DIGESTIVE SYSTEM

NATSCI [MWF] 1 :30-2:30 PM

INTRODUCTION

The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are taken to where they are needed in the body.

FUNCTION OF DIGESTIVE SYSTEM

Prepares food for use by cells through “Five Basic Activities:”

1) INGESTION or the taking of food into the body

2) PERISTALSIS or the physical movement or pushing of food along the digestive tract

3) DIGESTION or the breakdown of food by both mechanical and chemical mechanisms

GOAL: Break down into :– Monosaccarides, amino acids, fatty acids– Absorbed through the epithelium

4) ABSORPTION or the passage of digested food from the digestive track into the cardiovascular and lymphatic systems for distribution of the body’s cells

5) DEFECATION or the elimination from the body of those substances that are indigestible and cannot be absorbed

Digestive System: “Gastrointestinal System”

The organs of digestion are part of two main groups.

• 1ST: DIGESTIVE TRACT

• 2ND: ACCESSORY ORGANS OF THE TRACT

Description: THE DIGESTIVE TRACT

(gastrointestinal (GI) tract)• Food passes through:

–starts at the mouth, –continues to the esophagus,– stomach, –small intestine, –large intestine (the colon / rectum)–And ends at the anus.

Description: THE DIGESTIVE TRACT

>>The entire system — from mouth to anus — is about 30 feet (9 meters) long.

Description:ACCESSORY ORGANS

• Food does NOT pass through:–Teeth–Tongue–Salivary glands–Liver–Gallbladder–Pancreas

THE DIGESTIVE TRACT

Mouth or oral cavity• “Buccal cavity”• The mouth is the beginning of the

digestive tract; • digestion starts here when taking

the first bite of food.

Mouth or oral cavity

Mouth or oral cavity

The food is chemically broken down by amylase-an enzyme in saliva that breaks down carbohydrates.

ACCESSORY ORGAN

Tongue • Consists of skeletal muscle covered

with mucous membrane

• Divided into symmetrical halves by septum called lingual frenulum

Tongue

Tongue

• Papillae – covers the upper surface and sides of the tongue

*Filiform papillae - found at the front of the tongue (rough and important in licking) –threadlike elevations covering

most of the tongue surface.

Papillae

-Fungiform papillae (contain taste buds)

–knoblike projections of the tongue scattered among the filiform papillae.

-Circumvallate papillae (contain taste buds)

–eight to twelve large papillae arranged in a V near the base of the tongue.

ACCESSORY ORGAN

Salivary glands• the one that secretes saliva in the

mouth,• Saliva is a watery substance located

in the mouths of organisms contains an enzyme - salivary amylase, –which breaks down starch.

ACCESSORY ORGAN

Three pairs of salivary glands:• Parotid gland—(secretory cell: serous)

• The submandibular or submaxillary gland—(secretory cell:mixed)

• The sublingual gland—– (secretory cell:mucous)

Salivary glands

Teeth-known as dentes

-are part of the skeletal system

-play a key role in

digestion

ACCESSORY ORGANS

ACCESSORY ORGANS

Teeth-In carnivores,

*are designed for killing and breaking down

meat.

-In Herbivores,

*for grinding plants and other food to ease them

through the digestion process

ACCESSORY ORGANS

₪ Tooth is composed of:

-the crown--(covered with enamel)

-the neck or cervix

-the root

Tooth

ACCESSORY ORGANS

“The Four types of teeth”

Four types of teeth

(1) The Incisors• The 8 front teeth • are used to cut

food (2) The Canine (4

eyeteeth)• Used to tear food• are used to cut

food• Having only 1 cusp

or cuspids

(3) The Molars (back teeth) are used for chewing and grinding food.

(4) The 8 Premolars (bicuspids) have a flat biting surface, they tear and crush food .

THE PHARYNX

FUNCTION:• Is to begin the

process of swallowing or deglutition

Is a common passageway for food and air.

