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123 terms

Davis: Digestive System

Digestive System
Digestive System
converts food to usable form and moves it to the bloodstream
Functions of the Digestive System
1. Ingestion
2. Digestion
3. Mechanical Digestion
4. Chemical Digestion
5. Absorption
6. Elimination
Mechanical Digestion
1. break down of large particles into small food particles
2. Achieved by teeth and digestive juices
Chemical Digestion
1. breakdown of small food particles via enzymes into food molecules
2. Via mouth by saliva and finished in the small intestine
uptake of organic molecules, water, electrolytes and other nutrients
removal of undigested material and waste products
Removes cellulose and bacteria
Structures of the Digestive Tract or Alimentary Canal
continuous tube that begins with mouth and ends with
1. anus
2. Oral cavity
3. Pharynx
4. Esophagus
5. Stomach
6. Small intestine
7. Large intestine
8. Rectum
9. Anus
Role of Accessory Organs
play a role in the process of digestion
Accessory Organs to Digestive Tract
1. Teeth
2. Tongue
3. Liver
5. Gallbladder
6. Salivary glands
7. Pancreas
study of the digestive system
study of the colon and the large intestine
Gastrointestinal Tract
1. Stomach
2. Small Intestine
3. Large Intestine
4 Tissue Layers of Digestive Tract - outer to inner most tunics
1. Serosa
2. Muscularis
3. Submucosa
4. Mucosa
Ct layer, immediately beneath peritoneum
2 sheets of smooth muscle with a bundle of nerves (myenteric plexus) between sheets
a. Movement of digestive tract
b. Controlled by Enteric Nervous System
thick layer of CT
a. Contains lots of nerves, BV, and small digestive glands
b. Controlled by Enteric Nervous system
lining of digestive system
a. Directly opens to lumen of digestive tract
b. Mucus membrane
c. Carries out secretions and absorption of digestive tract
serous membrane which covers the inside walls of abdominal cavity and most abdominal organs
1. Most digestive organs are covered by the peritoneum
2. Secretes lubricating fluid
a. Parietal Peritoneum - forms lining of body walls
b. Visceral Peritoneum - covers the organs
c. Peritoneal Cavity - space between with peritoneal fluid
sheets of CT that suspend most of the organs in abdomen
a. Mesentery Proper - supports small intestine
b. Lesser Omentum - binds liver and stomach to diaphragm
c. Greater Omentum - supports transverse colon by binding it to the stomach
i. Contains long double fold on stomach that holds fat - omental bursa - "Fatty apron"
Organs that are Retroperitoneal
not suspended in peritoneum
a. Kidneys
b. Urinary bladder
c. Adrenal glands
d. Rectum
e. Ascending and descending colon
f. Pancreas
g. Duodenum - part of small intestine
inflammation of abdominal cavity due to abdominal infections
a. Results from surgery or injury
b. Fast acting infection
Oral Cavity
i. Bounded anteriorly by lips
ii. Laterally by cheeks
iii. superiorly by hard palate
iv. inferiorly by muscular wall
v. posterior fasces (openings) connect to oropharynx
2 Chambers in the oral cavity
1. Vestibule
2. Oral Cavity Proper
front of mouth, space between lips and cheeks, and alveolar processes, teeth
Oral Cavity Proper
anything behind the teethe
muscular structures, orbicularis muscles
1. Fleshy structures with thin skin (blood vessels give the pink color)
2. Frenula
tissue piece that is bound to alveolar processes
Functions of the Labia
a. Hold food
b. Form words through sound
c. Conveyor of facial expression
1. hold food
2. Shape words
3. made of Buccinators muscles
4. contain Buccal fat pads - give the rounded shape of cheeks
primary teeth
deciduous teeth
a. Fall out when as you get older
b. Erupt 6 mo-24 mos.
