M3.7 -Exchange surfaces and breathing

how come diffusion alone is enough to supply the needs of single-celled organisms?

• The metabolic activity of unicellular organisms is usually low

• so O2 demands and CO2 production of the cell are low

• The SA:V of the organism is large.

• so the distance which substances have to diffuse over is short

why do larger organisms need specialized exchange surfaces?

• bigger organisms = smaller SA:V

• distance that substances need to travel from outside to reach the cells at centre of the body get longer

• so it is impossible to absorb enough O2 through the available SA to meet needs of the body

• high metabolic demands

• need lots of O2 for cellular respiration

• lots of waste products produced that need to be removed

Is metabolic activity higher in unicellular or multicellular organisms?

multicellular

Features of an efficient exchange system

• large SA:V

• good blood supply/ ventilation »» CG

• Short diffusion distances

why is an increased Surface Area important for efficient gaseous exchange?

increases the area over which gases and other substances can be transported into and out of the organism, via diffusion and active transport.

example of large SA

(to increase rate of diffusion)

• root hair cells - plants

• villi - small intestine

• folded membranes -mitochondria

why are thin layers/walls/short distances important for efficient gaseous exchange?

distances which substances diffuse over are short

so rate of diffusion is faster and more efficient

as particles do not have to travel as far

examples of thin layers

(to increase rate of diffusion)

• alveolar walls- lungs

• villi - small intestine

why is a good blood supply/ steep concentration gradient important for efficient gaseous exchange?

• steeper CG = Faster diffusion

• good blood supply means substances are constantly delivered to and removed from exchange surface

• so more efficient exchange

examples of good blood supply

(to increase rate of diffusion)

• alveoli - lungs

• gills - fish

• villi- small intestine

why is good ventilation important for efficient gaseous exchange?

• creates steep CG

• create a high partial pressure (of oxygen in the alveoli.)

examples good ventilation

(to increase rate of diffusion)

• alveoli- lungs

• gills- fish

  (flow of water carrying dissolved O2)

why do large organisms/ mammals have a high metabolic rate?

• they are active

• maintain their body temperature independent of the environment

what does the mammalian gaseous exchange system consist of?

• nasal cavity

• trachea

• bronchus

• bronchioles

• alveoli (lungs)

Passage of air flow through the body

1. NASAL CAVITY - inhalation

2. TRACHEA - continues below larynx

3. BRONCHUS - trachea divides (forms left bronchus and right bronchus)

4. BRONCHIOLES - bronchi divide into smaller tubes

5. ALEVOLI - main site of gas exchange

features of the nasal cavity

• Large SA and good blood supply

• hairy lining

• moist surfaces

importance of the large SA and good blood supply in the nasal cavity

Warms the air to body temp

» so air entering lungs is similar temp to body temp

• Ensures appropriate exchange of carbon dioxide and oxygen,

• To prevent diseases.

importance of the hairy lining in the nasal cavity

• secretes mucus to trap dust and bacteria

• this protects delicate tissue from irritation and infection

• (provides additional humidity to the inhaled air)

importance of moist surfaces in the nasal cavity

• increases humidity of incoming air

• reduces evaporation from exchange surfaces

• ensures cilia do not dry out and continue functioning

features of the trachea

• strong, flexible cartilage

• ciliated epithelial cells

• goblet cells

importance of cartilage in the trachea

• prevents collapsing of trachea

structure of cartilage in trachea and importance of that structure

• rings of cartilage

• rings are incomplete so food can easily move down the oesophagus behind the trachea

importance of ciliated epithelial cells in trachea

• cilia beat and move the mucus along

• move any trapped dirt and microorganisms away from lungs

where does most of the wafted mucus from the cilia end up?

• into the throat

• swallowed and digested

what effect does cigarette smoke have on cilia?

• stops cilia beating

• paralyze the cilia and eventually destroy them

what causes ‘smokers cough’

• toxins destroy cilia

• cilia are less effective at keeping lungs clear

• coughing attempts to remove mucus from lungs

importance of goblet cells in trachea

• secrete mucus onto lining of trachea

• to trap dust and microorganisms

  (that have escaped the nose lining)

where are goblet cells located?

between and below the epithelial cells

features of bronchi (bronchus)

• similar structure to trachea

  but

• narrower in size

feature of bronchioles

• smaller bronchi but no cartilage rings

• walls of smooth muscle

• lined with a thin layer of flattened epithelium

• clusters of alveoli at the end

importance of smooth muscle in bronchioles

• smooth muscles contract - bronchioles constrict

• smooth muscles relax - bronchioles dilate

This changes the amount of air reaching the lungs

importance of thin layer of flattened epithelium in bronchioles

• makes gaseous exchange possible

• permits rapid diffusion of oxygen and carbon dioxide.

features of alveoli

• thin flattened epithelial cells

• collagen and elastic fibres

• large SA:V

• good blood supply

• coated in lung surfactant

diameter of alveoli

200-300 μm

what is elastic recoil of the lungs?

