Waste Excretion and Internal Equilibrium Topic 12.1 PDF

Waste Excretion and Internal Equilibrium Topic 12.1  Waste Products I’ve alluded to “waste” many times but really we’ve only talked about CO2 Where is the other waste coming from and what is it made of? E.g. the liver transforms toxins (like booze) into less harmful sub...

Waste Excretion and Internal Equilibrium Topic 12.1  Waste Products I’ve alluded to “waste” many times but really we’ve only talked about CO2 Where is the other waste coming from and what is it made of? E.g. the liver transforms toxins (like booze) into less harmful substances and sends them to the kidney to be excreted  Waste Products Come to think of it… tons of stuff gets sent to the kidneys 1) Excess protein Excess protein 🡪 converted to carbs 🡪 forms an amino group in the process This is called deamination The amino groups forms ammonia 🡪 very toxic 🡪 sent to kidney  Waste Products 2) Liver combines CO2 with ammonia to form urea which is then sent to the kidney 3) Uric acid is formed during the breakdown of nucleic acids and must be sent to the kidney  Water Balance Hrm… the kidneys seem kinda important but wait, there’s more! They are responsible to controlling your body’s water balance. Water is more important than food. You lose some everyday and so you must replenish it. If not, you could die within 3 days Think back to circulation – we already know one reason that water is so important and it is: Anatomy of the Urinary System Anatomy of the Urinary System Renal arteries branch from the aorta and bring blood to the kidney The kidney may hold as much as 25% of the body’s blood at a time Waste from the blood is filtered by the kidney and sent to the bladder via the ureters Anatomy of the Urinary System The urine stays in the bladder until the bladder becomes it becomes too full At which time a message is sent to the brain that it’s “time to go” As the bladder fills the message becomes more urgent When you eventually urinate, the urinary sphincter relaxes and allows the urine to flow into the urethra Anatomy of the Kidney  Anatomy of the Kidney Outer layer of connective tissue – cortex The next layer in is called the medulla A hollow tube joins the kidney with the ureter – renal pelvis Functional units of the kidney are called nephrons  Anatomy of the Nephron The nephron is the functional unit of the kidney They are supplied with blood by the afferent arteries Afferent arteries continue to branch the kidney becoming capillary beds called glomeruli (single – glomerulus)  Anatomy of the Nephron The blood that leaves the glomerulus does not go to a vein but another arteriole system, the efferent arterioles (Remember “A” comes before “E” in the alphabet) These arterioles become a capillary bed again, this time surrounding the kidney tubule, called the peritubular capillaries This capillary bed finally joins with the renal VEIN  Anatomy of the Nephron The glomerulus is surrounded by the Bowman’s capsule Bowman’s capsule becomes the proximal tubule Proximal tubule becomes the Loop of Henle This becomes the distal tubule Eventually becoming the collecting duct  Anatomy of the Nephron Located in the cortex: Bowman’s capsule Afferent and efferent arteriole Glomerulus Proximal and distal tubules Located in the medulla: Peritubular capillaries Loop of Henle  Formation of Urine There are 3 steps: Filtration Fluid from blood into the Bowman’s capsule Reabsorption Transfer of “good stuff”(solutes and water) back into the blood Secretion Transport of materials from the blood into the nephron  1. Filtration The glomerulus has a lot more pressure than your regular ol’ capillary This allows water and dissolved solutes to pass into the Bowman’s capsule Once again, cells, platelets and proteins are too big to fit through  1. Filtration What does fit through? Water Salt (sodium chloride) Glucose Amino acids Hydrogen ions urea  2. Reabsorption On average 600 mL of fluid flows through the kidney per minute (120 mL in the nephrons) That would be a lot of urine produced and many washroom breaks if you didn’t reabsorb most of it! 1 mL of this actually becomes urine – phew!  2. Reabsorption Happens by both passive (no energy needed) and active (energy needed) transport Active Transport - pumps Na+ across the membrane - negative ions follow the positive charge - Cl- and HCO3- - not all salt can be pumped out of nephron - the nephron reaches a threshold level  2. Reabsorption Active Transport Continued… - glucose and amino acids will also be sent back into the blood - if there is excess however, they will remain in the urine Because so much “stuff” (solutes) have been transported across the membrane, the concentration in the blood is much higher than in the nephron. What do you expect will happen?  2. Reabsorption Passive Transport - Water will diffuse to follow the high concentration of solutes in the blood - urea and uric acid will follow (but not as much as what will remain in the urine) Most of the water reabsorption occurs in the Loop of Henle Loop of Henle - ascending portion is pumping out Na+ ions into the blood and surrounding tissue by active transport - because ascending and descending are right beside each other, this makes the descending portion of the loop very hypotonic - this forces water out of the loop by osmosis This process also occurs in the collecting duct for similar reasons.  3. Secretion Active transport of substances into the urine by cells in the distal tubule Into blood and surrounding tissue NaCl and HCO3- Into nephron K + and H+ Let’s PRACTICE!!!!!!!!!!!!!!! http://www.youtube.com/watch?v=glu0dzK4dbU &feature=related  Hormones That Affect Renal Function 1. ADH (Anti-diuretic Hormone) Produced in the hypothalamus and released by the pituitary gland Acts on the collecting duct to increase water reabsorption The more ADH in the bloodstream, the more water reabsorbed, the more concentrated the urine When would your body release this hormone?  ADH Production and Release Osmoreceptors detect changes in osmotic pressure There are osmoreceptors in a part of your brain called the hypothalamus Once activated the hypothalamus sends a message to the pituitary gland The pituitary gland releases ADH into the bloodstream The higher the osmotic pressure the greater the release of ADH Positive feedback  Diuretics Block the release of ADH What would this cause? Examples?  Hormones That Affect Renal Function 2. Aldosterone Has the same overall effect as ADH – it decreases urine production and increases water reabsorption but with some important differences Released by the adrenal glands Acts on the distal tubule and the collecting duct to increase the active transport of Na+ back into the blood Water moves due to concentration gradient