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Key Characteristics to Gas Exchange:
Moist membranes that cover lots of surface area
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Bacterial/protist gas exchange
movement of oxygen or carbon dioxide into/out of cell
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Cindarians gas exchange
Simple gas exchange from fluid in a branching or simple gastrovascular cavites into cells
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Annelids gas exchange
- gas exchange through skin common is small thin organisms
- Worms have larger surface area with bumps,
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Arthopod gas exchange
- respiratory tubes called trachea open into spiracles
- subdivide into many branches to get close to many cells
- no oxygen carrier or special cells needed, no blood stream intermediate, more fast efficient
- Direct diffusion of gas limits size
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Gas exchange in amphibians
- Usually breathe through skin even though they have small lungs
- Need to be moist
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Larger animals key to gas exchange:
- SA internally is larger than skin via branching or folding
- Do internally because external would dry out on land (ex: birds reptiles)
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Gas exchange in Reptiles
Use lungs and some use cloaca as secondary and exchange unit
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Gas exchange in Birds
- are homeotherms, maintain constant body temperature
- Use muscle heat to maintain
- Use lungs similar reptiles but also have air sacs which allow fresh to flow through lungs during exhalation
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Air Sacs
- Use lungs similar reptiles but also have air sacs which allow fresh to flow through lungs during exhalation
- Holds more air than lungs can take in so on exhale old air and inhale has excess air, new air to use air flows only one direction (unlike mammals)
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Gills
- Breathe in water through branching gastrovascular cavities
- Simple tubular projections from the body with added SA
- Dont have to worry about keeping moist
- Must be more efficient at removing oxygen from water because only holds a fraction of oxygen that air does
- Blood vessel so thin only blood can pass through one cell at a time
- Four gill arches are found on either side of the head in thin filaments just out from each bony arch
- Each filament has 100's of lamellae where diffusion of oxygen into blood happens
- *Key aspect blood is flowing toward head of fish and water flowing toward tail as swims
- Countercurrent exchange
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Counter Current
- favors high diffusion
- high oxygen moves along blood across the gill gradient (moves in opposite direction) in order to encounter the highest gradient difference in concentrations

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Mammalian Gas Exchnge
- Circulatory system is needed to bridge gap between lungs and cells
- End in blind sacs called alevoli
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Alevoli
Dense net of capillaries which oxygen diffuses and co2 is excreted
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Pathway of air in mammals
- nose to mouth, air entrees pharynx across larynx (lies within tachea)
- trachea goes into two bronchi and further into bronchioles
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Breathing Partial Pressues
- Deoxygenated blood enters lunch capillary
- Low partial pressure of oxygen
- Inhaled air has high partial pressure
- Therefore oxygen moves into capilariess
- CO2 opposite so it moves out of body
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Erythopoltin
hormone released by kidneys increases red blood cells
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Erythocyte
Red Blood Cell
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Hemiglobin and Allosoteric Loading
Made of four subunits capable of biding to four oxygen molecules
Loading becomes easier after the first oxygen
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Bohr Effect
- Hemigobin losses oxygen more easily in acidic environments
- Carbonic acid from krebs cycles makes more acidic
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Arthopods Circulatory System
- An open circulatory system
- No distrinction between blodd and intestitual fluid (hemolymph)
- Ventilation system in insects is completely distinct
- Tracheal tubes bring oxygen throughout hemolymph to pick up oxygen
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Annelids Circulatory System
- First Closed circulatory system
- Diffusion of gases and nutrients occur into and out of blood
- Blood and interstitial fluid dont mix
- oxygen and nutrients diffuse out of blood into interstitial fluid from fluid to cells
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Two Chambered Hearts-Fish
- One atrium where blood is recieved
- One ventrical pumps blood back out of gills
- No oxygened blood flows into heart because only oxygenated by gills
- Swimming movements help push blood through body
- One circuit out to gills through body and back to heart
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Three chambered Heart
- In reptile and amphiians
- Two separate atria and one larger ventricle
- Two circuit-out to lungs 1st then body stop at heart between ciruit, may be an evolutionary development from lungs
- More efficient because blood can be delivery with high velocity for each circuit (stops at heart in between)
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Three Chambered Heart, Elongated Septum
- Division that almost cuts ventricle in half
- Progression to four chambers allows for separation of oxygenated and deoxygenated blood
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Four Chambered Heart
- Mammals and birds
- Double Circuit
- Each side has own pump
- Right pump deoxygenated blood to lungs
- Left side pumps oxygenated to aorta and out of body
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What are the four chambers of heart
- Two upper receiving chambers are artia
- Two lower are ventricles, muscular
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AV-Atrivoentricular Valuves
- Between artia and Ventricle prevent back flow of blood into atria
- Semilunar valuves in pulmonary artery prevent back flow of blood into lungs
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Systole
Period between ventricles contracting and forcing blood into luncgs and aorta
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Diastole
ventricles contract and fill with blood
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Blood Pressure
- Force/ area blood exerts on walls of blood vessels
- Systole/Diastole #
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Veins
Often collapse on themselves when not filled with blood
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Arteries
Contain an open lumen and can contract against themselves to propel blood away from heart
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Aorta
Maiin artery leading away from left ventricle
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Precapillary Spincters
Small bands of muscles that close off capilaries when not in use (not enough blood in the body to keep them always open)
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Temperature Regulatation
- Spincters close when cold to restrict heart losse
- More blood near surface means more heat lost
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Vasodilation
- Keeping lots of blood vessels in extremities open
- Helps sweat and cooling body
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