Digestion

Fundus

The area of the stomach just below the cardia. It makes up the upper half of the stomach. Gastric secretions can be found here. This holds food before being mixed with chyme. As food is held here, salivary enzymes (such as amylase) continue to do its work.

Lingual frenulum

A flap of skin under the tongue. If a person had severe ankyloglossia, this would have to be cut so they could speak.

Somatostatin

A hormone in the stomach mucosa of the pyloric antrum and the duodenum. It is stimulated by the presence of food in the stomach and is used for restricting gastric secretions and emptying the stomach.

Ghrelin

A hormone that is found in the stomach mucosa of the fundus. It is activated by the fasting state. It is used to stimulate feelings of hunger and satisfaction.

Pancreatic juice

A juice secreted by the pancreas. It is rich in enzymes.

Pancreas

A long, pear shaped organ that secretes amylase (digests carbs), nucleases (digests nucleic acids), trypsinogen (digests proteins after being activated to trypsin) and sodium bicarbonate (to buffer acidic chyme).

Mixing wave

A unique type of peristalsis that mixes and softens the food with gastric juices to create chyme. Each wave happens in intervals of 20 seconds.

Cuspids

Also called canines. They are used to pierce tougher foods.

Voluntary phase

Also called the oral phase. It is the first phase of swallowing. It is consciously and voluntarily controlled.

Cephalic phase

Also known as the reflex phase. It is brief and takes place before food enters the stomach. It is stimulated by the senses, such as sight and taste. This is a conditioned reflex and occurs if you like a particular food. It increases gastric secretions.

Lingual lipase

An enzyme in the saliva that helps breaks down carbs. It has a minor role in breaking down fats, but this doesn't take full effect until it hits the stomach.

Acinus

An exocrine cell cluster found in the pancreas. It secretes enzyme rich pancreatic juice.

Gingivae

Another name for the gums. These surround teeth.

Labia

Another name for the lips. They are controlled by the orbicularis oris muscle, which also controls what comes in or goes out of the mouth. As someone chews, the muscle prevents food from falling out. This refers to the outer layer of the mouth that is covered by keratin.

Dentes

Another name for the teeth. These grind and tear food for mechanical digestion.

Deglutition

Another term for swallowing. It takes about 4 to 8 seconds for solid food and 1 second for soft foods. It is aided by mucus and saliva. It is controlled by skeletal muscle. It has three phases- the voluntary phase, the pharyngeal phase and the esophageal phase. The autonomic nervous system controls the last two.

Flora

Bacteria that live in the large intestine.

Incisors

Flat and sharp from teeth that are used for biting.

Upper esophageal sphincter

It acts as a gate that moves food from the pharynx to the esophagus. This is a muscle that contracts to close and relaxes to open.

Fungiform papillae

Mushroom shaped buds that cover a large area of the tongue. They are much larger in the back and smaller in the front of the tongue.

Tongue

One of the strongest muscles in the body. This facilitates ingestion, mechanical digestion, chemical digestion (lingual lipase), sensation of taste, texture and temperature of food, swallowing and vocalization. It is attached to the mandible. IT is covered in papillae on the superior surface.

Lesser curvature

The concave curve of the stomach. It is smaller and C shaped.

Salivary amylase

The enzyme that initiates the breakdown of carbs. It is inactivated by stomach acid.

Pepsinogen

The inactive proenzyme form of pepsin.

Pulp

The inner part of the tooth that contains blood vessels and nerves.

Esophagus

The long tube that extends from the pharynx to the stomach. It penetrates the diaphragm through the esophageal hiatus. It moves food through it via peristalsis. It is made up of non-keratinized stratified squamous epithelium, which protects it from erosion that can come from food particles. The upper third has smooth muscle, the middle has both skeletal and smooth muscle, and the lower third has smooth muscle. The most superficial layer is called the adventitia, not the serosa.

Dentin

The middle layer of a tooth. It is directly connected to the root.

Body

The middle part of the stomach.

Buccinator

The muscle that controls chewing and speaking. It is located in the cheeks.

Palatoglossal arch

The muscular fold that extends from the lateral side of the soft palate to the base of the tongue.

Palatopharyngeal arch

The muscular fold that extends from the lateral side of the soft palate to the side of the pharynx.

Fauces

The opening between the oral cavity and the throat.

Enamel

The outer coating of teeth. These are prone to mechanical and chemical erosion, also called tooth decay. Cavities are caused by these breaking down from bacteria that break down sugar that release acid that weaken this part of the tooth.

