Question

1. Explain how the epidermis and the external morphology of shark, mudpuppy, snake, bird, pig are adapted to the lifestyle of each animal.

2. Trace the path of food from its entrance into the body to its exit from the body for each of the five organisms, indicating all organs that are involved in the digestion of food.

3. Indicate one unique digestinve feature for each organism and indicate its function.

Answer 1

SHARKS:

Sharks’ ability to sustain life as the apex of the aquatic ecosystem for more than 400 million years speaks volumes about their physical and behavioral adaptations.

This predator, known for razor-sharp teeth and swift movements, combines such attributes with a range of behaviors to carry on necessary processes inherent to survival and supremacy at the top of the food chain in the ocean habitat.

Sharks combine physical adaptations such as sharp teeth, heightened senses and a forceful body and tail with behavioral techniques to catch prey. Sharks are nocturnal predators of the ocean, feeding at night between low and high tide, and typically in shallow water near reefs.

Sharks use their speed, agility, body weight and the force of their teeth to attack their prey without exerting a large amount of energy. This helps them retain calories needed for migrating long distances, hunting and mating.

MUDPUPPY:

Mudpuppies are between 20 and 33 cm in length. They are neotenic and retain large, maroon colored external gills throughout their life. Mudpuppies that live in cold water with high oxygen concentrations have shorter gills than those living in oxygen depleted waters.

The spotting pattern ranges from a few spots, to many spots, or spots merging to form stripes. The belly is whitish to grayish, and sometimes has bluish black spots. There are two generally recognized subspecies.

Necturus m. maculosus individuals have rusty brown to gray dorsa with conspicuous spotting. The underside is gray, and may or may not be spotted. Louisiana waterdogs have light yellowish brown to tan dorsa. The dorsal side is marked with large spots and sometimes a dorsal stripe. The belly is light colored with no spots.

The head of all mudpuppies is flat and the tail is short and laterally compressed for swimming. Four toes are present on each of four well-developed limbs. Males and females look very similar.

However, male cloacae have two prominent papillae directed backward. In the breeding season, males have swollen cloacae. Female cloacae are slit-like and usually surrounded by light coloration. Young mudpuppies are black with longitudinal yellow stripes.

SNAKES:

Although it is known that the epidermis of snakes consists of six main layers, there has not been a single study comparing the cross-section architecture of these layers between different snake species inhabiting different environments and preferably using different modes of locomotion.

From previous studies, it is known that between different snake species the scale surface microstructure can vary significantly even between representatives of the same family. That is why these microstructures have been used for taxonomic purposes, but with a limited success.

Scale microstructures vary between dorsal, lateral and ventral body regions within a single species. In a few experimental studies, these microstructures have been shown to influence frictional properties of different skin regions.

Furthermore, depending on function, the scale surface microstructure may also vary within one body region.

For instance, the surface structure of the infrared imaging pit organ scales reveals indistinguishable geometrical parameters in contrast to the surrounding surface and other body scales.

BIRDS:

The skin of birds is fundamentally adapted to their life as active homoiothermic animals. It is largely concealed by the feathers, and its properties have been shaped by them.

The ordinary skin is usually pale pink or bluish pink, elastic, often translucent, and thinner in birds than in mammals of equal size. Over most of the body, a bird fits loosely inside its skin, like a baby in a sleeper, having the freedom of movement required for flight.

The skin is firmly attached with little or no modification on the skull, the wing tips, and other regions. The integument is unfeathered, solidly attached to the skeleton, and highly modified on the beak, the feet, and certain other parts.

PIGS:

The pig’s epidermis contains high levels of alkaline phosphatase in its supra-basal layers (feature solely found in pigs) and a much denser stratum corneum compared to humans.

Hair follicle density is also relatively low in the domestic pig, but only when considering adult animals (~10–20/cm2) as opposed to neonatal pigs (~730/cm2). In contrast, small animals typically used for wound healing research have an abundant fur with follicle density assessed as high as ~1600/cm2 in rat, 1800/cm2 in rabbit, and ~5000/cm2 in mouse skin.

In pigs, so-called “eccrine” sweat glands are histologically distinct (they are branched tubular glands with a secretory epithelium), and are found only on the snout, lips and carpal organ. On the rest of the skin, pigs have another type of gland: the “apocrine” sweat glands. The term “apocrine sweat gland” is a remarkable misnomer for two reasons:

1) these glands have little to do with sweating,

2) they have a merocrine (not apocrine) type of secretion.

DIGESTIVE SYSTEMS:

SHARKS:

Most sharks swallow their food whole or bite it into relatively large pieces. Sharks have U-shaped stomachs that use very strong acids and enzymes to dissolve most of what is eaten.

The stomach produces an easily absorbed, soupy mush. Only this liquid mush enters the intestines because the pyloric valve is small. Indigestible things, are vomited.

Absorption of nutrients takes place in the intestines. Although the intestines are short, they have a large surface area due to infolding of the inner surface of the intestines. Some shark intestines are arranged in folds, some are in a spiral pattern, like a spiral staircase enclosed within a cylinder.

MUDPUPPY:

The digestive system of the mud puppy differs very little from that of the dogfish shark. There are, however, several evolutionary advances. A spiral valve is no longer present and, to compensate for the resulting reduction in internal surface area, there has been an increase in the length of the small intestine.

