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Chapter: 17 Excretory System and Liver • All animals excrete nitrogenous waste products and some animals also balance water and solute concentrations. • The chemical composition of the blood is regulated by the liver. I. Nitrogenous waste products and excretion A. Excretion: process of removing metabolic wastes and helps to maintain homeostasis by regulating the content of water and other substances in the blood 1. Blood plasma of an animal is a constantly changing solution 2. Blood supplies the substances needed for an animal’s metabolism and removes molecular waste products from tissues 3. Blood needs to be continuously filtered and cleaned B. Waste products from the metabolism of amino acids 1. Body has no way to store excess amino acids (not needed for protein synthesis) 2. Deamination: chemical changes in which the amine group (NH2) is removed 3. Amine group is incorporated into 3 types of waste molecules a) Ammonia b) Urea c) Uric acid 4. Kidney: all mammals and some other animals use it to filter and clean the blood of urea and other wastes 5. Malpighian tubules: structures in insects to filter the blood C. Evolutionary history, habitat, and the type of nitrogenous waste 1. Nitrogenous waste: contains one or more atoms of nitrogen from deamination of amino acids a) Animals form of nitrogenous waste is based on ancestral origins and the emerging species is most likely to use the same nitrogenous waste type b) Animals can’t evolve an entirely new physiology even when they undergo enough change to qualify as a new species Nitrogenous waste slides 2. Fish: use ammonia a) Aquatic habitat means that they have an unlimited watery supply that they can use to dilute and flush out the highly toxic ammonia b) Ammonia is very energy inexpensive Paramecium 3. Mammals: produce and excrete urea a) Urea is only toxic at relatively high concentration levels and mammals can cope with certain levels of urea b) Level of urea needs to be kept under control by the constant filtering of the kidneys c) Urea is a component of urine and can be stored in the bladder d) Water is not as accessible to mammals like it is to fish, so their system needs less water for dilution and elimination compared with ammonia 4. Birds and reptiles: egg that is self-contained for nutrients and water for development and hatching a) Ammonia can’t be stored within egg, so evolutionary solution was uric acid b) Uric acid is not water soluble and can be stored within the egg, but it is energy expensive to produce c) Adult bird continue to produce uric acid and allows them to require less water 5. Insects: uric acid using Malpighian tubules a) Insects have an open circulatory system, so their internal organs are bathed in blood b) Malpighian tubules: small tubes that lie within the pools of blood i) Closed at distal end and open into the insect’s gut at the proximal end ii) Nitrogenous waste (uric acid), water and many salt ions (Na+, K+, Cl-) remain in the tubules are eliminated iii) Useful substances, non-excess water, and unused nutrients from the blood are transported back into the pool of blood of the body cavity Note: Humans and other vertebrates have a closed circulatory system: Blood is contained in vessels Slides D. Anatomy and function of the kidney 1. Function: Filter waste products from the blood 2. Two bean-shaped organs located in the back behind the stomach and liver 3. Urine: fluid produced by the kidneys that consists of water and dissolved waste products that have been removed from the blood 4. Structure a) Cortex: outermost portion b) Medulla: inner portion c) Renal pelvis: funnel-shaped structure in the center in which urine is collected d) Renal artery: transports nutrients and wastes into the kidneys e) Renal vein: carries filtered blood out of kidneys Draw a kidney Structure of the Kidneys Section 38-3 Kidney Nephron Bowman’s capsule Cortex Capillaries Glomerulus Medulla Renal artery Renal vein Ureter Collecting duct Vein To the bladder Artery Loop of Henle To the ureter E. Nephrons: filtering units of kidneys 1. Each kidney has 1.25 million nephrons 2. Nephron structure includes a) Glomerulus: capillary bed which filters various substances from the blood b) Bowman’s capsule: surrounds the glomerulus c) Small tubule that extends from Bowman’s capsule i) Proximal convoluted tubule ii) Loop of Henle iii) Distal convoluted tubule d) Peritubular capillary bed: second capillary bed that surrounds the three part tubule Nephrons 3. Materials are exchanged between tubule and blood by three major processes a) Ultrafiltration: process by which various substance are filtered through the glomerulus from the blood into Bowman’s capsule b) Reabsorption: process that recovers needed substances are returned to the blood c) Secretion: process in which substances (waste) pass from blood into filtrate in the distal convoluted tubule Kidney processes Section 38-3 