Digestive System

By: Isaías Quezada, Emely Rivera, Carlos SandovalPer.5

Overview The digestive system consists of the Alimentary canal:

1.Mouth

2.Pharynx

3.Esophagus

4.Stomach

5.Small intestine

6.Anal canal

Accessory structures:

1.Salivary glands

2.Liver

3.Gallbladder

4.Pancreas

Structure of the Alimentary Canal’s Walls Its' walls consist of four distinct layers that are developed to

different degrees from region to region. Certain regions are specialized for certain functions. These layers are:

1.Mucosa

2.Submucosa

3.Muscular Layer

4.Serosa

Mucosa formed of surface epithelium, lamina propria(connective

tissue), and a small amount of smooth muscle

Function are protection, secretion, and absorption

Submucosa Contains loose connective tissue, glands, blood vessels,

lymphatic vessels, and nerves

Function is to nourish surrounding tissues and carry away any absorbed materials

Muscular Layer

consists of two coats of smooth muscle tissue arranged in circular and longitudinal groups

Provides movement of the tube and its contents

Serosa

outer covering of the tube and comprised of visceral peritoneum, which is formed of epithelium on the outside and connective tissue beneath

Its function is both protection and lubrication

Types of Movement

There are two main motor functions of the alimentary canal; mixing & propelling

Types of Movement: Mixing

Occurs when smooth muscles in small segments of the tube contract rhythmically

When the stomach is full, waves of muscular contractions move along its wall from one end to the other.

The waves occur every twenty seconds and they mix foods with the digestive juices that the mucosa secretes

Types of Movement: Propelling

a wave-like motion called peristalsis occurs

a ring of contraction appears in the wall of the tube, yet just ahead the muscular wall relaxes

This action begins when food expands the tube

Mouth

First portion of alimentary canal

Receives food

Begins mechanical digestion

Breaks food into smaller pieces

Organ of sensory and speech

Cheeks

Lateral walls of mouth

Consist of outer layers of skin

Pads of subcutaneous fat

Muscles that help with expressions and chewing

Moist inner layers moist, stratified squamious epithelium

Lips

Mobile structures surrounding mouth

Contain skeletal muscle

Judges temperatures and texture of food

Reddish color comes from amount of blood cells

External borders mark boundaries between skin of face and mucous membrane that lines in alimentary canal

Tongue

Muscular organ rest on the bottom of the mouth

Covered by mucous membrane

Connected by midline to the floor by membranous fold, lingual frenulum

Composed of skeletal muscle fibers that run in several directions

Papillae

Root held by hyoid bone

Posterior covered in lingual tonsils

Palate

Roof of oral cavity

Hard anterior , soft posterior

Hard palate formed by palatine processes of maxillary

soft palate forms a muscular arch

Uvula

Muscles here help with swallowing

Palatine tonsils

Pharyngeal tonsils.

Teeth

Hardest structures in body

Not considered part of the skeletal system

Develop in sockets in alveolar process of mandibular and maxillary bones

Permanent teeth come at about six years old

They break food into smaller particles, thus beginning the mechanical process

Helps mix food with saliva

Salivary Glands

Secretes saliva

minor glands are found on mucosa of the mouth

Constantly secreting fluid to keep mouth moist

There are 3 pairs of major glands, parotid, submandibular, sublingual

Secretion

Secretory cells within the glands, Serous, and Mucous cells

Serous cells contain salivary amylase.

Enzymes split starch and glycogen molecules, they then become disaccharides

This begins chemical digestion

Mucous cells secrete mucus

Glands have parasympathetic and sympathetic nerves

Pharynx

Connects nasal and oral cavity with larynx and esophogus

Nasopharynx

oLocated: superior to the soft palate

oCommunicates with the nasal cavity and provides a passageway for air during breathing

Oropharynx

oLocated: posterior to the mouth

oPassageway from the mouth for air moving to and from the nasal cavity

Pharynx (continued)

Laryngopharynx

oLocated: inferior to the oropharynx

oExtends from the upper boarder of the….downward to the lower boarder of the cyroid cartilage of the larynx and is a passageway to the esophagus

Esophagus

Straight, collapsible tube that is about 25 cm. long

Provides a passageway for food

Cardiac Sphincter

Remain contracted

Close entrance to the stomach

Prevents regurgitation

Parts of the Stomach: Cardiac Region A small are near the esophageal opening, or cardia

This is where the contents of the esophagus empty into the stomach

Parts of the Stomach: Fundic Region Serves as a temporary storage area and sometimes fills with

swallowed air

This produces a gastric air bubble which may be used as a landmark on a radiograph of the abdomen

Parts of the Stomach: Body Region The main portion of the stomach and located between the

fundic and pyloric portions

The main chamber for containing food

Parts of the Stomach: Pyloric Region Funnel-shaped

Shape narrows and becomes the pyloric canal as it approaches the small intestine

At the end, the circular layer of fibers in its muscular wall thickens and forms the muscle Pyloric Sphincter, which acts as a valve that controls gastric emptying

Gastric Secretions

The stomach’s mucous membrane is studded with gastric pits, located at the ends of tubular gastric glands

Their structure and composition of their secretion vary in different parts of the stomach

All gastric glands generally contain 3 types of secretory cells

Secretory Cells

Mucous Cells: found in the necks of the glands near the openings and is responsible for lining the stomach from digestive juices

