Gaseous Exchange

THE DELIVERY OF OXYGEN FROM THE LUNGS TO THE BLOODSTREAM, AND THE ELIMINATION OF CARBON DIOXIDE FROM THE BLOODSTREAM TO THE LUNGS AND OUT OF THE BODY.

In multicellular organisms the cells are far away from external environment where oxygen is obtained.

They have specialised gas exchange surface.

So that he oxygen from external environment can diffuse into the body, and carbon dioxide can be diffuse out.

Functions :

clean and warm the incoming air Maximise surface area for diffusion of O2

and CO2

Minimise distance fro diffusion Maintain adequate gradient for diffusion

Air enters the body through the mouth and nose, from here it moves to the pharynx (throat), passes through the larynx (voice box) and enters the trachea.

The trachea splits into two branches, the left and right bronchus, each bronchus divides many times into smaller branches called bronchioles.

trachea

Bronchusbronchioles

Each bronchiole finally leads to a bunch of tiny air sacs, called alveoli, which inflate during inhalation, and deflate during exhalation.

Gas exchange is the delivery of oxygen into bloodstream, and the elimination of carbon dioxide out of the body. It takes place in the alveoli.

The alveoli walls are surrounded by blood capillaries. the O2 from alveoli diffuse into the capillaries and the CO2 diffuse into alveoli and to be exhaled out of the body. Both O2 and CO2 move from high concentration to low concentration areas.

Lungs

Located in the thoracic (chest) cavity surrounded by pleural membrane (airtight).

Pleural membrane contains small amount of fluid

To allow friction free movement when lungs ventilates.

Cartilage

Found in trachea(c shape) and bronchus (irregular shape)

Keeps airways open and air resistance low

Prevent collapsing or bursting of the passage as different air pressure change when breathing

Bronchiles

Has no cartilage Surrounded by smooth muscles Smooth muscles contract and

reflex to adjust diameter of airways

During exercise the muscles relax to allow big flow of air into alveoli.

Warming and Cleaning The Air

Air from nose to trachea are warmed to body temperature and moistened by evaporation from the lining

To protect the surface inside lungs from desiccation

Particles larger than 5-10µm are trapped on the hairs inside the nose and the mucus lining the nasal passages & other airways

mucus

Production of goblet cells of the ciliated epithelium

Slimy solution of mucin Contains

1. glycoprotein with many carbohydrate chain that make them sticky

2. Lysozyme, the enzyme in lysosome which causes lysis( breakdown of bacteria)

Some chemical pollutants eg: SO2 and NO2

can dissolve in mucus and forms acid solute that irritates lining of airways

Between the goblet cells ciliated cells

Continual beating of their cilia carries the carpet of mucus upwards towards the larynx (1 cm/ min)

When mucus reaches the trachea, it is usually swallowed so that pathogens are destroyed by stomach acid

Macrophages

Phagocytic white blood cell Act as police for small particles

o Kills small particles (dust and bacteria) o the surfaces of airways

During infection, other phagocytic cells will leave the capillaries to help remove pathogens

Alveoli

300 millions in each lung Super thin membrane (squamous epithelial

cells) Surrounded by many blood capillaries carrying

deoxygenated blood Alveolar walls contains elastic fibres

o Stretch during breathing o Recoils during expiration, help to force air out

The elasticity ables the alveoli to expand to increase the volume of air

Increses the surface area for diffusion & air is expelled efficiently when elastic fibres recoil

Breathing rate

Calculate by Spirometer At rest, we require 6dm3 of air per minute &

about 0.35dm3 enters the alveoli Lungs cannot be emptied with air. At least

1dm3 remains = Residual Volume

Tidal volume = volume of air in and out per breath (0.5 dm3 )

Vital capacity = max volume of air that an be moved in and out per breath ( 5 dm3 )

Residual volume = volume of air that remains in the lungs after biggest possible exhalation (1.5dm3 )

Ventilation rate = tidal volume x breathing rate

One breath

Pulse rate

Stroke volume = volume of blood pumped out per minute

Cardiac output = total volume pumped out per minute

Pulse rate = stretch and recoiling of aorta and arteries as blood travels

Pulse rate is identical to heart rate

Is an indication of aerobic fitness

An average person = 60-100 beats per min

Blood pressure

Systolic pressure = Maximum arterial pressure during the ventricular systole

Diastolic pressure = Minimum pressure in the arteries o It reflects the resistance of the small arteries

and capillaries Typical blood pressure is 120/80 mm Hg

Hypertension

when systolic and diastolic pressure are high at rest, and the heart is working too hard

High blood pressure occurs• Contraction of smooth muscles in the walls of small arteries

and arterioles , which is a result of hormone noradrenaline

Long term hypertension imposes a strand on the cardiovascular system.

Known as the silent killer ( no prior warning for stroke , heart failure and heart attack)

Causes of hypertension

• Excessive alcohol intake

• Smoking

• High salt levels in diet

• Genetic predisposition

• obesity