The Kidney and Osmoregulation

What you need to know

Reflections and Exam tips

Kidney and osmoregulation

Every person has 2 bean-shaped kidneys located on the sides of our bodies just below the ribs.

Kidneys control the levels of water and salts in our bodies. The control of water and salts is called osmoregulation. (osmo= to do with osmosis, regulation = control).

The kidney is mainly involved in the removal of urea from the blood. Urea is a by-product of protein metabolism.

When you eat protein, this is what happens:

Protein in diet —›Digested into amino acids —›Some amino acids used, Excess amino acids broken down into Urea by the Liver —› Urea goes into blood.

• The blood circulates around the body and when it reaches the kidney, Urea must be removed into urine.

Gross structure of the kidney

Kidney diagram comes here

The kidney is made up of:

• an outer pale region called the cortex- this is the main area of blood filtration
• a darker middle region called the medulla- its made of a number of oval pyramids- this is the main area of balancing body fluids through reabsorption
• an inner central white region called the pelvis- this collects the urine and sends it to the bladder via the ureters.

Inside the kidney

Everything to do with the kidney is refered to as renal (From French renes= kidneys)

Nephron diagram comes here

Blood enters the kidney through the renal artery, blood leaves through the renal vein.

Inside the kidney is a system of vessels which divides into a series of tubes which carry out the functions of the kidney. Each system of tubules is called a nephron, it is the functional unit of ecah kidney- the smallest unit which carries out the functions. Each kidney has more than a million nephrons enabling a large volume of blood to be filtered each hour.

The Nephron

Blood enters the nephron through the renal artery.

The renal artery divides into lump of capillaries called the Glomerulus. The capillary walls are single-celled with tiny pores for filtration. Pressure here forces small molecules out into the Bowmans capsule.

• Water
• Urea
• Salts
• Glucose

What remains in the blood are:

• Proteins
• Blood cells- These are too big to pass through the pores
• Some water

-The Glomerulus is enclosed in a cup shaped Bowman's capsule. This collectd the filtrate from the Glomerulus.

-The capillaries of the Glomerulus rejoin to form the renal vein which carries filtered (clean) blood back to the body.

-The Bowman's Capsule connects to a folded tube which goes down from the Cortex and makes a U-turn in the medulla.

-The U-shaped tube is called the Loop of Henle. This is where useful substances are reabsorbed back into blood.

-The reabsorption happens by active transport so it requires energy- these cells must have a lot of mitochondria.

What is reabsorbed?

• Some Water (by osmosis)
• Some salts (Na, Cl, K- by active transport)
• All glucose (by active transport)

Urea is not reabsorbed - all of it passes into urine.

Comparing parts of the kidney:

Kidney Failure

Sometime people's kidneys begin to fail to do their jobs properly. This means that toxins like urea begin to accumulate and cause damage to other body organs.

Some signs of kidney failure

• Tiredness
• Blood in urine
• Fluid accumulation- swollen feet

Kidney failure-risk factors

• Diabetes
• Genetic factors
• Alcoholism
• High blood pressure
• Physical damage

Kidney transplants

A matching kidney from a donor is transplanted to the patient.

Advantages

• Prolongs the patient's life
• One-off procedure, no need to revisit hospital every week

Disadvantages

• Shortage of matching donors- antigens have to match
• Transplant waiting times may be very long
• Cost of the procedure
• Use of immuno-supressants- the patient has to take drugs which suppress their immune system otherwise it will attack the new kidney as a foreign organ. This exposes them to other infections.
• Ethics of transplants- some people may not want to have a kidney from a dead/unkown person.

Dialysis

During dialysis, blood is taken into a machine from a vein in the arm and returned into an artery. In the machine, blood is forced to flow next to a Dialysis fluid seperated by a semi-permeable membrane.

This is athe comparison of dialysate (fluid) with blood.

As blood flows against the dialysis fluid, Urea and excess salts Diffuse into the dialysis fluid, leaving the blood clean. The patient has to be connected to the maching for a few hours, several times a week.

Advantages

No immunosupressants, less risk of other infections

Prolongs people's lives

No waiting lists

Disadvantages

Diet has to be restricted

Restricts lifestyle- attached to a machine for 4 hours, 3 times a week.