What affect does the urinary system have on the blood pressure? What affect does the renal What is the purpose of taking the drug cyclosporine following kidney transplantation? Where in the body are the ureters located? How long are these tubes? Are the kidneys inferior to the lungs? What organ system does the kidney belong to? What organ system does the liver belong to? What is the major function of the kidney?
Small mammals have much higher mass-specific metabolic rates than large mammals. Compared with large mammals, the apical membranes in the kidney tubules of small mammal epithelial cells have more infoldings, increasing surface area for absorption. Increased metabolism will lead to more waste products and a greater demand on the filtration capacity of the kidneys. Therefore the number of nephrons must increase as body size increases, which in turn increases the relative amount of cortex the area of the kidney where most of the nephron is located , at the expense of the medulla.
The relative thickness of the medulla is related to urine-concentrating ability because the medulla contains the loops of Henle. Hence larger animals, even the camel, cannot produce urine as concentrated as that of smaller mammals, because their kidney medulla is relatively small compared with its cortex. Small mammals such as rodents and bats tend to have relatively thicker medullas than larger mammals, which can be correlated with their production of concentrated urine Figure Rodents generally have kidneys with a larger medullary area and produce more concentrated urine than bats and other mammals.
The thicker medulla of small desert rodents could therefore be viewed as a desert adaptation superimposed on a basic body-size-dependent pattern.
Most loops of Henle in desert rodents are of the juxtamedullary type, and the epithelial cells have densely packed mitochondria with more cristae per unit volume than a horse's loop of Henle.
What is the significance of the greater concentration of mitochondria and more cristae per unit volume of mitochondria in the epithelial cells of loops of Henle in desert rodents compared with those of the horse? Conservation of water by the kidney is of crucial importance for the kangaroo rat, which does not drink and can obtain water only from catabolism.
Other desert rodents obtain water from their diet. The degu Octodon degus , found in Northern Chile, lives in semi-arid desert country, known as matorral, which is characterised by evergreen scrub plants.
Degus survive on limited amounts of water obtained primarily from their food, which comprises scrub foliage, grass and seeds. There is seasonal variation in the water content of plants; in summer the plant foliage dries out and contains just 3—6 per cent water; in winter, foliage contains 70—80 per cent water. Bozinovic et al. Water intake and efflux were measured by use of the doubly-labelled water technique in degus kept in a secure enclosure within the matorral.
Urine osmolality was measured in wild-captured degus using microhaematocrit capillary tubes to obtain samples from the urethra. Note: whereas osmolarity measures the number of osmotically active particles of a particular substance in a volume of fluid, osmolality measures the equivalent number in a mass weight of fluid.
For most biological systems the molarity and molality of a solution are nearly exactly equal. For our purposes osmolarity and osmolality can be regarded as equivalent. Drawing on the data provided in Table 4, summarise the physiological strategy for water economy in the degu.
In winter when water content of plants is 70—80 per cent, the rate of water intake is relatively high at In contrast, in the summer the rate of water intake is relatively low at The kidney is able to concentrate urine, thereby reducing water loss in the summer when the diet provides very little water. Variation in the osmolality of urine is not in itself unusual. Such responses result from the physiological regulation of body water content.
Recall that the permeability of the epithelium of cortical and medullary collecting ducts is controlled by the hormone ADH antidiuretic hormone, also known as vasopressin.
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Free course Animals at the extremes: The desert environment. Figure 26 Exhaled air temperatures of seven species of bird and the kangaroo rat at various ambient temperatures. Much the same relationship applies in many small mammals. Comparison of Nephrons in Mesic and Desert Animals. Relationship between Environmental Conditions and Medullary Thickness. Brent Cornell. Cell Introduction 2. Cell Structure 3.
Membrane Structure 4. Membrane Transport 5. Origin of Cells 6. Cell Division 2: Molecular Biology 1. Metabolic Molecules 2. Water 3.
Protein 5. Enzymes 6. Cell Respiration 9. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4.
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