Excretion Flashcards
Why do we need excretion?
To remove harmful metabolic waste products
What are the 3 main waste products that need excreting?
CO2 from respiration
Nitrogenous waste (e.g urea)
Other compounds like bile pigments (found in faeces)
What are the 4 main excretory organs?
Lungs
Liver
Kidneys
Skin
What may occur if CO2 isn’t excreted properly?
Build up of CO2
Dissolves into blood plasma forming H2CO2 (carbonic acid)
Dissociates to form H+ which changes the pH of blood
This can change the shape of haemoglobin reducing the affinity of erythrocytes to O2
How does the body ensure that CO2 doesn’t build up
High CO2 concentrations detected by the medulla oblongata
Increases breathing rate to remove the CO2
What is the pH threshold of the blood and what does it cause if the pH drops below this value?
pH 7.35
Respiratory Acidosis
Why does the body not excrete excess amino acids?
They contain lots of energy that can be used in respiration
What is the name of the process where the harmful amino group is removed?
Deamination
Where does deamination occur?
Liver
What is the equation for deamination?
amino acid + oxygen = keto acid + ammonia
What is ammonia converted to after deamination?
Urea
What is the equation for the formation of Urea?
ammonia + carbon dioxide = urea + water
What is the name of liver cells?
Hepatocyes
Why must the liver have a good blood supply?
it is involved in many metabolic processes so requires O2 for respiration
What are the 2 sources of blood supply TO the liver?
Hepatic artery
Hepatic portal vein
What blood is found in the Hepatic Artery?
Oxygenated blood from the heart
provides oxygen for aerobic respiration of the hepatocytes
What blood is found in the Hepatic Portal Vein?
Deoxygenated blood from the digestive system
Rich in the products of digestion
any toxic compounds that have been absorbed must be removed
What blood vessel does blood leave the Liver by?
Hepatic Vein
What is the fourth vessel that is connected to the liver?
Bile duct
What is the function of Bile in the liver?
aid digestion of fats
Contains pigments (bilirubin) that must be excreted
Created by liver cells as a result of haemoglobin breakdown.
Describe the histology of the liver
Divided into lobes and then further into lobules
Inter lobular vessels (branches of the hepatic artery and hepatic portal vein) deliver their fluids into a sinusoid
It then reaches the intra lobular vessel in the centre where it leaves the liver via the Hepatic vein
What is a sinusoid?
A cavity surrounded by hepatocytes where blood flows through as toxins are removed
What is a bile canaliculus?
A cavity where bile flows into as it is produced by the hepatocytes
Flows into bile duct were bile is transported to gall bladder
What is the function of Kupffer cells?
Specialised macrophages that breakdown old erythrocytes
How might hepatocytes be specialised to carry out metabolic reactions?
Dense cytoplasm
High numbers of specific organelles
What are the metabolic functions of the liver?
control of blood glucose, amino acid and lipid levels
synthesis of bile, plasma and cholesterol
synthesis of RBC’s
storage of vitamins (A, D, B12)
Detoxification of drugs and alcohol
breakdown of hormones
breakdown of RBC’s
Storage of glycogen
In what form does the liver store glycogen?
Granules in the cytoplasm of hepatocytes
Describe 2 enzymes the liver uses to detoxify compounds?
Catalase - converts H2O2 to H2O
Cytochrome P450 - Break down drugs such as cocaine and various medicinal drugs. Can interfere with other metabolic functions giving the side affects of drugs
Ethanol dehydrogenase - turn ethanol to acetate and H+ which are used used in respiration
Why does alcohol lead to hepatitis or liver cirrhosis?
Too much NAD is used to remove H+ produced when alcohol is broken down
Not enough NAD available for fatty acid breakdown
fat builds up on liver causing hepatitis or cirrhosis
What is the ornithine cycle?
Conversion of ammonia (NH3) to urea (CO(NH2)2)
Why must ammonia be converted immediately after it is formed in deamination?
it is highly soluble and highly toxic
Where does urea go after it is created?
to the kidneys
it is then filtered out of the blood
excreted in the urine
What are the two main blood vessels connected to the kidneys?
Renal Vein
Renal Artery
What is the other vessel connected to the kidneys and what is its function?
Ureter
transport urine from kidneys to the bladder
What are the 3 main sections of the kidneys?
Cortex - outer region
Medulla - inner region
Pelvis - centre connected to the pelvis
What is the name of the tine tubules that make up the kidneys?
Nephrons
What is the name of the structure at the start of a nephron?
Bowman’s capsule
What is the name of the knot of capillaries in the Bowman’s Capsule?
Glomerulus
what is the name of the process where blood is pushed into the Bowman’s capsule?
Ultrafiltration
How is the Bowman’s capsule specialised to carry out ultrafiltration?
