Homeostasis- Kidneys Flashcards
(47 cards)
What are the kidneys homeostatic roles?
1) Excretion of metabolic waste chemicals
2) Osmoregulation
3) Water balance
4) Blood pH
What are the features of the kidney?
- Two reddish brown, bean shaped organs
- Located at rear of abdominal cavity
- Have a very good blood supply
- Receive blood from paired renal arteries and blood exits into paired renal veins
- Each kidney attached to a ureter that carries excreted urine to the bladder
Gross anatomy of kidneys:
1) CAPSULE
- tough, fibrous covering that is covered by fat to provide protection
2) CORTEX
- dark outer layer
- filtering of blood takes place here
- glomerulus, bowman’s capsule, and convoluted tubules located here, lots of capillaries
3) MEDULLA
- lighter in colour, inner layer
- collecting ducts and Loops of Henle located here
4) PELVIS
- central chamber that the collecting ducts drain into
- connected to ureter
Blood supply to kidneys:
1) RENAL ARTERIES
- branch directly from aorta
- carry oxygenated blood to kidneys
2) RENAL VEINS
- drain blood from the kidneys into inferior vena cava
What is a nephron?
Microscopic and functional unit of kidney
What components make up the nephron?
1) Glomerulus
2) Bowman’s Capsule
3) Proximal Convoluted Tubule
4) Loop of Henle
5) Distal Convoluted Tubule
6) Collecting Duct
What parts of the nephron are located in the Medulla vs Cortex?
CORTEX -Glomerulus -Bowman's Capsule -Proximal Convoluted Tubule -Distal Convoluted Tubule MEDULLA -Loop of Henle -Collecting Duct
What is ultrafiltration?
Filtration on a microscopic scale
How does ultrafiltration occur in Bowman’s Capsule?
1) Small molecules and ions are filtered out of the blood and pass into the lumen of Bowman’s Capsule, forming glomerular filtrate
2) Cells that make up capillary walls of glomerulus are leaky because they have fenestrations, so mass flow of plasma occurs
3) Plasma passes through basement membrane that has a filtering function
4) Inner wall of Bowman’s Capsule made from PODOCYTES that have a filtering function because they create filtration slits
This is a triple filter process
How do podocytes have a filtering function?
- Podocytes have extensions called pedicels that wrap around glomerular capillaries
- Pedicels form filtration slits between them
- Filtration slits stop blood cells and large plasma proteins, such as albumin leaving the blood plasma
- Fluid that reaches inside of Bowman’s Capsule contains almost same substances as in blood and at almost the same concentrations
- Main substances are urea, glucose and salt as Na+ and Cl-
- Fluid called glomerular filtrate
What are the main functions of the nephrons after Bowman’s Capsule?
- Selective reabsorption
- Producing urine
- Osmoregulation
Where does selective reabsorption occur?
- Both convoluted tubules
- Loop of Henle
- Collecting Duct
Selective reabsorption in Proximal Convoluted Tubule:
1) All glucose, amino acids, vitamins and hormones are selectively reabsorbed by active transport from the glomerular filtrate in the blood
2) A large proportion of sodium ions are selectively reabsorbed by active transport
3) A large proportion of chloride ions are selectively reabsorbed by diffusion
4) A large proportion of water molecules are selectively reabsorbed by osmosis
5) By end of proximal convoluted tubule, 80% of volume of glomerular filtrate has been selectively reabsorbed into the blood
Why is the proximal convoluted tubule longer than the distal?
Because majority of the volume of the glomerular filtrate (80%) is selectively reabsorbed into the blood and therefore more time is needed, hence its longer
What are the two function of the Loop of Henle?
1) Creates a high concentration gradient of sodium and chloride ions in the tissue fluid that is in between the cells of the medulla
2) Allows mammals to produce urine that is more concentrated than their blood
What are the adaptations of the Loop of Henle?
1) Descending limb is permeable to water but relatively impermeable to sodium and chloride ions
2) Ascending limb is permeable to sodium and chloride ions but relatively impermeable to water
This means that as loop descends into the medulla, the tissue fluid becomes more salty (lower water potential)
3) Blood vessels that surround loop have a blood flow that is in the opposite direction to the filtrate flow in both limb, allowing counter-current exchange
Hypertonic definition:
A solution outside the cell with a lower water potential compared to the inside of the cell
Isotonic definition:
A solution outside the cells with the same water potential as the solution inside the cell
Hypotonic definition:
A solution outside the cell with a higher water potential compared to the inside of the cell
Ascending Limb of the Loop of Henle:
- In lower part of ascending limb, sodium and chloride ions move from the filtrate into the tissue fluid of the medulla by diffusion
- In the upper part of the ascending limb, sodium and chloride ions are pumped from the filtrate into the tissue fluid of the medulla by active transport
- Ascending limb is impermeable to water, so water cannot move from filtrate into tissue fluid by osmosis
- A high concentration and a concentration gradient of sodium and chloride ions is produced in the tissue fluid of the medulla
- Dilute filtrate is produced at the top of the ascending limb as is hypotonic to the blood plasma
Descending Limb of the Loop of Henle:
- Filtrate entering descending limb is isotonic to the blood plasma
- Water moves out of the filtrate into the tissue fluid around the medulla cells by diffusion
- Happens because ascending limb has created a high concentration of sodium and chloride ions in medulla’s tissue fluid
- Water in tissue fluid then diffused back into the blood plasma in the vasa recta
- Descending limb impermeable to sodium and chloride ions so that they do not diffuse back into the filtrate
- Filtrate at the bend is hypertonic to blood plasma
Selective reabsorption in Distal Convoluted Tubule:
1) Water balance of blood plasma regulated in distal convoluted tubule
2) Dilute filtrate produced at top of ascending limb of Loop of Henle
3) Filtrate has lower water potential than blood plasma
4) Water permeability of cells that make up distal convoluted tubule controlled by ADH
5) More or less water leaves filtrate and enters blood plasma by diffusion
6) If blood plasma has too little sodium and chloride ions then they are pumped by active transport into tissue fluid so that they diffuse into blood
7) Blood pH also regulated here
Selective reabsorption in the Collecting Duct:
1) Main part of creating volume and concentration of urine happens here
2) As urine flows through collecting duct, water leaves urine and moves into tissue fluid of medulla by diffusion, then back into blood plasma
3) This produces urine that is either:
- Hypertonic (concentrated) when body needs to reduce water loss
- Hypotonic (dilute) when body needs to increase water loss
4) Permeability of walls to water controlled by ADH
What is the vasa recta?
- Straight arterioles and straight venules of the kidney
- Capillaries connect the arteriole to the venule
- Lie parallel to the loop of Henle
- Counter current flow arrangement so substances can diffuse into blood plasma
