plasma

Examples of plasma in the following topics:

• Blood Plasma

  • Plasma comprises about 55% of total blood volume.
  • One percent of the plasma is salt, which helps with pH.
  • Human blood plasma volume averages about 2.7–3.0 liters.
  • Plasma contains molecules that are transported around the body.
  • Albumins, produced in the liver, make up about two-thirds of the proteins in plasma.

• Transfusions of Whole Blood

  • Whole blood refers to blood drawn directly from the body from which none of the components, such as plasma or platelets, have been removed.
  • Most blood banks now split the whole blood into two or more components, typically red blood cells and a plasma component such as fresh frozen plasma, which is extracted frozen plasma from the blood splitting process.
  • Centrifuge quickly separates whole blood into plasma, buffy coat, and red cells by using centrifugal force to drop the cellular components to the bottom of a container.
  • Sedimentation, in which whole blood sits overnight, causing the red blood cells and plasma to settle and slowly separate by the force of normal gravity.
  • Whole blood is sometimes "recreated" from stored red blood cells and fresh frozen plasma for neonatal transfusions.

• Potassium Balance Regulation

  • The acid base status controls the distribution between plasma and cells.
  • A high plasma potassium increases aldosterone secretion and this increases the potassium loss from the body, restoring balance.
  • This change of distribution with the acid base status means that the plasma K+ may not reflect the total body content.
  • Therefore, a person with an acidosis (pH 7.1) and a plasma K+ of 6.5 mmol/l could be depleted of total body potassium.
  • Conversely, a person who is alkalotic with a plasma K+ of 3.4 mmol/l may have normal total body potassium.

• Renal Clearance

  • In renal physiology, the clearance is a measurement of the renal excretion ability, which measures the amount of plasma from which a substance is removed from the body over an interval of time.
  • For example, certain pharmaceuticals have the tendency to bind to plasma proteins or exist unbound in plasma.
  • It is also important to note that renal clearance is not the only form of clearance that occurs for the substances within the plasma of the body.
  • These types of clearance all add up to a summation known as total body clearance, which refers to the removal of a substance from the plasma over time, incorporating all routes of removal in the body.

• Sodium Balance Regulation

  • The plasma and interstitial sodium is about 140 mmol/l with an extracellular volume of about 13 litres, 1,800 mmol are in the extracellular space.
  • The major physiological controller of aldosterone secretion is the plasma angiotensin II level which increases aldosterone secretion.
  • A high plasma potassium also increases aldosterone secretion because besides retaining Na+ high plasma aldosterone causes K+ loss by the kidney.
  • Plasma Na+ levels have little effect on aldosterone secretion.
  • When aldosterone has been activated to retain sodium the plasma sodium tends to rise.

• Regulation of Urine Concentration and Volume

  • ADH is a hormone secreted from the posterior pituitary gland in response to increased plasma osmolarity (ie. increased ion concentration in the blood), which is generally due to increased concentration of ions relative to volume of plasma, or decreased plasma volume.
  • The increased plasma osmolarity is sensed by osmoreceptors in hypothalamus, which will stimulate the posterior pituitary gland to release ADH.
  • ADH will then act on the nephrons of the kidneys to  cause a decrease in plasma osmolarity, and an increase in urine osmolarity.
  • After ADH acts on the nephron to decrease plasma osmolarity (and leading to increased blood volume) and increase urine osmolarity, the osmoreceptors in the hypothalamus will inactivate, and ADH secretion will end.
  • A diuretic is any substance which has the opposite effect of ADH, by increasing urine volume, decreased urine osmolarity and leading to an increased plasma osmolarity and often reduced blood volume.

• Postabsorptive State

  • Combined deficiency of insulin and glucagon results in an initial drop in plasma glucose levels, but is followed by an increase in plasma glucose levels.
  • This indicates that there is support of post-absorptive plasma glucose concentrations from glucagon, when in concert with insulin.
  • Changes in plasma glucose concentrations also result from changes in glucose production, but not from glucose utilization.
  • Both scenarios result in much higher plasma glucose concentrations.
  • Increases in plasma glucose levels are ultimately followed by plateaus.

• Calcium and Phosphate Balance Regulation

  • The plasma concentration of Ca++ is 2.2 mmol/l and phosphate is 1.0 mmol/l.
  • The solubility product of Ca and P is close to saturation in plasma.
  • However, the distribution from bone to plasma is controlled by both the parathyroid hormones and vitamin D.
  • Calcium in plasma exists in three forms: ionized, nonionized and protein bound.
  • Plasma phosphate has no direct effect on parathyroid hormone secretion; however, if it is elevated it combines with Ca++, decreasing ionized Ca++ in plasma, and thereby increasing parathyroid hormone secretion.

• Regulation of Water Intake

  • Osmoreceptors detect changes in plasma osmolarity (ie. concentration of solutes dissolved in the blood).
  • That is, they expand when the blood plasma is more dilute and contract with higher concentration.
  • When the osmoreceptors detect high plasma osmolarity (often reperesenting a low blood volume), they send signals to the hypothalamus, which creates the biological sensation of thirst, and also stimulates vasopressin (ADH) secretion, which starts the events that will reduce plasma osmolarity to normal levels.
  • The renin-angiotensin system is a complex homeostatic pathway that deals with blood volume as a whole, as well as plasma osmolarity and blood pressure.
  • Note that the renin-angiotensin system, and thus thirst, can be caused by other stimuli besides increased plasma osmolarity or a decrease in blood volume.

• Water Balance Disorders

  • Hypotonic dehydration causes decreased plasma osmolarity, while hypertonic dehydration will cause increased plasma osmolarity.
  • Isotonic dehydration will not change plasma osmolarity, but it will reduce overall plasma volume.
  • Hypovolemia is specifically a decrease in volume of blood plasma.
  • Plain water restores only the volume of the blood plasma, inhibiting the thirst mechanism before solute levels can be replenished.