Respiratory Systems

Respiratory Systems

• What is a respiratory system? How does it work?• What are the functions of respiratory systems?• What are the different respiratory strategies that animals

use?

Definitions

Respiration – sequence of events that result in the exchange of oxygen and carbon dioxide between the external environment and the mitochondria

External respiration – gas exchange at the respiratory surface

Internal respiration – gas exchange at the tissues

Mitochondrial respiration – production of ATPATP via oxidation of carbohydrates, amino acids, or fatty acids. Oxygen is consumed and carbon dioxide is produced

Gas molecules move down concentration gradients

Mitochondrial respiration

Mitochondria consume O2 to produce ATPATP

Produce CO2 in process

Organisms must have mechanisms to obtain O2 from the environment and get rid of CO2

→ External respiration

• Unicellular and small multicellular organisms rely on diffusion for gas exchange

• Larger organisms must rely on a combination of bulk flow and diffusion for gas exchange, i.e., they need a respiratory system

Respiratory strategies of animals

Respiratory systems - physics

Diffusion

Diffusion is the movement of molecules from a high concentration to a low concentration

• Slow over long distances• Fast over short distances

Respiratory systems - diffusion

The Fick equation

J= -DAdC/dx

J = rate of diffusion (moles/sec)D = diffusion coefficientA = area of the membranedC = concentration gradientdx = diffusion distance

For gases, we usually use partial pressure rather than concentration

Rate of diffusion will be greatest when the diffusion coefficient (D), area of the membrane (A), and energy gradients (dC/dx) are large, but the diffusion distance is small

Consequently, gas exchange surfaces are typically thin, with a large surface area

Respiratory systems - diffusion

J= -DAdC/dx

For gases, we usually use partial pressure rather than concentration

• Total pressure exerted by a gas is related to the number of moles of the gas and the volume of the chamber

Ideal gas law: PV = nRT

P- total pressure; V- Volume; n – number of moles of gas molecules; R – gas constant (8.314472 J · K-1 · mol-1) T – temperature in Kelvin

Gas Pressure

Gas Pressure cont.

• Air is a mixture of gases: nitrogen (78%), oxygen (21%), argon (0.9%) and carbon dioxide (0.03%)

• Dalton’s law of partial pressures: in a gas mixture each gas exerts its own partial pressure that sum to the total pressure of the mixture

Gases Dissolve in liquids

Gas molecules in air must first dissolve in liquid (water or extra-cellular fluid) in order to diffuse into a cell

Henry’s law: [G] = Pgas x Sgas

Gases Dissolve in liquids

CO2 is much more soluble in water than is O2. Thus, at the same partial pressure, more CO2will be dissolved in a solution than will oxygen

Diffusion Rates

Graham’s lawThe relative diffusion of a given gas is

proportional to its solubility in the liquid and inversely proportional to the square root of its molecular weight:

Diffusion rate solubility/MW

• O2 32 atomic mass units

• CO2 44 amu

• In air “solubilities” are the same (1000 ml/L at 20oC)

• Oxygen diffuses about 1.2 times faster than CO2

• However, CO2 is about 24 times more soluble in aqueous solutions than O2. So CO2 diffuses about 20 times faster than O2 in water

Diffusion Rates at a constant temperature

Combining the Fick equation with Henry’s and Graham’s laws:

Diffusion rate dPgas x A x Sgas / X x (MW)

At a constant temperature the rate of diffusion is proportional to

•Partial pressure gradient (dPgas)

•Cross-sectional area (A)

•Solubility of the gas in the fluid (Sgas)

And inversely proportional to •Diffusion distance (X)•Molecular weight of the gas (MW)

Fluid Movement: Bulk flow

• Bulk flow: Mass movement of water or air as the result of pressure gradients

• Fluids flow from areas of high to low pressure

• Boyle’s Law: P1V1 = P2V2

Temperature and the number of gas molecules remain constant

Bulk flow and Boyle’s law

Respiratory systems use changes in volume to cause changes in pressure!

P1V1 = P2V2 P2V2 P1 = P2

P1V1 = P2V2 P2 P1 = P2 V2

Surface Area to Volume Ratio

• As organisms grow larger, their ratio of surface area to volume decreases

• This limits the area available for diffusion and increases the diffusion distance

J= -DAdC/dx

Respiratory strategies of animals

• Unicellular and small multicellular organisms rely on diffusion for gas exchange

• Larger organisms must rely on a combination of bulk flow and diffusion for gas exchange, i.e., they need a respiratory system

Respiratory Strategies

Animals more than a few millimeters thick use one of three respiratory strategies• Circulating the external medium through the body

• Sponges, cnidarians, and insects

• Diffusion of gases across the body surface accompanied by circulatory transport

• Cutaneous respiration• Most aquatic invertebrates, some amphibians, eggs of birds

• Diffusion of gases across a specialized respiratory surface accompanied by circulatory transport

