Your Digestive System

The digestive system consists of:

Digestive tract,Oral cavity,Salivary glandsPharynx,Esophagus,StomachintestinesLiverGallbladderpancreasRectum Anus

ITS JOB

Ingest food

Break it down

Absorb nutrients and water

Get rid of waste

Supply the body with energy to perform

steps

Ingestion: materials enter the mouthMechanical processing: tearing and crushing with teeth and squashing with tongue making it easier for food to travel through the digestive tractDigestion: breakdown of food into smaller fragmentsSecretion: glandular organs and epithelium release water, acids, enzymes, buffers, and salts.

steps

Absorption:  the movement of organic substrates, electrolytes (inorganic ions), vitamins, and water across the digestive epithelium and into the interstitial fluid of digestive tract.

Excretion: eliminate waste products from body. A process called defecation.

*eliminates materials as feces.

Its lining:

The lining of the digestive tract protects surrounding tissues against the effects of digestive acids and enzymes. 

Bacteria.

*If bacteria reaches the lamina propria it will be attacked by macrophages and by other cells of the immune system.

Major layers of digestive tract

Mucosa: its the inner lining, consists of a layer  of an epithelium moistened by glandular secretions and an underlying layer of areolar tissue, called the lamina propria.

Submucosa: layer of dense irregular connective tissue. Surrounds the muscularis mucosae.

Has large blood cells and lymphatic vessels. 

Major layers of digestive tract

Muscularis externa: mostly smooth muscle.  Covered by Serosa.

Responsible for mechanical processing and movement along the digestive tract.

Serosa

Oral cavity

Digestion begins even before food is ingested. Just by the sight, smell or even thinking about  food.The sight of food stimulates the salivary gland.When food is taken into the mouth it gets prepared for digestion in a process known as mastication.Teeth tear down the food making it into smaller pieces.Tongue rolls these pieces into boluses.

saliva

Parotid, sublingual, and submandibular glands produce saliva

Breaks down food, Make food easy to swallowLubricate the mouth when you eat and moisten foodSalivary gland produces 1.0-1.5 liters of saliva each day.99.4% water the remaining 0.6% includes electrolytes, buffers, antibodies, enzymes, and waste products. 

About saliva

mucins is responsible for the lubricating action of saliva.Salivary secretions are controlled by autonomic system.Nauseas will keep your mouth wet; increases saliva production.70% of saliva originates in the submandibular salivary glands 25% in the parotids 5% in the sublingual cavity.

tongue/taste buds

Detect: sweet, salt, bitter and sour.Olfactory nerves contribute by sending the aroma to the brain.Everyone's taste buds are different.They will change as you get older.Fast fact: when you were a baby you had taste buds, but not only in your tongue, but on the sides and roof of your mouth. You were sensitive to different foods.

Taste buds disorders

Medications, smoking, not getting enough of the right vitamins, injury to the head, brain tumors, chemical exposure, and the effects of radiation can cause taste disorders.

facts

We have almost 10,000 taste buds inside our mouths, even on the roofs of our mouths.

Girls have more taste buds than boys.

Taste is the weakest of the five senses.

The Pharynx

Passageway for solid food, liquids, and air.

Nasopharynx, oropharynx, and laryngopharynx.

Food passes through the pharynx and laryngopharynx to the esophagus.

Swallowing

Voluntarily, automatically once it begins.

Buccal phase

Pharyngeal phase

Esophageal phase

.

When the bolus of food is swallowed, the epiglottis closes the trachea.

Food is forced to the esophagus 

Epiglottis opens up again

esophagus:

Receives blood from inferior phrenic arteries.

Prevents air from entering.

Movements of Materials: Peristalsis

Smooth muscle tissue is able to move in a wave of contraction.Bolus move through the esophagus with the help of contractions called Peristalsis. The contractions occur behind the bolus pushing it down the digestive tract. 2 or 3 seconds.

stomach

Shape of an expanded J.A short lesser curvature forms the medial surface of the organ, and a long greater curvature forms the lateral surface.The anterior and posterior surfaces are smoothly rounded.An average stomach, the lesser curvature has the length of approximately 10cm  (4in.) and the greater curvature about 40 cm (16 in.)

The stomach extends between the levels of the vertebrae T7 and L3.Stomach has four regions: The cardia: the smallest part of the stomach. 3 cm (1.2 in.) it contains abundant mucous glands whose secretions coat the connection with the esophagus and help protect that tube from the acids and enzymes of the stomach.

