Comparative Physiology of Sheep, Mice, and Humans - Outline Example

Comparative Physiology of Sheep, Mice, and Humans COMPARATIVE PHYSIOLOGY OF SHEEP, MICE, AND HUMANS Probably the first point to make about the reproductive system of humans, sheep, and mice is that they are quite similar as they are all mammals. To begin with, while the size and shape in reference to the male and female reproductive system in all three are different, they all work in a similar way. In this case, the mouse has the shortest vagina of all three animals, while they have a plate or vaginal closer that raptures following birth (Waters, 2009: p47). However, humans and sheep do not have a vaginal plate prior to birth. In addition, the embryo in mice grows in approximately 33 to 34 days, compared to 145-152 days in sheep and nine months in humans. The ovaries of all three are paired, although they are spherical for mice and ovoid in humans (Parker, 2010: 9). Ovaries in mice are attached through the mesovarium to the dorsal body around the kidneys’ caudal poles, as well as being enclosed by the elastic bursa. The ovarian bursa in the mouse closes off the abdominal cavity from the peri-ovarian space, although there is a small opening that allows nerves and blood vessels to access the ovarian hilus (Hollen, 2011: p62). In humans, just as in sheep, the ovaries float within the pelvis and are attached to the pelvic sidewalls and uterus by associated ligaments. During sexual maturity, the ovary surface becomes nodular due to development of corpus lutea and follicles during menstrual/estrus cycles in humans and mice. With regards to their oviducts, mice have narrow, coiled, and 1.8 cm long tubes connecting the peri-ovarian space to the uterine horn (Kardong, 2012: p28). Its oviduct is suspended by the mesotubarium from the dorsal body, which are continuous with the uterine mesometrim, ovarian bursa, and mesovarium (Walker & Wood, 2013: p39). The oviduct in humans is also referred to as the fallopian tube and has a similar appearance to that of the mouse, although it is not as tightly coiled, while it is twice as long as muscular in nature. Just as with the mouse, human oviducts are made up of the isthmus, a fimbriated end, an infundibulum, an ampulla, and an intra-muscular portion. The intramuscular portion resides within the uterine wall and, in mice; it slightly extends into the uterus through the dorsolateral wall of the uterus and is called the colliculus tubarius (Knobil & Neill, 2013: p72). In a sheep, the oviduct opens near the ovary through the infundibulum that is funnel-shaped. For all three animals, the oviduct is involved in transporting the sperm to fertilize the ovum, followed by subsequent transport of the embryo to the uterus for sheep mice, as well as the zygote for humans. The uterus in mice is bicornuate with two lateral horns joint to a single corpus distally (Khanna & Yadav, 2010: p66). For humans, the uterus is pear-shaped and has a single cavity that is triangular-shaped. However, the size of the uterus varies more greatly in humans than mice depending on the presence of leiomyomata, prior pregnancies, and hormonal status (Klosterman, 2010: p59). The uterus of mice is suspended by the mesometria from the dorsal body, which have broad and heavy ligaments that carry lymphatic and blood vessels, as well as many nerves. In humans, the uterus is also suspended by similar ligaments, although it is attached to the lateral pelvic walls. The uterus of sheep, humans, and mice are made up of cervical and cranial segments and, for mice, the cervix segment consists of one cavity that extends to the vagina, while the cranial segment is divided by the median septum into two cavities (Rogers, 2011: p55). In sheep, the uterus is made of two different coruna or horns, which can contain more than foetus during birth, just as with mice. However, this is not the case in humans. In mice, the vagina is muscular and short and extends to an opening dorsal of the urethra from the uterine corpus (Lang 2010: p38). It is connected loosely to the urethra ventrally and dorsally to the rectum. The ventral aspect of the vagina in mice is elevated by the clitoris at the exterior opening, which is covered by skin and hair and has a clitoral fossa that is a depression at the clitoral tip where the urethra opens into (Vandenbergh, 2013: p82). Additionally, the mouse also has paired clitoral glands in the subcutaneous tissue that have one duct opening into the clitoral fossa through its lateral walls. While the human vagina is muscular as well and extends all the way starting the vulva to the cervix, it has ridges that are as a result of folds within the outer part of the vagina called rugae. In a sheep, the duration of estrus is mainly influenced by age, just as in humans and mice, although there is an additional influence related to breed of the sheep and seasons. For instance, the period of estrus occurring during fall are more intense and longer, while younger sheep have a less intense and shorter estrus compared to mature sheep (Marshall Cavendish Corporation, 2010: p42). The human digestive system is larger in size compared to mice, although it should be noted that they are relatively the same size in proportion to their body sizes. Sheep, on the other hand, have longer digestive systems because they are ruminants. In addition, whereas humans have a simple digestive system, which in sheep and