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ANIMAL
PHYSIOLOGY
BIOL 3151:
Principles of Animal
Physiology
Dr. Tyler Evans
Email: [email protected]
Phone: 510-885-3475
Office Hours: F 8:30-11:30 or appointment
Website: http://evanslabcsueb.weebly.com/
PREVIOUS LECTURE
CARDIOVASCULAR PHYSIOLOGY
CHARACTERISTICS OF CIRCULATORY SYSTEMS
• circulatory systems can either be OPENED or CLOSED
• in a CLOSED circulatory system, fluid remains within blood vessels at all points and
substances must diffuse across the walls of blood vessels to enter tissues
• in an OPEN circulatory system, fluid enters a SINUS (space) at some point and
there comes into direct contact with tissues allowing exchange
• there is often uncertainty as to which type of system an animal possesses
• decapod crustaceans have both
sinuses and fine branching blood
vessels. Their circulatory systems
are usually classified as open, but
like closed systems, diffusion can
across the membrane of some fine
blood vessels
textbook Fig 8.8 pg 356
PREVIOUS LECTURE
CARDIOVASCULAR PHYSIOLOGY
ADVANTAGES OF A CLOSED CIRCULATORY SYSTEM
• closed circulatory systems provide two main advantages over open systems:
1. ability to generate high pressure and flow rates
2. ability to better control and direct blood flow to specific tissues
• these features are important for oxygen delivery to metabolically active
tissue and closed systems tend to be found in highly active organisms or
those living in low-oxygen environments
PREVIOUS LECTURE
CARDIOVASCULAR PHYSIOLOGY
VERTEBRATE CIRCULATORY SYSTEMS
• although left and right sides of the heart are joined together in a single organ, in
birds and mammals these sides are functionally separated
• functionally, more like a single circuit with two pumps
• having separated pulmonary and systemic circuits has an important advantage:
allows pressure in each circuit to be different
• in lungs, capillaries must be thin to allow for gas exchange and cannot withstand
high pressure
• in contrast high pressure is needed in the systemic circuit to force blood
throughout the body
PREVIOUS LECTURE
VERTEBRATE CIRCULATORY SYSTEMS
• trade-off to completely separated circuit is that the circulatory system becomes
relatively inflexible
• for example, if a mammal holds it’s breath, blood must still flow to the lungs
despite that the fact that blood is not becoming oxygenated when it arrives
• because breathe continuously, has been selection pressure to divert blood flow
from pulmonary circuit
• unlike birds and mammals, amphibians and reptiles have incompletely divided
hearts and because ventricles of the heart are interconnected, blood can be
diverted from pulmonary to systemic circuit or vice-versa.
textbook Fig 8.13 pg 362
TODAY’S LECTURE
WHAT IS A HEART?
• chambered hearts, like those in humans, evolved from simple pulsatile blood
vessels or tubular peristaltic hearts independently many times in different
animals
• for this reason we find substantial differences in the structure and function of
hearts among animals and the difference between a heart and a contractile
blood vessel can be cloudy
textbook Fig 8.6 pg 355
HEARTS
ARTHROPOD HEARTS
• Hemolymph is the circulating fluid of open circulatory systems
• When hemolymph enters sinuses, it mixes with other fluids like
EXTRACELLULAR FLUID and LYMPH (fluid with only small molecules and
few proteins)
• because these fluids are constantly mixing it is difficult to distinguish each
fluid and it is instead referred to as HEMOLYMPH
HEARTS
ARTHROPOD HEARTS
• arthropod hearts generally pump HEMOLYMPH out into the circulation via
arteries and blood returns to the heart via a series of holes or OSTIA.
