The Digestive System by oU58Dz6o


									The Digestive System
   Digestive System: Overview
• The alimentary canal or gastrointestinal
  (GI) tract digests and absorbs food
• Alimentary canal – mouth, pharynx,
  esophagus, stomach, small intestine, and
  large intestine
• Accessory digestive organs – teeth,
  tongue, gallbladder, salivary glands, liver,
  and pancreas
           Greater Omentum

• Greater - covers small intestines like an apron.
• This is the visceral fat that is detrimental to your
Where does she carry most of
        her weight?
    Mesentery and Mesocolon

• Mesentery of small intestines holds many blood vessels
• Mesocolon anchors colon to posterior body wall
Peritoneum – serous membrane
of the abdominal cavity
     Visceral – covers external
     surface of most digestive
     Parietal – lines the body
Peritoneal cavity- small space
between visceral and parietal
     Lubricates digestive organs
     Allows them to slide across
     one another
            Stages of Digestion
• Mechanical digestion
  – physical breakdown of food into smaller particles
  – teeth and churning action of stomach and intestines
• Chemical digestion
  – series of hydrolysis reactions that break macromolecules
    into their monomers
  – enzymes from saliva, stomach, pancreas and intestines
  – results
     • polysaccharides into monosaccharides
     • proteins into amino acids
     • fats into glycerol and fatty acids
         Digestive Processes
• Motility
  – muscular contractions that break up food, mix
    it with enzymes and move it along
• Secretion
  – digestive enzymes and hormones
• Membrane transport
  – absorption of nutrients
   Motility in the Small Intestine
• The most common motions of the small intestine
  is segmentation and peristalsis
• Segmentation ensures mechanical digestion in
  the SI and to ensure the enzymes mix with
  proper substrates for maximal absorption.
• After nutrients have been absorbed:
   – Peristalsis moves contents steadily toward the
     ileocecal valve( ileum meets the cecum)
     • Meal remnants, bacteria, mucosal cells, and debris
       are moved into the large intestine
   Histology of the Alimentary
• From esophagus to the anal canal the
  walls of the GI tract have the same four
  layers (tunics)
  – From the lumen outward they are the mucosa,
    submucosa, muscularis externa, and serosa
• Each tunic has a predominant tissue type
  and a specific digestive function
                Anatomy of the Alimentary Canal




Blood vessels

• The innermost layer epithelial layer that lines the
  lumen of the alimentary canal
• Stomach and small intestine mucosa contain:
   – Enzyme-secreting cells that aid in the
     absorption of nutrients for of digestion
   – Mucus producing cells protects the lumen from
     hydrolytic enzymes while aiding the movement food
     through the alimentary canal
• Has many lymphatic vessels that protection
  against infectious disease
  Other layers of the Alimentary Canal
• Submucosa –
  –   Dense connective tissue containing elastic fibers
  –   Blood and lymphatic vessels
  –   Lymph nodes
  –   Nerves (Submucosal Nerve Plexus)
• Muscularis externa –
  – Composed of involuntary smooth muscle innervated
    by the (Myenteric Nerve Plexus)
  – responsible for segmentation and peristalsis
• Serosa
  – the protective visceral peritoneum
  – Outer most layer
                Enteric Nervous Control

Myenteric Nerve Plexus
Submucosal Nerve Plexus
      Enteric Nervous Control
• Is often referred to the second brain because it
  can regulate digestive tract mobility, secretion
  and blood flow independently of CNS.
  – It is thought that there are more neurons in the ENS
    than the spinal cord.
• Composed of two nerve networks
  – submucosal plexus
     • controls glandular secretion and muscular
       contraction of the mucosa
  – myenteric plexus
     • controls peristalsis
     • contractions of muscularis external
Autonomic Function in Digestion
                • Parasympathetic nervous
                  system has many neural
                  connections to the ENS.
                   • It stimulates digestive
                     activities via the vagus
                   • Sympathetic nervous
                     system inhibits
                     digestive activity by
                     shunting blood away
                     from the gut and to the
                     heart and skeletal
Phases of Digestion
                 Cephalic Phase
• Excitatory events include:
   – Sight or thought of food
   – Stimulation of taste or
     smell receptors
• Inhibitory events include:
   – Loss of appetite or
   – Decrease in stimulation of
     the parasympathetic
     Digestive Processes in the Mouth

•   Food is ingested
•   Mechanical digestion begins (chewing)
•   Propulsion is initiated by swallowing
•   Salivary amylase begins chemical breakdown of
    – Mouth is at a fairly neutral Ph. Ideal for amylase
• The pharynx and esophagus serve as a
  passage way for food from the mouth to the
Salivary Glands

