Circulatory Systems I

Circulatory Systems I
Primary Functions

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.
Circulatory Fluids

Interstitial Fluid
◦ Extracellular fluid directly bathes tissues

Blood
◦ Closed circulatory systems.

Hemolymph
◦ Open circulatory systems
Diversity of Circulatory Systems
Sponges, Cnidarians and Flatworms

All lack a true circulatory system.

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.
