Cell Signaling and the Hormonal Response to Exercise Flashcards
Neuroendocrine system:
Endocrine system releases hormones
Nervous system uses neurotransmitters
Endocrine glands =
Release hormones directly into the blood
Hormones =
Alter the activity of tissues that possess receptors to which the hormone can bind
Several classes based on chemical makeup
> Amino acid derivatives
> Peptides/protein
> Steroids
The effect of a hormone on a tissue is determined by:
Plasma concentration of hormone
Rate of secretion of hormone from endocrine gland
Rate of metabolism or excretion of hormone
Quantity of transport protein
Changes in plasma volume
Rate of secretion of hormone from endocrine gland =
Magnitude of input
Stimulatory versus inhibitory input
Rate of metabolism or excretion of hormone =
At the receptor and by the liver and kidneys
Incretin =
gut-derived peptide hormone that are rapidly secreted in response to a meal – stimulate B cells to postprandially secrete insulin
The overarching role of insulin in the body:
regulate the body’s energy supply or glucose by transporting glucose intracellularly to cells, tissue
To be used as energy and to maintain blood glucose levels at a ‘normal’ level which ideally is less than 100mg/DL of blood – over 126 is indicative of diabetes
Contributing factors to increase insulin secretion by the pancreas are:
increased plasma glucose levels
glucose circulating in the blood stream
increased amino acid
automonic nervous system adjustment from both SNS and PSNS
incretins
Hormone-Receptor Interactions
Hormones only affect tissue with specific receptors
Hormones have to be congruent with a receptor inorder to activate the cell
Magnitude of effect of Hormone-Receptor Interactions dependent on:
Concentration of the hormone
Number of receptors on the cell
Affinity of the receptor for the hormone
Speed with which hormone is metabolized
Downregulation =
Decrease in receptor number in response to high concentration of hormone
Upregulation =
Increase in receptor number in response to low concentration of hormone
Mechanisms of Hormone Action
Altering activity of DNA to modify protein synthesis
Activating second messengers via G protein
= Cascade of events leads to a second messenger = Cyclic AMP, Ca++
Altering membrane transport = Insulin via tyrosine kinase = large class of transmembrane receptors; play a key role in regulation of glucose homeostasis
Hormones are secreted from endocrine glands:
Hypothalamus and pituitary glands
Thyroid and parathyroid glands
Adrenal glands
Pancreas
Testes and ovaries
endocrine system is comprised of:
pineal gland
thymus
ovary
testicle
hypothalamus
pituitary gland
thyroid gland
parathyroid glands
pancreas
adrenal glands
placenta - during pregnancy
Hypothalamus =
Stimulates release of hormones from anterior pituitary gland
Provides hormones for release from posterior pituitary gland
Hypothalamus function:
Coordinates the endocrine system: main function is to keep body in homeostasis
Body Temperature
BP
Hunger and Thirst
Satiety
Mood
Libido
Sleep
Anterior Pituitary Gland
hormones released:
ACTH
FSH
LH
MSH
TSH
Prolactin
GH
Adrenocorticotropic hormone (ACTH)
Stimulates cortisol (stress = increased levels) release from adrenal glands
Follicle-stimulating hormone (FSH)
Sexual development & reproduction
Luteinizing hormone (LH)
Stimulates production of testosterone and estrogen
Melanocyte-stimulating hormone (MSH)
Stimulates production of melanin
Thyroid-stimulating hormone (TSH)
Controls thyroid hormone (growth, metabolism) release from thyroid gland
Prolactin
Stimulates release/production of breast milk
Growth hormone (GH)
Controls height, bone length, and muscle growth
Growth Hormone and Performance
More adverse effects than benefits
Irreversible acromegaly
Heart disease
Diabetes
Not advocated as anti-aging therapy = Increased lean body mass but no change in strength
GH increases protein synthesis in muscle and long bone growth
Used to treat childhood dwarfism
Also used by athletes and older adults = Increased release during exercise
GH injections
Increase exercise capacity and muscle mass in conjunction with resistance training
Posterior Pituitary Gland hormones released:
oxytocin
ADH
Oxytocin =
Stimulates smooth muscle during childbirth and milk production
Antidiuretic hormone (ADH) =
Reduces water loss from the body to maintain plasma volume
Favors reabsorption of water from kidney tubules to capillaries
Release stimulated by high plasma osmolality and low plasma volume
Due to sweat loss without water replacement
Increases during exercise >60% VO2 max (moderate to vigorous exercise) = To maintain plasma volume
Thyroid Gland
butterfly-shaped gland locatedat the base of the neck, just below the larynx or Adam’s apple
produces hormones that regulate heart rate, blood pressure, body temperature and weight
Stimulated by TSH (Anterior Pituitary)
releases:
Triiodothyronine (T3)
Thyroxine (T4)
Calcitonin
Triiodothyronine (T3) and thyroxine (T4)
Establishment of metabolic rate
Permissive hormones = Permit full effect of other hormones
Latent period but long lasting
Increased secretion in CV exercise
Calcitonin =
Regulation of plasma Ca++
Opposes effect of parathyroid
Parathyroid Gland
releases parathyroid hormone = Primary hormone in plasma Ca++ regulation
Parathyroid hormone =
Stimulates Ca++ release from bone
Stimulates reabsorption of Ca++ by kidneys
Converts vitamin D3 into a hormone that increase Ca++ absorption from GI tract
High intensity exercise > 50 minutes or low intensity exercise > 5 hours increases parathyroid hormone levels
