Gastrointestinal tract

Question 1

What organs are involved in the gastrointestinal tract?

Answer 1

• mouth
• oesophagus
• stomach
• small intestine
• large intestine

Question 2

What is the GI tract?

Answer 2

a tube, differentiated along its length for sequential processing of food

Question 3

What anchors the suspended intestines within the abdominal cavity?

Answer 3

mesenteries (membranes)

Question 4

What are immunologic omentum?

Answer 4

immunological organ that is a source if inflammatory cells & stem cells that play a role in the control of infection through wound-healing & regeneration

Question 5

What separates the different hollow organs?

Answer 5

sphincters & secretory accessory glands/organs

Question 6

What are sphincters?

Answer 6

muscular rings - control the progression of the food from 1 section to the next. They also prevent the backflow of material from one section to the previous one.

Question 7

What is the function of GI tract?

Answer 7

• motility propels ingested food
• secretions from associated glands
• digestion/hydrolysis into absorbable molecules
• absorption into the bloodstream of nutrients, electrolytes, water

Question 8

What are the 2 layers of the GI tract?

Answer 8

• mucosal layer
• submucosal layer

Question 9

What is in the mucosal layer?

Answer 9

in touch with contents of the lumen - contains epithelial cells.
- either absorbable or secretory cells
- lamina propria (connective tissues with blood & lymph vessels)
- thin muscularis mucosae

Question 10

What is in the submucosal layer?

Answer 10

connective tissue (collagen, elastin), glands larger blood vessels (that transport molecules, as well as removing & metabolites

Question 11

What shape are the 2 smooth muscle layers (enteric neurones between)?

Answer 11

circular + longitudinal

Question 12

What is serosa?

Answer 12

squamous epithelia

Question 13

What is the function of the mouth?

Answer 13

• mechanical disruption of food
• (mastication) aims to increase the surface area to attack by enzymes & chemicals later in the GI tract.
• also lubricate the food with the secretions of these 3 glands.

Question 13

What can be found in the multi-parted exocrine glands?

Answer 13

ligual lipase + amylase initiates lipid + starch

Question 13

What are the 3 sections of the salivary glands?

Answer 13

• parotid gland
• submandibular gland
• sublingual gland

Question 13

What are the roles of saliva?

Answer 13

• lubricate food (bolus)
• antimicrobial - resists bacterial infection
• buffering - neutralises acid
• dissolves food - detection by taste buds

Question 14

What controls the level of mastication & swallowing?

Answer 14

the brainstem (CNS) will control the level of mastication & swallowing

Question 14

What receptors relay sensory information to the CNS?

Answer 14

mechanoreceptors (found in mouth & teeth) & chemoreceptors relay sensory information to brainstem

Question 14

How do later parts of the GI tract prepare for the arrival of food?

Answer 14

they start to secrete, in preparation for the arrival of the bolus

Question 14

What does stimulation of the central nervous system enable?

Answer 14

enables later sections of the GI tract to get ready for the arrival of food?

Question 15

What does swallowing do?

Answer 15

move the bolus into the oesophagus

Question 16

What is the oesophagus lined with?

Answer 16

lumen lined with stratified squamous epithelia

Question 17

What is the benefit of having stratified squamous epithelia on the lumen of the oesophagus?

Answer 17

loose cells at the surface allow cells to be lost without causing damage to the underlying tissue, as they are in contact with the bolus

Question 18

How does the swallowing reflex work?

Answer 18

• closes upper oesophageal sphincter.
• initiates primary peristaltic wave, coordinates sequential contractions
• continued distension (food in the oesophagus) initiates secondary peristaltic wave (by ENS - enteric nervous system - the nervous system within the GI tract)

Question 19

What initiates the second peristaltic wave?

Answer 19

continued distension - food in the oesophagus - with activates the ENS (enteric nervous system)

Question 20

What is the ENS (enteric nervous system)?

Answer 20

nervous system within the GI tract

Question 21

What does the vasovagal reflex control?

Answer 21

lower oesophageal sphincter (LOS) tone

Question 22

How does the PNS (parasympathetic nervous system) vagus nerve control the LOS (lower oesophageal sphincter) opening?

Answer 22

by releasing VIP neurotransmitter

Question 23

What is the autonomic nervous system made up of?

Answer 23

- sympathetic nervous system - parasympathetic nervous system - enteric nervous system

Question 24

What are the extrinsic part of the nervous system that regulate the GI tract?

Answer 24

sympathetic & parasympathetic

Question 25

What are the intrinsic part of the nervous system that regulate the GI tract?

Answer 25

enteric nervous system

Question 26

What modifies the enteric nervous system?

Answer 26

the brain - 2 MAIN plexuses

Question 27

What are the 2 main plexuses in the brain?

Answer 27

- ganglia within submucosal - myenteric plexuses (including pancreases + biliary system)

Question 28

How does neural control of the GI tract work?

Answer 28

- parasympathetic ganglia within plexuses coordinates information received from PNS and relay to smooth muscle, endocrine & secretory cells - postganglionic neurones are either cholinergic (release ACh) or peptidergic (release peptides)

Question 29

What do sympathetic postganglionic nerve fibres release?

