Download Circulatory System

Circulatory System
Most animals have a circulatory system
including a pumping device – heart
• Open Circulatory System – system may
have large open spaces (sinuses) where
definite vessels are absent (mollusks,
insects) organs are bathed in blood – less
efficient oxygen delivery
• Closed Circulatory System – blood stays
enclosed in vessels throughout system
(earthworms, all vertebrates)
Circulation in Vertebrates
Closed system consisting of:
• Arteries – carry blood away from the heart – branch into smaller
vessels called arterioles
• Capillaries – tiny vessels where exchange occurs (walls are only
one or two cells thick)
• Venules – small vessels that lead away from capillaries – branch
into the larger
• Veins – vessels that carry blood back to the heart
– Veins have valves to assist in moving blood up to the heart
(against gravity) and also depend on squeezing from muscles
William Harvey (1628) – published work marked the beginning
of modern science of Physiology (understanding bodily
processes in terms of chemistry and physics)
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Circulation Pathway in Humans
4 chambered heart – 2 separate pumps separated by
the septum
Coronary arteries supply the heart itself with oxygenated
blood
Heart Circulation:
Deoxygenated blood returns to heart through superior
(head, neck, and arms) and inferior (lower body) vena
cava
Right atrium – through tricuspid valve
Right ventricle – through semilunar valve
Pulmonary arteries to lungs – gas exchange takes place
and blood is oxygenated – blood returns to the heart
through pulmonary veins
Left atrium through mitral valve (bicuspid) to
Left ventricle through semilunar valve to
Aorta - very large artery carries oxygenated blood to the
body
(Tricuspid)
(Bicuspid)
Circulation outside of the heart is divided into:
• Pulmonary circulation – pulmonary arteries
carry deoxy. blood to lungs and pulmonary
veins carry oxy. blood to heart
• Systemic circulation – aorta, arteries and
arterioles carry oxg. blood to cells – venules
and veins carry deoxy. blood back to heart
Structure of Blood Vessels
Walls composed of three layers:
• Outer connective tissue layer – provides elasticity
• Middle layer of smooth muscle
• Inner layer of connective tissue lined with endothelium
1. Arteries have a thick layer of smooth muscle (very strong
and elastic – can withstand high pressure)
– Inner diameter is small
2. Veins are much less elastic (don’t have as much pressure)
– Smooth muscle layer is thinner and inner diameter is
wider
3. Capillary walls are 1 or 2 cells thick to allow exchange
between blood and tissues
Circulation in other Vertebrates
• Four chambered hearts characteristic of birds and
mammals
– High metabolic rates necessitate efficient oxygen
delivery system (no mixing of oxy. and deoxy. blood)
• Fish have a two chambered heart – systemic
circulation under very low pressure, blood moves
sluggishly
• Amphibians and reptiles have three chambered
heart – 2 atria and 1 ventricle
– Oxy. and deoxy. blood mix in ventricle
– Reptiles show beginning of development of septum
(reduces mixing)
Contraction of the Heart
• Cardiac cells tend to contract naturally
– Contraction of one heart cell stimulates contraction of
neighboring cells
• Heartbeat is initiated by the sinoatrial node
(pacemaker)
– located in wall of right atrium
• Impulse is carried to ventricles by atrioventricular
node located on septum between atria
– Bundle of His – fibers that extend from AV node into
walls of ventricles
– Purkinje fibers further branch into all parts of ventricular
muscle
• Contraction of atria is initiated by SA node – wave
of contraction passes through atria to AV node –
impulse transmitted to ventricles and wave
continues
• Cardiac muscle cells are electrically
coupled by intercalated disks between
adjacent cells
Cardiac Cycle
• Alternating contraction and relaxation of the heart
chambers
• Contraction phase called systole, and relaxation phase
called diastole
• Heart sounds heard with stethoscope are caused by
closing of the valves
• Sound pattern is “lub-dup, lub-dup, lub-dup”
• First heart sound (“lub”) created by closing of AV valves
