Circulatory SystemMost 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 VertebratesClosed 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 beginningof modern science of Physiology (understanding bodilyprocesses in terms of chemistry and physics)

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:1. Deoxygenated blood returns to heart through superior

(head, neck, and arms) and inferior (lower body) vena cava

2. Right atrium – through tricuspid valve3. Right ventricle – through semilunar valve4. Pulmonary arteries to lungs – gas exchange takes place

and blood is oxygenated – blood returns to the heart through pulmonary veins

5. Left atrium through mitral valve (bicuspid) to6. Left ventricle through semilunar valve to 7. 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 VesselsWalls 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 anddecreases 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 Blood1. 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)

2. 7 – 9% - plasma proteins (fibrinogen, albumins, and globulins – important for osmotic pressure in plasma, help to transport substances, blood clotting)

3. Organic nutrients (glucose, fats, phospholipids, amino acids, lactic acid, cholesterol)

4. Nitrogenous wastes – urea, ammonia and uric acid5. Hormones – regulatory chemicals6. 3 gases found in small amounts – nitrogen, oxygen and

carbon dioxide

Composition of BloodCells 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 Blood2. Red Blood Cells – erythrocytes

• 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)