respiratory system

human anatomy and physiology lecture 14

functions of the respiratory system

• moves air to and from surfaces of lungs

• provides an extensive surface area for gas exchange between the air and the circulating blood

• protects respiratory surfaces from dehydration, temperature changes, environmental variations and defense against pathogens

• producing sounds involved in communication

• facilitating the detection of olfactory stimuli

anatomical organization of the respiratory system

upper respiratory system above the larynx, lower respiratory system below and including the larynx

structures of the upper respiratory system

nose, nasal cavity, pharynx

structures of the lower respiratory system

larynx, trachea, bronchi terminal and respiratory bronchioles, alveoli

structures of the conducting zone of the respiratory system

nose, nasal cavity, pharynx, larynx, trachea, bronchi, terminal bronchioles

structures of the respiratory zone of the respiratory system

respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli

direct path from larynx to alveoli

larynx → trachea → primary bronchi → secondary bronchi → tertiary bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli

conducting zone

• includes passageways which are rigid conduits for gas exchange

• acts to cleanse, humidify, and warm incoming air

respiratory zone

site of gas exchange

olfactory epithelium

specialized tissue located on the roof of the nasal cavity, contains olfactory receptor cells that detect the stimulus of smell

air filtration in conducting zone

• nasal conchae/turbinate bones create turbulence in air, suspending dust particles

• pseudostratified ciliated columnar epithelium filters the air

air warming in conducting zone

blood vessels in the mucus membrane warm the incoming air

air humidification in conducting zone

mucus secreted on the membrane humidifies incoming air

pharynx

chamber shared by digestive and respiratory systems, extending from internal nares to entrances to larynx and esophagus

sections of the pharynx

• nasopharynx

• oropharynx

• laryngopharynx

larynx

cartilaginous structure that surrounds the glottis

glottis

narrow opening leading to the trachea

vocal cords

open and close the glottis and produce sound as passing air makes them vibrate

epiglottis

folds back as the larynx is elevated during swallowing, preventing entry of food and liquids into the respiratory tract

mucociliary escalator

cilia on pseudostratified columnar ciliated epithelial cells from the nasal cavity to the smaller bronchi sweep mucus with dust particles trapped in it towards the upper respiratory tract

metaplasia

transition from pseudostratified columnar cells to stratified squamous cells due to damage

tracheal cartilages

strengthen and protect airway and maintain it open, discontinuous where trachea contacts esophagus

bronchioles

have no cartilage, dominated by smooth muscle controlled by autonomic nervous system

bronchodilation

dilation of bronchi and bronchioles caused by sympathetic autonomic nervous system, reduces resistance and increases airflow

bronchoconstriction

constriction of the bronchi and bronchioles caused by the parasympathetic autonomic nervous system or histamine release, increases resistance and decreases airflow

changes from conducting zone to respiratory zone

• passageway diameters decrease

• cartilage rings become irregular and eventually disappear

• epithelium changes from pseudostratified, to simple cuboidal, to simple squamous

• mucus coating gradually thins

• ciliated and mucosal cells eventually disappear

• smooth muscle disappears in respiratory zone

bronchopulmonary segment

portion of lungs with its own bronchus and artery

pulmonary lobule

alveolar ducts, alveolar sacs, and alveoli, connected to a stalk (respiratory bronchiole)

lung tissue

does not contract, but its elasticity allows it to change shape

visceral pleura

membrane directly on the outer surface of lung tissue

parietal pleura

membrane attached to the inner wall of the thoracic cavity

pleural cavity

fluid-filled space between the visceral and parietal pleura

inhalation

air is drawn into the lungs

exhalation

air is expelled from the lungs

thoracic cavity

closed, contains two lungs

intrapulmonary cavity

air-filled alveoli where pressure fluctuations drive air in and out

muscles contracted during normal ventilation

diaphragm and external intercostal muscles contract during normal inhalation

tidal volume

amount of air moved in and out of lungs in a single normal respiratory cycle

normal ventilation

characterized by the use of only the diaphragm and external intercostal muscles

dorsal respiratory group (DRG)

• controls normal ventilation

• inspiratory center only

• receives input from baroreceptors and chemoreceptors

accessory muscles recruited for forced inhalation

sternocleidomastoid and serratus anterior

accessory muscles recruited for forced exhalation

internal intercostal muscles and rectus abdominis

inspiratory center of the ventral respiratory group (VRG)

• activated at the same time as the DRG during forced breathing

• receives input from mechanoreceptors in the alveoli that sense loss of tension when lungs deflate below tidal volume

• turns off the VRG expiratory center

expiratory center of the ventral respiratory group (VRG)

• active while the DRG rests

• receives input from mechanoreceptors in the smooth muscle of bronchioles which sense lung overexpansion

• stops the DRG and VRG inspiratory center

inspiratory reserve volume (IRV)

maximum amount of additional air that can be drawn into lungs during forced breathing

expiratory reserve volume (ERV)

maximum amount of additional air that can be drawn out of lungs during forced breathing

vital capacity

tidal volume + inspiratory reserve volume + expiratory reserve volume

residual volume

volume of air left in lungs after forceful exhalation

mechanics of normal breathing

activity of the dorsal respiratory group stimulates inspiratory muscles, DRG neurons become inactive during exhalation

mechanics of forced inhalation

increased activity in the DRG, stimulates the inspiratory center of the ventral respiratory group to recruit accessory inspiratory muscles

mechanics of forced exhalation

expiratory center of the ventral respiratory group recruits accessory expiratory muscles

effect of airway diameter on air flow

smaller airway = greater resistance = slower airflow

factors that influence resistance

• foreign object caught

• mucus accumulation (brinchitis)

