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Lecture 12

DEV2022: Lecture 12 notes

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DEV2022 – LECTURE 12 Functions of abdominal wall muscles: The abdominal pressure can be increased or decreased. The abdominal muscles also bring stability to the vertebral column via the attachment to the roots. When they contract or relax have an action upon the structures to which they are attached – the trunk and the pelvis. Via the agency of the diaphragm, forms the top of the container of the abdominal cavity is essential in breathing. Raising intra-abdom pressure: If you increase abdominal pressure, structures inside are influenced. Segmental cutaneous innervation: The skin overlying the trunk and particularly the abdominal cavity is innervated in a dermatome type pattern. Major features of the abdomen: The abdominal cavity is not really a ‘cavity’ as there are no empty spaces. The cavity is filled with organs. However, the space between organs is a cavity, where that cavity is filled with fluid. Abdominal cavity: Extends superiorly to the diaphragm. It merges with the pelvic cavity. This cavity is completely closed in males from the external environment. In females, it is open to the external environment. The cavity is a sac, which is lined by a membrane. A serous sac is a membrane that secretes a serous or watery fluid. Abdominal-peritoneal-body cavity: The cavity is lined by a serous membrane (simple, squamous epithelium with supporting connective tissue, which secretes fluid). This is why an organ inside the abdom cavity is called a viscous (wet and sticky). They are kept wet and sticky by the serous membrane. Parietal covering walls Visceral covering all the organs inside the enclosed space. Development: Visceral peritoneum covering over the organs. Visceral nerves and vessels coming from a origin – spinal cord, autonomic nerves, aorta, etc. and they transit from their origin to the viscera. Parietal layer receives it nerves and vascular supply from the body wall, so they have somatic nerve supply (motor and sensory). The visceral layer is not innervated by somatic nerves, but the nerves supply to the viscera, which is the autonomic nervous sytem. Hence pain associated with something wrong with the viscera is not highly localized to a dermatome because there are not dermatomes. It is diffuse and wide spread because it's a member of the autonomic nervous system. Mesenteries: As it’s developed during embryogenesis, it is invaginating into the body cavity, and its taking its parietal and visceral membranes with it to produce an attachment. 2 sheets of surround membrane equal a mesentery. This allows structures to reach the viscera and in converse, structures from the viscera return to the body wall – nerve, veins, arteries, lymphatics. The mesenteries, in addition to providing a supply line of structures – vessels, nerves and lymphatics – also allow mobility of the gut. The mesentery is thin and delicate, like a rubber band where they can stretch and return to its original state. Mobility in some organs in the abdominal cavity is important for grinding food and processing food into packets, where we eventually expel as faeces. Vessels and nerves: Mesentery is a thin sheet, double layered serous membrane. Intraperitoneal viscera of GI tract: If they are intraperitoneal, these organs are suspended by mesenteries in the cavity. If something is being suspended, they will have mobility. Other organs are behind the peritoneal cavity where we call them posterior peritoneal organs. They include the kidneys, adrenals and ureters. They do not have a mesentery, as they are not free to move – they are fixed. Retro-peritoneal organs: Their mesentery during embryogenesis has fused with the parietal peritoneum. So they are no longer suspended in any way. The net result in this is that the organs in the retroperitoneal cavity are fixed, while some are mobile. Those, which are mobile, can expand (stomach). Mesenteries are not only the supply chain but they also allow the gut that they suspend to be mobile, and also allow expansion and contraction. The gut and associated organs: The gut tract is a tube from the mouth to anus. Derived from endoderm. The digestive tube is different as it has glands that are derived from that primitive gut tube (liver, pan
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