Respiratory system

what is respiration?

the exchange of oxygen and carbon dioxide between an organism and the external environment

what is external respiration?

the act of breathing

what isi internal respiration?

the utilisation of oxygen by cells in metabolism

what gaseous exchange occurs during respiration?

the absorption of oxygen and excretion of carbon dioxide

what is olfaction?

the sense of smell

by specialist nerve endings in the nasal cavity and transmitted to the brain by the first cranial nerve (olfactory)

name some functions of the respiratory system

• gaseous exchange

• olfaction

• speech - via vocal cords in the larynx

• homeostasis - via O₂ and CO₂ exchange

• protection - via the immune system and mucus production

describe the structure of the nose in relation to its function

lined by epithelial cells with tiny hairs which filter incoming air and secrete a sticky fluid to trap dust and bacteria to prevent them entering the lungs

in the nose air is warmed and filtered

organ of smell

describe the structure of the nasopharynx in relation to its function

lies behind the nose - continues to warm air

at the back of the nasopharynx are the adenoids which are made up of dense lymphoid tissue and fight infections

Eustachian tubes connect the nasopharynx to the middle ear and have a key role in equalising pressure in the ear to atmospheric pressue

describe the structure of the pharynx in relation to its function

large and muscular tube which lies behind the mouth and between the nasopharynx and larynx

serves as both an air and food passage

at the back are the tonsils which are made up of dense lymphoid tissue

continue the process of warming inspired air

where are the tonsils located?

at the back of the pharynx

where are the adenoids located?

at the back of the nasopharynx

describe the structure of the larynx in relation to its function

short passage which connects the pharynx to the trachea

has rigid walls and contains the vocal cords - where air passes over these it creates sound

where are the vocal cords found?

the larynx

where is the epiglottis found?

at the opening from the pharynx to the larynx

during the act of swallowing food this is covered and closed by the epiglottis to prevent choking

labelled lungs diagram

describe the structure of the trachea in relation to its function

tube-like structure which extends from the larynx to the upper chest

made of 20 ‘C’ shaped rings of cartilage and smooth muscle

the ‘C’ shape of the cartilages allows expansion of the oesophagus when a bolus of food is swallowed

ensures the patency of the airway (being unobstructed)

describe the structure of the bronchi in relation to their function

where the trachea divides into two - similar in structure to trachea

lined with ciliated epithelial cells which secrete mucus and saline

the mucus traps solid particles and the cilia move them outwards so that they can be expelled by coughing

labelled diagram of airway epithelium

describe the mode of saline secretion by airway epithelial cells

1. NKCC (Na-K-Cl cotransporter) brings Cl- into epithelial cell from ECF

2. apical anion channels (at boundary of airway lumen), including CTFR, allow Cl- to enter the lumen

3. Na+ goes from ECF to lumen by the paracellular pathway, drawn by the electrochemical gradient

4. NaCl movement from ECF to lumen creates a concentration gradient so water also follows into the lumen

describe the structure of the bronchioles in relation to their function

cartilage is absent from the more terminal bronchioles, whose walls contain more smooth muscle

bronchi subdivides into bronchioles

what innervates the bronchi and bronchioles?

the autonomic immune system

muscarinic cholinergic receptors M3 cause bronchoconstriction

B2 adreno-receptors medicate bronchodilation

describe the structure of the alveoli in relation to their function

functional unit for gas exchange

composed of type I and type II epithelial cells

type I cells - occupy 96-98% of the surface area - primary site for gas exchange - very thin to allow gas rapid diffusion

type II cells - occupy remaining 2-4% - synthesise a chemical known as surfactant, which reduces surface tension in the alveolus and therefore reduce resistance during inhalation and exhalation

describe how and why the alveoli are supplied with blood

gas exchange occurs in the alveoli through a dense network of capillaries

blood vessels fill 80-90% of the space between alveoli forming a continuous ‘sheet’ of blood in close contact with air-filled alveoli

the proximity of capilalry blood to alveolar air is essential for the rapid exchange of gases

what is the thin protective membrane that covers the lungs called?

pleural membrane