Excretion and Osmoregulation in Insects, Fish etc.

Osmoregulation

• the maintenance of a constant internal osmotic environment despite changes in the external environment

• this involves maintaining the WATER and SOLUTE content in blood

Excretion

• the removal of metabolic waste products from the body

Secretion

Secretion is the release of useful substances from cells, including hormones or digestive fluids

Egestion

• removal of undigested waste products from the body

  • not excretion as the only ‘metabolic waste’ they excrete is bile pigments

Osmoregulators vs Osmoconformers

• osmoregulators actively control the internal osmotic conditions of their body

• osmoconformers; allow their body to equilibrate with the osmotic conditions of their external environment

Functions of Excretion and Osmoregulation ( why r they important)

1. regulation of pH - excretion of H+ and HCO3-

2. removal of unwanted metabolic products - to maintain rate of reactions, as many reactions are reversible and and removal of waste products will allow the reaction to favour the left → right

3. controlling salt levels - salts dissociate into ions, these ions are important for muscle contractions, enzyme activity and nervous coordination

4. regulating water content in the body - ensure not too much or too little water is conserved

5. removal of toxic wastes - if accumulate r toxic to body, enzyme inhibitors

Types of Excretory products

• Co2 - respiration

• O2 - photosynthesis

• nitrogenous wastes - proteins, amino acids or nucleic acids

• bile pigments - breakdown of haem

Explain Nitrogenous Products

• these are waste products containing nitrogen.

• First one produced is ammonia - deamination of proteins

• ammonia is HIGHLY toxic and can only be safely excreted in large volumes in dilute concentration - marine animals do this as they readily have access to water

• urea - less toxic, formed in liver through ornithine cycle

• uric acid - insects, requires much less water to excrete, safely stored in tissues as its a solid, does require atp tho

ammonia is mainly secreted by organism + habitat

• ammoniotelic organisms, living in freshwater

amphibian larvae, protozoans, freshwater teleost

Urea - habitat and organism

• Ureotelic Organisms

• terrestrial organisms or aquatic marine organisms such as marine teleost or mammals

Uric Acid - habitat and organism

• Uricotelic organisms

• terrestrial

• birds, reptiles and terrestrial insects

Excretory Structures (lowkirkenuinely not superduper important just know a few)

• cell surface membrane of protozoans

• kidneys, liver, gills and skin - fish/larval amphibians

• kidneys, liver lungs and skin of adult amphibians repitles birds and mammals

• Malpighian tubules and tracheae of insects

• protonephridia - flatworms and metanephridia of annelids

Explanation of skin,lungs and liver as excretory surfaces

→ Skin; water, urea and salts are secreted by the sweat glands as sweat

→ lungs; carbon dioxide and water vapour diffuse out

→ liver; bile pigments (breakdown of haemoglobin) and formation of urea

Osmoregulatory Structures (lowkirkenuinely not superduper important just know a few)

1. contractile vacuoles in protozoans

2. protonephridia of flatworms and metanephridia of annelids

3. malpighian tubules of insects

4. gills and kidneys in fish

5. kidneys in mammals

Why are osmoregulatory and excretory structures so similar

• because nitrogenous wastes must be excreted using water, hence a balance must be achieved to ensure wastes are safely eliminated without using too much water

Adaptations of Insects to live on land (waterloss related)

1. impermeable waxy layer covering exoskeleton

2. spiracles which have valves to control opening and closing

3. excrete a semi-solid not liquid

4. eggs have an impermeable shell

→ Malpighian Tubules!

Nitrogenous Excretion and Osmoregulation in Insects

• blind ending extensions found at the junction between the midgut and hind gut

• uric acid and salts enter from the blood its bathed in via active transport

• water follows

• salts are actively reabsorbed by epithelial cells and returned to blood - water follows by osmosis

• amount of water reabsorbed is controlled by salt reabsorption

• uric acid then mixes with undigested products in the hindgut and rectum

• forms solid crystals and excreted via the anus with the rest of undigested material

Nitrogenous Excretion and Osmoregulation in Freshwater Teleosts

• gills and kidneys act as excretory and osmoregulatory organs

• these fish are HYPERTONIC to their environment so they face swelling by excess water entering and loss of solutes as they move out

• prevent this by 1. excreting ammonia in large volumes of dilute concentration. 2. impermeable scales and mucus on the outercovering 3. active uptake of solutes from the external environment

Nitrogenous Excretion and Osmoregulation in Marine Teleosts

• organisms are HYPOOSMOTIC to their environment, so loss of water and entry of salts

• any salts absorbed from drinking water are actively excreted and eliminated from the blood by gill epithelium

• small amounts of conc urine contains such salts which ARENT removed by gills

• impermeable outer covering by gills