Transcript Digestive System

Role of Digestive System
A. Prepare food for absorption and utilization by all the body cells
B. Excess food material (not absorbed) becomes feces to be eliminated
C. Ingestion vs. Digestion
1. Ingestion – process of taking food into the GI tract
2. Digestion - food undergoes a chemical process called
hydrolysis
a. food and fluid is broken down into their
smallest parts so the body can use them to
build and nourish cells, along with providing energy
b. absorption – movement of nutrients into internal
environment
A. Gastrointestinal (GI) Tract [aka alimentary canal] (listed in order of food pathway)
1.
2.
3.
4.
5.
6.
mouth
oropharynx
pharynx
esophagus
stomach
small intestine
a. duodenum
b. jejunum
c. ileum
7. large intestine
a. cecum
b. colon
1.
2.
3.
4.
8. rectum
9. anus
B. Accessory Organs
1.
2.
3.
4.
5.
6.
7.
salivary glands
tongue
teeth
liver
gallbladder
pancreas
vermiform appendix
ascending colon
transverse colon
descending colon
sigmoid colon
Layers of the walls of the gastrointestinal (GI) tract
1. (deepest) mucosasubmucosamuscularisserosa (most superficial)
2. Tissue layers have variation in different organs
Mouth and Pharynx
• Buccal Cavity
– Lips – external is skin; internal is mucous
membranes
– Cheeks – lined by mucous membranes;
contain mucous secreting glands
– Hard and Soft Palates
• Hard palate – four bones
• Soft palate – muscle; forms partition
between mouth and nasopharynx; uvula extend from soft palate
– Tongue – muscle covered by mucous membrane
• mastication (chewing) and deglutition (swallowing)
• papillae – surface of tongue; some contain taste buds
• lingual frenulum – mucous membrane fold that anchors tong to
bottom of mouth
Mouth and Pharynx
• Salivary Glands
– Secrete about 1L of saliva/day
• Salivary amylase – enzyme in saliva that converts starch to sugar
– Three pairs of glands (parotid, submandibular, sublingual)
Mouth and Pharynx
•
Teeth
– Anatomy
• crown - covered in enamel
• neck – connects crown to root
• root – fits into socket in the gum
– Types
• Deciduous teeth (20 baby teeth)
–
–
–
–
Incisors
Canines
first molars
second molars
• Permanent Teeth (32 adult teeth)
–
–
–
–
–
•
incisors
canine
premolars
1st & 2nd Molars
third molars – wisdom teeth
Pharynx – tube through which bolus (chewed
ball of food) passes when moved from mouth to
esophagus (deglutition)
Esophagus and Stomach
• Esophagus
– Extends from pharynx
to stomach
– Resides in both
abdominal and
thoracic cavities
– Peristalsis begins
Esophagus and Stomach
• Stomach
– Functions
• reservoir for food until it is partially digested and
moved along GI tract
• secretes gastric juice
• breaks food into small particles and mixes them with
gastric juice
• limited absorption
• helps protect body from bacteria swallowed with food
• produces gastrin – hormone that causes the stomach
to produce acid
Esophagus and Stomach
•
Stomach
– Sphincter Muscles
• lower esophageal sphinter (LES)/cardiac sphincter controls opening of esophagus into stomach
• pyloric sphincter - controls opening of stomach into
small intestine (duodenum)
– gastric reflux – sphincter working improperly causing
heartburn
– Stomach wall
• Gastric mucosa
– Rugae – folds in lining of the stomach
• gastric glands – below rugae; secrete most of gastric
juice
– chief cells – secrete the enzymes of gastric juice
– parietal cells - secrete HCl
» Zantac – reduces HCl formation in stomach
– endocrine cells – secrete gastrin
• Gastric muscularis – thick layer of muscle that allows
stomach to contract
•
•
•
•
•
•
Helicobacter pylori – bacteria that causes peptic ulcers
Stomach lining replaces itself every 3 days
Chyme – liquefied food; form that food leaves the stomach
Gastroenteritis – stomach inflammation
Emesis – vomiting
35 million digestive glands in the stomach
Gastroesophageal Reflux
Gastric Ulcer
Small Intestine
• Proximal to stomach
duodenumjejunumileum
• Microvilli (villus) allow for
absorption (increase surface
area by hundreds)
• Where majority of substances
are absorbed
• 22 feet long
• Food can stay here for up to 4
hours
Large Intestine
Large Intestine
• Proximal to small intestine
cecum ascending colontraverse colondescending
colonsigmoid colon rectum
• Haustra – pouchlike structures
• Constipation – movement of lower colon and rectum
contents at a rate slower than normal
• Diverticulosis – outpouchings of intestinal wall
• Colitis – inflammation of large intestine
• 5 feet long
• Waste stays 10-12 hours
• Main function is water absorption in order to eliminate
feces
Appendix and Peritoneum
• Vermiform Appendix
– function not fully known; but thought to provide safe
place for good bacteria
– appendicitis
• inflammation of appendix
• not common in elderly
• appendectomy – surgical removal of appendix
• Peritoneum
– large, continuous sheet of serous membrane
– parietal and visceral portions
– mesentery – extension of parietal peritoneum that
anchors GI tract to abdominal wall.
