Today I watched a beautiful short (7 min) film “Oxygen – The Old Man and His Bed” directed by Marc Issacs. Bob, who suffers from a severe (un-named) respiratory condition, last went outside in 1982 to get permission to be put on oxygen.
Warning: this Film is somewhat confronting (yes, there were tears)
We explored how carbon dioxide is produced when sugars are broken down during cellular respiration on Monday and now understand why we must breathe out, but why exactly do we need the oxygen that we get when we breathe in?
What exactly is the big deal with breathing? Why do we breathe? Always. It must be pretty important….so important that most of the time our body does it automatically. Respiration (a fancy-pants word for breathing) is more than just breathing in oxygen and breathing out carbon dioxide. The nutrients (sugars, proteins and fats) that you eat travel through the circulatory system to the cells and are broken down and their energy converted into ATP (adenosine triphosphate) through stacks of complicated processes that go under the banner cellular respiration. ATP is kind of like the universal energy currency of cells. Australia has the dollar, Europe the euro and cells have ATP. Most things that happen inside cells (like moving, replicating and making things) have a cost that is paid in ATP. Each cell even has its own money mints to print the ATP – the mitochondria.
While we’re hard to knock off the top of the food chain, humans aren’t known for holding their breath. We’re not designed for diving deep into the ocean like the humpback whale which can hold its breath for 45 minutes or longer. But how long can a human hold its breath. How long can you? Give it a go….I dare you……
So, how did you go? Me? I grimaced my way through 48 seconds (with a few strange looks from my housemates). I admit it, I’m no humpback whale. And my effort definitely pales in comparison to the world record breath-hold of 20 minutes and 21 seconds by 26 year old Brazillian Ricardo da Gama Bahia. Although I admit that the full 24 minute video below isn’t exactly Oscar winning material, it’s worth it for the cheesy music; the build-up and climax at the record breaking moment is nothing short of inspirational.
Now we know how aquatic eggs (amphibians and fish) breathe, let’s explore how eggs that are normally laid on land exchange their respiratory gases. The amniotes (reptiles, birds and mammals) mostly lay their eggs on the land, in burrows or in nests high up in the trees. Like any living thing, the embryo within the egg needs to exchange respiratory gases (oxygen and carbon dioxide) with the environment. To do this they have tiny little pores (holes) in their eggshells. Domestic hen eggs have ~7500 pores. Just beneath the surface of the eggshell lie membranes (amnion, chorion and allantois) that have many little blood vessels where the gases can be exchanged and carried to the embryo. Two of these membranes, the chorion and the allantois become joined in older bird embryos to form the chorioallantoic membrane or CAM which is the major site of gas exchange in bird embryos.
Basically, oxygen can diffuse (move down its concentration gradient) through the pores in the eggshell. It enters the bloodstream of the embryo by diffusing though the membrane just beneath the shell into a blood vessel (e.g. capillary) and binds (joins) to haemoglobin which helps increase how much oxygen the blood can carry. The oxygen is then pushed through the blood vessels by the pumping heart of the embryo and can reach every cell in the embryos body. At the cells the carbon dioxide waste is created (futures blogs will explore exactly why the cells need oxygen and create carbon dioxide waste). The carbon dioxide travels back through the blood vessels (although without the help of haemoglobin which usually only joins to oxygen) diffuses through the membrane and out of the pores into the environment.
Yes, embryos inside eggs need to breathe! This is going to be a big two-parter and we will explore how egg-laying amniotes (reptiles, birds and monotremes) eggs breathe in part two. First, let’s discover how amphibian (frogs and salamanders) and fish eggs that are normally laid in water exchange their respiratory gases.
Amphibian and fish eggs are mostly made up of jelly. In the centre of the egg, the vitelline membrane envelopes the fluid which surrounds the embryo. Most amphibians and fish lay their eggs in the water so they aren’t at risk of drying out. Unlike amniote eggs (see next blog) which have a shell to provide some resistance to drying, the jelly layers easily dry out. The oxygen in the water diffuses (moves down its concentration gradient) through the jelly layer, across the membrane, through the perivitelline fluid and into the embryo (through the skin and/or external gills). Carbon dioxide moves in the opposite direction also by diffusion. No energy is needed because diffusion is a passive process. Cilia (tiny hairs) on the surface of amphibian embryos move around to create water currents inside the pervitelline fluid and help speed up diffusion.
