Zoo Respiration

Gas exchange in animals External respiration: not to be confused with cellular respiration, although purpose is to provide oxygen and eliminate carbon dioxide Single-celled organisms achieve this by simple diffusion Larger organisms need specialized breathing organs

Getting the air into the body is one challenge Circulatory system needed to distribute oxygen to the tissues Specialized blood cells can transport oxygen (solubility in plasma is very low)

The process of breathing Air has much more oxygen than water (20% vs 0.9%) Gas diffuses more rapidly in air; water is much more dense and viscous Therefore aquatic animals are highly efficient at extracting oxygen form water However, they must expend much more energy to do so (up to 20% vs 1-2% of resting metabolism)

Respiratory surfaces must be thin and wet so that gas can diffuse through an aqueous phase between environment and circulation (also to maintain cells themselves) Air breathers have adapted specialized invaginations of the body to “take in” air Ventilation-mechanisms to move air into and out of the body Evaginations (gills) for water breathing Invaginations (lungs and tracheae) for air

Types of respiratory organs Direct diffusion (cutaneous respiration) protozoa, sponges, cnidarians, some worms Possible because these animals have large areas relative to their mass (and all cells are close to the outer surface). See where a circulatory system comes in?

Larger animals (amphibians, eels) supplements breathing with cutaneous respiration Skins are heavily vascularized Hibernating frogs and turtles can exchange all gases through skin while submerged Presence of gills can vary through animal development All chordates have gill slits at some point

Gills: efficient gas exchange in water Many different types of gills external extensions of body surface dermal papulae: sea stars bracheal tufts: marine worms, aquatic amphibians internal gills- fishes, arthropods lots of vasculature- blood flow is opposite to flow of water across gills (countercurrent flow)

Operculum (gill cover) closes when mouth opens

Water passes over gills and out operculum

Countercurrent exchange

Maximizes transfer of oxygen from water to blood

Gills must be continuously in water (I.e., in aquatic animals) or they will collapse and dry out Terrestrial animals require internal tubes to move air into the body tracheal systems lungs

Air vs water Much higher concentration of oxygen in air Gases diffuse faster in air; less ventilation and less energy required of the animal Internalizing the respiratory tubes minimizes water loss

Tracheal systems branch throughout body

Larger (and/or flying insects) require ventilation

Body movements; flight muscles help pump air through tracheal system Mitochondria are “available” to use oxygen in aerobic respiration Tracheal system is separate from an insect’s circulatory system

Lungs confined to a specific region of the body Pulmonate snails, spiders, scorpions, some crustaceans) have rudimentary lungs (book lungs unique to spiders) Use muscle movements to provide rhythmic exchange of air

Amphibians: saclike or subdivided Reptiles: interconnecting air sacs Mammalian lungs: alveoli system that exchanges gases with capillaries. Greatly increases surface available for gas exchange Not particularly efficient: approximately 20% of air is never expelled

Breathing in amphibians: positive pressure Reptiles, birds and mammals use negative pressure: expand thoracic cavity to pull in air Frogs draw air into the mouth, then drive it into the lungs by closing nares , raising mouth floor and driving air into the lungs Mouth cavity is vascularized; often frogs do not use their lungs

Birds’ system has evolved to meet the demands of flight

Birds have lost part of their digestive systems and make room for air sacs

Mammalian respiratory system

Properties of lungs Compliance- ability to expand when stretched Elasticity- ability to return to original size Surface tension exerted by fluid in alveoli Surfactant helps prevent alveoli from collapsing RDS-surfactant lacking in the lungs of premature babies ARDS- alveolar permeability and reduced surfactant

Control of breathing; gas level detectors

Why can’t you hold your breath indefinitely?

Partial pressures of oxygen and carbon dioxide Most O2 in blood is bound to RBCs (0.3ml out of 20 ml/100 ml blood is dissolved in plasma) Increasing PO2 in blood increases rate of diffusion to tissues Arterial levels are significant because they reflect lung function

Respiratory pigments help transport gases (metallic ion confers color and binds oxygen) Hemocyanin- copper ion; found in arthropods and many mollusks Hemoglobin- iron; vertebrates Oxygen is bound reversibly

Hemoglobin and oxygen transport Loading (in lungs) deoxyhemoglobin becomes oxyhemoglobin; reversed in tissues Affinity for oxygen decreases in lower pH and higher temperature 2,3-DPG (unique to RBCs) also reduces affinity of oxyhemoglobin for oxygen (this works if oxygen levels are low or in anemia) Net effect: favors unloading of oxygen into tissues

Carbon dioxide transport and acid-base balance Carbon dioxide is converted to carbonic acid by carbonic anhydrase in red blood cells Hydrogen ions are produced; these combine with hemoglobin This promotes unloading of oxygen from hemoglobin

Much cooperation between circulatory and respiratory system Objective: to deliver oxygen efficiently through body Circulatory system also delivers nutrients from digestive system to cells Contains elements to maintain itself (hemostasis) and regulate fluid levels (nervous, endocrine) Also defense against disease (white blood cells)