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Circulatory System
A system that transports fluids, nutrients, gases, and wastes through an animal’s body
Open Circulatory System
A system in which the circulatory fluid is not completely enclosed in vessels
Closed Circulatory System
A system in which the blood is confined to vessels and kept separate from interstitial fluid
Hemolymph
The circulatory fluid in open systems; mixes with interstitial fluid
Blood
The circulatory fluid in closed systems; kept separate from interstitial fluid
Heart
A muscular pump that powers circulation by rhythmic contraction
Vessel
A tube-like structure that carries circulatory fluid through the body
Arteries
Vessels that carry blood away from the heart
Veins
Vessels that carry blood back to the heart
Capillaries
Thin-walled vessels where exchange of gases, nutrients, and wastes occurs
Gas Exchange
The process of swapping O₂ and CO₂ across respiratory surfaces
Respiratory Surface
A thin, moist, large surface where diffusion of gases occurs
Essential Conditions for Respiratory Surfaces
Must be thin, moist, and have a large surface area
Single Circulation
Blood flows through the heart once per circuit (seen in fish)
Double Circulation
Blood flows through the heart twice per circuit (seen in mammals and amphibians)
Pulmonary Circuit
The path of blood from the heart to the lungs and back
Systemic Circuit
The path of blood from the heart to the body and back
Two-Chambered Heart
A heart with one atrium and one ventricle (seen in fish)
Three-Chambered Heart
A heart with two atria and one ventricle (seen in amphibians)
Four-Chambered Heart
A heart with two atria and two ventricles (seen in birds and mammals)
Right Atrium
Receives deoxygenated blood from the body
Right Ventricle
Pumps deoxygenated blood to the lungs
Left Atrium
Receives oxygenated blood from the lungs
Left Ventricle
Pumps oxygenated blood to the rest of the body
Pulmonary Artery
Carries deoxygenated blood from the right ventricle to the lungs
Pulmonary Vein
Carries oxygenated blood from the lungs to the left atrium
Aorta
Largest artery; carries oxygenated blood from the left ventricle to the body
Vena Cava
Largest vein; returns deoxygenated blood from the body to the right atrium
Atrium
Heart chamber that receives blood
Ventricle
Heart chamber that pumps blood out
Gills
Gas exchange organs in aquatic animals; extract O₂ from water
Countercurrent Exchange
A system where blood and water flow in opposite directions to maximize O₂ diffusion
Tracheal System
A network of air tubes in insects for direct gas exchange
Lungs
Internal gas exchange organs found in mammals, birds, reptiles, and amphibians
Alveoli
Tiny air sacs in mammalian lungs where gas exchange occurs
Negative Pressure Breathing
A breathing system where air is pulled into the lungs by expanding the thoracic cavity
Diaphragm
A sheet of muscle that contracts to enlarge the chest cavity during inhalation
Intercostal Muscles
Muscles between ribs that assist with chest expansion during breathing
Inhalation
Diaphragm contracts and moves downward; air is drawn into the lungs
Exhalation
Diaphragm relaxes and moves upward; air is pushed out of the lungs
Partial Pressure
The pressure exerted by an individual gas in a mixture of gases
Diffusion of Gases
Gases move from areas of higher partial pressure to lower partial pressure
Oxygen Transport
Carried by hemoglobin in red blood cells
Carbon Dioxide Transport
Carried dissolved in plasma, bound to hemoglobin, or as bicarbonate ions
Hemoglobin
A respiratory pigment in red blood cells that binds and carries oxygen
Affinity of Hemoglobin
Changes with pH and CO₂ levels; lower pH reduces O₂ binding (Bohr effect)
Bohr Shift
A drop in pH lowers hemoglobin’s affinity for oxygen, aiding O₂ delivery to tissues
Breathing Control Centers
Located in the medulla oblongata; respond to blood pH and CO₂ levels
CO₂ and pH
An increase in CO₂ lowers blood pH, triggering increased breathing rate
Fick’s Law of Diffusion
Rate of gas diffusion depends on surface area, concentration gradient, and membrane thickness
Circulation in Amphibians
Three-chambered heart allows some mixing of oxygenated and deoxygenated blood
Circulation in Birds and Mammals
Four-chambered heart completely separates oxygenated and deoxygenated blood
Circulation in Fish
Two-chambered heart supports single circulation through gills and body
Breathing in Amphibians
Can use lungs, skin, and lining of the mouth for gas exchange
Breathing in Birds
Use unidirectional airflow with air sacs to maintain high O₂ levels during both inhalation and exhalation
Unidirectional Airflow
In birds, air flows through the lungs in one direction, not tidal; highly efficient gas exchange
Air Sacs in Birds
Store air and ensure continuous flow through the lungs