Homeostasis- The Kidneys Flashcards
What is one of the main functions of the kidneys?
To excrete waste products such as urea
What do the kidneys regulate?
The water potential of the blood
What is ultrafiltration?
As blood passes through capillaries in the cortex of the kidneys, substances are filtered out of the blood and into long tubules that surround the capillaries
What is selective reabsorption?
Useful substances (such as glucose and the right amount of water) are then reabsorbed back into the blood
What happens to the remaining unwanted substances?
They pass along to the bladder and are excreted as urine
What are the nephrons?
Long tubules along with the bundle of capillaries where blood is filtered
How many nephrons are in each kidney?
Around a million
How does blood enter the kidney?
From the renal artery enters smaller arterioles in the cortex of the kidney
What does each arteriole split into?
A structure called a glomerulus
What is a glomerulus?
A bundle of capillaries looped inside a hollow ball called a Bowman’s capsule
Where does ultrafiltration take place?
The glomerulus
What is the afferent arteriole?
The arteriole that takes blood into each glomerulus
What is the efferent arteriole?
The arteriole that takes the filtered blood away from the glomerulus
Why is the blood in the glomerulus under high pressure?
Because the efferent arteriole is smaller in diameter than the afferent arteriole
What does the high pressure mean?
It forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule
What three layers do the liquid and small molecules pass through to get into the Bowman’s capsule and enter the nephron tubules?
The capillary wall, a membrane (basement membrane) and the epithelium of the Bowman’s capsule
Why do larger molecules like proteins and blood cells stay in the blood?
They can’t pass through
What are the substances that enter the Bowman’s capsule known as?
The glomerular filtrate
How does the glomerular filtrate pass out the kidney?
Along the rest of the nephron and useful substances are reabsorbed along the way —> flows through the collecting duct —> passes out of kidney along ureter
When does selective reabsorption take place?
As the glomerular filtrate flows along the proximal convoluted tubule, through the loop of Henle, and along the distal convoluted tubule
What do useful substances do?
They leave the tubules of nephrons and enter the capillary network that’s wrapped around them
Why does the epithelium of the wall of the PCT have microvilli?
To provide a large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood
What happens to useful solutes like glucose?
The are reabsorbed along the PCT by active transport and facilitated diffusion
Why does water enter the blood by osmosis?
Because the water potential of the blood is lower than that of the filtrate- water is reabsorbed from the PCT, loop of Henle, DCT and the collecting duct
What is the filtrate that remains?
Urine which passes along the ureter to the bladder
What is urine usually made up of?
Water and dissolved salts, urea, other substances such as hormones and excess vitamins
What does urine not usually contain?
Proteins and blood cells as they’re too big to be filtered out of the blood, glucose because it’s actively reabsorbed back into the blood
