Excretion 5.2 Flashcards
What is excretion?
The removal of metabolic waste from the body
What is the difference between excretion and egestion?
Excretion is removing waste that was produced from cells and egestion is removing waste from the digestive system
What is metabolic waste?
Substances produced from chemical reactions that may be toxic at high levels in the body
What are examples of metabolic waste?
- CO2
- nitrogenouswaste (urea)
- bile pigments found in faeces
What is the importance of excretion?
Allowing metabolic products to build up can be fatal and interfere with cell processes by altering pH
How can toxins be made harmless?
through processes like oxidation, reduction or combining them with another molecule
What is the histology (structure) of the liver?
- lobes
- lobules
- hepatocytes
- hepatic artery
- hepatic portal vein
- hepatic vein
- inter-lobular vessels (between cells)
- Intra-lobular vessels (inside cell)
- kupffer cells
- sinusoids
- bile canaliculi
What shape do liver lobules have?
Hexagonal shape
What are kupffer cells?
The are cells found in the sinusoids that act like phagocytes so engulf and digest old RBC and bacteria
What is a sinusoid?
A wide capillary inside the liver lobule which is lined with hepatocytes
What is the other vessel that leaves the liver but does not carry blood?
Bile duct
Which blood vessel connected to the liver is the bigger one?
Vena cava
How can you tell the difference between the bile duct and the blood vessels?
The bile duct is lined with hepatocytes too and does not connect to the sinusoid
What is the lumen of the vessel that carries the bile called?
Bile caniculus
What is the hepatic portal vein?
A small vein going from the small intestine to the liver carrying deoxygenated blood containing lots of nutrients so the liver can store the nutrients and detoxify the blood
What are the functions of the liver?
- controls glucose conc. and lipid levels
- controls amino acid levels (deamination/ transamination)
- removes toxins and unwanted proteins
- produces bile from breakdown of RBC
- synthesis of plasma proteins and cholesterol
- stores vitamins
What happens to glucose in the liver?
Only a limited amount can be stored as glycogen so any excess is converted into lipids for storage elswhere
How does the liver store sugars?
In the form of glycogen
What is detoxification?
The breakdown of alcohol into acetyl coenzyme A which is used in respiration
What is the process of detoxification?
Ethanol - Ethanal - Ethanoic acid - Acetyl Coenzyme A - Respiration
What is the enzyme that catalyses the dehydrogenation of ethanol?
Ethanol Dehydrogenase
What is the enzyme that catalyses the dehydrogenation of ethanal?
Ethanal Dehydrogenase
What happens when ethanol is converted to ethanal and ethanal is converted to ethanoic acid?
Hydrogen atoms are relased which reduces NAD into NADH
What happens to the hydrogen that NAD picks up?
It provides the hydrogen for the electron transport chain
What is NAD also used for in the liver? (not detoxification)
Oxidise and breakdown fatty acids for use in respiration
What enzyme is needed to convert ethanoic acid into acetyle coenzyme A?
Coenzyme a
What happens to cause cirrhosis of the liver?
- if the liver has to detoxify too much alcohol stores of NAD are used up
- not enough NAD to breakdown fatty acids
- fatty acids converted back to lipids and stored in hepatocytes
- causes liver to become enlarged (fatty liver)
- too much build up can stop liver function and causes liver to scar (cirrohsis)
What happens to cholesterol in the liver?
It is used in cell membranes and excess cholesterol is excreted by the liver
What is the process of proteins turning into urea?
- Proteins broken down into amino acids by hydrolysis
- amino acids broken down into ammonia and keto acids by deamination
- ammonia broken down into urea by ornithine cycle
What happens during the ornothine cycle?
Ammonia and carbon dioxide combine and cause a series of reactions which produce water and urea
Why is ammonia turned into urea?
It is less toxic and soluble so can be excreted from the body in urine
What is the equation for ammonia turning into urea?
Ammonia + carbon dioxide —> water + urea
Is urea more or less soluble than ammonia?
Less soluble
What is transamination?
The process of turning one amino acid into another one
Why is transamination needed?
Diet does not always provide the exact amino acids that we need and transamination helps overcome this problem but some amino acids cannot be made
What is deamination?
The removal of the amine group
How man essential amino acids are there?
8
What happens to protein hormones in the Liver?
They are deaminated in the liver
What happens to steroid hormones in the liver?
