UNIT 5: EXCRETION AND WASTE MANAGEMENT

EXCRETION:

is the process by which dissolved metabolic wastes are separated from body fluids and removed from the body.If these metabolic wastes were not removed, the organism would die.(Eg: water, salt, CO2, urea)

RECALL: ELIMINATION or EGESTION:

•is the process that removes undigested materials from the large intestine only as part of the digestive system NOT excretory system.

FUNCTIONS OF THE EXCRETORY SYSTEM:

1.Removal of metabolic waste by:
i)Excretory system collects fluids from somewhere inside the body, usually from the blood or spaces between the organs.
ii)It modifies the fluid by reabsorbing substances that the body needs to keep, and by transporting waste substances into the excretory product
iii)It then provides a way to expel the excretory product from the body.
2.Removal of excess heat by the excretory system that helps the temperature of the body constant.
3.Maintaining the body fluids' pH level, water and salt balance.

EXCRETORY ORGANSof the body include:

➢Kidneys ➢Lungs ➢Skin

Metabolic Waste Product Origin of Waste Product Excretory Organ

AMMONIA Breakdown of amino acids in the liver Kidneys
UREA (NITROGENOUS WASTE)Conversion of ammonia in the liver Kidneys, skin
CARBON DIOXIDE Cellular respiration (breakdown of glucose in cells)Lungs
WATER Cellular respiration (breakdown of glucose in cells)Kidneys, lungs, intestines skin (sweat)
MINERAL SALTS Food and water Kidneys, skin (sweat)

In addition, excretory organs control the excretion of:

➢SPICES: Onion, garlic, and some spices have volatile components that leave the body through the lungs, whereas the rest leave the body through the kidneys and skin.➢DRUGS AND HORMONES: Penicillin and other drugs are removed primarily by the kidneys and the drugs or the products of their breakdown can be detected in the urine.

ROLE OF LIVER:

1.DETOXIFICATION:
-converting toxic substances into forms that arelesspoisonous tothe body
-Removes harmful substances such as bacteria, drugs, and hormones from the blood.
-Within the liver these substances are changed into inactive or less poisonous forms.
-Therefore,the liver purifies or detoxifies the blood. Inactive forms of the substances are returned to the blood and excreted from the body by the kidneys.
2.DEAMINATION: REMOVAL OF NITROGENOUS WASTES
❑Proteins are digested and broken into amino acids.
❑If more proteins are eaten than is needed by the body then excess amino acids must be removed.

HOW DOES DEAMINATION OCCUR?

❑The amino group NH2must be removed.
❑Ammonia (NH3)is one of the products of deamination and is very toxicin concentrated solutions.
❑Ammonia is converted to a less toxic substance called UREAin the liver before beingreleased into the bloodstream and removed from the body by the kidneys

SUMMARY:

Dietary protein →digests into amino acids in the digestive track→excess amino acids broken down into AMMONIA AND THEN INTO UREA→then travels through the bloodstream to the kidneys and is removed in urine

ROLE OF THE LUNGS:

The lungs are considered part of the excretory system because they rid the body of carbon dioxide and water (water vapor) during cellular respiration.
C6H12O6 + O2 \> H20 + CO2 + ATP
Function:Carbon dioxide diffuses out of the body cells into the blood. Carbon dioxide is carried by the blood to the lungs, where it is released and expelled from the body.

ROLE OF THE SKIN:

The skin is made up of many different kinds of tissues, and performs a number of functions. One of these functions is excretion of wastes.
Function:
i)Protection: The skin keeps microorganisms and other foreign materials from entering the body.
ii)Since the outmost layer of skin is waterproof, the skin also keeps the body from drying out.
iii)The skin excretes a small amount of urea and salts in sweat, which is 99% water.
iv)The skin also removes excess body heat.

