Anatomy And Physiology Digestive System Notes Pdf

anatomy and physiology digestive system notes pdf

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To survive, we need to take nutrients from the food that we eat. This is achieved by digestion, a complicated process that takes place in our gut. Although food contains all of the nutrients we need for good health, they are locked up in large, complex compounds.

The digestive system uses mechanical and chemical activities to break food down into absorbable substances during its journey through the digestive system.

Quick Anatomy Lesson: Human Digestive System

The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body. Although the small intestine is the workhorse of the system, where the majority of digestion occurs, and where most of the released nutrients are absorbed into the blood or lymph, each of the digestive system organs makes a vital contribution to this process.

Figure 1. All digestive organs play integral roles in the life-sustaining process of digestion. As is the case with all body systems, the digestive system does not work in isolation; it functions cooperatively with the other systems of the body. 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; they do not return blood directly to the heart. Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing before blood completes its circuit back to the heart. At the same time, the digestive system provides nutrients to the heart 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 as endocrine cells of the pancreas, the stomach, and the small intestine, contribute to the control of digestion and nutrient metabolism. In turn, the digestive system provides the nutrients to fuel endocrine function. The easiest way to understand the digestive system is to divide its organs into two main categories.

The first group is the organs that make up the alimentary canal. Accessory digestive organs comprise the second 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 function of the digestive system.

The main function of the organs of the alimentary canal is to nourish the body. This tube begins at the mouth and terminates at the anus. Between those two points, the canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the body.

Both the mouth and anus are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Each accessory digestive organ aids in the breakdown of food. Within the mouth, the teeth and tongue begin mechanical digestion, whereas the salivary glands begin 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 accessory organs because 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.

Even after development is complete, they maintain a connection to the gut by way of ducts. 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.

Figure 2. The wall of the alimentary canal has four basic tissue layers: the mucosa, submucosa, muscularis, and serosa. The mucosa is referred to as a mucous membrane, because mucus production 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 thin, smooth muscle layer, called the muscularis mucosa not to be confused with the muscularis layer, described below. As its name implies, the submucosa lies immediately beneath 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 transport absorbed nutrients , and a scattering of submucosal glands that release digestive secretions. Additionally, it serves as a conduit for a dense branching network of nerves, the submucosal plexus, which functions as described below. The third layer of the alimentary canal is the muscalaris 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, pharynx, anterior part of the esophagus, and external anal sphincter, the muscularis is made up of skeletal muscle, which gives you voluntary control over swallowing and defecation.

The basic two-layer structure found in the small intestine is modified in the organs proximal and distal to it. The stomach is equipped for its churning function by the addition of a third layer, the oblique muscle.

While the colon has two layers like the small intestine, its longitudinal layer is segregated into three 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 alimentary canal superficial to the muscularis. Present only in the region of the alimentary canal 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 have a dense sheath of collagen fibers called the adventitia. These tissues serve to hold the alimentary canal in place near the ventral surface of the vertebral column.

As soon 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 be without taste, but you would also be unable to feel either the food or the structures of your mouth, and you would be unable to avoid biting yourself as you 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 system, which runs from the esophagus to the anus, and contains approximately million 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 , 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.

Extrinsic innervations of the alimentary canal are provided by the autonomic nervous system, 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 motility. In contrast, parasympathetic activation the rest-and-digest response increases GI secretion and motility by stimulating neurons of the enteric nervous system.

The blood vessels serving the digestive system have two functions. They transport the protein and carbohydrate nutrients absorbed by mucosal cells after food is digested in the lumen. Lipids are absorbed via lacteals, tiny structures of the lymphatic system.

Specifically, the more anterior parts of the alimentary canal are supplied with blood by arteries branching off the aortic arch and thoracic aorta. Below this point, the alimentary canal 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 nutrient-rich blood from the small intestine where most absorption occurs empty into the hepatic portal system.

This venous network takes the blood into the liver where the nutrients are either processed or stored for later use. Only then does the blood drained from the alimentary canal viscera circulate back to the heart.

The digestive organs within the abdominal cavity are held in place by the peritoneum, a broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue. It is composed of two different regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs. The peritoneal cavity is the space bounded by the visceral and parietal peritoneal surfaces.

A few milliliters of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum. Figure 3. A cross-section of the abdomen shows the relationship between abdominal organs and the peritoneum darker lines.

Inflammation of the peritoneum is called peritonitis. Chemical peritonitis can develop any time the wall of the alimentary canal 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 severe peritonitis is associated with bacterial infections seen with appendicitis, colonic diverticulitis, and pelvic inflammatory disease infection of uterine tubes, usually by sexually transmitted bacteria. Peritonitis is life threatening and often results in emergency surgery to correct the underlying problem and intensive antibiotic therapy.

When your great grandparents and even your parents were young, the mortality from peritonitis was high. Aggressive surgery, improvements in anesthesia safety, the advance of critical care expertise, and antibiotics have greatly improved the mortality rate from this condition.

Even so, the mortality rate still ranges from 30 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 adjacent organs. The five major peritoneal folds are described in Table 2. Note that during fetal development, certain digestive structures, including the first 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. Watch this short video of what happens to the food you eat , as it passes from your mouth to your intestine. Along the way, note how the food changes consistency and form. How does this change in consistency facilitate your gaining nutrients from food? The digestive system includes the organs of the alimentary canal and accessory structures. The alimentary canal forms a continuous tube that is open to the outside environment at both ends.

The organs of the alimentary canal are the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The accessory digestive structures include the teeth, tongue, salivary glands, liver, pancreas, and gallbladder. The wall of the alimentary canal is composed of four basic tissue layers: mucosa, submucosa, muscularis, and serosa.

The enteric nervous system provides intrinsic innervation, and the autonomic nervous system provides extrinsic innervation. Answer the question s below to see how well you understand the topics covered in the previous section. Skip to main content. Module 7: The Digestive System. Search for:.

Gastrointestinal system anatomy

Food that is chewed in the oral cavity then swallowed ends up in the stomach where it is further digested so its nutrients can be absorbed in the small intestine. The salivary glands, liver and gall bladder, and the pancreas aid the processes of ingestion, digestion, and absorption. These accessory organs of digestion play key roles in the digestive process. Each of these organs either secretes or stores substances that pass through ducts into the alimentary canal. Six salivary glands, located around the oral cavity, secrete saliva.

23.2 Digestive System Processes and Regulation

The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body. Although the small intestine is the workhorse of the system, where the majority of digestion occurs, and where most of the released nutrients are absorbed into the blood or lymph, each of the digestive system organs makes a vital contribution to this process. Figure 1.

The gastrointestinal tract , GI tract , GIT , digestive tract , digestion tract , alimentary canal is the tract from the mouth to the anus which includes all the organs of the digestive system in humans and other animals. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled as feces. The mouth , esophagus , stomach and intestines are all part of the gastrointestinal tract. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines.

Anatomy & Physiology of Digestion: 10 Facts That Explain How the Body Absorbs Nutrients

The digestive system is a kind of processing plant inside the body. It takes in food and pushes it through organs and structures where the processing happens.

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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 1. The Digestive System. We need food for cellular utilization: →nutrients as.

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Intro to A & P: Digestive Anatomy; Ziser Lecture Notes, 1. The Digestive System. We need food for cellular utilization: →nutrients as building blocks for.

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