Cardia

The part of the stomach that connects to the esophagus. It is just below the diaphragm.

Oral vestibule

The pocket like part of the mouth that is framed on the inside by the gums and teeth, and on the outside of the cheeks and lips.

Absorption

The process of absorbing nutrients into the bloodstream where they are put to work. This occurs primarily in the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through epithelial cells that make up the mucosa.

Mastication

The process of chewing. This involves tongue movements and jaw movements that help break down food into smaller pieces and mix it with saliva.

Salvation

The secretion of saliva. It is regulated by the autonomic nervous system. This increases in the presence of food and decreased by anxiousness. It increases after swallowing to allow for cleansing.

Esophageal phase

The third and final phase of swallowing. Peristalsis is initiated here. Mucus glands secrete mucus to lessen friction and the lower esophageal sphincter is opened. It is also involuntary.

Pharynx

The throat. It is used in both digestion and respiration. It has three subdivisions called the nasopharynx (no food is supposed to be here), the oropharynx and the laryngopharynx (Which are both used in breathing and digestion).

Uvula

The tip at the back of the mouth. It prevents food from going into the nasal cavity. It is also responsible for snoring.

Chief cells

These are found at the bottom of gastric cells. These secrete pepsinogen.

Enteroendocrine cells

These are found in gastric glands. THese secrete various hormones such as gastrin into the interstitial fluid of the lamina propria.

Haustra

These are found in the large intestine. They are created by smooth muscle bands and are responsible for the wrinkled appearance in the colon.

Parietal cells

These are found in the middle region of gastric glands. These are highly specialized, more so than other epithelial cells in the body. These produce HCl and intrinsic factor.

Gastric pits

These are pores that are found on the inner walls of the stomach.

Sublingual glands

These are the salivary glands which secrete through a duct underneath the tongue. These use the lesser sublingual ducts to secrete saliva into the oral cavity under the tongue.

Teniae coli

These are three bands of smooth muscle found in the large intestine, except in the terminal end. The individual pouches are known as haustra.

Salivary glands

These produce 1 to 1.5 liters of saliva a day. These produce more saliva if food is present and helps break down carbs. The major glands in the mouth include submandibular glands, sublingual glands and parotid glands.

Mucous neck cells

These secrete a thin and acidic mucus. The role is unknown.

Filiform Papillae

Thin and long, these are considered the taste buds of the tongue. These have touch receptors that move food around as well. These create a rough surface to help chew food.

Intrinsic factor

This is a vital glycoprotein for the absorption of vitamin B12 in the small intestine.

Plica circulares

This is the circular fold which is a deep ridge in the mucosa and submucosa, running from the proximal part of the duodenum to the middle of the ileum.

Gastric gland

This is the gland that secretes acidic gastric juice.

Lower esophageal sphincter

This is the muscular gate that leads from the esophagus to the stomach. It does not completely close, which can lead to reflux.

Labial frenulum

This is the non keratinized layer that connects the inner surface of the lip to the gum. It is a mucus membrane that is a thin line. It is made up of non-keratinized stratified squamous epithelium.

Lesser Omentum

This is the peritoneal fold that attaches to the greater curvature of the stomach and is a pathway for structures to the liver. It suspends the stomach from the inferior border of the liver.

Digestion

This is the processing of food through six steps. These steps include ingestion, propulsion, mechanical/physical digestion, chemical digestion, absorption and defecation.

Visceral peritoneum

This is the serous membrane covering the organs in the abdominal cavity.

Parietal peritoneum

This is the serous membrane lining the abdominal cavity.

Molars

Used to crush foods to ease swallowing.

Premolars

Used to mash food.

Lacteals

Vessels in the small intestine where lipids are absorbed and transported via lymphatic vessels to the bloodstream.

Lingual glands

these are found in the lamina propria of the tongue. This secretes mucus and a watery serous fluid that contains the enzyme lingual lipase.

Histamine

A hormone in the stomach mucosa. It is stimulated by the presence of food in the stomach and is used to stimulate parietal cells to release HCl.

Serotonin

A hormone in the stomach mucosa. It is stimulated by the presence of food in the stomach. It is used to contract stomach muscles.

Segmentation

A process of mechanical digestion that takes place in the small intestine. It is made up of localized contractions of circular muscle of the muscularis of the alimentary canal. These contractions isolate small sections of the intestine, which moves their contents back and forth while subdividing, breaking up and mixing the contents. This back and forth motion allows food to move through the intestinal lumen and mix with digestive juices, which allows for absorption.

