GI System

Question 1

What structures are apart of the tubular GI tract?

Answer 1

Mouth, pharynx, esophagus, stomach, small and large intestine

Question 2

What are the accessory organs?

Answer 2

teeth, tongue, salivary glands, liver, gall bladder and pancreas

Question 3

Describe what occurs in the mouth.

Answer 3

Tongue - tastes and guides food
Teeth - grind food
Saliva - mixes food

Question 4

Describe what occurs during the swallowing reflex

Answer 4

• tongue pushed against soft pallet
• respiration inhibited by epiglottis blocking larynx
• food pushed into esophagus from pharynx

Question 5

What is the esophagus and how does it perform its function?

Answer 5

A tube that moves food to the stomach by peristalsis

Question 6

What is peristalsis?

Answer 6

muscular contractions of the digestive tract

Question 7

Describe what occurs in the small intestine

Answer 7

• peristalsis
• digestion of all nutrients
• main site of nutrient absorption

Question 8

What are the three parts of the small intestine?

Answer 8

1. duodenum
2. jejunum
3. ileum

Question 9

How do the liver and pancreas aid in digestion?

Answer 9

liver - provides bile salts and bilirubin via gall bladder

pancreas - provides bicarbonate and various enzymes

Question 10

What occurs in the large intestine (colon)?

Answer 10

• mass movement
• absorption of water and electrolytes
• storage of fecal material for expulsion

Question 11

What is the structure of the GI tract wall (4 layers)?

Answer 11

1. Mucosa
2. submucosa
3. muscularis (contraction)
4. serosa
   networks of neurons - submucosal plexus and myenteric plexus

Question 12

What are the specialized cell of the mucosa and what is their function?

Answer 12

TRANSPORT cells - secrete acid, bicarbonate, absorb nutrients, water and vitamins
ENTEROENDOCRINE cells - secrete hormones into blood
EXOCRINE cells - secrete enzymes, mucous etc.
- goblet cells: secrete mucous
- paneth cells: secrete antimicrobial compounds

Question 13

Myenteric plexus

Answer 13

regulates motility (contraction)

Question 14

Submucosal plexus

Answer 14

regulates secretion and absorption

Question 15

How does the PNS control the digestive system?

Answer 15

vagus nerve synapses on enteric system neurons, postganglionic fibres release ACETYLCHOLINE

• increase gut muscle activity
• relax sphincters
• increase secretion

Question 16

How does the SNS control the digestive system?

Answer 16

postganglionic neurons innervate entire GI tract, releasing NORADRENALINE

• inhibit gut movements
• constrict sphincters
• reduce secretion

Question 17

How does the GI tract regulate its own activity?

Answer 17

1. neural mechanisms
2. hormonal mechanisms
3. local mechanisms ie. pH, physical/chemical stimulation

Question 18

What arteries supply the stomach, small and large intestine?

Answer 18

Stomach - celiac artery
Small - superior mesenteric artery
Large - superior and inferior mesenteric srteries

Question 19

Describe blood flow from the GI tract and in the liver.

Answer 19

Blood from GI tract returns to the heart via the liver.

• hepatocytes clean blood of harmful substances
• hepatic portal vein and artery blood pools in sinusoids
• moves to central veins, drains into hepatic veins and returns to heart

Question 20

How does the GI smooth muscle operate as a single unit?

Answer 20

cells are connected by gap junctions and action potentials travel in all directions

Question 21

What causes contractions of GI smooth muscle?

Answer 21

slow waves must exceed threshold - determines frequency of APs

force and duration of contraction are directly related to the amplitude and frequency of APs

Question 22

Interstitial cells of Cajal

Answer 22

• generate slow waves and action potentials

- located between nerve fibres and smooth muscle cells

Question 23

What causes depolarization of Interstitial cells of Cajal and how often does it occur?

Answer 23

Ca2+ entry

depolarizes ~3/min in stomach and ~12/min in duodenum