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Circulatory System
Chapter 42
What you need to know!
• The circulatory vessels, heart chambers, and route of
mammalian circulation.
• How red blood cells demonstrate the relationship of
structure to function.
• The pathway a molecule of oxygen takes from the air
until it is picked up by the hemoglobin of a red blood cell.
Cardiovascular System
• System combining both the circulatory system and the
respiratory system
• Organs of exchange  body cells
(lungs, gills)
Circulatory System
Components:
1. Heart
2. Blood
3. Vessels
Variation of Circulatory Systems
• Open circulatory system
(CS) in arthropods and
mollusks:
• Heart, and some main
vessels filled with
hemolymph (not blood)
bath organs
• Closed CS in vertebrates:
• Blood remains in heart
and vessels at all times
Types of Blood Vessels
1. Arteries
2. Capillaries
3. Veins
• Pathway (in closed CS):
Heart  arteries  
arterioles  arterial capillaries
 venous capillaries 
venules  veins  back to
heart
Arteries
• Always carry blood away from
the heart
• High pressure
• Thick walls
• Branch into smaller arterioles in
organs
• Once deep in the tissue they
become…
Capillaries
• Microscopic blood vessels
in the tissue
• Deliver blood to every cell
• Thin walls facilitate
diffusion and osmosis
• Exchange of gas,
nutrients, and waste
• Converge into…
Veins
• Always carry blood back to the heart
• Venules are small veins (much like arterioles are small
arteries)
• Venules converge into larger veins
• Low pressure
• Thin walls
• Valves prevent blood from flowing back into the tissue
• Supported by surrounding smooth muscles
• Superficial
The Heart
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Hollow, muscular organ
Pumps blood
Chambers:
Atria: entrance chambers
Ventricles: main chambers
Cardiac muscle surrounds the chambers
Muscle contracts  constricts chamber  pumps blood out
Valves prevent back flow
Birds and Mammals
• 4 chambers
• 2 atria
• 2 ventricles
• Separated pulmonary
circuit
• High oxygen demands for
endotherms and large
brains
Reptiles and Amphibians
• 3 chambers
• 2 atria, 1 ventricle
• Oxygen rich and oxygen
poor blood mix together in
the ventricle
Fish
• 2 chambers
• 1 atrium
• 1 ventricle
• Lower oxygen demand (exothermic)
• Single pathway heart  gills  body  back to heart
• Muscle movement helps pump blood
• Gills and arteries use counter-current exchange for
maximum diffusion of O2 and CO2
Heart Rhythm
Cycles:
• Systole: contractions of chambers (pumping)
• Diastole: relaxation of chambers (filling)
• Atrial systole and ventricular diastole are simultaneous
• Atrial diastole and ventricular systole are simultaneous
Regulation: muscle cells contractions are orchestrated by:
1. Sinoatrial node (pacemaker) and
2. Atrioventricular nodes (delayed)
• They are situated in the cardiac muscle and give off
electrical impulses
• Independent from the brain (involuntary)
• Hearts can continue to beat after brain-dead (vegetable)
Blood
• A tissue
Contains:
• Cells
• Red blood cells (RBC) and
• White blood cells (WBC)
• Plasma, and
• Cell fragments
• Platelets
Red Blood Cell (Erythrocytes)
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Shaped like disks
Produced by bone marrow in hollow bones
Loose nuclei during maturing (in humans)
Lifespan 120 days
Aged cells (3-4 months) are reabsorbed by the spleen and
liver
Blood type antigens
Contains hemoglobin (protein with iron) for gas transport and
exchange
O2: bound loosely by hemoglobin in the lung, and is released
as blood travels through the body
CO2: 70% reacts with H2O (carbonic acid), 30% reacts with
empty hemoglobin
RBC Blood Types
• A, B, AB, O encoded on genome inherited from parents
• Determined by a surface antigen on erythrocytes
Rhesus Factors of antigen (D):
• Presence of antigen D = Rh +
• Absence of antigen D = Rh –
• Blood work at the beginning of a pregnancy is important
to help prevent Rh- mothers from producing antibodies
against an Rh+ child
White Blood Cells (leucocytes/lymphocytes)
• White blood cells are the largest portion of your immune
response
• 9 different types of WBCs (i.e. macrophages, b cells, t
cells, etc.)
• Have nucleus (unlike RBCs)
• 1% of the blood
• They identify and attack foreign substances and
microorganisms (i.e. viruses, bacteria, and transplanted
organs)
• Also found in the lymphatic system
Plasma
• Straw colored liquid
Contains:
• H2O – 90%
• Salts (isotonic to cell cytoplasm)
• Proteins
• Antibodies (as a result of inheritance as well as previous
infections and vaccinations)
Platelets
• Pinched off from bone marrow cells
• They release sticky networks of protein fibers (fibrin)
when stimulated by air
• Stops blood flow
Lymphatic System
• Plasma and protein can leak into tissue from the
capillary beds
• The lymphatic system returns this fluid (lymph) to the
vena cava
• Before returning the fluid it is filtered through lymph
nodes (WBC filters) to remove viruses and bacteria
Consists of:
• Tonsils, thymus gland, spleen, and lymphatic vessels