THE KIDNEY - HOW IT WORKS By the end, you will know about…  Nephrons  Ultrafiltration  Selective Reabsorption  Control of Water Balance  Kidney Damage and possible treatments….

OBJECTIVES Key Objective  Describe the structure and function of the kidneys Outcomes  Describe how the amount of urine produced is affected by water intake, heat and exercise (D)  Describe the basic structure of the kidney and how it works (C)  Explain how the structure of the kidney tubule is related to filtration of the blood and formation of urine (B)  Explain how the concentration of urine is controlled by the anti-diuretic hormone (ADH), produced by the pituitary gland (A)  l Understand how ADH production is controlled by a negative feedback mechanism (A*)

STARTER Where do we get water from? Where do we lose water?

Excretion  We need to excrete certain things that may otherwise build up and be poisonous to us, eg:  Carbon dioxide (lungs)  Urea (kidney)  Faeces (from digestion)

The Kidney  You have two kidneys in your body.  They are located towards your back, near your waist.  They filter the blood, and remove any harmful or excessive substances, eg. Urea, water, salts, hormones.

Inside the Kidney  The kidney has an outer CORTEX.  The middle section is the MEDULLA.  There are pyramid-like structures in the medulla.  The centre part is known as the PELVIS.  The tube that carries urine to the bladder is the URETER.

The Nephron  Nephrons are small subunits that make up the kidney. They do the filtering!  There are millions of these tiny structures inside the kidney, and all eventually drain into the ureter.

Ultrafiltration  Blood had to be filtered to stay “clean”.  It has to be filtered under high pressure. ULTRAfiltration!  The blood enters the kidney through the RENAL ARTERY.  It enters the GLOMERULUS – a tiny knot of capillaries.

Bowman’s Capsule  As the blood goes from artery to glomerulus, it creates extremely high pressure.  This forces everything small enough to leave the blood and enter the first part of the nephron; Bowman’s Capsule.  Proteins and cells are too big, so stay in the blood.

First Coiled Tubule  After the filtrate trickles down from Bowman’s Capsule, it contains water, salts, urea, glucose, any hormones and drugs.  However, the body needs to reabsorb the useful products back into the blood.  The first coiled tubule is the first section of the nephron, near the Bowman’s capsule. It is long and coiled.  In the first coiled tubule, glucose is reabsorbed into the capillaries surrounding the nephron.

The Loop of Henlé  The next section of nephron is the Loop of Henlé. It is a long loop, that goes into the medulla of the kidney.  It is here that water and some useful salts are reabsorbed.

Second Coiled Tubule  This is the third section of the nephron. It is another coiled tubule.  Anything else that needs reabsorbing will be reabsorbed here (eg. water and more salt if necessary).

Collecting Duct  All the leftover substances end up in the collecting duct.  This includes urea, excess water and salts, any drugs and other waste products from the body’s chemical reactions.  If the body gets dehydrated, water gets absorbed from the collecting duct.  This leftover waste liquid is known as URINE.

Urine  Urine can be important in diagnosis of certain diseases.  If there are certain substances in the urine that should have been filtered out by the kidneys, then it can be an indication of kidney damage.  Glucose in the urine is an indication of diabetes.

PRACTICAL Analysing urine samples Sample Result with glucose testing strip Result with protein testing strip Result with powdered sulfur A B C D Conclusion Urine sample ____________________ is from a healthy person. Urine sample ____________________ is from a person with diabetes. Urine sample ____________________ is from a person with kidney disease. Urine sample ____________________ is from a person with jaundice.

Water Balance  The levels of water in the body need to be properly controlled to avoid death by dehydration.  This is an example of HOMEOSTASIS – keeping the environment inside you at a constant.  Think of it like a driver trying to stick to the speed limit!

ADH  Anti-diuretic hormone is produced by the pituitary gland in the brain.  Changes in water levels in the blood are detected by the HYPOTHALAMUS in the brain. It controls release of ADH by the pituitary.

Water Balance cont…  When you drink a lot, there is a lot of water in your blood.  Your hypothalamus detects this, and stimulates the pituitary to release LESS ADH.  This means the collecting ducts become LESS permeable to water.  LESS water is reabsorbed into the blood.  Therefore you produce a greater amount of weak, pale urine.

Water Balance cont…  When you don’t drink enough, the hypothalamus stimulates the pituitary to release MORE ADH.  The collecting ducts become MORE permeable to water.  MORE water is reabsorbed into the blood.  Therefore you produce a small amount of very yellow, concentrated urine.

Kidney Damage  The kidneys can be damaged due to diabetes, high blood pressure, developing kidney stones, etc.  You can survive with one working kidney, as the blood can still be filtered by the remaining kidney.  If both kidneys fail, there are only two possible treatments to stop the toxins and salts building up to fatal levels in the body.

Treatments – Dialysis  The patient is hooked up to a dialysis machine – this is like an artificial kidney.  The patient’s blood runs out of the body, through tubes into machine where excess fluids and toxins are drawn off. Tubes take blood back into the body.

Treatments - Transplants  A donor kidney must be found that matches the patient’s own tissue type.  The donor kidney must be removed from the donor less than an hour after death.  The kidney is put in the groin, and attached to a vein and an artery.  The patient will have to take anti-rejection drugs for the rest of their life.