Chapter 8 - The Digestive System

Accessory organs

“aid with digestion, but are not part of the digestive system.” More accurate to say they are not DIRECTLY part of the digestive system because food does not pass through these structures.

• liver

• galllbladder

• pancreas

gastrointestinal tract or GI tract

structures of the digestive system are also described as the

upper GI tract

consists of the mouth, esophagus, and stomach.

lower GI tract

made up of the small and large intestines (bowels), plus the rectum, and anus.

Major structure of the oral cavity (mouth)

• lips

• hard and soft palates

• salivary glands

• tongue

• teeth

• periodontium

lips (labia)

form the opening to the oral cavity (singular, labium). The same term also refers to parts of the female genitalia

during eating, the lips hold food in the mouth and aid the tongue and cheeks in guiding food between the teeth for chewing

also important roles in breathing, speaking, and the expression of emotions

Upper and lower labial frenum

are narrow bands of tissue that attach the lips to the jaws

Hard palate

the bony anterior portion of the palate that is covered with a specialized mucous membrane

Rugae

irregular ridges or folds in this mucous membrane (singular, ruga)

Soft palate

the flexible posterior portion of the palate.

it has the important role of closing off the nasal passage during swallowing to prevent food and liquid from moving upward into the nasal cavity.

Uvula

hangs from the free edge of the soft palate. During swallowing, it moves upward with the soft palate. Also plays and important role in snoring and the formation of some speech sounds.

Tongue

• very strong flexible, and muscular

• aids in speech

• moves food during chewing and swallowing

Dorsum

Upper surface of the tongue.

This surface has a protective covering and, in some areas, small bumps known as papillae (singular, papilla).

Sublingual surface

of the tongue and the tissues that lie under the tongue are covered with delicate, highly vascular tissues

Sublingual

under the tongue

Highly vascular

containing many blood vessels

Lingual frenum

attaches the tongue to the floor of the mouth and limits its motion

Periodontium

consists of the bone and soft tissues that surround and support the teeth

odont/o

teeth

Gingiva (gums)

the specialized mucous membrane that surrounds the teeth, covers the bone of the dental arches, and lines the cheeks.

Dental Arches

• The boney structures of the oral cavity consist of the maxillary and mandibular arches

• Commonly referred to as the upper and lower jaws

• Firmly hold teeth in position to facilitate chewing and speaking

Temporomandibular joint (TMJ)

• is formed at the back of the mouth where the maxillary and mandibular arches come together

• The maxilllary arch, which is part of the skull, does not move

• The mandibular arch, whcih is a seperate bone, is the moveable component of this joint

Dentition

the natural teeth arranged in the upper and lower jaws

incisors

biting and tearing

canines (cuspids)

Biting and tearing

premolars (bicuspids)

chewing and grinding

molars

chewing and grinding

Primary dentition (deciduous dentition/baby teeth)

• consists of 20 teeth that are normally lost during childhood and are replaced by the permanent teeth.

• These teeth include:

  • 8 incisors

  • 4 canines

  • 8 molars

  • No premolars

Permanent dentition

• 32 teeth that are designed to last a lifetime

• These teeth include:

  • 8 incisors

  • 4 canines

  • 8 premolars

  • 12 molars

Edentulous

means without teeth

Occlusion

describes any contact between the chewing surfaces of the upper and lower teeth

Malocclusion

any deviation from the normal positioning of the upper teeth against the lower teeth

Crown

The portion of a tooth that is visible in the mouth

Enamel

covers the crown. It is the hardest substance in the body

Roots

hold the tooth securely in place within the dental arch.

Cementum

protects the roots. This is strong but not as hard as enamel.

Cervix

neck of the tooth is where the crown and root meet

dentin

makes up the bulk of the tooth structure and is protected on the outer surfaces by the enamel and cementum

pulp

consists of a rich supply of blood vessels and nerves that provide nutrients and innervation to the tooth. In the crown, the pulp is located in the pulp cavity. In the roots, the pulp continues through the root canals

Saliva

colorless liquid that moistens the mouth, begins the digestive process. and lubricates food during chewing a swallowing.

parotid glands

located on the face in front of and lsightly lower than each ear. The ducts for these glands are on the inside of the cheek near the upper molars

Sublingual glands and their ducts

located on the floor of the mouth under the tongue

submandibular glands and their ducts

located on the floor of the mouth near the mandible

Pharynx

common passageway for both respiration and digestion,commonly known as the throat, allows food, liquids, and air to pass through it

Epiglottis

a lid like structure that closes off the entrance to the trachea (windpipe) to prevent food and liquids from moving into the laryngopharynx during swallowing

Esophagus

muscular tube through which ingested food passes from pharynx to stomach

lower esophagea, sphincter (cardiac sphincter or gastroesophageal sphincter)

a muscular ring that controls the flow between the esophagus and stomach. Normally opens to allow the flow of food into the stomach and closes to prevent stomach contents from regurgiating into the esophagus

regurgitating

means to flow backward

stomach

a sac like organ composed of the fundus (upper, rounded part), body (main portion), and antrum (lower part).

Rugae

the folds in the mucosa lining the stomach. Glands located within these folds produce gastric juices that aid in digestion and mucus to create a protective coating on teh lining of the stomach.

