5.2 Excretion Flashcards
What is excretion?
The removal of metabolic waste from the body
What is metabolic waste?
A chemical produced by the metabolic processes in the cells, and can be toxic
Why does waste need to be excreted?
At high concentrations, waste can:
- Inhibit enzyme activity
- Become toxic
- Affect pH
Name 3 excretory products.
- Carbon Dioxide
- Nitrogenous waste e.g. urea
- Other compounds such as bile pigments in faeces
What is egestion?
The elimination of faeces from the body.
What are the main excretory organs?
- Lungs
- Liver
- Kidneys
- Skin
What do the lungs excrete?
Carbon dioxide
What is bilirubin?
A bile pigment
How is urea transported?
Dssolved in blood plasma
What is the main role of the kidneys?
To remove urea from the blood and make urine
How is the skin involved in excretion?
Sweat released through the skin contains salts, urea, water, uric acid and ammonia, which are all excretory products.
In what form is carbon dioxide transported in the blood?
Hydrogen carbonate ions
HCO 3-
Which enzyme promotes carbonic acid dissociation?
Carbonic anhydrase
How is carbonic acid formed in erythrocytes?
Carbon dioxide + water > carbonic acid
Why is an acidic pH in red blood cells bad?
It changes the tertiary structure of haemoglobin, reducing its affinity for oxygen (haemoglobinic acid)
What happens to carbon dioxide that is not converted to hydrogencarbonate ions?
It combines directly with haemoglobin, forming carbaminohaemoglobin.
What happens if the blood pH drops a small amount?
Change is detected by the respiratory centre in medulla oblongata, which makes breathing rate increase to remove the excess carbon dioxide (CO2 causes more H+ to be produced)
What is respiratory acidosis?
When blood pH drops below 7.35 and can cause headaches, confusion etc.
Urea is less _____ and less ______ than ammonia
Toxic and soluble
Why does the body not excrete excess amino acids?
The body can’t store them, and it would be wasteful to excrete them without releasing their energy
What is a hepatocyte?
A specialised liver cell
What is the function of the hepatic artery?
To provide oxygenated blood for aerobic respiration in hepatocytes.
What is the function of the hepatic portal vein?
To take deoxygenated, digestive product rich blood from the digestive system into the liver.
What is bile?
Bile is a secretion from the liver which has functions in digestion (emulsifies lipids, neutralises stomach acid).
Bile is made in the _____ and stored in the _____.
Made in liver, stored in gall bladder.
What is the function of the bile duct?
To carry bile from the liver to the gall bladder.
How are bile pigments made?
They are produced by the breakdown of red blood cells in the liver
Why do hepatocytes have loads of peroxisomes?
Peroxisomes contain powerful enzymes which breakdown toxins and poisons
Where is glycogen stored?
The liver
What does a Kuppfer cell do?
It’s a specialised macrophage which breaks down old red blood cells
What is the livers main roles?
Breakdown of excess amino acids and detoxification
Why must nitrogenous substances be removed from the body?
They can’t be stored, and in excess they can be damaging
What is deanimation?
The removal of the nitrogen containing amino group from an amino acid making ammonia and organic keto acid
What is the use of organic keto acid?
They can be respired to make ATP, or converted to carbohydrates and stored as glycogen
What is urea made of?
Ammonia + Carbon dioxide
What part of the ornithine cycle occurs in the mitochondria?
Ornithine> Citruline
Why can’t ammonia be excreted directly?
It’s too toxic and soluble
What is detoxification?
The breakdown of harmful substances into less harmful compounds that can be excreted
How is ethanol detoxified in the liver?
Ethanol> Ethanal> Acetic acid
What is liver cirrhosis?
Excess alcohol causes liver cells to die and scar tissue blocks blood flow
Why must paracetamol be broken down?
An excess amount in the blood can lead to liver and kidney failure
Why must excess insulin be broken down?
In excess it can cause problems with blood sugar
Where in the digestive system does the hepatic portal vein bring blood from?
Small intestine
What are liver lobules?
Cylindrical structures made of hepatocytes that are arranged in rows, radiating from the centre outwards.
What connects the hepatic artery and hepatic portal vein to the central vein?
Capillaries called sinusoids
How is the bile duct connected to the central vein?
Canalculi tubes
What is the main function of the kidney?
To excrete waste products from the body, e.g. urea
How does blood enter the kidney?
The renal artery
From outwards to inwards, what is the kidney structure?
