Inside Nature's Giants

Who: herbivore

What: eats leaves

Where & When: middle or top layers of canopy, particularly the tall and thorny acacia trees; daytime

Neck: The long neck enables a high reach to the middle or top of a tree.

Lips and tongue: The upper lip is long and pointy, which allows it to be inserted between sharp acacia spines to grab leaves. The tongue is also very long and flexible, allowing it to grasp leaves from between the spines and withdraw them into the mouth. The tongue colour is blue-black.

Cheeks: The inside surface of the cheeks is lined with stiff, papillae-like projections, making a rough surface with much surface area. The function of this rough texture is not known, but may relate to protection while chewing thorny plants, or it may help shred the food.

Saliva: Extra slimy spit lubricates food for swallowing with no water. It contains enzymes that begin digestive process. It also neutralizes the stomach acids preventing irritation of the oesophagus during regurgitation of cud.

Mastication: There are no upper incisors, only lower incisors that function to grasp leaves by trapping them against the hard palate. The lower jaw is narrower than the upper jaw. The means that the lower jaw is shifted back and forth between the right and left sides during chewing. The miss-match causes the molar teeth to be in occlusion on only one side at a time. When they are occluded on the right side, they are not lined up in occlusion on the left. This relationship reverses when the lower jaw shifts to the left to line up the left lower molar teeth with the left upper molar teeth.

Stomach: Giraffes are artiodactyls (ruminants), and therefore have the typical four-chambered stomach. Each chamber has a distinctive texture to is lining and a unique folding pattern of its walls that corresponds to its function. The first and largest chamber is called the rumen. This chamber serves as a settling chamber, which allows liquid portion of the food to flow onwards to the second stomach chamber, while trapping the heavier particulate matter. Once the liquid has been separated off, the larger particles are sent back up to the mouth to be chewed again as cud, thereby causing more of it to be further broken down.

Contractions are designed to push fermentation gas back to the oesophagus for eruction (burping). The second chamber is the reticulum. This chamber holds the smaller particles that have passed the first stage of digestion. Here, food is mixed with microbe-laden liquid that will aid in further food breakdown. This mixture is then passed onto the third chamber called the omasum. Particulate matter is retained here while fluids are passed on to the fourth chamber, called the abomasum. This last chamber is homologous to the stomach of non-ruminant animals, and contains the glandular tissue that secretes digestive acids. It also secretes an enzyme that kills the excess of bacteria that were functional in the earlier chambers but are not necessary in this last chamber.

Intestines: Food passes from the stomach to the small intestines, where nutrient absorption takes place. It then passes to the large intestines where fluid absorption takes place.

Dung: Most of the dung produced is dead bacteria and indigestible plant parts. All digestible plant parts are absorbed earlier in the digestive tract. That's why giraffes produce such small stool pellets, approximately the size of a walnut. They are very efficient at extracting as much as they can out of the plant products they ingest.