The kidneys

• The main job of the kidneys is to filter the blood and remove waste products like urea, which is made in the liver during deamination
• The kidneys also regulate the levels of ions like sodium and potassium, as well as water in the body
• Water regulation is crucial because cells can lose or gain water through osmosis, affecting their size and function
• Inside each kidney are around a million structures called nephrons, which are responsible for filtering blood
• Kidney tubules absorb small molecules like water, glucose, amino acids, and urea during the filtration process
• Selective reabsorption occurs in the kidney tubules, where only the substances that the body needs are reabsorbed, forming urine with the waste products
• The hypothalamus in the brain detects water concentration in the bloodstream and signals the release of antidiuretic hormone (ADH) from the pituitary gland if water levels are too low
• ADH travels to the kidneys and instructs the tubules to reabsorb more water into the blood, reducing urine production
• This process of water regulation is a negative feedback loop, where the body constantly monitors and adjusts water levels to maintain balance
• The three main roles of the kidneys are to:

  • Remove waste products like urea from the blood
  • Regulate the levels of ions in the blood
  • Regulate the amount of water in the blood
• Blood cycles through the kidneys, passing in through the renal arteries and out through the renal veins
• The kidneys produce urine from the blood, which passes down the ureters and is stored in the bladder until it is urinated out through the urethra
• Filtration is where some of the liquid part of the blood is forced from the glomerulus into the Bowman's capsule
• Only small substances like water, amino acids, urea, glucose, and ions can be filtered through to the Bowman's capsule
• About 20% of the plasma in the blood is filtered through to the Bowman's capsule
• The kidneys reabsorb substances like glucose and amino acids back into the blood vessels
• Selective reabsorption is the process of reabsorbing only the substances that are needed back into the blood vessels
• Selective reabsorption happens throughout the entire region of the tubule
• Parts of the nephron include:

  • Glomerulus
  • Bowman's capsule
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
• Fluid that passes out of the collecting duct is classified as urine
• Urine passes down the ureter to the bladder and can then be released as waste