Digestive system

Question 1

Gastrointestinal segmentation involves contraction of what?

Answer 1

circular and longitudinal muscles in short segments of intestine.

Question 2

What does GI segmentation do?

Answer 2

Pushes bolus’ of food back and forth, with a small amount being pushed further down the gut.

Question 3

What is the purpose of GI segmentation?

Answer 3

To mix the chyme with digestive juices and bring it into contact with absorbing surfaces.

Question 4

Which muscles act as the pacemaker for GI segmentation?

Answer 4

Longitudinal muscles

Question 5

What phenomenon determines the frequency of contractions?

Answer 5

The base electrical rhythm

Question 6

What determines the strength of segmentation contraction?

Answer 6

The frequency of action potentials from the central nervous system.

Question 7

Where does segmentation contraction receive their parasympathetic and sympathetic innervation from?

Answer 7

Parasympathetic= Vagus and ENS
Sympathetic= ENS

Question 8

What happens to the BER along the length of the gut, oral to anal end?

Answer 8

The BER decreases in strength.

Question 9

What is the function of peristalsis?

Answer 9

To push bolus distally along the GI tract.

Question 10

Where does the migrating motility complex begin and end?

Answer 10

The MMC begins at the gastric antrum and terminates at the iliocaecal junction.

Question 11

What is the purpose of the MMC?

Answer 11

Prevent bacterial colonisation, move undigested food to the large intestine and move digested food onto absorbing surfaces.

Question 12

Which hormone is involved in the MMC initiation?

Answer 12

Motilin

Question 13

What can induce the MMC to start?

Answer 13

If the smooth muscle of the lumen is distended, the oral end contracts and the anal end relaxes, to push food.

Question 14

Which neurone plexus mediates the MMC?

Answer 14

The myentric plexus.

Question 15

Explain the gastroileal reflex?

Answer 15

when the bolus of food arrives at the ileocaecal junction, the distention causes the sphincter to open. When the bolus has entered the colon, distention of the colon will cause the cause the sphincter to close.

Question 16

What do colonic bacteria digest/ferment undigested material into?

Answer 16

Vitamine K., Short chain fatty acids and various gases.

Question 17

What is mass movement contraction?

Answer 17

The intense contraction of the colon to push a mass of faeces towards the rectum.

Question 18

After the mass movement contraction has occurred, what induces the urge to defaecate?

Answer 18

Stretch receptors in the rectum sense the distension and cause the urge.

Question 19

How does defaecation occur?

Answer 19

The rectum contracts and the internal and external sphincters relax.

Question 20

Which nervous system controls defaecation?

Answer 20

Parasympathetic and somatic nerves.

Question 21

What are the main functions of the stomach?

Answer 21

Sterilise the intake, begin protein digestion and secrete B12 intrinsic factor.

Question 22

Which stomach functions occur in the body of the stomach?

Answer 22

Secretions and storage.

Question 23

Which stomach functions occur in the antrum?

Answer 23

Mixing, grinding an secretion of gastrin.

Question 24

What is the purpose of stomach rugae?

Answer 24

the wrinkles allow for expansion when full

Question 25

What type of epithelium is found in the stomach?

Answer 25

Simple columnar cells.

Question 26

What is the gateway to the gastric gland?

Answer 26

The gastric pit

Question 27

What do gastric pits lead to?

Answer 27

The gastric glands.

Question 28

Which three cells are found in the base of the gastric gland?

Answer 28

Parietal, Chief and G cells

Question 29

Which two cells are found in the upper gastric gland and gastric pit?

Answer 29

Mucous neck cells and surface mucous cells.

Question 30

What do Chief cells secrete and what is its purpose?

Answer 30

Pepsinogen- the inactive form of pepsin, which digests proteins.

Question 31

What do Parietal cells secrete and what is its purpose?

Answer 31

HCl to activate the pepsinogen and to sterilise the stomach. | B12 intrinsic factor which allows for the absorption of B12 in the distal ileum.

Question 32

What do G-cells secrete and what is its function?

Answer 32

Gastrin is a hormone involved in the control of digestion further down the tract.

Question 33

How do parietal cells synthesise H+ ions?

Answer 33

CO2 diffuses into the cell and combines with water to form H2CO3. The hydrogen ion dissociates and enters the apical membrane of the stomach lumen.

Question 34

How do Parietal cells get Cl-?

Answer 34

They pump HCO3- into the blood in exchange for CL-

Question 35

How do Cl- and H+ become HCl?

Answer 35

They are both pumped into the stomach of the lumen (with H+ exchanged for K+) and in water form aqueous HCl.

Question 36

Which receptor does gastrin bind to?

Answer 36

Parietal CCK-B receptors.

Question 37

By which pathway do does gastrin cause an increase in intracellular Ca2+?

Answer 37

Inositol bisphosphate pathway.

Question 38

What does an increase in intracellular Ca2+ result in?

Answer 38

Phosphorylates kinases to increased activity in the K+/H+ pump (increased formation of HCl)

Question 39

What do enterchromaffin cells secrete?

Answer 39

Histamine

Question 40

What does histamine bind to and what does it activate?

Answer 40

Parietal G-coupled H2 receptor which activates adenylase cyclase.

Question 41

Which reaction does parietal adenylase cyclase catalyse?

Answer 41

ATP to cAMP

Question 42

What does cAMP do in parietal cells?

