Circulation and gas transport (continued)

IB-202-14

3/19/06

Blood Clotting• A cascade of complex reactions

– Converts fibrinogen to fibrin, forming a clot

Plateletplug

Collagen fibers

Platelet releases chemicalsthat make nearby platelets sticky

Clotting factors from:PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)

Prothrombin Thrombin

Fibrinogen Fibrin5 µm

Fibrin clotRed blood cell

The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Plateletsadhere to collagen fibers in the connective tissue and release a substance thatmakes nearby platelets sticky.

1 The platelets form a plug that providesemergency protectionagainst blood loss.

2 This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via amultistep process: Clotting factors released fromthe clumped platelets or damaged cells mix withclotting factors in the plasma, forming an activation cascade that converts a plasma proteincalled prothrombin to its active form, thrombin.Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM).

3

Figure 42.17

A baby aspirin per day makes the platelets lazy!

Hemophiliacs

Cardiovascular Disease• Cardiovascular diseases

– Are disorders of the heart and the blood vessel and account for more than half the deaths in the United States

• One type of cardiovascular disease, atherosclerosis– Is caused by the buildup of cholesterol within arteries (low

density lipoprotein complexes with cholesterol)

Figure 42.18a, b

(a) Normal artery (b) Partly clogged artery50 µm 250 µm

Smooth muscleConnective tissue Endothelium Plaque

Plaques sites of inflammation and can cause a clot to form if plaque splits open! Aspirin!

Thrombus!

• Hypertension, or high blood pressure– Promotes plaque formation 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– Either by plaque build up or a clot (thrombus) formed

elsewhere and lodging in the vessel. Angina (pain in chest) Nitroglycerin-explosive! Releases nitric oxide relaxe arterioles.

• A stroke– Is the death of nervous tissue in the brain, usually

resulting from rupture or blockage of arteries in the head (clot dissolving enzymes useful if administered immediately).

• Concept 42.5: Gas exchange occurs across specialized respiratory surfaces

• Gas exchange– Supplies oxygen for cellular respiration and

disposes of carbon dioxide

Figure 42.19

Organismal level

Cellular level

Circulatory system

Cellular respiration ATPEnergy-richmoleculesfrom food

Respiratorysurface

Respiratorymedium(air of water)

O2 CO2

Oxygen is final electron acceptor in electron transport chain!!

• Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases– Between their cells and the respiratory medium

which can be either air or water

• Gills are outfoldings of the body surface specialized for gas exchange in aquatic animals

• In some invertebrates– The gills have a simple shape and are

distributed over much of the body

(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.

Gills

Tube foot

Coelom

Figure 42.20a

• Many segmented marine worms (Annelids) have flaplike gills

– That extend from each segment of their body

Figure 42.20b

(b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gillsand also function incrawling and swimming.

Gill

Parapodia

• The gills of clams, crayfish, and many other animals– Are restricted to a local body region

Figure 42.20c, d

(d) Crayfish. Crayfish and other crustaceanshave long, feathery gills covered by the exoskeleton. Specialized body appendagesdrive water over the gill surfaces.

(c) Scallop. The gills of a scallop are long, flattened plates that project from themain body mass inside the hard shell.Cilia on the gills circulate water around the gill surfaces.

Gills

Gills

• The effectiveness of gas exchange in some gills, including those of fishes– Is increased by ventilation and

countercurrent flow of blood and water

Countercurrent exchange. Very efficient for extracting oxygen from water!

Figure 42.21

Gill arch

Water flow Operculum

Gill arch

Blood vessel

Gillfilaments

Oxygen-poorblood

Oxygen-richblood

Water flowover lamellaeshowing % O2

Blood flowthrough capillariesin lamellaeshowing % O2

Lamella

100%

40%

70%

15%

90%

60%

30% 5%

O2

Ram jet ventilation!

Figure 42.22a

Tracheae

Air sacs

Spiracle

(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.

Tracheal Systems in Insects• The tracheal system of insects

– Consists of tiny branching tubes that penetrate the body

• The tracheal tubes– Supply O2 directly to body cells

Airsac

Body cell

Trachea

Tracheole

TracheolesMitochondria

Myofibrils

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

Air

Lungs

• Spiders, land snails, and most terrestrial vertebrates have internal lungs.

Spiders, land snails, and most terrestrial vertebrates have internal lungs.

In mammals a system of branching ducts conveys air to the lungs

Branch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole

Branch from thepulmonaryartery(oxygen-poor blood)

Alveoli

Colorized SEMSEM

50 µ

m

50 µ

m

Heart

Left lung

Nasalcavity

Pharynx

Larynx

Diaphragm

Bronchiole

Bronchus

Right lung

Trachea

Esophagus

Figure 42.23

Capillary web over alveoli

• In mammals, air inhaled through the nostrils– Passes through the pharynx into the trachea,

bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs across a thin layer of water and the plasma membrane!

