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BIOL 381 Final Exam


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Describe properties of myogenic pacemakers.
1. MYOGENIC - initiated within the cell, not by an outside source
2. Pacemaker potential - slow, positive increase in electric current over the cell membrane that occurs between the beginning and end of APs
3. Rhythmic, self-regenerating APs

Describe the transmission of excitation through the mammalian heart.
The excitation wave begins in the sinoatrial node and heads to both atria, and from there to the ventricles through the atrioventricular node via junctional fibers.

The junctional fibers are also connected to nodal fibers, which are connected to the bundle of His and Purkinje fibers, which innervate the ventricular myocardium.

The contraction of the ventricular myocardium as an excitation wave passes from the endocardium to the epicardium enables what?
The separate, synchronous contraction of the atria and ventricles.
What are gap junctions and intercalated disks involved with?
Transmission of excitation.

Excitation is transmitted by cells in close proximity (intercalated disks) through channels called gap junctions.

Describe the steps of blood flow in a single heartbeat.
1. AV valves and aortic valves open; ventricles/atria relaxed; blood flows from venous system to ventricles
2. Atria contracts to top off ventricles (30% of final ventricle blood volume)
3. AV and aortic valves closed; ventricle undergoes isometric contraction to raise pressure
4. Aortic valve opens and ventricle squirts blood into aorta

What factors influence stroke volume (via influence over end-systolic volume)?
1. Venous filling pressure
2. Atrial contraction pressure
3. Elasticity of ventricular wall
4. Time available

Where is the mammalian heart innervated and what function do the nerves carry?
SA node innervated by sympathetic (norepi) and parasympathetic (ACh) nerves. Para nerves slow heart rate, sympa nerves raise heart rate.
What sorts of animals have a rigid pericardium, what sorts of animals have a compliant pericardium, and what are the implications of each pericardium type?
Elasmobranchs - rigid pericardium that augments cardiac output

Mammals - compliant pericardium with little effect on cardiac output, protective

Why are some reptile ventricles partially divided?
To prevent some movement of deoxygenated blood back to the tissues
How does circulation change in a mammalian fetus at birth?
Ductus arteriosus joins the pulmonary artery and systemic arch; lungs inflate; shift from placental to pulmonary circulation
What are the main functions of the arterial system?
Distributes blood, pressure reservoir
What affects blood flow in capillaries?
Pressure difference between arterial and venous systems
How do baroreceptors and mechanoreceptors help regulate blood flow?
Baroreceptors monitor blood pressure-- unmyelinated baroreceptors only react to blood pressures above normal. Mechanoreceptors react to heart rate and blood filling in the atria.
What are some cardiovascular responses to diving in mammals?
Bradycardia, peripheral vasoconstriction, reduction in heart rate and cardiac output
What are some cardiovascular reactions to exercise in mammals?
Increased sympathetic nerve activity to increase heart rate and force of contraction, hyperemia to increase blood flow to muscles, 1.5x increase in stroke volume
What affects arterial blood pressure?
As cardiac output increases, ABP increases.

If capillary flow increases, ABP falls.

Normally cardiac output/capillary flow are evenly matched and ABP changes little.

What affects blood movement in and out of capillaries to tissues?
Osmotic differences and blood pressure (blood is exchanged with interstitial fluid)
What are the primary functions of the venous system?
Blood reservoir and system for returning blood to the heart
How does the lymphatic system operate?
Blind-ending lymphatic capillaries collect interstitial fluid from tissues and carry it back to the circulatory system, entering at a point of low pressure called a thoracic duct.

Reptiles and amphibians have lymph hearts to help move lymph.

