Reptiles Flashcards
Describe reptiles as ectotherms.
Reptiles do not generate their own heat for maintaining core body temperature. They rely on environmental sources of heat – radiant heat from basking in the sun in heliothermy or heat gain from hotter surroundings by direct conduction in thigmothermy or by radiated heat.
When is gular fluttering used?
If reptiles get too hot they can potentially move away from sources of heat but if the whole environment is hotter than they are, the only way they can dissipate heat is via evaporate cooling via gular fluttering.
What is gular fluttering?
This is where they rapidly move air in and out via throat fluttering movements to evaporate water from the oral cavity and upper airway.
Give an example of how reptiles can regulate body temperature using behavioural and physiological mechanisms.
Vasodilation of cutaneous blood vessels during basking enables them to heat up quickly and cutaneous vasoconstriction as the environment cools conserves body heat so that they cool down slowly.
Give an example of how ectothermy limits activity in space and time.
The leopard gecko can be active at night in hot tropical environments but would not be able to be nocturnal in cooler temperate environments, particularly during colder winter seasons.
Distinguish sternothermal and eurythermal.
Some reptiles are stenothermal, they can survive over a narrow temperature range.
Other reptiles are eurythermal, they can survive over a wide temperature range.
Describe a reptile’s preferred optimal temperature zone.
- Species specific and is the temperature range for optimum function of body processes.
- Can survive at temperatures just outside their POTZ but they will be stressed and so less likely to reproduce and are more prone to infection.
- POTZ will also depend activity like digestion or spermatogenesis.
- If suffering infection, reptiles can show a behavioural fever where they actively seek extra heat at the upper end of their POTZ.
What is the impact of ectothermy on metabolic rate?
Considerably lower (1 5th or 7th) than a comparably sized mammal. Will depend on body temperature and will increase by up to 17 times during digestion.
- So more adapted to anaerobic, glycolytic metabolism with less dependence on aerobic, oxidative metabolism.
- But does not mean reptiles are slow, as the strongest and fastest muscle fibres have the highest glycolytic and lowest aerobic capacity.
- But are not able to sustain maximal exercise rate for long and will fatigue more rapidly than mammals.
What allows reptiles to thrive in poorly productive environments?
One day’s food for a small avian insectivore could last a comparable reptilian insectivore 35 days. Sit and wait predators such as pythons, may only eat once a month.
Describe the efficiency of the reptilian respiratory system.
- Less efficient than mammalian
- Despite a relatively large lung volume, reptiles have a respiratory exchange surface area of only 1% of that of a comparable mammal.
- But does not need to be very efficient as the lower metabolic rate results in a lower oxygen requirement
Describe reptilian respiration.
- Triphasic breathing with expiration, inspiration and breath-holding phases, which can make it problematic administering gaseous anaesthetics.
- Ventilation rate is matched to oxygen requirements and as temperature is a major factor determining metabolic rate.
- Similarly to mammals, ventilation rate is also increased by high PaCo2 and low PaO2.
Describe a respiratory adaptation in chelonia.
Some chelonians can further increase their time spent submerged by absorbing oxygen via their skin, pharyngeal mucosa a even their cloaca.
How do crocodiles differ from other reptiles?
In having a completely separated 4 chambered heart. But most reptiles have a 3 chambered heart with separate atria and a ventricle that is incompletely divided by septa.
Describe mixing of blood in the reptilian heart.
- Despite having a single ventricle, a combination of the timing of contractions, the valve-like action of the septa and the momentum of the blood ensures that there is normally relatively little mixing of oxygenated and deoxygenated blood in the heart.
- A bit of mixing of oxygenated and deoxygenated blood is not such an issue in a reptile with lower oxygen requirements compared to a mammal.
What is shunting and how is this controlled in reptiles?
- 3 chambered heart is adapted to allow shunting of blood between systemic and pulmonary circulations, which is not possible in the separated mammalian CVS system.
- This shunting is not something that is determined by control of the heart, but rather by control of the relative resistances of the systemic and pulmonary circulations.
Describe how vasodilation and vasoconstriction are used to regulate reptilian body temperature.
Cutaneous vasodilation in warming up: decreases resistance of the systemic circulation. Shifts the balance of blood flow towards the lower resistance systemic circuit to the skin and less to the lungs. This is fine as the reptile is not exercising and has a lower oxygen requirement.
Cutaneous vasoconstriction in cooling down: increases resistance of the systemic circulation and more blood flows through the lungs to meet increased oxygen requirements of the higher metabolic rate.
