Excretory SystemExcretory System

ExcretionExcretion

is the process by which the body rids itself is the process by which the body rids itself of metabolic wastes.of metabolic wastes. The lungs eliminate carbon dioxideThe lungs eliminate carbon dioxide The large intestine eliminates toxic digestive The large intestine eliminates toxic digestive

wastewaste The liver changes toxin and products of The liver changes toxin and products of

protein metabolism into soluble compounds protein metabolism into soluble compounds that the kidney can collect and eliminate.that the kidney can collect and eliminate.

The role of the liver:The role of the liver:Excess protein is converted to carbohydrates by a Excess protein is converted to carbohydrates by a process called process called deaminationdeamination. This involves the . This involves the removal of an removal of an amino groupamino group from amino acids to from amino acids to produce a carbohydrate and produce a carbohydrate and ammoniaammonia (a toxic gas). (a toxic gas).Two molecules of toxic ammonia react with carbon Two molecules of toxic ammonia react with carbon dioxide to produce dioxide to produce ureaurea. Urea is about 100,000 x less . Urea is about 100,000 x less toxic than ammonia and can be safely transported toxic than ammonia and can be safely transported through the bloodstream.through the bloodstream.Nucleic acidsNucleic acids are also broken down into are also broken down into uric aciduric acid. . Excess uric acid can cause kidney stones or gout.Excess uric acid can cause kidney stones or gout.

All of the waste products made by the liver travel All of the waste products made by the liver travel through the blood and are then filtered by the kidney.through the blood and are then filtered by the kidney.

The role of the kidneys:The role of the kidneys:

1. Main role: Removal of poisonous 1. Main role: Removal of poisonous nitrogenous wastesnitrogenous wastes

2. Maintenance of blood pH2. Maintenance of blood pH

3.3. Maintenance of water balanceMaintenance of water balance

4.4. Maintain blood pressureMaintain blood pressure

Urinary SystemUrinary System

Blood is carried to the paired kidneys from Blood is carried to the paired kidneys from renal arteriesrenal arteries that branch off the aorta. that branch off the aorta. The kidney’s can hold as much as 25% of The kidney’s can hold as much as 25% of the entire blood supply at any given time. the entire blood supply at any given time. Wastes are then filtered by the kidneys Wastes are then filtered by the kidneys and taken to the and taken to the urinary bladder urinary bladder via the via the ureters.ureters.

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Urinary System AnatomyUrinary System Anatomy

A A sphincter musclesphincter muscle at the base of the urinary at the base of the urinary bladder acts as a valve and released stored urine bladder acts as a valve and released stored urine through the through the urethra urethra when the muscles relax. The when the muscles relax. The signal to urinate is relayed to the brain when the signal to urinate is relayed to the brain when the bladderbladder is about 200 mL full of urine. The liquid in is about 200 mL full of urine. The liquid in the bladder cause the walls to stretch, stimulating the bladder cause the walls to stretch, stimulating receptors. At 400 mL volume, the signal will be of receptors. At 400 mL volume, the signal will be of increasing strength and urgency, and at a 600 mL increasing strength and urgency, and at a 600 mL volume, the sphincter muscles relax, voluntary volume, the sphincter muscles relax, voluntary bladder control is lost and urination occurs.bladder control is lost and urination occurs.

Howstuffworks "Urination"

Remember, that when you drink fluids, the fluid Remember, that when you drink fluids, the fluid goes to your stomach first, and is then absorbed goes to your stomach first, and is then absorbed by the body. The loss of bladder control only by the body. The loss of bladder control only occurs when much more than 600 mL is occurs when much more than 600 mL is processed, absorbed, filtered and finally processed, absorbed, filtered and finally collected in the bladder.collected in the bladder.

The bottom line:The bottom line:

You won’t lose bladder control from drinking a You won’t lose bladder control from drinking a Big Gulp or Slurpee. Input doesn’t equal output Big Gulp or Slurpee. Input doesn’t equal output when it comes to excretion. Your body retains when it comes to excretion. Your body retains much of the fluid it consumes for normal much of the fluid it consumes for normal processes.processes.

