The Kidney Is Crucial in Osmoregulation and ExcretionThe kidney filters water and solutes from blood plasma, then selectively reabsorbs the substances the body needs.This makes it central to both osmoregulation and excretion, the two jobs that keep the internal environment stable.Structure of a Human KidneyNoteOsmoregulation controls the water and solute balance of the blood.Excretion removes the waste products of metabolism from the body.Osmoregulation Keeps the Blood's Water Balance StableDefinitionSee other references1OsmoregulationOsmoregulation is the process of maintaining the balance of water and solutes in the body.Osmoregulation controls the water and solute balance of the body's fluids.It keeps the osmotic concentration of blood stable at about 300 mOsm/L.The kidney does this by adjusting how much water it reabsorbs and how concentrated the urine becomes.Theory of KnowledgeHow does the nephron of a desert mammal reflect evolutionary adaptation to a dry environment?Excretion Removes Metabolic Waste Such as UreaDefinitionExcretionExcretion is the removal of metabolic waste products.Excretion is the removal of the waste products of metabolism.Urea is the main nitrogenous waste, formed in the liver from the deamination of excess amino acids.The kidney filters urea from the blood and removes it dissolved in urine.Excess ions, drugs, and pigments are excreted the same way.ExampleUrochrome, a pigment from the breakdown of haemoglobin, gives urine its yellow colour.The Nephron Is the Kidney's Functional UnitEach kidney contains about a million nephrons, the tiny tubes that actually filter the blood and make urine.Filtrate flows through four regions in order, each doing a different job.The kidney and nephronThe Four Regions of the NephronGlomerulus and Bowman's CapsuleBlood is filtered here, forcing water and small solutes into the tubule while proteins and cells stay in the blood.Proximal Convoluted Tubule (PCT)Most useful substances, such as glucose and water, are reabsorbed back into the blood here.Loop of HenleIt sets up a salt concentration gradient in the medulla that lets the kidney concentrate urine.Distal Convoluted Tubule and Collecting DuctFinal adjustment of water and ions happens here, tuning urine to the body's needs.Process of Urine Formation in a NephronNoteThe detailed mechanisms of each region are covered in the next three subtopics.How Osmoregulation and Excretion Work TogetherAs filtrate passes through the nephron, the kidney reclaims what the body needs and lets waste continue toward the bladder.By choosing how much water to reabsorb, the kidney regulates blood water balance and removes urea in the same process.Active recallWhat is the difference between osmoregulation and excretion?Where is urea produced, and from what?What is the functional unit of the kidney?Name the four regions filtrate passes through in the nephron, in order.Roughly what osmotic concentration does the kidney keep the blood at?