URINARY SYSTEM

The urinary system is made up of:
i)KIDNEYS:humans have two kidneys. They are bean-shaped organs, approximately 11.5 cm long, situated in the abdominal cavity, just below the ribcage, one on either side of the spine. They are embedded in fatty tissue for protection. The kidneys make up less than 0.5% of the human body weight, and they use about 10% of the human body's oxygen and energy just moving blood to the kidneys and cleansing it.
The kidneys are essentially blood filters. Blood is brought to the kidneys to be filtered by the renal artery. After filtering, the blood is taken away again by the renal vein.
ii)URETERS:are the tubes that connect the kidneys to the urinary bladder
iii)URINARY BLADDER:is a smooth muscular bag where urine is stored
iv)URETHRA:is the tube that leads from the bladder to the outside of the body. During urination, urine travels through this tube.

ROLE OF KIDNEYS:

ROLE OF KIDNEYS:
The kidney functions as the bloodfiltration and water balancing system
➢it removes metabolic wastes for excretion
The kidneys are essentiallyblood filters.Blood is brought to the kidneys to be filtered by the renal artery.After filtering, the blood is taken away from the kidney by the renal vein.
The kidneys filter about 125 millilitresof blood every minute, which adds up to about 180 litres per day. We obviously don't excrete 180 litres of urine per day, so most of the water filtered out of the blood is returned to the circulatory system.The body excretes only about two litres of urine every day.
Water isn't the only substance that is reabsorbedinto the circulatory system. All the glucose that is filtered out of the blood is reabsorbed.This important nutrient necessary for the production of ATP is actively transported back into the circulatory system so that it reaches the cells. Salt concentration in the blood also needs to remain constant. The amount of salt excreted and reabsorbed into the blood depends on how much salt we get from the foods we eat. If we take in a lot of salt, some is reabsorbed into the bloodstream, and more is excreted into the urine.
MAJOR FUNCTIONS:
1.Excretion ofnitrogenous waste (UREA) and other metabolic wastesforming urine
2.Balancing pH of the blood
3.Reabsorption of useful substances in the blood
4.Regulation of body's salt and water content (maintain homeostasis of body fluids)... OSMOREGULATION

STRUCTURE OF THE KIDNEYS:

The kidney has THREE main parts:
i)Renal Cortex:
-outer region where blood is filtered in NEPHRONS
ii)Renal Medulla:
-middle region made up of tubes called collecting ducts, which forms the pyramids
This is wherethe filtrate (filtered substances) is carried to the pelvis
iii)Renal Pelvis:
-inner region that is a cavity that connects into the ureter(holds urine)

NEPHRONS:

•Nephrons are the basic functional unitsof the kidneys
•Each kidney has about 1.25 million nephrons.
•Part of each nephron is found in the cortex, and the medulla.
WHY DOES EACH KIDNEY HAVE SO MANY NEPHRONS?➢Having millions of microscopic nephrons rather than one or a few large ones help to increase the surface area, which therefore helps to increase the efficiency of the kidney in filtering blood forming urine.

PARTS OF THE NEPHRON AND BLOOD SYSTEM:

BLOOD VESSELS
GLOMERULUS
BOWMAN'S CAPSULE
NEPHRON TUBULE
LOOP OF HENLE
COLLECTING TUBULE

BLOOD VESSELS

BLOOD VESSELS:each nephron has its own blood supply. Blood enters the kidneys through the RENAL ARTERIES. Each nephron has one arteriole that carries blood from the renal artery into the nephron. The arteriole branches to form the network of capillaries that connects to the venule, and then leaves the kidneys through the RENAL VEINS.

GLOMERULUS

GLOMERULUS.: At the upper end of the nephron is the glomerulus. It is a group of capillaries that form a tight ball that blood from the arteriole pass through.

BOWMAN'S CAPSULE

BOWMAN'S CAPSULE:The glomerulus is surrounded by a double-walled, cup-shaped structure, which is called the Bowman's capsule. From the blood in the glomerulus, substances are filteredinto the Bowman's capsule.

NEPHRON TUBULE

NEPHRON TUBULE(AKA: RENAL TUBULE): The filtrate thenexits the Bowman's capsule through the nephron tubule. Thenephron tubule has four main parts: the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

LOOP OF HENLE

LOOP OF HENLE:The middle section of the nephron tubule forms a long loop called the loop of Henle. This extends into the medulla. Some reabsorption of necessary nutrients occurs here.

