Transport oxygen and nutrients to actively metabolizing tissues.
Remove carbon dioxide and other waste products from tissues.
Transport signaling molecules and immune cells throughout the body.
Diffusion
Unicellular organisms and some small metazoans lack cardiovascular systems.
Rely on diffusion to transport molecules.
Slow across long distances.
Diffusion
Bulk Flow
Limitation on the rate of diffusion so larger animals move fluids through their body by a process called bulk flow
Occurs within a series of chambers & tubes.
Faster across long distances than diffusion
Bulk Flow
One way valves ensure unidirectional flow through the system.
Circulation Time Mammal Elephant Horse Human Rat Shrew
Body Mass (kg) 4000 700 70 0.2 0.003
Circulation Time (sec) 140 90 50-60 12 4
Exercising Human = 12 seconds Exercising Shrew = 1 second
Circulatory Systems
3 Main Components: 1. 1≤ pumps apply force to drive fluid flow. 2. A system of tubes, channels, or spaces through which the fluid can flow. 3. A fluid that circulates through the system.
Substantial diversity among animals
Pumping Structure
3 main types: ◦ Contractile Chamber
◦ External Pump ◦ Peristaltic Contraction
Pumping Structures
Pumping Structures
Chambered hearts: ◦ Chamber(s) that circulatory fluid first enters is/are called atrium/atria ◦ Function as both reservoirs and pumps. ◦ Fluid flows from an atrium into a muscular chamber called a ventricle. ◦ Functions as primary pump.
Pumping Structures
Skeletal muscles can be used to develop pressure gradients.
Pumping Structures
Tube-like hearts found in some invertebrates move blood by peristalsis.
Circulatory Systems
Open Circulatory Systems
Closed Circulatory Systems
Open Circulatory Systems
Circulatory fluids flow through open spaces called sinuses.
Sinuses allow circulatory fluids to make direct contact with tissues.
Circulatory fluids therefore mix with extracellular fluids.
Closed Circulatory Systems
Circulatory fluids flow through enclosed blood vessels.
Blood vessels have specialized lining that separates circulatory fluids from tissues.
Complete separation of circulatory fluid and extracellular fluid.
All have mechanisms for propelling fluid around their bodies.
The bulk flow of fluids is part of a combined respiratory, digestive, and circulatory system.
Sponges, Cnidarians and Flatworms
The bulk flow of fluids is part of a combined respiratory, digestive, and circulatory system.
Annelids
Most have closed circulatory systems ◦ Polychaetes = tube worms Some have open circulatory systems
◦ Oligochaetes = earth worms Series of small blood vessels connect large dorsal and ventral blood vessels
Mollusks
Most have open circulatory systems ◦ All have hearts or contractile organs ◦ Some have blood vessels
Mollusks: Squid, Octopuses, & Cuttlefish
Have completely closed circulatory systems.
Mollusks: Squid & Octopuses
Have 3 muscular chambered hearts:
The systemic heart pumps oxygenated blood to the body.
Deoxygenated blood flows into the two branchial hearts that pump blood through the gills.
From the gills the oxygenated blood flows back into the systemic heart.
Arthropods
All have open circulatory systems ◦ Almost all have 1≤ hearts and some BVs.
Vertebrates
All have closed circulatory systems. ◦ Blood remains within blood vessels throughout all points of circulation.
Advantages: ◦ Ability to generate high pressure and flow ◦ Ability to control and direct blood flow to specific tissues
Blood
Circulatory fluid in closed systems.
Plays many roles: ◦ Provide constant internal environment ◦ Transports – nutrients, oxygen, wastes products, immune cells, and signaling molecules around the body.
Composition of Vertebrate Blood
Composition of Vertebrate Blood
Blood Plasma: ◦ mostly water (93% by volume) ◦ contains dissolved proteins, glucose, clotting factors, dissolved ions, hormones and CO2
White Blood Cells = Leukocytes ◦ Immune System Cells
Red Blood Cells (RBCs) = erythrocytes ◦ Main Function = transport of oxygen
Red Blood Cells
Mammalian RBCs lack nuclei, mitochondria, and other organelles including ribosomes.
Most mammalian RBCs are shaped like biconcave disks.
Contain oxygen high concentration of binding protein hemoglobin (Hb).
Red Blood Cells
Hb: increases the maximum amount of oxygen that blood can carry by 50x
When you increase Hb you increase you oxygen storage capacity of blood and your ability to deliver oxygen to tissues.
Red Blood Cells
Hematocrit (HCT) = % blood that is made up of erythorcytes (RBCs)
Varies substantially among vertebrates (20-65%)
Acclimation of humans to high altitude causes an increase in HCT.
Circulatory Plan of Vertebrates
Circulatory Plan of Vertebrates
Arteries: carry blood away from heart
Arterioles: arteries branch into arterioles
Capillary Beds: dense networks of thin walled capillaries
Venules: capillaries coalesce into venules
Veins: venules coalesce into veins, which return blood to the heart
Blood Vessels - Wall Structure
Blood vessels are hollow and tubular ◦ Lumen = hollow area
Composed of up to 3 Layers: ◦ Tunica Intima ◦ Tunica Media ◦ Tunica Externa
Blood Vessels - Wall Structure
Tunica Intima – inner-most layer ◦ Inner lining called the vascular endothelium
Tunica Media – middle layer ◦ Composed of smooth muscle and elastin ◦ Vasodilatation and vasoconstriction
Tunica Externa – outer-most layer ◦ Composed of collagen fibers ◦ Support and reinforce blood vessel
Blood Vessels - Wall Thickness
Arteries: large diameter & thick-walled ◦ Aorta - highly elastic with a thick tunica externa. ◦ Arteries farther from heart have a thicker tunica media and are highly muscular.
Blood Vessels - Wall Thickness
Arterioles: thinner walls and lack extensive tunica externa. ◦ Larger arterioles - extensive tunica media ◦ Smaller arterioles = single layer of smooth muscle around the endothelium allows for vasoconstriction and vasodilatation
Blood Vessels - Wall Thickness Capillaries:
lack tunica media and
externa. Very small diameter Extremely thin walled:
◦ composed of a single sheet of epithelial cells. ◦ Allows substances to pass between the blood and tissues.
Capillaries
Substances can move across walls by: ◦ Diffusion – lipid-soluble substances ◦ Vesicle transport – proteins ◦ Paracellular pathway – small molecules like water and ions can pass through pores between cells of the capillary walls.
Capillaries – Tunica Intima
Continuous capillaries: ◦ seal between cells not usually complete allowing fluids and small molecules to pass.
Fenestrated capillaries: ◦ Cells of vascular endothelium have many pores. Passage of small molecules and fluids is easy.
Sinusoidal capillaries: ◦ Most porous of all capillaries. ◦ Allows proteins to move across capillary wall.
Blood Vessels - Wall Thickness
Capillaries empty into venules, which lead to veins that return blood to the heart.
Vein usually has a thinner wall and larger lumen than a similarly sized artery. Thin tunica media, thick tunica externa.
