Chapter 42 gas exchange and circulatory system
1 / 75

Chapter 42: Gas Exchange and Circulatory System - PowerPoint PPT Presentation

  • Uploaded on
  • Presentation posted in: General

Chapter 42: Gas Exchange and Circulatory System. Presented by: McQuade and Verpooten. Circulatory Systems Reflect Phylogeny. In unicellular organisms Exchanges occur directly with the environment For most of the cells making up multicellular organisms

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Download Presentation

Chapter 42: Gas Exchange and Circulatory System

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Chapter 42: Gas Exchange and Circulatory System

Presented by: McQuade and Verpooten

Circulatory Systems Reflect Phylogeny

  • In unicellular organisms

    • Exchanges occur directly with the environment

  • For most of the cells making up multicellular organisms

    • Direct exchange with the environment is not possible

Gastrovascular Cavities

  • Wide diversity of animals is paralleled by the diversity in circulatory systems.

  • Simple animals, such as cnidarians

    • Have a body wall only two cells thick that encloses a gastrovascular cavity

  • The gastrovascular cavity

    • Functions in both digestion and distribution of substances throughout the body


Open and Closed Circulatory Systems Overcome limitations of Diffusion

  • More complex animals

    • Have one of two types of circulatory systems: open or closed

  • Both of these types of systems have three basic components

    • A circulatory fluid (blood)

    • A set of tubes (blood vessels)

    • A muscular pump (the heart)


Hemolymph in sinusessurrounding ograns


Anterior vessel

Lateral vessels

Tubular heart

Figure 42.3a

(a) An open circulatory system

  • In insects, other arthropods, and most molluscs

    • Blood bathes the organs directly in an open circulatory system



Small branch vessels in each organ

Dorsal vessel(main heart)

Ventral vessels

Auxiliary hearts

(b) A closed circulatory system

Figure 42.3b

  • In a closed circulatory system

    • Blood is confined to vessels and is distinct from the interstitial fluid

Survey of Vertebrate Circulation

  • Humans and other vertebrates have a closed circulatory system

    • Often called the cardiovascular system

    • Clearly the most advanced/efficient system

  • Blood flows in a closed cardiovascular system

    • Consisting of blood vessels and a two- to four-chambered heart

3 Main Types of Blood Vessels: Arteries, Veins, & Capillaries

  • Arteries carry blood to capillaries

    • The sites of chemical exchange between the blood and interstitial fluid

  • Veins

    • Return blood from capillaries to the heart


  • A fish heart has two main chambers

    • One ventricle and one atrium

  • Blood pumped from the ventricle

    • Travels to the gills, where it picks up O2 and disposes of CO2


  • Frogs and other amphibians

    • Have a three-chambered heart, with two atria and one ventricle

  • The ventricle pumps blood into a forked artery

    • That splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit

Reptiles (Except Birds)

  • Reptiles have double circulation

    • With a pulmonary circuit (lungs) and a systemic circuit

  • Turtles, snakes, and lizards

    • Have a three-chambered heart

Mammals and Birds

  • In all mammals and birds

    • The ventricle is completely divided into separate right and left chambers

  • The left side of the heart pumps and receives only oxygen-rich blood

    • While the right side receives and pumps only oxygen-poor blood

  • A powerful four-chambered heart

    • Was an essential adaptation of the endothermic way of life characteristic of mammals and birds

Gill capillaries

Lung and skin capillaries

Lung capillaries

Lung capillaries





Right systemicaorta






Heart:ventricle (V)









Atrium (A)













Systemic circuit

Systemic circuit


Systemic capillaries

Systemic capillaries

Systemic capillaries

Systemic capillaries

Figure 42.4

  • Vertebrate circulatory systems

  • Double circulation in mammals depends on the anatomy and pumping cycle of the heart

  • The structure and function of the human circulatory system

    • Can serve as a model for exploring mammalian circulation in general

  • Heart valves

    • Dictate a one-way flow of blood through the heart

  • 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 to the body tissues by the left ventricle