Describe water homeostasis in the reptilian kidneys.
- Lack a loop of Henle and are unable to concentrate urine greater than isosmotic.
- 30-50% is reabsorbed by the proximal tubule, but urine still represents a major potential route for water loss.
- Posterior pituitary produces a structurally similar neuropeptide called arginine vasotocin (not mammalian ADH).
- Does not affect water permeability of the collecting ducts, but does have a water conserving role by constricting the afferent renal arteriole and therefore decreasing glomerular filtration rate.
Describe nitrogenous excretion in reptiles.
- Unable to maintain the excretion of nitrogenous waste despite a reduction in glomerular filtration rate, as only a small proportion of nitrogenous waste is excreted by glomerular filtration.
- Major route is via secretion of uric acid/urates from the peritubular capillary network into the renal tubule.
- This is independent of glomerular filtration rate as blood is supplied by the renal portal vein.
When can water be lost in reptiles?
- Keratin layer of their dry skin coupled with the underlying mesos lipid layer restricts water loss through the skin.
- But this barrier function is lost during ecdysis/skin shedding, which can dramatically increase water loss.
How does water conservation occur?
- Aided by excreting nitrogenous waste as uric acid in terrestrial species, which requires less water than excretion in the form of urea.
- Further water reabsorption can occur by reflux of urine from the uroderm of the cloaca back into the colon by reverse peristalsis.
- Most reptiles do not have a urinary bladder to store urine, but there is evidence of reabsorption from the urinary bladder in chelonians and some lizard species that possess one.
How do desert reptiles decrease water loss?
Desert adapted reptiles may estivate/summer hibernation in their burrows during the intense heat of summer months to decrease water loss.
How do marine, desert and some herbivorous reptiles regulate salt content?
Have an extra renal salt gland that can excrete a salt load to maintain osmotic and ionic balance (except tortoises).
Describe reptilian genomics.
Genotypic determination is chromosomally based, but like birds and unlike reptiles, the female is heterogametic sex with ZW sex chromosomes and the male is homogametic sex with ZZ sex chromosomes.
But, temperature of incubation can alter sex ratios in many reptile species.
What is an environmental factor affecting reproduction in reptiles?
As in mammals and birds, reproductive activity and females is affected by photoperiod, often triggered by increasing day length, as well as being influenced by having sufficient energy reserves, but unlike mammals and birds, environmental temperature is also a significant factor triggering breeding.
What is a main difference between reptilian and mammalian male reproductive tracts?
Unlike mammals, the male reproductive tract does not have accessory glands and instead, part of the renal tube called the sexual segment secretes a fluid with a similar role to seminal fluid, which is mixed with spermatozoa in the cloaca.
What is a main difference between reptilian and mammalian female reproductive tracts?
But unlike mammals and like birds, there is a significant sperm storage in the female reproductive tract and sperm can remain viable for years in some species.
Which reptiles reproduce asexually?
- A few species of snake and a few of reptiles, including Komodo dragons, can switch between sexual reproduction and reproducing asexually, without fertilisation, which is known as parthenogenesis.
- A few reptile species including some geckos only reproduce asexually.
Describe oviparity in reptiles.
- Typically lay a clutch of eggs at once.
- Crocodilians and some turtle and geckos lay hard-shelled eggs, but most reptiles have softer, less calcified eggs.
- Resist water loss, while allowing exchange of O2 and CO2.
- Oestrogen stimulates yolk lipoprotein production by the liver via vitellogenesis.
- Oestrogen mobilises calcium ion from bone for shell calcification.
Describe behaviour surrounding oviposition.
- Most reptiles abandon their eggs after laying them, but a few species of snake, especially pythons show maternal care by brooding tehri clutch of eggs.
- Bask in the sun to increase their body temperature and then return to their clutch and coil around the eggs to incubate them.
- This behaviour also reduces water loss, albeit at the expense of decreasing rate of gas exchange.
- Many python species generate heat by shivering. This shivering thermogenesis can increase the clutch temperature by up to 7˚C above environmental temperature.
What is ovoviviparity and the advantage of this to reptiles?
- Most of these species are ovoviviparous, meaning that they incubate their eggs internally, where they hatch before being born.
- This has the advantage of the mother being able to control temperature of incubation by her thermoregulatory behaviour.
What is a viviparous reptile?
- Very few species, including anacondas, are fully viviparous, in which a placenta exchanges nutrients and gases between mother and foetus.
- In this case, the corpora lutea somehow recognise implantation and maintain progesterone production.
