Transcript Ch. 25: GI System part A

C. Chace Tydell, DVM
25-1


Veterinarian/surgeon for more than 15 years
Immunology researcher for 10 years




UCI
Caltech
Scientific publications
Taught Developmental Biology at Caltech
25-2



Your name
Your career goals
One disease about which you would like to know
more

Does someone in your family have a health problem?
Diabetes?

Heart attack?
Stroke?
A disease or disorder that you have heard about?
Lupus?
Leprosy?
Hepatitis?
25-3
Chapter 25
Lecture Outline
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
25-4

-osis = condition or process


-itis = inflammation


eg- gastritis, colitis, hepatitis
-ostomy = a surgically created opening for waste
products to move out of the body


eg- cyanosis, cirrhosis, leukocytosis
colostomy, ileostomy, ostomy
-scopy = to view, to have a look

colonoscopy, gastroscopy, endoscopy
25-5

Mechanical digestion
physical breakdown of food into smaller particles
 teeth and churning action of stomach and intestines


Chemical digestion



series of hydrolysis reactions that break macromolecules into
their monomers
enzymes from saliva, stomach, pancreas and intestines
results
 polysaccharides into monosaccharides
 proteins into amino acids
 fats into glycerol and fatty acids
25-6

Ingestion


Digestion


breakdown of molecules
Absorption


intake of food
uptake nutrients into blood/lymph
Defecation

elimination of undigested material
25-7

Motility


Secretion


muscular contractions that break up food, mix it with
enzymes and move it along
digestive enzymes and hormones
Membrane transport

absorption of nutrients
25-8

Digestive tract (GI tract)


30 foot long tube extending
from
mouth to anus
Accessory organs

teeth, tongue, liver,
gallbladder,
pancreas, salivary glands
25-9

Mucosa





Submucosa
Muscularis externa



epithelium
lamina propria
muscularis mucosae
inner circular layer
outer longitudinal layer
Adventitia or Serosa

areolar tissue or mesothelium
25-10
25-11


Able to function independently of CNS
Composed of two nerve networks

submucosal plexus
 controls glandular secretion of mucosa
 contractions of muscularis mucosae

myenteric plexus
 controls peristalsis
 contractions of muscularis externa
Peristalsis is alternate waves of longitudinal and
circular muscular contraction that pushes food along
the alimentary canal.
25-12
25-13




Serous membrane that lines the peritoneal cavity of the
abdomen and covers the mesenteries and viscera
Of the GI tract, only duodenum, pancreas and parts of
large intestine are retroperitoneal
Dorsal mesentery suspends GI tract and forms serosa
(visceral peritoneum) of stomach and intestines
Ventral mesentery forms lesser and greater omentum

lacy layer of connective tissue that contains lymph nodes,
lymphatic vessels, blood vessels
25-14


Lesser - attaches stomach to liver
Greater - covers small intestines like an apron
25-15


Mesentery of small intestines holds many blood vessels
Mesocolon anchors colon to posterior body wall
25-16

Neural control
short myenteric reflexes (swallowing)
 long vagovagal reflexes (parasympathetic
stimulation of digestive motility and secretion)


Hormones


messengers diffuse into bloodstream, distant
targets
Paracrine secretions

messengers diffuse to nearby target cells
25-17
25-18

Cheeks and lips




Tongue is sensitive, muscular manipulator of food



keep food between teeth for chewing; essential for speech
and suckling in infants
vestibule - space between teeth and cheeks
lips: cutaneous area versus red area (vermilion)
papillae and taste buds on dorsal surface
lingual glands secrete saliva, tonsils in root
Hard and soft palate


allow breathing and chewing at same time
palatoglossal and palatopharyngeal arches
25-19


Baby teeth (20) by 2 years; Adult
(32) between 6 and 25
Occlusal surfaces and cusp
numbers differ
25-20
25-21

Periodontal ligament is
modified periosteum




Cementum and dentin
are living tissue
Enamel is noncellular
secretion formed during
development
Root canal leads into
pulp cavity


anchors into alveolus
nerves and blood vessels
Gingiva or gums
25-22

Breaks food into smaller pieces to be swallowed


 surface area exposed to digestive enzymes
Contact of food with sensory receptors triggers
chewing reflex
tongue, buccinator and orbicularis oris manipulate
food
 masseter and temporalis elevate the teeth to crush
food
 medial and lateral pterygoids swing teeth in side-toside grinding action of molars

25-23

Functions of saliva





moisten
begin starch and fat digestion
cleanse teeth
inhibit bacteria
bind food together into bolus
25-24

