Circulation and Gas Exchange

Chapter 42

Overview: Trading with the Environment• Every organism must exchange materials &

energy with environment• Exchanges ultimately occur at the cellular

level

• In unicellular organisms, exchanges occur directly with environment

In multicellular organisms, direct exchange with environment not possible with all internal cells

Diffusion always at cellular level BUT diffusion over long dist (lung to internal cells) too slow

Therefore developed physiological systems specialized for transport (circulatory) & exchange (respiration)

Concept 42.1: Circulatory systems reflect phylogeny

• Diffusion alone not adequate for transporting substances over long distances within animals

• Therefore complex animals have internal transport systems (circulatory systems) that circulate fluid & connect the organs of exchange with the body cells for exchg

Invertebrate Circulation

• The wide range of invertebrate body size & form plus differences in environmental pressures = diversity in circulatory systems

Gastrovascular cavities

Open and Closed Circulatory Systems

Complex animals with many cell layers have: - open circulatory system- closed circulatory system

Both have 3 components in common:1. circulatory fluid (blood or hemolymph2. set of tubes (blood vessels)3. muscular pump (heart provides pressure

to move fluid)

In insects, other arthropods, & molluscs bloodbathes organs directly in open circ system

no distinction between blood & interstitial fluid; general body fluid = hemolymph

Closed circulatory system = blood confined to vessels & distinct from interstitial fluid

Closed systems more efficient at transporting circ fluids to tissues & cells (worm is an example)

Vertebrate Circulation

Humans & other vertebrates blood flows in closed circulatory system (blood vessels & 2- 4-

chambered heart) = cardiovascular system

- arteries: carry blood to capillaries, sites of

chemical & gas exchange between blood & interstitial fluid (single cell layer that

gas exchanges)

- veins: return blood from capillaries to heart

Fishes• 2 main chambers: ventricle & atrium• Blood pumped from the ventricle travels to the

gills, where it picks up O2 and disposes of CO2

Amphibians• Frogs and other amphibians have a three-

chambered heart: 2 atria & 1 ventricle

R atrium L atrium

Ventricle

Reptiles

One can say that the reptile heart has 3 chambers, 2 atria & 1, partially divided, ventricle. Or one may argue that reptiles have 4-chambered hearts with 2 atria & 2 ventricles, but the wall between the ventricles is incomplete.

Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit

Mammals and Birds In all mammals & birds, ventricle divided into

separate R & L chambers

L side : pumps & receives only O2-rich blood R side: receives & pumps only O2-poor blood

A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds

Endotherms need 10x energy as equal-sized ectotherm so mustdeliver more via blood

Concept 42.2: Double circulation in mammals depends on anatomy & pumping cycle of heart

The human circulatory system serves as a model for exploring mammalian circulation

Mammalian Circulation: The Pathway• Heart valves dictate a one-way flow of blood

through the heart• Blood begins its flow with R ventricle pumping

blood to lungs• In lungs, blood loads O2 & unloads CO2

• O2-rich blood from lungs enters heart at L atrium & into L ventricle where then pumped to body tissues

• Blood returns to heart at R atrium

The Mammalian Heart: A Closer Look provides a better understanding of dbl circ

Valves

Cardiac cycle

- contraction, or pumping, phase = systole

- relaxation, or filling, phase = diastole

Heart sounds, heard with stethoscope, caused by closing of valves.

“lub-dup, lub-dup”

Lub=close AV

Dub=close semilunar

Heart murmur = defect in valve detectable as a hissing sound when blood squirts backward through it

Rheumatic fever can cause

Heart rate = pulse = beats per minute

Cardiac OP = volume blood pumped into systemic circ per minute

Stroke vol = amt blood pumped by L ventricle per contraction________________________________________

Av stroke vol … 75 mlAv ht rate ……..70/min

Cardiac OP: 75 * 70 = (5,250 ml) 5.25 L/min

Heart’s Rhythmic BeatCardiac muscle stims self = contract without signal from nervous syst

Pacemaker influenced by nerves, hormones, body T, & exercise

Impulses during cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)