Renal capsule, cortex, medulla, pelvis
What are nephrons?
Long tubules with a bundle of capillaries
Where does ultrafiltration take place?
Glomerulus and Bowmans capsule
What is the difference between the afferent and efferent arteriole?
Afferent- takes blood to the glomerulus
Efferent- takes blood away from glomerulus
Why does the efferent arteriole have a smaller diameter than the afferent arteriole?
To increase the pressure, which forces liquid and molecules out of the capillary and into the Bowmans capsule
What layers must a molecule pass through to get into Bowmans capsule?
The capillary endothelium, the basement membrane, and the podocyte/Bowmans capsule epithelium
Why is the proximal convoluted tubule convoluted?
To increase the surface area for diffusion
Where does selective reabsorption take place?
Proximal CT, Loop of Henle, Distal CT, collecting duct
What is completely selectively reabsorbed into the blood from the glomerular filtrate?
Glucose and amino acids
What is mostly reabsorbed (but dependant on conditions)?
Water and ions
What is reabsorbed in the Proximal convoluted tubule?
Most water, and all glucose and amino acids
How does selective reabsorption of glucose and amino acids work?
Na+ pumped out of cell, then diffuse back in with cotransport protein which brings back glucose and amino acids
What is the purpose of the loop of Henle?
To decrease the water potential of the tissue fluid in medulla, by removal of water and addition of ions
What happens in the descending limb of loop of Henle?
Water is removed by osmosis, and Na+ and Cl- diffuse in
What happens in the ascending limb of the loop of Henle?
Na+ and Cl- pumped out
What happens in the distal convoluted tubule?
K+ pumped in by active transport
What does ADH do?
Increase the collecting ducts permeability to water by aquaporins, so more water is reabsorbed.
What happens in the collecting duct?
Water gradually lost to decrease the water potential, but it remains above that of the surrounding tissue (allowing max water to be reabsorbed)
What is the equation for deamination?
Amino acid + Oxygen > Keto acid + Ammonia
What does the ornithine cycle require to start?
ATP and Carbon Dioxide
What is the equation for the formation of urea?
Ammonia + Carbon Dioxide > Urea + Water
What is the equation for the reaction that catalase catalyses?
Hydrogen peroxide > Water + Oxygen
Where does detoxification occur in hepatocytes?
The smooth endoplasmic reticulum
What enzyme catalyses ethanol > ethanal ?
Ethanol dehydrogenase
What enzyme catalyses ethanal > ethanoic acid?
Ethanal dehydrogenase
What are fenestrations?
Pores between capillary endothelium
What is osmoregulation?
The control of water potential in the body, by controlling salt and water levels
Where is ADH secreted from?
Posterior lobe of pituitary gland
Where are osmoreceptors found?
Hypothalamus
What is hypertension?
High blood pressure
What is acute kidney failure?
Fast development, short acting, easily treatable
What is chronic kidney failure?
Slow developing, long acting, hard to treat
What are the treatments for kidney failure?
Haemodialysis, peritoneal dialysis, kidney transplant
What is the peritoneum?
The layer of tissue lining the abdominal cavity
What do pregnancy tests test for?
HCG
Osmoregulation is an example of _________ feedback.
Negative
In haemodialysis, where is blood added back to the body?
Vein
Describe peritoneal dialysis.
- Dialysis fluid put into body through catheter and left in peritoneal cavity
- Takes around an hour, happens multiple times a day
How do pregnancy tests work?
Monoclonal antibodies with blue bead test for HCG in urine
What 4 ways are the cells lining the proximal convoluted tubule specialised?
- Plasma membrane is highly folded to form microvilli
- Cotransport proteins are in the plasma membrane
- Membrane close to the capillary has microvilli and Na/K pumps
- Many mitochondria
Which part of the nephron is impermeable to water?
Ascending loop of Henle
What mechanism does the loop of Henle create?
The countercurrent multiplier mechanism
What does the countercurrent multiplier mechanism do?
Helps to reabsorb water back into the blood
What are osmoreceptors?
Receptor cells in hypothalamus which monitor the water potential of the blood
What is water potential?
The tendency of water to move from one place to another.
What is the effector to control the body’s water content?
The kidneys
What are aquaporins?
Vesicles containing water permeable channels
How does the cell membrane remove water permeable channels in the collecting duct?
It folds in on itself to create more new vesicles that remove water permeable channels.