  • Blood returns to the heart

    • Through the right atrium

Capillaries of

head and



vena cava













of right lung


of left lung








Left atrium



Right atrium


Left ventricle

Right ventricle



vena cava

Capillaries of

abdominal organs

and hind limbs

Figure 42.5

  • The mammalian cardiovascular system

Pulmonary artery




Anterior vena cava


Right atrium






Posterior vena cava

Right ventricle

Figure 42.6

Left ventricle

The Mammalian Heart: A Closer Look

  • A closer look at the mammalian heart

    • Provides a better understanding of how double circulation works

  • The heart contracts and relaxes

    • In a rhythmic cycle called the cardiac cycle

  • The contraction, or pumping, phase of the cycle

    • Is called systole

  • The relaxation, or filling, phase of the cycle

    • Is called diastole

  • The heart rate, also called the pulse

    • Is the number of beats per minute

  • The cardiac output

    • Is the volume of blood pumped into the systemic circulation per minute

  • Some cardiac muscle cells are self-excitable

    • Meaning they contract without any signal from the nervous system

  • A region of the heart called the sinoatrial (SA) node, or pacemaker

    • Sets the rate and timing at which all cardiac muscle cells contract

  • Impulses from the SA node

    • Travel to the atrioventricular (AV) node

  • At the AV node, the impulses are delayed

    • And then travel to the Purkinje fibers that make the ventricles contract

Signals pass

to heart apex.

Signals spread


Pacemaker generates wave of signals to contract.

Signals are delayed

at AV node.


AV node

SA node(pacemaker)








Figure 42.8

  • The control of heart rhythm

  • Structural differences in arteries, veins, and capillaries

    • Correlate with their different functions

  • Arteries have thicker walls

    • To accommodate the high pressure of blood pumped from the heart

Direction of blood flowin vein (toward heart)

Valve (open)

Skeletal muscle

Valve (closed)

Figure 42.10

  • In the thinner-walled veins

    • Blood flows back to the heart mainly as a result of muscle action

Blood Pressure

  • Systolic pressure

    • Is the pressure in the arteries during ventricular systole

    • Is the highest pressure in the arteries

  • Diastolic pressure

    • Is the pressure in the arteries during diastole

    • Is lower than systolic pressure

  • The critical exchange of substances between the blood and interstitial fluid

    • Takes place across the thin endothelial walls of the capillaries

  • The lymphatic system

    • Returns fluid to the body from the capillary beds

    • Aids in body defense

  • Blood is a connective tissue with cells suspended in plasma

  • Blood in the circulatory systems of vertebrates

    • Is a specialized connective tissue

Blood Composition and Function

  • Blood plasma is about 90% water

  • Among its many solutes are

    • Inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes

  • Blood consists of several kinds of cells

    • Suspended in a liquid matrix called plasma

  • The cellular elements

    • Occupy about 45% of the volume of blood

Plasma 55%


Major functions

Solvent for

carrying other



Icons (blood electrolytes






Osmotic balance

pH buffering, and

regulation of




Plasma proteins





Osmotic balance,

pH buffering



Substances transported by blood

Nutrients (such as glucose, fatty acids, vitamins)

Waste products of metabolism

Respiratory gases (O2 and CO2)


Figure 42.15

  • The composition of mammalian plasma

Cellular Elements

  • Suspended in blood plasma are two classes of cells

    • Red blood cells, which transport oxygen

    • White blood cells, which function in defense

  • A third cellular element, platelets

    • Are fragments of cells that are involved in clotting


Cellular elements 45%


Cell type

Numberper L (mm3) of blood

  • The cellular elements of mammalian blood

Erythrocytes(red blood cells)

Transport oxygenand help transportcarbon dioxide

5–6 million

Defense andimmunity

Leukocytes(white blood cells)









Blood clotting

Figure 42.15


  • Red blood cells, or erythrocytes

    • Are by far the most numerous blood cells

    • Transport oxygen throughout the body

  • The blood contains five major types of white blood cells, or leukocytes

    • Monocytes, neutrophils, basophils, eosinophils, and lymphocytes, which function in defense by phagocytizing bacteria and debris or by producing antibodies

Pluripotent stem cells(in bone marrow)

Lymphoidstem cells

Myeloidstem cells


B cells

T cells







Figure 42.16

  • Erythrocytes, leukocytes, and platelets all develop from a common source

    • A single population of cells called pluripotent stem cells in the red marrow of bones

Cardiovascular Disease

  • Cardiovascular diseases

    • Are disorders of the heart and the blood vessels

    • Account for more than half the deaths in the United States

Smooth muscle

Connective tissue



(a) Normal artery

(b) Partly clogged artery

50 µm

250 µm

Figure 42.18a, b

  • One type of cardiovascular disease, atherosclerosis

    • Is caused by the buildup of cholesterol within arteries

  • 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

Respiratorymedium(air of water)




