8.5 - Kidneys Flashcards
(18 cards)
Purpose of kidneys
Part of the excretory system
- Filters blood, removing nitrogenous wastes, and maintaining optimal levels of salt and water (osmoregulation)
- Osmoregulation - adds excess water to other waste, making urine.
- Vitamin D activation
Prevents the buildup of waste
Kidney structure
Blood enters through the renal artery –> filtered through nephrons –> renal vein back to the heart. Waste passes through the ureter to the bladder.
Cortex:
- The cortex is the outer part of the kidney
- This is where the blood is filtered by nephrons. (Bowman’s capsule and the proximal and distal tubules are found in the cortex).
- Capillaries are so tiny that RBC pass through single file
Medulla
- Inside part of the kidney
- This is where the amount of salt and water is maintained, by the loop of Henle and the collecting tubule (collecting duct) which protude down into the medulla.
Pelvis
* Where urine is collected
How do kidneys work
Each kidney is made up of about a million filtering units (nephrons) - containing a filter called the glomerulus and a tubule.
180L are filtered every 24 hours
Nephron
Renal artery divides into arterioles, and then into the network of capillaries in the glomerulus.
In the cortex:
- Glomerulus - a network of capillaries, connected to the arteriole. There is a lot of pressure that forces fluid, nutrients and waste out of the glomerulus and into the tubules. It also prevents blood and large molecules such as proteins from passing through.
- Bowman’s capsule : beginning of the nephron where filtration first happens.
- Proximal tubule - nutrients are secreted
- And then the distal tubule (after the Loop of Henle)
In medulla
- Loop of Henle
- End of the collecting duct - takes urine into the calex through the ureters to get to the bladder
Nephron function
First step: filtration
- Blood enters the arterioles from the renal artery
- Passes through the glomerulus (network of capillaries). These are a lot thinner than the arteriole, and therefore blood flows through at high pressure.
- These pressure causes fluid to diffuse into the bowman’s casule. E.g. 20% of blood plasma exits. These are called glomerular filtrate (nitrogenous wastes, amino acids, glucose, ions, water)
- Bigger proteins, blood cells remain in the blood vessel.
- The filtrate then moves to the tubules of the nephron
Second step: reabsorption. This is essential, otherwise we’d get dehydrated so fast.This returns useful substances from the filtrate back to the blood. E.g. 90% of filtrate goes back into the blood stream.
- These include: amino acids glucose, sodium and potassium ions, some vitamins.
- This occurs in the proximal convoluted tubule. Water and nutrients (sugar, vitamins) are reabsorbed (diffusion) back into the bloodstream. 2/3 of water filtered is reabsorbed here (osmosis - due to higher solute concentration)
- Salts taken in by active transport occurs in the loop of Henle and collecting ducts in the medulla.
- The medulla becomes increasingly salty as it descends, the solute concentration increases, and water follows (osmotic gradient from the Henle into the bloodstream).
- At the ascending nephron loop, it is impermeable to water. Sodium and chloride ions are actively transported out of the bloodstream into the medulla. This active transport makes osmosis possible in the Loop of Henle possible.
- Distal convoluted tubule and collecting duct - water can diffuse out. This is dependent on osmoregulation, on the secretion of anti-diueretic hormone (controls the permeability of distal convoluted tubule and collecting ducts)
Third step: secretion
Active removal of toxic substances from blood into the nephron tubules. These are actively transported, as they are not diffusing from the blood capillaries into the nephron for elimination. However, urea and ammonia diffuse.
- Includes: hydrogen ions, ammonia, urea, uric acid, drugs.
- This occurs in the proximal tubule and the descending limb of the loop of Henle
Fourth step: excretion
This is not part of the nephron, but it’s the end result: - Collecting duct is connected to several nephrons. Here, urea is and other waste is collected from the nephrons. Connects to the ureter to the bladder.
Renal Artery
External to kidney
Passes through arterioles, with all the essential and waste in the blood that needs to be filtered. E.g. nitrogenous wastes such as urea, water, salts, glucose, and amino acids.
Glomerulus
In the cortex
- Blood passing through the glomerulus is under high pressure. Substances are thus forced out of the blood in this knot of capillaries into Bowman’s capsule.