• Gills (evaginations) or lungs (invaginations)• Vertebrates

Circulating the external medium through the body

Parazoa and Cnidaria

Circulating the external medium through the body

Tracheal systemSeries of narrow tubes leading from surface to deep within bodyGases move in the tubes via a combination of diffusion and bulk flow

Cricket spiracle

Most animals have a circulatory system

Respiratory surface

TissueCirculatory

systemExternal medium

• Diffusion of gases across a specialized respiratory surface accompanied by circulatory transport

O2O2

Cutaneous respiration

Respiration through skin

Found in some aquatic invertebrates and a few vertebrates

Disadvantages: relatively low surface area

Conflict between respiration and protection

Salamander Annelid Lake Titicaca frog

External gills

Gills originate as outpocketings (evaginations)

• Advantages: high surface area, exposed to medium

• Disadvantages: easily damaged, not suitable in air

Polychaete

Salamander

Internal gills

• Advantages: High surface area, protected

• Disadvantages: not usually suitable in air

Lungs

Originate as infoldings (invaginations)

• Advantages: High surface area, protected, suitable for breathing air

• Disadvantages: not suitable in water

Ventilation

The active movement of the respiratory medium (air or water) across the respiratory surface

Ventilation of respiratory surfaces reduces the formation of static boundary layers i.e. improves efficiency of gas exchange

Types of ventilation• Nondirectional - medium flows past the respiratory

surface in an unpredictable pattern• Tidal - medium moves in and out• Unidirectional - medium enters the chamber at one

point and exits at another

Animals respond to changes in environmental oxygen or metabolic demands by altering the rate or pattern of ventilation

Nondirectional ventilation

PO2 = 160mmHg

40 60 80 100 120 140 160 160

O2

Flow

Medium flows past the respiratory surface in an unpredictable pattern

Effect of increased boundary layer

Tidal ventilation

PO2 = 160mmHg

PO2

100mmHg40 40

6080 90

95

100 100

Flow

Lung

Blood vessel

Medium moves in and out

Gas exchange – unidirectional ventilation

Cocurrent flow

Countercurrentflow

Blood

Medium

Resp. surface

Blood

Medium

Resp. surface

Crosscurrent flow

Medium

Resp. surface

Blood

Medium enters the chamber at one point and exits at another

With unidirectional ventilation, the blood can flow in three ways relative to the flow of the medium

Orientation of Medium and Blood Flow

PO2 of medium and blood will equilibrate


PO2 of blood approaches that of the inhalant medium


Found in birdsInitial-parabronchial (PI; ) and End-parabronchial values (PE). Mixed venous (Pv) blood; Arterial blood (Pa).

The PO2 of arterial blood is derived from a mixture of all serial air-blood capillary units and exceeds that of PE.

Ventilation and Gas Exchange

Because of the different physical properties of air and water, animals use different strategies depending on the medium in which they live

Differences• [Oair] 30x greater than [Owater]• Water is more dense and viscous than air• Evaporation is only an issue for air breathers

Strategies• Unidirectional: most water-breathers• Tidal: air-breathers• Air filled tubes: insects

Ventilation and Gas Exchange in Water

Strategies• Circulate the external medium through an

internal cavity• Various strategies for ventilating internal and

external gills

Ventilation in water- invertebrates

Sponges and Cnidarians

• Circulate the external medium through an internal cavity• In sponges flagella move water in through ostia and out

through the osculum• In cnidarians muscle contractions move water in and out

through the mouth

Molluscs

Two strategies for ventilating their gills and mantle cavity• Beating of cilia on gills move water across the gills

unidirectionally • Blood flow is countercurrent• Snails and clams

• Muscular contractions of the mantle propel water unidirectionally through the mantle cavity past the gills

• Blood flow is countercurrent• Cephalopods (squid)

Crustaceans

• Barnacles (filter feeding) or small species (copepods) lack gills and rely on diffusion

• Shrimp, crabs, and lobsters, have gills derived from modified appendages located within a branchial cavity

• Movements of the gill bailer propels water out of the branchial chamber; the negative pressure sucks water across the gills

copepod

Echinoderms – sea stars, sea urchins, sea cucumbers• Most sea stars and sea

urchins use their tube feet for gas exchange

• Water is sucked in and exits through the madreporite

• Sea stars also have external gill-like structures (respiratory papulae); cilia move water over the surface

Echinoderms, cont.