Is divided into:– the NASOPHARYNX– The OROPHARYNX

and– The

LARYNGOPHARYNX

Division of Pharynx

Nasopharynx• Region posterior

to the nasal cavity, from the internal nares (choanae) to soft palate

Division of Pharynx

Oropharynx• Region

posterior to the root of the tongue

Division of Pharynx

Laryngopharynx• Region posterior

to, behind larynx, from the epiglottis to cricoid cartilage (larynx)

THE ESOPHAGUS

Is to secrete mucus and transport food to the stomach through an opening in the diaphragm called the esophageal hiatus

THE DIGESTIVE TRACT

THE ESOPHAGUS

it uses PERISTALSIS – involuntary waves of muscle contraction to help push food down to the stomach through the lower esophageal sphincter

THE DIGESTIVE TRACT

lower esophageal sphincter

--Functions as to keep food and stomach acid from coming back up in to the esophagus

THE STOMACH

Begins the chemical breakdown of proteins through the enzyme pepsin

Breaks up food mechanically by churning its contents

THE DIGESTIVE TRACT

THE STOMACH

It has folds called rugae and is a big muscular pouch which churns the bolus and mixes it with gastric juice- a mixture of stomach acid, mucus and enzymes.

4 parts of stomach

Cardia• Surrounds the gastroesophageal

sphincter

4 parts of stomach

Fundus• The rounded

portion above and to the left of the cardia

4 parts of stomach

The body• The large

central portion of the stomach below the fundus

4 parts of stomach

Pylorus or antrum• The narrow inferior

region that connects with the duodenum of the small intestine via the pyloric sphincter

4 parts of stomach

Dual function:

(a) Its acini produce digestive enzymes that get carried by the pancreatic duct to the duodenum of the small intestine

THE DIGESTIVE TRACT

THE PANCREAS

(b) Its pancreatic islets secrete the hormones insulin and glucagon into the blood to control blood sugar levels

THE DIGESTIVE TRACT

THE PANCREAS

Divided into :• The head- is the widest part of the

organ • The body - the tapered left side that

extends slightly upward • The tail -

THE PANCREAS

The pancreas is made up of two types of glands:• Exocrine

secretes:digestive enzymes. These enzymes are secreted into a network of ducts that join the main pancreatic duct, which runs the length of the pancreas.

• Endocrine

consists of the islets of Langerhans, secretes hormones into the bloodstream.

THE PANCREAS

• Largest organ of the body

• Produces bile• Break up fats• Functional units

– lobules

THE LIVER

ACCESSORY ORGAN

It stores copper, iron and vitamins A,D,E, and K.

It stores or transforms poison into less harmful substances

THE LIVER

Division of the liver (a) right lobe (b) left lobe

It stores and concentrates bile produced by the liver lobules

ACCESSORY ORGANTHE GALLBLADDER

Where the major portion of absorption and digestion occurs

Approximately:• Length: 21 feet • Diameter:1 inch

Divided into 3 portions

THE DIGESTIVE TRACTTHE SMALL INTESTINE

The three portions : 1st: duodenum

• The shortest part • Length: 10 inches

long 2nd: jejunum

• Length: 10 inches long

• Extends to the 3rd part

3rd: ileum• Length: 12 feet long• Joins the large

intestine

THE DIGESTIVE TRACT

Length: 5 feet Diameter: averages

2.5 inches FUNCTIONS:

• Absorption of water• Manufacturing and

absorption of certain vitamin

• Formation and expulsion of the FECES

THE LARGE INTESTINE

Attached to the posterior wall of the abdomen by extensions of its visceral peritoneum known as mesocolon

THE DIGESTIVE TRACTTHE LARGE INTESTINE

Four principal regions (1) the cecum

• The pouchlike first part of the large intestine

• Attached to the close end of the cecum is the twisted tube known as the vermiform appendix (length 3 inches)

THE LARGE INTESTINE

(2) the colon

• The largest part.• Looks like a tube of consecutive

pouches• The pouches are called haustrae• Parts:

– Ascending Colon– Tranverse colon– Descending colon– Sigmoid colon

(3) the rectum• The last 7-8 inches of the

gastrointestinal tract• Eliminate feces• What’s left over?

– undigested materials:– mainly cellulose from plants– called roughage or fiber – keeps everything moving & cleans out

intestines

• It is situated anterior to the sacrum and coccyx.

(4) anal canal• The terminal 1 inch of the rectum

• It is situated anterior to the sacrum and coccyx.