COLLECTING TUBULE

COLLECTING TUBULE:The distal convoluted tubule empties into the collecting tubule then empties into the renal pelvis, and then waste travels to the ureter.

HOW IS URINE FORMED? REMOVING NITROGENOUS WASTE FROM BLOOD

Urine is made in the nephrons in THREE processes: I)FILTRATIONII)REABSORPTIONIII)SECRETION

FILTRATION:

Filtration is the process by which:
Fluid and some small dissolved substances from the blood are forced through the thin walls of the GLOMERULUS INTO THE BOWMAN'S CAPSULE from the arteriole.
➢The materials that are filtered are called the FILTRATE.
How is blood moved?
Blood in the glomerulus is at a relatively high pressure andthis forcemovesthe dissolved substancesin the blood through the capillary walls by passive transport.
➢*Pressure created by blood entering the kidney forcessubstances into the nephron.
IMPORTANCE:
During this stage, both useful substances and wastes are removed from the blood and end up in the filtrate.
➢SUBSTANCES INCLUDED in FILTRATE:
water, urea, glucose, amino acids, vitamins, various salts, and ions from the blood. ➢NOT INCLUDED:
Blood cells (RBC, WBC, and platelets) fats, and plasma proteins are too large to pass through the walls and remainoutside the nephronand DO NOTenter the glomerulus/Bowman's Capsule

REABSORPTION:

Reabsorptionis the process by which Beneficial(good)substances are absorbed back into the capillaries that surround the PROXIMAL CONVOLUTED TUBULE AND THE LOOP OF HENLE andTHE DISTAL CONVOLUTED TUBULE.
How are substancesmoved?
Substances are moved by active transport and require the use of energy(ATP)and passive transport (osmosis)
•Reabsorption of salts (sodium) occurs in the distal convoluted tubule by active transport.
•99% of water is reabsorbed by osmosisinto the capillaries surrounding the nephron tubule.
IMPORTANCE:
-During this stage;Important material, previously removed from the blood at the Bowman's capsule, is RETURNED to the blood ➢SUBSTANCES INCLUDE: All the glucose, amino acids, hormones, vitamins, some salts, and water.

SECRETION:

SECRETION:Secretion is the process by whichAdditional waste substances, not previously filteredmove out of the blood and into the nephron tubules from the capillaries into THE DISTAL CONVOLUTED TUBULE AND COLLECTING TUBULE
How are substances moved?
➢These substances are secreted by active transportor as a result ofdiffusionacross the membrane.
➢SUBSTANCES INCLUDE:hydrogen ions (H+), potassium ions (K+), ammonia (NH3), and certain drugs.
➢These substancessuch as potassium ions and hydrogen ions, that were too large to pass through the glomerulus into the Bowman's capsule, are secreted from the blood in thecapillaries directly into the nephron tubule by active transport into the filtrate.
IMPORTANCE: Afterthis Stage:Remaining filtrateafter the three processes of filtration, reabsorption, and secretion now form the composition of URINE
•COMPOSITION OF URINE: Urine is composed of: urea, water, mineral ions (salt ions) drugs, toxins
PATHWWAY OF URINE:Urine is made in the renal cortexthen moves into the renal medulla via the collecting ductsand isemptied into the renal pelvis.From there is it transported to the ureter, then to the urinary bladder and eventually leaves the body through the urethra.

WHEREDOES THE PROCESS OCCUR?Include both nephron part and blood vessel.

