Reptiles are a diverse group of vertebrates that can be found in many different habitats. They have a number of unique anatomical features that make them interesting to study.
The skin of most reptiles is keratinized and has fewer skin glands than amphibians. The scales of a reptile are usually large and plate-like, with the junction between them providing a flexible hinge. These may be modified into crests, spines and horn-like processes.
Reptiles breathe by changing the volume of their body cavities. This is done by contraction of the rib muscles and expansion of the lungs. The lungs are simple saclike structures with small pockets, called alveoli, within the walls. An increase in the surface area of the lungs increases the efficiency of gas exchange.
The trachea opens 도마뱀분양 into two lungs that lack bronchioles in all but colubrids and crocodiles, the latter of which have a multichambered lung system with bronchioles that each end in faveoli. The Savannah monitor lizard, however, has one lung that is divided into multiple chambers by a few large septa. This increased structural complexity probably decreases the potential for ventilation-perfusion (V / Q) heterogeneity that can constrain gas exchange efficienc 도마뱀분양 y in vivo.
The lungs empty into the stomach which has a small duodenum and a pylorus that separates the jejunum from the ileum. The pylorus also contains the pancreas and gall bladder. The large intestine terminates in the cloaca. The anterior cloaca receives feces while the posterior cloaca collects urogenital secretions and sperm.
Before the evolution of lungs, vertebrates had an undivided heart. The single cardiac ventricle had internal ridges that allowed some functional separation of the oxygenated and deoxygenated sides of the circulation. In reptiles, the left ventricle receives deoxygenated blood from the systemic circulation via the right and left pulmonary veins while the right ventricle pumps oxygenated blood to the lungs via the cavum pulmonale and cavum arteriosum.
During ventricular systole, these structures remain closed allowing the two aortic arch arteries to communicate through a hole in the aortic wall known as the foramen of Panizza (Holmes, 1975). In non-crocodile reptiles, the aortic valves open during this phase while the foramen closes during diastole.
The aortae exit the single ventricle and fuse to form a single abdominal aorta that extends caudally through the coelomic cavity. There is also a paired iliac arteries that supply the lower extremities. The iliac arteries may converge at the point of the pylorus, where they split into a renal and cranial artery. This allows for the concentration of drugs that are nephrotoxic or that require renal clearance.
Many reptiles, such as chameleons, can change their colour using special skin cells called iridophores. These cells contain tiny particles that directly influence how light passes through the body, giving it different colours.
The reptile stomach is a muscular sac containing a fluid-filled cavity known as the chyme that holds food until it can be digested. This is important because reptiles do not chew their food, but swallow it whole.
Snakes have a small cloaca that acts as a general collecting area for waste products and secretions. It has three chambers; the anterior one, the coprodeum, receives faeces and urine. The middle chamber, the urodeum, receives the male intromittent organs and the female scent glands. The posterior chamber, the proctodeum, acts as a dumping area for excretory wastes.
Reptile kidneys are composed of nephrons that include glomeruli for filtering plasma, Bowman capsules that collect the filtrate and tubules for reabsorption of water. They also regulate acid-base balance, excrete wastes and produce hormones and vitamins.
Unlike mammals, reptiles have a common cloacal opening that receives waste from the lower digestive, reproductive and urinary tracts. The lungs of reptiles are simpler in composition (not having alveoli) and rely on the movement of blood through the coelomic cavity to supply oxygen to the body.
The copulatory organs of reptiles are paired structures called hemipenes that protrude into the female during mating. The ducts of a male’s testes empty into the cloacal and are filled with blood through spaces in the hemipenis to create an erection.
Reptiles have a three chambered heart with two atria and one partly split ventricle, which allows them to redirect the flow of blood away from the lungs to conserve energy or to allow aquatic reptiles to dive for longer periods. This ability to alter blood flow can also save reptiles from hypoxic conditions by eliminating the need for them to pump deoxygenated blood to the lungs.
Radiography can be very useful in evaluating the cardiovascular system of reptiles, but it is important to have a normal radiograph from a matched conspecific to refer to. Cardiac size varies considerably among taxa and a good understanding of the normal anatomy is essential for accurate cardiac measurements in reptiles.
Like mammals, reptiles have a large lymphatic system. It drains the perivascular spaces around the major vessels and the viscera. The caudal large intestine empties into the coprodeum portion of the cloaca, which is common emptying chamber for the digestive, urinary and reproductive systems.
Snakes have paired adrenal glands located either in front of or just behind the gonads. These pinkish, spongy-like glands are secretory of corticosterone, which suppresses the immune response and is an important stress hormone.
During larval development, urodele amphibians (newts and salamanders) have 8 to 18 pairs of LHs for a total of 18 lymphaticovenous connections10. However, during ontogeny the number of LHs declines. This correlates with decreased regeneration ability in urodeles9. In addition to the LHs, a frog has a pair of large subcutaneous lymphatic sacs. These connect the limb lymphatics to the TLyLL. ICG injection of a frog forelimb revealed that lymph flow into the sacs was rapid and peaked within 10-15 minutes. Similarly, the hindlimb lymphatics ran posteriorly to an axilla network that was connected to the TLyLL through the right and left lateral LHs.