Discuss the functions of the uriniferous tubule.

(N/A) The filtrate produced by the glomerulus is approximately similar to blood plasma. As it gradually passes through the uriniferous tubule,its composition changes,and urine is formed.
$(1)$ Proximal Convoluted Tubule $(PCT)$: $PCT$ is lined by simple cuboidal brush border epithelium,which increases the surface area for reabsorption.
Nearly $2/3$ of water and $NaCl$ are reabsorbed here.
$PCT$ also helps to maintain the $pH$ and ionic balance of the body fluids by selective secretion of $H^{+}$ ions,$NH_{3}$,and $K^{+}$ into the filtrate and absorption of buffer $HCO_{3}^{-}$.
The filtrate and blood plasma become isotonic.
$(2)$ Descending Limb of the Loop of Henle: Reabsorption in this part is minimal.
It plays a significant role in the maintenance of high osmolarity of medullary interstitial fluid. It is permeable to $H_{2}O$ but impermeable to electrolytes.
This concentrates the filtrate as it moves down.
The filtrate becomes hypertonic compared to blood plasma.
$(3)$ Ascending Limb of the Loop of Henle: It is impermeable to water but allows the transport of electrolytes actively or passively.
Therefore,as the concentrated filtrate passes upward,it gets diluted due to the passage of electrolytes.
$(4)$ Distal Convoluted Tubule $(DCT)$: Conditional reabsorption of $Na^{+}$ and $H_{2}O$ takes place here.
It is also capable of reabsorption of $HCO_{3}^{-}$ and selective secretion of $H^{+}$ and $K^{+}$ ions and $NH_{3}$ to maintain the $pH$ and $H^{+}-K^{+}$ balance in the blood.
$(5)$ Collecting Duct: This long duct extends from the cortex of the kidney to the inner parts of the medulla.
Large amounts of $H_{2}O$ are reabsorbed to produce concentrated urine.
It allows the passage of small amounts of urea into the medullary interstitium to maintain osmolarity,and the selective secretion of $H^{+}$ and $K^{+}$ ions maintains $pH$ and ionic balance.