Chapter 23

Facilitating ExchangesCirculatory systems ensure O2, CO2, nutrients,

and wastes get to their specific sites in the bodyImportant for animals to large to survive by

diffusion aloneCnidarians and flatworms have gastrovascular

cavities that serve in digestion and distributionCells can exchange directly with water surrounding

themAnimals with multiple layers of cells need a true

circulatory systemMuscular pump (heart) and circulatory fluid (blood)

Molecular ExchangeO2 and nutrients must

enter cellsCO2 and wastes must

exitLarger organisms have

smaller outer surfaces than innerAll cells must be in an

aqueous environmentFolds and alternate

structures within to facilitate

Circulatory SystemsDirect exchange not between blood and body

cellsCells bathed in interstitial fluid that diffusion

must passOpen circulatory system

Many invertebrates including molluscs and all arthropods

Closed circulatory system Often called a cardiovascular systemEarthworms, squids, octopuses, and vertebrates

Open Circulatory SystemFluid pumped through

open-ended vessels out to cellsNo distinction between

blood and interstitial fluidBody movements

circulate fluid to allow exchange

Heart with pores that allows fluid return and prevents backflow

Respiratory exchange through tracheal system

Cardiovascular SystemBlood confined to vessels

Separate from interstitial fluid

3 kinds of vesselsArteries (red) blood Away

from heartVeins (blue) blood to heartCapillaries transport

blood between the 2Heart with atrium and

ventricle pumps blood to body cells

Arteries to arterioles to capillaries in capillary beds to venules to veins back to heart

Cardiovascular System EvolutionSingle Circuit pumps blood to capillaries

which diffuses to body tissuesDouble circulation pumps blood a second

time after losing pressure in the capillariesPulmonary circuit carries blood between the

heart and lungsSystemic circuit carries blood between the

heart and rest of the body

Single Circuit2 chambered heartBlood to gill

capillaries where pressure is reduced considerably

Flow maintained by organism’s movements

Pressure to low for complex circulation

Double CirculationAmphibians have 3

chambered heartPulmocutaneous circuit

because gas exchange in lungs and across skin

Mixing occurs, but most blood to proper location

Birds and mammals have 4 chambered heartsSupports higher

metabolic ratesDifferent ancestral

evolution so demonstrates convergent evolution

Human Cardiovascular SystemR. ventricle to lungs via

pulmonary arteriesCO2 and O2 exchange

Pulmonary veins back to L. atria to L. ventricle

Through aorta to systemic circuitBranches to upper body

and lower body separately

O2 poor blood back to R. ventricle via S. and I. vena cava

(heart to lungs to heart to body tissue to heart)

Cardiac CycleSequence of pumping

and filling of the heartHeart pumps O2 poor

blood to lungs and O2 rich blood to body

Diastole=entire heart relaxed, ventricles fill with blood

Systole=atria then ventricle contraction

Left stronger because blood to body, but volume is same in both sides=cardiac output

The Beating HeartHeart rate and cardiac rhythm can vary

Age and fitness can effectBoth increase with increasing activity levelsBlood flow controlled by internal valves

Open when pushed from behind and close when pushed from in front

Heart beat sounds = lub-dub AV and semilunar valves’ closing respectively

Heart murmur sound when blood squirts backwards

Beating to its Own Rhythm

Cardiac muscle tissue cycle without neural input Pacemaker sets the contraction rate AV node coordinates, delay to ventricle

Electric shock can be used to reset pacemaker during a heart attackArtificial pacemaker when self system fails

Cardiovascular diseaseDisorders of heart and blood vessels

Heart attack is the damage or death of cardiac tissue from blockage of coronary arteries

Stroke is death of brain tissue from vessel blockage to the head

Most caused by arterosclerosis, or plaque build up, which narrows vessel openingsClots trapped or blood flow is slowed

Anti-inflammatories, angioplasty, and clot-dissolvingTendency to be inherited, but smoking can increase

while exercise and low cholesterol diets can decrease

Blood Vessel FunctionsMust connect with all

body tissuesRemarkable length,

close enough for diffusion to occur

Into interstitial fluid first

Transport blood, nutrients, and wastes to disposal organs

Role in homeostasis and the environment of cells

Blood Vessel StructureCapillaries

Thin walls of single layer epithelial tissueWrapped in a basal lamina

Larger structuresSame epithelial structure, but reinforcedSupported by elastic fiber layer and smooth muscleArteries and arterioles

Thicker and sturdier to accommodate high pressure from heartVeins and venules

Blood to heart at lower pressure One way valves to prevent backflow

Blood FlowBlood pressure is the force blood exerts against

vessel wallsPumped to arteries faster than it can flow =

stretching of vessels, detected as pulsePressure reduces from arteries to capillaries as

resistance from vessel walls decreasesSmaller, but more numerous vesselsRelaxing muscles allows vessel dilation = drop

pressurePressure almost zero at veins

1 way valves and muscle to propel back to heart

Muscle ControlEvery part of body has

blood supply at all timesCertain areas always

full, others are rationed by need

Smooth muscle controls arteriole flow

Precapillary sphincters controlThoroughfare channel is

always openRelaxed vs. contracted

Digestive System

While eating

While exercising

CapillariesOnly vessels that can allow diffusion between blood

and interstitial fluidExchange of substances by diffusion (O2 and CO2),

carried by endocytosis and released by exocytosis, or leaks in wall (water, sugars, and salts)

Direction of movement depends on osmotic and blood pressure differencesArteriole end blood pressure drives fluid out of capillaryVenous end blood pressure drops so osmotic drives into

Fluid that leaves one end generally reenters at other Rest returned via lymphatic system

Blood Composition

RBC CountSet number needed for healthy organismsBroken down and recycled every 3-4 months

Fe returned to bone marrow to form new RBCsLow RBC count = anemia

Excessive tiredness due to lack of O2Most commonly due to low Fe (women more likely); also

blood loss, vitamin and mineral deficiency, or cancersNegative feedback sensitive to O2

Low O2, kidneys produce erthropoietin (EPO) to stimulate bone marrow production of RBCs

Increased RBC production in individuals at high altitudesConnections to athletic training, blood doping, and

artificial EPO injections

Blood Clots

Blood platelets and plasma protein fibrinogen prevent death from minor cuts, enable clotting

Upon damage vessel constricts to reduce blood lossPlatelets adhere to epithelium and form a sticky plug to halt

blood lossClotting factors released from plug to form reinforced patch

Fibrinogen converted to fibrin which traps other blood cells

Stem CellsUnspecialized cells in red marrow of bones

that can differentiate into different blood cellsLymphoid stem cells produce lymphocytes for

immune systemMyeloid stem cells produce RBCs, WBCs, and

plaeletsFormed in early embryo and make all blood

cells for life

LeukemiaCancer of white blood cells or leukocytes

Protect against infections and cancersCells become cancerous, grow uncontrollably, and

crowd RBCs and plateletsSevere anemia and impaired clotting results

Usually fatal unless treatedNot all responsive to radiation and chemoBone marrow transplant, often from a sibling

Lifelong treatment with drugs to avoid rejection of cells Can treat infected marrow to remove most cancer cells and re-

injectUmbilical cord blood has potential, but unsuccessful

so far