Circulation and Gas Exchange

Chapter 42

Overview:

• Every organism must exchange materials with its environment

• Natural selection resulted in 2 basic adaptations that permit effective exchange for all animals– Body Plan that places many or all cells in direct

contact with environment• Gastrovascular Cavities – serves both in digestion and distribution of

substances throughout body

– Circulatory Systems (large animals)• System move fluids

Figure 42.2b

(b) The planarian Dugesia, a flatworm

Gastrovascularcavity

Mouth

Pharynx2 mm

General Properties of Circulatory Systems

Evolutionary Adaptation: A circulatory system minimizes the diffusion distance in animals with many cell layers

• A circulatory system has– A circulatory fluid (blood)– Blood Vessels (tubes)– Muscular pump (heart)

• Function: The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of wastes

Digestivesystem

Circulatorysystem

Excretorysystem

Interstitialfluid

Cells

Nutrients

Heart

Animalbody

Respiratorysystem

Blood

CO2FoodMouth

External environment

O2

50 µ

m

A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM).

10 µm

Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM).

The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM).

Unabsorbedmatter (feces)

Metabolic wasteproducts (urine)

Anus

0.5 cm

In Circulation, what needs to be transported

• Nutrients (fuel from digestive system)• Respiratory (O2 and CO2 gas exchange)• Excretory (waste from cells)• Protection (blood clotting, immune defenses)• Regulation (hormones)

Open Circulatory Systems

• Blood bathes the organs directly• No distinction between blood and interstitial fluid, and

this general body fluid is called hemolymph• Evolutionary advantage: lower hydrostatic pressure

less costly• Ex. insects, other arthropods,

and most molluscs,

• Blood is in vessels and is distinct from the interstitial fluid• More efficient at transporting circulatory fluids to tissues/cells• Evolutionary advantage:

– increase blood pressure effective delivery of O2 & nutrients to cells of larger/more active animals.

– Regular distribution of blood to different organs• Ex. Annelids, cephalopods, and vertebrates

Closed Circulatory Systems

Organization of Vertebrate Circulatory Systems

Cardiovascular System• Humans and other vertebrates have a closed

circulatory system called the cardiovascular system• The three main types of blood vessels are arteries,

veins, and capillaries• Blood flow is one way in these vessels

Why do veins have valves and arteries do not?

Veins move blood against gravity without benefit of the heart contraction

Blood flow: Heart arteries arterioles capillaries venules veins heart

Arteries: Away from heartVeins: Toward heart

• Vertebrate hearts contain two or more chambers• Blood enters through an atrium and is pumped out through

a ventricle

• Double circulation maintains higher blood pressure in the organs than does single circulation

Evolutionary Trends:

Figure 42.5

Amphibians Reptiles (Except Birds)

Pulmocutaneous circuit Pulmonary circuit

Lungand skincapillaries

Atrium(A)

Atrium(A)

LeftRight

Ventricle (V)

Systemiccapillaries

Systemic circuit Systemic circuit Systemic circuit

Systemiccapillaries

IncompleteseptumIncompleteseptum

Leftsystemicaorta

LeftRight

Rightsystemicaorta

A A

V V

Lungcapillaries

Lungcapillaries

Pulmonary circuit

A AV V

LeftRight

Systemiccapillaries

Key

Oxygen-rich bloodOxygen-poor blood

Mammals and Birds

How has natural selection shaped the double circulation of birds and mammals?

• The mammalian cardiovascular system meets the body’s continuous demand for O2

• Endotherms use 10x as much energy as same sized ectotherms. Need 10x as much fuel and O2 and need to remove 10x as much CO2 and other wastes

Mammalian Circulation

• Blood begins its flow with the right ventricle pumping blood to the lungs

• In the lungs, the blood loads O2 and unloads CO2

• Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle

• The aorta provides blood to the heart through the coronary arteries

• Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs)

• The superior vena cava and inferior vena cava flow into the right atrium

• Video: Heart pumping mechanism video• Video: How your heart pumps blood• Video: 3D pumping heart

Superior vena cava

Pulmonaryartery

Capillariesof right lung

Pulmonaryvein

Aorta

Inferiorvena cava

Right ventricle

Capillaries ofabdominal organsand hind limbs

Right atrium

Aorta

Left ventricle

Left atrium

Pulmonary vein

Pulmonaryartery

Capillariesof left lung

Capillaries ofhead and forelimbs

Figure 42.6

Figure 42.7

Pulmonary artery

Rightatrium

Semilunarvalve

Atrioventricularvalve

Rightventricle

Leftventricle

Atrioventricularvalve

Semilunarvalve

Leftatrium

Pulmonaryartery

Aorta

• The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle

• The contraction, or pumping, phase is called systole• The relaxation, or filling, phase is called diastole

