234 Development of the Digestive System
Digestive System Development
The digestive system is an endoderm-derived structure that begins developing about the fourth week of embryogenesis.
Learning Objectives
Outline the development of the embryonic digestive system
Key Takeaways
Key Points
- Around the 16th day of human development, the embryo begins to fold and the ventral surface becomes concave in two directions. The sides of the embryo fold in on each other and the head and tail fold toward one another, forming the primitive gut.
- During fetal life, the primitive gut is divided into three segments: foregut (mouth to duodenum ), midgut (duodenum to colon ), and hindgut (majority of colon and rectum ).
- The stomach and colon (derived from the gut proper), develop as swellings of the primitive gut. In contrast, gut-related derivatives (e.g. those structures that derive from the primitive gut, but are not part of the gut proper), generally develop as out-pouchings of the primitive gut.
Key Terms
- midgut: The portion of the embryo from which most of the intestines develop.
- foregut: The anterior part of the alimentary canal of an embryo, from the mouth to the duodenum.
- hindgut: The posterior (caudal) part of the alimentary canal. In mammals, it includes the distal third of the transverse colon and the splenic flexure, descending colon, sigmoid colon, and rectum.
Development of Digestive System: Sagittal section of embryo at about four weeks showing the primitive gut.
The gut is an endoderm-derived structure. At approximately the 16th day of human development, the embryo begins to fold ventrally (with the embryo’s ventral surface becoming concave) in two directions: the sides of the embryo fold in on each other and the head and tail fold toward one another. The result is that a piece of the yolk sac, an endoderm-lined structure in contact with the ventral aspect of the embryo, begins to detach and become the primitive gut. The yolk sac remains connected to the gut tube via the vitelline duct. Usually this structure regresses during development. In cases where it does not, it is known as Meckel’s diverticulum.
During fetal life, the primitive gut can be divided into three segments: foregut, midgut, and hindgut. Although these terms are often used in reference to segments of the primitive gut, they are also used regularly to describe components of the definitive gut as well. Each segment of the gut gives rise to specific gut and gut-related structures in later development. Components derived from the gut proper, including the stomach and colon, develop as swellings or dilatations of the primitive gut. In contrast, gut-related derivatives (structures that derive from the primitive gut, but are not part of the gut proper), generally develop as out-pouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development. The foregut is the esophagus to the first two sections of the duodenum, liver, gallbladder, and superior portion of pancreas. The midgut is the lower duodenum, leading to the first two-thirds of the transverse colon, jejunum, ileum, cecum, appendix, ascending colon, and first two-thirds of the transverse colon. The hindgut includes the last third of the transverse colon, descending colon, rectum, and upper part of the anal canal.
Aging and the Digestive System
Aging can result in changes in the digestive system due to decreased nerve sensitivity, muscle loss, and increased infection rate.
Learning Objectives
Analyze the affects of aging on the digestive system
Key Takeaways
Key Points
- Individual digestive tract organs can be targeted by pathologies specific to that organ.
- Common changes in the upper intestinal tract include periodontal disease, difficulty swallowing, gastritis, and peptic ulcer disease.
- Changes in the small intestine include appendicitis, duodenal ulcers, malabsorption, maldigestion. acute pancreatitis, jaundice, and gallbladder problems.
Key Terms
- jaundice: A yellowish pigmentation of the skin, the whites of the eyes (sclera), and other mucous membranes caused by increased levels of bilirubin in the blood that build up in extracellular fluid, usually due to liver disease.
- gastritis: Inflammation of the lining of the stomach, characterized by nausea, loss of appetite, and upper abdominal discomfort or pain.
The changes associated with aging of the digestive system are largely caused by decreased nerve sensitivity, loss of muscle tone, and increased susceptibility to bacterial infection because of a weakened immune system. Thus, changes include loss of strength and tone of muscular tissue and supporting muscular tissue, decreased secretory mechanisms, decreased motility of the digestive organs, changes in neurosensory feedback regarding enzyme and hormone release, and diminished response to internal sensations and pain.
Digestive Tract: Several aspects of the digestive tract are labeled in this diagram, including the mouth, large intestine (colon), rectum, anus, ileum, small intestine, stomach, and esophagus.
In the upper GI tract, common issues include:
- Periodontal disease, which is caused by bacterial infection and affects alveolar bone, periodontal ligament, cementum, and/or gingiva.
- Difficulty swallowing due to loss of muscle tone.
- Reduced sensitivity to mouth irritations and sores, likely caused by nerve damage.
- Loss of taste, which can be caused by local damage and inflammation that interferes with the taste buds stemming from radiation therapy, tobacco use, and denture use.
- Gastritis, an inflammation of the stomach lining that can develop after traumatic injury or severe infection.
- Peptic ulcer disease, largely due to weakened immune systems unable to clear the bacterial infection.
Issues common in the small intestine include:
- Appendicitis
- Duodenal ulcers
- Malabsorption of nutrients due to inflammatory bowel disease, radiation enteritis, digestive failure, and malnutrition.
- Maldigestion.
Other pathologies that increase in occurrence with age include acute pancreatitis, jaundice, and gallbladder problems. Large intestinal changes such as hemorrhoids and constipation may also occur. Cancer incidence in general increases with age, including risk for rectal cancer.
