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Ch 15 Notes
DIGESTIVE SYSTEM AND NUTRITION
DIGESTION
Digestion – breakdown of foods and the
absorption of the resulting nutrients.
 Two kinds

 Mechanical
– breaks large pieces into smaller ones
without chemically alteration. (chewing)
 Chemical – breaks food into simpler chemicals
(enzymes)
DIGESTIVE SYSTEM COMPOSITION

Alimentary canal
 From
mouth to anus
 Secretes substances used in digestion
 Organs – mouth, pharynx, esophagus, stomach,
small intestine, large intestine, rectum, and anus
 Accessory organs – salivary glands, liver,
gallbladder, pancreas
 Surface area – 186 square meters
STRUCTURE OF ALIMENTARY CANAL

Mucosa – Innermost Layer
 epithelium,
connective tissue, and some smooth
muscle
 lumen – folds that increase surface area
 tubular glands that secrete mucous
STRUCTURE OF ALIMENTARY CANAL

Submucosa
 loose
connective tissue
 glands, blood vessels, lymphatic tissue, nerves
 Nourishes surrounding tissues and carries away
absorbed materials
STRUCTURE OF ALIMENTARY CANAL

Muscular Layer
 Two
coats of smooth muscle
 Inner coat – circular fibers that decrease diameter
 Outer coat – longitudinal fibers that shorten the
tube
STRUCTURE OF ALIMENTARY CANAL

Serosa/Serous Layer – Outermost layer
 Outside
epithelium and connective tissue
 Also called visceral peritoneum
 Lubricates outer tube to reduce friction between
surfaces in the abdominopelvic region
FIG 15.3
MOTOR FUNCTIONS OF ALIMENTARY CANAL

Mixing



Rhythmic contraction of
smooth muscles mixes
content with gastric
juices
Stomach and small
intestine
Contents move in many
directions at one time
MOTOR FUNCTIONS OF ALIMENTARY CANAL

Moving (Propelling)



Peristalsis – wavelike
motion of smooth muscle
As wave moves, contents
are pushed ahead of it
Only moves in one
direction
FUNCTIONS OF ORGANS
Fill out the table with the functions of each
organ in the digestive system.
 We will do the enzyme part later.

Organ Functions Table
TEETH
Function: Begin mechanical digestion
 Types

 Incisors
(8) – bite off pieces of food
 Canine (4) – grasp and tear food
 Bicuspid (8) – grind food particles
 Molar (12) – grind food particles

Two main parts
 Crown
 Root
STRUCTURE OF TEETH - CROWN



Crown is covered by
enamel
Dentin – harder than
bone
Pulp – blood vessels,
nerves, connective
tissue
STRUCTURE OF TEETH - ROOT


Root is covered by
cementum – thin,
bonelike layer
Periodontal ligament –
blood vessels and
nerves, attaches tooth
to jaw
SALIVARY GLANDS
Secrete saliva – dissolves food; begins chemical
digestion
 Two types of secretory cells: serous and mucous
 Serous – salivary amylase


splits starch and glycogen into disaccharides (for
carbohydrate digestion)
Mucous – coats food for swallowing
 Why is it difficult to swallow something that tastes
nasty?

MAJOR SALIVARY GLANDS

Parotid glands – in front of the ear
 Largest
 Rich

in salivary amylase
Submandibular – floor of mouth, near lower jaw
 Equally

serous and mucous
Sublingual – under the tongue
 Primarily
mucous
PHARYNX
No digestion – just a passageway
 Pharynx – only oropharynx and laryngopharynx
are for food

SWALLOWING
Three stages
 Voluntary

 Tongue
rolls food into bolus and pushes it into
oropharynx
SWALLOWING

Involuntary
 Soft
palate raises, epiglottis closes off larynx,
tongue presses soft palate
 Longitudinal muscles in pharyngeal wall pull the
pharynx upward
 Esophagus opens
 Peristalsis pushes food downward
SWALLOWING
During steps 1 and 2, breathing momentarily
ceases
 Involuntary – Peristalsis pushes food from
esophagus to the stomach.

