GI Anatomy and Physiology

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1

List digestive system functions:

  • Movement
  • Secretion
  • Digestion
  • Absorption
  • Circulation
  • Nervous and Hormonal control
2

List the organs of the alimentary canal:

  1. Mouth
  2. Pharynx
  3. Esophagus
  4. Stomach
  5. Small intestine
  6. Large intestine
  7. Anus
3

List the accessory organs of the GI:

  1. Tongue
  2. Salivary gland
  3. Liver
  4. Pancreas
4

Mechanical breakdown of food in the GI involves:

  • Chewing
  • Churning
  • Segmentation
5

Propulsion of things through the GI involves:

  • Swallowing
  • Peristalsis
6

Absorption of nutrients primarily occurs where?

Small intestine

7

Absorption of water primarily occurs where?

Large intestine

8

Innermost layer of epithelial cells that

  • secretes mucus, digestive enzymes and hormones
  • Absorb digestion products into blood
  • Protect against infectious dz

Mucosa

9

List the structures located in the mucosa

  • Epithelium
  • Lamina propria
  • Muscularis mucosae
10

Part of the mucosa with a rich lining of mucus secreting cells

Epithelium

11

Part of the mucosa that is connective tissue and mucosa-associated lymphoid tissue (MALT) containing lymphocytes, plasma cells, and macrophages

Lamina propria

12

Part of the mucosa that produces local movement

Muscularis mucosae

13

Dense connective tissue that contains part of the enteric nerve system; elastic fibers that allow stretching

Submucosa

14

Responsible for segmentation and peristalsis (longitudinal/circular muscle), contains part of the enteric nerve system

Muscularis externa

15

Outermost protective layer, visceral peritoneum, consisting of squamous cells.

Serosa

16

T/F: The oral cavity, pharynx, and rectum have adventitia instead of serosa

True

17

Local constriction of the small intestine and, to a lesser extent, the large intestine to mix food w digestive juices and increase exposure to the intestinal wall

Segmentation

18

Alternating waves of contraction and relaxation of smooth muscle to propel food through the GI tract

Peristalsis

19

Contract and relax to control movement or holding of luminal content

Sphincters

20

T/F: Segmentation and peristalsis are phasic, while sphincters are tonic

True

21

What kind of muscle is involved in segmentation?

Circular

22

Describe the "Law of the Gut"

Peristaltic reflex pushes intestinal contents from the oral to the aboral direction

23

Describe the three steps in peristalsis

  1. Contraction of circular muscle behind food mass
  2. Contraction of longitudinal muscle ahead of food mass
  3. Contraction of circular muscle layer forces food mass forward
24

List the three major types of GI control

  1. Neural - enteric nervous system
  2. Hormonal - peptides produced by endocrine cells
  3. Local - physical, chemical, pH
25

T/F: The ENS possesses afferent, efferent , and interneurons and has an abundance of short reflexes.

True

26

List the two major plexuses of the ENS

  1. Myenteric plexus (Auerbach's)
  2. Submucosal plexus (Meissner's)
27

Which plexus is responsible for contraction and relaxation of GI tract smooth muscle (GI motility)

Myenteric plexus (Auerbach's)

28

Which plexus is responsible for secretory and absorptive functions as well as local blood flow?

Submucosal plexus (Meissner's)

29

When stimulated, the main effects of the Myenteric plexus (Auerbach's) are:

  1. ↑ tonic contraction ("tone") of gut wall
  2. ↑ intensity of rhythmical contractions
  3. slight ↑ rate of rhythm of contraction
  4. ↑ velocity of conduction of excitatory waves along gut wall
30

Where is the Myenteric plexus (Auerbach's) plexus located?

bw circular and longitudinal muscle layers along length of gut

31

Where is the Submucosal plexus (Meissner's) located?

Submucosa of small and large intestine

32

T/F: Intrinsic primary afferent nerves involved in sight, smell, taste, or the thought of food eventually acts through the extrinsic primary nerves and can induce GI secretions. This is why you may salivate at the thought of your favorite food

False

33

Summarize the movement of the GI tract:

  1. Bolus brushes against EC cells causing 5HT to be released
  2. 5HT binds receptors on IPANs activating interneurons in the myenteric plexus
  3. Ascending excitatory interneurons in circular muscle cause contraction in ascending (oral) side of bolus via motor neurons
  4. Descending inhibitory interneurons in circular muscle cause relaxation in descending (aboral) direction via motor neurons
  5. Bolus moves aborally
34

Which NT almost always inhibits GI activity?

