CHAPTER 42CIRCULATION AND GAS

EXCHANGE

Word List:

aorta - the biggest and longest artery (a blood vessel carrying blood away from the heart) in the body. It carries oxygen-rich blood from the left ventricle of the heart to the body.inferior vena cava - a large vein (a blood vessel carrying blood to the heart) that carries oxygen-poor blood to the right atrium from the lower half of the body.left atrium - the left upper chamber of the heart. It receives oxygen-rich blood from the lungs via the pulmonary vein.left ventricle - the left lower chamber of the heart. It pumps the blood through the aortic valve into the aorta.mitral valve - the valve between the left atrium and the left ventricle. It prevents the back-flow of blood from the ventricle to the atrium.pulmonary artery - the blood vessel that carries oxygen-poor blood from the right ventricle of the heart to the lungs.pulmonary valve - the flaps between the right ventricle and the pulmonary artery. When the ventricle contracts, the valve opens, causing blood to rush into the pulmonary artery. When the ventricle relaxes, the valves close, preventing the back-flow of blood from the pulmonary artery to the right atrium.pulmonary vein - the blood vessel that carries oxygen-rich blood from the lungs to the left atrium of the heart.right atrium - the right upper chamber of the heart. It receives oxygen-poor blood from the body through the inferior vena cava and the superior vena cava.right ventricle - the right lower chamber of the heart. It pumps the blood into the pulmonary artery.septum - the muscular wall that separates the left and right sides of the heart.superior vena cava - a large vein that carries oxygen-poor blood to the right atrium from the upper parts of the body.tricuspid valve - the flaps between the right atrium and the right ventricle. It is composed of three leaf-like parts and prevents the back-flow of blood from the ventricle to the atrium.

• Get nutrients/wastes in/out of cells

• Diffusion – 100 sec. -> 1mm; 3hrs. -> 1cm! NOT EFFICIENT.

• Diffusion - needs thin, flat bodies - 2 cell layer or diploblastic - in hydra (cnidaria), branching Gastrovascular cavity and flat/thin body in planaria (Platyhelminthes)

Why is there a circulatory system?

• Circulatory system in all higher phyla:

• Heart - why?, blood vessels - closed or open system, circulatory fluid - hemolymph/blood

Why is there a circulatory system?

• Open circulatory system- blood bathes organs directly. There is no distinction between blood and interstitial fluid, collectively called hemolymph.

• insects, other arthropods, and most mollusks

Fig. 42.2a

•Closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid (liquid bathing cells). Earthworms - heart is a tube.

•earthworms, squid, octopuses, and vertebrates

•Open circulatory system, hemolymph flows through open vessels and is not distinct from the interstitial fluid. Heart (long tube) pumps fluid into body spacs called sinuses and fluid reaches back through openings called ostia.

•Molluscs, arthropods, echinoderms like seastars

What are the advantages and disadvantages of open circulation?

-less energy needed to work it, build, and maintain

-serves as skeleton in molluscs

-less effective at transport

What are the advantages of closed circulation?-very effective at transport

-higher hydrostatic pressure in vessels

-great for increased metabolic need/larger size

• The closed circulatory system

• Heart consists of atria, (receive blood returning to the heart), ventricles, (pump blood out of the heart).

• Arteries (away from heart to capillaries), veins (towards heart from capillaries), and capillaries - blood vessels.

• Arteries -> arterioles -> capillary bed -> venules -> veins

• Need a mechanism for oxygenating the blood (lungs, skin, gills)

Cardiovascular system -Vertebrates

• Fish heart has two chambers, one atrium and one ventricle. One loop of circulation.

• Ventricle to the gills (the gill circulation) -> For Oxygenation

• Systemic (body) circulation- Oxygenated blood -> body

-Deoxygenated blood -> heart

Fig. 42.3a

• Frogs and other amphibians - a three-chambered heart with two atria and one ventricle.

• Two loops of circulation

• Pulmocutaneous -Deoxygenated blood ->taken to lung + skin foroxygenation

• Systemic circulations

- Oxygenated blood -> body

- Deoxygenated blood -> heart

Fig. 42.3b

• Reptiles - double circulation with pulmonary (lung) and systemic circuits.

• less mixing of oxygen-rich and oxygen-poor blood (ventricle is partially divided).

