Mouth to Stomach

Question 1

Describe anatomical components oral cavity, function in chewing

Answer 1

lips: guide/retain food within oral cavity
tongue: guide food during chewing (keep bolus under teeth) and during swallowing. skeletal, voluntary
palate: roof of cavity, separate from nasal.
teeth: tearing, grinding, mixing

chewing- breaks into smaller pieces, mixes bolus with saliva, stimulates taste buds

chewing is initially voluntary, then reflexive (reflexive skeletal muscle contraction of jaw, lip, cheek, tongue mediated by sensory afferents)

Question 2

describe components of salivary secretions

Answer 2

produced by parotid, submandibular and sublingual glands
= 99.5% water, 0.5% electrolytes and protein (amylase which, lysozyme, mucus)
fluid- stimulate buds, aid in speech, keep mouth clean
mucus- thick/slipper glycoprotein helps food bind in bolus, lubricates it
amylase- breaks down poly –> maltose. initiates carb digestion
lysozyme- lyses cell wall bacteria, protect
HCO3-: acts as buffer, prevent carries

Question 3

motility- describe sequence of events contributing to, and controlling swallowing

Answer 3

1. oral phase: pushing food bolus toward back of oral cavity and up against palate. requires tongue (voluntary)
2. pharyngeal: pharynx located at posterior of oral cavity, at its junction with nasal passages. touch/pressure receptors activated by bolus, send info to medulla via CNV. initiates reflexive component
3. esophageal- swallowing center relaxes pharyngoesophageal sphincter. swallowing center initiates primary peristaltic waves by interacting with ENS

Question 4

identify nutrients/substances that are digested in mouth, how?

Answer 4

minimal. digestion occurs in mouth, pharynx, esophagus bc of amylase

Question 5

role esophagus in swallowing. what is peristalsis

Answer 5

connects pharynx –> stomach
large ring of circular muscle, a sphincter at each end
pharyngoesophageal sphincter closed except during swallowing to prevent air entering stomach

primary peristalsis: inner circular layer of muscularis externis contracts. outer longitudinal contracts, propagates along esophagus, pushing luminal contents to stomach. takes 5-9 sec

secondary: reflexive, does not involve swallowing center. luminal contents become lodge, stimulates ENS, strong wave.

gastroesophageal sphincter opens when wave pushes bolus against region. reflexive relaxation

Question 6

anatomical components of stomach, function for each

Answer 6

fundus: portion lying above gastroesophageal sphincter
body: middle
antrum: distal, thick muscularis externa

Question 7

differentiate btw gastric filling, storage, mixing processes in stomach. state the control mechanism

Answer 7

filling- stomach reflexively relaxed upon food entry “receptive relaxation”. mediated via short loop ENS inhibition muscularis externa.

storage- food stored in body. weak persistaltic contractions move it toward antrum by contractions resulting from fundal pacemaker cells

mixing- slow wave propagation and muscularis externa contractions generate powerful antral peristaltic waves, force toward pyloric sphincter. result in mixing. pyloric sphincter open enough to let small amounts liquids through. solid contents diverted back

Question 8

describe processes gastric emptying, why regulated

Answer 8

volume of chyme entering duodenum. depends on

• strength contraction of pyloric sphincter
• # peristaltic waves / time

gastric contents are v acidic, duodenum needs basic envir. stomach receives variable input, needs stable enviro to duo… therefore tight regulation

influenced by gastric (amount of chyme, fluidity) and duodenal factors (ENS, ANS, CCK,gastrin, secretin) to control strength/rate. influenced by modulation of slow waves in SM cells of muscularis externa

Question 9

differentiate btw gastric glands and pits, list products secertes

Answer 9

pits/glands = infoldings of mucosa
divided into oxyntic mucosa lining fundus/body and
pyloric gland area lining antrum

pit = neck at the top, continuous with glands
gland = secretes

Question 10

describe gastric exocrine secretions, functions, control

Answer 10

• mucus secreted from mucous cells in gastric pits. lubricate, inhibits pepsin to protect against auto-digest, neutralizes acid
• HCL from parietal cells in gastric glands of oxyntic mucosa. converts pepsinogen –> pepsin, breakdowns connective tissue/fibers, breaks teritary structure proteins, kills micoorganisms
• intrinsic factor from parietal cells in gastric glands. required for absorption Vit B12, RBC formation
• pepsinogen from chief cells in gastric glands of oxyntic mucosa. activated by HCl, cleaves peptide bonds

Question 11

describe gastric paracrine and endocrine secretions, function, factors controllin

Answer 11

1. Histamine from ECL cells in gastric glands of oxyntic mucosa in response to ACh, gastrin. stimulates parietal cell H+ production
2. gastrin from G cells in gastric glands of PGA

Question 12

explain carb/protein digestion

Answer 12

carb: begins in mouth with amylase, continues in food bolus as it is stored in body of stomach. no further amylase secreted by stomach
protein: result from pepsinogen and acid exposure in antrum

Question 13

does stomach absorb nutrients?

Answer 13

stomach absorbs:
EtOh- partially liq soluble, diffuse across epithelial membrane, enter blood
aspirin- weak acid remain un-ionized in acidic gastric juice, making it lipid soluble