Circulatory and respiratory Systems: An anatomical and physiological analysis
Circulatory and respiratory systems form the most important organ systems in any animal as they are both responsible for transporting the life sustaining element of oxygen to every cell and tissue in the body, while also collecting the wastes and disposing of them through various organs. However, the anatomy and the physiology of these systems differ radically in each classification of animals, in effect throwing light on the various stages of evolution in different types of animals. In this paper we shall discuss the circulatory and respiratory systems in four animals with regards to their anatomy and physiology so as to compare and contrasts the different kinds of systems present in each of these organisms.
Earthworms have long tube like bodies with a simple closed circulatory system which is complete in a sense that a separate respiratory system is not required. The circulatory system comprises of two main blood vessels that run throughout the body of the earthworm parallel to each other. The ‘ventral’ blood vessel leads blood to the posterior end while the ‘dorsal’ blood vessel leads it to the anterior end. The blood is pumped from the posterior to anterior through the dorsal vessel which acts as a contractile pump. A series of hearts which are simple aortic arches are used for this purpose and the blood is pumped into the ventral vessel. From the ventral vessel, the blood is distributed on to the capillaries that reach to the body wall and to a vascular sinus in the gut wall where nutrients and bodily gases are exchanged. The earthworm’s skin is always kept moist so that the exchange of the bodily gases is possible with the outside environment. (Edwards & Bohen, 2005)
Advantages. The system is fairly simple with two major blood vessels doing the majority of work that includes oxygenation, waste removal and interacting with the gut wall where the gases and nutrients required for the body are exchanged.
Disadvantages. The earthworm’s body surface, the epidermis, always needs to be kept moist for the system to work. If the earthworm stays in sun out for long and its outer surface dries up, it will die as oxygenation is no longer possible.
Insect respiration occurs without the faculty of lungs, like in the earthworms. But their physiology is a little more advanced, with an outer exoskeleton and an open circulatory system. The respiratory system consists of internal tubes and sacks which diffuse oxygen directly to the tissues and the circulatory system in turn acts like a hose getting rid of the waste materials into the atmosphere. Accordingly, the circulatory system has no veins or capillaries, instead consisting of a single perforated dorsal tube which pulses peristaltically. The gas exchange patterns in insects can either be of continuous ventilation or discontinuous. Some species of insects can also breathe underwater through the aid of gills or other physiological organs.
Advantages. The circulatory system consisting of the dorsal tube divides into chambers towards the thorax acting as the insect’s heart, the opposite end of which it acts as the aorta pumping hemolymph which provides oxygen and the vital nutrients to the cells. The air is taken in through openings on the sides of the abdomen called spiracles (Shneiderman, 1960).
Disadvantages. The system works only when the insect is active as discussed above, as only some insects have the provision to breathe and circulate even when they are resting. This causes decreased lifetime and lower variety of actions that an insect could perform.
Fishes exchange gases through the use of gills, which consist of fine structures in the shape of a thread. These are called filaments and they are present on either side of their pharynx. Fishes pull the water, which is rich in oxygen through their mouths and then pump over their gills where the actual exchange of gases occurs (Anderson, 2010). The circulatory system of the fish can be considered as a closed-loop system, with the heart consisting of two chambers, an entrance and an exit. While one chamber pumps blood into the fish’s body, the other chamber sends the de-oxygenated blood to the gills for oxygenation. The liver and pancreas of the fish add enzymes to the food as it moves through the digestive track and the nutrient absorption occurs after the food moves through the intestines. The nutrients thus supplied to the fish’s body, after they are absorbed by the tissue, release waste gases into the blood.
Advantages. The double chambered heart makes sure that oxygenated blood is pumped to all the bodily tissues and the deoxygenated blood is received for waste disposal. The gills are responsible for the fish to directly take oxygen from the water.
Disadvantages. The gills can only absorb oxygen from water and specific fish survive in specific kinds of water, which makes their chances of survival very little when their environment is shifted. Although different fish have evolved different varieties of respiratory organs that allow them to survive in different environments (some even on land), the lack of lungs means that the process of oxygenation occurs outside the body which is dangerous and uncontrollable at times (Helfman et al., 1997).
Humans have a complex respiratory and circulatory systems replete with a pair of lungs, a four chambered heart and a network of veins and arteries that run throughout the body. The air is taken into the body through nasal cavities and is sent to the lungs where the oxygen is extracted and supplied to the blood. The oxygenated blood is pumped into the heart and then into the arteries and capillaries. The deoxygenated blood is received into the heart and pumped into the lungs again. The intestines absorb nutrients from the food and diffuse them into the blood supplying it to all the tissues. The wastes collected are filtered through the kidneys.
Advantages. The circulatory system and respiratory system together ensure that all the impurities of the atmosphere are filtered before they reach the tissues.
Disadvantages. Since all systems are inside the human body, there is no scope for survival in a different environment like underwater, decompressed or zero-gravity environments, etc.
Edwards. C. A. Bohlen. P.J. (Eds.). (2005). Biology and Ecology of Earthworms (3rd ed.). New York: Springer.
Shneiderman. H. A. (1960). Discontinuous respiration in insects: Role of spiracles. Biological Bulletin, 119, 494-528. Retrieved October 14, 2011 from http://www.biolbull.org/content/119/3/494.abstract
Anderson. P. (2010). Fish and Shark Information. Retrieved October 14, 2011 from http://schoolworkhelper.net/2010/05/fish-and-shark-information
Helfman. G. Collette. B. Facey. D. (1997). The diversity of fishes. Massachusetts: Wiley-Blackwell.