Chapter 42: Circulation and Gas ExchangeAP Biology 2013

Gas Exchange❖ Unicellular organisms - gas

exchange occurs directly with the environment

❖ Multicellular organisms - direct gas exchange is not possible

❖ Gills are and example of a gas exchange mechanism

❖ O2 diffuses from water to blood vessels

❖ CO2 diffuses from blood to water

Fig. 42.1

Circulatory System and Phylogeny❖ Transport systems connect the organs of

exchange with body cells

❖ Internal transport systems circulate fluid that provides a link between the aqueous cell environment and the exchange organs (lungs)

❖ Invertebrate circulation

❖ Simple animals (like cnidarians) have a body wall only two cells thick with a gastrovascular cavity (functions in both digestion and distribution of substances throughout the body)

❖ More complex animals have either an open or closed circulatory system

❖ Both have a circulatory fluid (blood), set of tubes (vessels), and a muscular pump (heart) Figs. 42.2 & 42.3

Circular canal

Mouth

Radial canals 5 cm

(a) The moon jelly Aurelia, a cnidarian (b) The planarian Dugesia, a flatworm

Gastrovascular cavity

Mouth

Pharynx 2 mm

(a) An open circulatory system

Heart

Hemolymph in sinuses surrounding organs

Pores

Tubular heart

Dorsal vessel

(main heart)

Auxiliary hearts

Small branch vessels in each organ

Ventral vessels

Blood Interstitial fluid

Heart

(b) A closed circulatory system

1

2

3

Cardiovascular System❖ Vertebrates - closed circulatory system called a

cardiovascular system

❖ Blood flows in a closed system consisting of blood vessels and a two to four chambered heart

❖ Arteries carry blood to capillaries (site of chemical exchange between blood and intestinal fluid)

❖ Veins return blood from capillaries to heart

❖ Fish - heart has two chambers (one ventricle and one atrium)

❖ Blood pumped from ventricle travels to gills where it picks up O2 and disposes of CO2

❖ Amphibians - have a three chambered heart with two atria and one ventricle

❖ Ventricle pumps blood into a forked artery and splits the output into pulmocutaneous circuit and systemic circuit

(a) Single circulation

Artery

Heart: Atrium (A) Ventricle (V)

Vein

Gill capillaries

Body capillaries

Key Oxygen-rich blood Oxygen-poor blood

Amphibians

Pulmocutaneous circuit

Lung and skin capillaries

Atrium (A)

Atrium (A)

Left Right Ventricle (V)

Systemic capillaries

Systemic circuit

Key

Oxygen-rich blood Oxygen-poor blood

Figs. 42.4

& 42.5

Cardiovascular System❖ Reptiles - have double circulation

with a pulmonary circuit and a systemic circuit

❖ Turtles, snakes, and lizards have a three-chambered heart

❖ Mammals and birds - ventricle is completely divided into separate right and left chambers

❖ Left side of the heart pumps and receives only oxygen-rich blood

❖ Right side receives and pumps only oxygen-poor blood

❖ Four-chambered heart was an essential adaptation of the endothermic way of life

(b) Double circulation

Systemic circuit

Systemic capillaries

Right Left

A A V V

Lung capillaries

Pulmonary circuit

Key Oxygen-rich blood Oxygen-poor blood

Figs. 42.4

& 42.5

Reptiles (Except Birds)

Pulmonary circuit

Systemic circuit

Systemic capillaries

Incomplete septum

Left systemic aorta

Left Right

Right systemic aorta

A V

Lung capillaries

Atrium (A)

Ventricle (V)

Key

Oxygen-rich blood Oxygen-poor blood

Double Circulation❖ Depends on anatomy and pumping cycle

of the heart

❖ Structure and function of the human circulatory system can serve as a model for exploring mammalian circulation in general

❖ Heart valves - dictate one-way flow of blood through the heart

❖ Pattern of flow:

❖ Blood flow begins with the right ventricle pumping blood into the lungs (loads O2 and unloads CO2)

❖ Oxygen-rich blood then enters the left atrium and is pumped to the body tissues by the left ventricle

❖ Blood returns to the heart through the right atrium Fig. 42.6

Superior vena cava

Pulmonary artery

Capillaries of right lung

Pulmonary vein

Aorta

Inferior vena cava

Right ventricle

Capillaries of abdominal organs and hind limbs

Right atrium

Aorta

Left ventricle

Left atrium

Pulmonary vein

Pulmonary artery

Capillaries of left lung

Capillaries of head and forelimbs

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5

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Mammalian Heart❖ Contract and relaxes in a

rhythmic cycle called the cardiac cycle

❖ Systole - contraction/pumping phase

❖ Diastole - relaxation/filling phase

❖ Heart rate is called the pulse (beats per minute)

❖ Cardiac output - volume of blood pumped into the systemic circulation per minute