Pylorus

the narrow passage that connects the stomach with the small intestine

Pyloric sphincter

the ring like muscle that controls the flow from the stomach to the duodenum of the small intestine

Small intestine

• Extends from the pyloric sphincter to the first part of the large intestine

• Coiled organ, reaches up to 20 feet in length

• Consists of 3 sections where food is digested and the nutrients are absorbed into the bloodstream:

  • duodenum, jejunum, ileum

Duodenum

the first portion of the small intestine; extends from the pylorus to the jejunum

Jejunum

the middle portion of the small intestine; extends from the duodenum to the ileum

Ileum

the last and longest portion of the small intestine; extends from the jejunum to the cecum of the large intestine

Large intestine

• Extends from the end of the small intestine to the anus

• About twice as wide as the small intestine

• 1/4th as long as small intestine

• Waste products of digestion are processed here in preparation for excretion through the anus

• Major parts: cecum, colon, rectum, anus

Cecum

a pouch that lies on the right side of the abdomen

extends from the end of the ileum to the beginning of the colon

Ileocecal sphincter

the ring like muscle that controls the flow from the ileum of the small intestine into the cecum of the large intestine

Vermiform appendix (appendix)

hangs from the lower portion of the cecum

vermiform

refers to a worm like shape

Colon

the longest portion of the large intestine; subdivided into four parts: ascending, transverse, descending, sigmoid

Ascending colon

travels upward from the cecum to the undersurface of the liver

Transverse colon

passes horizontally from right to left toward the spleen

Descending colon

travels down the left side of the abdominal cavity to the sigmoid colon

Sigmoid colon

an S shaped structure that continues from the descending colon above and joins with the rectum below

Sigmoid

means curved like the letter s

Rectum

the widest divison of the large intestine, makes up the last 4 inches of the large intestine and ends at the anus

Anus

the lower opening of the digestive tract. The flow of waste through the anus is controlled by the internal anal sphincter and external anal sphincter

Anorectal

refers to the anus and rectum as a single unit

an/o

anus

rect/o

rectum

Accessory Digestive Organs

• Play a key role in the digestive process

• Food does not travel through these structures

  • liver

  • biliary tree

  • gallbladder

  • pancreas

Liver

• A large organ located in the right upper quadrant of the abdomen

• Important functions related to removing toxins from the blood and turning food into fuel and nutrients the body needs

• Removes excess glucose from bloodstream and stores it as glycogen, a form of starch

• When the blood sugar level is low, the liver converts glycogen back into glucose and releases it for use by the body

• Destroys old erythrocytes

• Removes toxins from the blood

• Manufactures some blood proteins

Bilirubin

the pigment produced from the destruction of hemoglobin, is released by the liver in bile

Bile

a digestive juice that aids in the digestion of fats; secreted by the liver. Bile travels from the liver to teh gallbladder, where it is concentrated and stored

Biliary tree

provides the channels through which bile is transported from the liver to the small intestine

Biliary

pertaining to bile

Common hepatic duct

the trunk, just outisde the liver, is known as

Cystic duct

Bile travels from the liver through the common hepatic duct to the gallbladder where it enters and exits through the narrow ___

Common bile duct

the cystic duct leaving the gallbladder rejoins the common hepatic duct to form the _______

Gallbladder

• Pear shaped organ about the size of an egg

• Located under the liver

• Stores and concentrates bile for later use

• When bile is needed, the gallbaldder contracts, forcing the bile out through the biliary tree

Cholecyst/o

gallbladder

Pancreas

• A soft, 6 inch long oblong gland

• Located behind the stomach

• Important roles in digestive and endrocrine functions

• The pancreas produces and secretes pancreatic juices that aid in digestion and contain sodium bicarbonate to help neutralize stomach acids and digestive enzymes

Pancreatic juices

leave the pancreas through pancreatic duct that joins the common bile duct just before the entrance into the duodenum

Digestion

the process by which complex foods are broken down into nutrients in a form the body can use

Digestive enzymes

responsible for the chemical changes that break foods down into simpler forms of nutrients for use by the body

Nutrient

a substance, usually from food, that is a neccessity for normal functioning of the body

Primary nutrients

carbohydrates, fats, proteins

Essential nutrients

vitamins, minerals (required in small amounts)

Metabolism

Includes all of the processes involved in the bodys use of nutrients

metabol

change

-ism

condition

Anabolism

The building up of body cells and substances from nutrients. Opposite of catabolism

Catabolism

The breaking down of body cells or substances, releasing energy and carbon dioxide. Opposite of anabolism.

Absorption

• the process by which completely digested nutrients are transported to the cells throughout the body

• the mucosa that lines the small intestine is covered with finger like projections called villi. Each villus contains blood vessels and lacteals

• The blood vessels absorb nutrients directly from the digestive system into the bloodstream for delivery to the cells of the body

Mastication (chewing)

breaks down food into smaller pieces, mixes it with saliva, and prepares it to be swallowed

bolus

a mass of food that has been chewed and is ready to be swallowed

Peristalsis

a series of wave like contractions of the smooth muscles in a single direction

Gastric juices

of the stomach contain hydrochloric acid (HCI) and digestive enzymes to begin the digestive process. Few nutrients enter the bloodstream through the walls of the stomach.