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Transcript of Circulation and Gas Exchange Chapter 42. Overview: Every organism must exchange materials with its...
Circulation and Gas Exchange
Chapter 42
Overview:
• Every organism must exchange materials with its environment
• Natural selection resulted in 2 basic adaptations that permit effective exchange for all animals– Body Plan that places many or all cells in direct
contact with environment• Gastrovascular Cavities – serves both in digestion and distribution of
substances throughout body
– Circulatory Systems (large animals)• System move fluids
Figure 42.2b
(b) The planarian Dugesia, a flatworm
Gastrovascularcavity
Mouth
Pharynx2 mm
General Properties of Circulatory Systems
Evolutionary Adaptation: A circulatory system minimizes the diffusion distance in animals with many cell layers
• A circulatory system has– A circulatory fluid (blood)– Blood Vessels (tubes)– Muscular pump (heart)
• Function: The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of wastes
Digestivesystem
Circulatorysystem
Excretorysystem
Interstitialfluid
Cells
Nutrients
Heart
Animalbody
Respiratorysystem
Blood
CO2FoodMouth
External environment
O2
50 µ
m
A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM).
10 µm
Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM).
The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM).
Unabsorbedmatter (feces)
Metabolic wasteproducts (urine)
Anus
0.5 cm
In Circulation, what needs to be transported
• Nutrients (fuel from digestive system)• Respiratory (O2 and CO2 gas exchange)• Excretory (waste from cells)• Protection (blood clotting, immune defenses)• Regulation (hormones)
Open Circulatory Systems
• Blood bathes the organs directly• No distinction between blood and interstitial fluid, and
this general body fluid is called hemolymph• Evolutionary advantage: lower hydrostatic pressure
less costly• Ex. insects, other arthropods,
and most molluscs,
• Blood is in vessels and is distinct from the interstitial fluid• More efficient at transporting circulatory fluids to tissues/cells• Evolutionary advantage:
– increase blood pressure effective delivery of O2 & nutrients to cells of larger/more active animals.
– Regular distribution of blood to different organs• Ex. Annelids, cephalopods, and vertebrates
Closed Circulatory Systems
Organization of Vertebrate Circulatory Systems
Cardiovascular System• Humans and other vertebrates have a closed
circulatory system called the cardiovascular system• The three main types of blood vessels are arteries,
veins, and capillaries• Blood flow is one way in these vessels
Why do veins have valves and arteries do not?
Veins move blood against gravity without benefit of the heart contraction
Blood flow: Heart arteries arterioles capillaries venules veins heart
Arteries: Away from heartVeins: Toward heart
• Vertebrate hearts contain two or more chambers• Blood enters through an atrium and is pumped out through
a ventricle
• Double circulation maintains higher blood pressure in the organs than does single circulation
Evolutionary Trends:
Figure 42.5
Amphibians Reptiles (Except Birds)
Pulmocutaneous circuit Pulmonary circuit
Lungand skincapillaries
Atrium(A)
Atrium(A)
LeftRight
Ventricle (V)
Systemiccapillaries
Systemic circuit Systemic circuit Systemic circuit
Systemiccapillaries
IncompleteseptumIncompleteseptum
Leftsystemicaorta
LeftRight
Rightsystemicaorta
A A
V V
Lungcapillaries
Lungcapillaries
Pulmonary circuit
A AV V
LeftRight
Systemiccapillaries
Key
Oxygen-rich bloodOxygen-poor blood
Mammals and Birds
How has natural selection shaped the double circulation of birds and mammals?
