Amphibian and Reptilian Anatomy and Physiology

1. Amphibian and Reptilian Anatomy and Physiology

2. Learning Objectives List the taxonomic orders in the classes Reptilia and Amphibia. Define ectothermic and explain how ectothermic animals regulate their body temperatures. List the unique features of the reptilian and amphibian integumentary systems. Describe the process of ecdysis. List the unique features of reptilian and amphibian vision and hearing. List the components of the reptilian and amphibian heart and describe the flow of blood through the heart. Describe the unique features of the reptilian and amphibian respiratory and gastrointestinal systems. Describe the structure of the kidneys of reptiles and amphibians. Describe the factors that determine the sex of offspring of reptiles and amphibians. List the unique features of the musculoskeletal systems of reptiles and amphibians.

3. Taxonomy • Class Reptilia - four orders: • Crocodylia (alligators and crocodiles) • Squamata (snakes and lizards) • Chelonian (turtles and tortoises) • Rhyncocephalia (tuataras)

4. Taxonomy • Class Amphibia - three orders: • Gymnophiona (caecilians) • Anura (frogs and toads) • Caudata (salamanders and newts)

5. Metabolism • Ectothermic animals are unable to generate body heat internally. • Body temperature depends on environmental temperature • Some reptiles can raise body temperatures via metabolic processes (e.g., muscular contractions) • Herptiles - maintain body temperatures via behavioral thermoregulation (e.g., postural changes)

6. Ectothermy • Related to energy conservation • Animal regulates temperature depending on metabolic needs • Allows many herptiles to survive on very small amounts of food • Depends on access to temperatures within the preferred optimal temperature zone (POTZ) • POTZ: range of temperatures in which the animal can perform all necessary metabolic functions

7. Reptile Integument • Keratinized skin • Alpha keratin - soft, flexible, found in interscalar skin • Beta keratin - rigid, found in scales • Limited subcutaneous space

8. Reptile Integument • Dermis - dense connective tissue • Blood and lymph vessels, nerves, and chromatophores (pigment-containing cells) • Chromatophores allow some lizards to change skin color and pattern • Osteoderms: bony plates within dermis of some lizards and crocodilians

9. Reptile Integument • Scales - formed by epidermal folds in most reptiles • Vary in size and shape • Brille (spectacle): modified scales that may cover eyes • Other epidermal structures may be present • Crests, tubercles, spines, and dewlaps

10. Reptile Integument Scale and scute nomenclature - aids in species identification and medical recording

11. Ecdysis Shedding of the skin Occurs with growth and in response to skin injury Process is controlled by thyroid gland Shed in pieces or in one large piece Shed skin: exuvia

12. Ecdysis Cells replicate new epidermis Enzyme-containing lymph secreted between old and new epidermal layers Skin color dulls; spectacle opacifies Lymph - resorbed prior to ecdysis Mechanical rubbing on objects

13. Amphibian Integument • Epidermis - single or few layers of keratinized cells • Aquatic amphibians - no keratinized cells • Extremely permeable • Absorb water directly from environment • “Drink patches”: areas of increased permeability on ventral surfaces • Dermis - chromatophores and glands • Glands produce secretions which help protect the amphibian’s skin

14. Amphibian Integument • Toxic secretions - produced by some glands within dermis and epidermis • Defense mechanisms • Dermis: little subcutaneous space in salamanders and caecilians • Anurans: looser attachments of dermis (more subcutaneous space) • Amphibians regularly shed outer layers of epidermis

15. Vision • Reptiles – iris made up of skeletal muscle under voluntary control • Pupillary light reflex: consensual reflexes usually not seen • Lower lid usually more mobile than upper

16. Vision • Some species of lizards have thin, transparent lower lids • Allows for a degree of vision even when lids are closed • Cartilagenous pads (tarsal pads): found in lids of some reptiles • Nictitans: well-developed, mobile in many reptiles

17. Vision • Snakes, some lizards - no true eyelids • Clear, fused scale (spectacle) • Tear film - between cornea and spectacle in subspectacular space • Tears drain into mouth through nasolacrimal duct system

18. Vision • Most reptiles - poorly developed extraocular muscles • Exception - chameleons; eyes move freely and independently of one another • Chelonians - no nasolacrimal ducts; tears spill over the lid margin

19. Vision • Lacrimal and harderian glands present in most reptiles and amphibians • Produce secretions that combine to form the tear film • Eyelids absent in some aquatic species • Caecilians - eyes covered with skin • Amphibian eyes - often protrude ventrally into the oral cavity when animal swallowing

20. Vision • Ossicles: scleral bones present in most reptiles (except snakes and crocodilians) • Lens: more fluid in reptiles than mammals (more rigid in snakes) • Accommodation • Chelonians - lens is squeezed through the pupil • Snakes - lens moves back and forth due to pressure changes within the aqueous and vitreous humors

21. Vision • Reptiles - avascular retinas • Nutrition and waste removal via choroidal vessels in vitreous • Conus papillaris: in lizards, extends into vitreous from optic disc • provides nutrition and waste removal • Crocodilians have a tapetum • Parietal eye - found in some reptiles • Rudimentary retina and cornea, no iris, lids, or musculature • Exact function unknown • May play a role in light-cycle-mediated hormone function

22. Cardiovascular System • Location of the heart varies • Chelonians - on midline just caudal to thoracic girdle, ventral to the lungs • Most lizards - within thoracic girdle • Crocodilians and some lizards - farther back in the coelomic cavity • Snakes - usually at junction of the first and second third of the body length • Fairly mobile within the coelomic cavity

23. Heart Two atria One ventricle

24. Heart Ventricle Regions Cavum venosum: paired aortic arches, lead to systemic circulation Cavum arteriosum: receives blood from pulmonary veins and directs oxygenated blood to cavum venosum Cavum pulmonale: receives blood from right atrium and directs flow into pulmonary circulation

