Excretion The removal from the body of the waste products of metabolism Includes removal through the lungs, skin, urinary system and kidney Done through osmoregulation The maintenance of a proper balance of water and dissolved substances in the organism

Types of Nitrogenous Waste Type of WasteOrganismAdvantagesDisadvantages AmmoniaFishLittle energy required Toxic; must be removed from the animal quickly UreaMammalsMedium energy to produce; only toxic in abnormal amounts Requires water for dilution and removal from the body Uric acidBirdsInsoluble and can be easily stored; little to no water required Requires a lot of energy to produce

Malpighian Tubes Found in insects Selectively permeable Open in the insects guts and closed at the other end Reabsorption of non- excess water and nutrients Waste and excess water are released into the gut Waste is released with the feces

Osmoregulators vs Osmoconformers Osmoregulators Internal solute concentration is different than the environment Mechanisms are in place to regulate water balance High energy cost Osmoconformers Internal and external solute concentration is almost identical No need to regulate water Restricted to one environment

Diagram of the Kidney

The explanation Humans have two kidneys near the lower back Each kidney has a renal artery leading to it and a renal vein and ureter leading away from it Renal vein removes clean blood from the kidney Ureter takes urine to the bladder

Annotated Glomerulus

The explanation The functional unit is the nephron Renal artery Takes blood to the kidney for filtration Renal vein Removes clean blood from the kidney Afferent vessel Takes blood to the glomerulus Efferent vessel Takes blood away from the glomerulus Vasa recta Blood vessels around the nephron Takes away reabsorbed materials

The explanation Glomerulus Extensive capillary bed Provides ultra-filtration Bowman’s capsule First part of the nephron Receives filtrate from the glomerulus Proximal convoluted tubule Most reabsorption of glucose, salt, and water takes place here Loop of henle Reabsorption of salt Reabsorption of water Distal convoluted tubule Reabsorption of salt Collecting duct Reabsorption of urea Reabsorption of salt Reabsorption of water Regulated by ADH

Ultra-filtration The fluid of the blood is pushed out of the glomerulus into the nephron The substances that the body doesn’t want to lose (glucose) are reabsorbed into the blood Waste substances (ammonia) are secreted into the filtrate to be removed by the urine Diameter of the afferent vessel is larger than the efferent vessel Puts the blood under high pressure allowing ultra-filtration Pushes some of the liquid and small dissolved molecules into the bowman’s capsule for filtration All the blood circulates through the kidney every 5 minutes and 15%-20% goes through the bowman’s capsule

Reabsorption of water Bowman’s capsule Where the filtrate of the glomerulus enters the nephron Joins the proximal convoluted tubule Fluid here is similar to plasma Contains glucose, amino acids, vitamin, hormones, urea, salts and water Most of the glucose, amino acids, vitamins, hormones and most salt and water is reabsorbed here into blood vessels Driven by osmosis for water and active transport for everything else Has microvilli to increase the surface area for absorption Lots of mitochondria to provide energy for active transport

Roles of the different parts Loop of Henle In the descending loop water is removed through osmosis Some salt diffuses here as well The ascending loop is impermeable to salt and water Helps maintain the concentration gradients Medulla Concentration gradient is maintained by a countercurrent No direct exchange between the filtrate and the blood

Collecting Duct Wall is permeable and water can pass from the ultra-filtrate into the blood vessels to be carried away ADH Anti-diuretic hormone Increases the permeability of the walls of the distal convoluted tubule and the collecting duct Released from the posterior lobe of the pituitary gland when the amount of solutes in the blood is too high When absent no water can be absorbed

Osmoregulation The regulation and control of water balance of the blood, tissue and cytoplasm Maintains homeostasis Evens out: The amount of water ingested Sweating Ventilation (water is actually lost while breathing)

Hydration Levels DehydrationOverhydration SleepinessChange in behavior ConstipationBlurred vision Dry mouth/skinMuscle cramps Dizziness/headacheNausea/vomiting

The liquids Blood plasma In the renal artery is rich in oxygen and contains more urea, more salt and possibly more water than what the body requires In the renal vein contains carbon dioxide, less urea and the optimum amounts of water and salts No change in proteins and no glucose Glomerular filtrate Found in the bowman’s capsule Similar to the plasma but no large molecules Urine (compared to glomerular filtrate) Contains less water, less salt, no glucose, no proteins or amino acids Lots of urea

Urine Testing Glucose In diabetics with insulin deficiency will have higher blood glucose when it arrives at the kidney If the blood glucose is too high it is not all reabsorbed into the blood and spills out into the urine Blood Cells Sign of infection or internal bleeding Proteins Usually too large to fit through the glomerous In pregnancy it is a sign of preeclampsia Drugs Often filtered out into the urine

Kidney Failure Dialysis External filtration of the blood Takes several hours Must be done every 1-3 days Kidney transplant New kidney must have correct protein matches so the immune system does not attack it Possible to live with 1 healthy kidney