THE CIRCULATORY SYSTEM
I.
II.
Blood vessels
A.
Arteries—carry blood away from the heart (usually oxygenated—the only exception is
the pulmonary artery)
1.
3 layers thick; expandable walls
a.
endothelium—thin, inner membrane (smooth lining)
b.
middle layer—smooth muscle w/ elastic fibers for expansion
c.
outer layer—tough connective tissue w/ collagen for strength and
elastin for elasticity
2.
are “highways” for blood and its components
3.
branch into narrower arterioles, which further branch into capillaries
B.
Capillaries
1.
are the major exchange system for gases, water, nutrients, wastes, hormones,
etc.
2.
blood moves through due to narrow passage ways (called capillary action)
3.
capillary “beds” are the only place where veins and arteries meet
C.
Veins
1.
carry blood back toward the heart
2.
structure varies a bit from arteries
a.
layers are the same, but thinner
b.
have valves to prevent backflow of blood
c.
narrow into venules, then into venous capillaries
D.
“Portal” systems
1.
veins w/ networks of capillaries at each end
2.
type of “portal” depends on organism
Ex: renal portal system (most reptiles), hepatic portal system (mammals)
The Heart
A.
Location
1.
middle of thoracic cavity
2.
behind sternum and between lungs
B.
Structure
1.
fist-sized (~0.4 kg) organ covered with pericardium
a.
pericardium = double-walled sac containing fluid to reduce friction in
tissues
2.
main part of heart is myocardium (the muscle w/ both skeletal and involuntary
features
a.
oxygen and carbon dioxide exchange occurs in coronary arteries and
veins (coronary circulation)
3.
chambered—divided into left and right sides by a septum
a.
atria (-um)—2 relatively thin-walled upper chambers
b.
ventricles—thick-walled (esp. the left) comprising the lower half of the
heart
c.
valves separate the 4 chambers
1)
atrioventricular (AV) valves—between atria and ventricles; open
when the heart contracts
2)
semilunar valves—between ventricles and major blood vessels;
opened by pressure from contraction of ventricles
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III.
4.
lining = endocardium
Cardiac cycles and controls
A.
Sino-atrial (SA) node
1.
located in rear wall of right atrium
2.
is the “pacemaker” of the resting (base) heart rate
3.
electrical signal causes atria to contract in unison
B.
Atrioventricular (AV) node embedded in the septum between ventricles causes the
ventricles to contract in unison when the atria relax
C.
Phases of the cardiac cycle
1.
systole—when chambers are contracting
2.
diastole—when chambers are relaxed
3.
entire cycle lasts approx.. 0.85 seconds (figures don’t add up due to overlap)
a.
atrial systole = 0.15 seconds
b.
ventricular diastole (occurs when atria are in systole) = 0.55 seconds
c.
atrial diastole = 0.70 seconds
d.
ventricular diastole = 0.30 seconds
D.
Blood pressure
1.
pressure exerted on arterial walls as the heart pumps blood
2.
measured in millimeters of mercury (mmHg)
3.
“top number” is the systolic (working) pressure
4.
“bottom number” is the diastolic (resting) pressure
a.
average adult = 120/80 (but most doctors want to see the bottom #
even lower)
E. Blood flow
1.
right side of heart pumps blood to lungs (pulmonary circulation)
2.
left side pumps to body (systemic circulation)
Path of blood:
Right atiumtricuspid valveright ventriclepulmonary semilunar valvepulmonary artery (branches
into the left and right pulmonary artieries)(gas exchange occurs at alveolar capillaries)left and right
pulmonary veinpulmonary semilunar valveleft atriumbicuspid valveleft ventricleaortic
semilunar valveaorta rest of the body
Fetal vs. adult circulation
1)
2)
3)
