Transcript DIGESTION and ABSORPTION

DIGESTION and ABSORPTION
Learning Objectives:
• Understand the physical and chemical
processes of digestion
• Learn the function of each organ in the
digestive system
• Gain an understanding of common
Gastrointestinal Disorders
TASTE and SMELL
The Chemosenses
1. Olfactory Cells:
• Stimulated by odors around us
• Found high inside the nose, connect directly to
the brain
2. Gustatory Cells:
• React to food and beverages
• Clustered into taste buds
• TASTE: salty, sweet, bitter, sour, and umami
TASTE and SMELL
The Chemosenses
3. Common Chemical Sense
• Thousands of nerve endings on the moist
surfaces of the eyes, nose, mouth, and throat
accent our sense of smell and taste
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FLAVOR = texture, temperature, common
chemical sense, taste, and odor
CEPHALIC (preabsorptive)
PHASE RESPONSE
In response to sensory stimulation, your
body primes its resources to better absorb
and use anticipated nutrients
 EXAMPLE:
Sound (Hearing a description of food) can
cause the salivary glands to increase the
flow of saliva
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Important Structures
ASSISTING ORGANS
PHYSICAL PROCESSES
Chewing
 Peristalsis – the wavelike, rhythmic
muscular contractions of the GI tract that
move chyme down its tract
 Segmentation – periodic squeezing and
partitioning of the SI which mixes the
chyme and promotes close contact with
digestive juices and absorbing cells
 Sphincters – regulate the flow of food
particles
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CHEMICAL PROCESSES
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Enzymes: protein compounds that facilitate
chemical reactions but are not altered in the
process
CHEMICAL PROCESSES
Acid in the stomach (hydrochloric acid)
 Base in the small intestine (bicarbonate)
 Bile
 Mucus
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MOUTH
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Saliva
Amylase – breaks down starches into small
sugar molecules (only about 5%)
Lingual Lipase – breaks down fats, but only
in a miniscule amount
Epiglottis – guards entrance to the trachea
STOMACH
GASTRIC JUICE:
• Water
• Hydrochloric Acid (pH = 2) page 77
• Mucus
• Enzymes
• Hormones
• Intrinsic Factor
NUTRIENT ABSORPTION in
the STOMACH
Only:
• Some lipid-soluble compounds
• Weak acids, such as alcohol and
aspirin
SMALL INTESTINE
 Almost
all digestion of protein, fat, and
carbohydrate is performed in the SI
Divided into three parts:
• Duodenum (the first 10-12 inches)
• Jejunum (~ 4 feet)
• Ileum (~ 5 feet)
NUTRIENT DIGESTION in the
SMALL INTESTINE
 SECRETIN
is released upon the
appearance of chyme in the SI 
SECRETIN stimulates the release of
BICARBONATE from the pancreas
 BICARBONATE neutralizes the
chyme
NUTRIENT DIGESTION in the
SMALL INTESTINE
 The
neutralization is important because
the enzymes in the SI need a neutral
environment
 Pancreatic juice and secretions from
the intestinal wall cells contain a
variety of digestive enzymes that help
to digest fats, carbohydrates, and
proteins
NUTRIENT DIGESTION in the
SMALL INTESTINE
 BILE
is released from the gall bladder
upon the appearance of fat in the SI
 BILE acts as an emulsifier, and
without it, lipids might not come into
contact with pancreatic lipase, and
would not be properly digested
NUTRIENT DIGESTION in the
SMALL INTESTINE
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With pancreatic and intestinal enzymes
working together, digestion creates
smaller compounds of protein, fat, and
carbohydrate which can then be easily
absorbed
Minerals, vitamins, and cholesterol are
not broken down and are generally
absorbed unchanged
NUTRIENT ABSORPTION in
the SMALL INTESTINE
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Most absorption occurs in the SI – 90%
Provides the surface area equivalent to a
tennis court!
