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20. Amphibian and Reptilian Anatomy and Physiology
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20. Amphibian and Reptilian Anatomy and Physiology

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20. Amphibian and Reptilian Anatomy and Physiology 20. Amphibian and Reptilian Anatomy and Physiology Presentation Transcript

  • Amphibian and Reptilian Anatomy and Physiology
  • 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.
  • Taxonomy
    • Class Reptilia - four orders:
      • Crocodylia (alligators and crocodiles)
      • Squamata (snakes and lizards)
      • Chelonian (turtles and tortoises)
      • Rhyncocephalia (tuataras)
  • Taxonomy
    • Class Amphibia - three orders:
      • Gymnophiona (caecilians)
      • Anura (frogs and toads)
      • Caudata (salamanders and newts)
  • 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)
  • 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
  • Reptile Integument
    • Keratinized skin
      • Alpha keratin - soft, flexible, found in interscalar skin
      • Beta keratin - rigid, found in scales
    • Limited subcutaneous space
  • 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
  • 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
  • Reptile Integument
    • Scale and scute nomenclature - aids in species identification and medical recording
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
    • 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
    Vision
  • 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
  • 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
  • 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
  • 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
  • Heart
    • Two atria
    • One ventricle
  • 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
  • Heart
    • Pressure differences of outflow tracts and muscular ridge that partially separates cavum venosum and cavum pulmonale maintain separation of oxygenated and deoxygenated blood
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • Pulmonary Tissues
    • Honeycomb appearance
    • Openings of honeycomb end at faveoli
      • Fixed structures surrounded by capillaries
      • Site of gas exchange
    • Tracheal rings incomplete (except chelonians)
  • Reptile Lungs
    • Unicameral lung
      • Simple, saclike
      • Cranial portion: site of gas exchange
      • Caudal portion: avascular, comparable to avian air sac
  • Reptile Lungs
    • Multicameral lung
      • Many compartments
      • Intrapulmonary bronchi
  • Reptile Lungs
    • Paucicameral Lung
      • Characteristics of both unicameral and multicameral lungs
  • Reptile Respiratory System
    • No true diaphragms
    • Action of intercostal muscles and parts of axial musculature used for respiration
  • 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
  • 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
  • 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
  • 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
  • Feeding Strategies
    • Carnivorous, omnivorous and herbivorous reptiles all exist
    • Snakes, crocodilians, and adult amphibians are strict carnivores
    • Some diets are very specialized
  • 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
  • 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
  • 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
  • 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)
  • 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
  • Dentition
    • Turtles and tortoises
    • No teeth
    • Tomia (keratinized beaks)
    • Other reptiles: 3 types of dentition
  • Types of Dentition
    • Thecodont dentition: teeth arise from sockets in skull bones (crocodilians)
    • Pleurodont dentition: teeth attached to medial aspect of periosteum on mandibles and maxillae (snakes and iguanid lizards)
    Types of Dentition
  • Types of Dentition
    • Acrodont dentition: teeth fused to biting edge of mandible and maxillae (some lizards)
  • Dentition
    • Snakes have 6 rows of teeth: two mandibular, two maxillary, two on palantine/pterygoid bones
    • Aglyphous snakes lack fangs
  • Dentition
    • Venomous snakes - specialized dentition for venom delivery
    • Proteroglyphous and opisthoglyphous - fangs are fixed upright
    • Solenoglyphous - fangs are folded on roof of mouth when mouth is closed and are erect when snake bites
  • Dentition
    • Venom-delivering teeth: hollow with an opening near end where venom expelled
    • Fangs receive venom through a duct from venom gland at its base
    • Contraction of muscles around venom gland forces venom out through the fang
    • Snakes can control amount of venom delivered with each bite
  • Dentition
    • Most amphibians have teeth
    • Caecilians and salamanders - both maxillary and mandibular teeth
      • Palatal teeth in some species
    • Maxillary dentition present in some anuran species
    • Odontoid process: cutting plates on rostral mandibles of some frogs
  • Esophagus
    • Reptile - thin and distensible
      • Unique morphology reflects type of prey
    • Amphibian esophagus very short and wide, especially in anurans
  • Stomach
    • Reptile - variable size and shape
      • Snakes - highly distensible
      • Crocodilians - thick muscle comparable to avian gizzard
    • Amphibian - anurans capable of prolapsing stomach through the mouth; gastric prolapse is a terminal event in dying animals