• Mumps is a contagious viral infection that can
  cause painful swelling of the parotid glands.
• Mumps can lead to hearing loss and meningitis
  (inflammation of the meningeal layers the brain
  and spinal cord)
• Functions of saliva
  – moisten, begin starch and fat digestion, cleanse teeth,
    inhibit bacteria, bind food together into bolus
• Composed of 99.5% water and solutes
  –   salivary amylase, begins starch digestion
  –   lingual lipase, digests fat activated by stomach acid
  –   mucus, aids in swallowing
  –   lysozyme, enzyme kills bacteria
  –   immunoglobulin A, inhibits bacterial growth
  –   electrolytes = Na+, K+, Cl-, phosphate and bicarbonate
• pH of 6.8 to 7.0
Anatomy of the Oral Cavity: Mouth
Hiatal Hernia
       • Part of the esophagus
         and upper part of
         stomach get trapped in
         the thoracic cavity.
       • Acid gets trapped in the
         esophagus which can
         mimic symptoms of a
         heart attack.
       • Over time it will erode the
         esophagus resulting in
         strictures, hemorrhage or
         even cancer.
       Digestion in the Stomach
• The stomach:
  –   Holds ingested food
  –   Digests food both mechanically and chemically
  –   Delivers chyme to the small intestine
  –   Enzymatically digests proteins with pepsin
       • Lingual lipase activated.
  – Secretes intrinsic factor required for absorption of
    vitamin B12
     • Vitamin B12 is necessary for the production of many
        different type of cells including nerve and red
        blood cells
           – Pernicious anemia can result from a lack of either Vitamin B12 or
             intrinsic factor.
    Chemical breakdown of proteins
    and to a lesser extent fats begins
    and food (bolus) is converted to
•   Cardiac region –connects the
    esophagus to stomach.
•   Muscularis –Is composed of 3
    muscular layers
     – Allows the stomach to churn,
       mix, and pummel food
•   Rugae: folds in the stomach when
    empty stomach
•   The pylorus is continuous with the
    duodenum through the pyloric
     – Regulates how rate that food
       enters into the small intestines.
            Glands of the Stomach
• Gastric glands of the fundus and body have a variety of
  secretory cells
   – Mucous neck cells – secrete mucus to protect
     stomach from acid environment.
   – Parietal cells – secrete H+Cl- and intrinsic factor
   – Chief cells – produce pepsinogen
      • Pepsinogen is activated to pepsin by H+Cl- in the
   – Enteroendocrine cells – secrete hormones that
     regulate digestion and gastric motility.
      • G-cells secrete gastrin : hormone that increases
        secretory activity and Gastric mobility
          – Stimulated by the Vagus nerve and rising pH
            levels in the stomach
Microscopic Anatomy of the Stomach
                           Gastric Phase
•   Excitatory events include: Stimulate
    Gastrin release
     – Stomach distension (stomach
       expands as bolus enters)
     – Activation of stretch receptors
       stimulates the Vagus nerve
     – Activation of chemoreceptors:
       presences of proteins buffer
       stomach acid ↑pH

•   Inhibitory events include:
     – As food exits out the pylorus the pH
        may drop below 2
     – There will be less distension.
     – Emotional upset that overrides the
        parasympathetic division and
        activate the sympathetic division
Control of Gastric Secretion
                   Gastric Secretions

• 2 to 3 L of gastric juice/day (H2O, HCl and pepsin)
• Parietal cells contain carbonic anhydrase (CAH)
    – CO2 + H2O  H2CO3  HCO3- + H+
    – H+ is pumped into stomach lumen by H+K+ATPase
       • antiporter uses ATP to pump H+ out and K+ in
    – HCO3- exchanged for Cl- (chloride shift)
       • Cl- pumped out to join H+ forming HCl
       •  HCO3- in blood causes alkaline tide (blood pH )
    Healthy Mucosa and Peptic Ulcer

