What do you know about the Digestive System?

Think-Pair-Share On a scratch sheet of

paper, jot down some thoughts about what you know about the digestive system

Be prepared to share your ideas…

HOW LONG DOES GUM

REALLY STAY IN YOUR

DIGESTIVE SYSTEM?

BONUS OPP…

DIGESTIVE SYSTEMChapter 14

Course of Study10.) Identify structures and functions of the

digestive system.

Tracing the pathway of digestion from the mouth to the anus using diagrams Identifying disorders affecting the digestive system Examples: ulcers, Crohn's disease, diverticulitis

Tracing the pathway of digestion from the mouth to the anus using diagrams

Next Slide…(Picture in your Notes) Be prepared to explain this step by step on the test!

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Structures and Functions of the Digestive System

Anatomy of the Digestive System

Alimentary Canal Accessory Digestive Organs

AKA: Gastrointestinal (GI) Tract Performs the whole menu of digestive

functions (ingests, digests, absorbs, & defecates)

Is a continuous, coiled, hollow, muscular tube that winds through the ventral body cavity and is open at both ends

Organs include: mouth, pharynx, esophagus, stomach, small intestine, & large intestine

In a cadaver, the alimentary canal is approximately 9m long, but in a living person, it is considerably shorter because of its relatively constant muscle tone

Food material within this tube is technically outside the body, because it has contact only with cells lining the tract and the tube is open to the external environment at both ends.

Includes teeth, tongue, & several large digestive glands

Assist the process of digestive breakdown

Mouth Food enters the digestive tract through the mouth or “oral cavity” Mucous membrane-lined cavity As food enters the mouth, it is mixed with saliva and masticated

(chewed) The cheeks and closed lips hold the food between the teeth during

chewing and the tongue continually mixes food with saliva and initiates swallowing.

Thus, the breakdown of food has begun before it even leaves the mouth!

Also, as you already know, the papillae containing taste buds on the tongue surface allow us to enjoy and appreciate food as it is eaten….thank goodness

Mouth Parts include:

Lips(labia): protect its anterior opening

Cheeks: Form its lateral walls Hard Palate: forms its anterior

roof Soft Palate: forms its posterior

roof Uvula: Fleshy fingerlike

projection of the soft palate Tongue: Occupies the floor of

the mouth…has bony attachments like the hyoid bone and the styloid process in the skull

Lingual frenulum: secures the tongue to the floor of the mouth and limits its movements (short frenulum=tongue tied in children…gets cut)

Tonsils: part of the body’s defense system

Pharynx Subdivided into the:

1. Nasopharynx: Part of the respiratory passageway

2. Oropharynx: Posterior to the oral cavity3. Laryngopharynx: Continuous with the

esophagus below Walls of the pharynx contain to skeletal

muscle layers The cells of the inner layer run longitudinally The cells of the outer layer run around the wall

in a circular fashion Alternating contractions of these two

muscle layers propel food through the pharynx into the esophagus below

This propelling mechanism is called peristalsis

Esophagus “Gullet” Runs from the pharynx

through the diaphragm to the stomach

About 25 cm (10in) long It is essentially a

passageway that conducts food by peristalsis to the stomach

Stomach C-shaped On the left side of the abdominal

cavity nearly hidden by the liver and the diaphragm

25cm (10in) long, but its diameter depends on how much food it contains

When it is full, it can hold about 4 liters (1 gallon) of food…when it is empty, it collapses inward on itself

Acts as a temporary “storage tank” for food as well as a site for food breakdown

Stomach Physical

Breakdown: Besides the longitudinal

and circular muscle layers, its wall contains a third obliquely arranged later in the muscularis external…this arrangement allows the stomach not only to move food along the tract, but also to churn, mix and pummel the food, physically breaking it down to smaller fragments

Chemical Breakdown: Chemical breakdown of proteins

begins in the stomach, a few ways:○ The mucosa of the stomach

produces large amounts of mucus○ The lining of the stomach is dotted

with millions of deep gastric pits, which lead into gastric glands that secrete the solution called “gastric juices”

Chief cells produce protein-digesting enzymes, mostly pepsinogens, and parietal cells produce corrosive hydrochloric acid

After food has been processed in the stomach, it resembles heavy cream and is called “chyme”

Chyme enters the small intestine through the pyloric sphincter

SMALL INTESTINE The body’s major digestive organ Within its twisted passageways,

usable food is finally prepared for its journey into the cells of the body

It is the longest section of the alimentary tube, with an average length of 2.5-7meters (8-18 feet) in a living person

Except for the initial part of the small intestine, the small intestine hangs in sausage-like coils in the abdominal cavity

SMALL INTESTINE Has 3 subdivision:

Duodenum 5% of lengthJejunum 40% of lengthIleum 60% of length

The small intestine is able to process only a small amount of food at one time

The pyloric sphincter (literally “gatekeeper”) controls food movement into the small intestine from the stomach and prevents the small intestine from being overwhelmed

Chemical Digestion in the Small Intestine

The duodenum has interesting featuresSome enzymes are produced by the intestinal

cells of the intestineMore important enzymes are produced by the

pancreas which are ducted into the duodenum through the pancreatic ducts, where they complete the breakdown of foods in the small intestine

Bile (formed by the liver) also enters the duodenum through the bile duct

Absorption in the Small Intestine

Nearly all food absorption occurs in the small intestine The small intestine is well suited for its function. It has 3

structures that increase the absorptive surface tremendously:Microvilli

○ Tiny projections of the plasma membrane of the mucosa cells that give the cell surface a fuzzy appearance; sometimes referred to as the “brush border”

Villi○ Fingerlike projections of the mucosa that give it a velvety appearance

and feel…within each villus is a rich capillary bed…the digested foodstuffs are absorbed through the mucosal cells into the capillary beds.

