Excretion (liver and the kidney) Flashcards
What is excretion?
The removal of the waste products of metabolism from the body
What makes up metabolism?
All the chemicals reactions that take place in the body
What are the functions of the liver?
-The removal of excess amino acids
- The removal of harmful substances from the body
- Stores glycogen
How are excess amino acids broken down by the liver?
- The amino groups (NH2) are removed from proteins, forming ammonia and organic acids. This process is called deamination.
- Ammonia is then binded with CO2 in the ornithine cycle to create urea.
- The urea is then released from the liver into the blood . The kidneys then filter the blood and remove the urea as urine. The urine is then excreted from the body.
What harmful substances, other than urea, does the liver break down?
- Alcohol
- Drugs
- Unwanted hormones
What is detoxication?
The breakdown of harmful substances, such as drugs, alcohol and unwanted hormones, into less harmful substances, which can them be removed from the body
Describe how the liver breaks down alcohol (ethanol)?
- Ethanol is a toxic substance that can damage our body cells
- The liver breaks down ethanol into ethanal.
- Ethanal is consequently broken down into a much less harmful substance called acetic acid, which is excreted from the body
What happens to us if there’s excess alcohol in the body?
- This can lead to cirrhosis of the liver.
- This is where the cells of the liver die and scar tissue blocks the blood flow
Why is paracetamol broken down by the liver?
Because excess paracetamol in the blood can lead to liver and kidney failure
What is insulin ?
A hormones that controls blood glucose concentration
Why is insulin broken down by the liver?
Because excess insulin can cause problems with blood sugar levels
What are the main veins, arteries, and ducts of the liver?
- The hepatic artery
- The hepatic vein
- The hepatic portal vein
- The bile duct
What does the hepatic artery do?
- It supplies the liver with oxygenated blood from the heart, so the liver has a good supply of oxygen for respiration.
What does the hepatic vein do?
- It takes deoxygenated blood away from the liver
What does the hepatic portal vein do?
- Brings blood from the small intestine rich in the products of digestion to the liver.
- This allows for any ingested harmful substances to be filtered out and broken down by the liver straight away.
What does the bile duct do?
It takes bile to the gallbladder to be stored
Is the hepatic artery narrower than the hepatic vein?
Yes, because it is transporting high pressure oxygenated blood from the heart to the liver
What is the liver made up of?
- Lobules.
- These are cylindrical structures made up of hepatocyte cells that are arranged in rows radiating from the centre
What does each lobule have in the middle?
A central vein that connects to the hepatic vein.
What are the hepatic artery and the hepatic portal vein connected to the central vein by?
Veins called sinusoids
How does blood run through the sinusoids?
- Past the hepatocytes that remove harmful substances and oxygen from the blood
- These harmful substances are broken down into less harmful substances by the hepatocytes and they then reenter the blood.
- The blood runs to the central vein and the central veins from all lobules conect up to form the hepatic vein
What are kupffer cells attached to ?
The walls of the sinusoids
What do kupffer cells do?
Remove bacteria and break down old red blood cells
Which cells in the liver produce bile?
The hepatocytes
What nitrogenous waste is produced by fish?
Ammonia
What nitrogenous waste is produced by birds and insects?
Uric acid
Where is the liver located in the body?
Below the diaphragm
What is a nickname for the kuoffer cells?
The macrophages of the liver
Bike from hepatocytes->
Into canaliculi -> into bile ducts -> into gall bladder
What are the functions of the kidneys?
-to excrete waste products
- to regulate the water potential of the blood
Give an overview of how the kidney excretes waste products
- Blood enters the kidney through the renal artery and then passes through the capillaries in the cortex of the kidneys.
- As the blood passes through the capillaries, substances are filtered out of the blood and into long tubules that surround the kidneys. This process is known as ultrafiltration.
- Useful substances, like glucose, are reabsorbed back into the blood from the tubules in the medulla and the cortex. This is called selective reabsorption
- The remaining unwanted substances pass along the tubules, then along the ureter to the bladder, where they’re passed out as urine.
- The filtered blood passes out of the kidneys through the renal vein
What are nephrons?
the long tubules along with the bundle of capillaries where teh blood is filtered out
How many nephrons are there in each kidney?
around 1 million
Describe the process of filtration in the nephrons?
- Blood from the renal artery enters smaller arterioles in the cortex.
- Each arteriole splits into a structure called a glomerulus, a bundle of capillaries looped inside a hollow balled called the Bowman’s capsule.
- The glomerulus is where ultrafiltration takes place.
- The arteriole that takes blood in blood into each glomerulus is called the afferent arteriole, ad the arteriole that takes the filtered blood away is called the efferent arteriole.
- The efferent arteriole is smaller in diameter than the afferent arteriole, so the blood in the glomerulus is under high pressure.
- The high pressure in the glomerulus forces liquid and small molecules in the blood out of the glomerulus and into the bowman’s capsule.
- The liquid and small molecules pass through 3 layers to get into the Bowman’s capsule and enter the nephron tubule: the basement membrane and the epithelium of the bowman’s capsule.
- The liquid and small molecules, now called filtrate, pass along the rest of the nephron and useful substances are reabsorbed along the way.
- Finally, the filtrate flows through the collecting duct and passes out of the kidney along the ureter.
Where does selective reabsorption take place?
as the filtrate flows along the proximal convulated tubule (PCT), through the loop of Henle, and along the distal convulated tubule
is it true that useful substances leave the tubules of the nephrons and enter the capillary network that’s wrapped around them?
yes
why is the epithelium of the wall of the proximal convulated tubule covered in microvilli?
to provide a large surface area for the reabsorption of useful materials from the filtrate into the blood
what useful substances are reabsorbed along the proximal convulated tubule?
glucose, amino acids, vitamins, and some salts
why does water enter the blood surrounding the proximal convulated tubule by osmosis?
because the water potential of the blood is lower than that of the filtrate
How is water lost by the body?
- through sweat
- during excretion
Where does selective reabsorption take place?
As the filtrate flows along the proximal convulated tubule, through the loop of henle and along the distal convulated tubule
Why does the epithelium of the wall of the proximal convulated tubule have microvilli?
To provide a large surface area for the reabsorption of useful materials from the filtrate into the blood
What happens if the water potential of the blood is too low?
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This results in the urine being more concentrated and less water being lost during excretion
What happened if the water potential of the blood is too high?
Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means that the urine is more dilute, so more water is lost during excretion
What 2 limbs is the loop of henle made up of?
The descending limb and the ascending limb. They have a mechanism called the countercurrent multiplier mechanism. This mechanism helps to reabsorbed water back into the blood
Describe the process of the countercurrent multiplier mechanism in the loop of henle
1) Near the top of the ascending limb, sodium and chloride ions are actively pumped out of the loop of henle and into the medulla.
The ascending limb is impermeable to water, so the water stays inside the tubule.
This creates a low water potential in the medulla because there’s a high concentration of ions in the medulla.
2) Because there’s a lower water potential in the medulla than in the descending limb, water moves out of the descending limb and into the medulla by osmosis.
As a result, the filtrate becomes more concentrated and the water in the medulla is reabsorbed into the blood through the capillary network
3) Near the bottom of the ascending limb, sodium and chloride ions diffuse out into the medulla
4) Hence, the ion concentration in the medulla massively increases and its water potential lowers.
This causes water to move out of the collecting duct by osmosis
The water in the medulla is reabsorbed into the blood through the capillary network
What type of receptors does the hypothalmus have?
osmoreceptors