• The rebound of the lungs

• after having been stretched by inhalation

importance of flattened thin epithelial cells in alveoli

• single epithelial cell thick

• short diffusion distance

• between the air in the alveolus and the blood in the capillaries

• diffusion rate much faster more efficient

importance of elastic fibres in alveoli

• allow alveoli to stretch during inhalation

• as return to resting size, air is squeezed out

  » elastic recoil

what are elastic fibres in the alveoli composed of?

elastin

how many alveoli are there per adult lung?

300-500 million

what is the alveolar SA for gaseous exchange in the two lungs combined?

50-75m²

why is a large SA of the alveoli essential for gaseous exchange in the lungs?

• speeds up diffusion because gases have more area over which to diffuse.

• otherwise without the alveoli, the lungs would not be big enough for

• amount of oxygen needed to diffuse into the body

How many capillaries supply the millions of alveoli in each lung?

280 million capillaries

importance a good blood supply in the alveoli

• constant flow of blood through capillaries

• » brings CO2 and carries off O2

• maintains a steep CG for CO2 and O2

• between air in the alveoli and blood in the capillaries

• so rate of diffusion is faster

importance of lung surfactant in the alveoli

• keeps alveoli inflated

• prevents alveoli from collapsing

• reduces surface tension at the air-liquid interface in the alveoli

• allows O2 to dissolve in water before in blood

• »increases rate of diffusion

define surfactant

substance which reduces tension and helps substances dissolve in water

what is the lung surfactant composed of? (chemical mixture)

• phospholipids

• hydrophilic proteins

• hydrophobic proteins

where is the lung surfactant found?

coats the surfaces of the alveoli

what happens if surface tension is too high?

• alveoli can’t expand anymore

• lung collapse

• unable to breathe in

what creates surface tension?

• alveolar walls lined with thin film of water

• tension from the forces acting on the liquid surfaces

function of the rib cage

• protects vital organs in the thoracic cavity

• assists in respiration

• supports the weight for the upper extremities

how many types of rib are there?

• true ribs

• false ribs

• floating ribs

what are true ribs?

• 1-7 ribs are true ribs

• they articulate directly with sternum by costal cartilages

what are false ribs?

( vertebrochondral ribs)

• indirectly articulate with the sternum

• their costal cartilages are attached to the costal cartilage of the seventh rib

• 8,9,10 are false ribs

what are floating ribs?

• do not articulate with the sternum at any point

• 11, 12 are floating ribs

structure of ribs, rib cage

• basket-like structure

• expansible and semi-rigid

• twelve pairs of ribs

• formed from ribs - corresponding attachments to sternum and vertebral column

• protects lungs and heart » 2 vital organs

what happens to external intercostal muscles during inhalation?

contract

what happens to the ribs during inhalation?

move upwards and outwards

what causes the ribs to move upwards and outwards during inhalation?

the diaphragm and external intercostal muscles contract

what happens to the diaphragm during inhlation?

• contracts

• flattens

• lowers

what happens to the internal intercostal muscles during inhalation?

relax

what happens to the volume of the thorax during inhalation?

increases

why does the pressure in the thorax decrease during inhalation?

• volume of thorax increases

• so pressure decreases

• pressure and volume are inversely proportional at a constant

During inhalation, how does the air pressure in the thorax compare to atm?

• pressure in thorax reduced to below atmospheric air

• causes a pressure gradient

• so air from outside moves inwards - down a pressure gradient

• equalises pressure inside and outside chest

what happens to the alveoli during inhalation?

they stretch

Describe the process of inspiration

1. external intercostal muscles contract whereas the internal ones

   relax

2. cause the ribs to raise upwards, outwards

3. The diaphragm contracts, flattens.

4. the intercostal muscles and diaphragm cause the volume inside the thorax to increase

5. thus lowering the pressure inside the thorax

6. » below ATM

7. difference between the pressure inside lungs and ATM creates a pressure gradient

8. causing the air to enter the lungs (thru nasal cavity etc)

» until pressure inside and outside lungs is equalised

is Inspiration an energy using process?

yes - active phase of ventilation

Is expiration an energy using process?

no - Expiration is passive in the normal individual during quiet breathing

what allows expiration to be a passive process?

