Excretion Flashcards
what is excretion?
the removal of the waste products of metabolism from the body
describe the structure of the liver.
the liver is made up of liver lobules- made of cells called hepatocytes
each lobule has a central vein in the middle that connects to the hepatic vein
hepatic artery- supplies the liver with oxygenated blood from the heart so that the liver has a good supply of oxygen for respiration
hepatic vein- takes deoxygenated blood away from the liver
hepatic portal vein- brings blood from the small intestine so it’s rich in nutrients, any ingested harmful substances are filtered out and broken down straight away
bile duct- takes bile to the gallbladder to be stored
sinusoids- capillaries that connect the hepatic artery and hepatic portal vein to the central vein
kupffer cells- remove bacteria and breakdown old red blood cells
hepatocytes- produce bile and secrete it into tubes called bile canaliculi
what is the ornithine cycle?
converts excess ammonia into urea in the mitochondria of liver cells
what happens during deamination?
nitrogen containing amino groups are removed from any excess amino acid forming ammonia and organic acids
this process is called deamination
amino acids—–> ammonia + organic acids
what happens in the ornithine cycle?
the organic acids can be respired to give ATP or converted to carbohydrate and stored as glycogen.
ammonia is too toxic for mammals to excrete directly so it’s combined with Co2 in the ornithine cycle to create urea and water
ammonia + carbon dioxide—-> urea + water
the urea is released from the liver into the blood. the kidneys then filter the blood and remove urea as urine
What happens during detoxification?
the liver breaks down other harmful substances into less harmful compounds that can then be excreted from the body, these include:
alcohol- is broken down into ethanal which is then broken down into a less harmful substance called acetic acid
alcohol over long period can lead to cirrhosis of the liver (liver cells die and scar tissue blocks blood flow)
paracetamol- broken down by the liver. excess paracetamol in the blood can lead to liver and kidney failure
insulin- is broken down by the liver as an excess can cause problems with blood sugar levels
how is glucose stored in the body?
the liver converts glucose in the blood to glycogen in a process called glycogenesis.
the glycogen is then stored as granules in the liver cells until the glucose is needed for energy
what is the process of excretion of waste products?
blood enters the kidney through the renal artery and then passes through the capillaries in the cortex of the kidney
ultrafiltration- as blood passes through the capillaries, substances are sorted out of the blood and into long tubules that surround the capillaries
selective reabsorption- useful substances are reabsorbed back into the blood from the tubules in the medulla and cortex
the remaining unwanted substances pass along the tubules then along the ureter to the bladder where they are expelled as urine
blood passes out of the kidneys through the renal vein
what is the nephron?
the long tubules along with the bundle of capillaries where the blood is filtered
what happens during ultrafiltration in the nephron?
blood from the renal artery enters smaller arterioles in the cortex. Each arteriole splits into a structure called a glomerulus- a bundle of capillaries inside the Bowman’s capsule. The arteriole that takes blood into the glomerulus is called the afferent arteriole and the one that takes blood away is called the efferent arteriole.
The latter is smaller in diameter so the high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule. The liquid and small molecules pass through the three layers to get into the Bowman’s capsule and enter the nephron tubule- the capillary endothelium, basement membrane and the epithelium of the Bowman’s capsule.
Larger molecules can’t pass through and stay in the blood. The filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way; it flows through the collecting duct and passes out the kidney along the ureter
what happens during selective reabsorption of the nephron?
reabsorption of the useful substances takes place as the filtrate flows along the PCT through the loop of Henle and along the DCT, they leave the nephron and enter the capillary network wrapped around it.
epithelium of the PCT has microvilli to provide a large SA for absorption of useful materials from the filtrate by active transport and facilitated diffusion. Some urea is also reabsorbed by diffusion.
water enters the blood by osmosis because the WP of the blood is lower than that of the filtrate its is reabsorbed from the loop of Henle, DCT and the collecting duct.
the filtrate that remains is urine which passes along the ureter to the bladder
what is urine made of?
urine is usually made up of water and dissolved salts, urea and other substances such as hormones and excess vitamins.
It doesn’t contain proteins or blood cells as they’re too big to be filtered out of the blood.
glucose amino acids and vitamins are actively reabsorbed back into the blood so they’re not usually found in the urine either
How do the kidneys regulate water potential?
WP of blood too low- more water is reabsorbed by osmosis into the blood from the tubules of the nephron. urine is more concentrated so less water is lost during excretion
WP of blood too high- less water is reabsorbed by osmosis into the blood from the tubules of the nephron. urine is more dilute so more water is lost during excretion
the volume of water reabsorbed is controlled by hormones
How does the counter-current multiplier mechanism work?
top of ascending limb- Na+ and Cl- ions are actively pumped out into the medulla, AL is impermeable to water so it stays inside the tubule
low WP is created in the medulla than in the descending limb so water moves out of the DL into the medulla by osmosis; this makes it more concentrated.
the water in the medulla is reabsorbed into the blood through the capillary network
bottom of ascending limb- Na+ and Cl- ions diffuse into the medulla, further lowering WP.
this causes water to move out of the collecting duct by osmosis.
water in the medulla is reabsorbed into the blood through the capillary network
What is the loop of Henle length different in some animals?
the longer an animals loop of Henle, the more water they can reabsorbed from the filtrate
when the AL is longer, more ions are actively pumped out into the medulla which creates a really low WP in the medulla
this means more water moves out of the nephron and collecting duct into the capillaries giving very concentrated urine
animals that live in areas with little water usually have long loops to save as much water as possible.
