Download Digestive System

• Ingestion
• Secretion (release of water, acid, buffers &
enzymes into the GI tract)
• Mixing & propulsion
• Digestion
1. Chemical
2. Mechanical
• Absorption from the GI tract into the blood &
lymph
• Defecation
•
GI Tract
1. Mouth
2. Pharynx
3. Esophagus
4. Stomach
5. Large & small intestine
• Accessory digestive organs
1. Teeth
2. Tongue
3. Salivary glands
4. Liver
5. Gallbladder
6. Pancreas
• Mucosa
– 1. Mucus membrane that lines the lumen of the GI
tract
– 2. Mouth, pharynx & esophagus contains
nonkeritanized stratified squamous epithelium
– 3. Simple columnar lines stomach and intestine
– 4. contains exocrine cells that secrete mucus
– 5. Lamina propria
• A, Aerolar connective Tissue
• B. Contains lymphatic & blood vessels for nutrient
absorption
•
C. Contains mucosa associated lymphoid tissue (MALT)
that houses cells that protect against disease
6. Musculairs mucosae
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A. Thin layer of smooth muscle
B. Causes folds that increase surface area
Submucosa
– 1. Consists of areolar tissue
– 2. Contains submuscosal plexus
•
A. Regulates movement of muscosa & vasoconstriction
of blood vessels
• Muscularis
– 1. Upper portion & anal sphincter contains skeleton
muscle
– 2. Rest contains smooth muscle
– 3. Mix and propel food
– 4. Myenteric plexus controls muscular movements
• Serosa
– 1. Superficial layer of organs in abdominopelvic
cavity
– 2. Composed of connective tissue & simple
squamous epithelium
• Largest serous membrane in the body
• Parietal peritoneum lines the abdominpelvic
cavity
• Visceral peritoneum covers some of the organs
and forms their serosa
• Peritoneal cavity
• Folds
– 1. Mesentery
• A. Outward fold of the serous membrane of the small
intestine
• B. Bids small intestine to abdominal wall
– 2. Mesocolon
• A. Binds large intestine to posterior abdominal wall
• B. Carries blood & lymphatic vessels
– 3. Falciform ligament
• A. Attaches liver to anterior abdominal wall & diaphragm
• B. Liver is the only organ attached to anterior abdominal
wall
– 4. Lesser omentum
• A. Suspends stomach & duodenum from liver
– Greater omentum
• A. Hangs loosely over transverse colon
• B. Contains large amounts of adipose
• Formed by cheeks, hard & soft palates &
tongue
• Uvula
– 1. Muscular process
– 2. Drawn superiorly, closes off nosopharynx during
swallowing
• Covered by nonkeritanized stratfied stratfied
squamous
• Any cell or organ that releases saliva into oral
cavity
• Normally keep oral cavity moist
• Secretions increase when food enters &
chemical digestion starts
• Major salivary glands
– 1. Parotid glands
• A. Located inferiorly and anteriorly to ears between ears
& masseter muscle
• B. Secertes through paroyid duct into vestibule opposite
second maxillary molar
– 2. Submandibular glands
• A. Found beneath tongue
• B. Submandibular ducts excrete under tongue
– 3. Sublingual glands
• A. Superior to submandibular gland
• B. Open in floor of oral cavity
• Composition of saliva
– 1. 99.5% water & .5% solutes
– 2. Amylase
– 3. Lingual lipase
• Accessory organ compose of skeletal muscle &
covered with a mucous membrane
• Pushes food
• Fungiform Papillae
– 1. Mushroom like elevations
– 2. Contains taste buds
– 3. More numerous near tip of tongue
• Circumvallate Papillae
– 1. Form inverted V shape
– 2. All contain taste buds
• Filiform Papillae
– 1. Whitish conical projections
– 2. Lack taste buds
– 3. Increase friction of tongue and food
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Crown (visible portion)
Neck (constricted junction at gum line)
Roots (area below gum line)
Composition
– 1. Dentin
• A. Calcified connective tissue
• B. Harder than bone because of more calcium salts
– 2. Pulp
• A. Connective tissue
• B. Contains blood vessels, nerves & lymphatic vessels
– 3. Enamel
• A. Covers teeth
• B, Hardest substance in the body
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Collapsible
Pierces diaphragm through esophageal hiatus
Contains mucosa, submucosa & muscularis
Superficial layer called adventitia (attaches
esophagus to surrounding structures)
• Secretes mucous & transports food
• Passage of food regulated by esophageal
sphincter
• Cardiac sphincter relaxes to let food into
stomach
• Peristalsis (circular muscles contract &
longitudinal relax)
• Acid reflux is a result of the improper closing of
cardiac sphincter
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J shaped enlargement of the GI tract
Connects esophagus to duodenum
Serves as mixing vat & holding reservoir
Anatomy
– 1. Cardia surrounds superior opening
– 2. Fundus is superior & left of Cardia
– 3. Body (central portion)
– 4. Pylorus (connects stomach to duodenum)
– 5. Stomach communicates with small intestine
through pyloric sphincter
• Has the same basic four layers of the GI tract
• Functions
