Module 5.1.2- Excretion

• Excretion


  Process by which metabolic wastes are eliminated from the body including carbon dioxide, nitrogenous waste and bile pigments
• Bile pigments


  Formed from the breakdown of haemoglobin from old red blood cells in the liver. They are excreted in the bile from the liver into the small intestine via the gall bladder and bile duct
• What vessel supplies oxygenated blood to the liver


  hepatic artery
• What vessel collects blood from the liver and returns it to the heart


  hepatic vein
• Hepatic portal vein


  carries nutrient-rich blood with products of digestion straight from the intestines to the liver
• Hepatocytes (liver cells)


  prominent Golgi apparatus, large nuclei, lots of mitochondria, lots of ER
• Sinusoids


  blood from hepatic artery and blood from hepatic portal vein is mixed in these spaces increasing oxygen content of the blood
• Kupffer cells


  macrophages in the liver ingesting foreign particles
• Hepatocytes secrete...


  bile into bile canaliculi
• Structure of the liver

  
• Carbohydrate metabolism- function of liver


  Insulin, glucagon

  1) gluconeogenesis: making glucose to be sent to the body

  2) glycogen storage: to store energy when needed

  3) glycogenolysis --> (glucose released into bloodsteam): breaking down that glycogen in glycogenolysis, which will then release glucose into the bloodstream.
• Transamination- function of liver


  the conversion of one amino acid into another
• Deamination- function of liver


  the removal of an amino group from an amino acid
• Why is deamination important


  So any ingested excess protein would not be excreted and wasted
• Deamination process


  amino group (NH2) must be removed, converted to ammonia (NH3) then to urea
• Ornithine cycle


  A series of biochemical reactions that convert ammonia to urea since ammonia is highly toxic

  
• What are the rest of the amino acids used for after deamination


  Can be used for respiration
• Detoxification- function of liver


  Detoxified chemicals are secreted by the liver as part of bile or modified so that they can be excreted by the kidney.

  example:

  hepatocytes contain catalase -> breaks down hydrogen peroxide hepatocytes contain alcohol dehydrogenase -> ethanol to ethanal
• What is the structure of a nephron


  Bowman's capsule,

  proximal convoluted tubule,

  loop of Henle,

  distal convoluted tubule,

  collecting duct

  
• Bowman's capsule- nephron


  contains the glomerulus, more blood goes into the glomerulus than leaves it due to ultrafiltration processes that take place
• Proximal convoluted tubule- nephron


  found in the cortex of the kidney. this is where many substances needed by the body are reabsorbed into the blood
• Loop of Henle- nephron


  a long loop of tubule that creates a region with a very high solute concentration in the tissue fluid deep in the kidney medulla descending limb and ascending limb
• Distal convoluted tubule- nephron


  A second twisted tubule where the fine-tuning of the water balance of the body takes place.

  Further regulation of the ion balance and pH of the blood also takes place

  Permeability of the walls to water varies inresponse to the levels of anti diuretic hormone (ADH) in the blood.
• Collecting duct- nephron


  urine passes down the collecting duct through the medulla to the pelvis. more fine tuning of the water balance takes place- the walls of this part of the tubule are also sensitive to ADH.
• What is the function of the cortex in the kidneys


  It's where the filtering of the blood takes place and it has a very dense capillary network carrying the blood from the renal artery to the nephrons. (It is a dark outer layer when seen through a microscope)
• What is the function of the medulla in the kidneys


  It contains the tubules of the nephrons that form the pyramids of the kidney and the collecting duct
• What is osmoregulation


  the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations.
• State the 4 steps in ultrafiltration


  1. Different lumen sizes of Afferent and Efferent arterioles creates a filtration pressure in glomerulus

  2. Fluid passes through the basement membrane and gaps in the endothelium that act as a 1st filter

  3. The podocytes in the Bowman's capsule wall act as a 2nd filter as they have pedicels that wrap around the capillaries. further stopping the entry of any RBCs, WBCs and large plasma proteins

  4. The filtrate which enters the capsule contains glucose, water, salt (Na+, Cl-), urea, amino acids, hormones, vitamins
• Wall of Bowman's Capsule


  • Cells (podocytes) have processes (pedicels) that wrap around glomerular capillaries.
  • Spaces between pedicels (filtration slits) allow passage of small molecules across a slit membrane.

  
• Adaptations of the proximal convoluted tubule


  covered with microvilli, increasing the surface area over which substances can be reabsorbed

  many mitochondria to provide ATP needed in active transport systems
• Adaptations of the loop of Henle


  different areas of the loop have different permeabilities to water which acts as a counter-current multiplier, using energy to produce concentration gradients that result in the movement of substances
• In the descending limb, this is the region where water moves _____ of the filtrate down a concentration gradientThe upper part is ___________ to water whilst the lower part is ___________ to water and runs down the medulla

  out,impermeable,permeable
• What happens to the salt concentration as you go further down the medulla


  It increases
• The descending limb is impermeable to sodium and chloride ions so...


  no active transport takes place in the descending limb
• Ascending limb is ___________ to water whilst the first section of the ascending limb is _____________ to sodium and chloride ions. They then move _____ of concentrated solution _____ the concentration gradient. In the second section, sodium and chloride ions move ______ the concentration gradient actively pumped out increasing the salt ion concentration in the medulla diluting the filtrate.

  impermeable,permeable,out,down,against
• Importance of counter-current multiplier system


  to increase the concentration of solute and ions within the interstitium of the medulla produce urine that is more concentrated than the blood

  
• Adaptations of distal convoluted tubule


  lots of mitochondria for active transport

  ADH levels vary with permeability of walls of the tubules
• Adaptations of collecting duct


  water moves out of collecting duct by diffusion down a concentration gradient as it passes through the renal medulla

  water is moved all the way along its length since as you keep going down from cortex -> medulla, salt ion increases decreasing water potential causing water to diffuse out by osmosis
• Osmoregulation- function of kidney


  regulation of solute concentrations and water balance e.g. through ADH (negative feedback system)

  
• ADH is produced by the ______________ and then secreted into the ________ ___________ gland where it is stored


  hypothalamus, posterior pituitary (gland)