Oxygen capacity
The maximum quantity of oxygen that will combine chemically with the hemoglobin in a unit volume of blood; 1.34 ml of O2 per gm of hb or 20 ml of O2 per 100 ml of blood.
Oxygen content
How much oxygen makes up a certain mixture of gases (ex. the atmosphere)
Percent saturation
The amount of oxygen dissolved in the water sample compared to the maximum amount that could be present at the same temperature.
Hemoglobin that has an Fe3+ instead of Fe2+; cannot carry oxygen; bluish-brown
Bohr effect
An increasing concentration of protons and/or carbon dioxide will reduce the oxygen affinity of hemoglobin
Describe the role of hemoglobin in the transfer of
oxygen and carbon dioxide.
Hemoglobin binds to oxygen with its iron heme and increases the amount of oxygen that can be dissolved in the blood.
Describe the effects of gravity on the distribution of
blood in the human lung. What effect does alveolar
pressure have on lung blood flow?

Lungs are supplied by pulmonary (deoxygenated) and systemic (oxygenated) blood. Birds/Mammals have lower pulmonary pressure than systemic pressure to ensure liquid does not pool in the lung. In human lungs blood flow is minimal at the top of the lung, and can cease when alveolar pressure is greater than arterial pressure.
Compare and contrast ventilation of the mammalian
lung and the bird lung.
Mammals have a sac-like lung suspended by the diaphragm, while birds have a series of parabronchial tubes that form the lung. In birds a horizontal septum closes the thoracic cage, and air sacs connected to the lung are squeezed to force air into it. In mammals air is only exchanged by opposing movements (inspiration/expiration) while birds change air with every movement.
Lipoprotein complexes that bestow a very low surface tension on the liquid-air interface. Lung surfactants not only reduce the effort associated with breathing but also help prevent collapse of alveoli.
How do insects avoid transporting O2 in the blood?
Insects have direct tubes from the atmosphere to their tissues and take advantage of the high amount of O2 dissolved in the air.
How does a rete mirabile help fish to maintain high swimbladder pressures?
The rete structure allows blood to flow into the bladder
wall without a concomitant large loss of gas from the

How is O2 moved into a swimbladder?
Blood passes first through the arterial capillaries of the rete, then through a secretory epithelium (gas gland) in the bladder wall, and finally back through the venous capillaries in the rete.
How are lungs and gills different?
The density and viscosity of water is 1000x that of air, and oxygen diffuses in water 10,000x more slowly than in air. Air breathing requires reciprocal movement; water breathing is unidirectional. The fish gill is designed to minimize diffusion distances in the water, and the distribution of O2 in the air compared to the lung is lower than in the water compared to the gill. Respiratory area compared to body weight is greater in air breathers.
Why is the ventilation-to-perfusion ratio higher in fishes?
Water contains only about one-thirtieth as much dissolved
oxygen as an equivalent volume of air at the same Pq and temperature. Thus, in fishes, the ratio of water flow and blood flow through the gills is between 10 : 1 and 20 : 1, much higher than the li,/Q ratio in air-breathing mammals.
What is the function of the central chemoreceptors?
Mammals and probably other air-breathing vertebrates
also have central chemoreceptors, located in the medulla,
that drive ventilation in response to decreases in the pH of
the cerebrospinal fluid (CSF), usually caused by elevations
in Pco,. Stimulation of this system is required to maintain
normal breathing: if body PCol falls, or is held at a low level
experimentally, breathing will cease. These central
chemoreceptors have little ability to respond to falling O2
levels; the peripheral chemoreceptors have this role and
are important in increasing ventilation during periods of

What is the Hering-Breuer reflex?
Inflation of the lungs decreases the frequency of breathing.
How does a mammal acclimate to hypoxic conditions at high altitudes?
The reduction in air Po2 leads to a reduction in blood Po2. This stimulates carotid/aortic chemoreceptors and leads to an increase in lung ventilation, which eliminates more CO2. The decrease in blood Pco2 leads to an increase in the pH of the cerebrospinal fluid, and ventilation is reduced. Blood and CSF pH return to normal levels eventually via the excretion of bicarbonate.
What is the effect of carbonic anhydrase being located in the red blood cells?
The reaction of CO2 with H2O to form HCO, is slow
and has an uncatalyzed time course of several seconds. But
in the presence of the enzyme carbonic anhydrase, this reaction approaches equilibrium In much less than a second.

