The domes are produced by: the liver on the right, with some contribution from the right kidney and the right suprarenal gland, and the fundus of the stomach and spleen on the left, with contributions from the left kidney and the left suprarenal gland.
Although the height of these domes varies during breathing, a reasonable estimate in normal expiration places the left dome at the fifth intercostal space and the right dome at rib V. This is important to remember when percussing the thorax.
During inspiration, the muscular part of the diaphragm contracts, causing the central tendon of the diaphragm to be drawn inferiorly. This results in some flattening of the domes, enlargement of the thoracic cavity, and a reduction in intrathoracic pressure. The physiological effect of these changes is that air enters the lungs and venous return to the heart is enhanced.
There is blood supply to the diaphragm on its superior and inferior surfaces:
Superiorly, the musculophrenic and pericardiacophrenic arteries, both branches of the internal thoracic artery, and the superior phrenic artery, a branch of the thoracic aorta, supply the diaphragm.
Inferiorly, the inferior phrenic arteries, branches of the abdominal aorta, supply the diaphragm (see Fig. 4.143).
Venous drainage is through companion veins to these arteries.
Innervation of the diaphragm is primarily by the phrenic nerves. These nerves, from the C3 to C5 spinal cord levels, provide all motor innervation to the diaphragm and sensory fibers to the central part. They pass through the thoracic cavity, between the mediastinal pleura and the pericardium, to the superior surface of the diaphragm. At this point, the right phrenic nerve accompanies the inferior vena cava through the diaphragm and the left phrenic nerve passes through the diaphragm by itself (see
Fig. 4.143). Additional sensory fibers are supplied to the peripheral areas of the diaphragm by intercostal nerves.
The bean-shaped kidneys are retroperitoneal in the posterior abdominal region (Fig. 4.149). They lie in the extraperitoneal connective tissue immediately lateral to the vertebral column. In the supine position, the kidneys extend from approximately vertebra TXII superiorly to vertebra LIII inferiorly, with the right kidney somewhat lower than the left because of its relationship with the liver. Although they are similar in size and shape, the left kidney is a longer and more slender organ than the right kidney, and nearer to the midline.
Relationships to other structures
The anterior surface of the right kidney is related to numerous structures, some of which are separated from the kidney by a layer of peritoneum and some of which are directly against the kidney (Fig. 4.150):
A small part of the superior pole is covered by the right suprarenal gland.
Moving inferiorly, a large part of the rest of the upper part of the anterior surface is against the liver and is separated from it by a layer of peritoneum.
Medially, the descending part of the duodenum is retroperitoneal and contacts the kidney.
The inferior pole of the kidney, on its lateral side, is directly associated with the right colic flexure and, on its medial side, is covered by a segment of the intraperitoneal small intestine.
The anterior surface of the left kidney is also related to numerous structures, some with an intervening layer of peritoneum and some directly against the kidney (Fig. 4.150):
A small part of the superior pole, on its medial side, is covered by the left suprarenal gland.
The rest of the superior pole is covered by the intraperitoneal stomach and spleen.
Moving inferiorly, the retroperitoneal pancreas covers the middle part of the kidney.