Lecture 17/18: The Gastrointestinal System

Question 1

What are the main components of the Gastrointestinal Tract and the order they come in?

Answer 1

• Oral cavity
• upper esophogeal sphincter
• Esophagus
• lower esophogeal sphincter
• Stomach
• pyloric sphincter
• Small intestine
• ileocecal valve
• Colon (Large intestine)
• anal sphincter
• Rectum
• are main comp and - are the sphincters making sure insides only flow one way

Question 2

What is the Gastrointestinal Tract?

Answer 2

• large surface area of body exposed to external environment (ie what comes into body)
• detects food and potentially toxic substances
• sense to expel vomit and diarrhea
• specialized populations of T cells localized to the intestinal mucosa ex: peyer’s patches, mesenteric lymph nodes * specifically help to protect against what exposed to

Question 3

What are unique properties of the GI tract

Answer 3

• 28 ft long (extensively folded
• large surface area due to micro villi/villi
• food spends 30-80 hours in tract
• has residence gut microbiome (bacteria) and protects against pathogenic microbes that enter tract
• has own intrinsic nervous system

Question 4

What are the 4 basic processes of the of the GI?

Answer 4

• Motility
• Digestion
• Absorption (water & nutrients)
• secretion (salica/mucous, antibodies (IgA), digestive enzymes, bile, bicarbonate)

Question 5

What is the Cephalic Phase of Digestion?

Answer 5

• chemical and mechanical digestion beginning in mouth
• chewing (mastication)
• Salivary secretion is under autonomic control (stim by SNS and PNS) which lubricates food and provides enzymes liek amylase and some lipase

Question 6

Does protein digestion begin in the cephalic phase of digestion

Answer 6

• no (think don’t want muscles in mouth to break down, only in things with barrier)
• amylases breaks down carbs and some lipids broken down by lipase

Question 7

What is the Gastric Phase of Digestion?

Answer 7

• secretory cells of gastric mucosa
• digestion of proteins and fat
• carbs not broken down (amylase is pH sensitive)
• pepsin and gastric lipase secreted
• secretion stimulated by acetylcholine (PNS regulates this think its in charge of resting things)

Question 8

What is the small intestine phase of digestion?

Answer 8

• where most digestion takes place
• enzymes released are primarily secreted by pancreas
• enzymes that break down protein are released in inactive form ( Zymogen) prevents autodigestion
• inactive enzymes are activated by trypsinogen (note ogen= not yet activated)
• trypsinogen activated by enterokinase in brush border of duodenum

Question 9

What are the components of small intestine?

Answer 9

• top- bottom
• duodenum
• jejunum
• lleum
• gall bladder, liver, pancreas and stomach sit above
• relseases inactive: carboxypeptidase, chymotrypsin(ogen), lipase, amylase

Question 10

What structures are associated with pancreas?

Answer 10

• gall bladder: stores bile

- liver: produces bile

Question 11

What helps promote absorption of nutrients?

Answer 11

lined villi on small intestine (increased surface area)

Question 12

How are glucose and galactose absorbed?

Answer 12

• active transport
• transporter: SGLUT1
• **requires sodium to move across (co-transport)
• would not see in muscle (GLUT1 in muscle)

Question 13

How is fructose absorbed?

Answer 13

• facilitated transport
• transporter: GLUT5
• wont be found in skeletal muscle or in adipose

Question 14

What is maltose?

Answer 14

2 glucose

Question 15

What is sucrose?

Answer 15

1 fructose and one glucose

Question 16

What is lactose?

Answer 16

galactose and glucose

Question 17

What is starch?

Answer 17

glucose, glucose, glucose….

Question 18

Why is sodium in sports drinks

Answer 18

• promote glucose uptake (drink should be about 6-8% glucose)
• required to provide energy
• water follows sodium, fluid absorption will also be improved
• drink designed for recovery not during excersise

Question 19

What happens if an individual has a deficiency in lactase?

