Anatomy Lecture 13/14 Part 2 (II)

respiratory cycle

one complete breath, inspiration and expiration

quiet respiration

breathing while at rest; effortless and automatic

forced respiration

deep or rapid breathing, such as during exercise or playing an instrument

flow of air in and out of lung depends

on a pressure difference between air within lungs and outside body

respiratory muscles do what…

change lung volumes and create differences in pressure relative to the atmosphere

what are the principal muscles of respiration?

diaphragm and intercostal muscles

diaphragm

prime mover of respiration; accounts for 2/3 of airflow

what does contraction of the diaphragm do?

flattens it towards the abdomen, enlarging thoracic cavity and pulling air into lungs

what does relaxation of the diaphragm do?

allows it to buldge upward towards the thoracic cavity, compressing the lungs and expelling air

internal and external intercostal muscles

assist diaphragm; located between ribs; contribute to enlargement and contraction of thoracic cage; add about 1/3 of the air that ventilates the lungs

accessory muscles of respiration act mainly

in forced respiration

deep inspiration also uses

the sternocleidomastoid, scalenes, pectoralis minor, and serratus anterior

normal quiet inspiration

active process using the diaphragm and external intercostal muscles

normal quiet expiration

energy saving passive process achieved by the elasticity of the lungs and thoracic cage; as inspiration muscles relax, structures recoil to original shape and original size of thoracic cavity; results in airflow out of lungs

forced expiration

greatly increased abdominal pressure pushes viscera up against diaphragm increasing thoracic pressure, forcing air out; rectus abdominis, internal intercostals, and external oblique

neural control of breathing

depends on repetitive stimulation of skeletal muscles from brain and will cease if spinal cord is severed high in neck

breathing is controlled at two levels of brain:

cerebral and conscious vs unconscious and automatic

brainstem respiratory centers

automatic, unconscious breathing is controlled by respiratory centers in the medulla oblongata and pons

what are the two pairs of respiratory centers in the medulla oblongata?

ventral respiratory group and dorsal respirtory group

ventral respiratory group

primary generator of the respiratory rhythm; reverberating circuits of inspiratory neurons and expiratory neurons, produces a respiratory rhythm of 12 breaths per min

dorsal respiratory group

functions in both quiet and forced breathing, modifies the rate and depth of breathing by affecting VRG

both VRG and DRG receive input from…

external sources → pons, medulla, receptors in lungs, and higher brain centers

central chemoreceptors

brainstem neurons that respond to changes in pH of cerebrospinal fluid; regulate respiration to maintain stable pH; ensures stable CO2 levels in blood

what does the pH of cerebrospinal fluid reflect.

the CO2 level in the blood (lower the pH, the more CO2 in blood)

peripheral chemoreceptors

located in carotid and aortic bodies; respond to the O2 and CO2 contents in blood and pH of blood

stretch receptors

in smooth muscle of bronchi and bronchioles, and in visceral pleura; respond to inflation of lungs

inflation (Hering-Breuer) reflex

triggered by excessive inflation; protective reflex that inhibits inspiratory neurons and stops inspiration to stop excessive inflation/stretching of lung tissue

irritant receptors

nerve endings amid the epithelial cells of the airway; respond to smoke, dust, pollen, chemical fumes, cold air, and excess mucus

what do irritant receptors trigger?

bronchoconstriction, shallower breathing, apnea, or coughing

where does voluntary control over breathing originate?

the motor cortex of the frontal lobe of the cerebrum; sends impulses down corticospinal tracts to respiratory neurons in spinal cord, bypassing brainstem

breaking point

when CO2 levels rise to a point where automatic controls override one’s voluntary will

respiratory airflow is governed by…

the same principles of flow, pressure, and resistance as blood flow

blood flow

the flow of a fluid is directly proportional to the pressure difference between two points; the flow of a fluid is inversely proportional to the resistance

atmospheric (barometric) pressure

the weight of the air above us; lower at higher elevations

intrapulmonary pressure

air pressure within lungs; changes with lung volume according to Boyle’s law

Boyle’s law

governs air flows into and out of the lungs: at a constant temperature, the pressure of a given quantity of gas is inversely proportional to its volume (P= 1/V)

if lungs contain a quantity of gas and the lung volume increases,

their internal pressure (intrapulmonary pressure) falls

if the pressure falls below atmospheric pressure…

air moves into the lungs

if lung volume decreases…

intrapulmonary pressure rises

if the pressure rises above atmospheric pressure…

air moves out of the lungs

during inspiration…

the lungs expand and follows the expansion of the thoracic cage because of intrapleural pressure

intrapleural pressure

the slightly negative pressure that exists between the two pleural layers

recoil of lung tissue and tissues of thoracic cage…

causes lungs and chest wall to be pulling in opposite directions

how do layers of the pleura stay together?

cohesion of water

as the alveoli increase in volume…

the intrapulmonary (alveolar) pressure drops below atmospheric pressure

charles’s law

the volume of a gas is directly proportional to its absolute temperature

expiration

passive process in quiet expiration; achieved mainly by elastic recoil of thoracic cage; recoil compresses lungs; raises intrapulmonary pressure

the intrapleural pressure in both inhalation and exhalation…

is always negative

pneumothorax

presence of air in pleural cavity; thoracic wall in punctured; inspiration sucks air through the wound into the pleural cavity

what happens to the potential space in pneumothorax?

