Digestion, Absorption, and Transport

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Digestion, Absorption, and Transport

• Chapter 3

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To become part of your body, food must first
be digested and absorbed.
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• Digestion The process by which food is broken
  down into absorbable nutrients
• Absorption The passage of nutrients from the GI
  tract into either the blood or the lymph

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Anatomy of the gastrointestinal (GI) tract
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The Gastrointestinal Tract
Salivary glands
Pharynx
Mouth
Epiglottis
Trachea (to lungs)
Upper esophageal sphincter
Esophagus
Lower esophageal sphincter
Lower esophageal sphincter
Stomach
Liver
Liver
Gall bladder
Pancreas
Pyloric sphincter
Pancreatic duct
Bile duct
Small intestine (duodenum, jejunum, ileum)
Ileocecal valve
Appendix
Appendix
Large intestine (colon)
Rectum
Rectum
Anus
Anus
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Start at the beginning

• The mouth- Teeth crush your food saliva blends
  with the food.

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The Teeth
Incisors have chiseled edges that cut
Canines (cuspids) have pointed crowns that tear
Premolars (bicuspids) and molars have
ridged surfaces that crush and grind
Tongue
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The Teeth
Enamel
Crown
Dentin
Pulp cavity
Neck
Gum (gingiva)
Bone
Root
Blood vessels and nerves in pulp
Root canal
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Digestion

• Pharynx- Tube shared by the digestive and
  respiratory systems.
• Epiglottis- Cartilage that prevents food from
  entering the lungs during swallowing.

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Normal Swallowing and Choking
Tongue
Food
Esophagus (to stomach)
Larynx rises
Trachea (to lungs)
Epiglottis closes over larynx
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Next

• Esophagus- the food pipe a long tube that
  carries a food bolus from the pharynx to the
  stomach.
• Preventive measures Esophageal sphincters
• two sphincters on each end of the esophagus.
• They function to
• 1. Upper ES- allow food into the esophagus
• 2. Lower ES- allow food into the stomach and
  prevents backflow of stomach contents.

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An Example of a Sphincter Muscle
Esophagus
Circular muscle
Longitudinal muscle
Esophagus muscles relax, opening the passageway.
Diaphragm muscles relax, opening the passageway.
Stomach
Esophagus muscles contract, squeezing on the
inside.
Diaphragm muscles contract, squeezing on the
outside.
When the circular muscles of a sphincter
contract, the passage closes when they relax,
the passage opens.
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What happens in the stomach?

• A bolus enters the stomach via the lower
  esophageal sphincter.
• The stomach gradually transfers the bolus from
  the upper portion to the lower portion of the
  stomach.
• Stomach acids are added and the food is ground by
  muscular forces
• The bolus is now called chyme.
• The stomach slowly releases chyme through the
  pyloric sphincter into the small intestine.

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Stomach Muscles
Longitudinal
Circular
Diagonal
The stomach has three layers of muscles.
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Still going

• Small intestine Made of three parts-
• 1. The duodenum
• 2. The jejunum
• 3. The ileum

In beginning of the small intestine, fluids from
the gallbladder and pancreas, flow through the
common bile duct and interact with the chyme.
The chyme then moves through the 3 parts of the
small intestine.
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The Small Intestine
Pyloric Sphincter
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The surface area of the small intestine is
roughly the size of a tennis court.
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And going through the large intestine

• Chyme passes through the Ileocecal valve, the
  entrance to the large intestine.
• Chyme bypasses the appendix.
• Chyme travels through the large intestine water
  is withdrawn and a semi-solid mass forms.
• The mass moves to the rectum rectal muscles
  relax.
• 2 sphincters of the anus relax, thus passing the
  mass through the anus.

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The Colon or Large Intestine
Transverse colon
Ascending colon
End of small intestine
Opening from small intestine to large intestine
Descending colon
Appendix
Rectum
Anus
Sigmoid colon
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The whole picture
Esophagus
Stomach
Large Intestine
Small Intestine
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The Digestive Fate of a Sandwich
MOUTH CHEWING AND SWALLOWING, WITH LITTLE
DIGESTION
STOMACH COLLECTING AND CHURNING, WITH SOME
DIGESTION
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The Digestive Fate of a Sandwich
SMALL INTESTINE DIGESTING AND ABSORBING
LARGE INTESTINE REABSORBING AND ELIMINATING
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How does food move through?

