Lecture 21: The Mammalian Kidney Flashcards
What are the 4 structures of the mammalian excretory system?
- Kidneys (2)
- Ureter (2)
- Urinary bladder
- Urethra
Describe kidneys, state their 3 main functions?
kidney shaped organs near back that have 3 main functions:
- Excretion
- Osmoregulation
- Homeostasis
Describe excretion
1 of 3 main kidney functions
the disposal of nitrogenous waste (ex. urea in mammals) and toxins in the blood that need to be filtered out
Describe osmoregulation
1 of 3 main kidney functions
regulates the loss of water and the reabsorption of essential molecules
Describe homeostasis
regulates blood pH through balancing H+ and bicarbonate (HCO3-) molecules
Describe nephrons and their function. What are the 2 kinds of nephrons?
Nephrons are the excretory/functional units of the kidney. They filter blood and produce urine and they are the location of where substances are secreted out of or absorbed back into the blood
There are 2 kinds:
- cortical nephrons
- Juxtammedullary nephrons
Describe cortical nephrons and juxtamedullary nephrons and state the difference
CORTICAL NEPHRONS:
- include most nephrons
- located mostly in the RENAL CORTEX (partly extend into the medulla)
JUXTAMEDULLARY NEPHRONS:
- less common
- lengthier tubules that extend deep into the medulla
What are the 3 processes (in order) that result in the production of urine?
- filtration
- secretion
- reabsorption
Describe the process of FILTRATION in terms of urine production and in which structures does this step occur?
The initial filtration is a rough filtering of the blood to remove molecules of a small size (toxins and urea are small molecules). This filtering can also remove some useful molecules because it is based solely on SIZE.
In the ARTERIOLE (moves blood away from heart), there are useful and harmful molecules
There must be a filter to remove harmful molecules into the EXCRETORY TUBULES (one of the tubules that makes up a nephron)
Filtration occurs in the BOWMAN’S CAPSULE and GLOMERULUS
Describe the process of SECRETION in terms of urine production and in which structures does this step occur?
Secretion is the removal of harmful ions like hydrogen and NH3 and other toxins from the blood stream –> interstitial fluid —> proximal tube.
this occurs at the proximal tube and again at the distal tubule
Describe the process of REABSORPTION in terms of urine production and in which structures does this step occur?
Reabsorption is the process of bringing back the useful ions (water, glucose, Na, Cl) that were lost during filtration to the blood stream.
from the proximal tubule –> interstitial fluid —> capillaries/blood stream
this occurs at the proximal tubule and again at the distal tubule
How does the structure of the juxtamedullary nephrons relate to an organism’s environment? discuss desert, aquatic, and moist terrestrial environments/organisms.
Desert mammals: have longer (JN) loops of Henle to allow for more water reabsorption and the production of more concentrated urine –> less water loss!
Fresh water mammals: have short loops to allow for less opportunity of water reabsorption and to produce diluted urine
Moist terrestrial mammals: intermediate length loops to balance it
How are substances moved in the nephron and between the nephron, interstitial fluid, and blood?
Substances are transferred between the tubules of the nephron, the interstitial fluid, and the blood
How are capillaries related to the nephron?
certain parts of the nephron are always in close contact with capillaries because these are the exchange sites for toxins/harmful molecules and useful molecules and water
- substances regulated by the nephrons circulate in the blood
- toxins in blood and waste products are removed from the blood by nephrons
- water and useful ions are reabsorbed from the nephron into the blood
Describe interstitial fluid in a closed circulatory system
fluid that bathes body cells, organs, and tissues and acts as an intermediary between capillaries and, in an excretory system, the secretory tubules of the nephrons
Describe interstitial fluid in a closed circulatory system
fluid that bathes body cells, organs, and tissues and acts as an intermediary between capillaries and, in an excretory system, the secretory tubules of the nephrons
T or F: Capillaries are always surrounding the tubules of the nephron. Why/why not?
TRUE because that is how exchange happens between the blood and the nephron via the interstitial fluid
T or F: Capillaries are always surrounding the tubules of the nephron. Why/why not?
