Why does the crayfish have such a short intestine

Most animals with soft bodies use this type of digestion, including Platyhelminthes flatworms , Ctenophora comb jellies , and Cnidaria coral, jelly fish, and sea anemones. Invertebrates with Extracellular Digestion : Invertebrates like grasshoppers have alimentary canals with specialized compartments for digestion. Their food is broken down in their digestive tract extracellular digestion , rather than inside their individual cells intracellular digestion.

Ingested material enters the mouth and passes through a hollow, tubular cavity. The food particles are engulfed by the cells lining the gastrovascular cavity and the molecular are broken down within the cytoplasm of the cells intracellular.

The alimentary canal is a more advanced digestive system than a gastrovascular cavity and carries out extracellular digestion. Most other invertebrates like segmented worms earthworms , arthropods grasshoppers , and arachnids spiders have alimentary canals. The alimentary canal is compartmentalized for different digestive functions and consists of one tube with a mouth at one end and an anus at the other.

Once the food is ingested through the mouth, it passes through the esophagus and is stored in an organ called the crop; then it passes into the gizzard where it is churned and digested.

From the gizzard, the food passes through the intestine and nutrients are absorbed. Because the food has been broken down exterior to the cells, this type of digestion is called extracellular digestion. The material that the organism cannot digest is eliminated as feces, called castings, through the anus.

Most invertebrates use some form of extracellular digestion to break down their food. Flatworms and cnidarians, however, can use both types of digestion to break down their food. Vertebrates may have a single stomach, several stomach chambers, or accessory organs that help to break down ingested food. Vertebrates have evolved more complex digestive systems to adapt to their dietary needs.

Some animals have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive system adapted to eating un-masticated un-chewed food. Humans and many animals have a monogastric digestive system. The process of digestion begins with the mouth and the intake of food. The teeth play an important role in masticating chewing or physically breaking down food into smaller particles.

The enzymes present in saliva also begin to chemically break down food. The esophagus is a long tube that connects the mouth to the stomach. Using peristalsis, the muscles of the esophagus push the food towards the stomach. In order to speed up the actions of enzymes in the stomach, the stomach has an extremely acidic environment, with a pH between 1. The gastric juices, which include enzymes in the stomach, act on the food particles and continue the process of digestion.

In the small intestine, enzymes produced by the liver, the small intestine, and the pancreas continue the process of digestion. The nutrients are absorbed into the blood stream across the epithelial cells lining the walls of the small intestines. The waste material travels to the large intestine where water is absorbed and the drier waste material is compacted into feces that are stored until excreted through the rectum.

Mammalian digestive system non-ruminant : a Humans and herbivores, such as the b rabbit, have a monogastric digestive system. However, in the rabbit, the small intestine and cecum are enlarged to allow more time to digest plant material. The enlarged organ provides more surface area for absorption of nutrients. Birds face special challenges when it comes to obtaining nutrition from food.

They do not have teeth, so their digestive system must be able to process un-masticated food. Birds have evolved a variety of beak types that reflect the vast variety in their diet, ranging from seeds and insects to fruits and nuts. Because most birds fly, their metabolic rates are high in order to efficiently process food while keeping their body weight low.

The stomach of birds has two chambers: the proventriculus, where gastric juices are produced to digest the food before it enters the stomach, and the gizzard, where the food is stored, soaked, and mechanically ground. The undigested material forms food pellets that are sometimes regurgitated. Most of the chemical digestion and absorption happens in the intestine, while the waste is excreted through the cloaca. Bird digestive system : The avian esophagus has a pouch, called a crop, which stores food.

Food passes from the crop to the first of two stomachs, called the proventriculus, which contains digestive juices that break down food. From the proventriculus, the food enters the second stomach, called the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Birds do 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 from the digestive process. This waste is excreted through an opening called the cloaca.

Ruminants are mainly herbivores, such as cows, sheep, and goats, whose entire diet consists of eating large amounts of roughage or fiber. They have evolved digestive systems that help them process vast amounts of cellulose. They use their lower teeth, tongue, and lips to tear and chew their food. From the mouth, the food travels through the esophagus and into the stomach.

To help digest the large amount of plant material, the stomach of the ruminants is a multi-chambered organ. The four compartments of the stomach are called the rumen, reticulum, omasum, and abomasum. These chambers contain many microbes that break down cellulose and ferment ingested food. This is where gastric juices are secreted. The four-compartment gastric chamber provides larger space and the microbial support necessary to digest plant material in ruminants.

