PHS 301 Respiratory tract

Question 1

Types of respiratory control

Answer 1

Chemical control mechansim
Nervous control mechanism

Question 2

What is chemical control of respiration (and stimulation)

Answer 2

carries out by chemoreceptors, these are sensory nerve ending that responds to changes in the chemical constituent of blood

they can be stimulated by:
i. Hypoxia (low O2)
ii. Hypercapnea (increase PCO2)
iii. Increased [H+]

Question 3

Types of chemoreceptors

Answer 3

i. central
ii. peripheral

Question 4

Central chemoreceptors

Location, function & stimulant

Answer 4

Central chemoreceptors are situated in the deeper part of the medulla oblongata, close to the dorsal respiratory group of neurons.
They form synapse with the respiratory centres, especially the DRG
Chemoreceptors are in close contact with blood and CSF. They act slowly but effectively and are responsible for 70% to 80% of increased ventilation through the chemical control of respiration.
The main stimulant for central chemoreceptors is the increased [H+] conc.
Whenever [H+] conc. increases in the blood, it cannot stimulate the central chemoreceptors because the hydrogen ions from blood cannot cross the BBB and blood-CSF barrier.
However, if CO2 increases in the blood, it can easily cross the BBB and blood­ CSF barrier and enter the interstitial fluid of the brain or the CSF.

There CO2 combines with H2O to form carbonic acid: CO2+ H2O → H2CO3 → H+ + HCO3–
Carbonic Acid immediately dissociates into H+ & HCO3-
[H+] stimulates the central chemoreceptors and impulses are passed from the chemoreceptors to the DRG. Resulting in increased ventilation (increased rate and force of breathing).
Because of this, excess CO2 is washed out and respiration is brought back to normal.

Question 5

PERIPHERAL CHEMORECEPTORS

Answer 5

Peripheral chemoreceptors are situated in the carotid and aortic bodies

The carotid bodies are bilaterally located at the bifurcation of the common carotid artery. The afferent nerve fibers passes through the Herring’s nerve and to the dorsopharyngeal nerve, then to dorsorespiratory area of the medulla. The aortic bodies are located along the arch of the aorta. The afferent nerve fibers pass through the vagi and to the dorsal respiratory area of the medulla.
The main stimulant for the peripheral chemoreceptors is decreased in PO2. Whenever there is a decrease in PO2, peripheral chemoreceptors are stimulated and impulses are sent through the aortic and Herring’s nerve fibres to the respiratory area, especially DRG. The DRG sends impulses to the respiratory muscles. DRG sends impulses and this causes an increase in ventilation, hence hypoxia is being inverted so that the PO2 is increased.

Question 6

Describe the nervous control of respirations

Answer 6

Respiratory centres are composed of several groups of neurons, which are bilaterally located in the medulla oblongata and pons of the brainstem

Types:
1. Medullary Centres
2. Pontine Centres

Question 7

MEDULLARY CENTERS

Answer 7

Composed of:
1. Dorsal Respiratory Group of Neurons (DRG)
2. Ventral Respiratory Group of Neurons (VRG)

Question 8

Dorsal Respiratory Group of Neurons

Answer 8

Dorsal respiratory group of neurons are located in the nucleus of tractus solitarius (solitary tract) in the upper medulla. All the neurons of the dorsal respiratory group are inspiratory and generate inspiratory ramp by their autorhythmic property and are responsible for the basic rhythm of respiration

Question 9

Ventral Respiratory Group of Neurons

Answer 9

Located anteriorly and laterally to the nucleus of tractus solitarius. They are composed of a nucleus ambiguous and a nucleus retroambiguous. Have both inspiratory and expiratory neurons.
They are normally inactive during quiet breathing and become active during forced breathing.

Question 10

PONTINE CENTERS are divided into

Answer 10

Pneumotaxic Center
Apneustic Center

Question 11

Apneustic Center (location and function)

Answer 11

The apneustic center is situated in the reticular formation of lower pons, it increases the depth of inspiration by acting directly on dorsal group neurons.