FILTRATION
Between the glomerulus and into Bowman's capsule
REABSORPTION
Between the proximal convoluted tubule/Loop of Henle/distal convoluted tubuleand surrounding capillaries
SECRETION
Between the distal convoluted tubule/collecting tubule and capillaries surrounding

DESCRIBE THE MAIN PROCESS

FILTRATION
Movement of water and dissolved substances out of the blood into nephron. This forms the FILTRATE.Both BENEFICIAL AND HARMFUL substances moved out of blood Using high pressure but a passive process (no ATP required)
REABSORPTION
Movement of BENEFICIAL substances including water and dissolved substances out of the kidney tubules back into the blood Note that this process prevents substances needed by the body from being lost in the urine
SECRETION
Movement of ADDITIONAL WASTE material not previously filtered such as waste, ions or drug out of the bloodcapillariesand into the kidney tubules, where they are eventually eliminated in the urine.

State what MATERIALS ARE INVOLVED

FILTRATION
GlucoseWaterVitamins/mineralsUreaSaltsamino acids/fatty acidshormonesdrugstoxinsNOTE: Blood cells and plasma proteins are too large to pass
REABSORPTION
GlucoseSome Watervitamins/mineralssome salt ionamino acids/fatty acidssome hormones
SECRETION
hydrogen ions (H+) potassium ions (K+)ammonia (NH3)certain drugs

Is the process Active or Passive transport?

FILTRATION
PASSIVE
REABSORPTION
ACTIVE/ PASSIVE(urea &salt) (water)
SECRETION
ACTIVE

COMPARE THE SUBSTANCE FOUND IN THE VARIOUS REGIONS ON THE NEPHRON:

•Glomerulus →makes FILTRATE (both beneficial and harmful substance)
•Nephron →reabsorbedbeneficial substances
•Collecting Tubule →Reabsorbedwater(with ADH)
•Collecting Tubule →substances excreted as urine(water, urea, salt, drugs)

REGULATING BODY'S WATER CONTENT:

1.ADH (antidiuretic hormone) (water balance: osmoregulation)2.Aldosterone(salt balance)➢Both maintain the balance of blood volume and composition through negative feedback mechanisms.

HOW DOES THE BODY KNOW WHEN TO RESPONDFOR OSMOREGULATION?

Receptors in the hypothalamussense when the body's levels are not with normal range due to:
ofluid intake is low
owhen blood volume decreases
owhen the sodium concentration in blood increases.

REGULATING BODY'S WATER CONTENT

ANTIDIURETIC HORMONE (ADH) (aka vasopressin) is a hormone released by the posterior pituitary gland of the brain.
FUNCTION:
-regulates water balance by controlling reabsorptionof the remaining water in the distal convoluted tubule and collecting tubule.
-ADHincreases the permeabilityof the nephron to water.(forms aquaporins)More water is, therefore, reabsorbed back into the circulatory system.
➢ADH increases reabsorption of water from the urine.
➢Loss of waterfrom the body stimulates ADH secretionwhich in turn slows downthe loss of water from urine.The body may detect a decrease ofits water content in one of two ways:
i)a reduction in blood volume(ie severe bleeding)
ii)an increase in the concentration of blood plasmaproteindue to the loss of water from sweatingThe thirst center of the brain is called the hypothalamus. The shrinkingof the hypothalamus initiates a behavioral response, the sensation of thirst.

If the WATER CONTENT OF THE BLOOD IS TOO LOW

ADH is secreted from the pituitary gland
The hormone makes cells of the collecting duct MOREpermeable to water and removes water from the filtrate by osmosis. (forms aquaporins)
LARGE VOLUME OF WATER REABSORBED FROM COLLECTING DUCT
A small volume of concentrated urine is produced.

If the WATER CONTENT OF THE BLOOD IS TOO HIGH

ADH is NOT secreted from pituitary gland
Collecting duct becomes LESSpermeable to water, little water is reabsorbed as the filtrate passes down the collecting duct
LITTLE/NOVOLUME OF WATER REABSORBED FROM COLLECTING DUCT
A large volume of dilute urine is produced.

RELEASE OF WASTES:

All the urea, excess water, salts, and ions continue through the collecting duct into the renalpelvis, where they are collected and pass as urinevia the ureterinto the urinary bladder, from where it is excreted through the urethra.

