Bio chapter 22-gas exchange

lungs in tetrapod that live on land, such as

§ amphibians, § reptiles including birds, and mammals.

Reviewing the concepts

· Gas exchange in humans involve breathing, transport of gases, and exchange with body cells. Gas exchange, the interchange of oxygen and carbon dioxide between organism and its environment, provide oxygen for cellular respiration and remove its waste product, carbon dioxide · Animals exchange oxygen and carbon dioxide across moist body surfaces. Respiratory surfaces must be thin and moist for diffusion of oxygen and carbon dioxide to occur. Some animals use their entire skin as gas exchange organ. In most animals, gills, a tracheal system, or lungs provide large respiratory surfaces for gas exchange · Gills are adapted for gas exchange in aquatic environments. Gills absorb oxygen dissolved in water. in fish, gas exchange is enhanced by ventilation and countercurrent flow of water and blood · The tracheal system of insects provides direct exchange between air and body cells. A network of finely branched tubes transport oxygen directly to body cells and move carbon dioxide away from them · The evolution of lungs facilitated movement of tetrapods onto land. Skeletal adaptations of air-breathing fish may have helped early tetrapods move onto land · In mammals, branching tubes convey air to lungs located in chest cavity. Inhaled air passes through pharynx and larynx into trachea, bronchi, and bronchioles to alveoli. Mucus and cilia in respiratory passages protect lungs · Negative pressure breathing ventilates your lungs. Contraction of rib muscles and diaphragm expands thoracic cavity, reducing air pressure in the alveoli and drawing air into lungs · Breathing is automatically controlled. Breathing control centers in brain coordinate breathing with body needs by sensing and responding to pH of cerebrospinal fluid, which indicate carbon dioxide level in blood. A drop in blood pH trigger increase in rate and depth of breathing · Blood transport respiratory gases. Heart pump oxygen-poor blood to lungs, where it picks up oxygen and drop off carbon dioxide. Oxygen-rich blood return to heart and is pumped to body cells, where it drops off oxygen and pick up carbon dioxide · Hemoglobin carries oxygen, help transport carbon dioxide, and buffers the blood. Human fetus exchange gases with mother's blood. Fetal hemoglobin enhances oxygen transfer from maternal blood in placenta. At birth, rising carbon dioxide in fetal blood stimulates the breathing control centers to initiate breathing.

Hemoglobin-multipurpose;

· also help transport carbon dioxide & assist in buffering the blood o Most of carbon dioxide that diffuse from tissue cells into capillary enter RBC where some of it combine with hemoglobin. o The rest react with water, forming carbonic acid, which then break apart into a hydrogen ion and a bicarbonate ion o Hemoglobin bind most of H+ produced by this reaction, minimizing change in blood pH o The bicarbonate ions diffuse into plasma, where they're carried to the lungs

Partial pressure of oxygen in tissue reflect

· how much oxygen the cells are using and determine how much oxygen is unloaded

Cellular respiration requires

continuous supply of oxygen and the disposal of carbon dioxide

Without healthy cilia, smokers must

cough to clear dirty mucus from the trachea.

Most CO2 in the blood

enters red blood cells.

Respiratory surfaces are made up of

living cells; plasma membranes must be wet to function; therefore, always moist

However, air-breathing animals

lose water through their respiratory surfaces.

Main problem facing air-breathing animal, however, is

loss of water to air by evaporation

Compared to water, using air to breathe has two big advantages.

o Air contains higher concentrations of O2 than water. o Air is lighter and easier to move than water.

At birth

o CO2 in fetal blood increases and o breathing control centers initiate breathing.

water contain

oxygen as dissolved gas o however, concentration of oxygen dissolved in water is low, only about 3% of that in an equivalent volume of air o warmer and saltier the water, less oxygen it holds o efficiency of fish gills provided by countercurrent exchange, the transfer of substances such as oxygen between two fluids flowing in opposite directions. In this case, fluids are water and blood.

A drop in blood pH increases

rate and depth of breathing.

