Collecting Ducts

The collecting ducts, which consist of cortical and medullary segments, reabsorb the final 5 to 7% of the filtered Na+. The epithelium forming the collecting ducts consists of two distinct cell types: principal cells and intercalated cells. The relative preponderance of the two cell types varies along the length of the collecting duct and between nephron segments. Principal cells are responsible for the reabsorption of Na+ and the secretion of K+ (Fig. 21.5). Na+ enters the principal cell from the tubular fluid through a unique and highly selective epithelial Na+ channel, ENaC. Intercalated cells reabsorb HCO3~ and K+ and secrete H+. Normally, H+ is secreted into the urine and HCO3~ is reabsorbed, while


principal cell


(filled circle)

intercalated cell

H4^ HCO3

Constipation Prescription

Constipation Prescription

Did you ever think feeling angry and irritable could be a symptom of constipation? A horrible fullness and pressing sharp pains against the bladders can’t help but affect your mood. Sometimes you just want everyone to leave you alone and sleep to escape the pain. It is virtually impossible to be constipated and keep a sunny disposition. Follow the steps in this guide to alleviate constipation and lead a happier healthy life.

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