Nutrients are trapped in folds of the
intestinal wall and absorbed through the
microvilli
Each villus contains blood vessels and a
lymph vessel which transport nutrients
NUTRIENT ABSORPTION in
the SMALL INTESTINE
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Water-soluble nutrients are absorbed
directly into the bloodstream
Fat-soluble lipid compounds are
absorbed into the lymph rather than the
blood
NUTRIENT ABSORPTION in
the SMALL INTESTINE
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Duodenum and Upper Jejunum: most
minerals (except sodium, chloride, and
potassium)
Jejunum and Upper Ileum: carbohydrates,
amino acids, water-soluble vitamins
Jejunum: lipids and fat-soluble vitamins
Terminal Ileum: Vitamin B12
LARGE INTESTINE
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Is ~ 5 feet long and includes the
cecum, colon, rectum, and anal canal
NUTRIENT DIGESTION in the
LARGE INTESTINE
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Little digestion occurs in the large
intestine
The large population of bacteria
digests small amounts of fiber
This bacterial activity forms: Vitamin
K, Vitamin B12, Thiamin, Riboflavin,
Biotin, and gases
NUTRIENT ABSORPTION in
the LARGE INTESTINE
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Little absorption occurs in the large
intestine
However, it does absorb: water,
sodium, potassium, chloride, and some
of the Vitamin K produced by bacteria
It does not absorb Vitamin B12
Healthy Bacteria
Probiotics are live microorganisms (in most
cases, bacteria) that are similar to beneficial
microorganisms found in the human gut.
 Probiotics are available to consumers
mainly in the form of dietary supplements
and foods.
 Look for “live and active cultures”. The
good bacteria most often comes from two
groups: Lactobacillus or Bifobacterium.
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Prebiotics are not digested in the SI, and
are used as food by bacteria
NUTRITION and GI DISORDERS
CONSTIPATION
• Occurs when the colon absorbs too much water, or
if the colon’s muscle contractions are slow and
sluggish
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CAUSES:
Not enough liquids in the diet
Not enough fiber in the diet
Sedentary lifestyle
Some medications
Abuse of laxatives
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TREATMENT?
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NUTRITION and GI DISORDERS
DIARRHEA
• Occurs when the colon absorbs too little water
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CAUSES:
Most common: infection from bacteria, viruses, or
parasites
Antibiotics
Chronic diarrhea may signal a more serious
medical problem (Inflammatory Bowel Disease)
TREATMENT
BRAT diet (bananas, rice, applesauce, toast)
Rehydrate and replace electrolytes
NUTRITION and GI DISORDERS
Gastroesophageal Reflux Disease
• Basically, chronic “heartburn”
CAUSES:
• Hiatal Hernias
• Foods that relax the lower esophageal
sphincter (LES)
• Frequently occurs in people with asthma,
irritable bowel syndrome, and
developmental disabilities
• Concern because of increased risk of
esophageal cancer
TREATMENT
• Avoid foods that relax the LES
• Don’t lie down or exercise too soon after
eating, raise the head of the bed
• Wear loose fitting clothing
• Medications
NUTRITION and GI DISORDERS
DIVERTICULOSIS
• Result of rising pressure in the colon, believed to
be caused by low-fiber diet and constipation
DIVERTICULITIS
• Infected or inflamed diverticulum (fecal matter or
bacteria gets trapped)
• May experience abdominal pain, indigestion, fever
• Diverticulum may rupture causing infection, or
can form scar tissue and create an obstruction
Diverticulosis/itis
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TREATMENT
Diverticulosis – high fiber diet
Diverticulitis – low fiber diet
NUTRITION and GI DISORDERS
IRRITABLE BOWEL SYNDROME
• Disorder that interferes with normal functions of
the colon. Symptoms are abdominal pain,
bloating, constipation, and diarrhea
• People with IBS have more sensitive colons and
react more strongly to: stress, large meals, certain
foods, caffeine, or alcohol
• Diagnosed by symptoms and the absence of other
diseases
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TREATMENT
Reduce stress
Change diet
Medications
NUTRITION and GI DISORDERS
ULCERS
CAUSES:
• Helicobacter pylori infection (most common),
chronic use of anti-inflammatory drugs, and
disorders that cause excessive gastric acid
secretion
• Not caused by spicy foods or stress
TREATMENT
• Antibiotics
• Medications (acid suppressors)
NUTRITION and GI DISORDERS
LACTOSE INTOLERANCE
CAUSES:
• Inability to digest lactose, caused by a shortage of
lactase
• Symptoms: nausea, cramps, bloating, gas, and
diarrhea
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TREATMENT
Don’t eat dairy products! Or eat less, and more
processed types (ex. Yogurt vs. milk )