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Digestive System

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Digestive System The System in Brief: Food enters via the mouth. dig system animation Breaks down food, absorbs nutrients and eliminate wastes Food must be broken ... – PowerPoint PPT presentation

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Title: Digestive System


1
Digestive System
2
The System in Brief
dig system animation
  • Food enters via the mouth.

3
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

4
2 Forms of Breakdown Mechanical and Chemical
  • 1. MECHANICAL
  • in the mouth teeth cut and grind the food into
    small pieces

5
Mechanical
2. in the stomach strong muscles mix and churn
the food
6
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)

7
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
8
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
9
  • 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
10
  • The bolus enters the stomach through the cardiac
    sphincter.

11
Functions of Stomach
  1. Store Food (chyme)
  2. digestion of proteins, produces digestive enzymes
  3. Kills bacteria in food with addition of HCl

12
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
13
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)

14
Gastrin
  • (a hormone) stimulates the secretion of HCl at
    gastric glands
  • Triggered by high protein meal
  • Increase production of gastric juices

15
Mucus
  • protects the stomach lining from digesting
    itself! (the lining is replaced every few days)
  • Prevention of Ulcers

16
  • 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
17
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