Functions of the Kidneys & the Nephron: Extended

 

What Are the Kidneys?

• Your kidneys are two bean-shaped organs located in your lower back.
• They act as filters, cleaning your blood and removing waste products like urea, excess water, and ions, which are excreted as urine.

Part	Role
Cortex	Outer part of the kidney where filtration happens.
Medulla	Inner part of the kidney containing the nephrons and collecting ducts.
Nephron	The functional unit of the kidney that filters blood and forms urine.

 

Overview of Kidneys functions

 

Function	What Happens
Ultrafiltration	Removes waste products like urea, excess water, and ions from the blood.
Selecctive Reabsorption	Takes back useful substances like glucose, some water, and ions into the blood.
Urine Formation	Produces urine from waste products and excess substances.

 

 

The Nephron 

• The kidneys contain millions of small nephrons. These also can be called renal tubules or kidney tubules.
• These nephrons are located inbetween the cortex and medulla in the kidney. They start at the cortex, loop into the medulla and return back to the cortex.
• What the nephrons have collected is drained into the most inner part of the kidneys where the urine collects to flow through the ureter and bladder

 

Part of the Nephron	Role
Glomerulus	Filters water, glucose, urea, and ions from the blood.
Proximal Tubule	Reabsorbs all glucose, some ions, and most water back into the blood.
Loop of Henle	Concentrates the urine by reabsorbing water and ions.
Collecting Duct	Final site where urine is formed and transported to the ureter.

 

A: Ultrafiltration

 

 

• Bowman's capsule contains many capillaries twisted together. These twisted capillaries are the glomerulus.
• The capillaries get more narrow as they get closer to the bowmans capsule. This increases the blood pressure and also forces the small molecules in the blood to move from the blood into the bowman's capsule. 
• This forms the filtrate. This process is called ultrafiltration.
• Water, urea, glucose and ions are forced out of the capillaries and can be reabsorbed into the blood if needed

 

 

B: Selective Reabsorption

 

 

• Glucose is reabsorbed by active transport in the proximal convoluted tubule.
• Active transport requires energy, due to this there are a lot of mitochondria in the nephron.
• Due to the energy required for active transport reabsorbtion can only take place  in the proximal convoluted tubule in the nephron.
• People with diabetese are not able to regulate their blood glucose. So in a normal person reabsorbtion would absorb all the glucose, someone with diabetes are not able to.
• This causes the glucose to not be filtered out and continue to the filtrate and end up in the urine

 

Summary of the Journey of Blood Through the Kidneys

1. Blood Enters Through the Renal Artery:

   • Blood carrying waste products flows into the kidney.

2. Filtration in the Glomerulus:

   • Water, glucose, urea, and ions are filtered out of the blood into the nephron.

3. Reabsorption in the Nephron:

   • Useful substances like glucose, some ions, and most water are reabsorbed back into the blood.

4. Urine Formation in the Collecting Duct:

   • The remaining waste (urea, excess water, and ions) forms urine.

5. Urine Leaves Through the Ureter:

   • Urine is transported to the bladder, where it’s stored before being excreted.

 

 

Key Substances in Urine

Substance	Why It’s There
Urea	Waste from the breakdown of excess amino acids in the liver.
Excess Water	Removes extra water to maintain body balance.
Excess Ions	Removes surplus salts to maintain the right concentration in the blood.