Download CHAPTER 16 Digestive System

CHAPTER 16
Digestive System
Pictures from Essentials of Anatomy & Physiology, Third Edition
Overview
• Provides fuel (food) to cells and enzymes and chem.
to the body.
• Mouth, pharynx, esophagus, stomach, small
intestine, large intestine, rectum, anus.
• Accessory organs – salivary glands, gallbladder,
liver, pancreas.
• Absorption - substances pass through the wall of
intestine & enter circulation system.
• Reabsorption - water is removed from wastes &
returned to body.
6 processes of the digestive system
1.
Ingestion – food enters digestive tract thru mouth.
2.
Mechanical processing – physical handling of solid foods (by
tongue, teeth, mixing motions of dt).
3.
Digestion – chem. breakdown of food so it can be absorbed by
epithelium.
4.
Secretion – water, acids, enzymes, buffers by digestive tract &
accessory organs.
5.
Absorption – small organic (C) molecules, electrolytes,
vitamins, water that move across the digestive epithelium into
the interstitial fluid.
6.
Excretion – removal of waste products from body (compacted).
Components of digestive system Fig. 16-1
Structure of small intestine Fig. 16-2
Peristalsis Fig. 16-3
Muscle contractions along the digestive tract that move materials along.
Oral cavity Fig. 16-4
•
4 Functions
1.
Examine material before swallowing.
2.
Mechanically chew food via teeth, tongue, surfaces of the palate (mouth).
3.
Lubricate food by mixing w mucous and salivary secretions
4.
Begins digestion of carbs & lipids w help of salivary enzymes.
Tongue - moves food around, sensory info – bitter, sweet, etc.
Salivary Glands Fig. 16-5
• Produce saliva …1-1.5
liters of saliva each
day; 99.4% water w
some ions, buffers,
enzymes. Lubricates
the mouth, controls
bacteria.
• Salivary amylase enzyme that breaks
down carbs that can by
absorbed by digestive
tract.
Teeth Fig. 16-6
• Dentin - bulk of the tooth,
made of mineralized sub
similar to bone.
• Crown - top of the tooth,
coated with enamel.
• Enamel - crystalline form
of calcium phosphate –
hardest biologically
manufactured sub. Protects
tooth
• Root - below gum, root
dentin covered by
cementum.
Pharynx
• Passage… for solid food, liquids, air.
• Smooth muscles propel food down the esophagus.
Esophagus
• Begins at pharynx & ends at stomach - ~ 1 ft long &
diam of .75 “
• Lies behind trachea in neck.
• Secretions of mucous glands keep food from
sticking to the sides.
• Peristalsis contractions move materials down the
esophagus.
Esophageal hiatus Fig. 16-7g
• Enters peritoneal
cavity thru opening in
diaphragm before
empting into the
stomach
• Hiatal hernia –
abdominal organs
slide into thoracic
cavity thru esophageal
hiatus
Stomach Fig. 16-8
•
Ingested food …mixes w secretions from glands of
stomach.
•
4 functions
–
Temporary storage of food.
–
Mechanical breakdown of food.
–
Acids & enzymes break down chem. bonds of food.
–
Production of intrinsic factor – compound
necessary for absorption of vitamin B12.
Chyme
• Viscous, highly acid mixture of partially digested
food.
• Forms from the action of gastric and salivary
secretions mixed w food.
Pyloric sphincter
• Muscular valve . . . that regulates the flow of chyme
from stomach to small intestine.
Rugae
• Ridges & …folds in the lining of the empty stomach
that disappear as the stomach expands to digest food.
• Covered with … alkaline mucous to protect the stomach
lining from acids & enzymes when empty.
• As the stomach stretches …the gastric pits & gastric
glands secret gastric juice.
• Mucous epithelium – secretes mucous that covers &
protects lining from acids, etc
• Gastric pits – opening to gastric glands that secrete
gastric juice
Stomach Anatomy Fig. 16-8c,d
Gastric wall
• Lined by …mucous epithelium
• Intrinsic factor – helps absorption of vit B12 in the intestine.
• Hydrochloric acid (HCl) – lowers pH of gastric juice to 1.5-2.0. Kills
microorganisms, breaks down cell walls & connective tissues in foods,
activates enzymatic secretions of other cells.
• Pepsinogen (inactive form of pepsin) - secreted by cells in stomach.
HCl converts pepsinogen to pepsin – enzyme that splits proteins.
• Gastrin – stimulated by … stretch receptors in stomach (from eating)
stimulate gastrin.
– Gastrin triggers secretion of …intrinsic factor,HCl & pepsinogen.
– Chyme is being formed and …and the “food” is being “digested”.
• Gastritis – inflammation of …gastric mucous.
• Peptic ulcer – digestive aids & enzymes ... erode the
stomach lining or part of the small intestine.
– Caused from much acid being produced or
inadequate production of mucous lining. 80%
caused by bacteria
– Little or no nutrient absorption occurs in the stomach
although digestion begins here. Most carbs, lipids &
proteins are only partially broken down.
Small Intestine
• 90% of nutrient absorption occurs here – rest in
large intestine.
