acid base

what is homeostasis

the principle of maintaining a stable internal environment

why is homeostasis important

disruptions to homeostasis often lead to disease

how is acid-base homeostasis achieved

Balance is achieved when the production of acids (H+) is matched by their removal, keeping body fluid pH within a narrow, healthy range

what is a major challenge regarding acid-base homeostasis and why

The major challenge is preventing a fall in pH (acidosis), since normal metabolism produces large amounts of acids

why is acidosis dangerous

because H+ ions:

• Break chemical bonds

• Alter the shape and function of proteins and enzymes 

• Disrupt cell membranes 

Maintaining acid-base balance is therefore critical for…

cell function, enzyme activity and overall health 

what is an acid

a chemical compound that produces hydrogen ions when dissolved in water

what is a base

a chemical compound that accepts hydrogen ions when dissolved in water

what is a strong acid and example

• an acid that ionises completely, releasing all of its H+

• HCL or H2SO4

what is a weak acid

• an acid that partially ionises

• Eg. carbonic acid

what is pH

• the measure of the acidity or basicity of a solution

• Pure water has a pH of 7

• Values below 7 are acidic = high concentration of H+

• Values above 7 are basic = low concentration of H+

how do you calculate pH

• pH = -log[H+]

• pH + pOH = 14

what is the normal pH range of blood

7.35-7.45

what Ph range is incompatible with life

outside 6.8-7.8

what is the pH range of acidosis

plasma pH <7.35

what is the pH range of alkalosis

plasma pH >7.45

what is the normal intracellular pH

7.0 - 7.3

what is a fixed acid

• Fixed acids do not leave a solution. Once produced they remain in the body fluids until they are eliminated by the kidneys

• Include metabolic acids such as lactic acid (from anaerobic production of ATP), ketone bodies (from metabolism of fats - acetoacetate, beta-hydroxybutyrate, & acetone*), and HCl, sulphuric acid (H2SO4) & phosphoric acid (H3PO4) from amino acid & nucleic acid metabolism

what is a volatile acid

• Volatile acids can vaporize into a gas and leave the body via the lungs (exhalation)

• The main volatile acid is carbonic acid (CO2)

• In addition, some of the ketone bodies are volatile. For example, acetone can be smelt on the breath in people on a ketogenic diet.

• Other volatile acids include short to chain fatty acids, such as butyric acid, which is produced by bacteria in the colon. However, this is almost completely metabolized in the colon epithelia and does not enter the blood

how does the respiratory system regulate the level of volatile acids in the blood

through ventilation

what is a buffer

A buffer is any substance that can reversibly bind H+, therefore controlling the concentration of free H+ in solution, making it an effective way to protect against acid-base changes

what is the main buffer system in ecf

HCO3-

what is the main buffer system in icf

phosphates and proteins (amino acids)

what is the main buffer system in rbc

Hb

what is the main buffer in urine

phosphates and ammonia

explain the bicarbonate buffer system

ok

explain the phosphate buffer system

ok

explain the protein buffer system

ok

explain the urinary buffer system

ok

glutamine enters ____ ____ cells from the bloodstream through specific ____ ____ ____ on the ____ membrane of the ____ ____ cells

Glutamine enters renal tubular cells from the bloodstream through specific amino acid transporters on the basolateral membrane of the tubular epithelial cells

Inside the epithelial cells, glutamine is broken down by the enzyme ____, which catalyses its hydrolysis into ____ and ____

Inside the epithelial cells, glutamine is broken down by the enzyme glutaminase, which catalyses its hydrolysis into ammonia (NH3/NH4+) and alphakeloglutarate (α-KG)

where do the products of glutamine go (ammonia and α-KG)

• The ammonia diffuses into the tubular fluid and is eliminated in the urine

• The α-KG is metabolized to produce ATP and HCO3. The HCO3- diffuses into blood

what is acidosis/acidaemia

low blood pH <7.35, or the process leading to the increased acidity

what is alkalosis/alkalemia

high blood pH >7.45, or the process leading the the increased alkalinity

when do acid-base abnormalities occur and how do we classify them

when blood pH moves outside its normal range and is classified by aetiology and type

what is aetiology and type

Aetiology: what fundamentally led to this problem 

• Metabolic: primary abnormality is in bicarbonate level or non-volatile acid production or elimination 

• Respiratory: primary abnormality is in CO2 control

• Mixed: both situations occurring

Type 

• Acidosis (decreased pH)

• Alkalosis (increased pH)

what changes to cause metabolic acid-base disorders

concentration of bicarbonate ions [HCO3-] or concentration of non-volatile acid

what does primary loss of HCO3- cause and give example

metabolic acidosis eg diarrhoea

what does primary gain of HCO3- cause and give example

metabolic alkalosis eg chronic antacid use

what does excessive H+ production/ failure to excrete H+ cause and give examples

metabolic acidosis e.g. tissue anoxia, lactic acidosis or diabetic ketoacidosis and renal failure

what does loss of H+ from gastric contents cause and example

metabolic alkalosis eg. chronic vomiting

what changes to cause respiratory abnormalities

arterial CO2 levels (PaCO2)

what is hypercapnia

• Hypercapnia (PaCO2 > 45 mmHg) causes respiratory acidosis.

• Hypercapnia can develop when there is defective ventilation, or...

• Defective diffusion (e.g. pulmonary oedema, ventilation-perfusion mismatch).

what is hypocapnia

• Hypocapnia (PaCO2 < 35 mmHg) causes respiratory alkalosis.

• Hypocapnia generally occurs with hyperventilation.

• It can be seen in anxiety, fever, and cerebral disease. Also in aspirin overdose

what is Mixed acid-base abnormalities 

• A mixed acid-base disturbance occurs when a patient simultaneously exhibits characteristics of both metabolic and respiratory acid-base imbalance.

• Mixed disturbances can make diagnosis and treatment more complex, as they may require addressing both underlying conditions and their respective compensation mechanisms.

what is compensation

Compensation for an acid-base disturbance is the way that the body attempts to correct for the abnormal pH if it cannot reverse the underlying condition. It is an effort to maintain acid-base homeostasis.

what is compensation for respiratory abnormalities

• involves adjusting H+ and HCO3- excretion in kidneys. This is called metabolic compensation.

• E.g. A respiratory acidosis will be compensated for by an increase in [HCO3-] in the blood.

• Metabolic compensation usually takes several days to achieve a noticeable effect.

what is compensation for metabolic abnormalities

• involves adjusting PaCO2, by changing alveolar ventilation (i.e. changing rate and depth of breathing)

• E.g. a metabolic acidosis will be compensated for by hyperventilation, which will decrease PaCO2.

• Respiratory compensation typically begins relatively quickly, within a matter of minutes.