ESOPHAGUS
~25 cm long
 Penetrates the diaphragm through the
esophageal hiatus
 Mucous glands throughout to lubricate food
 Lower espohageal sphincter – closes entrance
to stomach so contents don’t come back into
the espophagus

STOMACH
Receives food from esophagus
 Mixes with gastric juices

 Rugae
– gastric folds
Starts protein digestion
 Limited absorption

 Small

amounts of water, salts, alcohol
Moves food to small intestine
STOMACH - STRUCTURE
Cardia – area near esophogeal opening
 Fundus – balloons inferior to cardia; temporary
storage area
 Body region – main part of the stomach
 Pylorus – Area that tapers to the duodenum

 Pyloric
canal – approaches the small intestine
 Pyloric sphincter – muscle valve that controls
gastric emptying
STOMACH - SECRETIONS

Gastric glands – have gastric pits at the end.
 Mucous
cells – secrete thick mucous to prevent the
stomach from digesting itself
 Chief cells – secrete enzymes
 Parietal cells – secrete hydrochloric acid

Intrinsic factor – helps small intestine absorb
Vitamin B12.
STOMACH – ENZYME

Pepsinogen + HCl -> pepsin
 Starts
the digestion of protein
GASTRIC SECRETION REGULATION

Secretion is regulated by both the brain and by
hormoes
 Stomach
– gastrin
 Small intestine - cholecystokinin
When you see, smell, or taste food, your
stomach begins releasing gastric juices.
 As food moves into the intestine, gastric juice
secretion is inhibited

STOMACH ACTIONS
Mixing creates a semifluid paste called chyme.
 When chyme reaches the pylorus, it relaxes the
pyloric sphincter, pushing it into the small
intestine

STOMACH ACTIONS

Food content determines time
 Liquids
– fastest
 Carbs – very fast
 Proteins – a little slower
 Lipids – very slow
PANCREAS
Pancreas has both endocrine and exocrine
qualities.
 Secretes digestive fluids called pancreatic
juices.

PANCREAS STRUCTURE

Located behind the
stomach, with its head
in the c-shaped curve of
the duodenum and its
tail against the spleen
PANCREAS STRUCTURE
Mostly made up of pancreatic acinar cells that
produce pancreatic juices
 These lead into a pancreatic duct, which carries
juices to the duodenum.

 Coincides

with the bile duct from the gall bladder.
Hepatopancreatic sphincter controls release.
PANCREATIC JUICE - ENZYMES
Pancreatic amylase – breaks down carbs
 Pancreatic lipase – breaks down lipids
 Nucleases – breaks down nucleic acids
 Trypsin, chymotrypsin, carboxypeptidase –
break down proteins

 Several
are necessary because no one enzyme can
break all peptide bonds.
 Cannot be activated until they come into contact
with other enzymes (i.e. – enterokinase,
cholecytokinin)
PANCREATIC SECRETION - REGULATION
Controlled by nervous and endocrine systems
 When chyme reaches the duodenum, the
hormone secretin is released, which stimulate
the release of pancreatic juice into the
duodenum.
 Pancreatic juice, high in bicarbonate ions,
neurtalizes the acid in the chyme to provide a
more favorable environment in the intestine

LIVER



Location – Upper right
quadrant just under the
diaphragm
Well supplied with blood
vessels
Heaviest organ – weighs
about 3 lbs
LIVER


Enclosed by fibrous
capsule and split into
the left and right lobes
by connective tissue.
Lobes are subdivided
into hepatic lobules –
hepatic cells radiating
from a central vein.
LIVER - STRUCTURE
Blood from digestive tract’s hepatic portal vein
bring absorbed nutrients in
 In the hepatic sinusoids, there are large
phagocytic macrophages called Kupffer cells.

 They
remove bacteria and other foreign particles
that enter through hepatic portal vein

Hepatic cell secretions -> bile canuliculi -> bile
ductules -> hepatic ducts ->common hepatic
duct
LIVER - FUNCTIONS
Carbohydrate metabolism – controlled by
hormones insulin and glucagon which can
lower or raise blood glucose levels
 Lipid metabolism – breaks down, synthesizes
cholesterol, converts sugars to fats for storage
 Protein metabolism – forms urea, makes
plasma proteins (clotting factors), changes
amino acids into other amino acids

LIVER - FUNCTIONS
Storage – Vitamins A, D, B12, and iron
 Protection – destroy defective red blood cells,
phagocytize foreign substances and toxins (i.e.
– alcohol)
 Secretes bile

BILE
Yellowish-green liquid secreted by hepatic cells
 Contains – water, bile salts, bile pigments (i.e.
biliruben), cholesterol, and electrolytes
 Bile salts are the only substances that have
digestive function.