Loop of Henle
Salt and water are reabsorbed, controlled by ADH and aldesterone (acting on collecting duct)
Collecting ducts
Located in the pelvis
Materials remaining after reabsorption are the wastes that move into the collecting tubule. As these wastes move through the tubule, more water is taken back into the bloodstream from the tubule. The waste in the collecting tubuel is urine, which is passed down into the pelvis of the kidney.
Hormonal regulation
Aldosterone stimulates the reabsorption of salt in the loop of Henle, to regulate salt and water balance in the kidney (medulla)
The hormone antidiueretic hormone stimulates the reabsorption of water in the kidney (collecting duct and distal convoluted tubule)
Filtrate
Loss of kidney function
Symptoms:
- Nausea
- Vomiting
- Fatigue and weakness
- Changes in urine volume
- Decreased alertness
- Muscle twitches and cramps
- Swelling of feet and ankles
- High blood pressure
Causes:
- Diabetes - too much glucose in the blood, and the kidneys are overworking to reabsorb glucose into the body.
- Chronic high pressure - reduce function of nephrons (too much high pressure forcing the blood into bownman’s capsule)
- Recurrent infections - damage to nephrons which can be exacerbated by prolonged use of medications used to treat infection
- Kidney stones - blockage of urine causes increased pressure which will damage kidneys
Note: just remember diabetes
Bowman’s capsule
In the cortex
– a cup-shaped structure surrounding the glomerulus that collects materials forced out of the blood
Peritoneal dialysis
Peritoneal dialysis
Dialysis can also be carried out within the body by a process known as peritoneal dialysis.
* In this instance, the dialysis solution is passed into the abdonem of the patient by a catheter (fine tube).
* The lining of the abodmen (peritoneum) serves as a natural filtering membrane.
* After a dwell time, wastes diffuse from the underlying blood vessels (equlibrium reached) to the now-used dialysis fluid, which is then drained out by another catheter.
* This process avoids the necessity to circulate the blood from the patient’s body, with the possible risk of blood clotting and infection.
Advantages:
- Portable - can be done at home, when travelling, etc. Doesn’t need visits to a dialysis centre. Can be done during sleep.
- Allows for more unrestricted diet and fluid intake.
- No needles required
- Gentler on the heart and blood pressure as exchange is more gradual, and the slower, more continuous filtration maintains a steady blood pressure.
Disadvantages:
- Less effective, and must be run for several hours to produce comparable results. (8-10 hours overnight, or several exchanges throughout the day)
- Risk of peritonitis (infection of the abdomen).
- As it is done personally, strict hygiene and daily committment is required.
Hemodialysis
In people who have impaired kidney function, waste products can be removed from their blood using a process called renal dialysis.
- Blood is filtered outside the body by passing through a dialysis machine.
- The blood of the patient is passed through several thin coils. These are separated by a membrane from a saline solution which has the same concentration as healthy blood (dialysate).
- The dialysis membrane is permeable to water and to nitrogenous and other waste products of metabolism, especially urea. Diffussion, osmosis removes this waste. Solute to modify pH, medication and anti-coagulants can also be present in dialysate to improve patient’s blood health.
- Cleaned blood returns to the body.
- Surgery is required to create a vascular access - inserting a graft or fusing a fistula which would sustain the high pressure of blood pumping.
- At a dialysis centre 4–5 hours about three times a week, the blood of the patient is circulated through the haemodialysis machine.
Advantages
- Performed by medical professionals - less responsibility by patient, and reduced risk of infection.
- Efficient and fast waste removal - especially important for emergenices.
- Allows off days
Disadvantages
- Rapid fluid and waste removal can cause fatigue, low blood pressure, cramps, and dizziness after sessions.
- Because treatments are spaced out, patients need to limit fluid, potassium, sodium, and phosphorus intake more strictly.
- Treatment schedule is fixed, not portable - limited flexibility.
Disorder that causes kidney damage
Diabetic nephropathy
Diabetes (type 1 and type 2, in which insulin does not sufficiently regulate glucose) can cause diabetic nephropathy - kidney damage that can result in chronic kidney disease
Cause:
- Insufficient presence of insulin impairs glucose regulation. This chronic high level of glucose in the blood can damage glomerular membranes, therefore impairing the nephrons.