c. Fall out at 5-11 years and replaces with Secondary teeth
d. Kids grow 20 deciduous teeth
Secondary teeth (Permanent Teeth)
1. Replaced by mid adolescence except for Wisdom teeth - erupt between 24-32 years
2. Adults have 32 permanent teeth
species that grow multiple types of teeth
Dental Formula
on rt and left sides, top and bottom
1. 2-1-2-3
2. Incisors (2) - cutting teeth, 1 root
3. Canines (1) - tearing teeth, 1 root
4. Premolars (2) - grinding teeth, 2 roots
5. Molars (3) - crushing teeth, 4 roots
Tooth Structure
1. Crown - top surface
2. Contains an enamel - hard substance
3. Calcified Tissue - dentin
4. Pulp - surrounds cavity with soft tissue, receives blood vessels
5. Caries or Cavities
6. Roots - bounded to alveolar processors to CT Tissue
Functions of teeth
a. Primary organ for mastication
i. Beginning of mechanical digestion
ii. Enlarging S. A. of chemical digestion
b. Shape voice
c. Digestion
large muscular organ
1. Posteriorly attached to hyoid bone
2. Anterior portion is free moving
3. Phrenulum - binds floor of mouth to bottom of tongue
Functions of the Tongue
a. Primary speech organ
b. Primary gustation organ (taste)
c. Holds food and moves it during mastication
d. Shapes your food into a ball - bolus
e. Pushes bolus into oropharynx
3 Pairs of Salivary Glands
a. Parotid - large, anterior to ears and above the jaw
b. Submandibular - 1 on each side of jaw base
c. Sublingual - beneath the tongue
d. There are also many little ones like coiled tubes in epithelium of mouth
Functions of Salivary Glands
secrete saliva
1. mixture of serous and mucus fluids
2. 1 L produced per day
3. Contains 2 types of enzymes
- Salivary Amylase - carb digester
- Lingual Lipase - fat digester
4. Overall facilitates 5% of digestion in the mouth
1. Keeps oral mucosa moist
2. Facilitates gustation (taste)
3. Lubricate food to pass to pharynx
4. Antibacterial function - lysozymes that kill bacteria in the mouth
5. Begins process of digestion
Salivation Reflex
autonomic response
1. Closely tied to sensory data
2. Begins with taste, smell, sight, and thought of food
Pharyngeal Constrictors
1. within the oropharynx, 3 pairs of smooth muscles that push food downward
2. Lined with stratified squamous epithelium to resist against abrasion
What type of tissue is Laryngopharynx lined with?
1. Lined with stratified squamous epithelium to resist against abrasion
1. Regulated by pons and medulla oblongata
2. 3 Phases
3 phases of Deglutination
a. Voluntary Phase
b. Pharyngeal Phase
c. Esophageal Phase
Voluntary Phase
tongue pushes bolus against hard palate and moves it into oropharynx
Pharyngeal Phase
reflexive, unconscious control
i. Soft palate elevates to close nasopharynx
ii. Oropharynx elevates to receive bolus of food
iii. Pharyngeal constrictors contract to force food into laryngopharynx
iv. At the same time, epiglottis folds posteriorly to close glottis to prevent food from traveling into respiratory tract
v. Upper Esophageal sphincter - pressure against will open it to push food into esophagus
Esophageal Phase
movement of food from esophagus to stomach, longest phase
d. Moves food via peristalsis
e. Lower Esophageal Sphincter will open when food is pressed on it and move into the stomach
long muscular tube
i. 25 cm long
ii. Anterior to vertebral column, posterior to trachea
iii. Thick wall with 4 tunics
iv. Superior end - made of skeletal muscle for voluntary control
v. Inferior end - made of smooth muscle for unconscious control
vi. Inner layer - lined with mucus to move food
vii. Upper Esophageal sphincter
viii. Lower esophageal sphincter - boundary between esophagus and stomach
ix. Esophagus passes through diaphragm through an opening - Hiatus
Hiatal Hernia
1.condition where the stomach bulges over the diaphragm due to injury, congenital diseases, or digestive diseases
ii. Causes lower esophageal sphincter to improperly close leading to back flow of gastric juices into esophagus
Hiatal Hernias lead to..
a. Reflux
b. Esophagitis
c. Gastritis
d. Stomach ulcers
immediately inferior and slightly behind the heart
i. Between esophagus and small intestine
ii. Sac-like, bean shaped when full
1. Expands up to 2 liters
iii. Floppy when empty
iv. Cardia - upper region
v. Fundus - curved region superior to cardia
vi. Pyloric Part - inferior end
vii. 2 curvatures - greater (left side facing) and lesser (rt side facing)
viii. Diaphragm is superior
ix. Pancreas is inferior
x. Lesser omentum - binds stomach to diaphragm
3 Sheets of Stomach smooth muscle tissue
1. Churns contents
2. Vertical - outer longitudinal
3. Horizontal - middle circular
4. Oblique - middle oblique
Submucosa and Mucosa layers of the stomach have?
