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OSMOREGULATION IN MARINE MAMMALS - Coggle Diagram
OSMOREGULATION IN MARINE MAMMALS
Pinnipeds (seals and sea lions)
Solute & water
loading & infusions
Loading of fresh water causes:
-Increase urine volume & fractional clearance of electrolyte & water
-Causes an increase in GFR
-Decreases plasma and osmolality of urine
Harbor seals contain a volume receptor that regulates differently than that in humans
Apnea
(forced diving)
Blood diversion from kidneys during
longer dives (> ADL) → lesser O2
intake by kidneys and elevate oxygenated
blood distribution to other tissues
Decreased GFR due to regional
diversion of blood flow to the kidneys
Non-diving conditions → the kidneys have
large oxygen consumption and acquire
significant volume of blood for filtration
Fasting & feeding
Fasting animals maintain water balance by using the metabolism of fat, protein stores and pre-formed water
Kidney activity is reduced and resorption of endogenous electrolyte and body water is increased in order to maintain fluid and electrolyte homeostasis during fasting
Feeding animals uses water from metabolism of their food and pre-formed water
Water immersion
Spend >75% of their time in water → Pressure impacts of water immersion were contrived in harbor seals via continuous negative-pressure breathing → no change in urine production was prompted
Henry-Gauer reflex is absent in seals
Metabolic water & drinking
Salt supplements or low-salt diet could be implemented to prevent hypothermia in captured pinnipeds in fresh water
The incidental ingestion linked with feeding may be vital for maintaining electrolyte homeostasis - but drinking is not necessary for sustaining water balance
Hormonal regulation
4 hormones responsible for
osmoregulation → angiotensin (I, II, III),
atrial natriuretic peptide (ANP),
aldosterone and vasopressin (AVP)
RAAS (renin-angiotensin-aldosterone system)
→ regulate electrolyte balance under
normonatremic conditions
AVP and RAAS mediate water and electrolyte resorption
Hyponatremic circumstances → mediation
by pituitary-adrenal axis → satiate salt concentrations
Apnea elevate ANP levels, reducing angiotensin II
and AVP → indicates that diving has an
impact on these hormones
Dolphins & whales
Solute and water loading
Dolphins
- Hypertonic saline load → raise urine flow
- Freshwater load → diuresis was not induced
- :check: An increase in urine osmolality was observed 2h after the freshwater administration
- :check: The increased diuresis following a hypertonic infusion was the result of extracellular fluid expansion
The stomach tube is used to load the solutes and water.
Other points of interest
Creatinine clearance is a valid way to calculate GFR in whales.
Low respiratory water loss in dolphins, pinnipeds and whales compared to that of any land mammals of similar body mass
Pinnipeds: :check: Secretion of creatinine from the renal tubules into the filtrate
Dolphins: :red_cross:Secretion of creatinine
Drinking, fasting and feeding
Pinnipeds
After feeding, GFR, RPF, and urine flow rate increased, causing in an increase in electrolyte excretion which is induced by increased nitrogen-loading on the kidney
Whales
Fasting whales/extreme dehydration → stimulus → metabolic water production → increased free water excretion → have dilute urine
Dolphins
- Under fasting condition, dolphins drink sea water.
- Also, 70% of total water flux is replenished through dolphins' skin.
- If dolphins exposure to a hypo-osmotic environment, they may gain freshwater.
Hormonal regulation
Renin
- Increase blood pressure
- Induce a vascular pressor effect as in other mammals
- Pressor effect is dose-dependent
- The response is graded until it reaches a point where it causes a prolonged rise in blood pressure.
Renin+ aldosterone
- RAAS is present and active in bottlenose dolphins as evidenced by a positive association between plasma renin activity and aldosterone
- Sea lions have the same slope of correlation regressions as dolphins
- Bottlenose dolphins have also shown positive correlations in adrenal steroid levels (aldosterone, cortisol and corticosterone), suggesting the presence of a functioning pituitary-adrenal axis.
Aldosterone and vasopressin (AVP)
- The plasma-extracted AVP from whales tissue are known to help determine how much water was retained in water-loaded rats by measuring the electrical conductivity of the urine.
- Little or no AVP was detected at dolphins' tissue
.
- No correlation observed between urine flow rate and plasma AVP in fasting dolphins. Thus, AVP has no effect on water retention or urine volume in dolphins.
