Lecture 25 Flashcards
Secretion in the GIT (107 cards)
1
Q
What is the epithelial membrane called in the GIT lumen side?
A
Apical membrane
2
Q
What is the epithelial membrane lining the blood and lymph lumen?
A
Basal membrane
3
Q
What is the epithelial membrane between the gap junction?
A
Lateral membrane
4
Q
What are the two pathways of diffusion from the GIT lumen to the blood and lymph?
A
Transcellular pathway and paracellular pathway
5
Q
What is the transcellular pathway?
A
Across the cell membrane and through the cytoplasm
6
Q
What is the paracellular pathway?
A
Between the cells through the tight junction
7
Q
What is secretion?
A
The movement of solutes and water from the body to the GIT lumen. Can occur via the paracellular and/or transcellular pathway
8
Q
What is absorption?
A
The movement of solutes and water from the GIT lumen into the body. Can occur via the paracellular and/or transcellular pathway
9
Q
What is endocrine secretion?
A
Hormones into the blood
10
Q
What is exocrine secretion?
A
Secretions produced by the epithelia
11
Q
What are the components of exocrine secretions in the GIT?
A
Mucus, electrolyte solutions and digestive enzymes
12
Q
What is the function of mucus?
A
To protect and lubricate and also aid in mechanical digestion
13
Q
What is the function of electrolyte solutions?
A
Dilutes food and provides optimal pH as well as being essential for digestive enzymes
14
Q
What is the function of digestive enzymes?
A
Essential for chemical digestion of food and also aids absorption
15
Q
Why is RE-absorption important for secretion?
A
Because we secrete 8L/day of fluid from 3L of plasma therefore need to recycle it
16
Q
How many salivary glands do we have?
A
3
17
Q
How much fluid do the salivary glands secrete per day?
A
1.5L
18
Q
How much fluid does basal (resting) secretion secrete?
A
0.3mL/min
19
Q
How much fluid does stimulated secretion secrete?
A
1.5mL/min
20
Q
What is the composition of saliva?
A
Musus, dilute solutions of NaHCO3 and NaCl (electrolytes) and digestive enzymes
21
Q
What s the function of electrolytes in saliva?
A
To dilute food for tasting, swallowing and also talking. Provides the optimal pH for digestive enzymes and for hygiene
22
Q
What are the digestive enzymes of the salivary glands?
A
Lingual lipase and salivary amylase
23
Q
What does lingual lipase do?
A
Chemical digestion of fats
24
Q
What does salivary amylase do?
A
Chemical digestion of starch
25
What is secretion of the salivary glands regulated by?
The autonomic nervous system
26
What are the two components of the autonomic nervous system?
Parasympathetic and sympathetic
27
What does the parasympathetic nervous system do for the salivary glands?
Stimulates secretion of copious quantities of fluid
28
What does the sympathetic nervous system do for the salivary glands?
Stimulate secretion of less and more viscous fluid
29
How much fluid does the stomach secrete per day?
2-3L
30
What is the volume of stomach secretion between meals?
Slow rate of 15-30mL/hr
31
What cells are active between meals in the stomach?
Goblet cells on the surface of the stomach
32
What do the goblet cells secrete?
Mucus and bicarbonate
33
What does bicarbonate do?
Protects the proteins in the lining of the stomach from the acid, preventing denaturing
34
What cells are active while eating in the stomach?
Goblet cells, parietal cells and chief cells
35
What do the parietal cells secrete?
HCl acid and intrinsic factor
36
What is the purpose of HCl in the stomach?
To denature proteins and convert pepsinogen to pepsin. Also protects from microbes
37
What is the purpose of intrinsic factor in the stomach?
To bind to vitamin B12 in the stomach and then help its absorb in the ilium (SI)
38
What do the chief cells secrete, and why?
Pepsinogen, a precursor for pepsin that starts chemical digestion of proteins
39
What is the source of hydrogen ions for HCl in the stomach?
Carbonic anhydrase and production of H+ and HCO3- from H2O and CO2
40
What is the process of secretion of stomach acid (H+) in the stomach?
H+ - K+ ATPase in the apical membrane of parietal cells pumps the H+ ions into the GIT lumen in exchange of K+ (into cell lumen) which returns to the GIT lumen through a passive channel
41
What is the source of chloride in the stomach?
Anion counter transporter in the basolateral membrane of parietal cells imports Cl- ions into the cell in exchange for ejecting HCO3- into interstitial fluid
42
What is the process of the secretion of Cl- in the stomach?
Cl- diffuses across the cell into the lumen via Cl- channel in apical membrane
43
What are the three phases of gastric secretion and what proportion of gastric secretions do they provide?
Cephalic 20%, gastric 70%, intestinal 10%
44
What is the function of the cephalic phase?
To prepare the stomach for the arrival of food
45
What is the stimulus of the cephalic phase?
Seeing, smelling, tasting or thinking about food + chewing
46
What is the stimulus of the cephalic phase detected by?
CNS
47
What is the response from the CNS in the cephalic phase?
PSN stimulates ENS (submucosal plexus) via the vagus nerve
48
What are the effectors of the cephalic phase?
Goblet cells, chief cells, parietal cells, G cells
49
What are G cells?
A type of enteroendocrine cell
50
What do the G cells do?
Secrete gastrin into blood which stimulates chief and parietal cells (for the second time)
51
What is gastrin?
A hormone secreted by G cells (an EEC) into the blood
52
What do goblet cells secrete?
Mucus and bicarbonate
53
What do chief cells secrete?
Pepsinogen
54
What do parietal cells secrete?
HCL acid
55
What is the outcome of the cephalic phase?
Increased secretion of mucus, HCO3-, HCl acid and pepsinogen in the stomach
56
What is the function of the gastric phase?