The Nephron Reabsorption Filtration Most filtration occurs in the glomerulus. Blood pressure forces water, salt, glucose, amino acids, and urea into Bowman’s capsule. Proteins and blood cells are too large to cross the membrane; they remain in the blood. The fluid that enters the renal tubules is called the filtrate. As the filtrate flows through the renal tubule, most of the water and nutrients are reabsorbed into the blood. The concentrated fluid that remains is called urine. Secretion Substances such as hydrogen ions are transferred from the blood to the filtrate. F. Blood is ultrafiltered within Bowman’s capsule 1. Afferent arteriole: small branch of the renal artery that brings unfiltered blood to the nephron 2. Inside Bowman’s capsule, afferent arteriole branches into the glomerulus a) Glomerulus walls have fenestrations (small slits) that open when blood pressure is increased b) Efferent arteriole: drains blood from the glomerulus and has a smaller diameter than afferent c) Connecting a larger diameter blood vessel to a smaller diameter creates a higher pressure where they join in the glomerulus 3. Ultrafiltration: process by which various substances are filtered through the glomerulus under unusually high blood pressure in the capillary bed 4. Filtrate: fluid that is ultrafiltered from the glomerulus passes through the basement membrane (prevents large molecules like proteins from becoming a part of the filtrate) 5. Filtrate then enters the proximal convoluted tubule 6. Blood that did not get filtered, including all of the cells, proteins, and other molecules, exit the Bowman’s capsule by the efferent arteriole G. Reabsorption recovers substances that are needed 1. Filtrate: contains needed substances that body can’t lose as a part of the urine a) Most of water b) Many salt ions c) All of the glucose 2. These substances are reabsorbed back into the blood Note: Total volume of blood is filtered about 25 times each day. Reabsorption is very important. 3. Much of reabsorption occurs in proximal convoluted tubule a) Substances leave the tubule and are put back into the blood via the peritubular capillary bed (surrounds (peri-) the tubule) b) Proximal convoluted tubule wall is a single cell thick made up of a single ring of cells i) Lumen: interior of the tube that filtrate flows through ii) Microvilli: located on the interior side of the cells to increase surface area for reabsorption 4. Types of transport mechanisms for reabsorption a) Salt ions (Na+, Cl-, and K+): leave the filtrate and are returned to the blood i) Actively transported into the tubule cells ii) Move into the intercellular fluid outside the tubule iii) Salt ions are taken into the peritubular capillary bed b) Water: moves by osmosis following the movement of the salt ions i) Water moves from a hypotonic region to a hypertonic region following the pathway of the solutes ii) Water remains in the filtrate awaiting a control mechanism that will determine how much water the body can eliminate in the urine c) Glucose: active transport moves all of the glucose in the filtrate back into the blood H. Secretion: substances pass from blood into filtrate in the distal convoluted tubule 1. Wastes and toxic materials 2. Hydrogen ions to adjust pH of blood I. Formation of urine: remaining fluid and wastes in the distal convoluted tubule form urine 1. Flows into a collecting duct where more water moves out 2. 99% of water is returned to the blood by the end of the process Process J. Kidney nephrons and osmoregulation 1. Water is the solvent of life and is in almost all body fluids a) Cytoplasm, blood plasma, lymph, and intercellular fluid b) Some water needs to be eliminated in the urine each day 2. Amount eliminated depends on many physiological factors a) Total volume of water ingested as liquid and food b) Perspiration rate: exercise level and environmental temperature c) Ventilation (breathing) rate: water is exhaled when we breathe out: dependent on activity/exercise level 3. Osmoregulation: body’s response mechanisms that attempt to maintain homeostatic levels of water 4. Loop of Henle creates a hypertonic environment in the medulla of the kidney a) Remaining water and dissolved solutes enters the descending portion of the loop of Henle b) Segment of the loop is permeable to water but impermeable to salt ions loop of Henle c) Filtrate then enters the ascending portion of the loop of Henle: impermeable to water, but permeable to salt ions d) Filtrate moves up the ascending portion of the loop, salt ions are pumped out and enter the intercellular fluid e) Loop of Henle extends down into the medulla of the kidney: medulla is an area with many ions (hypertonic) in comparison with the fluids within the tubules f) Some water moves out of the descending portion by osmosis, the filtrate that moves up the ascending loop and into the distal convoluted tubule is still hypotonic (high water content) Nephrons Kidney 5. ADH