The Human Digestive System

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The Human Digestive System
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What is digestion?

• The process of breaking down foods into molecules
  the cells of the body can use.
• Where does digestion occur?

The gastrointestinal tract
(AKA- alimentary canal) Muscular tube approx. 9
meters long!
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Organs of the Alimentary Canal and their
accessory organs
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Mechanical vs. Chemical Digestion

• Mechanical Digestion The physical breakdown of
  food into smaller pieces
• Chemical Digestion Breaking the bonds in food to
  change the chemical nature of it

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Mouth (Buccal Cavity)

• Mechanical Digestion (mastication)
• - Teeth break down food
• - Tongue manipulates food against the hard
  palate (bony roof of mouth) and contains bumps
  (papillae) that provide friction for moving food
  around.
• - The frenulum connects the tongue to the floor
  of the mouth.

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Mouth cont.

• Chemical Digestion
• - Salivary glands that line the mouth produce
  saliva.
• - Saliva moistens food particles, binds them
  together, allows tasting, helps to cleanse the
  mouth and teeth, and begins carbohydrate
  digestion.
• - Saliva is a mixture of water, mucus and an
  enzyme called amylase (breaks down carbs).
• - The mucus lubricates and holds the food
  together forming a ball called a bolus.
• INTERESTING FACT
• Halitosis results when food particles accumulate
  in the mouth and bacteria flourish. Saliva helps
  wash away these food particles.

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Three pairs of Salivary Glands
1-1.5 L / day for digestion lubrication
(swallowing) moistening (tasting)

• Parotid lateral side of face, anterior to ear
  watery saliva
• Submandibular floor of mouth Sublingual
  inferior to tongue thick saliva

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Pharynx

• The pharynx connects the nasal and oral cavities
  with the larynx and esophagus and is divided into
  a nasopharynx (top portion), oropharynx (middle
  portion), and largyngopharynx (bottom portion).
• Sensory receptors in the pharynx sense food,
  which triggers swallowing reflexes.

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Esophagus

• When food is swallowed it passes the pharynx and
  into the esophagus.
• The esophagus is a muscular tube approx. 10
  inches long.
• What type of muscle lines the esophagus?
• Contractions and relaxations of these muscles
  move the bolus down the esophagus. This process
  is called- PERISTALSIS
• Peristalsis is very effective Can drink upside
  down

Peristalsis
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Cardiac Sphincter

• Circular muscle that opens to allow food to pass
  from the esophagus into the stomach.
• What if the cardiac sphincter doesnt work
  properly?
• Gastroesophageal reflux disease- GERD
• A condition in which the liquid content of the
  stomach regurgitates (backs up or refluxes) into
  the esophagus. The liquid can inflame and damage
  the lining of the esophagus. The regurgitated
  liquid usually contains acid and pepsin that are
  produced by the stomach.

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Achalasia

• The term achalasia means "failure to relax" and
  refers to the inability of the cardiac sphincter
  to open and let food pass into the stomach. Also,
  the muscle that lines the esophagus does not
  contract properly. As a result, patients with
  achalasia have difficulty in swallowing food.

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StomachThe stomach is divided into the cardiac,
fundus, body, and pylorus regions.
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CS
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Stomach

• Mechanical Digestion in Stomach
• - The stomach is lined with smooth muscle.
  This lining is folded and the folds are called
  rugae. Smooth muscle of the stomach twists and
  turns the stomach, physically breaking down food.
• - If the stomach is empty, then it growls. This
  is due to the sounds made by the contractions of
  the muscles.

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A Real Stomach!!!
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Stomach cont.

• Chemical Digestion
• - Innermost lining of the stomach is a mucous
  membrane that has openings called gastric pits.
• - Gastric pits are the openings through which
  secretions are released into the stomach.
• - These secretions (called gastric fluid)
  include mucus, pepsinogen (breaks down
  proteins), and hydrochloric acid.
• - The mucous coating of the stomach protects it
  from the acid. If it breaks down ULCER!
• - Food usually stays in the stomach for 3-4
  hours.
• - The mixture produced from mechanical/chemical
  digestion is called chyme (fats, sugars,
  vitamins, minerals, and proteins).

