BI 233 - Respiratory System Lecture

The respiratory system is an organ system that takes in air rhythmically and expels it from the body to deliver ____

oxygen to tissues and remove carbon dioxide

Boyle's Law states:

the pressure of a given quantity of gas is inversely proportional to its volume (assuming constant temperature)

Charles's Law states that ____

the volume of a fixed amount of gas is directly proportional to its absolute temperature when the pressure is maintained steadily

Dalton's Law states that _____

the total pressure of a gas mixture is equal to the sum of the partial pressures of its individual gases

Henry's Law states that ____

at the air-water interface, for a given temperature, the amount of gas that dissolves in water is determined by the partial pressure of that gas in the air and by its solubility in water

The main organs apart of the respiratory system are ____

nose, pharynx, larynx, trachea, bronchi, and lungs

Alveoli sacs provide a large surface area for ____

gas exchange

Squamous (type 1) alveolar cells cover 95% of _____

alveolar surface area (but are less numerous than type II alveoli)

Squamous (type 1) alveolar cells are very thin, allowing for ____

rapid gas exchange by simple diffusion

Great (type 2) alveolar cells are round/cuboidal cells that cover the other ____

five percent of alveolar surface

Great (type 2) alveolar cells cells repair ____

alveolar epithelium

Great (type 2) alveolar cells secrete ___

pulmonary surfactants

Alveolar macrophages (dust cells) are most numerous of all cells in the _____

lungs

Alveolar macrophages (dust cells) wander lumens of ___

alveoli and connective tissue between

Alveolar macrophages (dust cells) phagocytose _____

dusts, debris, and pathogens

Alveolar macrophages (dust cells) minions (will edit) die each day as they ride up the ____

mucociliary escalator

Visceral pleura lines ___

the surface of the lungs

Parietal pleura lines ____

the mediastinum (central compartment in the thoracics), inner surface of the rib cage, and superior surface of the diaphragm

The pleural cavity is the potential space between ___

the two pleurae. Also, houses the lungs

Intrapleural pressure is the slight negative pressure (suction) that exists between ___

the two pleural membranes, usually about -5cm H2O

Atmospheric (barometric) pressure is the weight of the ___

air above us (760mm Hg at sea level, lower at higher elevations)

Intrapulmonary pressure is the air pressure within ___

the lungs (changes with lung volume)

What makes fluids passively flow from one area to another?

flow down gradient: fluids flow from an area of higher pressure to an area of lower pressure

Pulmonary ventilation requires a ____

pressure gradient

Flow (F) is proportion (∝) to the difference (Δ) in pressure (P) divided by

resistance (R)

mm Hg =

millimeter of mercury

mm Hg is used to measure ____

pressure in many contexts (including atmospheric pressure)

For respiratory flow we use ____

cm H2O

If the pressure in the pulmonary alveoli is -2cmH2O, that means that the pressure in the alveoli fell ___

2cmH2O below the ambient atmospheric pressure

Inspiration requires ____

negative intrapulmonary pressure

Contraction of breathing muscles (diaphragm and intercostals) and expansion of thoracic cavity is a requirement for what?

inspiration

Pleural pressure is a requirement for what?

inspiration

Warming of air as it reaches the alveoli (Charles's Law) is a requirement for what?

inspiration

What is the overall overview of the inspiration process?

thoracic cavity expands - diaphragm contracts - ribs and parietal pleura attached to it are pulled down and out - visceral pleura clings to the parietal pleura and is thus pulled also, taking the alveoli on the surface of the lung with it - the surface alveoli expand and pull on neighboring alveoli - the whole lung volume expands - increased volume --> decreased pressure within the alveoli (intrapulmonary/alveolar pressure gradient - as inhaled air is warmed, it expands, contributing to lung inflation - when resp muscles stop contraction, pressure equilibrium is reached and flow stops

Relaxed expiration is a ____

passive process

What is the overall overview of the expiration process?

diaphragm relaxes and thus rises - rib cage contracts - lungs are compressed (smaller volume) - intrapulmonary pressure is now positive in relation to outside - air flows out, down pressure gradient - Pause

Inhaled current of air never actually gets to the alveoli due to ____

the tiny spaces it would have to travel (resistance!)

The air current gets only to terminal bronchioles, the rest of the journey to alveoli has to be ____

[slow] simple diffusion. Same for CO2 leaving the alveoli

Our lungs never completely empty. Leftover air is called ____

residual volume

Bronchodilation can be caused by ____

epinephrine and sympathetic stimulation

Bronchoconstriction can be caused by ____

histamine, parasympathetic stimulation, CO2, cold air, and chemical irritants

Pulmonary compliance is the ease with which the lung can ___

expand

Pulmonary compliance can be reduced by ____

degenerative lung diseases (lungs are stiffered by scar tissue)

Anatomical dead space refers to ____

the portion of air in the respiratory system, typically about 150 mL, that does not participate in gas exchange

Physiological (total) dead space is the sum of anatomical dead space and ___

any pathological dead space

Alveolar ventilation rate (AVR) is the amount of ____

air ventilating alveoli per minute (total volume inhaled - volume of air in dead space) x respiratory rate

Pneumothorax refers to ___

a collapsed lung

A collapsed lung (pneumothorax) is when the air or another gas leaks out of the lungs and into ___

the pleural cavity (the space between the parietal and visceral pleura which should ONLY have serous fluid)

