Your Digestive System

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Your Digestive System
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The digestive system consists of

• Digestive tract,Oral cavity,Salivary glands
• Pharynx,Esophagus,Stomach
• intestines
• Liver
• Gallbladder
• pancreas
• Rectum 
• Anus

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ITS JOB

• Ingest food
• Break it down
• Absorb nutrients and water
• Get rid of waste
• Supply the body with energy to perform

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steps

• Ingestion materials enter the mouth
• Mechanical processing tearing and crushing with
  teeth and squashing with tongue making it easier
  for food to travel through the digestive tract
• Digestion breakdown of food into smaller
  fragments
• Secretion glandular organs and epithelium
  release water, acids, enzymes, buffers, and salts.

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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.

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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.

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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. 

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Major layers of digestive tract

• Muscularis externa mostly smooth muscle.
   Covered by Serosa.
• Responsible for mechanical processing and
  movement along the digestive tract.
• Serosa

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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.

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saliva

• Parotid, sublingual, and submandibular glands
  produce saliva
• Breaks down food, Make food easy to swallow
• Lubricate the mouth when you eat and moisten food
• Salivary 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. 

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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.

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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.

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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.

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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.

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The Pharynx

• Passageway for solid food, liquids, and air.
• Nasopharynx, oropharynx, and laryngopharynx.
• Food passes through the pharynx and
  laryngopharynx to the esophagus.

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

• Voluntarily, automatically once it begins.
• Buccal phase
• Pharyngeal phase
• Esophageal phase

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• 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.

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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.

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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.)

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• 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.

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• The fundus superior to the junction between the
  stomach and esophagus. Contacts the diaphragm
• The 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.

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• 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 rugae
• Rugae 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.

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Active stomach

• Mixes w/ gastric juices for 3 hours.
• When filled up its walls begin to contract
  downward in a swaying motion

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• 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.

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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.

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Cells

• Parietal and chief cells.
• Together they secrete 1500 ml of gastric juice
  each day.

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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

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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 .

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Chief cells

• Secrete pepsinogen, then converted to Pepsin.
• Pepsin functions as a strong acidic pH of 1.5-2.0

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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.

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Small Intestine

• 6 m (20ft.) in length
• Absorb 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 L4
• Enzymes released from liver, gallbladder,
  pancreas break bolus down.

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• Jejunum chemical digestion and nutrient
  absorption occur in the Jejunum.
• Ileum final segment of the small intestine.
• Undigested food enters the large intestine

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Intestinal villi

• Has folds of Plicae.
• Does not disappear when stomach fills.
• Small intestine contains 800 Plicae.
• It increases the area  available for absorption

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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.

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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.

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Small intestine movements

• When chyme enters the duodenum it is then moved
  with peristaltic contractions towards jejunum.
• Nervous system controls this.

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pancreas

• Has two distinct functions endocrine and
  exocrine
• Produces digestive enzyme and buffers
• Pancreatic 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.

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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 lipasebreak down complex lipids,
  release products like fatty acids.
• - Proteolytic Enzyme break proteins apart
• Secrete insulin and glucagon into the bloodstream.

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liver

• The largest organ in the body
• Functions 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

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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

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gallbladder

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

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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

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• 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.

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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.

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• 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

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Intestinal absorption

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

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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.

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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.

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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.)

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colon

• Four regions 
• ascending colon
•  transverse colon
• Descending colon
• Sigmoid colon

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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.

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Three parts

• Divided in three parts
• Cecum- first portion of the large intestine.
• The colon- largest portion
• Rectum- end of the digestive tract.

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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.

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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.

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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

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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.