Amphibians Flashcards
Cutaneous respiration
- capillary beds within the lower epidermis
eg adult salamanders no lungs and gills
frogs rely on 50%
SA to BW ratio important here
Amphibian digit/limb integurment
Has raised/calluses of codified epithelium on digits and limbs during the breeding season
leydig cells in amphibians
secrete product = inhibits bacteria and virus into skin
Frog and salamander glands
mucous and granular glands
mucous = continuous, moist skin + limited pathogen protection
Granular = poison - milky, distasteful secretion (often poisonous int injected in blood of ingested into blood
both glands multicellular
Chromatophores
found in dermis + some in epidermis
aposematic colouration
warning to predators about posion
Dermis attachment in amphibians
In salamanders and caecilians, the dermis is firmly attached to the underlying muscles; however, in frogs and toads there are large lymphatic sinuses between the dermis and epidermis which permit considerable movement of the epidermis relative to the underlying structures.
amphibians respiratory system
most have a buccal pump for getting O2 to the lungs, as modern amphibians have short and often fused ribs.
4 steps of the buccal pump
- With the glottis closed and the nares open, fresh air is sucked into the buccal cavity by expanding the buccal cavity.
- The glottis then opens rapidly and, with nares still open, expired air escapes from the body under pressure from the elastic lungs. Expired air passes across the dorsal aspect of the buccal cavity thus minimising mixing with the fresh air retained in the buccal cavity.
- The nares then close and the floor of the buccal cavity rises, forcing fresh air into the lungs via the open glottis.
- The glottis closes, retaining the air in the lungs, and the nares open again, returning to step 1
this also helps vocalisation
structure of amphibian lungs
partitioned by septa, containing capillaries, these divide the lungs into small compartments called faveoli
how are faveoli different to an alveoli
Inspired air passes from the trachea into a central chamber, from where it diffuses into the faveoli. Thus, faveoli differ from mammalian alveoli in that they open onto a central chamber rather than an airway, as is the case with mammalian alveoli.
Larval stages of amphibians retain gills
may be internal, external, or both as in larval salamanders. Internal gills are ventilated by a pumping action of the buccal cavity (similar to the buccal pump), while external gills are held out in a moving stream of water, or waved around, in order to facilitate gas exchange. Gills are lost at metamorphosis.
amphibian skeleton 5 main adaptions
Vertebrae have articular process which interlock = greater rigidity
pectoral girdle = not fused with skull = cervical vertebrae development
Pelvic girdle goes from one bone to three
Sacral region has developed and articulates
5 digits hind
4 digits fore
Digestive tract amphibians
tongue = muscular + frog stuff
oesophagus = short with ciliated and goblet cells
stomach –> coiled small intestine –> short straight LI
LI = terminates at cloaca
bladder = terminates at cloaca
Amphibian heart
sinus venosus, left and right atria divided by a complete septum
- deep trabeculae = keep two blood streams seperate between oxygenated and deoxygenated
he left atrium receives oxygenated blood from the lungs via the pulmonary vein which empties into the atrium directly. The right atrium receives deoxygenated systemic blood via the sinus venosus
due to two seperate circulations blood pressure in the dorsal aorta of frogs is double that of fish. The development of a lymphatic system is a consequence of this increased blood pressure. Isn’t evolution fascinating?!!
Amphibian Excretory System
wolffian duct (archinephric duct) transport both the kidney waste and testis sperm
some species are advanced enough with there own urinary tract, but the sperm still goes through the wolffian duct.
bladder is formed by ventral diverticulum of the cloaca
curiously, because the Wolffian ducts enter the cloaca dorsally, the urine must cross to the other side of the cloaca to enter the bladder! In more terrestrial species, such as toads, where dehydration is a constant threat, some water may be resorbed from the bladder.
Because many species of amphibians live in freshwater, they are hyperosmotic compared to their environment and so they need to eliminate copious quantities of dilute urine.
most excretion is salts
Amphibian Reproduction
external fertilisation with the female laying eggs and the male laying sperm over the top during amplexus
Alternatively, in salamanders the male produces a spermatophore which consists of a cap of sperm atop a gelatinous stalk which the female picks up using her cloaca.
Amphibians have two ovaries and two oviducts – note that ovaries, unlike testes, do not share excretory ducts with the kidneys. The oviduct is coiled and glandular. Eggs receive a jelly-like coating in the distal oviduct and, in the rare instances where eggs are hatched and develop internally, this takes place in the oviduct.
In some species, sperm may be stored in a pocket of the cloaca called the spermatheca, for deposition at a favourable time.
Amphibian Central nervous system
The spinal cord is circular in cross-section. The brain shows very little development from that seen in the lobe-finned fishes. The lateral line is present in aquatic larvae but is lost in terrestrial adults.
Amphibian Neoteny
Neoteny is the process by which somatic development has slowed relative to sexual development, and so animals become sexually mature and are able to reproduce while still at the larval stage, before having undergone metamorphosis to the adult form.
eg axolotl
A familiar example is the axolotl, or Mexican walking fish, which is the larval form of the tiger salamander (Ambystoma tigrinum). In its larval axolotl form, the tiger salamander lives in cool mountain ponds in the Mexican plateau, where it reproduces and never metamorphoses. However, in the USA, at lower elevations and warmer temperatures, the axolotl metamorphoses to the adult salamander. The difference comes down to the hormone thyroxine which is responsible for amphibian metamorphosis: the cold temperatures in Mexico inhibit the secretion of thyroxine and so the axolotyl never undergoes metamorphosis.
