5.1.2: Excretion Flashcards
Excretion
The removal of waste products of metabolism from the body.
Functions of the liver
- Carbohydrate metabolism
- Deamination of excess amino acids
- Detoxification
Which vessel supplies the liver with blood containing products of digestion?
Hepatic portal vein
Hepatic portal vein
supplies the liver with blood containing products of digestion.
Which vessel supplies the liver with oxygenated blood?
Hepatic artery
Which vessel removes deoxygenated blood from the liver?
Hepatic vein
(bile) Canaliculus
Spaces into which bile is secreted.
How to identify the bile canaliculus as distinct from the sinusoids?
Bile canaliculus does not empty into the hepatic vein
Lobule
functional unit of the liver; star-shaped structure made of many sinusoids going towards the central vein
Hepatocyte function
- Synthesise plasma proteins
- Carry out transamination
- Carry out deamination
- Carry out detoxification
- Carbohydrate metabolism
Structure of hepatocyte
- Large prominent nucleus
- Many free ribosomes
- (possibly) visible Golgi apparatus
Two processes required for formation of urea
- Deamination
* Ornithine cycle
Deamination (process)
Amino acid + O₂ ⟶ Keto acid + Ammonia
Problems with ammonia
- Very toxic
* Very soluble (lots of water required, messes up water potential)
Detoxification of hydrogen peroxide equation
2H₂O₂ –catalase–> 2H₂O + O₂
What is the ornithine cycle?
Series of enzyme-controlled reactions that convert ammonia (from deamination of amino acids) into urea.
What is transamination?
The conversion of one amino acid to another by a hepatocyte.
Why is transamination necessary?
- The free amino acids available in the body (from diet) may not match the body’s requirements
- Only works for non-essential amino acids
Steps in ultrafiltration
1) Fenestrated capillary endothelium
2) Basement membrane = main filter
3) Pedicels of the podocytes
What is filtered out in ultrafiltration?
• Anything with Mr of less than 69,000 e.g. ⟶ Water ⟶ Amino acids ⟶ Glucose ⟶ Urea ⟶ Inorganic ions (Na+, K+, Cl-)
What remains in the blood during ultrafiltration (assuming kidney is healthy)?
- Blood cells
- Proteins
- Substances with a Mr of over 69,000
Glomerular filtrate
substances that enter the Bowman’s capsule (are filtered out of the blood)
Basement membrane
specialised extracellular matrices
⟶ Important for compartmentalising tissues, providing substrata
Where does selective reabsorption occur?
Proximal Convoluted Tubule (PCT)
How is the PCT specialised for selective reabsorption?
- Many co-transporter/transport proteins
- High SA (brush border)
- Many mitochondria (supply ATP for active transport)
What is selectively reabsorbed by the PCT?
- All glucose
- All amino acids
- Some salts
- Some water
Selective reabsorption is a largely active/passive process?
active
Where does ultrafiltration takes place?
The glomerulus (within the Bowman’s capsule)
Parts of the Loop of Henle
- Descending limb
- Apex (hairpin bend)
- Ascending limb
The Loop of Henle is important because
it allows mammals to produce urine that is more concentrated than their blood.
How does the Loop of Henle allow mammals to produce urine more concentrated than their blood?
The Loop of Henle creates a low water potential in the medulla by transporting Na+ and Cl- ions out of the glomerular filtrate (ascending limb)
Descending limb of the Loop of Henle
• Permeable to water
Ascending limb of the Loop of Henle
- Impermeable to water
* Highly permeable to Na+ and Cl-
Osmoregulation
Control of the water balance of the blood
Functional unit of the kidney
Nephron
Renal cortex
- Dark outer layer of kidney
- Where filtration takes place
- Dense capillary network: blood carried from renal artery to nephron
Renal medulla
- Inner region of the kidney
- Lighter in colour than the renal cortex
- Contains the tubules of the nephron and the collecting ducts
Renal pelvis
- Central chamber of the kidney
* Where urine collects before passing to the bladder via the ureter
Ureter
Tube that carries urine away from the kidney
Urethra
Carries urine from the bladder to the outside of the body
Sphincter
Muscle that opens to allow urine to be removed from the bladder
Describe selective reabsorption in the PCT
1) Na⁺ actively transported out of cells of PCT into tissue fluid and then blood plasma, which generates a concentration gradient between the filtrate and the PCT cells
2) Na⁺ enters cells from the lumen by facilitated diffusion, down the concentration gradient; glucose and amino acids are co-transported with these Na⁺ ions.
3) Increase in solute concentration due to influx of Na⁺ leads to osmosis of water into the PCT cells.
Glucose and amino acids will pass into the blood (other side) through facilitated diffusion; blood flow maintains a concentration gradient.
Effects of kidney failure
- Loss of electrolyte balance (body cannot excrete excess Na⁺ etc, eventually leading to death).
- Osmotic imbalance in the tissues
- Build up of urea in the blood (toxic)
- High blood pressure (because the kidneys help regulate this –> still researching how)
- Weakened bones: without proper control, calcium ions diffuse out of blood
- Anaemia: kidneys fail to produce crythropoetia (hormone that promotes formation of new RBCs)
How to detect kidney failure
- Reduction in glomerular filtration rate (levels of creatine used to estimate GFR as creatine is a breakdown product of muscles)
- Higher creatine conc. in blood = lower filtration rate
Treatment methods for kidney failure
- Dialysis
* Transplant
Pros of dialysis
✔︎ More readily available
✔︎ No surgery or immunosuppressants needed
Cons of dialysis
✖️ Long term more expensive than transplant
✖️ Need regular sessions - treatment needed repeatedly
✖️ Must monitor diet carefully
Pros of transplant
✔︎ Long-term is cheaper than dialysis
✔︎ No dietary monitoring/restrictions
✔︎ Single surgery could enable normal function
✔︎ Able to be more independent
Cons of transplant
✖️ Need surgery (infection risk) and immunosuppressants
✖️ Need frequent checks for signs of organ rejection
✖️ Not always readily available; long donor waiting list and must find a match
What is haemodialysis?
- Involves use of a dialysis machine
* Usually done in hospital
What is peritoneal dialysis?
- Dialysis done inside the body - makes use of the natural dialysis formed by the peritoneum (lining of the abdomen)
- Can be carried out at home and patient can go about normal life while this is taking place
How does a pregnancy test work?
- Test for hCG (chemical produced at site of developing placenta) using monoclonal antibodies
- Test contains mobile monoclonal antibodies that have coloured beads attached to them
- hCG in urine binds to mobile monoclonal antibodies to form hCG/antibody complex
- At first window, there are immobilised monoclonal antibodies that only bind to the hCG/antibody complex –> proves woman is pregnant or not
- At second window, there are immobilised monoclonal antibodies that binds to mobile antibodies regardless of whether hCG is present -> proves pregnancy test is working
How can excretory products be used in medical diagnosis?
- Pregnancy testing
* Drugs testing e.g. anabolic steroids in sport
How to detect drugs in urine
- Use an immunoassay (monoclonal antibodies bind to the drugs or its metabolite(s))
- Use of gas chromatograph/mass spectrometer