The KidneysThe Kidneys

A cross section of the A cross section of the kidney reveals the kidney reveals the anatomy of three anatomy of three major structures:major structures:

1. The cortex1. The cortex

2. The medulla2. The medulla

3. The renal pelvis3. The renal pelvis

Cortex

Renal Pelvis Medulla

Detailed Kidney StructureDetailed Kidney StructureA cross-section of the kidney reveals the A cross-section of the kidney reveals the anatomy of three major structures: cortex, anatomy of three major structures: cortex, medulla, and renal pelvismedulla, and renal pelvis

ureters ureters – tubes that conduct urine from the – tubes that conduct urine from the kidneys to the bladderkidneys to the bladder renal artery renal artery -- delivers blood to the kidneydelivers blood to the kidneyrenal vein renal vein – sends blood back to the body– sends blood back to the bodyrenal calyces renal calyces – outer extensions of the renal – outer extensions of the renal pelvis that filter bloodpelvis that filter bloodcortex cortex – outer layer of connective tissue– outer layer of connective tissuemedullamedulla – inner layer beneath the cortex, hold – inner layer beneath the cortex, hold the major part of the nephronthe major part of the nephronrenal pelvisrenal pelvis – hollow chamber that joins the – hollow chamber that joins the kidney with the ureterkidney with the ureter

The NephronThe NephronBlood PathwayBlood Pathway::

The nephron is the functional unit of the kidney. The nephron is the functional unit of the kidney. There are about 1 million of these slender There are about 1 million of these slender tubulestubules in the kidney. These tubules are in the kidney. These tubules are supplied with blood from the supplied with blood from the afferent arteriolesafferent arterioles which branch from the renal artery. They lead which branch from the renal artery. They lead into a high pressure capillary bed called the into a high pressure capillary bed called the glomerulusglomerulus. This is where filtration occurs. . This is where filtration occurs. Blood leaves the glomerulus via the Blood leaves the glomerulus via the efferent efferent arteriolesarterioles and is carried to a capillary network, and is carried to a capillary network, called the called the peritubular capillariesperitubular capillaries, that wraps , that wraps around the kidney tubule. Blood is then around the kidney tubule. Blood is then transferred to a transferred to a renal veinrenal vein. Then back to the . Then back to the venous blood systemvenous blood system

http://www.wisc-online.com/objects/AP2504/AP2504.swf

Filtrate Pathway:Filtrate Pathway:The glomerulus is surrounded by a cup-like The glomerulus is surrounded by a cup-like portion of the nephron called portion of the nephron called Bowman’s Bowman’s capsulecapsule. The cortex contains Bowman’s . The cortex contains Bowman’s capsule, afferent and efferent arterioles. Fluids capsule, afferent and efferent arterioles. Fluids to be processed into urine enter Bowman’s to be processed into urine enter Bowman’s capsule from the glomerulus. Next, fluids move capsule from the glomerulus. Next, fluids move through the through the proximal/distal tubulesproximal/distal tubules and then and then into the into the collecting ductscollecting ducts which collect urine which collect urine from many different nephrons and merge into from many different nephrons and merge into the the renal pelvisrenal pelvis..

kidney patient guide - healthy kidney

Urine Formation- Removal of WastesUrine Formation- Removal of Wastes

Formation of urine depends on filtration, re-absorption and Formation of urine depends on filtration, re-absorption and secretion.secretion.

FiltrationFiltration – is accomplished by the movement of fluid into – is accomplished by the movement of fluid into Bowman’s capsuleBowman’s capsule. Blood moves through the afferent . Blood moves through the afferent arteriole to the glomerulus and small dissolved solutes arteriole to the glomerulus and small dissolved solutes (glucose, aa, urea, uric acid, ammonia, and salts) and (glucose, aa, urea, uric acid, ammonia, and salts) and water pass into Bowman’s capsule (much lower water pass into Bowman’s capsule (much lower pressure). The pressure gradient allows only some pressure). The pressure gradient allows only some substances to be filtered. Red blood cells, plasma substances to be filtered. Red blood cells, plasma proteins, white blood cells, platelets are proteins, white blood cells, platelets are too largetoo large to to pass through. pass through.

Nephron Information Center

Re-absorptionRe-absorption – involves the transfer of essential – involves the transfer of essential solutes (glucose, aa, vitamins, salts, K+,and solutes (glucose, aa, vitamins, salts, K+,and H+) and water H+) and water from the nephron, back into the from the nephron, back into the bloodblood. This is very important in maintaining . This is very important in maintaining the body’s water balance. About 85% of the body’s water balance. About 85% of filtrate is re-absorbed. (Remember the Big filtrate is re-absorbed. (Remember the Big Gulp: If you drink a 1L Big Gulp, about 850 mL Gulp: If you drink a 1L Big Gulp, about 850 mL of the fluid is reabsorbed, and only 150 mL is of the fluid is reabsorbed, and only 150 mL is collected in the bladder. You don’t even feel collected in the bladder. You don’t even feel like you have to “go” yet.)like you have to “go” yet.)

