EICM contraction causes : (1) Elevation of the ribs and the sternum causing an increase in the volume of the thoracic cavity in the dorso-ventral axis (2) Elevation of the ribs and the sternum causing an increase in the volume of the thoracic cavity in the antero-posterior axis (3) Depression of the ribs and the sternum causing an increase in the volume of the thoracic cavity in the dorso-ventral axis (4) Depression of the ribs and the sternum causing an increase in the volume of the thoracic cavity in the antero-posterior axis........// IF YOU DONT KW THE ANSWER DONT TYPE DUM I NEED CORRECT ANSWERS
Answers
Answer:
The correct sequence of events in the initiation of respiration is:
(i) The contraction of external intercostal muscles raises the ribs and sternum
(ii) The volume of thorax increases in the dorsoventral axis
(iv) Diaphragm contraction
(vi) The volume of thorax increases in the anterior-posterior axis
(iii) Intrapulmonary pressure decreases
(v) Air rushes into lungs
So, the correct answer is '(i),(ii),(iv),(vi),(iii),(v)'.
Answer:
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Explanation:
Pulmonary ventilation, more commonly referred to as breathing, is the movement of air into and out of the lungs. Inhalation is the act of drawing air into the lungs, and exhalation is the expulsion of that air out of the lungs. This action follows Boyle’s law, which explains that the pressure of a gas decreases as the volume increases if the temperature is held constant.[1] Increasing the volume of the thoracic cavity causes a decrease in the intrathoracic pressure and an influx of air. Meanwhile, decreasing the volume, typically through the relaxation of the muscles of inspiration, causes an increase in intrathoracic pressure and results in exhalation. The thoracic wall is essential to this process and is made up of the sternum, 12 pairs of ribs, 12 thoracic vertebrae, and the muscles, fascia, and skin that connect to this bony cage.
Structure and Function
The structures of the thoracic wall protect the heart, lungs, and great vessels as well as some abdominal organs. Additionally, the bony structures provide attachment points for muscles and allow for the mechanical function of ventilation.
Ribs are curved, flat bones that attach posteriorly to vertebrae and anteriorly to the sternum. Ribs originate at each thoracic vertebra. The head of each rib has 1 or 2 facets for articulation with the costal facets on the bodies of thoracic vertebrae. Ribs 1, 10, 11, and 12 have a single facet on their head that only articulates with its respective vertebra. Ribs 2 through 9 all have 2 facets on their heads; the superior facet articulates with the vertebra above the rib, while the inferior facet articulates with the respectively named vertebra. In addition, ribs 1 through 10 have tubercles with facets that articulate with the costal facet of the transverse process of each respective vertebra.[2]. Ribs 11 and 12 have no tubercle and therefore do not articulate with the transverse process of their respective vertebra.
The sternum is composed of 3 parts: the manubrium, body, and xiphoid process.[3] The manubrium is the widest portion and contains the jugular, or sternal notch as well as the clavicular notch. The sternal angle, or angle of Louis, is where the manubrium joins the body of the sternum. The second rib attaches at this point. The xiphoid process is attached inferiorly to the body of the sternum and provides an attachment point for the diaphragm and rectus abdominis, but no ribs.
Ribs 1 through 7 are considered true, or vertebrocostal, ribs and attach directly to the sternum. Ribs 8 through 10 are considered false, or vertebrochondral, ribs in which the cartilage of each rib attaches to the cartilage of the rib above it which terminates where the seventh rib attaches to the sternum. Ribs 11 and 12 are considered floating, vertebral, or free, ribs because they terminate in the posterior abdominal musculature and do not attach to the sternum. The costal cartilage of ribs 1 through 10 facilitates the elastic recoil of the thoracic wall which contributes to passive exhalation.
Embryology
The thoracic wall forms part of the axial skeleton and is comprised of bone, muscle, and connective tissue. It develops from the mesoderm where blocks become somites from which the sclerotome separates. The sclerotome is the origin of the vertebrae and transverse elements which begin elongating into ribs during the fifth week of gestation. Ossification begins during the fetal period but will not be complete until adulthood.[4] The myotome gives rise to the muscles of the thoracic wall. The sternum forms from sternal bars that meet in the midline and begin to fuse during the seventh week of gestation. Fusion starts superiorly and ends inferiorly by the tenth week.[5]
Blood Supply and Lymphatics
Each intercostal space receives its blood supply from 3 arteries, a posterior intercostal artery and a pair of anterior intercostal arteries. The posterior arteries of the first 2 intercostal spaces are fed from the superior (supreme) intercostal artery which comes off the subclavian artery.[6] The remaining pairs of posterior intercostal arteries and a pair of subcostal arteries emerge directly from the thoracic aorta.[7] These posterior arteries enter the costal groove near the angle of each rib where they travel between the intercostal vein and nerve. The posterior and anterior intercostal arteries anastomose laterally.
The internal thoracic artery is another branch of the subclavian artery that supplies the anterior intercostal arteries of spaces 1 through 6 before dividing into the superior epigastric and musculophrenic arteries.[8] The musculophrenic artery supplies the anterior intercostal arteries of spaces 7 through 9. The 2 most inferior intercostal spaces are supplied from the posterior intercostal arteries and their collateral branches and do not have anterior intercostal arteries.