Figure 42.8-1

Atrial andventricular diastole

0.4sec

1

Figure 42.8-2

Atrial andventricular diastole

Atrial systole and ventricular diastole

0.1sec

0.4sec

2

1

Figure 42.8-3

Atrial andventricular diastole

Atrial systole and ventricular diastole

Ventricular systole and atrialdiastole

0.1sec

0.4sec

0.3 sec

2

1

3

• The heart rate, also called the pulse, is the number of beats per minute

• The stroke volume is the amount of blood pumped in a single contraction

• The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume

• Four valves prevent backflow of blood in the heart• The atrioventricular (AV) valves separate each atrium

and ventricle• The semilunar valves control blood flow to the aorta

and the pulmonary artery

• The “lub-dup” sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves

• Backflow of blood through a defective valve causes a heart murmur

Maintaining the Heart’s Rhythmic Beat

• Some cardiac muscle cells are self-excitable, meaning they contract without any signal from the nervous system

• The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract

• Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)

• The pacemaker is regulated by two portions of the nervous system: the sympathetic and parasympathetic divisions

• The sympathetic division speeds up the pacemaker• The parasympathetic division slows down the

pacemaker• The pacemaker is also regulated by hormones and

temperature

Components of Blood (Humans have ~5L of Blood)red blood cells (erythrocytes)* biconcave discs, approx 7µ in diameter* most numerous (5-6 billion / mL of blood)* one RBC contains ~250 million molecules of hemoglobin which carry O2

white blood cells (leucocytes)* 5 different types, some with granulated cytoplasm* fight infection* produce antibodies to ‘tag’ foreign cells for destruction* perform phagocytosis

platelets (thrombocytes)* incomplete cells (cytoplasmic fragments)* important for blood clotting (controlling blood loss from damaged vessels)

plasma* fluid matrix composed of 90% H2O, clear yellow in color* transports glucose, electrolytes, hormones, CO2, waste, proteins, lipids, etc* helps regulate fluid and pH levels in blood

YWBC

o

Red Blood Cells Structure and Function

• Biconclave shape increases surface area to enhance O2 uptake and release.

• Each RBC contains about 250 million molecules of hemoglobin, and each hemoglobin molecule can bind up to four molecules of O2.

• Lack nuclei, which increases space for hemoglobin.• Lacks mitochondria, O2 so is not consumed.

Concept 42.3: Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels

• The physical principles that govern movement of water in plumbing systems also influence the functioning of animal circulatory systems

Blood Vessel Structure and Function

• A vessel’s cavity is called the central lumen• The epithelial layer that lines blood vessels is called the

endothelium• The endothelium is smooth and minimizes resistance

Figure 42.10 Artery

Red blood cells

Endothelium

Artery

Smoothmuscle

Connectivetissue

Capillary

Valve

Vein

Vein

Basal lamina

Endothelium

Smoothmuscle

Connectivetissue

100 m

LM

Venule

15

mL

M

Arteriole

Red blood cell

Capillary

• Capillaries have thin walls, the endothelium plus its basal lamina, to facilitate the exchange of materials

• Arteries and veins have an endothelium, smooth muscle, and connective tissue

• Arteries have thicker walls than veins to accommodate the high pressure of blood pumped from the heart

• In the thinner-walled veins, blood flows back to the heart mainly as a result of muscle action

Blood Flow Velocity

• Physical laws governing movement of fluids through pipes affect blood flow and blood pressure

• Velocity of blood flow is slowest in the capillary beds, as a result of the high resistance and large total cross-sectional area

• Blood flow in capillaries is necessarily slow for exchange of materials

Figure 42.11

Aorta

Arterie

sArte

riole

s

Capill

arie

sVen

ules

Veins

Venae

cava

e

Systolicpressure

Diastolicpressure

020406080

100120

01020304050

Pre

ss

ure

(mm

Hg

)V

elo

cit

y(c

m/s

ec

)A

rea

(c

m2)

01,0002,0003,0004,0005,000

Blood Pressure

• Blood flows from areas of higher pressure to areas of lower pressure

• Blood pressure is the pressure that blood exerts against the wall of a vessel

• In rigid vessels blood pressure is maintained; less rigid vessels deform and blood pressure is lost

Changes in Blood Pressure During the Cardiac Cycle

• Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries

• Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure

• A pulse is the rhythmic bulging of artery walls with each heartbeat

Regulation of Blood Pressure

• Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles

• Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure

• Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall

• Vasoconstriction and vasodilation help maintain adequate blood flow as the body’s demands change