• Second sound (“dup”) created by closing of semilunar
valves
• Heart murmers – occur when valves are damaged and do
not shut completely, some blood leaks backward resulting
in a hissing sound
• Electrocardiograms – used to detect electrical changes
during contraction (can detect abnormalities)
Blood Pressure and Rate of Flow
• During systole, heart contracts and blood is
forced into arteries under high pressure
• During diastole, heart relaxes and blood
pressure falls in arteries
• Blood pressure is measured to record the
regular cycle of pressure in the arteries as
the heart contracts
– Usually measured in upper arm (brachial artery)
with a sphygmomanometer and stethoscope
– Average pressure for young adult male is 120
(systolic)/80 (diastolic)
Blood pressure varies by location in body and
decreases with distance from the heart
• Resulting gradient of pressure causes continuing
flow of blood – fluids move from regions of high
pressure to regions of low pressure
• Differences in systolic and diastolic pressures
diminish with distance from heart
• By the time blood reaches capillaries the flow is
constant (rather than surging as in the arteries)
• Pressure continually drops through arterioles and
capillaries, lowest in veins closest to heart
• Rate of flow highest in arteries
• Rate of flow lowest in capillaries
• Increases again in veins
Capillary Function
• Extremely small in diameter – RBCs pass through single
file
•Highly branched to
increase total cross –
sectional area
•results in low pressure and
slower flow (more time for
exchange btw blood and
cells)
•Large surface area for
exchange and penetration
into all tissues
Mechanisms for Exchange between Blood
and Tissue
• Diffusion
• Materials are picked up by vesicles in cell
membrane of capillary endothelial cell
(endocytosis) travel across cell and are
expelled by exocytosis
• Water and dissolved molecules (not
proteins) filter through clefts between
adjacent endothelial cells
Composition of Blood
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Plasma – liquid matrix constituting 50 – 60% of whole
blood plasma is 90% water with a variety of dissolved
substances:
• 0.9% - inorganic cations (Na+, Ca+2, K+, Mg+2) and
organic anions (Cl-, HCO3-)
 concentrations are kept relatively stable to maintain
homeostasis (even slight shifts in concentration can
cause dysfunction or cell death)
7 – 9% - plasma proteins (fibrinogen, albumins, and
globulins – important for osmotic pressure in plasma, help
to transport substances, blood clotting)
Organic nutrients (glucose, fats, phospholipids, amino
acids, lactic acid, cholesterol)
Nitrogenous wastes – urea, ammonia and uric acid
Hormones – regulatory chemicals
3 gases found in small amounts – nitrogen, oxygen and
carbon dioxide
Composition of Blood
Cells found in blood:
1. White blood cells – leucocytes
• Five major types: monocytes, neutrophils, basophils,
eosinophils, and lymphocytes
• Fight infections
• Monocytes and neutrophils are phagocytes
• Eosinophils fight infection against parasites
• Basophils release histamine – causes vasodilation
(increases blood flow to injured site) – part of
inflammatory response
• Lymphocytes – B cells and T cells – part of specific
immune response resulting from exposure to an antigen
(foreign substance in body)
 B cells produce antibodies (globulin proteins) to
destroy antigen – specifically fight antigen that
stimulates production
Composition of Blood
2. Red Blood Cells – erythrocytes
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Biconcave, disc-shaped, lack nuclei
Approx 5 million/mm3 of blood
Live approx 120 days – destroyed by liver and
spleen
Formed in red bone marrow (in long bones,
skull, ribs, and pelvis)
Filled with hemoglobin (carries oxygen, gives
red color)
•Some animals (mollusks and
arthropods) have hemocyanin –
contains Cu instead of Fe –
dissolved in plasma not in cells
• Whole blood – blood as it is in the
circulatory system
• Blood plasma – whole blood without
formed elements
• Blood serum – plasma without fibrinogen
Blood Clotting
• Fibrinogen comes out of solution and converts to
fibrin (forms a hard lump or clot)