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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
4
5
6
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)
7
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
13
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)
16
17
18
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
24
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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