  • Amphibian Intestinal Tract
    • Indistinct regions
    • Liver may contain melanomacrophages involved in immune function
    • Pancreas - between stomach and proximal segments of intestine
  • Reptilian Intestinal Tract
    • Varies according to diet
      • Herbivores - longer intestinal tracts than carnivores
    • Snakes - relatively straight intestinal tracts
  • Reptilian Intestinal Tract
    • Colon - large and complex in herbivores
      • Hindgut fermentation for digestion
    • Cecae - site of hindgut fermentation in herbivorous lizards and chelonians
    • Liver - usually large and bi-lobed
  • Cloaca
    • Common outflow tract for GI and urogenital tracts (all reptiles and amphibians)
    • Three chambers: coprodeum, urodeum and proctodeum
  • Reptile Kidney
    • Usually oblong and smooth-surfaced
    • Snakes - kidneys that are lobulated
    • Ureters empty into dorsolateral aspects of the urodeum
      • Some species do not have urinary bladders
  • Reptile Kidney
    • No distinct renal pelvis
    • Distal collecting tubules join into collecting ducts that merge to form the ureter
    • No loop of Henle present
    • Not able to concentrate urine as mammals do
    • Water can be absorbed from urine through wall of the urinary bladder, rectum, or cloaca
  • Amphibian Kidney
    • Nephrostomes - connect the coelomic cavity to the renal tubules; filter blood and coelomic fluid
    • Kidneys usually lobulated and in caudodorsal coelomic cavity
  • Amphibian Kidney
    • Some amphibians excrete ammonia as a nitrogenous waste product; others excrete urea, some excrete uric acid
    • No ability to concentrate urine
    • Urinary bladders and cloacal anatomy similar to reptiles
  • Reptile Reproductive System
    • Males have internal testes located in dorsal coelomic cavity
    • Ductus deferens leads from testes to dorsal wall of the urodeum
    • Most also have a sexual portion to the kidney tubules
      • Develops in response to high levels of circulating sex hormones
      • Probably provide secretions that contribute to the seminal fluid
  • Reptile Reproductive System
    • Copulatory organs vary in structure
      • Crocodilians and chelonians - phallus of erectile tissue rising from
      • floor of cloaca
      • Snakes and lizards - paired hemipenes everted from the tail base through the vent
  • Reptile Reproductive System
    • Females - paired ovaries in dorsal coelomic cavity
    • Paired oviducts lead to cloaca and end at genital papillae in dorsal wall of the urodeum
  • Reptile Reproductive System
    • Oviducts - 5 regions: infundibulum, magnum, isthmus, uterus, and vagina
    • Albumin and shell - in oviparous species, added to ova in the oviduct prior to egg laying
    • In viviparous species, fetuses are retained in uterine portion of oviduct
  • Reptile Reproductive Cycle
    • Vitellogenesis - development and maturation of the follicles
      • Triggered by environmental cues that stimulate release of FSH and estrogen
    • Vitellogenin - lipid substance added to yolk within developing follicle
      • Large amounts of calcium are also added
    • In viviparous reptiles - some support of fetus
      • Some lizards have true placentas
  • Reptile Reproductive Cycle
    • Oviposition - many reptiles dig nests to lay eggs
      • Without suitable nesting material, female may experience dystocia
    • Chelonians and lizard species may excavate deep holes to deposit eggs
  • Reptile Reproductive Cycle
    • After oviposition or parturition, reptiles not involved with care of eggs or offspring
      • Exceptions - crocodilians protect their nests and young for a period of time following hatching
      • Pythons and cobras - protect their nests until hatching
  • Egg Incubation
    • Development and hatching requires proper temperature, humidity, and gas composition of nest
    • Incubation time and temperature varies
    • Reptile eggs should not be rotated during incubation
  • Sex Determination in Reptiles
    • Determined by genotype or temperature at which eggs are incubated
    • Sex chromosomes:
      • Females are heterozygous (ZW) and males are homozygous (ZZ)
  • Sex Determination in Reptiles
    • Some species do not have sex chromosomes
      • Higher incubation temperatures produce males in crocodilians and lizards
      • Opposite occurs in chelonians
      • Temperature range within the nest allows for production of a mixed clutch of hatchlings
  • Secondary Sex Characteristics
    • Snakes - no real sexual dimorphism
    • In some species, pelvic spurs can be larger in males
      • Pelvic spurs: remnants of pelvic limbs; provide tactile stimulation to females
  • Secondary Sex Characteristics
    • Male chelonians may have concave plastron and more distally located vent
      • Allows closer apposition of the cloacas when the male mounts the female
    • Some lizards show obvious dimorphism
      • Example: male Jackson’s chameleon has three well-developed horns on its face
  • Amphibian Reproduction
    • Sexual dimorphism in some species
      • Poison dart frog males have enlarged toe pads
      • Large tympanic membranes in some male anurans
      • Prominent cloacal glands in male salamanders
  • Amphibian Reproduction
    • Paired gonads in dorsocaudal coelomic cavity
    • Bidder’s organs - ovarian remnants near testes in male toads
    • Most caecilians are viviparous
    • Most anurans and salamanders are oviparous
