Osmoregulation

Question 1

define osmoregulation

Answer 1

The regulation of osmotic concentration (water content and solutes) in the body

Question 2

define excretion

Answer 2

Is the elimination of waste products (potentially toxic products) from the body

Question 3

What helps maintain homeostasis?

Answer 3

Excretion and osmoregulation

Question 4

Deine osmosis

Answer 4

The spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration in the direction that tends to equalize the solute concentrations on the two sides

Question 5

Define isotonic

Answer 5

The solution has an effective osmole concentration that is the same as the solute concentration of a cell

Question 6

define hypertonic

Answer 6

Solution has a higher concentration of solutes outside the cell than inside the cell

Question 7

define hypotonic

Answer 7

Solution has a lower concentration of solutes outside the cell than inside the cell

Question 8

define osmoconformer

Answer 8

Are iso-osmotic (same osmole []) with their surroundings and do not regulate their osmolarity

Question 9

define osmoregulator

Answer 9

Spend energy to control water loss and uptake in a hyperosmotic or hypo-osmotic environment

Question 10

define stenohaline

Answer 10

Describes organisms (most animals) that cannot tolerate substantial changes in external osmolarity (salinities)

Question 11

define euryhaline

Answer 11

Describes organisms that can survive large fluctuations in external osmolarity (salinities)

Question 12

define excretion

Answer 12

It is the elimination of waste products from the body.

Question 13

the movement of water and ions

Answer 13

Relative osmotic and ionic conditions exist between marine, freshwater, and terrestrial invertebrates and their environments

Question 14

osmoregulation in fresh water

Answer 14

Constantly take-in water from their hypo-osmotic environment
Salts lost by diffusion are replaced by foods and water uptake across the gills
Some invertebrates living in temporary ponds, can lose almost all their body water when pond dries out and survive in a dormant state = anhydrobiosis

Question 15

examples of anhydrobiotes

Answer 15

Tardigrades (‘water bears’) (Phylum Tardigrada)
Nematodes (Phylum Nematoda)
Rotifers (Phylum Rotifera)
Springtails (Phylum Arthropoda; Sub-class Collembola)
Midge larvae (Phylum Arthropoda; Class Insecta)

Question 16

osmoregulation in marine environments

Answer 16

Most marine invertebrates are osmoconformers (e.g. starfish, anemones)
Therefore require little to no energy to maintain osmotic balance.
Organisms living in coastal environments must survive fluctuating conditions (fresh water, lack of water, desiccation, etc)
As a result, some coastal invertebrates are efficient osmoregulators – they maintain optimal salt concentrations regardless of changes in the environment.

Question 17

example of osmoregulation in marine environments

Answer 17

Example: shore crab body fluids are hypertonic to brackish water (mixture of salt and fresh water) - gills remove salts from water and put into blood while excretory organs excrete excess water that diffuses in

Question 18

osmoregulation on land

Answer 18

In terrestrial environments, lack of water is often a constraint. There are several ways arthropods can gather water
1. Drinking
2. Metabolic water
3. Water vapour absorption (oral & rectal uptake)

Question 19

drinking arthropods on land

Answer 19

Drinking in arthropods is widespread, especially if they are dehydrated
Several species can take up capillary water from the soil against considerable water tension (termites)
Desert animals may drink condensation from vegetation and other surfaces
The Namib desert beetle Onymacris unguicularis climbs dunes in the early morning (fog-basking behaviour) and drinks water that condenses on its body, and trickles to its mouth

Question 20

examples of drinking arthropods

Answer 20

Lepidochora beetle species dig trenches and fog condenses on the ridges
Beetles return later and close down the trenches, drinking the condensate

Question 21

Metabolic water

Answer 21

Many species obtain water by processing food ingested (recall gas exchange lecture)
Carbohydrate= 0.033ml water / kJ
Lipid= 0.027ml water / kJ

Energy and water requirements have to be balanced

Increased O2 requirements or O2 limitation may mean that metabolising lipid has no advantage for particular organisms

Question 22

Water vapour absorbtion

Answer 22

Several (> 50) species of arthropods can absorb water vapour from unsaturated air by using mouthparts or rectum:

Mouthparts: uptake of H2O in cockroaches, booklice (Psocoptera), lice, ticks, mites, and pleopods in isopods

Rectal uptake in a variety of insects (some beetle and lepidopteran larvae, silverfish (fish moths) and fleas) from air ventilated into the rectum
Association of Malpighian tubules and rectum to form a cryptonephridial complex
K+ (potassium) ions are actively pumped into Malpighian tubules by leptophragmata cells, water cannot follow owing to perinephric membrane
Water moves from the rectal lumen into the peri-rectal fluid at humidity’s above c. 88%
A water impermeable (periphrenic) membrane keeps the osmotic concentration of the peri-rectal fluid high
Water moves from the perirectal fluid to the tubule
A counter-current system may be important

Question 23

what is filtration

Answer 23

the excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure accros the selectively permeable membranes of a cluster of capilaries and into the excretory tubules.