• valves within the ostia open and close to regulate the flow of hemolymph
• neurons of the CARDIAC GANGLION send a signal to close the ostia and initiate
contraction, squeezing blood out of the heart and around the body
• arthropods hearts are attached to SUSPENSORY LIGAMENTS, so that after the
heart contracts these ligaments pull the heart to increase volume
• as this occurs, the ostia open and hemolymph is drawn into the heart, ready for
the next contraction
(i.e. contraction)
(i.e. relaxation)
textbook Fig 8.16 pg 368
HEARTS
STRUCTURE OF VERTEBRATE HEARTS: FISH
• Bony Fish hearts contain four-chambers arranged in a series: blood enter the
SINUS VENOSUS, flows into the ATRIUM, then into the muscular VENTRICLE
and finally through the BULBOUS ARTERIOSIS
• all components except the
BULBOUS ARTERIOSIS are
contractile in bony fish
textbook Fig 8.18 pg 370
HEARTS
STRUCTURE OF VERTEBRATE HEARTS: AMPHIBIANS
• amphibians have a three-chambered heart: two atria and one ventricle
• the ventricle pumps blood through the CONUS ARTERIOSIS to both the
PULMONARY (lung) and SYSTEMIC (whole-body) circuit
• oxygenated blood returns to the
left atrium, while deoxygenated
blood flows into the right atrium
• the two atria supply blood to the
single ventricle, which is either
pumped ot the lungs or the rest of
the body
• mechanisms separating
oxygenated and deoxygenated are
not fully understood, but involves
re-direction using a SPIRAL FOLD
textbook Fig 8.18 pg 370
HEARTS
STRUCTURE OF VERTEBRATE HEARTS: MOST REPTILES
• non-crocodilian reptiles have five-chambered hearts
• two atria as in amphibians, but the ventricle is divided into three interconnected
compartments: CAVUM VENOSUM, CAVUM PULMONALE, CAVUM ARTERIOSUM
• despite incompletely separated ventricle, oxygenated and de-oxygenated blood
are typically separated.
• de-oxygenated blood
enters right atrium and
flow to cavum venosum,
then across the muscular
ridge to the cavum
pulmonale
• oxygenated blood enters
right atrium, then into
cavum areteriosum and
out aortas to rest of body
textbook Fig 8.19 pg 371
HEARTS
STRUCTURE OF VERTEBRATE HEARTS
• reptiles can also distribute blood selectively between pulmonary and systemic
circuits-called a SHUNT.
• in a shunt, some fraction of oxygenated poor blood bypasses the pulmonary
circuit and re-enters the systemic circuit (and vice-versa too)
• reptiles are intermittent breathers often holding their breath for long periods of
time and allows for blood to be directed to the body diving rather than to the
non-functional lungs
HEARTS
STRUCTURE OF VERTEBRATE HEARTS: MOST REPTILES
• in crocodiles, the ventricles are separated and shunting occurs with the help of a
special valve a the entrance of the pulmonary artery (going to lungs)
• rather than opening or closing in response to changes in pressure like most cardiac
valves, this valve in controlled by the hormone EPINEPHRINE
• when crocodiles are at rest underwater, epinephrine is low and the valve is closed
diverted blood away from the pulmonary circuit
• when active, epinephrine is higher and the valve is open
• crocodiles can remain submerged for several hours
HEARTS
STRUCTURE OF VERTEBRATE HEARTS: BIRDS & MAMMALS
• birds and mammals have four chambered hearts
• the left side of the heart consists of a thin-walled atrium and a thick walled
ventricle, on the right side the ventricle is much thinner
textbook Fig 8.20 pg 373
• left ventricle pumps blood
through the high resistance
systemic circuit and must
therefore contract more
forcefully than the right
ventricle
• ATRIOVENTRICULAR VALVES
allow blood to flow from
artium to ventricle, but not
in reverse.
• SEMILUNAR VALVES on
blood vessels prevent blood
from flowing back into
ventricles
HEARTS
THE CARDIAC CYCLE
• the vertebrate heart acts as a integrated organ, with each chamber contracting at
appropriate times to properly move blood
FISH
• In fish, each chamber contracts in series
• Starts in SINUS VENOSUS-too thin walled to be involved in moving blood long
distances, but instead important in initiating contraction
• pressure in sinus venosus opens valve and blood flows to atrium
• building pressure opens valve from
atrium and blood flows into the
ventricle
• contraction of the ventricle propels
blood through the body
• the bulbus arteriosis is stretchy and
helps dampen blood pressure
changes
HEARTS
THE CARDIAC CYCLE
• the vertebrate heart acts as a integrated organ, with each chamber contracting at
appropriate times to properly move blood
MAMMALS
• in mammals, blood entering atria first flows passively into the ventricles as the
AV valves are open.
• the atria then contract pumping additional blood into the ventricles, reaching
END DIASTOLIC VOLUME (max amount of blood in ventricle)
• as pressure builds in the ventricles, the semilunar valves are forced open and
blood flows out into the arteries in the VENTRICULAR EJECTION PHASE
• at this point ventricles have reached minimum or END-SYSTOLIC VOLUME
• throughout ventricular contraction, the atria are relaxed so blood is once
again passively entering these chambers and the cycle repeats.
