Osmoregulation and Excretion Flashcards
What is homeostasis?
Homeostasis – maintaining a healthy internal environment
» eg thermoregulation: maintaining body temperature by balancing heat loss and gain
What, other than homeostasis, do animals need to regulate?
Animals also need to regulate chemical composition of body fluids by balancing uptake and loss of chemicals and fluids
What is Osmoregulation?
Active control of the movement of solutes between internal fluids and external environment
» Balances uptake and loss of water and solutes
What is Osmosis
Cell membrane is permeable to water molecules (aquaporins), but generally impermeable to charged ions (require channels or pumps)
What is Osmolarity?
Osmolarity = solute concentration
» Lower osmolarity = hypoosmostic (hypotonic)
» Higher osmolarity = hyperosmotic (hypertonic)
» Same osmolarity = isoosmotic (isotonic)
How does osmolarity work?
Water moves from hypoosmotic side to hyperosmotic side until both sides have same osmolarity (isoosmotic)
» Osmolarity of human blood = 300 mOsm/L
» Osmolarity of seawater = 1,000 mOsm/L
What are the two strategies of Osmoregulation?
» Osmoconformer → isoosmotic w/ environment
» Osmoregulator → control internal osmolarity independent of external environment
Are marine invertebrates osmoconformers or osmoregulators?
Most marine inverts are osmoconformers
» Don’t need to control water movement
» Still need to control specific ion concentration
• eg Mg+ in seawater is 50 mM, but Mg+ in haemolymph of lobster is 9 mM
Are marine vertebrates osmoconformers or osmoregulators?
Many marine vertebrates (and some inverts) are osmoregulators
» Big challenge -ocean is a strongly dehydrating environment
» Drink lots of seawater, then specifically eliminate salts through gills and kidneys
What does mOsm stand for?
Milli-osmolarity
Are fresh water animals osmoconformers or osmoregulators?
- Freshwater (≈0.05% salt) has very low osmolarity (≈1 mOsm/L) compared to blood (≈300 mOsm/L)
- All freshwater animals are osmoregulators
» Must avoid excess gain of water (by osmosis) and loss of solutes (by diffusion)
» Drink almost no water, excrete lots of it (in dilute urine)
» Actively take up salts across gills and from diet
Draw the Fresh vs. saltwater regulators diagram
book
What is the difference between Anadromous species and Catadromous species?
Some animals migrate between fresh and salt water habitats
» Anadromous: live in sea, spawn in fresh (eg salmon)
» Catadromous: live in fresh, spawn in sea (eg eels)
What is a major osmoregulatory problem for land animals and what adaptions are key to their survival?
- Dehydration
- Adaptations are key
» Physical adaptations, eg. impermeable outer layer to avoid water loss (waxy layers, shell, dead skin cells)
» Behavioural adaptations (eg nocturnal)
How do animals maintain their water balance?
» Drinking
» Eating moist food
» Producing water through
cellular respiration
What is dessication?
Dessication (extreme dehydration) is lethal for most animals
» eg, humans: up to 12%; camels: up to 25%
What do some animals do to avoid dessication when they don’t have access to water?
Some can go into inactive state and survive (“anhydrobiosis”)
» eg, tardigrade: up to 98%
Albatross live on the ocean, drink seawater, how do they survive without fresh water?
- Specialised glands excrete salt
» Counter-current exchange
What is excretion?
- Metabolic processes produce waste, which cannot be used by the organism (not poo, just stuff in our blood after we have digested the food that we have to filtre out), eg.
» Cellular respiration produces CO2 and H2O
» Biosynthesis and catabolism produces nitrogen compounds
What is the general process of excretion and why do we need it?
- Most metabolic wastes are dissolved in water → excretion tightly linked to osmoregulation
- Need to eliminate that waste, lest it accumulates in tissues
- Most metabolic wastes are dissolved in water → excretion tightly linked to osmoregulation
What does the amount and type of Nitrogenous wastes excreted depend on?
The animal’s evolutionary history, their habitat and especially how much water is availability
What are the three types of nitrogenous waste?
Ammonia, Urea and Uric acid
What animals produce ammonia?
Most aquatic animals including most bony fish
What animals produce Urea?
