5 - MZH - Homeostasis 6 - Excretion and the Kidneys Flashcards
Define:
Excretion
Osmoregulation
Excretion = The emilination of metabolic waste including
Osmoregulation = The balancing and control of of the water potential in the blood
What is the approximate human blood pH?
pH = 7.4
Fill in the table and give examples of each
Summarise 2 main functions of the kidneys
- Act as excretory organs - Removes nitrogenous and other waste from the body
- Important role in homeostasis - Helps to regulate blood pH, water and Na+ conc in the blood and tissue fluids
What waste fluid do mammalian kidneys produce?
Urine which is more concentrated than the body fluids
Lable the diagram
Lable the diagram of the kidney
Name the 2 different types of nephron
-
Cortical nephrons
- Allow only minor water conservation
- Used in normal water availabilty conditions
-
Juxtamedullary nephrons
- Allow water conservation
- More present in animals that need to conserve more water
Name a type of animal that has more of:
- Cortical nephrons
- Juxtamedullary nephrons
WHY?
- Beaver, otta or platypus - No problem with having access to frsh water.
- Camel - Need to conserve max volume of water
What is the name of the functional unit of the kidney?
Nephron
What does it mean?
Afferent and efferent?
Afferent = A blood vessle supplying blood to a structure
Efferent = A blood vessle carrying blood away from a structure
Lable the diagram of the nephron
Briefly describe how blood travels through the kidneys
- Blood enters each kidney via the left/right renal arteries that branch into arterioles.
- Each arteriole divides into a knot of capillaries called the glomerulus. Each glomerulus is found in the cup of each renal capsule/Bowman’s capsule.
- Blood leaved the glomerulus into the efferent vessel which is an arteriole and divides into the second capillary network which surrounds the PCT, DCT and loop of Henle.
- Blood from this capillary network then drains into venules and finally into the renal vein.
- Kidney filtrate is formed in the renal capsule and flows down the nephron via the PCT, loop of Henle and DCT and enters the collecting duct which emties it into the pelvis.
What are the 3 main processes that occur in the kidneys?
-
Ultrafiltration - From glomerulus to Renal/Bowman’s capsule
- Water and soluble substances pass from the blood into the lumen of the renal capsule. This becomes the filtrate which is now in the nephron, it contains excretory products & useful products.
-
Selective reabsorption - Mainly PCT
- Useful substances e.g. glucose are reabsorbed into the blood.
-
Concentration - Loop of Henle and collecting duct
- Loop of Henle creates the right conditions in the medulla allowing a conc gradient to occur.
What makes up the renal corpuscle?
Bowman’s capsule and the glomerulus
What is ultrafiltration?
Ultrafiltration = High pressure filtration of blood between the glomerular capillaries and the renal/bowman’s capsule and results in the formation of glomerular filtrate which will pass down the length of the nephron
How is a high pressure created during ultrafiltration? (3)
- High blood pressure in renal arteries
- Narrow glomerular capillaries
- Wider afferent arteriole and narrow efferent arteriole
What are podocytes?
Podocytes = Specialised cells found in the epithelium of the Bowman’s capsule. They’re wrapped around the capillaries
Ultrafiltration:
What step is this in the process?
Describe the process
What does the filtrate contain? (7)
What remains in the blood and why? (2)
- It’s the 1st step
- The high pressure in the glomerulus results in a high hydrostatic pressure which forces water and solutes from the blood plasma into the renal capsule forming filtrate.
- Filtrate consists of:
- Dissolved ions
- Glucose
- Vitamins
- Amino acids
- Fatty acids
- Glycerol
- Urea
- Blood cells and plasma proteins are too large to be filters so they remain in the blood.
What layers are there to the filtration barrier in ultrafiltration? (3)
There’s 3 layers:
-
Endothelium of capillary
- Pores allow fluid passage but hinder blood cells
-
Basement membrane is the actual filter
- Made of a mesh of collagen fibres
- Blocks molecules > Mr 69,000
- Large proteins blocked due to size & repelled by negative charges on callagen
-
Epithelium of renal capsule
- Contains podocytes
- Filtration slits allow passage of fluid into filtrate
What step occurs right after ultrafiltration?
What is it’s purpose?
Where does this occur in the kidney?
- Selective reabsorbtion occurs after ultrafiltration.
- It retunrs the useful substances from the filtrate back into the blood.
- It occurs mainly in hte PCT (proximal convoluted tubule)
Selective reabsorbtion:
Where does it occur? What particular about the structure of this location and how is it adapted to carry out this process? (6)
Mainly in the PCT. The PCT is composed of a single layer of epithelial cells.
- Large SA - Relatively long PCT. Microvilli on tubule cells also increase SA.
- Convolutions - Slows down flow rate, more time for reabsorbtion.
- Maintain conc gradient - Many blood capillaries close to the tubule.
- Short distance between filtrate and blood.
- Many mitochondria - Produce ATP for active transport.
- Specific carrier/ transport proteins in the cell membranes.
Describe how selective reabsorbtion happens
- Na+/K+ pump in the proximal tubule cell membrane uses ATP made by the mitochondria. As ATP is being used K+ ions are pumped into the cell and Na+ ions out to increase the K+ ions conc and reduce the Na+ ions conc inside the cell.
- Na+ ions actively transported into the basal channels but they can only be transported if they are paired up with a glucose molecule. Simultaneously glucose can enter the cell via a symport protein.
- Glucose leaves the cell by facilitated diffusion
Cotransporter proteins and their role in selective reabsorbtion?
In this case it’s when Na+ ions are holding onto something else e.g. glucose. Unless it’s paired with a glucose moelcule it can not be transported by that cotransporter protein.
Different cotransporters bring about the reabsorbtion of all the other substances that need to be removed from the filtrate as well.
What happens to these substances in the selective reabsorbtion stage?
- Glucose
- Water
- Urea
- Small proteins
- Glucose - Filtrate → Epithelium → Basal Channels → Blood
- Water - Continuous solute removal to blood maintains a water potential gradient for reabsorbtion of water into blood by osmosis
- Urea - Up to 50% is unfortunately reabsorbed by diffusion
- Small proteins - Uptake by pinocytosis & lysosomes liberates amino acids. Amino acids used by cell or enter the same pathway as glucose: Filtrate → Epithelium → Basal Channels → Blood