4. Answer the following questions about the ventilation cycle (a) Which muscles

Question

4. Answer the following questions about the ventilation cycle (a) Which muscles are important for ventilation? Explain what happens to these muscles during inspiration and during expiration (b) Pleural membranes also aid in ventilation, particularly in inspiration. How does the high surface tension of pleural aid in expanding the lungs? (c) What are the two pressure gradients responsible for inspiration? (d) How do the high surface tension of pleural fluids and elastic recoil of tissues aid in expiration?

Explanation / Answer

( a) primary Muscles

The primary inspiratory muscles are the external intercostals and the diaphragm and the primary expiratory muscles are the internal intercostals, intercostalis intimi, and subcostals.

The muscles of inspiration , the ribs and sternum, and the muscles of expiration depress .

Accessory Muscles

The accessory inspiratory muscles are the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, the inferior fibres of serratus anterior and latissimus dorsi, the serratus posterior anterior it will help inspiration also the iliocostalis cervicis

The accessory expiratory muscles are the abdominal muscles: rectus, abdominis, external oblique, internal oblique and transversus abdominis. And in the thoracolumbar region the lowest fibres of iliocostalis and longissimus, the serratus posterior inferior and quadratus lumborum.

Diaphragm

Origin: Xiphoid process (posterior surface), lower six ribs and their costal cartilage (inner surface) and upper three lumbar vertebrae as right crus and upper two lumbar vertebrae as left crus.

Insertion: central tendon

Nerve Supply: Motor nerve supply by Phrenic nerve (C3 C4 C5) and sensory supply by phrenic nerve to central tendon and lower 6 or 7 intercostal nerve to peripheral parts.

Intercostal muscles

They are three types: External intercostal muscles, internal intercostal muscles, and innermost intercostal muscles.

External intercostal muscles:

Internal intercostal muscles:

Innermost intercostal muscles:

Nerve supply: all the intercostal muscles are supplied by intercostal nerves

(b) advantages of having surfactant and the low surface tension of pleural aid in expanding the lungs

1.It increases the compliance of the lung

2.It reduces the work of expanding of the lung with each breath

3.It stabilises the alveoli (thus the smaller alveoli do not collapse at the end-expiration)

4.It keeps the alveoli dry (as the surface tension tends to collapse alveoli, it also tends to suck fluid

into the alveolar space from capillaries).

(c)For these purposes, pulmonary pressures will be referred to inrelative terms to atmospheric pressure (0 = 760 mm Hg, or1 atmosphere). Mouth pressure (P

m) is always 0 unless positive pressure is applied to the airway Pressure at the body surface (Pbs ) isalso always 0, unless the patient is being ventilated with a negative pressure ventilator.Alveolar pressure (Palv) will vary throughout the respiratory cycle. Pleural pressure (Ppl),which is normally negative during quiet breathing, will also vary throughout the breathing cycle.Differences between these pressures are calledpressure gradients.There are three key pressure gradients involvedin the mechanics of breathing: thetransrespiratory,thetranspulmonary,and thetransthoracic pressure gradients.

As inspiration begins, the muscles of inspiration work to expand the thorax.Thoracic expansion increases the transthoracic pressure gradient by causing a drop inpleural pressure. As the pleural pressuredrops, the transpulmonary pressure gradient widens, causing the alveoli to expand

(d)eastic recoil of the tissues of the lung and thoracic cage together with surface tension of the membranes to deflation of the lungs

The at elastic tissue in the lungs tends to recoil and pull the lung inward. the lung moves away from the thoracic wall, the cavity becomes slightly large

lung is high due to the lung's abundant elastic tissue and surfactant's ability to lower the surface tension of the alveolar fluid

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