• Nitric oxide is a major inducer of vasodilation• The peptide endothelin is an important inducer of

vasoconstriction

Blood Pressure and Gravity

• Blood pressure is generally measured for an artery in the arm at the same height as the heart

• Blood pressure for a healthy 20-year-old at rest is 120 mm Hg at systole and 70 mm Hg at diastole

Blood pressure reading: 120/70

120

70

Soundsstop

Soundsaudible instethoscope

120

Arteryclosed

1 2 3

Figure 42.12

• Fainting is caused by inadequate blood flow to the head

• Animals with longer necks require a higher systolic pressure to pump blood a greater distance against gravity

• Blood is moved through veins by smooth muscle contraction, skeletal muscle contraction, and expansion of the vena cava with inhalation

• One-way valves in veins prevent backflow of blood

Direction of blood flowin vein (toward heart) Valve (open)

Skeletal muscle

Valve (closed)

Figure 42.13

Gas exchange across specialized respiratory surfaces

Gas exchange (respiration): supplies O2 for cellular respiration and disposes of CO2

Respiration Media• Animals can use air or water as a source of O2

• Gas exchange is more difficult in aquatic animals– There is less O2 available in water than in air– Water has greater density and viscosity – Obtaining O2 from water requires greater efficiency than air

breathing

Respiratory Surfaces

• Part of an animal’s body where gases are exchanged with the surrounding environment.

• It can be the body wall, skin, gills, tracheae, lungs

• General characteristics of respiratory surfaces include:– Must be moist– Favorable surface area/volume ratio. Respiratory surfaces

are often extensively folded or branched (structure/function)– Closely related with vascular system of larger animals

Gills in Aquatic Animals

• Gills are outfoldings of the body that create a large surface area for gas exchange

• Ventilation: increases flow over the respiratory surface• Advantage of countercurrent exchange: Water and blood

flow in opposite directions “across” one another so oxygen can continually diffuse into blood

How do insects meet their high metabolic demands for oxygen with an open circulatory system?

• Contain tracheal system– tiny branching tubes that penetrate the body– supply O2 directly to body cells– respiratory and circulatory systems are separate– Larger insects must ventilate their tracheal system to

meet O2 demands

Mammalian Respiratory Systems: LUNGS

Ventilation in Mammals: Breathing

Pathway of Oxygen to Lungs• Pharynx : Air inhaled through the nostrils is warmed,

humidified, and sampled for odors (nasal and oral cavities)

• Larynx: upper part of respiratory tract• Trachae: windpipe• Bronchi• Bronchioles• Alveoli : air sacs clustered at the end of bronchioles

Figure 42.25

Pharynx

Larynx(Esophagus)

Trachea

Right lung

Bronchus

Bronchiole

Diaphragm(Heart)

Capillaries

Leftlung

Dense capillary bedenveloping alveoli (SEM)

50 m

Alveoli

Branch ofpulmonary artery(oxygen-poorblood)

Branch ofpulmonary vein(oxygen-richblood)

Terminalbronchiole

Nasalcavity

• Air sacs clustered at ends of bronchioles in the lungs• Thin, most and large surface area• Associated with the capillary beds.• Oxygen diffuses into the blood by passing through the

thin membrane of an alveolus and through the thin membrane of a capillary, into the blood, and attached to the hemoglobin molecule in a RBC.

• Carbon dioxide diffuses from the capillaries across the epithelium and into the air space

Alveoli : Structure and Function

Interaction of Circulatory and Respiratory System

• What is the passage of oxygen as it enters your nasal passageway and is used by tissues in your big toe?

Respiratory Pigments: Increase efficiency of oxygen transport

– Hemocyanin in arthropods and molluscs; Cu is the binding component

– Hemoglobin vertebrates; Fe is binding component; each holds 4 O2 molecules; relies on cooperativity!

• Drop in pH lowers affinity for oxygen, active tissues with more carbon dioxide (lower pH) will have more oxygen dropped off

– Increased metabolic activity lowers pH by increasing the concentration of CO2 in the blood. CO2 reacts with water to form carbonic acid, which dissociates into a bicarbonate ion and a hydrogen ion. As blood pH drops, the rate and depth of respiration increase.

• Breathing is influenced by pH, which is an indirect indication of blood CO2 levels.

Figure 42.30aExhaled air Inhaled air

Pulmonaryarteries

Systemicveins

Systemicarteries

Pulmonaryveins

Alveolarcapillaries

AlveolarspacesAlveolar

epithelialcells

Heart

SystemiccapillariesCO2 O2

Body tissue

(a) The path of respiratory gases in the circulatory system

CO2 O2

8 1

2

37

6 4

5