Three phases of gas exchange occur in humans and other animals with lungs:

1. breathing 2. transport of oxygen and carbon dioxide in blood 3. exchange of gases with body cells

You should now be able to

Describe the three main phases of gas exchange in a human. Describe four types of respiratory surfaces and the kinds of animals that use them. Explain how the amount of oxygen available in air compares to that available in cold and warm fresh water and cold and warm salt water. Explain how the structure and movements of fish gills maximize oxygen exchange. Explain why breathing air is easier than using water for gas exchange. Describe the tracheal system of insects. Describe the respiratory structures of the fossil animal Tiktaalik. Explain how the metabolic rate of a vertebrate corresponds to the nature of its respiratory system. Describe the structures and corresponding functions of a mammalian respiratory system. Describe the impact of smoking on human health. Compare the mechanisms and efficiencies of lung ventilation in humans and birds. Explain how breathing is controlled in humans. Explain how blood transports gases between the lungs and tissues of the body. Describe the functions of hemoglobin. Explain how a human fetus obtains oxygen prior to and immediately after birth.

aiding oxygen uptake by fetus is

Fetal hemoglobin o attracts O2 more strongly than adult hemoglobin and o takes oxygen from maternal blood.

respiration

Gas exchange occurring as we breathe

In the body tissues, blood drops off

O2 and picks up CO2.

respiratory surface

Part of animal's body where gas exchange with environment occur

Breathing rate must also be coordinated with

activity of circulatory sys. which transport blood to and from alveolar capilaries

Gases are exchanged between

air in alveoli and blood in capillaries.

Breathing is

alternate inhalation and exhalation of air (ventilation).

In many insects,

alternating contraction & relaxation of flight muscles rapidly pump air through tracheal system

Gas exchange take place by

diffusion

Exchange of gases between capillaries and cells around them occur by

diffusion of gases down gradients of pressure o Mixture of gases, such as air, exert pressure. o You see evidence of gas pressure whenever you open can of soda, releasing pressure of carbon dioxide it contains o Each kind of gas in mixture account for portion of total pressure of mixture o Thus each gas has partial pressure o Molecules of each kind of gas diffuse down gradient of their own partial pressure independently of other gases

For small/slow moving insect,

diffusion through tracheae bring in enough oxygen to support cellular respiration

After delivery, placental gas

exchange with mother ceases, and baby's lungs must begin to work o Carbon dioxide act as signal o As soon as carbon dioxide stop diffusing from fetus to placenta, carbon dioxide levels rise in fetal blood Resulting drop in blood pH stimulate breathing control centers in infant's brain, and newborn gasps and take its first breath

Not all air is expelled during

exhalation. o Some air still remains in the trachea, bronchi, bronchioles, and alveoli. o This remaining air is "dead air." o Thus, inhalation mixes fresh air with dead air.

Gills-

extensions, or outfoldings, of body surface specialized for gas exchange.

Lower oxygen levels delay

fetal development and growth, resulting in higher incidence of premature birth, low birth weight, and brain and lung defects

Increasing this flow ensure

fresh supply of oxygen & removal of carbon dioxide

Blood that has lost carbon dioxide and gained oxygen return to

heart and is then pumped out to body tissues

Oxygen-poor blood return to

heart from capillaries in body tissues o Heart pump this blood to alveolar capillaries in lungs

Some CO2 combines with

hemoglobin.

Insect in flight has

high metabolic rate & consume 10-200 times more oxygen than it does at rest.

Continual movement of air as you inhale and exhale maintain

high oxygen and low carbon dioxide concentrations at respiratory surface

Gases move from areas of

higher concentration to areas of lower concentration. o Gases in the alveoli of the lungs have more O2 and less CO2 than gases in the blood. § O2 moves from the alveoli of the lungs into the blood. § CO2 moves from the blood into the alveoli of the lungs. o The tissues have more CO2 and less O2 than gases in the blood. § CO2 moves from the tissues into the blood. O2 moves from the blood into the tissues.

Oxygen isn't

highly soluble in water

A human fetus does not breathe with

its lungs. Instead, it exchanges gases with maternal blood in the placenta.

