Osmoregulation Flashcards
(28 cards)
How are osmoregulation, volume regulation and ion regulation linked?
Osmoregulation is mostly the regulation of ions, as well as some proteins or sugars.
Concentration of solutes is (solutes/volume) so it involves volume regulation by the amount of water solutes are dissolved in
What are the two ways that water can move between compartments? Where is each found?
Osmotic movement - diffusion across cell membranes
Hydrostatic pressure - In kidneys and other excretory organs
What does the tight epithelium in the kidney, gut, and respiratory system do?
Forms a tube to separate the body from the outside environment (inside tube)
What is the need for osmoregulation in marine bony fish?
Have an ECF concentration of 1/3 seawater, but need to drink to take up water, this causes ion absorption. To counteract this, they produce a small amount of urine, and excrete many ions through the gills
What is the general osmoregulatory problem in freshwater environments?
Freshwater fish have same osmotic concentration as marine, but freshwater is even lower. The main problem is osmotic water influx and losing ions to the environment
What is osmoregulation like in terrestrial environments?
There is no osmotic water movement and no ion exchange from the air, ion intake comes from food and water is evaporated.
Problems are like marine - not enough water, too many ions - so water is conserved, animals drink, and produce concentrated urine
What is the {ion} and {osmotic} like in sharks in comparison to seawater? How do they maintain it?
The {osmotic} is similar to salt water, so they do not need to drink in order to gain water, thus they do not absorb the salt.
{ion} is maintained by producing urine
What are the major differences between freshwater and marine fish in terms of osmo and ion regulation?
Freshwater fish - hyperosmoregulating ionoregulators
- osmotic water influx is dumped by kidneys with as many ions as possible reclaimed from urine
- Ion loss is replaced by ion uptake at gills
Marine fish - hypo-osmoregulating ionoregulators
- Must drink to absorb water, but absorb ions with it. These are excreted through gills
- Minimize water loss in urine
What are the pieces of the three compartment model in ion exchange?
Outside - lumen of gut, lumen of nephron, air side of lung, etc.
Intracellular - Inside cells of tight epithelium - ICF
Inside - extracellular fluid (ECF)
In which direction do ions travel? Is it possible to go against that?
Ions move down electrochemical gradients
It is possible to go against it, but in total it requires energy input
What is the simplified version of the Nernst equation?
What does it calculate?
mV = 58 log10(concentration(out)/concentration(in) x valency
Valency is +1 or -1
It finds the balance point between electrical potential difference and concentration different for a single ion across a barrier
Where do the ions flow through if it is passive transport? Active?
Passive - movement through tight junctions
Active - active across either apical OR basolateral membrane, and passive through the other
What are the steps to determining flow of ions in fish?
Determine which way the ions are moving across the epithelium - eg. Marine move outward
Use the Nernst equation to determine whether the movement is active or passive by comparing the reference to the measured potential
If it is passive, it is through the tight junction.
If it is active, determine which barrier is active and which is passive
What ions are exchanged at the gill epithelium? Which are linked in exchangers?
Where can something similar be found in mammals?
Na+ - H+
Na+ - NH4/NH3
Cl- - HCO3
An Na+/H+ exchanger that can also exchange Na+/NH4 can also found in mammal kidneys
How do ion exchangers in the gill control pH?
If the Na+/H+ exchanger has a higher rate than the Cl/HCO3 exchange, there is a higher H+ (acid) excretion, raising pH level.
The opposite is true for higher base excretion and lowering pH
What are the three common Nitrogenous waste products and what types of animals use them?
Ammonia/ammonium
- little energy, and can be toxic
- Used by aquatic animals
Urea
- requires energy to synthesize but can be excreted in high concentrations
- used by terrestrial animals like mammals
Uric acid - or salt form, urate
- requires less water, but not soluble and uses a lot of energy to synthesize
- Done by birds, lizards and insects
What is the first step of an excretory organ? How do vertebrates perform it?
What does it select for?
They filter everything
Use blood pressure to filter blood plasma across Bowman’s capsule
Allows ions, water, simple sugars and amino acids to flow through, but not proteins, complex lipids or carbohydrates
What is the second step of an excretory organ? How is it performed?
The reclaiming of all nutrients, ions and water.
The proximal convoluted tubule in vertebrates reabsorbs 2/3 of filtrate.
This is done by Na+ transport causing an electrochemical gradient to absorb Cl. The change in osmotic concentration then causes water uptake through aquaporins
What is the third step of an excretory organ?
The regulated uptake of water and ions in the distal convoluted tubule
The transport of ions and water are regulated by aldosterone and ADH
What are the functions of aldosterone, chloride and ADH in uptake of water and ions?
Aldosterone - increases number of Na+ and K+ channels, increasing Na uptake in exchange for K
Chloride is co-transported with Na+ from collecting duct
ADH increases water permeability of epithelium by increasing number of aquaporin channels and causes concentrated urine
What is used to cause concentrated urine mammals?
The loop of Henle - the countercurrent multiplier creates a concentration gradient with NaCl transport
What is the process in the loop of Henle?
Active NaCl transport in thick ascending loop
NaCl leaves ascending thin loop passively because of a higher concentration gradient
How is urea affected in the loop of Henle?
Urea concentration increases the more water is reabsorbed.
Proximal convoluted tubule, descending loop and, if ADH is present, the distal convoluted tubule all absorb water
The lower part of the collecting duct is permeable to urea so it moves into the medulla of the kidney
What is the role of the vasa recta?
The vasa recta is a vascular loop that allows the reabsorbed water to return to the blood vessels
It is a countercurrent exchanger with a net uptake of water
