The Digestive System

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The Digestive System
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Functions of the Digestive System

• Take in Food
• Break down the food
• Absorb the digested molecules
• Provides Nutirents

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The Tissue

• Four Tunics
• mucosa
• submucosa
• muscularis
• serosa

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The peritoneum

• The peritoneum is a serous membrane that lines
  the abdominal cavity and covers the organs
• Mesenteries are double layers of peritoneum that
  extend from the body wall to the many organs
• Retroperitoneal organs are behind the peritoneum

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The oral cavity

• Lips and cheek muscles involved in mastication
• The tongue muscle is involved in speech ,
  mastication and swallowing
• 32 permanent teeth for chewing
• Hard and soft palate
• Salivary glands produce serous and mucous
  secretions

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Teeth

• 32
• Incisors, canines, premolars and molars
• Each tooth is made of a crown , neck and root
• Cut , tear and crush the food

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Salivary Glands

• Exocrine
• NAMES
• Parotid
• Submandibular
• Sublingual
• secrete Amylase which digests starches
• and Mucin which provides lubrication

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Tongue

• muscle that will push food from the oral cavity
  into the pharynx

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Pharynx

• Nasopharynx
• Oropharynx only site of food entry
• Laryngophaynx
• Once food is pushed into the oropharynx, the soft
  palate closes the nasopharynx and the epiglottis
  closes the laryngopharynx. The food is then moved
  into the esophagus

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Esophagus

• Long tube that is located between the pharynx
  and the stomach
• Once food is pushed into the esophagus waves of
  constricitons of the esophageal muscles called
  Peristalsis moves the food down the esophagus to
  the stomach

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Esophageal function
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The Stomach

• The stomach begins where the esophagus ends and
  ends where the first part of the small intestines
  begins
• Its opening at the esophagus is called the cardia
• Its opening at the duodenum is called the pylorus
• The wall is made up of three muscle layers
  longitudinal, circular and oblique

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The Stomach Secretions

• Mucus-protects the stomach lining
• Hydrochloric Acid- kills microorganisms and
  activates pepsin
• Pepsin- starts protein digestion
• Intrinsic Factor- aids in vitamin B12 absorption
• Gastrin-helps regulate stomach secretions

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Stomach
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Regulations of
Stomach Secretions

• Cephalic Phase
• Gastric Phase
• Intestinal Phase

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Movement of the Stomach

• Mixing waves mix the stomach contents with the
  stomach secretions and form a substance called
  Chyme
• Peristalsis moves the chyme from the stomach into
  the duodenum( first part of the small intestine)

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The Small Intestine

• Divided in to three parts
• Duodenum
• Jejunum
• Ileum
• Along the surface are circular folds, villi, and
  microvilli which increase the surface area for
  the absorption of food
• Most of all nutrient absorption from food occurs
  along the duodenum and jejunum

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Secretions from the Small Intestine

• Mucus secreted from duodenal glands
• Multitude of enzymes that aid in digestion of
  carbohydrates, proteins and fats
• Stimulated by tactile irritation, vagal nerve
  stimulation and secretion

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Movement of the Small Intestine

• Segmental Contractions- occur over short
  distances and mix intestinal contents
• Peristaltic Contractions- occur the length of the
  intestine and propel chyme through the intestine

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Parts of the Small Intestine
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The Large Intestine (colon)

• The colon is divided into 4 parts
• ascending
• transverse
• descending
• sigmoid
• The colon begins where the ileum (last part of
  small intestine begins).
• The Cecum forms a blind sac at the end of the
  junction of the small and large intestine
• The Appendix forms a blind sac off the cecum

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Function of the Large Intestine

• Absorbs water
• Converts Chyme to Feces
• Eliminates Feces Trough the process of
  Defecation
• note it takes longer for the material to
  move through the large intestine than the small
  intestine. Mass movements occur 3-4 times a day

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Large Intestine
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Liver

• Consists of Four Lobes
• Produces a substances called Bile which leaves
  the liver to enter the duodenum through a system
  of ducts. The right and left hepatic ducts empty
  into the common hepatic duct
• Bile consists of bile salts that will emulsify
  fats
• The Liver also stores and makes nutrients, makes
  new molecule, detoxifies molecules and makes
  blood proteins

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Gall Bladder

• A small organ on the undersurface of the liver
  that stores the bile that has been made by the
  liver.
• Extending from the gall bladder is the cystic
  duct which connects to the hepatic duct to form
  the common bile duct

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The Pancreas

• Located behind the stomach and duodenum
• Both an Endocrine and Exocrine gland
• Endocrine- alpha and beta cells which
  make glucagon and insulin for control of blood
  nutrient levels
• Exocrine produces bicarbonate and
  digestive enzymes . Acidic chyme stimulates the
  release of this bicarbonate which neutralizes
  acidic chyme. The enzymes are released in
  response to fatty and amino acids

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Digestion/ Absorption

• Digestion is the chemical breakdown of organic
  molecules ( carbohydrates, lipids and fats) into
  their component parts by various digestive
  enzymes
• Absorption the process by which these
  components are taken up by the digestive system
  and transported across the intestinal wall into
  the blood to be circulated around to the rest of
  the body tissues

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The Rectum and Anal Canal

• The Rectum is a straight tube at the end of the
  Large Intestine
• The Anal Canal is at the end of the rectum. It is
  surrounded by an internal anal sphincter (smooth
  muscle )and an external anal sphincter ( skeletal
  muscle) which regulate the defecation process

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The Organic Molecules

• Carbohydrates
• Proteins
• Fats

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Digestion / Absorption

• Digestion is the chemical breakdown of these
  organic molecules of into their component parts .
  
• After the molecules are digested , these
  components are then either transported across the
  intestinal wall or diffuse through the intestinal
  wall

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Carbohydrates

• Carbohydrates are made up of chains of sugar (
  saccharide) molecules
• Mono
• Di
• Poly

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Digestion and Absorption of the
Polysaccharide

• Poly saccharides are split by salivary amylase
  into disaccharides by salivary amylase and then
  again by pancreatic amylase
• Disaccharides are broken down to monosaccharides
  by disaccharidases on the surface of the
  intestinal epithelium
• Monosaccahrides are absorbed by active transport
  into the blood and carried by the hepatic portal
  vein to the liver where glucose is store or used
  as needed by other tissues

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Digestion and Absorption of
Proteins

• Polypeptides, Di -peptides, Amino acids
• Proteins are split into small polypeptides by
  the enzymes in the stomach( pepsin) and on the
  surface of the intestinal epithelium( trypsin)
• Peptidases on the surface of the intestinal
  epithelium breakdown polypeptides and di-
  peptides into amino acids
• Amino acids are then absorbed intestinal cells
  by active transport under the influence of growth
  hormone and insulin
• Once absorbed into the blood they will go to be
  used as building blocks for new proteins

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Digestion and Absorption of the Lipids

• Bile Salts made by liver
• Pancreatic Lipase breaks down lipids . These
  break down products of lipids are mixed with the
  bile salts to form micelles
• Micelles come close to the intestinal epithelium
  and their contents diffuse into intestinal cells
  where they are packaged and released into the
  lymphatic system
• From the lymphatics lipids are transported to
  Adipose tissue and the liver to be stored for use
  as energy when needed

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Water and Minerals

• 99 of the water that enters you intestine is
  absorbed Most is absorbed in the large
  intestine
• Minerals ( Calcium, phosphorous, Magnesium, Iron
  ) are actively transported across the intestinal
  wall