Physiology Exam #4b: Acid-Base

Normal arterial blood pH

7.35-7.45

3 Systems body uses to maintain pH

• Buffers

• Respiratory System (adjusts CO2, QUICK)

• Kidneys/ Metabolic System

  • (remove acid or keep bicarbonate, LONG TERM)

  • regulate bicarbonate and hydrogen ions

Acidosis

• pH too LOW

  • too many H⁺ ions

  • decreased enzyme activity

  • confusion, lethargy

  • weak heart contractions

  • low bp

Alkalosis

• pH too HIGH

  • few H⁺ ions

  • muscle twitching or cramping

  • abnormal heart rhythms

  • over-excitable nerves, (seizures)

2 Measurements of Respiratory and Renal Systems

• PCO₂ (partial pressure of carbon dioxide, respiratory)

• HCO₃⁻ (bicarbonate, metabolic)

PCO₂

Partial Pressure of Carbon Dioxide (35–45 mmHg)

controlled by RESPIRATORY system/ lungs

• > 45= TOO MUCH CO2 in blood

  • acidic blood/ acidosis

  • lots of hydrogen ions

  • ↓ pH

  • lungs aren’t properly removing CO2

  • ex: shallow breathing

• < 35= TOO LITTLE CO2 in blood

  • alkalosis

  • few hydrogen ions

  • ↑ pH

  • lungs exhaling too much

  • ex: hyperventilation

HCO₃⁻

Bicarbonate (22–26 mEq/L)

regulated by METABOLIC system

Buffers pH by “soaking up" extra hydrogen ions (H⁺)

• HIGH= too much HCO₃⁻

  • alkalosis

  • ↑ pH

• LOW= low HCO₃⁻

  • acidosis

  • ↓ pH

Define Buffer

• Keeps sudden pH changes stable

  • pick up extra hydrogen ions (H⁺) when the body becomes too acidic

  • or release hydrogen ions when body becomes too basic

4 Major Buffers

• Bicarbonate

• Protein

• Phosphate

• Hemoglobin

What happens to CO₂ once it enters the blood?

• CO₂ mixes with water (H₂O) & forms carbonic acid (H₂CO₃)

  • carbonic acid breaks into H⁺ and HCO₃⁻ (bicarbonate)

CO₂ in the blood essentially acts like an acid!!!

2 parts of Bicarbonate Buffer System

in blood plasma and extracellular fluid

• Bicarbonate (HCO₃⁻)

• Carbonic Acid (H₂CO₃)

Bicarbonate Buffer System: Bicarbonate

acts as the BASE in the pair, neutralizes

• TOO acidic

  • bicarbonate combines within excess H⁺ to form carbonic acid

  • carbonic acid → CO2 and water

  • removes H⁺ from solution, ↑ pH!!

Bicarbonate Buffer System: Carbonic Acid

acts as the ACID in the pair, neutralizes

• TOO Alkaline

  • carbonic acid can dissociate and release a hydrogen ion into solution

  • increases H⁺ concentration, ↓ pH

What happens if there is more CO2 in the blood than normal?

• CO₂ will combine with water and produce hydrogen ions

• makes the blood more acidic

  • bicarbonate will kick in and raise pH

  • or lungs can increase respiratory rate and release more carbon dioxide

What happens if there are too many hydrogen ions in blood?

• Blood is acidic

  • kidney reabsorbs more bicarbonate, to raise pH

What happens if there are too few hydrogen ions in blood?

• Blood is alkalotic

  • kidney excretes extra bicarbonate in urine, to lower pH

Protein Buffer System

in cells and plasma

• AMINO ACIDS can either accept or donate hydrogen ions

  • Acidic: grabs extra H+, helps raise pH

  • Alkaline: release H+, helps lower pH

Phosphate Buffer System

in cells and kidneys

• 2 forms of phosphate

  • HPO₄²⁻ (base)

  • H₂PO₄⁻ (weak acid)

• too many H+ (acidic): HPO₄²⁻ → H₂PO₄⁻

  • grabs hydrogen to prevents pH from dropping too much

• too few H+ (alkaline): H₂PO₄⁻

  • releases hydrogen, prevents pH from rises too high

Hemoglobin Buffer System

in RBCs

• RELEASES Oxygen

  • more O2 available to pick up hydrogen ions (↑ pH)

  • prevents blood from being too acidic

• PICKS UP Oxygen

  • less O2, more hydrogen will be released (↓ pH)

  • prevents blood from being too alkaline

Most CO₂ in the blood is carried as…

bicarbonate

Alveolar Ventilation

movement of air into and out of the alveoli

• Keep oxygen high & CO2 controlled

  • ↑ ventilation= CO₂ falls

  • ↓ ventilation= CO₂ raise

• (CO₂ acts like an acid in the body!!)

What 2 ways do the kidneys regulate acid-base balance?

1. Secreting H⁺ into the urine

2. Reabsorbing bicarbonate back into the blood

Most hydrogen ion secretion begins in the…

• Proximal convoluted tube

  • Na⁺/H⁺ exchanger uses sodium movement to push H⁺ into the filtrate