• Crocodiles, birds, and mammals- the ventricle is completely divided

• Left – Oxygenated Blood

• Right – Deoxygeneated blood

• Double circulation- meets needs of

endotherm (higher metabolic rate)

Fig. 42.3c

• Right ventricle -> pulmonary artery - >

• Lungs - > capillaries load up oxygen, unloads CO2 -> pulmonary veins ->

• Left atrium - > (pulmonary circulation)

• Left Ventricle -> Aorta -> arteries -> capillaries near body cells (systemic circulation)

• -cells get oxygen and give back CO2 to blood in capillaries

• Capillaries -> venules -> veins -> venacava

• Right Atrium

• -> Right ventricle

• DOUBLE CIRCULATION

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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 42.5

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• Coronary arteries- supply the heart!

• Cardiac cycle - one complete sequence of contraction (systole) and relaxation (diastole).

• Cardiac output (L/min.) depends on two factors: the rate of contraction or heart rate (number of beats per second) and stroke volume (the amount of blood pumped by the left ventricle in each contraction).

• The average stroke volume for a human is about 75 mL.

• The typical resting cardiac output, about 5.25 L / min, is about equivalent to the total volume of blood in the human body.

• Cardiac output can increase about fivefold during heavy exercise.

• Heart rate can be measured indirectly by measuring your pulse - the rhythmic stretching of arteries caused by the pressure of blood pumped by the ventricles.

• Four valves in the heart, each consisting of flaps of connective tissue, prevent backflow and keep blood moving in the correct direction.

• Atrioventricular (AV) valve – (A and V)

• Two sets of Semilunar valves- (LV and Aorta; RV and Pulmonary artery)

•The first heart sound (“lub”) is created by the recoil of blood against the closed AV valves.

•The second sound (“dup”) is the recoil of blood against the semilunar valves.

•Defect in valve= heart murmur (swoosh, clicks)

• The cardiac cycle is regulated by electrical impulses that radiate throughout the heart.

• Pacemaker – Sinoatrial (SA) Node - sets heart rate and pumping- in right atrium; Self- excitation of heart muscle starts here(myogenic vs neurogenic)

Fig. 42.7

•Cardiac muscle cells are electrically coupled by intercalated disks between adjacent cells.

•Stimulus spreads to Atrioventricular (AV) node at the junction of right atrium and right ventricle; Signal waits for 0.1 sec here (allows atrium empty fully before ventricles contract)

•Purkinje fibers then carry contraction impulse to rest of heart

• Currents can be detected by electrodes and recorded as an electrocardiogram (ECG or EKG).

What influences heart rate?

• Exercise

• Sex

• Age

• Flight or fight response

• Temperature

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• Outside- a layer of connective tissue with elastic fibers allows the vessel to stretch and recoil.

• Middle layer -smooth muscle and more elastic fibers.

• Endothelium- Lining the lumen (cavity), a single layer of flattened cells - capillaries have only this layer- WHY???

Structural differences of arteries, veins, and capillaries correlate with their functions

Thick middle layer- maintains pressure in vessels even if heart is relaxed

Thin middle layer- low velocity and pressure as blood flows back

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• Will blood flow faster in a big fat aorta or thin capillaries?

Fig. 42.9

•Blood flows >1000 times faster in Aorta than capillaries

•Will blood flow in veins be faster/slower than capillaries?• Faster- flow depends on total cross sectional area

Blood flow review

• Heart contracts (systole)

• Aorta-> Arteries -> Arterioles ->

• Capillaries

• Venules -> Veins -> Venacava

• Heart relaxes (diastole)

• Blood back to heart

What is a diastole?What is a systole?Blood pressure, the

hydrostatic force that blood exerts against vessel walls, is much greater in arteries than in veins and is highest in arteries when the heart contracts during ventricular systole, creating the systolic pressure (120 mm Hg)

Fig. 42.10

The elastic walls of the arteries snap back during diastole, but the heart contracts again before enough blood has flowed into the arterioles to completely relieve pressure in the arteries- the diastolic pressure (80 mmHg)This is called peripheral resistance Blood pressure depends on peripheral resistance and cardiac output (hmmm???)

• A sphygmomanometer measures blood pressure (depends on cardiac output and peripheral resistance; gravity, stress, exercise, age, sex…???)

• 120 mm Hg at systole and 70 mm Hg at diastole.

Fig. 42.11

• Capillaries have sphincters- control flow

• Solutes and water leave the capillaries and move into space around cells (interstitial fluid)- WHY?

Fig. 42.12

Fig. 42.13

•85% of the fluid that leaves reenters

•Remaining 15% is eventually returned to the blood by the vessels of the lymphatic system.