The fermentation process produces large amounts of gas in the stomach chamber, which must be eliminated. As in other animals, the small intestine plays an important role in nutrient absorption, while the large intestine aids in the elimination of waste.

Ruminant mammal digestive system : Ruminant animals, such as goats and cows, have four stomachs. The first two stomachs, the rumen and the reticulum, contain prokaryotes and protists that are able to digest cellulose fiber. The ruminant regurgitates cud from the reticulum, chews it, and swallows it into a third stomach, the omasum, which removes water. The cud then passes onto the fourth stomach, the abomasum, where it is digested by enzymes produced by the ruminant.

Some animals, such as camels and alpacas, are pseudo-ruminants. They eat a lot of plant material and roughage. Digesting plant material is not easy because plant cell walls contain the polymeric sugar molecule cellulose. The digestive enzymes of these animals cannot break down cellulose, but microorganisms present in the digestive system can. Since the digestive system must be able to handle large amounts of roughage and break down the cellulose, pseudo-ruminants have a three-chamber stomach.

In contrast to ruminants, their cecum a pouched organ at the beginning of the large intestine containing many microorganisms that are necessary for the digestion of plant materials is large. When it supplies answers to all the questions which fall under these four heads, the Zoology of Crayfish will have said its last word.

As it matters little in what order we take the first three questions, in expanding Natural History into Zoology, we may as well follow that which accords with the history of science. After men acquired a rough and general knowledge of the animals about them, the next thing which engaged their interest was the discovery in these animals of arrangements by which results, of a kind similar to those which their own ingenuity effects through mechanical contrivances, are brought about.

They observed that animals perform various actions; and, when they looked into the disposition and the powers of the parts by which these actions are performed, they found that these parts presented the characters of an apparatus, or piece of mechanism, the action of which could be deduced from the properties and connections of its constituents, just as the striking of a clock can be deduced from the properties and connections of its weights and wheels.

Under one aspect, the result of the search after the rationale of animal structure thus set afoot is Teleology ; or the doctrine of adaptation to purpose. Under another aspect, it is Physiology ; so far as Physiology consists in the elucidation of complex vital phenomena by deduction from the established truths of Physics and Chemistry, or from the elementary properties of living matter. We have seen that the crayfish is a voracious and indiscriminate feeder; and we shall be safe in assuming that, if duly supplied with nourishment, a full-grown crayfish will consume several times its own weight of food in the course of the year.

Nevertheless, the increase of the animal's weight at the end of that time is, at most, a small fraction of its total weight; whence it is quite clear, that a very large proportion of the food taken into the body must, in some shape or other, leave it again.

In the course of the same period, the crayfish absorbs a very considerable quantity of oxygen, supplied by the atmosphere to the water which it inhabits; while it gives out, into that water, a large amount of carbonic acid, and a larger or smaller quantity of nitrogenous and other excrementitious matters. From this point of view, the crayfish may be regarded as a kind of chemical manufactory, supplied with certain alimentary raw materials, which it works up, transforms, and gives out in other shapes.

And the first physiological problem which offers itself to us is the mode of operation of the apparatus contained in this factory, and the extent to which the products of its activity are to be accounted for by reasoning from known physical and chemical principles.

We have learned that the food of the crayfish is made up of very diverse substances, both animal and vegetable; but, so far as they are competent to nourish the animal permanently, these matters all agree in containing a peculiar nitrogenous body, termed protein , under one of its many forms, such as albumen, fibrin, and the like.

With this may be associated fatty matters, starchy and saccharine bodies, and various earthy salts. And these, which are the essential constituents of the food, may be, and usually are, largely mixed up with other substances, such as wood, in the case of vegetable food, or skeletal and fibrous parts, in the case of animal prey, which are of little or no utility to the crayfish. The first step in the process of feeding, therefore, is to reduce the food to such a state, that the separation of its nutritive parts, or those which can be turned to account, from its innutritious, or useless, constituents, may be facilitated.

And this preliminary operation is the subdivision of the food into morsels of a convenient size for introduction into that part of the machinery in which the extraction of the useful products is performed. The food may be seized by the pincers, or by the anterior chelate ambulatory limbs; and, in the former case, it is usually, if not always, transferred to the first, or second, or both of the anterior pairs of ambulatory limbs.

These grasp the food, and, tearing it into pieces of the proper dimensions, thrust them between the external maxillipedes, which are, at the same time, worked rapidly to and fro sideways, so as to bring their toothed edges to bear upon the morsel.