• Brittle stars and sea cucumbers have internal invaginations

• Brittle stars used cilia to move water into bursae

• Sea cucumbers use muscular contractions of the cloaca and the respiratory tree to breathe water tidally though the anus

Lamprey and hagfish have multiple pairs of gill sacs

Jawless Fishes - Hagfish

Hagfish• A muscular pump (velum) propels water through the respiratory cavity• Water enters the median nostril!!!! and leaves through a gill opening• Flow is unidirectional• Blood flow is countercurrent

Ventilation - hagfish

Gills sacs are arranged for counter current flow

Water flow

Jawless Fishes - Lamprey

Lamprey• Ventilation is similar to that in hagfish when not feeding • When feeding the mouth is attached to a prey (parasitic)• Ventilation is tidal though the gill openings

Elasmobranchs – sharks, skates and rays

Steps in ventilation• Expand the buccal cavity• Increased volume sucks fluid

into the buccal cavity via the mouth and spiracles

• Mouth and spiracles close• Muscles around the buccal

cavity contact forcing water past the gills and out the external gill slits

Blood flow is countercurrent

Water flows in via the mouth, out via the opercular opening

Teleost Fishes

Teleost Fishes

VP

Fish Gills

Fish gills are arranged for countercurrent flow

Ventilation and Gas Exchange in Air

Two major lineages have colonized terrestrial habitats

• Vertebrates• Arthropods (eeeekkkk)

• Unidirectional ventilation of gills common in water-breathing animals

• Tidal ventilation of lungs common in air-breathing animals

Ventilation in air

Insects

Vertebrates

MolluscsSpiders

Ventilation – terrestrial molluscs

• The “pulmonate” molluscs lack gills (or have highly reduced gills

• Instead, mantle cavity is highly vascularized and acts as a lung

• Garden snails and terrestrial slugs are pulmonates• Pumping of the mantle cavity moves air in and out of

these lungs

Arthropods (eeeeeeek)

• Crustaceans (crabs, woodlice and sowbugs)• Chelicerates (spiders and scorpions)• Insects

Gift from Agnes Lacombe

Crustaceans

Terrestrial crabs• Respiratory structures and the processes of ventilation are

similar to marine relatives, but• Gills are stiff so they do not collapse in air• Branchial cavity is highly vascularized and acts as the

primary site of gas exchange• Movements of the gill bailer propels air in and out of the

branchial chamber

Terrestrial isopods (woodlice and sowbugs)• Have a thick layer of chitin on one side of the gill for support and

the other side is thin walled and used for gas exchange• Anterior gills contain air-filled tubules (pseudotrachea). Oxygen

diffuses down the pseudotrachea and dissolves in the interstitial fluid

Chelicerates - Spiders and scorpions

Have four book lungs• Consists of 10-100

lamellae• Open to outside via

spiracles• Gases diffuse in and out

Some spiders also have a tracheal system – series of air-filled tubes• Oxygen diffuses into the

trachea and dissolves in the interstitial fluid before diffusing into the tissues

Insects

• Have an extensive tracheal system - series of air-filled tubes• Tracheoles – terminating ends of tubes that are filled with

hemolymph• Oxygen dissolves in the hemolymph• Open to outside via spiracles• Gases diffuse in and out• High diffusion coefficient of oxygen in air allows oxygen to

diffuse through the tracheal system

Ventilation in insects

• Some species can expand and compress the trachea

• Changes in tracheal volume cause changes in pressure, which causes air to flow through the system

Images of insect trachea obtained using X-ray synchrotron radiation

Insect Ventilation

3 Types• Contraction of abdominal muscles or

movements of the thorax• Can be tidal or unidirectional (enter anterior

spiracles and exit abdominal spiracles)

• Ram ventilation (draft ventilation) in some flying insects

• Discontinuous gas exchange• Phase 1 (closed phase): no gas exchange; O2

used and CO2 converted to HCO3-; in total P

• Phase 2 (flutter phase): air is pulled in

• Phase 3: total P as CO2 can no longer be stored as HCO3

-; spiracles open and CO2 is released

Ventilation in insects - Discontinuous gas exchange

• Phase 1 (closed phase): no gas exchange; O2 used and CO2 converted

to HCO3-; in total P

• Phase 2 (flutter phase): air is pulled in• Phase 3: total P as CO2 can no longer be stored as HCO3

-; spiracles open and CO2 is released

Aquatic insects

• Most aquatic insects breathe air

• Mosquito larvae have “snorkel”

Hydrofuge hairs

How insects keep their snorkels dry

Water beetle (Dytiscus)

• Water beetles carry scuba tanks (air bubbles)

Air breathing vertebrates

Air breathing evolved in fishesAquatic habitats can become hypoxicUnder these conditions, the ability to breathe air

is a substantial benefit

Vertebrates

• Fish

• Amphibians

• Reptiles

• Birds

• Mammals

Evolution of air breathing

Some fish use “aquatic surface respiration” when hypoxic

Swim to the surface and ventilate gills with water from the thin well-oxygenated water layer near surface

Some fish can gulp air into mouth (buccal cavity)

Buccal cavity highly vascularized for gas exchange

Fish

Air breathing has evolved multiple times in fishes

Types of respiratory structures• Reinforced gills that do not collapse in air• Mouth or pharyngeal cavity for gas exchange (highly vascularized)• Vascularized stomach• Specialized pockets of the gut• Lungs

