Excretory & Digestive

Excretory & Digestive - The liver is important in...

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The liver is important in excretion because it synthesizes urea - Carrier of excess nitrogen resulting from protein breakdown. - Excess nitrogen must be converted to urea because free ammonia is toxic. Selective reabsorption – usually occurs in the PCT Just like the digestive system, we have voluntarily and involuntarily-controlled sphincters (external and internal sphincters, respectively) Plasma proteins are too large to pass through the filter (and immunoglobulins) glucose passes through the filtrate, and must be reclaimed during selective reabsorption (diabetics have a problem with glucose reabsorption). - Out of albumin, glucose, and sodium, the latter two are present in the filtrate in Bowman’s capsule in concentrations similar to those seen in blood. Roughly 70% of the volume of filtrate is reabsorbed in the PCT - The PCT is selective in that it chooses what to reabsorb, but it is not overly regulated since it reabsorbs “as much as possible” . Secretion in the distal nephron/DCT as a “back-up” method that ensures what needs to be eliminated, gets eliminated. - Most secretion takes place in the DCT and collecting duct - Primary way that many drugs and toxins are deposited in the urine . The distal tubule is not permeable to water - Diuresis – water loss in the urine - Caffeine – an example of a diuretic - ADH – “antidiuretic hormone” (fitting name, huh?) Alcoholics cause people to diurese because it inhibits ADH secretion by the posterior pituitary . People with high BP have to avoid salty foods. - Why? salt ingestion causes aldosterone release, which induces sodium reabsorption in the DCT. Following the sodium would be water, which would ultimately increase the ECF volume, thereby increasing BP even further - The release of aldosterone leads to increased thirst and consequential water retention, which raises BP. - When the BP is high, aldosterone is not released sodium is lost in the urine plasma osmolarity (solute concentration) decreases. ADH – stimulates water reabsorption in the collecting duct . - Normally, the lumen of the collecting duct is impermeable to water. ADH makes it permeable via aquaporins . - Works to increase BP
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The renal medulla normally has a high osmolarity, which causes water to exit the lumenal tubule into the renal medulla via osmosis. - Why? in the distal nephron, water is kept inside the lumen, making the urine more dilute this increases the osmolarity of the medulla (since water is not flowing out of the nephron to dilute the solutes present in the medulla) Descending loop of Henle – thin – usually made of non-metabolically active simple squamous epithelial cells Ascending loop of Henle – thick – usually made of metabolically active cuboidal epithelial cells. Countercurrent multiplier
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Excretory & Digestive - The liver is important in...

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