7.3: Excreting Wastes

Control and Regulation of Metabolic Wastes•Waste products must be removed from the body to maintain life processes.

Examples:Lungs remove CO2.

Large intestine removes toxic wastes.

Liver

Transforms toxins such as alcohol and heavy metals into soluble compounds.

Transforms products of protein metabolism into metabolites.

Kidneys remove waste, balance blood pH and maintain water balance.

What happens to excess Protein?

• Converted into carbohydrates

• Amino group must be removed from the body – Deamination

Deamination

• Occurs in the liver• Byproduct is ammonia, which is water

soluble and extremely toxic• Ammonia combines with CO2 to form urea,

which is 100 000 times less toxic• Uric Acid is formed by the breakdown of

nucleic acids• Ammonia, Urea and Uric Acid are all

removed by the Kidneys

Excretion in Unicellular Organisms

• Waste moves directly out of the cell.

• Excess water is regulated by contractile vacuoles that pump out excess water.

• Multicelluar organisms need specialized cells and structures to get rid of waste.

Removal of Metabolic WastesWaste Origin of waste Organ of

excretion

Ammonia Deamination of a.a.s by the liver Kidneys

Urea Deamin. Of a.a.s by the liver

Ammonia combined with CO2kidneys

Uric acid Product of breakdown of nucleic acids

kidneys

CO2 Waste product of cellular resp. Lungs

Bile pigments Breakdown of hemoglobin Liver

Lactic acid Product of anaerobic resp. Liver

Solid waste By product of digestible and indigestible material

Large intestine

Some Key Terms:

• Deamination the breaking up of amino acids (removal of an amino group from an organic compound)

– (NH3 = toxic and must be further processed)

• Urea 2 molecules of highly insoluble, toxic ammonia (NH3) mixed with one molecule of CO2 = soluble (made in liver)

– (waste product of amino acid – NH3)

• Uric acid waste product formed from the breakdown of nucleic acids

• Liver responsible for removing/breaking down waste in the blood which is then sent to the kidneys to be filtered into the bladder

• Section 7.3 Questions, pp. 345, # 1-4

7.4: The Urinary System

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

Nephrons

http://www.wisc-online.com/objects/AP2204/AP2204.swf

Cortex:Bowman’s capsule, efferent and afferent arterioles are located here

Medulla:Loop of Henle descends into this portion.

*See kidney above.

*Concentration of solute in the interstitial fluid increases from the cortex down to the medulla – this facilitates movement of water and solutes during reabsorption.

Section 7.4, pp. 348, #1-4

http://www.biologymad.com/resources/kidney.swf

7.5: Formation of Urine• There is a lot going on here! The main point is that the

nephron is able to expel unneeded or harmful substances and retain or reabsorb substances useful to the body. You would be rather dysfunctional and have to pee a lot if this didn’t happen!

• For every 120 mL of fluid (amount filtered by kidneys each minute), 1 mL of urine is formed, 119 mL of fluid and solutes need to be reabsorbed.

• Urine is formed by:1. filtration of the blood2. reabsorption into the blood3. secretion from the blood

Filtration• Structures involved – glomerulus and

Bowman’s capsule pressure in capillary bed = 2 kPa, pressure in

glomerulus = 8 kPa• Blood moves from the afferent arteriole into the

glomerulus (high pressure filter)

• Dissolved solutes such as H2O, NaCl & H+ pass into the Bowman’s capsule

• Large molecules such as protein, blood cells and platelets cannot pass through the glomerulus.

Reabsorption• Structures: convoluted tubules, loop of

henle• Selective reabsorption occurs by both

active and passive transport• Carrier molecules move Na+ ions across

cell membranes, negative ions (Cl-) follow • Reabsorption occurs until the threshold

level is reached.• Excess salt remains in the nephron and is

excreted with the urine.

Reabsorption

• On average, 600 mL of fluid in kidney/minute• ~ 120 mL of that fluid is filtered into the

nephrons• 1 mL of urine is formed and 119 mL of fluid is

reabsorbed by active and passive transport into the blood stream

• reabsorption occurs until the threshold level is reached (maximum amount of material that can be moved across the nephron)

Reabsorption Continued

• Glucose and amino acids attach to carrier molecules, which drives them out of the nephron and into the blood.

• Solutes actively transported out of the nephron create an osmotic gradient that draws water from it.

• A second osmotic force is created by proteins helps reabsorption.

• Proteins remain in the blood stream and draws water from interstitial fluid into the blood.

Reabsorption Continued

• As water is reabsorbed from the nephron, remaining solutes become more concentrated.

• Urea and uric acid diffuse from the nephron back into the blood but less is reabsorbed than was originally filtered.

• On average 600 ml of fluid flows through the kidneys every minute

• Approx. 120 ml of that fluid is filtered into the nephrons.

• 1 ml of urine is formed and 119ml of fluid is reabsorbed by active and passive transport into the blood stream.

Secretion• Occurs in distal/proximal tubule

• Wastes from the blood move into the nephron

• Nitrogen-containing wastes, excess H+ and K+ secreted

• Cells loaded with mitochondria line the distal tubule

• Tubular secretion occurs by active transport therefore require mitochondria.

Site Process

1. glomerulus/Bowman’s capsule

*FILTRATION

The movement of fluids from the blood into the Bowman's capsule of the nephron

blood plasma forced through walls of glomerulus into Bowman’s capsule by pressure

water and dissolved solutes (Na+Cl-, glucose, proteins, amino acids, H+) move out of blood via fluid pressure into Bowman’s Capsule

REABSORBTION takes place in the region – Loop of Henle

2. proximal tubule*REABSORBTIO

N

The transfer of essential solutes and most water back into the blood stream.

passive: water by osmosis, K+ active: NaCl (Na+, Cl- follows) , HCO3-, Glucose,

Amino acids Na+ ions leave (active) … take –ve ions with

them (attraction) As solutes are drawn out of the nephron into the

cells surrounding the nephron they create an osmotic gradient.

Summary of Urine Formation

3. descending limb(permeable to water)*REABSORBTION

water follows (passively) due to concentration gradient, ions actively pumped from nephron – (as water leaves) salt becomes concentrated in filtrate at bottom of descending loop

4. ascending limb(permeable to salt)*REABSORBTION

thin portion of ascending is permeable to salt – salt leaves with concentration grad. (passively)Salt continues to leave in thick segment of loop (actively pumped)

5. distal tube*REABSORBTION

More substances transported out of the nephron into the blood (i.e. bicarbonate – for pH adjustment )water follows – more leaves with the concentration grad.Drugs, poisons can be removed from blood into filtrate here too.The stuff left in the nephron that is not reabsorbed is the filtrate

*SECRETION Formation of urine … purposeto release any toxins and drugs that have not been filteredMaintain the electrolyte balance of the body (if positive sodium ions are reabsorbed then positive ions like potassium must be secreted to keep the balance).Acid-base balance (usually it is an acid being secreted, essentially a proton plus whatever it is attached to).Note: Acidic juices like cranberry cause our urine to be quite acidic which helps protect against UTIs and prevent kidney stones.Note: The bicarbonate ion is never secreted since it is used as a buffer in the maintenance of our blood pH.Wastes removed from body – sent to bladder via

6. collecting duct

What is a kidney stone?= hard mass developed from crystals that separate from the urine within the urinary tract. Do not normally form due to inhibitors in urine. Common type of stone contains calcium in combination with either oxalate or phosphate.

http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0041-swf_micturition_re.swf

Section 7.5, pp. 352, # 2-6

Target Practice Quiz: Kidney