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Questions and Answers
What is the primary reason bicarbonate is maintained in the bloodstream?
During cellular metabolism, what two products are primarily produced?
What role does the kidney play in relation to bicarbonate?
In the bicarbonate buffer system, what does bicarbonate primarily react with?
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What happens to the hydrogen ions that are produced during glycolysis?
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What is the role of carbon dioxide in the context of acid-base balance?
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What does the enzyme carbonic anhydrase do in relation to acid-base balance?
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How does the kidney contribute to maintaining acid-base balance?
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What happens to H2CO3 after its formation in the acid-base balance reaction?
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What ions are produced from the reaction of water and carbon dioxide in acid-base balance?
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What role does bicarbonate play in acid-base balance regulation?
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What happens when the pH of the blood becomes too basic?
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Which muscle is responsible for contracting the bladder during urination?
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Which of the following statements about the external urethral sphincter is true?
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What type of nerve innervates the external urethral sphincter?
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Study Notes
Acid-base Balance and the Kidney
- During aerobic metabolism, cells produce carbon dioxide (CO2).
- CO2 reacts with water (H2O) in the presence of carbonic anhydrase to form carbonic acid (H2CO3), which quickly dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-).
- The equation for this reaction is: H2O + CO2 <=> H2CO3 <=> H+ + HCO3-
- The kidney plays a vital role in maintaining acid-base balance by eliminating H+ and reabsorbing HCO3-.
- By reabsorbing HCO3-, the kidney helps to maintain a slightly basic pH in the blood (around 7.4).
- When H+ are produced during glycolysis, they can combine with HCO3- in the blood, forming H2CO3, which is further converted back to CO2 and H2O.
- This process is known as the bicarbonate buffer system.
Micturition Reflex and Urinary Dysfunction
- The micturition reflex is the process of urination.
- The urinary bladder is composed of three main parts:
- Detrusor muscle: contracts to empty the bladder.
- Internal urethral sphincter: muscle that controls urine flow from the bladder to the urethra.
- External urethral sphincter: muscle that is under voluntary control and allows us to choose when to urinate.
- The detrusor muscle and the internal sphincter are innervated by both the sympathetic and parasympathetic nervous systems.
- The external sphincter is innervated by the pudendal nerve, which is part of the somatic nervous system.
Spinal Cord Injuries and Urinary Dysfunction
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Upper motor neuron (UMN) bladder
- Occurs with lesions above the conus medullaris.
- Results in a spastic bladder (reflexive bladder).
- The bladder contracts easily, leading to frequent urination.
- The bladder often doesn’t empty completely, causing a higher risk of urinary tract infections (UTIs).
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Lower motor neuron (LMN) bladder
- Sometimes referred to as a flaccid bladder.
- Occurs with lesions below the conus medullaris.
- The bladder is relaxed and unable to contract.
- The bladder fills up without voluntary control.
- The bladder can become over-distended, causing leakage.
- Increased risk of UTIs and bladder damage.
- Both UMN and LMN bladder dysfunction can cause urinary incontinence.
- UMN bladder incontinence is characterized by frequent small spurts of urine.
- LMN bladder incontinence is characterized by continuous urine leakage.
- Both types can cause urine to back up into the kidneys, leading to kidney damage.
Bladder Function
- The bladder is a high-compliance tissue, stretching out as it fills with urine.
- As the bladder expands, pressure rises gradually, creating a low initial pressure increase.
- Micturition contractions occur when the bladder reaches a certain volume, typically around 200 milliliters.
- These contractions increase bladder pressure, causing a urge to urinate.
- The urge diminishes as the bladder relaxes, allowing urine retention until the next contraction.
- The external urethral sphincter is responsible for controlling urine flow, allowing the urge to be tolerated.
Kidney Function and Glomerular Filtration Rate (GFR)
- GFR is the volume of plasma filtered by the kidneys per minute, typically around 90-120 ml/min/1.73 m2.
- A sudden decrease in GFR is a sign of acute kidney injury.
- A gradual decrease in GFR over time is a sign of chronic kidney disease.
- Autoregulation involves the afferent and efferent arterioles, independently vasoconstricting or vasodilating to maintain a stable GFR at various blood pressures.
- Creatinine, a metabolic byproduct of creatine phosphate, is filtered but minimally reabsorbed in the kidneys.
- High blood creatinine levels indicate poor glomerular filtration.
Hypertension and Kidney Damage
- Hypertension leads to increased blood pressure in the glomerulus, causing glomerular hypertension.
- Prolonged glomerular hypertension causes damage and scar tissue formation, hindering filtration capacity.
- Damage also extends to the tubular system, impairing reabsorption and secretion processes.
- Hypertension contributes to chronic kidney disease by impairing the entire nephron's function.
- It affects the kidneys' ability to control blood flow due to damage to the afferent and efferent arterioles.
- Protein losing nephropathy occurs when proteins are filtered from the glomerulus and excreted in the urine.
- This can lead to decreased plasma colloid osmotic pressure, impacting fluid balance and distribution.
Diabetes and Kidney Dysfunction
- Both type 1 and type 2 diabetes result in elevated blood glucose levels, leading to increased glucose filtering into the renal tubular system.
- Glucose transporters become saturated due to excess glucose, causing glucose to be excreted in the urine (diabetes).
- Sodium reabsorption is increased in conjunction with glucose, placing a higher workload on the kidneys.
- Excessive sodium reabsorption further elevates glomerular filtration rate, potentially causing glomerular damage and hyperfiltration.
- This hyperfiltration can lead to a cascade of events that result in chronic kidney failure, including glomerular scarring, proteinuria, and tubular damage.
Kidney Dysfunction & Exercise
- Individuals with kidney dysfunction may experience fatigue, exercise intolerance, and delayed recovery from exercise.
- Kidney dysfunction can lead to issues with acid-base and electrolyte balance, potentially resulting in cramps, muscle damage, and impaired muscle performance.
- Chronic kidney disease can affect muscle metabolism over time, leading to muscle weakness and increased risk of falls.
- Altered vitamin D and calcium metabolism in individuals with chronic kidney disease can increase bone fracture risk.
- Electrolyte imbalances and protein-losing nephropathy can contribute to edema in patients with kidney disease.
- Kidney disease can impair skeletal muscle contraction and increase the risk of arrhythmias.
- In severe cases, kidney disease can affect oxygen sensing and erythropoietin secretion, leading to anemia and reduced exercise tolerance.
- Medications metabolized by the kidneys may require dosage adjustments in individuals with kidney dysfunction to avoid side effects and toxicities.
- Patients with chronic kidney disease often have complex medical conditions beyond kidney dysfunction, such as atherosclerosis and diabetes mellitus.
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Description
This quiz covers the essential concepts of acid-base balance and kidney function, particularly how carbon dioxide and bicarbonate ions are regulated by renal processes. It also explores the micturition reflex and the role of the urinary bladder in urination. Test your understanding of these critical physiological processes.
