Renal system
60 flashcards covering Renal system for the MCAT Biology & Biochemistry section.
The renal system, centered on the kidneys, is your body's primary waste filtration and regulation mechanism. It processes blood to remove toxins, excess salts, and water through structures like the nephrons, while also balancing electrolytes, pH levels, and blood pressure. This system ensures homeostasis by adjusting urine composition based on the body's needs, making it crucial for overall health and preventing conditions like dehydration or kidney failure.
On the MCAT, the renal system frequently appears in biology and biochemistry questions that assess physiological processes, such as glomerular filtration, tubular reabsorption, and hormone regulation like renin-angiotensin or ADH. You'll encounter multiple-choice questions based on passages, diagrams, or experiments, with common traps including confusing similar terms (e.g., filtration vs. secretion) or overlooking the role of feedback loops in homeostasis. Focus on integrating anatomy with functions and practicing application-based problems.
A solid tip: Draw and label nephron diagrams to visualize key processes.
Terms (60)
- 01
Kidney
The primary organ of the excretory system that filters blood to remove waste, regulate electrolytes, and maintain fluid balance.
- 02
Nephron
The basic structural and functional unit of the kidney, consisting of a glomerulus and tubules, where filtration, reabsorption, and secretion occur to form urine.
- 03
Renal cortex
The outer region of the kidney containing most nephrons and responsible for initial blood filtration and reabsorption.
- 04
Renal medulla
The inner region of the kidney with loops of Henle and collecting ducts that help concentrate urine through osmotic gradients.
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Glomerulus
A network of capillaries in the nephron where blood is filtered under pressure to produce glomerular filtrate.
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Bowman's capsule
The cup-like structure surrounding the glomerulus that collects the filtrate and funnels it into the renal tubule.
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Afferent arteriole
The blood vessel that delivers blood to the glomerulus, and its diameter helps regulate glomerular filtration rate.
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Efferent arteriole
The blood vessel that carries blood away from the glomerulus, influencing pressure and filtration in the process.
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Proximal convoluted tubule
The segment of the nephron where most reabsorption of water, ions, and nutrients from the filtrate occurs via active and passive transport.
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Loop of Henle
A U-shaped structure in the nephron that creates an osmotic gradient in the renal medulla, essential for urine concentration.
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Descending limb of Loop of Henle
The permeable part of the loop of Henle that allows water to exit and concentrate the filtrate as it descends into the medulla.
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Ascending limb of Loop of Henle
The impermeable-to-water segment of the loop of Henle where sodium and chloride are reabsorbed, contributing to the medullary osmotic gradient.
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Distal convoluted tubule
The section of the nephron where fine-tuning of electrolyte balance occurs, influenced by hormones like aldosterone.
- 14
Collecting duct
The final structure in the nephron that collects urine from multiple nephrons and adjusts its concentration based on ADH levels.
- 15
Glomerular filtration
The passive process in the glomerulus where blood plasma is filtered into Bowman's capsule, driven by hydrostatic pressure.
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Tubular reabsorption
The selective process by which useful substances like glucose, amino acids, and water are transported from the renal tubule back into the blood.
- 17
Tubular secretion
The active process where substances like hydrogen ions, potassium, and drugs are moved from the blood into the renal tubule for excretion.
- 18
Glomerular filtration rate (GFR)
The volume of fluid filtered from the glomeruli per unit time, typically around 125 mL/min, and a key indicator of kidney function.
- 19
Filtration fraction
The proportion of plasma flowing through the glomeruli that is filtered, calculated as GFR divided by renal plasma flow, usually about 20%.
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Countercurrent multiplier
The mechanism in the loop of Henle that establishes and maintains the osmotic gradient in the renal medulla for urine concentration.
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Countercurrent exchanger
The process in the vasa recta that preserves the osmotic gradient in the medulla by exchanging solutes and water without dissipating it.
- 22
Vasa recta
The capillary network around the loop of Henle that supplies blood to the medulla and helps maintain the osmotic gradient for urine concentration.
- 23
Juxtaglomerular apparatus
A structure at the end of the loop of Henle that senses sodium levels and releases renin to regulate blood pressure and fluid balance.
- 24
Renin
An enzyme released by the kidneys in response to low blood pressure that initiates the renin-angiotensin-aldosterone system to conserve sodium and water.
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Angiotensin II
A potent vasoconstrictor produced in the renin-angiotensin system that increases blood pressure and stimulates aldosterone release.
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Aldosterone
A hormone from the adrenal cortex that promotes sodium reabsorption and potassium secretion in the distal tubule and collecting duct.
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Antidiuretic hormone (ADH)
A hormone released by the posterior pituitary that increases water reabsorption in the collecting duct by making it more permeable to water.
