Exercise Physiology Exam 3

Where is the cardiovascular control center located?

The pons and medulla

What is the vasomotor center?

The 4 areas of the medulla that are vital for cardiovascular control

What are the 4 areas of the medulla that are vital for cardiovascular control?

1. Pressor area

2. Depressor area

3. Cardioacceleration center

4. Cardioinhibitory center

What is the function of the pressor area of the medulla?

Induces vasoconstriction to raise BP

What is the function of the depressor area of the medulla?

inhibits nerves that cause vasoconstriction in order to decrease BP

-BP falls because vasoconstrictor tone is reduced

What is the function of the cardioacceleration center of the medulla and when is it activated?

increases HR

-activated when pressor area is stimulated

What is the function of the cardioinhibitory center of the medulla?

Associted with vagus nerve activity

decreases HR

What is the function of the anterior hypothalamus?

controls vasodilation of skin vessels for temp regulation

What is the function of the posterior hypothalamus?

vasoconstriction in response to a drop in body temp

Where does the cardiovascular control center receive input from to determine the level of Q and peripheral resistance during exercise?

- Central command

- Hypothalamus

- Baroreceptors

- Chemoreceptors

- Muscle afferents

Where are baroreceptors located?

- Heart

- Major arteries especially carotid sinus and aorta, and pulonary vessels

What is the function of baroreceptors?

senses stretch/pressure and in respone signals back to Cardiovascular control center affecting

- Heart rate

- cardiac contractility

- vascular resistance and compliance

(CO provides the pressure/stretch)

*INVOLVED IN THE REGULATION OF BP

What do arterial baroreceptors stimulate the release of when BP is low?

vasopressin and vasoconstrictor hormone

(when BP low baroreceptor activity decreases stimulating the release of these hormones)

How does the baroreceptor set point change at the start of exercise and why is this beneficial?

At the start of exercise baroreceptor set point increases stimulating an increase in HR and blood pressure

- this is beneficial as it prevents baroreceptors from firing too soon and dampening the increase in CO needed to deliver oxygen to working muscles

How does training affect baroreceptor set-point and why is this beneficial?

The baroreceptor set point is higher in trained humans

- allows for the increase in HR and CO needed to deliver oxygen to working muscles

How do baroreceptors regulate blood pressure?

baroreceptors establish a BP set point to maintain homeostasis

If pressure increases the baroceptors fire and send impulses to the CVCC to reduce sympathetic tone in order to lower BP (decreases HR and TPR)

If pressure drops baroreceptors sense this and trigger an increase in sympathetic tone

(increases HR -> increases CO

which increases BP, also increases TPR which increases BP)

When does baroreceptor activity decrease?

once BP is back to the set point

How do baroreceptors effect skeletal muscle circulation?

By inhibitinh the CVCC pressor area stimulating vasodilation when BP increases and vasoconstriction when BP decreases

Where are chemoreceptors located?

Aorta and carotid arteries

What is the function of chemoreceptors?

repond to decreased PO2, Decreased pH, and increased PCO2 and sends impulses to the pressor area of the CVCC

(increases vasoconstriction and BP)

What causes the drive to breathe?

high PCO2 levels

(hyperventilation blows off CO2)

Where are the muscle afferents located?

skeletal muscle

What is the fuction of the muscle afferents?

Send signals to the CNS regarding the metabolic status of the muscle

Helps balance blood flow to muscles and maintenance of BP

(tells brain whats going on at muscle level/ metabolic status)

How many types of muscle afferents are there?

4

What types of muscle afferents affect cardiovascular function?

III and IV

(I and II are not involved with cardiovascular function)

What are the properties of type I and II muscle afferents?

highly myelinated fibers

involved in CNS activity

No effect on cardiovascular funciton

What stimulates Type III and IV muscle afferents?

stimulated by mechanical (muscle contraction), thermal (increase in heat), and chemical (pH) stimuli to send signals to the CVCC to increase BP via an increase in HR

What is the function of type III and IV muscle afferents?

signal CVCC to increase BP by increasing HR

(limits vagus nerve and increases sympathetic response)

also increases the strength of myocardial contraction (increases CO and BP) and vasoconstricts blood vessels (splenic region and non-active muscle)

How do type III and IV muscle afferents increase BP?