Fetus obtains nutrients & oxygen from maternal blood
wastes such as carbon dioxide are eliminated via fetal circulation
liquid wastes are removed by the allantoic duct
**there is no direct connection between mom and the fetus!!
4)
The indirect connection is the placenta (one placenta/fetus)
--capillaries within the placenta allow diffusion of oxygen & nutrients…carried via the umbilical
vein--> some branches go to the LIVER, the joins the INFERIOR VENA CAVAheartcarries oxygen and
nutrients through the bodydeoxygenated blood leaves via the UMBILICAL ARTERIES
5)
After birth, the DUCTUS VENOSUS becomes the LIGAMENTUM VENOSUM (a liver ligament)
6)
umbilical arteries + umbilican vein + allantoic duct = umbilical cord
**NOTE: The fetus makes its own blood, which interfaces with mom’s blood within the capillaries of the
placenta
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Other FETAL CIRCULATORY STRUCTURES
1)
Foramen ovale—an opening in the interatrial septum (this acts to shunt most of the incoming
blood into the left atrium, bypassing the (nonbreathing) lungs
2)
Ductus arteriosus—a temporary vessel connecting the pulmonary trunk with the aorta (another
by-pass mechanism)
AFTER BIRTH:
Umbilical vein—becomes the round ligament of the liver
Umbilical arteries—becomes fibrous tissue
Ductus venosus—becomes the ligamentum venosum
Foramen ovale—closes and leaves a slight depression (the fossa ovalis)
Ductus arteriosus—becomes the ligamentum arteriosum
**patent ductus arteriosis and patent foramen ovaleresult in the mixing of oxygenated and
deoxygenated blood (this is what is meant when you hear someone say they have a “hole in the heart”)
IV.
The blood
A.
Components
1.
formed elements (hematocrit) = 3 types of cells
a.
erythrocytes (red blood cells, or rbc’s)
1) biconcave discs w/ no nucleus when mature
2) carry hemoglobin
a)
globin=protein composed of 4 polypeptides chains
b)
heme=complex containing an iron ion, which binds
loosely to oxygen
c)
carries some carbon dioxide, but most CO2 is in the form
of bicarbonate ion
3) lifespan of about 120 days
a)
removed from blood by phagocytic cells in liver and
spleen
b)
Hb released; Fe recovered and delivered back to bone
marrow
c)
heme degraded and excreted as a bile pigment (
biliirubin)
b.
leukocytes (white blood cells)—immune system warriors
c.
thrombocytes (platelets)—clotting
2.
Plasma = liquid portion of blood
a.
contains water, inorganic salts, gases, urea, uric acid, ammonia,
hormones, vitamins, etc.
b.
plasma proteins: assist in transport of large organic molecules
(hormones, bilirubin, fat-soluble molecules, cholesterol, etc.)
1) gives “viscosity” to blood (thickness); needed to exert blood
pressure on blood vessels & important in blood movement
2) maintains blood volume for proper blood pressure; albumin
helps osmotic pressure
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3)
B.
C.
some plamsa proteins have functions that can’t be duplicated by
any other protein
a)
fibrinogen = blood clotting
b)
gamma globulins = antibodies
Blood clotting functions
1.
coagulation of blood occurs at open injuries
a. serum is squeezed out of the clot
1) contains all the components of plasma except fibrinogen
b. blood clots
1) 12 clotting factors (proteins) + thrombocytes = clot
a)
fibrinogen and prothrombin are the primary proteins
needed for clot formation
Infection-fighting function of blood
1.
leukocytes
a.
appearance
1) larger than red blood cells
2) have nuclei
3) no hemoglobin
4) white when not stained
b.
different types
1) granular leukocytes—have granules in cytoplasm which contain
digestive enzymes
a)
neutrophils—most common WBC’s
i)
many-lobed nucleus
ii)
granules stain lavender
iii)
phagocytize bacteria
b)
eosinophils
i)
granules stain red
ii)
many-lobed nucleus
iii)
phagocytize antigen-antibody complexes
c)
basophils—least common
i)
granules stain deep blue
ii)
many-lobed nucleus
iii)
release histamine when stimulated (part of
allergic response)
2) Agranular leukocytes
a)
produced in bone marrow
b)
some mature in thymus glgand
c)
stored in spleen, tonsils, & other lymphoid tissues
d)
2 types
1)
monocytes—largest WBC’s, with a single
nucleus; important in chronic infections for
phagocytizing bacteria and viruses
2)
lymphocytes—commonly called B-cells and Tcells; have a single indented nucleus
--B-cells produce antibodies in blood
--T-cells phagocytize antigens and produce
lymphokines (part of the immune response)
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D.
E.
Antibodies
1.
produced by B-cells in response to antigens
a.
antigens = foreign substances capable of stimulating an immune
response
2.
are antigen-specific (determinant site on surface of antigen)
3.
forms a complex w/ the antigen (agglutination); prepares for phagocytosis and
activation of complement (series of immune responses)
Inflammatory response
1.
occurs at site of injury to tissues or capillaries
2.
bradykinin is secreted which initiates nerve impulses in pain receptors
3.
histamines are released by basophils
4.
capillaries dilate and become permeable to neutrophils (causes redness &
edema)
5.
neutrophils engulf Ag-Ab complex
6.
pus forms (dead tissue, dead neutrophils & bacteria, live WBC’s, etc)
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