How an Amphibian Breathes

• An amphibian such as a frog– Ventilates its lungs by positive pressure

breathing, which forces air down the trachea.– Mammals ventilate using negative pressure

breathing.– Reptiles also use negative pressure but have

no diaphragm

How a Mammal Breathes• Mammals ventilate their lungs

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

Air inhaled Air exhaled

INHALATIONDiaphragm contracts

(moves down)

EXHALATIONDiaphragm relaxes

(moves up)

Diaphragm

Lung

Rib cage expands asrib muscles contract

Rib cage gets smaller asrib muscles relax

Figure 42.24

How a Bird Breathes• Besides lungs, bird have eight or nine air sacs

– That function as bellows that keep air flowing through the lungs in a one way direction

INHALATIONAir sacs fill

EXHALATIONAir sacs empty; lungs fill

Anteriorair sacs

Trachea

Lungs LungsPosteriorair sacs

Air Air

1 mm

Air tubes(parabronchi)in lung

Figure 42.25

• Air passes through the lungs– In one direction only

• Every exhalation– Completely renews the air in the lungs.– Thus birds are much more efficient in extracting

oxygen from the air and thus can fly at altitudes of 30,000 feet. Humans can barely climb stair at this elevation (Mount Everest climbers need oxygen!)

Control of Breathing in Humans• The main breathing control centers

– Are located in two regions of the brain, the medulla oblongata and the pons

Figure 42.26

PonsBreathing control centers Medulla

oblongata

Diaphragm

Carotidarteries

Aorta

Cerebrospinalfluid

Rib muscles

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 medulla’s control center also helps regulate blood CO2 level. Sensors in the medulla detect changes in the pH (reflecting CO2

concentration) of the blood and cerebrospinal fluid bathing the surface of the brain.

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.

The control center in themedulla sets the basic

rhythm, and a control centerin the pons moderates it,

smoothing out thetransitions between

inhalations and exhalations.

1

Nerve impulses trigger muscle contraction. Nerves

from a breathing control centerin the medulla oblongata of the

brain send impulses to thediaphragm and rib muscles, stimulating them to contract

and causing inhalation.

2

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.

6

5

3

4

• 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

• Sensors in the aorta and carotid arteries– Monitor O2 and CO2 concentrations in the blood– Exert secondary control over breathing– At high altitudes the oxygen sensors kick in and

causes deep rapid breathing. This “blows” off excess carbon dioxide making ones blood alkaline and gives one head aches (don’t feel well either). Some people more susceptible to altitude sickness than others (10,000 ft for some).

Respiratory pigments bind and transport gases

• The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2. The amount is more than can be physically dissolved in solution! Thus the need for respiratory pigments.

Composition of air and solubility of gases in water

• Air pressure at sea level =760 mmHg• Air is 78% Nitrogen, 21% Oxygen and .2%

Carbon dioxide. Each gas exerts it pressure independently of the other.

• Thus the partial pressure of O2 =.21 X 760= ~160 mmHg, N2 600 mmHg and CO2 .23mmHg

• Solubility of pure gas in one liter of water. O2 = 49 ml/l, N2 =24 ml/l,CO2 = 1713 ml/l

• Temperature decreases, increase solubility• Salt decreases solubility• Thus, an aquatic animal living in a tropical tide

pool doesn’t have access to much oxygen in the water.

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

• Gases diffuse down pressure gradients in the lungs and other organs

• In the lungs and in the tissues– O2 and CO2 diffuse from where their partial

pressures are higher to where they are lower

Inhaled air Exhaled air

160 0.2O2 CO2

O2 CO2

O2 CO2

O2 CO2 O2 CO2

O2 CO2 O2 CO2

O2 CO2

40 45

40 45

100 40

104 40

104 40

120 27

CO2O2

Alveolarepithelialcells

Pulmonaryarteries

Blood enteringalveolar

capillaries

Blood leavingtissue

capillaries

Blood enteringtissue

capillaries

Blood leaving

alveolar capillaries

CO2O2

Tissue capillaries

Heart

Alveolar capillaries

of lung

<40 >45

Tissue cells

Pulmonaryveins

Systemic arteriesSystemic

veinsO2

CO2

O2

CO 2

Alveolar spaces

12

43

Figure 42.27

Exhaled air contains a lot of oxygen because of mixing in dead end space!

0.5 liter tidal volume

4.8 l vital capacity

1.2 l residual space

Need for Respiratory Pigments

• Respiratory pigments are proteins that bind and transport oxygen

• Can only dissolve 4.5 ml of oxygen in a liter of blood without Hb. – Greatly increase the amount of oxygen that

blood can carry (200 ml of oxygen /liter)

Oxygen Transport

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

• In invertebrates that have pigments they are hemocyanin, a large copper containing protein that circulates free in solution ( not housed in cells like hemoglobin).

