Water / Salt Physiology Flashcards
Water-Salt relations in a freshwater animal (crayfish)
Recall, water moves towards a higher concentration of salts, and salts move down their concentration gradient. A freshwater animal, such as a crayfish, faces challenges because of passive water and salt exchange. The freshwater animal tents to gain water and lose salts, especially across the gills. To combat this, crayfish have copious amounts of very dilute urine, as well as active (energy requiring) absorption of Na+ and Cl- on their gills. These adaptations allow them to gain/maintain as much salt as possible, while removing large amounts of water.
Active Na+ and Cl- transport in gills of freshwater fish
-Active ion transport pumps exist within single epithelial cells on the gills.
-CO2(from metabolism) and H2o (from body water) are combined into H2CO3, which is then separated into HCO3- (bicarbonate) and H+ (Proton).
-Protons are exchanged via pump for Na+ ions, and bicarbonate is exchanged via pump for Cl- ions
Gill structure
Picture a gill, boomerang in shape. The gill has 2 main components, the gill arch and gill filaments. The gill arch is the structure that the gill filaments attach to, like the hairs on a broom. On the gill arches, there are ribbed structures called secondary lamellae, which increase surface area allowing for better oxygen uptake. These lamellae also have mitochondria-rich cells also called chloride cells
Animals that are Isosmotic to seawater (7)
- Mussels
-Squids
-Crabs
-Sea urchins
-jellyfish
-Hagfish
-Octopus
Mitochondria-rich cells (aka chloride cells) (MRC)
Are densely filled with mitochondria (duh) and have an extensive intracellular tubular system composed of branching tubules. These Tubules are continuous (connected) with both basal and lateral cell membranes, and extend throughout the entire cell. Additionally, the lateral membranes are externally surrounded by pavement cells
Basal vs lateral
Basal = connected to the basement (bottom) membrane, a structural component
lateral = surfaces that connect to neighboring cells
Pavement cells
Pavement cells act as a protective layer for the more specialized cells below, helping to prevent water loss, maintain internal temperature, and resist the intrusion of external materials.
NaCl excretion in gills of saltwater fish
The NKCC brings in K+ ,Cl- into the cell against their gradients and Na+ along its gradient into the MCR. The sodium/potassium pump removes excess Na+ across the basolateral membrane back into the blood to maintain the cells polarity, while bringing in more K+. The excess K diffuses through an ion channel back into the blood. The chlorine in the MRC then diffuses into the ocean through a ion channel. Excess Na+ in the blood diffuses directly into the seawater.
Apical vs basolateral membrane
Basolateral = membrane between MRC and blood
apical = membrane between MRC and seawater
NKCC
Na-K-2CL cotransporter
Water-salt relations in freshwater vs saltwater fish (5 each + 2 that both do)
Freshwater:
-Hyperosmotic to ambient water
-Salt loss from diffusion and water gain from osmosis on gills
-Active uptake of Na+ and Cl- on gills
-Large amounts of very dilute urine
-Do not drink the water
Saltwater:
-Hyposmotic to ambient water
-Salt gain from diffusion and water loss from osmosis on gills
-Active excretion of Cl- and passive diffusion of Na+ on gills
-Small amounts of urine
-Ingest salts and water from seawater (net water gain)
Both:
-Gain salt and water from food
-excrete salt and water in feces
Salt excretion in birds
The salt glands of birds are located above the eyes. Ducts carry the secretion of salts to the nasal passages, where they drip out of their nostrils. The glands themselves consist of many long lobes, which each contain a great number of branching secretory tubules arranged radially around a central canal.
Chemical structure of urea
H2N - C - NH2 With a double bonded O attached to the top of C
Salt - water relations in sharks (6)
-Hyperosmotic but also hyperionic to ambient water
-Salt gain by diffusion and water gain by osmosis across the gills
-Modest amount of urine which is hypoosmotic to plasma
-Rectal gland secretes feces rich in NaCl plus other salts and water
-do not drink
-Gain salts and water from food
Types of osmotic regulators
Hyper-isosmotic regulators: typically found in freshwater animals that enter brackish waters.
hyper-hyperosmotic regulators : typically found in shore crabs
Trout experiment
A brown trout that was living in freshwater was transferred into seawater. After 60 days in the seawater, the abundance of NKCC and sodium potassium pumps per unit of gill tissue increased from about 5 to 35. The trout was placed back in freshwater, then the abundance of NKCC had dropped to about 20 and the sodium potassium pump dropped to about 25 after 10 days.
Mussels experiment
Two populations of blue mussels were collected, one from the north sea (ambient salinity 30g/kg) and one form the Baltic sea (15g/kg). Their initial cilia activity was measured. Cilia are what pump water into the mussel for food and o2 collection. The mussels were then swapped into opposite salinities and left for 30 days. After 30 days, their cilia activity resembled the opposite populations initial rate. In other words, after 30 days the Baltic mussels were acting like north mussels and vice versa.
Insect water loss and temprature
In insects, evaporative water loss typically increases as temperature increases, then spikes after hitting the “transition temperature”
Temp of exhaled air effect on water retention
Deep-body temperature in 37c in mammals and 39c in birds. The air these animals inhale is warmed to the deep-body temperature in the lungs, but cooled to be closer to the ambient air temp by the time it is exhaled - resulting in a large amount of water saved as less evaporated water molecules can be stored in the exhaled air.
Rate of evaporative water loss in a phylogenetic group
Within a phylogenetic group, water loss is a function of body weight, where the larger the animal in the group, the less evaporative water loss it will experience
Urine Concentration and body size
as body size increases, maximum urine concentrating ability decreases
Water turnover
Water turnover is the amount of water lost and gained in a day. On average, reptiles turn over the least and birds turn over the most with mammals in the middle
Arboreal frogs
Arboreal frogs secrete a protective lipid over their skin which drastically reduces evaporative water loss