25. Heart Pressure differences of outflow tracts and muscular ridge that partially separates cavum venosum and cavum pulmonale maintain separation of oxygenated and deoxygenated blood

26. Heart Rate • Depends on species, size, temperature, activity level, and metabolic function • Heart rate = 33.4 × (Weight in kg-0.25) • Lizards - vasovagal reflex induces drop in heart rate, blood pressure, and a catatonic state • Triggered by applying gentle pressure to both eyeballs through closed lids • Lizard recovers with cessation of pressure or mild stimulation

27. Blood Cells Reptilian red blood cells: oval and nucleated RBC life span between 600 and 800 days Immature erythrocytes occasionally seen, especially in juveniles and during ecdysis

28. Blood Cells • Heterophils: round with eosinophilic rod-shaped granules and round to oval nuclei • Analogous to mammalian neutrophils without peroxidase and acid phosphatase • Reptiles produce caseous pus instead of liquid material • Eosinophils: similar appearance to heterophils but granules are round • Basophils: small round cells with deeply basophilic cytoplasmic granules that may obscure the nucleus

29. Blood Cells • Lymphocytes: vary in size; usually round cells with large nuclei, large nuclear-to-cytoplasm ratio, and no cytoplasmic granules • Monocytes: oval or lobed nuclei, blue-grey cytoplasm, may contain small vacuoles or very fine granules • Some reptile monocytes have small azurophilic granules (azurophils) • Thrombocytes: small, oval, nucleated cells; colorless cytoplasm may contain small granules

30. Respiratory System • Reptiles capable of surviving long periods without breathing • Because of large pulmonary volume, reptiles have efficient anaerobic metabolism and cardiac shunting capabilities. • Respiration driven by oxygen levels in blood

31. Respiratory System Glottis of most amphibians and reptiles: rostral portion of oral cavity Glottis very mobile in snakes; protrudes from mouth to allow respiration during ingestion of prey Paired arytenoid cartilages: border glottal opening; open during respiration

32. Respiratory System • No vocal cords • Only vocalizations possible are hissing, grunting, bellowing • Frogs and toads - vocal sacs arise from trachea • Glottal keel present in some species of snakes • Increases volume of vocalizations

33. Pulmonary Tissues • Honeycomb appearance • Openings of honeycomb end at faveoli • Fixed structures surrounded by capillaries • Site of gas exchange • Tracheal rings incomplete (except chelonians)

34. Reptile Lungs • Unicameral lung • Simple, saclike • Cranial portion: site of gas exchange • Caudal portion: avascular, comparable to avian air sac

35. Reptile Lungs • Multicameral lung • Many compartments • Intrapulmonary bronchi

36. Reptile Lungs • Paucicameral Lung • Characteristics of both unicameral and multicameral lungs

37. Reptile Respiratory System No true diaphragms Action of intercostal muscles and parts of axial musculature used for respiration

38. Reptile Respiratory System • Crocodilians - muscular septum caudal to lungs • Cranial aspect of liver is attached to septum • Caudal aspect of liver is attached to pubis by diaphramaticus muscle • Lung inflation results from contraction of diaphramaticus moving the septum caudally

39. Amphibian Respiratory System • Simple saclike lungs • Some salamanders have no lungs • Cutaneous respiration • Pulmonary ventilation results from pumping of buccal cavity and pharynx • Gas exchange can also occur across mucous membranes of buccal cavity, pharynx, and cloaca

40. Hearing • Ears - both sides of head, usually caudal to eyes • Tympanum - may lie in depression and/or be covered by folds of skin (some lizards and crocodilians) • Columella - single bone in middle ear of reptiles • Connects to tympanum and quadrate bone • Transmits vibrations to oval window of cochlea • Converted to nerve impulses and transmitted to the brain via the vestibulocochlear nerve

41. Hearing • Semicircular canals control balance and equilibrium (reptiles) • Snakes - no external ears; columella articulates with quadrate bone • Allows snakes to be very sensitive to ground vibrations transmitted through the mandibles • Snakes also able to hear aerial sounds • Salamanders and caecilians - no tympanic membranes; columella may be degenerate

42. Feeding Strategies Carnivorous, omnivorous and herbivorous reptiles all exist Snakes, crocodilians, and adult amphibians are strict carnivores Some diets are very specialized

43. Oral Cavity • Snakes and lizards: deeply forked tongues • Function as particle delivery system for vomeronasal organ (accessory olfactory organ) • Allow for detection of particle gradients

44. Oral Cavity • Chameleons: specialized projectile tongues designed for capturing prey from long distances • Sticky end which the prey items stick to • Turtles and tortoises: typically thick, fleshy, relatively immobile tongues

45. Oral Cavity • Crocodilians: immobile tongue attached to intermandibular space • Muscular flaps from base of tongue and dorsal pharynx allow for opening of mouth while submerged without ingesting or inhaling water

46. Oral Cavity Tongue used to capture prey (most amphibians) Anurans, most terrestrial salamanders: caudodorsal aspect of tongue is flipped cranioventral to prehend food (lingual flipping)

47. Oral Cavity • Numerous salivary glands • Salivary secretions provide lubrication that aids in ingestion of large prey • Also has enzymatic properties • Venom glands (some snakes, lizards) - modified salivary gland

48. Dentition Turtles and tortoises No teeth Tomia (keratinized beaks) Other reptiles: 3 types of dentition

49. Types of Dentition Thecodont dentition: teeth arise from sockets in skull bones (crocodilians)

50. Types of Dentition Pleurodont dentition: teeth attached to medial aspect of periosteum on mandibles and maxillae (snakes and iguanid lizards)