The Digestive System

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The Digestive System
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Digestive System

• Alimentary Canal
• Gastointestinal Tract (GI Tract)
• Mouth, Pharynx, Esophagus, Stomach, Small
  Intestine, Large Intestine, Anus
• Technically Outside the Body
• Accessory Organs
• Teeth, Tongue, Gallbladder, Salivary Glands,
  Liver, Pancreas

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Digestive Processes

• Ingestion
• PropulsionSwallowing, Peristalsis
• Mechanical DigestionChewing, Mixing,
  Segmentation
• Chemical Digestion
• Absorption
• Defecation

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Peristalsis
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Digestive System

• LumenOutside the body.
• Digestive Activity is provoked by a range of
  mechanical and chemical stimuli.mechanoreceptors
  and chemoreceptors in the wall of the tract
  organs. These may initiate reflexes, activate or
  inhibit secretion, and mix contents.
• Controls of Digestive Processes are both
  extrinsic and intrinsicin-house nerve plexuses
  (enteric)
• Hormone Producing Cells
• Short Reflexes Long Reflexes

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Structure of the Digestive System

• Most in the abdominopelvic cavity.
• Covered with serous membranes
• Peritoneum (visceral parietal)
• Serous fluid
• MesentaryFunctions
• Parts of the small intestine, most of the
  pancreas, and parts of the large intestine lie
  posterior to the peritoneum and have no
  mesentary.
• Retroperitoneal
• Intraperitoneal
• Periotonitis

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Basic Structure of the Wall of the Alimentary
Canal

• Lumen
• Mucosaepithelial membrane secretion,
  absorption, protection.
• 3 Layers
• Lining Epitheliumsimple columnar with goblet
  cells.
• Lamina proprialoose areolar connective tissue.
  Blood and Lymph System.
• Muscularis mucosaesmooth muscle. Produce local
  movements.

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Structure of the Wall of the Alimentary Canal

• Submucosadense connective tissue. Blood, Lymph,
  and nervous tissue. Lots of Elastic Fibers.
• Muscularis ExternaInner Circular Layer and Outer
  Longitudinal Layer of musclesResponsible for
  peristalsis and segmentation. May also form
  sphincters.
• SerosaVisceral Periotoneum Adventitia

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Enteric Nervous System

• Within the Nervous system.
• Intrinsic nerve plexuses
• Submucosal Nerve Plexusregulates glands in the
  mucosa tunic.
• Myenteric plexusfound in muscularis externa.
  Control Gastric Mobility. Peristalsis
  Segmentation.
• Linked to the CNS

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Mouth, Pharynx, Esophagus

• Mouth (oral or buccal cavity)
• Oral orifice
• Oropharynx
• Stratified squamous epithelium
• Defensins
• Palate
• Hard palate
• Soft palate
• uvula

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The Tongue

• Skeletal muscle
• Aids in chewing and mixing food with saliva.
• Forms a bolus.
• Helps in speaking consonants.
• Intrinsic muscles
• Extrinsic musclesextend from the bones of the
  skull and the soft palate.
• Lingual frenulum
• ankyloglossia

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The Salivary Glands

• Salivacleanses, moistens, dissolves food,
  contains enzymes.
• Extrinsic salivary glandsmake most of the
  saliva. (parotid, submandibular, sublingual, and
  the tubuloalveolar glands)
• Intrinsic or buccal glands
• Mumpssterility
• Composed of serous cells and mucous cells.

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Saliva

• 97-99 water
• Slightly acidic
• Contains ions, mucin, amylase, lysozyme, IgA
  antibodies, defensins
• Nitric oxide
• 1000-1500 ml are made per day
• Controlled by the parasympathetic nervous system.
• Sympathetic control may cause dry mouth.

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Teeth

• Mandible and maxilla
• Mastication
• Primary dentitions
• Deciduous teeth
• 20 total
• Permanent dentitions
• 32 total
• third molars or wisdom teeth may not erupt.
• Impacted Teeth.

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Teeth

• Incisors4
• Canines--2
• Premolars or bicuspids--4
• Molars6
• Structure
• Crownenamel (hydroxyapaptite)
• Ginvivagums
• Neck
• Root
• Periodontal ligament--gomphosis

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Teeth

• Root Canal
• Dental caries
• Dental plaque
• Tartar
• Gingivitis
• Periodontitis
• Connections to heart disease

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Food Pathways

• Mouth
• Pharynx
• Epiglottis
• Esophagus
• Cardiac Sphincter
• Stomach
• Pyloric Sphincter
• Small intestine
• Pancreas

• Liver
• Gallbladder
• Large Intestine

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The Mouth

• Chewing
• Surface Area
• Salivary Glands
• Amylase
• Pharynx

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Pharynx Esophagus

• Oropharynx
• Laryngopharynx
• Esophagus
• 10 inches long
• Epiglottis
• Esophogeal hiatus
• Cardiac sphincter
• Diaphragm
• Heartburn
• Hiatal hernia
• Esophageal ulcers
• Has same 4 layers as other parts of the GI tract.

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The Mouth, Esophagus, and Pharynx

• Chemical breakdown, little absorption,
  mastication, deglutition
• Deglutition
• Buccal phasevoluntary. Bolus forced into the
  oropharynx.
• Pharyngeal-esophageal phaseinvoluntary
• Talking or laughing while eating.