The termiHal portion of the digestive tract, the rectum or large intestine, has become differentiated into a more stnlctmally distinct organ. Thus the digestive tract of the mud puppy illustrates the early tetrapod stage, but it retains many larval features, such as a vertical transverse septum, gill slits, and a poorly formed tongue.

SNAKES:

Directly inside the mouth of snakes is the buccal cavity. This leads to the esophagus of the snake. In snakes, the esophagus is long and can cover up to half the length of the body.

The esophagus of snakes has more internal folds than other reptiles, which allows for the swallowing of large, whole prey. Peristaltic movement within the esophagus moves the food downward towards the stomach.

The stomach is a j-shaped organ in which most of the digestion occurs in snakes. The 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 rate of digestion is dependent of body temperature because they are cold-blooded animals.

BIRDS:

The mouth of birds distinctly different from mammals. They have no teeth and their jaws are covered by a beak, which is seen in remarkably different forms. Birds do not really masticate, and mechanical disruption of food is accomplished by the beak and gizzard.

The esophagus is large in diameter, particularly in birds that swallow large meals. Swallowing is accomplished by esophageal peristalsis, and in most birds appears to be aided by extension of the neck.

Most but not all birds have a crop, which varies from a simple expansion of the esophagus to one or two esophageal pouches. Depending on the state of contraction of the stomach, food being swallowed is diverted into the crop, then later propelled into the stomach by waves of peristalsis in the crop.

Birds have a glandular stomach, or proventriculus, and muscular stomach or gizzard. The glandular stomach receives food from the esophagus, and secretes mucus, HCl and pepsinogen, similar to what is seen in the mammalian stomach.

The gizzard is a disk shaped, very muscular and in many birds contains small stones that facilitate grinding of foodstuffs. One of the gizzard's two orifices receives ingesta from the glandular stomach and the other empties into the duodenum.

A complex cycle of contractions involving the two stomachs force feed back and forth between the two, grinding it and increasing exposure to digestive enzymes.

There is also periodic retropulsion of duodenal contents back into the stomachs, again presumably facilitating mixing of ingesta with enzymes. A final type of motility is seen in the regurgitation of pellets of bones, hair and feathers from the stomach of raptors.

Birds have a small intestine that seems very similar to the small intestine of mammals. A duodenum, jejunum and ileum are defined, although these segments are not as histologically distinct as in mammals.

The proximal small intestine receives bile from the liver and digestive enzymes from the pancreas, and the absorptive epithelial cells are decorated with essentially the same battery of enzymes and transporters as in mammals.

The large intestine consists of a short colon and, typically, a pair of ceca. Short villi extend into the lumen of the colon, unlike what is seen in mammals. The cloaca is an expanded, tubular structure that serves as the common opening of the digestive, reproductive and urinary systems, which opens to the outside of the bird as the vent.

PIGS:

The digestive tract of the pig has five main parts: the mouth, esophagus, stomach, and small and large intestines. The following discussion explains how each part digests nutrients.

The mouth is where food enters the digestive tract and where mechanical breakdown of food begins. The teeth chew and grind food into smaller pieces. Saliva, produced in the mouth, acts to soften and moisten the small food particles. Saliva also contains an enzyme which starts the digestion of starch. The tongue helps by pushing the food toward the esophagus.

The esophagus is a tube which carries the food from the mouth to the stomach. A series of muscle contractions push the food toward the stomach. Swallowing is the first of these contractions. At the end of the esophagus is the cardiac valve, which prevents food from passing from the stomach back into the esophagus.

The stomach is the next part of the digestive tract. It is a reaction chamber where chemicals are added to the food. Certain cells along the stomach wall secrete hydrochloric acid and enzymes. These chemicals help break down food into small particles of carbohydrates, protein, and fats.

Some particles are absorbed from the stomach into the bloodstream. Other particles that the stomach cannot absorb pass on to the small intestine through the pyloric valve.

The small intestine is a complex tube which lies in a spiral, allowing it to fit in a small space. Its wall has many tiny finger-like projections known as villi, which increase the absorptive area of the intestine. The cells along the small intestine's wall produce enzymes that aid digestion and absorb digested foods.

At the first section of the small intestine called the duodenum, secretions from the liver and pancreas are added. Secretions from the liver are stored in the gall bladder and pass into the intestine through the bile duct. These bile secretions aid in the digestion of fats.

Digestive juices from the pancreas pass through the pancreatic duct into the small intestine. These secretions contain enzymes that are vital to the digestion of fats, carbohydrates, and proteins.

Most food nutrients are absorbed in the second and third parts of the small intestine, called the jejunum and the ileum. Undigested nutrients and secretions pass on to the large intestine through the ileocecal valve.

A "blind gut" or cecum is located at the beginning of the large intestine. In most animals, the cecum has little function. However in animals such as the horse and rabbit, the cecum is very important in the digestion of fibrous feeds.

The last major part of the digestive tract, the large intestine, is shorter, but larger in diameter than the small intestine. Its main function is the absorption of water. The large intestine is a reservoir for waste materials that make up the feces. Some digestion takes place in the large intestine.

Mucous is added to the remaining food in the large intestine, which acts as a lubricant to make passage easier. Muscle contractions push food through the intestines. The terminal portion of the large intestine is called the rectum.

The anus is an opening through which undigested food passes out of the body. Food that enters the mouth and is not digested or absorbed as it passes down the digestive tract is excreted as feces.