Intestinal phase

It is made up of excitatory and inhibitory elements. It occurs when chyme enters the duodenum. Gastrin increases gastric juice production.

Pharyngeal phase

It is the second phase of swallowing. It is controlled by the medulla oblongata and is involuntary. Breathing ceases for a bit during deglutition apnea. This is where the upper esophageal sphincter relaxes and lets food enter the esophagus.

Gastric phase

It lasts 3-4 hours. It is triggered when food enters the stomach.

Gastric emptying

Rhythmic mixing waves force 3 mL of chyme at a time through the duodenum. Only a small amount is released to prevent the small intestine from being overwhelmed. Chyme in the duodenum activates receptors that inhibit gastric secretion. High fat meals stay in the stomach the longest due to fats taking a long time to digest in the small intestine. Carb laden meals are process the fastest. Protein rich meals stay in the stomach for an average period of time.

Peristalsis

The act of swallowing. It is involuntary. It is facilitated by smooth muscles which allow it to contract and relax walls within the alimentary canal. This propels food along and play a role in mixing food with digestive juices. It is strong enough so that you can swallow food and liquids and guide them to your stomach even if you're upside down.

Ingestion

The first process of digestion. It refers to the entry of food to the alimentary canal through the mouth. Within the mouth, the food is chewed and mixed with saliva. This saliva contains enzymes that being the breakdown of carbs found in the food along with some fat digestion done by lingual lipase. The action of chewing allows the food to become bolus and increases its surface area. Swallowing is one of the two voluntary acts in the digestive system. The process of taking in food through the GI tract.

Greater curvature

The larger bulge of the stomach. It is J shaped. It is considered convex.

Defecation

The last step in digestion. Here, undigested materials are excreted from the body in the form of feces. This takes place in the anal canal/rectum.

Pylorus

The lower part of the stomach. It connects the stomach to the duodenum. The antrum connects to the body, which the canal connects to the duodenum, which is bordered by a sphincter made up of smooth muscle. There are several mucus cells here to help make chyme less acidic. It also has the ability to secrete gastrin within its mucus cells.

Propulsion

The movement of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary process of peristalsis.This is what happens when food leaves the mouth when the tongue and the pharyngeal muscles propel it into the esophagus.

Saliva

The watery substance that is found in the mouth. It is 95.5% water. The other 4.5% contains some ions, glycoproteins, enzymes, growth factors and waste products. It contains immunoglobulin A to prevent microbes from penetrating the epithelium and lysozyme to make it antimicrobial. It is usually swallowed with food to prevent fluid loss.

Mucosal barrier

These are cells that protect the stomach from digesting itself. Mucus is alkaline, which makes it perfect for the job. These are found in the glands of the pylorus and cardia. Within the pylorus, gastrin is also secreted. This mucus is rich in bicarbonate. Tight junctions prevent gastric juice from going into deeper layers.

Chemical digestion

This is the enzymatic breakdown of food that occurs in the digestive system. It starts in the mouth with saliva, which helps break down carbs. Digestive secretions facilitate this by breaking down complex food molecules into their chemical building blocks, such as when proteins get seperated into amino acids. These secretions vary in composition, but typically contain water, various enzymes, acids and salts. This is completed in the small intestine.

Mechanical digestion

This is the physical part of digestion and does not change the chemical composition of the food. This makes the ingested food smaller to increase its surface area and its mobility. Chewing and stomach churning are examples of this.

Chyme

This is what bolus becomes when it gets processed through the stomach. It is acidic due to passing through the stomach and being exposed to digestive juices.

Hydrochloric acid

This is what gives stomach acid its low pH of 1. It is needed to activate the protein digesting enzyme of pepsin. It converts pepsinogen to pepsin.

Palate

This is what gives the mouth its characteristic arch shape. This allows for both digestion and respiration to coexist.

Omentum

This is what holds the stomach in place.

Stomach

This is where chemical digestion primarily occurs. It is about the size of the fist empty, but can expand up to 4 liters (75 times the starting volume). It serves as a chamber for access food before it gets processed in the small intestine. Regardless of when it was eaten, it will always process food into chyme, which is released to the small intestine. Carbs continue their digestion, but very little nutrient absorption occurs here. It has four main regions, which include the cardia, fundus, body and pylorus.