Which Nerve Plexus Controls The Motility Along The Length Of The Gut?
23.1 Overview of the Digestive System
Learning Objectives
By the finish of this section, y'all will exist able to:
- Draw the organs of the comestible canal from proximal to distal, and briefly state their function
- Identify the accessory digestive organs and briefly state their function
- Describe the four fundamental tissue layers of the comestible canal and the function of each layer
- Contrast the contributions of the enteric and autonomic nervous systems to digestive system functioning
- Explicate how the peritoneum anchors the digestive organs
The function of the digestive arrangement is to pause down the foods y'all eat, release their nutrients, and blot those nutrients into the trunk. Although the small-scale intestine is the workhorse of the system, where the bulk of digestion occurs, and where almost of the released nutrients are captivated into the blood or lymph, each of the digestive system organs makes a vital contribution to this procedure (Figure 23.1.i).
Equally is the case with all torso systems, the digestive system does not piece of work in isolation; information technology functions cooperatively with the other systems of the trunk. Consider for example, the interrelationship between the digestive and cardiovascular systems. Arteries supply the digestive organs with oxygen and processed nutrients, and veins drain the digestive tract. These intestinal veins, constituting the hepatic portal system, are unique in that they do not return claret direct to the centre. Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing before blood completes its excursion back to the middle. At the aforementioned time, the digestive system provides nutrients to the middle muscle and vascular tissue to support their functioning. The interrelationship of the digestive and endocrine systems is also critical. Hormones secreted by several endocrine glands, as well equally endocrine cells of the pancreas, the breadbasket, and the small intestine, contribute to the control of digestion and nutrient metabolism. In plow, the digestive organization provides the nutrients to fuel endocrine function. Table 23.1 gives a quick glimpse at how these other systems contribute to the functioning of the digestive system.
| Contribution of Other Body Systems to the Digestive System (Tabular array 23.1) | |
|---|---|
| Body system | Benefits received past the digestive system |
| Cardiovascular | Blood supplies digestive organs with oxygen and processed nutrients; absorption of nutrients |
| Endocrine | Endocrine hormones assist regulate secretion in digestive glands and accessory organs |
| Integumentary | Pare helps protect digestive organs and synthesizes vitamin D for calcium assimilation |
| Lymphatic | Mucosa-associated lymphoid tissue and other lymphatic tissue defend confronting entry of pathogens; lacteals absorb lipids; and lymphatic vessels transport lipids to bloodstream |
| Muscular | Skeletal muscles support and protect abdominal organs |
| Nervous | Sensory and motor neurons assistance regulate secretions and muscle contractions in the digestive tract |
| Respiratory | Respiratory organs provide oxygen and remove carbon dioxide |
| Skeletal | Bones aid protect and support digestive organs |
| Urinary | Kidneys convert vitamin D into its active form, allowing calcium absorption in the pocket-size intestine |
Digestive System Organs
The easiest mode to understand the digestive system is to divide its organs into two principal categories. The commencement group is the organs that brand up the comestible canal. Accessory digestive organs comprise the 2nd group and are critical for orchestrating the breakdown of food and the assimilation of its nutrients into the body. Accessory digestive organs, despite their name, are critical to the office of the digestive organization.
Alimentary Canal Organs
Besides called the gastrointestinal (GI) tract or gut, the gastrointestinal tract (aliment- = "to nourish") is a ane-style tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured later death, one time smooth muscle tone is lost. The primary function of the organs of the alimentary culvert is to nourish the torso by digesting food and absorbing released nutrients. This tube begins at the mouth and terminates at the anus. Between those ii points, the canal is modified every bit the pharynx, esophagus, stomach, and modest and large intestines to fit the functional needs of the torso. Both the oral fissure and anus are open to the external surround; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Only through the procedure of absorption practise the nutrients in food enter into and nourish the body'south "inner space."
Accessory Structures
Each accessory digestive organ aids in the breakup of food (Figure 23.1.2). Within the mouth, the teeth and tongue begin mechanical digestion, whereas the salivary glands begin chemical digestion. Once nutrient products enter the small intestine, the gallbladder, liver, and pancreas release secretions—such as bile and enzymes—essential for digestion to continue. Together, these are called accessory organs considering they sprout from the lining cells of the developing gut (mucosa) and augment its function; indeed, you could not live without their vital contributions, and many significant diseases result from their malfunction. Fifty-fifty afterwards development is complete, they maintain a connection to the gut by style of ducts.
