Digestive System

Assimilation

The process by which nutrients from foods are taken into the cells of the body after the food has been digested and absorbed.

Absorption

The process by which nutrient molecules pass through the wall of the digestive system into the blood

Bolus

A term used to describe food after it has been chewed and mixed with saliva

Chyme

Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.

Digestion

Breakdown of food substances into simpler forms that can be absorbed and used. There are two kinds.

Defecation

Elimination of feces

Ingestion

The intake of food from the environment into the alimentary canal

Mechanical Digestion

Physical breakdown of large pieces of food into smaller pieces (chewing and intestinal compression)

Chemical Digestion

Process by which enzymes break down food into small molecules that the body can use (Stomach acid and saliva)

Digestive System

Extends from mouth to anus and consists of:

Alimentary Canal and Accessory Organs

Alimentary Canal

Mouth, Pharynx, Esophagus, Stomach, Small Intestines, Large Intestines, Rectum, and Anus.

Accessory Organs

Salivary Glands, Liver, Gallbladder, and Pancreas.

Alimentary Canal: Mouth

Hollow chamber with roof, floor, and walls.

Receives the food (ingestion) and begins mechanical (chewing) and chemical (saliva) digestion (chemical digestion of carbohydrates)

Alimentary Canal: Pharynx

Tube-like structure made of muscle and lined with mucous membranes

Connects nasal/oral cavities with larynx/ esophagus.

Three parts: Nasopharynx, Oropharynx, and Laryngopharynx

Alimentary Canal: Esophagus

Peristalsis pushes food to stomach.

Alimentary Canal: Stomach

Secretes acid and enzymes. Mixes food with secretions to begin enzymatic digestion of proteins

Alimentary Canal: Small Intestines

Mixes food with bile and pancreatic juice.

Final enzymatic breakdown of food molecules; main site of nutrient absorption

Tubular organ, about 7 meters (20 feet) long that completes digestion and facilitates absorption.

Transports remaining residue to the large intestine which takes 3 - 10 hrs.

Alimentary Canal: Large Intestines

Absorbs water and electrolytes to form feces. Consists of ascending, traverse, descending, and sigmoid colons.

Alimentary Canal: Rectum

Regulates elimination of feces. Temporary storage site for undigested material before defecation.

Alimentary Canal: Anus

Opening at the end of the alimentary canal through which solid waste matter leaves the body

Accessory Organs: Salivary Glands

Secretes about 1 liter per day to help moisten and bind food particles.

Amylase begins chemical digestion of carbohydrates. Stimulated by sight, smell, taste or thought of food.

Accessory Organs: Liver

Produces bile, which emulsifies fat

Accessory Organs: Gallbladder

Stores bile and introduces it into small intestine

Accessory Organs: Pancreas

Produces and secretes

pancreatic juice, containing

digestive enzymes and

bicarbonate ions,

into small intestine

Tongue

Mainly consists of skeletal muscle and help move the food to the back of the oral cavity. Contains taste buds.

Esophagus

A muscular, mucous-lined tube about 25cm (10 in.) long which serves as a passageway for food.

It connects the pharynx with the stomach and descends posterior to the trachea. Peristalsis pushes food to stomach. Contains the esophageal hiatus.

Stomach

A hollow, muscular organ that serves as a pouch which can hold about one liter.

Divided into three areas: Fundus, Body, and Pylorus. It connects to the duodenum and controls the emptying of chyme.

Gallbladder

A pear-shaped sac whose main function is to

store bile. Fats in chyme "trigger" release of Cholecystokinin or CCK which stimulates contractions. Cystic duct + common hepatic duct = common bile duct.

Duodenum

C-shaped section where most chemical digestion occurs

Jejunum

The middle section of the small intestine; connects the duodenum and ileum

Ileum

Joins the large intestine at the ileocecal valve.

Appendix

A small, fingerlike extension of the vertebrate cecum; contains a mass of white blood cells that contribute to immunity.