mice is more, specialized due to their different diets from humans (Moyes & Schulte, 2010: p33). While mice do not have gall bladders, humans and sheep possess gall bladders that act as accessory glands within their digestive systems to help in digestion of fats. Also, whereas humans do not have fermentation chamber, mice and sheep have fermentation chambers that aid in the digestion of cellulose that is abundant in their diet of grains/seeds and foliage respectively (Smith & Morton, 2011: p61). Because all three animals are mammals, the physiology of their digestive system is similar with little dissimilarity. These dissimilarities exist as a result of their different diets that require different digestive capabilities. Generally, mice eat seeds that mainly contain cellulose, meaning that they have a specialized chamber for fermenting the hard cellulose chains in seeds. Mice and sheep have enlarged caecums that contain micro-organisms to carry out the fermentation of cellulose. In mice, other than the lack of a gall bladder, they have a digestive system that begins from the oral cavity that contains salivary glands to the anus, just as in sheep and humans (Sjaastad et al, 2010: p47). The human digestive system is not essentially specialized, unlike that of sheep and mice, because humans have a generalized food habit without any specific food type that is critical to maintain life. However, the accessory organs of the human digestive system are more prominent, specifically because humans consume a wider variety of foods compared to mice and sheep (Wiedersheim & Parker, 2010: p78). The presence of fats and proteins during ingestion means that the accessory organs play a more important role than in mice. Presence of the gall bladder ensures that animal fats are digested, while the gall bladder of sheep ensures that plant oils are digested properly (Stevens, 2009: p19). The human digestive system is, however, not adapted to breaking down cellulose as discussed for sheep and mice, which means that their digestive tracts do not digest cellulose. In addition, while the large intestines of both mice and sheep have specialized cells to take up the bi-products of digested cellulose, humans lack this specialization (Cormack, 2011: p34). In mice, the small intestine is divided into the duodenum, jejunum, and the ileum, just as in both humans and sheep. All three animals also have pancreases that produce glucagons and insulin to stabilize blood sugar that can be elevated from the diets of all three animals (Windelspecht, 2014: p51). Sheep and mice have specialized lips and tongues used for tearing and grasping, while their premolars and molars are well developed for grinding and move laterally, which is different in humans that have vertical movement. Moreover, especially in sheep, the dental pad replaces their upper teeth, while a gap between molars enables the tongue to break down food into smaller portions for swallowing. Unlike humans that bring food to their mouth, mice and sheep take their mouth to food and sheep regurgitate their food, which mice and humans do not. Whereas human intake of proteins is via ingestion, both sheep and mice can satisfy their protein needs from micro-organisms in their digestive tract (Frandson et al, 2009: p49). Moreover, while humans can forcefully eject food from their digestive systems through vomiting, sheep and mice do not. References Cormack, D. H. (2011). Essential histology. Philadelphia: Lippincott Williams & Wilkins. Frandson, R. D., Wilke, W. L., & Fails, A. D. (2009). Anatomy and physiology of farm animals. Ames, Iowa: Wiley-Blackwell. Hollen, K. H. (2011). The reproductive system. Westport, CT: Greenwood Press. Kardong, K. V. (2012). Vertebrates: Comparative anatomy, function, evolution. Boston: McGraw-Hill. Khanna, D. R., & Yadav, P. R. (2010). Biology of mammals. New Delhi: Discovery Pub. House. Knobil, E., & Neill, J. D. (2013). Physiology of the reproductive system. New York: Raven Press. Klosterman, L. (2010). Reproductive system. Tarrytown, NY: Marshall Cavendish Benchmark. Lang, A., Bernard, H. M., Bernard, M., & Haeckel, E. (2010). Text-book of comparative anatomy: [Part I]. Charleston, SC: BiblioLife. Marshall Cavendish Corporation. (2010). Mammal anatomy: An illustrated guide. New York: Marshall Cavendish. Moyes, C. D., & Schulte, P. M. (2010). Principles of animal physiology. San Francisco: Pearson Benjamin Cummings. Parker, S. (2010). Digestive and reproductive systems. Mankato, MN: New Forest Press. Rogers, K. (2011). The reproductive system. New York, N.Y: Britannica Educational Pub., in association with Rosen Educational Services. Sjaastad, O. V., Hove, K., & Sand, O. (2010). Physiology of domestic animals. Oslo: Scandinavian Veterinary Press. Smith, M. E., & Morton, D. G. (2011). The digestive system. Edinburgh: Churchill Livingstone. Stevens, C. E. (2009). Comparative physiology of the vertebrate digestive system. Cambridge: Cambridge University Press. Vandenbergh, J. G. (2013). Pheromones and Reproduction in Mammals. Oxford: Elsevier Science. Walker, P., & Wood, E. (2013). The reproductive system. San Diego: Lucent Books. Waters, S. (2009). The female reproductive system. New York: Rosen Pub. Group. Windelspecht, M. (2014). The digestive system. Westport, Conn: Greenwood Press. Wiedersheim, R., & Parker, W. N. (2010). Comparative anatomy of vertebrates. LaVergne, TN: Nabu Public Domain Reprints. Read More