Functions of saliva


moisten, begin starch and fat digestion, cleanse teeth, inhibit
bacteria, bind food together into bolus
Hypotonic solution of 99.5% water and solutes



salivary amylase, begins starch digestion
lingual lipase, digests fat activated by stomach acid
mucus, aids in swallowing
lysozyme, enzyme kills bacteria
 immunoglobulin A, inhibits bacterial growth
 electrolytes = Na+, K+, Cl-, phosphate and bicarbonate


pH of 6.8 to 7.0
25-25


Small intrinsic glands
found under mucous
membrane of mouth,
lips, cheeks and
tongue - secrete at
constant rate
3 pairs extrinsic
glands connected to
oral cavity by ducts



parotid
submandibular
sublingual
25-26




Compound tubuloacinar
glands (see pg 177)
Mucous cells secrete
mucus
Serous cells secrete thin
fluid rich in amylase
Mixed acinus has both
25-27



Total of 1 to 1.5 L of saliva per day
Cells filter water from blood and add other substances
Food stimulates receptors that signal salivatory
nuclei in medulla and pons



parasympathetic stimulation  salivary glands produce thin
saliva, rich in enzymes
sympathetic stimulation  produce less abundant, thicker
saliva, with more mucus
Higher brain centers stimulate salivatory nuclei so sight,
smell and thought of food cause salivation
25-28
25-29

Skeletal muscle


deep layer –
longitudinal
orientation
superficial layer –
circular
orientation
 superior, middle
and inferior
pharyngeal
constrictors
25-30

Straight muscular tube 25-30 cm long




Extends from pharynx to cardiac stomach passing
through esophageal hiatus in diaphragm


nonkeratinized stratified squamous epithelium
esophageal glands in submucosa
skeletal muscle in upper part and smooth in bottom
inferior pharyngeal constrictor excludes air from it
Lower esophageal sphincter closes orifice to reflux
25-31
25-32
25-33


Series of muscular contractions coordinated by
centers in the brain
Buccal phase


tongue collects food and pushes it back into oropharynx
Pharyngeal-esophageal phase



soft palate rises and blocks nasopharynx
infrahyoid muscles lift larynx; epiglottis folded back
pharyngeal constrictors push bolus down esophagus
 liquids in 2 seconds -- food bolus may take 8 seconds
 lower esophageal sphincter relaxes
25-34
25-35

Mechanically breaks up food, liquifies food and begins
chemical digestion of protein and fat


resulting soupy mixture is called chyme
Does not absorb significant amount of nutrients

absorbs aspirin and some lipid-soluble drugs
25-36

Muscular sac (internal volume from 50ml to 4L)
J - shaped organ with lesser and greater curvatures
 regional differences






cardiac region just inside cardiac orifice
fundus - domed portion superior to esophageal opening
body - main portion of organ
pyloric region - narrow inferior end
 antrum and pyloric canal
Pylorus - opening to duodenum

thick ring of smooth muscle forms a sphincter
25-37
Cardia
Fundus
Body
Pylorus

Notice: bulge of fundus, narrowing of pyloric region, thickness
of pyloric sphincter and greater and lesser curvatures
25-38

Innervation by
parasympathetic fibers from vagus
 sympathetic fibers from celiac plexus


All blood from stomach enters hepatic portal
circulation and is filtered through liver before
returning to heart
25-39
25-40

Mucosa



simple columnar glandular epithelium
lamina propria is filled with tubular glands (gastric pits)
Muscularis externa has 3 layers

outer longitudinal, middle circular and inner oblique layers
25-41
25-42

Mucous cells


Regenerative cells


secrete HCl acid and intrinsic factor
Chief cells



divide rapidly to produce new cells
that migrate to surface
Parietal cells


secrete mucus
secrete pepsinogen
chymosin and lipase in infancy
Enteroendocrine cells

G cells
 Make gastrin

Others secrete hormones and
paracrine messengers
25-43
25-44

Parietal cells contain carbonic anhydrase (CAH)
CO2 + H2O  H2CO3  HCO3- + H+
 H+ is pumped into stomach lumen by H+K+ATPase
  HCO3- in blood causes alkaline tide (blood pH )

2 to 3 L of gastric juice/day
(H2O, HCl and pepsin)
25-45


Activates pepsin and lingual lipase
Breaks up connective tissues and plant cell walls


Converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+)


liquefies food to form chyme
absorbed and used for hemoglobin synthesis
Destroys ingested bacteria and pathogens
25-46

Intrinsic factor



Pepsin - protein digestion



essential for B12 absorption by small intestine
RBC production (lack causes pernicious anemia)
secreted as pepsinogen (inactive)
HCl converts it to pepsin (active)
Gastric lipase and chymosin
lipase digests butterfat of milk in infant
 chymosin curdles milk by coagulating proteins

25-47
25-48

Many produced by enteroendocrine cells
hormones enter blood  distant cells
 paracrine secretions  neighboring cells


Gut-brain peptides

signaling molecules produced in digestive tract and
CNS
25-49