- This kidney damage is very subtle, as symptoms do not occur until it has affected 80 to 90% of the kidneys. This is due to the extreme efficiency and redundancy in the kidneys (millions of nephrons), and can continue to operate even when damaged - therefore, when complications do appear, it is near total kidney failure.
Key impacts on patient health:
- Due to kidney damage, blood is not filtered properly, resulting in a build up of toxins in the body, electrolyte imbalance, water retention (swelling as it is not removed from the body).
- It also causes high blood pressure, as retained fluid increases blood volume, and therefore pressure.
- Damaged kidneys incorrectly stimulate the secretion of aldosterone that encourages promotes salt and water retention.
- As high blood pressure only continues to damage kidneys, chronic blood pressure forms a vicious cycle with damaged kidneys.
Can be treated with dialysis when kidney failure is reached. However, kidney transplant is preferred.
Disorders that cause kidney damage
Kidney stones (calcium oxalate)
There are four types of stones - calcium oxalate is one of them.
Causes:
* Unbalanced diet, with too little water that results in a solid mass forming in the kidney when urine is being produced.
* With too little liquid and too much oxalate, it “sticks” to calcium, forming a stone. When there is too much waste and too little liquid in the kidneys, crystals begin to form. This attracts other elements, and the stone grows larger.
Impact on patient health:
* The impacts of kidney stones are felt when it causes irritation of blockage. If the stone is large, it can back-up fluid as it is passing from the kidneys through the ureter, bladder, or urethra. This causes severe pain in the lower back, and can even result in blood in urine, nausea or vomiting.
Kidney stones are often just passed after a period waiting: painkillers are prescribed and water intake increased to ensure urine remains dilute. In severe cases, extracorporeal shock wave lithotripsy can be used to break up the stone into smaller pieces that can be passed.
Fabry disease
Overview
- A rare genetic lysosomal storage disorder, where there is an insufficient amount of alpha-GAL enzyme to break down sphingolipids. The inability of the body to adequately break down sphingolipids causes them to collect in blood vessels and tissues
- Affects heart, kidneys, brain, central nervous system, and skin. In the kidneys: deposits of sphingolipids can enlarge the kidneys, leading to the decrease of kidney function. Renal manifestations of Fabry disease often ultimately result in end-stage kidney failure.
- In the classic type, symptoms appear during childhood or adolescence and progressively become worse over time. Common symptoms are numbness, tingling, or burning sensation in hands and feet, high levels of protein in urine, diarrhea, constipation, or abdominal pain
- X-linked inheritance, a genetic mutation of the GLA (galactosidase alpha) gene causes it to produce insufficient alpha-GAL enzyme
Enzyme replacement therapy
- Addresses the insufficiency of alpha-GAL enzymes by supplying the patient’s body with a lab-engineered enzyme similar to alpha-GAL. The name of these enzymes are Replagal or Fabrazyme. Treatment is conducted through an intravenous infusion every 2 weeks
- The lab-engineered enzymes break down sphigolipids in the blood, preventing them from accumulating in blood vessels
- Advantages: enzyme replacement therapy alleviates the symptoms of Fabry disease, as the lab-engineered enzymes substitute the function of the deficient alpha-GAL enzymes. Early implementation of this treatment can help prevent kidney failure in a patient, as well as preventing heart failure and nerve damage associated with the disease. Also, Replagal and Fabrazyme are subsidised by the Australian Government through its Life Saving Drugs Program, making enzyme replacement therapy more accessible to individuals in need
- Disadvantages: enzyme replacement therapy does not solve the genetic defect that causes Fabry disease, so patients will have to commit to lifelong treatments at regular and frequent intervals. This can limit the flexibility of their lives, for example imposing restrictions on their ability to travel. Moreover, enzyme replacement therapy may not be accessible to individuals living in remote regions where there is poor access to medical facilities that can provide the treatment. Also financial barrier: ERT is expensive as it depends on conspicuous amounts of the recombinant enzyme
Jenisha judgement: while it can be inconvenient, it can be life-saving and prevent the degeneration of important organs like kidneys in the long term. So it is useful.
