Renal system

• Renal system function

  • The renal system has 2 main functions;
  • Excretion or removal of nitrogenous waste in the form of urea
  • Osmoregulation or regulation of the water balance in the body (endocrine system)
• • Proteins and nucleic acids both contain nitrogen. We normally take in more nitrogen-containing compounds in our food than we need daily.
  • Any excess is converted by the liver to urea. The urea is transported in the blood to the kidneys where it is removed from the body when urine is being formed.
  • The renal system is sometimes called the urinary system and is closely connected to the reproductive system. The 2 systems together are sometimes called the genitourinary.
• • The renal system consists of 2 kidneys with emerging tubes (called the ureters) running down the posterior abdominal wall to the bladder.
  • The passage from the bladder to the outside is called the urethra, and the flow of urine is controlled by a sphincter muscle located just below the bladder.
  • The kidneys are supplied by short renal arteries coming off the main artery of the body, the aorta.
  • Renal veins take the blood from the kidneys straight into the vena cava, the main vein of the body.
• Function of kidney

  1. Filtration of waste products and toxins from the blood
  2. Formation of urine
  3. Regulation of water and salt balance in the body
  4. Maintenance of the normal pH balance in the blood
• Kidney

  • The two kidneys are bean-shaped organs. They lie on the posterior wall of the abdomen, partly protected by the lower rib cage.
  • The right kidney is slightly lower than the right, due to the space taken up by the liver.
  • Each kidney has over 1 million nephrons (filtration units) which are responsible for filtering blood to produce urine. Healthy kidneys filter about half a cup of blood every minute, removing waste and extra water to make urine
• Removal of waste products from the blood

  • The two kidneys are bean-shaped organs. They lie on the posterior wall of the abdomen, partly protected by the lower rib cage.
  • The right kidney is slightly lower than the right, due to the space taken up by the liver.
  • Each kidney has over 1 million nephrons (filtration units) which are responsible for filtering blood to produce urine. Healthy kidneys filter about half a cup of blood every minute, removing waste and extra water to make urine
• Each tubule has a knot of capillaries (the glomerulus) in a cup-shaped Bowman's capsule leading to a long coiled bent tubule
• Glomerular filtration is the first step in making urine
• It is the process that kidneys use to filter excess fluid and waste products out of the blood into the urine collecting tubules of the kidney
• This process allows for the elimination of waste products from the body
• As the filtrate leaks from the glomerulus into the cup and down into the tubule, useful substances such as glucose, amino acids, and some water are reabsorbed back into the capillaries around the tubules
• Protein molecules and blood cells are too big to pass into the Bowman's capsule unless the nephron has been damaged
• Ureters 


  are slim tubes that join the kidneys to the bladder. Urine passes mainly by gravity but the muscular walls of the tube can also carry out peristalsis
• Bladder 


  the bladder is a hollow organ with muscular walls, that expands. It stores urine until the person can go to the toilet. A healthy bladder can hold 300-400mls of urine in the day and 800mls during sleep.
• Urethra

  urethra is the tube that carries urine from the bladder to the exterior. In females it is quite short (4cm) but in males it runs through the penis so it is longer. (18-20cm)
• Kidney affect on blood pressure

  • The cardiovascular system plays a big play in blood pressure
  • The kidneys also influence blood pressure by; changing the circulating blood volume.
  • The enzyme Renin and hormones Aldosterone and Antidiuretic hormone all play a part. It is called the renin-angiotensin system. Renin stimulates the system into action
  • If blood pressure drops, salt content is low. Aldosterone increases the uptake of sodium (salt) and water back into the blood. This increases the volume of fluid in the body and increases the blood pressure.
• Antidiuretic hormone and water balance

  • Antidiuretic Hormone (ADH) from the pituitary gland controls fluid balance, known as osmoregulation
  • If a lot of water has been drunk and absorbed into the blood, volume increases and ADH production is reduced so that less surplus water is reabsorbed and more goes into the urine until the balance is restored
  • On the other hand, if the body is lacking water, more ADH is secreted and more water is reabsorbed to regain balance.