- However recent research of free-range dolphins has discovered greater AVP concentration which might help in future assays.
Otters
Freshwater otter
Have ability to concentrate its urine
Higher blood urea nitrogen (BUN) (urinary sodium and chloride levels approx. 6.5x and 10x greater than sea otter)
Sea otter
Slightly better urine-concentrating ability than river otter (max. urine osmolality 30% greater)
Lower BUN - can excrete sodium and chloride more than in surrounding environment
Can actively drink sea water and gain free water to eliminate urea-nitrogen load
Have lobulate kidney, larger than other marine mammals
Similar plasma chloride conc. in both sea otter and freshwater otter
High-protein diet
GFR and RPF associated with feeding and fasting
No hormonal data found
Manatees & Dugong (Sirenians)
Plasma data
Lower osmotic and ionic concentration
For wild freshwater manatees, they access to salt occasionally
Temporary inhabit in marine environment
Consuming salt content from aquatic vegetation
For captive manatees, they will be having hyponatremia (Sodium level in blood is lower than normal)
No updated study regarding renal hemodynamics in sirenians
High consumption of fresh water
Hormonal Regulation
Freshwater manatees (Usually found in sodium depleted habitat) inhabit in salt water for 4 days, significant decrease in RAAS, increase when returning to fresh water
High sensitivity of RAAS (A complex multi-organ endocrine system in regulating blood pressure balanced by fluid and electrolyte in blood).
Oral intubation - caused neuroendocrine stress response - RAAS response increase
Plasma osmolality increase, AVP (Vasopressin) stimulated and released
Drinking
Have the ability to concentrate its urine
Sea water drink by the manatees for maintaining homeostasis fluid
Not drinking the sea water voluntarily
Water consumed are used for the metabolic water production during food deprivation periods
Urine Concentration
Consumption of seawater is not a must by marine mammals. They do not rely on seawater to maintain their fluid balance, as they do not regularly produce urine that have higher concentration Na+ and Cl− compared to seawater.
Martine mammals can produce urine that has higher osmolality compared to seawater (Highest urine osmolality = 2658 mosmol l−1).
Mammals found in freshwater habitats remains their urine-concentrating abilities, as they could concentrate their urine responding to hyperosmolality environment.
The thickness of the cortical:medullary thickness of the West Indian manatees is related to the production of urine that has higher osmolality compared to seawater.
Freshwater manatees did not concentrate their urine when exposed to saltwater as source of freshwater was maintained by feeding normal diet that has high water content.
Urine osmolality by wild animals in seawater is approximate 1200 mosmol l−1.
Positive correlation between urine osmolality and plasma osmolality in marine mammals
.
Kidney Structure
Main organs that involve in the regulation of water and electrolyte
Multilobed kidney is found in Pinnipeds and Cetacea, similar to otters and bears. These kidneys consists of individual lobes or reniculi, each contains separate cortical tissue and single medullary pyramid in single calyx.
The kidney of manatees, order of Sirenia (Sea cows) is superficially lobulated (lack true reniculi and cortex is unbroken).
Kidney of Cetacean different compared to terrestrial mammalian kidneys due to diving behaviour
Lacking bundles of medullary blood vessels.
Lacking a layer of collagen, smooth muscle and elastic fibers that separate cortex from medulla (sporta perimedullaris musculosa).
Lacking specialized of glycogen store in proximal convoluted tubules epithelial cells
Kidney of Sirenians varies based on the habitats of each species (freshwater & saltwater), different compared to pinnipeds and cetaceans.
Kidneys of West Indian manatees (inhabit both freshwater and saltwater) has several large lobes with continuous cortex.
Kidneys of marine dugongs is elongated, similar to kidneys of camel and horse.
Kidneys in marine animal living in a hyperosmotic environment have thick medullary but they are poor urine concentrators of urine (slightly better compared to humans, but lower compared to desert rodents). Mammals tend to adapt to hyperosmotic environment by hormonal regulation of urine concentration and rate of formation of urine.
Introduction
Marine mammals adapted to hyperosmotic environment
Physiological mechanism tends to conserve fresh water for preventing dehydration
Aquatic mammals diverged and started to live in freshwater
Physiological mechanism needs to conserve electrolyte
Some marine mammals in arid terrestrial environments
A stronger physiological mechanism needed to stand for prolonged fasting, maintain water balance and the electrolyte homeostasis.
