pH

(noun)

In chemistry, pH is a measure of the activity of the hydrogen ion concentration.

Related Terms

Examples of pH in the following topics:

  • Regulation of H+ by the Lungs

    • Acid-base imbalances in blood pH can be altered by changes in breathing to expel more CO2, which will raise pH back to normal.
    • Since maintaining normal pH is vital for life, and since the lungs play a critical role in maintaining normal pH, smokers have yet another reason to quit smoking.
    • Acid–base imbalance occurs when a significant insult causes the blood pH to shift out of the normal range (7.35 to 7.45).
    • When blood pH drops too low (acidemia), the body compensates by increasing breathing thereby expelling CO2, shifting the above reaction to the left such that less hydrogen ions are free; thus the pH will rise back to normal.
    • When blood pH drops too low, the body compensates by increasing breathing to expel more carbon dioxide.

  • Chemical Buffer Systems

    • Chemical buffers such as bicarbonate and ammonia help keep blood pH in the narrow range compatible with life.
    • The body is very sensitive to its pH level, so strong mechanisms exist to maintain it.
    • Its pH changes very little when a small amount of strong acid or base is added to it.
    • Many life forms thrive only in a relatively small pH range so they utilize a buffer solution to maintain a constant pH.
    • Several buffering agents that reversibly bind hydrogen ions and impede any change in pH exist.

  • Alkalosis

    • Alkalosis is the increased alkalinity of blood and other tissues, generally occurring when the blood pH is above 7.45.
    • Generally, alkalosis is said to occur when pH of the blood exceeds 7.45.
    • The opposite condition is acidosis (when pH falls below 7.35).
    • Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range (7.35-7.45 ).
    • As the pH of blood increases, the protein in the blood becomes more ionized into anions.

  • Disorders of Acid-Base Balance

    • In the fetus, the normal range differs based on which umbilical vessel is sampled (umbilical vein pH is normally 7.25 to 7.45; umbilical artery pH is normally 7.18 to 7.38).
    • Acidosis refers to a low pH in tissue.
    • Acidemia refers to a low pH in the blood.
    • Alkalosis refers to a high pH in tissue.
    • Alkalemia refers to a high pH in the blood.

  • Chemical Composition of Bone

    • In the fetus, the normal range differs based on which umbilical vessel is sampled (umbilical vein pH is normally 7.25 to 7.45; umbilical artery pH is normally 7.18 to 7.38).
    • Acidosis refers to a low pH in tissue.
    • Acidemia refers to a low pH in the blood.
    • Alkalosis refers to a high pH in tissue.
    • Alkalemia refers to a high pH in the blood.

  • Chemoreceptor Regulation of Breathing

    • The goal of this system is to keep the pH of the blood stream within normal neutral ranges, around 7.35.
    • The respiratory chemoreceptors work by sensing the pH of their environment through the concentration of hydrogen ions.
    • Central chemoreceptors: These are located on the ventrolateral surface of medulla oblongata and detect changes in the pH of spinal fluid.
    • As bicarbonate levels decrease while hydrogen ion concentrations stays the same, blood pH will decrease (as bicarbonate is a buffer) and become more acidic.
    • The chemoreceptors are the sensors for blood pH, the medulla and pons form the integrating center, and the respiratory muscles are the effector.

  • Local Regulation of Blood Flow

    • Blood flow is regulated locally in the arterioles and capillaries using smooth muscle contraction, hormones, oxygen, and changes in pH.
    • Local responses to stretch, carbon dioxide, pH, and oxygen also influence smooth muscle tone and thus vasoconstriction and vasodilation.
    • Generally, stretch and high oxygen tension increase tone, and carbon dioxide and low pH promote vasodilation.
    • Brain arterioles are particularly sensitive to pH, with reduced pH promoting vasodilation.

  • Acidosis

    • Acidosis describes increased acidity in the blood and other tissues, usually measured as arterial pH below 7.35.
    • Acidosis is said to occur when arterial pH falls below 7.35, while its counterpart (alkalosis) occurs at a pH over 7.45.
    • In humans, the normal pH of arterial blood lies between 7.35 and 7.45.
    • Blood pH values compatible with life in all mammals are limited to a pH range between 6.8 and 7.8.
    • The Henderson-Hasselbalch equation is useful for calculating blood pH, because blood is a buffer solution.

  • Gastric Phase

    • Ingested food stimulates gastric activity in two ways: by stretching the stomach and by raising the pH of its contents.
    • Small peptides also buffer stomach acid so the pH does not fall excessively low.
    • But as digestion continues and these peptides are emptied from the stomach, the pH drops lower and lower.
    • Below pH of two, stomach acid inhibits the parietal cells and G cells: a negative feedback loop that winds down the gastric phase as the need for pepsin and HCl declines.

  • The Role of the Kidneys in Acid-Base Balance

    • Outside the range, pH becomes incompatible with life; proteins are denatured and digested, enzymes lose their ability to function, and the body is unable to sustain itself.
    • To maintain this narrow range of pH the body has a powerful buffering system.
    • The kidneys also play an important role in maintaining acid-base homeostasis by regulating the pH of the blood plasma.
    • The kidneys are slower to compensate than the lungs, but renal physiology has several powerful mechanisms to control pH by the excretion of excess acid or base.