Renal: Tubular Structure and Function Flashcards
Label the different parts of the renal tubule
The tubular cells are different in the different segments in height, microvilli and mitochondria
What are the 2 types of nephrons in the kidney?
Cortical nephrons (85%) Short LoH, doesn’t extend into medulla Extensive capillary network round entire tubule
Juxtamedullary nephrons (15%) Long LoH, penetrates deep into medulla which allows more water reabsorption Long afferent arteriole extending from glomerulus to outer medulla This is subdivided into small capillaries (vasa recta) which lie next to LoH
Describe the proximal convuluted tubule
Majority of the reabsorption including 65% of water
Tall cells w many mitochondria and microvilli= large SA for substance exchange and increases energy for AT.
Malfunction causes acidosis and “fanconisyndrome”- defective PCT reabsorption. AAs, glucose, Na+, K+ etc all elevated in urine
Describe the LOH
The descending loop of Henle: water permeable, thin, flat epithelial cells w less mitochondria. Osmotic gradient increases down the loop, so hay mucho water reabsorption
The ascending limb has thicker cells, w mitochondria. Impermeable to water, but reabsorbs mucho electolytes, esp Na.
Plays critical role in conc/diluting urine by adjusting fluid secretion/reabsorption rate
Describe the distal convuluted tubule
Tall cells with numerous mitochondria
Includes the juxtaglomerular apparatus
Low water permeability, but ADH can increase this
Main function is solute reabsorption which dilutes the tubular fluid
Basolateral Na+/K+ ATPase activity aids Na+ reabsorption in the DCT
DCT plays a role in acid-base balance by secreting ammonia which increases urine pH
Describe the collecting duct
Responsible for water absorption. 2 major cell types:
Principal cells: tall, responsible for Na absorption and ADH action
Intercalated cells:more microvilli, numerous mitochondria, responsible for acid secretion
Other solutes, esp NaCl, continue to be reabsorbed in the CD, maintaining medullary hyperosmolarity. This facilitates water reabsorption in presence of ADH by maintaining osmotic gradient
Explain the action of ADH/Vasopressin in water transport
ADH stimulates insertion of aquaporins into luminal membrane
Water is reabsorbed down osmotic gradient
Tubular fluid becomes more concentrated
ADH also increases CD permeability to urea
Sin ADH, no water or urea is reabsorbed. NaCl absorption continues. Large volume of dilute urine (diuresis)
ADH secretion= antidiuresis
What is the counter current multiplier in the loop of Henle, and the counter current exchanger?
CCM: Na,Cl,K are pumped out from the ascending limb. This forms hyperosmolar medulla which drives water reabsorption
Counter current exchanger: Absorbed water is returned to the circulatory system via the vasa recta. Because the blood flow through the Vrecta is slow, any solutes reabsorbed diffuse back into the ISF. This maintains the solute conc gradient in the medulla.
How is Na and glucose reabsorbed in the PCT at the same time?
Glucose needs to cross the apical surface of the renal tubule cells. But glucose conc inside the cells> tubule, so for glucose to cross the apical surface requires energy.
Na electrochemical gradient is sufficient to pull 2 Na + AND 1 glucose molecule into the tubule cell via SGLT (secondary a.t).
The intracellular glucose conc is high in the tubule so it quickly moves basolaterally into peritubular capillaries via GLUT1 or GLUT2 (facilitated dif).
How is Na reabsorbed in the PCT?
Na/H+ exchanger pumps Na into the cell and H+ from the cell into the lumen.
This aids HCO3- reabsorption and is regulated by Ang II
Describe Na reabsorption in the loop of Henle
25% Na is further reabsorbed in the TALof Henle. This segment is impermeable to water, so no water is reabsorbed along w sodium.
Na, K and Cl- is reabsorbed through the NKCC2 cotransporter. ADH stimulates NKCC2, increasing sodium, chloride and potassium reabsorption.
How is Na reabsorbed in the DCT?
In the distal tubule a Na-Cl cotransporter reabsorbs both sodium and chloride.
Sodium is also reabsorbed by ENaCs in response to aldosterone in the DCT.