1. Rugae
2. Gastric pits
gastric folds
a. Expands when needed
b. Made of simple columnar epithelium - not able to absorb
Gastric Pits
small openings that lead to gastric glands
Functions of the Stomach
1. Mixing chamber using gastric juices
2. Form acidic liquid with food - chime
3. Stores fluid and slowly releases into small intestine
4. Absorption is a tertiary function
Gastric Juice
1. Mucus - lubrication of stomach and protects its lining from acid
2. HCl - breaks down food, pH <2
3. Pepsinogen - protein that turns into pepsin in the presence of HCl
a. Pepsin - breaks down proteins
4. Intrinsic Factor - aids reabsorption of B-12
5. Gastrin - regulates other stomach secretions
6. Histamines - ensures good blood flow
7. Body produces 2-3 L/ day
Phases of Gastric Juice Release
a. Cephalic Phase - begins in response to sensory stimuli that will secrete gastric juices
b. Gastric Phase - stimulated by movement of food, caffeine, or alcohol
i. Elevated level of gastric juices
c. Gastrointestinal Phase - secretion decreases when food leaves the stomach
Contractions of the stomach
1. Churns once every 20 sec. by weak contraction - mixing waves
a. Performs 80% of action
2. Peristaltic Waves - forceful churns
a. Performs 20% of action
b. Forces chime to pyloric sphincter during peristaltic waves, chime will slowly secrete into pyloric sphincter.
c. Empties in 2-6 hours
i. Carbs are broken down the fastest
ii. Fats are the slowest
Stomach growling
mixing waves occurring when the stomach is empty
a. Hunger pains - mixing waves start to cause pain
Heart Burn
1. acid reflux
2. Originates in cardiac region of the stomach
3. Reflux of acid chyme into esophagus
4. Causes painful burning sensation
Causes of Heart Burn
i. Overeating, especially fatty foods
ii. Lying down after eating
iii. Alcohol, caffeine, or nicotine can trigger reflux
iv. Tight clothing - constricting stomach to push chime into esophagus
v. Stress
vi. Hiatal Hernias
Gastroesophageal/Reflux Disease (GERD)
1. chronic acid reflux
2. caused by Stress, Poor diet, Long term smokers and alcoholics, Caffeine, and Hiatal hernias
forceful ejection of stomach content due to irritation of stomach lining
a. Overfilling of GI tract
b. Toxins and bacteria can cause irritation of mucosa of stomach lining
c. Sensory stimuli can stimulate vomiting - usually sights or smells of decay
How does the body vomit?
d. Stomach will contract to push contents into esophagus
e. Undergo reverse peristalsis
f. Reflexively take a deep breathe
g. Glottis will close
h. Soft palate closes nasopharynx
i. Upper esophageal sphincter opens
j. Diaphragm will forcefully contract
Small Intestine
primary organ of digestion and absorption
i. Narrow tube, highly coiled (5.5-6m long)
ii. Bounded by mesenteries
iii. Peritoneal, only duodenum is retroperitoneal
iv. 3 Regions (proximal to distal)
1. Duodenum
2. Jejunum
3. Ileum
1. proximal end attaches with stomach- 25cm long
2. Originates at pyloric sphincter
3. Ends at bend of jejunum
4. Walls contain openings of small ducts that lead to pancreas and liver
5. High level of mucus protection, protects against chime
6. Chemical digestion is primarily completed
7. Lining is heavily folded with circular folds
Circular Folds of Duodenum contain?
