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Lecture 4

BIOB32H3 Lecture Notes - Lecture 4: Ontogeny, Aorta

Biological Sciences
Course Code
jason brown

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4 Feb 2019
4 - Comparative Physiology of the Heart.pptx
How is the heart of Daphnia regulated? Use drugs to determine whether myogenic or neurogenic by
looking at its heart under microscope and measure heart rate
Evolution of animals heart: what is a heart? 2 ways of defining:
1. Functional definition: organ in body to circulate fluid throughout animal
2. Anatomical definition: based on its structure: a true heart is sth that has a chambered structure (u
have 4 chambers) => if u have a true heart, u contrast that with a pumping vessel
pic shows heart of insect: heart is basically a thickened rgn of one of the blood vessel, muscular and help
prepare fluid through that vessel => this pic doesn't have a chamber => anatomically not a heart, but
functionally is => bc not chambered but circulates blood, it’s called a pumping vessel (not a heart)
Only 2 groups of animals that have a true anatomical chambered heart (pump): vertebrates (fish, human,
etc.) and molest(?)
In other animal groups, they have peristaltic pumps (not a true heart): pepperl blood through one
direction: arthropods, some molests, analits,
Animals that have neither (no circ system) => rely on diffusion to get ox and waste move throughout
their body
- Diff very slow over long distances => if u fall within this category^, u r either a very small animal
(target brase?: their ancestor had peristaltic pump, but they don’t now and it’s probably bc they
r so small that they don’t even need it) OR u have a very small/slow metabolism (no need for
high speed delivery of ox/nutrients to their tissues)
Ontogeny (development of individual organism) recapitulates (plays out again) phylogeny (development
of evolutionary linear over time) => if u look at indi organism, u can see the evolutionary past
Look at human heart development: look at day 20: development start to occur, no actual heartbeat yet
=> depend on diffusion still , day 22 heart beats but a tubular heart (not a real heart, just like a tubular
vessel), in later days there is development of the tubular heart into an adult heart at day 35 => u can see
how the heart development evolution was just by looking at embryo, also since heart is one of the first
organs to develop, it suggests that we can’t grow without it
Looking at peristaltic pumps in arthropods (mainly in insects): structure labeled heart (in a functional
way, no proper chamber), aorta opens up into a cavity (called hemocoel: to dump out extracellular fluid)
=> insects have an open circulatory system, all organs inside hemocoel and CF bathes all tissues
Insects don't have a blood, their CF is called hemolymph:
- blood in a closed circ sys animals, interstitial fluid bathes cells
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- but hemolymph used when we refer to an open circ sys animal whose blood and interstitial fluid
r mixed together
Dorsal vessel runs along the backside of insects and pumps the ECF (plays the heart role), when it pumps
it brings the flow forward. how dorsal vessel works?
- There are openings called ostium (arrows show blood flow from hemocoel through ostium into
heart), what’s the deriving force to get hemolymph in heart is the pressure inside heart
- Dorsal diaphragm inside connected to the heart (dorsal pump), it can be a muscle or an elastic
a) If it’s a muscle, when insect wanna draw hemolymph into dorsal vessel it’ll contract
muscle of diaphragm and pull posterior part of dorsal open => heart vol increase =>
pressure of hemolymph inside decrease => pressure derives hemolymph from
hemocoel through ostium into heart
- When muscles relax (contract inside), squeeze inside, pressurizing it, ostium has no valve =>
only way for hemolymph is to go out through aorta
b) In case of elastic ligament, heart contract stretches ligament and when heart relaxes
the ligaments go back to original length . Also, ligament plays as a valve (let hemolymph
in, but not out)
Insects use stomach to assist pump blood (help heart), heart may not even be the biggest contributor to
If heart was the major producer of hemolymph circulation, there should be a perfect correlation between
heartbeat and when hemolymph pressure rises => heart may not even be the heart! => abdominal pump
job is to get the hemo flow started and heart keeps it going
Insects have a lot of accessory pulsatile organs (accessory heart) that r present to ensure hemo circulates
through apandogen (?)
Antennal hearts at base of each antenna there’s a structure comprised of a vessel running up to antenna,
it opens at en, fluid flows into vessel and dumps out through antenna
Look at the pic: DM (diallater muscle) contracts, pulls ampulla, pressure low, hemo in ostium, when filled
with hemo and DM relaxes and back to original volm, it goes upto vessel into antenna to be dumped out
Mantennal heart makes sure that hemo actually gets into antenna, without antennal heart it won't
happen: blood circulates through hemocoel but not in antenna bc it’s very narrow => need accessory
organs to flow
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