Digestive%20System

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Digestive System
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The System in Brief
dig system animation

• Food enters via the mouth.

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Polymer
Monomer

• Breaks down food, absorbs nutrients and eliminate
  wastes
• Food must be broken down so that the pieces are
  small enough to pass through the walls of the
  intestinal villi

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2 Forms of Breakdown Mechanical and Chemical

• 1. MECHANICAL
• in the mouth teeth cut and grind the food into
  small pieces

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Mechanical
2. in the stomach strong muscles mix and churn
the food
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CHEMICAL

• in the mouth saliva is mixed with the food
• Saliva functions to
• Lubricates esophagus
• Moisten food
• Contain enzyme salivary amylase
• salivary amylase begins the chemical breakdown of
  starch into maltose
• (starch H2O?maltose)

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Swallowing

• The tongue rolls food into a ball (bolus) and
  moves food to back of pharynx
• The soft palate closes off the nasopharynx, and
  the epiglottis covers the opening to the trachea
  (glottis)

Swallowing X-Ray
Swallowing Animation
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Peristalsis

• Once the food enters esophagus, peristalsis
  begins.
• muscular contraction that move bolus towards
  stomach.
• an involuntary action throughout the alimentary
  canal

Laryngoscopic Trachea vs Esophagus
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• The cardiac sphincter is located between the
  esophagus and the stomach
• Ring of muscle that acts as a valve, opening to
  allow the food bolus entry to the stomach,
  closing to prevent back flow of acidic chyme
  into the esophagus (causing burning sensation
  known as a heart burn)

Esophagus
Cardiac Sphincter
Duodenum
Stomach
Pyloric Sphincter
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• The bolus enters the stomach through the cardiac
  sphincter.

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Functions of Stomach

1. Store Food (chyme)
2. digestion of proteins, produces digestive enzymes
3. Kills bacteria in food with addition of HCl

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Stomach
Gastric Pit

• Muscular stomach wall churns food (peristalsis)
• Lining of stomach contains gastric pits which
  lead to gastric glands (produces gastric juice
  containing enzyme pepsin, HCl and mucus)

Gastric Gland
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Gastric Juices

• HCl
• Causes highly acidic environment (pH of 2)
• Kills bacteria
• converts pepsinogen to pepsin
• Pepsinogen
• an inactive form of pepsin, (protein H2O --gt
  polypeptides)

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Gastrin

• (a hormone) stimulates the secretion of HCl at
  gastric glands
• Triggered by high protein meal
• Increase production of gastric juices

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Mucus

• protects the stomach lining from digesting
  itself! (the lining is replaced every few days)
• Prevention of Ulcers

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• Helicobacter pylori (commonly referred to as h.
  pylori)is a bacterium that infects the mucus
  lining of the stomach. Many peptic ulcers and
  some types of gastritis are caused by H. pylori
  infection, although most humans who are infected
  will never develop symptoms. This bacterium lives
  in the human stomach exclusively and is the only
  known organism that can thrive in that highly
  acidic environment. It is helix-shaped (hence the
  name helicobacter) and can literally screw itself
  into the stomach lining to colonize.
• H. Pylori infections
• It is estimated that about two thirds of the
  world population are infected by helicobacter
  pylori. Actual infection rates vary - the
  Western/Developed nations have rates around 25
  and less developed nations have much higher rates
  of infections. In the United States, infection is
  primarily in the older generations (about 50 for
  those over the age of 60 compared with 20 under
  40 years) and the poorest. This is largely
  attributed to higher hygiene standards and
  widespread use of antibiotics. However,
  antibiotic resistance is appearing in H. pylori.
  There are already metronidazole resistant strains
  present in the UK population.
• There is also evidence of a higher incidence of
  symptoms in people who eat spicy foods,
  apparently because of the effect these foods have
  on the stomach lining. When the protective lining
  is reduced from certain foods, h. pylori is
  better able to spiral into the stomach wall. This
  is one of the reasons that it was (and still is)
  commonly thought that spicy foods caused stomach
  ulcers. In actual fact, it is the h pylori that
  causes the stomach ulcers, but the spicy foods
  creates the conditions for h. pylori to cause
  problems.
• In the absence of any treatments, H. pylori
  infection apparently persists for life our
  immune systems are not able to eradicate it.

Peptic ulcer
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