The lymphatic system returns fluid to the blood and aids in body defense

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Blood has RBCs (erythrocytes) and WBCs (leukocytes), and platelets (clotting) as cellular elements

Fluid in blood = Plasma (50%)

Has water, ions, proteins like immunoglobins (antibodies),

Blood transports nutrients, gases, wastes,hormones

Blood is made in bone marrow from adult stem cells

EPO - hormone stimulates RBC production (doping)

CHAPTER 42 GAS EXCHANGE

Fig. 42.18

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Gas exchange is the uptake of O2 and the discharge of CO2

Aquatic

Simple Diffusion

“Aquatic”

Skin – respiratory organ!

“Aquatic”

Gills– respiratory organ

“Aquatic”

Gills– respiratory organ

“Terrestrial”

Tracheae– respiratory organs

“Terrestrial”

Lungs– respiratory organs

• Gills = Aquatic environment; need ventilation (movement of water over gills)

Fig. 42.19

Fig. 42.20

• Fish Gills =Counter current exchange -water moves opposite to blood in gills

• Blood meets water with MORE oxygen at every point. Diffusion gradient all along the capillary favors oxygen exchange

•The tracheal system of insects is composed of air tubes that branch throughout the body (why is this different from lungs?).

•WHY AIR IS BETTER THAN H2O

•More O2 in air than in water (less dissolved O2 in warm/salty ocean water)

•Gases diffuse faster in air – less ventilation

•Air is lighter

•Problem – evaporation; Solution – Closed Circulatory System

LUNGS: Spiders, terrestrial snails, and vertebrates

• System of branching tubes: trachea, bronchi, bronchioles, alveoli

• Respiratory surface – capillary network surrounding alveoli

• Circulatory system transports gases between the lungs and the rest of the body.

Negative pressure breathing.

• This works like a suction pump, pulling air instead of pushing it into the lungs. Muscle action (diaphgram and rib muscles) changes the volume of the rib cage and the chest cavity,and the lungsfollow suit.

Fig. 42.24

• The volume of air an animal inhales and exhales with each breath is called tidal volume.

• About 500 mL in resting humans.

• The maximum tidal volume during forced breathing is the vital capacity,

• about 3.4 L and 4.8 L for college-age females and males, respectively.

• The lungs hold more air than the vital capacity, but some air remains in the lungs, the residual volume, because the alveoli do not completely collapse (stale and fresh air mix)

HOW MUCH AIR???

• Besides lungs, birds have eight or nine air sacs that do not function directly in gas exchange, but act as bellows that keep air flowing through the lungs. Birds can carry more oxygen = better performance under some conditions such as???

Fig. 42.25

• Breathing control centers are located in two brain regions, the medulla oblongata and the pons.

• medulla and pons -trigger contraction of the diaphragm and rib muscles (rate of breathing).

• Stretch receptors in ribs inhibits the breathing center (Negative-feedback mechanism)

• Sensors in aorta, and other arteries detect O2 changes and signal medulla to

Control centers in the brain regulate breathing

What are alveoli?

• Partial pressure- the contribution of a particular gas to the overall total pressure.

• At sea level, the atmosphere pressure = 760 mm Hg.

• 21% oxygen; the partial pressure of oxygen (abbreviated PO2) is 0.21 x 760, or about 160 mm Hg.

• The partial pressure of CO2 is only 0.23 mm Hg.

Gases diffuse down pressure gradients

• A person exercising consumes almost 2 L of O2 per minute, but at normal body temperature and air pressure, only 4.5 mL of O2 can dissolve in a liter of blood in the lungs.

• If 80% of the dissolved O2 were delivered to the tissues (an unrealistically high percentage), the heart would need to pump 500 L of blood per minute - a ton every 2 minutes.

Respiratory pigments transport gases and help buffer the blood

• O2 is bound to special proteins called respiratory pigments instead of dissolved in solution.

Hemocyanin - Arthropods

Hemoglobin -Vertebrates

• Coopertive binding of Oxygen To Hemoglobin: Dissociation Curve and Bohr’s Shift

• Hemoglobin protein has 4 subunits- binding of one subunit to oxygen causes other 3 subunits to bind O2 faster

• Release of one oxygen also leads to release of the other 3 co-operatively

Fig. 42.29

Fig. 42.29, continued

What does pollution do to your lungs?

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Deep-diving air-breathers stockpile oxygen and deplete it slowly

Fig. 42.30

• Diving vertebrates not only start a dive with a relatively large O2 stockpile, but they also have adaptations that conserve O2.

• They swim with little muscular effort and often use buoyancy changes to glide passively upward or downward.

• Their heart rate and O2 consumption rate decreases during the dive and most blood is routed to the brain, spinal cord, eyes, adrenal glands, and placenta (in pregnant seals).

• Blood supply is restricted or even shut off to the muscles, and the muscles can continue to derive ATP from fermentation after their internal O2 stores are depleted.