The fundus: superior to the junction between the stomach and esophagus. Contacts the diaphragmThe body: between the Fundus and the curve of the J. the largest region, acts as a mixing tank for ingested food.Gastric glands  secrete most of the acids and the enzymes.The pylorus: the curve of the J. it's divided into pyloric antrum that is connected to the body and pyloric canal, which empties to the duodenum. When the mixing movements occur the pylorus changes shape.

Pyloric sphincter regulates how much chyme its release into the duodenum. The volume of the stomach increases while you eat, then decreases when chyme enters the small intestine.When stomach is relaxed (empty), the mucosa is thrown into prominent folds called rugaeRugae is a temporary feature that lets gastric lumen expand.When your stomach fills the rugae flattens out. When its full the rugae almost disappears. When  full: it can expand to contain 1-1.5 liters of material.

Active stomach

Mixes w/ gastric juices for 3 hours.

When filled up its walls begin to contract downward in a swaying motion

The oblique layer assist in the mixing and churning essential to the formation of chyme.Alkaline mucous layer protects epithelial cells against the acids and enzymes in the gastric lumen.The stomach receives blood from the left gastric artery, which supplies the left gastroepiploic artery and the common hepatic artery supplies the right gastric Then drained by the gastric and gastroepiploic veins.*When food is liquefied in the stomach, it is slowly released into the small intestine for further processing.

Stomach lining

It contains Hydrochloric acid (HCI) and enzymes (pepsin) that break down food.When food enters HCI is released.Gastric pits openings to the gastric mucosa.Gastric epithelial cells has a life span of 3-7 days.

Cells

Parietal and chief cells.

Together they secrete 1500 ml of gastric juice each day.

parietal

Parietal cells secrete intrinsic factor. This facilitates the absorption of vitamins B12. They also secrete hydrochloric acid. HCI is not produced in the cytoplasm because it's such a strong acid that would destroy the cell.H+ and C1- form HCI and are transported by different mechanisms

Parietal/ G Cells

The acidity of gastric juices kills most of the microorganisms ingested in food.The acidity break down plant cell walls and the connective tissues in the meat.G cells produce gastrin.Gastrin stimulates the secretion of both parietal cells and chief cells.They also help the contractions when mixing the food .

Chief cells

Secrete pepsinogen, then converted to Pepsin.

Pepsin functions as a strong acidic pH of 1.5-2.0

Three phases of gastric control

Cephalic phase: Begin when you see, taste,  or smell food. Prepares your stomach to receive food. Only lasts minutes.- increase volume of gastric juices by stimulating mucus, enzyme and acid prod.Gastric phase: begins with the arrival of food. 3 – 4 hrs.-consists of Neural response, Hormonal response, Local response.Intestinal phase: starts when chyme enters the small intestine.

Small Intestine

6 m (20ft.) in lengthAbsorb minerals, vitamins, carbohydrates, proteins, and fats.Divided into three sections: Duodenum, Jejunum, and Ileum.90% of the absorption of nutrients occur in here.Duodenum: a mixing bowl that receives chyme from the stomach. It curves in a C that encloses the pancreas. It's between vertebrae L1 and L4Enzymes released from liver, gallbladder, pancreas break bolus down.

Jejunum: chemical digestion and nutrient absorption occur in the Jejunum.

Ileum: final segment of the small intestine.

Undigested food enters the large intestine

Intestinal villi

Has folds of Plicae.

Does not disappear when stomach fills.

Small intestine contains 800 Plicae.

It increases the area  available for absorption

Villi Structure

Each villus is covered by epithelial cells which contain microvilli.

Increases absorption

The Lamina Propria of each villus contain a network of capillaries.

Carry absorbed nutrients & deliver it to the liver & send it to the bloodstream to get to the body cells.

movements

Contractions move the villi back and forth.

The movements of the villi squeeze the lacteals, and they move lymph out of the villi.

Capillaries contain lymphatic capillary called Lacteal.

Transport materials that aren't able to enter blood capillaries.

Small intestine: movements

When chyme enters the duodenum it is then moved with peristaltic contractions towards jejunum.

Nervous system controls this.

pancreas

Has two distinct functions: endocrine and exocrineProduces digestive enzyme and buffersPancreatic duct: delivers secretions to the duodenum.Three enzymes in pancreatic juice which digest carbohydrates, lipids, and proteins.Lipases and pancreatic juices break down fat into fatty acids and glucerol, while proteinases continue to breakdown proteins into amino acids.