Because surfactant production don't begin until

late in fetal development, babies born 6 week/more before due date often have difficulty inflating their alveoli during inhalation

In the placenta, capillaries of

maternal blood and fetal blood run next to each other. The fetus and mother do not share the same blood. Capillaries exchange gases with maternal blood that circulate in placenta, and mother's circulatory system transport gases to and from her lungs

Neural circuits in a part of brain called

medulla oblongata form pair of control centers that establish breathing rhythm o Nerves from medulla signal the diaphragm and rib muscles to contract, causing you to inhale o Between inhalations, muscles relax, and you exhale o When you're at rest, these nerve signals result in about 10 to 14 inhalations per minute

Major branches of respiratory system are lined by

moist epithelium covered by cilia and thin film of mucus o Cilia and mucus are respiratory system's cleaning sys. o Beating cilia move mucus with trapped dust, pollen, and other contaminants upward to pharynx, where it's usually swallowed

Ventilation occur by

negative pressure breathing, system in which air is pulled into lungs

This type of ventilation is called

negative pressure breathing.

As blood flow through capillaries in the lungs, reaction is

reversed Bicarbonate ions combine with H+ to form carbonic acid; carbon acid converted to carbon dioxide and water; and carbon dioxide diffuse from blood to alveoli and leave body in exhaled air

Tracheae are reinforced by

rings of chitin, the tough polysaccharide that also make up insect's exoskeleton

Other CO2 reacts with

water, forming carbonic acid, which then breaks apart into o hydrogen ions and o bicarbonate ions in a reversible reaction. o Hemoglobin binds most of the H+ produced by this reaction, minimizing the change in blood pH.

In the lungs, blood picks up

O2 and drops off CO2.

Most animals transport

O2 bound to proteins called respiratory pigments. o Blue, copper-containing pigment is used by § molluscs and § arthropods. o Red, iron-containing hemoglobin § is used by almost all vertebrates and many invertebrates and § transports oxygen, buffers blood, and transports CO2.

Enlarged portions of tracheae form

air sacs near organs that require large supply of oxygen

Alveoli are highly susceptible to

airborne contaminants o Defensive WBC patrol them and engulf foreign particles o However, if too much particulate matter reach alveoli, the delicate lining of these small sacs become damaged and efficiency of gas exchange drops o There's significant association between exposure to fine particles and premature death o Air pollution & tobacco smoke-two sources of these lung damaging particles

Respiratory problems-

alveoli are so small & thin walled that surface tension would cause their moist surfaces to stick shut if it weren't for specialized secretions called surfactants

In general, size and complexity of lungs correlate with

animal's metabolic rate and thus oxygen need For example, lungs of birds & mammals, whose high body temperatures are maintained by high metabolic rate, have greater area of exchange surface than lungs of similar sized amphibians and nonbird reptiles, which have much lower metabolic rate

Gas exchange involve

both respiratory & circulatory systems in servicing your body's cells

Figure illustrates how medulla regulate

breathing in response to changes in level of carbon dioxide in blood 1. Normal blood pH is about 7.4 2. You exercise vigorously, causing metabolism to speed up. Your body cells use more oxygen and generate more carbon dioxide as waste product. Higher carbon dioxide concentration lead to increase in concentration of H+, lowering blood pH and cerebrospinal fluid 3. Sensors in medulla, as well as in major blood vessels, detect this change 4. Breathing control centers in medulla respond by signaling diaphragm and rib muscles to increase rate and depth of breathing 5. Excess carbon dioxide is eliminated in exhaled air, the pH of blood rises, and your breathing return to normal.

As enlargement on diagram show,

bronchioles dead-end in grapelike clusters of air sacs called alveoli o Each of lungs contain millions of these tiny sacs o Inner surface of each alveolus lined with thin layer of epithelial cells o When inhaled air reach an alveolus, oxygen dissolve in film of moisture on epithelial cells o It then diffuses across epithelium and into dense web of blood capillaries that surround each alveolus o This close association between capillaries and alveoli also enable carbon dioxide to diffuse opposite way-from capillaries, across epithelium of alveolus, into air space, and finally out in exhaled air

