F214 - Excretion Flashcards
Excretion
Definition
The removal of metabolic waste from the body
I.e. the removal of by-products or unwanted substances from normal cell processes
Why is it important to remove waste carbon dioxide from the body?
Excess carbon dioxide is toxic
- most CO2 is carried as hydrogen carbonate ions in the blood but at red blood cells this also forms hydrogen ions which compete with oxygen to bind with haemoglobin
- CO2 can also bind directly with haemoglobin to form carbaminohaemoglobin
- respiratory acidosis is where CO2 combines with water to form carbonic acid. Carbonic dissociates to form H+ ions which make the blood more acidic. Breathing rate is increased to try to remove excess CO2 but the change in blood pH causes headaches, tremors and confusion
Why is it important to remove nitrogenous waste from the body?
The body cannot store proteins or amino acids but they do contain a large amount of energy so it would be wasteful to excrete them
They are transported to the liver and the potentially toxic amine group is removed, deamination
This forms ammonia which is converted into urea and transported to the kidneys for excretion
The Liver
Hepatic Artery
Carries highly oxygenated blood from the aorta
This is essential as hepatocytes are very metabolically active so have a high respiration rate
The Liver
Hepatic Portal Vein
Carries blood from the digestive system
High in glucose for respiration
High in toxic products for break down
The Liver
Hepatic Vein
Blood leaves the liver via the hepatic vein
The Liver
Sinusoid
A specialised chamber where oxygenated blood from the heart is mixed with the blood from the digestive system
The sinusoid is lined with hepatocytes which remove molecules from and pass molecules into the blood
The Liver
The Bile Duct
A primary function of hepatocytes is to produce bile which is secreted into the bile duct and taken to the gallbladder where it is stored
From there it is secreted into the top of the small intestine where it neutralises stomach acid to protect the intestinal walls and emulsified fats to make them easier to digest
Adaptations of Hepatocytes
Microvilli
Increase the surface area for diffusion
Adaptations of Hepatocytes
Mitochondria
Hepatocytes he a a high metabolic rate so have to respire more than other cells to produce the energy require for their metabolic processes
Adaptations of Hepatocytes
Protein Synthesis
Hepatocytes contain more of the organelles required for protein synthesis than other cells as the have to make more membrane proteins and enzymes that other cells
Adaptations of Hepatocytes
Kupffer Cells
Specialised macrophages in the sinusoid
They break down old red blood cells
One product of the break down of haemoglobin is bilirubin which is excreted in to the bile duct
Gross Structure of the Liver
Liver
Two Lobes (Left and Right)
Each lobe is split into four segments
Each segment is made up of lobules
Functions of the Liver
Control of blood glucose, amino acid and lipid levels Storage of glycogen, iron, vitamins Detoxification of alcohol and drugs Breakdown of hormones Destruction of red blood cells
The Liver
Deamination
AminoAcid + Oxygen ->
KetoAcid + Ammonia
The Liver
Formation of Urea
The Ornithine Cycle
Ammonia + CO2 -> Urea + Water
The Liver
Detoxification of Alcohol
Ethanol is oxidised by ethanol dehydrogenase to form ethanal, this releases 2H
Ethanal is oxidised by ethanal dehydrogenase to form ethanoic acid, this also releases 2H
EthanoicAcid + Co-enzyme A
-> Acetyl Co-enzyme A
Which is required for the Kreb’s Cycle in respiration
The 2H reduce NAD to form NADH
The Liver
Dangers of Alcohol (reduction of NAD)
During the detoxification of alcohol NAD is reduced to form NADH
NAD is required for the break down of triglycerides, NADH cannot perform this role
Too much alcohol causes a build up and storage of fats and lipids as there is very little NAD left to break them down
Where can reduced NAD be reoxidised?
The cristae / inner mitochondrial membrane
Detoxification
Definition
The conversion of toxic molecules to less or non toxic molecules
The Kidney
The Glomerulus
The efferent arteriolar has a smaller lumen than the afferent arteriole so blood pressure increases
This high blood pressure forces smaller molecules out of the blood, there is NO DIFFUSION
There are spaces between the capillary endothelial cells to allow fluid to quickly leave the blood vessel rather than diffusing through cells
The Kidney
Bowman’s Capsule (Renal Capsule)
The basement membrane of the capsule is a sieve like structure made of collagen fibres and glycoproteins
This prevents anything with a relative molecular mass greater than 69000 from leaving the blood, ultrafiltration
The epithelial cells, podocytes, are shaped to create spaces between them for fluid to move through rather than diffusing through cells
At Bowman’s capsule water, urea, sodium, water and small proteins are filtered out of the blood, blood cells, larger proteins and some fluid remains in the blood
The Kidney
Proximal Convoluted Tubule
(filtrate to PCT epithelial cells)
Sodium, glucose, and 85% of water reabsorbed
- sodium moves by facilitated diffusion from the filtrate into the epithelium through a co transporter protein with either glucose or amino acids
- this reduces the water potential of the cell allowing water to move in by osmosis through a protein channel from the filtrate
- epithelial cells have a brush border of microvilli to increase the surface are for diffusion
The Kidney
Proximal Convoluted Tubule
(PCT epithelial cells to blood)
- sodium and potassium ions are pumped out of the epithelial cells by active transport in to the tissue fluid
- this alters the relative concentration of glucose on either side of the membrane allowing glucose to move by facilitated diffusion through a glucose specific carrier protein into the diffusion
- this lowers the water potential of the tissue fluid so water moves by osmosis through protein channels into the tissue fluid
- sodium and glucose then diffuse into the blood
- water moves by osmosis into the blood stream
The Kidney
Loop of Henle
