lecture 26 objectives Flashcards
Compare and contrast tubular reabsorption and secretion with respect to the direction of solute movement and the tubule segments in which each process occurs. - tubular reabsorption
Direction of Solute Movement: Movement of solutes from the filtrate (inside the nephron) back into the bloodstream (peritubular capillaries).
Key Locations:
Proximal convoluted tubule (PCT): Most reabsorption occurs here (e.g., glucose, amino acids, Na+).
Loop of Henle: Water is reabsorbed in the descending limb, while Na+ is reabsorbed in the ascending limb.
Distal convoluted tubule (DCT) & Collecting duct: Reabsorption of Na+, water, and other ions like calcium and chloride occurs.
Process Involved: Active transport (e.g., Na+/K+ pump), facilitated diffusion, osmosis.
Compare and contrast tubular reabsorption and secretion with respect to the direction of solute movement and the tubule segments in which each process occurs. - tubular secretion
Direction of Solute Movement: Movement of substances from the blood (peritubular capillaries) into the filtrate (nephron tubules).
Key Locations:
Proximal convoluted tubule (PCT): Secretion of substances like H+, drugs, and urea.
Distal convoluted tubule (DCT): Secretion of K+ and H+ in exchange for Na+ (regulated by aldosterone).
Process Involved: Active transport, countertransport (e.g., Na+/H+ exchange), facilitated diffusion.
Describe specific mechanisms of transepithelial transport that occur in different parts of the nephron (e.g., active transport, osmosis, facilitated diffusion, electrochemical gradients).
Active Transport
Example: Na+/K+ pump in the PCT and DCT, actively pumping Na+ out of the cells and K+ into cells.
Facilitated Diffusion
Example: Glucose reabsorption in the PCT via GLUT transporters. No energy required, but transport proteins are needed.
Osmosis
Example: Water reabsorption in the PCT and descending limb of the loop of Henle. Water moves through aquaporins in response to osmotic gradients.
Electrochemical Gradients
Example: Na+ movement across the nephron creates electrochemical gradients that enable transport of other ions (Cl-, K+).
Give examples of each type of transepithelial transport, including the substance being transported, any membrane proteins involved, and the direction of movement across the tubule wall
Na+ transport
glucose transport
water transport
potassium transport
Na+ transport (substance, mechanism, direction)
Substance: Sodium (Na+)
Mechanism: Active transport (Na+/K+ ATPase pump) in the PCT, loop of Henle, DCT, and collecting duct.
Direction: From tubule cells into the interstitial space or bloodstream.
glucose transport (substance, mechanism, direction)
Substance: Glucose
Mechanism: Facilitated diffusion (GLUT transporters) in the PCT.
Direction: From tubule lumen to blood.
water transport (substance, mechanism, direction)
Substance: Water
Mechanism: Osmosis via aquaporins (PCT, descending limb, collecting duct).
Direction: From nephron lumen to the blood.
potassium transport (substance, mechanism, direction)
Substance: Potassium (K+)
Mechanism: Active transport in the DCT (via Na+/K+ exchange).
Direction: From blood into the lumen of the nephron.
For the important solutes of the body (e.g., Na+, K+, glucose, urea), describe how each segment of the nephron handles the solute -> sodium
Proximal convoluted tubule (PCT): Reabsorbed actively (via Na+/K+ pump).
Loop of Henle: Reabsorbed in the thick ascending limb.
Distal convoluted tubule (DCT): Regulated by aldosterone (Na+ reabsorption).
For the important solutes of the body (e.g., Na+, K+, glucose, urea), describe how each segment of the nephron handles the solute -> potassium
PCT: Small reabsorption.
Loop of Henle: Minimal reabsorption.
DCT: Secreted, especially when aldosterone is active.
For the important solutes of the body (e.g., Na+, K+, glucose, urea), describe how each segment of the nephron handles the solute -> glucose
PCT: Reabsorbed completely under normal conditions via active transport.
For the important solutes of the body (e.g., Na+, K+, glucose, urea), describe how each segment of the nephron handles the solute -> urea
PCT: Reabsorbed passively.
Loop of Henle: Urea reabsorption occurs in the inner medullary collecting duct (contributes to high osmolarity).
State the equation for clearance of a solute and explain how inulin clearance is used to determine glomerular filtration rate (GFR).
