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Bio 103
Winter Quarter
Lake Tahoe Community College
Instructor: Sue Kloss
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Ch. 42 - Circulation and Gas Exchange
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Most organisms need specialized systems for gas, nutrient and waste exchange. Gills have lots of surface area, lots of
blood vessels provide lots of surface area for other animals.
I. Circulatory systems reflect phylogeny
A. Intro
1. diffusion takes too long for transporting substances over long distances in animals
2. 1 sec. for given quantity of glucose to diffuse 100 um, it will take 100 sec. to diffuse 1 mm and 3 hrs
to diffuse 1 cm.
3. rapidly transporting fluid (blood) with substances ensures that no substance will need to diffuse far
4. blood ---> interstitial fluid -------> cells and back again.
B. Invertebrate circulation
1. gastrovascular cavities
a. hydras and other cnidarians
1. fluid in cavity is continuous with surrounding fluids
2. both inner and outer tissue layers are bathed in water/fluids
b. planarians also have g.v.’s
c. in all cases, diffusion distances are short for a gv. system to work
C. Open and Closed Circulatory systems1. both have blood, blood vessels, heart or muscular pump
2. blood pressure causes blood to flow powered by the heart
3. open systems - no difference btn blood and interstitial fluids
4. advantages of open systems a. lower metabolic costs
b. may serve as hydrostatic skeleton
5. Advantages of closed system
a. more effective at transporting material than open systems
b. can cause more growth and better metabolism in animals
D. Survey of Vertebrate Circulation (Fig. 42.4)
1. vertebrate circulation generally powered by cardiovascular system
a. heart- 2 atria and 2 ventricles
b. arteries, veins and capillaries 2 main kinds of blood vessels
c. capillary beds- networks of capillaries infiltrating tissue.
d. arterioles and venules
e. vertebrates have various forms of this, via natural selection
2. Fishes
a. 2 main chambers in heart= 1 ventricle, 1 atrium
b. gill circulation and systemic circulation
3. Amphibs
a. 3 chambered heart and 2 circuits of blood flow
b. pulmocutaneous circuit and systemic circuit - ridge in ventricle sends most O2 rich blood
into systemic circuit and most O2 poor blood into pulmocutaneous circuit
c. double circulation - pumped a second time after losing pressure in capillary beds
4. Reptiles
a. pulmonary circuit and systemic circuit
b. septum in heart further reduces mixing of blood
c. separate artery brings O2 poor blood to the systemic circuit
5. Mammal and Birds
a. 4 chambered heart, one side is all O2 rich, other side is all O2 poor
b. double circulation - blood is pumped again after getting reoxygenated
c. endothermy required powerful heart for max energy production - need 10x as much fuel, O2
as ectotherms
II. Double Circulation in Mammals depends on the anatomy and pumping cycle of the heart
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A. Mammalian circulation - the Pathway (Fig. 42.5)
1. learn all structures and pathways in the figure
B. Mammalian Heart (Fig. 42.6)
1. learn all structures and pathways in figure
2. cardiac output = hr x sv - avg in humans is 75 ml
a. can increase 5x during heavy exercise - equivalent to pumping an amt. of blood matching
the persons body mass every 2-3 min.
3. AV valves - atrio ventricular
4. semilunar valves - 2 exits - pulmonary artery and aorta
a. lub dub = lub- recoil of blood against AV valves, dub = recoil of blood against semilunar valves
5. pulse - rhythmic stretching of arteries caused by pressure of blood leaving ventricles
C. Maintaining heart’s rhythmic beat
1. brain cells die in a few min. if no O2.
2. to ensure continuity of heart beat, a couple features
a. some cardiac muscle cells are self excitable - will beat if removed from heart
b. SA (sinoatrial) node, or pacemaker intrinsic to heart - controls and coordinates contractions
1. composed of specialized muscle tissue located in wall of right atrium near s. vena
cava entry
2. called a myogenic heart
3. arthropods have neurogenic heart, beat arises from nerves outside heart
4. SA node generates electrical impulse much live a nerve impulse
5. heart muscle cells connected by intercalated discs, to spread impulses rapidly
6. impulse soon gets to AV node, in wall between right atrium and right ventricle
a. impulse delayed about .1 sec. before spread to ventricles, to allow
full emptying of atria
7. special muscle fibers called bundle fibers and purkinje fibers conduct signal to apex
of
heart thru ventricular walls
c. pacemaker is influenced by:
1. nerves that influence tempo
2. temperature - increase of 1C increases hr by 10 bpm (e.g. . fever)
3. hormones- fight or flight
III. Physical principles govern blood circulation
A. Blood vessel structure and function
1. connective tissue surrounds smooth muscle, both with elastic fibers. Inside lumen in surrounded by
VERY smooth epithelium to minimize resistance to blood flow
a. differences in veins and arteries (fig. 42.9)
2. capillaries lack 2 outer layers- epithelium and basement tissue for max exchange capacity
3. low pressure of veins (less muscle, and little to no heart action affecting them); flaps in them keep
blood flowing in right direction (Fig. 42.10)
B. blood flow velocity - blood travels over 1000x faster in aorta (30 cm/sec) than in capillaries (.026 cm/sec)
1. total cross sectional area of capillaries is much higher than veins or arteries (Fig. 42.11) so blood
speeds up when it gets to veins
2. pressure very low in veins - rhythmic contractions of smooth muscle in veins and contractions of ‘
skeletal (voluntary) muscle help squeeze blood thru veins
a. inhaling causes expansion of venae cavae in chest and they fill with blood
C. Capillary function
1. only about 5-10% of capillaries have blood in them
a. each tissue has many capillaries so every part of body is supplied with blood
1. heart, brain, kidneys and liver capillaries are usually maxed out
2. other parts of body - depends on activity
a. ie. if you eat, digestive system gets blood.
b. exercising muscles get blood, etc.
