Human Digestion and Absorption

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Human Digestion and Absorption

• Chapter 4

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Organization of the Human Body

• Chemical Level
• Atoms combine to form molecules
• Cell Level
• Molecules form organelles
• Use ATP
• Tissue Level
• Similar cells make up tissues

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Organization of the Human Body

• Organ Level
• Different tissues combine to form organs
• Organ System Level
• Organs make up an organ system
• Organism Level
• Organ systems make up an organism

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Digestive Organ System

• GI tract
• Mouth, esophagus, stomach, small intestine, large
  intestine
• Accessory organs Liver, pancreas and gall bladder

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Digestive Organ System
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Digestive System Overview

• Digestion
• Process of breaking down foods into a form the
  body can use
• Absorption
• Uptake of nutrients from the GI tract into the
  blood or lymph

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Anatomy of the GI Tract

• GI tract
• Long hollow muscular canal. Nutrients pass
  through the wall of the canal to be absorbed
• Four layers (listed from inner most layer to
  outermost layer)
• Mucosa
• Submucosa
• Muscle
• Serosa

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GI Motility

• Peristalsis
• Contractions of the GI tract, mainly in
  esophagus, stomach, and small intestine
• Segmentation
• Back and forth movement-happens in small
  intestine so there is mixing with digestive
  juices
• Mass movements
• Slow peristalsis over widespread area- in large
  intestine to help propel fecal matter to rectum
• Elimination

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One Way Street
Sphincters Ring like muscles along the GI tract
that control the flow of contents
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Mouth (Oral Cavity)

• Chewing breaks up food and increases surface
  area. These smaller food particles are mixed with
  saliva and forms a bolus.
• Saliva
• Lysozyme
• Break down bacteria
• Amylase
• Break down starch
• Mucus
• Lubricate and hold bolus together

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Taste and Smell

• Taste buds on the tongue and soft palate
• Salty (from metal ions)
• Sour (from acids)
• Sweet (from organic compounds)
• Bitter (many diverse compounds like
  phytochemicals)
• Umami or savory (from amino acids)
• Olfactory glands
• Sense of smell (enhances sense of taste)

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Esophagus

• Swallowing
• Moves bolus from the mouth to the esophagus
• Epiglottis
• Prevents food from lodging in the trachea
• Covers the larynx
• http//youtu.be/sM6uxd1uS6M

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Stomach

• Bolus goes through lower esophageal sphincter
  into stomach
• Mixed with stomach secretions becomes chyme
• Pyloric sphincter allows chyme into the small
  intestine
• Gastric inhibitory peptide (hormone) slows
  release of chyme into the small intestine to
  allow time for acid neutralization and digestion
  (only one teaspoon is allowed into the SI at a
  time).

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Stomach Secretions

• Chief cells produce
• Pepsinogen (an inactive protein-digesting enzyme)
• Other secretions include,
• Gastric lipase
• Gastrin
• Hormone stimulated when food is in stomach
  controls release of HCl and pepsinogen and
  stimulates motility
• Mucus
• Protects the stomach from being digested

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Stomach Secretions

• Parietal cells produce hydrochloric acid which
• Inactivates proteins
• Destroys bacteria and viruses
• Aids in mineral absorption (dissolves them)
• Converts pepsinogen (protein digesting enzyme)
  into pepsin (active form)

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Small Intestine

• Most digestion and absorption occurs here
• Sections
• Duodenum, Jejunum
• Ileum

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Small Intestine

• Villi (finger like projections on interior of SI)
  that are lined with
• Goblet cells make mucus
• Endocrine cells produce hormones
• Cells (enterocytes) that produce enzymes for
  absorption

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Hormones OF the Small Intestine

• Gastrin
• Also released by stomach, stimulates intestinal
  motility
• Cholecystokinin (CCK)
• Stimulated by dietary fat in chyme, stimulates
  release of pancreatic enzymes and bile
• Secretin
• Stimulated by acidic chyme, stimulates release of
  pancreatic bicarbonate
• Gastric Inhibitory peptide
• Stimulates stomach to limit gastric juices, slows
  motility

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Accessory Organs Liver, Gallbladder and Pancreas

• Liver
• Provides bile
• Needed to emulsify fat (disperse into droplets
  and suspend in water) so it can be absorbed
• Gallbladder
• Bile storage
• Pancreas
• Produces sodium bicarbonate, lipases, proteases
  and pancreatic amylase

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Accessory Organs Liver, Gallbladder and Pancreas
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Large Intestine

• Functions Absorption of water and electrolytes,
  house bacterial flora, and form and expel feces.
• Colon
• Cecum, ascending colon, transverse colon,
  descending colon and sigmoid colon
• Rectum
• Anus

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Large Intestine
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Absorption
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Absorption

• Passive (fat, water, some minerals)
• High concentration to low
• Facilitated (ex. fructose)
• High concentration to low carrier protein
• Active (amino acids, glucose)
• Low concentration to higher energy
• Endocytosis (large proteins like immune factors)
• Engulfment

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Absorption
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Moving Nutrients

• Cardiovascular System
• Includes heart, blood vessels and blood
• Water-soluble nutrients transported via
  capillaries in villi to portal vein, which leads
  to liver
• Allows liver to process nutrients before entering
  general circulation

• Lymphatic System
• Includes lymph
• Fat-soluble nutrients and large particles
  transported via lacteals into the lymph vessels
  to thoracic duct, where it connects to the blood
  stream.

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Bacterial Flora

• Beneficial bacterial flora
• Controls pathogenic bacteria
• Synthesize Vitamin K and Biotin
• Aid lactose digestion and fermentation
• Pro-biotic
• Live bacteria
• Pre-biotic
• Non digestible carbohydrates that promote the
  growth of beneficial bacteria

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Putting it all together

• Be able to trace the pathway of food from when
  you first eat it until it is eliminated or
  absorbed
• Know the major function of each organ and if it
  secretes any major enzymes or hormones

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Digestion Gone Awry

• Heartburn and Gastroesphogeal reflux (GERD)
• Causes
• Overweight, alcohol, smoking, pregnancy
• Foods that increase reflux
• Citrus, caffeine, chocolate, fatty foods, spicy
  foods, onion, garlic and tomato based foods
• Medications include
• H2 blockers (blocks histamine formation) and
  proton pump inhibitors

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Digestion Gone Awry
Heartburn and Gastroesphogeal reflux (GERD)
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Digestion Gone Awry

• Ulcers
• Causes
• H pylori, alcohol, aspirin and smoking (not
  stress)
• Treatment
• Medications (abx, same as GERD)
• Avoid foods that increase symptoms

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Digestion Gone Awry

• Gallstones
• Food Intolerances
• Lactose, gluten, MSG
• Intestinal Gas
• Flatulence
• Air and undigested CHO in large intestine

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Digestion Gone Awry
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Digestion Gone Awry

• Constipation
• Fiber, fluid and exercise
• Laxative use (bulk, osmotic, stimulants,
  softeners, and lubricants)
• Diarrhea
• Replace fluid and electrolytes
• Irritable bowel
• Cause unknown, examine dietary factors
• Hemorrhoids