They are excreted in bile
What does the liver contain that helps detoxify substances?
enzymes (catalase and cytochrome P450)
What is cytochrome P450?
A group on enzymes used to breakdown drugs such as cocaine and medicenal drugs
What processes is cytochrome P450 used in other than detoxification?
Metabolic reactions such as the electron transport chain during respiration
What are the negatives of cytochrome P450?
It can interfere with other metabolic roles and can cause unwanted side effects of some medicenal drugs
What are the functions of the kidney?
- filtration of waste products from the blood
- homeostasis of water and ions
- produce urine
What are the four sections of the kidneys?
- cortex (outer region)
- medulla (inner region)
- pelvis (centre)
- ureter (leading off from pelvis)
What are the small structures that the kidney consists of and how are they positioned in the kidney?
- nephrons
- bowman’s capsule and PCT is in the corex, loop of henley is in the medulla, DCT is in the cortex and collecting duct is in the medulla
What are the components of a nephron?
- glomerulus
- bowman’s/ renal capsule
- proximal convoluted tubule
- loop of henle
- distal convoluted tubule
- collecting duct
What are the blood vessels associated with the kidneys?
- renal artery
- afferent arteriole
- efferent arteriole
- renal vein
What is the difference between afferent and efferent arteriole?
Afferent is going towards the nephron and efferent is going away
What is filtered out the blood by the kidneys?
- glucose
- urea
- ions
- water
- amino acids
What is reabsorbed into the blood by the kidneys?
- glucose (all)
- ions (some)
- water (some)
- amino acids (all)
What stays in the urine after being filtered out the blood?
- urea
- ions (some)
- water (some)
What is left in the capillaries?
- blood cells, proteins and some water
- creates a low water potential which is important for reabsorption
What is ultrafiltration?
Filtration of the blood at a molecular level under pressure
How does the process of ultrafiltration work?
- afferent artriole is wider than efferent arteriole
- this ensures blood in he glomeulus is maintained at a higher pressure than the blood in the bowman’s capsule
- pressure difference pushes fluid blood into the bowman’s capsule through the triple layer filtration
What does a triple filtration layer consist of?
- endothelium of capillaries
- basement membrane
- epithelium of renal capsule
What are the adaptations of the endothelium of the capillaries?
- very thin
- perforated with thousands of spores
- provides a barrier to cells but not plasma proteins
What are the adaptations of the basement membrane?
- meshwork of collagen and glycoprotein fibres
- water and small molecules can pass through
- proteins are too large and are repelled by negative charges on the fibres
(chronic high blood pressure can damage the fibres)
What are the adaptations of the epithelium of the renal capsule?
- made of cells which are modified for filtration
- podocytes
What are podocytes?
- cells with foot like projections that wrap around capillaries and interlink with neighbouring cells
- contain gaps called filtration slits (25nm wide) allowing filtered fluid to pass through
Where do the collecting ducts lead to?
Pelvis
Where does the majority of selective reabsorption happen?
Proximal convoluted tubule
How is the nephron suited for reabsorption in the PCT?
- plasma membrane inside the nephron is highly folded (microvilli)
- has co-transporter proteins (transport glucose/ amino acids with Na+)
- outer membrane is highly folded
- has sodium potassium pumps
- mitochondria in cytoplasm
What are the steps to reabsorption?
- Na+ ions actively transported out of cells lining the tubule an K+ ions pumped in
- conc. of Na+ ions in cytoplasm decreases creating a conc. gradient
- Na+ ions move into cell through a cotransporter protein by facilitated diffusion
- Na+ ions have to be carrying a glucose/ amino acid
- water moves into cells by osmosis
- glucose/ amino acids diffuse into blood
How are small proteins reabsorbed?
Endocytosis
What is the role of the loop of henle?
To decrease the water potential of the tissue fluid of the medulla (make it salty again), role of homeostasis
What is counter current multiplication?
The process of using energy to generate an osmotic concentration that enables you to reabsorb water from the fluid inside the nephron and produce concentrated urine
- fluids flow in opposite directions
- multiplies osmotic gradient between fluid within the tube and tissue fluid in the medulla
Where id the majority of the water reabsorbed?
Distal convoluted tubule
How does the loop of henle maintain a low water potential in the medulla?