- increases HR (CO)

-increases strength of contraction (CO)

- increases vasoconstriction (TPR)

Why do type III muscle afferents respond very quickly while Type IV take longer?

Type III respond quickly because they are stimulated by muscle contraction

Type IV respond slower because they respond more to chemical stimuli such as, potassium and decreased pH, which take longer

Why are muscle afferents (type III and IV) very important in regulating cardiovascular control during exercise?

They tell the brain more blood flow is needed and where it has to go

Where are type III and IV most active?

In working muscle

-not very active in "inactive muscle" fire much more in working muscle

(ex: if on a run they are more actie in legs than arms)

What is the overall goal of cardiovascular control during (dynamic) exercise?

supply blood to working muscles and maintain BP (central component is CO which is primarily regulated by SV)

What are the steps that occur under cardiovascular control during exercise? (11)

1. Start of exercise, central command stimulates the CVCC

(increase HR, Increase strength of cardiac contraction and regional vasoconstriction)

2. Vagus tone decreases

(HR and BP increase)

3. muscle pump facilitates venous return to the heart

(increases SV which increases CO which increases BP)

4. Baroreceptor set point is raised

(results in CVCC stimulation to increase HR, strength of contraction, and vasoconstriction)

5. Hypothalamus stimulated by raise in body temp (stimulates CVCC and vasodilation to skin and sweat to cool)

6. Type III muscles are stimulated by contraction and stretch (stimulates CVCC)

7. release of catecholamines from adrenal glands (Increases HR and force of contraction, vasodilates working muscle blood vessels for greater perfusion)

8. Sympathetic stimulation produces vasoconstriction (cardiovascular triage)

9. local changes in metabolism stimlates vasodilation and increased muscle blood flow (increases perfusion to accomodate increased CO)

10. As intensity increases the activity of type III and IV muscle afferents increase (stimulates vasoconstriction in active muscle to maintian BP)

11. As exercise continues, signals from central command, the CVCC, hypothalamus, baroreceptors, chemoreceptors, and muscle afferents ate balanced

How does the baroreceptor during rest compare to during exercise and why is this important?

The threshold is higher during exercise than rest

- important bc we need a higher CO to provide oxygen to working tissues and a higher BP for greater perfusion of working tissues

What are the 4 causes for the upper limit to oxygen consumption during maximal exercise (VO2max)?

1. the respiratory system and limitations to pulmonary function

((a-v)O2 diff)

2. the heart and its capacity to pump blood

(LIMITING FACTOR- SV)

3. the peripheral circulation and extent to which blood vessels of active muscle can vasodilate and receive blood without an excessive rise in BP

(not limiting)

4. The metabolic capacity of the active tissues namely the oxidative capacity of the mitochondrial enzymes

(not limiting)

Why does addition of more active tissue during exercise at VO2max cause no further increase in Q or oxygen uptake?

the heart cannot provide enough blood flow for all the muscles which results in blood redistribution

(ex: running at max intenstiy and adding bicep curls will not increase oxygen uptake only take blood away from legs)

What exercise uses 100% of muscle mass?

none

VO2max in humans is acheived by intense activation of only about 50% of the total muscle mass

How is total vascular conductance and arterial pressure maintained when aditional muscles are activated at VO2max?

By vasoconstriction in active muscle NOT increased blood flow

- closed system

(evidence for Q being primary limitation to oxygen uptake)

What is evidence for Q being the primary limitation to oxygen uptake?

The capacity of the muscles to consume oxugen each minute far exceeds what the heart can deliver

(heart is the limitation, limited by max HR and max SV)

What happens if someone is doing a single-leg exercise at VO2max and they add in their other leg?

single leg blood flow is reduced as the body shunts blood from one leg to the other

What is the prime function of respiration?

To allow oxygen to move from the air into the venous blood and carbon dioxide to move out

What does Fick's law of diffusion state?