 They
break fat molecules into much smaller
droplets (emulsification) so they can more easily be
digested
 Also help with absorption of vitamins A, D, E, and K.
GALLBLADDER
Pear-shaped sac connected to the cystic duct
and to the hapatic duct.
 Epithelium lined with strong muscles
 Stores bile, absorbs water, releases bile into
small intestine

GALLBLADDER AND LIVER CONVERGE



Common hepatic duct
and cystic duct join to
form the bile duct.
Bile duct empties into
small intestine.
Controlled by
hepatopancreatic
sphincter.
RELEASE OF BILE
Bile is released when the hormone
cholocytokinin relaxes the hepatopancreatic
sphincter.
 It is released along with the pancreatic juices.

SMALL INTESTINE
Tubular organ that goes from pyloric sphincter
(stomach) to the large intestine.
 Receives secretions from the pancreas and
liver, completes digestion of chyme, absorbs
products of digestion, transports residues to
large intestine.

SMALL INTESTINE – PARTS


Doudenum
Jejunum (2/5) – bigger in
diameter, more active


Ileum (3/5)
Connected to posterior
abdominal wall by the
mesentery


Blood vessels, nerve and
lymphatic tissue,
Ileocecal Sphincter
INSIDE THE SMALL INTESTINE LINING

Intestinal villi line the inside of the mucosa.
 Increase
surface area
 Aid in absorption
 Lymph vessel (lacteal) and blood vessels inside,
which carry away absorbed nutrients.
 Nervous Tissue
SMALL INTESTINE ENZYMES
Peptidase – Breaks down peptides (proteins)
into amino acids
 Sucrase, maltase, lactase – Breaks down
disaccharides into monosaccharides
 Instestinal Lipase – Breaks down fats into fatty
acids and glycerols

REGULATION OF SECRETION

Chyme offers both mechanical and chemical
stimulation in the duodenum and along the
intestinal wall.
ABSORPTION – SMALL INTESTINE
Small intestine is the most important
absorption organ on the alimentary canal.
 Very little absorbable material reaches the
large intestine.
 Carbs – Easily absorbed into blood capillaries
by facilitated diffusion or active transport.

ABSORPTION – SMALL INTESTINE
Amino acids (from proteins) – absorbed into the
blood.
 Fats – Broken down, reassembled, covered in
protein coat (chylomicrons), absorbed by lymph
vessels, which then take it to blood vessels
 Also absorbs – electrolytes and water

MOVEMENTS OF THE SMALL INTESTINE
Mixing – segmentation mixes the contents and
“swishes” them back and forth.
 Moving – peristalsis over 3 to 10 hours
 If contents move too quickly, water and
electrolytes that would normally be absorbed
are not. This causes diarrhea.

LARGE INTESTINE
Has a larger diameter than small intestine.
 Four main parts: cecum, colon, rectum, anal
canal
 Absorbs water and electrolytes from chyme.
 Forms and stores feces.

PARTS


Cecum – Connection to
ileum
Appendix – lymphatic;
no known digestive
function
PARTS

Colon





Ascending
Transverse
Descending
Sigmoid
Rectum
PARTS


Anal canal
Anus


Two sphincter muscles:
internal anal sphincter
muscle and external anal
sphincter muscle
Skeletal muscle –
voluntary control
LARGE INTESTINAL WALL
Lacks villi
 Longitudinal muscle fibers form 3 distinct
bands

FUNCTIONS
Little to no actual digestive properties.
 Mucous is the large intestine’s only major
secretion.
 Will absorb water and electrolytes in the first
half.
 Substances that remain become feces and are
stored in the second half.

FUNCTIONS – INTESTINAL BACTERIA
Bacteria that live in colon (intestinal flora) can
break down some materials that are still useful
to it at this point. (i.e. cellulose)
 They make Vitamins K, B12, thiamine, and
riboflavin
 They may also make intestinal gas

MOVEMENTS OF LARGE INTESTINE
Mixing and moving like small intestine, but
slower.
 Waves happen only 2-3 times a day.
 Typically mass movements follow a meal –
gastrocolic reflex
 Voluntary – defecation reflex
 Internal and external anal sphincters relax

FECES
Material not absorbed during digestion, water,
electrolytes, mucus, shed intestinal cells,
bacteria
 Pigmentation and odor are due to bacterial
action
