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Functions of the kidney. • filtration – fluid pressure forces water and dissolved substances out of blood. • reabsorption – returns useful items as blood ...
Typology: Study notes
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Karen L. Lancour National Rules Committee Chairman – Life Science
include carbon dioxide, water, salt, urea and uric acid. All excreted wastes travel at some time in the blood.
∑ Lungs - removal of excess carbon dioxide ∑ Liver - produces urea and uric acid as a by-product of the breakdown of proteins ∑ Skin - removal of excess water, salt, urea and uric acid ∑ Urinary System - kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid
∑ Humans produce waste products that must be removed from their body. ∑ Most animals have a system that deals with nitrogen-rich wastes from the breakdown of proteins and nucleic acids. ∑ Ammonia (NH 3 ) is toxic. ∑ It helps maintain homeostasis – balancing osmotic action and pH.
∑ Excrete toxins and nitrogenous waste ∑ Regulate levels of many chemicals in blood ∑ Maintain water balance ∑ Helps regulate blood pressure
Kidney – filters blood and forms urine- receives 20-25 % of arterial blood
Homeostatic device – regulates composition of the blood Filtration – removes waste
Ureter – carries urine to the urinary bladder Muscles contract and relax to move urine out of kidneys every 10 to 15 seconds to prevent infection
Urinary Bladder – holds urine – it can hold up to 16 oz of urine for 2-5 hours
Urethra – releases urine from the body by relaxing the sphincter muscle (circular muscle around the bladder opening to keep it from leaking) at bottom of bladder and contracting the bladder muscles
∑ Glomerular filtration – into Bowman’s Capsule o substances move from blood in glomerulus to the Bowman’s capsule
∑ Tubular Reabsorption of solutes and water o Solute Reabsorption – from proximal tubule to capillary o substances move from renal tubules into blood of peritubular capillaries ß glucose, water, urea, proteins, creatine ß amino, lactic, citric, and uric acids ß phosphate, sulfate, calcium, potassium, and sodium ions
o Water Reabsorption – from proximal tubule and Loop of Henle to capillary
∑ Tubular Secretion – from capillary to distal o substances move from blood of peritubular capillaries into renal tubules o drugs and ions
D. Intrinsic Controls: Regulation of Glomerular Filtration
a. low concentration -> vasodilation b. high concentration -> vasoconstriction
Tubular Reabsorption: Reabsorbing the Glomerular Filtrate
A. Overview of Reabsorption
B. Active Tubular Reabsorption
A. Movement from Capillaries to Tubular Cells
C. Formation of Dilute Urine
Renal Clearance
A. Renal Clearance (RC) – the rate at which the kidney can remove a substance from the blood RC = U/P X V concentration of substance in urine (mg/ml) U/P = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - concentration of substance in plasma (mg/ml) V = rate of the formation of urine (ml/minute) (normal = 1 ml/minute) B. Glomerular Filtration Rate = 125 ml/minute; (determined by challenge with “Insulin”)
Characteristics and Composition of Urine
A. Physical Characteristics
Composition of Urine
Normal GFR = 125 mL/min or 7.5 l/hr or 180 l/day
GFR– amount of filtrate formed per minute in all nephrons of both kidneys
GFR = UV = Urine concentration x Rate of Urine Flow = g/ml x ml/min = ml/min P Blood Plasma Concentration g
Note: Cranberry juice acidifies the urine which can help prevent bacterial growth and some types of kidney stones. It also reduces the adherence of bacteria onto the walls of the urinary tract reducing the risk of urinary tract infections.