surface are covered with fingerlike projections - villi
i. Villi contain hair like projections - microvilli
ii. Absorbs nutrients
How do the villi absorb nutrients
1. Contains lots of capillary beds
2. Lymphatic capillaries - lacteals absorbs lipids
3. Increases available surface area for absorption
4. Villi and microvilli increase absorption by 600 fold
structurally similar to duodenum
a. Narrows further along and decreases in circular folds along tube
a. Continues to absorb, less folds as tube narrows
b. Contains peyer patches to kill off bacteria
c. Terminates at Ileocecal Sphincter - opens into large intestine
d. Ileocecal Valve - prevents back flow from large intestine to small intestine
Movement of the Small Intestine
v. Movement is by Peristalsis - local reflex
1. 2 types of contractions - Segmental Contraction and Peristaltic Contraction
Segmental Contractions
small amount of movement
i. Mix chyme and pancreatic juices
Peristaltic Contraction
squeeze chyme through small intestine
Large Intestine
i. Begins at Ileocecal Junction
ii. Ends at anus
iii. Cecum - proximal end
iv. Verbiform Appendix
v. Colon
vii. Rectum
Functions of Large Intestine
1. Convert non-digestive material into feces to be removed
2. Major role in reabsorption of water and salts, in chyme
3. Breaks down some vitamins and nutrients like vitamin K and milk solids
1. Receiving chamber for non-digested material
2. 6cm long
3. receives non-digestible fibers, Bacteria (living and dead), and Cellular Debris
Verbiform Appendix
1. Permanent patches of lymphatic tissue
2. Vestige that can be removed
inflammation due to obstruction or bacterial infection
b. Sudden sharp abdominal pain
c. In lower rt quad
Mc Burney's Point
- 1/3 between ilium and naval
makes up most of large intestine
1. 1.5-1.8 m long
2. Ascending Colon - cecum to liver
3. Rt. Colic Flexure - fold of rt. colon
4. Transverse Colon
5. Left Colic Flexure - bend of transverse colon
6. Descending Colon - inferior spleen to pelvis
7. Sigmoid Colon
8. Teniae Coli
9. Epiplocic Appendages
10. Haustra
11. Crypts
Transverse Colon
bound to greater omentum
a. Runs under small intestine
b.From liver to spleen
Sigmoid Colon
s-shaped colon
a. Bounds medially and inferiorly to rt.
Teniae Coli
-band of smooth muscle that contracts to move feces through colon
Epiplocic Appendages
fatty deposits along Teniae Coli
pouches on colon
a. Holding places for feces
small straight glands that release mucus to lubricate and bind feces
a. Some absorption of water and salts
straight muscular tube with thick muscularis
1. Narrows to anal canal - 2-3 cm in length
Anal Canal
a. Storage chamber for feces
b. contains Internal Superior Anal Sphincter - smooth muscle sphincter
c. Contains External Inferior Sphincter -at anus
i. Skeletal muscle for conscious control
undigested material from food
1. Made of mucus, water, bacteria, debris
gas byproduct
Movement of the Large Intestine
i. Slow peristalsis that occurs in response to taste and smell of food
ii. Distension of the stomach
1. Entry of chyme through duodenum
iii. Occurs for 30-40 minutes stops, and restarts after 8-12 hours
iv. Later, commonly occurs in the morning
unabsorbed water due to inflammation and muscle thickening of colon which cannot absorb water
Defecation Reflex
stimulated by distension of fecal wall.
1. Stretch receptors send a signal to the spine which will relay a message to put pressure on the internal anal sphincter to push on external anal sphincter
a. Similar to Micturition Reflex
b. Body is able to control when the defecate
1. largest internal organ
1. 1.4 kg in average adult
2. Located upper right quad of abdomen
3. Rests on inferior surface of diaphragm
4. Surrounded by CT capsule
5. Bare area - place that touches diaphragm no CT protection
External Division of Liver
i. 2 lobes (anterior) - joined by falciform ligaments
ii. 2 lobes (posterior) - quadrate and caudate lobes - joined to left lobe of liver, separated by fold of greater omentum
1. Inferior vena cavae is between lft lobe and caudate
2. Gallbladder is between rt lobe and quadrate
iii. Between caudate and quadrate lobes - Porta Hepatis
Internal Division of Liver
8 segments
i. Unrelated to external lobes, overlap into each lobe
ii. Functionally independent of each other and can be removed individually
iii. Most regenerative, damaged lobe can regenerate
Porta Hepatis
is an opening for nerves, BV, and liver ducts within the liver
cells of the liver
Porta Hepatis
blood passes through via Hepatic Artery and Hepatic Portal Vein
i. RT and Left Hepatic ducts carry bile from gallbladder to duodenum
Functions of the Liver
i. Bile production
ii. Storage
iii. Engages in Nutrient Interconversion
iv. Detoxification
v. Phagocytic
vi. Synthesis Functions - Produces proteins
