In this IBDP Biology Blog, we will be looking at how the kidney works, and what functions it carries out, let's go!

Structure of Kidney and Functions

• Blood enters the kidneys via the 

renal artery and exits the kidneys via the renal vein

• Blood is filtered by specialised structures called 

nephrons which produce urine

• The urine is transported from the kidneys via the 

ureter, where it is stored by the bladder prior to excretion

• The kidney contains specialised structures called nephrons which function to filter the blood and 

eliminate wastes

How do the malphigian tubules work? 

• 1. Cells lining the outside of the 
• Malphigian tubules actively transport ions and uric acid from the hemolymph into the tubules' lumens.
• This means that water is drawn out of the 
• hemolymph into the lumens by osmosis.
• 2. The tubules empty into the 

gut.

• 3. In the hindgut water and 

salts are reabsorbed. Nitrogenous waste is excreted within feces.  

Protein, Glucose, Urea in blood, glomerulus

Proteins: Present in blood plasma, but not present in glomerular filtrate or urine. This is because proteins cannot pass across the basement membrane during ultrafiltration and thus cannot form part of the filtrate

Glucose: Present in blood plasma and glomerular filtrate, but not present in urine (normally). This is because the glucose is selectively reabsorbed in the proximal convoluted tubule. It is reabsorbed from the filtrate into the blood by active transport (symport with Na+ ions)

Urea: Present in blood plasma, glomerular filtrate and urine. Only about 50% of urea is reabsorbed (some urea is reabsorbed to help regulate the medullary osmolarity gradient). Because water is reabsorbed from the filtrate (by osmosis, due to the hypertonicity of the medulla), urea becomes more concentrated in urine. The concentration of urea in the urine will depend on the amount of water in the urine.  

Ultrafiltration

In IBDP Biology, we know that ultrafiltration occurs when hydrostatic pressure forces blood through a semi-permeable membrane, separating blood cells and large proteins from the remainder of the serum. Ultrafiltration occurs between the glomerulus and the Bowman's capsule and requires two things to form the filtrate:

Hydrostatic Pressure

The glomerulus increases BP by forming narrow branches (also increases surface area)

• This pressure is maintained by a 
• narrow efferent arteriole, which restricts the outflow of blood 
• The net pressure gradient in the glomerulus forces blood into the 

capsule space

• Basement Membrane (filtration barrier)

The basement membrane is a fine mesh that restricts the passage of blood cells and proteins

• It lies between the glomerulus and Bowman's capsule

Blood can exit the glomerulus directly through pores as the capillaries are fenestrated, and enter Bowman's capsule. 

What happens when blood has a high solute concentr 

• The hypothalamus signals to the
•  pituitary gland to secrete ADH.
• The ADH makes the walls of the 
• distal convoluted tubule and the collecting duct more water permeable.
• All the way down the collecting duct most of the water is reabsorbed via 

osmosis, thanks to the high solute concentration in the medulla.

• A small volume of urine with a high solute concentration is produced.
• The 

solute concentration of the blood is decreased 

Glucose in the urine of diabetic patients 

• The urine of non-diabetic patients should contain no glucose as it is selectively reabsorbed from the filtrate in the 
• proximal convoluted tubule
• Diabetics have higher levels of blood glucose due to either a 
• lack of insulin secretion (type I) or insensitivity to insulin secretions (type II)
• Because of this, not all of the glucose in diabetics is reabsorbed into the 

blood (protein pumps in tubule wall become saturated)

• This results in the presence of glucose in the urine of untreated diabetics, which can be detected using test strips 

That's the main points in the Structure and ultrafilteration of the kidney, good job!

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References:

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2F92183123610101339%2F&psig=AOvVaw160EAU5GWw63cw2QGGFGeF&ust=1625300261365000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCNj-j7r5w_ECFQAAAAAdAAAAABAU

https://ib.bioninja.com.au/higher-level/topic-11-animal-physiology/113-the-kidney-and-osmoregu/kidneys.html

https://www.google.com/url?sa=i&url=http%3A%2F%2Figcse-biology-notes.blogspot.com%2F2017%2F06%2F272-describe-ultrafiltration-in-bowmans.html&psig=AOvVaw0pxDbpmPZOsbPEDC7rty67&ust=1625301544897000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCIDi2p3-w_ECFQAAAAAdAAAAABAD

Drafted by Venetia (Biology)