2. Ureters Composed of smooth muscle tissue ~25cm long Connects kidneys to bladder Undergoes peristaltic contraction to move urine to bladder

Transcription

1 Section 6: The Urinary System A) Organs of the Urinary system 1. Kidneys 2. Ureters 3. Bladder 4. Urethra 1. Kidneys Paired organs located on either side of vertebral column in upper part of abdominal cavity Embedded in dorsal muscles behind peritoneum (peritoneum= lining of the abdominal cavity) Partly protected by floating ribs Bean shaped, reddish brown in color Concave side has a depression where renal artery enters kidney and renal veins and ureter exit kidney Renal artery transports blood to kidney to be filtered Renal vein -transports filtered blood away from kidney 2. Ureters Composed of smooth muscle tissue ~25cm long Connects kidneys to bladder Undergoes peristaltic contraction to move urine to bladder 3. Bladder Stores urine until it is expelled Contains smooth muscle tissue that allows it to expand Stretch receptors embedded in bladder wall Send sensory nerve signal to spinal cord Motor response from spinal cord to bladder cause bladder to contract and sphincters to relax so urination can occur 4. Urethra Small tube that connects bladder to exterior of body Lined with mucus membrane to trap any pathogens trying to enter body

2 B) Functions of the Urinary system (all happens in Kidney): 1. Excretion of metabolic waste 2. Maintenance of salt/water balance 3. Maintenance of acid-base (ph) balance 4. Contribution to hormonal function 1. Excretion of metabolic waste (esp nitrogen waste) a) Urea end product of amino acid breakdown made in the liver Ammonia (toxic) + CO2 urea (less toxic) breakdown of aa in the liver releases ammonia which is very toxic to cells- the liver rapidly combines ammonia with CO2 to produce urea which is less toxic this is taken via the bloodstream to the kidney for disposal b) Uric acid (byproduct of digestion) formed from breakdown of nucleotides of nucleic acids Nitrogen from nitrogen bases in nucleotide is converted to a less toxic form of nitrogen waste and expelled through the kidneys c) Creatinine nitrogen waste formed from the end product of creatine phosphate breakdown Creatine phosphate is a hi energy reserve molecule in skeletal muscles when it breaks down it forms creatinine this is expelled through the kidneys 2. Maintains salt/water balance Maintains the level of salt (Na + + Cl - ) and water in the blood the amount of salt in the blood effects blood pressure so in that way, kidneys regulate blood pressure by regulating the amount of salt in the blood Regulates blood pressure by regulating blood volume think of osmosis the higher the salt concentrations are in the blood the more water will diffuse into the blood stream and therefore the greater the blood pressure Maintains the level of other ions in the blood: K + needed for nervous impulse HCO3 - (bicarbonate) needed for transport of CO2 Ca 2+ needed in muscle contraction

3 3. Maintains acid-base (ph) balance ph of blood ~7.4 kidney monitors blood ph and regulates it by excreting H+ (acid) and reabsorbing HCO3- (base) as needed 4. Contributes to hormonal function Secretes erythropoietin (hormone) to increase RBC production if O2 carrying capacity of blood decreases Secretes renin, an enzyme that stimulates the release of hormones to regulate the salt/water balance of blood C) Kidney structure 1. Macroscopic Structure 3 regions 1) Renal cortex outer granulated layer dips down into kidney between the: 2) Renal medulla o radially striated inner layer o consists of cone shaped tissue called renal pyramids o renal pyramids composed of collecting ducts and loops of nephron 3) renal pelvis -central space or cavity in kidney where collecting ducts deposit urine 2. Microscopic Structure = nephron + collecting ducts Contains millions of nephrons = kidney tubules that produce urine which flow into collecting ducts then into renal pelvis

4 2 parts - blood supply around the nephron and the nephron itself... a) Blood supply: Renal artery afferent arteriole glomerulus efferent arteriole peritubular capillary network venule renal vein o Afferent arteriole larger than efferent because blood pressure higher - Transports blood to be filtered to glomerulus o Glomerulus - Knot of capillaries inside the glomerular capsule (also called Bowman s capsule) of nephron

