Chordata
The Chordate is of the Phylum Chrodata, which taxonomically includes three subphyla: Tunicata,
Cephalochordata, and the Craniata. In this phylum, the common attributes of Chordates include having, for
at least some period of time in their life cycles, an endostyle, a notochord, a hollow dorsal nerve chord,
pharyngeal slits, and a post-anal tail. Some animals in the phylum include Hagfish, sea squirts, fish, and
other marine animals.
The Digestive System of the Chordate
Similar to humans but unlike some other phylum, Chordates eat through ingestion rather than absorption. In the Chordata
phylum the species can be herbivores, carnivores, or even omnivores. Since there are over 450,000 species in the Chordata
phylum, there are many different forms and ways of digestion. So instead of attempting to go through all the digestive
systems, here is the digestive systems of three of the species that make up a vast majority of the phylum: the fish, the snake
(reptiles), and the rabbit.
The Digestive System of the Fish
Fishes' jaws allow them eat wide variety of food, including plants and other organisms.
Fish ingest food through the mouth and break it down in the esophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches called pyloric caeca, which secrete digestive enzymes and absorb nutrients. Organs such as the liver and pancreas add enzymes and various chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption. As with many aquatic animals, most fish release their nitrogenous wastes as ammonia. Some of the wastes diffuse through the gills. Blood wastes are filtered by the kidneys.
Saltwater fish tend to lose water because of osmosis. Their kidneys return water to the body. The reverse happens in freshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater.
Saltwater fish tend to lose water because of osmosis. Their kidneys return water to the body. The reverse happens in freshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater.
The Digestive System of the Snake (Reptiles)
Snakes eat only occasionally, because of the large meals that they have. All snakes are carnivorous, although they do not chew but swallow their prey hole. Their jaws are especially designed to allow snakes to eat prey much larger in diameter than themselves.
The thick-walled, spindle-shaped stomach is muscular and distensible. The small intestine is relatively uncoiled but has several short transverse loops tightly enveloped by dorsal mesentery. It empties into the colon that may store faeces. The large intestine is relatively wide and is separated from the cloaca by a distinct fold. A small caecum projects from the proximal colon in Boidae. In the snake digestion takes place in its j-shaped stomach, where cells of the stomach secrete digestive enzymes and gastric juices that breakdown proteins. The food then passes through the pyloric valve and into the small
intestines.The small intestines is a long narrow coiled tube
where absorbance of nutrients takes place. The small intestines is divided into
three regions: the duodenum, the ileum, and jejunum. The liver, which primarily
functions in excreting nitrogenous wastes, storing nutrients, and producing
bile, excretes digestive enzymes into the duodenum of the small intestines.
Also, the pancreas, which produces insulin and glycogen as well, produces
digestive enzymes such as lipases, proteases and carbohydrases and secretes them
into the duodenum. At the junction of the small intestines and large
intestines is the caecum. The large intestines is the least muscular and most
thin-walled structure of the snake digestive system. It passes into the cloacae
chamber. This chamber is divided into a copradaeum for receiving feces and a
urodaeum for urine and products of the genital organs. The cloaca plays an
important role in the reabsorption of water.
The Digestive System of the Rabbit
The initial stages of rabbit digestion are the same as most mammals. When a rabbit eats, the food travels from the mouth, down the oesophagus, into the stomach, and on to the small intestine. The small intestine is responsible for absorbing the nutrients from the food. As food travels along it, enzymes break the food down into individual nutrients that are small enough to pass through the lining of the intestine and be absorbed into the blood stream. Enzymes can’t breakdown fiber, so in most mammals the fiber portion of the food would travel on through the colon and be excreted as waste. However, in rabbits the colon sorts the fibre into two types, digestible and indigestible.
Digestible fibre has nutrients locked away inside it, so the colon diverts it to the caecum for processing. The left over indigestible fibre doesn’t contain any useable nutrients, but it is still essential to the digestive process, as it has helped carry the food through the digestive system. Its job is now complete, so the colon forms it into the hard round droppings your rabbit leaves in his litter tray and it passes out of the body as waste.
Meanwhile, in the caecum, a colony of special bacteria ferment the digestible fiber, breaking it down to release the stored nutrients. The caecum can absorb some of the nutrients but most need to go back through the small intestine to be absorbed. To achieve this, the fermented fibre moves back into the colon, where it is coated in protective mucus, before being excreted from the body as special droppings, called cecal droppings. The rabbit eats these droppings (a process called cacography) so they pass through the digestive tract again. In their new format, the small intestine can easily absorb the nutrients.
Digestible fibre has nutrients locked away inside it, so the colon diverts it to the caecum for processing. The left over indigestible fibre doesn’t contain any useable nutrients, but it is still essential to the digestive process, as it has helped carry the food through the digestive system. Its job is now complete, so the colon forms it into the hard round droppings your rabbit leaves in his litter tray and it passes out of the body as waste.
Meanwhile, in the caecum, a colony of special bacteria ferment the digestible fiber, breaking it down to release the stored nutrients. The caecum can absorb some of the nutrients but most need to go back through the small intestine to be absorbed. To achieve this, the fermented fibre moves back into the colon, where it is coated in protective mucus, before being excreted from the body as special droppings, called cecal droppings. The rabbit eats these droppings (a process called cacography) so they pass through the digestive tract again. In their new format, the small intestine can easily absorb the nutrients.