AAP2 Unit 3 Respiratory System

respiratory system

consists of a system of tubes that delivers air to the lungs; oxygen diffuses into the blood, carbon dioxide diffuses out

9 functions: respiration, communication, olfaction, pH balance, BP regulation, blood/lymph flow, platelet production, blood filtration, expulsion of abdominal contents

respiratory system organs

nose, pharynx, larynx, trachea, bronchi, lungs

conducting zone

includes those passages that serve only for airflow, no gas exchange; nostrils through major bronchioles

• nasal cavity → pahrynx → trachea → main bronchi → lohbar bronchi → segmental bronchi → bronchioles → terminal bronchioles

respiratory zone

consists of alveoli and other gas exchange regions

• respiratory bronchioles → alveolar ducts → atrium → alveolus

automatic breathing

unconscious; controlled by respiratory centers in reticular formation (medulla oblongata and pons)

ventral respiratory group (VRG)

respiratory center in medulla

primary generator of the respiratory rhythm, produces a respiratory rhythm of 12 breaths per minute

in quiet breathing (eupnea), inspiratory neurons fire for about 2 sec, expiratory neurons fire for about 3 sec

dorsal respiratory group (DRG)

respiratory center in medulla

modifies the rate and depth of breathing, receives influences from external sources (pons, chemo-sensitive center of medulla oblongata, and higher brainstem emotional centers)

pontine respiratory group (PRG)

respiratory center in pons

modifies rhythm of VRG by outputs to both VRG and DRG

adapts breathing to special circumstances such as sleep, exercise, vocalization, and emotional responses

central chemoreceptors

brainstem neurons that respond to changes in pH of CSF (reflects CO2 level in the blood)

regulate respiration to maintain stable pH; ensures stable CO2 level in blood

peripheral chemoreceptors

carotid and aortic bodies; respond to the O2 and CO2 content and the pH of blood

stretch receptors

found in smooth muscles of bronchi and bronchioles, and in visceral pleura

respond to inflation of lungs: inflation reflex (Hering–Breuer) triggered by excessive inflation

inflation reflex

 protective reflex that inhibits respiratory neurons and stops inspiration

irritant receptors

nerve endings amid the epithelial cells of the airway

respond to smoke, dust, pollen, chemical fumes, cold air, and excess mucus

trigger protective reflexes such as bronchoconstriction, shallower breathing, breath-holding (apnea), or coughing

voluntary control

originates in the motor cortex of frontal lobe of the cerebrum

sends impulses down corticospinal tracts to respiratory neurons in spinal cord, bypassing brainstem

overridden by CO2 level rise

arterial blood levels

• pH: 7.35 to 7.45

• PCO2: 40 mm Hg

• PO2: 95 mm Hg

breathing stimuli

pH, followed by high CO2 , and least significant is low O2

pulmonary ventilation for brain pH

change in respiration due to central chemoreceptors in medulla (75%) and H+ stimulating peripheral chemoreceptors (25%)

CO2 crosses blood–brain barrier and reacts with water in CSF to produce carbonic acid; its H+ stimulates central chemoreceptors

hydrogen ions

stimulate peripheral chemoreceptors, which produce 25% of the respiratory response to pH changes

respiratory acidosis/alkalosis

pH imbalances resulting from a mismatch between the rate of pulmonary ventilation and the rate of CO2 production

acidosis

blood pH lower than 7.35

Hypercapnia (PCO2 greater than 43 mm Hg) is most common cause

alkalosis

blood pH higher than 7.45

Hypocapnia: PCO2 less than 37 mm Hg (normal 37 to 43 mm Hg); Most common cause of alkalosis

hyperventilation

response to acidosis; “blowing off” CO2 faster than the body produces it

pushes reaction to the left: CO2 (expired) + H2O ← H2CO3 ← HCO3− + ↓ H+

reduces H+ (acid), raises blood pH

hypoventilation

response to alkalosis; CO2 is retained and accumulates in body fluids

pushes reaction to the right: CO2 + H2O → H2CO3 → HCO3− + H+

raising the H + concentration, lower pH

ketoacidosis

caused by rapid fat oxidation releasing acidic ketone bodies (seen in diabetes mellitus)

kussmaul respiration

hyperventilation that reduces CO2 concentration and compensates (to some degree) for acidity of ketone bodies

chronic hypoxemia

PO2 < 60 mm Hg; stimulates ventilation (hypoxic drive)

can occur in emphysema, pneumonia, daily high elevation

hypoxia

deficiency of oxygen or inability to use oxygen; respiratory disease consequence

hypoxemic (low arterial PO2), ischemic (low blood circulation), anemic (low oxygen transport), histotoxic (poisons/cyanide), cyanosis (blue skin)

hyperbaric oxygen

used to treat premature infants; discontinued due to retinal damage

CO2 direct effects

rise at beginning of exercise may directly stimulate peripheral chemoreceptors and trigger ventilation more quickly than central chemoreceptors

exercise respiration

when the brain sends motor commands to the muscles, it also sends to respiratory centers

they increase pulmonary ventilation in anticipation of exercising muscle needs

muscle/joint proprioceptors

stimulated by exercise, transmit excitatory signals to brainstem respiratory centers