5 - Have specialized cells on exterior surface of these capillaries called podocytes which make pores to allow easy passage of small molecules out of capillaries and into the nephron o Efferent arteriole - Smaller than afferent because as molecules leave blood and enter nephron, the blood volume decreases - Transports blood from the glomerulus to the peritubular capillaries o Peritubular capillary network - Surrounds the nephron - Allows transport of molecules from bloodstream into nephron (tubular secretion) and from the nephron (tubular reabsorption) Then the peritubular capillary network feeds into the venule and then into the renal vein and back to the heart b) Parts of the Nephron o Glomerular capsule - Located in renal cortex the outer layer of the kidney - Cuplike structure - Receives molecules filtered from blood from glomerulus = glomerular filtration o Proximal convoluted tubule - Located in renal cortex - Proximal means close to and it is the tubule closest to the glomerular capsule - Has microvilli = brush border that increases surface area for reabsorption of filtered molecules from the nephron back into the bloodstream via the peritubular capillaries - Have mitochondria in the cells of the proximal convoluted tubule to provide energy to assist reabsorption by active transport of molecules o Loop of Nephron - Located in renal medulla - Helps reabsorption of water, extrusion of salt = salt/water balance

6 - Descending limb allows water to leave H2O NaCl Ascending limb interior surface has no aquaporons therefore water can t leave - extrudes salt ions Na + and Cl - o Distal convoluted tubule - Located in renal cortex - Distal means far or distant further from glomerular capsule - Has lots of mitochondria but No microvilli - Moves molecules from blood TO nephron = tubular secretion (opposite to tubular reabsorption) o Collecting ducts - NOT part of the nephron - Several nephrons enter 1 collecting duct - All the collecting ducts feed into the renal pelvis - then renal pelvis feeds into the ureter to the bladder to the urethra and out... D) Urine Formation 3 processes: 1. glomerular filtration 2. tubular reabsorption 3. tubular secretion

7 1. Glomerular filtration Blood to nephron (blood pushed thru coarse filter into container) How and why: a passive process works on blood pressure -afferent arteriole is larger than efferent high blood pressure in the glomerulus acts like a coarse filter pushing anything smaller then about 3-5 nm into the glomerular capsule so end up with ~ same contrns of these molecules in the blood and filtrate. Controls juxtaglomerular apparatus responds to conctrn of NaCl in filtrate if it detects a fall in NaCl respond by dilation of the afferent arteriole allowing increase blood so increase filtration / if it detects high NaCl, leads to constriction of afferent arteriole to lower amount that is filtered. Renin is released from juxtaglomerulus apparatus (juxtaglomerulus apparatus occurs at contact point between afferent arteriole and distal convoluted tubule juxta = next to, so juxtaglomerulus means next to glomerulus, and apparatus refers to a bunch of cells working together) when blood pressure and volume decreases too low for filtration this leads to secretion of Aldosterone from adrenal glands (on kidney) promotes reabsorption of Na+ followed by reabsorption of water increase blood press and vol. Glomerular Filtrate: Filterable (small molecules) Non filterable (large molecules) Water RBC Nitrogenous waste urea/uric acid WBC Nutrients aa/ glucose Platelets salts proteins o Non filterable stays in efferent arteriole 2. Tubular reabsorption Nephron to Blood (blood stream reclaims everything the body needs from the container) How and why: the total volume of our blood plasma is filtered thru our kidneys in about 20 min so if almost all of it was NOT reabsorbed our bodies would be drained in about 30 min almost immediately when the filtrate enters the proximal convoluted tubule 100% of glucose and amino acids (if all carriers in use, can have excretion of glucose or aa in urine )and ~99% of water and other