– 1. Mixes saliva, food & gastric juice into chyme
– 2. Reservoir for holding food
– 3. Secretes gastric juice which contains HCL,
Pepsin, intrinsic factor & gastric lipase
– 4. HCL kills bacteria & denatures proteins; pepsin
begins the digestion of proteins; intrinsic factor aids
in absorption of vitamin B12; gastric lipase aids in
digestion of triglycerides
Pancreas
• Made of clusters of epithelial cells called Acini
• Acini secrete pancreatic juice
• Composition and function of pancreatic juice
– 1. Pancreatic enzymes digest carbohydrates
– 2. Trypsin, chymotrypsin, carboxypeptidase and
elasatse break down proteins
– 3. Pancreatic lipase breaks down triglycerides
Pancreas
continued
– 4. Ribonucleases & deoxyrobonucleases
break down nucleic acids
Liver & Gallbladder
• Liver divided into large left & small right
lobe by falciform ligament
• Liver composed of hepatocytes
• Liver has no capillaries but has epithelial
lined sinosoids
• Sinusoids contain phagocytes (Kupffers
cells)
• Secretes bile into hepatic duct
• Hepatic duct joins cystic duct to form
common bile duct
Liver & Gallbladder
continued
• Role & composition off bile
– 1. Bile salts (emulsification of lipid)
– 2. Biliruben
• Functions of liver
– 1. Carbohydrate metabolism: maintains a
normal blood glucose level by breaking down
stored glycogen
– 2. Lipid metabolism: Hepatocytes store
triglycerides
– 3. Protein metabolism: break down amino
acids; NH3 converted to urea
Liver & gallbladder
continued
– 4. Synthesis of alpha & beta globulins
(antibodies) & fibrogen that helps clot blood
– 5. Processing of drugs & hormones: detoxify
& chemically alter hormones
– 6. Excertion of biliruben: derived from heme
portion of broken down blood cells
– 7. Synthesis of bile salts: emulsification &
absorption of lipids
– 8. Storage: glycogen & some vitamins and
minerals
Liver & gallbladder
continued
– 9. Phagocytosis: Kupffers cells phagocytize
bacteria & old red and white blood cells
Small intestine
• Major sire of digestion & absorption
• Begins at pyloric sphincter & ends at large
intestine
• Anatomy
– 1. Duodenum (shortest region)
– 2. Jejunum (about 3 ft long & extends to ileum
– 3. Ileum (last and largest part of the small
intestine; joins large intestine at ileocecal
sphincter
Small Intestine
continued
• Histology
– 1. Mucosa forms fingerlike villi that increase
surface area
– 2. Simple columnar epithelium with many
microvilli and goblet cells
• Functions
– 1. Mixes chyme
– 2. Peristalsis
– 3. Completion of digestion
– 4. Absorbs 90% of nutrients
Small intestine
continued
• Roles of intestinal juices
– 1. Mix with pancreatic juice to absorb
nutrients from chyme
Chemical digestion in small
intestine
• Carbohydrates
1. Starches not broken down by amylase
are broken down by pancreatic amylase
2. Sucrase breaks sucrose into glucose and
fructose
3. Lactase breaks lactose into glucose and
galactose
4. Maltase breaks maltose into glucose and
glucose
Chemical digestion in small
intestine continued
• Proteins
1. Starts in stomach by pepsin
2. Trypsin, chemotrypsin,
carboxypeptidase and elastase
breaks down proteins into peptides
3. Amino peptidase cleaves terminal Amino
acids
4. Dipeptidase splits dipeptides into Amino
Acids
Chemical digestion in small
intestine continued
• Lipids
1. Lipases split triglycerides into fatty acids
and glycerol
2. Bile salts emulsify triglycerides, which
increase surface area exposed to
pancreatic lipases
3. Pancreatic lipases and gastric lipases
cleave off two fatty acids chains leaving a
monoglyceride
Absorption in small intestine
• Monosaccharides
1. 120 grams per hour
2. passes through lumen by facilitated
diffusion or active transport
3. move out of epithelial cells into
capillaries
Absorption in small intestine
continued
• Amino acids, dipeptides, and tripeptides
1. Absorbed by active transport in
duodenum, and jejunum
2. Half absorbed from food and half
from dead cells
3. 95-98% absorbed
4. enter blood by diffusion
5. if not filtered and used by hepatocytes
they enter general circulation
Absorption in small intestine
continued
• Lipids
1. By simple diffusion
2. Monoglycerides follow same path as
nucleic acids
Large intestine
• Anatomy
1. Ileocecal sphincter allows material to pass
into large intestine
2. Cecum
a. pouch about 2.4 cm long
b. Has appendix attached
3. Colon
a. Divided into ascending, transverse
descending and sigmoid portions
Large intestine continued
• Colon continued
b. Hepatic flexure (ascending)
c. Splenic flexure ( descending)
d. Sigmoid enters rectum
4. Rectum
a. Anal canal
b. Guarded by internal and external
sphincter
Large intestine continued
• Absorption and feces formation
1. Chyme becomes semi-solid after 3-10
hours in large intestine
2. Feces is composed of water, inorganic
salts, dead cells, bacteria, unabsorbed
digestive material, and indigestible food
parts
3. Water is absorbed in large intestine