Hormonal Response to Exercise

Hormonal Response to Exercise

• Hormones are released into the blood via the endocrine system
• Nerves use neurotransmitters to relay responses via the nervous system

Growth Hormone

• Released by the anterior pituitary gland
• Targets all cells in the body
• Responsible for development and enlargement of body tissues until maturation
• Increases the rate of protein synthesis
• Increases fat mobilization and oxidation
• Increases gluconeogenesis in the liver

Catecholamines

• Includes norepinephrine and epinephrine
• Released by the adrenal medulla
• Maintains blood pressure and plasma glucose homeostasis

Insulin

• Secreted from the beta cells of the pancreatic islets
• Targets liver, skeletal muscle, and adipose tissue
• Increases glucose and amino acid uptake in tissues

Glucagon

• Released by alpha cells
• Targets the liver and adipose tissue
• Increases liver glycogenolysis
• Promotes mobilization of free fatty acids from adipose tissue
• Increases gluconeogenesis in the liver

Testosterone

• Released by the gonads (testes)
• Promotes muscle growth
• Anabolic steroid ineffectiveness: Due to incorrect doses and lack of understanding of the body's response

Female Athlete Triad

• Characterized by an interrelationship of three conditions: disordered eating, intense exercise, and energy availability
• Can result in low bone mass density and amenorrhea (absence of period)
• Athletic amenorrhea originates in the hypothalamus, an endocrine gland

The Nervous System

• Major divisions include: central nervous system (CNS), peripheral nervous system (PNS), somatic nervous system, autonomic nervous system (ANS), sympathetic, and parasympathetic

Afferent vs. Efferent Neurons

• Afferent neurons carry sensory information to the CNS
• Efferent neurons carry motor commands away from the CNS

Sympathetic vs. Parasympathetic Neurons

• Sympathetic neurons release norepinephrine
• Parasympathetic neurons release acetylcholine

Neuron Structure

• Dendrites receive signals
• The cell body processes signals
• The axon sends signals
• Axon terminals release neurotransmitters

Resting Membrane Potential (RMP)

• Caused by ion distribution (Na+, K+) across the membrane
• Maintained by sodium-potassium pumps
• RMP in neurons is typically between -65 to -70 mV

Action Potential

• Depolarization occurs due to Na+ influx
• Repolarization occurs due to K+ efflux
• Restoration of RMP is achieved by ion pumps

Cardiovascular Control & Hemodynamics

• Transports of gases, nutrients, wastes, and hormones
• Regulates fluid balance, blood pressure, pH, and thermal balance
• Protection via clotting and transport of WBCs and antibodies

Cardiac E-C Coupling

• Calcium-induced calcium release
• Involves calcium influx through L-type channels, which triggers further calcium release from the sarcoplasmic reticulum (SR)
• A small increase in Ca2+ in the vicinity of the SR leads to a much larger Ca2+ release from the SR
• Calcium influx triggers further release from the SR, enhancing contraction strength

Refractory Period

• Skeletal Muscle: The refractory period is very short compared to the time required for tension development with repeated stimulation resulting in summation and tetanus (max tension)
• Cardiac Muscle: The refractory period is almost as long as the entire muscle twitch, which prevents tetanus

Electrical Activity of the Heart

• SA node → AV node → Bundle of His → Purkinje fibers
• Parasympathetic activity decreases vagal tone
• Sympathetic nerve activity (SNA)

ECG Waves

• P wave: Atrial depolarization
• QRS complex: Ventricular depolarization
• T wave: Ventricular repolarization

Stroke Volume (SV)

• SV = EDV - ESV (end-diastolic volume minus end-systolic volume)

Frank-Starling Mechanism vs. Contractility

• Contractility is independent of volume and improves force of contraction
• Defined as the strength of contraction at a given diastolic volume without change
• Frank-Starling mechanism states that increased venous return increases EDV, which stretches the muscle and improves contraction and stroke volume

Mechanisms for Increased Venous Return

• Skeletal muscle pump
• Respiratory pump
• Venoconstriction

Blood Vessel Wall Layers

• Tunica intima: Endothelium
• Tunica media: Smooth muscle
• Tunica externa: Connective tissue

Vascular Smooth Muscle Tone Regulation

• Controlled by ion flow, mainly Ca2+, for contraction or relaxation
• Regulated by intracellular calcium concentration

Blood Flow

• Blood Flow (Q) = ΔP / R (pressure difference divided by resistance)

Resistance Vessels

• Arterioles

Factors Affecting Resistance (R)

• Viscosity: Increased viscosity decreases blood flow
• Vessel length
• Vessel radius: Increased size decreases resistance and increases blood flow

Baroreceptors

• Detect changes in BP and adjust heart rate

Cardiovascular Responses to Exercise

• O2 delivery (cardiac output) increases
• O2 utilization (a-vO2 diff) increases
• Muscle metabolism increases, needing more ATP
• Increased venous return to the heart
• Increased EDV increases force of contraction
• Increased SNA increases contractility

Mechanisms controlling blood flow to skeletal muscle

• Endothelial control releases nitric oxide, causing vasodilation
• Mechanical control from the muscle pump increases AP, increasing muscle blood flow
• Myogenic control causes vasoconstriction
• Neural vasoconstriction
• Metabolic muscle metabolism increases, increasing metabolites, which causes vasodilation in skeletal muscle

Fick Principle

• VO2 = Q x (a-vO2 diff)
• Cardiac output is the difference in arterial and venous blood

Fick Equation

• VO2 = Q x (CaO2 - CvO2)

a-vO2 Difference

• Amount of oxygen extracted by tissues, which increases during exercise

Intrinsic vs. Extrinsic Control of Blood Flow

• Intrinsic: Vasodilation from metabolites
• Extrinsic: Sympathetic nervous system

Blood Pressure Response to Exercise

• Systolic blood pressure rises
• Diastolic blood pressure remains unchanged

Respiration During Exercise

• Pulmonary refers to has exchange in lungs
• Cellular refers to use of oxygen in mitochondria

Muscles Involved in Ventilation

• At rest, the diaphragm and external intercostals are primarily involved in passive process
• During exercise, more muscles assist, including the sternocleidomastoid, scalenes, and pectoralis minor for inspiration
• Abdominal muscles and internal intercostals assist with active expiration

Inspiration vs. Expiration

• Inspiration: The diaphragm contracts and moves down, external intercostals lift rib cage, increasing thoracic volume, which decreases pressure in the lungs, drawing air in
• Expiration: At rest, passive due to elastic recoil of the lungs. During exercise, internal intercostals and abdominal muscles contract to force more air out

Dalton's Law

• States that the total pressure of a gas mixture equals the sum of the partial pressures of each individual gas

Pulmonary Diffusion

• Pulmonary diffusion occurs because O2 moves from alveolar air to blood
• CO2 moves from blood to alveolar air
• Gas exchange occurs in alveoli across the respiratory membrane

Factors that influence the rate of diffusion across the blood-gas interface

• Higher surface area increases the rate of diffusion
• A thinner membrane increases the rate of transfer

Fick's Law of Diffusion

• Asserts that the rate of diffusion is directly proportional to surface area and the difference in gas partial pressures, and inversely related to membrane thickness
• Increased thickness decreases the rate of diffusion

Mechanisms for Transporting O2 & CO2 in the Blood

• Hemoglobin transports O2
• 1% dissolves in plasma