NE

35

Neuropeptide from tachykinin family that serves as a cotransmitter w ACh. Stimulates smooth muscle contrations

SP

36

High concentrations of 5HT in the gut can lead to:

N/V

37

Stimuli responsible for the release of 5HT:

  • Stretch (intraluminal distention/food ingestion)
  • Vagal nerve stimulation
  • Osmolarity, pH of contents
  • End products of digestion (taste receptors)
  • Infection
  • Cytotoxic cancer agents
38

List the roles of 5HT

  1. Signaling - Stimulates intrinsic nerves to initiate reflexes or extrinsic nerves to initiate their responses
  2. Produce motor fxns - acts directly on smooth muscle to initiate contration or release mucosal secretions
  3. NT - released to act on other neurons to release excitatory/inhibitory mediators such as ACh, NO, VIP
39

T/F: All 5HT receptors are GPCR except 5HT2 which is a ligand-gated ion channel

False

40

Which 5HT receptors are in GI tract on enterocytes, enteric neurons, GI smooth muscle, and immune cells?

1-4, 7

41

Which 5HT receptor is found on intrinsic primary sensory afferents and can cause depolarization of the afferent nerves when stimulated?

5HT1P

42

Which 5HT receptor is located on intrinsic and extrinsic primary sensory afferents and stimulation causes depolarization of these nerves?

5HT3

43

Which 5HT receptor is located presynaptically on post-ganglionic nerves to ENHANCE release of ACh and can cause an increase in GI secretions. Also involved in peristaltic reflex

5HT4

44

Which 5HT receptor releases inhibitory substances such as VIP and NO

5HT1A

45

Summarize GI motility in the submucosal plexus ascending pathway:

  1. EC cells respond to stimuli by releasing 5HT
  2. 5HT binds 5HT1P on IPANs
  3. IPANs release ACh which binds to nicotinic receptors on enteric interneurons in submucosal plexus
  4. Enteric interneurons release ACh to ascending motor neurons
  5. Motor neurons release ACh to M3 receptors (and SP to NK1 receptors) on smooth circular muscle causing contraction
46

Summarize GI motility in the submucosal plexus descending pathway:

  1. EC cells respond to stimuli by releasing 5HT
  2. 5HT binds to 5HT1P receptors on IPANs
  3. IPANs release ACh which binds to nicotinic receptors on enteric interneurons in the submucosal plexus
  4. Enteric interneurons release ACh to descending motor neurons
  5. Motor neurons release NO and VIP to smooth circular muscle causing relaxation
47

Summarize GI motility in the myenteric plexus (longitudinal muscle)

  1. EC cells respond to stimuli by releasing 5HT
  2. 5HT binds to 5HT3 receptors on IPANs
  3. IPANs release ACh which binds to nicotinic receptors on enteric interneurons in the myenteric plexus
  4. Enteric interneurons release 5HT (and probably ACh) to motor neurons
  5. Motor neurons release ACh to longitudinal smooth muscle causing contraction (relaxation is possible through another mechanism, but contraction is predominant)
48

T/F: Longitudinal contraction prevents bulging

True

49

Summarize GI motility in the myenteric plexus (long reflex)

  1. EC cells respond to stimuli by releasing 5HT
  2. 5HT binds to 5HT3 receptors on EPANs
  3. Action potentials are carried to the CNS via the vagus nerve and can result in nausea, vomiting, or pain through the medulla oblongata.
  4. Efferents interact with myenteric or submucosal plexuses causing contraction, relaxation, secretion, etc.
50

List the three classes of hormone signaling in GI:

  1. Endocrine - circulation (Gastrin)
  2. Paracrine - local (5HT, his)
  3. Neurocrine - secreted by neurons (NE, ACh)
51

List the roles of GI hormones:

  1. Muscle tone
  2. Secretions
  3. Absorption
  4. Tissue growth
  5. Release of other hormones
52

Hormones are ____________ secreted by ______________

Peptides; enteroendocrine cells

53

Which hormone:

  • Stimulates gastric acid release
  • releases histamine
  • stimulates growth of gastric mucosa
  • May inhibit gastric emptying

Gastrin

54

Which hormone:

  • secretion of bicarbonate & water from pancreatic ducts
  • secretion of bile from liver
  • may inhibit gastric emptying – Nature’s Antacid

Secretin

55

Which hormone:

  • release of bile from gallbladder
  • secretion of pancreatic enzymes from acinar cells
  • may inhibit gastric emptying
  • inhibits acid secretion in the stomach

Cholecystokinin (CCK)

56

Which hormone:

  • slows stomach motility and secretions (Enterogastrones)
  • releases insulin

Gastric inhibitory Peptide (GIP)

57

Which hormone:

  • stimulates overall GI tract motility during interdigestive period

Motilin

58

List the pancreatic secretions

  1. Protease
  2. Lipase
  3. Amylase - starch hydrolysis
  4. Water and bicarb
  5. insulin
59

List the liver secretions:

  1. Bile
  2. Bile salts
60

Where is bile stored?

Gallbladder

61

__________ stimulates bicarb secretion (therefore bile) from the liver and bicarb from the pancrease

Secretin

62

_______ causes the contraction of gallbladder and inhibits stomach emptying

Cholecystokinin (CCK)

63

CCK relaxes sphincter of _______

Oddi

64

A concretion in the gallbladder or a bile duct, composed chiefly of a mixture of cholesterol, calcium bilirubinate, and ca carbonate; may cause jaundice and acute pancreatitis

Gallstones