Ventilation is tidal using buccal force similar to other fish

Amphibians - ventilation

• Amphibians have simple sac-like lungs

• Form as outpocketings of the gut

Amphibians

Types of respiratory structures• Cutaneous respiration• External gills• Simple bilobed lungs; more complex in terrestrial frogs

and toads

Ventilation is tidal using a buccal force pump

Amphibians – external gills

• Advantages: high surface area, exposed to medium

• Disadvantages: easily damaged, not suitable in airPolychaete

Salamander

Amphibians

Reptiles

* Most have two lungs; in snakes one lung is reduced or absent

* Can be simple sacs with honeycombed walls or highly divided chambers in more active species• More divisions result in more surface area

Ventilation• Tidal• Rely on suction pumps• Results in the separation of feeding and respiratory

muscles• Two phases: inspiration and expiration• Use one of several mechanisms to change the volume of

the chest cavity

Reptiles: mechanisms to change the volume •Snakes and lizards: use intercostal muscles.

Contraction of the intercostals moves the ribs forward and outward, increasing the volume•Turtles and tortoises: Use abdominal muscles that expand and compress the lungs•Crocodilians: Hepatic septum is attached to the anterior side of the liver. Paired diaphramaticus muscles run from the hepatic septum to the pelvic girdle. Diaphramaticus muscles contract which decreases the volume in the abdominal cavity and increases the volume of the lungs. As a result pressure in the lungs decreases

Reptiles

Ventilation in birds and mammals

• Birds use unidirectional ventilation

• Mammals use tidal ventilation

Birds

• Lung is stiff and changes little in volume

• Rely on a series of flexible air sacs

• Gas exchange occurs at parabronchi

Bird lungs – crosscurrent flow

Oxygen extraction efficiency high (up to 90%)

Bird Ventilation

Requires two cycles of inhalation and exhalation

Air flow across the respiratory surfaces is unidirectional

Bird Ventilation

Mammals

Two main parts• Upper respiratory tract: mouth, nasal cavity, pharynx,

trachea• Lower respiratory tract: bronchi and lungs

Alveoli are the site of gas exchange

Both lungs are surrounded by a pleural sac

Mammalian lungs

Mammalian lungs - alveoli

Type I cells gas exchange

Type II cells surfactant secretion

Airways:

LarynxTracheaBronchiiBronchiolesAlveoli

Mammalian lungs

Its Friday

Compliance:• Distensibility (stretchability):

• Ease with which the lungs can expand.

• 100 x more distensible than a balloon.• Compliance is reduced by factors that produce resistance

to distension.

Elasticity:• Tendency to return to initial size after distension.• High content of elastin proteins.

• Very elastic and resist distension.• Recoil ability.

Physical Properties of the Lungs

•Pulmonary ventilation involves different pressures:• Atmospheric pressure • Transpulmonary pressure• Intraalveolar (intrapulmonary) pressure • Intrapleural pressure

• Atmospheric pressure is the pressure of the air outside the body.

•Transpulmonary pressure is the pressure difference across the wall of the lung. Keeps the lungs against chest wall.

• Intraalveolar pressure is the pressure inside the alveoli of the lungs.

•Intrapleural pressure is the pressure within the pleural cavity. Pressure is negative, due to lack of air in the intrapleural space

Physical Properties of the Lungs

Insert fig. 16.15

Lungs, pleura, and chest wall

Airway resistance

• Flow = P/R• If resistance increases, a greater P

is needed to maintain the same flow• Airway resistance is inversely

proportional to airway radius to the 4th power (1/r4)

• Bronchoconstriction – reduction in airway radius

• Bronchodilation – increase in radius

Bronchoconstriction and Bronchodilation

Bronchoconstriction: stimulation of parasympathetic nervous

systemHistamineIrritants

Bronchodilation:stimulation of sympathetic nervous systemCirculating epinephrine(binds to beta-2 receptors)High alveolar PCO2

Mammal Ventilation

Tidal ventilation

Steps• Inhalation

• Somatic motor neuron innervation

• Contraction of the external intercostals and the diaphragm

• Ribs move outwards and the diaphragm moves down

• Volume of thorax increases

• Air is pulled in

• Exhalation• Innervation stops

• Muscle relax

• Ribs and diaphragm return to their original positions

• Volume of the thorax decreases

• Air is pushed out via elastic recoil of the lungs

During rapid and heavy breathing, exhalation is active via contraction of the internal intercostal muscles

Mammals

Mammalian lungs - ventilation

Air moves into and out of the lungs along pressure gradients that are the result of volume changes

Surfactants

• Surfactants – reduce surface tension by disrupting the cohesive forces between water molecules

• Results in an increase in lung compliance and a decrease in the force needed to inflate the lungs

• In humans, surfactant synthesis does not begin until late gestation

Dead Space

Tidal volume – total volume of air moved in one ventilatory cycle

Dead space – air that does not participate in gas exchange• Two components

• Anatomical dead space – volume of the trachea and bronchi

• Alveolar dead space – volume of any alveoli that is not being perfused with blood

