Gastrointestinal System Flashcards Preview

MD2001 > Gastrointestinal System > Flashcards

Flashcards in Gastrointestinal System Deck (64):
1

What is the primary function of the GI?

Absorption of dietary nutrients, a process maximised by secretions added along the "tube" that convert large molecules to smaller ones - digestion

2

What are other functions of the GI system?

+ Storage
+ Excretion

3

What is the mucosa?

A single cell layer forming a continuous inner lining of GI tract

Mucosa = epithelium + lamina propria + muscularis mucosa

4

How often is the mucosal epithelia shed and replaced?

Every 2-3 days

5

Where does the apical side of the mucosal epithelium layer face?

GI lumen

6

Where does the basolateral side of the mucosal epithelium layer face?

Interstitium & vasculature

7

What are features of the mucosa in regards to the muscularis mucosa?

+ Thin layer of smooth muscle

+ Further increases surface arrea by creating ridges and folds

8

What are the features of the mucosa in regards to villi and crypts?

+ Extent of villi and crypts vary with GI section function e.g absorption vs motility

9

What are the features of the mucosa in regards to the lamina propria

+ Loose CT made up of elastin & collagen fibres

+ Contain sensory nerves, blood & lymph vessels, and secretory glands

10

What are the 4 different GI layers?

1. Mucosa
2.Submucosa
3. Muscularis externa (ME)
4. Serosa

11

What are features of the submucosa layer of the GI?

+ Thick layer with similar compostition to lamina propria

+ Incorporates blood vessels and nerve bundles that form a submucosal plexus (Meissner plexus - integral part of enteric nervous system

12

What are features of the muscularis externa (ME) layer of the GI?

ME = circular muscle + myenteric plexus + longitudinal muscle (Auerbach plexus)

+ Muscle layers named based on circulation

+ ENS co-ordinated contractions to mix and move contents between compartments

+ Sphincters regulate flow from one compartmetn to the next

13

What is the ENS?

Enteric nervous system: a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system

14

What are features of the Serosa layer of the GI

+ Outermost layer of CT and layer of squamous epithelial cells

+ Some GI tract sections do not have a serosal layer (e.g oesophagus) but connect directly with adventitia (i.e CT that blends into abdominal or pelvic wall)

15

Gi function is regulated by which 3 divisions of the autonomic nervous system (ANS)?

+ Parasympathetic (PSNS)
+ Sympathetic (SNS)
+ Enteric (ENS)

16

Where is innervation derived from in the PSNS?

+ Vagus (medulla oblongata)
+ Pelvic-splanchnic nerces (S2-S4)

17

What do the sensory and motor components of the PSNS respond to?

+ Stretch
+ Pressure
+ Temperature
+ Osmolarity

18

In the PSNS, what primary NTs are used?

+ Acetylcholine (ACh)
+ Gastric releasing peptide
+ Substance P

19

What is the role of the PSNS in the GI system?

PSNS stimulates:
- GI secretions
- motility facilitating digestion
- absorption of nutrients

20

Where do the nerves of the SNS originate?

+ T5-T12
+ L1-L3

21

Where do the nerves of the SNS synapse?

In 1 of 3 ganglia:
- celiac
- superior mesenteric
- inferior mesenteric
(for lower GI system)

22

What are features of the SNS?

+ Upper GI tract innervates by nerves that synapse in superior cervical ganglion

+ Generally decreases GI secretions and motility

23

What are features of the ENS?

+ PSNS & SNS usually synapse with ENS components and modulate the ENS

+ But ENS can operate autonomously via intrinsic regulation & sensory reflexes

+ ENS nerves are organised into myenteric & submucosal plexuses

24

What are features/functions of the myenteric plexus?

+ A dense parallel neuronal configuration

+ Primary role of regulating intestinal smooth muscle

+ Participates in tonic & rhythmic contractions

25

What are features/functions of the submucosal plexus?

+ Primarily regulates intestinal secretions & local absorptive environment

+ Can also synapse on blood vessels, circular & longitudinal muscle, muscularis mucosa

26

What are ENS neurones supported by?

Enteric glial cells - resemble brain astrocytes

27

What are the plexuses of the ENS?

+ Myenteric
+ Submucosal

28

How are reflex actions in the ENS regulated?

+ Neural circuits involving mechanoreceptor/chemoreceptor stimulation in the mucosa regulate many GI reflex actions

+ Signal transmitted back to neurons in submucosal plexus, which stimulate other neurons in submucosal or myenteric plexus that regulate endocrine or secretory cells

29

What are some NTs of the ENS?

+ Enkaphalins: constrict circular muscle around sphincters
+ VIP, substance P, ACh, nitric oxide, serotonin (5-hydroxytryptamine (5-HT))

30

What hormones are involved in the GI system?

+ Cholecystokinin (CCK)
+ Glucose-dependent insulinotropic peptide
+ Gastrin
+ Motilin
+ Secretin

31

What are the 1) releasing cells, 2) associated structures and 3) functions of CCK?

1. I cells

2. Pancreas, gallbladder, stomach

3. Increases enzyme secretion; contracts gallbladder; increases gastric emptying

32

What are the 1) releasing cells, 2) associated structures and 3) functions of glucose-dependent insulinotropic peptide?

1. K cells

2. Pancreas, stomach

3. Releases insulin; inhibits acid secretion (H+)

33

What are the 1) releasing cells, 2) associated structures and 3) functions of gastrin?