Figs. 42.7 & 42.8

Pulmonary artery

Right atrium

Semilunar valve

Atrioventricular valve

Right ventricle

Left ventricle

Atrioventricular valve

Semilunar valve

Left atrium

Pulmonary artery

Aorta

Atrial and ventricular diastole

Atrial systole and ventricular diastole

Ventricular systole and atrial diastole

0.1 sec

0.4 sec

0.3 sec

2

1

3

Heart Rhythm❖ Some muscle cells are self-excitable (contract without any signal from the nervous system)

❖ Sinoatrial (SA) node (pacemaker) - sets the rate and timing at which all cardiac muscle cells contract (influenced by nerves, hormones, body temperature, and exercise)

❖ Impulses from the SA node travel to the atrioventricular (AV) node

❖ Impulse is delayed at the AV node and then travels to the Purkinje fibers that make the ventricles contract

❖ Impulses can be recorded by an electrocardiogram (ECG or EKG)

Fig. 42.9

SA node (pacemaker)

AV node Bundle

branches Heart apex

Purkinje fibers

ECG

1 2 3 4

Blood Circulation❖ Same physical properties that

govern water flowing through a pipe govern blood circulation.

❖ All blood vessels are built of similar tissues and have three similar layers

❖ Structural differences in arteries, veins, and capillaries correlate with different functions

❖ Arteries have thicker walls to accommodate high pressure blood pumped from the heart

❖ Veins have thinner walls because blood flows back to the heart as a result of muscle contraction

Fig. 42.10

& 42.13

Artery

Red blood cells

Endothelium

Artery

Smooth muscle Connective tissue

Capillary

Valve

Vein

Vein

Basal lamina

Endothelium

Smooth muscle

Connective tissue

100 µm

LM

Venule

15 µ

m

LM

Arteriole

Red blood cell

Capillary

Direction of blood flow in vein (toward heart) Valve (open)

Skeletal muscle

Valve (closed)

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8

9

Blood Circulation❖ Velocity of blood flow varies in the

circulatory system

❖ Slowest in the capillary beds because of high resistance and large total cross-sectional area

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

❖ Systolic pressure is the pressure in the arteries during ventricular systole (highest pressure in the arteries)

❖ Diastolic pressure is the pressure in the arteries during diastole (lower than systolic pressure)

❖ Determined by cardiac output and resistance

Figs. 42.11 & 42.12Aorta

Arte

ries

Arterio

les

Capilla

ries

Venules

Vein

s

Venae

ca

vae

Systolic pressure

Diastolic pressure

0 20 40 60 80

100 120

0 10 20 30 40 50

Pres

sure

(m

m H

g)

Velo

city

(c

m/s

ec)

Are

a (c

m2 )

0 1,000 2,000 3,000 4,000 5,000

Blood pressure reading: 120/70

120

70

Sounds stop

Sounds audible in stethoscope

120

Artery closed

1 2 3

Capillaries❖ Usually filled to capacity

❖ Two mechanisms that regulate distribution of blood in capillary beds:

❖ One mechanism involves contraction of smooth muscles in the wall of an arteriole to constrict the vessel

❖ Second involves precapillary sphincters to control the flow of blood between arterioles and venules

❖ Critical exchange of substances between the blood and interstitial fluid takes place in the thin endothelial wall of the capillaries

Precapillary sphincters

Thoroughfare channel

Arteriole

Capillaries Venule

(a) Sphincters relaxed

Arteriole Venule

(b) Sphincters contracted

Fig. 42.14

Capillaries❖ Difference between blood pressure and osmotic pressure drives fluid out of

the capillaries at the arteriole end and into the capillaries at the venule end

❖ The lymphatic system returns fluid from the body from the capillary beds and also aids in defense

❖ Fluid directly reenters circulation at the venous end of the capillary bed and indirectly through the lymphatic system

Fig. 42.15

INTERSTITIAL FLUID Net fluid movement out

Blood pressure

Osmotic pressure

Arterial end of capillary Direction of blood flow

Venous end of capillary

Body cell

10

11

12

Lymphatic System❖ Returns fluid that leaks out

from the capillary beds

❖ Fluid (called lymph) reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system which drains into veins in the neck

❖ Valves in the lymph vessels prevent the backflow of fluid

❖ Lymph nodes filter lymph and help in body defenses Fig. 42.16

Blood❖ Connective tissue with cells

suspended in plasma

❖ Consists of several kinds of cells (45% of blood)

❖ Red blood cells (transport oxygen)

❖ White blood cells (defense)

❖ Platelets (involved in clotting)

❖ Blood plasma is about 90% water with solutes like inorganic salts in the form of dissolved ions (electrolytes)

❖ Plasma also contains proteins which influence pH, osmotic pressure, and viscosity. These proteins also function in lipid transport, immunity, and blood clotting.