The amount of gas that moves across a sheet of tissue is proportional to the area of the sheet but inversely proportional to its thickness

(want big surface area and thin walls)

How do oxygen and carbon dioxide move between air and blood?

simple diffusion

-from high to low partial pressure

The rate of gas diffusion in the airways is_____ and the distance covered is ______.

rapid, short

what is resting CO?

5 L/min

What is tidal volume?

Normal breathing

What is functional residual capacity?

The volume of gas in the lung after normal expiration

What is vital capacity?

Maximal expiration following maximal inspiration (NOT total lung volume)

What is residual volume?

Gas that remains in the lung after a maximal expiration

Total lung capacity- vital capacity= residual volume

How is ventilation affected prior to beginning exercise?

Ventilation starts to increase in anticipation for exercise

How is ventilation affected during the first 30 seconds of exercise and why is it important?

at the start of exercise ventilation rises rapidly within the first 30 sec

(this big initial increase in ventilation is needed to accomodate the increase in CO driven by the increase in HR

-we need to oxygenate that CO)

When does the rapid increase in ventilation begin to slow?

After ~ 2 min the rapid rise in ventilation stops and ventilation rises slowly thereafter

When does ventilation plateau?

over 4-5 min during SUBMAXIMAL exercise

(during maximal exercise ventilation continues until either maximal voluntary ventilatio or point of fatigue is reached)

What is resting pulmonary blood flow equal to?

resting CO

What neural-humoral factors control ventilation during exercise?

change in pH, change in temp, neural factors

What 3 factors does ventilation VOLUME depend upon?

1. work rate (intensity)

2. training status

3. muscle group used

How does training affect ventilatory volumes reached during exercise compared to ventilation rates in trained vs untrained individuals?

Trained: higher ventilatory volume reached, lower ventilatory rate

untrained: lower ventilatory volume reached, higher ventilatory rate

When is ventilation (rate) higher in untrained vs. trained individuals?

ventilation is higher in untrained vs. trained individuals for a given absolute and relative workload REGARDLESS OF MUSCLE MASS INVOLVED

Why does Ventilation increase during exercise?

due to an increase in both tidal volume and breathing frequency

How much can both tidal volume and breathing frequency increase from rest to exercise?

several fold

How does intensity impact the increase in tidal volume compared to breathing frequency?

at low relative intensity both increase proportionally

at high relative intensity tidal volume plateaus and increases in Ve are due to breathing frequency

How is VE calculated?

tidal volume X breathing frequency

What causes the increase in tidal volume and how is this affected by intensity?

at the start of exercise the increase in tidal volume is due to decreases in both Inspiratory reserve volume and expiratory reserve volume

at high intensity and Ve, ERV levels off and further increases are due to further decreases in IRV

What drives the increase in breathing frequency eith exercise?

reduction in both inspiratory and expiratory times

What neural factors control/regulate ventilation?

Three basic elements of respiratory control

1. SENSORS which gather information and feed it to

2. CENTRAL CONTROLLER in the brain which processes the information and sends impulses to the

3. EFFECTORS (RESPIRATORY MUSCLES) which cause ventilation

Where does the auromatic process of breathing originate?

in impulses that come from the brainstem

What are inspiration and expiration controlled by?

neurons located in the pons and medulla

(this area has been designated the respiratory centers)

What are the three main groups of neurons responsible for inspiration and expiration?

1. medullary respiratory center

2. apneustic center

3. pneumotaxic center

Where is the medullary repiratory center located?

in the reticular formation of the medulla

What are the two distinct areas of the medullary respiratory center and what do they control?

cells in the dorsal region of the medulla (dorsal respiratory group) are mainly for inspiration

cells in the ventral area of the medulla (vental respiratory group) are mainly for expiration

Where is the apneustic center located?

the lower pons

What is the function of the apneustic center?

Impulses from this center have an excitatory effect on the inpiratory area of the medulla (dorsal area)

*drives inspiration

Where is the pneumotaxic center located?

upper pons

What is the function of the pneumotaxic center?

this center inhibits inspiration and thus regulates inpiratory volume and inspiratory rate

What other parts of the brain can alter the pattern of breathing in states such as rage and fear?