Although plasma has a higher total CO2 content than red
blood cells, most of the CO2 entering and leaving the
plasma does so via erythrocytes, because carbonic anhydrase
is present in red blood cells but not in the plasma.
Therefore, formation of HCO3 ions in the tissues and CO2
in the lungs occurs predominantly in red blood cells.

What is the function of the medullary respiratory center?
MRC enables extremely fine control of air flow, as is required for such complex actions in humans as singing, whistling, and talking, as well as simply breathing. It has both inspiratory and expiratory neurons.
How are heat and water loss affected by gas transfer?
Increases in lung ventilation not only increase gas transfer
but also result in more loss of heat and water.

Air in contact with the respiratory surface becomes saturated
with water vapor and comes into thermal equilibrium with the blood. Cool, dry air entering the lung of mammals is humidified and heated. Exhalation of this hot, humid air results in considerable loss of heat and water, which will be proportional to the rate of ventilation of the lung surface.

The cooling of exhalant air in the nasal passages results in the conservation of both heat and water.

What are the components of circulatory systems?
Blood vessels

Dynamic properties of flowing blood
Transport of O2/nutrients is limited by _____.
As a cell becomes larger, it has ____ surface area in relation to ____.
smaller, volume
If you have less surface area in relation to volume, diffusing substances take ___ to diffuse.
Demand for O2/nutrients increases with _____ ____.
metabolic rate
Circulatory systems permit evolution of structures with ___ ____ ___ and ___ ___ ___.
large surface areas, small diffusion distances
Traits of circulatory systems
O2/nutrient uptake time reduced
Requires a moving liquid medium (blood)
Flows to large body surfaces separated from environmental O2 by thin membranes (skin, gills, lungs)
Diffusion area, distance and concentration gradient favor rapid diffusion into blood
Concentration gradient favors diffusions of waste/secretions from tissues into blood
Blood force provided by pump (heart)

Pressure =
The heart determines what?
Concentration of O2 in blood
O2 concentration gradient between blood/tissues
O2 delivery rate to tissues

Receives blood from body
Sends blood to ventricle
Pumps blood from heart to O2 collecting organs and the rest of the body
Prevent reversal of blood flow between atria/ventricles
What converts the kinetic energy of blood motion into heat?
Friction between vessel walls and blood
Blood viscosity
As the number of blood cells in blood increases, the blood viscosity ____.
Percentage of blood occupied by blood cells
Hematocrit in mammals
Hematocrit in birds
Flow =
The ____ of blood vessels is ____ important than the viscosity of blood when determining blood flow.
radius, more
A 2x increase in vessel radius decreases resistance by ___x.
Substance that stimulates urine production
How does the heart make blood flow?
The heart produces enough pressure to overcome flow resistance
Open Circulatory System
– Slow blood flow
– Slow oxygenation
– Slow oxygen delivery
- No microcirculation
– Return of blood to heart
depends on body
movements, gravity
– No ultrafiltration
– Appropriate for animals
with slow metabolism
(low oxygen needs)

Closed Circulatory System
– Fast blood flow
– Fast oxygenation
– Fast oxygen delivery
– Microcirculation
– Return of blood to heart
depends on pressure in
blood vessels
– Ultrafiltration
– Appropriate for animals
with fast metabolism
(high oxygen needs)