The function of the loop of Henle is to establish a water potential gradient going down into the medulla
- the descending limb is permeable to water and sodium and chloride ions
- water moves out by osmosis into the interstitial tissue
- sodium and chloride ions move into the nephron by diffusion
- sodium and chloride ions can still diffuse in at the lower part of the ascending limb
- but further up the limb the membrane becomes increasingly impermeable to water and salt ions
- at the top of the limb sodium and chloride ions are actively pumped out
The Kidney
Distal Convoluted Tubule
Active transport is used to adjust the concentration of different salts in the filtrate
The Kidney
Collecting Duct
Because of the water potential gradient established at the loop of Henle the water potential of the tissue surrounding the collecting the duct should always be lower than the filtrate
This means that water can be reabsorbed at every point along the collecting duct by osmosis into the medullary tissue and then into the blood stream
In the presence of ADH the collecting duct becomes more permeable to water
hCG
Human Chorionic Gonadotropin
Released by the blastocyst into the parents bloodstream once it has implanted into the uterine lining
Has a relative molecular mass of 36700
If hCG is present in the urine it indicates that the woman is pregnant
Urine Testing
Testing for hCG
Urine moves up wick
If hCG is present mobile, monoclonal hCG antibodies which are attached to a marker will bind to the hCG
At the first window hCG (if present) will also bind to a line of immobilised hCG antibodies, this lines up all of the markers causing a line to appear in the first window
At the second window mobile antibodies (not bound to hCG) bind to immobilised antibodies, this lines up the markers causing a line to appear in the second window
The second window is a test, a line should always appear
A line will only appear in the first window if the pregnancy test is positive
What do anabolic steroids do ?
They are able to pass into cells and inside the nucleus
They affect transcription which increases protein synthesis and therefore causes a build up if tissue especially in the muscles
Urine Testing
Testing for Anabolic Steroids
Gas chromatography
The sample is vaporised and passed along a tube lined with an absorption agent
Each substance stays in the tube for a different retention time
Then passes into a detector where it is analysed to produce a chromatogram
To identify the substance this must be compared with a chromatogram of known substances which was carried out under the same conditions
Sources of Water
Food
Drink
Respiration
Sources of Water Loss
Urine
Sweat
Evaporation through breathing
Osmoregulation
Production and Storage of ADH
ADH is manufactured in the cell body of specialised neurones called neurosecretory cells
The cell body is in the hypothalamus
Once produced ADH moves down the axon to the terminal bulb which is in the posterior pituitary gland, it is stored there
When the cell is stimulated it sends an action potential down the axon which causes ADH to be released from the terminal bulb into the blood stream
Osmoregulation
Detection of Low Water Potential
The water potential of the blood is monitored by osmoreceptors in the hypothalamus
When the water potential of the blood is low water moves out of the cells by osmosis causing them to shrink
This stimulates neurosecretory cells which triggers an action potential causing ADH to be released into the blood stream
Osmoregulation
The Effect of ADH at the Collecting Duct
ADH is transported in the blood to the collecting duct
The cells that make up the walls of the collecting duct have receptors which the ADH binds to
This causes a chain of enzyme controlled reactions inside the cell
Vesicles containing aquaporins fuse with the cell surface membrane
This makes the collecting duct more permeable to water
Osmoregulation
Less ADH at the Collecting Duct
In the absence of ADH the vesicles containing the aquaporins reform so the collecting duct becomes less permeable to water and less water is reabsorbed
Osmoregulation
High Blood Water Potential
When the blood water potential is high osmoreceptors don’t lose water so no action potential is triggered and ADH is not releases from the neurosecretory cells
The ADH that is already in the blood has a half life of about 20 minutes so over time it breaks down
The concentration of ADH in the blood is reduced and less water is reabsorbed
Causes of Kidney Failiure
Diabetes mellitus (Type I & Type II)
Hypertension
Infection
What are the two treatments for kidney failure?
Transplant
Dialysis
Treating Kidney Failure
Transplant
Old kidneys usually left in place
New kidney is implanted into the lower abdomen and attached to the blood supply and bladder under anaesthesia
Patients have to take immunosuppressants for life to prevent rejection of the donor organ
Advantages of kidney transplant
Freedom form time consuming dialysis
Diet is less limited
Feeling better physically
Better quality of life
Disadvantages of Kidney Transplant
Major surgery under general anaesthetic Immunosuppressants Risks of surgery, infection bleeding surrounding organ damage Frequent checks for organ rejection Side effects
Treating Kidney Failure
Dialysis
Patients blood is passed over a dialysis membrane which is partially permeable which allows the exchange of fluids between the blood and the dialysis fluid
Dialysis fluid contains idea,concentrations of salts, urea and water, for the blood plasma
Dialysis must be combined with a carefully controlled diet
What are the two types of dialysis?
Haemodialysis
Peritoneal Dialysis
Haemodialysis
Blood from a vein is passed into a machine that contains an artificial dialysis membrane
Heparin is added (an anticoagulant to prevent clotting)
Usually performed three times a week in hospital
Peritoneal Dialysis
The abdominal membrane, the peritoneum, is used as the dialysis filter
A surgeon implants a permanent tube into the abdomen
Dialysis fluid is poured into the tube and fills the space between the abdominal wall and organs
After several, hours the fluid is drained