controls reabsorption of water in the collecting duct a) Filtrate that enters collecting duct is a dilute form of urine with a high amount of water b) Some of the water is reabsorbed through the wall of the collecting duct c) Collecting duct is differentially permeable to water and depends on the presence or absence of antidiuretic hormone (ADH) d) ADH is secreted from the posterior lobe of the pituitary gland and targets the tissue of the kidney collecting ducts e) ADH present: collecting duct becomes permeable to water and water moves by osmosis out of the collecting duct and into the medulla interstitial fluid to the peritubular capillary bed and into the blood f) ADH absent: collecting duct becomes impermeable to water and water stays in the collecting duct and urine is more dilute ADH 6.Longer loop of Henle is an adaptation for water conservation a) Kidneys are highly diverse organs when you compare different species i) Frogs and toads have virtually no loops of Henle and are unable to conserve water by mechanism involving a hypertonic medulla and reabsorption of water from the collecting duct so their urine is dilute ii) Vertebrate animals that live in the desert means that they have adaptions for water conservation iii) Kangaroo rat: recycle almost all of their water and lose very little water to urine due to a very long loop of Henle that produces a large hypertonic area for water reabsorption using ADH mechanism K. What changes do the kidneys make to the blood? 1. Comparison of the composition of blood entering a kidney and blood leaving the kidney a) b) c) d) e) f) Lowered amount of urea Lowered amount of salt ions Lowered amount of water Nearly identical amount of glucose Nearly identical amount of protein No change in blood cells 2. Osmoregulators: animals with internal tissues that have a different solute concentration compared with environment a) Need mechanisms that regulate water balance and expend energy to achieve it b) Most animals are osmoregulators 3. Osmoconformers: animals that have internal tissues that have the same solute concentration as their environment (iso-osmotic) a) Do not need mechanisms to take in or to eliminate water as water moves in and out freely because of the osmotic balance b) Animals are restricted to living in only those environments to which they are isoosmotically matched L. Kidney failure: 2 options for patient 1. Kidney dialysis/hemodialysis: patient’s blood is pumped into a device that contains a large surface area of a membrane (dialysis membrane) a) One side of membrane is patient’s blood and the other is dialysate (solution similar in the makeup of blood but without the urea at the start of process) b) Urea from blood diffuses through the membrane and enters the dialysate c) Balance of water and some ions can be regulated by adjusting which fluid on either side of the dialysis membrane has a greater concentration of each substance d) Dialysis takes several hours each session and must be repeated every 1-3 days Dialysis Video Kidney Dialysis Section 38-3 Blood in tubing flows through dialysis fluid Blood pump Vein Artery Used dialysis fluid Shunt Air detector Dialysis machine Fresh dialysis fluid Compressed air 2. Kidney transplant: receive a new kidney from a donor a) Patient’s and donor’s tissues must match to minimize rejection of the organ by the patient’s immune system: still need to take immunesuppressing drugs b) Can live normally with one kidney, so a family member with a tissue match can donate c) Long waiting list for a kidney from a deceased donor M. Other medical issues related to the kidneys 1. Kidney stones: crystalline structures that form within the kidneys and can cause blockages and severe pain (especially if they pass through ureter) a) Can be broken up into smaller pieces by ultrasound so they can pass through the normal urinary tract 2. Testing urine for chemical composition: can provide doctor with information concerning you physiology a) Glucose: healthy person should have no glucose in urine: should be reabsorbed in proximal convoluted tubule: can indicate diabetes if glucose is present in urine b) Blood cells: Glomerular filtrate should have no blood cells since they are too large to fit through the fenestrations of the glomerulus i) Sign of kidney malfunction ii) Infection iii) Bleeding in renal tubes c) Proteins: too large to fit through the glomerulus and shouldn’t be found in urine could indicate many different diseases or conditions including kidney disease, low blood sugar in diabetics, high blood pressure, and problems during pregnancy d) Drugs: most drugs are filtered in the kidneys and it has become common for employers and sports teams to test individuals for prescribed or unauthorized chemicals 3. Dehydration: too little water intake video 4. Overhydration: too much water intake Symptoms for both can be serious because water tis the solvent component of our blood and cytoplasm Urine