Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Internal Organs
General Overview of Internal Organs
Development of Body Cavities

To properly understand the Cytology/cytology/67.html">Development and Structure of the Internal Organs, let us examine the Water/144.html">Origin of the cavities that contain them. All of these cavities develop from the embryonic coelom.

Even at the Early stages of embryonic development, each of the lateral mesoderm plates splits into two layers: the visceral (splanchnic) and parietal (somatic) layers. A cavity, the coelom, appears between them (Fig. 4.1). This is a paired cavity; it arises behind the foregut in the mesoderm surrounding The Heart primordium and extends to the right, left, and caudally along the sides of the trunk gut. Both cavities communicate with each other in front of the heart primordium. The outer layer of each coelomic sac lines the inner body wall, fuses with it, and is therefore called the parietal layer; the inner layer, facing the median sagittal plane of the body, lies adjacent to the sides of the gut tube and forms the visceral layer. Both visceral layers come into contact and fuse with each other along the sagittal plane, dorsal and ventral to the gut tube. This gives rise to the dorsal and ventral mesenteries, which anchor the gut between the dorsal and ventral body walls. Later, part of the ventral mesentery disappears, leaving most of the intestine suspended only from the posterior body wall by the dorsal mesentery. Blood Vessels from the Abdominal Aorta and nerves grow into it. In the region of the Liver, the ventral mesentery is preserved. In the adult human, it is represented by the falciform ligament of The Liver and the hepatogastric ligament (lesser omentum).

Class="center">

Fig. 4.1. Early stages of coelom and mesentery development (after Patten):

1 — amnion; 2 — neural groove; 3 — somite; 4 — intraembryonic coelom; 5 — yolk sac wall; 6 — primitive gut; 7 — extraembryonic coelom; 8 — dorsal aorta; 9 — mesonephros; 10 — coelom; 11— gut; 12 — dorsal mesentery; 13 — ventral mesentery; 14 — neural tube; 15 — notochord; 16 — aorta; 17 — Kidney primordium; 18 — liver; 19 — ventral ligament of the liver; 20 — gonad primordium

The division of the coelom into separate cavities begins with The formation of the septum transversum between the ventricles of The Heart and the liver. It grows from the ventral to the DORSAL SIDE OF the body, dividing the coelom into the pericardial and peritoneal cavities. This gives rise to the primordium of the Diaphragm—its ventral part (up to the floor of the primitive gut). The dorsal part of the diaphragm is formed later by the growth of the pleuroperitoneal folds. Myoblasts migrate into the septum and folds from the cervical myotomes, and Muscle tissue develops. Dorsal to the gut, the anterior and posterior PARTS OF THE coelom are connected by short pleural canals. The lung buds later grow into these canals, expanding greatly to become the pleural cavities. They are separated from the pericardial and peritoneal cavities by paired tissue folds. In male embryos, two more small cavities evaginate from the caudal part of the peritoneal cavity into the Scrotum, surrounding the gonad (Testis).

Review Questions

1. Which internal Organ Systems do you know?

2. Describe the Body Cavities: pleural, pericardial, and abdominal.

3. What are the visceral and parietal Peritoneum?

4. Peritoneal derivatives: omenta, ligaments, and mesenteries.

5. Stages of Body Cavity Development in ontogeny.