BMSC 208 - Midterm 1

List the four major functions of the respiratory system

List the four major functions of the respiratory system

1. Exchange of gases between atmosphere and blood

2. Homeostatic regulation of body pH

3. Protection from inhaled pathogens and irritating substances

4. vocalization

What are the 3 structures involved in ventilation and gas exchange?

1. Conducting system or air ways (nasal cavity, pharynx, larynx, trachea, bronchii, bronchiole)

2. Alveoli

3. Bones and muscles of the thorax (ex. SCM, scalenes, intercostals, diaphragm, abdominal muscles)

What is the upper respiratory system?

• Anything not in thoracic cavity

• Nasal cavity, pharynx, larynx

What is lower respiratory system?

• Anything in the thoracic cavity

• Trachea, bronchii, bronchiole, alveoli

What lung is larger in size?

• Right lung

• Left is smaller due to cardiac notch

The lungs are surrounded by what structure?

Fluid filled pleural sac

What are the 2 layers of the pleural sac?

1. Visceral pleura – outside surface of lungs

2. Parietal pleura – inside surface of thoracic cavity

2 functions of pleura

1. Creates moist slippery surface (decreases friction)

2. Holds lungs tight to thoracic wall (holds lungs open)

Pathway of air through respiratory system

• Nasal cavity or mouth

• Pharynx

• Larynx

• Trachea

• Bronchus

• Bronchiole

• Alveoli

What structure is the voice box/vocal cords?

-        Larynx

What structure is the windpipe?

-        Trachea

Structure of trachea

-        Semi-flexible tube held open with 15-20 cartilage rings

How is the branching of the respiratory system similar to the CV system?

Branching increases down the respiratory system causing an increase in total cross-sectional area (even though there is a decrease in single pathway CSA)

Velocity of air flow is _________ proportional to total cross-sectional area

• Inversely

• V=Q/A

Velocity _____ as CSA increases?

-        Decreases

Velocity _______ as CSA decreases?

-        Increases

The major role of the upper airways and bronchi is?

-        Conditioning the air before it reaches the alveoli

What are the 3 ways upper airways and bronchi condition the air before reaching the alveoli?

1. Warming air to body temp

2. Adding water vapor (liquid in alveoli needed for gas exchange)

3. Filtering out foreign material (nasal hairs, shape of nasal airways causes particles to embed in mucus in back of pharynx and slide down to esophagus)

How is air filtered in the trachea and bronchi? i.e. What types of cells line the airways, what do these cells produce, and what is their function?

• Airways are lined with ciliated epithelial cells and goblet cells

• Ciliated epithelial cells produce saline

• Goblet cells produce mucus (overtop the saline) which contain immunoglobulins

• Ciliated epithelial cells push the mucus towards the pharynx (mucocilliary escalator)

Explain why saline is necessary for mucocillary escalator function?

• Cilia move the saline layer which pulls mucus layer upward towards the pharynx

• Without the saline layer, cilia would become embedded in thick mucus and unable to move

How is saline produced?

• produced by epithelial cells

• Cl- secreted into lumen by apical CFTR channel (cystic fibrosis transmembrane regulator channel)

• Secretion of Cl- creates electrochemical gradient which draws Na+ into lumen paracellularly (between epithelial cells)

• NaCl movement lumen creates an osmotic/concentration gradient, so water flows into lumen producing saline

What causes cystic fibrosis?

• CFTR channel non-functioning = reduced production of saline

• Without saline layer, cilia trapped in mucus and can no longer move

• Mucus cannot be cleared, bacteria colonize the airways, resulting in recurrent lung infections.

Alveoli are the site of?

-        Gas exchange

Where are alveoli?

-        Clustered at ends of bronchioles

Alveoli are ________ vascularized and have _______ surface area, optimal for gas exchange

• Heavily

• Huge (very short diffusion distance for increased gas exchange)

Alveoli are __% surface area

-        95%

Function of Type 1 alveolar cell

-        Gas exchange

Function of type 2 alveolar cell

-        Synthesizes surfactant

Alveolar macrophage

-        Ingests foreign material

How does air exchange occur by?

-        Bulk flow

Air exchange occurs by bulk flow and follow what 3 principles that also govern bulk flow through the CV system?

1. Flows from high to low pressure

2. Muscular pump creates pressure gradient

3. Resistance is primarily influenced by diameter of tubes (remember that viscosity and length also affect flow, however these are relatively constant in respiratory system)

What is the flow, pressure, resistance relationship?

F= ∆P/R

Pulmonary circulation has _____ flow and _____ pressure

• High

• Low

Why does pulmonary circulation have high flow?

• Low blood volume and equal CO to systemic circuit

• Cardiac output in pulmonary system = systemic circuit (this means that as much blood flows through the lungs in 1 minute as flows through the rest of the body)

• Low blood volume = greater turnover of blood

Why does pulmonary circulation have low pressure?