Histology of the Gastrointestinal tract
Throughout its length, the alimentary tract is composed of the same four tissue layers; the details of their structural arrangements vary to fit their specific functions. Starting from the lumen and moving outwards, these layers are the mucosa, submucosa, muscularis, and serosa, which is continuous with the mesentery (see Figure 23.1.ii).
The mucosa is referred to as a mucous membrane, because mucus product is a characteristic feature of gut epithelium. The membrane consists of epithelium, which is in direct contact with ingested food, and the lamina propria, a layer of connective tissue analogous to the dermis. In addition, the mucosa has a sparse, smooth muscle layer, called the muscularis mucosa (not to be dislocated with the muscularis layer, described below).
Epithelium—In the mouth, pharynx, esophagus, and anal canal, the epithelium is primarily a non-keratinized, stratified squamous epithelium. In the stomach and intestines, information technology is a unproblematic columnar epithelium. Find that the epithelium is in direct contact with the lumen, the space inside the comestible canal. Interspersed amidst its epithelial cells are goblet cells, which secrete mucus and fluid into the lumen, and enteroendocrine cells, which secrete hormones into the interstitial spaces between cells. Epithelial cells take a very cursory lifespan, averaging from but a couple of days (in the mouth) to about a calendar week (in the gut). This process of rapid renewal helps preserve the health of the gastrointestinal tract, despite the clothing and tear resulting from continued contact with foodstuffs.
Lamina propria—In improver to loose connective tissue, the lamina propria contains numerous blood and lymphatic vessels that transport nutrients absorbed through the alimentary culvert to other parts of the body. The lamina propria also serves an allowed part by housing clusters of lymphocytes, making upward the mucosa-associated lymphoid tissue (MALT). These lymphocyte clusters are particularly substantial in the distal ileum where they are known as Peyer's patches. When y'all consider that the alimentary culvert is exposed to foodborne bacteria and other foreign matter, it is not hard to capeesh why the immune system has evolved a ways of defending against the pathogens encountered inside it.
Muscularis mucosa—This thin layer of smooth musculus is in a constant state of tension, pulling the mucosa of the tummy and minor intestine into undulating folds. These folds dramatically increment the area bachelor for digestion and absorption.
As its name implies, the submucosa lies immediately beneath the mucosa. A broad layer of dense connective tissue, information technology connects the overlying mucosa to the underlying muscularis. It includes claret and lymphatic vessels (which transport absorbed nutrients), and a handful of submucosal glands that release digestive secretions. Additionally, it serves as a conduit for a dumbo branching network of fretfulness, the submucosal plexus, which functions as described below.
The 3rd layer of the alimentary canal is the muscalaris (also chosen the muscularis externa). The muscularis in the pocket-sized intestine is made up of a double layer of smooth muscle: an inner circular layer and an outer longitudinal layer. The contractions of these layers promote mechanical digestion, expose more of the food to digestive chemicals, and move the nutrient forth the culvert. In the most proximal and distal regions of the alimentary culvert, including the mouth, throat, anterior part of the esophagus, and external anal sphincter, the muscularis is made up of skeletal musculus, which gives yous voluntary control over swallowing and defecation. The basic two-layer structure institute in the small intestine is modified in the organs proximal and distal to it. The tummy is equipped for its churning function past the addition of a tertiary layer, the oblique muscle. While the colon has two layers like the modest intestine, its longitudinal layer is segregated into iii narrow parallel bands, the tenia coli, which make it look like a series of pouches rather than a simple tube.
The serosa is the portion of the comestible canal superficial to the muscularis. Present only in the region of the gastrointestinal tract within the abdominal cavity, it consists of a layer of visceral peritoneum overlying a layer of loose connective tissue. Instead of serosa, the mouth, pharynx, and esophagus accept a dense sheath of collagen fibers chosen the adventitia. These tissues serve to hold the alimentary canal in identify near the ventral surface of the vertebral cavalcade.