• pulmonary edema

• bronchoconstriction (asthma or allergic reaction)

visceral pleural membrane

anchored onto alveoli

parietal pleural membrane

anchored to muscles

intrapleural pressure

negative relative to the atmospheric pressure (-4 mmHg)

pneumothorax

pleural membrane is punctured and air gets into the intrapleural space, lung collapses

boundaries across which gas exchange occurs in the alveoli

• alveolar epithelium

• fused basement membrane

• endothelial cells lining the wall of the capillary

alveolar epithelium

type 1 pneumocytes lining the wall of alveoli

surfactant

amphipathic lipid produced by type 2 pneumocytes that spreads on the inside of the alveoli to reduce surface tension by interrupting cohesive forces between water molecules to keep alveoli open

atelectasis

deflation of a localized group of alveoli, results in reduced gas exchange

concordance between ventilation and perfusion

the quality of air reaching the alveoli and blood flow to that alveolar capillary should correspond

• blood is diverted to areas of the lungs with high O₂ content

• air is diverted to areas of the lungs with high CO₂ content to evacuate

lung compliance

a measure of the lungs’ ability to stretch and influences how much air can be collected

compliance in pulmonary fibrosis

non-elastic scar tissue builds up, compliance is low and alveoli fill with much less air

compliance in COPD (emphysema)

compliance is higher than normal because the elastic fibers are compromised, the ability to push air out of the lungs is compromised and air gets trapped in alveoli, compromising gas exchange

emphysema

condition when the delicate septa of the alveoli and the elastin fibers around the alveoli are destroyed, the alveolar sac occupies a greater volume but there is less surface area for gas exchange, causing decreased function in the lung

chronic obstructive pulmonary disease (COPD)

condition when mucus builds up in the airways, mucus pools in the lower respiratory tract

residual volume greater than 25% of vital capacity

increased compliance, obstructive condition (bronchitis, emphysema, asthma), greater total volume

residual volume less than 25% of vital capacity

decreased compliance, restrictive condition (fibrosis, tuberculosis), smaller total volume

external respiration

in the lungs

• O₂: lungs → blood

• CO₂: blood → lungs

internal respiration

in the tissues

• O₂: blood → cells

• CO₂: cells → blood

characteristics of erythrocytes

• filled with hemoglobin to carry O₂ and CO₂

• non-nucleated reticulocytes → more room left for hemoglobin and can have biconcave shape

• biconcave shape → high surface area:volume ratio that maximizes gas exchange

• no mitochondria → generates energy anaerobically to not use up oxygen being carried

hemoglobin

protein with iron hemes to bind oxygen

• 4 hemes per hemoglobin

• 1 iron per heme → 4 oxygen per hemoglobin

percentages of CO₂ in the blood

• 69%: as bicarbonate (HCO₃^-)

• 25%: bound to globin in red blood cells

• 6%: dissolved in blood

percentages of O₂ in the blood

• 98.5%: bound to heme in hemoglobin

• 1.5%: dissolved in blood

cooperativity

hemoglobin has a high affinity for oxygen when the oxygen concentration is high, affinity between O₂ and heme increased if other hemes are already bound to O₂

activity of hemoglobin in metabolically active tissues

• metabolically active tissues use O₂ for respiration → low O₂

• low O₂ decreases the affinity of O₂ for hemoglobin → hemoglobin releases O₂ to supply tissues

• metabolically active tissues produce CO₂ through cellular respiration → high CO₂

• CO₂ binds to hemoglobin, causing a conformational change

• change further reduces hemoglobin’s affinity for O₂

• CO₂ is an allosteric inhibitor

carbonic anhydrase

enzyme in red blood cells that combines CO₂ with H₂O to form carbonic acid, which then spontaneously dissociates into an H⁺ ion and an HCO₃^- ion

• carbonic ion exits the red blood cell and travels in the plasma

• H⁺ binds to hemoglobin, causing a conformational change in protein (increasing acidity in the red blood cell)

  • change further reduces hemoglobin’s affinity for O₂

acidosis

caused by hypoventilation (more CO₂ → more carbonic acid → more H⁺)

alkalosis

caused by hyperventilation (less CO₂ → less carbonic acid → less H⁺)

factors influencing gas exchange

• high temperature

• age of red blood cells

• altitude

• paralysis or injury of muscles involved in breathing

• reduced lung compliance

• obstructed airway

• pulmonary edema

• alveoli with broken septa

effect of high temperature on gas exchange

high temperature reduces the affinity of hemoglobin for oxygen

effect of age of red blood cells on gas exchange

older red blood cells have low 1,3-bisphosphoglycerate levels and bind to O₂ with much more affinity (bad for gas exchange)

law of partial pressure

• partial pressure in blood is a measure of number of molecules of dissolved gasses in a given volume

• law of diffusion: high concentration to low concentration

• greater concentration gradient → faster gas exchange

effect of altitude on gas exchange

ambient oxygen levels are lower → speed of gas exchange decreases

even at substantially lower oxygen levels, hemoglobin is able to be nearly saturated with O₂ (95%), not a huge impact

effect of paralysis or injury of muscles involved in breathing on gas exchange

can hinder pressure gradient between lungs and environment → speed of gas exchange decreases

effect of reduced lung compliance on gas exchange

can hinder the pressure gradient between lungs and environment

effect of obstructed airway on gas exchange

air can’t leave or enter alveoli

• foreign object

• mucus accumulation

• bronchoconstriction

effect of pulmonary edema on gas exchange

left ventricle is unable to propel blood forward → excess fluid accumulates in pulmonary circuit → interstitial fluid bulks up thickness of the respiratory membrane → slows gas exchange

effect of alveoli with broken septa on gas exchange

reduces area available for gas exchange