Due to low resistance (shorter length circuit, more distensible and larger total cross-sectional area of arterioles

What law describes the pressure-volume relationship of gasses?

• Boyles law

• P1V1=P2V2

If the volume of a container decreases, the pressure will?

-        Increase

If the volume of a container increases, the pressure will?

-        decrease

What are the muscles and their functions in quiet inspiration?

• 60-75% of inspiratory volume change is due to diaphragm contracting to move downward/flatten

• 40-25% due to movements of the rib cage

  • Pump handle: external intercostals of upper ribs and scalenes attached to sternum pull the sternum outward

  • Bucket handle: external internal intercostals of lower ribs pull ribs up and out

What are the muscles involved in quiet expiration?

• No contraction of muscles, passive process with relaxation of inspiratory muscles

• Diaphragm, external intercostals, and scalene muscle relax

What are the 4 different lung volumes?

1. Tidal volume

2. Inspiratory reserve volume

3. Expiratory reserve volume

4. Residual volume

Do lung volumes overlap?

-        NO

Tidal volume

-        Amount of air that enters/exits the lungs during quiet respiration

Inspiratory reserve volume

Additional air that could still be inspired after quiet inspiration

Expiratory reserve volume

At end of quiet expiration, the volume of remaining air that can be expired

Residual volume

The amount of air that will always remain in the lungs

Two important functions of residual volume

1. Prevents airway collapse, if collapsed would take an unusually large pressure to re-inflate it

2. Allows continuous exchange of gases

Total pulmonary ventilation

• Total ventilation during rest

• Tidal volume x frequency of breaths

What are the 4 lung capacities?

1. Total lung capacity

2. Functional residual capacity

3. Inspiratory capacity

4. Vital capacity

Total lung capacity

The sum of all 4 lung volumes (IRV, TV, ERV, RV)

Functional residual capacity

• Capacity of air remaining in lungs after quiet expiration

• ERV+RV

Inspiratory capacity

• Maximal amount of air that can be inspired after quiet expiration

• IRV+TV

Vital capacity

• Maximal achievable air moved with a single breath

• IRV+TV+ERV

Label

1. inspiratory reserve volume IRV

2. Inspiratory capacity

3. Tidal volume TV

4. Vital capacity

5. Total lung capacity

6. Expiratory reserve volume ERV

7. Functional residual capacity

8. Residual volume

Explain how pressure and lung volumes change during normal breathing and how that affects air flow in the respiratory system.

• Inspiration: alveolar volume increases resulting in decreased pressure below atmospheric pressure, resulting in air flow from the atmosphere into alveoli

• Expiration: alveolar volume decreases resulting in increased pressure above atmospheric pressure, resulting in air flow from the alveoli to the atmosphere

True or false: the lung is directly attached to the diaphragm and thoracic wall, so breathing occurs from diaphragm pulling lungs downward and ribcage outward

• False

• The lungs are attached to the pleural sac

What is the intrapleural pressure within the parietal sac

• About -3 mmHg

The lungs have a natural tendency to go inwards or outwards?

• Inwards

• They have a natural recoil

The chest wall has a natural tendency to go inwards or outwards?

-        Outwards

The natural inward recoil of the lungs and the natural outward recoil of the chest wall creates a?

• Negative intrapleural pressure

• The inspiratory muscles pull the parietal layer of pleura away from visceral layer, increasing the volume of the intrapleural cavity and thus decreasing the intrapleural pressure

True or False, the apex of the lungs are more positive in intrapleural pressure?

-        False, the apex is more negative

Explain how lungs expand in inspiration with the intrapleural cavity

• Inspiratory muscles expand chest cavity which increases the intrapleural volume

• Increase in intrapleural volume decreases to an even more negative value

• Lungs are drawn to more negative intrapleural pressure and thus expand

Fill in the blanks. Inspiration: Diaphragm and inspiratory intercostals _________. Thorax ______. Intrapleural pressure becomes _________. Lungs ________. Alveolar pressure becomes _________. Air flows _______.

• Contract

• Expands

• More Sub atmospheric (more negative)

• Expand

• Sub atmospheric (more positive)

• Into alveoli

Fill in the blanks. Expiration: Diaphragm and inspiratory intercostals ________. Chest wall _______. Intrapleural pressure _______. Lungs ______. Air in alveoli becomes _________. Alveolar pressure becomes _______. Air flows ________.

• Relax

• Recoils inward

• Becomes more positive and moves back toward preinspiration value

• Recoil toward preinspiration size

• Compressed

• Greater than atmospheric pressure

• Out of lungs

Traumatic pneumothorax

-        Puncture of parietal or visceral pleura

Spontaneous pneumothorax

-        Lung and visceral pleura rupture

The degree of lung expansion at any time is _______ to the change in pressure

-        Proportional

What is compliance?