• Peristalsis- wavelike muscular contractions that
  push contents along.
• Segmentation- the circular muscles of the small
  intestine rhythmically squeeze and contract the
  contents chyme is mixed with digestive juices,
  etc.
• Sphincter contractions- opening and closing of a
  sphincter to allow contents to enter or exit.

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Peristalsis and Segmentation
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Digestive Secretions

• Source Secretion
• Salivary Glands Saliva
• Stomach Gastric juice
• Pancreas Pancreatic juice
• Liver (via gallbladder) Bile
• Small intestine Intestinal Flora

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The Salivary Glands
Salivary glands
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The pH Scale
pHs of common substances
Basic
Concentrated lye
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Oven cleaner
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Household ammonia
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Baking soda
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Bile
Pancreatic juice
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Blood
pH neutral
Water
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Saliva
Urine
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Coffee
5
Orange juice
4
Vinegar
3
Lemon juice
2
Gastric juice
1
Battery acid
Acidic
0
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Absorption

• The small intestine
• Villi- Small intestinal projections
• Microvilli- Microscopic hairs on the villi
• Crypts- crevices between the villi
• All of these components make up the massive
  absorptive area of the intestine.

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Absorption of Nutrients
Carrier loads nutrient on outside of cell . . .
Outside cell
Carrier loads nutrient on outside of cell . . .
Cell membrane
Energy
Energy
. . . and then releases it on inside of cell.
. . . and then releases it on inside of cell.
Inside cell
ACTIVE TRANSPORT
FACILITATED DIFFUSION
SIMPLE DIFFUSION
Absorption of nutrients into intestinal cells
typically occurs by simple diffusion or active
transport.
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The Small Intestinal Villi
Stomach
Folds with villi on them
Small intestine
Circular muscles
Longitudinal muscles
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The Small Intestinal Villi
Lymphatic vessel (lacteal)
Capillaries
A villus
Goblet cells
Crypts
Artery
Vein
(contd next slide)
Lymphatic vessel
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The Small Intestinal Villi
Microvilli
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Nutrient Transport

• The nutrient crosses the cell and can
• 1. Enter the blood stream (water soluble)
• or
• 2. Enter the lymphatic system
• Water soluble nutrients and smaller fat products
  are released into the bloodstream.
• Larger fats, fat-soluble vitamins and turned into
  chylomicrons and released into the lymphatic
  system

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The Vascular System
Head and upper body
Lungs
Pulmonary vein
Pulmonary artery
Aorta
Aorta
Left side
Left side
Right side
Heart
Heart
Hepatic artery
Hepatic artery
Hepatic vein
Portal vein
Portal vein
Liver
Arteries Capillaries Veins Lymph vessels
Digestive tract
Digestive tract
Lymph
Entire body
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The Vascular System

• Blood delivers Oxygen and Nutrients to organs and
  tissues CO2 and waste products are carried away
  by the blood.
• The digestive system supplies nutrients to the
  blood.
• Heart Arteries Capillaries
• Veins

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The Vascular System (cont.)

• Blood leaving the digestive system is taken to
  the liver via a vein.
• The liver is the bodies major metabolic organ.
• It receives nutrients and other products from the
  digestive system a gatekeeper.

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Route of blood from intestines to heart.

• Heart Arteries Capillaries
• (in intestines)
• Vein Capillaries Veins
• (in liver)

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The Lymphatic System

• A route for fluid from tissue to enter the blood.
• Large fats and fat-soluble vitamins use the lymph
  system
• Ultimately end up in the heart
• Once in the blood stream, the nutrients can be
  delivered to cells, organs, etc.

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Chylomicron travels via the Lymphatic System
Hydrophilic head
Hydrophobic tail
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Common GI Problems

• Choking- improper closing of the epiglottis, food
  lodged in the pharynx, etc.
• Vomiting- stomach contents expelled sometimes
  the contents of the duodenum are expelled.
• Diarrhea- frequent loose stools, lack of
  absorption and increased water in the intestine
  fast motility
• Constipation- inability to defecate

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Common GI Problems (cont.)

• Gas- excessive gas in the GI tract
• Belching-excessive gas in the stomach
• Reflux- relaxation of the lower esophageal
  sphincter, causing stomach acid to touch the
  lining of the esophagus
• Ulcers- erosion of the lining of the GI tract
• Diseases of the GI tract

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Diverticula in the Colon
Diverticula (plural)
Diverticulum (singular)
Diverticula may develop anywhere along the GI
tract, but are most common in the colon.
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In-text Figure Page 74
Eat a variety of food to keep your
gastrointestinal tract happy.