Expose to such pollutants can cause

continual irritation and inflammation of lungs & lead to chronic obstructive pulmonary disease (COPD) o COPD encompass two main conditions-chronic bronchitis and emphysema o In emphysema, delicate walls of alveoli become permanently damaged & lungs lose elasticity that help expel air during exhalation o With COPD, both lung ventilation & gas exchange are severely impaired Patients experience labored breathing, coughing, and frequent lung infections

Earthworms and other skin-breathers must live in

damp places/in water because whole body surface has to stay moist o Animals that breathe only through skin generally small, and many are long and thin/flattened o These shapes provide high ratio of respiratory surface to body volume, allowing sufficient gas exchange for all cells in body

Maximum volume of air that can be inhaled and exhaled with

each breath-vital capacity o Lungs actually hold more air than vital capacity o Because alveoli don't completely collapse, residual volume of dead air remain in lungs even after you blow out as much air as you can o As lungs lose elasticity with age/result of disease, such as emphysema, less air exit exhalation and residual volume increase at expense of vital capacity

Current fossil evidence support hypothesis that

earliest changes in front fins & shoulder girdle of tetrapod ancestors may have been breathing adaptations that enabled fish in shallow water to push itself up to gulp in air

Oxygen concentration in blood usually has little

effect on breathing control centers o However, sensors monitor concentration of oxygen in arterial blood as it leave heart o When oxygen level drops very low, these sensors signal breathing control centers, which respond by causing increase in rate and depth of breathing. o This response may occur, for example, at high altitudes, where atmospheric pressure is so low that you can't get enough oxygen by breathing normally

In most animals, skin surface not extensive enough to

exchange gases for whole body o Instead, certain body parts have adapted as highly branched respiratory surfaces with large SA o Such gas exchange organs include gills, tracheal systems, lungs o Many animals have adaptations that improve ventilation, flow of water/air over respiratory surface o Example: movement of operculum in ray-finned fishes pass water over gills

Tracheal system of insects-

extensive system of branching internal tubes with thin, moist epithelium forming respiratory surface at their tips o Smallest branches exchange gases directly with body cells. o Thus, gas exchange in insects require no assistance from circulatory system

Hemoglobin molecule consist of

four polypeptide chains of two different types, depicted with two shades of purple in the figure. o Attached to each polypeptide is chemical group called heme (colored red), at center of which is an iron atom (gray). o Each iron atom binds one oxygen molecule o Thus, every hemoglobin molecule can carry up to four oxygen molecules o Hemoglobin load up with oxygen in lungs and transport it to body's tissues o There, hemoglobin unload some/all of its cargo, depending on oxygen needs of cells o Partial pressure of oxygen in tissue reflect how much of oxygen the cells are using and determine how much oxygen is unloaded

Some animals use their entire outer skin as

gas exchange organ; e.g. earthworm

Alveoli are well adapted for

gas exchange with high surface areas of capillaries.

Control centers use

information about changes in internal environment to coordinate breathing rate with your body's need for oxygen o Sensors in medulla monitor the pH of cerebrospinal fluid, which surrounds the brain and spinal cord, as indicator of carbon dioxide level in blood. o The reason pH can be used in this way is that blood carbon dioxide is the main determinant of pH of cerebrospinal fluid o Carbon dioxide diffuse from blood to cerebrospinal fluid, where it reacts with water and form carbonic acid o Carbonic acid can then break apart into a hydrogen ion and a bicarbonate ion, shown below

SA of respiratory surface must be

large enough to take up sufficient oxygen for every cell

The first tetrapods on land diverged into three major lineages.

o Amphibians use small lungs and their body surfaces. o Nonbird reptiles have § lower metabolic rates and § simpler lungs. o Birds and mammals have § higher metabolic rates and § more complex lungs.

A mixture of gases, such as air, exerts pressure.

o Each kind of gas in a mixture accounts for a portion of the total pressure of the mixture. o Thus, each gas has a partial pressure. o The exchange of gases between capillaries and the surrounding cells is based on partial pressures. o Molecules of each kind of gas diffuse down a gradient of its own partial pressure, moving from regions of § higher partial pressure to § lower partial pressure.

