C31 - Kidney Functions and Malfunctions Flashcards
What’s the gross structure of the kidney?
Vertebrates have 2 kidneys, located just below the ribs on either side of the spine.
Each receives and removes blood from the renal artery and renal vein.
Urine produced passes through a tube called the ureter into the bladder, where it’s stored.
What are the components of a kidney?
Pelvis of kidney Medulla Cortex Renal artery Renal vein
What are the organs/components of the excretory system?
Vena cava
Aorta
Renal artery
Renal vein
Kidney
Ureter
Bladder
Urethra
What are the 3 regions of the kidney?
Cortex (outer region)
Medulla (inner region, consisting of renal pyramids, which are composed of sections of nephrons)
Renal pelvis (most central region which leads into the ureter)
What’s excretion?
Removal of waste products of metabolism.
E.g. CO2 and water from the lungs or water and salts in sweat from skin.
What does the ultrastructure of the nephron consist of?
The nephron begins in the kidney’s cortex.
It has a cup-shaped structure called the Bowman’s capsule which surrounds a dense network of capillaries known as the glomerulus.
The nephron is then divided into four sections:
- proximal convoluted tubule
- loop of Henle
- distal convoluted tubule
- collecting duct
What’s the Bowman’s capsule?
Cup shaped structure in nephrons surrounding the glomerulus.
What’s the glomerulus?
A dense network of capillaries in the Bowman’s capsule of nephrons.
Where does deamination mainly occur?
Liver cells
How is ammonia removed from the body?
As urea
Ammonia is formed when excess amino acids are deaminated.
Ammonia is then combined with CO2 in the Ornithine cycle and converted into urea.
Urea is less toxic than ammonia but must be removed via excretion by the kidneys.
What happens in the glomerulus?
Blood pressure is very high, which causes water, ions, urea, glucose and amino acids to be forced from the blood and filtered into the nephron.
This is known as ultrafiltration.
What’s selective reabsorption?
A process in nephrons where useful substances, e.g. glucose, most water and some ions, are reabsorbed back into the tissue fluid and blood capillaries.
Unwanted substances travel to the collecting duct.
What is the waste fluid from nephrons, which reaches the end of the collecting duct, called?
Urine.
This moves through the renal pelvis, down the urethra and into the bladder.
Urine is excreted from the bladder via a tube called the urethra.
From where is urine excreted?
From the bladder via a tube called the urethra.
What’s ultrafiltration?
Filtration of molecules in the glomerulus of the kidney nephrons.
Large molecules remain in the blood meanwhile smaller molecules pass into the Bowman’s capsule.
What occurs in ultrafiltration?
Hydrostatic pressure in the capillaries of the glomerulus is greater than the pressure in the Bowman’s capsule.
Blood is brought into the glomerulus by the afferent arterioles and leaves via the efferent arteriole.
The smaller diameter of the efferent arteriole causes the build-up of hydrostatic pressure.
This causes water and small molecules (ions, amino acids, glucose) to be forced into the Bowman’s capsule.
How does the structure of capillaries in the glomerulus and Bowman’s capsule act as a filter?
Endothelium cell’s in capillaries are separated by narrow gaps called fenestrations, which prevents blood from escaping.
The basement membrane of capillaries is composed of a fine mesh of collagen and glycoprotein. This prevents large proteins from being filtered out of the plasma.
Epithelial cells of the capsule have finger-shaped projections to create small gaps between cells. These cells are called podocytes and the gaps are known as filtration slits.
Where does selective reabsorption occur?
In the proximal convoluted tubule (PCT) of nephrons.
All glucose is reabsorbed here, as well as acids and some ions.
How are cells lining the proximal convoluted tubule (of nephrons) specialised for reabsorption?
- They have microvilli (which increase SA)
- There are co-transporter proteins present. These allow facilitated diffusion of glucose or amino acids, in association with Na+ ions, from tubule fluid. They can then diffuse into blood capillaries.
- Na/K pumps in the membrane next to PCT cells, adjacent to capillaries. They pump Na+ out of the PCT and into tissue fluid.
This results in a low Na+ concentration in PCT cells which allows co-transport of glucose or amino acids. - High concentration of mitochondria, which provide energy for active transport.
What remains in the nephron filtrate after selective reabsorption?
Toxic compounds (urea), excess water and some ions, which will be excreted as urine.
In what order does fluid move around parts of the nephron?
1) Glomerulus
2) Bowman’s capsule
3) Proximal convoluted tubule (PCT)
4) Descending and ascending loop of Henle
5) Distal tubule
6) Collecting duct
What does the loop of Henle consist of?
A descending and ascending limp, arranged as a hairpin countercurrent multiplier.
This means that a fluid passing in opposite directions close to each other enables exchange of substances between the 2 limbs.
How are ions and water transferred in the loop of Henle (within nephrons)?
Fluid enters the descending limb from the proximal convoluted tubule.
Water diffuses out the descending limb by osmosis and is reabsorbed by capillaries.
At the bottom of the loop, ion concentration is very high and water potential is very low.
Na+ and Cl- diffuse out of the nephron at the base of the ascending limb and into the tissue fluid in the medulla.
Water is unable to leave the ascending limb as its wall is impermeable to water.
The filtrate leaves the ascending limb and travels to the distal convoluted tubule. The filtrate has high water potential (and low solute concentration).
A low water potential has been created in the medulla, through which the collecting ducts pass.
What happens in the collecting duct (of nephrons)?
Fluid reaches the collecting duct via the distal convoluted tubule (DCT).
The fluid has a high water potential, meanwhile the surrounding medulla tissue has low water potential. Thus water will move out the duct and into the medulla and capillaries via osmosis.
However, permeability of the collecting duct can be altered to control how much water gets reabsorbed.