Organismal level

Circulatory system

Cellular level

Energy-richmoleculesfrom food


Cellular respiration

Figure 42.19

Gas Exchange Occurs Across Specialized Respiratory Surfaces

  • Generally referred to as Respiration

    • Do not confuse with cellular respiration which refers energy transformations

  • Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide

Remember key biological concept….lots of body structure have numerous folds to increase surface area for chemical reaction

  • The part of an animals body where gas exchange occurs is called a respiratory surface

  • Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases

    • Between their cells and the respiratory medium, either air or water

    • Rate of diffusion is proportional to surface area across which diffusion occurs and inversely proportional to the square of the distance molecules must move

  • As a result respiratory surfaces tend to be thin and have large surface areas

Critical Thinking: Who will have more surface area in their respiratory surfaces, ectotherms or endotherms? Explain.

Endotherms. While respiratory area depends mainly on the size of the organism and whether it lives in a terrestrial or aquatic environment, endotherms utilize more energy (ATP) and so must do more cellular respiration than a similarly sized ectotherm

Skin as a Respiratory Organ

  • Some animals use entire outer skin as a respiratory organ

    • Earthworms and amphibians

  • Moist skin exchanges gasses by diffusion across entire body

    • Respiratory surface must remain moist requiring these organisms to live in water or damp places

    • Organisms usually small (thin or flat)with high surface area to volume ratios

3 Most Common Respiratory Organs

  • Gills: out-foldings of body surface suspended in water

    • Respiratory medium= water

    • The warmer and saltier the water, the less dissolved O2

  • Trachea: made up of air tubes that branch throughout the body

    • Most common respiratory system of terrestrial animals (insects)

  • Lungs: most familiar respiratory system

(a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange.



Figure 42.20a

Tube foot

  • In some invertebrates

    • The gills have a simple shape and are distributed over much of the body


Gill arch



Blood vessel

Gill arch





Water flow







Blood flowthrough capillariesin lamellaeshowing % O2

Water flowover lamellaeshowing % O2


Figure 42.21

Countercurrent exchange

  • The effectiveness of gas exchange in some gills, including those of fishes

    • Is increased by ventilation and countercurrent flow of blood and water

      • Ram ventilation

      • Appendages that “paddle” water past the gills

Advantages & Disadvantages to Air as the Respiratory Medium

Advantages of air

Disadvantages of air

Respiratory surfaces must be large and MOIST

Air dries things out

  • Higher concentration of dissolved oxygen

  • Oxygen and carbon dioxide diffuse much faster in air than water, so respiratory surfaces have to be ventilated much less vigorously in air than water

    • When ventilation does occur in terrestrial animals it requires less energy because air is lighter than water and easier to pump

Air sacs



(a) The respiratory system of an insect consists of branched internaltubes that deliver air directly to body cells. Rings of chitin reinforcethe largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid(blue-gray). When the animal is active and is using more O2, most ofthe fluid is withdrawn into the body. This increases the surface area of air in contact with cells.

Figure 42.22a

Tracheal Systems in Insects

  • The tracheal system of insects

    • Consists of tiny branching tubes that penetrate the body

Body cell



Body wall






(b) This micrograph shows crosssections of tracheoles in a tinypiece of insect flight muscle (TEM).Each of the numerous mitochondriain the muscle cells lies within about5 µm of a tracheole.

Figure 42.22b

2.5 µm

  • The tracheal tubes

    • Supply O2 directly to body cells

With virtually all body cells within a very short distance of respiratory medium, the open circulatory system of insects is not involved in transporting O2 and CO2

For small insects, diffusion through the trachea brings in enough oxygen and removes enough carbon dioxide to support cellular respiration

Larger insects with higher energy demands ventilate their tracheal systems with rhythmic body movements that compress and expand the air tubes like bellows


Unlike the branching tracheal system of insects, lungs are confined to 1 location

Because the respiratory surface of a lung is not in direct contact with all other body cells, the gap must be bridged by the circulatory system

Evolution of Lungs

  • Lungs have evolved in spiders, terrestrial snails, and most vertebrates

  • Amphibians have small poorly developed lungs due to the gas exchange in their skin

