Do All Animals Have A Digestive System

Learning Outcomes

• Compare and dissimilarity different types of digestive systems

Invertebrate Digestive Systems

Animals have evolved different types of digestive systems to assistance in the digestion of the unlike foods they consume. The simplest example is that of a gastrovascular crenel and is found in organisms with but one opening for digestion. Platyhelminthes (flatworms), Ctenophora (comb jellies), and Cnidaria (coral, jelly fish, and sea anemones) use this type of digestion. Gastrovascular cavities, equally shown in Effigy 1a, are typically a blind tube or cavity with only 1 opening, the "oral fissure", which also serves as an "anus". Ingested textile enters the oral fissure and passes through a hollow, tubular cavity. Cells within the cavity secrete digestive enzymes that suspension down the food. The food particles are engulfed past the cells lining the gastrovascular cavity.

The comestible canal, shown in Figure 1b, is a more than avant-garde system: information technology consists of ane tube with a mouth at one cease and an anus at the other. Earthworms are an case of an animal with an alimentary canal. One time the food is ingested through the rima oris, it passes through the esophagus and is stored in an organ chosen the crop; then it passes into the gizzard where information technology is churned and digested. From the gizzard, the food passes through the intestine, the nutrients are absorbed, and the waste is eliminated every bit feces, called castings, through the anus.

Figure 1. (a) A gastrovascular cavity has a single opening through which food is ingested and waste product is excreted, as shown in this hydra and in this jellyfish medusa. (b) An alimentary canal has ii openings: a mouth for ingesting nutrient, and an anus for eliminating waste, as shown in this nematode.

Vertebrate Digestive Systems

Vertebrates have evolved more circuitous digestive systems to adapt to their dietary needs. Some animals have a single breadbasket, while others have multi-chambered stomachs. Birds accept developed a digestive system adapted to eating unmasticated food.

Monogastric: Single-chambered Stomach

As the word monogastric suggests, this type of digestive system consists of ane ("mono") stomach chamber ("gastric"). Humans and many animals have a monogastric digestive system as illustrated in Figure 2a and 2b. The procedure of digestion begins with the mouth and the intake of nutrient. The teeth play an important role in masticating (chewing) or physically breaking down food into smaller particles. The enzymes nowadays in saliva besides begin to chemically suspension downwards food. The esophagus is a long tube that connects the oral cavity to the breadbasket. Using peristalsis, or moving ridge-like smooth muscle contractions, the muscles of the esophagus push the food towards the tummy. In order to speed up the actions of enzymes in the breadbasket, the stomach is an extremely acidic environment, with a pH betwixt one.5 and two.5. The gastric juices, which include enzymes in the stomach, act on the food particles and go on the process of digestion. Further breakdown of food takes place in the small intestine where enzymes produced past the liver, the small intestine, and the pancreas continue the procedure of digestion. The nutrients are absorbed into the blood stream beyond the epithelial cells lining the walls of the pocket-sized intestines. The waste product cloth travels on to the big intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until information technology is excreted through the rectum.

Figure 2. (a) Humans and herbivores, such as the (b) rabbit, have a monogastric digestive organization. Notwithstanding, in the rabbit the small-scale intestine and cecum are enlarged to allow more time to digest plant fabric. The enlarged organ provides more surface expanse for absorption of nutrients. Rabbits assimilate their food twice: the first time food passes through the digestive system, it collects in the cecum, and and so information technology passes every bit soft feces chosen cecotrophes. The rabbit re-ingests these cecotrophes to further digest them.

Avian

Birds face special challenges when information technology comes to obtaining nutrition from food. They do not have teeth so their digestive system, shown in Figure iii, must be able to process un-masticated food. Birds take evolved a variety of beak types that reverberate the vast variety in their diet, ranging from seeds and insects to fruits and nuts. Considering most birds wing, their metabolic rates are high in order to efficiently process food and keep their body weight depression. The stomach of birds has ii chambers: the proventriculus, where gastric juices are produced to digest the nutrient before it enters the stomach, and the gizzard, where the nutrient is stored, soaked, and mechanically basis. The undigested material forms food pellets that are sometimes regurgitated. Almost of the chemical digestion and assimilation happens in the intestine and the waste is excreted through the cloaca.