Exposure to pollutants can cause continual irritation and inflammation of the lungs.

o Examples of common lung pollutants include § air pollution and § tobacco smoke. o Chronic obstructive pulmonary disease (COPD) can result, limiting § lung ventilation and § gas exchange.

Tetrapods seem to have evolved in shallow water.

o Fossil fish with legs had lungs and gills. o Adaptations for air breathing evident in their fossils include flat skull with strong, elongated snout, as well as muscular neck and shoulders that enabled animal to lift head clear of water and into unsupportive air o Strengthening of long jaw may have facilitated pumping motion that early air breathing tetrapods are presumed to have used to inflate their lungs: frogs today still employ this pumping motion o Legs may have helped them lift up to gulp air. o The fossil fish Tiktaalik § lived about 375 million years ago and § illustrates these air-breathing adaptations.

Air enter respiratory system through nostrils.

o It's filtered by hairs and warmed, humidified, and sampled for odors as it flow through maze of spaces in nasal cavity. o Can also draw in air through mouth, but mouth breathing don't allow air to be processed by nasal cavity o From nasal cavity/mouth, air pass into pharynx, a common passageway for air & food o When you swallow food, larynx (upper part of respiratory tract) move upward and tips epiglottis over opening of trachea, or windpipe o Rest of time, air passage in pharynx is open for breathing

How does negative pressure work?

o Key: create pressure gradient by changing volume of lungs o During inhalation, muscles between ribs contract, causing ribs to move upward and out, and diaphragm contracts and move downward o These contractions expand volume of thoracic cavity o The lungs, which have natural elasticity, expand along with thoracic cavity o Air pressure in alveoli decrease-it become lower than atmospheric pressure, which explain why mechanism is called negative pressure breathing o Air, moving from region of higher pressure to lower pressure, flow from surrounding atmosphere through nostril and into lungs

The process of gas exchange is sometimes called respiration, the interchange of

o O2 and the waste product CO2 o between an organism and its environment.

In alveoli,

o O2 diffuses into the blood and o CO2 diffuses out of the blood.

Exhalation reverse pressure gradient

o Rib muscles and diaphragm relax, reducing volume of thoracic cavity o Lungs return to their relaxed, unstretched position o Resultant increase in alveolar air pressure forces air up breathing tubes and out of body

The micrograph shows how these tubes branch repeatedly

o Smallest branches, called trachioles, extend to nearly every cell in insect's body. o Their tiny tips have closed ends and contain fluid o Gases are exchanged directly with body cells by diffusion across moist epithelium that lines these tips Thus, circulatory system of insects is not involved in transporting gases

The heart pumps blood to two regions.

o The right-side pumps oxygen-poor blood to the lungs. o The left side pumps oxygen-rich blood to the body.

Gas exchange with water has its limits.

o Water holds only about 3% of the oxygen in air. o Cold water holds more oxygen than warm water. o Fresh water holds more oxygen than saltwater. Turbulent water holds more oxygen than still water

Pictures: circle represent cross section of animal's body through respiratory surface

o Yellow areas represent respiratory surfaces; green outer circles represent body surfaces with little/no role in gas exchange o Boxed enlargements show gas exchange occurring across respiratory surface

Gills

o are extensions of the body, o increase the surface to volume ratio, and o increase the surface area for gas exchange. § Oxygen is absorbed. § Carbon dioxide is released.

In mammals, air is inhaled through the nostrils into the nasal cavity. Air is

o filtered by hairs and mucus surfaces, o warmed and humidified, and o sampled for odors.

Smoking also

o increases the risk of heart attacks and strokes, o raises blood pressure, and o increases harmful types of cholesterol.

Smoking can cause

o lung cancer, o cardiovascular disease, and o emphysema.

Respiratory surfaces must be

o moist for diffusion of O2 and CO2 and o thin, to best facilitate diffusion.

Insect tracheal systems use tiny branching tubes that

o reduce water loss and o pipe air directly to cells.

One-way flow of air in birds

o reduces dead air and increases their ability to obtain oxygen.

The diaphragm

o separates the abdominal cavity from the thoracic cavity and o helps ventilate the lungs.

