How many air sacs to birds have? Where are they located?
Cranial to Caudal:
2 anterior thoracic
2 posterior thoracic
Where does gas exchange take place in the avian respiratory system?
Parabronchi capillary network
Through what structures does air enter the avian respiratory system?
Nares (upper beak)
After the nares, past what structure does air move to get to the glottis at the base of the tongue?
Choana - cleft in upper palate
After the getting past the glottis, through what structures does air move to reach the lungs of a bird?
Trachea (complete cartilaginous rings)
Syrinx (voice box)
In what direction can air travel through the paleopulmonic lung of the parabronchi in the bird?
Cranial to caudal only, ie., during inspiration.
In what direction can air travel through the neopulmonic lung of the parabronchi in the bird?
The neopulmonic lung, branching tubes running laterally alongside the paleopulmonic tubes, takes up 25% of the lung tissue. Air can move both cranial to caudal and caudal to cranial in the neopulmonic lung.
What percentage of respiratory volume is taken up by the bird's nine air sacs?
What are the three main roles of the air sacs in birds?
1. act as a reservoir of air for the respiratory system.
2. act as bellows to aid respiration
3. lighten the weight of the abdomen and so aid flight
What happens in the parabronchi & air sacs during INSPIRATION in the bird?
Air passes down the trachea, through the syrinx (voice box) divides into the primary bronchi and passes through the neopulmonic parabronchi which filter and clean the air, then into the caudal air sacs (abdominal air sacs).
The caudal air sacs, assisted by the effects of gravity on the sternum and some muscular activity, inflate. The sacs act as reservoirs for air.
At this stage oxygenated air is already in the paleopulmonic parabronchi of the lungs from the previous respiratory cycle and gaseous exchange with capillaries is occurring.
The cranial air sacs (cervical, anterior & posterior thoracic) are filling with deoxygenated air as it leaves the lungs, having given up their oxygen to the blood.
What happens in the parabronchi & air sac during EXPIRATION in the bird?
The inflated cranial air sacs expel air out of the trachea.
The inflated caudal air sacs expel oxygenated air through the paleopulmonic parabronchi (where oxygen absorption takes place).
This air continues to pass through the lung tissue, with increasing amounts of oxygen being removed into the capillaries until oxygen-depleted air refills the cranial sacs.
What is the system in the lungs that enables diving birds & those that fly at high altitudes to exchange the oxygen in inhaled air with their blood in their lungs so much more efficient than in mammals?
The cross-current exchange system.
Air flows in one direction through the paleopulmonic tubes while capillaries flow across them, so oxygen diffusion is maximised.
What are gill rakers and what is their function in fish respiration?
Gill rakers are stiff projections on the gill bar that face cranially. The gill rakers overlap each other slightly and form a filtering screen. This prevents food and any damaging particles in the incoming water from reaching the delicate gill filaments.
What structures inside fish gills are responsible for gas exchange?
The secondary lamellae are capillaries inside the primary lamellae, also known as gill filaments. The gas exchange takes place in the secondary lamellae.
Insects do not have a respiratory system that exchanges gases from inhaled air into the blood, nor do they have a circulatory system to transport gases around the body.
How then, do insects exchange and transport gases around their bodies?
They absorb air through diffusion into external openings called spiracles, which lead into tubes called tracheae, which branch into smaller tracheoles. These end in fluid-lined cells of the body, such as muscle cells.
The oxygen that diffuses into the insect tubules ends up dissolving into the solution within the cells. Waste gases pass out the same way.
In larger insects, such as locusts/grasshoppers, there are air sacs at the end of the tracheae that expand and compress with breathing movements.
Which of the following have a diaphragm to aid respiration?
A. Only mammals have diaphragms.
Which muscles do snakes & lizards use to ventilate?
Rib muscles: internal & external intercostal muscles.
How do chelonia (turtles, tortoises) ventilate their lungs? What muscles do they use?
They use their limb muscles, as their ribs are fused to their carapace & therefore they can't use their rib muscles.
All chelonia force air in and out of the lungs by moving their limbs in and out of the shells. There are some smooth muscles within the lung to contract the lung itself. All chelonia compensate for the restricted diaphragmatic movement either by the movement of the front legs or the pelvic girdle, (or indeed sometimes both), which create an extra pumping action, helping to draw more air into the lungs.
How many chambers does an amphibian (eg. frog) heart have?
Three: two atria, one ventricle.
Usually they exchange gases through skin.
What is special about the reptile heart besides having two atria and a ventricle?
There are two aortic arches. One carries mixed/partly oxygenated blood to the systemic circulation while the other brings it into the lung capillaries for full oxygenation. From there it returns to the left atrium, to be mixed in the ventricle.
How many lungs does the snake have?
Usually just one. The caudal aspect of the lung tends to be an air sac.
Older snake species have a really big right lung that extends all the way down toward the vent into an air sac, and a small left lung.
What if a reptile stops breathing because, as in the example of a snake, it is feeding and its glottis closes? How does it oxygenate its blood?
Reptile blood collects oxygen by passing through the lung(s). The heart has two atria and one ventricle. Although the ventricle is not divided by complete walls, there are incomplete septa. The heart contracts in a wave around the ventricle. Therefore oxygenated and de-oxygenated blood is kept separate.
If the lungs are not filled with air, blood is shunted across the heart and does not go to the lungs. Blood is not wasted to the lungs if the animal is not breathing, for example, during diving.
What is special about the crocodile heart compared with other reptile hearts?
It has four chambers.
What does poikilothermic mean, and what is a poikilothermic species?
Poikilothermic means a highly variable internal temperature. Fish, amphibians & reptiles are poikilothermic.