Kidney in Detail

Standard Grade Biology

Excretion by the Kidney

• Urea

-nitrogenous waste

-made by liver

-excess amino acids in blood

-toxic

• Why must nitrogenous waste be excreted?

1 – Filtration by the Kidney

Renal artery

Ureter

Renal vein

•Supplied with blood from renal artery

•Inside it splits into many fine capillaries

•Each capillary supplies blood to hundreds of thousands of tiny filtration units called nephrons

Lets have a look at a nephron!!!

1. Glomerulus brings a large surface area of blood capillaries in close contact with Bowman’s capsule

2. Liquid filtered from blood under pressure (filtration)

3. Glomerular filtrate produced containing:-water-glucose-salts-urea

(Protein molecules and red bloodcells do not pass into tubule asthey are TOO BIG!!!!)

Blood from renal artery enters wide capillary

Blood travels through narrow capillary towards renal vein

Glomerular filtrate

Filtration

Think…

• Which feature of the glomerulus helps the process of filtration?

• Which 4 components of unfiltered blood appear in the glomerular filtrate?

• Why do blood cells and protein molecules not appear in the glomerular filtrate?

Key Words!!

Nephron: structure in the kidney that acts as a microscopic filtration unit

Glomerulus: dense mass of very fine blood capillaries at the nephron that act as a filter

Bowman’s capusle: cup-shaped part of the nephron that holds a glomerulus and collects the products of filtration from it

Glomerular filtrate: liquid removed from the blood by filtration in the kidney

2 – Reabsorption by the Kidney

• Once the main components of glomerulur filtrate enter the bloodstream

-they are no longer in bloodstream

• If nothing more happened in the nephron then all the useful stuff would be lost in the urine!

• Therefore, glucose, water and some salts need to be reabsorbed!

Glucose reabsorbed

Variable amounts of water and salts reabsorbed and filtrate gradually turning into urine

More water reabsorbed

Final urine containing:

-excess water

-unneeded salts

-waste urea

Think….

• Which three components of the glomerular filtrate are reabsorbed?

• Why is it important for these to be reabsorbed?

• Which substances are present in the final urine?

• Summary of kidney function

2 – Controlling Water Concentration

• Blood-important part of internal environment-constantly changing water concentration-e.g. exercising

drinking lots of water

• The body uses negative feedback control to regulate water content of the blood

How does it work?

• Control of Water animation

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