(4) anal canal• The terminal 1 inch of the rectum

THE DIGESTIVE TRACT

ANUS

The opening of the anal canal to the exterior

The last part of the digestive system

Human digestive system

THE ENZYMES Mouth:

secretes Salivary Amylase which down starches into sigars

Stomach: -Secretes Pepsin which breaks

down proteins and hydrochloric acid which provides an acid environment to kill bacteria

Pancreas: • secretes amylase, which continues

the breakdown of starch, • trypsin which continues the break

down of proteins• Lipase which breaks down fats

Small Intestine:Secretes peptidase and maltase

which converts the remaining sugars into glucose

Liver:• Secretes Bile which breaks down

fats and stores it in the gallbladder

HISTOLOGY

The walls of the alimentary canal from the esophagus to the anal canal have the same arrangement of tissue layers.• These layers are referred to as

“coats” or “tunics”

HISTOLOGY

The Four Coats or TUNICS of the tract

(From the inside out)

1)The MUCOSA2)SUBMUCOSA3)MUSCULARIS4)ADVENTITIA or SEROSA

Tunics

1) Tunica mucosa:

• This layer is composed of epithelium, connective tissue and muscle.  These tissues can usually be found in distinct layers as follows:

Tunica mucosa

THREE LAYERS

1) lamina epithelialis mucosae: –consists only of epithelium

2) lamina propria mucosae: –consists of either loose areolar or

reticular connective tissue3) lamina muscularis mucosae:

–consists of smooth muscle–which permits the mucosa to

dynamically move and fold.

THREE LAYERS:

Tunics

The magnification of all four images is identical and the epithelial layer is oriented toward the top.

2) Tunica Submucosa?

• Consists of loose connective tissue that binds the tunica mucosa to the next layer, the tunica muscularis,nerves, blood vessels, and glands in some organs

3) Tunica muscularis:

• consists of at leasttwo layers, an inner circular and an outer longitudinal with parasympathetic ganglia located between the layers

Tunics

4) Tunica Adventitia or

Tunica Serosa: • consists of loose connective

tissue.  * If the organ is surrounded by other tissues, this layer is called a tunica adventitia and its connective tissueblends with that of the surrounding tissues. 

* If the organ is suspended in the body cavity, this layer is called a tunica serosa and it is covered by a simple squamous epithelium that is called mesothelium. 

DIGESTIVE SYSTEM DISORDERS

Ulcerative Colitis

-An inflammatory disease -affects only the large intestine. Diarrhea occurs when waste products move through the large intestine too quickly; constipation results when this movement is too slow.

GERD(Gastroesophageal reflux disease) -occurs when the lower esophageal sphincter relaxes at the wrong times, allowing acid from the stomach to enter the esophagus.

GERD-possible cause:

a hiatal hernia, a protrusion of this same sphincter and the upper portion of the stomach into the chest

cavity

What is a fart exactly?

Why Do Farts Smell Bad?• The more sulfur-rich your diet is, the more

terrible your farts will smell. Some foods contain more sulfur than others, which is why eating things like beans, cabbage, cheese, soda, and eggs can cause gas that will peel the paint off the walls!

1) Farts Are Flammable

2) If You Hold Them In, They'll Just Come Out When You Sleep

3) People Even Fart After Death

TOP 10 FOOD MYTHS Myth #1:

Drinking water in between your meals will mess up your digestion

Myth #2:Having fruits immediately after a meal is not good for you

Myth #3: Papaya should be avoided during pregnancies

Myth #4:The skin of an apple contains no nutrients

Myth #5: Eating after 7 pm will make you fat

Myth #6: Having milk immediately after eating fish 

Myth #7:You should not swim/shower immediately after a meal

Myth #8: Having chocolate causes acne

Myth #9: Having kesar (saffron) during pregnancy makes your baby fair

Myth #10: If you swallow a chewing gum, it stays in your stomach for seven years before it gets digested 

Facts and fallacies Ulcers

-Spicy food and stress cause stomach ulcers. False.

almost all stomach ulcers are caused either by infection with a bacterium called Helicobacter pylori (H. pylori) or by use of pain medications such as aspirin, ibuprofen, or naproxen, the so-called nonsteroidal anti-inflammatory drugs (NSAIDs).

Heartburn

Smoking a cigarette helps relieve heartburn. False.

Actually, cigarette smoking contributes to heartburn.