Spirometry

Method for measuring pulmonary function

Lung Volumes and Capacities

Emphysema

• In emphysema, the walls of the alveoli break down

• Increases lung compliance, but reduces lung elastance

Gas Transport

• Sponges, cnidarians, and insects circulate external fluid past almost every cell in their bodies and can rely on diffusion

• Larger animals use circulatory systems

Ventilation-perfusion matching

• Ventilation of the respiratory surface must be matched to the perfusion of the respiratory surface

• VA/Q quantifies this. Should be close to 1

• Humans: VA ~ 4-5 L/min and Q ~ 5L/min

Gas transport

Bulk flowVentilation

DiffusionBulk flowCirculation

Diffusion

Gas transport

Bulk flowVentilation

Diffusion

Bulk flowCirculation

Diffusion

Oxygen Transport

• Solubility of oxygen in aqueous fluids is low

• Metalloproteins contain metal ions which reversibly bind to oxygen and increase oxygen carrying capacity by 50-fold

• By binding oxygen to carriers, PO2 in the blood remains low and results in improved oxygen extraction

Amount of oxygen that can dissolve in plasma is limited at physiological PO2 (Henry’s Law [G] = Pgas * Sgas)

Respiratory pigments

• Respiratory pigments help to increase the amount of O2 in blood

• Oxygen-binding molecules• Contain metal ions• Gives them a strong colour (e.g. hemoglobin – red)• Oxygen binds reversibly to the metal ion• Bind to the pigment at the lungs• Releases from the pigment at the tissues

Types of respiratory pigment

• Hemoglobin - vertebrates, nematodes, some annelids, some crustaceans, some insects

• Hemerythrin - sipunculids, priapulids, brachiopods, and one family of annelids

• Hemocyanin - arthropods and molluscs

Respiratory Pigments

Metalloproteins are referred to as respiratory pigmentsThree major types

• Hemoglobins• Most common• Vertebrates, nematodes, some annelids, crustaceans, and

insects• Consist of a protein globin bound to a heme molecule

containing iron• Usually located within blood cells• Appears red when oxygenated• Myoglobin is a type of hemoglobin found in muscles

• Hemocyanins• Arthropods and molluscs• Contain copper• Usually dissolved in the hemolymph• Appears blue when oxygenated

• Hemerythrins• Sipunculids, priapulids, brachiopods, some annelids• Contains iron directly bound to the protein• Usually found inside coelomic cells• Appears violet-pink when oxygenated

Hemoglobin

•Vertebrate hemoglobins are tetramers•Two alpha chains•Two beta chains•Each contains a heme group•Each heme group can bind 1 molecule of oxygen•Therefore 1 Hb molecule can bind 4 oxygen molecules

Myoglobin (Mb)

• Type of hemoglobin found in vertebrate muscle

• Monomer• Each Mb molecule

binds one molecule of oxygen

Hemocyanin

• Arthropods & molluscs• Contain copper instead of iron• Copper is complexed directly to amino acids in the

protein• Multimeric (up to 48 subunits)• Blue when oxygenated

Hemerythrins

•Sipunculids, priapulids, brachiopods, and one family of annelids•Do NOT contain heme•Iron is bound directly to amino acids in the protein

subunits (usually 2 iron molecules per subunit)•Molecules are usually trimeric or octomeric•Very pretty violet colour when oxygenated, colorless

when deoxygenated

Oxygen carrying capacity of blood

• Carrying capacity = the maximum amount of oxygen that can be carried in blood

• Total O2 in blood = dissolved O2 + O2 bound to respiratory pigment

• Increased amount of respiratory pigment = increased capacity for carrying oxygen

• Because of the low solubility of oxygen in aqueous solutions, only a small amount of oxygen can dissolve in blood

• PO2 is equal in plasma and lungs, but oxygen content of plasma is much lower


• If an oxygen carrier such as hemoglobin is present, some of the oxygen will bind to the pigment

• This oxygen no longer contributes to PO2

• PO2 is the same as in the previous example, but oxygen content is higher


• At low environmental PO2, the PO2 of the plasma is low

• Less oxygen dissolves in plasma

• The amount of oxygen bound to the pigment may also decrease somewhat (if the plasma PO2 is low enough)

• But, the total oxygen content of the blood is still higher than if no pigment were present


Oxygen Equilibrium Curves

• Shows the relationship between partial pressure of oxygen in the plasma and the percentage of oxygenated respiratory pigment in a volume of blood

• As partial pressure increases, more and more pigment molecules will bind oxygen, until the saturation point

• P50 – oxygen partial pressure at which the pigment is 50% saturated


• Obey the law of mass action

• Hb + O2 HbO2

• If oxygen concentration increases, reaction shifts to the right

• If oxygen concentration decreases, reaction shifts to the left

Shapes of Oxygen Equilibrium Curves

• Can be either hyperbolic or sigmoidal

• Each molecule of myoglobin binds oxygen independently and therefore has a hyperbolic shape