    • Amplexus - Male frogs and toads fertilize eggs as they are laid while grasping the female
  • Amphibian Reproduction
    • Phallodeum - portion of cloaca in caecilians that is everted to deposit semen into female’s cloaca
    • Spermatophores - packets of sperm deposited onto substrate by male salamanders
      • Picked up by the female salamander’s cloaca
      • Spermatotheca - pocket in cloaca of female salamanders where sperm can be stored
  • Amphibian Reproduction
    • Eggs are usually deposited in or near water
    • Some parental care of eggs and/or young in anurans and most salamanders
    • Larval anurans (tadpoles) have completely aquatic lives prior to metamorphosis
    • Tadpole metamorphosis - usually complete within 90 days
      • Metamorphosis is stimulated by thyroid hormones
  • Endocrine System
    • Single thyroid gland (except lizard)
      • Crocodilians - bilobed thyroid has a thin isthmus between lobes
    • Size of thyroid gland varies according to season and metabolic state
    • Parathyroid glands and ultimobrachial bodies in cervical region
  • Endocrine System
    • Adrenal glands - usually within the ligaments that suspend the gonads
    • Produce epinephrine, norepinephrine, aldosterone, and corticosterone
    • No distinct separation of adrenal cortex and medulla
    • Exact location of endocrine organs in amphibians varies
  • Reptile Nervous System
    • Three major divisions of reptilian brain
      • Forebrain - olfactory lobes, cerebral hemispheres, diencephalon
      • Midbrain - optic lobes, cerebral peduncles, nerve fibers connecting forebrain and hindbrain
      • Hindbrain - cerebellum, medulla oblongata
    • No surface gyri or sulci on the brain
  • Reptile Nervous System
    • Brain meninges: pia-arachnoid layer and dura mater
    • 12 cranial nerves
    • Depend on spinal segmental reflexes and locomotor centers for control of movement
  • Amphibian Nervous System
    • Brain - well developed for basic functions (sight, olfaction, and movement)
    • 10 cranial nerves
    • Spinal cord extends to the tip of the tail in amphibians and caecilians; ends in lumbar region in frogs and toads
    • Animal dependent upon spinal segmental reflexes to control movement
  • Reptile Musculoskeletal System
    • Types of skulls
    • Anapsid: no temporal openings; chelonians
    • Diapsid: temporal openings in the skull
  • Reptile Musculoskeletal System
    • Snake skulls -extremely mobile
    • Mandibular symphysis is connected by ligaments that allow jaws to move independently of each other
  • Snake Skulls
    • Mandibular symphysis connected by ligaments allows jaws to move independently
    • Quadrate bones - allow wider opening of mouth
    • Moveable bones of maxillae and palate
  • Reptile Musculoskeletal System
    • Spine - extremely flexible; presacral, sacral, and caudal-vertebral regions
    • Single occipital condyle forms the articulation between skull and spine
    • Well-developed ribs
      • Exceptions: chelonians’ spine and ribs are fused to the bony shell
  • Amphibian Musculoskeletal System
    • Skulls of anurans - broad and fenestrated
    • Parts of the skull involved with olfaction and hearing are well developed
    • Palate - poorly developed with reduced dentition
    • Caecilians - compact, well-ossified skulls with well-developed dentition
  • Amphibian Musculoskeletal System
    • Highly variable number of vertebrae
    • Vertebrae - no distinctions of regions
      • Salamanders and anurans also possess sacral vertebrae
    • Anurans’ vertebrae are fused
      • Urostyle - last caudal vertebra
    • Caecilians lack a sternum
    • Sternum is a small cartilaginous plate in salamanders
  • Axial Skeleton
    • Tail autonomy - defensive mechanism
      • Some lizards and salamanders
      • Discarded tail usually continues to wiggle and distract predator
    • The species capable of tail autonomy have “fracture planes” along which tails break
      • Little to no blood loss
    • Lost tail can regenerate; regenerated tail stiff and cartilaginous
  • Reptile Appendicular Skeleton
    • Pectoral girdle - scapula and coracoid bone with muscular attachments to the body
    • Pectoral limbs - humerus, radius, ulna, carpal bones, metacarpal bones, and phalanges
    • Pelvic limb - femur, tibia, tarsal and metatarsal bones, and the phalanges
      • Usually five digits on both front and rear feet
  • Reptile Appendicular Skeleton
    • Spurs - vestigial pelvic limbs of some snake species
      • Found on either side of the vent
      • Used in courtship behavior
    • Some lizards have very reduced limbs
      • “ Legless lizards” retain vestigial thoracic and pelvic limb structures
  • Amphibian Appendicular Skeleton
    • Pectoral girdle - primarily cartilaginous; consists of precoracoid, coracoid and scapula
      • Exception - anurans’ pectoral girdle is completely ossified and consists of scapula, clavicle, and coracoid
    • Pectoral limb - similar to reptile, except for radioulna (fused radius and ulna in anurans)
      • Four toes usually present on the pectoral limbs
    • Pelvic girdle - ilium, ischium and pubis
  • Amphibian Appendicular Skeleton
    • Pelvic limb - elongated and well developed for swimming and jumping
      • Elongated metatarsal bones in anurans
      • Usually five toes are present
  • Muscular Structure
    • In four-limbed amphibians and reptiles, musculature is somewhat analogous to that of mammals.
    • Snakes: epaxial muscles and segmental muscles