• Gastric and Peptic ulcers are linked to the acid tolerant
  bacteria Helicobactor pylori and excessive use of
• Proton pump inhibitors block the H+K+ATPase pump thus
  reducing acid production in the stomach.
                     Intestinal Phase
• Baroreceptor: detects distension
  of duodenum.
• Chemoreceptors : detects
  presence of fatty acids,
  carbohydrates and proteins.
   – monitor osmolarity (
      concentration of food stuff)
   – pH changes (acidic chyme
      reduces pH)
   – Initiates inhibition of local
      reflexes that inhibit vagal
      stimulation (PNS) while exciting
        • Closes the pyloric sphincter
                         Intestinal Phase
•     Once food (Chyme) enters the small intestines duodenal
      enteroendocrine cells secrete various hormones that inhibit gastric
      secretion :
    –    CCK, (Cholecystokinin) VIP (Vasoactive Intestine Peptide )
         GIP( Gastric inhibitory peptide) and Secretin
•      These collectively inhibit stomach secretions of HCL and gastrin from
      the G-cells thus reducing stomach motility.
•     Pyloric sphincter tightens limiting admission of more food into the
    –    Allows the duodenum time to work on the chyme that has already
         Small Intestine – 3 Segments
• Has three subdivisions: duodenum, jejunum, and ileum
• Runs from pyloric sphincter to the ileocecal valve
                     Small Intestine
• Duodenum (10 in.)
   – receives stomach contents through the pyloric sphincter
   – pancreatic juice and bile aid in chemical digestion of chyme.
   – neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH
     increase, pancreatic enzymes hydrolyze their specific substrate.
   – Mostly digestion with minimal absorption occurs here
   – retroperitoneal along with pancreas (curves around head of pancreas)
• Jejunum - next 8 ft. (in upper abdomen)
   – has large tall circular folds; walls are thick, muscular
   – nutrient digestion and absorption occurs here
• Ileum - last 12 ft. (in lower abdomen)
   – has peyer’s patches – clusters of lymphatic nodules
   – ends at ileocecal junction with large intestine
   – Primarily nutrient absorption occurs here
Microscopic Anatomy of the Small Intestine
          Small Intestine: Histology
• Lined simple columnar epithelium which functions in
  absorption and secretion.
   – Villi
      • fingerlike extensions of the mucosa containing
        blood and lymph vessels for the absorption of
   – Microvilli
      • tiny folds in the individual simple columnar
        epithelial cells that further increase digestive
        surface area.
      • Brush-border enzymes
           – hydrolytic enzymes responsible for chemical
             digestion of organic molecules and activation
             of pancreatic enzymes.
• Pancreatic enzymes and bile enter the duodenum
  through for the sphincter of Oddi
               Liver: Functions
• The largest gland in the body
• Liver cells( Hepatocytes) functions include:
  – Production of bile (emulsification of fat)
  – Detoxification( removes or dilutes toxins in the body
  – Storage of fat-soluble vitamins ( ADEK)
  – Gluconeogenesis :Formation of Glycogen from
    non-carbohydrates ( used to elevate BGL’s)
  – Formation of cholesterol including HDL and LDL
     • Used to transport fat throughout the circulatory system.
  – Water soluble nutrients absorbed in the digestive
    system must go the liver first via the hepatic portal
    circulation before returning to general circulation.
             The Gallbladder
• A green muscular sac on the ventral surface of
  the liver is palpable in the right upper quadrant.
• Stores and concentrates bile that was produced
  in the liver
• Bile is released in response to the hormone
   – Facilitate fat and cholesterol absorption
   – GB releases bile into the cystic duct, which
     flows into the bile duct.
   – From the bile duct it goes through the
     Sphincter of Oddi into the duodenum.
   – Promotes short term satiety
    • Exocrine function
       – Acini (clusters of secretory
         cells) digestive enzymes
       – Secretes pancreatic juice
         which breaks down all
         categories of foodstuff

    • The pancreas also has an
      endocrine function
        – release of insulin and
Acinus of the Pancreas
         Composition and Function of
             Pancreatic Juice
• Secretin causes the release of HCO3– which neutralizes
  acid chyme
   – Water solution of electrolytes and HCO3–
       • Alkaline pH helps neutralize acidic chyme providing an optimal
         environment for pancreatic enzymes
• CCK stimulates the pancreas to release the following
  Digestive enzymes:
   – Amylase : polysaccharide → monosaccharides
   – Lipase: (lipid digestion) triglycerides → glycerol and 3 fatty acids
   – Protease: (trypsinogen, chymotrypsinogin, procarboxypeptidase)
       • (Protein digestion) polypeptides → amino acids.
   – Nucleases: digestion of nucleic acids into pentose sugars,
     nitrogenous bases and phosphate ions
            Emulsification of Fats by Bile
• Main role of bile is to emulsify fat (break into smaller
• Emulsified fat droplets have a greater surface area
  for pancreatic lipase to work.
Emulsification of Fats
      Chemical Digestion: Fats
• Absorption: bile salts and pancreatic lipase
  results in FFA and Glycerol
• FFA diffuse into intestinal cells where they:
  – Combine with proteins and form chylomicrons
  – Enter lacteals and are transported to systemic
    circulation via lymphatic system.
• Glycerol and short chain fatty acids are:
  – Absorbed into the capillary blood in villi
  – Transported via the hepatic portal vein
Fatty Acid Absorption
Carbohydrate Digestion - Small Intestine
         Carbohydrate Metabolism

