Osmoregulation Flashcards
What are the main functions of excretory organs?
- maintain osmotic concentrations
- maintain body fluid volume
- maintain proper concentration of ions
- remove metabolic end products
- remove foreign substances/toxins/anything that is in excess
What is osmolarity?
The concentration of moles of active solutes per litre of solvent
What is osmotic pressure?
Force associated with the movement of water
What are osmolality and tonicity?
Osmolality - conc. of solutes per KG of solvent
Tonicity - conc. of IMPERMEABLE solutes per litre of solvent
How do excretory organs control the osmolarity and volume of extracellular fluids?
- By excreting water and solutes that are in excess
* By conserving water and solutes in short supply
In what different ways are Nitrogen excreted?
Different animals deal with nitrogen in different ways
• converted to ammonia - most toxic and need a lot of water to get rid of it
• converted to urea (human)
• converted to uric acid - least toxic and requires least amount of water to excrete
How is urea synthesised?
Urea is synthesised from - carbon dioxide - water aspartate - ammonia • in a metabolic pathway called the UREA CYCLE
Where is urea synthesised?
Liver
Excretory function for marine animals
Have to conserve water and excrete excess salts
Excretory function for freshwater animals
Have to excrete excess water and conserve salts
Excretory function of terrestrial animals
Must conserve water and salts
What is an osmoconformer
- Marine organisms that maintain an internal environment which is osmotic to their external environment.
- Osmotic pressure of their cell and the surrounding environment is equal
- do no have physiological systems to perform osmoregulation
What is an osmoregulator?
- Organism who actively regulate their osmotic pressure in different environments
- Can survive in varied environments by maintaining the osmolarity of their body
What are teleost fish?
Most bony fish that can be in either salt or fresh water (osmoregulators)
- They are cartilaginous - have cartilage instead of bone
What happens when the teleost fish internal environment is hypo-osmotic to the external environment?
- Higher salt concentration in the surrounding en/v
- water lost via osmosis, and salts gained
- fish drink seawater to replace the water lost to the en/v
- produce little, more concentrated urine (kidney)
- eliminate the salts ingested fro salt water
What is the principle nitrogenous waste in aquatic invertebrates and bony fish?
- Ammonia
- easily removed because very soluble in water
- Excreted by diffusion across the gill membranes directly into water
What are the different ways terrestrial animals obtain water and get rid of it?
In: 1. drinking 2. water in food 3. metabolic Out: 1. evaporation 2. urine 3. faeces
What are the behavioural strategies of desert animals to minimise water loss?
- Avoid the daytime heat and emerge at night
* Aestivation: low metabolic activity so low H20 Turnover (similar to hibernation - stay burrowed during dry seasons)
What are some structural/physiological changes in desert animals to minimise water loss?
- Have a thick keratinised cuticle - high lipid content
* Have efficient kidneys and excrete highly concentrated urine (long loops of Henle)
Nephron
functional unit of the vertebrate kidney, and consists of a glomerulus and renal tubule
Glomerulus
- Dense ball of capillaries which filters blood plasma to produce a fluid lacking cells, proteins and other large molecules
- Where blood is filtered across the walls of a mesh of capillaries
Renal tubule
Processes the filtrate into urine
Bowman’s capsule
Receives renal filtrate from glomerulus, mainly water and small molecules such as glucose, amino acids and ions (salts).
Why is the rate of filtration high in the glomerulus?
- high glomerulus blood pressure
- high permeability of glomerulus capillaries and their podocytes (which wrap around capillaries and leave slits between them)
What happens in tubular reabsorption?
- Glomerular filtrate flows into the renal tubule
* here it is modified by reabsorption of water and ions
Why do you not produce 200L of urine even though it is amount of water filtered by the glomerulus?
Most of the water and solutes filtered out of the glomerulus are reabsorbed and do not appear in urine
Where does most of the water reabsorption take place?
- 75% in the proximal convoluted tubule - resulting in a filtrate that is iso-osmotic to blood
- remainder occurs in the rest of the renal tubule resulting in the filtrate that is more concentrated than blood
Describe the structural features of the proximal convoluted tubule and each of their functions
- PCT cells are cuboidal with increased surface area due to microvilli
- large numbers of mitochondria near the apical surface - PCT cells are highly metabolically active
- the PCT cells actively transport Na+, glucose and amino acids out of the filtrate & back into tissue fluid
• This causes water to follow by osmosis (water & solutes are taken up by peri-tubular capillaries )
What are aquaporins?
Water channel molecules which assist osmosis
What is the function of aquaporin 1?
AQP1 regulates the movement of water molecules in the proximal convoluted tubule (PCT).
What happens in mice who have AQP-1 that does not properly function?
Mice cannot concentrate their urine because there is no movement of water from renal filtrate in the PCT.
What 3 components make up the loop of Henle?
- thick ascending limb
- thin ascending limb
- descending limb
