Lab 10: The Digestive System

order of structures of alimentary canal

1. mouth

2. pharynx

3. esophagus

4. gastroesophageal sphincter (GES)

5. stomach

6. pyloric sphincter

7. small intestine

8. ileocecal valve

9. large intestine

10. anus

order of structures in the intestines

1. pyloric sphincter

2. duodenum

3. jejunum

4. ileum

5. ileocecal valve

6. cecum

7. ascending colon

8. transverse colon

9. descending colon

10. sigmoid colon

11. rectum

12. anal canal

parietal peritoneum

lines the outer abdominal wall

visceral peritoneum

lines the digestive organs themselves

mesentery

supports the small intestine

greater omentum

hangs between stomach and transverse colon like a fatty apron

lesser omentum

hangs between liver and lesser curvature of stomach

mesocolon

supports large intestine

retroperitoneal organs in digestive system

1. esophagus

2. kidney

3. portions of large intestine: cecum, appendix, ascending + descending colon, rectum

esophagus

1. function: peristalic contractions to move food from pharynx to stomach

2. stratified squamous

3. longitudinal + circular muscle

stomach

1. mechanical + chemical breakdown

2. simple columnar

3. gastric pits

4. longitudinal, circular, oblique

5. rugal folds

small intestine

1. absorption of nutrients into bloodstream and chemical digestion

2. simple columnar

3. peyer’s patches, villi, microvilli

4. lacteals

5. longitudinal, circular

6. circular folds

large intestine

1. contraction + storage of stool; nutrient + water resorption

2. simple columnar

3. longitudinal + circular

4. haustra, epipolic appendages, teniae coli

3 types of folds that maximize the SA of small intestine

1. circular folds

2. villi

3. microvilli

vitamins that are produced and absorbed in the large intestine

1. vitamin K

2. vitamin B

amount of baby teeth on maxilla + mandible

10 on each

how many adult teeth on the maxilla + mandible

16 on each

Incisors

shearing, cutting, biting

Canines

gripping, tearing, ripping

Pre-molars

crushing, tearing, grinding

molars

crushing, grinding, breaking down food into smaller pieces

3 sets of salivary glands

1. parotid

2. submandibular

3. sublingual

which set of salivary glands empties saliva by the upper molars

parotid

how does saliva aid in digestion

1. chemical breakdown (amylase + lipase)

2. dissolves food particles, allowing them to interact with taste buds

organ that makes bile

liver

organ that stores and secretes bile

gallbladder

alkalinity of pancreatic enzymes serves what purpose

neutralizes acidic chyme

pancreatic fluids are secreted into which part of the small intestine

duodenum

if a gallstone gets stuck in the opening where the bile duct enters the small intestine, which other organ will have the backup of its secretion?

pancreas—condition is gallstone pancreatitis

are the same organs retroperitoneal in cats as in humans

no organs are retro in cats

main functions of the digestive system

1. take in food

2. break it down into nutrient molecules

3. absorb molecules into bloodstream

4. rid body of any indigestible remains

alimentary canal

continuous muscular tube that runs from mouth to anus

functions of the AC

1. digests food: breaks down into smaller fragments

2. absorbs fragments through lining into blood

organs of the AC

1. mouth

2. pharynx

3. esophagus

4. stomach

5. small intestine

6. large intestine

7. anus

where does the AC constrict

sphincter

where does the AC dilate

stomach

accessory glands of the AC

1. salivary glands

2. tongue

3. teeth

4. pancreas

5. liver

6. gallbladder

teeth + tongue function

mechanical breakdown

digestive glands

produce secretions that help break down foodstuffs

salivary glands function

moisten food

liver function

1. produces bile

2. filters blood

3. stores glycogen

pancreas function

1. endocrine: secretes insulin and glucagon

2. exocrine: secretes H

why is it beneficial to have non-keratinized stratified squamous epithelium in the mouth, esophagus, and anus

1. many layers

2. resistance to abrasions and friction

why is it beneficial to have simple columnar epithelium in the stomach, small intestine, and large intestine

1. apical side faces lumen of AC

2. basal side faces bloodstream

3. one-way absorption of molecules

membrane proteins =

transporters

functions of saliva

1. cleanses mouth

2. dissolves food chemicals for taste

3. moistens food; compacts into bolus

4. begins breakdown of starch with enzyme amylase

major salivary glands include

1. parotid

2. submandibular

3. sublingual

parotid

1. anterior to ear and external to masseter muscle

2. Parotid duct opens into oral vestibule next to second upper molar

submandibular

1. medial to body of mandible

2. Duct opens at base of lingual frenulum

sublingual

1. anterior to submandibular gland under tongue

2. Opens via 10–12 ducts into floor of mouth

teeth location

lie in sockets in gum-covered margins of mandible and maxilla

mastication

process of chewing that tears and grinds food into smaller fragments

dentition and the dental formula

1. all but 3rd molars (wisdom teeth) are in by end of adolescence

2. 3rd molars may or may not emerge around 17-25 years of age

incisors

rip/tear flesh of apple

canines

pierce flesh

premolars (bicupsids)