• Salivary amylase gets denatured in stomach (pH < 4.5)
• Pancreatic amylase further hydrolyzes carbohydrates.
• Brush border enzymes maltase, sucrase, lactase
  complete the hydrolysis resulting in monosaccharides
  that can be absorbed.
   – Maltase → Hydrolyzes maltose into 2 glucose molecules
   – Sucrase → hydrolyzes sucrose leaving maltose and glucose ,
   – Lactase → hydrolyzes lactose into Galactose and glucose
• Absorption: via co-transport with Na+, and facilitated
   – Enter the capillary bed in the villi
   – Transported to the liver via the hepatic portal vein
Protein Digestion
           Protein Digestion
– Enzymes for protein digestion are released in
  inactive forms to avoid digesting the pancreas and
  associated ducts prior to reaching its appropriate
– Enzymes include:
   • Trypsinogen is activated by brush border enzyme
     entrokinase to trypsin
   • Chymotrypsinogin is activated to Chymotrypsin by trypsin
   • Procarboxypeptidase is activated by trypsin to
– Both break down proteins into A.A via hydrolysis
              Alcohol metabolism
Alcohol can be absorbed directly through the stomach.
   – Food acts as a buffer
• Can cross the blood brain barrier of the brain
   – Impaired judgment cognitive and physical abilities.
   – DWI can result in sharing a cell with a guy named Bubba
• Pound for pound females usually can’t tolerate as much
  alcohol as their male counterparts because they
  naturally produce less of the enzyme that breaks it down.
      (Alcohol dehydrogenase)
   – The heavier you can usually tolerate more alcohol.
   – Tolerance varies between different ethnicities.
• With a lot of practice you will make more of the enzyme
  and be able to hold your Liquor.
           Absorption of Polar Molecules
• The absorption of water soluble polar molecules
  (carbohydrates, amino acids, nucleotides, electrolytes
  and water) is accomplished by specific transport
  proteins located on the cell membranes of the
  absorptive cells. Membrane proteins utilize
   – secondary active transport: Sodium dependant co-
    transport proteins is necessary for the absorption of glucose
    , Galactose, amino acids and many minerals
      • 95% of the water is absorbed in the SI via osmosis
        following the osmotic gradient established by the Na+,K+-
        ATPase (pump
  – Digestion requires a lot of ATP! Should this
    influence the frequency of your meals if you’re
    trying to loss weight.
     Carbohydrate Absorption

