Chatper 42 (5)

__ is the uptake of moleuclar O2 from the environment and the discharge of CO2 to the environment.
__ is the pressure exerted by a particular gas in a mixture of gases.
- To do so, we need to know the pressure that the mixture exerts and the fraction of the mixture represented by a particular gas.

Calculating __ for a gas dissolved in liquid, such as water, is traightforward. When water is exposed to air, the amt of a gas that dissolves in the water is proportional to its partial pressure in the air and its solubility in water. Equilibrium is reached when gas moleucles enter and leave the solution at the same rate.

At equilibrium, the __ of the gas int eh solution equals the partial pressure of the gas int he air.
- The __ of O2 in the air and water differ substantially because O2 is much less soluble in water than in air.

The conditions for gas exchange vary considerably, depending on whether the __- the source of O2- is air or water.
- O2 is plentiful in air, making up about __ of Earth's atmosphere by volume. Compared to water, air is much less dense and less vicous, so it is easier to move and force through small passageways. As a result, breathing air is relatively easy and need not be particularly efficient.

Gas exchange with water as the __ is much more demanding. The amt of O2 dissolved in a given volume of water varies but is always less tahn in an equivalent volume of air: Water in many marine and freshwater habitats contains only 4-8 mL of dissolved O2 per liter, a concentration roughly 40 times less than in air. The warmer and saltier the water is, the less dissolved O2 it can hold. Water's lower O2 content, greater density, and greater viscosity mean that aquatic animals must expend considerable energy to carry out __.

Specialized for gas exchange is apparent in the structure of the respiratory surface, the part of an animal's body where __ occurs. Like all living cells, teh cells that carry out gas exchange have a plasma membrane that must be in contact with an aqueous solution. Respiratory surfaces are therefore always moist.

The movement of O2 and Co2 across moist respiratory surfaces takes place entirely by __. The rate of _- is proportional to the surface area and is inversely proportional to the square of the distance through which molecules must move.

THe structure of a respiratory surface depnds mainly on the size of teh animal and whether it lives in water or on land, but it is also influenced by metabolic demands for __. Thus, an endotherm generally has a larger area of respiratory surface than a similar-sized ectotherm.

Some animal's plasma membrane is clsoe enough to the environment for diffusion; but the bulk of the body's cell lack immediate access to the environment. The respiratory surface in these animals is a thin, moist __ that constitutes a respiratory organ. T

The skin serves as a respiratory organ in some animals, including earthworms and some amphibians. Just below the skin, a dense network of capillaries facilitates the exchange of gases between the __ and teh environment. BEcause the respiratory surface must remain moist, earthworms and many other skin-breathers can survive for extended periods only in damp places.

The general body surface of most animals lacks sufficient area to exchange gases for teh whole organism. The solution is a respiratory that is extensively folded or branched, thereby enlarging the availbale surface area for gas exchange.
- __, __, and __ are three such organs.

__ are outfoldings of the body surface that are suspended in the water. THe distribution of __ over the body can vary considerably. Regardless of their distribution, __ often have a total surface area much greater than that of the rest of the body.

Movement of the respiratory medium over the respiratory surface, a process called __, maintains the partial pressure gradients of O2 and CO2 across the gill that are necessary for gas exchange. To promote __, most gill-bearing animals either move their gills through teh water or move water over their gills.

The arrangement of capillaries in a fish gill allows for __, the exchange of a substance or heat between two fluids flowing in opposite directions.
- In a fish gill, this process maximizes gas exchange efficiecy. Because blood flows in the direction opposite to that of water passing over the gills, at each point in ts travel blood is less saturated with O2 than the water it meets. As blood enters a gill capillary, it encounters water that is completing its passage through the gill. Depleted of much of its dissolved O2, this water nevertheless has a higher __ than the incoming blood, and O2 transfer takes place. As the blood continues its passage, its __ steadily increaeses, but so does that of the water it encounters, since each successive position in the blood's travel corresponds to an earlier position in the water's passage over the gills. Thus a partial pressure gradient favoring the diffusion of O2 from water to blood exists along the entire length of the capillary.

__ mechanisms are remarkably efficient. In the fish gill, more than 80% of the O2 dissolved in the water is removed as it passes over teh respiratory surface. __ also contributes to temp regulation and to the functioning of the mammalian kidney.

Although the most familiar respiratory structure among terrestrial animals is the __, the most common is actually the __ of insects. Made up of air tubes that branch throughout the body, this system is one variation ont he theme of an internal respiratory surface.

The largest tubes, called __ open to the outside. The finest branches extend close to the surface of nearly every cell, where gas is exchanged by diffusion across the moist epithelium that lines the tips of the tracheal branches. Becuasase the __ brings air within a very short distance of virtually all body cells in an insect, it can trtansport O2 and CO2 without the participation of the animal's open circulatory ststem.

This works for small insects,but for larger insects meet their higher energy demands by ventilatig their __ with rhythmic body movements that compress and expand the air tubes like bellows.

Unliek tracheal systems, which branch through the insect body, __ are localized respiratory organs. Representing an infolding of the body surfac,e they are typically subdivided into numerous pockets. Because the respiratory surface of a __ is not in direct contact with all other parts of the body, the gap must be bridged by the circulatory system, which transports gases between the lungs and the rest of the body. __ have evolved in organsism with open circulatory systems, such as spiders and land snails, as well as in vertebrates.

Explain amphibian lungs.

Explain turtle gas exchange.

In general, the size and complexity of lungs are correlated wih an animal's __ (and hence its rate of _)

n mammals, a system of branching ducts conveys air to the lungs, which are located in the __.
-Explain the path.

intersection where the paths for air and food cross

The epithelium lining the major branches of this respiratory tree is covered by cilia and a thin film of __. THe __ traps dust, poollen and other particulate contaminants and the beating cilia move the mucus upward to teh pharynx, where it can be swallowd into the esophagus.

Gas exchange occurs in the __, air scacs clustered at the tips of the tinest bronchioles.
-Oxygen in the air entering the alveoli dissolves in the moist film lining hteir inner surfaces and rapidly diffuses across the epithelium into a web of capillaries that surrounds each alveolus. Carbon dioxide diffuses in the opposite direction, fromt eh capillaries across teh epithelium of the alveolus and into the air space.

Alveoli are so small that specialized secretions are required to relieve the surface tension in the fluid that coats their surface. These secretions, called __, contains a mixture of phospholipids and proteins. Without them, alveoli collapse, blocking air's entry.

Lacking cilia or significant air currents to remove particles from their surface, alveoli are highly susceptible to contamination. __ patrol alveoli, engulfig foreign particles. If too much reaches the alveoli, the defenses can rbreak down, leading to diseases tha treduce the efficiency of gas exchange.