Answer 29

they are adrenergic (release norepinephrine)

Question 30

What are nerve fibres a mix of?

Answer 30

mixed afferent & efferent i.e sensory & motor information is relayed between GI tract & CNS, coordinated by the plexuses

Question 31

What are the 3 phases to stomach motility?

Answer 31

1. receptive relaxation in thin-walled Orad stomach to receive food. 2. 3 muscular layers of Caudad region contract to mix food with gastric huice from mucosal glands (ANS control) forming chyme 3. Gastric emptying through pyloric sphincter into small intestine (SI) - fat content & H+ slows emptying

Question 32

What is chyme a mixture of?

Answer 32

- HCI (hydrochloric acid) - Pepsinogen - pepsin (protease) - Intrinsic factor - Mucus

Question 33

Why is there mucus in chyme?

Answer 33

to prevent the acid & proteins damaging the linin

Question 34

What is low level, weak contraction below the threshold called?

Answer 34

tone

Question 35

What are contractions called when there are action potentials on top of tone contractions?

Answer 35

phasic contractions

Question 36

How many sphincters are there in the Oddi?

Answer 36

6+

Question 37

What type of pressure is found in sphincters?

Answer 37

positive resting pressure

Question 38

What do sphincters regulate?

Answer 38

antegrade (forward) & retrograde (backward) movement of food

Question 39

What is the most contractile tissue?

Answer 39

unitary smooth muscle

Question 40

Why is unitary smooth muscle the most contractile tissue?

Answer 40

cells electrically coupled via gap junctions --> rapid spread of action potentials leading to coordinated contraction

Question 41

What are 2 types of contractions?

Answer 41

tonic - constant level of contraction/tone phasic - periodic contraction + relaxation (3-12/min)

Question 42

What cells are the gastrointestinal pacemaker cells?

Answer 42

interstitial cells of Cajal (ICC) in stomach, SI, LI

Question 43

What is contraction always preceded by?

Answer 43

electrical activity

Question 44

What is the function of the small intestine?

Answer 44

- digestion + absorption of nutrients - carbs, amino acids, fats, water & ions - chyme is mixed with digestive enzymes + pancreatic secretions - many hydrolytic enzymes embedded in membrane of brush border

Question 45

What are the 3 sections of the small intestine?

Answer 45

- duodenum - jejunum - ileum

Question 46

How does surface area increase?

Answer 46

plicae --> villi --> microvilli

Question 47

How much of exocrine secretion occurs into the duodenum per day?

Answer 47

1 litre

Question 48

Why is the exocrine solution rich in bicarbonate?

Answer 48

to neutralise the H+ delivered from the stomach

Question 49

From which cells is bicarbonate released from?

Answer 49

centroacinar & ductal cells

Question 50

How is pancreas secretion controlled by the autonomic nervous system?

Answer 50

PNS - stimulates secretion SNS - inhibits the 'rest & digest' response

Question 51

What do liver cells (hepatocytes) secrete?

Answer 51

bile

Question 52

When is CCK hormone ejected from the small intestine?

Answer 52

when chyme enters - following relaxation of Oddi

Question 53

What is bile made up of?

Answer 53

- water - amphipathic bile salts (lipid emulsification) - bilirubin - involved in erythrocyte breakdown - cholesterol - excretion & recirculation - phospholipids - emulsify fats - electrolytes - neutralise the acidic chyme

Question 54

How does 95% of bile acids get recirculated to the liver?

Answer 54

enterohepatic circulation

Question 55

What type of contractions are seen in the small intestine?

Answer 55

peristaltic contractions propel the chyme

Question 56

What do enterochromaffin cells release?

Answer 56

serotonin (neurocrine) - peristaltic reflex

Question 57

What happens to the material not absorbed in the small intestine?

Answer 57

passes through lleocaecal sphincter into the caecum of the large intestine

Question 58

What are the 3 types of GI peptides classified as?

Answer 58

- hormones - paracrines - neurocrines

Question 59

Where do GI pepetide hormones come from?

Answer 59

GI endocrine cells - e.g. GIP

Question 60

Where do GI pepetide paracrines come from?

Answer 60

from endocrine cells, act locally, e.g. somatostatin

Question 61

Where do GI peptide neurocrines come from?

Answer 61

released from neurones, following action potential

Question 62

What are the 3 main functions of the large intestine?

Answer 62

1. absorbs water & electrolytes: Na+, Cl-, HCO3, K+. 2. Make & absorb vitamins K+B. 3. Forming + propelling faeces (ferments indigestible food - bacteria), to be excreted.

Question 63

What increases Na+ absorption?

Answer 63

aldosterone

Question 64

What are the 2 parts of the large intestine?

Answer 64

- surface columnar epithelial cells (absorptive) - taenia coli - 3 bands of longitudinal muscle that is shorter than the large intestine caused bunching, forming small sacs - haustra

Question 65

How does food move through the large intestine?

Answer 65

- segmented contraction - caecum + proximal colon, mic contents - haustra.

Question 66

What reflex moves contents through the large intestine?

Answer 66

gastrocolic reflex