• Sodium-glucose transport proteins (SGLT) in
  membrane help absorb glucose and galactose
Pancreatic Islet
• Has both exocrine and endocrine cells and is
  located behind the stomach
  – Acinar cells produce an enzyme-rich juice used for
    digestion (98% of organ) (exocrine product)
  – Pancreatic islets (islets of Langerhans) produce
    hormones (endocrine products)
• The islets contain two major cell types:
   – Alpha () cells that produce Glucagon
   – Beta () cells that produce insulin
     • Remember: If your diabetic you Beta () have
       your insulin.
• Insulin:
   – Lowers blood glucose levels by increasing
     membrane permeability to both glucose and
     amino acids.
      • Considered an anabolic hormone
   – Target organs include muscle, liver and adipose
   – antagonizes Glucagon
• Insulin uses a second messenger which allows more
  glucose to enter the cell. Once in the cell insulin:
   – Increased utilization of glucose for ATP production
   – Glycogen is formed when anabolic enzymes
     stimulate dehydration synthesis of glucose.
   – Converts extra glucose to fat particularly in
     adipose tissue once glycogen stores are full.
   – Promotes cellular mitosis
• Hormone released when blood sugar levels
• Its major target is the liver where it promotes:
   – Glycogenolysis – the breakdown of
     glycogen to glucose
   – Gluconeogenesis – synthesis of glucose
     from lactic acid and non-carbohydrates
   – Release of glucose to the blood from liver
   – All will elevate blood glucose levels during
     fasting periods.
• From excess insulin injection or pancreatic islet
  – Causes hypoglycemia, weakness and hunger
   – triggers secretion of epinephrine, GH and
       • side effects: anxiety, sweating and  HR
• Insulin shock
   – uncorrected hyperinsulinism with
     disorientation, convulsions or
         Diabetes Mellitus (DM)
• Chronically elevated blood glucose levels results from
  hyposecretion or hypoactivity of insulin
• The three cardinal signs of DM are:
   – Polyuria – Frequent urination from excessive sugar
     levels spilling over in kidney filtrate. Water will follow
     the osmotic gradient to dilute the urine (filtrate).
   – Polydipsia – excessive thirst as a result if frequently
     urinating and dehydration.
   – Polyphagia – excessive hunger and food
     consumption because the body thinks its starving
     because the sugar is not able to get into the cell.
• Hyperinsulinism – excessive insulin secretion, resulting
  in hypoglycemia
          Types of Diabetes Mellitus
• Type I (IDDM) - 10% of cases
   – some cases have autoimmune destruction of 
     cells, diagnosed about age 12
   – treated with diet, exercise, monitoring of blood
     glucose and periodic injections of insulin
• Type II (NIDDM) - 90%
   – insulin resistance
       • failure of target cells to respond to insulin
       • Excessive weight gain increases intra-
         myocellular lipids which turns down
           – The body likes storing fat from an
             evolutionary perspective.
        Major Risk Factors
– 3 major risk factors are heredity, age (40+)
  and obesity
   • treated with weight loss program of diet and
   • oral medications improve insulin secretion
     or target cell sensitivity
       –Gastric bypass surgery has been shown
        to cure DM in 60-80% of cases. What’s
        they key?
           Pathology of Diabetes
• Acute pathology: cells cannot absorb glucose, rely
  on fat and proteins (weight loss, weakness)
  – fat catabolism  FFA’s in blood and ketone bodies
  – ketonuria promotes osmotic diuresis ( polyuria), loss of
    Na+ and K+
  – ketoacidosis occurs as ketones  blood pH
     • if continued causes dyspnea and eventually diabetic coma
• Chronic pathology
  – chronic hyperglycemia leads to neuropathy ( damage
    nerves) and cardiovascular damage from atherosclerosis
     • retina and kidneys (common in type I), atherosclerosis leads to
       heart failure (common in type II), and gangrene
                 Obesity Trends* Among U.S. Adults
                     BRFSS, 1990, 1999, 2009
                  (*BMI 30, or about 30 lbs. overweight )

             1990                                              1999


No Data   <10%      10%–14%   15%–19%      20%–24%   25%–29%   ≥30%
Have a Coke and a smile!
Anti-inflammatory Pyramid
                 Large Intestine
• Divided into 4 regions:
   – ascending colon: ascends up the right side of the
     abdominal cavity
      • cecum
         – Lies below the ileocecal valve
         – Contains a wormlike vermiform appendix
             » Acts as a reserve for good flora and other
               immune boosting cells following diarrhea.
              » Inflammation of appendix (appendicitis)
   – transverse colon: runs across the abdominal cavity
   – descending colon: descends down the left side of
     abdominal cavity.
   – sigmoid colon: S shaped leads to rectum where feces
     is stored until defecation occurs through the anal canal.
Functions of the Large Intestine
• 95% of water is absorbed in the small intestines
  following their osmotic gradient.
• The remaining water is absorbed in the large
• Other than digestion of enteric bacteria, no
  further digestion takes place
   – Vitamins, and electrolytes are reclaimed
• Its major function is propulsion of fecal material
  toward the anus
• Though essential for comfort, the colon is not
  essential for life
Neural Control of Defecation
          Digestive System Screen
•   Changes in appetite
•   Abdominal and chest pain
•   Nausea / Vomiting
•   Fatigue/ Weakness
•   Bowel movement changes such as constipation and Diarrhea
•   Dehydration
•   Psychological changes like depression and anxiety from nutritional deficiencies.
•   (gas) flagalence
•   Yellow skin, eyes and nails
•   Pancreatitis
•   Stones
•   Ulcer history
•   Hernias
•   Rebound tenderness
•   Hemorrhoids
               Case Study
• A 33 y/o female goes to her doctor with c/o
  bloating and diarrhea (3 years). She has
  gained 60 pounds in this time. She now is
  feeling depressed and has trouble getting
  more than 6 hours of sleep a night. She
  also reports occasional numbness and
  tingling in her feet.
  – What's going on with this patient?

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