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 Body Mass

(kg)

Circulation

Time (sec)

Elephant 4000 140

Horse 700 90

Human 70 50-60

Rat 0.2 12

Shrew 0.003 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.