The Excretory System

 The body has 2 kidneys  They hold ~ ¼ of our blood at any one time  They play a major role in homeostasis  Each has a mass of ~ 500 g  are made up of about 1 million nephrons

1. Remove Wastes 2. Balance Blood pH 3. Maintain Water Balance 4. Blood Pressure

 Such as urea and uric acid from the blood  Uric acid is formed from the breakdown of DNA (nucleic acids)  Urea is formed in a process called deamination

 It occurs in the liver  It is the conversion of amino acids in the blood to carbohydrates (urea is produced)

1.) NH 3 is removed from amino acids (ammonia – highly toxic…0.005 mg can kill you) 2.) 2 molecules of NH 3 combine with CO 2 to form urea (urea is 1000X less toxic)

 Both urea and uric acid enter the blood and will be removed from the body by the kidneys  The build up of uric acid is called gout

 Kidneys remove ions (E.g. H + ) from the blood keeping the pH in normal range between 7.3 and 7.5

 CO 2 from the peritubular capillaries combines with H 2 0 in the cells that line the nephon producing carbonic acid….  Carbonic acid breaks apart to form H + and HCO 3 - ions  CO 2 + H 2 O H 2 CO 3  H 2 CO 3 H + + HCO 3 -

 If the blood is too acidic  the H + is excreted in the urine and HCO 3 - is reabsorbed back to the blood …buffering the blood  If the blood is too basic  The HCO 3 - is excreted in the urine and H+ is reabsorbed back to the blood  This is aided by changes in breathing rate

 180 L moves through kidneys in one day  ~ 2L of water is lost per day from perspiration, exhaling, urine  178 L are reabsorbed!

 we can only survive a few days without water  1% loss of H 2 O = thirst,  5% loss of H 2 O = pain, collapse,  10% loss of H 2 O = death…E.g. heat exhaustion

 Two hormones regulate water concentration in the blood:  antidiuretic hormone (ADH)  aldosterone  Hormones are chemicals that travel in the blood and target cells in the body…. eliciting a response

 Targets the nephrons distal tubule and collecting duct  It increases H 2 O reabsorption into the bloodstream  It is produced by nerve cells in the hypothalamus  it is stored in the posterior pituitary gland and secreted when it is needed

Hypothalamus Pituitary

 H 2 O lost in the body causes H 2 O to move from the tissues into the bloodstream (shrinking body cells)  osmoreceptors in the hypothalamus detect low osmotic (H 2 O) pressure

 The hypothalamus responds by:  triggering thirst  sending a nerve message to the pituitary gland ….stimulating the release of ADH  ADH travels in the blood and targets the nephron

No ADH

ADH Present

 ADH causes the distal tubule and collecting duct to become permeable to H 2 O  The kidneys reabsorb more H 2 O  a more concentrated urine (dark yellow) is produced

 Cold weather, caffeine and alcohol all inhibit the release of ADH  reabsorption of the H 2 O can’t take place and urine volume is increased

 The kidneys help regulate blood pressure  Aldosterone:  is produced and secreted by the adrenal glands  It targets the ascending Loop of Henle, distal tubule and collecting duct

 It increases the amount of Na + reabsorption.. therefore increasing the reabsorption of H 2 O  This increases blood pressure

 It is detected by osmoreceptors in the juxtaglomerular apparatus ………cells located in the afferent arteriole near the glomerulus  cells in the juxtaglomerular apparatus release rennin  Rennin converts angiotensinogen (a plasma protein secreted by the liver) to angiotensin (active form)

Produces and releases aldosterone

Aldosterone Increases Sodium reabsorption

Na+

 angiotensin:  constricts blood vessels  causes aldosterone to be released from the adrenal glands (both of which increase BP)  Aldosterone causes an increase in Na + reabsorption from the ascending loop, distal tubule and collecting duct (nephron)

 H 2 O follows by osmosis and moves into the bloodstream therefore increasing blood volume and BP

 Draw and label the structures of the Urinary System

 Renal arteries:  branch from the abdominal aorta  they supply the kidneys with oxygenated, unfiltered blood  Renal veins:  remove deoxygenated, filtered blood

 Filter wastes from the blood  Are made up of 3 layers: a.) the cortex: outer layer of connective tissue b.) the medulla: inner layer..contains the nephrons (beneath the cortex) c.) the pelvis: hollow chamber joining kidney to ureter

 Are 2 tubes that filtered wastes from the kidneys passes through to reach the bladder

 storage for urine  holds about 200 mL of urine  at 400mL stretch receptors signal the brain that it is “time to go….”  after 600 mL is collected all voluntary control is lost!