Nerve Supply
Every bit before long as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves. Without these nerves, not only would your food exist without taste, but yous would also be unable to feel either the food or the structures of your mouth, and you lot would be unable to avoid biting yourself every bit you chew, an action enabled past the motor branches of cranial nerves.
Intrinsic innervation of much of the gastrointestinal tract is provided by the enteric nervous organisation, which runs from the esophagus to the anus, and contains approximately 100 million motor, sensory, and interneurons (unique to this system compared to all other parts of the peripheral nervous organization). These enteric neurons are grouped into two plexuses. The myenteric plexus (plexus of Auerbach) lies in the muscularis layer of the alimentary culvert and is responsible for motility, especially the rhythm and force of the contractions of the muscularis. The submucosal plexus (plexus of Meissner) lies in the submucosal layer and is responsible for regulating digestive secretions and reacting to the presence of food (see Figure 23.1.2).
Extrinsic innervations of the alimentary canal are provided by the autonomic nervous organization, which includes both sympathetic and parasympathetic nerves. In general, sympathetic activation (the fight-or-flight response) restricts the activeness of enteric neurons, thereby decreasing GI secretion and motility. In dissimilarity, parasympathetic activation (the remainder-and-digest response) increases GI secretion and motility by stimulating neurons of the enteric nervous arrangement.
Claret Supply
The blood vessels serving the digestive organization have two functions. They transport the poly peptide and carbohydrate nutrients absorbed by mucosal cells after food is digested in the lumen. Lipids are absorbed via lacteals, tiny structures of the lymphatic organization. The blood vessels' second office is to supply the organs of the alimentary canal with the nutrients and oxygen needed to bulldoze their cellular processes.
Specifically, the more anterior parts of the gastrointestinal tract are supplied with blood by arteries branching off the aortic curvation and thoracic aorta. Below this point, the alimentary culvert is supplied with blood by arteries branching from the abdominal aorta. The celiac trunk services the liver, tum, and duodenum, whereas the superior and junior mesenteric arteries supply blood to the remaining small and large intestines.
The veins that collect nutrient-rich blood from the small intestine (where well-nigh assimilation occurs) empty into the hepatic portal organisation. This venous network takes the blood into the liver where the nutrients are either candy or stored for later use. Only then does the blood tuckered from the alimentary canal viscera circulate back to the eye. To appreciate just how demanding the digestive process is on the cardiovascular system, consider that while you are "resting and digesting," about one-quaternary of the blood pumped with each heartbeat enters arteries serving the intestines.
The Peritoneum
The digestive organs within the abdominal cavity are held in place by the peritoneum, a wide serous membranous sac fabricated up of squamous epithelial tissue surrounded by connective tissue. It is composed of two dissimilar regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the intestinal organs (Effigy 23.i.3). The peritoneal cavity is the infinite bounded past the visceral and parietal peritoneal surfaces. A few milliliters of watery fluid act as a lubricant to minimize friction betwixt the serosal surfaces of the peritoneum.
Disorders of the…Digestive System: Peritonitis
Inflammation of the peritoneum is called peritonitis. Chemical peritonitis can develop any time the wall of the gastrointestinal tract is breached, allowing the contents of the lumen entry into the peritoneal cavity. For example, when an ulcer perforates the stomach wall, gastric juices spill into the peritoneal cavity. Hemorrhagic peritonitis occurs after a ruptured tubal pregnancy or traumatic injury to the liver or spleen fills the peritoneal cavity with blood. Even more astringent peritonitis is associated with bacterial infections seen with appendicitis, colonic diverticulitis, and pelvic inflammatory affliction (infection of uterine tubes, usually past sexually transmitted leaner). Peritonitis is life threatening and frequently results in emergency surgery to correct the underlying problem and intensive antibiotic therapy. When your great grandparents and even your parents were young, the bloodshed from peritonitis was loftier. Aggressive surgery, improvements in anesthesia safety, the accelerate of critical intendance expertise, and antibiotics have greatly improved the mortality rate from this condition. Even so, the bloodshed charge per unit still ranges from xxx to 40 percent.
The visceral peritoneum includes multiple large folds that envelope various abdominal organs, holding them to the dorsal surface of the body wall. Within these folds are blood vessels, lymphatic vessels, and nerves that innervate the organs with which they are in contact, supplying their next organs. The five major peritoneal folds are described in Tabular array 23.2. An of import 1 of these folds is the mesentery which attaches the small intestine to the body wall allowing for blood vessels, fretfulness, and lymphatic vessels to have a secure structure to travel through on their way to and from the minor intestine. The mesocolon is the portion of the mesentery serving the colon and is considered function of the larger mesentery organ. Note that during fetal development, certain digestive structures, including the first portion of the small intestine (chosen the duodenum), the pancreas, and portions of the large intestine (the ascending and descending colon, and the rectum) remain completely or partially posterior to the peritoneum. Thus, the location of these organs is described as retroperitoneal.
| The Five Major Peritoneal Folds (Table 23.2) | |
|---|---|
| Fold | Description |
| Greater omentum | Frock-like structure that lies superficial to the small intestine and transverse colon; a site of fat deposition in people who are overweight |
| Falciform ligament | Anchors the liver to the anterior abdominal wall and inferior border of the diaphragm |
| Lesser omentum | Suspends the stomach from the inferior edge of the liver; provides a pathway for structures connecting to the liver |
| Mesentery | Vertical band of tissue inductive to the lumbar vertebrae and anchoring all of the small intestine except the initial portion (the duodenum) |
| Mesocolon | Attaches ii portions of the large intestine (the transverse and sigmoid colon) to the posterior abdominal wall |
External Website
By clicking on this link yous can watch a curt video of what happens to the food you eat, every bit it passes from your mouth to your intestine. Along the mode, note how the food changes consistency and form. How does this change in consistency facilitate your gaining nutrients from food?
Affiliate Review
The digestive system includes the organs of the gastrointestinal tract and accessory structures. The alimentary culvert forms a continuous tube that is open to the exterior environment at both ends. The organs of the alimentary culvert are the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The accompaniment digestive structures include the teeth, tongue, salivary glands, liver, pancreas, and gallbladder. The wall of the alimentary canal is composed of 4 basic tissue layers: mucosa, submucosa, muscularis, and serosa. The enteric nervous system provides intrinsic innervation, and the autonomic nervous system provides extrinsic innervation.
Interactive Link Questions
By clicking on this link, you tin watch a curt video of what happens to the food yous eat as information technology passes from your mouth to your intestine. Along the way, annotation how the nutrient changes consistency and course. How does this change in consistency facilitate your gaining nutrients from nutrient?
Answers may vary.
Review Questions
Critical Thinking Questions
1. Explain how the enteric nervous system supports the digestive system. What might occur that could upshot in the autonomic nervous system having a negative bear upon on digestion?
ii. What layer of the alimentary canal tissue is capable of helping to protect the torso confronting disease, and through what mechanism?
Glossary
- accessory digestive organ
- includes teeth, tongue, salivary glands, gallbladder, liver, and pancreas
- alimentary canal
- continuous muscular digestive tube that extends from the mouth to the anus
- motility
- motion of food through the GI tract
- mucosa
- innermost lining of the gastrointestinal tract
- muscularis
- muscle (skeletal or smooth) layer of the gastrointestinal tract wall
- myenteric plexus
- (plexus of Auerbach) major nerve supply to alimentary canal wall; controls motility
- retroperitoneal
- located posterior to the peritoneum
- serosa
- outermost layer of the alimentary canal wall present in regions inside the abdominal crenel
- submucosa
- layer of dense connective tissue in the alimentary canal wall that binds the overlying mucosa to the underlying muscularis
- submucosal plexus
- (plexus of Meissner) nervus supply that regulates activity of glands and smoothen muscle
Solutions
Answers for Critical Thinking Questions
- The enteric nervous system helps regulate gastrointestinal tract move and the secretion of digestive juices, thus facilitating digestion. If a person becomes overly anxious, sympathetic innervation of the alimentary canal is stimulated, which can result in a slowing of digestive activity.
- The lamina propria of the mucosa contains lymphoid tissue that makes up the MALT and responds to pathogens encountered in the alimentary canal.
Which Nerve Plexus Controls The Motility Along The Length Of The Gut?,
Source: https://open.oregonstate.education/aandp/chapter/23-1-overview-of-the-digestive-system/
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