CONCENTRATION OF THE URINE:

❑Since most of the water is reabsorbed, the substances left in the filtrate are highly concentrated.
❑After reabsorption, the fluid remaining in the tubules is urine. It is made up of water, urea, and various salts. About 2 L of urine is produced per day.
❑Wastes flows from distal convoluted tubule into the collecting ducts. The walls of the collecting ducts are permeable to water, and additional water is removed resulting in the actual concentration of urine increasing.

FACTORS THAT INFLUENCE THE PRODUCTION OF URINE:

1.Temperature: ↑body temp ↑water loss by sweating ↓ urine production
2.Water Consumption↑water consumption ↑water volume in body ↑urine production
3.Exercise : ↑exercise ↑metabolic rate ↑waste production ↑ urine production
4.Protein Consumption↑protein consumption ↑amino acids in body ↑water reabsorption for deamination ↑urea produced ↑urine production
5.Salt Consumption↑salt consumption ↑water reabsorption for salt removal ↑waste salt produced ↑urine production(small volume and concentrated)

EFFECTS OF ALCOHOL AND CAFFEINEon Urine Production

-both are diureticsthat suppress the production and release of the hormone ADH.This results in less water being reabsorbedand too much water being released in urine.Beverages high in alcohol cause excessive urination and lead to dehydration.

REGULATING BODY'S SALT CONTENT:

▪In addition to removing wastes, the kidneys also control the level of sodium in the blood by removing and absorbing sodium ions.

ALDOSTERONE

ALDOSTERONEis a hormone secreted by theadrenal cortex of the kidney.FUNCTION: Aldosteroneregulates the reabsorption ofsodiumfrom the filtratein the distal convoluted tubule and collecting duct of the nephron.
➢Aldosterone also helps to regulate water balance.
➢Factors that cause its release arelow bloodvolume and low blood pressure.
➢Aldosterone causes the reabsorption of sodium into the circulatory system.
➢Water follows the sodium(recall rule "Salt Sucks"), and blood volume and pressure are restored.
➢Aldosterone helps control the osmotic pressure of the blood, and maintainsblood pressure.
➢The body's sodium content (and volume of water) depends upon the balance betweenthe intake of salt in the diet and that lost in the urine.

BALANCING pH OF THE BLOOD:

The kidneys also regulate the pH of the blood by filtering out hydrogen ionsand allowing bicarbonate ions to be reabsorbed back into the blood. This then buffers the blood. Recall: the hydrogen ions decrease blood pH levels and make the blood more acidic.

NEGATIVE FEEDBACK MECHANISMWITH DECREASE IN FLUID INTAKE:

STIMULUS:Intense physical activity without fluid intake
CHANGE: WATER VOLUMEin the bloodstream is LOWERED
RECEPTOR: OSMORECEPTORin the hypothalamus detect change and send a message to the pituitary gland
REGULATORY CONTROL CENTER: HYPOTHALAMUS AND PITUITARY GLAND in the brain coordinate response.
EFFECTOR: PITUITARY GLAND RELEASES ADH(antidiuretic hormone)
RESPONSE:ADH travels to the kidneys, and causes the reabsorption of water out of the collecting ducts (more permeable to water) and places it back into the blood.This leads to LESS urine volume produced (concentrated)\******Feeling of thirst also leads to drinking of fluids\********
CHANGE: WATER CONCENTRATION in the bloodstream is RAISED to normal level

NEGATIVE FEEDBACK MECHANISMWITH INCREASE IN FLUID INTAKE:

STIMULUS:Increase influid intake
CHANGE: WATER VOLUMEin the bloodstream is RAISED
RECEPTOR: OSMORECEPTOR in the hypothalamus DO NOT detect change REGULATORY CONTROL CENTER: HYPOTHALAMUS AND PITUITARY GLAND in the brain DO NOT cause a response.
EFFECTOR: PITUITARY GLAND DOES NOT RELEASES ADH(antidiuretic hormone)
RESPONSE:No reabsorption of water out of the collecting ducts This leads to MOREurine volume produced (Diluted)
CHANGE: WATER CONCENTRATION in the bloodstream is LOWERED to normal level

KIDNEY THRESHOLD LEVEL:

Most substances have what is called a KIDNEY THRESHOLD LEVEL. If the concentration of a substance in the blood is greater thana certain level, the excess substance is NOT reabsorbed. The excess remains in the urine and is excreted from the body.
❑Example: the blood sugar levels of a person who has diabetes is so high that not all of the glucose in the filtrate can be reabsorbed. As a result, glucose appears in the urine. Diabetes have this problem

EXPLAIN HOW DRUGS AND ALCOHOL CAN BE DETECTED BYA URINE TEST?

