Exrectory System

Topics: Nephron, Kidney, Glomerulus Pages: 11 (3499 words) Published: February 28, 2013
Excretory System Review

Main Concepts:

Describe the major gross anatomical structures of the excretory system. Kidneys: receive about 25% of the cardiac output; produce urine (a fluid containing water, ions, and small soluble compounds) Ureters: receive urine from the kidneys and conduct it to the urinary bladder. Urine movement involves a combo of gravity and the peristaltic contractions of smooth muscle in the walls of the ureters Urinary Bladder: receives and stores urine prior to elimination from the body. Urination is driven by the contraction of smooth muscle layers in the walls of the bladder Urethra: passageway that conducts urine from the urinary bladder to the exterior

List and describe the functions of the excretory system.
Adjusting blood volume and blood pressure
Regulating plasma concentrations of sodium, potassium, chloride, and other ions Stabilizing blood pH
Conserving valuable nutrients
Removing drugs and toxins from the bloodstream

Explain the functions of the components of a nephron, and relate those functions to cellular and histological specializations. SegmentGeneral FunctionsSpecific Functions
Renal CorpuscleFiltration of plasma; generates approximately 180 L/day of filtrate similar in composition to blood plasma but without proteinsFiltration: Water and inorganic and organic solutes from plasma

Plasma proteins and blood cells
Proximal Convoluted TubuleReabsorption of 60-70% of the water (108-116 L/day), 99-100% of the organic substrates, and 60-70% of the sodium and chloride ions in the original filtrateActive Reabsorption: glucose, other simple sugars, amino acids, vitamins, ions (including sodium, potassium, calcium, magnesium, phosphate, and bicarbonate Passive Reabsorption: urea, chloride ions, lipid-soluble materials, water Secretion: hydrogen ions, ammonium ions, creatinine, drugs and toxins Nephron LoopReabsorption of 25 % of the water and 20-25% of the sodium and chloride ions present in the original filtrate; creation of the concentration gradient in the renal medullaReabsorption: sodium and chloride ions, water Distal Convoluted TubuleReabsorption of a variable amount of water (usually 5% of 9L/day) under ADH stimulation, and a variable amount of sodium ions under aldosterone stimulationReabsorption: sodium and chloride ions, sodium ions (variable), calcium ions (variable), Secretion: hydrogen ions, ammonium ions, creatinine drugs, and toxins Collecting SystemReabsorption of a variable amount of water under ADH stimulation, and a variable amount of sodium ions under aldosterone stimulationReabsorption: sodium ions (variable), bicarbonate ions (variable), water (variable) Secretion: potassium and hydrogen ions

Peritubular CapillariesRedistribution of water and solutes reabsorbed in the renal cortexReturn of water and solutes Vasa RectaRedistribution of water and solutes reabsorbed in the renal medulla, and stabilization of the concentration gradient of the renal medullaReturn of water and solutes from the peritubular fluid to the general circulation

Describe the excretory / circulatory interface.
The goal of urine production is to maintain homeostasis by regulating the volume and composition of blood. This process involves the excretion of solutes—specifically, metabolic waste products, including urea, creatinine, and uric acid.

Explain what is meant by renal threshold, and the contribution of filtration, secretion and reabsorption. The renal threshold is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine. When the renal threshold of a substance is exceeded, reabsorption of the substance by the proximal renal tubuli is incomplete; consequently, part of the substance remains in the urine. Renal thresholds vary by substance – the low potency poison urea, for instance, is removed at much lower concentrations than glucose. Indeed, the most common reason for the glucose...
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