analysis lab N. Elimination of urine 1. Urine from collecting ducts enters the renal pelvis 2. Ureter: narrow tube that leads from each kidney to bladder 3. Urinary bladder: muscular sac that stores urine 4. Urethra: tube from bladder that leads out of the body Section 38-3 The Urinary System Vein Kidney (Cross Section) Kidney Cortex Medulla Ureter Urinary bladder Urethra Artery 5. Body must remove 500 ml of urine each day to remove toxic materials from body 6. Adult removes 1.5 L to 2.3 L a day II. Excretory system A. Kidneys: primary organs of the excretory system 1. Life –threatening situation if kidneys fail 2. Can survive using one kidney B. Lungs 1. Eliminate carbon dioxide 2. Carry out detoxification: altering harmful substances so that they are not poisonous C. Skin: secretes sweat to remove excess water and salt 1. Person working in extreme heat can excrete 1L of water per hour by sweating 2. 10-30 g of salt per day Types of excretion Calculation How much blood does the glomerulus (kidneys) filter per day? 125 mL of blood is filtered per min Answer 125 ml/min x 60 min x 24 hr = 180,000 mL /day 1 hr 1 day 180,000 mL x 1 L = 180 L / day 1000 mL 180L is 47.5 gallons III. Functions of the liver: remove some substances from the blood and add others A. Circulation of blood to and from the liver 1. Liver receives blood from two major blood vessels and is drained by one a) Hepatic artery: branch of aorta and carries oxygenated blood to the liver tissues b) Hepatic portal vein: supplies blood to liver c) Sinusoids: capillaries of the liver that blood is carried into d) Hepatic vein: drains the sinusoids and blood vessel that takes blood away from liver 2. Hepatic portal vein receives blood from the capillaries within the villi of the small intestine and blood within portal vein varies in two ways from blood that normal enters an organ a) Low pressure and deoxygenated since it has already been through a capillary bed b) Varies in the quantity of nutrients (glucose) depending on the types of food and timing of ingestion, digestion, and absorption of food 3. Hepatic vein blood is also low-pressure and deoxygenated blood, but it doesn’t vary in nutrients 4. Stabilization of nutrients within the hepatic vein represents one of the major functions of the liver a) Storage of nutrients b) Release of those nutrients when needed 5. Portal system of circulation: blood travels through two capillary beds before returning to the heart to be re-pumped B. Sinusoids are the capillaries of the liver 1. Hepatocytes (liver cells): job is to remove or add substances 2. Sinusoids: where exchanges occur between the blood and the hepatocytes a) Oxygen-rich blood from hepatic artery and sometime nutrient-rich blood from hepatic portal vein both flow into sinusoids 3. Sinusoids differ from typical capillary beds a) Wider than capillaries b) Lined by endothelia cells with gaps between them c) Gaps allow large molecules like proteins to be exchanged d) Hepatocytes are in direct contact with blood components making all exchanges with blood more efficient e) Sinusoids contain Kupffer cells that help break down hemoglobin released form older erythrocytes for recycling cell components f) Sinusoids receive a mixture of oxygenated blood (hepatic artery) and nutrient-rich blood (hepatic portal vein) which eventually drains into small branches of the hepatic vein C. Liver removes toxins from the blood 1. Humans ingest a lag number of toxic substance each day that our bodies eliminate a) Pesticides and herbicides added to food produce b) Food preservatives and food flavor enhancers c) Medications and alcohol 2. Kupffer cells: line the inside of sinusoids and use phagocytosis to remove old erythrocytes and bacteria from the blood a) Contain many lysosomes b) Specialized leucocytes (white blood cells) 3. Hepatocytes: most numerous and most active in removing and processing chemical toxins from the blood a) They are bathed with the plasma components of the blood b) Extract toxins from the plasma and do a two step process to eliminate the toxins i) Chemically modify the toxin to make it less destructive ii) Add chemical components that make it water soluble c) Water soluble substance is added back to blood so it can be eliminated by the kidneys in urine D. Alcohol consumption damages liver cell over time 1. Hepatic portal vein brings absorbed alcohol to the liver first and any alcohol not removed the first time will be brought back through the liver sinusoids by the hepatic artery 2. Each time the blood passes through the liver the hepatocytes attempt to remove the alcohol from the blood, so it has a magnified effect on liver tissue 3. Long-term alcohol abuse has three primary effects on the liver a) Cirrhosis: scar tissue left when areas of hepatocytes, blood vessels, and ducts have been destroyed by exposure to alcohol (areas no longer function) b) Fat accumulation: damaged areas of liver will build up fat in place