Anfibios 2


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Anfibios 2

  1. 1. Phylum Chordata: Class Amphibia & Class Reptilia 17.1Lab #17 -- Biological Sciences 102 – Animal BiologyEvolution of AmphibiansThe evolution of characteristics that allow animals to survive in a variety of terrestrialhabitats will be an important topic for the remaining vertebrate groups we will discuss.Amphibians were the first tetrapods to evolve from fish ancestors during thelate Devonian period, some 360-370 million years ago. The nameamphibian, suits its nature - being derived from the Greek amphibiosmeaning "a double life". Despite this distinction, however, some species areconfined to the land, while other species have a completely aquatic existenceAmphibians most likely evolved from either the lobe-fin fishes(Crossopterygii) or the lungfishes (Dipnoi) of the Early Devonian Period(lasting from 408 to 387 million years ago). These fishes had an advantageover other fishes by the fact that they had lungs. In time of shortage ofwater, these fishes probably came out of the pools which were drying out ontheir muscular fins to search for other water. They might have added insectsand other small arthropods to their diet while moving and over time becameless dependent on water. A caecilian fossil from the Paleocene Epoch (66.4to 57.8 million years ago) has been found in Brazil.In water, there is little problem with support. However, on land, supportstructures must be modified to allow adequate support of the body, to prevent lungs fromcollapsing under the weight of the body, and to permit locomotion.The first land animals included the labyrinthodont amphibians, in which the pectoral andpelvic fins were modified into short, powerful legs. The vertebral column was strengthened bythe development of interlocking processes and the replacement of the notochord by bonyringlike vertebrae.Gills were replaced by lungs, which evolved from the swim bladder, an organ to controlbuoyancy. Tear glands prevent drying of eyes. The terrestrial ear may have evolved fromportions of the lateral line structure of fish.The oldest known land vertebrates, the ichthyostegids, retained a tail fin and a lateral linesystem, suggesting that they spent most of their time in water.Fifty million years after the first appearance of amphibians, a major breakthrough invertebrateevolution occurred: a group of small labyrinthodont amphibians evolved the ability to lay theireggs on dry land, away from water. The early reptiles developed a lighter, more flexible bodycovering consisting of the protein keratin, rather than the bony scales of their amphibian andfish ancestors.Although a few amphibian species live their lives in water, most live a portion of their lifecycleon land. They are distributed worldwide, but the majority is found in the tropical regions of theEarth. Most amphibians have an aquatic larval, or tadpole, stage that metamorphoses into anadult.Only one of the 3 major groups of ancient amphibians evolved into the modern salamanders,frogs, toads, and caecilians. Today amphibians have invaded almost every environment wherefresh water is available for some period of time. Some toads survive in deserts in undergroundburrows and only emerge during the occasional monsoon rains that fill temporary ponds.ÇPhylum Chordata: Class Amphibia & Class Reptilia 17.2Lab #17 -- Biological Sciences 102 – Animal BiologyAmphibians have many unique characteristics that distinguish them from othervertebrate classes. Amphibian skin is glandular and lacks scales, feathers, or hairs. The
  2. 2. skin is also permeable allowing for water and gas exchange. This restricts amphibianactivity to wet and/or humid conditions, but this trait also allows amphibians to respireand absorb water through the skin from the surrounding environment. This is only oneof the methods of amphibian breathing. Respiration is also accomplished by the use oflungs, gills, and buccal pumping, where the animals swallow air and force it into thelungs (frogs are positive pressure breathers). The amphibian egg is also a distinctivefeature. It is shell-less and lacks the embryonic membranes of the amniotic egg of theother tetraopod classes, therefore development is restricted to a moist environment.Go to the following websites for more information about Acanthostega and Ichthyostegawhichare two different intermediate fossil forms between fish and amphibians.: of AmphibiansClass AmphibiaOrder Gymnophiona (jimno-fyo-na) (Gr. gym nos, naked, +ophioneos, of a snake) (Apoda): caecilians. Body elongate;limbs and limb girdle absent; mesodermal scales present inskin of some; tail short or absent; 95 to 285 vertebrae;pantropical, 5 families, 33 genera, approximately 