Answer 42

Increases K+/H+ pump activity by phosphorylating kinases.

Question 43

What does the vagus nerve secrete and to which receptor does this bind to?

Answer 43

The vagus nerve secretes acetylcholine and this binds to muscarinic-3 receptors.

Question 44

What is the effect of Ach release on parietal cells?

Answer 44

Increase in intracellular Ca2+ and K+/H+ pump activity.

Question 45

What do prostaglandins do to parietal cells?

Answer 45

Deactivates the G-1 proteins to inhibit HCl production.

Question 46

What is the cephalic phase of gastric acid stimulation?

Answer 46

The 'thought' phase initiates the vagus nerve to stimulate acid production.

Question 47

What is the gastric phase of gastric acid stimulation?

Answer 47

Gastric distension invokes enteric and vagal reflexes to secrete more HCl. Peptide presence induces gastrin cells to secrete gastrin, which is inhibited at low pH.

Question 48

What is the intestinal phase of gastric acid stimulation?

Answer 48

Acid in the duodenum stimulates the splanchnic reflex for s-cells to secrete secretin. Fat in the duodenum causes the release of GIP.

Question 49

What do GIP and secretin both do?

Answer 49

Decreases the effectiveness of gastrin.

Question 50

What is the precursor of pepsin?

Answer 50

The zymogen pepsinogen is inactive.

Question 51

At which pH does pepsin become active?

Answer 51

Lower than 3.

Question 52

What is the role of mucous in the stomach?

Answer 52

Cytoprotective and mechanicoprotective role.

Question 53

What cannot occur if there is no B12 intrinsic factor?

Answer 53

B12 won't be absorbed and this causes pernicious anaemia.

Question 54

What happens in pernicious anaemia?

Answer 54

RBC don't fully mature and therefore don't gain their biconcavity, vital for their function?

Question 55

How long can the body survive without intake of B12?

Answer 55

The liver has 3 years' worth of stores, meaning that B12 deficiency doesn't usually become symptomatic until then.

Question 56

How frequent are peristaltic waves?

Answer 56

Roughly 3 per minute?

Question 57

Which cells in the duodenum secrete HCO3-?

Answer 57

Submucosal brunners glands.

Question 58

What stimulates duodenal HCO3-?

Answer 58

Secretin and vagal/ENS reflexes

Question 59

What inhibits secretin in a -ve feedback loop?

Answer 59

Acid

Question 60

In terms of digestion, is the pancreas exocrine or endocrine?

Answer 60

Exocrine.

Question 61

By which structure does the common bile duct enter the duodenum, and where is it?

Answer 61

The sphincter of oddi is at the major papilla.

Question 62

How are zymogens activated when they exit the sphincter of oddi?

Answer 62

Enterocyte bound enterokinases, on the duodenal brush border, activate trypsinogen to trypsin. Trypsin activates other zymogens in the duodenum.

Question 63

How are zymogens stimulated to be secreted?

Answer 63

Secretin, amino acids and lipids stimulate CCK. CCK stimulates zymogen secretion.

Question 64

What is, and where are, hepatic portal triads?

Answer 64

A portal vein, systemic artery and a bile canaliculus are found on the edge of each corner of liver lobule.

Question 65

What is in the centre of a liver lobule?

Answer 65

A systemic vein

Question 66

What carries blood across a lobule?

Answer 66

Sinusoid capillaries.

Question 67

What are the main components of bile?

Answer 67

Bile acids, lecithin and cholesterol.

Question 68

What else may be found in bile, but in smaller concentrations?

Answer 68

Bilirubin and detoxified metals.

Question 69

What colour is bilirubin and what colour does it become?

Answer 69

It is yellow, giving yellow bile its colour. In the colon, it is digested by bacteria and become brown.

Question 70

How much of the bile salts need to be synthesised every day?

Answer 70

Around 0.5g because most of the bile salts can be recuperated and recycled from the ileum.

Question 71

What are bile salts synthesised from?

Answer 71

Cholesterol.

Question 72

What conjugates bile salts to acids?

Answer 72

Glycine or taurine residues.

Question 73

How does the gall bladder concentrate bile?

Answer 73

It pumps Na+ across the basal membrane and water follows it. This concentrates it.

Question 74

Where in the small intestine does most of the digestion take place?

Answer 74

Duodenum.

Question 75

What occurs 95% of the time in the jejunum

Answer 75

The absorption of nutrients.

Question 76

What does the ileum do?

Answer 76

Reabsorb NaCl (and therefore water) and concentrate the chyme.

Question 77

What do villus cells do?

Answer 77

Absorb: salt, water, amino acids, monosaccharides, lipids, minerals and vitamins.

Question 78

What do Crypt cells do?

Answer 78

Secrete Cl- and H2O

Question 79

How are amino acids transported into the epithelial cell?

Answer 79

Co-transported with sodium.

Question 80

How is sodium transported into the blood?

Answer 80

In an Na+/K+ antiporter

Question 81

How are lipids transported out of the lumen?

Answer 81

They diffuse cross the membrane into the villi lacteal, which drain into the lymphatic system.

Question 82

What are the layers of the alimentary canal?

Answer 82

Mucosa, submucosa, muscularis externa and serosa.

Question 83

The lamina propria, a layer of the mucosa, contains what?

Answer 83

Lymph and blood vessels