-both drugs and alcoholare toxins that are secreted into the distal convoluted tubule and then sent to the urinary bladder and removed with the urine.
-Therefore urine tests can prove the use of drugs and alcohol.

URINALYSIS:

Urine is a product of osmoregluation, excretion and metabolism. These processes can be disrupted by illness or drug abuse.Urinalysis is a clinical procedure that examines urine for any deviation from normal composition.
When visiting the doctor, you may be asked to provide a urine sample. What does the presence of cetain chemical composition such as glucose, blood cells, proteins, and drugs tell the doctor concerning your physiology. Urinalysis test strips indicate for pH, protein levels and glucose levels in the urine.

DISEASES:

A number of diseases affect proper kidney function.

KIDNEY STONES:

Sometimes substances crystallize out of the urine in the urinary tract, or kidney. These crystallized substances are called kidney stones.If the stones are too big to be passed with the urine, they must be surgically removed, or shattered into small pieces with sound waves or lasers.

NEPHRITIS OR BRIGHT'S DISEASE:

Nephritis is not a single disease, but a broad description of many diseasescharacterized by the inflammation of the nephrons.It is believed that toxins produced by invading microbes destroy the tiny blood vessels, and alter the permeability of the nephron.Proteins and other large molecules including blood cells are able to pass into the nephron.Proteins remain in the nephron and draw water into the nephron, increasing the output of urine.

DIABETES:

Caused by inadequate secretion of insulin, result in increased in blood sugar levels. Water remains in the nephron due to disruption in osmotic pressure, and water is lost in the urine.\**** presence of glucose in urine\***

KIDNEY FAILURE

If the kidney stops working, the second kidney can take over its work and live a normal life. Kidney failure can occur for a number of reasons, but most commonly occurs:
❑as a complication from diabetes
❑chronic high blood pressure as a result of diabetes If both kidneys fail, excess fluid and waste build up rapidly in the body, and can lead to death. An artificial kidney machine or dialysis machine may be used to filter the blood. This process is known as HEMODIALYSIS.

DIALYSIS (HEMODIALYSIS)

Blood flows from the body into the dialysis machine, where wastes are filtered out, thenthe filtered blood is returned to the body.

HOW DOES DIALYSIS WORK?

oBlood flows from the body via artery into the dialysis machine
oA steady flow of blood passes over an artificial semi-permeable membrane in the dialysis machine.
oThe small waste products in the blood pass through the membrane, the larger blood cells and proteins cannot.
oThe purified blood is then returned to the patient via a veinoWorks on the principle of a conc. gradient... high urea conc in the blood moves to low conc. of urea in the dialysate solution by diffusion.By undergoing about 20 hours of dialysis each week, a person can live for years after kidney failure.
➢Permanent cure available is a kidney transplant

Identify four differences between blood entering the kidney and the blood leaving the kidney. Identify 2 similarities.

\n RENAL ARTERY--oxygenated-contains high urea-contains high salt-higher water content-brings blood into kidneys-Unfiltered blood

RENAL VEIN--deoxygenated-contain little urea-contains less salt-lower water content-carriesblood out of the kidney-filtered blood

SIMILARITIES:

BOTH CONTAIN:Beneficial substances: glucose, amino acids, vitamins, hormones, blood cells, blood plasma proteinsBOTH are blood vessels associated with blood flow in kidneyBOTH contain no filtrate

OSMOREGULATION

is the regulation/control of water and salt concentration to maintain a consant osmotic pressure of fluids within the organism