Effigy iii. The avian esophagus has a pouch, chosen a crop, which stores nutrient.

In the avian digestive system, food passes from the crop to the outset of 2 stomachs, called the proventriculus, which contains digestive juices that break downwardly food. From the proventriculus, the food enters the 2d stomach, chosen the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to assist the grinding process. Birds practise not have separate openings to excrete urine and feces. Instead, uric acid from the kidneys is secreted into the large intestine and combined with waste product from the digestive process. This waste is excreted through an opening called the cloaca.

Avian Adaptations

Birds accept a highly efficient, simplified digestive system. Recent fossil evidence has shown that the evolutionary divergence of birds from other land animals was characterized by streamlining and simplifying the digestive arrangement. Unlike many other animals, birds do not have teeth to chew their food. In identify of lips, they have sharp pointy beaks. The horny beak, lack of jaws, and the smaller tongue of the birds tin exist traced back to their dinosaur ancestors. The emergence of these changes seems to coincide with the inclusion of seeds in the bird nutrition. Seed-eating birds have beaks that are shaped for grabbing seeds and the two-compartment stomach allows for delegation of tasks. Since birds need to remain low-cal in order to fly, their metabolic rates are very high, which means they assimilate their food very speedily and demand to eat oft. Contrast this with the ruminants, where the digestion of plant matter takes a very long time.

Ruminants

Ruminants are mainly herbivores similar cows, sheep, and goats, whose entire nutrition consists of eating big amounts of roughage or fiber. They accept evolved digestive systems that help them assimilate vast amounts of cellulose. An interesting feature of the ruminants' mouth is that they practice non take upper incisor teeth. They use their lower teeth, natural language and lips to tear and chew their food. From the mouth, the food travels to the esophagus and on to the stomach.

To assistance digest the large amount of plant material, the tum of the ruminants is a multi-chambered organ, as illustrated in Figure four. The iv compartments of the tum are called the rumen, reticulum, omasum, and abomasum. These chambers incorporate many microbes that break down cellulose and ferment ingested food. The abomasum is the "true" tum and is the equivalent of the monogastric stomach bedchamber where gastric juices are secreted. The 4-compartment gastric bedroom provides larger infinite and the microbial back up necessary to digest plant material in ruminants. The fermentation process produces large amounts of gas in the tummy bedchamber, which must be eliminated. Equally in other animals, the modest intestine plays an of import role in nutrient absorption, and the large intestine helps in the elimination of waste.

Figure 4. Ruminant animals, such equally goats and cows, take four stomachs. The showtime ii stomachs, the rumen and the reticulum, contain prokaryotes and protists that are able to digest cellulose cobweb. The ruminant regurgitates cud from the reticulum, chews it, and swallows it into a third stomach, the omasum, which removes water. The cud so passes onto the fourth tummy, the abomasum, where it is digested by enzymes produced by the ruminant.

Pseudo-ruminants

Some animals, such as camels and alpacas, are pseudo-ruminants. They eat a lot of establish cloth and roughage. Digesting plant cloth is not piece of cake because plant cell walls contain the polymeric sugar molecule cellulose. The digestive enzymes of these animals cannot break downward cellulose, simply microorganisms present in the digestive system can. Therefore, the digestive system must exist able to handle large amounts of roughage and break down the cellulose. Pseudo-ruminants have a three-bedchamber stomach in the digestive system. Even so, their cecum—a pouched organ at the outset of the big intestine containing many microorganisms that are necessary for the digestion of plant materials—is big and is the site where the roughage is fermented and digested. These animals practice non take a rumen only have an omasum, abomasum, and reticulum.

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