Cortex, limbic system, and hypothalamus

What are the muscles of respiration?

-diaphragm

-intercostals muscles

-abdominal muscles

-accessory muscles such as sternomastoids

What is responsible for making sure these various muscle groups work together in a coordinated manner?

the central controller

(it is critically important they all work in a coordinated manner)

What is a chemoreceptor?

a receptor that responds to change in the chemical composition of the blood and other fluid

Where are the most imprtant chemoreceptors involved in the minute-by-minute control of ventilation located?

near the ventral surface of the medulla

(near the area involved in the control of expiration)

How does local application of H or dissolved CO2 in the ventral surface of the medulla (where central chemoreceptors are located) affect respiration?

stimulates breathing within a few seconds

What do the central chemoreceptors in the brain respond to and what are they surrounded by?

surrounded by brain extracellular fluid and respond to changes in its H concentration

-an increase in H stimulates respiration and a decrease inhibits it

What determines the composition of the extracellular fluid around the central chemoreceptors in the brain?

the composition of the extracellular fluid around the receptors is governed by the cerebrospinal fluid (CSF), local blood flow, and local metabolism

-CSF is the most important

What happens to central chemoreceptors when blood PCO2 rises?

CO2 diffuses into the CSF from cerebral blood vessels, liberating H ions which stimulate chemoreceptors

(stimulating respiration)

How does CO2 level in the blood regulate ventilation?

primarily by its effect on pH of the CSF

(drive to breathe driven by CO2 due to a decrease in CSF ph)

How does hyperventilation affect PCO2 of blood and therefore the CSF?

hyperventilatio reduces PCO2 in the bood and therefore the CSF

(also increases pH)

Where are peripheral chemoreceptors located?

carotid and aortic bodies

(above and below the aortic arch)

What do peripheral chemoreceptors respond to?

decreases in arterial PO2 and pH, and increases i PCO2

(low PO2, high PCO2 = increased ventilatory rate)

*RESPOND ALMOST IMMEDIATELY

What chemoreceptors are responsible for all the increases in ventilation that occurs in response to arterial hypoxemia (reduced PO2)?

Peripheral chemoreceptors

Which chemoreceptor is more responsive to PO2 levels? What about PCO2 levels?

Only peripheral receptors respond to PO2

While both respond to PCO2, the response of central chemoreceptors is much more important

What are the 4 other receptors that effect respiration (besides chemoreceptors)?

1. nose and upper airway receptors

2. Joint and muscle receptors

3. Gamma System

4. Pain and temperature

How do the nose and upper airway receptors affect respiration?

They respond similar to irritant receptors

How do joint and muscle receptors affect respiration?

impulses for contracting muscle stimulus to ventilation during exercise especially in early stages

How do gamma system receptors affect respiration?

many muscles including intercostals muscles and diaphram, contain muscle spindles wich sense elongation of the muscle

this info is used as a reflex to control strength of contraction

How do pain and temperature receptors affect respiration?

stimulation of afferent nerves can change ventilation

pain often causes a period of apnea (temporary cessation of breathinh) followed by hyperventilation

temp changes (like heating the skin) can cause hyperventilation

Overall what is the effect of exercise on ventilation?

Ve increases promptly and during strenuous exertion may reach very high levels

How does ventilation relate to O2 and CO2 during exercise?

THe increase in ventilation closely matches the increase in O2 uptake and CO2 output

How does exercise affect arterial pH?

Arterial pH will remain nearly constant for moderate exercise, and falls during heavy exercise due to lactic acid

What is responsible for the sharp rise in ventilation during the first few seconds/min of exercise?

Joint and muscle receptors

(takes time for chemical changes to occur)

passive movement of limbs stimulates ventilation resulting from joint and muscle receptors

What 4 factors stimulate increases in Ve during exercise?

-movement stimulates joint and muscle receptors

-slight oscillations in arterial PCO2 and PO2 can stimulate peripheral chemoreceptors even though mean levels remain unchanged

-increased body temp during exercise

-impulses from the motor cortex