Chapter 16 Part 1 - The Kidneys Flashcards
What do the kidneys do?
Excrete waste products (such as urea) and regulate blood water potential of the blood.
What happens as blood passes through the capillaries in the cortex (outer layer) of the kidneys?
Substances are filtered out of the blood and into long tubules that surround the capillaries - ultrafiltration.
What happens to useful substances after ultrafiltration?
Selective reabsorption of useful substances such as glucose and the right amount of water back into the blood.
What happens to the remaining unwanted substances after ultrafiltration?
They pass along to the bladder and are excreted as urine.
Where are the kidneys?
At the back of the abdominal cavity, 1 on each side of the spinal cord.
How many kidneys do we have?
2
What is a nephron?
Functional unit of the kidney - the long tubules along with the bundle of capillaries where the blood is filtered.
What are the long tubules along with the bundle of capillaries where the blood is filtered called?
Nephrons.
How many nephrons are there in each kidney?
Around 1 million in each kidney.
Fibrous capsule
Outer membrane protecting the kidney.
Cortex
Lighter coloured outer region made up of renal (Bowman’s) capsule, convoluted tubules and blood vessels.
Medulla
Darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels.
Renal pelvis
A funnel shaped cavity that collects urine into the ureter.
Ureter
A tube that carries urine to the bladder.
Renal artery
Supplies the kidney with blood from the heart via the aorta.
Renal vein
Returns blood to the heart, via the vena cava.
Describe the structure of a nephron
A narrow tube up to 14mm long, closed at 1 end with 2 twisted regions separated by a long hairpin loop.
What is each nephron made up of?
- Renal (Bowman’s) capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
What are the blood vessels associated with each nephron?
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Blood capillaries
Renal (Bowman’s) capsule
- The closed end at the start of the nephron.
- Cup-shaped.
- Surrounds a mass of blood capillaries (the glomerulus).
- Inner layer of renal capsule is made up of specialised cells called podocytes.
Proximal convoluted tubule
- Series of loops surrounded by blood capillaries.
- Its walls are made up of epithelial cells which have microvilli.
Loop of Henle
- Long, hairpin loop extending from the cortex into the medulla and back again.
- Surrounded by blood capillaries.
Distal convoluted tubule
- Series of loops surrounded by blood capillaries.
- Walls made of epithelial cells, but it is surrounded by fewer capillaries than the proximal convoluted tubule.
Collecting duct
- Tube into which a number of distal convoluted tubules from a number of nephrons empty.
- Lined by epithelial cells.
- Becomes increasingly wide as it empties into the pelvis of the kidney.
Afferent arteriole
- Tiny.
- Arises from renal artery.
- Supplies nephron with blood.
- Enters the renal capsule of the nephron where it forms the glomerulus.
Glomerulus
- A many-branched knot of capillaries from which fluid is forced out of the blood.
- The glomerular capillaries recombine to form the efferent arteriole.
Efferent arteriole
- Tiny.
- Leaves renal capsule.
- Smaller diameter than afferent arteriole so causes an increase in blood pressure within the glomerulus.
- Carries blood away from renal capsule and later branches to form the blood capillaries.
Blood capillaries
- A concentrated network of capillaries that surrounds the proximal convoluted tubule, loop of Henle and the distal convoluted tubule and from where they reabsorb mineral salts, glucose and water.
- They merge together into venules that in turn merge to form the renal vein.
Where in the nephron is blood filtered?
At the start
Explain the process of ultrafiltration
1) Blood from renal artery enters smaller arterioles in the cortex of the kidney.
2) Each arteriole splits into a glomerulus.
3) This is where ultrafiltration takes place.
4) The afferent arteriole that takes blood into each glomerulus and the efferent arteriole takes the filtered blood away from the glomerulus.
5) The efferent arteriole is smaller in diameter than the afferent arteriole, so blood in the glomerulus is under high pressure.
6) The high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule.
7) The liquid and small molecules pass through three layers (the glomerular capillary endothelium, basement membrane and the epithelium of the Bowman’s capsule) to get into the Bowman’s capsule and enter the nephron tubules.