Cecum

First part of large intestine which is pouch-like. Contains the Vermiform appendix which serves no important digestive function in humans but contains lymphatic tissue.

Large Intestine

1.5 meters (5 feet) long. Takes care of undigested and unabsorbed food.

Absorbs some water and electrolytes.

Forms and stores feces.

Anus

Opening of the anal canal to the outside which is guarded by two sphincter muscles:

Internal anal sphincter (smooth muscle under involuntary control) and External anal sphincter (skeletal muscle under voluntary control).

Salivary Gland: Parotid

The largest of the salivary glands which lie inferior to each ear

Salivary Gland: Submandibular

These open into the mouth on either side of the lingual frenulum

Salivary Gland: Sublingual

The smallest of the salivary glands. These open into the floor of the mouth

Bile Duct

A tube that carries bile from the liver and gallbladder to the intestine

Pancreatic Duct

Extends the length of the pancreas

connects with duodenum at major duodenal papillae

General Characteristics of the Alimentary Canal

About 8 meters long (27ft), Muscular / irregular tube, Open at both ends, Passes through the ventral cavity. Different areas have particular functions, however, the structure of its walls, innervation (nerve structure), and how it moves food is the same throughout.

Four Distinct Layers of the Alimentary Canal Walls

Mucosa, Submucosa, Muscularis, and Serosa.

Mucosa

(The mucous membrane) 1st layer from inside out.

Lines the lumen (open inside area) of the GI tract.

Simple columnar epithelium designed for absorption, secretion, protection.

Submucosa

2nd layer from inside out.

Connective tissue layer which contains many blood vessels and nerves.

Muscularis

Third layer from the inside out.

2 layers: outer longitudinal and inner circular.

Peristalsis within the tube ( involuntary waves which produce movement).

Mixing and mechanical breakdown of larger food particles.

Serosa

Outermost layer from inside out.

Cells produce serous fluid which provides moisture and lubrication and allows organs within the abdominal cavity to slide freely against one another.

Peristalsis

Propelling movements created by a ring of muscle that contracts then relaxes

Serous Fluid

Fluid having a thin and watery appearance

Palate

Forms the roof of the mouth and is divided into the hard and soft portions. Helps to prevent choking.

Uvula

Prevents food or liquids from entering the nasal cavities.

Teeth

Responsible for the initial mechanical digestion. 20 Deciduous and 32 Permanent.

Deciduous begin erupting around 6 months of age. Permanent begin erupting around 6 years of age.

Amylase

An enzyme that digests starch into disaccharides. Secreted by salivary glands and by the pancreas.

Lingual Frenulum

Fold of mucous membrane that connects the tongue to the floor of the mouth

Three Major Pairs of Salivary Glands

Parotid, Submandibular, and Sublingual glands

Wharton's Duct

The excretory duct of the submandibular gland

Stenson's Duct

The excretory duct of the parotid gland

Nasopharynx

Located above the soft palate and is the passageway for air.

Oropharynx

Located behind the mouth and is a passageway for food and air.

Laryngopharynx

The passageway to the esophagus.

Esophageal Hiatus

The opening where the esophagus pass through the diaphragm

Fundus

Enlarged portion to the left and above esophagus.

The region of the stomach most associated with secretion of acid and enzymes.

Body

Central or main part of the stomach and lies between the fundic and the pyloric region.

Pylorus

Lower narrow section that ends with the Pyloric sphincter

Three Areas Of The Stomach

Fundus, Body, and Pylorus

Main Functions of the Stomach

Stores swallowed food. Mixes the food with acids.

Begins the second phase of digestion: breakdown of proteins. Sends the formed chyme to the small intestine.

Gastric Juices

Contain hydrochloric acid and enzymes.

Constantly being produced though the rate varies.

Seeing, smelling, or tasting appetizing food stimulates increased production.

Digestive enzymes:

-Pepsinogen

-Activated by HCl (Hydrochloric Acid)

-Forms Pepsin

--begins protein digestion in stomach

--turns bolus into chyme

Pepsinogen

The inactive form of pepsin that is first secreted by specialized cells located in gastric pits of the stomach.

