Slide 9

Question 1

What are the basic processes of the digestive system?

Answer 1

digestion (biochemical breakdown of complex food)
motility (muscular contractions that mix and move food forward in digestive tract)
secretion (digestive juices)
absorption (small monomers and water)

Question 2

Trace the path of the digestive system.

Answer 2

oral cavity, esophagus, stomach, small intestine, large intestine, rectum

Question 3

Describe the phyiosological features of the stomach and the small intestine.

Answer 3

stomach: fundus, body, antrum -> have pyloric sphincter: pinches opening to small intestine so chime is released bit by bit
rugae: folds disappear when there is stomach distension

small intestine: duodenum, jejunum, ileum
plica: folds that remain there even when there is distension and have villi and microvilli on it to increase the surface area for max. absorption
each villus has its own artery and vein to absorb nutrients

Question 4

What is mesentery?

Answer 4

connective tissue that holds organs in place an blood vessels in their places so not everything clumps together when you stand up straight

Question 5

Describe the layers of tissue in the digestive tract from outside to inside.

Answer 5

serosa: connective tissue + peritoneum
submucosa: gland in submucosa + duct from gland
mucosa: mucous epithelium, basal lamina, muscularis mucosae
muscularis: circular layer and longitudinal layer

Question 6

What is the mucosa? What are the 3 layers?

Answer 6

lines luminal surface
highly folded surface increasing absorptive areas

1. mucous membrane: epithelium
   secretion and absorption
   exocrine: digestive juices and endocrine: into blood or tissues
2. lamina propria: thin layer of CT
   houses GALT lymphoid tissue for defense of intestinal bacteria
3. muscularis mucosa: sparse layer of smooth muscle

Question 7

Describe the epithelial lining of stomach.

Answer 7

highly folded called rugae marked by depressions = gatric pits [des creux]

coiled glands are found under mostly in the fundus and body of stomach

Question 8

Describe the secretion and mesentery in the serosa.

Answer 8

secretes serous fluid: lubricates and prevents friction between digestive organs and surrounding viscera

mesentery is continuous throughout much of the tract and provides:
attachment for fixation
support to digestive organs in the proper place while having freedome of propulsive movements and mixing

Question 9

What kind of secretions can be found in the mouth/oral cavity?

Answer 9

-saliva: produced by salivary glands {parotid, submandibular, sublingual} composed mostly of water and electrolytes

moistens food to swallow
rich in bicarbonate buffers since amylase works best at slightly alkaline pH

-amylase (begins CHO digestion by serous cell), mucus (lubrication), lysozyme(antibacterial action)

Question 10

Describe the esophagus.

Answer 10

flattened in the resting state

lined with stratified squamous epithelium

between pharynx and stomach

has sphincters at both ends:

• pharyngoesophageal sphincter keeps entrance closed so not huge amounts of air enter esophagus
• gastroesophageal sphincter prevents reflux of gastric contents

Question 11

What are the GI tract contractions?

Answer 11

peristalsis: promotes forward movement
segmental: contractions promote mixing

Question 12

What is gastric motility?

Answer 12

mixing action in the stomach of both repulsion (back ward) and propulsion (forward)

as peristaltic contractions become stronger: liquid chyme squirts out of pyloric sphincter into duodenum

stomach continues to mix chime while it gradually releases the chyme

Question 13

Describe the steps in gastric emptying.

Answer 13

1. direction of movement of peristaltic contraction (from fundus to antrum)
2. peristaltic contraction
3. movement of chime squirts through the pyloric sphincter slowly

Question 14

How does the duodenum control gastric emptying?

Answer 14

1. fat: digested and absorbed more slowly than other nutrients
2. acid: HCL secretion+highly acidic chime neutralized in duodenum by bicarb secreted by pancreas
   * unneutralized acid in duodenum inhibits further gastric emptying
3. hypertonicity: amino acid and glucose molecules slows gastric emptying
   if increase osmolarity of duodenal contents, stomach closes
4. distension: too much chime in the duodenum inhibits emptying of more gastric contents

Question 15

What are the three responses of the duodenum to gastric emptying?

Answer 15

fat, hypertonicity, acid, distension trigger:

-neural response enterogastric reflec acts to slow peristaltic activity [smooth muscle contraction]

-hormonal response
release of GIP [gastric inhibitory peptide] act on gastric muscle to decrease peristalsis and slow passage of food into the duodenum

-additional factors
emotions: sadness + fear = decrease motility
anger+ aggression = increase motility
intense pain= inhibit motility

Question 16

Where do gastric secretions come form? What are the gastric sections?

Answer 16

gastric juices secretions

oxyntic mucosa
lines the body and fundus

pyloric gland area [PGA]
lines the antrum

Question 17

Describe the phases in gatric empyting.

Answer 17

cephalic

• sensation or thought relayed to brainstem
• response: parasympathetic signals to gastric mucosa
• stimulates gastric juice secretion

gastric

• stomach distension of stomach caused by presence of food
• triggers parasympathetic reflexes that increase secretion of gastric juice
• Gastrin (by endocrine G cells) is a digestive hormone secreted by mucosa in the presence of food to cause increased gastric juice

intestinal phase
-once food enters the small intestine
-stomach activity is inhibited by less gastric juice secretion
-via GIP, CCK and secretin
=oppose gastric juice secretion and gastrin action
=stimulate bile ejection from pancreas to neutralize HCL in duodenum

Question 18

Where are the gastric pit located?

Answer 18

in the middle portion of the mucosa of the stomach

Question 19

In the stomach, in the oxynctic mucosa, what are the endocine cells?

