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The Plan
• Introduction – general concepts
• Anatomy
• Mechanics – moving air into the lungs
– Structures, pressure changes
• Gas Exchange – moving air from the lungs
to blood and tissues
– Moving O2 in and CO2 out of tissues
• Control mechanisms
– Local
– CNS
1
Readings - Respiratory
• McKinley, O’Loughlin, and Bidle,
Anatomy and Physiology An integrative
Approach, p 883-931.
• Control mechanisms: nervous and others
911-915
2
Objectives
• Describe the general controls of the respiratory
system involving skeletal muscles.
• Understand local controls involving dilation and
constriction of blood vessels and bronchioles
• Explain inputs and controls involving voluntary
and involuntary centers in the CNS
• Describe the functions of the dorsal and ventral
respiratory groups
3
Controls of Respiration
cognition
Higher CNS centers
brain stem
Respiratory control center
body
respiratory
system
Respiratory Centers and Reflex Controls
spinal cord
Motor neurons
4
Control of Respiration
• How do you control respiration? – what cells
directly control inhalation & exhalation?
– Control = skeletal muscles involved in inhalation
and exhalation
• These cells control respiratory minute volume.
How do you control these cells?
– Motor neurons control skeletal muscle. Respiratory
minute volume involves the frequency and volume of a
respiratory cycle.
• Is this control voluntary or involuntary?
– Both … from several CNS control centers
5
Control of Respiration
• How does one know when control is
needed? Where do the signals originate?
– Cognitive input & input from the 5 senses
(visual, auditory, olfactory, gustatory,
touch) – function through control centers
in the brain stem
– Sensory inputs from the body also function
through control centers in the brain stem
• Chemoreceptors
• Baroreceptors
• others
6
Mechanisms that control breathing
1. Motor neurons control skeletal muscles
(diaphragm, intercostals and accessory
muscles for increased breathing)
2. ● Local controls for systemic blood flow in
arterioles. ● Local controls in the lung for
blood flow and air flow in the lung.
3. Input from (peripheral) sensory receptors:
chemo-, baro-, and proprio-receptors
4. Control centers within the CNS
7
1. Controls of
‘Respiratory’
muscles
8
Control Mechanisms & Respiration
• The distribution of gases (O2 and CO2) associated with blood
or the spaces in the lung is carefully coordinated.
• The movement of gases is influenced by:
– Partial pressures, gradients, pH, temperature, gas solubilities
– Changes in blood flow
– Changes in depth and rate of respiration
• This involves:
– responses to stimuli from a systemic (the body) location &
– excellent coordination between the respiratory and
cardiovascular systems called -
– Ventilation-Perfusion Coupling
Air/Gas
Blood flow
9
Controls: flow of a gas or liquid
•
To increase the amount of a gas or liquid, you open up the
tube – you dilate that tube …
faster
•
= vasodilate & bronchiodilate
To slow (restrict) flow of a gas or liquid, you constrict the
tube …
slower
•
= vasoconstrict or bronchioconstrict
Remember: O2 is good and CO2 is bad so …
–
•
you want to remove CO2 and bring in O2
Scenerio: muscle cells in interstitium are very active, so …
–
O2 is needed for metabolism; O2 is donated to cells so O2 in blood
decreases … also
–
CO2 is produced after metabolism and PCO2 in blood increases10
Control of gas movement in
blood or air spaces
• Constriction & dilation occurs in arterioles and
bronchioles
– these are the ‘control’ points for the cardiovascular and
respiratory systems
– because they have smooth muscles oriented around
their small lumens and their branches support many cells
• Constriction or dilation in arterioles or bronchioles
results in:
– altered blood flow through capillaries.
– altered air flow into and out of alveoli.
11
2. Controls: Systemic Gas flow in the
organ systems, eg. muscle cells
Muscle cells in interstitium are very active.
According to the partial pressure
gradients:
Systemic
capillary
- O2 is given to muscle cells for metabolism
- CO2 is being produced after metabolism and
released
In the systemic capillary:
- PO2 is decreased from 95 to 40mm Hg
- PCO2 is increased from 40 to 45mm Hg
The control Released CO2 causes smooth muscle cells around systemic
BVs to relax = vasodilation
Blood flow increases, CO2 leaves & more O2 enters via blood
12
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings
2.Controls: within the lungs
Ventilation-Perfusion Coupling
1.
Blood flow through alveolar capillaries is directed toward
2.
lung lobules where PO2 levels are relatively high and
(CO2 levels are low)
Smooth muscle cells in walls of bronchioles are sensitive
to CO2
–
Increased PCO2 causes bronchiodilation
13
Ventilation-Perfusion Coupling
Ventilation-Perfusion Coupling
 For gas exchange to be optimal in the lung, perfusion through blood
vessels has to match air compositions in the alveoli
- if alveoli are well ventilated = high O2 and low CO2 – pulmonary arterioles
dilate and blood flow is directed to that area to pick up O2.