Mammals, most amphibians, sharks and some bony fish
What animals produce Uric acid?
Birds and many other reptiles, insects, land snails.
What are the pro’s and con’s of Ammonia?
Pro’s:
- Small molecule, readily lost by diffusion across membranes
Con’s:
- Toxic even at low concentration
- Requires lots of water to excrete (≠ land animals)
What are the pro’s and con’s of Urea?
Pro’s
- 100,000× less toxic than NH3
- Less water required for excretion than NH3
- Can be stored
Con’s
- Energetically expensive to produce
- Still requires some water (≠ desert, flying)
What are the pro’s and con’s of Uric Acid?
Pro’s
- Even less toxic than urea
- Excreted as a semi-solid paste, almost no water required
Con’s
- Energetically very expensive to produce
From lowest to highest, rank the toxicity, size, Amount of water needed to excrete and energy needed to produce for ammonia, urea and uric acid.
Toxicity:
Uric Acid -> Urea - > Ammonia
Size of Molecule:
Ammonia -> Urea -> Uric Acid
Amount of water needed to excrete:
Uric Acid -> Urea -> Ammonia
Energy needed to produce:
Ammonia -> Urea -> Uric acid
What are the different functions of the Excretory system?
- Filtration
- Reabsorption
- Secretion
- Excretion
Draw the stylised version of the excretory system
book
What happens in Filtration?
- The Excretory tubule collects a filtrate from the blood.
- Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule.
What happens in Reabsorption?
The transport epithelium reclaims valuable substances from the filtrate and returns them the body fluid.
What happens in Secretion?
Other substances such as toxins and excess ions, are extracted from the body fluids and added to the contents of the excretory tubule.
What happens in Excretion?
The altered filtrate (Urine) leaves the system and the body.
How is a flatworms excretory system different to humans?
- Flatworms (Planaria) lack a coelom (body cavity) and have a system of protonephridia (Networks of dead end tubules connected to external opening)
- Filtrate collected and emptied into surrounding environment
What is a protonephridia excretory system?
Where there are networks of dead-end tubules connected to external opening to release the waste instead of one main excretory exit.
How is a Earthworms excretory system different to humans?
- They have Metanephridia excretory organs (Each segment of an earthworm has this system)
- Also osmoregulation
» Nitrogenous waste excreted
» Valuable solutes reabsorbed
» Lots of water in environment (damp soil), so urine is dilute
What do Metanephridia excretory organs do?
Collect fluid directly from the coelom and release into surrounding environment
What kind of excretory system do insects have?
- Insects and terrestrial arthropods have Malpighian tubules
» Remove nitrogenous wastes
» Osmoregulation - Dead-end tips immersed into haemolymph open into digestive tract
- Nitrogenous waste (mostly insoluble uric acid) excreted with faeces
- Conserves lots of water
How does excretion in Vertebrates work
- Specialised organ: Kidneys
- Both excretion and osmoregulation
- Network of tubules, counter-current exchange
- Nitrogenous wastes excreted as urea
- Collecting duct carries hyperosmotic urine → bladder
» Except in birds, which have no bladder (weight saving) and produce uric acid
What is so special about the kidneys?
≈10 cm long, on left and right side of body
- Filter 1,000 - 2,000 L blood per day
- Produce 180 L of urine per day
- We excrete ≈1.5 L of urine per day, so kidneys reabsorb ≈99% of water!
What are Kidney stones?
» Calcium salts accumulate and form a mass
» Caused intake of foods rich in oxalate (beets, nuts, spinach, rhubarb, chocolate)
What is Renal failure?
» Nephrons are damaged (by infection, tumors, shock, toxic compounds etc) and cannot perform regulatory and excretory function
» Requires dialysis
• Removes waste and excess water from blood
What is a Nephron?
Each of the functional units in the kidney, consisting of a glomerulus and its associated tubule, through which the glomerular filtrate passes before emerging as urine.
What are soe unique adaptions in animals in their excretory sstems?
- Desert animals have very particularly long loop of Henle → maximise water reabsorption
- Vertebrates that live in water have very short loop of Henle
Draw the Nephron Organisation Diagram
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