• Hemoglobin exhibits a sigmoidal curve because of cooperativity – hemoglobin has a higher affinity for oxygen when more of its heme groups are bound to oxygen

Log[Y/(1-Y)] vs. Log(PO2)


Factors that can affect the shape of the oxygen equilibrium curve

• Molecular structure of the respiratory pigment• Environmental factors such as pH, CO2, allosteric

modifiers, temperature

Shapes of Oxygen Equilibrium Curves

Structure of the pigment

Fetal hemoglobin has a lower P50 than maternal hemoglobin

• Myoglobin has a lower P50 than Hemoglobin

• Myoglobin has higher oxygen affinity

• Also note the difference in the shapes of the curve

• The hemoglobin curve is sigmoidal

• Myoglobin curve is hyperbolic

Structure of the pigment

Conditions That Affect Oxygen Affinity

pH and PCO2

• Bohr effect or shift – a decrease in pH or increase in PCO2 reduces oxygen affinity - right shift

• This facilitates oxygen transport to active tissues and facilitates oxygen binding at the respiratory surfaces


Temperature• Increases in temperature decrease oxygen affinity;

right shift• Promotes oxygen delivery during exercise

Organic modulators (e.g., 2,3-DPG, ATP, GTP)• Increases in these modulators decrease oxygen

affinity; right shift• Helps oxygen unloading at tissues

Carbon monoxide and Hb

• Carbon monoxide is a byproduct of combustion

• Carbon monoxide (CO) can bind to hemoglobin

• CO has 250 times the affinity for hemoglobin than O2

• Hb becomes 100% saturated with CO at PCO = 0.6 mm Hg

• Hb becomes 100% saturated with O2 at PO2 = 600 mm Hg


pH and PCO2

•Root effect – a Bohr effect with a reduction in the oxygen carrying capacity

•Seen in hemoglobin of many teleost fishes•Helps in oxygen delivery to eye and swim bladder

Swim bladder

• Fish • Many bony fish have a swimbladder that helps

to maintain neutral buoyancy• Gas-filled sac• Fill with gas to increase buoyancy• Remove gas to reduce buoyancy• In most species this gas is oxygen

Swim bladder

•Gas gland excretes lactic acid •Acidity causes hemoglobin

of the blood to lose its oxygen

•Oxygen diffuses into the bladder while flowing

through a complex structure known as the rete mirabile

Carbon Dioxide Transport

• Carbon dioxide is more soluble in body fluids than oxygen

• However, little CO2 is transported in the plasma

• Some CO2 binds to proteins (carbaminohemoglobin)

• Most CO2 is transported as bicarbonate

• CO2 + H2O H2CO3 (carbonic acid) HCO3-

(bicarbonate) + H+

• Carbonic anhydrase catalyzes the formation of HCO3

-

Carbon Dioxide Equilibrium Curve

• Shows the relationship between PCO2 and the total CO2 content of the blood

• The shape of the curve depends on the kinetics of HCO3

- formation

• Deoxygenated blood can carry more CO2 than oxygenated blood (Haldane effect)

Haldane effect

• Removal of oxygen from hemoglobin increases hemoglobin’s affinity for carbon dioxide

• Allows CO2 to be carried bound to hemoglobin

Vertebrate Red Blood Cells and CO2 Transport• Carbonic anhydrase is located within RBCs

• Reactions to synthesize HCO3- occur in the

RBCs even though most of this HCO3- is carried

in the plasma

Carbon dioxide transport – at tissues

• CO2 is produced by aerobic metabolism• Rapidly diffuses out of tissues and into red cell• Carbonic anhydrase catalyzes formation of bicarbonate• the H+ formed by this reaction binds to Hb• the bicarbonate ions are moved out the the RBC by a transporter protein

(band III)• Bicarbonate does not readily diffuse through membranes• if it were not removed, build up within red

cell would inhibit CA reaction• Band III exchanges HCO3

- for Cl- (Chloride shift)

Carbon dioxide transport – at respiratory surface

• PCO2 of air/water is lower than blood

• CO2 diffuses out of plasma across respiratory

surface• CO2 diffuses out of RBC into plasma

• Equilibrium of CO2-bicarbonate reaction is shifted• Bicarbonate ions move from plasma into RBCs

(reverse-chloride shift)• Bicarbonate and H+ from carbonic acid and then

CO2

• CO2 diffuses out of RBC into plasma and

then across respiratory surface

Regulation of Respiratory Systems

Vertebrate respiratory and circulatory systems work together to regulate gas delivery by• Regulating ventilation• Altering oxygen carrying capacity and affinity• Altering perfusion

• Respiratory systems are closely regulated• Respond to changes in external and internal environment• Must be able to supply sufficient oxygen to meet metabolic

demands• Must be able to remove carbon dioxide to prevent pH

disturbance

pH homeostasis

Buffer systems:

Buffer: moderates changes but does not prevent changes in pHProteins, Phosphate Ions and bicarbonate

Lungs:Via respiratory compensation

Kidneys:Use ammonia and phosphate buffers

Disturbance H+ pH HCO3-

AcidosisMetabolic

Acid Base disturbances – Metabolic acidosis

CO2 + H2O H2CO3 HCO3- + H+

Step by step:Causes include lactic acid accumulation, ketoacids (from breakdown of fats or amino acids ). Can also be due to loss of bicarbonate

1. Hydrogen concentration increases, pH decreases2. Equilibrium shifts to the left3. HCO3

- buffer is used up and CO2 increases4. Response of body: CO2 can be blown off at the lungs.