Chief Cells: also known as peptic cells are a key component of gastric juices

Parietal Cells: also known as oxyntic cells. When the chief cells secrete enzymes and parietal cells release a hydrochloric acid solution, they form the gastric juices

Major Components of Gastric Juices

Components Source Function

Pepsinogen Chief Cells of the Gastric glands

Inactive form of pepsin

Pepsin Pepsinogen in the presence of hydrochloric acid

Protein-splitting enzyme that digests all dietary protein

Hydrochloric acid Pepsinogen in the presence of hydrochloric acid

Protein-splitting enzyme that digests all dietary protein

Mucus Goblet cells and mucous glands

Provides viscous alkaline protective layer on the inside of the stomach wall

Intrinsic factor Parietal cells of the gastric glands

Aids in vitamin B12 absorption

Phases of Gastric secretions

Phase Action

Cephalic phase Sight, taste, or thought of food triggers parasympathetic reflexes. Gastric juice is secreted in response

Gastric phase Food in stomach chemically & mechanicaly stimulates release of gastrin, stimulating secretion of gastric juice; reflex response also stimulate gastric juice secretion

Intestinal phase As food enters small intestine, it stimulates intestinal cells to release intestinal gastrin, promoting the secretion of gastric juice from the stomach wall.

Pancreas Endocrine Gland/exocrine function

Secretes pancreatic juices

Pancreas (structure) Located posterior to parietal peritoneum

Pancreatic acinar cells: produce pancreatic cells

Aclai: clusters around tiny tubes which release their secretions

Small tubes connect to pancreatic duct

Pancreatic duct connects with duodenum

Stomach

A J-shaped pouch like organ in the abdominal cavity

It receives food from the esophagus, mixes it with gastric juices, initiates the digestion of proteins, carries on limited absorption, and transports food into small intestine

Divided into four sections;

1.Cardiac region

2.Fundic section region

3.Body regions

4.Pyloric regions

Liver

• Largest gland in the body• Weights 3.2 – 3.7 pounds• Detoxifies blood• Creates bile for stomach• Stores vitamins, iron, simple sugar glucose• Converts ammonia to urea• Very Likely to get disease due to the mass of functions it

carries out

Gallbladder

• Pear shaped• Stores conventrate bile• Stores any bile that is not used • Cholecystokinin causes the release of bile to

small intestine• Cholestoral, bile salts, can create Gallstones

Regulation of Bile Release

Small Intestine A tubular organ that extends from the pyloric sphincter

to the beginning of the large intestine Recieves secretions from the pancreas and liver Completes digestion of the nutrients in chym

Macromolecules

Carbohydrates Begins in the mouth Parctially digested carbs travel to esophagus and then the

stomach Move to the small intestine where they are broken down by

enzymes from the pancreas Then absorbed into the blood stream Fiber passes through undigested LipidsSome digested in mouth and stomach Mainly in the small intestineBile produced in liver is sent to gallbladder Fatty acids combine with cholesterol and bile Transported to veins of chest and the blood carries fat to be

stored in adipose tissue

Macromolecules (cont)

ProteinsDigested into amino acids Begins in stomach with gastric juicePotent enzymes from pancreasContinues to the small intestineAmino acids absorbd into the blood

Duodenum

Shortest and most fixed portion of the small intestine C-shapedRecieves the partly digested food

JejunumGreater diameterThicker wall More vascularMore activeSupport absorption of carbohydrates and protiens

IleumMore lymph nodules Higher bacterial populationAbsorb chyme

Large Intestine 1.5 meters long

Consists of cecum, colon, rectum, and anal canal

Begins in iliac region of pelvis

Joined together with small intestine

Continues across and down the abdominal cavity, and ends at the anus

Takes 16 hours to digest

Transports waste and re-absorption of water before it gets secreted.

Absorbs water and vitamins

Reduces Acidity

Produces antibodies

Cecum Tube like structure in lower abdominal cavity

Receives undigested food from small intestine

Absorbs fluids and salts that remain after intestinal digestion and absorption

Mixes the contents with mucus

Has a thick layer of mucous membrane

Layer of muscle that makes churning and rubbing movements

Colon Removes water, salt, and nutrients that form stool

Muscles squeeze the contents through the intestine

Bacteria is found along the walls of the colon

4 parts, descending, ascending, transverse, and sigmoid

Supported by peritoneum

Rectum 10 to 12 cm

Dilates towards the anus

Stores feces

Stretch receptors in walls tell when the body needs to defecate

When the rectum storage is full, the pressure pushes the feces to the anus

Body temperature can checked from rectum area

Anal Canal

3-5 cm

Lubricates feces as it comes from rectum

Has muscular sphincter system that closes lumen

External anal sphincter surrounds anal canal and acts like a clamp. Similar to the puborectalis muscles that covers rectum from behind.

Both of which are voluntarily controlled

Internal anal sphincter relaxes so blood in anal cushions drain, which allows feces to go through

HormonesHormone Function

Gastrin Produce acid to dissolve food

Intestinal gastrin Increase activity of gastric glands

Inner/Somatostatin Inhibits secretion of acid

Cholecystokinin Decrease activity of gastric glands; stimulates pancrease; stimulates gallbaldder

Secretin Stimulates pacreas to secrete fluid

Hormone Function

Ghrelin Stimulates appetite

Paptide YY Inhibits appetite

Leptin Tells the body it is full