Alveolar surface is covered with a thin film of ____

water, for gas exchange to occur

Due to cohesion of water (result of hydrogen bonding) alveoli can collapse during ____

expiration thus decreasing pulmonary compliance

Surfactant is produced by the great alveolar cells to decrease _____

surface tension and prevent collapse of alveoli

Pulmonary surfactant is made of ____

phospholipids (and other lipids) and proteins

Partial pressure:

the separate contribution of each gas in a mixture

Example: atmospheric pressure of air is 760 mm Hg and oxygen is 20.9% of its composition, so the partial pressure of oxygen (PO2) is:

760 mm Hg × 0.209 = 159 mm Hg

Composition of inspired and alveolar air ____

differs

Air is humidified by contract with mucous membranes. Alveolar partial pressure of H2O is more than _____

ten times higher than inhaled air

Alveolar air mixes with residual air. Oxygen gets diluted and air is ____

enriched with CO2 that was part of residual volume

Alveolar air exchanges O2 and CO2 with ___

blood

Oxygen must move from the air in alveoli, across thin film of water, across the respiratory membrane into ____

the blood vessel

Oxygen must move from the air in alveoli, across thin film of water, across the respiratory membrane into the blood vessel. Carbon dioxide must do the same in _____

the opposite direction

Each gas moves by simple diffusion down its own ____

gradient

At the air-water interface, for a given temperature, the amount of gas that dissolves in water is determined by ___

the partial pressure of that gas in the air and by its solubility in water (Henry’s Law)

For gases to be loaded and unloaded into erythrocytes, the cells must spend enough time in ____

capillaries to allow this action (0.25 seconds required)

Both O2 and CO2 diffuse down their own ____

partial pressure (concentration) gradients

Blood unloads CO2 and loads O2 at the ____

alveolus

Several variables determine the rate and thus efficiency of gas exchange such as:

pressure gradients of gasses, solubility of gasses, distance needed to diffuse (membrane thickness), and ventilation-prefusion coupling

Pressure gradients of gases, normally:

PO2 = 104 mm HG in alveolar air versus 40 mm Hg in blood arriving in the lungs

PCO2 = 46 mm Hg in blood arriving versus 40 mm Hg in alveolar air

Gradients will differ at high altitude and during ___

hyperbaric oxygen therapy

Carbon dioxide is 20 times more soluble in water as ____

oxygen (oxygen is two times as soluble as nitrogen gas)

Although pressure gradient of oxygen gas is much greater, the exchange rate of carbon dioxide and oxygen is _____

the same due to solubility differences

The membrane thickness of respiratory membrane is usually ___

0.5μm

Edema thickens the layer of water and thus slows ___

exchange rate (not enough time to load)

Membrane surface area:

healthy lungs have ~70 m2, and the 100 mL of blood in alveolar capillaries is spread very thinly for efficient loading/unloading of gasses

Emphysema and lung cancer decrease ___

membrane surface area

~ 1.5% of oxygen in the blood is dissolved in ____

plasma or cytosol or RBC

Remaining oxygen is reversibly bound to ___

hemoglobin

Carbon dioxide is transported in three forms:

1. It is hydrated (reacts with water) to form carbonic acid, which dissociates into bicarbonate and protons (hydrogen ions). 90% of CO2 transported like this.

2. About 5% of CO2 binds to the amino groups of plasma proteins and hemoglobin to form carbamino compounds. CO2 does not compete for the same site as oxygen, so both can be transported.

3. 5% of CO2 is carried as dissolved gas

Blood gives up the dissolved CO2 gas and from the carbamino compounds more easily than ___

CO2 in bicarbonate when gases are exchanged in alveoli

Central and peripheral chemoreceptors monitor the composition of ____

the blood and CSF, and send information to the brainstem respiratory centers

Breathing is regulated by the ____

central nervous system, no autorhythmic pacemakers in the lungs

There are 3 pairs of respiratory centers in the _____

reticular formation of the medulla and pons

What are the three pairs of respiratory centers in the reticular formation of the medulla and pons?

the ventral respiratory group (VRG), the dorsal respiratory group (DRG), and the pontine respiratory group (PNG)

Ventral respiratory group (VRG) - sets the basic circuit for ____

the rhythm of breathing

a. inspiratory neurons

b. expiratory neurons

Dorsal respiratory group (DRG) is the main modifier of the _____

VRG due to inputs from receptors

The pontine respiratory group (PNG) modifies the length of each _____

inspiration or expiration (as opposed to the whole cycle)

Central chemoreceptors is the brainstem neurons that respond to changes in the _____

pH of the cerebrospinal fluid. The pH of the CSF reflects the CO2 level in the blood

Peripheral chemoreceptors are located in carotid and aortic bodies in the arteries above the heart and respond to ____

CO2 and O2 and pH in the blood. Glossopharyngeal and vagus nerves send the info to DRG

Stretch receptors are in smooth muscles of bronchi, bronchioles, visceral pleura and respond to ______

inflammation of the lungs and signal to DRG by vagus nerve

Irritating Receptors are nerve endings amid the epithelial cells of the airway that respond to _____

smoke, pollen, dust, chemical fumes, cold air, and excess mucus. Message via vagus nerve to DRG, which then results in shorter breaths, breath holding, bronchoconstriction.

Voluntary control of breathing originates in the ____

motor cortex of the cerebrum

Output is sent down corticospinal tracts to integrating centers in the spinal cord, bypassing the ___

brainstem centers

Holding one's breath raises CO2 to a point when ____

the automatic controls override one's will