The Kidney Flashcards
The endothelium of the capillary
Narrow gaps between cells of the endothelium of the capillary cell wall. The cells contain pores celled fenestrations. Blood plasma and dissolved substances pass in and out of the capillary.
The basement membrane
consists of a fine mesh of collagen fibres and glycoproteins. Mesh prevents the passage of large molecules so most proteins and all blood cells are held in the capillaries of the glomerulus.
The epithelial cells of the Bowman’s capsule
The podocytes have a specialised shape that hold cells away from the endothelium of the capillary ensuring here are gaps between cells. Fluid from the blood in the glomerulus can pass between these cells into he lumen of the Bowman’s capsule.
Ultrafiltration
The filtering of blood at a molecular level
Efferent and afferent arterioles
Blood flows into the glomerulus (Arrives) at the Afferent arteriole. The efferent arteriole carries blood away from the glomerulus (exits).
The afferent is wider than the efferent to ensure the blood in the capillaries of the glomerulus maintains a pressure higher than the pressure in the Bowman’s capsule. This pressure difference pushes blood from he glomerulus into the Bowman’s capsule.
What is filtered out of the blood?
Water Amino acids Glucose Urea Inorganic mineral ions
How are the cells of the proximal convoluted tubule specialised to achieve absorption?
- highly folded micro villi to increase surface area for reabsorption
- plasma membrane contains cotransporter proteins to transport glucose or amino acids with sodium ions into the cell
- cell cytoplasm has many mitochondria to provide ATP
The mechanism of reabsorption
- sodium ions are actively pumped out of the cells lining the tubule
- concentration of sodium ions in the cell cytoplasm decreases creating a concentration gradient
- sodium ions diffuse through cotransport protein carrying glucose or an amino acid
- water moves into the cell by osmosis
- Glucose/amino acids diffuse into the blood
In the descending loop of henle…
mineral ions diffuse in so water potential becomes more negative, water moves out of the descending limb and enters the capillaries.
In the ascending loop of henle…
Mineral ions leave the fluid. At the base, this is by diffusion and at the top this is by active transport.
This creates a higher water potential in the ascending limb and decreases the water potential in the tissue fluid of the medulla.
In the collecting duct…
As it passes through tissues with always decreasing water potential, there is always a water potential gradient allowing water to move out of the collecting duct by osmosis.
Concentration changes in the tubule fluid
- [glucose] decreases as it is selectively reabsorbed from the proximal tubule
- [Na+] increases as they diffuse into the descending limb, concentration decreases as they are pumped out of the ascending limb
- [urea] rises as water moves out of the tubule. Urea is also actively moved into the tubule.
- [Na+] and [K+] increases as water is removed from the tubule
Osmoregulation
Is the control of water potential in the body. This involves controlling levels of salt and water.
The mechanism of osmoregulation
The kidneys alter the volume of urine produced by altering the permeability of the collecting duct.
If you need to conserve less water, the walls of the collecting ducts become less permeable so less water is reabsorbed, more urine produced.
If you need to conserve more water, collecting duct becomes more permeable so more water is reabsorbed, less urine produced.
Altering the permeability of the collecting duct (ADH)
The cells in the walls of the collecting duct have membrane bound receptors for ADH. When ADH binds a series of enzyme controlled reactions is triggered which end in vesicles containing aquaporins to bind to the plasma membrane making the walls more permeable.
If ADH levels fall, membrane folds inwards to create new vesicles to remove the aquaporins from the membrane. This makes walls less permeable.