Also, renal compensation


AcidosisRespiratory

Acid Base disturbances – Respiratory acidosis


Step by step:Hypoventilation results in an increase of carbon dioxide and elevatedPCO2.

1. Plasma CO2 levels increase; H+ increases2. pH decreases3. Equilibrium shifts to the right4. Hydrogen and bicarbonate concentrations increase5. Response of body: Renal compensation


AlkalosisMetabolic

Acid Base disturbances – Metabolic alkalosis


Step by step:Loss of protons due to vomiting of acid stomach contents orexcessiveIntake of bicarbonate-containing antacids

1. H+ decreases2. pH increases 3. Equilibrium shifts to the right, CO2 decreases and bicarbonate goes

up4. Response of body: Adjust respiration and renal compensation


AlkalosisRespiratory

Acid Base disturbances- Respiratory alkalosis


Step by step:Due to hyperventilation.

1. CO2 decreases, pH increases2. Equilibrium shifts to the left, protons and bicarbonate decrease3. Response of body: Renal compensation

Responses to Acid-base disturbances

Metabolic Acidosis:1.Hyperventilate (blow off CO2) PCO2 decreases2.Renal System - Secretion of H+ and reabsorption of bicarbonate

Respiratory Acidosis:1. Renal System: Secretion of H+ and reabsorption of bicarbonate

Metabolic Alkalosis:1.Hypoventilation PCO2 increases. Corrects pH problem but increases bicarbonate (only short term)2.Renal System: bicarbonate excreted and H+ reabsorbed

Respiratory Alkalosis:1.Renal System: bicarbonate excreted and H+ reabsorbed

Regulation of Ventilation

• Rhythmic firing of central pattern generators within the medulla initiate ventilatory movements

• Pre-Botzinger complex is an important respiratory rhythm generator in mammals

Ventilation is automatic

• Ventilation is an automatic process

• Continues even when we are unconscious

• Central pattern generator in medulla

• Exact location within the medulla varies among species

Regulation of Ventilation

• Chemosensory input helps modulate the output of the central pattern generators

• Chemoreceptors detect changes in CO2, H+, and O2

• Oxygen is the primary regulator in water-breathers while CO2 is the primary regulator in air-breathers

• Rhythm generation neurons of the preBotzinger complex send output via motor neurons

• Motor neurons innervate intercostal muscles, diaphragm, and abdominal muscles

• Cause muscle contraction, resulting in either inspiration or expiration

Regulation of ventilation


• Ascending sensory input comes from chemosensory neurons in carotid and aortic bodies, in vasculature of lungs, and chemoreceptors in the medulla

• Modulates the rate and depth of breathing• Negative feedback loop to maintain blood PO2 and PCO2 within

a narrow range

Homeostatic feedback loop for the regulation of ventilation


Carotid and aortic chemoreceptors

Glomus cells = chemosensory cells

Mechanisms in carotid body

• Glomus cells contain oxygen-gated K+ channels

• Oxygen sensor detects low PO2

• Closes K+ channels• Cell depolarizes• Causes release of dopamine• Stimulates sensory neuron

Mechanisms in central chemoreceptors

• Most important controllers in mammals

• Sensitive to changes in PCO2 and pH

• CO2 crosses blood/brain barrier

• Carbonic anhydrase converts CO2 to HCO3

- and H+

• H+ stimulates receptor• Stimulates ventilation

Chemoreceptor reflex

Chemoreceptor reflex

•Most of the response is mediated by central chemoreceptors

•Increased PCO2 stimulates increased ventilation

Irritant receptors/stretch receptors

• Trigger bronchoconstriction• Trigger coughing• Trigger sneezing

Irritant receptors/stretch receptors

• Hering-Breuer inflation reflex• Reduces ventilation when

lungs are over-inflated• Usually only experienced

during/after intense exercise

Regulation of ventilation in water breathers

• Water-breathers such as fish are typically more sensitive to PO2 than PCO2

• Decreases in PO2 increase ventilation• Most species are sensitive to blood PO2

• A few species are thought to be sensitive to environmental PO2

Environmental Hypoxia

• Hypoxia – lower than normal levels of oxygen

• Can be caused by environmental hypoxia, inadequate ventilation, reduced blood hemoglobin content

