Exam #3 Study Guide

Respiratory

Structures of pulmonary system – NOT ON STUDY GUIDE

• Lobes (3 on right, 2 on left) - segments – lobules

• Blood vessels serve the pulmonary system

• Chest wall/thoracic cage

• Diaphragm: involved in ventilation – dome shaped muscle that separates the thoracic and abdominal cavities

• Mediastinum: space between lungs containing heart, great vessels, and esophagus

• Conducting airways

o Upper airways: warms and humifies air

▪ Nasopharynx and oropharynx

o Larynx: connects upper and lower airways

o Lower airways

▪ Trachea, bronchi, terminal bronchioles

• Carina: ridge where the trachea divides into the right and left bronchi

• Hila: where the right and left bronchi enter the lungs, along with blood and lymph vessels

• Goblet cells: produce mucus

• Cilia: hair-like structures – work with goblet cells to propel foreign material up and enable it to be coughed up

• Pleura: serous membrane – adheres firmly to the lungs and folds over itself

o Visceral: covering the lungs; Parietal: lining the thoracic cavity

o Pleural space: fluid lubricates the pleural surfaces allowing them to slide over each other

▪ Pressure in pleural space: negative (-4 to –10); keeps lungs from collapsing

▪ Inspiration – chest cage pulled outward on lungs creates greater negative pressure

Understand basic structure and function of alveoli

• Gas exchange airways: acinus - “berry”

o Respiratory bronchioles

o Alveolar ducts

o Alveoli

▪ Primary gas exchange units

▪ Oxygen enters the blood and carbon dioxide is removed

▪ Epithelial cells

• Type 1 alveolar cells: provide alveolar structure

• Type 2 alveolar cells: surfactant production – prevents lung collapse

▪ Contain alveolar macrophages: ingest foreign material and remove it through lymphatic system

Surfactant – its function and where it comes from

• Detergent like substance secreted by type 2 alveolar epithelial cells in lungs

• Keeps alveoli open and free of fluid and pathogens (collectins)

• Decrease surface tension by blocking H20 and H+ binding in alveolar space – prevents collapse – allow airflow in

more easily

Understand the mechanics of the pulmonary circulation and how it relates to systemic circulation

• Pulmonary circulation functions:

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o Facilitate gas exchange

o Deliver nutrients to lung tissue

o Acts as a blood reservoir for the left ventricle

o Serves as a filtering system that removes clots, air, and other debris from the circulation

o Pulmonary system pressure is 18 mmHg compared to systemic circulation of 90 mmHg

o Gas exchange airways are served by the pulmonary circulation

▪ Low pressure system, high flow – Supplies venous blood from all parts of the body to the

alveolar capillaries where O2 is added and CO is removed; contains 100% of CO

o Bronchi and other lung structures are served by systemic circulation – bronchial circulation

▪ High pressure system, low flow – supplies blood to trachea, bronchial tree, bronchioles, and out

coats (adventia) of pulmonary arteries and veins; contains 1-3% of CO

• Pulmonary circulation

o Begins at the pulmonary artery, which receives venous blood from the right side of the heart. The

pulmonary artery divides into the left and right branches and forms the capillaries that surround the

alveoli. After blood is oxygenated via gas exchange, blood returns to the left side of the heart through

the pulmonary veins.

• Pulmonary artery and accompanying smaller arteries and arterioles have large diameter; systemic vessels are

small

o Gives the pulmonary artery tree large compliance - accommodate stroke volume and pressure from RV

• Pulmonary capillaries surround the acinus

• Alveolocapillary membrane

o Formed by shared alveolar and capillary walls

o Contains the pulmonary capillaries

o Where gas exchange occurs

• Mechanics of breathing

o Major and accessory muscles – The major muscle of breathing is the diaphragm, which performs 80% of

the work of breathing. External intercostals function as accessory muscles to raise the ribs up and out,

often during respiratory distress.

o Alveolar surface tension –Surfactant plays a major role in alveolar surface tension, pulmonary surfactant

functions to decrease alveolar surface tension to increase lung compliance and ease the work of

breathing.

o Elastic properties of the lung and chest wall – The lung and chest wall have elastic properties that permit

expansion during inspiration and return to resting volume during expiration. Elastic recoil is the

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tendency of the lungs to return to the normal resting state after inspiration. Compliance is the measure

of the lung and chest wall distensibility. Increased compliance indicates the lungs are abnormally easy

to inflate and has lost some elastic recoil. A decrease in compliance indicates the lungs are abnormally

stiff and difficult to inflate.

o Airway resistance – Airway resistance is the resistance of the respiratory tract to airflow during

inspiration and expiration. Airway resistance is increased with bronchitis, asthma, mucous, edema, or

spasm.

