chapter 16 the digestive system. functions of the digestive system 1.take in food 2.break down food...
TRANSCRIPT
Chapter 16The Digestive System
Functions of the Digestive SystemFunctions of the Digestive System
1. take in food
2. break down food
3. absorb digested molecules
4. provide nutrients
5. eliminate wastes
Two Divisions of the Digestive SystemTwo Divisions of the Digestive System
1. alimentary canal (digestive tract)
• digests and absorbs
• oral cavity to anus
2. accessory digestive organs
Organs of the Digestive SystemOrgans of the Digestive System
Figure 14.1
Digestive TractDigestive Tract
muscular tube approximately 9 M long
open at both ends
Wall has 4 layers with some variation due to specific function.
Layers of Digestive TractLayers of Digestive Tract
innermost: mucosa
epithelial cells which line cavity
attached to connective tissue
surrounded by thin muscular layer
protects tissues of canal
carries out secretion and absorption
Layers of Digestive TractLayers of Digestive Tract
next: submucosa
thick layer of loose connective tissue housing blood vessels, lymph vessels, and nerves
nourishes surrounding layers of tract
Layers of Digestive TractLayers of Digestive Tract
next: muscular layer
inner: circular smooth muscle
outer: longitudinal smooth muscle
propels food through digestive tract
contains lots of nerves to control movement and secretion
Layers of Digestive TractLayers of Digestive Tract
outermost: serosa
visceral peritoneum
protects underlying tissue
secretes serous fluid to keep tract from sticking to other tissues of abdominal cavity
Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs
Figure 14.3
Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy teeth – 32 total in adults
incisors, premolars, molars, wisdom teeth
tongue – thick, muscular organ functions in digestion,
taste and speech attaches to posterior
part of mouth and by frenulum
covered by mucous membrane
houses taste buds within papillae salty, sweet, sour,
bitter
Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy
tonsils lingual and palatine
palate – roof of oral cavity hard = bone soft = muscle and
connective tissue separates oral and
nasal cavities uvula – fleshy
projection of the soft palate
Salivary GlandsSalivary Glands
produce saliva – mixture of mucous and serous fluids keeps mouth moist contains enzymes that aid in chemical digestion
3 pairs in oral cavity parotid – located anterior to ears
secrete serous and mucous fluids submandibular – base of jaw
ducts open below tongue secrete more serous than mucous fluids
sublingual – smallest, below tongue duct opens into floor of oral cavity secretes thick, stringy mucous fluid
SalivaSaliva produce 1 liter a day serous fluid: parotid and submandibular glands
contains amylase, enzyme to break down starches lysozyme: reduces bacterial growth in mouth mucous: contains mucin for lubrication regulated by parasympathetic stimulation (involuntary
nervous system) increase in secretions with sight, smell, thought of
food
Processes of the MouthProcesses of the Mouth
mechanical digestion mastication (chewing) of food mixing of food with saliva by tongue
chemical digestion salivary amylase breaks down starches
allow for the sense of taste NO food absorption occurs in mouth.
SwallowingSwallowing
tongue, soft palate, pharynx and esophagus phase 1: voluntary (mouth)
Bolus (food mass) is forced into pharynx by tongue. phase 2: involuntary (pharynx)
Pharynx connects mouth and esophagus. Receptors in pharynx sense food which triggers
swallowing reflexes. Epiglottis covers larynx.
phase 3: involuntary (esophagus) Esophagus connects pharynx to stomach. Peristalsis moves food from esophagus to stomach. Lower esophageal sphincter helps prevent regurgitation
of food.
Stomach AnatomyStomach Anatomy
Slide 14.15a
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located on the left side of the abdominal cavity
Food enters at the cardiac opening.
Stomach FunctionsStomach Functions
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acts as a storage tank for food
site of food breakdown
start of protein digestion
very little absorption
delivers chyme (processed food) to the small intestine
Slide 14.15b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Regions of the stomach
Cardiac region – near the heart
Fundus – most superior part
Body
Pylorus – funnel-shaped terminal end
Food empties into the small intestine at the pyloric sphincter.
Stomach AnatomyStomach Anatomy
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Figure 14.4a
Muscles of the stomach
• different than rest of digestive tract• 3 layers
1. outer longitudinal layer
2. middle circular layer
3. inner oblique layer
• produce churning action – mechanical digestion
Specialized Mucosa of the StomachSpecialized Mucosa of the Stomach
gastric glands – secrete gastric juice
3 types of cells
1. mucus cells – produce a sticky alkaline mucus which protects stomach lining
2. chief cells – secrete protein-digesting enzymes (pepsinogen which becomes pepsin)
3. parietal cells – secrete hydrochloric acid
rugae – internal folds of the mucosa allows stomach to stretch when full
Other Stomach SecretionsOther Stomach Secretions
• gastrin – hormone that increases stomach secretions• intrinsic factor – aids in absorption of vitamin B12• cholecystokinin – hormone that stimulates gastric
secretions
Production of gastric juices is regulated by hormones and the nervous system.
Humans produce about 2 L per day.
