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Define the term “excretion”.

The removal of metabolic waste products from the body.


Explain the importance of excretion in maintaining metabolism and homeostasis.

- Waste products can be toxic if allowed to build up.
- Maintains water balance and PH.


Name the 3 main metabolic waste products in mammals, describe where they come from and where they are excreted.

1) Carbon dioxide - gas waste product of cellular respiration.
2) Bile pigments - formed from break down of haemoglobin from old RBCs in the liver. Excreted in the bile from the liver into the small intestine via the gall bladder and bile duct.
3) Nitrogenous waste products (urea) - formed from the breakdown of excess amino acids by the liver.


Name the nitrogenous waste products in mammals, fish, birds and insects.

1) Mammals - urea
2) Fish - ammonia
3) Birds/ insects - uric acid.


Describe the location of the liver in mammals and draw and label a diagram to show the blood vessels going to and from the liver.

- Present just below the diaphragm.
- Oxygenated blood is supplied to the liver by the hepatic artery.
- Hepatic portal vein carries blood to the liver of a low oxygen concentration but is rich in the products of digestion as it has come from the intestines.
- The hepatic vein carries deoxygenated away from the liver.


What are the sinusoids?

Spaces surrounded by the hepatocytes (liver cells). Blood from the hepatic portal vein and the hepatic artery mixes here. This mixing increases the oxygen concentration of the blood from the HPV, supplying the hepatocytes with enough oxygen for their needs.


Name the type of cell which makes up the liver and describe the adaptations they have for their functions.

- Hepatocytes.
- Large nuclei, prominent golgi apparatus, lots of mitochondria.


Draw and label a diagram to show the arrangement of tissues within the liver.

- Spaces called sinusoids are surrounded by hepatocytes.
- The bile canaliculi are also present alongside the hepatocytes.
- The kuppffer cells are present in the sinusoids.


Label and annotate a photomicrograph of liver tissue at low and high power to show key histological features.

Under low magnification (x34):
- Central vein visible as a large white blob.
- Sinusoids visible as small white lines between hepatocytes.
- Hepatocytes visible as small pink dots with dark blue dots within them (the nuclei).

Under high magnification (x3 500)
- Hepatocytes visible as large pink blobs dotted with dark blue spots (mitochondria) and a large light purple blob as the nucleus.
- Sinusoids visible as white spaces filled with RBCs presenting their biconcave shape.
- Kupffer cells visible as grainy light purple blobs as the edge of the sinusoids.


Describe the role of Kupffer cells in the liver.

- Sinusoids contain Kupffer cells.
- They act as a macrophage by ingesting foreign particles to help protect against disease.


Describe how bile is formed and how it travels to where it is stored.

- Bile is formed by the hepatocytes from the breakdown of blood and is then secreted into the bile canaliculi.
- From these, the bile drains into the bile ductules which take it the gall bladder.


Name the 6 roles of the liver.

- Carbohydrate metabolism
- Deamination of excess amino acids
- Production of urea (ornithine cycle)
- Protein metabolism
(- Transamination)
- Detoxification
- Production of bile


Describe the role hepatocytes play in the control of blood glucose concentration.

- Carbohydrate metabolism.
- When blood-glucose concentration rises, the level of insulin rises and insulin stimulates the hepatocytes to convert glucose to glycogen.
- This lowers blood-gluc conc.
- Same happens with glucagon and the conversion glycogen to glucose. Raises blood glucose conc.


Define the terms “transamination” and “deamination”.

Transanimation - the conversion of one amino acid into another. Important because the diet does not always contain the right balance of amino acids.

Deamination - the removal of an amine group from a molecule. Important because the body can't store amino acids or proteins.


Draw a diagram to show the process of deamination.

- The amine group of the amino acid is removed.
- The amine group is converted to ammonia which is very toxic.
- The rest of the amino acid is used in respiration.
- This ammonia is converted to urea in the ornithine cycle.


Draw a diagram to show how urea is produced from excess amino acids via the ornithine cycle.

1) Ornithine + NH3 + CO2 → H20 + Citruline
2) Citruline + NH3 → H2O + Arginine
3) Arginine + H20 → Urea + Ornithine

2NH3 + CO2 → H2O + Urea.


Define the term “detoxification” and describe two examples of detoxification by the liver.

- The removal or breakdown of toxins.
- The breakdown of hydrogen peroxide. Split into oxygen and water.
- Detoxification of ethanol. Ethanol is broken down into enthanal and then ethanoate.