CARDIAC CYCLE OF MAMMALS
Textbook Fig 8.21 pg 374
HEARTS
THE CARDIAC CYCLE-MAMMALS
• remember that although the two ventricles of the mammalian heart contract
simultaneously, the left ventricle contracts much more forcefully than the right
ventricle…
WHY?
textbook Fig 8.20 pg 373
HEARTS
CONTROL OF CONTRACTION
• clearly, cardiac contraction must be tightly regulated
• unlike the muscles described previously that required neural stimulus (i.e.
NEUROGENIC), vertebrate CARDIOMYOCYTES (i.e. heart muscle cells) are
MYOGENIC, they produce rhythmic spontaneous depolarizations that initiate
contraction
• cardiomyocytes are electrically coupled by __________________, so that
depolarizations can spread from once cell to another.
Rate of spontaneous depolarization
varies (i.e. some faster, some slow),
but those with the fastest rates are
called PACEMAKER CELLS
In vertebrates (except fish), the
pacemakers cells are located in the
SINOATRIAL (SA) NODE
PACEMAKER CELLS
•
•
•
•
HEARTS
pacemaker cells are small, have few myofibrils, and thus do not contract
these cells have unstable resting membrane potentials
slowly drift up from -60mV until an action potential is initiated
The result of a FUNNY CURRENT (names for unusual behavior)
• FUNNY CHANNELS open during
textbook Fig 8.23 pg 376
hyperpolarization (i.e. after action
potential) and allow Na+ to gradually
enter cell.
• when membrane potential hits
threshold, voltage gated calcium
channels open that add to depolarization
and trigger an action potential
• during repolarization, K+ channels open
(more slowly than muscle cells though).
• processes is repeated during
hyperoplarization
HEARTS
ENDOCRINE SIGNALS REGULATE PACEMAKER CELLS
• endocrine signals alter the rate of pacemaker potentials from the SA node
• NOREPINEPRHINE and EPINEPHRINE bind to beta-adrenergic receptors on
pacemaker cells
• this binding alters the activity of the funny channels and calcium channels, in
effect speeding the rate of Na+ depolarization and increases the frequency of
action potentials and ultimately increases heart rate
Pathway
to
increase
heart rate
textbook Fig 8.24 pg 377
HEARTS
ENDOCRINE SIGNALS REGULATE PACEMAKER CELLS
• ACETYLCHOLINE acts to reduce heart rate
• binding of acetylcholine to MUSCARINIC RECEPTORS on pacemaker cells increases
permeability of K+ and causes increased hyperpolarization
• hyperpolarization means longer for Na+ and calcium to reach threshold
• slows the rate of action potential generation and thus heart rate
textbook Fig 8.25 pg 378
HEARTS
ELECTRICAL ACTIVITY
• in addition to electrical signals in the heart are spread via special conduction
pathways
• gap junctions spread signal within a chamber, but contraction at different
chambers at different times relies on alternative pathway
• after an action potential in the AV node, the depolarization spreads along an
INTERNODAL PATHWAY to the ATRIOVENTRICULAR (AV) node
• The AV node delays the signal, then passes on through the BUNDLE OF HIS and
PURKINJE FIBERS to the ventricles
• delay ensures that atria finish contracting before ventricles start contraction
textbook Fig 8.27 pg 380
HEARTS
ELECTRICAL ACTIVITY
• cardiac muscle cell depolarization produces a strong electrical signal that can be
detected by an ELECTROCARDIOGRAM
• the fluctuations represent the combined effects of all action potentials
• The P-WAVE is the atria depolarizing
• The QRS-COMPLEX is the result of ventricle depolarization and atrial repolarization
• VENTRICULAR FIBRILLATION
results form uncoordinated
contraction and results in
effective pumping of blood to
cells
• A DEFRIBRILLATOR machine
rapidly depolarizes all the
cells, reseting the system and
allowing the pacemaker cells
to take over
LECTURE SUMMARY
• structure of vertebrate and invertebrate hearts (i.e. # of chambers)
• importance of SHUNTING in reptiles and the ability to divert blood away from
the pulmonary circuit when holding breath
• described the CARDIAC CYCLE in fish and mammals
• control of heart contraction
• FUNNY CHANNELS and FUNNY CURRENTS
• Role of endocrine signals like acetylcholine, epinephrine and
norepinephrine
• the spread of electrical signal across the heart and the role of the INTERNODAL
PATHWAY
• ended by describing the causes of the fluctuations on electrocardiogram
NEXT LECTURE
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