L6: Digestive 1

Question 1

Digestive system overview of function

Answer 1

responsible for processing, digestion, and absorption of food material

also elimination of wastes or indigestible residue

Epithelium lining of digestive tube and associated glands is derived from endoderm

gut lining secretes mucus which functions to aid passage of contents down the digestive tract, protect against corrosive HCL and protect against enzymatic degradation of epithelial lining

Question 2

what are the 3 general sections of the digestive tract

Answer 2

oral cavity (mouth)

digestive tube (esophagus, stomach, small and large intestines)

digestive glands (pancreas and liver)

Question 3

Tongue and oral cavity (epithelium, submucosa structure)

Answer 3

lined by stratified squamous epithelium (nonkeratinizing); except keratinized on gums, dorsal surface of tongue, and hard palate

epithelium (mucosa) underlain by submucosa of dense irregular CT with collagen and elastic fibers

• contains small mucous and mucoserous glands (in submucosa). These glands secrete mucus and digestive enzymes (salivary amylase –> breaks down carbs)
• underlying CT is immunologically active (tonsils=collections of lymphoid tissue in submucosa in pharynx region)

Question 4

Muscles of the tongue

Answer 4

composed of skeletal muscle sheathed in a mucous membrane continuous with that of the oral cavit

muscle fibers are both intrinsic (confined to the tongue) and extrinsic (originate outside of tongue)

between muscle fibers are mucous glands (at base of tongue), serous glands (in the body of the tongue), and mixed acinar glands (at tip of tongue)

serous glands of the tongue are called von Ebner’s glands= act to wash taste buds free of stimulus molecules to allow new tasting

Question 5

Von ebner’s glands

Answer 5

act to wash taste buds free of stimulus molecules to allow new tasting

Question 6

Lingual papillae

Answer 6

projections of mucosal surface with submucosal core

anterior 2/3 of the tongue covered with these

Question 7

filiform papillae

Answer 7

located over entire surface, slender and conical

Question 8

fungiform

Answer 8

located singly among rows of filiform, more numerous towarsd tip.

mushroom shaped with secondary papillae of CT

Question 9

circumvallate

Answer 9

only 10-14 in humans
located along central sulcus of tongue

surrounded by circular furrow

taste buds present in lateral walls

Question 10

foliate papillae

Answer 10

leaf-like folds on posterolateral margins

taste buds occur in grooves between folds

rudimentary in humans

well developed in rabits

Question 11

tongue muscle: dorsoventral intrinsic

Answer 11

move tip of tongue

Question 12

tongue muscle: lateral intrinsic

Answer 12

move tongue sideways, cup tongue

Question 13

tongue muscle: extrinsic

Answer 13

protrude tongue

Question 14

taste buds

Answer 14

barrel-shaped neuroepithelium (taste receptor cells, sustentacular cells, basal cells); opens via taste pore

Question 15

taste receptor cells

Answer 15

chemoreceptors, respond to dissolved molecules

Question 16

salivary glands, general

Answer 16

compound exocrine glands, developed from epithelial lining

Question 17

Parotid salivary gland

Answer 17

located below and anterior to ear in humans

ducts open to cheek opposite 2nd upper molar, ducts prominent

serous secretion (enzymes [amylase] and polysaccharides)

compound tubuloalveolar

enclosed by dense irregular CT capsule

secretory unit empties to intercalary duct –> secretory ducts (modify ionic composition) –> excretory ducts –> main duct

divided into lobes and lobules by septa (from capsule)

Question 18

submandibular salivary gland

Answer 18

lies in floor of mouth beneath the body of the mandible (lower jaw)

duct opens below tip of tongue- ducts prominent

mixed secretion (mostly serous)

mucous secretory units often capped with cresent-shaped serous demilunes

compound alveolar or tubuloalveolar, encapsulated.

Question 19

sublingual salivary gland

Answer 19

lies underneath tongue

multiple ducts open near submandibular ducts, fewer ducts within the gland.

mixed secretion (mucous predominates)

compound tubuloalveolar

CT capsule less well-developed

Question 20

4 regions of the digestive tube

Answer 20

Divided into 4 regions (organs) by sphincters
(muscular valves)…

1. Esophagus
2. Stomach
3. Small Intestine
4. Large Intestine (colon)

Question 21

4 layers of the digestive tube

Answer 21

1. mucosa
2. submucosa
3. muscularis externa
4. serosa (adventitia)

Although all regions of the digestive tract show common structural arrangement, each particular region is modified according to its function.