Inverts have ____ instead of blood. They may have compounds in the blood that function similarly to a _____ in verts.
Hemocoel, hemoglobin
Large veins serve as blood _____.
What enables the elasticity of the aorta?
Connective tissue and smooth muscle
Sum of all solute concentrations
Osmotic concentration is ___ in the plasma and ___ in the interstitial fluid.
higher, lower
Interstitial fluid is not absorbed back into the capillaries
At the upstream site of a capillary, H2O moves ___, and at the downstream site H2O moves ___ due to the ____ ____ ____.
out, in, osmotic pressure difference
All vessels to/in lungs
Sinoatrial/Atrioventricular nodes contain modified ____ ____ ___ capable of simultaneous ____ ____.
cardiac muscle cells, action potentials
What causes pacemaker potentials?
Leaky cell membranes with constantly open Na+ channels
Simultaneous action potentials only occur in the modified cardiac muscle cells in the SA/AV nodes because...
...they cannot contract.
The frequency of pacemaker cell action potentials is determined by the ____ ___ ____ ____, which is influenced by the __ of ___-___ ___ _____.
rate of pacemaker depolarization, number, "always-open" Na+ channels
How do action potentials propagate in the heart?
Axon-like extensions of cells
Directly through muscle cells connected end-to-end
The atrioventricular node is normally enslaved by the _____ ___.
sinoatrial node
The _____ side of the heart has ____ muscle because it has to push blood to the lungs and back.
right, less
What contracts first? Atria or ventricles?
Name the 5 stages of a heartbeat.
1. Mid-diastole (atria/ventricles relaxed, blood flows directly to ventricle from veins)
2. Late diastole (atrial contraction)
3. Early systole (isometric ventricular contraction)
4. Late systole (ventricular contraction ejecting blood into aorta)
5. Ventricular relaxation

Volume of blood pumped per unit time (e.g. L/minute)

CO = heart rate (bpm) X stroke volume (volume pumped by one heartbeat)

Vol blood/minute = beats/min X vol blood/beat

Frank-Starling mechanism
Describes the relationship between filling pressure (X) and stroke volume (Y) as a curve-- the top of the curve is the maximum amount of filling that can occur before stroke volume is impaired and maximum overlap between actin-myosin in the heart musclce cells
What are the extrinsic influences on heart rate and stroke volume?
Endocrine system (epinephrine) - heart rate and contraction strength
Autonomic nervous system (para/symp) - symp: HR/SV, myocytes innervated by symp neurons only - parasymp: HR

Parasympathetic neurons influence heart rate by the release of ___, which ____ the number of open Na+ channels.
Ach, decreases
What are the traits of the closed circulatory system in fish?
Oxygenated/unoxy blood completely separate
Blood in tissues fully oxygenated
Blood pressure/flow is slow because blood must pass gills before body

What are the traits of a closed circulatory system in amphibians/reptiles?
3 chambers
Oxy/unoxy blood not separate
Tissues do not receive fully oxy blood
Blood pressure/flow is fast

What is unique about the heart of a turtle compared to other reptiles?
Partially separated oxy/unoxy blood due to septa+valves
Frogs have how many of each heart chamber?
1 ventricle, 2 atria
Volume of air inhaled/exhaled by one breath
Volume of air in/exhaled in one minute
Number of breaths in one minute
Pulmonary Ventilation (V) =
Vt (tidal volume) X fR (respiratory frequency)

Analogous to cardiac output

How much air is taken in compared to how much air enters the blood
No contact with blood, but in lung
Fraction of atm pressure exerted by O2 =
1 atm =
760 mmHg = 760torr
O2 pressure at sea level =
760torr X .21 = 159torr
Solubility of O2 in H2O =
Perfusion of O2 into the blood depends on a difference in ___, not ____.
P(O2), [O2]
Why might P(O2)-lung = 100torr if the atmospheric P(O2) = 159torr?
During exhalation not all air is removed, remaining air is low in O2
Regulation of ventilation/blood flow maintains P(O2)-lung = ____torr.
In a water breather, perfusion requires a ____ delta-P(O2) and a ___ delta-P(CO2).
large, small
P(CO2) is higher in the gas-exchange organ of a ___-breather than in a ___-breather.
air, water
Under what condition are respiratory pigments especially useful?
High temperatures

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