Respiration in Animals How Animals Live

Why Do Animals Need to Breathe? Every cell in an animal requires oxygen to perform cellular respiration which gives off carbon dioxide and water as waste products. Respiration is the process by which animals exchange these gases with their environment. Animals have specialized systems of structures that help them to do this successfully and efficiently. Even a fish will drown if it cannot successfully breathe underwater!

How Mammals Breathe The chief organ in mammalian respiration is the lungs. The lungs are actively ventilated via a suction-pump mechanism of inhalation (breathing in) and exhalation (breathing out). Breathing depends on the rib muscles and the diaphragm, which is a structure located just beneath the lungs like a dome-shaped floor

Inhale Inhalation happens when the rib cage opens up and the diaphragm flattens and moves downward. The lungs can then expand into the larger space that causes the air pressure inside them to decrease, and the drop in air pressure inside the lung makes the outside air rush inside. 

Exhale Exhalation is the opposite process. The diaphragm and the rib muscles relax to their neutral state that causes the lungs to contract. The squashing of the lungs increases their air pressure and forces the air to flow out.

It Starts with the Nose In most mammals, the first place that air enters upon inhalation is the nose. It gets warmed, moistened, and filtered by cilia and mucus membranes which can trap dust and pathogens.

The epi-what? Air then reaches the epiglottis, which is the tiny leaf shaped flap at the back of the throat. The epiglottis regulates air going into the windpipe and closes upon swallowing to prevent food from being inhaled

Down to the Trachea Next, the air travels through a tube called a trachea. The trachea is a long structure of soft tissue surrounded by c-shaped rings of cartilage. In humans the trachea splits into two bronchi branches that lead to each lung.

Bronchi and Alveolus Each bronchi divides into increasingly smaller branches, until they form a big tree of tubes. The smallest branches are called the bronchioles Each bronchiole ends with a tiny air sac (no larger than a grain of sand) called an alveolus.  The tiny alveoli are important because they increase the surface area that can be used for gas exchange.

The In’s and Out’s of Breathing Capillaries are small blood vessels that take oxygen into the bloodstream. Oxygen is taken into the bloodstream for cells. Carbon dioxide is taken out of the bloodstream and sent outside the body.

It’s in Your Blood The blood is able to carry the fresh oxygen in red blood cells because of the hemoglobin protein, which can attach oxygen molecules. Think of hemoglobin like a bus that carries oxygen passengers. Each hemoglobin protein can carry four passengers of oxygen at one time.  When red blood cells are oxygen rich they are bright red, and when they are deoxygenated they are a deep purple.

The Heart of the Matter The heart pumps blood low in oxygen to the lungs In the lungs, the blood takes in oxygen then is pumped back into the heart to be sent out all over the body

How Reptiles and Amphibians Breathe Reptiles and amphibians both have lungs and exchange gases in the capillaries like mammals. Reptiles do not typically breathe the same way as mammals since many reptiles lack a diaphragm. Then how do they breathe?!

Pump it Up! Amphibians are capable of buccal pumping to push air into the lungs. This begins by muscles pulling air through the mouth or nose into a buccal cavity. Throat muscles then pump and move the floor of the mouth up in a way that is visible from the outside. This forces air out of the mouth and into the lungs. Look at this frog's throat constantly moving. 

Breathing for the Birds Birds have air sacs that collect air. They then force the air through their lungs like bellows stoking a fire.  When a bird inhales, air is brought into the posterior air sacs, which expand. Upon exhalation, the air is forced from the posterior air sacs into the lungs. This is where gas exchange takes place. A second inhalation will move the air from the lungs to the anterior air sac. A second exhalation will push the air out of the body. 

A fishy way to breathe In fish, respiration takes place in their gills. Gills can collect dissolved oxygen from the water and release carbon dioxide. Gills are much more complex than just a slit in the cheek of a fish. 

Gills Gills are comprised of gill arches with hundreds of gill filaments extending from them. Each filament is lined with rows of lamellae, and the gas exchange takes place as water flows through them. The frills and flaps increase the surface area to allow more gas exchange to take place, just as the alveoli do in the lungs.

How Insects Breath The respiratory apparatus in insects consists of a system of tubes, called tracheae, which directly ventilate the tissues. When an animal actively moves air to the site of gas exchange, it is called ventilation. The tubes divide and branch out into smaller and smaller tubes extending into all parts of the insect like plumbing pipes.