Excretory System

Question 1

Buildup of Ammonia

Answer 1

• A buildup of ammonia in the body can cause lethargy, rapid breathing, altered mental state and even death

Question 2

Osmolarity

Answer 2

• The sum of the concentration of all solutes that are dissolved in a solvent
• Salt and water balance are vital for our cardiovascular nervous systems
  *

Question 3

Erythropoietin

Answer 3

• Released from the kidney and promotes production of red blood cells or process called appropriately erythropoiesis

Question 4

Calcitriol

Answer 4

• Another hormone released by the kidney, which is also known as vitamin D3 that lets the digestive tract absorb calcium

Question 5

Anatomy of the Kidney

Answer 5

• The outer layer is the cortex
• the middle layer is the medulla
• The centre of the kidney where it starts to curve is the renal pelvis

Question 6

The renal Pelvis

Answer 6

• The renal pelvis connects to a tubular structure called the ureter, which helps transport the urine produced by the nephrons to the bladder before excretion

Question 7

The renal Pelvis

Answer 7

• The renal pelvis connects to a tubular structure called the ureter, which helps transport the urine produced by the nephrons to the bladder before excretion

Question 8

Function of the Kidney

Answer 8

• The kidneys are responsible for filtering the blood that’s constantly coming in through the renal artery.
• Once our blood has been cleaned, it drains out of the kidney and back to systemic circulation, via the renal vein.
• The functional unit of the kidney is the nephron and a million of these nephrons are working together in each one of our kidneys.

Question 9

Nephrons

Answer 9

• Each one of those nephrons as a tube made up of a simple epithelium lining
• The tube is broken down into five sections:
  
  • Bowmans Capsule
  • Proximal Convoluted tubule
  • loop of Henle
  • Distal convoluted Tubule
  • Collecting duct

Question 10

Bowman’s Capsule

Answer 10

• Surrounds a series of capillaries that are fed by the renal artery
• All the fluid and solutes that leave the capillaries and enter Bowman’s Capsule are called the filtrate.
• While the filtrate moves to the nephron from Bowman’s Capsule to the collecting duct, the nephron changes which solutes are present in the filtrate as well as their concentrations.

Question 11

Loop of Henle

Answer 11

• The loop descends into the medulla, then turns it around and descends back into the cortex of the kidney.
• After entering the cortex again, the filtrate enters the distal convoluted tubule

Question 11

Loop of Henle

Answer 11

• The loop descends into the medulla, then turns it around and descends back into the cortex of the kidney.
• After entering the cortex again, the filtrate enters the distal convoluted tubule

Question 12

Collecting Ducts

Answer 12

• The filtrate from each of those one million nephrons leaves the cortex and goes back into the medulla of the kidney through the collecting duct, which ends in the renal pelvis of the kidney

Question 13

Blood through the nephron

Answer 13

• Blood first enters the kidney through the renal artery, a mixture of red blood cells, ammonia, urea glucose, amino acids, vitamins and other molecules all suspended or dissolved in water.
• It enters the glomerulus of the nephron where blood pressure pushes some of those solutes along with water out of the capillaries and into Bowman’s capsule.
  
  • Solutes leave the glomerulus and enter Bowman’s capsule, or called the filtrate of the nephron.
  • The nephrons filter only by side, so sometimes valuable solutes get through. Some of the ones we want to hold on to are:
    
    • glucose
    • amino acids
    • vitamins
    • biocarbonate
    • sodium
    • chloride
  • To keep them the body need to selectively pull those thing out of the filtrate for re-entering into the blood.
    
