Circulation and Gas Exchange:
- Unicellular organisms exchange directly with environment.
- Multicellular organisms cannot exchange directly with environment
- Complex animals have internal transport systems that circulate fluid.
- Simple animals with two cell body walls enclose a gastrovascular cavity.
- This functions as digestion and distribution.
Open and Closed Circulatory Systems:
Present with complex animals.
List Three Basic Components of Both Circulatory Systems:
- Circulatory Fluid [blood(closed) hemolymph(open)]
- Set of Tubes (blood vessels)
- Muscular Pump (the heart)
Open Circulatory System:
- Blood bathes the organs directly
- Arthropods and Molluscs.
- Hemolymph = Blood + Internal Fluid.
Closed Circulatory System:
- Blood is confined to vessels and distinct from interstitial fluid.
- Closed systems are more efficient at transporting circulatory fluids.
Vertebrate Circulatory System:
- Vertebrates have a closed circulatory system.
- Called the cardiovascular system.
Three Main Blood Vessel Types:
Branch into arterioles and carry blood to capillaries.
- Network of capillaries called capillary beds.
- Site of chemical exchange.
- Venules converge into veins.
- Return blood from capillaries to heart.
- Contain two or more chambers.
- Blood enters through an atrium.
- Pumped out through a ventricle.
- Two-Chambered Heart
- Blood leaving heart passes two capillary beds before returning.
- Bony fishes, Rays, and Sharks.
- Amphibian, reptiles, and mammals have double circulation.
- O2-poor and O2-rich blood pump seperately from right and left sides of heart.
- Higher blood pressure in organs relative to Single Circulation.
- Oxygen-rich blood delivers oxygen through systemic circuit.
Oxygen-Poor Blood Flow in Double Circulation:
- Through pulmonary circuit to get oxygen from lungs. (Most)
- Through pulmocutaneous circuit to get oxygen from lungs and skin. (Amphibian)
Benefit of Double Circulation:
Can counteract gravity
- Three-chambered heart: two atria and one ventricle.
- Ventricle pumps blood into forked artery
- Ventricle output is split to pulmocutaneous circuit and systemic circuit.
- Blood flow to lungs is nearly shut off underwater.
Reptile (excluding Birds) Heart:
- Three-chambered heart: two atria and one ventricle.
- In crocodilians a septum divides the ventricle.
- Reptiles have a pulmonary circuit (lungs) and a systemic circuit.
Mammal and Bird Heart:
- Four-chambered heart with two atria and two ventricles.
- Left side pumps and receives only oxygen-rich blood.
- Right side receives and pumps only oxygen-poor blood.
- Endotherms require more O2 than ectotherms.
- Supplies oxygen for respiration and disposes carbon dioxide.
- Gas diffuses down pressure gradients in lungs and organs by partial pressure.
- Pressure exerted by a particular gas in a mixture of gases.
- A gas diffuses from region of high to low partial pressure.
- In the lungs and tissues O2 and CO2 diffuse.
- Animals use air or water as source of respiratory medium.
O2 in Water:
- There is less O2 available in water than in air.
- Getting O2 from water needs higher efficiency than breathing.
- Large, moist respiratory surfaces are needed for gas exchange.
- Gas exchange takes place by diffusion.
- Respiratory surfaces can include skin, gills, tracheae, and lungs.
Gills in Aquatic Animals:
Outfoldings of body creating large surface area for gas exchange.
- Moves respiratory medium over respiratory surface.
- Moving through water or moving water over gills for ventilation.
- Gills use countercurrent exchange system.
Countercurrent Exchange System:
- Blood flows in opposite direction to water passing over the gills.
- Blood is less saturated with O2 than water.
Tracheal System in Insects:
- Consists of tiny branching tubes that penetrate the body.
- Tracheal tubes supply O2 directly to body cells.
- Respiratory and circulatory systems are separate.
- Larger insects must ventilate their tracheal system to meet O2 demands.
- Infolding of body surface.
- Circulatory system transports gases between lungs and rest of body.
- Size and complexity of lungs correlate with metabolic rate.
Mammalian Respiratory System:
- System of branching ducts conveys air to lungs.
- Exhaled air passes over vocal cords to create sounds.
- Secretions called surfactants coat the surface of the alveoli.
Pathway of Inhaled Air:
Nostrils > Pharynx > Larynx > Trachea > Bronchi > Bronchioles > Alveoli
- Ventilating the lungs is breathing.
- Alternate inhalation and exhalation of air.
How an Amphibian Breathes:
- An amphibian ventilates lungs by positive pressure breathing.
- Forces air down the trachea.
How a Mammal Breathes:
- Mammals ventilate their lungs by negative pressure breathing.
- Which pulls air into the lungs.
- Lung volume increases as rib muscles and diaphragm contract.
- The tidal volume is volume air inhaled with each breath.
- The maximum tidal volume is the vital capacity.
- After exhalation residual volume of air remains in lungs.
How a Bird Breathes:
- Eight or nine air sacs function as bellows keeping air flow.
- Air passes through lungs in one direction.
- Every exhalation completely renews air in lungs.
Metabolic demands require blood to transport large quantities of O2 and CO2.
Blood Arriving in Lungs:
- Low partial pressure of O2.
- High partial pressure of CO2.
- Relative to air in the alveoli.
- O2 diffuses into blood.
- CO2 diffuses into air.
Partial pressure diffuses O2 into interstitial and CO2 into blood.
- Proteins that transport oxygen.
- Greatly increases amount of oxygen that blood can carry.
- Arthropods and molluscs have hemocyanin with copper as oxygen-binding component.
- Most vertebrates and some invertebrates use hemoglobin within erythrocytes.
- Can carry four molecules of O2.
- Small change in partial pressure of oxygen means large changes in O2 delivery.
- CO2 produced in respiration lowers blood pH and hemoglobin affinity for O2.
- Hemoglobin helps transport CO2 and assists in buffering.
- CO2 from respiring cells diffuse into blood and transport into either blood plasma, bound to hemoglobin, or bicarbonate ions (HCO3-).
- Deep-diving air breathers stockpile O2 and deplete it slowly.
- Weddell seals have high blood to body volume ratio.
- Also store oxygen in muscles via myoglobin proteins.