Amphibians

Question 1

Cutaneous respiration

Answer 1

• capillary beds within the lower epidermis
  eg adult salamanders no lungs and gills
  frogs rely on 50%
  SA to BW ratio important here

Question 2

Amphibian digit/limb integurment

Answer 2

Has raised/calluses of codified epithelium on digits and limbs during the breeding season

Question 3

leydig cells in amphibians

Answer 3

secrete product = inhibits bacteria and virus into skin

Question 4

Frog and salamander glands

Answer 4

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

Question 5

Chromatophores

Answer 5

found in dermis + some in epidermis

Question 6

aposematic colouration

Answer 6

warning to predators about posion

Question 7

Dermis attachment in amphibians

Answer 7

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.

Question 8

amphibians respiratory system

Answer 8

most have a buccal pump for getting O2 to the lungs, as modern amphibians have short and often fused ribs.

Question 9

4 steps of the buccal pump

Answer 9

1. With the glottis closed and the nares open, fresh air is sucked into the buccal cavity by expanding the buccal cavity.
2. 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.
3. The nares then close and the floor of the buccal cavity rises, forcing fresh air into the lungs via the open glottis.
4. The glottis closes, retaining the air in the lungs, and the nares open again, returning to step 1

this also helps vocalisation

Question 10

structure of amphibian lungs

Answer 10

partitioned by septa, containing capillaries, these divide the lungs into small compartments called faveoli

Question 11

how are faveoli different to an alveoli

Answer 11

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.

Question 12

Larval stages of amphibians retain gills

Answer 12

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.

Question 13

amphibian skeleton 5 main adaptions

Answer 13

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

Question 14

Digestive tract amphibians

Answer 14

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

Question 15

Amphibian heart

Answer 15

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?!!

Question 16

Amphibian Excretory System

Answer 16

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

Question 17

Amphibian Reproduction

Answer 17

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.

Question 18

Amphibian Central nervous system

Answer 18

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.

Question 19

Amphibian Neoteny

Answer 19

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.