• Hyper-, hypocapnia – higher or lower than normal levels of CO2

High Altitude PhysiologyHigh altitude8,000 - 12,000 feet[2,438 - 3,658 m]Very high altitude12,000 - 18,000 feet [3,658 - 5,487m]Extremely high altitude18,000+ feet (Everest 29,000ft)[5,500m]

Oxygen at Altitude

• Pressure declines as altitude increases• Oxygen delivery to body dependent on partial pressure of

oxygen• Concentration of oxygen doesn’t change but you get less

oxygen per breath• At 12,000ft you get ~40% less oxygen per breath

Physiological Response to Altitude

Moderate Altitude – initial symptoms

• Headache• Nausea• Fatigue• Loss of appetite• Difficulty sleeping• Frequent Urination

High Altitude – initial symptoms

• Confusion• Reduced mental acuity• Loss of coordination• Cerebral edema• Pulmonary edema• death

Physiological Response to Altitude

Response to Altitude - Respiratory

* Low inspired oxygen (PaO2 low)* CO2 production normal

• Arterial chemoreceptors sense low O2

• Increase rate and depth of breathing

Response to Altitude - Respiratory

* Hypocapnia* Reduces drive to breathe* Intermittent breathing (especially at night)* Causes difficulty sleeping

O2 Dissociation Curve

• Respiratory alkalosis shifts curve to left• Increased DPG shifts curve to right

Acclimatization to Altitude

Problems: * Hypoxia* Secondary hypocapnia

• Increased EPO• Increased hematocrit• Peripheral vasodilation

• Hypoxia persists• Therefore hyperventilation continues• Respiratory alkalosis• Compensate by increasing renal excretion of

HCO3-

* Hypoxia* Secondary hypocapnia

Acclimatization to Altitude

Pulmonary Blood Flow

• Inspired air low pO2

• Sensors in lung detect low oxygen• Causes vasoconstriction in lung• Reduces blood flow• Increases blood pressure• Can lead to pulmonary edema

High-Altitude Hypoxia

Llamas

• Moderate hematocrit• High affinity Hb• Very small RBCs

Deer Mice

Live at a variety of altitudes

Deer Mice

High Altitude mice have reduced DPG

Bar-headed Goose

• Migrates over Everest• Hb sequence differs by 1bp from all other geese• Greatly increases O2 affinity

Physiology of Diving

Physiology of Diving

Boyle’s Law

P1V1 = P2V2

• As pressure increases, volume decreases• As we dive, pressure increases

Breath-hold Diving

“The dive response”• Apnea• Bradycardia • Peripheral vasoconstriction• Redistribution of cardiac output• Limit breath-hold diving ~1 minute for humans

Animal adaptations to diving

• Modified body form• Increased oxygen stores• Ability to modify blood distribution• Ability to collapse lung• Regional hypothermia• Ability to buffer CO2

Limits to diving

Oxygen stores

Exercise Physiology

Initiation of muscle contraction

• Nervous signal initiates muscle contraction• ACh binds to receptor on motor end plate• Causes an action potential• Causes release of Ca2+ from SR• Initiates contraction

Fueling muscle contraction

• ATP• Phosphocreatine• Carbohydrates• Lipids (and proteins)

Exercise intensity and duration

• For short duration high-intensity exercise can use anaerobic pathways with PCr and carbohydrates as a fuel

• Results in lactate production• For longer duration exercise must switch to aerobic

pathways and lipids as a fuel• This requires oxygen• Blood flow to the exercising muscle must increase

Active hyperemia

• Increased muscle oxygen consumption

• Causes decrease in local oxygen concentration

• Release of local vasodilatory factors (e.g. nitric oxide)

• Causes vasodilation• Decreases resistance in arteriole

leading to muscle• Causes increased flow• Increases supply of oxygen to

working muscles

Blood flow during exercise• Misconception: Blood flow to brain increases during exercise • This is incorrect: Global cerebral blood flow to the brain is constant, approximately 750 ml/min, regardless of mental or physical activity • At rest: brain gets ca. 15% of total cardiac output per beat• As exercise intensity increases, cardiac output is redistributed (mostly to muscles) and the brain receives a lower percentage per beat.• At maximal intensity, the brain gets ca 4% of cardiac output per beat• However, this reduction is precisely offset by the overall increase in total cardiac output (the heart beats ca 4 times faster), resulting in a steady perfusion rate.

• Global oxygen and glucose uptake is also constant

Cardiac output

CO = HR x SV

• In untrained individuals CO increases from 5L/min - 20L/min; trained athletes up to ~35L/min during exercise

• Contribution of both heart rate and stroke volume

Blood flow

• Sympathetic nervous system causes generalized vasoconstriction• Reactive hyperemia causes increased flow to skeletal muscles• Net effect is a decrease in total peripheral resistance• Cardiac output (total blood flow) increases greatly• So what happens to blood pressure?

MAP = CO x TPR

Blood pressure

Ventilation during exercise

Exercise oxygen consumption

Ventilation during exercise

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Respiratory Systems

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