Download Human Anatomy & Physiology II

THE DIGESTIVE SYSTEM
Chapter 19
GASTROINTESTINAL (GI) TRACT
Tube that includes: mouth, Pharynx, Esophagus,
Stomach, Small intestine, Large intestine
 Accessory organs: teeth, tongue, salivary
glands, liver, gallbladder, and pancreas

FIGURE 19.1
OVERVIEW- OPERATIONS
 Ingestion:
eating
 Secretion: release of water, enzymes
& buffers
 Mixing
& propulsion: movement
along GI tract
 Digestion: mechanical and chemical
breakdown of foods
 Absorption: getting it into the body
 Defecation: dumping waste products
= defecation
WALL LAYERS- EVERYWHERE
4
layers
 Mucosa-
epithelium, connective layer, glands,
muscularis mucosae
 Submucosa-
connective tissue, blood vessels,
lymphatic vessels, enteric nervous system
 Muscularis-
circular layer, longitudinal
layer
In mouth, pharynx & upper esophagus –skeletal
muscle
 Also in external anal sphincter

 Serosa
or Visceral peritoneum
FIGURE 19.2
FIGURE 19.3A
FIGURE 19.3B
MOUTH
 Formed
by cheeks, hard & soft
palate & tongue
 Soft palate at back includes a “hangy
down” part = uvula

During swallowing uvula prevents
entry into nasal cavity
 Tongue

muscular accessory organ
maneuvers food for chewing
Adjusts shape for speech & swallowing
 Lingual
tonsils at base of tongue
SALIVARY GLANDS
 3 pairs of salivary glands
 Ducts empty into oral cavity
 Parotid inferior & anterior to ears
 Submandibular in floor of mouth, medial & inferior
mandible
 Sublingual
 Beneath tongue
submandibular
to
and superior to
 Saliva
contains 99.5% water, salivary
amylase, mucus and other solutes

Dissolves food & starts digestion of starches
FIGURE 19.4
TEETH
 Accessory
organs in bony sockets of
mandible & maxilla
 3 external regions:



3



Crown- above gums
Root- 1 or more parts embedded in socket
Neck – between crown and root near gum
line
layers of material
Enamel- covers crown
Dentin- majority of interior of tooth
Pulp cavity - nerve, blood vessel &
lymphatics
FIGURE 19.5
DIGESTION IN THE MOUTH
Mechanical
breakdown- chewing
Mixed with saliva by tongue
Salivary amylase chemically
breaks down polysaccharides
(starch)
maltose and larger fragments
Continues in the stomach until
acidified

Rounds
up food into a soft bolus
for swallowing
PHARYNX & ESOPHAGUS
 On
swallowing:
 Bolus of food  oropharynx
 Laryngopharynx esophagus

Muscular contractions in pharynx help
 Upper

Skeletal muscle –controls entry to
esophagus
 Lower

esophageal sphincter (UES)
esophageal sphincter (LES)
Smooth muscle- regulates entry to
stomach
FIGURE 19.6A,B
SWALLOWING
 Voluntary:
bolus forced into
oropharynx
 Triggers oropharyngeal stage
Involuntary & breathing interrupted
 Soft palate move up-close nasopharynx
 Epiglottis seals off larynx
 Bolus moves into esophagus through
UES

 Esophageal
stage peristalsis
moves it toward stomach
FIGURE 19.6C
STOMACH
 J-
shaped enlargement of tract
 Serves as mixing chamber and
holding reservoir
 Very elastic & muscular
 4 regions
Cardia- surrounds upper opening
Fundus- superior & to left of cardia
Body – large central portion
 Pylorus- lower part leading to pyloric
sphincter & duodenum



FIGURE 19.7
STOMACH WALL
 Mucosa:
 Folds called rugae
 Epithelium- simple columnar mucous
 Form gastric glands lining gastric pits
 Secretory cells: mucous neck cells
 Chief cells inactive enzyme pepsinoge
 Parietal cells HCl & intrinsic factor
 Collectively = gastric juice
 Muscularis-
3 Layers: longitudinal,
circular & oblique
FIGURE 19.8
FIGURE 19.9
DIGESTION & ABSORPTION
 Food entry stretch & rise in pH
 Nerve impulses  secretion & mixing
waves Food mixed with juice Chyme
 Small amount pushed through pyloric
sphincter
 = gastric emptying- Carb. foods fastest,
lipids next & proteins slowest
 Entry in duodenum feedback inhibition of
stomach activity
 Pepsin
digests protein peptides
 Little absorption- water, ions & some
drugs
PANCREAS
 Behind
stomach-


Produces pancreatic juice in acinar cells
to duodenum via pancreatic duct

Neutralize stomach acid and dilutes chyme

Proteases: chymotrypsinogen, trypsinogen, et.
al.
Activated by entreokinase from intestine
Starch digesting- pancreatic amylase
Pancreatic lipase
Nucleotidases – RNAase & DNAase
 NaHCO3
solution (pH 7.1-8.2)–
1000ml/day
 Panceas



digestive enzymes
LIVER & GALL BLADDER
 Largest
organ after the skin
 On right below diaphragm
 Functional unit is lobule

Hepatocytes around central vein
Open capillaries = sinusoids
 Bile
 canaliculi ducts hepatic
duct
 Gall bladder =Pear-shaped organ
on front (stores bile)
 cystic duct common bile duct
BILE
 Bicarbonate,
bile salts & waste. – 1000
ml/day
 Important for emulsifying fats