    • This is called reabsorption and occurs throughout the entire nephron

Question 14

Interstitial Fluid

Answer 14

• The fluid that fills spaces between cells
• The change in interstitial concentrations helps us understand what enters and leaves the nephrons.
• This is where osmolarity comes in. (it is the concentration of all the solutes are dissolved in the solvent)
  
  • This is important because all the osmolarity of the interstitial fluid, determines the osmolarity of the fluid in the nephrons.
  • When the body is in homeostasis, the osmolarity of blood in cells, is around 300 milli-osmols
• When interstitial fluid is in the cortex, its concentration is at its lowest, ranging from 100 to 300 milli-osmols
• The outer part of the medulla the osmolarity increases first to 600 and then to 1200 milli-osmoles as it reaches the inner medulla.
• To maintain these concentrations, solutes need to either be added to or removed from the fluid in the nephron.

Question 14

Interstitial Fluid

Answer 14

• The fluid that fills spaces between cells
• The change in interstitial concentrations helps us understand what enters and leaves the nephrons.
• This is where osmolarity comes in. (it is the concentration of all the solutes are dissolved in the solvent)
  
  • This is important because all the osmolarity of the interstitial fluid, determines the osmolarity of the fluid in the nephrons.
  • When the body is in homeostasis, the osmolarity of blood in cells, is around 300 milli-osmols
• When interstitial fluid is in the cortex, its concentration is at its lowest, ranging from 100 to 300 milli-osmols
• The outer part of the medulla the osmolarity increases first to 600 and then to 1200 milli-osmoles as it reaches the inner medulla.
• To maintain these concentrations, solutes need to either be added to or removed from the fluid in the nephron.

Question 15

Reabsorption in the Nephron

Answer 15

• At the start in Bowmans capsule the osmolarity is about 300 mOsm and then as it passes and into the proximal convoluted tubule about ⅔ of sodium ions in the filtrate will be reabsorbed by active transport.
  
  • Sodium can’t diffuse across the membrane because they’re positive charges.
  • Water will follow the sodium ions and chloride ions will passively follow the sodium ions as well, through the help of transport channels in the cell membrane
  • Both salt ions and water are reabsorbed to maintain the osmolarity at 300 mOsm in the intraretinal fluid.
• Next amnion acids, water soluble vitamins and glucose are reabsorbed by specific transporters.
• Before the filtrate moves from the proximal convoluted tubule into the descending loop of Henle, secretion needs to occur, to help increase the concentration of the filtrate.

Question 16

Reabsorption in the Nephron at the outer medulla

Answer 16

• As we know, the interstitial fluid in the outer medulla of the kidney increases to 600 milli-osmoles.
• To understand how this happens at the end of the proximal convoluted tubule, think of the change in concentration
• Remember the proximal convulated tubule is just one of two places in the nephron where solutes can be added to the filtrate, causing a raise in concentration.
  
  • To raise the concentrtaion, the nephron secretes solutes into the filtrate to increase the filtrate concentration up to 600 mOsm

Question 17

Secreted in the filtrate

Answer 17

• Four key solutes the body needs to secrete in the filtrate to prevent them from building up in the blood and making us sick
• “Dump the HUNK”
  
  • Hydrogen
  • Urea
  • Ammonia
  • Potassium
• The other solutes that out kidneys both filter at the glomerulus and secrete in the proximal tubule, such as creatine and creatinine from our muscles.
  
  • The first priority tho is to dump the HUNK

Question 18

Filtrate in the descending loop of Henle and in the inner medulla

Answer 18

• To increase the concentration to 900 and then 1200 mOsm, the filtrate must be continued to be concentrated.
• Since it is is no longer in the proximal convoluted tubule there can not be any more secretion, so the only other option is to reabsorb water out of the filtrate and into the interstitial fluid to increase the concentration
• The filtrate now has to reduce its concentration as it goes up the ascending loop of Henle toward the cortex
  
  • The ascending loop of henle is completely impermeable to water, so the only way to dilute the filtrate is to remove solutes.
• At the bottom of the loop of henle, sodium ions and chloride ions are reabsorbed passively due to the change in concentration
• But as the filtrate continues to move upwards towards the cortex and concentration gets closer to 300 mOsm, reabsorption becomes harder, so our nephrons invest some energy, recruiting many sodium potassium pumps in the larger tubular epithelial cells to help pump them out.
  
