Review Sheet 2 for Test #1 -- TRANSPORT IN ANIMALS B Circulatory Systems
Simplest animals (sponges, cnidarians, flatworms, roundworms) have no circulatory system; exchange is directly through skin or from digestive system
Components of Circulatory System: pump (heart) with vessels; blood
open circulatory system (insects) B low pressure, slow flow; independent of respiratory system
may have auxiliary pumps to help move blood through legs
closed circulatory system (annelids, vertebrates) B high pressure, rapid flow; necessary for rapid
delivery/removal of respiratory gases (O2 and CO2)
Functions of Circulatory System: (see page 906)
Blood B plasma: about 55%; cells: about 45%
Plasma with ions, nutrients, majority of CO2, wastes, hormones and proteins
Protein components include: transport proteins, clotting proteins, antibodies, albumins
Cells or Formed Elements: red and white blood cells, platelets; all formed in red bone marrow
1. Red blood cells (RBC=s; erythrocytes): small biconcave discs, good for squeezing through
capillaries as well as rapid exchange. Loaded with hemoglobin (Hb); O2 binds to Fe+ in heme; four
subunits to Hb. With 250 million Hb molecules per RBC, that means one RBC can carry one billion
molecules of O2!
During formation, initially have lots of ribosomes and mitochondria, but lose virtually all organelles
(including nucleus) before being released into the blood stream.
2. White blood cells (WBC=s; leukocytes): fight off infection; some phagocytotic, some produce antibodies
3. Platelets (thrombocytes): direct virtually all aspects of blood clotting
The Heart B receiving chamber: atrium; pumping chamber B ventricle
Evolution of the heart
Fish B two-chambered heart; blood through gills out to body and back
Amphibians B three-chambered heart: two atria and one ventricle. Both circuits (see below) have a
respiratory organ (lung & skin), so both circuits oxygenate.
Most reptiles B nearly four-chambered heart, with partial divider between the ventricles; keeps partial
separation between oxygenated and deoxygenated blood
Crocodiles, birds and mammals B four-chamber heart. Completely separate pulmonary and systemic
circuits for separating oxygenated and deoxygenated blood.
One-way valves between atria and ventricles, as well as
between ventricles and large arteries they feed.
Atrioventricular and semilunar respectively; closing of valves makes heart sounds.
Anatomy of the Human heart B Pathway for blood flow through the heart
Pulmonary Circuit B blood enters from right atrium into right ventricle through tricuspid valve, right ventricle
then pumps blood into pulmonary arteries through pulmonary semilunar valve, out to capillaries
in lungs for gas exchange (O2 in and CO2 out), back through pulmonary veins to left atrium.
Systemic Circuit B blood enters left ventricle from left atrium through bicuspid (mitral) valve, left ventricle
then pumps blood out into aorta through aortic semilunar valve, to all organs through many
branching arteries and smaller arterioles, into capillary beds for exchange of nutrients/wastes and gases
(O2 out and CO2 in), back through the veins into two large veins B the superior (drains head and
thorax) and inferior (drains body below diaphragm) vena cavae, which drain into the right atrium
Both ventricles contract together, so same amount of blood leaves both left and right ventricle with each beat.
Left ventricle pumps with greater pressure, however.
Cardiac Output = Stroke volume X Heart rate
Intrinsic conduction system -- nerve-like fibers that allow heart to beat independently:
Sinoatrial (SA) node B intrinsic pacemaker of the heart; sets pace, stimulates atria
Atrioventricular (AV) node B delays impulse from SA node (briefly), stimulates ventricles
Bundle/Purkinje fibers -- pass impulse to ventricular walls
can be modified by nervous connections and hormones
Blood pressure (B.P.) B force for transport; generated by contraction of the ventricles
Blood moves through the circulatory system due to a pressure gradient B highest in the large arteries, drops off precipitously in the arterioles and capillaries, low in the veins.
Capillary function B Exchange takes place here; basically the whole point of having a
types: continuous and fenestrated
precapillary sphincters in arterioles controls flow
two pressures are involved in exchanges at the capillaries B blood pressure forcing fluid out, and osmotic pressure drawing fluid back in
Lymphatic system B returns fluid lost at capillaries to circulatory system
vessels dead ended with lots of mini-valves to interstitial fluid
nodes cleanse the fluid, site of WBC proliferation to fight infection