FunMed: PBL 4 (Acid-Base Problems - Cystic Fibrosis) Flashcards
What type of acid-base disorder is cystic fibrosis and why?
Respiratory acidosis due to decreased ability to remove carbon dioxide from the body (hypoventilation) causing the extracellular fluid to become acidic (CO2 is acidic)
What is the cause of cystic fibrosis?
Autosomal recessive genetic disorder on chromosome 7 in gene which codes for the CFTR channel (inherits 2 faulty versions)
What is the role of the CFTR ion channel?
Cystic fibrosis transmembrane conductance regulator - chloride channel which pumps sodium and water out of cells into the extracellular space
Outline how CFTR channels function
ATP-gated anion (chloride) cahnnel which allows Cl- to flow down electrochemical gradient (out of cell) which creates a positive flow for Na+ and water to follow to create more watery mucus
Where are CFTR channels located?
Lungs, liver, pancreas, digestive tract, reproductive tract and skin
How is cystic fibrosis diagnosed?
Heelprick/Guthrie test (newborns) that detects trypsin in blood released by damaged pancreas, sweat test (saltier), carrier testing if family member has CF, or antenatal testing
What are the symptoms of cystic fibrosis?
Chronic lung infections, persistent coughing, shortness of breath, difficulty breathing, infertility (all men, most women), diabetes from pancreatic damage
Define ‘bronchiecstasis’
abnormal widening of the bronchi or their branches, in CF due to chronic thick mucus and repeated chest infections
What is the heterozygote advantage of a CFTR mutation?
May influence survival of people affected by diseases which involve loss of body fluid (cholera or typhoid etc.)
What are the most common types of bacteria which cause lung infections in CF patients?
Staphyloccus aureus, (MRSA), P. aeruginosa, H. influenza, S.maltophilia
Describe the treatment of cystic fibrosis
Daily physiotherapy (remove mucus and encourage exercise), pancreatic enzyme tablets (to take with fat-containing foods), higher calorie/protein diets, vitamin supplements (especially fat-soluble vitamins), oral/nebulised/IV antibiotics, transplants and potential gene therapy
Outline some of the complications of cystic fibrosis
diabetes, low bone mineral density (bone thinning), nephron/ototoxicity (hearing and kidney function loss) due to antibiotics taken, distal intestinal obstruction syndrome (blockages in stomach –> stomach pain, bloating, nausea and weight loss)
Which GI organ is affected by CF and how?
Due to CFTR mutation, the duct system of the pancreas is blocked by viscous secretions so digestive enzymes produced don’t reach duodenum –> self-digestion and can damage the Islets of Langerhans –> (can cause) diabetes
Why are CF patients so prone to lung infections?
Thick mucus lining of airways is warm and moist, and thick enough to resist ciliary action so mucus isn’t swept up –> optimal conditions for bacteria to culture and invade cells of airways
Why do pH levels have to be strictly controlled?
Enzyme function effectively to facilitate all essential metabolic processes
What are the 3 main mechanisms by which the body handles changes in serum pH?
Physiologic (chemical) buffers, renal compensation, pulmonary compensation
What are the 3 types of physiologic/chemical buffers?
Bicarbonate-carbonic acid (blood) Intracellular proteins (between cells) Phosphate buffers (bone)
Define ‘buffer’
Base and conjugate acid OR acid and conjugate base salt
Describe how renal compensation balances pH
Starts when other methods ineffective (6 hours later).
In acidosis: excrete H+ and retain HCO3-
In alkalosis: excrete HCO3- and retain H+
Describe how bone acts a buffer?
Contains large reservoir of bicarbonate and phosphate so can buffer significant acute acid load
Define alkalosis
pH > 7.45
Define acidosis
pH
What is normal serum pH?
7.40
Describe respiratory acidosis
pH less than 7.35, caused by alveolar hypoventilation (not enough CO2 - acid - removal). Relationship between pCO2 and HCO3- determine arterial pH