8) Larger molecules like proteins and blood cells can’t pass through, so stay in the blood. The substances that enter the Bowman’s capsule are known as the glomerular filtrate.
9) The glomerular filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way.
10) Finally, the filtrate flows through the collecting duct and passes out of the kidney along the ureter.
Where does blood go from the renal artery?
Arterioles in the cortex of the kidney.
What does each arteriole split into?
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?
Glomerulus.
What is the arteriole that takes blood into each glomerulus called?
Afferent arteriole
What is the arteriole that takes blood away from each glomerulus called?
Efferent arteriole
Which arteriole (afferent or efferent) is smaller in diameter?
Efferent
What does it mean as a result of the efferent arteriole having a smaller diameter than the afferent arteriole?
Means that blood in the glomerulus is under high pressure.
What does the high pressure of blood in the glomerulus do?
Forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule.
What does the liquid/small molecules that are forced out of the blood pass through to get into the Bowman’s capsule and enter the nephron tubules?
3 layers - the glomerular capillary endothelium, basement membrane and the epithelium of the Bowman’s capsule.
What are the 3 layers that need to be passed for filtration?
- Glomerular capillary endothelium
- Basement membrane
- Bowman’s (renal) capsule epithelium
Excretion
Removes waste products from metabolism (urea and creatinine).
Ultrafiltration
Blood is filtered at the glomerulus and passes into the renal capsule (only small components are filtered).
Selective reabsorption
Useful components of blood are reabsorbed, leaving behind waste products to be filtered.
Filtrate
Contents of the proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.
What does DCT stand for?
Distal convoluted tubule
What does PCT stand for?
Proximal convoluted tubule
What is a shorter way of writing distal convoluted tubule?
DCT
What is a shorter way of writing proximal convoluted tubule?
PCT
Explain how ultrafiltration occurs in terms of the pressure changes involved
- High pressure is created in the glomerulus and forces water and small molecule to be filtered out of the blood and into the renal capsule.
- High pressure is created as the diameter of the efferent arteriole is smaller than the diameter of the afferent arteriole.
- Also, coiling of the capillaries in the glomerulus further restricts blood flow so pressure increases.
What is the solute potential like in the glomerulus?
Low solute potential
Why is there low solute potential in the glomerulus?
Water is lost and plasma proteins stay behind.
What is the water potential like in the glomerulus?
HIgh water potential.
What is the pressure potential like in the glomerulus?
High pressure potential.
What is the solute potential like in the renal capsule?
High solute potential.
Why is there high solute potential in the renal capsule?
No plasma proteins.
What is another name for the renal capsule?
Bowman’s capsule.
What is another name for the Bowman’s capsule?
Renal capsule.
What is the pressure potential like in the renal capsule?
Relatively high pressure potential.
Why is the pressure potential relatively high in the renal capsule?
Because of all the fluid.
What is the water potential like in the renal capsule?
High water potential.
What does high pressure in the glomerulus do?
Forces the water and small components of blood to move from the glomerulus into the renal capsule.
What is the equation for water potential?
Water potential = Pressure potential + Solute potential
What does the glomerular capillary endothelium have?
Pores (fenestrations).
What does the basement membrane act as?
An effective filter.
What does the renal capsule epithelium have?
Podocytes that have large filtration slits.
Why can’t large molecules pass through into the Bowman’s capsule?
They are too large to pass through the basement membrane.
What can’t pass through the basement membrane?
Larger molecules like proteins and blood cells.
What are the substances that enter the Bowman’s capsule known as?
The glomerular filtrate.
Where are useful substances reabsorbed?
Along the nephron.
When does selective reabsorption take place?
As the glomerular filtrate flows along the PCT, through the loop of Henle, and along the DCT.
Where do useful substances move from and to?
Leave the tubules of the nephrons and enter the capillary network that’s wrapped around them.
What does the epithelium of the PCT have and why is this beneficial?