Pancreatic juice

Secrete about 1000 ml (1 qt) of pancreatic juice.Pancreatic enzymes: -pancreatic alpha- amylase, a carbohydrate. Breaks down starches. Identical to salivary amylase.- Pancreatic lipase:break down complex lipids, release products like fatty acids.- Proteolytic Enzyme: break proteins apartSecrete insulin and glucagon into the bloodstream.

liver

The largest organ in the bodyFunctions: metabolic regulation, hematological regulation, and bile production.The liver has more than 200 functions.It controls the excretion and production of cholesterol.Stores iron, maintains the hormone balance, fights infections, regulates blood clotting

Bile functions

Bile salts break down droplets apart.

90% of the bile salts are reabsorbed in the ileum.

This reabsorbed bile salts are collected and recycled by the liver

gallbladder

Stores bile; releases bile into small intestine. It can store 2 oz.Divided in three sections:-the Fundus- Body-neckTwo major functions: bile storage and bile modification.-Expandable.When full it can contain 40-70 ml of bile

The major hormones that control the functions of the digestive system

are produced and released by cells in the mucosa of the stomach and small intestine. These hormones are released into the blood of the digestive tract, travel back to the heart and through the arteries, and return to the digestive system where they stimulate digestive juices and cause organ movement

Gastric causes the stomach to produce an acid for dissolving and digesting some foods. Gastric is also necessary for normal cell growth in the lining of the stomach, small intestine, and colon.Secretin causes the pancreas to send out a digestive juice that is rich in bicarbonate. The bicarbonate helps neutralize the acidic stomach contents as they enter the small intestine. Secretin also stimulates the stomach to produce pepsin, an enzyme that digests protein, and stimulates the liver to produce bile.

hormones

CCK causes the pancreas to produce the enzymes of pancreatic juice, and causes the gallbladder to empty. It also promotes normal cell growth of the pancreas.

Ghrelin is produced in the stomach and upper intestine in the absence of food in the digestive system and stimulates appetite.

Peptide YY is produced in the digestive tract in response to a meal in the system and inhibits appetite

Intestinal absorption

Takes about 5 hours for materials to pass from duodenum to the end of the ileum.

cecum

The cecum, the first part of the large intestine,   the inner side of the ilium (the upper part of the hipbone).  a pouch or large tube like structure in the lower abdominal cavity that receives undigested food material from the small intestine and is considered the first region of the large intestine. It is separated from the ileum (the final portion of the small intestine) by the ileocecal valve  which limits the rate of food passage into the cecum and may help prevent material from returning to the small intestine. main functions: absorb fluids and salts that remain after completion of intestinal digestion and absorption & to mix its contents with  mucus.

The ileocecal valve

has two main functions. The first is to prevent the back flow of fecal contents from the colon to the small intestine. The second is to prevent the contents of the ileum from passing into the cecum prematurely.

Large intestine

Horseshoe-shaped.Begins at the end of the ileum ends at the anus.Major functions: reabsorption of water and compaction of intestinal contents into feces.-Absorptions of important vitamins.- storage of fecal material prior to defecation.Length of 1.5 meters (5ft.)

colon

Four regions 

ascending colon

 transverse colon

Descending colon

Sigmoid colon

l. intestine

10% nutrient absorption

Most of the bile salts that are in the large intestine are absorbed in the cecum and transported in blood to the liver for secretion into bile.

Three parts

Divided in three parts

Cecum- first portion of the large intestine.

The colon- largest portion

Rectum- end of the digestive tract.

Absorption in l. intestine

1500 ml of material enters your colon each day, only about 200 ml of feces is ejected.

- its 75% water 5% bacteria & rest a mixture of indigestible material and remains of epithelial cells.

movements

Takes hours for material to turn into feces.Mass movements- occur a few times each day.Contractions forces feces into the rectum and causes an urge to defecate.Peristaltic contractions force feces towards the anus.

Integration with other systems

Nervous: transmit signals to the digestive system to perform properly at a given time.Cardiovascular: absorbs fluid to maintain normal blood volumes. Absorbs vitamin K; liver excretes heme.Endocrine: provides nutrients and substrates to endocrine cells; endocrine cells of pancreas secrete insulin and glucagon;

Fun Facts

You get a new stomach lining every three days.Digestive problems cost Americans $50 billion each year in both direct costs and absence from work.Our saliva glands produce 2 liters of saliva everyday and we en up gulping most of them down. That's an average of 50,000 liters (5,500 gallons) for a lifetime.