Fig. 42.17Plasma 55%

Constituent Major functions

Water

Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate

Solvent for carrying other substances

Osmotic balance, pH buffering, and regulation of membrane permeablity

Plasma proteins Osmotic balance, pH buffering Albumin

Fibrinogen Immunoglobulins (antibodies)

Clotting Defense

Substances transported by blood Nutrients Waste products

Separated blood elements

Respiratory gases Hormones

Separated blood elements

Basophils

Neutrophils Monocytes

Lymphocytes

Eosinophils

Platelets

Erythrocytes (red blood cells) 5–6 million

250,000–400,000 Blood clotting

Transport of O2 and some CO2

Defense and immunity

Functions Number per µL (mm3) of blood Cell type

Cellular elements 45%

Leukocytes (white blood cells) 5,000–10,000

Blood Cells❖ Erythrocytes - red blood cells (transport oxygen)

❖ Leukocytes - white blood cells (defense)

❖ Monocytes, neutrophils, basophils, eosinophils, and lymphocytes

❖ Function by phagocytizing bacteria and debris by producing antibodies

❖ Stem cells help to replace worn out cells throughout an animal’s life

❖ All blood cells develop from a common source

Fig. 42.16

Stem cells (in bone marrow)

Myeloid stem cells

Lymphoid stem cells

B cells T cells

Lymphocytes

Erythrocytes Neutrophils

Basophils

Eosinophils Platelets Monocytes

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14

15

Clotting❖ When the endothelium of a blood vessel is damaged the mechanism of

clotting begins

❖ A cascade of reactions converts fibrinogen to fibrin forming a clot

Collagen fibers

1 2 3

Platelet Platelet plug

Fibrin clot

Fibrin clot formation

Red blood cell 5 µm

Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K)

Enzymatic cascade

Prothrombin Thrombin

Fibrinogen Fibrin

+

Fig. 42.18

Cardiovascular Disease❖ Disorders of the heart and blood vessels (account for more than half of the deaths in the U.S.)

❖ Atherosclerosis - caused by buildup of cholesterol within arteries

❖ Hypertension - high blood pressure (promotes atherosclerosis and increased risk of heart attack or stroke)

❖ Heart attack (myocardial infarction) - death of cardiac muscle tissue resulting from a blockage of one or more coronary arteries

❖ Stroke - death of nervous tissue in the brain usually from a rupture or blockage of arteries in the brain Fig. 42.20

Lumen of artery Smooth muscle

Endothelium Plaque

Smooth muscle cell

T lymphocyte

Extra- cellular matrix

Foam cell Macrophage

Plaque rupture

LDL

Cholesterol Fibrous cap

1 2

4 3

Gas Exchange

❖ Supplies oxygen for cellular respiration and disposes of carbon dioxide

❖ Animals require large, moist, respiratory surfaces for the adequate diffusion of respiratory gasses between the cells at the respiratory medium (either air or water)

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17

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Gills❖ Outfoldings of the

body surface specialized for gas exchange

❖ In some invertebrates the gills have a simple shape and are distributed all over the body

❖ Segmented worms have flaplike gills that extend over body segments

❖ Clams and crayfish are restricted to a local body region

Fig. 42.22Gills

Tube foot

(c) Sea star

Coelom

(b) Crayfish

Gills

Parapodium (functions as gill)

(a) Marine worm

Gills❖ Effectiveness of gas exchange in some gills (including fish)

❖ Increased by ventilation and countercurrent flow of blood and water

Gill arch

O2-poor blood

O2-rich blood

Blood vessels

Gill arch

Operculum Water flow

Water flow Blood flow

Countercurrent exchange PO (mm Hg) in water

2 150

PO (mm Hg) in blood 2

120 90 60 30

140 110 80 50 20 Net diffu- sion of O2

Lamella

Gill filaments Fig. 42.23

Tracheal Systems❖ Insects have a tracheal system that consists of tiny branching tubes that

penetrate the body

❖ The tubes supply oxygen directly to the body cells

Fig. 42.24

Tracheoles Mitochondria Muscle fiber

2.5 µ

m

Tracheae

Air sacs

External opening

Trachea

Air sac Tracheole

Body cell

Air

19

20

21

Lungs❖ Spiders, land snails, and most terrestrial vertebrates have internal lungs

❖ System of branching ducts that conveys air to the lungs

❖ Air passes through the nostrils passes through the pharynx, trachea, bronchi, bronchioles, and alveoli (where gas exchange occurs)

Fig. 42.25

Pharynx

Larynx (Esophagus)

Trachea Right lung

Bronchus

Bronchiole

Diaphragm (Heart)

Capillaries

Left lung

Dense capillary bed enveloping alveoli (SEM)

50 µm

Alveoli

Branch of pulmonary artery (oxygen-poor blood)

Branch of pulmonary vein (oxygen-rich blood)

Terminal bronchiole

Nasal cavity

Breathing❖ Ventilation of the lungs

❖ Amphibians ventilate by positive pressure breathing which forces air down the lungs

❖ Mammals ventilate lungs by negative pressure breathing (pulls air into the lungs)

❖ Lung volume increases as the rib muscles and diaphragm contract

Fig. 42.28

Rib cage expands.