Answer 19

causes lactose intolerance

Question 20

What happens if fructose is added to sports drinks

Answer 20

• now 2 transport systems
• more glucose uptake
• also have to consider that glucose will make water go back into intestine (dehyrate you)

Question 21

How are peptides and amino acids transported?

Answer 21

• amino acids cotransported with sodium
• di and tri peptides cotransported with H+
• small peptides carried intact across cell by transcytosis
• mostly amino acids absorbed
• intact proteins are not absorbed (would cause immune reaction, food allergy), may happen in cases of intestinal damage causing “leakiness”

Question 22

How do amino acid/protein supplements work?

Answer 22

• aa absorption requires transport (saturable process)

- amino acids go directly to liver, broken down and even transformed to other amino acids

Question 23

What is the maximum effective dose of protein?

Answer 23

25g (maybe 2x higher in older individuals)

Question 24

What does leucine do?

Answer 24

• ingestion of 5g+ of leucine has stimulatory effect on protein synthesis
• this is what you want

Question 25

How is fat emulsified?

Answer 25

Made soluble with bile:

• fat molecule in aqueous environment
• bile salts are amiphipathic (like soap or detergent both hydro and lipophilic)
• mechanically “busts up” fat globule

Brokendown by lipase:

• fat has triglycerides (3FA on glycerol backbone
• lipase from pancreas breaks down triglyceride
• broken down into fatty acids,
• arrange themselves into micelles, with polar ends facing out.

Question 26

How are fats absorbed and transported?

Answer 26

• absorbed as fatty acids and monoglycerides
• in intestinal cell gets reassembled into triglycerides and packed as chylomicrons (lipoprotein)
• chylomicrons too large to cross capillary wall, must be absorbed into lymphatic system
• enters circulation via thoracic duct near heart

Question 27

How is appetite regulated?

Answer 27

• secondary neurons and primary neurons
• stimulatory arm and inhibitory arm (primary neurons)
• G hrelin stim appetite
• PYY inhibits appetite
• insulin: inhibits appetite
• leptin: inhibits appetite

Question 28

How is dopamine related to appetite?

Answer 28

• dopamine linked to appetite

- hedonic (pleasure) eating

Question 29

What is gastric bypass surgery?

Answer 29

• Roux-en Y procedure: a small pouch is created in upper stomach attached directly to small intestine, bypass most of stomach and duodenum
• 40-50% weight loss within year of surgery

hormonal changes:

• increased PYY levels: dec appetite
• dec ghrelin levels (dec appetite)
• increased incretin levels postprandially (improves insulin secretion)
• can get incretin increased by diabetes drugs

Question 30

What is Gut Microflora?

Answer 30

• 10x as many microbes as human cells in the body
• assist with digestion: contain enzymes not present to add to supply
• assist with immune function
• synthesis of folate, B12 and K
• promote intestinal growth and differentiation of mucosals
• GI health is a balance between beneficial and harmful bacteria (bifidobacteria and lactobacillus (probiotics))

Question 31

How does gut microflora contribute to obesity

Answer 31

• inc levels bacteriodetes in lean
• inc levels of firmicutes in obese (promote breakdown and absorption of patty acids and polysaccharides)
• directly transferring “obese” microbiota into lean mice causes obesity
• co-housing ob mice with lean mice (with leam type microbiota) prevents weight gain due to exchange of fecal microbes
• lean mice not colonized by obese micrboes

Question 32

What is CCK

Answer 32

cholecystokinin

• released by duodenum
• when fat is sensed, sends feed back system to gall bladder to contract (bile then goes to small intestine)

Question 33

What is G hrelin

Answer 33

• stimulates app
• released by stomach
• stimulated by empty stomach

Question 34

What is PYY?

Answer 34

• inhibits app
• source: intestine
• simulated by bile, chyme, nutrients

Question 35

What is Leptin

Answer 35

• inhibits appetite
• source: adipose
• stimulated by inc in adipose mass

Question 36

What is Insulin (in relation to appetite)

Answer 36

• inhibits appetite
• source: pancreas
• stimulated by inc blood glucose