Osmoregulation
Dolphin and whales 
Drinking, fasting and feeding
Hormonal Regulation
the animals would become acutely dehydrated, which would trigger an increase in metabolic water production, culminating in an increase in free water excretion.
Conclusion: water absorption through the skin was implausible. Unlike pinnipeds, fasting cetaceans produce diluted urine.
• These investigations showed that (i) renin generates a vascular pressor effect in dolphins (and possibly other cetaceans), (ii) the pressor effect is dose-dependent, and (iii) the response is graded until a threshold is achieved that results in a sustained increase in blood pressure.
• However, the extract was provided to allow the trials to be repeated with known dose concentrations, shedding light on the renin-induced increase in blood pressure's sensitivity and kinetics..
• As seen by the matching in slopes of their correlation regressions, the RAAS appears to have the same sensitivity as the California sea lion.
• The only other reported bioassay of cetacean tissue was evaluating the electrical conductivity of urine to see how plasma-extracted AVP affected water retention in water-loaded rats.
• Renin was extracted from a bottlenose dolphin's kidney and injected into dogs in 4 ml and 2 ml.
The oral delivery of hypertonic NaCl to a bottlenose dolphin was one of the first tests on cetacean osmoregulation.
Manatees
Do not consume water voluntarily and obtain water by metabolizing the water product same with pinnipeds and cetaceans.
Freshwater manatees consume a large volume of water that leads to increase of glomerular filtration rate and renal plasma flow as a result of a hypervolemic-induced increase in blood pressure.
Renin-angiotensin-aldosterone system (RAAS) are present in manatees and function to regulate the Na+ balance. The RAAS are much more sensitive than in pinnipeds and dolphins.
Freshwater manatees exposed to salt water for 4 days exhibited a significant decrease in the response of the RAAS and subsequent increase upon returning to freshwater.
Kidney Structure
Sirenians
Strictly marine dugong (Dugong dugon)
Strictly freshwater Amazonian manatee (Trichechus inunguis)
West Indian (T. manatus)
West African (T. senagalensis) manatees
Several large lobes with a continuous cortex.
Externally elongated, with features similar to those found in the kidneys of the camel and horse.
Cetacean
Highly concentrated bundles of medullary blood vessels (vasa recta bundles).
Specialized glycogen stores in the proximal convoluted tubule epithelial cells.
The presence of a sporta perimedullar is musculosa, a layer of collagen, elastic fibers and smooth muscle separating the cortex from the medulla.
Otters
Similar to the kidneys of pinnipeds and cetaceans, possess a lobulate kidney but it is larger than that of other marine mammals.
Plasma CL- concentrations the two otter species are similar.
Very little comparative data on their osmoregulatory capabilities exists.
Species
Strictly freshwater habitat, the American river otter (Lutra canadensis)
Blood urea nitrogen (BUN) higher.
Strictly marine habitat, the sea otter (Enhydra lutris).
Possess a slightly greater urine-concentrating ability.
Baikal seal and West Indian manatee has retained the ability to concentrate its urine.
Urinary Na+ and Cl− levels are approximately 6.5- and 10-fold greater.
Can excrete Na+ and Cl− in greater concentrations and possess the ability to actively consume sea water and to gain free water.
Urine
There are only a few animals which are with higher osmolality than the sea water can produce urine
These animals have the ability to concentrate their urine to a higher osmolality than sea water.
Due to osmolality of urine being greater than sea water, it was predicted marine mammals drank sea water. An assumption was made by Portier (1910), the urine was mainly composed of Na⁺ and Cl⁻ .
The marine mammals would have to excrete Na+ and Cl− in concentrations greater than that in the water they drink to obtain a net positive gain in solute-free water
Seals and sea lions
Drinking, fasting and feeding
hormonal regulation
At least six of the 14 otariid (eared pinnipeds) species have been seen to engage in 'drinking' activity, particularly in males.
Drinking appears to be regulated by environmental temperature in otariids as a technique of reducing thermal stress.
Elephant seals appear to be more adapted than harbour seals to protracted periods of food shortage.
Grey seal pups did not sustain osmotic and ionic homeostasis to the same extent as elephant and harp seal pups when they were fasted.
Although most seals live in salty water, they do not drink it, and captive seals are at risk of hyponatremia which appears to be reconciled via the pituitary–adrenal axis
When Na+ availability is restricted, including in the case of fasting elephant seals, the sensitivity of the system is increased, according to the slopes of the regressions between plasma renin activity and aldosterone level for these two pinnipeds.
Dive diving has a significant impact on blood flow to the kidneys and glomerular filtration, leading in a reduction in renal function, which may affect vasoactive hormone responses.
Changes in vasoactive hormone levels shown during sleep apnea are likely to occur during breath-hold diving Changes in vasoactive hormone levels seen during sleep apnea are likely to occur during breath-hold diving
Group Member
Alvin Boo Chi Yuan (74047)
Choy Jing Yi (74466)
Dee Jie Ying (74589)
Exlia Marsheana Binti Marcus (74764)
Farm Yan Rou (74794)
Felicia Anak Nam (74819)