respiratory system

what are the main functions of the respiratory system ?

• internal and external respiration

• removal of inhaled foreign particles

• warming and humidification of air

• pH balance

• production of sound

external respiration

gas exchange between alveolar air and blood

internal respiration

gas exchange between blood and tissues

cellular respiration

oxidising food to co2 and water

what are the accessory muscles of inspiration ?

sternocleidomastoid and scalenus

what are the muscles of active respiration ?

internal intercostals and abdominals

what are the major muscles of inspiration ?

external intercostals and diaphragm

positive co-operativity

binding of each O2 to a given subunit increases the O2-binding affinity of the other subunits

what divides the upper and lower respiratory system ?

below larynx = lower

where does the conducting zone end ?

terminal bronchioles

role of upper respiratory tract

filters and humidifies air

the pharynx is further divided into

naso, oro and laryngopharynx

role of sinuses

• reduce skull weight

• modify and amplify sound

• cushioning effect

the lungs are located in

the thorax

the right lung has how many lobes ?

3 - left only 2

role of lower respiratory tract

allows airflow in and out of lungs

how many cm from larynx does the trachea bifurcate into L+R bronchi ?

10cm

conducting zone

nasal cavity to terminal bronchioles

warms and moistens air

why is the conducting zone referred to as anatomical dead space ?

no gas exchange (150ml)

respiratory zone

respiratory bronchioles to alveoli

site of gas exchange

how type I and II alveoli (pneumocytes) differ ?

type I - thin, delicate, flat

type II - produce surfactant

what % of alveolar surface is composed of type I pneumocytes ?

90 - 95

microorganisms and dust are removed from respiratory surfaces by

alveolar macrophages

apnoea

temporary cessation of breathing

asphyxia

tissue starvation due to lack of oxygen in air

cyanosis

blueness of skin from insufficient o2 in blood

dyspnoea

difficult of laboured breathing

hyperpnoea

increased pulmonary ventilation that matches increased metabolic demand

when not breathing pressure in lungs =

atmospheric

what happens to vol and pressure during inspiration ?

increased vol so decreased pressure

what happens to vol and pressure during exhalation ?

decreased vol. increased pressure

the lungs move due to…

contraction / relaxation of diaphragm and intercostal muscles

the lungs are connected to skeletal muscles of the thoracic wall via the

pleura

the visceral pleura lines

lungs

the parietal pleura lines

inner surface of thoracic cavity and rib cage

pressure in the pleural cavity compared to the lungs or atmosphere is

always negative

the diaphragm is innervated by

phrenic nerve

air flows in what direction ?

down pressure gradient

why is exhalation described as a passive process ?

lungs naturally want to recoil inwards

how does forced expiration differ from passive ?

contraction of accessory muscles further reduces volume of thoracic cavity

abdominal and internal intercostals

why do lungs have a tendency to recoil ?

elastic fibres - stretched during inspiration

surface tension

effect of surface tension

promotes alveolar collapse

causes irregular lung recoil

makes inspiration more difficult

surfactant

minimises surface tension

secreted by type II alveolar epithelial cells

increases lung compliance

NRDS

neonatal respiratory distress syndrome

developmental insufficiency of pulmonary surfactant and structural immaturity in lungs

what forces keep alveoli open ?

surfactant and alveolar interdependence

what forces promote alveolar collapse ?

surface tension and elastic recoil

alveolar interdependence

tendency of surrounding alveoli to pull open collapsing alveolus, resisting collapse

what proportion of respiratory work is required to overcome elastic recoil?

70% of total work

what is meant by respiratory work ?

energy and mechanical effort required to breathe

includes work to overcome elastic and airway resistance

what proportion of respiratory work is required to overcome airway resistance ?

30%

where is airway resistance greatest ?

medium sized bronchi

how does bronchoconstriction affect airway resistance?

decreases airway radius and increases resistance

airflow rate (F) =

pressure gradient / airway resistance

what is the atmospheric pressure at sea level ?

760mmHg

which part of the nervous system causes bronchodilation?

SNS sympathetic

which part of the nervous system causes bronchoconstriction ?