increase breathing due to moving muscles

increase pulmonary ventilation; keeps blood gas values normal despite elevated O2 consumption and CO2 generation by the muscles

respiratory muscles

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

diaphragm

prime mover of respiration; accounts for ⅔ of air flow

contraction flattens it, enlarging thoracic cavity and pulling air into lungs

relaxation allows it to bulge upward again, compressing the lungs and expelling air

normal quiet expiration

passive process achieved by the elasticity of the lungs and thoracic cage

as muscles relax, structures recoil to original shape and original (smaller) 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; important for “abdominal breathing”

rectus abdominis, internal intercostals, and other lumbar, abdominal, and pelvic muscles are involved

respiratory airflow

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 pressure

the weight of the air above us; 760 mm Hg at sea level, or 1 atmosphere (1 atm); drives respiration

lower pressure at higher elevations

Boyle’s Law

at a constant temperature, the pressure of a given quantity of gas is inversely proportional to its volume

describes air flow in and out of lungs during ventilation

Charles’ Law

volume of gas is directly proportional to its temperature

airway resistance

influenced by 2 factors: bronchiole diameter and pulmonary compliance (ease of lung expansion)

bronchodilation

via epinephrine and sympathetic stimulation = increase airflow

bronchoconstriction

via histamine, parasympathetic nerves, cold air, and chemical irritants = decrease airflow 

suffocation can occur from extreme ____ brought about by anaphylactic shock and asthma

pulmonary compliance

reduced by degenerative lung diseases that stiffen/scar lung, limited by surface tension of water film inside alveoli

surfactant

secreted by great cells of alveoli; mixture of phospholipids and proteins that coats the alveoli and prevents them from collapsing during exhalation

disrupts H+ bonds between water molecules, reducing the surface tension

alveolar air

only air that enters is available for gas exchange; about 150 mL fills the conducting zone of the airway

anatomic dead space

conducting zone of airway where there is no gas exchange;

can be altered somewhat by sympathetic dilation (increases dead space but allows greater flow)

physiological (total) dead space

in pulmonary disease, some alveoli unable to exchange gases

sum of anatomic dead space and pathological alveolar dead space

alveolar ventilation rate (AVR)

this measurement is crucially relevant to the body’s ability to get oxygen to the tissues and dispose of carbon dioxide

air that ventilates alveoli (350 mL) × respiratory rate (12 bpm) = 4,200 mL/min

Type I (Squamous) cells

thin cells allow rapid gas diffusion between air and blood

cover 95% of alveolar surface area

Type II (Great) cells

round to cuboidal cells that cover the remaining 5% of alveolar surface

repair the alveolar epithelium when the Type I cells are damaged

secrete pulmonary surfactant

alveolar macrophages (dust cells)

most numerous of all cells in the lung; wander lumens of alveoli and CT between them; keep alveoli free from debris by phagocytizing dust particles

100 million die daily as they ride up the mucociliary escalator to be swallowed and digested with their load of debris

respiratory membrane

thin barrier between alveolar air and blood

3 Layers: squamous alveolar cells, endothelial cells of blood capillaries, shared basement membrane

reabsorption

(osmotic uptake of water) overrides filtration and keeps the alveoli free of excess fluid

air composition

78.6% nitrogen, 20.9% oxygen, 0.04% carbon dioxide, 0% to 4% water vapor, depending on temperature and humidity

minor gases argon, neon, helium, methane, and ozone

partial pressure

the separate contribution of each gas in a mixture

• PN2 = 78.6% × 760 mm Hg = 597 mm Hg

• PO2 = 20.9% × 760 mm Hg = 159 mm Hg

• PH2O = 0.5% × 760 mm Hg = 3.7 mm Hg

• PCO2 = 0.04% × 760 mm Hg = 0.3 mm Hg

• PN2 + PO2 + PH2O + PCO2 = 760 mm Hg

Dalton’s law

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

Henry’s law

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

greater PO2 in alveolar air = more O2 picked up by blood

air composition variety

inspired and alveolar differ for 3 reasons;

air is humidified by contact with mucous membranes, alveolar air mixes with residual air, and changes O2 and CO2 with blood

relaxed breathing

passive process achieved mainly by elastic recoil of thoracic cage; recoil compresses the lungs = volume of thoracic cavity decreases

raises intrapulmonary pressure to about 1 cm H2O; air flows down the pressure gradient and out of the lungs

forced breathing

accessory muscles raise intrapulmonary pressure as high as +40 cm H2O

respiratory membrane

swapping of O2 and CO2 occurs across here; air in the alveolus is in contact with a film of water covering the alveolar epithelium