Question 12

Pneumotaxic Cente (location and function)

Answer 12

The pneumotaxic centre is situated in the posterolateral part of the reticular formation in the upper pons. It is formed by neurons of medial parabrachial and subparabrachial nuclei. The primary function of pneumotaxic centre is to control the medullary respiratory centres especially the DRG.
It acts through an apneustic centre.
Pneumotaxic centre inhibits the apneustic centre so that the dorsal group neurons are inhibited. Because of this, inspiration stops and expiration starts. Thus, pneumotaxic centre influences the switching between inspiration and expiration.

Question 13

Influence of the neural respiratory centre

Answer 13

The faster or slower the impulse, the faster or slower the breathing. Different factors can influence the rate at which impulses are released
Firstly, higher centres of the brain allow for the voluntary control of breathing. Also, the higher centres of the brain are important for the perception of pain, emotion and temperature. Hence, all these factors act on the pontine respiratory centres either positive or negative.

The pontine response centre will also be positive or negative, and the medullary response centre and hence stimulate or inhibit the rate of respiration.

Question 14

Hering-Breuer initiation reflex

Question 15

TYPES OF DEAD SPACE

Answer 15

Dead space is of two types:
1. Anatomical dead space
2. Physiologic dead space

Question 16

What is dead space?

Answer 16

Dead space is defined as the part of the respiratory tract, where gaseous exchange does not take place. Air
present in the dead space is called dead space air.

Question 17

Anatomical dead space (what it contains)

Answer 17

Anatomical dead space extends from the nose up to terminal bronchiole.

It includes the nose, pharynx, trachea, bronchi and branches of bronchi up to terminal bronchioles. These structures serve only as the passage for air movement. Gaseous exchange does not take place in these structures.

Question 18

Physiologic dead space/ total dead space

Answer 18

Includes anatomical dead space plus two additional volumes.

1. Air in the alveoli, which are non-functioning.

In some respiratory diseases, alveoli do not function because of dysfunction or destruction of the alveolar membrane.

2. Air in the alveoli, which do not receive adequate blood flow.

Gaseous exchange does not take place during inadequate blood supply.

Question 19

Normal range for dead space

Answer 19

150ml but can become expanded in physiologic conditions

Question 20

Surfactants

Answer 20

a surface-acting material or agent that reduces the surface tension of a fluid.
A surfactant that lines the epithelium of the alveoli in the lungs is known as a pulmonary surfactant and it decreases the surface tension on the alveolar membrane.

Question 21

Pulmonary surfactant is secreted by two types of cells:

Answer 21

1. Type II alveolar epithelial cells in the lungs, which are called surfactant-secreting alveolar cells or pneumocytes. A characteristic feature of these cells is the presence of microvilli on their alveolar surface.
2. Clara cells, which are situated in the bronchioles. These cells are also called bronchiolar exocrine cells

Question 22

Chemistry of surfactant

Answer 22

Surfactant is a lipoprotein complex formed by lipids, especially phospholipids, proteins and ions. Phospholipids form about 75% of the surfactant. The major phospholipid present in the surfactant is dipalmitoylphosphatidylcholine (DPPC). Other lipid substances of surfactant are
triglycerides and phosphatidylglycerol (PG).
Proteins of the surfactant are called specific surfactant proteins. There are four main surfactant proteins, called SP­A, SP­B, SP­C and SP­D.

SP­A and SP­D are hydrophilic, while SP­B and SP­C are hydrophobic. Surfactant proteins are vital components of surfactant and the surfactant becomes inactive in the absence of proteins.

Ions present in the surfactant are mostly calcium ions.

Question 23

Effect of surfactant deficiency

Answer 23

The absence of surfactant in infants causes collapse of the lungs and the condition is called infant respiratory distress syndrome or hyaline membrane disease. The rate of maturation of surfactant can be increased by glucocorticoids. Surfactants can also prevent pulmonary oedema. Cigarette smoking decreases lung surfactant.

Question 24

Describe the mechanics of respiration (chief muscle of respiration)

Answer 24

The chief muscle of respiration is the diaphragm. It is responsible for 25% of the change in intra-thoracic volume.
The diaphragm arches over the liver, It is attached to the bottom of the thoracic cage as it arches over the liver. And it’s contraction causes an increase in the thoracic cage