Water Reabsorption in the Renal Tubule | Aquaporin, Water Transport, Mechanism of Water Reabsorption

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Water Reabsorption in the Renal Tubule:
Water is filtered freely at the glomerulus. So osmolarity of filtrate is 300. The proximal tubule reabsorbs 65% of filtered water. The driving force for this reabsorption is the active reabsorption of solutes, which creates an osmotic gradient. The mechanisms are paracellular movement, as well as transcellular route, involving aquaporin 1. The osmolarity of the fluid at the end of the proximal tubule is the same 300 miliosmoles per liter. The thin descending limb reabsorbs 20% of filtered water. The driving force is medullary hyperosmolarity. And the mechanism is a transcellular movement, involving aquaporin 1. The osmolarity here gets as high as 600 to 1200. The ascending limb, and early distal tubule, do not reabsorb water. However, reabsorption of solutes here, makes the fluid hypoosmolar, with osmolarity getting as low as 100. The reabsorption from the late distal tubule, and collecting duct, occurs by transcellular route, involving aquaporin 2&3. The extent of this reabsorption depends on bodies needs. Normally, about 14% is reabsorbed, and 1% is excreted. So normal urine output is about 1.5 liters per day. When the body needs to conserve water, the vasopressin increases the reabsorption. In extreme cases, the excretion can decrease up to 0.3%, or 0.5 liters per day. The osmolarity in such cases, can get as high as 1200. On the other hand, when the body has access water, lack of vasopressin, decreases the reabsorption. In heavy water load, only 5% is reabsorbed. So up to 10%, or 20 liters of water is excreted. The osmolarity in such cases, can get as low as 30 miliosmoles per liter.

Chapters:
00:00 Introduction
00:18 Basic Points
01:39 Percentage of Water Reabsorbed in Different Segments
03:08 at Glomerulus (Filtration)
03:28 at Proximal Tubule: 65%
04:18 at thin Descending Limb: 20%
04:57 at Impermeable Segments: 0%
05:37 at Collecting Duct: 1%
06:20 Regulation by Vasopressin
07:52 Summary
10:14 Bonus Point

Dr Vipul Navadiya
Nonstop Neuron
Medical Animation
Medical Animation Videos
Physiology
#physiology
#humanphysiology

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