C= U xV/p
Where:
C = clearance of the solute,
U = concentration of the solute in urine,
V = urine flow rate,
P = concentration of the solute in plasma.
o Inulin Clearance for GFR:
Inulin is freely filtered at the glomerulus and neither reabsorbed nor secreted, so its clearance is equal to the glomerular filtration rate (GFR).
Trace the changes in filtrate osmolarity as it passes through the segments of the nephron.
o PCT: Filtrate is iso-osmotic to blood (osmolarity = 300 mOsm/L).
o Descending Limb of Loop of Henle: Water is reabsorbed, making the filtrate more concentrated (osmolarity increases).
o Ascending Limb of Loop of Henle: NaCl is actively reabsorbed without water, making the filtrate hypotonic.
o DCT and Collecting Duct: Fine-tuning of water and Na+ reabsorption based on hormonal regulation (ADH, aldosterone).
Explain the role of the nephron loop (of Henle), its permeability to water, and the high osmolarity of the interstitial fluid in the renal medulla in the formation of dilute urine.
o Descending Limb: Permeable to water, which is reabsorbed into the high osmolarity interstitial fluid.
o Ascending Limb: Impermeable to water, but Na+, K+, and Cl- are actively reabsorbed, diluting the filtrate.
o Role of the Medullary Osmotic Gradient: This gradient (high osmolarity in the renal medulla) allows for water reabsorption, which is crucial for concentrating urine when needed (with ADH).
composition of normal urine
Water (95%)
Urea (the main nitrogenous waste)
Creatinine (from muscle metabolism)
Uric acid
Electrolytes (Na+, K+, Cl-, etc.)
Small amounts of other metabolic waste products.
Identify and describe the gross anatomy and location of the ureters, urinary bladder, and urethra.
Ureters: Tubes that transport urine from the kidneys to the urinary bladder.
Urinary Bladder: Muscular organ that stores urine.
Urethra: Tube through which urine is expelled from the body.
microscopic anatomy of ureters
o Lining: Urothelium (transitional epithelium).
o Muscle Layers: Smooth muscle, including inner longitudinal and outer circular layers, facilitating peristalsis to move urine.
o Connective Tissue: Lamina propria (loose connective tissue) and adventitia (outer layer of fibrous tissue).
o Function: Transport urine from the kidneys to the bladder
microscopic anatomy of the urinary bladder
- Lining: Urothelium (transitional epithelium).
- Muscle Layers: Detrusor muscle, a thick layer of smooth muscle that contracts to expel urine.
- Connective Tissue: Lamina propria (loose connective tissue) and submucosa (connects lining to the detrusor muscle).
- Function: Stores urine and contracts to expel it into the urethra.
- Sphincters: Two sphincter muscles (internal and external) control urine flow
microscopic anatomy of the urethra
- Lining: Urothelium (transitional epithelium) in the proximal (closer to the bladder) two-thirds, and mucus-secreting epithelium in the distal (farther from the bladder) third.
- Muscle Layers: Smooth muscle, continuous with the bladder’s detrusor muscle, and the external urethral sphincter, a striated muscle under voluntary control.
- Connective Tissue: Loose connective tissue.
- Function: Transports urine from the bladder to the external urethral orifice
Compare and contrast the anatomy of the male urethra versus the female urethra.
o The male urethra is significantly longer (around 20 cm) and has four distinct parts, including the prostatic urethra, while the female urethra is shorter (around 4 cm) and lacks these specific sections, opening directly into the vestibule between the labia minora
Compare and contrast the locations, innervation and functions of the internal urethral sphincter and external urethral sphincter.
o The internal urethral sphincter (IUS) is located at the bladder-urethra junction, composed of smooth muscle and under involuntary (autonomic) control, while the external urethral sphincter (EUS) surrounds the urethra in the pelvic floor, made of skeletal muscle and under voluntary (somatic) control
Trace the path of urine from the collecting duct of the kidney to the external urethral orifice.
o Urine travels from the collecting duct of the kidney through the renal pelvis, ureter, urinary bladder, and finally exits the body through the urethra and the external urethral orifice
Describe the signals that cause release of aldosterone from the adrenal cortex and the effect of aldosterone on the nephron
o Aldosterone: Stimulated by low Na+ or high K+, it promotes Na+ reabsorption and K+ secretion in the DCT and collecting duct.