    • Some have no lungs at all

  • All mammals rely entirely on lungs

  • Exceptions

    • Turtles supplement lung breathing with gas exchange in the mouth and anus pew

    • lungfish, fish with lungs to live for short periods of time outside of water or in oxygen poor water

Branch from thepulmonaryartery(oxygen-poor blood)

Branch from the pulmonary vein (oxygen-rich blood)

Terminal bronchiole




Left lung



50 µm


50 µm

Right lung



Colorized SEM




Figure 42.23

Mammalian Respiratory Systems: A Closer Look

  • A system of branching ducts

    • Conveys air to the lungs

Mammalian Respiratory Systems: A Closer Look

  • Air enters the nostrils, is filtered by hairs, warmed, humidified, and sampled for odors

  • The nasal cavity leads to the pharynx, this is where paths for air and food cross

    • When food is swallowed, the larynx (the upper part of the respiratory tract) moves upward and tips the epiglottis over the glottis (the opening to the wind pipe) allowing food to enter the esophagus into the stomach


The larynx wall is reinforced with cartilage and in most mammals is adapted as a voice box

Inhaled air rushes past vocal chords in the larynx

Sounds are produced when voluntary muscles in the voice box are tensed stretching the chords so they vibrate

  • In mammals, air inhaled through the nostrils

    • Passes through the pharynx into

      • the trachea: windpipe  trachea forks into 

      • 2 bronchi: one leading to each lung

      • Bronchioles: within the lung, the bronchi branches repeatedly into bronchioles 

      • and dead-end alveoli, where gas exchange occurs

How an Amphibian Breathes

  • An amphibian such as a frog

    • Ventilates its lungs by positive pressure breathing

    • During a breathing cycle muscles lower the floor of the oral cavity drawing in air through the nostrils

    • With nostrils and mouth closed the floor of the oral cavity rises which forces air down the trachea

Rib cage expands asrib muscles contract

Rib cage gets smaller asrib muscles relax

Air inhaled

Air exhaled



INHALATIONDiaphragm contracts(moves down)

EXHALATIONDiaphragm relaxes(moves up)

Figure 42.24

How a Mammal Breathes

  • Mammals ventilate their lungs

    • By negative pressure breathing, which pulls air into the lungs

    • Pulls air in instead of pushing it in


How a Mammal Breathes

  • Muscles in the ribcage and diaphragm contract changing the volume of the chest cavity, and the lungs match these volume changes

  • Lungs are surrounded by a double walled sac with each wall separated by a thin layer of fluid

    • The inner layer adheres to the lungs

    • The outer layer adheres to the wall of the chest cavity

    • The layers can slide past each other but cant easily be pulled apart

Mammalian Breathing

  • Tidal Volume: the volume of air a mammal inhales and exhales with each breath

    • Averages about 500mL with each breath

  • Vital capacity: maximum tidal volume during forced ventilation

    • About 3.4 & 4.8L for college females and males respectively

  • Residual volume: the volume of air that remains in the lungs even after a forced exhale (our system doesn’t completely renew the air with every exhalation)



Anteriorair sacs



Posteriorair sacs


Air tubes(parabronchi)in lung

1 mm

EXHALATIONAir sacs empty; lungs fill

INHALATIONAir sacs fill

Figure 42.25

How a Bird Breathes

  • Besides lungs, bird have eight or nine air sacs

    • That function as bellows that keep air flowing through the lungs


The entire system of lungs and air sacs is ventilated when a bird breathes

  • Air passes through the lungs in one direction only regardless of whether they’re inhaling or exhaling

  • Instead of alveoli (dead-ends) the site of gas exchange in bird lungs are tiny channels called parabronchi through which air flows in only 1 direction

  • Every exhalation

    • Completely renews the air in the lungs

Control of Breathing in Humans

  • Most of the time breathing is regulated via automatic mechanisms

  • The main breathing control centers are located in two regions of the brain,

    • Medulla oblongata: sets basic breathing rhythm

    • Pons: control center

    • Secondary control is exerted via sensors in the aortic and carotid arteries which monitor O2 and CO2 concentrations, as well as pH

Medulla Oblongata

  • Sets breathing rhythm in response to changes of pH in tissue fluid(cerebrospinal fluid) bathing the brain

  • pH of cerebrospinal fluid is determined mainly by concentartion of CO2

  • CO2 diffuses from blood  CF where it reacts with water to form carbonic acid which lowers pH

  • This triggers the medulla oblingata to increase the rate and depth of breathing to eliminate excess CO2 which in turn brings the pH back up restoring homeostasis


The medulla’s control center

also helps regulate blood CO2 level.