2. rings of smooth muscle in arterioles can control blood flow to a particular capillary bed
3. precapillary sphincters at entrance to capillary beds control flow of blood as well
4. these 2 mechanisms are influenced by nerve signals and hormones
5. capillaries are very leaky - blood pressure pushes water, sugar, salt, O2 and urea into
interstitial fluid, not blood cells and blood proteins. These create osmotic pressure that pulls most (85%)
of fluid back in at other end of capillary bed
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a. other 15% is eventually returned to the CV system via the lymphatic system (Fig. 42.14)
IV. Blood is connective tissue with cells suspended in plasma
A. liquid matrix called plasma
1. about 90% water with lots of solutes
a. sometimes called electrolytes - esp. inorganic salts - help maintain osmotic pressure of blood
b. some ions help buffer blood, keep it at 7.4 pH
c. normal function of muscles and nerves depends on concentration of key ions in interstitial
fluid
2. plasma proteins
a. buffers of pH
b. help maintain osmotic pressure and viscosity
c. specific functions
1. escorts for lipids, which are insoluble in water and can travel in blood only when
bound to proteins
2. immunoglobulins or antibodies combat foreign agents
3. fibrinogens - clotting factors
3. plasma also contains
a. nutrients
b. metabolic wastes
c. respiratory gases
d. hormones
B. cellular elements (fig 42.15)
1. red blood cells- erythrocytes - small discs biconcave for max surface area
a. lack nuclei when mature, carry hemoglobin
b. no mitochondria - use anaerobic respiration so they are more efficient
c. contain hemoglobin - each rbc has 250 million hemoglobins, each carry 4 O2, so each
rbc can carry 1 billion molecules of O2
2. white blood cells - leukocytes - fight infection
a. monocytes, neutrophils, basophils, eosinophils and lymphocytes
3. platelets - fragments 2-3 um in diameter for blood clotting
V. Gas exchange occurs across specialized respiratory surfaces
A. respiratory surface- part of animal body where gases are exchanged - entirely by diffusion, so they tend to be
thin and have high surface area to increase rate of exchange
1. must be bathed in water, be moist so gases can dissolve in and diffuse across
a. protists use membrane
b. amphibs use skin and lungs or gills
c. other animals use lungs or tracheae most commonly, but lots of mechanisms (Fig. 42.20)
d. gills unsuitable on land, they collapse
2. Mammalian respiratory system (fig. 42.23)
a. larynx, vocal cords, trachea, bronchi, bronchioles, alveoli (100m2 of resp. surf)
VI. Breathing ventilates the lungs
A. How a mammal breathes - negative pressure breathing- open up space with diaphragm and rib muscles, and
lung expands to match increase in volume of the cavity pulling in air
B. control of breathing - in humans - (Fig. 42.26)
1. control center in medulla sets basic rhythm
2. pons smoothes it out
3. sensors ion aorta and carotid arteries monitor O2 and CO2 in blood and blood pH
a. when CO2 rises (exercise, for example) pH changes in blood (drops). medulla registers the
drop in pH in cerebrospinal fluid and increases rate and depth of breathing
Ch. 42 OBJECTIVES
1. Describe the need for circulatory and respiratory systems due to increasing animal body size.
2. Explain how a gastrovascular cavity functions in part as a circulatory system.
3. Distinguish between open and closed circulatory systems. List the three basic components common to both
systems.
4. List the structural components of a vertebrate circulatory system and relate their structure to their functions.
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5. Describe the general relationship between metabolic rates and the structure of the vertebrate circulatory system.
6. Using diagrams, compare and contrast the circulatory systems of fish, amphibians, non-bird reptiles, and mammals
or birds.
7. Distinguish between pulmonary and systemic circuits and explain the functions of each.
8. Distinguish between systole and diastole, and explain what causes the first and second heart sounds.
9. Define cardiac output and describe two factors that influence it.
10. List the four heart valves, describe their location, and explain their functions.
11. Define sinoatrial (SA) node and describe its location in the heart.
12. Distinguish between a myogenic heart and a neurogenic heart.
13. Describe the origin and pathway of the action potential (cardiac impulse) in the normal human heart.
14. Explain how the pace of the SA node can be modulated by nerves, hormones, body temperature, and exercise.
15. Relate the structures of capillaries, arteries, and veins to their functions.
16. Explain why blood flow through capillaries is substantially slower than it is through arteries and veins.
17. Explain how blood returns to the heart even though it must sometimes travel from the lower extremities against
gravity.
18. Explain how blood flow through capillary beds is regulated.
19. Explain how osmotic pressure and hydrostatic pressure regulate the exchange of fluid and solutes across
capillaries.
20. Describe the composition and functions of plasma.
21. Relate the structure of erythrocytes to their function.
22. Define gas exchange and define what a respiratory surface is.
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Describe the general requirements for a respiratory surface and list a variety of respiratory organs that meet these
requirements.
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For the human respiratory system, describe the movement of air through air passageways to the alveolus, listing
the structures that air must pass through on its journey
25. Describe negative pressure breathing. Explain how respiratory movements in humans ventilate the lungs.
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