  • The pumps are what make this part of the nephron thick.

Question 19

Filtrate in the cortex kidney

Answer 19

• When the filtrate enters the cortex of the kidney, its back to 300 mOsm
• The filtrate at this point has a very different solute profile than in the proximal covulated tubule
• After we enter the loop of henle, the only things reabsorbed the rest of the way are sodium, chloride and water
• As the filtrate moves to the distal convulated tubule, sodium and water are reabsorbed to keep the concentration at 300 mOsm
• Before entering the collecting duct, which is in the medulla of the kidney, the filtrate needs to become more concentrated.
• This is the second and final place where solutes can be secreted.
• Just like in the proximal convulated tubule, the kidney will secrete into the filtrate, again “dump the hunk”
• As the filtrate moves down the collecting duct towards the renal pelvis, water may be reabsorbed if the body is dehydrated
  
  • Any water and solutes that get to the ureter are lost and there is no way to reabsorb them at that point.

Question 20

Counter Current Multiplier System

Answer 20

• This system uses a vein called the vasa recta
• The vasa recta flows in the opposite direction from the nephron to pick up the solutes in water.
• It first picks up water from the collecting duct and sodium and chloride from the distal convulated tubule and ascending limb of the loop of Henle.
• As the blood continues to move through the vasa recta, it absorbs water from the descending loop of Henle.
• Finally it absorbs the glucose, amino acids, vitamins, ions and water from the proximal convoluted tubule
  
  • From here all of those solutes and all teh water, we return to the central ciculation via the renal vein so that teh rest of our body can use it.

Question 21

Osmoregulation

Answer 21

• The regulation of osmotic pressure in the body fluids of an organism to maintain homeostasis.
• This is achieved at the end of the nephron, in the distal convoluted tubule and collecting duct and is done using two hromones, a steroid → aldosterone and a peptide ADH

Question 22

ADH in Osmoregulation

Answer 22

• Osmoregulation is necessary when the blood is every over or underhydrated
  
  • Remember that the normal osmolarity of blood is 300 milli-osmoles, so concentration is too high or too low or non homeostatic
  • When we’re overhydrated, the osmolarity of our blood is below 300 milli-osmoles. In this situation the blood is too dilute.
    
    • Cells and tissues aren’t at the right concentrations, which means that they aren’t able to optimally access the nutrients and oxygen they need.
    • Overhydration also means an increase in blood volume which can raise blood pressure to dangerous levels.
    • The kidney’s respond by reabsorbing less water through the ascending loop of Henle and the collecting duct.
      
      • in this situation which we call “diuretic”, more fluid will leave the body in the formm of urine.
  • If the body is dehydrated, the osmolarity will be greater than 300 milli-osmoles,
    
    • Under normal circumstances, the collecting duct is relatively impermeable to water. However, the hypothalmus has osmosensors taht can detect and increase in the osmolarities when dehydration occurs.
    • The hypothalamus then responds by producing antidiuretic hormone or ADH, which is also called vasopressin, thats released by the posterior pituitary.
  • ADH affects the collecting duct by inserting aquaporins or water channels into the membrane so that water can be reabsorbed into the collecting ducts.
    
    • As water is reabsorbed, the osmolarity of the blood slowly corrects back down towards 300 milli-osmoles.

Question 23

Aldosterone in Osmolarity

Answer 23

• Aldosterone directly increases sodium reabsorption in the distal convoluted tubule and collecting duct
• To balance charge, chloride passively follows.
• Then because water follows salt, water will also be reabsorbed, as more sodium ions move out of the nephron.
• Now, if sodium, chloride and water are being reabsorbed, the osmolarity of the blood should remain at homeostasis, but the volume should increase
  
  • With an increase in blood volume, the blood pressure also increases
• Since increase in blood volume and blood pressure are the end result, aldosterone must be released when either blood volume, blood pressure or both are low.