• The mammalian cardiovascular system meets the body’s continuous demand for O2
• Endotherms use 10x as much energy as same sized ectotherms. Need 10x as much fuel and O2 and need to remove 10x as much CO2 and other wastes
Mammalian Circulation
• Blood begins its flow with the right ventricle pumping blood to the lungs
• In the lungs, the blood loads O2 and unloads CO2
• Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle
• The aorta provides blood to the heart through the coronary arteries
• Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs)
• The superior vena cava and inferior vena cava flow into the right atrium
• Video: Heart pumping mechanism video• Video: How your heart pumps blood• Video: 3D pumping heart
Superior vena cava
Pulmonaryartery
Capillariesof right lung
Pulmonaryvein
Aorta
Inferiorvena cava
Right ventricle
Capillaries ofabdominal organsand hind limbs
Right atrium
Aorta
Left ventricle
Left atrium
Pulmonary vein
Pulmonaryartery
Capillariesof left lung
Capillaries ofhead and forelimbs
Figure 42.6
Figure 42.7
Pulmonary artery
Rightatrium
Semilunarvalve
Atrioventricularvalve
Rightventricle
Leftventricle
Atrioventricularvalve
Semilunarvalve
Leftatrium
Pulmonaryartery
Aorta
• The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle
• The contraction, or pumping, phase is called systole• The relaxation, or filling, phase is called diastole
Figure 42.8-1
Atrial andventricular diastole
0.4sec
1
Figure 42.8-2
Atrial andventricular diastole
Atrial systole and ventricular diastole
0.1sec
0.4sec
2
1
Figure 42.8-3
Atrial andventricular diastole
Atrial systole and ventricular diastole
Ventricular systole and atrialdiastole
0.1sec
0.4sec
0.3 sec
2
1
3
• The heart rate, also called the pulse, is the number of beats per minute
• The stroke volume is the amount of blood pumped in a single contraction
• The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume
• Four valves prevent backflow of blood in the heart• The atrioventricular (AV) valves separate each atrium
and ventricle• The semilunar valves control blood flow to the aorta
and the pulmonary artery
• The “lub-dup” sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves
• Backflow of blood through a defective valve causes a heart murmur
Maintaining the Heart’s Rhythmic Beat
• Some cardiac muscle cells are self-excitable, meaning they contract without any signal from the nervous system
• The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract
• Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)
• The pacemaker is regulated by two portions of the nervous system: the sympathetic and parasympathetic divisions
• The sympathetic division speeds up the pacemaker• The parasympathetic division slows down the
pacemaker• The pacemaker is also regulated by hormones and
temperature
Components of Blood (Humans have ~5L of Blood)red blood cells (erythrocytes)* biconcave discs, approx 7µ in diameter* most numerous (5-6 billion / mL of blood)* one RBC contains ~250 million molecules of hemoglobin which carry O2
white blood cells (leucocytes)* 5 different types, some with granulated cytoplasm* fight infection* produce antibodies to ‘tag’ foreign cells for destruction* perform phagocytosis
platelets (thrombocytes)* incomplete cells (cytoplasmic fragments)* important for blood clotting (controlling blood loss from damaged vessels)
plasma* fluid matrix composed of 90% H2O, clear yellow in color* transports glucose, electrolytes, hormones, CO2, waste, proteins, lipids, etc* helps regulate fluid and pH levels in blood
YWBC
o
Red Blood Cells Structure and Function
• Biconclave shape increases surface area to enhance O2 uptake and release.
• Each RBC contains about 250 million molecules of hemoglobin, and each hemoglobin molecule can bind up to four molecules of O2.
• Lack nuclei, which increases space for hemoglobin.• Lacks mitochondria, O2 so is not consumed.
Concept 42.3: Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels
• The physical principles that govern movement of water in plumbing systems also influence the functioning of animal circulatory systems
Blood Vessel Structure and Function
• A vessel’s cavity is called the central lumen• The epithelial layer that lines blood vessels is called the
endothelium• The endothelium is smooth and minimizes resistance
Figure 42.10 Artery
Red blood cells
Endothelium
Artery
Smoothmuscle
Connectivetissue
Capillary
Valve
Vein
Vein
Basal lamina
Endothelium
Smoothmuscle
Connectivetissue
100 m
LM
Venule
15
mL
M
Arteriole
Red blood cell
Capillary
• Capillaries have thin walls, the endothelium plus its basal lamina, to facilitate the exchange of materials
• Arteries and veins have an endothelium, smooth muscle, and connective tissue
• Arteries have thicker walls than veins to accommodate the high pressure of blood pumped from the heart
• In the thinner-walled veins, blood flows back to the heart mainly as a result of muscle action
Blood Flow Velocity
• Physical laws governing movement of fluids through pipes affect blood flow and blood pressure
• Velocity of blood flow is slowest in the capillary beds, as a result of the high resistance and large total cross-sectional area
• Blood flow in capillaries is necessarily slow for exchange of materials
Figure 42.11
Aorta
Arterie
sArte
riole
s
Capill
arie
sVen
ules
Veins
Venae
cava
e
Systolicpressure
Diastolicpressure
020406080
100120
01020304050
Pre
ss
ure
(mm
Hg
)V
elo
cit
y(c
m/s
ec
)A
rea
(c
m2)
01,0002,0003,0004,0005,000
