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23 Cards in this Set

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What are the 4 phases of lung development, including the rough timing of each period?

- Embryonic period ( 0-7 weeks)

- Pseudoglandular phasde (5-17 weeks)

- Cannicular phase (13-27 weeks)

- Terminal Sac Period (24-40 weeks)

What occurs during the embryonic period of lung development?

Development of airways occurs (0-7 weeks)

- Outpouching of foregut forms primitive respiratory tube

- Primitive lung buds form

- Branches down to lobar branches

- Pulmonary vasculature begins to form

What occurs during the pseudoglandular phase?

Multiplication of airways occurs (5-17 wks)

- Bronchial branching completes

- Formation of muscle fibres, elastic

- diaphragm develops (hernias arise in this period)

What occurs during the cannicular phase?

Alveolar buds begin to form (13 - 27 weeks)

- cilia form in conducting airways

- alveolar buds and saccules form

- vascularisation of respiratory portion of lung

What happens during the terminal sac period?

Cilia, surfactant and alveoli development
(24-40 wks)

- Terminal sacs appear and divide in to alveolar ducts

- Epithelial cells of alveoli differentiate in to type 1 and 2

- at term, only primitive alveoli are formed

- surfactant production begins to occur
(preterm babies often have surfactant sufficiency)

Are alveoli fully formed at birth? What are the implications of this?

No, only primitive alveoli (saccules) are present at birth. These will continue to mature for several months after birth.

The implications of this is there is a decreased surface area for gas exchange

How many generations of bronchi are present at birth?


The final generations (23rd) don't form until around 14 years of age

How many divisions of bronchi form in a mature lung? When are the final divisions formed?

23 divisions in a mature lung.

Final division occurs at around 14 years of age.

When does alveoli formation end?

Alveoli continue to form until around 8-11 years of age

Diameter of infant airways is much smaller than adult airways. What is the functional implication of this?

The narrower lumen of the infant airway means there will be much more resistance to flow (remember R=1/r^4)

It also means that infant airways are much more effected by oedema and other things that might narrow the lumen.

What is ratio of heart to ribcage in adults vs infants?

Adults: 1/3 of ribcage

Infants: 1/2 of ribcage

What is the orientation of the infant ribs in comparison to adult ribs? What is the implication of this?

Oriented horizontally, meaning the bucket handle movements of the adult lungs can't occur. Instead, movement is directly out in a piston fashion, which is a less efficient movement and therefore less efficient ventilation results.

What is the difference in composition of the diaphragm in the infant and the adult? What is the implication of this?

The percentage of slow twitch muscle fibres is far less in the infant diaphragm. The implication of this is that the diaphragm is much more easily fatiguable.

What is the percentage of slow twitch muscle fibres in an adult, new born and preterm infant?

Adult = 55%

New born = 25%

Preterm = 10%

How many breaths per minute for:

- preterm infants

- infants

- children

- adult

Preterm: 50-70 breaths

Infant: 40 breaths

Children: 18-30 breaths

Adult: 12-15 breaths

How long do infants spend in REM sleep compared to adults? Why is this relevant for respiration?

Preterms spend 80% in REM sleep vs 20% in adults.

REM sleep has irregular respiration and may have apnoea

What are the metabolic demands of an infant vs an adult? What is the implication of this?

Newborn has 2x the rate of oxygen consumption of adults.

As a result, infants will progress to hypoxaemia much more quickly.

What is collateral ventilation?

The movement of air between alveoli, through pores of kuhn.

What is the difference between Haemoglobin concentration in infant vs adult blood?

Haemoglobin concentration is higher in infants, therefore higher O2 saturation.

O2 dissociation curve moves to left

Where is the haemoglobin saturation curve of an infant relative to an adult dissociation curve?

Infant curve is shifted to the left.

Therefore higher saturation in infants.

What are the functional implications to consider in infant respiration?

- higher resistance to airflow (due to narrow airways)

- dynamic compression of trachea (due to weak cartilage)

- Increased risk V/Q mismatch

- Increased work of breathing

What are the clinical signs of 6 respiratory distress?

- Increased respiratory rate

- Grunting on expiration

- Cyanosis

- Nasal flaring

- Head bobbing

- Apnoea

What is the difference between adults and infants in terms of work of breathing?

Work of breathing much higher in infants

- 40% at rest compared to 1-2% of adult