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Chapter 3

KNES 351 Chapter Notes - Chapter 3: Myocyte, Muscle Tissue, Second Messenger System

Course Code
KNES 351
Andrew Galpin

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Chapter 3: Endocrine Reponses to Resistance Exercise
Understand the concepts of endocrinology.
Explain the physiological roles of anabolic hormones.
Describe hormonal responses to resistance exercise.
Develop training programs reflecting the concepts of endocrinology.
Synthesis, Storage, and Secretion of Hormones
Hormones: chemical messengers that are synthesized, stored and released
into the blood by endocrine glands.
Endocrine glands receive signals and release hormones in response to a
o These hormones are released into the blood which then attach to
hormone specific receptors on the surface (peptide hormones) or in
the nucleus (steroid/thyroid hormones) of the target tissue.
Autocrine secretion is another source of hormone secretion: this is when a
hormone is released in the cell it is produced.
o The produced hormone never leaves the cell.
o Insulin growth factor I is an example: it is released inside the muscle
fiber upon stimulus of mechanical force production.
Paracrine secretion is another source of hormone secretion: this is when a
hormone is released to adjacent cells, disregarding the need for a transport
mechanism to reach the target cells.
Binding proteins circulating in the blood carry both peptide and steroid
hormones and act as storage sites for these hormones.
o They prevent the hormones from degrading; the hormones are not
activated until they are separated from their respective proteins.
Hormones interplay in a very complex system that not only affects muscle
tissue but the entire body’s physiology.
Muscle as the Target for Hormone Interactions
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Muscle tissue is multinucleated: the protein within a muscle fiber is
controlled by multiple nuclei.
o This is observable by the fact that the diameter of a muscle fiber is
different along a strand.
The remodeling of muscles involves the damage of muscles, which triggers
an inflammatory response, hormonal interactions, and the synthesis of new
proteins into sarcomeres.
o This process involves the interaction between the immune system,
endocrinal system, and immune system (neuroendocrine
The most prominent adaptation to resistance training is the increase in
myosin and actin filaments.
o There is also a change in myosin heavy-chain proteins; type IIx or IIa
can change to heavy chain proteins.
o These heavy chain proteins are responsible for the building of the
contractile proteins within the sarcomere.
Stimulation of protein synthesis begins at the gene level; the genes dictate
the quality and quantity of muscle over a period of time.
o There is a significant difference, however, between the changes
incurred across the different fiber types.
o For example:
Type I fibers depend on the reduction in protein degradation.
Type II fibers increase protein synthesis.
Anabolic & Catabolic
o Anabolic hormones: hormones that promote tissue building.
o Anabolic hormones counter the effects of catabolic hormones, which
degrade proteins to promote glucose synthesis.
Role of Receptors in Mediating Hormonal Changes
Hormones are specific to receptors: this is referred to as the lock-and-key
o However, cross-reactivity also occurs within the circulation of
hormones; receptors are partially interactive with hormones it was
not specifically designed for.
o To affect the change in DNA (which lacks direct binding receptors),
hormones must utilize secondary mechanisms.
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Allosteric binding sites: substances other than the hormones can enhance
or reduce the response to the primary hormone.
When an adaptation is no longer possible; the receptors atop those cells no
longer become responsive to a specific hormone.
o This is called downregulation of receptor function.
o The binding sensitivity of a receptor to a hormone and the actual
number of receptors present on a cell can be altered as a result of
training adaptation.
Steroid Hormones Versus Polypeptide Hormones
Steroid Hormone Interactions
o Steroid hormones are fat soluble, located in the adrenal cortex and
gonads, and passively diffuse across the sarcolemma.
o After its diffusion the hormone binds to a receptor to form a
hormone-receptor complex (H-RC).
This allows the transcription-translation process to occur,
triggering protein synthesis.
Polypeptide Hormone Interactions
o Polypeptide hormones are made up of amino acids, bind to receptors
in the blood (or receptors atop cell membranes), can have different
receptor domains.
o Polypeptide have three signaling pathways:
Cyclic AMP-dependent pathway.
Cytokine-activated JAK/STAT pathway.
Janus kinases (soluble tyrosine kinases) activate
transcription: signal transduction activating
transportation (STAT).
Once the hormone has affected the receptor, secondary
messengers act to produce the proper
o Polypeptide hormones are not fat soluble so they
cannot cross the membrane.
Prototypical growth factor, mitogen-activated signaling
Heavy Resistance Exercise and Hormonal Increases
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