Week 10 Bioscience

Question 1

Nose & Nasal Cavity

Answer 1

Nose
* Facilitates smell
* Hairs - filter

Nasal conchae
* Increased surface area
* Warm and humidify air
* Enhance air turbulence

Question 2

Mucosal epithelium

Answer 2

• Produces mucus humidifies incoming air traps particulates contains antibacterial compounds (lysozyme and defensins)
• bears cilia - moves contaminated mucous to the throat

Question 3

Pharynx

Answer 3

• Passageway for air and food

Question 4

Larynx

Answer 4

• Open passageway for air to reach the trachea
• Arrangement of cartilages
• Routes food and air into the correct passageways

Question 5

Trachea

Answer 5

• Windpipe
• C-shaped cartilage rings
• Mucociliary escalator

Question 6

Lungs

Answer 6

• Lie within the thoracic cavity - pleural cavities
• Left lung – 2 lobes ; Right lung – 3 lobes
• Large, soft and spongy organs – highly elastic

Question 7

The Lungs & pleura

Answer 7

Pleural fluid
* within the pleural space
* acts as a lubricant
* adheres lungs to the thoracic cavity wall

Adherence of the two pleural membranes to one another is absolutely essential for normal breathing

Question 8

The Respiratory Tree

Answer 8

• Branching network of airways starting from the trachea

Question 9

Conducting Zone

Answer 9

• Airways become smaller: diameter decreases
• Mucociliary escalator disappears
• Cartilage rings - cartilage plates
• Gain smooth muscle tissue and elastic fibres

Question 10

The Respiratory Zone

Answer 10

The respiratory zone is the only site of gas exchange.
* Alveolar sacs and alveoli are surrounded by capillaries
* The respiratory membrane
* Formed where the alveoli contacts the capillary
* Site of gas exchange

Question 11

Alveoli

Answer 11

• Alveolar pores connect neighbouring alveoli
• Type I alveolar epithelial cells form the major part of the alveolar walls
• Type II alveolar epithelial cells are scattered among the type I cells and produce surfactant
• Alveolar macrophages crawl around the alveolar surfaces to consume bacteria, dust and debris

Question 12

The Respiratory Membrane – the site of gas exchange

Answer 12

• formed where the Type I alveolar epithelial cells contact the capillaries
• formed where the Type I alveolar epithelial cells contact the capillaries
• Very thin (0.5µm wide)
  
  • Efficient gas exchange
• Alveolar surface is coated with alveolar fluid
  
  • Prevents damage
  • Facilitates gas exchange
  • Surfactant – prevents alveolar collapse

Question 13

Blood supply to the lungs

Answer 13

Blood ENTERS the lungs via 2 circulations:
1.Pulmonary circulation
* pulmonary arteries deliver blood requiring oxygenation
* nutrients for alveoli
2. Bronchial circulation
* bronchial arteries provide oxygenated blood to rest of the lung tissue

Blood LEAVES the lung via 1 circulation:
1. Pulmonary circulation
* Pulmonary veins return blood to the heart

Question 14

Innervation of the lungs

Answer 14

1. Sensory fibres
   * Degree of stretch
   * Presence of irritants (cause us to sneeze!)
   * Send messages to respiratory centre in the brainstem to influence respiratory rhythm
2. Sympathetic fibres
   * Dilate bronchioles via relaxing smooth muscle
3. Parasympathetic fibres
   * Constrict bronchioles via contracting smooth muscle

• changing bronchiole diameter alters resistance to air flow

Question 15

Muscles of respiration

Answer 15

The diaphragm and the external intercostal musclesare the muscles used in quiet breathing. These are often referred to together as our “respiratory muscles”. These muscles contract during inspiration and relax during expiration.

The internal intercostal muscles only play a role in forced expiration only. During forced expiration, these muscles contract to decrease thoracic volume and increase pressure.

Question 16

Expiration

Answer 16

• Involves muscle relaxation only
• Depends on recoil of the lungs (elasticity)
• Surface tension of the alveolar fluid

Question 17

What stops the lungs collapsing?

