The snake's heart is encased in a sac, called the pericardium, located at the bifurcation of the bronchi. The heart is able to move around, however, owing to the lack of a diaphragm. This adjustment protects the heart from potential damage when large ingested prey is passed through the esophagus. The spleen is attached to the gall bladder and pancreas and filters the blood. The thymus gland is located in fatty tissue above the heart and is responsible for the generation of immune cells in the blood. The cardiovascular system of snakes is also unique for the presence of a renal portal system in which the blood from the snake's tail passes through the kidneys before returning to the heart.
The vestigial left lung is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin. In the majority of species, only one lung is functional. This lung contains a vascularized anterior portion and a posterior portion which does not function in gas exchange. This 'saccular lung' is used for hydrostatic purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species. Many organs that are paired, such as kidneys or reproductive organs, are staggered within the body, with one located ahead of the other. Snakes have no colenary bladder or lymph nodes.
The vestigial left lung is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin. In the majority of species, only one lung is functional. This lung contains a vascularized anterior portion and a posterior portion which does not function in gas exchange. This 'saccular lung' is used for hydrostatic purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species. Many organs that are paired, such as kidneys or reproductive organs, are staggered within the body, with one located ahead of the other. Snakes have no colenary bladder or lymph nodes.
Respiratory System:
The respiratory system of snakes includes the trachea (windpipe), bronchi, lungs, and air sac. The anterior portion of the lungs is vascular (with blood vessels) and functions in gas exchange, but the second half of the lung is an avascular (without blood vessels) air sac that extends into the tail region. The air sac performs a hydrostatic function in most snakes, regulating pressure inside the body cavity. Because snakes do not have a diaphragm, air enters and leaves the lung due to action of the body muscles and movement of the ribs.
Digestive System: The digestive system is composed of the esophagus, stomach, small intestine, colon, and glands. In snakes, the esophagus has very little muscle and food is moved to the stomach more by movement of the entire body. The junction between the esophagus and the stomach is not well defined, and the stomach itself is not very advanced. The small intestine is relatively simple. There may be a few loops or folds, but for the most part it is a long tube that receives food from the stomach, absorbs nutrients from it, and transports it to the colon, or large intestine. The colon then carries the fecal matter to the cloacal opening where it is disposed. The cloaca is a common chamber, receiving products from the digestive, urinary, and reproductive systems.
The liver is the largest internal organ in a snake, filling the space between the heart and stomach. One of the many functions of the liver is to produce bile, a digestive enzyme. The gall bladder and spleen are found near the posterior tip of the liver. The gall bladder stores bile produced by the liver and releases it into the small intestine when needed. The pancreas also secretes digestive enzymes into the small intestine, as well as producing hormones that regulate blood sugar.
Digestive System: The digestive system is composed of the esophagus, stomach, small intestine, colon, and glands. In snakes, the esophagus has very little muscle and food is moved to the stomach more by movement of the entire body. The junction between the esophagus and the stomach is not well defined, and the stomach itself is not very advanced. The small intestine is relatively simple. There may be a few loops or folds, but for the most part it is a long tube that receives food from the stomach, absorbs nutrients from it, and transports it to the colon, or large intestine. The colon then carries the fecal matter to the cloacal opening where it is disposed. The cloaca is a common chamber, receiving products from the digestive, urinary, and reproductive systems.
The liver is the largest internal organ in a snake, filling the space between the heart and stomach. One of the many functions of the liver is to produce bile, a digestive enzyme. The gall bladder and spleen are found near the posterior tip of the liver. The gall bladder stores bile produced by the liver and releases it into the small intestine when needed. The pancreas also secretes digestive enzymes into the small intestine, as well as producing hormones that regulate blood sugar.
Cardiovascular System:
Two atria and one ventricle make up the three-chambered heart of a snake. The right and left atria receive blood from the lungs and body, respectively, and pass it to the ventricle to be circulated again. Encased in a sac, called the "pericardium," the heart is located at the bifurcation of the bronchi. The heart is able to move around, however, due to the lack of a diaphragm. This adjustment protects the heart from potential damage when large ingested prey is passed through the esophagus. The spleen is attached to the gall bladder and pancreas and functions to filter the blood and recycle old red blood cells. The thymus gland is located in fatty tissue above the heart and is responsible for the maturation of special immune cells in the blood.
Endocrine System:
The endocrine system is made up of glands that secrete hormones essential to normal body function. Snakes have the same endocrine glands as mammals. A few examples are the thyroid, parathyroid, and adrenal glands. The thyroid gland located in the throat area is responsible for proper growth and development, such as normal shedding of the skin. The parathyroid is a paired structure located near the thyroid and helps in the metabolism of calcium. The two adrenal glands are located in the tail region, suspended in a mesentery (membrane sheet attaching organs to the body wall) near the reproductive organs. They secrete the hormone epinephrine (adrenaline) that increases heart and respiratory rates when the animal is in a dangerous situation.
Genitourinary System:
The kidneys are the organs responsible for urinary output. In the snake, the kidneys are elongated, and the right kidney is situated closer to the head than the left. These organs filter the blood and remove waste products, which are then concentrated and transported, via the ureters, to the cloaca. The ureters are hollow tubes for transporting urine. In mammals, the ureters empty into the urinary bladder where the urine is stored and later expelled through another tube called the "urethra." Because snakes do not have a urinary bladder, the urine is not stored, and the ureters empty directly in the cloaca.
The paired gonads, testes in the male and ovaries in the female, are situated in a similar fashion, with the right being closer to the head than the left. They are also located closer to the head than the kidneys. In the female, the ovaries are near the oviducts, which carry eggs to the uterus before they enter the cloaca. Some snakes are oviparous (egg-laying) and some are viviparous (having live birth). In mammals, males have two ducts associated with each teste -- the epididymis and ductus deferens. Snakes lack epidiymides and the sperm are simply transported from the teste through the ductus deferens to the cloaca. The male also has organs called "hemipenes" that are located posterior to the cloacal opening. The hemipenes are paired copulatory organs, and they are both fully functional, though only one at a time is used to transfer sperm to the female. The hemipenes are closely associated with the scent glands, or musk glands, which are also present in the female.
The paired gonads, testes in the male and ovaries in the female, are situated in a similar fashion, with the right being closer to the head than the left. They are also located closer to the head than the kidneys. In the female, the ovaries are near the oviducts, which carry eggs to the uterus before they enter the cloaca. Some snakes are oviparous (egg-laying) and some are viviparous (having live birth). In mammals, males have two ducts associated with each teste -- the epididymis and ductus deferens. Snakes lack epidiymides and the sperm are simply transported from the teste through the ductus deferens to the cloaca. The male also has organs called "hemipenes" that are located posterior to the cloacal opening. The hemipenes are paired copulatory organs, and they are both fully functional, though only one at a time is used to transfer sperm to the female. The hemipenes are closely associated with the scent glands, or musk glands, which are also present in the female.
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