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Chapter 42
Invertebrate Circulation
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Hydras, flatworms, and jellies have gastrovascular
cavities (nutrients reach all cells via diffusion or simple
cavity branches)
Insects have open circulatory systems where ‘blood’ is
called hemolymph and is not distinguished from interstitial
fluid.
 Heart pumps hemolymph through pockets near organs
called sinuses, and returns to heart through pores called
ostia.
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Closed circulatory systems have blood that is kept
separate from interstitial fluid and is pumped through
increasingly small vessels to organs.
Vertebrate Circulation
Fish have a 2-chambered
heart where oxygen is pulled
from water (via gills) and goes
through the systemic circuit (to
organs) and then returns to the
heart.
 Amphibians have a 3chambered heart where blood
leaving and entering the heart
sometimes mix.

 Double circulation – blood is
pumped a 2nd time after it
moves through capillary beds.

Reptiles (except birds)
have a threechambered heart with
the ventricle partially
separated by cardiac
muscle. A right
systemic aorta also
brings mixed blood to
the systemic circuit.

Mammals and birds
(by convergent
evolution) have 4chambered hearts
for the highest
efficiency, where
blood leaving and
entering the heart
never mixes.
More on the Mammalian Heart
The contraction phase of the cardiac cycle is called
a systole, and a diastole is when the muscle
relaxes.
 Four valves (2 in ventricles, 2 in atria) keep blood
from flowing backwards.
 The sinoatrial node (pacemaker) is in the right
atrium and coordinates the muscle contractions of a
heartbeat (with help of intercalated discs in cardiac
muscle tissue).

Blood Vessels

Veins transport blood back to
the heart via smooth and
skeletal muscle contraction,
and sometimes have valves
to prevent backflow.

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Arteries take blood
to the
pulmocutaneous
and systemic
circuits, and have
thicker walls to
withstand changing
pressure from the
heart.
Capillaries have
thin walls so
oxygen can diffuse
through them.
Blood flow also
slows here.
More on Capillaries

Blood flow slows
because capillaries
have more surface
area than total
velocity of the
blood.

Precapillary sphincters
are made of smooth
muscle that contracts
and squeezes off blood
flow in the capillary bed,
except for one
thoroughfare channel.
Blood Cell Types and Composition
ALL BLOOD CELL TYPES COME FROM PLURIPOTENT STEM
CELLS IN BONE MARROW
Platelets – Cytoplasm pinched off from bone marrow,
aid in blood clotting
 Leukocytes (white blood cells) – Pathogen fighters,
usually in interstitial fluid

 5 types: basophils, eosinophils, neutrophils, monocytyes,
lymphocytes

Enthrocytes (red blood cells) – biconcave shape to
hold maximum oxygen
 No mitochondria or nucleus (use anaerobic respiration for
ATP)
 Hemoglobin enzymes transport oxygen for nitric oxide

Plasma – Liquid matrix surrounding blood cells
 Includes buffers to retain pH and protein escorts
Gas Exchange
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Amphibians use can use their skin to exchange
gases. They also use positive pressure breathing,
where air is pushed inside its body
Animals with gills ventilate (move water over
them)
Terrestrial animals have moist inner folds (lungs
with alveoli) and use negative pressure breathing,
where air is pulled inside the body.
 Respiratory pigments – proteins that load and unload
oxygen into the alveoli

Insects have a tracheal system – tubes on
abdomen draw in air directly to cells
Here’s what they look like:

Gills (bottom right),
lungs (bottom left),
tracheal system (top).
Credits
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http://www.unm.edu/~jimmy/vessels.jpg
http://bill.srnr.arizona.edu/classes/182/GasExchCirc/CircFish-2.jpeg
http://dtc.pima.edu/~biology/182/lesson11/11step3/11step3images/amphibianheart2.jpg
http://www.ambulancetechnicianstudy.co.uk/images/alveoli.gif
http://www.cartage.org.lb/en/themes/sciences/lifescience/generalbiology/Physiology/CirculatoryS
ystem/CirculatorySystem/Vertebrate/bloodvessels_3.gif
http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb6pg19_files/image002.jpg
http://cas.bellarmine.edu/tietjen/images/Sinus+animation.gif
http://gleesonbiology.pbworks.com/f/1160546416/capillaries.jpg
http://www.examstutor.com/biology/resources/studyroom/organs_and_systems/gas_exchange/pi
ctures/fig144c.gif