Acid-Base Balance PPT PDF

# Acid-Base Balance # ## Attendance ## - Please remember to check into the session via [App Name]. ## Session Guidelines ## | **MEDI11-102 Week 7** | | ----------- | | **Title** | Acid-base balance | | **Presenter** | Associate Professor Mike Todorovic | | **Why you should attend this session*...

# Acid-Base Balance # ## Attendance ## - Please remember to check into the session via [App Name]. ## Session Guidelines ## | **MEDI11-102 Week 7** | | ----------- | | **Title** | Acid-base balance | | **Presenter** | Associate Professor Mike Todorovic | | **Why you should attend this session** | To get a clear understanding of how buffers, and respiratory and renal mechanisms contribute to control of acid-base balance and how these systems compensate when acid-base disturbances occur. | | **What you will need to do in preparation** | Read session notes and chapter 26, 12th Edition Human Anatomy and Physiology, Marieb and Hoehn p. 1060-1069 | | **What you will need to bring** | Printed or downloaded session notes | ## Learning Outcomes ## By the end of this topic, you should be able to: - Outline central concepts of acid/base regulation including the roles of respiratory & renal systems - **LO 1:** The importance of maintaining acid-base balance - **LO 2:** The role of buffers in acid-base balance - **LO 3:** Respiratory control of acid-base balance - **LO 4:** Renal control of acid-base balance - **LO 5:** Acid-base imbalances ## What is pH? ## - The pH of blood is generally 7.35 - 7.45 ## What Does the pH Scale Represent ## - Image: A scale of pH values from 0 - 14. Each value is shown with the corresponding molar concentration of $H^+$. Values from 0 - 7 are acidic with values getting more acidic as they approach 0. Values from 7 - 14 are basic with values getting more basic as they approach 14. 7 is neutral. ## Why do we care so much about $[H^+]$? ## - Hydrogen is the smallest element and has a +1 charge. - It is highly reactive due to its *large charge to size ratio*. - It has a high affinity for negatively charged molecules such as proteins, enzymes, and cell receptors. ## Where Does the $H^+$ Come From? ## - **Acids** donate protons. - **Biological acids** are either *nonvolatile* or *volatile*: - **Nonvolatile acids** do not leave solution easily and must be excreted. (ex. phosphoric acid, sulphuric acid) - **Volatile acids** can leave solution easily. (ex. $CO_2$) ## The Three Main Buffer Systems ## - **Chemical:** *Bicarbonate Buffer System* - $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$ - **Respiratory** - Acts within minutes - Regulates the amount of $CO_2$. - **Renal** - Acts within hours to days - Regulates the amount of $HCO_3^-$ ## Phosphate Buffer System ## - Composed of salts of *dihydrogen phosphate* ($H_2PO_4^-$) and *monohydrogen phosphate* ($HPO_4^{2-}$) - Present in relatively *low concentrations in the plasma* - More important in *intracellular fluids* and urine. - $H^+ + HPO_4^{2-} \rightleftharpoons H_2 PO_4^-$ ## Protein Buffers ## - Proteins contain both carboxyl groups (-COOH) and amino groups (-NH2) - This allows them to act as both acids (donating $H^+$) and bases (accepting $H^+$) - Proteins are abundant in both ICF & ECF, providing a large capacity for buffering changes in pH. ## Respiratory Control of Acid-Base Balance ## - The *respiratory system* controls **alveolar ventilation**, the volume of fresh air that reaches the alveoli per minute. - This is the **short-term and immediate control of blood pH** - *Alveolar ventilation* is controlled by **chemoreceptors**: - **Central chemoreceptors** in the medulla - **Peripheral chemoreceptors** in the carotid body and aortic arch. - **Increased arterial $CO_2$** will result in **increased ventilation**(exhaling $CO_2$) and **increased $H^+$** concentration in the cerebral spinal fluid. ## Renal Control of Acid-Base Balance ## - The *renal system* provides **long-term control of pH**. - The renal system maintains plasma $HCO_3^-$ at approximately 24 mmol/L. ## Using Blood Values to Determine the Cause of Acidosis and Alkalosis ## 1. **Note the pH** - <7.35 = acidosis - >7.45 alkalosis 2. **Check the $pCO_2$** - High $pCO_2$ could indicate *respiratory acidosis*. - Low $pCO_2$ could indicate *respiratory alkalosis*. 3. **Check the bicarbonate level** - Low bicarbonate could indicate *metabolic acidosis*. - High bicarbonate could indicate *metabolic alkalosis*. ## Compensation ## - *Compensation* refers to when one system (respiratory or renal) attempts to correct an imbalance caused by another system. - **Example**: - If there is *respiratory alkalosis*, the renal system may try to compensate by *retaining HCO3-*.