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Atrial natriuretic peptide (ANP)
A hormone secreted by the heart in response to high blood volume that promotes sodium and water excretion by inhibiting renin and aldosterone.
- 29
Renal clearance
The volume of plasma completely cleared of a substance per unit time, calculated using urine and plasma concentrations to assess kidney function.
- 30
Inulin clearance
A method to measure GFR, as inulin is freely filtered and neither reabsorbed nor secreted, making its clearance rate equal to GFR.
- 31
PAH clearance
A measure of renal plasma flow, as para-aminohippuric acid is almost completely cleared from plasma by filtration and secretion.
- 32
Starling forces
The balance of hydrostatic and oncotic pressures across the glomerular capillaries that determines the net filtration pressure.
- 33
Effective filtration pressure
The net pressure driving filtration in the glomerulus, calculated as glomerular capillary pressure minus opposing forces.
- 34
Reabsorption of glucose
The process in the proximal tubule where glucose is actively reabsorbed via cotransport with sodium until the transport maximum is reached.
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Renal threshold for glucose
The plasma glucose concentration above which glucose appears in urine, typically around 200 mg/dL, indicating saturation of reabsorption.
- 36
Bicarbonate reabsorption
The process in the proximal tubule where bicarbonate ions are reabsorbed to help maintain acid-base balance in the blood.
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Hydrogen ion secretion
The mechanism in the distal tubule and collecting duct that excretes excess hydrogen ions to regulate blood pH.
- 38
Potassium handling
The balance of potassium reabsorption in the proximal tubule and secretion in the distal tubule, influenced by aldosterone levels.
- 39
Urine concentration
The process by which the kidneys produce hyperosmotic urine through the countercurrent system and hormonal regulation.
- 40
Autoregulation of GFR
The kidney's ability to maintain constant GFR despite changes in systemic blood pressure through myogenic and tubuloglomerular mechanisms.
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Myogenic mechanism
A process where smooth muscle in the afferent arteriole contracts or relaxes in response to changes in blood pressure to stabilize GFR.
- 42
Tubuloglomerular feedback
A feedback loop where the macula densa senses sodium chloride in the distal tubule and adjusts afferent arteriole resistance to regulate GFR.
- 43
Renal blood flow
The volume of blood delivered to the kidneys per unit time, about 1.1 L/min, which is regulated to ensure adequate filtration.
- 44
Renal plasma flow
The portion of renal blood flow that is plasma, typically measured using PAH and essential for delivering substances to the nephrons.
- 45
Formula for GFR
GFR can be estimated using the Cockcroft-Gault formula, which incorporates age, weight, serum creatinine, and gender to assess kidney function.
- 46
Example of clearance calculation
To calculate clearance, divide the amount of substance excreted in urine per minute by its plasma concentration, as in inulin clearance equaling GFR.
- 47
Common trap in filtration
Filtration does not involve active transport; it is a passive process based on size and charge, so proteins are typically not filtered.
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Strategy for nephron function
To understand nephron function, trace the path of filtrate from the glomerulus through each segment, noting key reabsorption and secretion sites.
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How ADH affects urine
ADH increases the permeability of the collecting duct to water, leading to more reabsorption and concentrated urine in response to dehydration.
- 50
Acid-base balance
The kidneys maintain blood pH by reabsorbing bicarbonate and secreting hydrogen ions, compensating for respiratory imbalances over hours to days.
- 51
Electrolyte balance
The kidneys regulate electrolytes like sodium, potassium, and chloride by adjusting reabsorption and secretion based on hormonal and dietary signals.
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Water balance
The kidneys control water balance by varying urine volume through ADH regulation, conserving water when dehydrated and excreting excess when hydrated.
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Diuretics mechanism
Diuretics increase urine production by inhibiting sodium reabsorption in the nephron, leading to more water excretion and used to treat hypertension.
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Osmolality of urine
The concentration of solutes in urine, which can range from 50 to 1200 mOsm/L depending on the body's hydration status and the countercurrent system.
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Free water clearance
A measure of the kidney's ability to excrete or retain water independently of solutes, calculated as urine volume minus osmolar clearance.
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Baroreceptor reflex
A neural mechanism where baroreceptors in blood vessels detect pressure changes and signal the kidneys to adjust renin release and fluid balance.
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Effects of sympathetic nervous system
Activation constricts renal blood vessels, reduces GFR, and promotes sodium retention to increase blood volume during stress or low blood pressure.
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Renal handling of urea
Urea is passively reabsorbed in the proximal tubule and loop of Henle, contributing to the osmotic gradient and urine concentration.
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Podocytes
Specialized cells in Bowman's capsule with foot processes that form filtration slits, preventing large molecules from entering the filtrate.
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Mesangial cells
Cells in the glomerulus that support capillary structure and can contract to regulate blood flow and filtration.