Elephants are herbivoroussingle stomached or monogastric animals. The major alimentary structures are similar to those of the horse. Elephants lack a gall bladder and rely on hind gut fermentation of fecal matter in their large cecum using bacterial symbiosis. The elephant digestive tract consists of (from oral to aboral) the mouth, pharynx, esophagus, stomach, small and large intestine, cecum, rectum and anus. Accessory organs such as molar teeth, tongue, salivary gland, liver and pancreas completethe system. The digestive system of elephant is not very efficient at absorption of nutrients. Elephants digest and absorb only about 44 percent of what they eat. The consumption of an adult Asian elephant is approximately 150-200 kilograms of food (10 percent of body weight) and 200 liters of water per day, although larger amounts of food may be required in some circumstances.
The opening of the mouth of the elephant is smaller relative to body size compared to many other mammals . The oral cavity has molar teeth, a tongue, and openings of the salivary ducts and salivary glands. The mouth is connected to the pharynx and the upper respiratory tract. The strong mandibular movement and coordination of teeth and tongue function are important in generating the horizontal grinding action of mastication of elephants.
The dental formula of adult elephants for both species is I 1/0 C0/0 PM 3/3 M 3/3, with a total number of 26 teeth,The two upper incisors are the tusks. The average weight of the teeth of elephants is approximately 5 kilograms. New born elephants have 2-3 teeth in each jaw quadrant, these teeth develop in the fetus and can be observed in jaw within a few months after the birth. Elephants have 6 sets of molar teeth during their life span but they cannot hold all 6 sets at one time. The molar teeth are shed periodically. They move foreword in the jaw to displace old and worn teeth that fragment and usually fall out on their own and are swallowed. The structure of the teeth of elephants is complex and very much like the structure of the teeth of other mammals,.They are comprised of cementum, enamel, dentin, a pulp cavity and pulp tissue that includes odontoblasts, odontocytes, vessels and nerves. All elephantteeth are held together by cementumwhich forms the foundation for the projections on the occlusal surfaces of the molars which are covered with light or white enamel. These ridges contrast with the grooves where the darker colored dentin is seen.. The shape of projections on molar occulsal surfaces can be used to identify theelephant species. Molar projections are lozenge shaped in African elephants and loop shaped in Asian elephants.
Figure 6. The molar teeth of an Asian elephant
Elephant tusks are the upper incisor teeth. The elephant tusk is a hypsodont tooth capable of growing through out the life of the elephant (elephant molar teeth are brachydont teeth). The deciduous tusks can found in new born elephants. The permanent tusks are observed in 2-3 year old elephants. Tusks normally grow about 15-18 centimeters per year. The structure of tusk is similar to that of a tooth except that enamel is only found on milk tusks. Elephant tusks have a unique characteristic refered to as the checered pattern (a net liked pattern) which can be seen in the cross section of the tusk. About 1/3 of the tusk length lies in the alvelolar socket of the maxillary bone. The sulcus is approximately the the length between the eye and the tusk sulcus. The pulp of the tusk extends about 2/3 of the tusk length, (see the figure 8). The position of the pulp is important for properly trimming the tusk.
Figure 7. The longitudinal section of an elephant head and tusk, a tusk (a), pulp (b), internal nare (c), air cavities (d), brain cavity (e) and molar teeth (f) (modified from GrÖning K, 1999)
Figure 8.The measuement useful for estimating the leghth of the pulp cavity in the elpehant (modified from Robinsom and Schmidt, 1986)
The esophagus extends from the pharynx to the stomach running in close relation to the trachea. Its structure is that of a musculomembranous tube, formed primarily by the tracheoesorphagial muscle. The esophageal mucosa has numerous mucous glands which secrete mucus to lubricate the food bolus as it passes through the esophagus.
The elephant stomachis cylindrical and approximately 75-90 centimeters in long in adult elephants. The capacity of adult elephant stomach is between 30 and70 litters.
Intestine, cecum and rectum
The length of small intestine of adult elephants is about 66 to74 feet. The intestines are divided into the duodenum (approximately 1.5 feet long), jejunum (approximately 11 feet long) and the ileum. The large intestine of an adult elephant is approximately 38-43 feet long divided into a 20 to 22 foot long colon followed by a 12 to 14 foot rectum the terminating at a muscular anus under the tail. The cecum is 5 to 7 feet long, located coming off of the junction of the ileum and the colon. It is a major site of fermentation in the elephant. The capacity of the small intestines of an adult elephant is approximately 135 liters and the large intestines and caecum hold approximately 480liters of matter.
Liver and pancreas
Although the elephants lack the gall bladder, bile is secreted and passes to the small intestine throughmultiple ducts. The bile functions to enhance lipid digestion and absorption in the intestine. Pancreatic secretions function to facilitate protein and carbohydrate digestion along with secretions from the glands in intestinal wall.
Circulatory, hemopoetic and lymphatic systems
The elephant heart is large ( about 12-21 kilograms). It is apple shaped with double ventricular apices. Large sinuses moderate the high blood pressure from cardiac contraction to prevent damage of peripheral blood vessels. These sinuses can found in both sides of the temporal area, along the trachea, sternum, axillae and inguinal areas. The vasculature of elephants is thicker walled and stronger than found in most other mammals.
The blood components of the elephant are similar to other mammals, except that the blood cells are larger.
Lymph and lymphoid organs
The thymus, tonsils, lymph nodes and spleen are the lymphoid organs of the elephant. The lymphatic system plays an important role in the elephant immune response.
The elephant nervous system is comprised of a brain, spinal cord and peripheral nerves. The brain to body size ratio is smaller than other mammals. The brains of male elephants weigh between 4.2-4.5 kilograms and the brains of female elephants weigh bewteen 3.6-4.2 kilograms. Although the elephants have a small brain to body size ratio, they are one of the most intelligent animals, with a highly complex and developed pattern of gyri and sulci. No intelligence difference has been observed between male and female elephants. The spinal cord of the elephant has two enlargements referred to as the cervical and lumbar enlargements. These enlargements contain numberous nerve cells that function in control of the limbs. ,
This system is comprised of bilateral kidneys, and ureters, a urinary bladder, urethra and urethal opening. Like the ox, elephant kidney s are multilobar. An elephant kidney has 5-7 lobules. The urinary bladder capacity of an adult elephant is isapproximtely 6-18 liters. Normal elephants urinate 10-15 times per day.