How Stomach Digests FoodHow Stomach Digests Food
1. As food enters digestive tract, gastrin is produced which causes production of gastric juices.
2. Food mixes with gastric juices and forms chyme which passes to pyloric region.
3. As food empties, secretions from stomach wall are inhibited by nervous system.
Stomach MovementStomach Movement
2 types resulting from stomach wall muscle contractions1. mixing – from weak contractions
mix ingested food with stomach secretions to form chyme
2. peristalsis – from stronger contractionsforce chyme toward and through pyloric sphincter
Structure of the Stomach MucosaStructure of the Stomach Mucosa
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Figure 14.4b, c
Small IntestineSmall Intestine
absorbs products of digestion
receives secretions from pancreas and liver
transports remaining residue to large intestine
6 meters long
ileocecal junction – joins ileum and large intestine
Ileocecal sphincter and ileocecal valve keep materials moving in right direction.
Subdivisions of the Small IntestineSubdivisions of the Small Intestine
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Duodenum
attached to the stomach
curves around the head of the pancreas
25 cm long
Common bile duct from liver and pancreatic duct join each other and empty into duodenum.
Jejunum
2.5 meters; attaches anteriorly to the duodenum
Ileum
3.5 meters, extends from jejunum to large intestine
Subdivisions of the Small IntestineSubdivisions of the Small Intestine
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Duodenum, jejunum and ileum have same structure except:
there is a gradual decrease in diameter
decrease in thickness of the walls
decrease in # of circular folds
decrease in # of villi
Chemical Digestion in the Small IntestineChemical Digestion in the Small Intestine
3 modifications to increase surface area up to 600 times
1. circular folds – run perpendicular to long axis of tract
2. villi – tiny finger-like projections formed by mucosa
3. microvilli – extensions of villi found in absorptive cells
Mucous Lining of Small IntestineMucous Lining of Small Intestinecomposed of simple columnar epithelium1. absorptive cells
have microvilliproduce digestive enzymesabsorb digested food
2. goblet cellsproduce protective mucus
3. granular cells protect intestinal epithelium from bacteria
4. endocrine cellsproduce regulatory hormones
Secretions of the Small IntestineSecretions of the Small Intestine
• lubricate and protect intestinal wall from acidic chyme and digestive enzymes
• keep chyme in liquid form
• produced by mucosa, pancreas, liver
• peptidases – break proteins into amino acids
• disaccharidases – break down complex sugars into monosaccharides
Absorption in the Small IntestineAbsorption in the Small Intestine
major function of small intestinemost in duodenum and jejunum
monosaccharides – absorbed through active transport or facilitated diffusion by villi
amino acids – absorbed through active transport by villi and carried away in blood
fatty acids – dissolve into cell membranes of villi and carried away by lymphatic vessels
water – absorbed through osmosis into villi electrolytes – absorbed by active transport by villi
Movement in the Small IntestineMovement in the Small Intestine
• mixing and propulsion – mechanical breakdown
• peristaltic contraction – causes chyme to move along tract; occur along entire digestive tract
• segmental contraction – short movements to mix contents
Large IntestineLarge Intestine
larger in diameter, but shorter than the small intestine 1.5 meters extends from ileocecal valve to anus major functions:
absorption of water, electrolytes, vitamins K and B elimination of indigestible food (feces) production of mucus for lubrication No digestion of food occurs here. Bacteria produce vitamin K and B.
Divisions of the Large IntestineDivisions of the Large Intestine
cecum – saclike first part of the large intestine appendix
accumulation of lymphatic tissue hangs from the cecum
colon ascending transverse descending S-shaped sigmoid (in pelvis)
rectum
anus external body opening contains 2 sphincters
Large IntestineLarge Intestine
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 14.8
Structures of the Large IntestineStructures of the Large Intestine
3 bands of longitudinal muscle arranged in teniae coli create haustra (pocket like sacs in wall)
large numbers of goblet cells
Absorption in the Large IntestineAbsorption in the Large Intestine
no digestive enzymes absorption of water and electrolytes and vitamins K and B
Propulsion in the Large IntestinePropulsion in the Large Intestine mass movements
slow, powerful contractions move contents toward anus occur two to three times per day cover more distance than peristaltic contractions
Presence of feces in the rectum causes a defecation reflex. Internal anal sphincter is relaxed. Defecation occurs with relaxation of the voluntary
(external) anal sphincter.
PancreasPancreas
located behind the stomach produces digestive enzymes that break down all categories
of food trypsin – protein digestion pancreatic amylase – starch digestion lipidase – fat digestion secreted into the duodenum
Alkaline fluid introduced with enzymes neutralizes acidic chyme.
LiverLiver
located on the right side of the body under the diaphragm
consists of four lobes capable of regeneration connected to the gall bladder via the common hepatic
duct metabolizes carbohydrates, lipids, proteins stores glycogen, vitamins A,D and B12, iron and blood filters blood, removes toxins and damaged blood cells secretes bile
BileBile
yellowish, green liquid includes water, bile salts, bile pigments, cholesterol
and electrolytes Bile salts
emulsify fats. aid in absorption of fatty acids, cholesterol and some
vitamins
Gall BladderGall Bladder
sac found beneath liver stores bile from the liver releases bile into the duodenum in the presence of fatty
food release controlled by sphincter muscles Crystallized bile causes gallstones.
Processes of the Digestive SystemProcesses of the Digestive System
Figure 14.11