Heart, Venous Return, Receptors Flashcards
What happens to venous return during exercise
Increases
Define venous return
Return of deoxygenated blood to the right side of heart via vena cava
What are the venous return mechanisms
Skeletal muscle pump
Respiratory pump
Pocket valves
Explain the skeletal muscle pump
When skeletal muscles contract they compress the veins which forces blood toward heart
Explain the respiratory pump
When muscles contract and relax during breathing in and out, pressure changes occur in the thoracic and abdominal cavities.
Changes in pressure compress nearby veins to assist blood return to heart
Explain pocket valves
These assist venous return in the veins and venues to prevent backflow
List 3 other factors affecting venous return
Thin layer of smooth muscle in walls of veins helps squeeze blood back towards heart
Gravity helps blood return to the heart from upper body
Suction pump action of heart = pressure difference between atria and veins ‘sucking’ blood towards the heart
What are the 2 importances of the venous return mechanism
During exercise to meet demands of the activity.
Immediately after exercise by performing active cool down to prevent blood pooling in veins
Define stroke volume
Volume of blood ejected from left ventricle per beat
ml
What does stroke volume depend on
Venous return
Elasticity of cardiac fibres
Define cardiac output
Volume of blood pumped out of the heart per minute
l/min
What’s starlings law
Suggests that SV is dependent on the elasticity of cardiac muscle fibres.
The greater the stretch of cardiac fibres, the greater the force of contraction
Define the ejection fraction
% of blood pumped out of left ventricle per beat.
Rest = normally around 55%
Exercise = rises to over 70%
Elite athletes = around 85% due to training.
What are the 3 steps to the cardiac cycle?
Atrial systole
Ventricular systole
Diastole
What does it mean that the heart is myogenic?
Generates its own impulses + can contract + relax rhythmically to its own accord.
List the order of the conduction system in which the impulses spread across the heart
SAN fires impulse causing atrial systole
Impulse is delayed at atrioventricular node
Passes through Bundle of His and Bundle branches to the apex of the heart
Along Purkinje fibres to cause ventricular systole
How is the delay of the electrical impulse caused?
By the non-conducive connective tissue
What is heart rate regulated by
Neural
Chemical
Intrinsic controls
What type of control is the CCC under?
Involuntary and is part of the autonomic nervous system
What are the two components of the autonomic nervous system
Sympathetic - Stimulates heart to beat faster
Parasympathetic - Slows HR down to resting levels
Define chemoreceptors
Tiny structures in carotid arteries and aortic arch that detects changes in acidity of the blood.
When ⬆️ acidity is detected, receptors stimulate sympathetic nervous system.
What lowers the pH of the blood?
CO2 and lactic acid = more acidic
Define baroreceptors
Special stretch receptors in walls of the aorta, vena cava and carotid arteries that detect changes in bp.
⬆️ in arterial pressure = ⬆️ stretch of the baroreceptors = ⬇️ in HR.
⬇️ in arterial pressure = ⬇️ in stretch of baroreceptors = ⬆️ HR.
Define proprioceptors
Sensory nerve endings in muscles, tendons and joints that detects change in movements and body position.
Start of exercise = send impulse to medulla, then sends through sympathetic nervous system to the SAN to ⬆️ HR.
Define thermoreceptors
Sensory cells in the body that detect changes in body temp and send info to CCC.
As body temp ⬆️ = thermoreceptors detect this = sends info to CCC to ⬆️ HR
Define capillaries
Form an extensive network that connects arteries and veins by uniting arterioles and venules.
How is blood flow maintained?
Cardiac output
Resistance to flow
What does resistance to flow depend on?
Blood viscosity
Blood vessel diameter
Explain vascular shunting mechanism/redistribution of blood during exercise
Skeletal muscles require more O2 so more blood is redirected to them to meet demand.
Skeletal muscles = 80-85% of total blood flow during exercise
15-20% to supply remaining organs and tissues.
Define the vascular shunting mechanism
The redirecting of blood flow to areas where it is needed the most.
What is blood pressure and blood flow controlled by?
the vasomotor centre in the medulla oblongata
Define vasodilation
Widening of blood vessels to ⬆️ blood flow to capillaries
Define vasoconstriction
Narrowing of blood vessels to ⬇️ blood flow to capillaries.
Define pre-capillary sphincters
Tiny rings of muscle located at the opening of capillaries that help with blood redistribution.
When they contract blood flow is restricted.
When they relax blood flow is ⬆️.
How does training affect vasomotor control?
Arteries ⬆️ in elasticity = control of blood flow becomes more efficient.
Explain how the CCC regulates HR during exercise
CCC located in medulla oblongata of brain + stimulated by chemo,baro+proprioceptors.
CCC initiates sympathetic + parasympathetic NS to stimulate SAN.
Symp. NS via accelerator nerve to stimulate heart to beat faster during ⬆️ intensity.
Paras. NS returns HR to resting levels via vagus nerve during ⬇️ intensity.
During exercise =
- Chemoreceptors detect CO2 ⬆️ to ⬆️ HR
- Baroreceptors establish a set point for blood pressure so a ⬇️ in arterial pressure = ⬆️ HR.
- Proprioceptors detect ⬆️ in muscle movement so ⬆️ HR.
