balance.
  • As sodium is always reabsorbed by active transport and water follows sodium to maintain osmotic balance, aldosterone manages not only sodium levels, but also the water levels in body fluids.
  • ANP affects salt release; because water passively follows salt to maintain osmotic balance, it also has a diuretic effect.
  • The renin-angiotensin-aldosterone system increases blood pressure and volume.