becomes an air-filled cavity causing the loss of negative intrapleural pressure allows lungs to recoil and collapse

atelectasis

collapse of part or all of a lung; can also result from an airway obstruction as blood absorbs gases from the alveoli cause a decrease in alveolar volume and subsequent alveolar collapse

other atelectasis causes

lung tumor, aneurysm, swollen lymph node, aspirated objected into airways

what two factors influence airway resistance?

bronchiole diameter and pulmonary compliance

bronchodilation

increase in diameter of bronchus or brinchiole

pulmonary compliance

ease with which the lungs can expand; change in lung volume relative to a given pressure change

how is compliance reduced?

degenerative lung diseases in which the lungs are stiffened by scar tissue (tuberculosis, black lung disease)

how is compliance increased?

emphysema (easier to expand and inhale, harder to exhale, trapping more air in the lungs)

how is compliance limited?

the surface tension of water film inside alveoli

what does surfactant do with surface tension?

secreted by great cells of alveoli disrupts hydrogen bonds between water molecules and thus reduces the surface tension, making them easier to fill with air

infant respiratory distress syndrome

premature babies lacking surfactant are treated with artificial surfactant until they can make their own

anatomical dead space

no gas exchange; can be altered somewhat by sympathetic dilation

spirometry

measuring pulmonary ventilation; aids in diagnosis and assessment of restrictive and obstructive lung disorders

restrictive disorders

reduction in pulmonary compliance, limit how much lungs can inflate; any disease that produces pulmonary fibrosis

examples of restrictive disorders

black lung disease and tuberculosis

obstructive disorders

interfere with airflow by narrowing or blocking the airway; make it harder to inhale or exhale a given amount of air

examples of obstructive disorders

asthma and chronic bronchitis

emphysema combines

elements of both restrictive and obstructive disorders

eupnea

relaxed, quiet breathing

apnea

temporary cessation of breathing

dyspnea

labored, gasping breathing; shortness of breath

hyperpnea

increased rate and depth of breathing in response to exercise, pain, or other conditions

hyperventilation

increased pulmonary ventilation in excess of metabolic demand

hypoventilation

reduced pulmonary ventilation leading to an increase in blood CO2

kussmaul respiration

deep, rapid breathing often induced by acidosis, diabetes-related ketoacidosis

dalton’s law

total atmospheric pressure is the sum of the contributions of the individual gases

partial pressure

the separate contribution of each gas in a mixture

why does composition of inspired and alveolar air differ?

air is humidified by contact with mucous membrane, alveolar air mixes with residual air, and alveolar air exchanges O2 and CO2 with blood

air is humidified by contact with mucous membrane

alveolar PH22O more than 10 times hgiher than inhaled air

alveolar air mixes with residual air

oxygen gets diluted and air is enriched with CO2

alveolar air exchanges O2 and CO2 with blood

PO2 of alveolar air is about 65% that of inspired air; PCO2 is more than 130 times higher

alveolar gas exchange

the movement of O2 and CO2 across the respiratory membrane

air in the alveolus is in contact with…

a film of water covering the alveolar epithelium

for oxygen to get into the blood…

it must dissolve in this water and pass through the respiratory membrane separating the air from the bloodstream

for carbon dioxide to leave the blood…

it must pass the other way and then diffuse out of the water film into the alveolar air

gases diffuse down their own gradient until…

the partial pressure of each gas in the air is equal to its partial pressure in water

henry’s law

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

the greater the PO2 in the alveolar air…

the more O2 the blood picks up

since blood arriving at an alveolus has a higher PCO2 than air…

it releases CO2 into the air

what is the efficiency of the unloading of CO2 and loading of O2 dependent on?

how long an RBC stays in alveolar capillaries

each gas in a mixture behaves…

independently (one gas does not influence the diffusion of another)

variables affecting alveolar gas exchange efficiency

pressure gradients, solubility, membrane surface area, membrane thickness, ventilation-perfusion coupling

pressure gradients of the gases

differ at high altitude and hyperbaric oxygen therapy; high elevations → partial pressures of all atmospheric gases are lower; pressure gradient for oxygen is lower so less diffuses into blood

hyperbaric oxygen therapy

treatment with oxygen at greater than 1 atm of pressure; larger gradient, so more oxygen diffuses into the blood

what is hyperbaric oxygen therapy used to treat for?

gangre, carbon monoxide poisoning

solubility of gases

CO2 is 20x more soluble than O2; equal amounts of CO2 and O2 are exchanged across the respiratory membrane because CO2 is more soluble and diffuses more rapidly

membrane surface area

100 mL of blood in alveolar capillaries, spread thinly over 70m2

what decreases surface area for gas exchange?

emphysema, lung cancer, and tuberculosis

membrane thickness

respiratory membrane only 0.5um thick, presents little obstacle to diffusion; when thicker, gases have farther to travel between blood and air and cannot equilibrate fast enough to keep up with blood flow

what cause the thickening of the respiratory membrane?

pulmonary edema and pneumonia

ventilation-perfusion coupling

air flow and blood flow are matched to each other; gas exchange requires both good ventilation of alveolus and good perfusion of the capillaries