Question 22

Mucosa of the digestive tube

Answer 22

3 layers:
epithelial membrane- lubricated by mucus.
lamina propria,
muscularis mucosae,

Question 23

lamina propria (mucosa)

Answer 23

underlying loose CT layer (rich in BV and lympathics, lymphatics involved in fat transport)

tends to become lymphoid (with lymph nodules)

Question 24

Muscularis mucosae (mucosa)

Answer 24

thin layer of smooth muscle forming boundary

contractions cause folding of mucous membrane

Question 25

Mucosa of the small intestines

Answer 25

shows finger-like projections or folds into lumen termed villi- act to greatly increase surface area for absorption/digestion. invaginations of epithelium form intestinal glands or "crypts" and gastric glands (stomach)

Question 26

submucosa

Answer 26

Loose CT between muscularis mucosae and muscularis externa • Supplied with blood vessels and lymphatics • Often contains accumulation of lymphoid tissue • Contains nerve plexus of autonomic fibers and ganglion cells = Meissner's Plexus - innervates muscularis mucosae • Contains mucus secreting glands in esophagus and duodenum of small intestine

Question 27

meissner's plexus

Answer 27

innervates muscularis mucosae

Question 28

muscularis externa

Answer 28

Consists of ≥ 2 layers of smooth muscle, more substantial than m. mucosae • Striated muscle replaces smooth in upper esophagus (associated with swallowing) • Layers: generally inner circular (constricts lumen), outer longitudinal (shortens gut, widens lumen) • Innermost oblique layer occurs in stomach • M. externa responsible for peristalsis → moving food along tract • Between inner circular and outer longitudinal layers lies Aeurbach's Plexus = Autonomic nerve fibers and ganglion cells - innervates m. externa, mostly parasympathetic

Question 29

aeurbach's plexus

Answer 29

autonomic nerve fibers and ganglion cells - innervate m externa, mostly parasympathetic

Question 30

serosa/adventitia

Answer 30

Outermost layer composed of somewhat denser areolar CT with elastic fibers • When lined by mesothelium = serosa, when outside of body cavity (retroperitoneal, portions of small intestine) = adventitia • Contains many blood vessels, lymphatics, nerves

Question 31

Describe the esophagus

Answer 31

Relatively straight tube extending from oral cavity to stomach, functions mainly in rapid transport of food • Mucosal epithelium is nonkeratinizing str. squamous in humans; in herbivorous mammals (swallow rough material) keratinized str. squamous is usually present • At upper and lower ends, mucosal glands (cardiac glands) present in lamina propria (secrete mucus) • Submucosal mucous glands present throughout

Question 32

Muscularis externa of the esophagus

Answer 32

upper esophagus: composed of skeletal muscle. middle esophagus: smooth begins replacing skeletal. lower esophagus: smooth musclein inner circular-outer longitudinal arrangement

Question 33

Esophagus submucosa/mucosa empty vs full

Answer 33

empty: folds in these layers extending into lumen full: distended response is allowed by prominent elastic fibers in submucosa (similar to remainder of digestive tract)

Question 34

stomach: 3 regions, function.

Answer 34

Muscular-walled reservoir capable of retaining food and digestion/absorption of food • Consists of 3 regions histologically: – Cardiac (anterior) – Fundic – Pyloric (posterior) • Food enters stomach as bolus of semisolid material, exits as chyme = semifluid pulp-like mass Absorption limited to salts, water, glucose, alcohol and some drugs • Gastric Juice secreted by stomach contains HCl, mucus, pepsin (a proteolytic enzyme), lipase (fat catabolism), rennin (curdles milk) • Submucosal/Mucosal folds into lumen

Question 35

Mucosal epithelium of the stomach: gastric glands, pits, and cardiac glands.

Answer 35

Mucosal epithelium = simple columnar, contains: – Gastric Glands = simple tubular or branched tubular glands – Gastric Pits = open to surface, 2 or 3 glands empty into one pit – Cardiac Glands = only for short initial portion of cardium, mucus-secreting, gastric glands short, gastric pits long; glands coiled and dilated with large lumen

Question 36

Rugae

Answer 36

submucosal/mucosal folds into the stomach lumen when empty

Question 37

surface of the stomach is lined with..

Answer 37

mucous columnar cells

Question 38

mucous neck cells of the gastric glands

Answer 38

found in "neck" region of gland, mucussecreting (acid mucopolysaccharides, proteoglycans, GAGs); basal cytoplasm basophilic, apical granules stain with PAS (contains carbohydrates)

Question 39

Parietal cells of gastric glands

Answer 39

scattered singly or in small groups throughout the length of gland acidophilic or pale cytoplasms secrete HCl

Question 40

chief cells in gastric glands

Answer 40

found at base of gland basophilic cytoplasm due to high number of ribosomes, secrete pepsinogen (converted to pepsin by HCl), protein hydrolysis is the result. Lipase--> lipid digestion

Question 41

Enteroendocrine cells

Answer 41

``` = found at base of gland; usually with clear unstained cytoplasm (stain with Ag2+, Cr2+; secrete serotonin, peptide hormones involved in digestion (secretin → stimulates pancreas secretion, gastrin → stimulates HCl secretion, cholecystokinin → stimulates pancreatic enzyme secretion), endorphins; ``` release secretion to lamina propria

Question 42

Germinative zone of gastric glands

Answer 42

occurs at isthmus/neck junction continuously replaces dead mucous columnar cells of pit and surface

Question 43

Cardiac glands (pit/gland lengths)

Answer 43

long dilated pits | short gastric glands

Question 44

Fundic glands (pit/gland length)

Answer 44

short pit | long gland

Question 45

Pyloric glands (pit/gland length)

Answer 45

long pits | medium glands