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I. Mammalian
circulation42.3
Birds and Mammals have developed
2 ventricles that completely separate
O2-
rich and
O2-poor
blood.
Q.What
are the advantages to 2 separate loops?
(a)
No mixing, better delivery of O2to
tissues
(b) better gas exchange in lung (greater
concentration difference) (c)
systemic and pulmonary circuits can operate at different
pressures
II.
Human heart42.4
A. Cardiac muscle
Blood is driven through the
circulatory system by the rhythmic contraction of th walls
of the heart, which are made up of a specialized type of
muscle cells; cardiac muscle.
1.
intrinsic rhythm
The cells spontaneously and
rhythmically contract. They don't need a signal from the
nervous system, like skeletal muscle. If you dissociate
embryonic heart cells into single cells in a culture dish,
they will beat spontaneously at all different frequencies.
When they divide and grow and touch each other to form a
sheet of cardiac muscle, they beat in unison.
Q.
What happened once the single cardiac muscle cells
touched each other?
- Gap junctions that allow ions and electrical charge to
cross between them formed.
Q.If
the individual cells were beating at different frequencies,
what determines the rate of beating of the sheet?
- the fastest cells
2.
initiation of contraction
Heart muscle cells (like
allmammalian cells) normally
have a negative membrane
potential( more negative
charges inside).
This results from the action of
anelectrogenic pump,
the Na+/K+ pump,
which sends 3 Na+ out for every 2 K+ that come in. So, like
neurons, heart muscle cells have a charge difference and a
concentration gradient for both K+ and Na+ between the
inside and the outside.
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