• ~ 20 - 25‘ long.
Fig. 16-11
• Intestinal mucosa has villi – increase surface area
for absorption.
Fig. 16-12
• Smooth muscle contractions
help move materials along.
• Intestinal glands secrete
intestinal juice, mucus &
hormones.
• Intestinal juice – moistens
chime, helps buffer acids,
dissolves digestive enzymes
and the prod of digestion.
• Most of the enzymes & buffers
are contributed by liver &
pancreas.
3 subdivisions of small intestine Fig. 16-10
Duodenum
• Pyloric valve (sphincter) opens to allow chyme to
enter duodenum.
• First foot closest to stomach.
• Receives chyme from stomach and secretions from
pancreas & liver.
Jejunum
• Next 8’.
• Most of chemical digestion & nutrient absorption.
• Weight control – removal of a significant portion of
jejunum
Ileum
• Last 12’.
• Ends in a valve that controls flow into the large
intestine.
• Continues process of nutrient absorption &
readsorption of water.
Pancreas Fig. 16-3
• Lies behind stomach, ~6" long, pinkishgray, lumpy, tissue is soft & easily torn.
• Primarily exocrine organ..
Pancreas function
• Exocrine - secrete water, ions, pancreatic juice (mixture
of digestive enzymes & buffer into small intestine.
• Endocrine - pancreatic islet (~1% of cells) - secrete
insulin & glucagon into blood.
Pancreatic enzymes secreted
• Lipases - attack lipids
• Carbohydrases – digest sugars & starches
• Proteases - ~70% of the total enzyme production break proteins apart
Liver Fig. 16-14
• Largest organ (>200 known functions), reddishbrown, firm texture, 2 lobes, mostly in the right
abdominopelvic region. Fig.
• Limited ability to regenerate
Liver lobule Fig. 16-15
• Basic functional unit of the liver. Blood comes from
hepatic artery & hepatic portal vein
• Hepatocytes - liver cells.
Common hepatic duct Fig. 16-16
• Smaller ducts carry bile thru liver, leaves thru chd flows into the duodenum (thru common bile duct)
or gallbladder (thru cystic duct).
Table 16-2 Major Functions of the Liver
• Refer to Table 16-2 for more of the functions
• Converts glucose to glycogen for storage
• Regulates composition of the blood
• Largest reservoir of blood in the body
• Produces bile
Bile
• Made in liver but stored & excreted by the
gallbladder into the lumen (central space) of
duodenum
• Mostly responsible for “emulsification” of lipids
Gallbladder Fig. 16-14, 16-16
Pear shaped just behind the right
(larger) liver lobe
2 major functions: bile storage & bile
modification/concentration
Gallstones – when bile sits too long in gallbladder &
becomes too concentrated (bile salts precipitate)
Hepatopancreatic sphincter Fig. 16-16c
• Valve that releases bile into the duodenum when
stimulated by other hormones
• More bile is released if the chyme contains large
amts of fats
Large Intestine Fig. 16-17
•Horseshoe-shaped, begins at end of ileum & ends
at anus.
• Lies below liver &
stomach, "frames" small
intestine.
• ~5' long, aka large
bowel. Divided into 3
parts.
Main functions
• Reabsorb water (removed from wastes & returned
to body) & compact feces.
• Absorb important vitamins made by bacterial
action.
• Store fecal material before defecation.
• Divided into 3 parts: cecum, colon, rectum
Cecum Fig. 16-17
• First portion; collects &
stores material from
ileum, begins process
of compaction.
• Sphincter (valve)
guards connection
between ileum & cecum
• Appendix attaches in
back – function with the
lymphatic system
Colon
• Divided into 4 regions:
ascending, transverse,
descending, sigmoid
• Larger diam & thinner
wall than small intestine.
• Pouches (haustra) that
permit enlargement &
elongation.
• Colon cancer occurs here.
• Reabsorption of water,
produces feces.
Rectum Fig. 16-7b
• End of digestive
tract.
• Feces exit thru
anus.
• Internal anal
sphincter &
external anal
sphincter
(voluntary muscle
control)
Absorption in the Large Intestine
• Efficiency of digestions, avg comp of feces: 75%
water, 5 % bacteria, rest if indigestible materials &
remains of epithelial cells
• Absorbs bile salts, & vitamins, organic waste
products (bilirubin from the breakdown of
hemoglobin) and toxins generated by bacteria
Bacteria in large intestine
• Responsible for generating
– vit K (needed by liver to produce clotting factor)
– biotin (needed to metabolize glucose)
– Vit B5 (needed for making steroid hormones &
neurotransmitters).
• Convert bilirubin (from the breakdown of
hemoglobin) into other products which are excreted
in the urine (yellow) or give feces it’s distinct color
• Break down peptides remaining in feces to generate
ammonia, hydrogen sulfide.
• Indigestible carbo (beans) used by bacteria &
produce intestinal gas
Lactose Intolerance
• Primary carbo in milk. Lactose - broken down by
lactase in the intestinal mucosa. If this stops =
intolerant