Monocalyceal kidney→ one single renal pelvis and set of papillae ex. mouse
one single renal pelvis + set of papillae = calyx
muticalyceal kidney→ divided into multiple calices ex. other mammals, humans
multirenuculated kidney→ separated into distinct lobes each individual lobe called reniculum acts as a separate little kidney having its own cortex and medullar ex. most marine mammals, few land mammals that need to conserve water
renicule = single unit of kidney and each has its own cortex, medulla and pelvis
Harbour Seal bladder
bladder has very muscular wall, capable of significant expansion
Nephrons
functional filtration units of the kidney
filter blood to remove metabolic wastes and excess minerals and excrete it as urine
filter out everything smaller than 68kDa and selectively reabsorb
deeper the medulla is relative to the cortex, the more concentrated the urine can become (longer loop of Henle), marine mammals have thicker medulla but no loop of Henle
nephrons function and urine concentrating ability is dependent upon the cortico-medullary axis of the kidney which establishes a counter current concentrator to produce urine
urine that mammals excrete is dependent upon
what is filtered out
what is reabsorbed
what is actively secreted
marine mammals have developed unique strategies to minimize water loss through increased reabsorption of water and increased filtration and secretion of salts and waste
Marine Mammals have unique challenges
coping with increased salt intake
coping with long fasting periods
finding fresh water
increasing number of reniculi→ Number of reniculi correlates with the salinity of the diet and is associated with an increased capacity to excrete urine
Marine mammals in salt water will have high salt intakes and will require more reniculi to remove the saline water it ingests with its food than a manatee or freshwater dolphin who lives in fresh water and has a lower salt content intake
Sirenia don’t have a true reniculated kidney, cortex is continuous. Dugong is close to man
drinking fresh water directly → fresh streams or ice
some live in freshwater lakes or rivers such as manatee or Amazon river dolphins
don’t worry much about removing huge amounts of mineral
pinnipeds like the Weddell seal have been seen chewing ice or snow and will drink from hose or trough in captivityDietary water sources→ manatees
H2O in food → most fish and invertebrates consist of 60-80% fresh water
West indian manatee maintain in salt water, deprived of fresh water but since they only at leafy green vegetables they still produced a normal urine output
metabolic water→ breakdown of fat or metabolism of protein
fatty acid catabolism
1 gram of Palmitate → 1.07g H20
Oxidation of NADH, FADH2
proteolysis
1 gram of protein → 0.4 H2O
sources of dietary fat and proteins as well as stored fat and protein will contain water
Mariposa→ intentional ingestion of sea water
may be beneficial to marine mammals who have high protein diets, as sea water can provide urinary osmotic space for urea, minimizes water loss
sea otter freely swallow seawater to help excrete high amount of urea it forms
northern fur seal, harbour seal and common dolphins also consume large amounts of sea water
non renal adaptions
pinnipeds have few sweat glands
cetaceans have NO sweat glands
water loss from breathing is reduced by conserving breaths and cooling expelled air (countercurrent exchanges)