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The Stomach

• Under the liver and diaphragm
• HCl pepsin
• Chyme
• Can hold up to 4 liters of food
• Rugae
• Cardiac region, fundus (below the diaphragm),
  body, pyloric region, pyloric sphincter

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The Stomach

• 4 tunics
• Mucosasimple columnar epitheliumproduce
  alkaline mucus. Contains gastric pits which lead
  to gastric glands which secrete gastric juice.
• Cell types found in these glands
• Mucous neck cellsproduce acidic mucus.
• Parietal cellssecrete HCl Intinsic factor
  (vitamin B12 absorption).
• Chief cellsproduce pepsinogen.Converted later
  to pepsin.
• Enteroendocrine Cellsproduce hormones
  includinggastrin, histamine, endorphines,
  serotonin, cholecystokinin, and somatostatin.

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Mucosal Barrier

• Bicarbonate-rich mucus
• Tight junctions between epithelial cells.
• Membranes of gastric glands are impermeable to
  HCl.
• Damaged cells are shed and replaced quickly.
  (completely replaced every 3-6 days.)
• Gastritis
• Gastric ulcers
• Peritonitis hemorrhage
• Heliobacter pylori
• May be linked to stomach cancer

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Digestion in the Stomach

• Protein Digestionpepsin renin
• Absorption in the stomach
• Intrinsic factor
• Pernicious anemiaanorexia, weight loss,
  neurological disturbances, red blood cell
  problems.

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Phases of Gastric Secretion

• Cephalicbefore food enters the mouth. Brain
  prepares the stomach. Conditioned reflex.
• Gastriclocal neural and hormonal mechanisms in
  the stomach initiate secretion of gastric juices.
  Low acidity, distension, and peptides in the
  stomach trigger this phase. Acetylcholine is the
  neurotransmitter involved.
• GastrinG cells make it. Stimulates the
  secretion of HCl and enzymes.
• IntestinalExcitatory portion is triggered when
  food enters the duodenum. Intestinal gastrin is
  secreted
• Enterogastric reflexinhibitory. Prevent
  additional food from entering the small intestine.

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Vomiting

• Emesis
• Stretching, toxins, alcohol,spicy foods, and
  drugs may stimulate this.
• Emetic Center of the Medulla
• Diaphragm and abdominal wall contract
• Cardiac sphincter relaxes.
• Soft palate rises

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Regulation of Gastric Secretions

• Neural Hormonal influences
• Parasympathetic nerves stimulate secretion,
  Sympathetic nerves inhibit secretion
• Gastrinstimulates secretion of enzymes and HCl
  and intestinal hormones.

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Esophagus and Stomach
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Functions of the Small Intestine

• Most digestion
• Most absorption of nutrients into the blood
• Structural adaptations
• Very long
• Circular folds
• Villi and microvilli
• Brush border--enzymes
• 200 square meters of surface area
• Capillaries
• Lacteals
• Crypts of Lieberkuhn
• Paneth cellslysozyme
• Effects of radiation therapy

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The Small Intestine

• 3 sections
• Duodenum
• Jejunum8 feet
• Ileum12 feet
• Ileocecal valve
• Duodenum10 inches
• Chyme
• Pancreatic duct
• Pancreas
• Alkaline fluid
• Digestive enzymes

• Pancreatic amylase
• Trypsin
• Peptidases
• Lipase
• Bile duct
• Liver4 lobes
• Bile
• Gallbladder

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The Accessory Organs

• 10,000 deaths per year
• Treatments
• Cirrhosis
• Gallbladder--Stores bile
• Bile duct
• Release affected by cholecystokinin. Also
  stimulates the secretion of pancreatic juices and
  allows these secretions to enter the duodenum.
• Gallstones
• Pancreas
• Pancreatic duct
• Produces digestive enzymes and an alkaline fluid
  (bicarbonate ion). (Amylase, lipases, nucleases,
  tryspin, etc
• Produces insulin
• Produces glucagon
• Islets of Langerhans

• Liver
• Secretes Bile-cholesterol derivates
• Emulsification of lipids.
• Absorption of fat and cholesterol
• bilirubin
• Makes plasma proteins
• Destroys old red blood cells
• Stores glycogen
• Produces urea
• Role of the hepatic portal vein.
• Hepatitis
• A and E transmitted enterically.
• Belevated risk of liver cancer
• Cchronic
• Other viral and nonviral causes

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Large Intestine

• 1.5 meters long
• Absorbs water
• Houses bacterial flora.
• Vitamins such as Vitamin K are synthesized.
• Formation of wastes
• Ileocecal valve
• cecum
• Appendix
• Appendicitis
• Ascending, Transverse, Descending Colon,
  Sigmoid colon, rectum

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Large intestine

• Anal canal
• Internal anal sphincter
• External anal sphincter
• Mass movements (2-3 times per day)
• Diverticulosisherniations of mucosa due to a
  lack of fiber in the diet.
• Diarrhea constipation
• Salmonella
• Bacteremia

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Digestion Absorption

• Chemical digestioncatabolism--hydrolysis
• Monomers
• Carbohydrate digestionamylase
• Lactose intolerance
• Protein digestion125 grams per day.
• Amino acids
• Pepsin, renin, trypsin, carboxypeptidase,
  dipeptidase
• Lipid digestion30 to 150 grams per day.
• bile, lipases
• Fatty acids and glycerol

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Absorption

• Lipids
• Micelles
• Lacteals
• Fat soluble vitamins
• Intrinsic factor
• Colon Cancer
• Metastasis
• 2nd largest cause of cancer deaths in US males.
• Polyps
• Genetic component

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