1. G cells

2. Stomach

3. Increases gastric acid secretion (H+)

34

What are the 1) releasing cells, 2) associated structures and 3) functions of motilin?

1. M cells

2. Gastrointestinal smooth muscle

3. Increases contractions and migrating motor complexes

35

What are the 1) releasing cells, 2) associated structures and 3) functions of secretin?

1. S cells

2. Pancreas, stomach

3. Releases HCO3-, water and pepsin, decrease gastric acid H+

36

What are features of paracrines involved in the GI system?

+ Released and act locally

+ Prostaglandins & somatostatin are more widespread in their release and actions than histamine

37

What paracrines are involved in the GI system?

+ Histamine
+ Prostaglandins
+ Somatostatin

38

What are the 1) releasing cells, 2) associated structures and 3) functions of histamine?

1. Enterochromaffin-like cells, mast cells

2. Stomach

3. Increases gastric acid secretion (H+)

39

What are the 1) releasing cells, 2) associated structures and 3) functions of prostaglandins?

1. Cells lining GI tract

2. Mucosa

3. Increases blood flow and mucus and HCO3- secretion, decreasing gastric acid (H+) secretion and maintaining GI barrier properties

40

What are the 1) releasing cells, 2) associated structures and 3) functions of somatostatin?

1. D cells

2. Stomach and pancreas

3. Inhibits peptide hormones and gastric acid secretion (H+)

41

Which GI NTs & NMs contract the wall muscle?

+ ACh
+ Substance P
+ Enkephalins

42

Which GI NTs & NMs relax the wall muscle?

+ Norepinephrine
+ Neuropeptide Y
+ Vasoactive intestinal peptide

43

What are the 3 digestive phases?

+ Cephalic
+ Gastric
+ Intestinal

44

What is involved in the cephalic phase of digestion?

+ Triggered by thought of food, conditions suggestive of previous food intake

+ Primarily neural & causes ACh & VIP release
- stimulates secretion by salivary glands, stomach, pancreas, intestines

45

What is involved in the gastric phase of digestion?

+ Begins when food and oral secretions enter stomach

+ Coincides with distension

+ Elicits neural, hormonal, paracrin GI response

46

What is involved in the intestinal phase of digestion?

+ Begins when stomach contents reach duodenum

+ Initiates primarily hormonal, but also paracrine & neural responses

47

What is secretion?

The act of transporting molecules or fluid from the body to the GI lumen

48

What is the role of the upper GI tract?

+ Minimal role in nutrient absorption

+ Transports and prepares food to be absorbed
- i.e breaking into smaller pieces, hydrating it to improve environment for enzymatic actions

49

What is the role of the mouth and associated structures?

Mouth: mechanical + chemical breakdown
- mastication = chewing

Teeth: cut, tear & pierce, crush and grind
- jaw muscles provide force and movement

Tongue: repositions food, tastes

50

What are features of the salivary glands and their secretions?

+ Saliva:
- watery fluid lubricates mouth - begins food digestion
- protective

+ 1-1.5 L saliva/day mainly by sblingual, submandibular and parotid glands

+ Hypotonic to plasma
- composition determined by ductal modification of primary secretion

51

What is peristalsis?

+ Series of co-ordinated muscle contractions/relacxtions (waves)

+ Commences after upper oesopheageal sphincter

+ Journey takes ~6-10s

52

What is the function of the stomach?

+ Accept & stores food
+ Mix food with secretions
+ Digest food
+ Deliver food to small intestine

53

What do pacemaker cells do in the stomach?

Initiate an action potential that drives waves of contraction thorugh the stomach, mixing and grinding its contents

54

What are the 3 sections of the stomach?

1. Fundus
2. Body
3. Antrum

55

What are the 3 primary motility functions of the stomach?

1. Accommodation via receptive relaxation
2. Mixing via slow wave-initiated contractions and retropulsion
3. Gastric emptying

56

What is included in gastric secretions?

+ Ions
+ Water
+ Mucus from mucous neck cells
+ Pepsinogen from chief cells
+ Intrinsic factor and H+ from parietal cells

57

Regulation of H+ secretion occurs at the level of the H+-K+ ATPase. What increases secretion of H+?

+ ACh from nerves
+ Gastrin from G cells
+ Histamine from enterochromaffin-like cells

58

Regulation of H+ secretion occurs at the level of the H+-K+ ATPase. What decreases secretion of H+?

+ Somatostatin from D cells
+ Prostaglandins

59

The small intestine id the longest section of GI tract: what does this comprise of?

+ Duodenum ~0.3m
+ Jejunum ~2.3m
+ Ileum ~3.4m

60

What occurs in the small intestine?

+ It is where most macronutrient, vitamin, and mineral absorption occurs:
- facilitated by huge surface area increase created by villi (10-fold) and microvilli (20-fold)

+ Mixing via segmentation; propulsion via peristalsis

61

What are the components of the large intestine?

1. Cecum
2. Ascending, transverse, descending, sigmoid colon
3. Rectum
4. Anus

62

What occurs in the large intestine?

+ Significant water and ion absorption

+ Motility of contents: segemtation via mixing, propulsion via peristalsis and mass movement

63

What is the role of the ileocecal sphincter?

To regulate the amount of chyme entering the large intestine

64

What is the tole of the internal and external anal sphincters?

To regulate the faeces exiting the GI system