The digestive system of mammals is formed by a long tube that runs from the mouth to the anus.
Various organs and glands produce digestive juices that "break down" the nutritive substances in foods (proteins, fats, sugars) until they are in "pieces" so small that the intestine can absorb them. The remains - which are not digested or used - are eliminated by the anus in the form of feces.
Some herbivores like ox, goat, sheep and giraffe are ruminant mammals. Like other mammals, they cannot digest cellulose, the type of sugar in plants. However, in the stomach of ruminants there are microorganisms (bacteria and protozoa) that digest the cellulose.
The teeth, surrounded by fleshy gums, are usually of 3 types (incisors to bite, cut or scrape, canines to grab and tear, premolars and molars to crush and grind the food). The shape and size of each tooth type varies by diet.
Keeping the body warm when the environment cools, for example, requires energy. Energy for mammalian homeothermia and general activities depends on respiration and circulation. In other words, obtaining energy depends on oxygen uptake and transport by the body as well as nutrients through the blood. Mammals get from the air the oxygen needed for their body's energy processes. All mammals are pulmonary beings, that is, air enters the airways to the lungs, which absorb oxygen. Even aquatic mammals have lungs, they must surface to breathe.
They present muscles located between the ribs, which act on the respiratory movements, and another called diaphragm.
Like the heart of birds, the heart of mammals has four cavities. Mammalian circulation is closed, double and complete without venous and arterial blood being mixed. Efficiency in blood circulation favors body homeothermia.
Like birds, mammals are endothermic or homeothermic, allowing them to remain active even at very high or very low temperatures. This justifies its widespread distribution in all habitat types, wider than any other animal (except birds).
In many mammalian groups, there are rituals of "dating" before mating. There is internal fertilization, the male places the sperm (which contains sperm) inside the female body, where the gametes meet. These beings called viviparous have offspring that are born after being raised in their mother's womb.
Most mammals breed their young inside the female's womb. Almost all mammalian pups are born directly from the mother's body and at an advanced stage of development.
Puppies kept inside the female's body for a longer period are better protected than those that finish their development inside eggs (as with birds and reptiles, for example).
Although viviparity limits the number of pups per pregnancy, it is an evolutionarily advantageous factor, increasing the chances of survival and reproductive success.
While the puppy is developing in the womb, it receives nutrients and oxygen through the placenta through the umbilical cord. The placenta is a structure formed by part of the mother's body and part of the fetus's body. It is also through the placenta that the fetus eliminates excreta, which is leftovers produced, for example, carbon dioxide.
This image shows a dolphin fetus at 8 weeks gestation.
This image shows an elephant fetus during pregnancy.
One or more pups may be born as the number varies depending on the species. After birth, the puppy feeds on breast milk and receives care from the mother - sometimes from the father - in the first phase of life. Babies of certain species of whales, for example, suckle five hundred liters of milk in one day.