Respiratory System

  

1. Respiratory System 

 

 

 

Topic 

 

Content 

Structure and Function of the 

respiratory system 

The exchange of gases between 

the internal and external 

environments of the body is 

facilitated by the structure and 

function of the respiratory 

system at the 

cell, tissue and 

organ levels 

 

Respiratory System Structure and Function

 

·

 

Nasal

 

cavity

 – warms, filters and moistens air

 

·

 

Pharynx-

 shared area of respiratory and digestive system

 

·

 

Epiglottis

- flap of cartilage tissue covering trachea when swallowing

 

·

 

Larynx 

– cartilage and mucous membranes produce sound & speech

 

·

 

Trachea

 – air way containing cartilage rings to keep the trachea 

open when inhaling and cilia and mucus producing epithelial cells 

that trap and waft material out of the trachea

 

·

 

Ribs 

– made of bone connective tissue for protection of lungs 

 

·

 

Intercostal muscles 

– skeletal muscles contract to raise the ribs up 

and out; lungs are “attached” to ribs via the pleural fluid/pleural 

membranes and therefore also increase in volume resulting in 

inhalation

 

·

 

Pleural membrane

 –line the lungs and ribs and secretes pleural fluid

 

·

 

Pleural fluid

 – lubricant, holds lungs to pleural membranes and in 

turn the ribs

 

·

 

Diaphragm

- skeletal muscle that contracts downwards into 

abdominal cavity increasing the volume of the thoracic cavity and 

thus the lungs resulting in inhalation 

 

·

 

Bronchioles 

–fine tubes extending from the bronchi with walls with 

smooth muscle that contract or relax to constrict or dilate the 

airways therefore regulating airflow to the lungs

 

·

 

Bronchus

- 2 large airways branching from the trachea

 

·

 

Alveoli

- small grape like structures at terminal of bronchioles which 

are the site of gas exchange

 

Breathing 

·

 

Inspiration

 

 

o

 

 Diaphragm contracts: flattens and pushes down into the 

abdominal cavity 

o

 

Intercostal muscles contract pulling the rib cage up and out 

o

 

Lung volume increases and pressure inside the lungs decreases 

o

 

Air flows from the area of high pressure outside the lungs into 

the area of low pressure inside the lungs 

·

 

Expiration

 

o

 

Diaphragm relaxes doming up into the thoracic cavity reducing 

lung volume 

o

 

At the same time the intercostal muscles relax lowering the rib 

cage causing ribs to move down and in 

o

 

Lung volume decreases and pressure inside the lungs increases 

o

 

Air flows from the area of high pressure inside the lungs into 

the area of low pressure outside the lungs 

Blood Flow in Pulmonary Circulation 

·

 

Pulmonary arteries

 –deoxygenated blood from heart to lungs

 

·

 

Pulmonary veins-

 oxygenated blood from the lungs to the heart

 

 

 

Exchange of gases

 

The efficient exchange of gases 

in the lungs is maintained by 

the actions of breathing, blood 

flow and the structure of the 

alveoli 

 

Passive diffusion of gases 

·

 

movement of gases from high concentration to low 

concentration, with/down the concentration gradient 

(diffusion), requires no expenditure of energy by the cell 

·

 

Simple diffusion of gases occurs directly through the cell 

membrane between alveoli and capillary as molecules are small. 

 

Alveoli features for gas exchange include

 

·

 

Many small alveoli

 – creates a large surface area which increases 

rate of diffusion

 

·

 

T

hin alveoli walls

 – simple epithelium allows less distance for gases 

to diffuse across and therefore increased rate of diffusion

 

·

 

Extensive blood capillary network

 –wrapped around the alveoli 

creating a large surface area for 

gas exchange

 between the blood 

and alveoli.

 

·

 

Moist surface

 – gases dissolve allowing for faster rate of diffusion.

 

 

Maintenance of gas concentration gradient

 b

etween air in alveoli and 

blood in capillaries 

·

 

Heart is always pumping - allows for a constant flow of blood to and 

from lungs. Blood passing the lungs will always have a low O

2

 

concentration and a high CO

2

 concentration

 

·

 

Constant 

breathing

 replaces O

2

 and expels CO

2

. Air in the lungs will 

always have a high O

2

 concentration and a low CO

2

 concentration

 

·

 

Cellular 

respiration

 uses O

2

 and produces CO

2 

as a waste, which 

returns to lungs in deoxygenated blood