of normal liver tissue c) Inflammation: swelling of damaged liver tissue as a result of alcohol exposure (alcoholic hepatitis) E. Regulation of nutrients in the blood 1. Solutes that are dissolved in blood plasma must stay within a normal homeostatic range or there will be problems in the body 2. Maintaining glucose levels in the blood a) Lowest in morning and highest after a meal b) Hepatic portal vein will contain blood with a very high concentration of glucose after a meal high in carbohydrates c) Blood enters sinusoids and some of the excess glucose is taken in by hepatocytes and converted to glycogen (helps to keep glucose level in the blood in normal range) d) Stored glycogen can be seen as large vesicles or granules e) Not eaten: blood glucose levels decrease so stored glycogen in granules is reconverted to glucose and added into blood in the sinusoids f) Homeostatic mechanisms are regulated by hormones from pancreas i) Insulin: stimulates hepatocytes to take in and convert glucose to glycogen when glucose level is high ii) Glucagon: stimulates hepatocytes to convert glycogen back to glucose when glucose level is low 3. Other nutrients that can be stored in liver F. Liver recycles components of erythrocytes and hemoglobin 1. Erythrocytes: life span of 4 months and need to be replaced by the blood cell forming tissue of the bone marrow a) Erythrocytes are anucleate (no nucleus) so they can’t undergo mitosis or code for new proteins within the cell 2. At the end of its cellular cycle the erythrocyte’s membrane becomes weak and ruptures (occurs in spleen, bone marrow or in bloodstream) a) Millions of hemoglobin molecules are released and circulate the bloodstream b) Circulating hemoglobin are ingested by Kupffer cells within the sinusoids by phagocytosis since hemoglobin is a very large protein c) Inside the Kupffer cells the hemoglobin is disassembled into its component parts i) Four globin proteins are hydrolyzed into amino acids ii) Amino acids are released back into blood and become available to any body cell for protein synthesis iii) Iron atom is removed from each heme group: some is stored in liver and some sent to bone marrow to make new erythrocytes iv) Bilirubin/bile pigment: Remaining heme group without iron is absorbed by hepatocytes and becomes a part of bile G. Hepatocytes produce and secret bile and plasma proteins 1. Bile: added to duodenum during digestion of fatty acid in order to emulsify fats a) Lipids tend to coalesce (clump) together which makes it difficult for lipase to digest the lipids b) When bile is added, the resulting emulsification does not chemically change the lipids but it breaks up the clumps and increases the surface area for lipase to catalyze the digestion 2. Hepatocytes produce bile by converting extra cholesterol into bile salt which are added to bilirubin making the bile a) Bile salts are the emulsifying portion of bile 3. Hepatocytes produce many types of plasma proteins (proteins that are added into the blood) a) Albumin: regulates blood osmotic pressure and acts as a carrier for bile salts and other fat-soluble substances b) Fibrinogen: gets converted to fibrin to form the mesh component of a blood clot 4. Plasma proteins secreted by hepatocytes by the following process a) DNA within nucleus of hepatocyte synthesizes a mRNA for a particular protein (transcription) b) mRNA exits the nucleus through pore c) mRNA finds ribosome on rough ER d) Plasma protein is synthesized (translation) e) Plasma protein is transported by a vesicle to the Golgi apparatus f) Golgi modifies the proteins and surround it in another vesicle g) Vesicle goes to the plasma membrane for exocytosis (secretion) h) Plasma protein enters the blood plasma H. Causes and consequences of jaundice 1. Jaundice: condition characterized by having too much bilirubin circulating in the bloodstream and within the body tissues 2. Bilirubin is a yellow pigment so people with jaundice have a yellow tinge to their skin and yellowing of the withes of their eyes 3. Bilirubin is formed when hemoglobin molecules are processed from dying erythrocytes d) Baby’s liver can then mature for full processing of bilirubin into bile e) Severe consequence of untreated jaundice is acute bilirubin encephalopathy (brain condition) in which excessive bilirubin is toxic to brain cells 4. Infant jaundice: typically in premature newborns because their livers are not yet capable of fully processing bilirubin into bile a) Bilirubin was processed by the mother’s placenta b) Soon after birth they may show signs of yellowing c) Common treatment: exposure to blue and green portion of the light spectrum which changes the shape and structure of bilirubin and then they can be eliminated in the baby’s urine and stool 5. Adult jaundice: symptom of an underlying cause of the liver not functioning properly a) Same symptoms and consequences as infant jaundice b) Many other symptoms if liver is not functioning