Liver
•
Anatomical units – lobes and lobules
–
–
–
left lobe
right lobe – biggest section of liver
hepatic lobules – branch of hepatic vein extends through each lobule (main anat unit)
•
•
•
Common bile duct – merger of the hepatic duct and cystic duct
Produces bile
–
–
•
Blood flows to hepatic lobules via branches of the hepatic artery and hepatic portal vein
Bile salts – aid in the absorption of fats; most essential part of bile
No enzymes
Functions of liver
– Detox
– Bile secretion – secrete 1 pint/day
– Metabolizes proteins, fats,
and carbohydrates
•
Misc. Info
– Hepatic refers to liver
– Largest gland in the body
– Hepatitis – inflammation of the liver
– Cirrhosis – degenerative liver
condition
– Removes harmful substances from
the blood
– Stores vitamins and sugars until your
body needs them
•
Gallbladder
– Stores bile (holds 30-50 ml bile)
– Cholecystokinin (CCK) – hormone that stimulates gallbladder to release
bile into duodenum (small intestine)
– Cholelithiasis - gallstones
– Cholecystectomy – surgical removal of gallbladder
– Below liver
– Pear shaped
Cholelithiasis - Gallbladder with
yellow cholesterol gallstones
Cholecystectomy
Gallbladder before removal
•
Pancreas
– Both endocrine and exocrine gland
– Pancreatic juice secreted by exocrine acinar cells
– Pancreatic cancer – form of adenocarcinoma
– Breaks down sugar
– Beta cells secrete insulin
Digestive Physiology
Mechanical Digestion
--Mastication
--Deglutition
--Peristalsis
Oral stage – mouth to oropharynx
- voluntary control
- bolus formed
- soft palate acts as valve to prevent
food from enetering
nasopharynx
Pharyngeal stage – oropharynx to
esophagus
- involuntary control
- epiglottis prevents bolus from
entering larynx to trachea
Esophageal stage – esophagus to
stomach
- involuntary control
Peristalsis
•wavelike ripple of smooth muscle
•ring of contraction occurs where GI wall is
stretched, pushing bolus forward
•stimulated by CCK – secreted by endocrine cells
in presence of chyme
Segmentation
•mixing movement
•forward and backward movement that
mechanically breaks down food and mixes it with
digestive juices
Organ
Mouth (teeth and tongue)
Pharynx
Esophagus
Stomach
Small Intestine
Ascending and
Transverse Colon
Descending Colon
Rectum
Mechanical
Process
Mastication
Deglutition
Deglutition
Deglutition
Peristalsis
Churning
Peristalsis
Segmentation
Peristalsis
Segmentation
Peristalsis
Mass peristalsis
Defecation
Chemical Digestion
Digestive enzymes
a. extracellular, organic (protein) catalysts
b. enzyme action
1. specificity
2. optimal pH
Stomach
pH
3.0
Jejunum
Ileum
Colon
6.0-7.0
7.5
6.8-7.3
3. catalyst
4. continually destroyed or eliminated,
so constantly being made
Digestive Enzyme Action
•proenzyme altered by kinase to form active enzyme
1. kinase removes prosthetic group to expose active
site
2. substrate (food) binds to active site of active
enzyme
3. enzyme splits substrate into components and
releases them
4. enzyme can now digest new substance
Carbohydrate digestion
(bread, potato, rice, pasta, fruit, vegetables)
•Starch and sugar are broken down by saliva,
pancreatic and small intestinal juices
salivary amylase,
pancreatic juices
* starch
small intestine
enzymes
maltose
absorbed into blood
glucose (monosac)
liver (stored or used)
small intestine enzymes
* sugar (sucrose)
glucose + fructose
absorbed into blood
* fiber – undigestible
•Cellulose cannot be broken down; eliminated in
feces
Pepsin
Trypsin
Lipid Digestion
•emulsification – bile breaks down fat
into small droplets within the small
intestine
•Steatorrhea - impaired fat absorption
producing large, greasy, foul-smelling
stool
micelle
•Fat-soluble vitamins – A, D, E, K
(stored in liver and fatty tissue)
•Pancreatic lipase – main fatdigesting enzyme
Digestive Juice
Enzyme
Substance
Digested
End Product
Saliva
Salivary
amylase
Starch
(polysacc)
Maltose (disacc)
Gastric Juice
Protease
(pepsin)
Protein
Partially digested protein
Pancreatic Juice
Protease
(trypsin)
Proteins
Peptides and a.a.
Lipase
Fats
Fatty acids, glycerol
Pancreatic
Amylase
Starch
(polysacc)
Maltose
Peptidases
Peptides
a.a.
Sucrase
Sucrose
Glucose, fructose
Lactase
Lactose
Glucose, galactose
Maltase
Maltose
Glucose (monosacc)
Intestinal
Disorders
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Mumps
Tooth Decay
Malocclusion
GERD (gastroesophageal reflux disease)
Ulcers
Pyloric stenosis
Appendicitis
Hemorrhoids
Proctitis
Diabetes
Gastroenteritis
Anorexia
Nausea
Emesis
Diarrhea
Constipation
Malabsorption
Diverticulitis
Colitis
Irritable Bowl Syndrome
Colorectal Cancer
Hepatitis
Cirrohsis
Pancreatitis
Pancreatic cancer