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Small Intestine

• Pyloric sphincter Circular muscle that opens to
  allow chyme into the small intestine from the
  stomach. It allows approx. 5-15 ml in at a time.
• The lengthy small intestine receives secretions
  from the pancreas and liver. The small intestine
  functions to complete digestion of the nutrients
  in chyme, absorb the products of digestion, and
  transport the remaining residues to the large
  intestine.
• If stretched out, the small intestine is 21 feet
  long! It is held together by a thin tissue layer
  called mesentery.
• The 3 parts of the small intestine include
• 1st Duodenum (10 inches)
• 2nd Jejunum (8 feet)
• 3rd IIleum (13 feet)

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Mesentery of Small Intestine
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Liver and Gall Bladder

• Liver
• - Large brownnish-red organ to the right of the
  stomach
• - Makes bile (important in fat digestion)
• Gall bladder
• - Stores the bile made by the liver
• - Bile travels from the liver to the gall
  bladder through the common hepatic duct and
  cystic duct.
• - When chyme is present in the small intestine
  (duodenum), the gall bladder releases bile
  through the cystic duct to the common bile duct
  which dumps into the small intestine at the
  duodenum.

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Human Digestion Small Intestine
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Gall Bladder Removal

• Why?
• Quick video of a removal

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Pancreas

• The pancreas secretes pancreatic fluid into the
  small intestine (duodenum). This helps breakdown
  the chyme.
• Pancreatic fluid leaves the pancreas through the
  pancreatic duct. The pancreatic duct joins the
  common bile duct just before it enters the small
  intestine.

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Absorption in the Small Intestine

• Digestion products are absorbed into the
  circulatory system through blood and lymph
  vessels.
• The lining of the jejunum and illeum has
  extensions called villi that increase surface
  area.
• Inside the villi are capillaries and lacteal
  (lymph vessels).
• Fatty acids enter lacteals
• Other substances diffuse into capillaries and
  carried to cells of the body

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Celiac Disease

• Celiac disease is when the small intestine lining
  (villi) is damaged and absorption of nutrients is
  hindered.
• The damage is due to a reaction to eating gluten,
  which is found in wheat, barley, rye, and
  possibly oats.
• The immune system incorrectly attacks villi
  because of the gluten they are absorbing.

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Large Intestine

• Once the remaining food enters the large
  intestine, it moves toward the anus by
  contractions of the smooth muscle in the lining
  of the large intestine.
• The large intestine consists of the cecum (pouch
  at the beginning of the large intestine), colon
  (ascending, transverse, descending, and sigmoid
  regions), the rectum, and the anal canal.
• As the matter moves through the large intestine,
  water is absorbed into the capillaries in the
  lining. This makes the matter more solid.
• The solid material is called feces.

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Large Intestine
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What is Feces??

• Feces is composed of undigested material, water,
  electrolytes, mucus, and bacteria.
• The color of feces is due to the action of
  bacteria on bile pigments.
• The odor of feces is due to the action of
  bacteria.
• What can we learn from our poop? Color, smell,
  consistency, curvature?

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What goes in must come out!
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Diverticulitis

• Diverticulosis happens when pouches (diverticula
  ) form in the wall of the colon . If these
  pouches get inflamed or infected (with feces), it
  is called diverticulitis. Diverticulitis can be
  very painful.
• Doctors aren't sure what causes diverticula in
  the colon. They think that a low-fiber diet may
  play a role. Without fiber to add bulk to the
  stool, the colon has to work harder than normal
  to push the stool forward. The pressure from this
  may cause pouches to form in weak spots along the
  colon.
• Diverticulitis happens when feces get trapped in
  the pouches (diverticula). This allows bacteria
  to grow in the pouches. This can lead to
  inflammation or infection.

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Facts at a Glance

• The average person eats 3 pounds of food a day.
  That's 1,095 pounds a year!
• An adult stomach holds 5 cups.
• 35 million glands produce acid in the stomach.
  The acid can dissolve a razor blade in one week!
• The body uses energy efficiently. (900 miles to
  the gallon!)

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Our own food breakdown factory!

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Why do we need our urinary system?

• To remove (excrete) metabolic waste from the
  bloodstream and carry it out of the body in the
  form of urine
• Metabolism Cells breaking down compounds for
  energy
• To regulate the water content in the body

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Functions of the organs of the human urinary
system

• Kidneys- Where blood is filtered and urine is
  produced
• Ureter- Narrow tube connected to each kidney that
  carries urine to the urinary bladder
• Urinary bladder- A muscular sac that stores urine
  and contracts to release urine
• Urethra- The tube that carries urine from the
  bladder out of the body

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Organs of the human urinary system
Kidney
Renal artery
Renal vein
Ureter
Urinary bladder
Urethra