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Osmoregulation in Marine Mammals, STH2203 ANIMAL PHYSIOLOGY - Coggle…
Osmoregulation in Marine Mammals
Introduction
Overview of osmoregulation:
The process by which organisms regulate water and salt balance in their bodies.
Importance of osmoregulation in marine mammals:
Due to their marine habitat, marine mammals face unique challenges in maintaining osmotic balance.
Seals & Sea Lions
Kidney Structure & Urine Concentrating Ability
The kidney is reniculate in structure, unlike those of terrestrial mammals (except bears), but these differences do not confer any greater concentrating ability.
Sources of Drinking
Seals can maintain water balance solely from pre-formed water in their diet and the subsequent metabolically derived water (Irving et al., 1971; Ortiz et al., 1978).
Drinking is not essential for maintaining water balance, but the incidental ingestion associated with feeding may be important for maintaining electrolyte homeostasis.
The Effect of Fasting, Feeding & Diving
Feeding increased GFR, RPF, urinary Na+, K+, and urea concentrations (Schmidt-Nielsen et al., 1959).
Because water is generally more available during feeding, the activity of the kidney is increased, allowing for increased excretion of dietary nitrogen and electrolytes.
During fasting, the activity of the kidney is reduced and the resorption of endogenous electrolytes and body water is increased to help maintain fluid and electrolyte homeostasis.
During periods of apnea and forced diving, GFR and RPF are reduced while the filtration fraction (GFR/RPF) remains relatively constant.
The Renal Responses to Infusions of Varying Salinity
Freshwater loads increase urine flow and decrease urine osmolality within 2 h (Albrecht, 1950; Bradley et al., 1954; Tarasoff and Toews, 1972; Hong et al., 1982; Skog and Folkow, 1994).
Continuous intravenous infusion of hyperosmotic saline resulted in the death suggesting that marine mammals do not have any greater resistance to seawater toxicity than terrestrial mammals (Albrecht, 1950).
Hormonal Regulation
Water and electrolyte resorption is mediated by AVP and the RAAS.
During hyponatremic conditions, mediation via the pituitary-adrenal axis may also be required to replete salt concentrations.
Vasoactive hormones are influenced by diving and may help regulate blood pressure and flow to the kidneys.
Otters
Kidney Structure & Urine Concentrating Ability
They possess a lobulate kidney (Hoover and Tyler, 1986) but, concerning body mass, it is larger than that of other marine mammals (Costa, 1982).
Sea otters possess a slightly greater urine-concentrating ability than river otters.
Sources of Drinking
They possess the ability to actively consume sea water and to gain free water as they can excrete Na+ and Cl- in greater concentrations than are found in their environment (Costa, 1982).
Sea otters are the only marine mammals reported actively to consume sea water and they do so as a means of eliminating urea-nitrogen load (Costa, 1982).
Fasting, and Feeding
The high-protein diet of otters suggests that changes in GFR and RPF may be associated with feeding and fasting.
Manatees & Dugongs
Kidney Structure & Urine Concentrating Ability
In manatees, the kidney is considered superficially lobulate since it lacks true reniculi and the cortex is continuous (Maluf, 1989).
The kidney of dugongs has been described as externally elongated.
Sources of Drinking
The manatees are capable to concentrate their urine.
Manatees do not consume seawater voluntarily and that, during periods of food deprivation, their water needs are met from metabolic water production, as in pinnipeds and cetaceans (Ortiz et al., 1999).
The Renal Responses to Infusions of Varying Salinity
Water flux studies have demonstrated that consumption of fresh water can be high, leading to lower osmotic and ionic concentrations (Ortiz et al., 1998; Ortiz et al., 1999).
An RPF and GFR may be elevated in these animals as a result of a hypervolemic-induced increase in blood pressure because freshwater manatees consume large volumes of water.
Hormonal Regulation
RAAS is present in manatees and is involved in the regulation of sodium (Na+) balance.
A neuroendocrine stress response in manatees led to an increase in the activity of the RAAS, which influence the regulation of water and electrolyte balance in manatees.
Increased plasma osmolality, a measure of solute concentration, appears to stimulate the release of AVP in manatees.
Dolphins & Whales
Kidney Structure & Urine Concentrating Ability
The kidney is reniculate in structure, unlike those of terrestrial mammals (except bears), but these differences do not confer any greater concentrating ability.
Drinking, Fasting, and Feeding
Dolphins do not drink seawater (Fetcher and Fetcher, 1942).
Fasting cetaceans have been shown to produce dilute urine (Bentley, 1963; Telfer et al., 1970; Hui, 1981).
GFR, RPF, and urine flow rate in dolphins increased after feeding, increasing electrolyte excretion (Malvin and Rayner, 1968; Ridgway, 1972).
The Renal Responses to Infusions of Varying Salinity
A hypertonic saline load increased urine flow (Fetcher and Fetcher, 1942; Ridgway, 1972).
Freshwater loading did not induce diuresis, although an increase in urine osmolality was observed 2 h after the administration (Malvin and Rayner, 1968).
Hormonal Regulation
Renin in dolphins (and probably all cetaceans) causes a vascular pressor effect.
AVP does not significantly regulate urine volume and, thus, water retention in these animals (Malvin et al., 1971).
STH2203 ANIMAL PHYSIOLOGY
GROUP MEMBERS:
BATRISYIA ADAWIYAH BINTI INDRA MALINDO (78951)
EVNEY EVLYN DARIUS (79370)
NURFARA NADIA BINTI AG JANIH (80759)
SHARIFAH NUR SHAHIRAH BINTI SYEED ZAINAL ABIDIN (81135)
ANNZLY ATTY DAVID (78860)
AARON KHOO BIN KHOO HOOI KEAN (77723)