-Re-absorption mostly occurs in the -Re-absorption mostly occurs in the proximal proximal tubule, tubule, with some minor solutes being re-with some minor solutes being re-absorbed in the absorbed in the distal tubuledistal tubule

-Most water re-absorption occurs in the -Most water re-absorption occurs in the descending limb of the descending limb of the Loop of HenleLoop of Henle

Steps involved in re-absorption:Steps involved in re-absorption:

1. Na+ is 1. Na+ is actively transportedactively transported out of the nephron. out of the nephron.2. Cl- and HCO3- follow Na+ by charge 2. Cl- and HCO3- follow Na+ by charge attraction.attraction.3. The resulting osmotic gradient draws water 3. The resulting osmotic gradient draws water from the nephron into the blood. (Remember, from the nephron into the blood. (Remember, water follows salt)water follows salt)4. An additional osmotic gradient is created by 4. An additional osmotic gradient is created by plasma proteins that stay in the blood. (They plasma proteins that stay in the blood. (They were too big to pass through Bowman’s capsule)were too big to pass through Bowman’s capsule)5. Urea and uric acid may diffuse out as well, but 5. Urea and uric acid may diffuse out as well, but will be reabsorbed laterwill be reabsorbed later

Re-absorption occurs Re-absorption occurs until a until a threshold levelthreshold level of substance is of substance is reached. Excess reached. Excess amounts of glucose and amounts of glucose and salts in the blood will salts in the blood will not be re-absorbed and not be re-absorbed and will be excreted in the will be excreted in the urine. This is why urine urine. This is why urine tests can tell us about tests can tell us about our blood chemistry.our blood chemistry.

Tubular SecretionTubular Secretion – involves the movement of – involves the movement of materials from the materials from the blood back into the blood back into the nephron.nephron. Nitrogen containing wastes (urea, Nitrogen containing wastes (urea, uric acid), histamines, excess H+ (that uric acid), histamines, excess H+ (that regulate pH), minerals, drugs, penicillin, etc. regulate pH), minerals, drugs, penicillin, etc. are all removed from the body by the cells in are all removed from the body by the cells in the distal tubule, which the distal tubule, which actively transportsactively transports these substances back to the nephron. The these substances back to the nephron. The distal tubule contains loads of mitochondria to distal tubule contains loads of mitochondria to keep up with this energy demand. keep up with this energy demand.

http://cpharm.vetmed.vt.edu/VM8314/http://cpharm.vetmed.vt.edu/VM8314/NephronMovie.swfNephronMovie.swf

Regulating Water BalanceRegulating Water Balance

Antidiuretic Hormone Antidiuretic Hormone (ADH)(ADH) helps regulate the helps regulate the osmotic pressure of body osmotic pressure of body fluids by causing the fluids by causing the kidneyskidneys to increase water re-to increase water re-absorptionabsorption, , producing more producing more concentrated urineconcentrated urine. ADH . ADH makes the makes the distal tubulesdistal tubules more permeable to the last more permeable to the last 15% of water can be re-15% of water can be re-absorbed into the blood. absorbed into the blood.

Special nerve receptors called Special nerve receptors called osmoreceptors osmoreceptors located in the located in the hypothalamushypothalamus in the brain in the brain detect changes in the osmotic detect changes in the osmotic pressure of the blood and pressure of the blood and stimulate or inhibit the secretion stimulate or inhibit the secretion of ADH. These receptors also of ADH. These receptors also elicit the thirst response, elicit the thirst response, inspiring you to increase fluid inspiring you to increase fluid consumption. Substances such consumption. Substances such as alcohol and caffeine as alcohol and caffeine decrease decrease the release of ADH, the release of ADH, resulting in increased urine resulting in increased urine output and dehydration.output and dehydration.

Blood PressureBlood PressureThe kidneys regulate blood pressure by The kidneys regulate blood pressure by regulating the amount of fluid in the blood. More regulating the amount of fluid in the blood. More fluid means higher pressure. The hormone fluid means higher pressure. The hormone aldosteronealdosterone, acts on the nephrons to , acts on the nephrons to increase increase sodium (salt) re-absorption from the distal sodium (salt) re-absorption from the distal tubuletubule, back into the blood. Chloride ions and , back into the blood. Chloride ions and water will follow, causing the blood volume to water will follow, causing the blood volume to increase. Aldosterone is secreted by the increase. Aldosterone is secreted by the adrenal cortexadrenal cortex, just above the kidney. A drop in , just above the kidney. A drop in blood pressure is detected by the blood pressure is detected by the juxtaglomerular apparatusjuxtaglomerular apparatus, located near the , located near the glomerulus. This causes the release of liver glomerulus. This causes the release of liver proteins, proteins, angiotensinogen angiotensinogen and and renninrennin, which , which stimulate the release of aldosterone from the stimulate the release of aldosterone from the adrenal gland.adrenal gland.http://www.wisc-online.com/objects/AP2204/http://www.wisc-online.com/objects/AP2204/AP2204.swfAP2204.swf

pH BalancepH Balance

Despite the variety of foods and fluids with Despite the variety of foods and fluids with different pH levels we consume, our bodies different pH levels we consume, our bodies maintain a relatively constant pH between about maintain a relatively constant pH between about 7.3 and 7.5. A relatively stable pH is maintained 7.3 and 7.5. A relatively stable pH is maintained by a buffer system that absorbs excess H+ ions by a buffer system that absorbs excess H+ ions or basic ions. Bicarbonate ions (HCO3-) are key or basic ions. Bicarbonate ions (HCO3-) are key components of this system:components of this system:HCOHCO33- + H+ - + H+ ====== H H22COCO33 ====== H H22O + COO + CO22