Increases surface area for digestion
 Pigment
is bilirubin- from broken-down
heme during RBC recycling
 Digested to strecobilin- brown color
 Bile salts reabsorbed at end of small
intestine- ileum
 recycle to liver in portal circulation
FIGURE 19.10
FIGURE 19.11A
FIGURE 19.11B
LIVER FUNCTION
 Maintains blood glucose
 Stores as glycogen
 Uses absorbed sugars & Converts
acids glucose
 Lipid metabolism
 Produces cholesterol
amino
& triglycerides, makes
bile
 Makes lipoproteins for lipid transport
 Excretion of bilirubin
 Processes drugs and other
 Store fat soluble vitamins
 Make active vitamin D
chemicals
SMALL INTESTINE
3 parts: duodenum, jejunum, ileum
 Where most of the digestion occurs
 Essentially all of the nutrient absorption
 Ends in ileocecal sphincter

FIGURE 19.12A
FIGURE 19.12B
WALL STRUCTURE
 Same
4 layers
 Epithelial- simple columnar
Absorptive cells with microvilli
 Goblet cells- secrete mucus

 Intestinal
glands- intestinal juice
& hormones

Secretin, cholecystokinin (CCK), Glucosedependent-insulinotrophic peptide (GIP)
 Lymphatic
tissue- defense
WALL STRUCTURE (CONT.)

Duodenal glands- alkaline mucus

Helps neutralize stomach acid
Circular folds- increase surface area
 Villi- finger like projections of mucosa

Increase surface area for absorption
 Include lacteals for lipid absorption

FIGURE 19.13
MOTILITY & SECRETIONS

Secretions: alkaline, some enzymes




Peptidases-breaks small peptides
Disaccharidases attached to wall
Water and salt to balance osmolality
~2000 ml/day
Segmentation activity- for mixing
 Peristalsis for movement after most absorption
completed- slow waves

DIGESTION & ABSORPTION
Chyme enters with partially digested
carbohydrates & proteins
 Bile + pancreatic juice + intestinal juice
completes the job
 Absorption is of monosaccharides; amino acids;
phosphate sugar & bases of DNA & RNA; fatty
acids & monoglycerides

CARBOHYDRATE DIGESTION

Amylases:


Starch & dextrin  maltose
Disaccharidases at surface:
Maltose: maltose  glucose
 Sucrase: sucrose  glucose & fructose
 Lactase: lactose glucose & galactose

PROTEIN & FAT DIGESTION

Trypsin, chymotrypsin, elastase,
carboxypeptidase & pepsin
 Proteins small
 Peptidases at surface:


peptides
Peptides amino acids & di- & tripeptides
Lipase:

glycerides fatty acids &
monoglycerides
ABSORPTION
 By
diffusion, facilitated diffusion,
osmosis & active transport
 Carbohydrates  monosaccharides

Via portal system to liver
 Proteins
acids

(jejunum & ileum) amino
Via portal system to liver
 Lipids
reformed to triglycerides
Packaged in chlyomicrons with protein
 Via lacteals  lymphatics

ABSORPTION (CONT.)

Water & salt


Primarily osmotic movement along with other
nutrients
Vitamins:
Fat soluble absorbed with fat
 Water soluble with simple diffusion
 B12 combines with intrinsic factor & absorbed by
active transport in ileum

FIGURE 19.14A
FIGURE 19.14B
LARGE INTESTINE
 Cecum,
colon, rectum, anal canal
 Ileocecal canal large intestine

Below is cecum with appendix

Few folds , little specialization for
absorption
 Colon-
ascending, transverse,
descending & sigmoid
  rectum anal canal
 Standard 4 layers with mucus
secretion
 Muscularis:
circular + bands of
longitudinal muscle
FIGURE 19.15A
FIGURE 19.15B
FIGURE 19.16
DIGESTION & ABSORPTION
Slow
emptying of ileum
Slow peristalsis
Mass peristalsis with food in
stomach

Moves from middle of colon  rectum
Bacterial
digestion
Produce some B-vitamins & Vit. K
 Produce gases= flatus
 Colon absorbs salt & water

DEFECATION REFLEX
 Stretch
of rectum wall neural
reflex
  contraction of longitudinal muscle
 Combined pressure +
parasympathetic activity relaxing
of internal anal sphincter
 External anal sphincter is voluntary
 Contraction of diaphragm &
abdominal wall muscles aid
defecation
CONTROL
 Rule:
activate forward and inhibit
behind
 three phases: Cephalic, gastric,
intestinal
 Cephalic- smell, sight, thought of
food

Neural signals stimulates salivary
glands & gastric glands
 Gastric
stretching, pH of stomach
Gastrin activates stomach & LES &
CONTROL (CONT.)
 Intestinal-
duodenum

responses to food entering
neural & endocrine
 CCK stimulated by AA &
 Pancreatic enzyme release
fats
Gall bladder contraction
Contraction of pyloric sphincter
 Acid


stimulates secretin
Stimulates HCO3- ions in pancreatic juice
Inhibits gastrin action in stomach
AGING
 Decreased
secretion, motility,
strength of responses
 loss of taste, periodontal disease,
hiatal hernia, gastritis & peptic
ulcer disease
 Increased incidence of gall bladder
problems, cirrhosis of liver,
pancreatitis, constipation,
hemorrhoids & diverticulitis