Circular Folds○ Deep folds of both mucosa and submucosa layers

All of these structural modifications increase the surface area and amount of food absorbed!

Large Intestine Much larger in diameter than the small

intestine but shorter in length…about 1.5m (5 feet).

Its major functions are to dry out the indigestible food residue by absorbing water and to eliminate these residues from the body as feces.

It frames the small intestine on 3 sides and has the following subdivisions:Cecum, appendix, colon, rectum, anal canal

Path of Food Through the

BodyYou are a piece of your favorite food…explain the path you take through the body from your oral cavity (mouth) to your anus…give specific details of things

you would go through as a piece of food…

Accessory Digestive Organs

Salivary Glands Teeth Pancreas Liver Gallbladder

Salivary Glands Three pairs of salivary glands empty their secretions

into the mouthParotid gland:

○ Lie anterior to the ears. Mumps, a common childhood disease in an inflammation of the parotid glands

Submandibular glands & Sublingual glands: ○ Empty their secretions into the floor of the mouth through tiny

ducts…their secretion is saliva-a mixture of mucus and serous fluids. The mucus moistens and binds food together in a mass called a bolus,

which makes chewing and swallowing easier. The serous contains an enzyme, salivary amylase, that begins the

process of starch digestion in the mouth. ○ Saliva also contains substances such as lysozyme and

antibodies that inhibit bacteria. ○ Last, but not least, saliva dissolves food chemicals so they can

be tasted! Thank Goodness!

Teeth Used to masticate or chew by opening and closing our jaws

and moving them from side to side while continually using our tongues to move the food between our teeth

Teeth tear and grind the food, breaking it down into smaller fragments

By the age of 21, two sets of teeth have been formed: Baby teeth: AKA Deciduous teeth, begin to erupt around six months

and a baby has a full set of teeth by 2 years Adult teeth: AKA Permanent teeth, as this second set of teeth enlarge

and develop, the roots of the baby teeth are reabsorbed, and between ages 6-12 they loosen and fall out. All of the permanent teeth but the third molars have erupted by the end of adolescence…the third molars “wisdom teeth” emerge later, between the ages of 17-25. Although there are 32 permanent teeth in a full set, the wisdom teeth often fail to erupt and sometimes are even absent!

Teeth Classified according

to shape and function as incisors, canines, premolars, and molarsIncisors: adapted for

cuttingCanines: “eye-teeth”

tearing or piercingPremolars and

molars: grinding

Teeth A tooth consists of 2 major

regions, the crown and the root The enamel-covered crown is the

exposed part of the tooth above the gum

Enamel is the hardest substance in the body and is fairly brittle because it is heavily mineralized with calcium salts

The portion of the tooth embedded in the jawbone is the root

The root and the crown are connected by the tooth region called the neck

Pancreas Soft, pink, triangular gland

that extends across the abdomen from the spleen to the duodenum

Produces enzymes that break down all categories of digestible food

The pancreatic enzymes are secreted into the duodenum in an alkaline fluid, which neutralizes the acidic chyme coming in from the stomach

Liver Largest gland in the body Located under the diaphragm to the

right side of the body and almost completely covers the stomach

It is one of the body’s most important organs…it has many metabolic and regulatory roles

Its digestive function is to produce bile…bile leaves the liver through the common hepatic duct and enters the duodenum through the bile duct

Bile Yellow-to-green, watery

solution that contains many components, but of the many only bile salts and phospholipids aid the digestive process

Bile does not contain enzymes, but its bile salts emulsify fats by physically breaking large fat globules into smaller ones, thus providing more surface area for the fat-digesting enzymes to work on

Gallbladder Small, thin-walled green sac that snuggles in a shallow fossa in the inferior

surface of the liver When food digestion is not occurring, bile backs up the cystic duct and enters the

gallbladder to be stored While being stored in the gallbladder, bile is concentrated by the removal of

water Later, when fatty food enters the duodenum, a hormonal stimulus prompts the

gallbladder to contract and spurt out stored bile, making it available for use again

Overview of Gastrointestinal Processes and Controls

1. Ingestion Food must be placed in the mouth to be acted on…this

active, voluntary process is called ingestion2. Propulsion

If foods are to processed by more than one digestive organ, it must be propelled from one organ to the next (peristalsis-discussed already)

3. Food Breakdown-Mechanical Mixing of food in the mouth, churning of food in the

stomach, and segmentation (movement in one direction) in the small intestine are all mechanical food breakdown…physically prepares food by physically breaking it down into smaller particles

Overview of Gastrointestinal Processes and Controls

4. Food Breakdown-Chemical The process of large food molecules being broken down

to their building blocks by enzymes is called chemical digestion

5. Absorption Transport of digested end products from the lumen of the

GI tract to the blood or lymph is absorption…for absorption to occur, the digested foods must enter the mucosal cells by active or passive transport…small intestine is major absorptive site

6. Defecation Elimination of indigestible residues from the GI tract

through the anus in the form of feces

Disorders of the Digestive System

Disorders of the Digestive System

1. Ulcers2. Crohn’s disease3. Diverticulitis4. Impacted teeth5. Gallstones6. Heartburn7. Pancreatitis8. Appendicitus9. Celiac disease10.Hernia11.Lactose intolerance