- if alveoli are poorly ventilated = low O2 and high CO2 – pulmonary
arterioles constrict and blood flow to that area is decreased.
 Bronchiole diameter parallels CO2 levels
a. if CO2
bronchioles dilate -- CO2 and O2 enters
b. if CO2
bronchioles constrict
14
Ventilation-Perfusion Coupling
BVs
lung
= CO2 increased
Increased O2 in lungs correlates with increased blood flow = vasodilation
15
Controls: bronchioles and
arterioles in the lung
(a) Changes in bronchioles
(b) Changes in arterioles
Increase CO2 causes bronchioles to dilate and arterioles to constrict
16
3.Controls: (peripheral) sensory
information into the CNS
• Sensory Modifiers of Respiratory Center Activities
– Chemoreceptors are sensitive to PCO2, PO2, or pH of blood or
cerebrospinal fluid
– Baroreceptors in aortic or carotid sinuses are sensitive to changes in
blood pressure
• Stretch receptors respond to changes in lung volume
– Proprioceptors from the periphery – signals indicating position in
space of limbs
– Irritating physical or chemical stimuli in nasal cavity, larynx, or
bronchial tree - COUGHING AND SNEEZING
– Other sensations including pain, changes in body temperature,
abnormal visceral sensations
17
Controls of Respiration
• Chemoreceptors Peripheral
– monitors changes pH either induced by PCO2 or
independent of PCO2 (kidney failure)
– in carotid or aortic bodies (in carotid & aortic blood
vessels)
– leads to increased rate and depth of respiration
when pH goes down
• Chemoreceptors Central
– monitors changes in pH due to changes in blood
PCO2 in the CSF – sensitive to 5mm Hg change
– on ventrolateral surface of medulla oblongata
– increased blood PCO2 causes a decrease in CSF pH
– causes increased rate and depth of breathing
18
Controls of Respiration
• Baroreceptors
1. monitor blood pressure; located in carotid sinuses and aortic arch
– when blood pressure falls - respiration rate increases
2. baroreceptors in bronchioles and visceral pleura also monitor
pressure and inhibit over stretching of lungs (Hering-Breuer reflex)
• Proprioreceptors
– monitor limb position is space
– Increase breathing when body movements increase
• Irritant receptors
– coughing and sneezing – require elevated intake of breath
19
3.Controls
of the
Respiratory
System
Irritant receptors
Baroreceptors
Receptors
of other
Reflexes
Internal
Chemoreceptors
Proprioceptors
20
4. Controls
of the
Respiratory
System
Pontine
respiratory center
Dorsal Respiratory Group (DRG)
Ventral Respiratory Group(VRG)
21
4. CNS Control of Respiration
The Respiratory Center = brain stem nuclei
• Pontine respiratory system
– modifies information into the medullary center and
regulates transition from inspiration to expiration
• Medullary respiratory system
– Dorsal respiratory system (DRG)
• Receives sensory information and relays information to the VRG
– **Ventral respiratory group (VRG)
• Initiates neural impulses for quiet breathing via the the spinal
cord and the diaphragm and internal intercostal muscles
22
Controls: from the CNS
• Voluntary Controls – input from higher brain centers
– Cognition into cortex; emotions from frontal cortex; limbic system;
hypothaIamus.
• into medullary respiratory system then to motor neurons in spinal
cord OR
• directly to motor neurons that control skeletal muscles associated
with respiration
• Involuntary Controls – input into brain stem nuclei
– Input from receptors (chemo-, baro-, proprio,etc.) in the body into DRG of
the medullary respiratory system. Output to VRG
– VRG signals the motor neurons controlling skeletal muscles associated
with respiration
23
Control of
Respiration
• Ventral Respiratory Group (VRG)
- Inspiratory center – controls
diaphragm and external intercostals
- Functions in quiet and forced
breathing
• Dorsal Respiratory Group (DRG)
- relays information to VRG
24
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings
Respiratory Rhythmicity
• Quiet Breathing
– VRG (ventral respiratory group: inspiratory neurons)
activated for 2 sec.
• Stimulates motor neurons and inspiratory muscles (diaphragm
and ext. intercostals)
– VRG inspiratory neurons inactivated by VRG expiratory
neurons for 3 sec.
• Allowing passive exhalation
• Altered Breathing Rate and Depth
– Sensory inputs (chemo, baro, proprio, etc.) into DRG
– Rate varies by altering inspiration vs expiration times
– Depth varied by engaging accessory muscles
25
Control of Respiration
• SIDS (sudden infant death syndrome)
• marked by the sudden death of an infant that is not
predicted by medical history (wikipedia)
– Some evidence of a disruption of the normal
respiratory reflex pattern
– May result from connection problems between
pacemaker complex and respiratory centers
–
http://en.wikipedia.org/wiki/Sudden_infant_death_syndrome
26
Controls of the
Respiratory System
27