o Work of breathing – The work of breathing is the amount of work that must be performed to overcome

the elastic and resistive properties of the lung, determined by lung recoil, chest wall recoil, and surface

tension of the alveoli

• Lymphatics

o Lymph vessels present in all supportive tissues of the lung

o Particulate material entering the alveoli is partly removed by the lymph channels – plasma protein

leaking from lung capillaries is removed from lung tissue

▪ Helps prevent pulmonary edema and supports the negative pressure in the lungs to help them

from collapsing – sucking motion

Understand the role of the ANS on the pulmonary system

• Phrenic nerve (c3-c5) innervates the diaphragm

o Receives voluntary and involuntary respiratory messages from CNS

• Respiratory center

o Located in the brainstem

o Dorsal respiratory group: sets the basic automatic rhythm

▪ Receives impulses from peripheral chemoreceptors in the carotid and aortic bodies – detects

the PaCO2 and the amounts of oxygen in the arterial blood

o Ventral respiratory group: contains inspiratory and expiratory neurons

▪ Becomes active when increased ventilatory effort is required

o Pneumotaxic and apneustic centers: are located on the pons

▪ Modifiers of the inspiratory depth and rate are established by the medullary centers

• Brainstem receives feedback

o Carbon dioxide and hydrogen

▪ Increased blood CO2 or H+ (decreased pH – acidic) stimulate brainstem respiratory centers to

increase respiration to allow blowing off CO2 and decrease blood acidity

▪ Increased CO2 and H+ (decreased pH– acidic) stimulate increased firing of aortic and carotid

bodies (peripheral chemoreceptors) -relay messages to brainstem via CN9 and CN10 to increase

respiration

o Oxygen

▪ Decreased PaO2; carotid and aortic bodies increase signaling to brainstem

o Exercise

▪ Motor cortex send direct innervation to stimulate brainstem

▪ Proprioceptive info from contracting skeletal muscle or nerve impulses generated locally for

skeletal hypoxia return to brainstem to stimulate respiratory center

o Hering-Breuer inflation reflex

▪ Stretch receptor in bronchiolar and bronchial tree send inhibitory impulses to brain stem that

limit excessive inspiration

• Central chemoreceptors

o Reflects PaCO2

o Stimulated by H+ (pH) in CSF – low pH/acidosis

o Increases respiratory rate and depth

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• Peripheral chemoreceptors

o Located in the aorta and carotid bodies

o Stimulated by hypoxia (PaO2)

o Responsible for all the increase in ventilation that occurs in response to arterial hypoxemia

Understand perfusion and ventilation and how it relates to each other, shunting

• Ventilation: amount of air getting to the alveoli

o Minute volume = RR x TV – normal is 6L/min

o Alveolar ventilation: how much air is getting to parts where gas exchange takes place – normal is 4.2L

min – accounts for dead space (150 mL)

▪ ABG – PaCO2

• Perfusion: amount of blood being sent to the lungs

• Normal V/Q ratio = 4L/min ventilation and 5L/min perfusion – 4/5 = 0.8

o Perfusion exceeds ventilation in the bases of the lungs because of gravity – lower ratio

▪ Low PaO2 and high PaCO2

o Ventilation exceeds perfusion in the apices of the lungs – higher ratio

▪ High PaO2 and low PaCO2

o Changes will change normal ratio – can be physiologically controlled

▪ Just by standing up! - V/Q mismatch

• Shunting – steps taken to normalize the ratio, control perfusion, increase efficiency

o Hypoxic (pulmonary artery) vasoconstriction

▪ V/Q ratio is low (too little ventilation or too much blood)

▪ Causes blood coming into the area to be directed to other parts of the lung

▪ Decreases the perfusion of the hypoxic region will raise the V/Q ratio and bring the arterial

blood gases closer to what we expect

▪ Most important cause: low alveolar partial pressure of oxygen (PaO2); also caused by acidemia

and inflammatory mediators

o Bronchoconstriction

▪ V/Q ratio is high (too much ventilation or not enough blood)

▪ Causes bronchi to constrict slightly to increase the resistance and decrease the amount of

ventilation coming into an area that is not well perfused

▪ Limits the amount of alveolar dead space that occurs and minimizes the ‘wasted work’

How is oxygen and carbon dioxide most commonly found in the body

• Oxygen delivery

o Ventilation of the lungs

o Diffusion of oxygen from the alveoli into the capillary blood

o Perfusion of systemic capillaries with oxygenated blood

o Diffusion of oxygen from systemic capillaries into cells

• Carbon dioxide removal

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