Has microvilli to provide a large SA for the reabsorption of useful materials from the glomerular filtrate (in the tubules) into the blood (in the capillaries).
Give an example of a useful solute
Glucose
Where are useful solutes like glucose reabsorbed and how?
Along the PCT by active transport and facilitated diffusion.
How does water enter the blood and why?
By osmosis because the water potential of the blood is lower than that of the filtrate.
Where is water reabsorbed from?
The PCT, loop of Henle, DCT and the collecting duct.
What is the filtrate that remains after selective reabsorption called?
Urine.
What happens to the filtrate that remains after selective reabsorption?
This is urine - it passes along the ureter to the bladder.
What is water potential?
The tendency of water to move from one area to another. Water will move from and area of higher water potential to an area of lower water potential - it moves down the water potential gradient.
What is urine usually made up of?
- Water and dissolved salts.
- Urea.
- Other substances such as hormones and excess vitamins.
What doesn’t urine contain?
- Proteins and blood cells - they’re too big to be filtered out of the blood.
- Glucose because it’s actively reabsorbed back into the blood.
Why doesn’t urine contain proteins and blood cells?
They’re too big to be filtered out (too large to cross the basement membrane).
Why doesn’t urine contain glucose?
It is actively reabsorbed back into the blood.
What does the volume of water in urine vary depending on?
How much you’ve drunk.
How much filtrate is reabsorbed in the PCT?
85% of filtrate.
What is the loop of Henle involved in in selective reabsorption?
Allows water to be reabsorbed from the collecting duct.
What is the DCT involved in in selective reabsorption?
Make final adjustments and where toxic substances can be secreted into filtrate.
Water reabsorption.
What is the collecting duct involved in in selective reabsorption?
Water reabsorption.
How is urine produced?
Ultrafiltration - Blood is filtered at the glomerulus and passes into the renal capsule (only small components are filtered).
Selective reabsorption - Useful components of blood are reabsorbed, leaving behind waste products to be filtered.
Filtrate - Contents of the proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.
What is reabsorbed in the PCT
Water, ions, glucose, amino acids, small proteins, urea.
By what process is urea reabsorbed in the PCT?
Passively - due to the absorption of water.
By what process are ions, glucose and amino acids reabsorbed in the PCT?
Active transport
By what process is water reabsorbed in the PCT?
Osmosis
What are adaptations of the PCT?
Microvilli, infoldings and mitochondria.
Explain the process of co-transport in reabsorption in the PCT
1) Sodium ions actively transported from PCT cells into blood. The blood carries sodium ions away.
2) Sodium ions diffuse into the PCT cells from the lumen of the PCT by facilitated diffusion.
3) Another molecule is carried with the sodium ions (glucose, or amino acids or chloride ions, etc).
4) The molecules then diffuse from the PCT into the blood.
What is the composition of filtrate at the end of the PCT like?
- 65% of water and ions have been reabsorbed.
- 100% of glucose and amino acids have been reabsorbed.
- Urea isn’t selectively reabsorbed but some urea will be reabsorbed passively by diffusion due to the loss of water.
- Concentration of urea increases.
What is the role of the loop of Henle in reabsorption?
Make medulla concentrated with ions, lowering the water potential and promoting the reabsorption of water by osmosis in the collecting duct.
What are the key features of the loop of Henle?
Descending limb = Permeable to water
Ascending limb = Impermeable to water
What happens in the descending limb of the loop of Henle?
Water leaves filtrate (reabsorbed), Sodium ions enter filtrate.
What happens in the ascending limb of the loop of Henle?
Sodium ions leave filtrate.
What happens in the collecting duct?
Water leaves filtrate (reabsorbed).
When in terms of its contents is the filtrate the most concentrated?
When there are the most ions present and the least water present (water potential is the lowest).
What is the water potential like at the start of the loop of Henle and why?
High as all the glucose and amino acids were reabsorbed in the PCT.
What is the water potential like at the end of the loop of Henle?
Lower
At what point of the loop of Henle is water potential the highest?
At the start
At what point of the loop of Henle is water potential the lowest?
At the end
