Excretory System

• The excretory system regulates the volume and composition of body fluids by excreting wastes and recycling some substances for reuse.
• The kidney is the primary filter of blood, with 20% of your blood always in your kidneys.
• The kidney is composed of three sections: cortex, medulla, and pelvis.
• In the cortex of the kidney, there are one million tiny filters called nephrons, which have five main parts: Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, and collection duct.
• Glomerular filtration moves water and solutes, except proteins, from blood plasma into the nephron, this filtered fluid is called filtrate.
• Tubular reabsorption removes useful substances such as sodium from the filtrate and returns them into the blood for reuse by the body systems.
• Tubular secretion moves additional wastes and excess substances from the blood into the filtrate.
• Water reabsorption removes water from the filtrate and returns it to the blood for reuse by body systems.
• During filtration, fluid moves from the glomerulus to the Bowman’s capsule.
• During reabsorption, all fluid must be removed first, nutrients are selectively reabsorbed from the filtrate, and the rest of the filtrate continues down the loop of Henle.
• During reabsorption, the descending part of the loop of Henle is permeable to water, thus water leaves the filtrate, and the ascending part is permeable to solutes (but not water), thus solutes leave the filtrate.
• During reabsorption, carrier molecules move Na+ ions across and negative ions such as Cl- follow because of attraction, glucose and amino acids are actively transported up to a limit, and high concentrations of ions outside of the loop create osmotic pressure that forces water to move out as well.
• Some nitrogenous wastes, excess ions, and minerals that are still in the blood that surrounds the distal tubule are actively transported into the distal tubule.
• Now, only urea, uric acid, and excess molecules (including salt, glucose, minerals) are left to flow to the collecting duct.
• Diabetes mellitus affects water retention due to excess sugar in the nephrons.
• Kidney stones are a build up of mineral solutes.
• Total loss of kidney function requires dialysis and eventually replacement.
• kidneys are located near the back of the body, separated from the thoracic cavity
• the kidney filters and recycle molecules, and a small amount goes into the bladder
• the collecting duct collects the urine and sends it to the ureters
• the medulla of the kidney contains the lower parts of the nephron (loop of Henle and collecting ducts)
• the glomerulus can only fit 1 red blood cell at a time
• molecules in blood are diffused from the glomerulus into the Bowman's capsule
• the liver detoxifies blood, which forms urea and diffuses out of the glomerulus
• the difference between urea and uric acid is that uric acid has more hydrogen
• ketosis is when proteins exit the blood and enter the filtrate
• proteins can leak into the filtrate if the glomerulus is damaged, or if there are too many proteins in the blood
• once the filtrate enters the proximal tubule, the capillaries remove carbon dioxide to be oxygenated and useful molecules (e.g. sodium) are reabsorbed in the capillaries via the concentration gradient
• when the body reabsorbs too much, the molecules diffuse back into the filtrate via the concentration gradient
• the reason why the color of urine depends on the amount of water drank is because more water dilutes the urea and ions, while less water concentrates urea since the water is absorbed into the blood
• blood should not be in urine, if it is in urine, it is a sign of kidney damage
• the filtrate flows in the opposite direction of blood flow
• water has to be absorbed into the filtrate in the descending loop of the tubule because the ascending loop is not permeable to water
• label the nephron diagram

  A) efferent arteriole

  B) afferent arteriole

  C) loop of henle

  D) proximal tubule

  E) distal tubule

  F) collecting duct

  
• the ascending loop of Henle only reabsorbs ions back into the capillaries
• diabetes mellitus directly impacts the kidneys. if there is too much sugar in the blood, the water has to dilute a lot of it which impacts water retention
• substances passively diffused out of the proximal are HCO3-, H2O (water), and K+
• substances actively diffused out of the proximal tubule are nutrients and NaCl
• the substance diffused out of the descending loop of Henle is H2O (water)
• NaCl is passively diffused out of the thin ascending loop of Henle, but actively diffused out of the thick ascending loop