Air inhaled.

Air exhaled.

Rib cage gets smaller.

1 2

Lung

Diaphragm

Breathing❖ Birds

❖ Also have air sacs that function as bellows which keep air flowing through the lungs

❖ Air passes through the lungs in one direction only (every exhalation completely renews the lungs) Fig.

42.27

Anterior air sacs

Posterior air sacs

Lungs

1 mm

Airflow

Air tubes (parabronchi) in lung

Anterior air sacs

Lungs

Second inhalation First inhalation

Posterior air sacs 3

2 4

1

4

3 1

2 Second exhalation First exhalation

22

23

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Control of Breathing

❖ Main breathing control centers are in two regions of the brain (medulla oblongata and the pons)

❖ Medulla regulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid

❖ Adjusts breathing rate and depth to match metabolic demands

❖ Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood and exert a secondary control Fig. 42.29

Homeostasis: Blood pH of about 7.4

CO2 level decreases. Stimulus:

Rising level of CO2 in tissues

lowers blood pH. Response: Rib muscles and diaphragm increase rate and depth of ventilation.

Carotid arteries

Aorta Sensor/control center: Cerebrospinal fluid

Medulla oblongata

Gas Transport❖ Gasses diffuse down pressure

gradients in the lungs and other organs

❖ Diffusion of a gas depends on differences in quantity called partial pressure

❖ Gases always diffuse from a region of high partial pressure to a region of low partial pressure

❖ In the lungs and tissues, O2 and CO2 diffuse from where their partial pressures are higher to where they are lower

Fig. 42.30

Exhaled air Inhaled air

Pulmonary arteries

Systemic veins

Systemic arteries

Pulmonary veins

Alveolar capillaries

Alveolar spaces Alveolar

epithelial cells

Heart

Systemic capillaries CO2 O2

Body tissue

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

CO2 O2

8 1

2

3 7

6 4

5

Inhaled air

160

(b) Partial pressure of O2 and CO2 at different points in the circulatory system numbered in (a)

1

Exhaled air

Part

ial p

ress

ure

(mm

Hg)

PO 2

120

80

40

0

2 3 4 5 6 7 8

PCO 2

Gas Transport❖ Respiratory pigments are the

proteins that transfer oxygen

❖ Hemoglobin is the respiratory pigment in almost all vertebrates

❖ Contained in erythrocytes

❖ Must reversibly bind O2 when loading in the lungs and unloading at the other body tissues

❖ Binding of O2 to one subunit of hemoglobin increases the O2 affinity in the other subunits

❖ Drop in pH lowers affinity for O2Heme group Iron atom

O2 loaded in lungs

O2 unloaded In tissues

Polypeptide chain

O2

O2

Fig. 42.312 (a) PO and hemoglobin dissociation at pH 7.4

Tissues during exercise

Tissues at rest

Lungs

PO (mm Hg) 2

0 20 40 60 80 100 0

20

40

60

80

100

O2 unloaded to tissues

during exercise

O2 unloaded to tissues at rest

O2 s

atur

atio

n of

hem

oglo

bin

(%)

(b) pH and hemoglobin dissociation

PO (mm Hg) 2

0 20 40 60 80 100 0

20

40

60

80

100

Hemoglobin retains less O2 at lower pH (higher CO2 concentration)

pH 7.2 pH 7.4

O2 s

atur

atio

n of

hem

oglo

bin

(%)

25

26

27

Gas Transport❖ Hemoglobin also

helps in the transport of CO2

❖ Also assists in buffering

❖ Carbon from respiring cells diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs

Fig. 42.32Body tissue

Capillary wall

Interstitial fluid

Plasma within capillary

CO2 transport from tissues CO2 produced

CO2

H2O

H2CO3 Hb Red blood cell Carbonic

acid

Hemoglobin (Hb) picks up

CO2 and H+.

H+ HCO3-

Bicarbonate +

HCO3-

To lungs

CO2

CO2

HCO3- CO2 transport

to lungs

H2CO3

H2O

H+ +

Hb Hemoglobin

releases CO2 and H+.

CO2

Alveolar space in lung

To lungs

HCO3-

CO2

CO2

CO2

Helpful Adaptations

❖ Migratory and diving mammals have adaptations that allow them to perform extraordinary feats

❖ Extreme O2 consumption of the antelope-like pronghorn allows it to run at high speeds over long distances

❖ Deep-diving air breathers have to stockpile O2 and deplete it slowly

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