notes on the digestive system

1. CHAPTER 19

2. 6 BASIC PROCESSES
 1. Ingestion
 2. Secretion
 3. Mixing and propulsion
 4. Digestion
 5. Absorption
 6. Defecation

4. LAYERS OF THE GI TRACT
 Mucosa- inner lining, direct contact with contents,
 Submucosa- blood vessels and lymphatic vessels, neutrons
for control
 Muscularis- consists of skeletal muscle for voluntary
swallowing and smooth muscle in the rest of the GI tract.
 Serosa and peritoneum- outermost layer, secretes watery
fluid to allow the tract to glide easily against other organs

8. THE MOUTH
 Hard palate- bones of maxillae and palatine of the
skull, roof of mouth
 Soft palate- muscular, near the back
 Uvula- prevents swallowed foods and liquids into the
nasal cavity
 Palatine tonsils- posterior to soft palate near the
opening of the oropharynx.

10. TONGUE
 Forms the floor of the oral cavity.
 Composed of skeletal muscle.
 Covered with papillae or taste buds.
 Scientists recognize 5 taste types.
 Sweet, sour, salty, bitter and umami.

11. SALIVARY GLANDS
 Parotid glands- between the ears and the masseter
muscle, lower jaw
 Submandibular glands- base of tongue and floor of
mouth
 Sublingual glands- anterior to submandibular
glands

13. TEETH
 Incisors-cut into food
 cuspids (canines)- tear and shred food
 bicuspids (premolars)- crush and grind food
 Molars- crush and grind

15. DIGESTION IN THE MOUTH
 Mechanical digestion in the mouth results from chewing
or mastication in which the food is manipulated by the
tongue, ground by the teeth and mixed with saliva.
 The food is reduced to a soft, flexible and easily
swallowed mass called a bolus.

16. PHARYNX AND ESOPHAGUS
 When food is swallowed, it passes from the mouth into the
pharynx.
 Muscular contractions move the bolus, into the
esophagus.
 The esophagus is a muscular tube and connects to the
stomach.
 It is lined with stratified squamous epithelium and mucous.
 Swallowing involves the mouth, pharynx and esophagus
helped by saliva and mucus.

21. Vocabulary Words
 Layers of GI tract (4 layers)
 Salivary glands (3)
 Mouth (4 structures)
 Teeth (4 types)
 Pharynx
 Esophagus

22. THE STOMACH
 J-shaped enlargement of the GI tract directly below the
diaphragm.
 Connects the esophagus to the duodenum, the first part of the
small intestine.
 Serves as a mixing chamber and holding reservoir for food.
 It is the most elastic part of the GI tract and can
accommodate a large amount of food.
 The diaphragm pushes and pulls the stomach with each
breath.

24. STRUCTURE OF THE STOMACH
 The stomach is composed of the same four layers as the rest of
the GI tract. (mucosa, submucosa, muscularis and serosa.)
 When empty, the muscosa lie in large folds called rugae.
 The stomach is connected to the duodenum by the pyloric
sphincter.
 The stomach contains many types of cells that secrete various
chemicals.

25. Vitamin B-
12
absorption

26. DIGESTION AND ABSORPTION IN THE
STOMACH
 Even before food enters the stomach, reflexes from the senses prepare
the stomach including injection of various digestion enzymes.
 Once the food reaches the stomach, the wall is stretched and pH
changes.
 Nerve impulses trigger mixing waves which are rippling movements
(peristalsis) of the muscles in the stomach.
 The waves macerate the food and mix it with the secretions of the
gastric juices producing chyme.
 Little absorption occurs except for certain medications, water and
alcohol.

28. PANCREAS
 Located behind the stomach, the pancreas secretes chemicals via the
pancreatic duct into the duodenum which unites with the common bile
duct from the liver and gallbladder.
 The pancreas is also part of the endocrine system, because it secretes
hormones.
 Pancreatic juice consists of water, salts, sodium bicarbonate and enzymes.
 Neurons and two hormones (secretin and cholecystokinin) regulate the
secretion of pancreatic juice.

29. Pancreas
Small intestine

32. Vocabulary Cards
 Stomach
 Bolus
 Chyme
 pancreas

33. LIVER AND GALLBLADDER
 The liver is the second largest organ in the body.
 The gallbladder is a pear-shaped sac that hangs from the lower part of the
liver.
 The liver’s lobes are made of many functional units called lobules.
 A lobule consists of specialized cells called hepatocytes arranged around a
central vein.
 Bile is secreted by hepatocytes that enter bile ducts and eventually form the
right and left hepatic ducts.
 The purpose of bile is to emulsify (turn into tiny droplets) triglycerides. (fat)

36.  These unite and exit the liver
through the common hepatic
duct.
 The hepatic duct joins with the
cystic duct from the gallbladder
forming the common bile duct.
 The gallbladder stores the bile
until it’s used.