- fluid in nephron flows from proximal convoluted tubule to descending limb of the loop of henle
- membrane of the limb is permeable to water
- water leaves due to osmosis, medulla has a lower water potential creating a water potential gradient
- as the fluid reaches bottom of the loop it now has a high concentration of ions and urea
- fluid moves into ascending limb of the loop of henle which is impermeable to water
- ions begin to leave the limb by facilitated diffusion
- as the fluid moves up the limb conc. of the ions in medulla decreases so the ions get actively transported out
- as the fluid reaches the collecting duct some more water leaves via osmosis and enters capillaries
What is the role of ADH?
To produce less urine
Where are the target cells for ADH?
Distal convoluted tubule and collecting duct
How is water potential in blood regulated by osmoregulation?
- water in the blood is monitored by osmoreceptors in the hypothalamus
- a lower water potential stimulates neurosecretory cells
- neurosecretory cells release ADH which is stored in the posterior pituitary gland
- ADH binds to receptors on the DCT and collecting duct which causes the release of the secondary messagers
- they cause a cascade of enzye cotrolled reactions
- this causes aquaporines to bind to the plasma membrane making it more permeable
- more water moves out and diffuses into the capillaries
- less ADH is released when water potential is high and more is released when water potential is low
What are aquaporins?
Water channels
How do aquaporins work?
- they respond to the level of ADH
- cells in the walls of the DCT and collecting duct have receptors for ADH
- when ADH binds to the receptors it causes more aquaporins to fuse with the membrane of the cells
- leads to more water being reabsorbed so urine is more concentrated
How is the distal convoluted tubule adapted to its function?
- cells have receptors for ADH so is involved in maintaining correct water potential in the blood
- cells have lots of mitochondria to actively pump out Na+ ions into the body if it lacks salt
- plays a role in balancing pH of the blood
How does a pregnancy test work?
- hCG bind to the mobile monoclonal antibodies that are also bound to a dye molecule
- the antibodies move up the strip with the fluid until they reach the test zone
- at the test zone there are immobilised antibodies that detect the antibodies that are already bound to hCG
- if it detects them the antibodies release the dye causing a coloured line to appear on the strip (positive result)
- antibodies that did not bind to the hCG continue moving up the strip until they reach the control zone
- at the control zone there are immobilised antibodies that bind to antibodies that are not bound to hCG
- the antibodies then release a dye again creating a line at the control strip showing that the test is not faulty
What do anabolic steroids do and how are they found?
- Increase protein synthesis
- banned from competitive sports
- found in urine
- stays in the blood for days
How does gas chromatography tests work?
- urine sample is vaporised with gas solvent and passed down the tube with absorbent lining
- each substance dissolves differently in the gas and has a different retention time
- eventually it is absorbed onto the lining and creates a chromatogram
- the results can then be compared to the chromatogram of standard drugs
- the first drug to show on the chromatograph is the most soluble
What are the causes of kidney failure?
- diabetes
- infection
- hypertension
- heart disease
What happens if kidneys fail?
They can no longer remove excess water or waste products from the blood
How is kidney failure tested for?
If the glomerular filtration rate is below the normal level
What is the glomerular filtration rate?
The rate at which water enters the nephrons
What are the three methods of treatment for kidney failure?
- haemodialysis
- peritoneal dialysis
- kidney transplant
How does haemodialysis work?
- removes waste, excess fluids and salts by passing blood over a dialysis membrane
- blood is taken from an artery and is passed into a machine
- the machine contains the artificial dialysis fluid
- heparin has been added to the blood to prevent it from clotting
- any air bubbles have to be removed before the blood is returned to the body
- carried out three times a week for 8 hours
- it can be done at home
How does a kidney transplant work?
- old kidneys are left in place unless they are at risk of causing cancer or infection
- donor kidney can be from a living or dead donor
- last 10 years
- surgeons implant the new organ into the lower abdomen and connects it to the blood supply and bladder
- patients feel immediately better after and it is the best life treatment
- patients take immunosuppressants to help prevent the body’s immune system rejecting the organ
What are the advantages of a kidney transplant?
- freedom from time consuming renal dialysis
- feeling physically better
- improved quality of life as they are able to travel
- improved self image and no longer have a feeling of being chronically ill
What are the disadvantages of kidney transplant?
- need to take immunosuppressant drugs
- need for major surgery under general anaesthetic
- need for regular checks for signs of rejection
- side effects of immunosuppressants (fluid retention, high blood pressure and susceptibility to infections)