Mucus and cilia in the respiratory passages

o sweep contaminant-laden mucus up and out of the airways and o can be damaged by smoking.

Exhalation occurs when

o the rib cage contracts, o the diaphragm moves upward, o the pressure around the lungs increases, and o air is forced out of the respiratory tract.

In mammals, inhalation occurs when

o the rib cage expands, o the diaphragm moves downward, o the pressure around the lungs decreases, and o air is drawn into the respiratory tract.

From the nasal cavity, air next passes

o to the pharynx, o then larynx, past the vocal cords, o into the trachea, held open by cartilage rings, o into the paired bronchi, o into bronchioles, and finally o to the alveoli, grapelike clusters of air sacs, where gas exchange occurs.

In a fish, gas exchange is enhanced by

o ventilation of the gills (moving water past the gills) and o countercurrent flow of water and blood.

The skin may be used for gas exchange in animals that are

o wet and o small. o Earthworms are an example.

When you exhale,

outgoing air rushes by pair of vocal cords in larynx, and you can produce sounds by voluntarily tensing muscles that stretch cords so they vibrate o You produce high pitched sounds when your vocal cords are tightly stretched and vibrating very fast o When cords are less tense, they vibrate slowly and produce low pitched sounds o From larynx, air pass into trachea o Rings of cartilage reinforce walls of larynx and trachea, keeping this part of airway open o Trachea forks into two bronchi, one leading to each lung o Within lung, bronchus branches repeatedly into finer and finer tubes called bronchioles o Bronchitis-condition in which these small tubes become inflamed and constricted, making breathing difficult

At bottom of figure, for instance, oxygen move from

oxygen-rich blood, through interstitial fluid, and into tissue cells because it diffuse from region of higher partial pressure to region of lower partial pressure o Tissue cells maintain this gradient as they consume oxygen in cellular respiration o Carbon dioxide produced as waste of cellular respiration diffuse down its own partial pressure gradient out of tissue cells and into capillaries o Diffusing down partial pressure gradients also account for gas exchange in alveoli

Breathing control centers in the brain

sense and respond to CO2 levels in the blood.

Surfactants are

specialized secretions required to keep the walls of the small alveoli from sticking shut. o Babies born 6 weeks or more before their due date often struggle with respiratory distress syndrome due to an inadequate amount of lung surfactant. o Artificial surfactants are now administered to preterm infants.

Larger insects may ventilate

their tracheal systems with rhythmic body movements that compress & expand air tubes like bellows.

At end of each trachea is

valve that allow insect to adjust size of opening to conserve moisture. o In dry climates, hairs surrounding opening also help minimize water loss

Tracheal system of insects,

with respiratory surfaces at tips of tiny branching tubes inside body, greatly reduces evaporative water loss

exchange of gases with body cells.

§ Body tissues take up oxygen and release carbon dioxide. § In process of cellular respiration that take place in mitochondria, oxygen is final electron acceptor in stepwise breakdown of fuel molecules § This process produce ATP that will power cellular work, and CO2 & H2O are waste products

Breathing

§ as you inhale, large, moist internal surface is exposed to air entering lungs. § Oxygen diffuse across cells lining lungs & into surrounding blood vessels § At same time, carbon dioxide diffuses from blood into lungs § As exhale, carbon dioxide leave body

transport of oxygen and carbon dioxide in blood

§ oxygen that diffused into blood attaches to hemoglobin in red blood cells § red vessels in figure are transporting oxygen rich blood from lungs to capillaries in body's tissues § CO2 is also transported in blood, from tissues back to lungs

In most terrestrial animals, respiratory surface is

· folded into body rather than projecting from it · Infolded surface open to air only through narrow tubes, an arrangement that help retain moisture that's essential for cells of respiratory surfaces to function

Most animals have specialized body parts that promote gas exchange

· gills in fish and amphibians, · tracheal systems in arthropods, and

Most terrestrial vertebrates have

· lungs which are internal sacs lined with moist epithelium. o As diagram indicate, inner surfaces of lungs are extensively subdivided, forming large respiratory surface o Gases are carried between lungs and body cells by circulatory system