• Stretchability

• How much any given change in pressure expands the lungs is dependent on compliance

What is elastance?

• The ability to resist being deformed

• Elastic recoil

Pulmonary fibrosis

• Formation of excess fibrous connective tissue in the lungs

• Decreased compliance, increased elastance

Emphysema

• Enzymes secreted by WBCs attack alveoli tissue causing them to merge, lose capillaries, lose surface area

• Increased compliance

• Loss of elastance

• Airway resistance

An important determinant of compliance and a major determinant of the lungs elastic recoil is the __________ at the air water interface of the airways.

-        Surface tension

What is surface tension

-        Measure of the force acting to pull a liquids molecules together at an air water interface

-        The water molecules on the fluid’s surface are attracted to other water molecules beside and beneath them but are not attracted to gases in the air at the air-fluid interface, therefore, the resultant force is downward

What direction is surface tension in alveoli?

• directed toward the center of the bubble and creates pressure in the interior of the bubble

What law is an expression of alveolar surface tension?

• Laplace

• P=2T/r

If the radius of an alveoli is small, the pressure is?

-        Greater

Increase radius = ______ alveolar pressure

• Decrease

Increase surface tension = _______ alveolar pressure

-        Increase

Decrease surface tension = _______ alveolar pressure

-        Decrease

_____ pressure is needed to keep a small bubble inflated

-        Increased

______ pressure is needed to keep a large bubble inflated

-        Decreased

What is surfactant?

-        Detergent like molecule

-        Secreted by type II alveolar cells

-        Reduces surface tension by decreasing density of water molecules

What are the 2 main functions of surfactant in the respiratory system?

1. Increases compliance

   1. a.Decreases the inward pressure, so easier to inflate

2. Ensures alveoli of all size inflate a. Smaller alveoli have more surfactant, which equalizes the pressure between large and small alveoli

What is infant respiratory distress syndrome?

• Developmental insufficiency of surfactant production and immaturity of lungs

• Prevalence decreases with gestational age

Bronchoconstriction/dilation is commonly under ______ control

-        Paracrine

What is the primary paracrine molecule that affects bronchiolar diameter?

-        Carbon dioxide

Increase CO2 in expired air leads to?

-        Bronchodilation

Decreased CO2 in expired air leads to?

-        Bronchoconstriction

_____ is a paracrine signal molecule that acts as a powerful bronchoconstrictor and is released by ____ cells.

• Histamine

• Mast

Circulating ________ binding to __ _______ receptors causes dilation

• Epinephrine

• B2

• Adrenergic

Parasympathetic nerves innervate bronchiole smooth muscle and activate _________ pathway via __ _______ receptor and cause constriction

• PLC-IP3

• M3 muscarinic

What is total pulmonary ventilation?

• Volume of air moved into and out of lungs each minute (minute ventilation)

• Total pulmonary ventilation = ventilation rate x tidal volume

• It is the effectiveness of breathing (similar to stroke volume)

What is alveolar ventilation?

• Alveolar ventilation = ventilation rate x (tidal volume – dead space)

• Amount of fresh air that reaches the alveoli

What is dead space?

• The conducting airways (trachea and bronchi) that do not exchange gases with the blood

• Some air that enters the respiratory system does not reach the alveoli because part of every breath remains in the conducting airways

Why does gas composition or PO2 and PCO2 remain relatively constant during quiet inspiration?

• Because O2 entering lungs is equal to O2 uptake

• And amount of fresh air that enters the lungs with each breath is only about 10% of total lung volume at end of inspiration

As alveolar ventilation increases (hyperventilation) alveolar PO2 ______ and PCO2 _______

• Increases (more O2 in than diffusion into blood)

• Decreases (removing CO2 more rapidly)

As alveolar ventilation decreases (hypoventilation) alveolar PO2 _______ and PCO2 ________

• Decreases (less O2 in than diffusion)

• Increases (build of CO2, exhale less)

Explain the local control mechanisms by which ventilation and perfusion are matched

• Gravity:

  • More negative intrapleural pressure at apex means alveoli are already partially open and filled even at rest, and therefor do not take in much air during ventilation

  • Apex gets less perfusion, base gets most

  • causes similar regions of lungs to receive matching ventilation and perfusion

• Regulating diameter of arterioles/bronchioles:

  • Increased PCO2 = bronchodilation, decreased PCO2 = bronchoconstriction

  • decreased PO2 = arterioles constrict

  • Constriction of arterioles diverts blood away from under-ventilated region to better ventilated parts of the lung

What is hypoxia? What is it usually associated with?

• Hypoxia: too little oxygen

• Hypercapnia: excess CO2