8 components such as salts (i.e, Na +, K +, HCO3 -, Mg2 + - actively or passively) are reabsorbed from nephron to blood either actively or passively in the descending limb of the loop, only water is passively transported into the blood through aquaporinsas you go back up the ascending limb there are no aquaporins but NaCl is passively (in lower part), then actively (in upper part) reabsorbed into the tissues, some reabsorption also happens in the distal convoluted tubule at this pt only about 10% of originally filtered NaCl and 25% of water remain in nephron most reabsorption from this pt on depends on body s needs. regulated by hormones mostly aldosterone Reabsorbed filtrate components Most H2O Nutrients Required salts Non reabsorbed filtrate components Some H2O Nitrogenous waste Excess salt Control: water reabsorption works on conctrn gradient so water reabsorption means reabsorption of salts back into the tissues has to happen as well then reabsorption of water can happen passively through osmosis. urea leaks from collecting duct into medulla add to salt concentration in inner medulla tissue Hormones regulate reabsorption of Na+ and water in the distal convoluted tubule (DCT) and collecting ducts to fine tune the body s needs. a) Aldosterone secreted by adrenal glands (on top of kidneys) promote excretion of K+ and reabsorb of Na+ from DCT into blood b) Renin hormone secreted by juxtaglomerular apparatus hormone release triggered by decreased blood pressure and blood volume when pressure and volume is insufficient for filtration, juxtaglomerulus releases renin, which in turn leads to secretion of aldosterone reabsorption of Na+ and so on... c) Antidiuretic hormone (ADH) water is not always reabsorbed in distal convoluted tubule ADH is secreted by pituitary (in brain) depending on osmolarity of the blood if our intake of water has been low ADH is secreted and more water is reabsorbed in distal convoluted tubule and collecting duct into blood.

9 d) ANH hormone secreted by atria of heart due to increased blood volume ANH inhibits secretion of renin and aldosterone leads to excretion of Na+, if ANH present, less water reabsorbs even if ADH is present as water reabsorption depends on salt concentration gradient. 3. Tubular Secretion Blood to Nephron (things are selectively put back or added into container from blood to fine tune body s chemical balance) How and why: selectively and actively moves undesirable substances from blood to nephron that either didn t make it into the filtrate (too big or associated with proteins) or were reabsorbed passively so need to be redumped back into nephron. Controls blood ph by secreting H + into nephron (& retain HCO3 - in blood) i.e, Hydrogen ions (H+), creatinine, and excess drugs such as penicillin moved by active transport from blood into the convoluted tubules. Side Note: Maintaining acid base balance in blood ph needs to stay near 7.4 for functioning of enzymes and regular metabolism 3 ways acid/base balance is maintained in blood... i. buffering system ii. respiratory control centre in brain iii. Kidneys i. Regulated by acid-base buffering system - Buffers -regulate blood ph by combining with excess H + ions (acid) or OH - ions (base) - One of most important buffers in blood is combination of carbonic acid (H2CO3) and bicarbonate ions (HCO3 - ) - These buffers are temporary solution to the change in H+ concentration ii. Also regulated by respiratory centre in brain covered in resp sectn - If concentration of H+ ions rises, increases ventilation, and as CO2 exhaled, concentration of H+ decreases because rxn shifts to the right H + + HCO3 - H2CO 3 H2O + CO2 (released)

10 iii. Acid base balance also regulated in the kidneys - Kidneys are slower acting then other 2 regulatory methods but has more powerful effect on ph - If blood is acidic, excretes H+ ions and reabsorbs bicarbonate - If blood is basic, H+ not excreted and HCO3 not reabsorbed - Urine is usually acidic therefore excess H+ ions are usually excreted - Ammonia, which is produced in tubule cells, also acts as a buffer and removes H+ ions H+ ions react with ammonia (NH3) to form ammonium NH4 + to remove H + from urine Urine contains substances that have come out of the blood through glomerular filtration and tubular secretion but have not been reabsorbed through tubular reabsorption This animation may help with understanding 9x7Q or google function of the nephron made easy!!