Essay: The digestive system of earthworms

Nutrition Structures and Mechanisms
The digestive system of the earthworm is divided into many different sections, each of which have a certain function. These different digestive systems consist of the oesophagus, the intestine the pharynx, the crop and the gizzard. Food is swallowed by the pharynx as it enters the earthworms mouth, this includes such thing as soil – decaying roots and leaves. This food then passes through the worms’ oesophagus, which contains calciferous glands. These glands help to rid the earthworm’s body of excess calcium by releasing calcium carbonate, they are also “believed to assist in adjusting the pH of the food material” (Merriam Webster, n.d.). This food then moves into the crop – where it is stored – after it passes through the oesophagus, and eventually moves into the gizzard. When it has moved into the Gizzard, the worm uses the stones that it has eaten to help grind the food completely. This food then moves into the intestines which use gland cells to release fluids to aid in the digestive process. The digested food is then absorbed and transported to the rest of the earthworm’s body through the bloods vessels which are contained in the intestinal wall.
The digestive system and the mechanisms of digestion are divide into many different sections within the toad. Food is consumed through the mouth (ingestion), with this including worms, insects, earthworms, snails etc. The toad uses its “sticky” tongue to help catch its prey and mixes it with saliva; as its teeth are weak and are not useful in catching agile prey. However, these teeth help in grinding the food that has been ingested before it is swallowed. The salivary glands help to produce saliva which is used to convert starch into sugar “and adds liquid to the ingested food” (TutorVista, n.d.). This food (which is mixed with the saliva) moves from the mouth to the pharynx and then it moves into the oesophagus. This food is then pushed further into “sac-like structure stomach” and is known as swallowing or “deglutition.” This food then mixes in with the enzymes and other fluids that are contained in the stomach, which occurs from the contraction of smooth muscles in the stomach. These food particles are propelled into the digestive tract – it is topped from moving back into the stomach through the sphincter valve. The now partially digested food then moves into the small intestine, this is where most of the digestion will occur. To help with the completion of digestion, juice from the pancreas and bile are secreted through the gall bladder (from the liver) to the small intestine. The small intestine absorbs the digestive nutrients – that are in the digestive system. However, the large intestine absorbs the unabsorbed nutrients and also reabsorbs water. Solids ate moved to the cloaca, while the liquid wastes are passed into the urinary bladder. Both the liquid and solid waste form the cane toad are “expelled” through the cloaca (“a slit that opens out finally in digestive system” – Tutor Vista, n.d.)
Gas Exchange Structures and Mechanisms
Earthworms do not have specialised respiratory organs like we do; instead they take in oxygen through their skin. These worms use diffusion to allow oxygen and carbon dioxide to pass through their skin. However, for diffusion to occur, the worm must have moist skin, to help with this mucous and body fluid from the excretory pores are released to keep its skin moist. This is linked to one of the reasons that earthworms usually surface at night, as it is cooler and the evaporating potential of the air is low. Similarly, the earthworm will spend most of its time– if not all (apart from certain night) – in the soil as this prevents their skin from drying out. The worms epidural layer has blood capillaries which are looped out from the vascular system circulating the blood. The gases can diffuse from the surrounding into and out of the blood through the skin and the capillary walls as the blood capillaries are so close to the skin. The gases circulate through the body through the haemoglobin in the blood solution. (Merriam Webster, n.d.)
Transport Structures and Mechanisms
Another important organ system in the worm is the circulatory system. The earthworm, like some invertebrates, has a closed circulatory system. This means that the blood is closed at all times within vessels of different size and wall thickness – blood is pumped by a heart through vessels, and does not normally fill body cavities. The earthworm circulates blood exclusively through vessels. Within the earthworm there are three main vessels that supply the blood to the organs around their body. These vessels are; the aortic arches, dorsal blood vessels and the ventral blood vessels. The aortic heart of the worm functions like a human heart. There are five pairs of aortic arches which all have the responsibility if pumping blood into the dorsal and ventral blood vessels. Blood is carries to the front of the earthworm’s body through the dorsal blood vessels. The ventral blood vessels are responsible for carrying blood to the back of the earthworm’s body. (Merriam Webster, n.d.)
Part C: Compare and Contrast the Different Mechanisms
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NUTRITION:
GAS EXCHANGE:
TRANSPORT: