Anatomy and Physiology Artlabeling Activity Figure 1321b 1 of 2

Learning Objectives

By the end of this section, you volition be able to:

• Identify the organs of the alimentary canal from proximal to distal, and briefly state their function
• Identify the accessory digestive organs and briefly state their office
• Describe the four fundamental tissue layers of the gastrointestinal tract
• Contrast the contributions of the enteric and autonomic nervous systems to digestive system functioning
• Explain how the peritoneum anchors the digestive organs

The function of the digestive system is to interruption down the foods you consume, release their nutrients, and absorb those nutrients into the body. Although the modest intestine is the workhorse of the organization, where the majority of digestion occurs, and where most of the released nutrients are captivated into the claret or lymph, each of the digestive organization organs makes a vital contribution to this process (Effigy 23.2).

Figure 23.2 Components of the Digestive System All digestive organs play integral roles in the life-sustaining process of digestion.

As is the case with all trunk systems, the digestive organization does not piece of work in isolation; information technology functions cooperatively with the other systems of the body. Consider for case, 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 arrangement, are unique; they practise not return blood directly to the center. Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing earlier claret completes its circuit back to the center. At the same time, the digestive organization provides nutrients to the heart musculus and vascular tissue to support their operation. The interrelationship of the digestive and endocrine systems is also disquisitional. Hormones secreted by several endocrine glands, likewise equally endocrine cells of the pancreas, the stomach, and the pocket-sized intestine, contribute to the control of digestion and nutrient metabolism. In plough, the digestive system provides the nutrients to fuel endocrine function. Table 23.1 gives a quick glimpse at how these other systems contribute to the performance of the digestive system.

Contribution of Other Body Systems to the Digestive System

Body system	Benefits received past the digestive system
Cardiovascular	Blood supplies digestive organs with oxygen and processed nutrients
Endocrine	Endocrine hormones help regulate secretion in digestive glands and accompaniment organs
Integumentary	Skin helps protect digestive organs and synthesizes vitamin D for calcium absorption
Lymphatic	Mucosa-associated lymphoid tissue and other lymphatic tissue defend against 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 help regulate secretions and muscle contractions in the digestive tract
Respiratory	Respiratory organs provide oxygen and remove carbon dioxide
Skeletal	Bones help protect and support digestive organs
Urinary	Kidneys convert vitamin D into its agile form, allowing calcium absorption in the small-scale intestine

Tabular array 23.1

Digestive Arrangement Organs

The easiest way to understand the digestive arrangement is to divide its organs into 2 master categories. The first grouping is the organs that make upward the gastrointestinal tract. Accessory digestive organs comprise the 2d grouping and are critical for orchestrating the breakdown of nutrient and the absorption of its nutrients into the body. Accessory digestive organs, despite their name, are critical to the function of the digestive system.

Gastrointestinal tract Organs

Likewise called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = "to nourish") is a one-way tube about 7.62 meters (25 anxiety) in length during life and closer to 10.67 meters (35 feet) in length when measured afterward death, once shine muscle tone is lost. The main function of the organs of the alimentary canal is to nourish the body. This tube begins at the oral fissure and terminates at the anus. Betwixt those two points, the canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the trunk. Both the oral fissure and anus are open up to the external environment; thus, food and wastes within the comestible canal are technically considered to exist outside the body. Only through the procedure of assimilation practice the nutrients in food enter into and nourish the torso's "inner space."

Accessory Structures

Each accessory digestive organ aids in the breakup of food (Figure 23.3). Within the mouth, the teeth and natural language begin mechanical digestion, whereas the salivary glands brainstorm chemical digestion. Once food 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 accompaniment organs because they sprout from the lining cells of the developing gut (mucosa) and augment its function; indeed, you could not alive without their vital contributions, and many pregnant diseases issue from their malfunction. Even later development is complete, they maintain a connection to the gut by way of ducts.

Histology of the Gastrointestinal tract

Throughout its length, the comestible tract is equanimous of the aforementioned 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 23.3).

Figure 23.3 Layers of the Comestible Canal The wall of the alimentary canal has iv basic tissue layers: the mucosa, submucosa, muscularis, and serosa.

The mucosa is referred to equally a mucous membrane, considering mucus product is a feature 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 thin, smoothen muscle layer, chosen the muscularis mucosae (not to exist dislocated with the muscularis layer, described below).

Epithelium—In the oral cavity, throat, esophagus, and anal canal, the epithelium is primarily a not-keratinized, stratified squamous epithelium. In the breadbasket and intestines, it is a simple columnar epithelium. Observe that the epithelium is in direct contact with the lumen, the space inside the gastrointestinal tract. Interspersed among 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 only a couple of days (in the oral fissure) to about a week (in the gut). This process of rapid renewal helps preserve the health of the alimentary canal, despite the wearable and tear resulting from continued contact with foodstuffs.

Lamina propria—In addition to loose connective tissue, the lamina propria contains numerous claret and lymphatic vessels that transport nutrients absorbed through the comestible canal to other parts of the body. The lamina propria also serves an allowed function by housing clusters of lymphocytes, making upwards the mucosa-associated lymphoid tissue (MALT). These lymphocyte clusters are particularly substantial in the distal ileum where they are known equally Peyer's patches. When you consider that the alimentary canal is exposed to foodborne bacteria and other strange matter, it is non hard to capeesh why the immune organization has evolved a means of defending against the pathogens encountered within it.

Muscularis mucosae—This thin layer of smooth muscle is in a constant state of tension, pulling the mucosa of the stomach and small intestine into undulating folds. These folds dramatically increase the surface area available for digestion and absorption.

As its proper noun implies, the submucosa lies immediately below the mucosa. A broad layer of dense connective tissue, it connects the overlying mucosa to the underlying muscularis. It includes blood and lymphatic vessels (which ship captivated nutrients), and a scattering of submucosal glands that release digestive secretions. Additionally, information technology serves every bit a conduit for a dense branching network of fretfulness, the submucosal plexus, which functions as described beneath.

The tertiary layer of the alimentary canal is the muscularis (also called the muscularis externa). The muscularis in the small 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 food along the canal. In the most proximal and distal regions of the alimentary canal, including the mouth, throat, inductive part of the esophagus, and external anal sphincter, the muscularis is fabricated up of skeletal muscle, which gives y'all voluntary control over swallowing and defecation. The bones 2-layer structure found in the small intestine is modified in the organs proximal and distal to information technology. The tummy is equipped for its churning function by the addition of a third layer, the oblique musculus. While the colon has two layers similar the small intestine, its longitudinal layer is segregated into three narrow parallel bands, the tenia coli, which make it wait similar a serial of pouches rather than a simple tube.

The serosa is the portion of the alimentary canal superficial to the muscularis. Present simply in the region of the alimentary culvert within the intestinal crenel, it consists of a layer of visceral peritoneum overlying a layer of loose connective tissue. Instead of serosa, the mouth, throat, and esophagus take a dense sheath of collagen fibers called the adventitia. These tissues serve to concord the gastrointestinal tract in place near the ventral surface of the vertebral cavalcade.

Nerve Supply

Equally soon equally food enters the mouth, it is detected by receptors that send impulses forth the sensory neurons of cranial nerves. Without these nerves, non only would your nutrient be without sense of taste, but you would also be unable to feel either the food or the structures of your oral fissure, and you lot would be unable to avoid bitter yourself as you lot chew, an action enabled by the motor branches of cranial nerves.

Intrinsic innervation of much of the alimentary canal is provided by the enteric nervous organisation, which runs from the esophagus to the anus, and contains approximately 100 meg motor, sensory, and interneurons (unique to this system compared to all other parts of the peripheral nervous system). These enteric neurons are grouped into two plexuses. The myenteric plexus (plexus of Auerbach) lies in the muscularis layer of the alimentary canal and is responsible for motility, specially 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 Effigy 23.3).

Extrinsic innervations of the alimentary canal are provided by the autonomic nervous organisation, which includes both sympathetic and parasympathetic nerves. In general, sympathetic activation (the fight-or-flight response) restricts the activity of enteric neurons, thereby decreasing GI secretion and motion. In contrast, parasympathetic activation (the balance-and-digest response) increases GI secretion and motility by stimulating neurons of the enteric nervous system.

Blood Supply

The claret vessels serving the digestive system have two functions. They transport the protein and carbohydrate nutrients captivated by mucosal cells subsequently nutrient is digested in the lumen. Lipids are absorbed via lacteals, tiny structures of the lymphatic organization. The blood vessels' second function is to supply the organs of the alimentary canal with the nutrients and oxygen needed to drive their cellular processes.

Specifically, the more anterior parts of the alimentary canal are supplied with claret by arteries branching off the aortic arch and thoracic aorta. Below this point, the gastrointestinal tract is supplied with blood by arteries branching from the abdominal aorta. The celiac trunk services the liver, stomach, and duodenum, whereas the superior and inferior mesenteric arteries supply blood to the remaining small and large intestines.

The veins that collect food-rich blood from the pocket-size intestine (where well-nigh absorption occurs) empty into the hepatic portal system. This venous network takes the claret into the liver where the nutrients are either processed or stored for later employ. Only and then does the blood drained from the gastrointestinal tract viscera circulate back to the heart. To appreciate merely how enervating the digestive process is on the cardiovascular system, consider that while y'all are "resting and digesting," most one-quaternary of the claret 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 broad serous membranous sac made upwards of squamous epithelial tissue surrounded past connective tissue. Information technology is composed of two dissimilar regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs (Figure 23.four). The peritoneal cavity is the space divisional by the visceral and parietal peritoneal surfaces. A few milliliters of watery fluid deed as a lubricant to minimize friction between the serosal surfaces of the peritoneum.

Figure 23.4 The Peritoneum A cross-section of the abdomen shows the human relationship between abdominal organs and the peritoneum (darker lines).

Disorders of the...

Digestive Organisation: Peritonitis

Inflammation of the peritoneum is chosen peritonitis. Chemic peritonitis can develop whatever time the wall of the alimentary culvert is breached, allowing the contents of the lumen entry into the peritoneal cavity. For example, when an ulcer perforates the tummy wall, gastric juices spill into the peritoneal cavity. Hemorrhagic peritonitis occurs later a ruptured tubal pregnancy or traumatic injury to the liver or spleen fills the peritoneal crenel with blood. Even more severe peritonitis is associated with bacterial infections seen with appendicitis, colonic diverticulitis, and pelvic inflammatory affliction (infection of uterine tubes, usually by sexually transmitted bacteria). Peritonitis is life threatening and oft results in emergency surgery to correct the underlying problem and intensive antibody therapy. When your great grandparents and fifty-fifty your parents were young, the mortality from peritonitis was high. Aggressive surgery, improvements in anesthesia safety, the accelerate of critical care expertise, and antibiotics accept greatly improved the mortality rate from this status. Withal, the mortality rate still ranges from 30 to forty per centum.

The visceral peritoneum includes multiple large folds that envelope diverse abdominal organs, holding them to the dorsal surface of the torso wall. Within these folds are claret vessels, lymphatic vessels, and fretfulness that innervate the organs with which they are in contact, supplying their adjacent organs. The five major peritoneal folds are described in Table 23.2. Notation that during fetal development, certain digestive structures, including the beginning portion of the small intestine (called 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

Fold	Description
Greater omentum	Frock-like construction 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 edge of the diaphragm
Bottom omentum	Suspends the stomach from the inferior border of the liver; provides a pathway for structures connecting to the liver
Mesentery	Vertical band of tissue anterior to the lumbar vertebrae and anchoring all of the pocket-sized intestine except the initial portion (the duodenum)
Mesocolon	Attaches two portions of the large intestine (the transverse and sigmoid colon) to the posterior intestinal wall

Table 23.2

Interactive Link

By clicking on this link you can sentinel a short video of what happens to the nutrient you eat, as it passes from your mouth to your intestine. Along the way, note how the food changes consistency and grade. How does this change in consistency facilitate your gaining nutrients from food?

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Source: https://openstax.org/books/anatomy-and-physiology-2e/pages/23-1-overview-of-the-digestive-system

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