TRUE because that is how exchange happens between the blood and the nephron via the interstitial fluid
List the molecules our bodies want to keep or reabsorb
- water
- glucose
- NaCl (dissociated as Na and Cl)
- proteins
- blood cells
List the molecules our bodies need to get rid of
- urea
- any other toxins
T or F: the main function of nephrons is to retain/reabsorb useful molecules (like water, glucose, proteins, etc.) and discard harmful molecules (urea, toxins)?
TRUE. the main purpose is to regulate water loss, retain useful ions and get rid of harmful toxins
T or F: the initial filtration step of the nephron will get rid of only the harmful molecules and allow all the useful ones to stay in the arteriole. why/why not?
FALSE. the initial filtration step filters out molecules of a certain size, the harmful ones happen to be small and most will filter out (NOT ALL), but some useful molecules are small too and will be filtered out too
Describe the Bowman’s Capsule and it’s functions and location in the nephron
The Bowman’s Capsule is the first part of the nephron, where blood enters. It is a cup-shaped, blind end of the tubule
- Blood is forced into a ball of capillaries called the GLOMERULUS where blood enters under PRESSURE.
- The pressure in the glomerulus pushes the small molecules out of the walls of the capillary
- The small molecules enter the filtrate through the Bowman’s capsule
Describe glomerulus
A ball of capillaries in the Bowman’s Capsule where blood enters
Describe glomerulus
A ball of capillaries in the Bowman’s Capsule where blood enters
What occurs in the Bowman’s capsule?
FILTRATION!
Most small molecules are removed from the capillaries and enter the filtrate tubule
All of the larger molecules (proteins, blood cells, etc) are retained in the arteriole and continue cycling in the blood stream
What occurs in the Bowman’s capsule?
FILTRATION!
Most small molecules are removed from the capillaries of the glomerulus and enter the filtrate tubule
All of the larger molecules (proteins, blood cells, etc) are retained in the arteriole and continue cycling in the blood stream
What occurs in the Bowman’s capsule?
FILTRATION!
Most small molecules are removed from the capillaries of the glomerulus and enter the filtrate tubule
All of the larger molecules (proteins, blood cells, etc) are retained in the arteriole and continue cycling in the blood stream
What processes occur after filtration?
secretion and reabsorption
Which important process occurs at the proximal tubule and where is it located within the nephron?
the second part of the nephron (in proximity to the Bowman’s capsule)
the proximal tubule now contains some of the useful ions and water that was lost during filtration and this is where the REABSORPTION of Na+, Cl-, water, bicarbonate (HCO3-) and important nutrients like glucose occurs.
Water moves with Na and Cl because of osmosis
Which 2 important processes occurs at the proximal tubule and where is it located within the nephron?
the second part of the nephron (in proximity to the Bowman’s capsule)
- the proximal tubule now contains some of the useful ions and water that was lost during filtration and this is where the (1) REABSORPTION of Na+, Cl-, water, bicarbonate (HCO3-) and important nutrients like glucose occurs.
(Water moves passively with Na and Cl because of osmosis) - some of the harmful toxins such as H+, NH3, and other toxins were not filtered out of the bloodstream initially and are now get (2) SECRETED from the blood through the interstitial fluid and into the PROXIMAL TUBULE
Reabsorption is the process of useful ions and water moving from ___ –> ____ –> ____
from the proximal tubule to the interstitial process to be replaced in the blood stream via the capillaries that surround the nephron
What function does reabsorbing bicarbonate (HCO3-) have for the blood?
Bicarbonate balances the pH of the blood in the capillaries
Secretion is the process of harmful toxins and ions moving from ____ –> ____ –> ____
from the BLOOD –> interstitial fluid —> proximal tubule
T or F: anything that remains in the proximal tubule (that doesn’t get reabsorbed or is transported into the proximal tubule) is going to be excreted from the body with/as urine
TRUE. the proximal tubule continues to the next parts of the nephron
Describe the DESCENDING LIMB OF THE LOOP OF HENLE
the third section of a nephron tubule that is permeable only to water and NOT NaCl.