160species.Order Urodela (yuruh-deluh) (Gr. oura, tail+ delos, evident) (Caudata): salamanders.Body with head, trunk, and tail; no scales;usually two pairs of equal limbs; 10 to 60vertebrae; predominantly holarctic; 10 livingfamilies, 61 genera, approximately 500species.Order Anura (uh-nuruh) (Gr. an, without, + oura, tail)(Salientia): frogs, toads. Head and trunk fused; no tail; noscales; two pairs of limbs; large mouth; lungs; 6 to 10vertebrae induding urostyle (coccyx); cosmopolitan,predominantly tropical; 29 families; 352 genera;approximately 4840 species. Phylum Chordata: Class Amphibia & Class Reptilia 17.3Lab #17 -- Biological Sciences 102 – Animal BiologyClassification of ReptilesClass ReptiliaSubclass Anapsida (a-napse-duh) (Gr. an, without, + apsis, arch): anapsids. Amniotes havingsome primitive features, such as a skull with no temporal opening.Order Testudines (tes-tudin-eez) (L. testudo, tortoise) (Chelonia): turtles. Body in a bonycase of dorsal carapace and ventral plastron; jaws with keratinized beaks instead of teeth;vertebrae and ribs fused to overlying carapace; tongue not extensible; neck usuallyretractable; approximately 300 species.Subclass Diapsida (di-apse-duh) (Gr. di, double, + apsis, arch): diapsids. Amniotes having askull with two temporal openings.Superorder Lepidosauria (lep-i-do-sor ee-uh) (Gr. lepidos, scale, + sauros, lizard). Diapsidlineage appearing in the Triassic; characterized by sprawling posture; no bipedalspecializations; diapsid skull often modified by loss of one or both temporal arches;transverse cloacal slit, skin shed in one piece.Order Squamata (skwa-mata) (L. squamatus, scaly, + ata, characterized by): snakes,lizards, amphisbaenians. Skin of horny epidermal scales or plates, which is shed;
  3. 3. quadrate movable; skull kinetic (except amphisbaenians); vertebrae usually concave infront; paired copulatory organs.Suborder Lacertilia (lay-sur-till ee-uh) (L. lacerta, lizard) (Sauria): lizards. Bodyslender, usually with four limbs; rami of lower jaw fused; eyelids movable; external earpresent; this paraphyletic suborder contains approximately 4600 species.Suborder Amphisbaenia (amfis-beenee-a) (L. amphis, double, + baina, to walk): wormlizards. Body elongate and of nearly uniform diameter; no legs (except one genus withshort front legs); skull bones interlocked for burrowing (not kinetic); limb girdlesvestigial; eyes hidden beneath skin; only one lung; approximately 160 species.Suborder Serpentes (sur-pentes) (L. serpere, to creep): snakes. Body elongate; limbs,ear openings, and middle ear absent; mandibles joined anteriorly by ligaments; eyelidsfused into transparent spectacle; tongue forked and protrusible; left lung reduced orabsent; approximately 2900 species.Order Sphenodonta (sfeno-dontuh) (Gr. sphen, wedge, + odontos, tooth): tuatara(Rhynchocephalia). Primitive diapsid skull; vertebrae biconcave; quadrate immovable;parietal eye present; two extant species in the genus SphenodonPhylum Chordata: Class Amphibia & Class Reptilia 17.4Lab #17 -- Biological Sciences 102 – Animal BiologyLAB PROCEDURENAME: LAB SCORE:You must answer ALL questions in the lab procedure for full credit.Finish them at home if you do not have time to complete them in lab.What is a tetrapod?Refer to textbook and Internet for diagrams, illustrations and reference text for this lab.Specifically, pay close attention to the frog dissection photos on the course website.Answer the following questions using supplementary lab atlas, textbook, instructorfeedback, the Internet and collective discussions with your classmates.Class Amphibia: Frogs, Toads, Salamanders and Caecilians¾ In the space below, briefly describe some important characteristics of this Class ofvertebrates.Your instructor will briefly review with you the basic lifecycle of a typical frog.¾ List a few characteristics that differentiate frogs from toads.¾ With regard to the musculoskeletal system, how does a salamander differ from a frog?¾ Which order of amphibians is most diverse? Provide an hypothesis for why this group isthe most diverse order? Phylum Chordata: Class Amphibia & Class Reptilia 17.5Lab #17 -- Biological Sciences 102 – Animal BiologyFROG DISSECTIONClass Amphibia Order Anura (Salientia) Family Ranidae Genus Rana (or similar genus)AFTER YOU HAVE COMPLETED THE CARDIAC PHYSIOLOGY PORTION OF THELAB ON PAGES 17.10 TO 17.13 THEN YOU MAY COMPLETE THE DISSECTIONTO OBSERVE THE STRUCTURES LISTED BELOW. All students at each lab tableshould observe one live frog. You need not write out your observations, but youshould think about the importance of the various frog adaptations you observe.Your instructor will double-pith a frog for your dissection which you will do ingroups of 3 or 4 students.