PNS parasympathetic

where does gas exchange occur in the lungs ?

between alveolar sacs and pulmonary capillaries

what air the main components of air ?

nitrogen, oxygen, co2

what % of air is nitrogen

78

how does emphysema affect gas exchange ?

decreases alveolar surface area, reducing gas exchange

what conditions increase respiratory membrane thickness?

• pulmonary oedema

• fibrosis

• pneumonia

what percentage of oxygen in blood is physically dissolved ?

3%

how is the majority of oxygen transported in the blood ?

bound to haemoglobin

what determines haemoglobin saturation with oxygen?

partial pressure of oxygen (PO₂)

PO₂ is a measure of

dissolved oxygen in blood

how many oxygen molecules can one haemoglobin bind ?

4

what are the two components of haemoglobin ?

globin (4 polypeptide chains) and 4 iron-containing haem groups

avg. haematocrit (% of RBCs)

45%

myoglobin

oxygen-binding protein in muscle

stores O₂ and binds only one molecule

what does the oxygen dissociation curve show ?

relationship between PO₂ and haemoglobin saturation

what is positive co-operativity in haemoglobin binding ?

binding of the first O₂ makes it easier for the next O₂ to bind

why is oxygen released from haemoglobin at tissues ?

PO2 decreases (CO2, acidity and temp increase)

reduce Hb affinity for O2

does arterial PO₂ equal alveolar PO₂ in health ?

yes

what are the 3 main ways CO₂ is transported in the blood?

• Physically dissolved in plasma (10%)

• Bound to haemoglobin as carbaminohaemoglobin (30%)

• As bicarbonate ions (most CO₂)

what determines the amount of CO₂ dissolved in plasma ?

the PCO2

how does CO₂ bind to haemoglobin ?

binds to globin portion, forming carbaminohaemoglobin (HbCO₂)

how is most CO₂ transported in the blood ?

as bicarbonate ions (HCO₃⁻) after reacting with water to form carbonic acid, then dissociating

which enzyme accelerates the conversion of CO₂ and water into carbonic acid ?

carbonic anhydrase - found in RBCs

why is bicarbonate an efficient CO₂ transport form ?

more soluble than CO₂ and can easily diffuse out of RBCs into plasma

what is the result of carbon manoxide binding to Hb ?

prevents O2 binding

what is hypercapnia ?

elevated CO₂ in the blood, usually due to hypoventilation

what condition does hypercapnia cause ?

respiratory acidosis lowers blood pH due to excess H⁺

hypocapnia

low CO₂ in the blood, usually due to hyperventilation

what condition does hypocapnia cause ?

respiratory alkalosis - increased blood pH due to reduced H⁺ production.

what is the normal plasma pH range ?

7.35 - 7.45

what pH values are incompatible with life ?

below 6.8 above 7.8

how is pH related to hydrogen ion conc. ?

a pH change of 1 = 10 fold change in conc. of hydrogen ions

what is a volatile acid ?

acids excreted via lungs eg. carbonic acid

short chain fatty acids

what are metabolic (non-volatile) acids ?

produced from sources other than CO2

not excreted by lungs

result of incomplete metabolism of carbs. fats, proteins

examples of metabolic acids

lactic acid

ketones

fatty acids

amino acids

what leads to gain of H+ in body

metabolic processes (produce CO2)

loss of bicarbonate (in diarrhoea and urine)

what leads to a loss of H+ in the body ?

vomiting or excretion via urine

what indicates a respiratory acid-base disturbance ?

abnormal PCO2

what indicates a metabolic acid-base disturbance ?

abnormal HCO3- (bicarbonate)

what defines acidosis ?

blood pH below 7.35

what defines alkalosis ?

blood pH above 7.45

what are the three mechanisms for maintaining pH balance?

1. Buffer systems (first line)

2. Respiratory compensation

3. Renal compensation

what is the major extracellular buffer ?

bicarbonate

how does the respiratory system compensate in metabolic acidosis ?

increases ventilation to remove CO2 and lower H+

how do the kidneys compensate for respiratory acidosis ?

excrete H⁺ and reabsorb/regenerate bicarbonate