Why is the descending limb of the loop of Henle permeable to water and not NaCl?
Because it has lots of AQUAPORINS (transport proteins that move water molecules quickly across membranes) and NO transport molecules for Na and Cl
Where will the water go if the body is trying to reabsorb it and not lose it in the urine? Which part of the nephron does it do this?
This occurs in the descending limb of the loop of Henle.
water moves to the interstitial fluid between the nephrons and capillaries via OSMOSIS and then diffuses into the surrounding capillaries
In the descending limb of the loop of Henle, the salt concentration at the bottom of the loop will be HIGHER or LOWER than the concentration at the top? why?
HIGHER because water is diffusing out of the descending limb, so there will be less water at the bottom of the loop, leaving behind a high concentration of Na and Cl.
What property should the interstitial fluid have to allow water to passively transport out of the entire length of the descending limb?
Water is moving by osmosis, which means there has to be a solute concentration gradient that has a higher concentration on the outside (interstitial fluid) than on the inside of the descending limb.
this means the Na and Cl concentration of the interstitial fluid increases from the cortex to the medulla (i.e. there is a high solute concentration in the renal medulla to allow water to continue coming out of the limb)
T or F: there are two distinct parts of the ascending limb of the loop of Henle
True.
Describe the 1st part of the ASCENDING limb of the loop of Henle. What process occurs here?
this is the fourth section of the nephron tubule, immediately following the descending limb. the first part of the ascending limb is the lower portion.
this part of the loop is NOT permeable to water, but it is permeable to Na and Cl.
Na and Cl ions move out of the lower part of the ascending limb by FACILITATED DIFFUSION due to the interstitial fluid have a lower solute concentration than the limb
The filtrate entering the ascending limb has a HIGHER or LOWER salt concentration than the interstitial fluid? why?
HIGHER because all the water has moved out of the descending limb so all that is left is Na and Cl
Why do Na and Cl move out of the lower portion of the ascending limb by facilitated diffusion?
because the interstitial fluid has a lower solute concentration (and solutes move from high –> low) than in the limb and facilitated diffusion is passive!
Describe the 2nd part of the ascending limb, where it is located, and what occurs here
The ascending limb is the 4th structure of a nephron. this second part is the top of the limb where it curves over.
Still not permeable to water, still permeable to Na and Cl
filtrate becomes less concentrated as it moves up the limb because Na and Cl have been diffusing into the interstitial fluid
in the second part of the ascending limb, Na and Cl ions move out by ACTIVE TRANSPORT because the interstitial fluid has become higher in solute concentration so they must go against their gradient.
the transport of Na and Cl out of the AL maintains the concentration gradient in the interstitial fluid.
Describe the distal tubule, where it is located, and what occurs here
5th section of the nephron, immediately following the ascending limb
*can remember distal –> DIST (distance from the bowman’s capsule).
- more REABSORPTION of water, sodium, chloride, and bicarbonate occurs here from the proximal tubule to the interstitial fluid
- more SECRETION of other unneeded ions like Potassium and Hydrogen occurs here
What does the reabsorption of bicarbonate and the secretion of hydrogen ions do for the blood stream?
helps balance the pH of the blood
Describe the steps that occur in the collecting duct and its location
The collecting duct is the final section of the nephron where…
- Na and Cl are actively transported from collecting duct to the interstitial fluid (to maintain concentration gradient)
- water follows NaCl into interstitial fluid as it nears the renal pelvis
- urine concentrates as water leaves the duct
**this is the big opportunity for the nephron to reclaim the last of the water it can before the water is excreted as urine
What is the Antidiuretic Hormone (ADH)?
it regulates the permeability of the collecting duct in response to blood osmolarity
ie. if you are dehydrated, it will be released and cause more reabsorption of water from urine –> why urine is so concentrated with lack of water
The main purpose of the loop of Henle is to….
reabsorb water and some NaCl