Hemoglobin a tetrameric molecule• Like all respiratory pigments

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

Heme group Iron atom

O2 loadedin lungs

O2 unloadedIn tissues

Polypeptide chain

O2

O2

Figure 42.28

• Loading and unloading of O2

– Depend on cooperation between the subunits of the hemoglobin molecule

• The binding of O2 to one subunit induces the other subunits to bind O2 with more affinity

• Cooperative O2 binding and release

– Is evident in the dissociation curve for hemoglobin

• A drop in pH– Lowers the affinity of hemoglobin for O2

O2 unloaded fromhemoglobinduring normalmetabolism

O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism

Tissues duringexercise

Tissuesat rest

100

80

60

40

20

0

100

80

60

40

20

0

100806040200

100806040200

Lungs

PO2 (mm Hg)

PO2 (mm Hg)

O2 s

atur

atio

n of

hem

oglo

bin

(%)

O2 s

atur

atio

n of

hem

oglo

bin

(%)

Bohr shift:Additional O2

released from hemoglobin at lower pH(higher CO2

concentration)

pH 7.4

pH 7.2

(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4

(b) pH and Hemoglobin Dissociation

Figure 42.29a, b

Arterial Blood O2 saturation and O2 content

0

20

40

60

Arterial blood

% O2saturation

PO2 (mm Hg)

OContent

(vol. %)(= mL O2

per 100mL blood)

2 80

100

30 60 90

0

10

20

5

15

O2 content vs PO2 for different animals

50 100

10

20

30

mL O2

per100 mLblood

(vol %)

PO2 (mm Hg)0

Human20 vol %

Mackerel 14 vol %

Bullfrog6 vol%

Dissolved O20.3vol%

Mud flatworm

Weddell seal~32 vol %

(diver)

(see also WSJ Fig. 7.23)

Carbon Dioxide Transport

• Hemoglobin also helps transport CO2 and assists in buffering the blood by forming bicarbonate.

• Carbon from respiring cells– Diffuses into the blood plasma and then into

erythrocytes and is ultimately released in the lungs

Figure 42.30

Tissue cell

CO2Interstitialfluid

CO2 producedCO2 transportfrom tissues

CO2

CO2

Blood plasmawithin capillary Capillary

wall

H2O

Redbloodcell

HbCarbonic acidH2CO3

HCO3–

H++Bicarbonate

HCO3–

Hemoglobinpicks up

CO2 and H+

HCO3–

HCO3– H++

H2CO3Hb

Hemoglobinreleases

CO2 and H+

CO2 transportto lungs

H2O

CO2

CO2

CO2

CO2

Alveolar space in lung

2

1

34

5 6

7

8

9

10

11

To lungs

Carbon dioxide produced bybody tissues diffuses into the interstitial fluid and the plasma.

Over 90% of the CO2 diffuses into red blood cells, leaving only 7%in the plasma as dissolved CO2.

Some CO2 is picked up and transported by hemoglobin.

However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed bycarbonic anhydrase contained. Withinred blood cells.

Carbonic acid dissociates into a biocarbonate ion (HCO3

–) and a hydrogen ion (H+).

Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thuspreventing the Bohr shift.

CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4).

Most of the HCO3– diffuse

into the plasma where it is carried in the bloodstream to the lungs.

In the lungs HCO3– diffuses

from the plasma into red blood cells, combining with H+ released from hemoglobin and forming H2CO3.

Carbonic acid is converted back into CO2 and water.

CO2 formed from H2CO3 is unloadedfrom hemoglobin and diffuses into the interstitial fluid.

1

2

3

4

5

6

7

8

9

10

11

Elite Animal Athletes

• Migratory and diving mammals– Have evolutionary adaptations that allow them to

perform extraordinary feats.– Weddell seals dive to 600 meters repeatedly during

a 20 minute dive and rest and breath for only about 10 minutes. There is no anaerobic metabolism during this dive pattern.

– If a very long dive then they can utilize anaerobic metabolism which provides energy, but then they need to rest for hours to get rid of lactic acid build up.

Weddell seal

Adaptations for deep diving

• Stores twice as much oxygen as humans—in greater volume of RBCs (twice as much blood as a human) and myoglobin in the muscles. RBCs also stored in spleen.

• During dive the heart rate slows to 10 beats /min and blood flow is maintained to brain, eyes, spinal cord, adrenal glands and placenta if pregnant

• How does the mother ensure that the fetus gets an adequate supply of oxygen during a dive?

Dissociation curve for Weddell seal blood of fetus and mother.

100

80

60

40

20

0

0 10080

604020

PO2 (mm Hg)

Fetus

Mother

O2

satu

ratio

n of

he

mog

lobi

n (%

)

Fetus hemoglobin has a greater Bohr effect.

The Ultimate Endurance Runner• The extreme O2 consumption of the antelope-like

pronghorn underlies its ability to run at high speed (60km/hr) over long distances. Greater lung surface, higher cardiac output and more mitochrondia per unit muscle.

Figure 42.31