Animal Physiology

Physiology is the branch of biology that studies the functioning of the organism, that is, the multiple mechanical, physical and biochemical functions in living beings.

We will now study animal physiology, which extends the methods of study of human physiology to nonhuman species. Let's start with digestion.


We unicellular beings, all survival problems are solved by the single cell. We multicellular, the execution of all survival-related tasks is hampered by the large number of cells. Not all are close to sources of food and oxygen. The distance from the innermost cells to the environment is large. The removal of excreta is laborious. The division of labor, exercised by different tissues and systems, became one of the main characteristics of these beings.

Adaptation to multicellular life then involved the organization of different systems, each intended for a particular task, but all maintaining interdependent relationships in order to perform their functions effectively.

Digestion: Breaking Food

Digestion is the process of transforming large molecules by enzymatic hydrolysis, releasing smaller units that can be absorbed and used by cells.

Thus proteins, fats and carbohydrates, for example, are broken down into amino acids, fatty acids and glycerol, glucose and other monosaccharides, respectively.

Two types of digestion: Extra and Intracellular

In protozoa, the digestion of food must be done inside the cell, characterizing the process of intracellular digestion. In general, digestive vacuoles are formed within which digestion is processed.

In the simplest multicellular animals, such as sponges, digestion is exclusively intracellular and occurs within special cells known as choanocytes and amoebocytes. In coelenterates and flatworms there is already a incomplete digestive cavity, that is, as a single opening - the mouth. In these animals, but the terminus is still intracellular.

As animal groups become more complex, digestion occurs exclusively in the digestive cavity, ie it is totally extracellular. This is what happens from the nematelminths, where the efficiency of the digestive process guarantees the total fragmentation of the food in the digestive cavity.

Undigested food waste is eliminated by the anus. The first animals with complete digestive cavity (mouth and anus) belong to the group of nematelminths.

In man and all vertebrates, digestion is extracellular and occurs entirely in the digestive tract cavity.

Digestive System Features

O human digestive tract presents the following regions; mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. The wall of the digestive tract has the same structure from the mouth to the anus, being formed by four layers: mucosa, submucosa, muscle and adventitia.

The teeth and the language prepare the food for digestion by chewing, the teeth reduce the food into small pieces, mixing them with saliva, which will facilitate the future action of the enzymes. The tongue moves the food by pushing it towards the throat so that it is swallowed. On the surface of the tongue are dozens of taste buds, whose sensory cells perceive the four primary flavors: sweet, sour, salty and bitter.

The presence of food in the mouth, such as sight and smell, stimulates the salivary glands to secrete saliva, which contains the enzyme salivary amylase or ptialin, as well as salts and other substances.