Viscera ( mammal )
Tagged: animal, cat, insect, mammalDigestive system
The alimentary canal is highly specialized in many kinds of mammals. In general, specializations of the gut accompany herbivorous habits. The intestines of herbivores are typically elongate, and the stomach may also be specialized. Subdivision of the gut allows areas of differing physiological environments for the activities of different sorts of enzymes and symbiotic bacteria, which aid the animal by breaking down certain compounds that are otherwise undigestible. In ruminant artiodactyls, such as antelopes, deer, and cattle, the stomach has up to four chambers, each with a particular function in the processing of vegetable material. A cecum is common in many herbivores. The cecum is a blind sac at the far end of the small intestine where complex compounds such as cellulose are acted upon by symbiotic bacteria. The vermiform appendix is a diverticulum of the cecum. The appendix is rich in lymphoid tissue and in many mammals is concerned with defense against toxic bacterial products. Hares and rabbits, the sewellel, or mountain beaverĀ (Aplodontia rufa), and some insectivores exhibit a phenomenon of reingestion called coprophagy, in which at intervals specialized fecal pellets are produced. These pellets are eaten and passed through the alimentary canal a second time. Where known to be present, this pattern seems to be obligatory. Reingestion is poorly understood, but it is generally supposed that the process allows the animal to absorb in the upper gut vitamins produced by the microflora of the lower gut but not absorbable there.
Excretory system
The mammalian kidney is constructed of a large number of functional units called nephrons. Each nephron consists of a distal tubule, a medial section termed the loop of Henle, a proximal tubule, and a renal corpuscle. The renal corpuscle is a knot of capillaries (glomerulus) surrounded by a sheath (Bowman’s capsule). The renal corpuscle is a pressure filter, relying on blood pressure to remove water, ions, and small organic molecules from the blood. Some of the material removed is waste, but some is of value to the organism. The filtrate is sorted by the tubules, and water and needed solutes are resorbed. Resorption is both passive (osmotic) and active (based on ion transport systems). The distal convoluted tubules drain into collecting tubules, which in turn empty into the calyces, or branches, of the renal pelvis, the expanded end of the ureter. The pressure-pump nephron of mammals is so efficient that the renal portal system of lower vertebrates has been completely lost. Mammalian kidneys show considerable variety in structure, relative to the environmental demands on a given species. In particular, desert rodents have long loops of Henle and are able to resorb much water and to excrete a highly concentrated urine. Urea is the end product of protein metabolism in mammals, and excretion is therefore called ureotelic.
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