Unit 15: Digestive System Flashcards
(37 cards)
What does the digestive system include?
1) Gastrointestinal (GI) tract
- tube from mouth to anus
2) Accessory organs
- teeth, tongue, salivary glands, pancreas, liver, gall bladder
What are the processes of the digestive system?
1) Ingestion
- food into oral cavity
2) Digestion
- large molecules broken down into smaller molecules
- 2 types:
a) mechanical = physical breakdown and motility (ex. =
chewing)
b) chemical = enzymes and acid secretions
3) Absorption
- end products of digestion enter blood or lymph
4) Defecation
- elimination of undigested material
What are the different parts of the digestive system - oral cavity and pharynx?
Oral cavity, salivary glands, dentition, oropharynx and laryngopharynx
Info on the oral cavity
Lined by a mucosa (mucous membrane) made of a stratified squamous epithelium and lamina propria. Includes:
a) lips
b) cheeks
c) palate
i. hard palate = 2 maxillae and 2 palatine bones
ii. soft palate (posterior to hard palate) = skeletal muscle,
and posterior projection is uvula which rises to close the
nasopharynx when swallowing
d) tongue
- attached to hyoid bone
- skeletal muscle
- projections of mucosa = papillae (taste buds)
Info about salivary glands
3 pairs:
a) parotid = inferior and anterior to ears; mumps = inflammation of 1 or both parotids
b) submandibular = floor of mouth
c) sublingual = below tongue on floor of mouth
- saliva = 99.5% water, and 0.5% solutes (ex. = enzymes)
Info about dentition (teeth)
- in maxillae and mandible
- child dentition = primary - deciduous (“baby”) teeth
- adult dentition = secondary - permanent teeth
*see chart on pg. 2 for number/types of teeth
Tooth structure:
a) crown = ABOVE the gum, dentin forms majority of tooth, enamel overlay is acellular, highly calcified = hard!
b) root = dentin w/ a cementum overlay
NOTE: dentin, enamel, and cementum is sim. to bone, but avascular
c) neck = enamel and cementum boundary (gums)
d) periodontal ligaments = attach root to bones
e) root canal extends to pulp cavity = contains CT, blood/lymph vessels, and nerves
Info about oropharynx and laryngopharynx
Only muscularis externa (skeletal muscle) and stratified squamous epithelium
What are the 4 basic layers of the gastrointestinal tract histology (esophagus to rectum)?
Mucosa, submucosa, muscularis externa, and serosa or adventitia.
Cavity = lumen.
Info about mucosa
1) Mucosa - 3 layers:
a) epithelium w/ numerous goblet cells
- stratified squamous: esophagus, anal canal
- simple columnar: stomach, small and large intestines,
rectum
b) lamina propria (areolar CT)
- contains blood, lymph vessels, lymph nodules/tissues
(immune)
c) muscularis mucosa
- smooth muscle - allows mvmt. of mucosa
Info about submucosa
- areolar CT
- contains: blood, lymphatic vessels, and a network of nerve cells
Info about muscularis externa
= 2 layers of smooth muscle separated by a second network of nerve cells
- inner circular layer (contraction constricts the lumen)
- outer longitudinal layer (contraction shortens gut length)
- contractions controlled by the nerve network cause motility (mixing and movement)
Upper 1/3 = skeletal muscle
Middle 1/3 = skeletal and smooth muscle
Lower 1/3 = smooth muscle
Info about serosa or adventitia
Serosa = double walled membrane
General info about the peritoneum
- serous membrane that lines the abdominopelvic cavity and MOST of the abdominal organs
- structure of serosa:
1) visceral peritoneum (against organ wall)
2) parietal peritoneum (against abdominal cavity wall)
3) peritoneal cavity (space btw. parietal and visceral
peritoneum)
- filled w/ serous fluid that minimizes friction btw. parts
of the digestive tract during motility
What are the two specializations of the peritoneum?
