Exam #4: Overview of Renal Physiology Flashcards
What are the three main regions of the kidney?
1) Cortex
2) Medulla
3) Papilla
What is the cortex?
Outer region of the kidney, located under the capsule
What is the medulla?
Central region of the kidney; it is divided into an inner & an outer medulla
What is the papilla?
Innermost tip of the inner medulla that empties into the minor & major calyces (extensions of the ureter)
What is the functional unit of the kidney?
Nephron
How many nephrons are contained within each kidney?
~1,000,000
What are the two major constituents of the nephron?
1) Glomerulus
2) Renal tubule
What is the glomerulus?
- A glomerular capillary network the emerges from an afferent arteriole
- These capillaries are surrounded by Bowman’s Capsule, creating Bowman’s Space
Which direction is blood filtered in in the glomerulus?
Across glomerular capillaries into Bowman’s Space
Beginning with Bowman’s Space, what are the parts of the nephron?
1) Proximal convoluted tubule
2) Proximal straight tubule
3) Loop of Henle
4) Distal convoluted tubule
5) Collecting ducts
What are the three parts of the Loop of Henle?
1) Thin descending limb
2) Thin ascending limb
3) Thick ascending limb
What is unique about the structure of the proximal convoluted tubule? How do these structural changes impact its function?
- Extensive development of microvilli, called a “brush border” on the luminal side
- Provides a large surface area of reabsorption
What are the two different types of nephrons?
1) Superficial cortical nephrons=
- Glomeruli in outer cortex
- Short Loops of Henle that descend only into the outer medulla
2) Juxtamedullary nephrons
- Glomeruli near corticomedullary border
- Large glomeruli
- Longer Loops of Henle that descend into the inner medulla & papilla
Which type of nephron functions in the concentration of urine?
Juxtamedullary nephrons
Describe the blood supply to the kidney.
- Renal arteries branch off the abdominal aorta
- Branches into
1) Interlobar arteries
2) Arcuate arteries
3) Cortical radial arteries - Afferent arterioles
*The afferent arterioles deliver blood to the glomerular capillaries, across which ultrafiltration occurs
Describe how blood leaves the kidney.
- Blood leaves the glomerulus via the efferent arterioles
- Efferent arterioles deliver blood to a 2nd capillary network, “peritubular capillaries”
- Blood from the peritubular capillaries flows from into the small vein
- Small vein drains into the renal vein
What is the function of the peritubular capillaries?
Solutes & water are reabsorbed into the peritubular capillaries
How does the blood supply of superficial cortical nephrons differ from juxtamedullary nephrons?
- Superficial cortical= peritubular capillaries branch off efferent arterioles & deliver nutrients to epithelial cells
- Juxtamedullary= peritubular capillaries contain vasa recta that serve as osmotic exchangers for concentrated urine
What is unique about the structure of the proximal convoluted tubule? How do these structural changes impact its function?
- Extensive development of microvilli, called a “brush border” on the luminal side
- Provides a large surface area of reabsorption
What are the two different types of nephrons?
1) Superficial cortical nephrons=
- Glomeruli in outer cortex
- Short Loops of Henle that descend only into the outer medulla
2) Juxtamedullary nephrons
- Glomeruli near corticomedullary border
- Large glomeruli
- Longer Loops of Henle that descend into the inner medulla & papilla
Which type of nephron functions in the concentration of urine?
Juxtamedullary nephrons
Describe the blood supply to the kidney.
- Renal arteries branch off the abdominal aorta
- Branches into
1) Interlobar arteries
2) Arcuate arteries
3) Cortical radial arteries - Afferent arterioles
*The afferent arterioles deliver blood to the glomerular capillaries, across which ultrafiltration occurs
Describe how blood leaves the kidney.
- Blood leaves the glomerulus via the efferent arterioles
- Efferent arterioles deliver blood to a 2nd capillary network, “peritubular capillaries”
- Blood from the peritubular capillaries flows from into the small vein
- Small vein drains into the renal vein
What is the function of the peritubular capillaries?
Solutes & water are reabsorbed into the peritubular capillaries
How does the blood supply of superficial cortical nephrons differ from juxtamedullary nephrons?
- Superficial cortical= peritubular capillaries branch off efferent arterioles & deliver nutrients to epithelial cells
- Juxtamedullary= peritubular capillaries contain vasa recta that serve as osmotic exchangers for concentrated urine
List the functions of the kidney.
1) Regulation of water & electrolyte balance
2) Regulation of arterial blood pressure
3) Excretion of metabolic waste
4) Excretion of foreign substances
5) Acid-base regulation
6) Regulation of RBC production
7) Last step of Vitamin D production
8) Gluconeogenesis (most happens in the liver, but the kidney does some during the long fast)
What is the lumen of the nephron?
The space inside of the nephron is the “lumen”
What is the luminal side of a tubular cell? What is the apical side of a tubular cell?
The cell surface touching the tubular lumen is the apical/ luminal side of the cell
What is the basolateral side of a tubular cell?
The cell surface facing the interstitial fluid is the basolateral side
What is the function of the Proximal Convoluted Tubule?
ISOSOMOTIC REABSORPTION OF SOLUTE & WATER
Water Reabsorption Na+, K+ & Cl- reabsorption Glucose reabsorption Protein reabsorption Secretion of organic anions, cations (esp. H+), and drugs
- Note that since water & solute are reabsorbed in the proximal convoluted tubule, this is referred to as “isosmotic”
- *Proximal convoluted tubule= isosmotic reabsorption
What is the function of the Loop of Henle?
The Loop of Henle is responsible for counter current multiplication, which is necessary for concentration & dilution of urine
*Note that the Thick Ascending Limb is referred to as the “Diluting segment;” REABSORPTION OF NaCl WITHOUT WATER i.e. NaCl is pumped out but water does NOT follow b/c the segment is impermeable to water
What is the function of the Distal Convoluted Tubule?
- Similar to thick ascending limb of henle; REABSORPTION OF NaCl WITHOUT WATER
- DILUTION OF TUBULAR FLUID
- Contains “principal cells” with receptors for aldosterone; reabsorbs Na+ & secretes K+
- Intercalated cells reabsorb K+ & secrete H+
What is the function of the Collecting Ducts?
- Respond to ADH–>concentration/ dilution of urine
Cortical portion= aldosterone receptors (principal cells)
Medullary portion= urea uniporters
How is protein reabsorbed in the proximal tubule?
- Peptides & small proteins are filtered across glomerular capillaries into Bowman’s Space; these proteins must be reabsorbed or proteinuria will result
- Small proteins are broken into amino acids, di, or tripeptides WITHIN the LUMEN of the PROXIMAL TUBULE, by peptidases on the apical membrane
- Larger proteins are taken up by endocytotic vesicles, broken down by lysosomes, and resultant amino acids leave across the basolateral membrane
Where does ADH act in the kidney?
ADH acts on the entire collecting duct
How does ADH control water concentration in urine?
1) Osmolarity of blood is measured by osmoreceptors in the hypothalamus
2) Osmoreceptors shrink when ECF is more concentrated than ICF i.e. high osmolarity in ECF
3) Signal sent to nuceli in hypothalamus to synthesize ADH
4) Posterior pituitary releases ADH
5) ADH acts on the collecting duct to produce more concentrated urine
Where is the Macula densa located?
Distal end of the thicken ascending Loop of Henle
What is the function of the Macula densa?
The macula densa controls vasodilation and vasoconstriction of the afferent arteriole as part of a mechanism for maintaining relatively constant GFR and renal blood flow despite changes in systemic arterial blood pressure