grind flesh

molars

best at grinding flesh due to “fit”

impacted tooth

1. a tooth that remains trapped in the jawbone

2. Can cause a good deal of pressure and pain

3. Wisdom teeth are most commonly involved.

4. Treatment: surgical removal

propulsion

involuntary, smooth muscle contractions propel and breakdown ingested food through GIT via peristalsis and segmentation

peristalsis

1. adjacent segments of the AC alternately contract and relax

2. food is moved along the tract

3. primarily propulsive

segmentation

1. nonadjacent segments of the AC contract and relax

2. back-and-forth sloshing mixes food and breaks it down mechanically

4 layers of AC

1. mucosa

2. submucosa

3. muscularis externa

4. serosa

mucosa functions

1. secretion

2. absorption

3. protection

submucosa

1. structural and elastic functions

2. contains blood and lymph vessel and nerve fibers

muscularis externa

1. deep circular layer (can form sphincters)

2. superifical longitudinal layer of smooth muscle for peristalsis and segmentation

serosa

1. made up of the visceral peritoneum

2. formed from alveolar CT covered with mesothelium (single layer of squamous epithelium) in most organs

peritoneum

1. serous membranes of abdominal cavity that consists of:

2. Visceral peritoneum: membrane on external surface of most digestive organs

3. Parietal peritoneum: membrane that lines body wall

Peritoneal cavity (the abdominopelvic cavity)

1. Fluid-filled space within the parietal peritoneum

2. Fluid lubricates mobile organs

mesentery functions

1. double layer of peritoneum; layers are fused back to back

2. Extends from posterior of abdominopelvic cavity wall to digestive organs

3. Provides pathway for blood vessels, lymphatics, and nerves

4. Holds organs in place and also stores fat

intraperitoneal organs

located within the peritoneal cavity

retroperitoneal organs

1. located outside, or posterior to, the peritoneum

2. Includes most of pancreas, duodenum, and parts of large intestine

Food passes from mouth to

oropharynx and then into laryngopharynx

pharynx function

1. Allows passage of food, fluids, and air

2. Stratified squamous epithelium lining with mucus-producing glands

3. External muscle layers consists of two voluntary skeletal muscle layers

4. inner layer of muscles runs longitudinally

5. Outer pharyngeal constrictors encircle wall of pharynx

esophagus

flat muscular tube that runs from laryngopharynx to stomach

esophagus is … when not involved in food propulsion

collapsed

Gastroesophageal sphincter GES

1. Keeps orifice closed when food is not being swallowed

2. Mucus cells on both sides of sphincter help protect esophagus from acid reflux

digestive processes in the stomach

1.Serves as holding area for food

2.Carries out mechanical breakdown of food (churns)

3.Denatures proteins using acidity (HCl)

•Denature means breaks bonds so unfolds proteins

4.Goblet cells secrete mucous to protect lining from acid (HCl)

5.Pepsin carries out enzymatic digestion of proteins

•Milk protein (casein) is broken down by rennin in infants

•Results in curdy substance

6.Delivers chyme to small intestine

anatomy of stomach

microscopic structure of esophagus

accessory organs are associated with small intestine

1. liver

2. gallbladder

3. pancreas

bile

fat emulsifier

pancreas function

supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid

small intestine

1. located between pyloric sphincter+ ileocecal valve

2. 20 feet long when relaxed

3. 3 divisions: duodenum, jejunum, ileum

circular folds

Permanent folds that force chyme to slowly spiral through lumen, allowing more time for nutrient absorption

villi

Fingerlike projections of mucosa with a core that contains dense capillary bed and lymphatic capillary called a lacteal for absorption

microvilli

Cytoplasmic extensions of mucosal cell that give fuzzy appearance called the brush border that contains membrane-bound enzymes brush border enzymes, used for final carbohydrate and protein digestion

Small intestine modifications and lymphoid nodules pattern

the abundance of small intestine modifications decrease in number over the small intestine, the number of Peyer’s Patches increase

teniae coli

three bands of longitudinal smooth muscle in muscularis

haustra

pocket-like sacs caused by tension of teniae coli

epiploic appendages

fat-filled pouches of visceral peritoneum

subdivisions of large intestine

1. cecum

2. appendix

3. colon

4. rectum

5. anal canal

cecum

first part of large intestine (retroperitoneal)

appendix

1. masses of lymphoid tissue

2. retroperitoneal

3. MALT

4. Bacterial storehouse capable of recolonizing gut when necessary

5. Twisted shape of appendix makes it susceptible

4 portions of colon

1. ascending—retro

2. transverse

3. descending—retro

4. sigmoid

ascending colon

travels up right side of abdominal cavity to level of right kidney

transverse colon

travels across abdominal cavity

descending colon

travels down left side of abdominal cavity

sigmoid colon

S-shaped portion that travels through pelvis

rectum

1. retro

2. 3 rectal valves stop feces from being passed with gas

anal canal

1. last segment of large intestine that ends at anus

2. 2 sphincters: internal and external