Answer 17

1. Surfactant reduces the surface tension of the alveolar fluid
2. Pleural fluid “sticks” the parietal and visceral pleural membranes together
3. Elasticity of the chest wall pulls the thoracic wall outwards

Question 18

Passive vs Forced Expiration

Answer 18

Passive (quiet) expiration
involves muscle relaxation only (external intercostals and diaphragm) depends on lung recoil

Forced expiration
physical activity or specific vocalizations
internal intercostal muscles CONTRACT - further depress the ribcage involves contraction of accessory muscles:
eg. rectus abdominus - pull ribcage down, increase intra-abdominal pressure and push the diaphragm further upwards

Question 19

Gas Flow / Ventilation

Answer 19

· In the conducting zone: air/gasses move down a pressure gradient via BULK FLOW
Gas flow through the lungs is dependant on a number of factors including:
- Resistance
- Alveolar surface tension
- Compliance

Question 20

Resistance

Answer 20

• Gas flow = Pressure/Resistance (same as blood flow)
  
  • Resistance = opposition to gas flow
  • friction between air and airway walls
  • dependant upon airway diameter
    
    • neural control

Question 21

Alveolar surface tension

Answer 21

Surface tension between water molecules in alveolar fluid

Surfactant – a lipid-protein complex produced by type II alveolar epithelial cells reduces surface tension of alveolar fluid

prevents alveolar collapse reduces effort required to expand alveoli - facilitates ventilation

Question 22

Compliance

Answer 22

A measure of the ability of the lungs and/or thoracic cavity to stretch/ expand
Depends on:
* lung elasticity
* alveolar surface tension (surfactant production)
* flexibility of muscles and joints of the thoracic wall

Question 23

External respiration (gas exchange at the alveoli)

Answer 23

• O2 diffuses from alveoli - pulmonary capillaries
• CO2 diffuses from pulmonary capillaries - alveoli

Question 24

Internal respiration (gas exchange at the tissues)

Answer 24

• O2 diffuses from blood - tissues
• CO2 diffuses from tissues - blood

Question 25

Oxygen transport

Answer 25

Problem = Oxygen is poorly soluble in water Solution = erythrocytes (Red Blood Cells) + haemoglobin (Hb) RBC are highly adapted for O2 transport: * large surface area to volume ratio * no organelles * stackable and flexible The chemical properties of Hb facilitate effective gas transport: Lungs: O2 levels are high - Hb binds O2 Tissues: O2 levels are low - Hb releases O2

Question 26

Carbon dioxide transport

Answer 26

* CO2 is a waste product * Different ways of transporting CO2

Question 27

PCO2 and pH are inversely related

Answer 27

when one variable is high, the other is low and vice versa

Question 28

Hypoxia

Answer 28

Decreased oxygen at tissues - homeostatic imbalance (flashback to week 1) Cyanosis – blue tinge to skin and mucosa (mouth and nail beds) Causes of hypoxia: * Anaemia: too few RBC or decreased Hb * Ischemia: blood circulation is reduced/blocked * Hypoxemia: reduced PO2 in blood (respiratory disease, decreased atmospheric O2 )

Question 29

Neural control of breathing

Answer 29

Respiratory centres (nuclei) in the brainstem set the respiratory rhythm * Respiratory rhythm = the rate and depth of breathing * neurons ‘fire’ in a cyclical manner to generate the repetitive cycle of inspiration: expiration * neurons innervate the diaphragm and intercostal muscles

Question 30

Factors that influence the respiratory centers/nuclei

Answer 30

* Stretch/inflation of the lungs – via stretch receptors * Emotions (eg angry, frightened, excited) – via the limbic system and hypothalamus * Choice (voluntary control) – controlled by primary motor cortex

Question 31

Changes in CO2 and O2 are detected by chemoreceptors

Answer 31

Central chemoreceptors: Located in the brainstem detect changes in CO2 levels Peripheral chemoreceptors: Located in the aortic arch and carotid sinuses and detect changes in CO2 , H+ and O2 levels

Question 32

The effect of altered PO2

Answer 32

* Under normal conditions (PO2 95-104 mm Hg) * O2 provides little stimulus for respiration O2 only becomes an important driver for ventilation when PO2 is very low (e.g. hypoxia * Small increases in blood PCO2 cause large increases in ventilation * Decreased blood PCO2 depresses breathing * Small fluctuations in arterial PCO2 have large affects on breathing