Hydrophobicity
The degree to which a molecule is insoluble in water. Such molecules are soluble in lipids.

Hydrogen bond
A weak attractive force between one electronegative atom and a hydrogen atom that is covalently linked to a second electronegative atom and a hydrogen atom that is covalently linked to as second electronegative atom.

Hydrogen uptake positive (Hup⁺)
A term used to describe a microorganisms that can assimilate or take up  hydrogen gas.

Hydrolase
Enzymes that catalyses hydrolysis reactions. These include lipases, Phosphatases, proteases and nucleases.

Hydrolysate
The product of hydrolysis such as a protein hydrolysate or casein hydrolysate.

Hydrolysis
Cleavage of a bond by the addition of water to yield two or more products.

Hydromechanical
stress See shear

Hydronium
ion The hydrate hydrogen ion (H₃O⁺).

Hydropathy
Exhibiting low affinity for water or hydrophobicity

Hydropathy plot
A measure of the hydrophobicity of a protein region and therefore the probability of residing in membranes.

Hydroxybutyrate dehydrogenase
See 2 HBD

Hydroxyl (-OH)
A chemical groups containing a hydrogen atom linked to an oxygen, as in alcohol.

Hydroxylation
A chemical reaction involving the addition of a hydroxyl (-OH) group to a compound.

Hydroxylysine
A posttranslational modification of lysine that occurs in collagen. Hydroxylation is catalysed by lysyl hydroxylase. Hydroxylysine serves as the point of attachment of O-linked polysaccharides.

Hyperacute graft rejection
Graft rejection caused by performed antibodies to antigens on the graft.

Humanised antibody
A genetically engineered mouse antibody in which the Fc ad sometimes the frame work region have been replace with human sequences to prevent a HAMA response

Humoral Immune response
The production of antibodies by B cells in response to the presence of an antigen.

Humoral immunity
An immunity that results from the presence of specific antibody.

Hyperalbuminaemia
An increase in albumin levels in blood. The most common cause of hyperalbuminaemia is dehydration as a result of osmotic diuresis. It may also occur due to venous stasis during blood collection or following over infusion of albumin. Hyperalbuminaemia is accompanied by an increase in total proteins and packed cell volume.

Hyperbilirubinaemia
Excess bilirubin in the blood.

Hypercalcaemia
Excess calcium in the blood

Hyperchloraemia
An increase in chlorides in the blood

Hyperchloraemic acidosis
Entry of chloride containing fluids such as urine into the ileum or colon, with loss of bicarbonate in exchange for chloride.

Hyperchlorhydria
Excessive hydrochloric acid in the gastric juice

Hyperchromatism
Increased staining of the nucleus due to excessive chromatin

Hyperchromic
An abnormal increase in the amount of haemoglobin in the erythrocytes

Hyperchromic effect
1. Refers to an increase in intensity of the absorption maximum or a change in the extinction coefficient to a higher value at the same absorption maximum. This is chiefly due to the presence of an auxochrome.

2. An increase in the UV absorbance of nucleic acid following denaturation.
Hyperchromicity, hypochromicity The change in the optical density of a nucleic acid solution upon denaturation or Renaturation. While denaturation causes an increase in optical density (hyperchromic shift) at 260nm, renaturation leads to a decrease in optical density (hypochromic shift)

Hyperemia
Excess blood in the area.

Hypergammaglobulinaemia
An increase in plasma gamma globulin levels. This may be polyclonal, involving all the fractions, or monoclonal, involving only a single immunoglobulin fraction

Hypergastrinaemia
Elevated level of gastrin in the blood

Hyperglycaemia
Elevated blood glucose concentration.

HyperlgM syndrome
Immune deficiency in which serum IgM levels are high and serum IgM is absent or very low.

Hyperimmunity
A state in which an extreme immune response is elicited by an antigen present in quantities that normally do not stimulate an immune response.

Hyperinsulinism
Excessive insulin secretion.

Hyperkalaemia
Elevated concentration of potassium in the blood.

Hyperkeratosis
Hypertrophy of the horny layer of the skin or cornea.

Hyperlink
A word or object in a hypertext document that is generally highlighted. This functions as a link to another document on the same computer or another computer linked to the internet.