 urine leaves the bladder through the urethra  sphincter muscles relax and urine is voided  It is shorter in women and as a result women are more susceptible to bladder infections…..closer contact to the outside

 The Nephron Handout: fill in structures  Note:  the cortex contains: the afferent, efferent arterioles and the Bowman’s capsule  The medulla contains: the Loop of Henle

 are the functional units of the kidney  Afferent arterioles  supply the nephrons with blood  branch into the capillary bed called the glomerulus

 Blood leaving the glomerulus:  Passes through the efferent arterioles  travels to the peritubular capillaries (they wrap around the tubules)  to the venule  then to the renal vein

 The glomerulus is surrounded by the Bowman’capsule (funnel-like part)  This tapers into the proximal tubule

 The proximal tubule connects to the loop of Henle  The loop of Henle connects to the distal tubule  The distal tubule empties into the collecting duct …these ducts merge in the renal pelvis

 Your Assignment: Page 380, 1-3

 It depends on 3 steps:  Filtration  Reabsorption  Secretion

 Filtration:  the movement of fluid from the blood (glomerulus) into the Bowman’s capsule  Reabsorption:  is the movement of essential solutes and water from the nephron back to the blood  Secretion:  involves the transport of materials from the blood into the distal tubule of the nephron

Filtration

 Occurs at the glomerulus  filtration rate: if the pressure  then filtration rate   blood enters nephron through the afferent arteriole (pressure is 2 kPa)  Then blood enters the glomerulus (pressure is 8 kPa) which acts like a high pressure filter

 Proteins, blood cells and platelets are too large to filter through glomerulus and move into the efferent arteriole  Plasma passes through the glomerulus into the Bowman’s capsule (E.g. Na +, Ca 2+, glucose, urea, uric acid etc.)

Reabsorption

 Solutes move from nephron into bloodstream  Most reabsorption (85%) occurs in the proximal tubule  It also occurs in the Loop of Henle and distal tubule  it occurs till the threshold level is reached

 600 mL of fluid moves through kidney per minute… about 120 mL of that is filtered into the nephron…and from that only 1 mL of urine is made  Both active and passive transport occur (large molecules require active transport)  glomerular filtrate (dissolved solutes) travels through the proximal tubule

 the proximal tubule contains a rich supply of mitochondria (ATP production) and microvilli  as the filtrate moves through the proximal tubule, Loop of Henle and distal tubule, H 2 O and certain ions are reabsorbed back into the bloodstream  This maintains proper water and ion balance

 Na +, glucose and amino acids are actively transported out of the nephron into the peritubular capillaries (bloodstream)  in the descending loop the filtrate is hypertonic and water diffuses out of nephron into bloodstream (osmosis)

 At the ascending loop, the filtrate is hypotonic Na+ is actively transported out …..to keep water from moving the wrong way  Cl - and HCO 3 - ions follow the Na + ions… due to charge attraction (passive transport)  There is limited energy for active transport so some solutes (E.g. NaCl) stay …..

 once the ions move out, an osmotic gradient is set up so water diffuses from tubules and Loop of Henle into bloodstream  filtrate becomes more concentrated as it moves along towards the distal tubule

Secretion

 movement of wastes from the bloodstream into nephron  Occurs at the distal tubule and involves active transport  urea, histamine, NH 3, K + ions, H + ions, HCO 3 ions, minerals, drugs such as penicillin etc. move from the blood into the distal tubule

 After secretion the urine moves into the collecting ducts  The collecting ducts lead to the renal pelvis then on to the ureters and bladder

 Filtration  glomerulus and Bowman’s capsule  passive transport  Reabsorption  proximal tubule (mainly), loop of Henle, distal tubule  active and passive transport  Secretion  distal tubule  active transport

 water (95%)  urea  uric acid  trace amino acids  electrolytes: Na +, K +, Cl -, SO 4 2-, PO 4 +3  excess vitamins, minerals, etc  The pH of urine ranges from 4 to 5 but can get as high as 8.5

Remains in Blood Filters into Capsule Reabsorbed RBCWaterWater (most of) WBCAmino acidsAmino acids (all) PlateletsGlucoseGlucose (all) FatsSaltsSalts (some) Blood ProteinUrea, uric acidUrea, uric acid (none)

ComponentPlasmaFiltrateUrine Urea Uric Acid Glucose to trace Amino Acid Salt0.72 ~1.5 Protein

 Comparing Solutes in plasma, Nephron, and Urine  Page 384

 Page 380, #’s 1-3  Page 383, #’s 4-5  Page 386, #’s 1-3,& 5