Bicarbonate ions in the blood remove excess H+ ions, Bicarbonate ions in the blood remove excess H+ ions, but the buffer must be restored for this system to but the buffer must be restored for this system to continue working indefinitely. The kidneys reverse this continue working indefinitely. The kidneys reverse this reaction. Carbon dioxide is actively transported from the reaction. Carbon dioxide is actively transported from the peritubular capillary and combines with water to produce peritubular capillary and combines with water to produce HCO3- and H+ ions. The bicarbonate ion diffuses back HCO3- and H+ ions. The bicarbonate ion diffuses back into the blood and the H+ ions combine with phosphate into the blood and the H+ ions combine with phosphate or ammonia and are excreted in the filtrate. or ammonia and are excreted in the filtrate. The pH balance is mostly controlled by the The pH balance is mostly controlled by the distal tubuledistal tubule of the nephronof the nephronAcid-Base BalanceAcid-Base Balance

Kidney DysfunctionKidney DysfunctionDiabetes MellitisDiabetes Mellitis – is caused by the – is caused by the inadequate secretion of insulin from the inadequate secretion of insulin from the pancreas. Without insulin, blood glucose pancreas. Without insulin, blood glucose levels are extremely high, and excess levels are extremely high, and excess glucose remains in the nephron. The high glucose remains in the nephron. The high osmotic gradient prevents water re-osmotic gradient prevents water re-absorption and increases urine production.absorption and increases urine production.Diabetes InsipidusDiabetes Insipidus – is caused by – is caused by inadequate production of Anti-Diuretic inadequate production of Anti-Diuretic Hormone (ADH). Without ADH, urine input Hormone (ADH). Without ADH, urine input increases dramatically, as much as 20 L per increases dramatically, as much as 20 L per day and the patient will be extremely thirsty.day and the patient will be extremely thirsty.

Nephritis Nephritis – ‘– ‘Bright’s DiseasesBright’s Diseases’ is inflammation of ’ is inflammation of the nephrons which can have a variety of causes. the nephrons which can have a variety of causes. Protein in the urine is a common symptom of Protein in the urine is a common symptom of nephritis. The osmotic gradient also causes an nephritis. The osmotic gradient also causes an increase in urine production. Nephritis can lead to increase in urine production. Nephritis can lead to irreversible kidney damage and eventual kidney irreversible kidney damage and eventual kidney failure.failure.

Kidney StonesKidney Stones – are caused by – are caused by

the precipitation of mineral solutes the precipitation of mineral solutes

form the blood. The stones lodge in the form the blood. The stones lodge in the

renal pelvis or the ureter, causing major pain and renal pelvis or the ureter, causing major pain and bleeding. Stones can be removed by surgery or by bleeding. Stones can be removed by surgery or by using ultrasonic waves that blast the stones into using ultrasonic waves that blast the stones into smaller fragments.smaller fragments.

Dialysis Dialysis – is used for patients whose kidneys no – is used for patients whose kidneys no longer function properly. longer function properly. HemodialysisHemodialysis – a machine is connected to the – a machine is connected to the patient’s circulatory system by a vein. Blood is patient’s circulatory system by a vein. Blood is pumped through a series of tubes submerged in pumped through a series of tubes submerged in solutes that removed waste from the blood.solutes that removed waste from the blood.kidney patient guide - Haemodialysis animationkidney patient guide - Haemodialysis animationPeritoneal DialysisPeritoneal Dialysis – is done through the lining – is done through the lining of the abdominal cavity. A catheter tube is of the abdominal cavity. A catheter tube is inserted and solution is fed into the abdominal inserted and solution is fed into the abdominal cavity for two to six hours. This fluid collects cavity for two to six hours. This fluid collects wastes from the body and is drained from the wastes from the body and is drained from the catheter when the process is complete.catheter when the process is complete.kidney patient guide - How Peritoneal Dialysis kidney patient guide - How Peritoneal Dialysis works animationworks animation

Kidney TransplantKidney Transplant

kidney patient guide - Kidney Transplant kidney patient guide - Kidney Transplant animationanimation