  4. 4. External Structures (entire frog)¾ head¾ trunk¾ sacral hump¾ cloacal opening¾ forelimbs (how many digits on each forefoot/hand?)¾ hindlimbs (how many digits on each hindfoot?)¾ eyes¾ nictating membrane¾ tympanic membrane¾ external naris (nares)Skeletal Structures(on frog skeleton and diagram in lab)¾ skull¾ axial skeleton¾ appendicular skeleton¾ nasal fossa¾ orbital fossa¾ auditory capsule¾ maxilla¾ dentary(middle portion of each side of the mandible)¾ vertebrae (ending in urostyle)¾ suprascapula and scapula¾ clavicle¾ humerus¾ radioulna¾ carpals¾ metacarpals¾ pelvis (urostyle, ischium and ilia;pubis is difficult to see)¾ femur¾ tibiofibula¾ calcaneus (with astragalus = tarsals)¾ metatarsals¾ phalanges (on all forefeet and hindfeet) Phylum Chordata: Class Amphibia & Class Reptilia17.6Lab #17 -- Biological Sciences 102 – Animal BiologyMuscles (see lab diagrams - can be removed from the frog once identified)¾ pectoralis major (ventral chest)¾ rectus abdominis (ventral abdomen)¾ external oblique (abdomen)¾ sartorius (ventral thigh)¾ gracilis major (ventral thigh)¾ adductor magnus (ventral thigh)¾ gastrocnemius (leg/shank) & Achilles tendon¾ latissimus dorsi (dorsal thorax)¾ triceps femoris (dorsal thigh)¾ biceps femoris (dorsal thigh)Head - Internal Structures¾ internal naris (nares)¾ teeth
  5. 5. ¾ tongue¾ opening to esophagusThoracic & Abdominal Organs – Internal Structures¾ liver¾ gallbladder¾ stomach¾ small intestines (supported by mesenteries)¾ large intestine¾ pancreas (as visible)¾ spleen (as visible)¾ mesonephric kidneys¾ urinary bladder¾ cloaca¾ gonads (ovary or testes)¾ oviducts (female)¾ lungs¾ heart¾ pericardial sac (around heart)¾ atria of heart¾ ventricle of heart¾ dorsal aorta (as visible)¾ posterior vena cava (as visible)¾ remove heart to view sinus venosus and interior of heart chambersPhylum Chordata: Class Amphibia & Class Reptilia 17.10Lab #17 -- Biological Sciences 102 – Animal Biology¾ VERTEBRATE CARDIAC PHYSIOLOGYThe heart undergoes a constant cycle of contractions and relaxations called the cardiac cycle.The period of ventricular contraction is called systole, while the period of ventricular relaxationis called diastole. Diastole begins as the ventricles start to relax. Soon the pressures within theaorta and pulmonary artery exceed ventricular pressures, causing the semilunar valves toclose. As the ventricular pressure falls below the atrial pressure the AV valves open and theventricles fill with blood. The ventricles fill to about 80% of capacity prior to contraction of theatria, the last event in diastole. As the ventricles start to contract, the ventricular pressuresoon exceeds the atrial pressure, causing the AV valves to close. As the ventricles continue tocontract, the ventricular pressure exceeds the arterial pressures causing the semilunar valvesto open. Blood is forcefully ejected out of the ventricles and into the aorta and pulmonaryartery.The heart is autorhythmic, meaning it generates its own rhythmic action potentialsindependent of the nervous system. The rhythmic beating of the heart is controlled by a smallgroup of cells in the wall of the right atrium, collectively called the sinoatrial node (SA node).Since the SA node controls heart rate, it is called the pacemaker of the heart. The electricalimpulse that arises in the SA node travels through gap junctions to the atrial myocardiumand then to the atrioventricular (AV) node. The impulse is delayed slightly in the AV node (AVnodal delay) before traveling into the bundle of His. The impulse then travels through thebundle branches, into the purkinje fibers and terminates in the ventricular myocardiumwhere it stimulates muscle contraction. The specialized structures that conduct the electricalimpulse through the heart are collectively called the conduction system.¾ Draw a diagram of the conduction system within the heart and label its parts.Phylum Chordata: Class Amphibia & Class Reptilia 17.11
  6. 6. Lab #17 -- Biological Sciences 102 – Animal Biology¾ Drugs that Effect the Vertebrate HeartBoth branches of the autonomic nervous system enervate the SA node and modify its activity.Sympathetic input (norepinephrine and epinephrine) increases heart rate, whileparasympathetic input (acetylcholine) decreases heart rate. Also, certain drugs can alter therate and strength of cardiac contraction. In today’s experiment you will record a frog’s cardiaccycle on the Biopac equipment using an exposed frog heart. You will also test the effects of thefollowing drugs on heart rate.Epinephrine: Epinephrine is a hormone secreted by the adrenal medulla. Epinephrine worksin concert with norepinephrine (a neurotransmitter secreted by the sympathetic nervoussystem) to increase both the strength and rate of cardiac contractions.Pilocarpine: Pilocarpine stimulates the release of acetylcholine from parasympathetic neuronsthat innervate the SA node, thus causing a decrease in heart rateAcetylcholine: Acetylcholine is a neurotransmitter secreted by the parasympathetic nervoussystem at the SA node of the heart. It causes a decrease in cardiac rate.Atropine: Atropine is a competitive inhibitor of acetylcholine. Atropine outcompetesacetylcholine for binding to the acetylcholine receptor. Atropine blocks the effects ofacetylcholine, thus inhibiting the parasympathetic activity of the heart.Eserine: Eserine is an inhibitor of Acetylcholinesterase, the enzyme responsible for thebreakdown of acetylcholine in the synaptic cleft of the neuromuscular junction.Potassium Chloride (KCl): The initiation and propagation of action potentials in the heart isdependent, in part, on the steep K+ concentration gradient between the ICF and ECF (higherconcentration of K+ on the inside of the cell than on the outside). An increase in extracellularK+ above normal (hyperkalemia) disrupts this gradient, causing a decrease in heart rate andcontractility. In extreme hyperkalemia, the conduction rate of action potentials may be sodepressed that ectopic pacemakers appear in the ventricles and fibrillation may develop, oftenwith fatal results