The other five pairs of jaws are no less active, and they thus crush and divide the food brought to them, as it is passed between their toothed edges to the opening of the mouth. As the alimentary canal stretches from the mouth, at one end, to the vent at the other, and, at each of these limits, is continuous with the wall of the body, we may conceive the whole crayfish to be a hollow cylinder, the cavity of which is everywhere closed, though it is traversed by a tube, open at each end fig. The shut cavity between the tube and the walls of the cylinder may be termed the perivisceral cavity ; and it is so much filled up by the various organs, which are interposed between the alimentary canal and the body wall, that all that is left of it is represented by a system of irregular channels, which are filled with blood, and are termed blood sinuses.

The wall of the cylinder is the outer wall of the body itself, to which the general name of integument may be given; and the outermost layer of this, again, is the cuticle , which gives rise to the whole of the exoskeleton. This cuticle, as we have seen, is extensively impregnated with lime salts; and, moreover, in consequence of its containing chitin , it is often spoken of as the chitinous cuticuta. Having arrived at this general conception of the disposition of the parts of the factory, we may next proceed to consider the machinery of alimentation which is contained within it, and which is represented by the various divisions of the alimentary canal, with its appendages; by the apparatus for the distribution of nutriment; and by two apparatuses for getting rid of those products which are the ultimate result of the working of the whole organism.

And here we must trench somewhat upon the province of Morphology , as some of these pieces of apparatus are complicated; and their action cannot be comprehended without a certain knowledge of their anatomy. The mouth of the crayfish is a longitudinally elongated, parallel-sided opening, in the integument of the ventral or sternal aspect of the head.

Just outside its lateral boundaries, the strong mandibles project, one on each side fig 3, B; 4 ; their broad crushing surfaces, which are turned towards one another, are therefore completely external to the oral cavity.

In front, the mouth is overlapped by a wide shield-shaped plate termed the upper lip, or labrum figs. These together constitute the metastoma fig. A short wide gullet, termed the oesophagus fig. It is divided by a constriction into a large anterior chamber cs , into the under face of which the gullet opens, and a small posterior chamber ps , from which the intestine hg proceeds.

In a man's stomach, the opening by which the gullet communicates with the stomach is called the cardia , while that which places the stomach in communication with the intestine is named the pylorus ; and these terms having been transferred from human anatomy to that of the lower animals, the larger moiety of the crayfish's stomach is called the cardiac division , while the smaller is termed the pyloric division of the organ. It must be recollected, however, that, in the crayfish, the so-called cardiac division is that which is actually furthest from the heart, not that which is nearest to it, as in man.

The gullet is lined by a firm coat which resembles thin parchment. At the margins of the mouth, this strong lining is easily seen to be continuous with the cuticular exoskeleton; while, at the cardiac orifice, it spreads out and forms the inner or cuticular wall of the whole gastric cavity, as far as the pylorus, where it ends in certain valvular projections.

The chitinous cuticle which forms the outermost layer of the integument is thus, as it were, turned in, to constitute the innermost layer of the walls of the stomach; and it confers upon them so great an amount of stiffness that they do not collapse when the organ is removed from the body. Furthermore, just as the cuticle of the integument is calcified to form the hard parts of the exoskeleton, so is the cuticle of the stomach calcified, or otherwise hardened, to give rise, in the first place, to the very remarkable and complicated apparatus which has already been spoken of, as a sort of gastric mill or food-crusher ; and, secondly, to a filter or strainer , whereby the nutritive juices are separated from the innutritious hard parts of the food and passed on into the intestine.

The gastric mill begins in the hinder half of the cardiac division. Here, on the upper wall of the stomach, we see a broad transverse calcified bar figs. The whole has, therefore, somewhat the shape of a cross-bow. Behind the first-mentioned piece, the dorsal wall of the stomach is folded in, in such a manner as to give rise to a kind of pouch; and the second piece, or what we may call the handle of the crossbow, lies in the front wall of this pouch.

The end of this piece is dense and hard, and its free surface, which looks into the top of the cardiac chamber, is raised into two oval, flattened convex surfaces t. The end which is articulated with the handle of the crossbow is produced into a strong reddish conical tooth mt , curved forwards and bifurcated at the summit; consequently, when the cavity of the stomach is inspected from the fore part of the cardiac pouch fig.

The joint which connects the handle of the crossbow with the hinder middle piece is elastic; hence, if the two are straightened out, they return to their bent disposition as soon as they are released. The upper end of the hinder middle piece pp is connected with a second flat transverse plate which lies in the dorsal wall of the pyloric chamber p.