Answer 19

mucous cell: secrete mucus to protect against the pepsin and acid (lines)

chief cells: pepsinogen when activated to pepsin and beings protein digestion

parietal cells: HCl

• activates pepsinogen
• denatures proteins
• breaks down connective tissue
• kills microrganisms
• intrinsic factor important for vit B12 absorption

ECL: secretes histamine stimulates parietal cells

Question 20

In the pyloric gland area, what is the function of the endocrine cells?

Answer 20

G cells: secrete gastrin which stimulates exocrine cells to secrete more gastric juice [high in HCl and pepsinogen]
has mechanism to ensure that when food is in stomach, there is enough juice to digest it = promotes digestion

D cells: produce inhibitory secretions ONLY = somatostatin
act to inhibit parietal cells [HCl], G cells [gastrin that increases the digestive secretion] and ECL cells

Question 21

What kind of cell types and secretions are there during the gastric phase?

Answer 21

1. mucous cells secrete
   -mucous - tonic with mucosa irritation to create a physical barrier between lumen and epithelium
   -bicarbonate - secreted with mucous to buffer gastric acid to prevent damage to epithelium
2. parietal cells secrete
   -gastric acid [HCl] to activate pepsin and kill bacteria
   -intrinsic factor to complexe with vitamin B12 for absorption
   as stimulus to release acetylcholine, gastrin, histamine
3. enterochromaffin like cell (ECL cells) secrete histamine to stimulate acetylcholine and gastrin to stimulate gastric acid secretion
4. Chief cells secrete
   -pepsinogen
   -gastric lipase
   to stimulate release of acetylcholine , acid and secretin to digest proteins and fats
5. D cells secrete somatostatins [inhibitory] to stimulate acid in stomach which inhibits gastric acid secretion
6. G cells secrete gastrin to stimulate acetylcholine, peptides and amino acids to stimulate gastric acid secretion

Question 22

What is the purpose HCl secretions and from where do they originate?

Answer 22

from parietal cells
activates pepsinogen to pepsin by providing acid medium for optimal pepsin activity
breaks down connective tissue and muscle fibres
denatures protein
kills most microorganism ingested with salivary lysozyme as a team

Question 23

How is HCl formed?

Answer 23

carbon dioxide + water = carbonic acid - dissociates to form H+

bicarbonate - exchange for Cl into parietal cells by open channels

combine H+ (H/K pump) and Cl- (diffuses) move into ducts

Question 24

What are the three ways HCl cannot enter into the cell?

Answer 24

1. luminal membrane gastric mucosal cells are impermeable to H+ so HCl cannot penetrate into cells
2. cells are joined by tight junctions so HCl cannot penetrate between them
3. mucous coating over the gastric mucosa protects even more.

Question 25

What happens when the gastric mucosal barrier is damaged?

Answer 25

H. pylori hide in the fundus form the HCl use flagella to go below mucous cells and cause damage to the barrier and tight junctions
allows HCl to damage tissue
treat with antibiotics

Question 26

What are the different systems and cell types in the pancreas?

Answer 26

mix of endocrine and exocrine tissues
elongated gland below stomach

endocrine function:
islets of Langerhan [regional cell cluster]
found throughout pancreas
-secrete insulin via Beta cells that cause glucose uptake
-glucagon release when glucose is low

Exocrine function: secretes pancreatic juice made of

• pancreatic enzymes [trypsinogen, lipases, nucleases] by acinar cells
• aqueous alkaline solution actively secreted by duct cells line pancreatic ducts to neutralize the duodenum

Question 27

What are pancreatic enzyme ?

Answer 27

exocrine regulated by secretin, CCK stimulate pancreatic juice act on the duct cells

proteolytic enzymes: (to digest protein)
trypsinogen and chymotrypsinogen

pancreatic amylase
converts poly to di amylase

pancreatic lipase is the only enzyme secreted throughout entire digestive system to digest fat

Question 28

What happens during protein digestion?

Answer 28

proteases catalyse hydrolysis of proteins

• intermediate proteoses then amino acids
• enzymes in gastric juices pepsinogen-pepsin are secreted with the common bile duct [running from liver passing by pancreas to duodenum]

Question 29

What is the role of the liver?

Answer 29

largest gland, most metabolic organ, detox

• bile secretion
• stores iron, vit. D, A, B12
• site of hematopoiesis

Question 30

What is the hepatic duct?

Answer 30

the hepatic duct fuses with the gallbladder cystic duct [where bile is stored] to form the common bile duct (passing through the pancreas) that enters into the duodenum

bile salts are formed in the liver from cholesterol
bile: actively secreted by liver and diverted to gallbladder between meals
lecithin (phospholipid) from cholesterol derived, converts large fat globules to liquid emulsion [emulsifies] for fat digestion and absorption into blood

Question 31

How are fats digested and absorbed?

Answer 31

1. large fat droplet from stomach = coated with bile salts from liver to break up the large fat droplet
2. become emulsions like micelles
   3.colipase and lipase come to digest the micelles
3. monoglycerides and fatty acids are moved out of micelles into the cell via diffusion
   or
   cholesterol is transported into the cell to the smooth ER
4. assembly of chylomicrons in Golgi
5. CM are released into the lymph [via lacteal] not into the capillaries

Question 32

What happens in the small intestines?

Answer 32

most digestions
and absorption

duodenum upper most part near the pyloric sphinter of the stomach
jejunum where tube turns vertical
ileum no clear mark

segementation contractions: initiated by pacemaker cells to mix chyme

secrete juice but has NO digestive enzymes

digestion via
pancreatic enzymes for CHO and protein
brush border enzymes for complete/final stages of enzymes CHO protein digestion
fat is digested entirely in the small intestine by pancreatic lipase

absorbs almost everything

LINING is REPLACED every 3 days

Question 33

What is the function of the large intestines?

Answer 33

motility, secretion of mucous, digest via gut microbiota, reabsorb electrolytes and wate, forms and stores feces