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Osmoregulation in marine mammal - Coggle Diagram
Osmoregulation in marine mammal
Dolphin and Whale
Drinking, fasting and feeding
Dolphin and cetacean don’t usually drink water to regulate their water-salt content
Under fasting condition, some species of dolphins do consume sea water. The skin is a major avenue of water flux (as much as 70 %) in fasting dolphins which is also dependent on the osmotic gradient of the environment.
Fasting cetaceans produce a dilute urine. They become acutely dehydrated, which would serve as a stimulus to increase metabolic water production (via fat oxidation), resulting in the increased excretion of free water
GFR, RPF and urine flow rate in dolphins increased after feeding, resulting in an increase in electrolyte excretion
Solute and water loading (Administration of hyperosmotic saline or fresh water)
The significant mechanism for maintaining water balance in cetaceans is because they have very low respiratory water loss
Hypertonic saline load increased urine flow, while freshwater loading (2.5 % of body mass) did not induce diuresis. However, an increase in urine osmolality was observed 2 hours after the administration. Increased diuresis following a hypertonic infusion was the result of extracellular fluid expansion.
Hormonal regulation
Positive correlations among adrenal steroid levels (aldosterone, cortisol and corticosterone) have exhibited in bottlenose dolphins, suggesting the presence of an active pituitary– adrenal axis
From dolphin samples taken, the AVP concentrations were very low as were the amounts in pituitary extracts. AVP does not significantly regulate urine volume and thus, water retention in these animals.
Kidney Structure
Possess reniculate kidneys made up of hundreds of individual lobes, or reniculi, each of which contains discrete cortical tissue and a single medullary pyramid inserted in a single calyx.
specialized glycogen stores in the proximal convoluted tubule epithelial cells, highly concentrated bundles of medullary blood vessels (vasa recta bundles), the presence of a sporta perimedullaris musculosa, a layer of collagen, elastic fibers and smooth muscle separating the cortex from the medulla.
Seals and Sea Lions
Metabolic water and drinking
Voluntary drinking of salt water (mariposia) - Assists with nitrogen excretion and thermal regulation in fasting animals living in warm conditions.
Seawater drinking
Ingestion of fresh water – form of ice consumption (yet unknown how fluid balance is maintained).
Incidental ingestion associated with feeding - maintaining electrolyte homeostasis
Fasting and feeding
Increased resorption of Na⁺ and K⁺ by the renal at the expense of H⁺, which may help to ease metabolic acidosis.
To increase the concentrations of Na⁺, K⁺, and urea in the urine.
Animals that are fed have the benefit of being able to use both the water generated by their food's metabolism and the pre-formed water in their diet.
Fasting decreases renal function while increasing resorption of endogenous electrolytes and body fluids to assist maintain fluid and electrolyte homeostasis.
Solute and water loading and infusions
Freshwater loads increase urine flow and decrease urine osmolality.
Urine flow and discharged Na⁺ and Cl⁻ both rise after infusions of hyperosmotic solutions of various concentrations.
The infusion of mannitol reduced plasma electrolyte and urea concentrations.
Urine volume and osmotic excretion were both enhanced when gelatine was infused.
Apnea / simulated diving
Effects of apnea (forced diving) on renal hemodynamics using the harbor seal- during periods of apnea and forced diving, GFR and RPF are reduced while the filtration fraction (GFR/RPF) remains relatively constant.
The apnea-induced decrease in GFR was associated with a decrease in urine flow and in excreted Na+ and K+.
Apnea and anoxia have similar effects on renal hemodynamics in the harbor seal.
Harbor seals trained to dive voluntarily and continuously without intermittent periods of breathing ( the two main differences between the earlier and most recent studies) - resulted in complete cessation of urine flow and GFR, which was attributed to an arterial constrictor response, within the first minute to the dive.
Water immersion
Henry-Gauer's reflex-arterial distention in the dog resulted in an almost immediate diuresis.
Pinnipeds - spend more than 75% of their time submerged in water, this reflex would be disadvantageous because of increased urinary water loss.
Pressure effects of water immersion were stimulated in harbor seals by continuous negative-pressure breathing - no change in urine output was induced.
Lack of a diuretic response to negative-pressure breathing- a Henry-Gauer reflex is not present in seals.
Hormonal Regulation
The primary hormones responsible for osmoregulation are angiotensin (angiotensin I, II or III), atrial natriuretic peptide (ANP), aldosterone and vasopressin (AVP).
The actions of ANP oppose those of angiotensin II and aldosterone by inhibiting
the synthesis and release of renin, thereby resulting in an increase in excreted Na+.
Most seals live in salt water, they do not drink sea water, and captive animals may be susceptible to hyponatremia.
Diving has profound effects on blood flow to the kidneys and on glomerular filtration, resulting in a decrease in renal activity, which could alter the response of vasoactive hormones (e.g. angiotensin II, AVP, ANP).
Apnea increases ANP levels and decreases angiotensin II and AVP levels, suggesting that these vasoactive hormones are also influenced by diving .
May help regulate blood pressure and flow to the kidneys.
Manatees and Dugong
Drinking
Consume sea water to maintain fluid homeostasis.
Manatees do not consume sea water voluntarily.
During periods of food deprivation, their water needs are met from metabolic water production.
Plasma Data
Consumption of fresh water can be high, leading to lower osmotic and ionic concentrations.
Plasma osmolality and electrolyte concentrations in wild freshwater manatees are similar to those of wild and captive animals in salt water.
Captive manatees held permanently in fresh water may be susceptible to hyponatremia, as are captive seals in a salt-depleted environment.
Freshwater manatees consume large volumes of water, renal plasma flow (RPF) and glomerular filtration rate (GFR) may be elevated in these animals as a result of a hypervolemic-induced increase in blood pressure.
Hormonal regulation
Manatees are commonly found in Na+ depleted environments and do not drink sea water as it can resulted in a neuroendocrine stress response.
Otter
Possess a lobulate kidney with respect to body mass.
Sea otters posses a slightly greater urine-concentrating ability than river otters.
Blood urea nitrogen is higher in the river otter
Sea otters can excrete Na+ and Cl- in greater concentrations than are found in their environment.
Possess the ability to actively consume sea water and to gain free water.
Only marine mammal to actively consume sea water and they do so to eliminate urea-nitrogen load.