BIOM 3200 Study Guide - Final Guide: Endoplasmic Reticulum, Heart Valve, Pulmonary Artery

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Unit 8/9: Cardiovascular System
Cardiac and Smooth Muscles
Cardiac muscle, like skeletal muscle, is striated and contains sarcomeres that shorten by sliding of thin
and thick filaments.
- Skeletal muscle (long fibrous muscle) requires nervous stimulation to contract
- Cardiac muscle can produce impulses and contract spontaneously
- Smooth muscles lack sarcomeres, but they do contain actin and myosin that produce
contractions in response to a unique regulatory mechanism
Skeletal muscles are voluntary effectors regulated by somatic motor neurons
Cardiac and smooth muscles are involuntary effectors regulated by autonomic motor neurons
All types of muscle contract by means of sliding of thin filaments over thick filaments
- Produced by the action of myosin cross bridges in all types of muscles, and excitation-
contraction coupling in all types of muscles involves Ca 2+
Cardiac Muscle
Myocardial cells are short, branched, and interconnected
- Each cell is tubular in structure and joined to adjacent myocardial cells by electrical synapses, or
gap junctions
- The gap junctions are concentrated at the ends of each myocardial cell, which permits electrical
impulses to be conducted primarily along the long axis from cell to cell.
Action potentials that originate at any point in a mass of myocardial cells (a myocardium) can spread to
all cells in the mass that are joined by gap junctions
- Since all cells in a myocardium are electrically joined, a myocardium behaves as a single
functional unit.
Skeletal muscles produce contractions that are graded depending on the number of cells
stimulated
A myocardium contracts to its full extent each time because all of its cells contribute to the
contraction
- The ability of the myocardial cells to contract, can be increased by the hormone epinephrine
and by stretching of the heart chambers
- The heart contains two distinct myocardia (atria and ventricles)
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Skeletal muscles require external stimulation by somatic motor nerves before they can produce action
potentials and contract
- Cardiac muscle is able to produce action potentials automatically
- Action potentials normally originate in a specialized group of cells called the pacemaker
The rate of this spontaneous depolarization, and the rate of the heartbeat, are regulated by
autonomic innervation
Skeletal muscles have a direct excitation-contraction coupling between the transverse tubules and
sarcoplasmic reticulum
Myocardial cells have voltage-gated Ca 2+ channels in the plasma membrane and the Ca2+ release
channels in the sarcoplasmic reticulum do not directly interact
- The transverse (or T) tubules come very close to a region of the sarcoplasmic reticulum
- Depolarization of the T tubules during an action potential opens voltage-gated Ca 2+ channels in
their plasma membrane, and the Ca 2+ that diffuses into the cytoplasm interacts with the
nearby Ca 2+ release channels in the sarcoplasmic reticulum
- Causes them to open and release the stored Ca 2+ into the cytoplasm to stimulate contraction
calcium-induced calcium release
- Ca 2+ serves as a second messenger from the voltage-gated Ca 2+ channels to the Ca 2+ release
channels
Excitation-contraction coupling is slower in cardiac than in skeletal muscle
Diffusion of Ca 2+ through the plasma membrane of the transverse tubules serves mainly to open the
channels in the sarcoplasmic reticulum
- The Ca 2+ release channels in the sarcoplasmic reticulum are 10 times larger than the voltage-
gated Ca 2+ channels in the plasma membrane, and so are primarily responsible for the rapid
diffusion of Ca 2+ into the cytoplasm, which then binds to troponin and stimulates contraction
- In order for the muscular chambers of the heart to relax, the Ca 2+ in the cytoplasm must be
actively transported back into the sarcoplasmic reticulum
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Structure of the Heart
The heart contains four chambers: two atria, which receive venous blood, and two ventricles, which
eject blood into arteries. The right ventricle pumps blood to the lungs, where the blood becomes
oxygenated; the left ventricle pumps oxygenated blood to the entire body
Divided into four chambers:
1. Right and left atria receive blood from the venous system
2. Right and left ventricles pump blood into the arterial system
3. Right atrium and ventricle (right pump)
4. Left atrium and ventricle (left pump)
The right and left pump are separated by a muscular wall, or septum
- Prevents mixture of the blood from the two sides of the heart
Between the atria and ventricles, there is a layer of dense connective tissue known as the fibrous
skeleton of the heart.
- Bundles of myocardial cells in the atria attach to the upper margin of this fibrous skeleton and
form a single functioning unit, or myocardium
- Myocardial cell bundles of the ventricles attach to the lower margin and form a different
myocardium
- The myocardia of the atria and ventricles are structurally and functionally separated
Special conducting tissue is needed to carry action potentials from the atria to the
ventricles.
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