Question 24

What is reabsorbtion?

Answer 24

the transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.

Question 25

what is secretion?

Answer 25

other substances such as toxins and excess ioins are extracted from the body fluids and added to the contents of the excretory tubule.

Question 26

Nitrogenous waste products - ammonia

Answer 26

First type of waste formed
Toxic and raises pH of body fluids
Requires energy (ATP) to form and large quantities of water to dilute it out of a biological system.
Aquatic animals tend to release ammonia into the water.
Ammonotelic.

Question 27

Nitrogenous waste products - Urea

Answer 27

This conversion prevents the build up of toxic ammonia
Urea cycle – converts ammonia to urea
This happens in the liver
Dependent on several enzymes, including the ornithine-based enzyme which, if lacking, leads to a build up of toxic ammonia
Ureotelic

Question 28

Nitrogenous waste products - Uric acid

Answer 28

Helps to deal with water scarcity on land
Major by-product of ammonia conversion in terrestrial species
Requires more energy and more complex than the ammonia-urea conversion
Excreted as a white paste or powder
Uricotelic

Question 29

the excretory system

Answer 29

Some aquatic invertebrates simply release excretory products across their skin. Examples include cnidaria, sponges, planaria

However, other invertebrates have more specialized structures. These are generally built on a network of tubules and include:

1. Protonephridria
2. Metanephridria
3. The bojanus and Kebers organs
4. Gills
   5 .Antennal gland
5. Malpighian tubules

Question 30

What is protonephridia?

Answer 30

Found in platyhelminthes, nemerteans, chordata, and rotifers (coelomates and acoelomates)
A protonephridium is a network of dead-end tubules lacking internal openings
Usually end in flame cells which excrete a dilute fluid
Due to large SA:V ratio, waste products can diffuse directly from cells to external environment.
Flame bulb: cap cell with cilia and tubule cell. Form a filtration membrane where the cells meet.
The cilia hang inside lumen of tubule
Beating of the cilia creates a pressure and pushes out small waste products
Larger waste products are pushed down through tubule, collected, and excreted through the nephridiopore
As fluid moves through tubules, reabsorption occurs and as a result, excreted product is dilute.

Question 31

What is metanephirdia?

Answer 31

Found in annelids, arthropods, molluscs

Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion

Each segment of an earthworm has a pair of open-ended metanephridia

Question 32

Annelids and metanephridia?

Answer 32

Earthworms have:
Nephrostome – aperture that opens into the coelom or body cavity. Ciliated. Collects fluid
Nephridiopore – terminal end, opens to the outside of the body, waste is discharged from here
Closed circulatory system - contains blood that is kept separate from the coelomic fluid
Ureotelic

Question 33

Molluscs – Kebers and Bojanus organs?

Answer 33

Molluscs have the basic metanephridia and sometimes possess specialized organs
Bojanus organ – two kidney-like structures derived from the coelom, situated below the pericardial cavity on either side of the vena cava
Kebers organ – pericardial gland used for excretion. Discharges waste into pericardium for collection by “kidneys”
Ammonotelic or uricotelic

Question 34

Crustaceans- gills?

Answer 34

Osmoregulation is very species-specific
Aside from metanephridia, gills play a principle role
Ion uptake and transport for haemolymph regulation, acid base balance, ammonia excretion
Generally in crustaceans – haemolymph osmotic and ion concentrations are slightly higher than surrounding medium
Have to compensate in lower salinity – more ion-transporting cells present in the gills for more ion uptake, more dilute urine, and active uptake of ions.

Question 35

Crustaceans - antennal glands

Answer 35

The green gland - a pair of glands in the head with an end sac containing podocytes, long excretory tubule, a bladder and excretory pore
Podocytes are specialized interlocking cells which allow some small compounds to pass through but retain larger molecules such as protein – ultrafiltration of blood
In a marine environment, ultrafiltration occurs with no water reabsorption and active secretion of substances
In a brackish environment ultrafiltration occurs with reabsorption where ions are resorbed followed the the active transport of water
Selective reabsorption.

Question 36

Malpighian tubules?

Answer 36

In insects and other terrestrial arthropods, malpighian tubules are found in the posterior region of the body
A system of branching tubules that increases contact with the haemolymph for maximum transport
Also lined with microvilli
Together with other rectal glands, they remove nitrogenous wastes from hemolymph and function in osmoregulation as well as excretion
Malpighian tubule indiscriminately uptakes ions from the haemocoel and empties “primary urine” into the gut, reabsorption occurs in the hindgut to further concentrate urine.
Insects, land snails (and some reptiles/birds) excrete uric acid as their major nitrogenous waste
Uric acid is largely insoluble in water and can be secreted as a paste with little water loss