human physiology 100 - respiratory system

What are the primary functions of the respiratory system?

1) Provide an extensive area for gas exchange between inhaled air and the circulation;

2) move air to and from the exchange surfaces of the lungs;

3) protect the respiratory surfaces from outside environment.

4) produce sounds

5) participates in the olfactory sense

6) indirectly contribute to regulation of blood volume, blood pressure, and pH.

What are the structures of the respiratory system?

Upper
- nose
- pharynx

Lower
- larynx (voice box)
- trachea
- bronchi —> larger bronchioles —> terminal bronchioles
- smaller (respiratory bronchioles)
- alveoli

What are the three main functions of the nose?

1. Warming, moistening and filtering air
2. Olfaction
3. Modifying speech vibrations

What is the pharynx divided into?

1. Nasopharynx
- contains tonsils
- equalises air pressure across eardrum

2. Oropharynx
- communicates with oral cavity

3. Laryngopharynx

What is the respiratory epithelium?

- pseudostratified columnar epithelium
- mucous cells and glands in lamina propria
- cilia on epithelia cells

Mucociliary escalator

What are the characteristics of the right and left lung lobes?

Right lobe
- three lobes
- speared by horizontal and oblique fissures

Left lobe
- two lobes
- separated by oblique fissure
- cardiac notch

Why are bronchioles dynamic airways?

- contains no cartilage
- are made up of smooth muscle innervated by Autonomic Nervous System and stimulated by circulating adrenaline

- parasympathetic —> bronchiole constriction
- sympathetic —> bronchiole dilation

- they are dynamic because they have significant capacity to change their diameter

What are the alveoli cell types?

Alveolar type I cells
- simple squamous
- site of gas exchange

Alveolar type II cells
- cuboidal epithelial
- microvilli
- secrete pulmonary surfactant which reduces surface tension

Alveolar macrophages
- wandering phagocytes that removes dust and debris

What are the three components of the respiratory membrane?

1. Squamous epithelial lining of alveolus
2. Endothelial cells lining an adjacent capillary
3. Fused basal laminae between alveolar and endothelial cells

What is Fick's Law?

States that the rate of diffusion (R) of a gas across a membrane is:

- proportional to the area of a membrane (A)
- inversely proportional to the thickness of the membrane (d)
- proportional to the difference in concentration or partial pressure

How to respiratory surfaces receive a blood supply?

A capillary network surrounds each alveolus

What are the pleural membranes?

They enclose each lung

1. Parietal pleura
- outer layer attached to wall of thoracic cavity

2. Visceral pleura
- inner layer covering surface of lung

3. Pleural cavity
- contains lubricating fluid secreted by membranes
- high cohesive forces

What is Boyle's law?

Defines the relationship between gas pressure and volume

Defines that pressure is inversely proportional to volume

This determines how air moves into and out of the lungs

Inhalation

The diaphragm and external intercostal muscles contract, increasing thoracic volume, decreasing pressure. Pressure of environment is greater and air flows into lungs down pressure gradient

Exhalation

The diaphragm and external intercostal muscles relax, decreasing thoracic volume, increasing pressure. The pressure inside the lungs is greater, air flows out of the lungs down the pressure gradient.

What are the important pressures in ventilation?

1. Atomspheric pressure
Approx 760 mmHg

2. Intrapulmonary pressure
Approx 760 mmHg

What is intrapleural pressure?

~ 756 mmHg

Due to the elasticity of the lung

How does the lung move with the thoracic cavity?

• No skeletal muscle in lung tissue

• Has to move with the thoracic cavity

2 critical factors:

1. Cohesive forces of intrapleural fluid

2. Transpulmonary pressure gradient across lung wall

What factors affect pulmonary ventilation?

1. Lung compliance
2. Elastance
3. Surface tension of alveolar fluid
4. Airways resistance

What are the two types of respiratory diseases?

1. Obstructive
- characterised by a difficultly to expire
• emphysema
• asthma
• bronchitis

2. Restrictive
- characterised by a difficulty to inspire
• respiratory distress syndrome
• lung fibrosis

What are the four lung volumes?

1. Tidal (500 ml)
2. Inspiratory reserve (3100 ml)
3. Expiratory reserve (1200 ml)
4. Residual (1200 ml)

What are the four lung capacities?

1. Inspiratory (3600 ml)
2. Functional residual (2400 ml)
3. Vital (4800 ml)
4. Total lung (6000 ml)

What is respiratory minute volume/ pulmonary ventilation?

Is the amount of air moved into and out of lung per minute

Respiratory rate x tidal volume

What is anatomic dead space?

The air within the trachea, bronchi and bronchioles which does not participate in gas exchange
Only ~ 70% of air reaches alveoli

What is alveolar ventilation?

= respiratory rate x (tidal volume - anatomical dead space)

What is Dalton's Law?

each gas in a mixture of gases exerts its own pressure

i.e the partial pressure, proportional to its concentration in the mixture and independently of other gases present

What is Henry's Law?

Quantity of gas that dissolves in a liquid is proportional to the partial pressure and solubility coefficient

Why doesn't nitrogen get absorbed into the bloodstream?

It is an inert gas

~ 560 mmHg in all compartments

What affect does pH have on haemoglobins affinity for oxygen?

Increasing the pH increases haemoglobins affinity for oxygen

What affect does temperature have on haemoglobins affinity for oxygen?

Increasing the temperature decreases haemoglobins affinity for oxygen

What affect does pCO2 have on haemoglobins affinity for oxygen?

Increasing the pCO2 decreases haemoglobins affinity for oxygen

What happens when the Hb saturation curve shifts to the right?

Increases unloading of oxygen from haemoglobin

What happens when the Hb saturation curve shifts to the left?

Decreases unloading of O2 from haemoglobin

What are the three levels of control of respiration?

1. Neural control
- involuntary establishment of basic breathing rhythm
- rhythm centre = medulla oblongata

2. Chemical control
- regulates O2 consumption and CO2 production

3. Voluntary control
- cerebral cortex

How does neural control of respiration work?

- nerve impulse from medullary respiration centres sent via motor neurons
• phrenic nerve to diaphragm
• intercostal nerves to intercostal muscles

- stimulate contraction = inhalation (active)
- when impulse ceases = expiration (passive)

What are the respiratory control centres?

1. Dorsal respiratory group (DRG)
- inspiratory centre
- functions in quiet and forced breathing

2. Ventral respiratory group (VRG)
- inspiratory and expiratory centre
- functions in only forced breathing

What adjusts the breathing rate and depth to match metabolic demand?

The neurons of the pons

What are the two types of chemoreceptors?

1. Peripheral chemoreceptors
- in the aorta and carotid arteries
- strongly detect changes in plasma pH
- weaker response directly to pO2, only responds when very low (< 60 mmHg ; < 90% saturation)

2. Central chemoreceptors
- in medulla
- detect changes in the pH in the cerebrospinal fluid caused by changes in arterial pCO2
- exert secondary control over breathing