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The Importance of Excreting Wastes. Why Pee?. The body runs chemical reactions necessary for life. The products of these reactions tend to be useful to the body but some are not – like carbon dioxide in cellular respiration.
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Why Pee? • The body runs chemical reactions necessary for life. The products of these reactions tend to be useful to the body but some are not – like carbon dioxide in cellular respiration. • These byproducts that are not used must be removed from the cells/body through excretion.
Protein Problems • Proteins are the working molecules and they are an absolute necessity for the body. • When proteins are broken down the amine group (NH2) is removed in a process called deamination. These must be excreted as they will form ammonia which is toxic to the body. • The ammonia is combined with carbon dioxide by the liver to form urea. • Nucleic acidsbreak down to give a similar product – uric acid.
What Else is Excreted? • See Table 1 on page 342. This table shows what gets excreted and who gets rid of it. • Ammonia, Urea and Uric Acid Kidneys • Carbon dioxide Lungs • Lactic Acid Liver • Solid Waste (Feces) Large Intestine
How to Get Urine Out • Cells dump their waste into the blood – kind of like a sewer system. The blood travels through the renal arteries to the kidneys. (Renal = Kidneys) • The kidneys are the major filtration organ of the body. They filter the blood and remove waste products. • The kidneys have three parts: • The renal cortex – the outer layer of the kidney. • The renal medulla – the middle area of the kidney which houses the nephrons. • The renal pelvis – the collecting area for urine.
Nephrons • The nephrons are the actual filtration units of the kidneys. They are microscopic and each kidney has over a million of them. • The nephrons are housed in the renal medulla. • Nephrons are composed of several parts – glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule and the collecting duct.
What Happens in the Nephron? • Blood with waste in it is carried by the afferent arteriole to the glomerulus. • Dissolved matter – both useful and waste products are “pushed” into the glomerulus within Bowman’s capsule. Blood continues in circulation through the efferent arteriole. • The good and bad stuff transported into the glomerulus is separated as it travels through the proximal tubule and the loop of Henle – the good stuff is reabsorbed into the blood while the bad stuff stays in the nephron.
After the Nephron? • The bad stuff leaves the nephron through the distal tubule and enters the collecting duct. • The collecting duct leads to the renal pelvis where it collects and is ready to leave the kidney. • Ureters extend down from the kidney to the urinary bladder and the urine travels down these tubes. • Urine collects in the urinary bladder that has cells that are capable of stretching. When stretched far enough a nervous impulse is sent to the brain that says “ya gotta go!”. • Urine exits the urinary bladder and the body through a tube called the urethra.
The Process of Peeing • Urination is the result of three steps or processes…Filtration, Reabsorption & Secretion. • Filtration – Stuff is removed from blood (everything except large plasma proteins, blood cells, and platelets); this occurs at relatively high pressure in the glomerulus and Bowman’s capsule. • Reabsorption – The good stuff we need to keep is brought back into the blood from the nephron and into the capillaries. • Secretion – Taking the bad stuff from the nephron, mixing it with water and expelling it from the body.
Interesting Information • Once you get to 600ml – you go – like it or not! • Luckily, only 1ml of every 120ml/minute that is filtered by nephron is turned into urine. The other 119ml is reabsorbed into the blood. • The body will reabsorb all the good stuff until it hits a threshold level for that substance – after that, good or not, it is going to go out in the urine.
Interesting Information • A dialysis machine does the same job as the kidneys and nephrons except that it can take up to 4hours a day, 3 times a week to do so. This is a time consuming and emotionally draining activity for people with kidney disease/failure. • There are two types of dialysis: hemodialysis and peritoneal dialysis. • Peritoneal dialysis is appropriate if the patient is otherwise relatively healthy. It requires only a simple pumping device, and it is possible to do once a day, generally overnight.