To maximise mechanical digestion and begin protein chemical digestion
57
What is the stimulus of the gastric phase?
The arrival of food through stretch of the stomach wall, increased pH and detection of undigested food (esp. protein)
58
What is the stimulus of the gastric phase detected by?
G cells (from peptides), gastric mechano- & chemoreceptors
59
What is the response from the G cells in the gastric phase?
Secrete gastrin to stimulate chief and parietal cells
60
What is the response from the receptors in the gastric phase?
Stimulus of the myenteric and submucosal plexus
61
What are the effectors of the submucosal plexus?
Goblet cells, chief cells, parietal cells, G cells
62
What are the effectors of the myenteric plexus?
Smooth muscle of the stomach to increase motility (retropulsion)
63
What is the outcome of the submucosal plexus stimulus in the stomach?
Increased secretion of mucus, HCO3-, HCl acid, pepsinogen and gastrin in the stomach
64
What is the outcome of the myenteric plexus stimulus in the stomach?
Increases motility; retropulsion, waves of peristalsis
65
What is the function of the intestinal phase?
To allow slow, controlled release of food to the small intestine
66
What is the stimulus of the intestinal phase?
Stretch of the duodenal wall, decreased pH from acid, arrival of fatty and amino acids in the duodenum
67
What is the stimulus of the intestinal phase detected by?
The duodenal enteroendocrine cells (EECs) and mechano- & chemoreceptors
68
What is the response from the EECs in the intestinal phase?
Secretion of duodenal hormones; CCK, GIP (fatty and amino acids) and secretin (pH)
69
What is the response from the receptors in the intestinal phase?
To stimulate the CNS (SNS) to inhibit the ENS - submucosal and myenteric plexus
70
What does inhibition of the submucosal plexus cause?
Decreased secretion of pepsinogen and HCl acid
71
What does inhibition of the myenteric plexus cause?
Inhibition of G cells to decrease gastrin and motility
72
What is the outcome of the intestinal phase?
Decreased secretion of HCl acid, pepsinogen and gastrin, decreased motility; retropulsion
73
What is the pancreas?
An endocrine and exocrine organ
74
How much fluid does the pancreas secrete per day?
1-1.5L
75
What are the two components of the pancreas?
The pancreatic acinar cells and pancreatic duct cells
76
What do the pancreatic acinar cells secrete?
Pancreatic digestive enzymes
77
What do the pancreatic duct cells secrete?
Alkaline fluid (HCO3-)
78
What stimulates the release of pancreatic juice with digestive enzymes from pancreatic acinar cells?
Cholecystokinin (CCK) from the duodenum EECs - CCK stimulated by the arrival of fatty acids and amino acids in the duodenum
79
How are digestive enzymes classified?
Based on what type of molecule they digest
80
What do nucleolytic enzymes digest?
Ribonuclease and deoxyribonuclease
81
What do lipolytic enzymes digest?
Fat; lipase
82
What do amylytic enzymes digest?
Carbohydrates; pancreatic amylase enzyme
83
What do proteolytic enzymes digest?
Peptides; trypsinogen, chymotrypsinogen, procarboxypeptidase
84
What are pancreatic proteolytic enzymes secreted as?
Inactive precursors that are activated in the duodenum
85
Why are pancreatic proteolytic enzymes secreted as precursors?
So that they don't digest proteins inside pancreatic acinar cells
86
What is the active form of Trypsinogen?
trypsin
87
What is the active form of chymotrypsinogen?
Chymotrypsin
88
What is the active form of procarboxypeptidase?
Carboxypeptidase
89
What converts trypsinogen to trypsin?
Enterokinase (enteropeptidase) which is bound to the duodenal membrane
90
What converts chymotrypsinogen and procarboxypeptidase to their active forms?
Trypsin
91
What stimulates the release of pancreatic juice with bicarbonate from pancreatic duct cells?
Secretin from the EECs - stimulated by the arrival of acidic chyme from the stomach in the duodenum
92
What does the alkaline fluid in the pancreatic duct cells do?
Neutralises acid in chyme from the stomach and provide the optimum pH for pancreatic enzymes
93
What volume of fluid does the liver secrete per day?
0.5L
94
What are the liver cells?
Hepatocytes
95
What do the hepatocytes make and secrete, and why?
Bile into the bile canaliculi for chemical digestion of fat
96
What do the bile duct cells secrete, and why?
Alkaline fluid which neutralises the acid in the chyme from the stomach
97
What does bile contain?
Excretory/waste products with bile pigments (bilirubin) from the breakdown of haem and also excess cholesterol
98
Where is bile sotred?
In the gallbladder where it is also concentrated
99
What stimulates the release of bile from the gallbladder into the duodenum?
CCK causes contraction of the wall of the gallbladder and relaxation of the hepatopancreatic sphincter
100
What stimulates the release of CCK?
Fatty acids in the duodenum
101
What happens to the bile after it is secreted through the duodenum?
About 95% is reabsorbed into the ilium and transported back to the liver via the enterohepatic circulation system where it can be reabsorbed and secreted again
102
How is the liver stimulated to produce more bile?
Through the return of bile to the liver via the enterohepatic circulation system because this signals to the hepatocytes that bile has recently been released from the gallbladder. Also stimulated through secretin (mildly)
103
What volume of fluid does the small intestine produce per day?
1.5L
104
Where does the secretion in the SI come from?
The glands (crypts)
105
What does the SI secrete?
Mucus and isosmotic fluid
106
What is isosmotic fluid?
An alkaline mixture of NaCl and NaHCO3 which helps neutralise acid and dilute food to aid digestion
107
What does the large intestine secrete?
Mucus
