Questions and Answers
What are the two types of functions of the kidneys?
What processes maintain fluid and electrolyte balance in the kidneys?
Glomerular filtration, tubular reabsorption, and tubular secretion
What is glomerular filtration?
The first process in urine formation where water, electrolytes, and small particles are filtered into the Bowman capsule.
What is the normal rate of glomerular filtration rate (GFR)?
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Glomerular filtration rate increases when the afferent arteriole is constricted.
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What occurs during tubular reabsorption?
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What is the renal threshold for glucose?
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What is tubular secretion?
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What hormones are produced by the kidneys?
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What role does renin play in the kidneys?
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How do prostaglandins affect kidney function?
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Study Notes
Functions of the Kidneys
- Kidneys perform regulatory and hormonal functions.
- Regulatory functions maintain fluid and electrolyte balance, as well as acid-base balance.
- Hormonal functions regulate red blood cell (RBC) formation, blood pressure, and activate vitamin D.
Regulatory Functions of the Kidneys
- Maintain fluid and electrolyte balance through urine elimination processes like glomerular filtration, tubular reabsorption, and tubular secretion.
Glomerular Filtration
- First step in urine formation; involves filtration of blood through the glomerulus.
- Small particles like water, electrolytes, creatinine, urea nitrogen, and glucose pass into Bowman capsule.
- Large particles, such as blood cells and proteins, remain in blood and are not present in urine.
Glomerular Filtration Rate (GFR)
- Normal GFR: 125 mL/min, totaling 180 L daily; approximately 1-3 L are excreted as urine.
- GFR self-regulated by blood pressure (BP) and blood flow through kidney constriction and dilation of arterioles.
- Low systolic BP (below 65-70 mmHg) impairs GFR regulation.
Tubular Reabsorption
- Second process in urine formation, where water and electrolytes are reabsorbed into peritubular capillaries.
- About 99% of filtered water is returned to circulation, affecting urine volume and concentration.
- Major reabsorption sites include the proximal convoluted tubule (PCT), descending loop of Henle, and distal convoluted tubule (DCT), influenced by hormones like ADH and aldosterone.
- Reabsorption of sodium, chloride, bicarbonate, calcium, and phosphate occurs primarily in the PCT.
- Approximately 50% of urea is reabsorbed, while creatinine is not.
Renal Threshold
- Refers to the maximum amount of glucose the kidneys can reabsorb; glucose level >180 mg/dL indicates threshold reached.
- Below this level, all glucose is reabsorbed into the bloodstream, preventing its presence in urine.
Tubular Secretion
- Third process of urine formation, allowing substances to be excreted from blood to urine.
- Important for maintaining fluid, electrolyte balance, and acid-base homeostasis through secretion of potassium and hydrogen ions.
Hormonal Functions of the Kidneys
- Produce renin, prostaglandins, erythropoietin, and activated vitamin D.
- Kinins influence blood flow and pressure within kidneys, affecting capillary permeability.
- Essential in breaking down and excreting substances like insulin and various drugs.
Renin
- Plays a vital role in blood pressure regulation.
- Secreted in response to low BP, blood volume, or sodium levels.
- Activates angiotensin II, which constricts blood vessels, and triggers aldosterone release to enhance sodium and water reabsorption in nephron, increasing BP.
Prostaglandins
- Regulate glomerular filtration, renal vascular resistance, and renin production.
- Promote renal excretion of sodium and water.
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Description
Explore the essential functions of the kidneys, including their regulatory and hormonal roles. Understand how kidneys maintain fluid and electrolyte balance while influencing red blood cell formation and blood pressure. Dive into details about glomerular filtration and the importance of Glomerular Filtration Rate (GFR).
