biol 3151: principles of animal physiology -...

BIOL 3151:

Principles of Animal

Physiology

ANIMAL

PHYSIOLOGY

Dr. Tyler EvansEmail: [email protected]

Phone: 510-885-3475

Office Hours: F 8:30-11:30 or appointment

Website: http://evanslabcsueb.weebly.com/

PREVIOUS LECTURE

CARDIOVASCULAR PHYSIOLOGY

• 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

CHARACTERISTICS OF CIRCULATORY SYSTEMS

textbook Fig 8.8 pg 356


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

PREVIOUS LECTURE

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 LECTUREVERTEBRATE 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.


TODAY’S LECTUREWHAT 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


HEARTSARTHROPOD 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

• 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

HEARTSARTHROPOD HEARTS


(i.e. contraction) (i.e. relaxation)

HEARTSSTRUCTURE 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


HEARTSSTRUCTURE 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


HEARTSSTRUCTURE 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


HEARTSSTRUCTURE 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

• 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

STRUCTURE OF VERTEBRATE HEARTS: MOST REPTILES

HEARTSSTRUCTURE 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

• 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

ventriclestextbook Fig 8.20 pg 373

HEARTSTHE 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

HEARTSTHE 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 MAMMALSTextbook Fig 8.21 pg 374

HEARTSTHE 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?


HEARTSCONTROL 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

HEARTSPACEMAKER CELLS

• 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

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


HEARTSENDOCRINE 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

HEARTSENDOCRINE 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


HEARTSELECTRICAL 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


HEARTSELECTRICAL 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

BLOOD

biol 3151: principles of animal physiology -...

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