O2 into blood

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

moves from alveolar air into plasma until equilibrium is reached

CO2 leaving blood

must pass opposite of O2, and then diffuse out of the water film into the alveolar air

alveolar air PP

PO2 = 104 mm Hg, PCO2 = 40 mm Hg

plasma PP

PO2 = 40 mm Hg, PCO2 = 46 mm Hg

tissue fluid PP

PO2 = 40 mm Hg, PCO2 = 46 mm Hg

capillaries PP

 PO2 = 95 mm Hg, PCO2 = 40 mm Hg

capillaries

oxygen moves from capillaries/blood into the tissue fluid, carbon dioxide moves into the capillaries

hydrogen

bumped off hemoglobin “seat” by oxygen

ion is taken up by bicarbonate to form carbonic acid; cleaved into CO2 and H2O

membrane thickness

only 0.5 micrometers thick, presents little obstacle to diffusion

when membrane is thicker, gases can’t equilibrate fast enough to keep up with blood flow; caused by pulmonary edema and pneumonia

ventilation-perfusion coupling

airflow and bloodflow are matched to each other; good ventilation of alveolus and good perfusion of capillaries is required for gas exchange

influenced by changes in diameter in pulmonary BV and bronchi

pulmonary blood vessels

can change diameter depending on air flow to area of lungs

if an area is poorly ventilated, pulmonary vessels constrict

bronchi

change diameter depending on blood flow to area of lungs

if an area is well perfused, bronchodilation occurs

hemoglobin oxygen transfer

oxygen is bound to the heme of hemoglobin, altering its shape into oxyhemoglobin

primary method of oxygen delivery is bicarbonate

gas transport

the process of carrying gases from the alveoli to the systemic tissues and vice versa

oxygen transport: 98.5% bound to hemoglobin, 1.5% dissolved in plasma

carbon dioxide transport

90% is hydrated to form carbonic acid (dissociates into bicarbonate ions);

5% is bound to proteins (carboamino compounds);

and 5% is dissolved as a gas in plasma

carbon dioxide exchange

70% of CO2 comes from carbonic acid;

23% comes from proteins;

and 7% comes straight from plasma

carbon monoxide (CO)

colorless, odorless gas in cigarette smoke, engine exhaust, fumes from gas furnaces

competes with O2 for binding sites on Hb (competitive inhibition)

carboxyhemoglobin

CO binds to iron of hemoglobin, more occupied in heavy smokers

CO2 loading

involves systemic capillaries; CO2 diffuses into blood, carbonic anhydrase in RBC catalyzes reaction to carbonic anhydrase

oxygen loading

H+ binds to HbO2, reduces its affinity for O2; makes hemoglobin release oxygen

venous reserve

amount of O2 remaining in blood after it passes through systemic capillary beds

CO2 unloading

Hb loads O2, its affinity for H+ decreases and H+ binds with HCO3-;

reverse chloride shift, HCO3- diffuses back into RBC in exchange for Cl-, free CO2 diffuses into alveoli to be exhaled

acidic blood

lower pH = more oxygen being released from hemoglobin

heat generated during exercise causes hemoglobin to lose binding affinity for oxygen

hemoglobin

 unloads O2 to match metabolic needs of different states of activity of the tissues; the more active the tissue, more oxygen is unloaded

oxygen unloading

4 factors adjust the rate of oxygen unloading to match needs: ambient PO2, temperature, ambient pH, bisphosphoglycerate (BPG)

ambient PO2

active tissue has low PO2, O2 is released from Hb

temperature

active tissue has high temp; O2 unloaded into tissue

ambient pH

active tissue has high CO2, lower pH promotes O2 unloading into tissue to make it more basic

bisphosphoglycerate (BPG)

produced by RBCS, binds to Hb; O2 is unloaded; RAISES body temp (fever)

thyroxine, GH, test, epinephrine all raise BPG and promote O2 unloading

more 2,3 BPG also causes hemoglobin to lose affinity for oxygen

alveolar capillary PCO2 increase

capillary diameter (blood flow) and bronchiole diameter (reduce the PCO2 pressure) would increase to promote expiration (capillaries to lungs)

pulmonary capillaries would constrict to redirect bloodflow to better ventilated regions

pleura

serous membrane that lines the thoracic wall and forms the surface of the lung; pulmonary ligament connects it to the diaphragm

2 layers: visceral and parietal

3 functions: reduction of friction (pleural fluid), creation of pressure gradient (inhale = expansion), compartmentalization (prevent infection spread)

pleural layers

visceral: forms surface of the lung and extends into fissures between lobes

parietal: adheres to mediastinum, inner surface of rib cage, and superior surface of diaphragm

pleural cavity

space between parietal and visceral layers; contains pleural fluid; potential space that wraps around the lung, not contains

pneumothorax

presence of air in pleural cavity; occurs during puncture; lungs recoil and collapse due to negative intrapleural pressure absence (atelectasis)

spirometer

measures pulmonary ventilation to assess severity of a respiratory disease or monitor

restrictive disorders

reduce pulmonary compliance, limiting amount lungs can be inflated

reduced Vital Capacity (VC); black lung disease, TB

obstructive disorders

interfere with airflow via blocking/narrowing airways, making it harder to inhale or exhale air; asthma and chronic bronchitis

measured via FEV (forced expiratory volume); percent of VC that can be exhaled (normal = 75-85%)

minute respiratory volume (MRV)

amount of air inhaled per minute; called MVV (maximum voluntary ventilation) during heavy exercise, where it is high

eupnea

relaxed, quiet breathing; TV of 500mL and respiratory rate of 12-15 bpm