Pepsin

Enzyme that breaks down proteins into smaller polypeptide fragments

HCl

Hydrochloric Acid (Stomach Acid)

Digestive Enzymes

Proteins found in digestive juices that act on food substances, causing them to break down into simpler compounds. Secreted by the Pancreas.

-Pepsinogen

-Activated by HCl (Hydrochloric Acid)

-Forms Pepsin

--begins protein digestion in stomach

--turns bolus into chyme

Pancreas

Lies behind the stomach in C shape of duodenum.

Has both and endocrine and exocrine functions:

Exocrine - secretion of the digestive juice

Endocrine - secretion of insulin.

Duodenal Papillae

Opening through which bile and enzymes from the pancreas enter the duodenum

Pancreatic Juice

The most important digestive juice.

Contains enzymes:

Pancreatic amylase - breaks down carbohydrates.

Pancreatic lipase - breaks down fats.

Trypsin, Chymotrypsin and Carboxypeptidase - act on proteins.

Contains sodium bicarbonate, an alkaline substance, that neutralizes HCl in gastric juice that enters the intestines.

Pancreatic Amylase

Breaks down carbohydrates.

Pancreatic Lipase

Breaks down fats.

Trypsin, Chymotrypsin and Carboxypeptidase

Act on proteins.

Liver

Fills entire upper right section of abdominal cavity and

sits just below diaphragm. It is and exocrine gland and the largest gland in the body. Divided into two lobes.

Each lobe has its own hepatic duct. Hepatic ducts merge to form the common hepatic duct.

Liver Functions

Responsible for: The metabolism of fats, proteins, and carbohydrates. Excretion of bilirubin, cholesterol, hormones, and drugs. Enzyme activation. Storage of glycogen, vitamins, and minerals. Synthesis of plasma proteins, such as albumin, and clotting factors. Blood detoxification and purification. Bile production and secretion.

Common Hepatic Duct

Name of the duct where all Liver ducts merge.

Bile

Contains cholesterol and bile salts. Allows for emulsification of fats and elimination of cholesterol from the body.

Enhances the absorption of fatty acids, cholesterol and the fat soluble vitamins A, D, E and K.

Lack of = poor lipid absorption, vitamin deficiencies. Stored in the Gallbladder.

Mesentery

Suspends the small intestines from the posterior abdominal wall. Is a double layered peritoneal membrane.

Plicae

Deep circular folds of the mucosa and submucosa that extend completely or partially around the circumference of the small intestine

Villi

Millions of fingerlike extensions of the intestinal mucosa that increase the surface area for absorption. Each contains: blood capillaries, lymphatic vessel (lacteal), and nerve fibers.

Microvilli

Brush-like border or the villi which further increases surface area

Vermiform Appendix

Worm-like projection of lymphatic tissue hanging off the cecum with no digestive function; may help to resist infection.

Ascending Colon

Begins at Cecum and travels upward. Becomes hepatic flexure.

Transverse Colon

Extends across front of abdomen. Becomes the splenic flexure.

Hepatic

Pertaining to the liver

Splenic

Pertaining to the spleen

Descending Colon

Down the left side of the abdomen

Sigmoid Colon

S-shaped segment. Terminates at the rectum

Anal Canal

The last 2.5 to 4 centimeters of the large intestine with its proximal end attached to the rectum

Functions of the Large Intestines

Receives undigested and unabsorbed food material. Some reabsorption of water and electrolytes. Little or no digestive function. Housing bacteria (called intestinal flora) inside. Synthesize certain vitamins such as K, B12, thiamine and riboflavin. Produce intestinal gas (flatus). Responsible for pungent odor.

Movements of Large Intestines

Peristalsis much slower. Normal passage is 3 - 5 days. Medical conditions (i.e. colitis or inflamed colon) can initiate more peristaltic waves.