Adrenal Medulla
Secretes the catecholamines
Part of the sympathetic nervous system
Dopamine, Epinephrine (E) and norepinephrine (NE)
Fast-acting hormones
Work to ensure stable blood pressure and plasma glucose
Released in response to physical and emotional stress
Bind to adrenergic receptors: Alpha and Beta
Adrenal Medulla - Effects depend on hormone used and receptor type
Can be both excitatory or inhibitory
Epinephrine
E = increase HR and force of contraction
Norepinephrine
N = vasoconstriction
Adrenal Cortex
Secretes steroid hormones
Mineralcorticoids = Aldosterone, Maintenance of plasma Na+ , K + and water balance
Regulation of blood volume and blood pressure
Part of renin-angiotensin-aldosterone system: All three hormones increase during exercise critical regulator of blood volume, electrolyte balance, and systemic vascular resistance
Adrenal Cortex Stimulated by:
Increased K+ concentration = plasma osmolality
Decreased plasma volume = hypovolemic
Adrenal Cortex Works to increase plasma volume
Glucocorticoids
> Cortisol
> Regulation of plasma glucose
Sex steroids
> Androgens and estrogens
> Support prepubescent growth
Adrenal glands =
suprarenal glands
small, triangular-shaped glands locatedon top of both kidneys
produce hormones that help regulate your metabolism, immune system, blood pressure, response to stress and other essential functions
Change in Renin, Angiotensin II, and Aldosterone During Exercise
With increased exercise intensity all 3 components of the R A A S increase for blood volume control
Cortisol - Maintenance of plasma glucose:
Promotes protein breakdown for gluconeogenesis =
stimulates glucose synthesis
Stimulates FFA mobilization from adipose tissue
Stimulated by:
> stress
> exercise
Cortisol secreted from adrenal glands is responsible for ___
gluconeogenesis = glucose production from non carbohydrate components
Mobilizes FFA from adipose tissue for production of glucose or gluconeogenesis
Stimulated by stress and exercise
In addition to storing triglycerides, adipose tissue also secretes hormones
leptin
adiponectin
With increased fat mass
> Higher leptin levels and lower adiponectin
> Leads to type 2 diabetes and low-grade inflammation
Leptin =
Influences appetite through the hypothalamus
Increases insulin resistance
Adiponectin =
Increases insulin sensitivity
Pancreas
Both exocrine and endocrine functions
Secretes:
Insulin (from beta cells)
> Transports glucose to cells for energy
> Lack of insulin = diabetes mellitus
Glucagon (from alpha cells)
> Stimulates conversion of glycogen to glucose primarily in the liver = glycogenolysis
Somatostatin = Controls rate of entry of nutrients into the circulation
Digestive enzymes and bicarbonate = Into the small intestine
Testosterone =
Released from testes
Anabolic steroid
> Promotes tissue (muscle) building
> Performance enhancement
Androgenic steroid
> Promotes masculine characteristics
Estrogen and Progesterone
> Released from ovaries
> Establish and maintain reproductive function
> Levels vary throughout the menstrual cycle
Anabolic Steroids and Performance
Increase lean body mass, muscle mass, and strength = Amplified when added with resistance exercise
Many negative side effects
> Mood and behavior disorders
> Cardiovascular disease
> Liver dysfunction
> Insulin resistance
Muscle as an Endocrine Gland
Skeletal muscle produces myokines when it contracts
> Regulation of lipid metabolism
Interleukin 6 (IL-6)
> IL-6 produced during exercise promotes anti-inflammatory effect
Regular exercise promotes anti-inflammatory environment
Reduction in chronic inflammation and reduced risk of heart disease, type 2 diabetes, and certain cancers
Muscle Glycogen Utilizatio
High intensity exercise = increase in plasma epinephrine = Glycogenolysis (glycogen to glucose) is related to exercise intensity
High-intensity exercise results in greater and more rapid glycogen depletion
Plasma glucose maintained through:
Mobilization of glucose from liver glycogen stores
Mobilization of FFA from adipose tissue
Gluconeogenesis from amino acids, lactic acid, and glycerol (mostly liver and kidneys)
Controlled by hormones
> Slow-acting = Thyroxine, cortisol, and growth hormone
> Fast-acting = Epinephrine, norepinephrine, insulin, and glucagon
Thyroid Hormones: Exercise
Act in a permissive manner to allow other hormones to exert their full effect
No real change in T3 and T4 during exercise
Slow-acting hormone (cortisol) Effects
Stimulate FFA mobilization from adipose tissue
Enhance gluconeogenesis in the liver
Decrease the rate of glucose utilization by cells
Cortisol: Effects of exercise
Decrease during low-intensity exercise
linear Increase during high-intensity exercise
> Above ~60% VO2 max
Growth Hormone: Exercise Effects
Supports the action of cortisol
> Decreases glucose uptake by tissues
> Increases free fatty acid mobilization
> Enhances gluconeogenesis in the liver
Exercise effect
> Increase in plasma GH with increased intensity
Epinephrine and Norepinephrine: Exercise
Fast-acting hormones
Maintain blood glucose during exercise
Muscle glycogen mobilization
Increasing liver glucose mobilization
Increasing FFA mobilization
Interfere with glucose uptake
Plasma E and NE increase during exercise
Also related to increased heart rate and blood pressure during exercise
Insulin and Glucagon: Exercis
Fast-acting hormones
Insulin
> Increased insulin sensitivity
> Decrease secretion
Glucagon
> Mobilization of glucose and FFA fuels
> Increased secretion
Insulin and glucagon secretion influenced by catecholamines