Sensorsin the medulla detect changes

in the pH (reflecting CO2 concentration)

of the blood and cerebrospinal fluid

bathing the surface of the brain.


The control center in the

medulla sets the basicrhythm, and a control centerin the pons moderates it,smoothing out thetransitions between

inhalations and exhalations.


Nerve impulses relay changes in CO2 and O2 concentrations. Other sensors in the walls of the aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed.


Breathing control centers

Nerve impulses trigger muscle contraction. Nervesfrom a breathing control centerin the medulla oblongata of the brain send impulses to thediaphragm and rib muscles, stimulating them to contractand causing inhalation.





In a person at rest, these nerve impulses result in about 10 to 14 inhalationsper minute. Between inhalations, the musclesrelax and the person exhales.


The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low.


Figure 42.26


Rib muscles

Control of Breathing in humans


  • The centers in the medulla

    • Regulate the rate and depth of breathing in response to pH changes in the cerebrospinal fluid

  • The medulla adjusts breathing rate and depth

    • To match metabolic demands

The Role of Partial Pressure Gradients

  • Gases diffuse down pressure gradients

    • In the lungs and other organs

  • Diffusion of a gas

    • Depends on differences in a quantity called partial pressure

Partial Pressure of

  • at sea level, the atmosphere exerts a total pressure of 760mmHg

  • This is a downward force equal to that exerted by a column of mercury 760mmHg high

  • Since the atmosphere is 21% oxygen by volume, the partial pressure of oxygen is

    PO2 = 0.21X 760 = 160mmHg

    PCO2 = 0.23mmHg

Partial Pressure

  • A gas always diffuses from a region of higher partial pressure to a region of lower partial pressure



Respiratory Pigments

  • Respiratory pigments

    • Are proteins that transport oxygen

    • Greatly increase the amount of oxygen that blood can carry

  • The respiratory pigment of almost all vertebrates is the protein hemoglobin, contained in the erythrocytes

    • Hemocyanin is a respiratory protein used in arthropods

Heme group

Iron atom

O2 loaded

in lungs


O2 unloaded

In tissues


Polypeptide chain

  • Like all respiratory pigments

    • Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body

Figure 42.28


Consists of 4 subunits each with a cofactor called a heme group that has an iron atom at its center

The iron binds the oxygen, thus each molecule of hemoglobin can carry four molecules of oxygen

A typical RBC has 250 million molecules of hemoglobin


The process of loading and unloading oxygen depends on cooperativity of the 4 subunits that make up hemoglobin

Binding of oxygen to 1 subunit induces the others to change shape slightly resulting in higher affinity for oxygen

When 1 subunit unloads oxygen the others quickly revert back to original shape lowering their affinity for oxygen

Review: What factors affect protein structure/function?

As with all proteins hemoglobins conformation is sensitive to a variety of factors including pH

Bohr Shift: when a drop in pH lowers the affinity of hemoglobin for oxygen

Because CO2 reacts with H2O to form carbonic acid (H2CO3) an active tissue lowers the pH of its surroundings and induces hemoglobin to release more O2

Carbon Dioxide Transport

  • In addition to transporting oxygen, hemoglobin also transports CO2 and assists in buffering

    • Preventing harmful changes in blood pH

      • Only 7% of CO2 released by respiring cells in transported dissolved in solution

      • 23% binds amino groups of hemoglobin

      • 70% is transported in the form of the bicarbonate ion HCO3-

CO2 Diffuses into the blood plasma and then into erythrocytes

  • It 1st reacts with water assisted by the enzyme carbonic anhydrase

  • To form H2CO3 which then dissociates a H+ ion and HCO3-

  • Most of the H+ attaches to hemoglobin and other blood proteins minimizing a shift in pH

  • The HCO3- diffuses into the plasma

  • As blood flows through the lungs the process is rapidly reversed as diffusion of CO2 out of the blood shifts the chemical equilibrium in favor of HCO3- CO2 which is ultimately released

Diving Mammals

  • Diving mammals have many adaptations for their way of life.

  • Deep-diving air breathers

    • Stockpile O2 and deplete it slowly

    • Lower heartrate and breathing during dives

    • Store O2 not only with hemoglobin, but also myoglobin in the blood and muscle

  • Login