• elastic recoil of the lungs

• relaxation of inspiratory muscles

• energy stored in the elastic lung tissue during inspiration being sufficient.

what happens to the diaphragm during expiration?

• relaxes

• moves upwards

• creates resting dome-shape

what happens to external intercostal muscles during expiration?

relax

what happens to internal intercostal muscles during expiration?

contract

what happens to the ribs during expiration?

• move down

• inwards

• under gravity

what happens to the elastic fibres in the alveoli during expiration?

• return to normal length

• elastic recoil

why do alveoli shrink/ recoil during expiration?

• to expel CO2 out of the lungs

what happens to the volume of the thorax during expiration?

decreases

what pressure changes take place in the thorax during expiration?

• pressure inside thorax increases

• to above atm

• creates a pressure gradient

• so air from inside is pushed outwards - down a pressure gradient

• equalises pressure inside and outside chest

Describe the process of expiration

1. external intercostal muscles relax whereas the internal ones contract

2. cause the ribs to move downwards, inwards

3. The diaphragm relaxes, moves up, forms dome-shape.

4. the intercostal muscles and diaphragm cause the volume inside the thorax to decrease

5. thus increasing the pressure inside the thorax

6. » above ATM

7. difference between the pressure inside lungs and ATM creates a pressure gradient

8. causing the air to move out of the lungs (thru nasal cavity etc)

» until pressure inside and outside lungs is equalised

process of forced expiration

1. uses energy

2. internal intercostal muscles contract

3. pulls ribs down hard, fast

4. abdominal muscles contract

5. forces diaphragm to move up (dome-shape)

6. increases pressure in lungs rapidly

what happens to the cells lining the bronchioles during an asthma attack?

• release histamines

what effect does histamine have during an asthma attack?

• histamine chemicals cause epithelial cells to become

• inflated and swollen

• stimulate excess mucus production in goblet cells

• smooth muscle in bronchiole walls to contract

» the airways narrow, fill with mucus, difficult to breathe

how is asthma treated/ helped?

• relievers

• preventers

where are asthma treating drugs delivered to in the body?

• straight into the breathing system

• using an inhaler

how do relievers work in treating asthma?

• give immediate relief from symptoms

• they attach to active sites

• on cell surface membranes of smooth muscle cells

• in the bronchioles

• makes them relax and dilate the airways

how do preventers work in treating asthma?

• they are often steroids

• taken every day

• to reduce sensitivity of lining of the airways

what does lung surfactant consist of?

• phospholipids

• hydrophilic proteins

• hydrophobic proteins

when do alveolar cells produce lung surfactant in babies during pregnancies?

• alveolar cells do not produce enough lung surfactant

• until the 30th week of pregnancy

why is lung surfactant a concern in premature babies?

• if baby is premature

• (born before 37 weeks)

• they alveolar cells may not have produced enough surfactant yet

• so due to not enough surfactant

• the alveoli collapse with each breath

• as they collapse , damaged cells collect in the airways

• leads to death

why can’t premature babies produce lung surfactant?

due to the immature development of type II pneumocytes

In what ways can the capacity of the lungs be measured?

• A peak flow meter

• Vitalographs

• A spirometer

what is a peak flow meter?

• show the amount and rate of air that can be forcefully breathed out of (and therefore into) the lungs (PEF)

• useful quick measure

when is a peak flow meter often used?

• in Asthma patients

• » monitor how well lungs are working

• » helps to diagnose Asthma

what is PEF (peak expiratory flow)?

amount and rate of air that can be forcefully breathed out of the lungs.

how to interpret results of a peak flow meter?

• When a patient is well their PEF is higher

• when the airways are narrow (as in asthma) » PEF is lower.

what is a vitalograph?

• (more complex peak flow meters)

• measures the FEV in 1 second » (FEV1)

• measures FVC

• produces graph, plots volume against time

what is FEV1 ?

• Forced expiratory volume (in 1 second)

• volume of air (in litres) exhaled in the 1st second during forced exhalation

• after maximal inspiration.

what is FVC?

• Forced vital capacity

• volume of air that can be forcibly exhaled

• from lungs

• after taking the deepest breath possible

how to interpret vitalograph?

• If the FVC and the FEV1 are within 80%

• results considered normal

• normal ratio value for the FEV1/FVC ratio is 70%

what is a spirometer?

• measures different aspects of lung volume

• investigate breathing patterns

• how well lungs are functioning

spirometer readings