Physiology 6: Waste Flashcards
What generates nitrogenous waste?
Breakdown of proteins and nucleic acids
- In digestive system
- For energy / conversion to fats / carbs
- Amino group (NH2) is removed
Why do we need to get rid of nitrogenous waste?
amino groups react with water to form ammonia
- Ammonia is highly toxic
- Ammonia raised pH of bodliy fluids
= inhibits key enzymes
How do organisms get rid of nitrogenous waste? (3 ways)
- Immediately, as ammonia: easy to do in aquatic environments
- Convert to urea
- Convert to uric acid
Describe why some organisms get rid of nitrogenous waste as ammonia
Doesn’t require energy to get rid of
Small molecule → rapid diffusion in aquatic environments
Highly soluble in water (need a high vol to get rid of effectively)
Which organisms excrete ammonia?
most bony fishes, aquatic life stages of amphibians, aquatic invertebrates
Describe urea (5)
- Urea produced in the liver
- Produced from Ammonia and Co2
- 1000x less toxic than ammonia
- Less soluble than ammonia, so requires less water to get rid of it
- Requires energy to make
which organisms excrete urea?
mammals, most amphibians, cartilaginous fish
How do elasmobranchs use urea to their advantage?
- They’re osmoconformers
- They use urea to maintain bodily fluids:
When urea (non toxic) stored in tissue, increases osmolarity of body fluids
= Elasmobranchs use this to make them isosmotic to salt water around them
Describe uric acid
- Larger molecule, semi-solid
- Insoluble (compared to urea and ammonia)
- Even less toxic than urea (can be stored for a long time and doesn’t affect pH)
- Excretes as a semi-solid → conserves water
- Requires 3x the amount of energy to make as urea
Which organisms excrete uric acid?
birds, reptiles, insects and some amphibians
Why is uric acids storing capabilities useful for some organisms?
Storing capabilities make it useful in egg development:
Egg is closed = unable to gain more water
Uric acid can build up inside without being toxic
Even urea would build up to toxic conc.s
Give some examples of how habitat is important in excreting nitrogenous waste
Terrestrial tortoises excrete uric acid (dry environ so limits water loss)
But, aquatic turtles excrete urea and ammonia (access to lots of water)
African lungfish can switch:
in mud during dry season excretes urea
in water during rainy season excretes ammonia
What is the nephrida
Excretory organ in annelid worms, molluscs, platyhelminthes
Describe how the nephrida functions
Nephrostome (ciliated funnel end) pumps water, ions & nitrogenous waste into highly vascularised tube (surrounded by capillaries)
Water reabsorbed from tube
Waste exits body through nephridiopore
What are malpighian tubes?
Excretory organ in insects
Tubules blind ended and open up into gut
What is the excretory organ in vertebrates?
Kidneys
What is the specialised excretory system in sea birds?
Nasal salt glands
Describe how nasal salt glands work in sea birds
Salt extracted from blood into tubules
Salt passes down ducts and is excreted from nostrils
Runs down beak and drips off
What is the specialised excretory system in fish?
Chloride cells
What are the features of the malpigian tubules?
Blind ended tubes
- Closed at one end, open into the gut at the other
Walls one cell thick
- to minimise diffusion distance
Between midgut and hindgut
Float in haemolymph
What is the number of malpigian tubules in insects dependent on?
Diet (= how much waste)
E.g Coddids have 2 tubules (low protein diet)
How much water to conserve
E.g Desert locusts have 250 (high protein diet + dry enviorn)
Describe the function of the malpigian tubules
Transport epithelium lining tubules actively transports solutes (salt, waste) from the hemolymph to the midgut lumen
Water follows by osmosis
Fluid in the midgut pumped to the rectum where most of the solutes are reabsorbed into hemolymph
Uric acid is excreted in dry matter as faeces
What are the benefits of the malpigian tubes?
Highly effective at conserving water
(Important due to insects high SA:V)
Describe, generally, how the human kidney works
Kidney works by filtering everything out, the selectively reabsorbing what the body needs
What are the 4 stages in kidney function?
- filteration
- Reabsorption
- Secretion
- Excretion of filtrate
Describe the renal medulla
- Located in the middle of the kidney
- Regulates water & salt conc. in blood
Describe the nephron
Single long tubules
Spans the kidney (cortex to medulla)
Associated with a network of capillaries
Each kidney has around 1 million
Describe the general process of kidney function (7 steps)
- Ultrafiltration
→ non-selective filtration
Starts in glomerulus. High blood pressure forces fluid into lumen of bowman’s capsule
Fluid contains water from blood + small solutes (e.g salt, glucose, nitrogenous waste, vitamins) but no larger molecules e.g blood cells - Fluid passes into proximal tubule
- Then to the Loop of Henle
- Descending / ascending limbs - Then to the Distal tubule
- Finally to the collecting duct
- Receives the filtrate from many nephrons - Filtrate passes to the renal pelvis
- Finally through the ureter
Describe the changing osmolarity of the nephron
- Fluid forced out of blood into glomerulus is at same osmolarity as the blood (~300Osm/L)
- As filtrate passes into proximal tubule, water is reabsorbed, active reabsorption of many salts
= no net change in osmolarity - Descending limb of the loop of Henle:
More water leaves filtrate by osmosis
= Increases osmolarity of the filtrate - Ascending limb of loop of Henle:
Salt leaves filtrate
Impermeable to water
= Decreases osmolarity of filtrate - Distal tubule:
Regulates salt conc.
Regulates pH
Regulates water balance
When a human is dehydrated, what type of urine will they produce?
Hyperosmotic
When a person has excess water, what type of urine will they produce?
Hypo-osmotic
What type of filtration is ultrafiltration?
Non selective
- Fluid is forced out of glomerulus into bowmans capsule due to high pressure
What does the fluid forced out of the glomerulus contain?
water from blood + small solutes (e.g salt, glucose, nitrogenous waste, vitamins) but no larger molecules e.g blood cells
Is the descending limb of the loop of Henle permeable or impermable to water?
Permeable
- water leaves filtrate by osmosis
= increases osmolarity of the filtrate
Is the ascending limb of the loop of Henle permeable or impermable to water?
Impermeable to water, permeable to ions
- Salt leaves filtrate
= Decreases osmolarity of filtrate
What is the function of the distal tubule?
Regulates salt conc.
Regulates pH
Regulates water balance
What does the countercurrent multipiler system in the kidneys maintain?
Steep osmotic gradient
Describe the countercurrent multipiler system in the kidneys
Tubule fluid in descending limb flows in opposite direction from ascending limb
Water leaves descending limb via osmosis
= high solute conc. in filtrate → hyperosmotic to surrounding medulla
Highest osmolarity ~1200Osm/L at the elbow of the loop
Maximises diffusion of salt from tubule
Ascending limb permeable to salt but not water
Diffusining NaCl helps to maintain high osmolarity in interstitial fluid
Means that water continues to diffuse out
How is the Countercurrent multiplier system in the kidneys different to the system in fish’s gills?
Theres active transport in the kidneys, not the gills