Many amphibian and fish species lay their eggs in jelly or foam masses. This can make it difficult for enough oxygen to move by diffusion through the egg mass. Some species make sure that there are water channels between the eggs for water (containing oxygen) movement. Symbiotic (mutual relationship) algae that produce oxygen when they photosynthesise live within the eggs of others like the spotted salamander.
Spotted salamander eggs with symbiotic algae
Photo by Richard Bonnett (some rights reserved)
Many frogs, such as the Victorian smooth froglet (Geocrinia Victoriana) their eggs on land and the tadpoles hatch when ponds are formed by the autumn (fall) rains. Gases are exchanged in exactly the same way as in water (see diagram); however, the eggs are at great risk of drying out (desiccating).
Stay tuned to discover how the shelled amniotic eggs (reptiles, birds and monotremes) breathe in the next blog!
Breathing is all about creating a difference in air pressure between the lungs and the environment. Air will then flow down its pressure gradient because gases (like air) always move from areas of high pressure to areas of lower pressure. Both frogs and mammals take advantage of this in different ways to move air into their lungs. Frogs and mammals create this pressure gradient in different ways. Frogs actively create a higher pressure in their mouths (positive pressure breathing) whereas mammals use their diaphragm to create a low pressure within their lungs (negative pressure breathing). Whatever the mechanism, the end result is the same. A pressure gradient is created (where the lungs are at a lower pressure) and air flows into the lungs.
I’ve always thought of myself as an air breather. It’s something that I do pretty well and, most of the time, manage to forget about completely. From time to time I have attempted (accidentally) to inhale liquids (water while swimming or a drink going down the wrong hole). While these events haven’t ended too badly (I’m still alive to tell the tale), there’s been a lot of coughing a sputtering and I’m fairly hesitant to label this choking as breathing. From my accidental attempts at liquid breathing it would be easy to proclaim that liquid breathing in humans is impossible. However, it turns out that humans can breathe a special type of liquid made from chemicals called perfluourocarbons.
(Check this out it’s amazing!)
This classic scene from James Cameron’s 1989 Sci-fi film “The Abyss” was actually filmed (according to the wiki) using a real rat breathing a perfluorocarbon liquid mixture. While searching for a lost nuclear submarine, the deep sea divers breathe liquid perfluorocarbons. This allows them to dive to great depths without getting nitrogen narcosis (poisoning) however, they perhaps have bigger problems on their hands when they encounter aquatic aliens (what the?). While I encourage you to maintain a healthy amount of scepticism about the idea of aliens in submarines at the bottom of the ocean, liquid breathing in humans is very real. Not only is it used during deep sea dives to prevent nitrogen narcosis, but also in medicine for treating premature babies, and its currently being developed for use in respiratory disorders in adults.
They may make your skin crawl and you might wish to think of them as a lower life form, but insects have a remarkably elegant and simple way of delivering oxygen to their body and removing the carbon dioxide waste.
Insects have a tracheal system rather than the complex respiratory (lungs and stuff) and circulatory (heart and blood vessels etcetera) systems we use to breathe and transport gases. As vertebrates, we have to move the respiratory gases (oxygen and carbon dioxide) through two convective (physical moving of the gases through fluids) and two diffusive (passive movement from high to low concentration) processes (stay tuned for details in a future blog!). The two convective processes (in the lungs and the circulatory system) cost energy. In comparison, many insects move the gases through the tracheal system via simple diffusion which is a passive process that doesn’t require any energy.
Yes, more than one animal does breathe through its bum. Dubbed, the “bum-breathing turtle” the Fitzroy river turtle (Elseya irwini) was discovered by the late “Crocodile Hunter” Steve Irwin and his father. Of course, bum breathing isn’t strictly correct. For starters, turtles don’t actually have a bum, instead they have one single opening for the intestinal, reproductive and urinary systems called a cloaca. In the females, pee, poo and eggs all come out of the same hole. So, we really should call this breathing cloacal breathing or cloacal respiration…..but let’s face it, bum breathing is just far more fun. The major way that the turtles breathe is by sucking air into their lungs via their nostrils, however, it is thought that bum breathing allows them to stay underwater for longer using less energy than would be needed to surface and take a breath.
Small fish such as pearlfish take advantage of the next well ventilated bum breather and actually live inside the anus (bum) of certain species of sea cucumber. The respiratory tree is the major breathing organ of several species of sea cucumber and is located inside the anus. The sea cucumber uses muscle contractions of the body wall to draw water in and out of the anus. This allows the water to move over the respiratory tree which extracts enough oxygen out of the water and releases carbon dioxide.
to breathe, or not to breathe 