Proteins That are made in the Liver
a. Albumin
b. Globulins
c. Heparin
d. Clotting factors
e. Fibrinogen
f. Hormones
Phagocytic Function of the Liver
1. Macrophages that phagocytize worn out blood cells, RBC and WBC - participates in immune clearance
2. Converts bilirubin into bile
3. Gobbles cellular debris and bacteria
breaks down harmful compounds informs that can easily be removed
1. Ammonia into urea
2. Alcohol into simple sugars
3. Breaks down any type of drugs
Nutrient Interconversion
1. Converts 1 organic molecule into another
2. Breaks amino acids - Deamination - into Glucose or ATP
3. Changes glucose to glycogen
4. Converts anything into fat
5. Breaks down fatty acids via beta oxidation to form ATP
6. Turns triglycerides into phospholipids
7. Changes lactic acid into glucose
Storage Function of the Liver
hepatocytes store vitamins and minerals
1. Fe, Cu, Zn, Vitamins K, B-12, D, E, K
2. Stores glycogen - excess glucose, 800-1200Kcal
Bile Production
makes bile, yellowish green fluid
1. Composed of bilirubin, cholesterols, fatty acids, and several hormones released into duodenum
2. Dilutes and neutralizes pancreatic juices
Hepatic Portal System
exists because of liver's role in processing nutrients
i. Capillary bed surrounding small intestines absorbs nutrients
ii. De-Oxy blood with nutrients are carried to the liver via Hepatic Portal Vein
iii. Portal Triads - point where hepatic portal vein, hepatic artery that contains Oxy blood empties into Hepatic Sinusoids
1. Capillary beds on the liver 2nd set of capillary beds
a. Nutrient and gas exchange occur
2. Blood exits via hepatic vein carrying De-oxy blood out of the liver
Production and Movement of Bile
1. Made by hepatocytes channeled away by bile canaliculi - channels that collect bile and transport to portal triads
2. Hepatic Duct - carry bile away from triads
a. Comprised of many small ducts
b. Converge to form rt and left hepatic ducts
c. Empty into common hepatic duct
i. Some bile is also directly emptied into gallbladder via cystic duct
3. Cystic Duct and common hepatic duct form common bile duct and Pancreas also sends pancreatic juice from pancreatic duct join to - leaves liver and arrives at Hepatopancreatic Ampulla (outside duodenum)
4. Then leads away from major duodenal papilla - empties both secretions into duodenum
sac-like organ posterior to liver
1. 8cm long, 4 cm wide, expandable
2. Serosa and muscularis layers
3. Inner mucosa has ruggae
4. Hepatocytes funnel excess bile into the gallbladder
5. Holds 40-70 mL of bile
6. Concentrates bile by adding bile salts
7. 95% of bile salts are reabsorbed in duodenum to travel back to liver
caused by hypercholesterolemia - condition in which body does not remove excess cholesterol
i. Can shift out of gallbladder and cause obstruction to cystic or pancreatic ducts
ii. Can require removal of gallbladder
iii. Removal of gallbladder will result in the body breaking down fats more slowly
1. Elongated spongy organ
2. 15cm long and 100g
3. Beneath and posterior to stomach
4. Head tucked in curve of duodenum
5. Tail runs into stomach
6. Endocrine and exocrine functions
a. Produce insulin and glucagon
cluster of exocrine cells that produce a fluid, pancreatic juice
i. Aqueous part is high in bicarbonate
ii. Enzymatic part - Secreted in inactive form and will activate in the presence of HCl
Pancreatic amylase - carb digester
Pancreatic Lipase - lipid digester
Nucleases - breaks nucleic acids
Proteolytic Enzymes - breaks proteins
i. Defecation < 2x/wk.
ii. Caused by
1. Dehydration
2. Diseases of intestinal tract
3. Changes in diet
4. Obstruction of colon
5. Frequent delays in defecation
6. Spinal cord injuries
7. Depression
Colon Polyps
inflamed growths on inside of colon
1. Develops as you age
2. More common in men
3. Causes
a. Digestive pain
b. Diarrhea
c. Left untreated can lead to cancer
Colon Cancer
2nd most deadly cancer
1. Can be prevented by high fiber diet - requires 25-35g/ day
2. Can be sneaky - isn't noticeable until too late
Crohn's Disease
1. Localized inflammation of digestive tract
2. Mainly affects colon and ileum
3. Progressive condition
4. Autoimmune condition
Ulcerative Colitis
inflammatory disorder
1. Autoimmune
2. Inflammation - edema mainly in the colon
3. Hemorrhaging of large intestine and rectum
4. Similar symptoms to Crohn's Disease
5. Signs, blood in feces
Irritable Bowel Syndrome (IBS)
1. Abnormal intestinal movements
2. Pain in lover left quad
Symptoms of IBS
a. Constipation and diarrhea
b. Correlated with environmental stress
c. Affects women more
d. Can be an inherited factor
e. No known physiological markers
f. Only diagnosed by symptoms
Causes of Crohn's Disease
a. Abdominal pain
b. Persistent fever
c. Extreme weight loss
d. Diarrhea