The Renal System Flashcards
The components of the renal system and the functions
Components
• Kidney
• Nephron
• Ureter
• Bladder
• Urethra
Functions of the renal system:
• removal of waste products from the body
• process of urine production
• role in osmoregulation
• role in homeostasis
Roles of the renal system
Osmoregulation-Maintains water/fluid and electrolyte balance. Excretion of waste products such as urea
Homeostasis of other functions- Regulation of acid/base balance Production of erythropoietin (Hormone) which stimulates red blood cell production. Control of blood pressure by renin (enzyme) production Conversion of vitamin D into an active form for the body
Nephron structure
• The blood vessels supplying the kidney and the capillary network surrounding the nephron.
• The renal corpuscle which is where fluid enters the nephron from the blood
• The two convoluted tubules – proximal and distal
• The loop of the nephron – this is the loop of Henle
• The collecting duct that drains into the renal pelvis
Nephrons
• Nephrons are the functional units of the kidney where the blood is filtered
• There are about 1 million of them in each kidney
• Nephrons are based in both the cortex and the medulla.
• They filter 125ml of fluid a minute and around 99% is reabsorbed leaving about 1ml of urine a minute.
• They can be damaged by high levels of glucose which damages the glomerulus and allows leakage of
unwanted substances into the filtrate such as protein and high blood pressure
What happens where in the nephron
• The different parts of the nephron all have different roles in reabsorbing or secreting substances that the body wants to retain or eliminate.
• The focus is on the process of water reabsorption and ‘water potential’
Ultrafiltration
• This is the process of how the fluid is removed from the blood stream and enters the Bowman’s capsule.
• The afferent arteriole is thicker than the efferent arteriole this increase pressure in the glomerulus so that
fluid is forced out of the blood into the nephron.
• This fluid is now called ‘filtrate’ and proceeds further into the nephron along with everything dissolved in it
• If nothing else happens then the fluid and dissolved content - water and urea, will end up going all the way through the nephron, down the ureter, through the bladder and into the toilet.
• However, the body needs to reclaim materials such as water and glucose which are still useful. This happens when they move out of the filtrate inside the nephron back into the capillary network that twists around the nephron through reabsorption.
• This is called selective reabsorption
Selective reabsorption
• Almost everything is reabsorbed in the proximal tubule mainly through co transport.
• The glomerular filtrate is then significantly (about 85%) reduced leaving fluid and some solutes remaining to continue through the nephron.
• Electrolytes (mineral ions such as sodium potassium etc) are reabsorbed later in the distal tubule to balance blood pH
Water potential
• Water potential describes the tendency of water to move out of a solution.
• Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane to reach equilibrium.
• A dilute solution has a high water potential (the right-hand side of the diagram below) and a concentrated solution has a low water potential (the left-hand side of the diagram below)
• Osmoreceptors are sensory receptors in the thirst centre in the hypothalamus that monitor the concentration of solutes and adjust feelings of thirst and ADH levels
The Loop of Henle
• As the filtrate moves down the descending loop it moved into an area of the medulla that has a higher contraction of salt than the filtrate. Water moves, through osmosis, out of the filtrate and into the tissue to try and balance water potential.
• In the ascending loop sodium ions are moved from the filtrate into the tissue to maintain the higher concentration of salt needed for osmosis
Role of Hormones - ADH
• Water balance is controlled by the secretion of the hormone
• ADH is the Antidiuretic Hormone and produced in the hypothalamus. It is then passed to be secreted from the pituitary gland into the blood.
• ADH increases the permeability of the collecting ducts so that more water is absorbed into the blood which lower the volume of urine produced.
• It does this by increase in the amount of aquaporins (water
channel proteins) present in cells of collecting duct, resulting in more water being reabsorbed into the blood so less loss in urine
Action of ADH
ADH has some key main effects which are:
• Increasing the water permeability of distal tubule as well as the collecting duct so that more water is retained by increasing the number of aquaporins present so more water is moved back into the body.
• Increases of sodium absorption across the ascending loop of Henle. This aids in water reabsorption later in the distal tubule and collecting duct because it makes the kidney tissue saltier than the filtrate (osmosis) so water moves out of the filtrate into the tissue for reabsorption.
• As more water is retained the volume of urine will be decrease and the colour will be darker
Urine and the bladder - excretion
• Urine at this stage moves into the ureters and flows into the bladder until expelled.
• Typically urine is about 95% water (depending on your fluid balance) and the remaining 5% is urea (2%) and trace minerals.
• Only about 0.8% of volume is removed from the blood by the kidneys, which shows how effective they are at recycling products
Urine
• The salts, chiefly sodium, must be excreted in order to maintain the right balance of fluids.
• The colour of urine comes from bilirubin (bile pigment). Normal urine is acidic (between pH 4.5 and pH8 ).
• Urine can be tested with ‘dip sticks’ which show what is present that can help diagnosis
