Late Filtrate Processing
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Page 1.

Introduction

• The final processing of filtrate in the late distal convoluted tubule and collecting ducts comes under direct physiological control. • In this region, membrane permeabilities and cellular activities are altered in response to the body's need to retain or excrete specific substances.

Page 2. Goals
• To understand the role of the hormone aldosterone in the reabsorption of sodium and secretion o f potassium. • To examine the role of the antidiuretic hormone in the concentration of urine. • To understand the role of the medullary osmotic gradient in the …ver más…

• Also notice the resulting increase in interstitial osmolarity. Water is not following the solute, because the luminal membrane is relatively impermeable to water unless it is stimulated by ADH.

Page 6. Filtrate Processing in the Late DCT and CCD: Role of Antidiuretic Hormone
• Under most normal conditions, an increase in aldosterone occurs along with an increase i n antidiuretic hormone. The reabsorption of salt is usually coupled with reabsorption of water, although they can occur independently. • The cell you see here has been stimulated as yet only by aldosterone, so it is still impermeable to water. • When stimulated by ADH, principal cells quickly insert luminal water channels, increasing their water permeability. • Notice that the interstitial osmolarity decreases. When water molecules can diffuse through a membrane, osmolarities on each side of the membrane equilibrate. • Label this diagram to show what happens when both aldosterone and ADH levels are high:

Page 7.

Response to Dehydration and Overhydration

• Now let’s look at two common conditions to demonstrate how these two hormones function in our everyday lives. • Dehydration: • In dehydration, which could be caused by hot weather, perspiration causes the body to lose both water and sodium. • In response, both ADH and aldosterone are released; they stimulate the kidney to conserve body fluid by increasing reabsorption of water and sodium ions from the filtrate.