BIOL 273 - Unit 5.4 + 5.5

Question 1

Rate of diffusion across lungs is

Answer 1

1. Proportional to partial pressure gradient
2. Proportional to the available surface area
3. Inversely proportional to the thickness of the membranes
4. Greatest over short distances

Question 2

Partial pressure gradient influenced by

Answer 2

1. Composition of inspired air
2. Alveolar ventilation
   - Can be affected by changes in airway resistance
   - Can be affected by changes in lung compiance

Question 3

What can be gas be transported in , in the blood

Answer 3

dissolved in plasma or in the RBS’s

Question 4

Describe the transport of oxygen in the blood

Answer 4

oxygen has low solubility in plasma

most O2 is transported by RBC (within RBC’s O2 is bound by haemoglobin)

• Each haemoglobin molecule can bind up to 4 oxygen molecules
  (oxyhaemoglobin HbO2)

Question 5

What three mechanisms of transport of carbon dioxide in the blood

Answer 5

1. Dissolved in plasma
2. Interact with proteins (haemoglobin via 4 terminal anime groups on the protein - carbaminohaemoglobin)
3. Converted to bicarbonate

Question 6

Explain how carbon dioxide can be transported in blood by converting to bicarbonate

Answer 6

• the majority of CO2 entering blood is converted by reaction catalyzed by carbonic anhydrase (in RBC)
• The bicarbonate ions are moved out of the RBC by a transporter protein which exchanges HCO3 for Cl in “chloride shift”

Question 7

the contraction of skeletal muscels is initiated by

Answer 7

medulla oblongata

Question 8

Network of neurons in medulla oblongata for ventilation

Answer 8

central pattern generator
(these neurons have intrinsic rhythmic activity)

Question 9

What are the two nuclei in the medulla oblongata associated with respiration and what does each control

Answer 9

1. Dorsal respiratory group (DRG) - inspiratory neurons (I neurons)

control external intercostal muscles and diaphragm (muscles of inspiration)

2. Ventral respiratory group (VRG) - expiration neurons (E neurons)

control internal intercostal and abdominal muscles (active expiration)

Question 10

Purpose of chemoreceptors

Answer 10

modify or adjust the rhythmicity of the central pattern generator neurons - based on composition of gases

Question 11

Two sets of chemoreceptors responsible for regulation of central pattern generator

Answer 11

1. Peripheral chemoreceptors
2. Central chemoreceptors

Question 12

Peripheral chemoreceptors

Answer 12

located in carotid (artery) bodies as glomus cells

sense changes in PO2 and pH of plasma or increase in PCO2 (which is set by alveoli)

Decrease PO2 or decreased pH or increase in PCO2 - up ventilation

Plasma PO2 must change radically before a signal is sent

Question 13

Central chemoreceptors

Answer 13

located in medulla oblongata (most important chemical controller of ventilation)

PCO2 increase in arterial blood - up ventilation

activated when CO2 crosses blood brain barrier into cerebrospinal fluid (CSF) - sense changes in pH

Sense changes in H+ in CSF and not arterial blood

Question 14

Purpose of mechanoreceptors

Answer 14

To control ventilation to protect the lungs

Question 15

Two types of mechanoreceptors that control ventilation to protect the lungs

Answer 15

1. Irritant receptors
2. Stretch receptors

Question 16

Irritant receptors (Mechanoreceptors)

Answer 16

located in airway mucosa
- stimulation triggers parasympathetic neurons that innervate bronchiolar smooth muscle
- lead to bronchoconstriction (to regulate breathing)

Question 17

Stretch receptors

Answer 17

located in airway smooth muscle
- triggered if lungs are over-inflated
- terminate ventilation - Hering-Beurer inflation reflex
- Reflex does not happen during quiet breathing or mild exertion