Blood Pressure
• Blood flows from areas of higher pressure to areas of lower pressure
• Blood pressure is the pressure that blood exerts against the wall of a vessel
• In rigid vessels blood pressure is maintained; less rigid vessels deform and blood pressure is lost
Changes in Blood Pressure During the Cardiac Cycle
• Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries
• Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure
• A pulse is the rhythmic bulging of artery walls with each heartbeat
Regulation of Blood Pressure
• Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles
• Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure
• Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall
• Vasoconstriction and vasodilation help maintain adequate blood flow as the body’s demands change
• Nitric oxide is a major inducer of vasodilation• The peptide endothelin is an important inducer of
vasoconstriction
Blood Pressure and Gravity
• Blood pressure is generally measured for an artery in the arm at the same height as the heart
• Blood pressure for a healthy 20-year-old at rest is 120 mm Hg at systole and 70 mm Hg at diastole
Blood pressure reading: 120/70
120
70
Soundsstop
Soundsaudible instethoscope
120
Arteryclosed
1 2 3
Figure 42.12
• Fainting is caused by inadequate blood flow to the head
• Animals with longer necks require a higher systolic pressure to pump blood a greater distance against gravity
• Blood is moved through veins by smooth muscle contraction, skeletal muscle contraction, and expansion of the vena cava with inhalation
• One-way valves in veins prevent backflow of blood
Direction of blood flowin vein (toward heart) Valve (open)
Skeletal muscle
Valve (closed)
Figure 42.13
Gas exchange across specialized respiratory surfaces
Gas exchange (respiration): supplies O2 for cellular respiration and disposes of CO2
Respiration Media• Animals can use air or water as a source of O2
• Gas exchange is more difficult in aquatic animals– There is less O2 available in water than in air– Water has greater density and viscosity – Obtaining O2 from water requires greater efficiency than air
breathing
Respiratory Surfaces
• Part of an animal’s body where gases are exchanged with the surrounding environment.
• It can be the body wall, skin, gills, tracheae, lungs
• General characteristics of respiratory surfaces include:– Must be moist– Favorable surface area/volume ratio. Respiratory surfaces
are often extensively folded or branched (structure/function)– Closely related with vascular system of larger animals
Gills in Aquatic Animals
• Gills are outfoldings of the body that create a large surface area for gas exchange
• Ventilation: increases flow over the respiratory surface• Advantage of countercurrent exchange: Water and blood
flow in opposite directions “across” one another so oxygen can continually diffuse into blood
How do insects meet their high metabolic demands for oxygen with an open circulatory system?
• Contain tracheal system– tiny branching tubes that penetrate the body– supply O2 directly to body cells– respiratory and circulatory systems are separate– Larger insects must ventilate their tracheal system to
meet O2 demands
Mammalian Respiratory Systems: LUNGS
Ventilation in Mammals: Breathing
Pathway of Oxygen to Lungs• Pharynx : Air inhaled through the nostrils is warmed,
humidified, and sampled for odors (nasal and oral cavities)
• Larynx: upper part of respiratory tract• Trachae: windpipe• Bronchi• Bronchioles• Alveoli : air sacs clustered at the end of bronchioles
Figure 42.25
Pharynx
Larynx(Esophagus)
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm(Heart)
Capillaries
Leftlung
Dense capillary bedenveloping alveoli (SEM)
50 m
Alveoli
Branch ofpulmonary artery(oxygen-poorblood)
Branch ofpulmonary vein(oxygen-richblood)
Terminalbronchiole
Nasalcavity
• Air sacs clustered at ends of bronchioles in the lungs• Thin, most and large surface area• Associated with the capillary beds.• Oxygen diffuses into the blood by passing through the
thin membrane of an alveolus and through the thin membrane of a capillary, into the blood, and attached to the hemoglobin molecule in a RBC.
• Carbon dioxide diffuses from the capillaries across the epithelium and into the air space
Alveoli : Structure and Function
Interaction of Circulatory and Respiratory System
• What is the passage of oxygen as it enters your nasal passageway and is used by tissues in your big toe?
Respiratory Pigments: Increase efficiency of oxygen transport
– Hemocyanin in arthropods and molluscs; Cu is the binding component
– Hemoglobin vertebrates; Fe is binding component; each holds 4 O2 molecules; relies on cooperativity!
• Drop in pH lowers affinity for oxygen, active tissues with more carbon dioxide (lower pH) will have more oxygen dropped off
– Increased metabolic activity lowers pH by increasing the concentration of CO2 in the blood. CO2 reacts with water to form carbonic acid, which dissociates into a bicarbonate ion and a hydrogen ion. As blood pH drops, the rate and depth of respiration increase.
• Breathing is influenced by pH, which is an indirect indication of blood CO2 levels.
Figure 42.30aExhaled air Inhaled air
Pulmonaryarteries
Systemicveins
Systemicarteries
Pulmonaryveins
Alveolarcapillaries
AlveolarspacesAlveolar
epithelialcells
Heart
SystemiccapillariesCO2 O2
Body tissue
(a) The path of respiratory gases in the circulatory system
CO2 O2
8 1
2
37
6 4
5