39. FUNCTIONS OF THE LIVER
 1. carbohydrate metabolism
 2. lipid metabolism
 3. protein metabolism
 4. processing of drugs and hormones.
 5. excretion of bilirubin (bile)
 6. storage of vitamins and minerals.
 7. activation of vitamin D.

43. SMALL INTESTINE
 Within 2-4 hours of eating a meal, the stomach has emptied its
contents into the small intestine where the major events of
digestion and absorption occur.
 The small intestine is about 10 feet long in a living person and 21
feet in a cadaver. Why the differences?
 It is divided into 3 sections.
 The duodenum attaches to the stomach, the jejunum is the
middle portion and the ileum is attached to the large intestine.

45.  Projections called circular folds are permanent
ridges in the muscosa.
 They enhance absorption by increasing surface
area and causing chyme to spiral rather than
go in a straight line as it passes in the small
intestine.
 The muscosa contains villi and microvilli.

48.  The villi are numerous fingerlike projections
consisting of simple columnar epithelium.
 The epithelium contains absorptive cells, mucus-
secreting goblet cells, and endocrine cells.
 The microvilli digest nutrients and move them to
the absorptive cells.

51. Mechanical Digestion in the Small
Intestine
 Segmentations are localized contractions that move
chyme back and forth, mixing it with digestive juices.
 Peristalsis moves the chyme forward into the small
intestine and the wave migrates down the small
intestine reaching the end in 90 to 120 minutes.
 The chyme generally remains in the small intestine 3-5
hours.

53. Chemical Digestion in the Small
Intestine
 The chyme entering the small intestine contains
partially digested carbohydrates and proteins.
 Pancreatic amylase, maltase, sucrase and lactase act
upon specific sugars in the chyme and break them into
smaller units to be absorbed.
 Peptidases break down proteins.
 Pancreatic lipase breaks down lipids.
 Nucleases digest nucleotides.

56. Vocabulary Words
 Small intestine (3
parts)
 Villi
 Microvilli
 Bile
 Liver
 Gallbladder
 Lobules
 hepatocytes

57. Large Intestine
 The large intestine is about 5 feet in length.
 The overall functions of the large intestine are
completion of absorption, production of
vitamins, the formation of feces and the
expulsion of feces.

58. Structure of the Large Intestine
 At beginning of the large intestine, the ileum
connects via a sphincter.
 The materials from the small intestine pass into the
large intestine here.
 The first segment of the large intestine is the
cecum with an attachment called the appendix.
 The appendix contains further digestive enzymes.

59.  The ascending colon goes up the side into the
transverse colon which is horizontal. This leads
into the descending colon which travels
downward.
 The sigmoid colon is an S-shaped part which
connects to the rectum and anus.
 The rectum stores feces.
 The anus is the opening to the outside of the
body.

64.  The walls of the large intestine differ from the small
intestine in that there are no villi or circular folds.
 The epithelium contain goblet cells for lubrication and
absorptive cells that function primarily in ion and water
absorption.
 Unlike the rest of the GI tract, the muscularis of the
large intestine is bundled in three longitudinal bands
giving the intestine a puckered appearance.

66. Digestion and Absorption
 Passage of chyme from the ileium into the cecum is regulated
by the sphincter.
 Immediately after a meal, a reflex intensifies peristalsis.
 Mass peristalsis is a characteristic of the large intestine which is
a huge wave driving the contents of the colon into the rectum.
 Food in the stomach initiates mass peristalsis which usually
takes place 3-4 times a day during or immediately after a
meal.

67.  The final stage of digestion occurs in the colon
through the activity of bacteria.
 Bacteria ferment any remaining carbohydrates and
create gases.
 These gases contribute to flatus.
 Several vitamins like B and K are absorbed in the
colon.
 Bile pigments are broken down into simpler pigments
which give feces the brown color.

68.  The large intestine absorbs a significant amount
of water.
 By the time chyme has remained in the large
intestine for 3-10 hours, it becomes feces.
 The defecation reflex results from mass peristalsis
of food contents into the rectum sending
impulses to the spinal chord which causes
contractions and the need to defecate.

70. 24 total Vocabulary
Words
 Mass peristalsis
 Large intestine (5
parts)
 appendix
 Rectum
 Anus
 Enzymes and
hormones (all on
one card)