The whole arrangement, thus far, may be therefore compared to a large cross-bow and a small one, with the ends of their handles fastened together by a spring joint, in such a manner that the handle of the one makes an acute angle with the handle of the other; while the middle of each bow is united with the middle of the other.

There are two small pointed teeth, one under each of the lateral teeth, and each of these is supported by a broad plate, hairy on its inner surface, which enters into the lateral wall of the cardiac chamber. There are various other simpler skeletal parts, but the most important are those which have been described; and these, from what has been said, will be seen to form a sort of hexagonal frame, with more or less flexible joints at the angles, and having the anterior and the posterior sides connected by a bent jointed middle bar.

As all these parts are merely modifications of the hard skeleton, the apparatus is devoid of any power of moving itself. The main functions of the colon are to extract the water and mineral salts from undigested food, and to store waste material.

Carnivorous mammals have a shorter large intestine compared to herbivorous mammals due to their diet. The rectum is the terminal end of the large intestine, as shown in Figure The primary role of the rectum is to store the feces until defecation. The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material.

Two sphincters between the rectum and anus control elimination: the inner sphincter is involuntary and the outer sphincter is voluntary. The organs discussed above are the organs of the digestive tract through which food passes.

Accessory organs are organs that add secretions enzymes that catabolize food into nutrients. Accessory organs include salivary glands, the liver, the pancreas, and the gallbladder. The liver, pancreas, and gallbladder are regulated by hormones in response to the food consumed. The liver is the largest internal organ in humans and it plays a very important role in digestion of fats and detoxifying blood.

The liver produces bile, a digestive juice that is required for the breakdown of fatty components of the food in the duodenum. The liver also processes the vitamins and fats and synthesizes many plasma proteins. The pancreas is another important gland that secretes digestive juices. The chyme produced from the stomach is highly acidic in nature; the pancreatic juices contain high levels of bicarbonate, an alkali that neutralizes the acidic chyme.

Additionally, the pancreatic juices contain a large variety of enzymes that are required for the digestion of protein and carbohydrates. The gallbladder is a small organ that aids the liver by storing bile and concentrating bile salts.

When chyme containing fatty acids enters the duodenum, the bile is secreted from the gallbladder into the duodenum. Different animals have evolved different types of digestive systems specialized to meet their dietary needs.

Humans and many other animals have monogastric digestive systems with a single-chambered stomach. Birds have evolved a digestive system that includes a gizzard where the food is crushed into smaller pieces.

This compensates for their inability to masticate. Ruminants that consume large amounts of plant material have a multi-chambered stomach that digests roughage. Pseudo-ruminants have similar digestive processes as ruminants but do not have the four-compartment stomach. Processing food involves ingestion eating , digestion mechanical and enzymatic breakdown of large molecules , absorption cellular uptake of nutrients , and elimination removal of undigested waste as feces.

Many organs work together to digest food and absorb nutrients. The mouth is the point of ingestion and the location where both mechanical and chemical breakdown of food begins. Saliva contains an enzyme called amylase that breaks down carbohydrates. The food bolus travels through the esophagus by peristaltic movements to the stomach. The stomach has an extremely acidic environment. An enzyme called pepsin digests protein in the stomach. Further digestion and absorption take place in the small intestine.

The large intestine reabsorbs water from the undigested food and stores waste until elimination. Skip to content Chapter Animal Nutrition and the Digestive System. Learning Objectives By the end of this section, you will be able to: Explain the processes of digestion and absorption Compare and contrast different types of digestive systems Explain the specialized functions of the organs involved in processing food in the body Describe the ways in which organs work together to digest food and absorb nutrients.

Herbivores, Omnivores, and Carnivores. Invertebrate Digestive Systems. Vertebrate Digestive Systems. Monogastric: Single-chambered Stomach. Parts of the Digestive System. Oral Cavity. Figure The human stomach has an extremely acidic environment where most of the protein gets digested.

Chyme is a mixture of food and digestive juices that is produced in the stomach. Food enters the large intestine before the small intestine.

In the small intestine, chyme mixes with bile, which emulsifies fats. The stomach is separated from the small intestine by the pyloric sphincter. Small Intestine. Villi are folds on the small intestine lining that increase the surface area to facilitate the absorption of nutrients. Absorptive cells that line the small intestine have microvilli, small projections that increase surface area and aid in the absorption of food.

The inside of the small intestine has many folds, called villi. Microvilli are lined with blood vessels as well as lymphatic vessels. The inside of the small intestine is called the lumen. Where is the gastric mill on a crayfish? What is a gastric mill? What has teeth in its stomach?

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