The endothelium of capillary - small gap between capillary and endothelium, also contains fenestrations which allow substances through
Basement membrane - a fine mesh of collagen and glycoproteins between capillary and endothelium, keep RBC’s in the capillary
Epithelia of Bowman’s capsule (Podocytes) - Have projections that make gaps between cells so fluid can pass into the lumen of the Bowman’s capsule
What the the 4 parts of a nephron tubule called?
Bowman’s capsule
Proximal convoluted tubule
loop of Henle
Distal convoluted tubule
What is filtered out of the blood in the kidneys?
Water Amino acids Glucose Urea Inorganic mineral ions (Na+, Cl-, K+)
What is the function of the nephron after ultra filtration?
selective reabsorption
What is reabsorbed into the blood in the proximal convoluted tubule?
Sugars, Mineral ions and some water
What happens in the descending limb of the loop of Henle?
mineral ions added back
water removed
water potential decreased
What happens in the ascending limb of loop of Henle?
mineral ions removed by active transport
water potential increased
What happens in the collecting duct?
Water removed
water potential decreased
What is the final product left in the collecting duct?
Urine
How are the cells lining the proximal convoluted tubule specialised to perform selective reabsorption?
surface membrane folded to form microvilli
surface membrane contains cotransporter proteins for moving glucose or amino acids into the cells
has lots of mitochondria to produce lots of ATP for active transport
Explain the role of Na+ in selective reabsorbtion
Na+ is actively transported out of the cell
It then diffuses back into the cell and acts as a cotransporter by bringing glucose or amino acids in against their concentration gradient
Known as secondary active transport
What are the two main parts of the loop of Henle?
Descending limb
Ascending limb
What is the function of the loop of Henle?
To reabsorb water from the filtrate
How does the loop of Henle regulate ion concentrations in the filtrate?
Filtrate entering decending limb is of high water potential
Water moves out down its osmotic gradient
Filtrate at the highest concentration at the bottom of the loop
Na+ and CL- are actively transported out of the ascending limb and water moves in
Filtrate is at its most dilute at the top of the ascending limb
Why must osmoregulation occur?
Too much or too little water could cause cell lysis or crenation
What hormone controls permeability of the collecting duct?
Antidiuretic Hormone (ADH)
What binds to cell surface or collecting duct cells in order to increase permeability?
Vesicles containing aquaporins
What happens when ADH concentration is high?
More aquaporins bind to cells in collecting duct
Increased permeability
more reabsorption of water
Urine becomes more concetrated
What happens when ADH concentrations fall?
Membrane invaginates to re-form vesicles
membrane permeability is reduced
less reabsorption of water
urine is more dilute
Where in the brain detects changes in water potential in the blood?
Osmoreceptors in the Hypothalamus
Where is ADH stored and released from?
posterior pituitary gland
By what process of movement is ADH released?
Exocytosis
What is the measure of Kidney function?
Glomerular filtration rate (GFR)
How do you measure GFR?
Analysis of urine for certain protiens
What is normal GFR, and what values would indicate issues?
Healthy = 90-120 cm3/min
Chronic kidney disease = <60 cm3/min
Kidney failure = <15 cm3/min
What are common causes of Kidney faliure?
Diabetes mellitus
Heart disease
hypertension
infection
What are the 2 main treatments for Kidney failure?
Renal Dialysis
Kidney transplant
What are the 2 types of renal dialysis?
Haemodialysis Peritoneal dialysis (PD)
describe the process of haemodialysis
Blood is passed into the machine containing the dialysis membrane
anti-clotting agent is added
Dialysis fluid flows in countercurrent direction to improve the efficiency of exchange
How often does haemodialysis need to be performed?
2-3 times /week at a clinic
Describe peritoneal dialysis?
The membrane is implanted in the bodys own abdominal membrane (peritoneum)
Dialysis fluid is poured into the abdomen via a tube and then must be drained after a few hours
What are the advantages of a Kidney transplant?
No need for time consuming dialysis
Feeling physically fitter
Ability to travel
Don’t feel chronically ill
What the disadvantages of a Kidney transplant?
Requires major surgery
Must take immunosuppressant drugs that can cause hypertension and make infections more common
Possibility for rejection
Organ waiting list is long so may take years to get a match
Give example of molecules that can be detected in urine analysis and where they are used in the world
Glucose in diabetes diagnosis
Alcohol to determine if drivers are drunk
Recreational drugs, tests done by police or employers
human chronic gonadotrophin (hCG) in pregnancy tests
anabolic steroids, in sporting competitions
What is used in pregnancy tests to test for hCG?
monoclonal antibodies
What process is used to test for anabolic steroids after a urine sample has been taken?
Gas Chromatography
