Renal system

• • collecting ducts of kidney converge to the renal papilla and are found in the inner medulla in a region known as the renal pelvis
  • papilla drain urine into the renal pelvis and out of the kidney via the ureter that feeds into bladder
• kidneys organized into outer layer = cortex, inner layer = medulla
• • 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
• renal capsule = connective tissue and peritoneum
• hilus= renal artery enters, rena vein exists, ureter exits
• 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
• 1. 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
• 1. 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
• 1. 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)