9.2 Blood Flow to the Kidneys; The Nephron; Urine formation, concentration & hormone influences Flashcards
Describe the passage of blood through the kidneys
- Renal artery
- Interlobular artery
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Peritubular capillary
- Vasa recta (loop of henle)
- Interlobular vein
- Renal Vein
- IVC
What are the three main components of a nephron?
- Renal corpuscle (water and solutes removed)
- Renal tubule (filtrate modification)
- Collecting system (urine from each nephron empties into minor calyces)
What are the three processes within kidney function?
- Filtration
- Rebasorption
- Secretion
Where does filtration occur in the nephron?
Only in the renal corpuscle
Describe the difference in diameter between the afferent and efferent arterioles of the glomerulus? Why is this important?
- Efferent has smaller diameter
- This causes a pressure gradient, enabling blood to move throughout the glomerulus and hence enabling filtration to occur
Describe the three layers of the filtration membrane of the glomerulus
- Fenestrated endothelium (capillary)
- Basement membrane (collagen -> -ve charge)
- Pedicels of podocytes
What three factors of the renal corpuscle enhance glomerular filtration?
- Thinness of filtration membrane
- BP gradient
- High surface area of capillaries
What does the fenestrated endothelium stop?
Some cells and platelets
What does the basement membrane stop?
Large proteins
What do filtration slits between pedicels of podocytes stop?
Medium sized proteins
What are some substances that can enter through the filtration membrane?
- Water
- Small proteins
- Amino acids
- Glucose
- Waste solutes
In what two ways does the basement membrane of the glomerulus act as a barrier?
- Charge (negative)
- Physical (blocks large proteins)
Briefly explain the role of mesangial cells in the renal corpuscle
- Control capillary diameter (and therefore blood flow rate)
- Keeps glomerular filter free of debris by phagocytosing trapped substances
What change occurs to tubular fluid at the PCT? What aids this?
- Essential substances (water, glucose, small proteins) are reabsorbed. Cells within PCT have microvilli to aid this
What change occurs to tubular fluid at the loop of Henle?
Descending: water is taken out of tubular fluid (so solute conc increases)
Ascending: Na+ and Cl- are reabsorbed out of tubular fluid along conc gradient
What percentage of initial filtrate volume reaches the DCT?
15-20%
What change occurs to tubular fluid at the DCT?
Final adjustment of filtrate composition via reabsorption and secretion
What change occurs to tubular fluid at the Collecting Duct?
- Filtrate is carried through osmotic gradient
- Water may/may not be reabsorbed depending on hydration status
Where does urine travel after leaving the papillary duct?
Collects filtrate from multiple collecting ducts and delivers it to the minor calyx
What are the main substances extreted?
- Waste products
- Toxins
- Urea (although this one is more complex)
Why do we expect to see more PCT cells than DCT cells in a H&E section of a nephron?
PCT is more tortuous than DCT (more windy)
Where is most of the filtrate reabsorbed? What are these substances?
- PCT
- Ions
- Simple molecules (glucose)
- Small proteins
What are two structures in PCT cells that can aid their function?
- Mitochondria (active transport)
- Microvilli (SA:V)
Describe the H&E appearance of PCT cells
- Centrally located nucleus
- Acidophilic (pink) cytoplasm
What is descending limb of the loop of henle similar to?
The PCT (branches off)
Describe the epithelium of the thin ascending limb
Simple squamous
What is the structure of the thick ascending limb of the loop of Henle similar to?
Similar to DCT (becomes DCT)
What vessels accompany the loop of henle?
- vasa recta
- Peritubular capillaries
Draw a diagram of the countercurrent multiplier mechanism. How do juxtamedullary nephrons aid in this process? How is urea recycling work?
What are the functions of the DCT?
- Na+ reabsorbed; K+ secreted (ATPase pump)
- Reabsorb bicarbonate (acidifies urine)
Describe the structure of DCT cells
- Few/no microvilli
- Lots of mitochondria
How and why do DCT cells look different to PCT cells in a H&E section?
Paler (less organelles; not main site of reabsorption, unlike PCT)
What are the two components of the juxtaglomerular apparatus
- Juxtaglomerular (JG) cells
- Macula densa
What is the function of the JG cells? Where are they located?
- Endocrine cells in the afferent arteriole
- Produce renin for RAAS system
- Causes increase resorption of sodium in the DCT
Where are macual densa located? What do they do?
- Part of DCT
- Monitor sodium conc in filtrate
Name two stimuli that can cause the release of renin from the JG cells of the JGA
- Sodium levels decrease in filtrate detected by Macula Densa
- Decreased blood pressure in afferent arteriole detected by JG cells
Structurally speaking, how are macula densa cells different from regular DCT cells?
More columnar
What are diuretics?
Increase excretion of sodium and water
What are some commonly encountered diuretics (colloquially speaking)
- Caffeine
- Alcohol
- Medications
What is hypohydration?
Water defecit; body water losses of >2% body mass
What are the three most important metabolic waste products excreted in urine?
- Urea
- Creatinine
- Uric acid
How is urea formed?
By-product of AA breakdown in liver
How is creatinine formed?
Formed in skeletal muscle through creatine phosphate breakdown (involved in muscle contraction)
How is uric acid formed?
By-product of recycling RNA nitrogenous bases
Which areas of the nephron does ADH act on?
Late DCT and collecting tube