Concept 42.3: Physical principles govern blood circulation

Structure/function: arteries, veins, & capillariesVelocity blood flow slowest in capillary beds

- arteries: thick wall + muscle- veins: blood flow result muscle action; valves

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- Exchange materials & gases at capillaries- BP at capillaries pushes fluid out into tissues

Fluid in tissues & 85% reenters at venous end Remaining 15% returned via lymphatic system

Critical exchange between blood & interstitial fluidtakes place across thin endothelial walls capillaries

Diff between BP & π drives fluids out capillaries at arteriole end & into capillaries at venule end

Fluid Return by the Lymphatic System

• The lymphatic system returns fluid to the body from the capillary beds

• This system role in body defense• Fluid reenters the circulation directly at the

venous end of the capillary bed & indirectly through the lymphatic system

Concept 42.4: Blood is a connective tissue with cells suspended in plasma

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Cellular ElementsSuspended in blood plasma

- red blood cells (erythrocytes) transport O2- white blood cells (leukocytes) body defenses

- platelets = frags cells & involved in clotting

Stem Cells & Replacement of Cellular Elementspluripotent stem cells in red marrow of bones

erythropoietin

Blood ClottingCascade rxs (fibrinogen to fibrin) = clot

hemophiliathrombus

Cardiovascular Disease disorders of heart & blood vessels account for > half deaths in United States

Artheroscloresis: accumulation cholesterol in arteries

Chlosterol transported as lipid:prot particlesLDL (low density lipoprot) = “BAD” cholesterolHDL (high density lipoprot) = “GOOD” cholesterol

Satd fats = ↑ tendency artherosclerotic plaques

• Hypertension, or high blood pressure, promotes atherosclerosis and increases the risk of heart attack and stroke

• A heart attack is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries

• A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head (can be side effect of heart attack)

Concept 42.5: Gas exchange occurs across specialized respiratory surfaces

Gas exchange = uptake O2 from environment & discharge CO2 (from cell resp) to environment

Animals require large, moist respiratory surfaces for adequate diffusion of gases between their cells & the respiratory medium…. air for terrestrial animals and water for most aquatic animals

Respiratorymedium(air or water)

Organismallevel

Cellular level

Energy-richfuel molecules

from food

Respiratorysurface

Circulatory system

Cellular respiration

CO2O2

ATP

Structure of respiratory surface depends on size of organism & whether it lives in water or on land

A. Water Habitat- Have gills = outfoldings of body surface suspended in water- Water [O2] low so special processes to ↑ efficiency of exchg

B. Terrestrial HabitatTracheal system of insects consists of tinybranching tubes that penetrate the body

The tracheal tubes supply O2 directly to body cells

LungsMost terrestrial vertebrates have internal lungs

system of branching ducts conveys air to lungsAir inhaled through the nostrils passes throughpharynx into trachea, bronchi, bronchioles, &dead-end alveoli, where gas exchange occurs

Mammals ventilate their lungs by neg pressure Inhale = ↑vol lung = pulls air into the lungs Exhale = musc relax & elastic fibers retract lung

Sensors in aorta & carotid arteries monitor O2 &CO2 concentration in blood = exert 2ndary control over breathing

Main breathing control center in brain which regulates rate & depth of breathing in response to pH changes in Cerebrospinal fluid

Gases diffuses from higher partial pressure (conc) to lower partial pressure

Oxygen TransportHemoglobin reversibly binds O2

- loads O2 in lungs - unloads it in other parts body

Drop in pH lowers affinity of hemoglobin for O

Carbon Dioxide Transport (mostly as HCO3)

CO2 diffuses into Red blood cells where + H2O forms carbonic acid which dissoc into

H+ & HCO3-

H+ binds to Hemoglobin

HCO3- diffuses into

plasma & carried to lungs

In lungs, reverse occurs

CO2 from respiring cells diffuses into

blood plasma & then into red

blood cells

CO2 from tissues carried

as HCO3- in

plasma of blood &

released in lungs

Baby steals O2 from mom’s blood