1) omenta
- folds of serosa btw. organs made of a sheet of 2 fused layers of VISCERAL peritoneum
- contains blood/lymph vessels and nerves
- examples:
a) greater omentum (“fatty apron”) - connects to
transverse colon, and forms large fold that hangs down
over transverse colon and small intestine
b) lesser omentum - connects liver to stomach
2) mesentery
- fold of serosa btw. the posterior abdominal cavity wall and the small/large intestine made of a sheet of 2 fused layers of PARIETAL peritoneum
- entry and exit point for blood vessels, nerves, and lymphatic vessels supplying digestive organs
What are the retroperitoneal organs?
- located posterior to the parietal peritoneum
- peritoneum lines only one side of the organ
- e.g. pancreas, duodenum
- anterior surface is covered by parietal peritoneum
- posterior surface is covered by adventitia that connects
the organ to the body wall
What are the parts of the digestive system (esophagus to anus)?
Esophagus, stomach, small intestine, large intestine
Info about the esophagus
- posterior to trachea
- passes through the diaphragm entering into the abdominal cavity
- histology of esophagus transitions from superior to inferior:
a) muscularis externa
- Upper 1/3 = skeletal muscle
- Middle 1/3 = skeletal and smooth muscle
- Lower 1/3 = smooth muscle
b) the outer layer is adventitia w/in thoracic cavity and
serosa w/in the abdominal cavity
General info about the stomach
- stores, partially digests, and regulates emptying of CHYME (food and gastric juices) into the small intestine
- has 4 regions:
a) cardiac region (cardia) = attached to interior esophagus
b) fundus = superior to esophageal entrance
c) body = middle portion
d) pyloric region (pylorus = gatekeeper) = inferior portion
of the stomach; the pyloric sphincter regulates release of
stomach contents into small intestine
What are the unique histological features of the stomach?
Mucosal surface
a) formed exclusively by mucous cells
b) has millions of gastric pits (invaginations of the epithelium) that are connected to underlying gastric glands
- gastric glands are exocrine glands that secrete gastric
juice into the gastric pits where it then enters the lumen
of the stomach
- gastric glands contain the following cell types:
a) goblet cells
b) chief cells - secrete enzymes for protein and fat digestion
c) parietal cells - secrete hydrochloric acid (HCI) which lowers
the pH of the stomach
d) G cells (enteroendocrine cells)- secrete a hormone INTO the blood that regulate activity
of parietal cells and other digestive processes
- secrete a hormone INTO the blood that regulate activity
Info about the rugae and muscularis externa of the stomach
1) rugae = folds of mucosa and submucosa due to contraction of muscularis mucosa
- visible when stomach is empty
- allows expansion of stomach w/out tearing
2) muscularis externa
- function = churning chyme
- 3 layers instead of 2:
i. INNER OBLIQUE
ii. middle circular
iii. outer longitudinal
General info on the small intestine
- pyloric sphincter to ileocaecal valve
- where most food digestion/absorption occurs
- histology = simple columnar epithelium 3 main cell types:
a) enterocytes = simple columnar cells (absorptive cells that form most of the mucosa)
b) goblet cells: secrete mucus
c) enteroendocrine cells:
i. located w/in intestinal glands
ii. secrete hormones into the blood that help regulate
digestive processes
What are the 3 segments of the small intestine?
a) duodenum
- first fold (short) - is retroperitoneal
- extra glands here secrete alkaline mucous to protect against stomach acid
- ducts of accessory organs (liver, gall bladder, pancreas) enter the digestive system here
b) jejunum
- middle section
c) ileum
- attached to caecum (part of large intestine)
- has groups of lymph nodules called Peyer’s patches
- prevent infection of small intestine and prevent bacteria
from entering blood
What are the segments of the small intestine specialized to increase absorption of surface area?
a) plicae circulares - submucosa thrown into large folds
b) villi - projections of mucosa into lumen of small intestine; contains blood capillaries and lacteals (are lymphatic capillaries that absorb fats)
c) microvilli - projections of the enterocyte cell membranes (so ARE part of the cell) that extend into the lumen of the small intestine, forming a fuzzy “brush border” on the surface of the mucosa
What is the general information about the large intestine?
- ileocaecal valve to anus
- basic functions:
a) absorption of water, electrolytes, vitamins
b) formation and temporary storage of feces - histology = mucosa has smooth surface w/ no folds or villi
