Digestive System of Reptiles-Anatomy and Function
written by Sidra BatoolThe reptile digestive system includes the mouth, esophagus, stomach, intestine, and cloaca. The cloaca is a single opening that serves as the exit for both the digestive and reproductive tracts.
The digestive systems of reptiles is complex and well-adapted to terrestrial life. Reptiles have evolved a number of adaptations to help them digest food, conserve water, and excrete waste products.
Digestive Organs of Reptiles
The digestive organs of reptiles work together to break down food into smaller pieces and absorb nutrients into the bloodstream.
| Organ | Function |
|---|---|
| Mouth | Grasps, tears, and grinds food; moistens food with saliva; starts the digestion of carbohydrates |
| Esophagus | Transports food from the mouth to the stomach |
| Stomach | Stores and breaks down food with gastric juices; absorbs some nutrients |
| Small intestine | Absorbs nutrients from food with bile and pancreatic juices |
| Large intestine | Absorbs water from food; stores waste products |
| Cloaca | Conserves water by reabsorbing it from the waste products |
1. Mouth
The mouth is the first organ involved in digestion. It contains teeth, tongue, and salivary glands.
2. Teeth
Reptiles have teeth that are adapted to their diet. For example, snakes have sharp, curved teeth for grasping and killing prey. Lizards have teeth that are flattened and sharp for cutting and slicing food. Turtles have horny beaks for crushing hard food items.
When a reptile eats, it uses its teeth to grasp, tear, and grind food. This helps to break down the food into smaller pieces that are easier to digest. The teeth also help to mix the food with saliva.
3. Tongue
The reptilian tongue is used to manipulate food and taste. It also helps to push food back into the throat so that it can be swallowed. Some reptiles have long, forked tongues that they use to smell.
Read our detailed article on Taste Buds/Gustation in Reptiles
For example, snakes use their forked tongue to flick the air and collect scent particles. These scent particles are then transferred to the Jacobson’s organ, which is located in the roof of the mouth. The Jacobson’s organ helps the snake to track its prey and identify other snakes.
4. Salivary glands
Salivary glands produce saliva, which moistens food and starts the digestion of carbohydrates. Saliva also contains enzymes that break down starch into sugars.
For example, the saliva of some lizards contains enzymes that break down cellulose, a component of plant cell walls. This helps the lizards to digest plant material.
5. Esophagus
The esophagus is a long tube that connects the mouth to the stomach. It is responsible for transporting food from the mouth to the stomach.
The esophagus uses peristalsis to move food down to the stomach. Peristalsis is a series of muscle contractions that push the food along.
6. Stomach
The stomach is a muscular organ that stores and breaks down food. It contains gastric juices, which are acids and enzymes that help to break down food.
The stomach mixes food with gastric juices and uses peristalsis to churn the mixture. This helps to break down the food into smaller pieces and absorb some of the nutrients.
Gastric juices contain hydrochloric acid, which kills bacteria and helps to break down proteins. Gastric juices also contain pepsin, an enzyme that breaks down proteins.
In addition to pepsin, the stomach also contains other enzymes that break down carbohydrates and fats. However, the digestion of carbohydrates and fats is primarily completed in the small intestine.
7. Small intestine
The small intestine is a long, coiled tube that absorbs nutrients from food. It is divided into three parts: the duodenum, jejunum, and ileum.
The duodenum is the first part of the small intestine. It receives bile from the liver and pancreatic juices from the pancreas. Bile helps to digest fats, while pancreatic juices contain enzymes that break down carbohydrates, proteins, and fats.
The jejunum is the middle part of the small intestine. It is responsible for absorbing most of the nutrients from food. The jejunum has a large surface area for absorption due to the presence of villi, which are finger-like projections that line the walls of the jejunum.
The villi are covered in microvilli, which are even smaller projections that further increase the surface area for absorption. The villi also contain capillaries, which are small blood vessels that transport the absorbed nutrients to the rest of the body.
The ileum is the last part of the small intestine. It is responsible for absorbing any remaining nutrients from food and water. The ileum also contains Peyer’s patches, which are aggregates of lymphoid tissue that play a role in the immune system.
8. Large intestine
The large intestine is a shorter, wider tube that absorbs water from food and stores waste products. It is divided into three parts: the colon, cecum, and rectum.
The colon absorbs water and stores waste products. The colon also contains bacteria that help to digest plant material.
The cecum is a small pouch that extends from the junction of the small and large intestines. The cecum is especially well-developed in herbivorous reptiles, where it plays a role in the digestion of plant material.
The cecum contains bacteria that help to break down cellulose and other complex carbohydrates. The bacteria also produce vitamins and minerals that are absorbed by the reptile.
The rectum stores waste products until they are excreted.
9. Cloaca
The cloaca is a single opening that serves as the exit for both the digestive and reproductive tracts. The cloaca helps to conserve water by reabsorbing it from the waste products.
Process of Digestion in Reptiles
The steps of digestion are as follows:
- Ingestion – This is the process of taking food into the body.
- Mechanical digestion – This is the process of breaking down food into smaller pieces using the teeth, tongue, and other muscles of the mouth and esophagus.
- Chemical digestion – This is the process of breaking down food into smaller molecules using enzymes. Chemical digestion begins in the mouth with the enzyme amylase, which breaks down starch into sugars. It continues in the stomach with the enzymes pepsin and lipase, which break down proteins and fats, respectively. Chemical digestion is completed in the small intestine with a variety of enzymes from the pancreas and liver.
- Absorption – This is the process of absorbing the broken-down food molecules into the bloodstream. Absorption takes place in the small intestine, where the villi (finger-like projections) increase the surface area for absorption.
- Egestion – This is the process of eliminating the undigested food and waste products from the body. Egestion takes place through the rectum and anus.
Adaptations of the reptilian digestive system
Reptiles have evolved a number of adaptations to their diet and lifestyle. For example, snakes have a long and flexible esophagus to accommodate large prey items. Lizards have teeth that are adapted to their diet, whether they are carnivores, herbivores, or omnivores. Turtles have a hard beak for crushing hard food items.
Reptiles are also able to excrete nitrogenous wastes in the form of uric acid. Uric acid is less toxic and requires less water to excrete than urea or ammonia, which are the nitrogenous wastes excreted by other vertebrates. This is an important adaptation for reptiles that live in dry environments.
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