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Physiology 1B > Gastrointestinal System > Flashcards

Gastrointestinal System Flashcards

1
Q

What are the functions of the digestive system?

A

Digestion of food stuff
Absorption of foodstuff into blood stream
Protection of the GI tract lining from acid and enzymes

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2
Q

What structures does foodstuffs pass through in digestion?

A 
Mouth
Pharynx
Oesophagus
Stomach
Duodenum
Jejunum
Ileum 
Colon
Rectum
Anus
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3
Q

What are the layers of the GI tract?

A

Mucosa
Submucosa
Muscularis externa
Serosa

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4
Q

What are the layers of the mucosa and what are their structures?

A

Epithelium- interface between lumen and body
Lamina propria- majority of mucosa, loose connective tissue
Muscularis mucosa- thin muscle layer for local movement

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5
Q

What is the submucosa made of?

A

Loose connective tissue with glands from bottom of oesophagus to top of duodenum

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6
Q

Which layer of the GI tract is the main driver of movement?

A

Muscularis externa

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7
Q

What are the layers in the muscularis externa?

A

Inner circular muscle and outer longitudinal muscle

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8
Q

Where is the submucosal plexus found?

A

Between submucosa and muscularis externa in the small intestine and colon

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9
Q

Where is the myenteric plexus found?

A

Between the muscle layers in the muscularis externa, along the whole GI tract

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10
Q

What is the serosa made of and what is its function?

A

Connective tissue to hold the tract together

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11
Q

What region of teh GI tract is specialised with gastric pits and gastric glands for acid secretion?

A

Stomach

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12
Q

What regional specialisations does the large intestine have?

A

Crypt packed with mucus secreting cells for protection

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13
Q

How is the small intestine adapted for absorbtion?

A

Villi

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14
Q

What are the levels of GI surface area amplification?

A

Circular/spiral folds
Villi
Microvilli

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15
Q

What are glycocalyx?

A

Protein network outside microvilli where final digestion products go for absorbtion

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16
Q

What are the two types of epithelial cells in the mucosa of the GI tract?

A

Secretory and absorbative

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17
Q

What are the 5 major sites of secretion in the GI tract?

A 
Salivary glands
Gastric glands
Exocrine pancreas
Liver biliary system
Small intestine
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18
Q

What is in secretions of the GI system?

A

Enzymes
Ions
Water
Mucus

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19
Q

What are the roles of secretions in the GI tract?

A 
Lubrication
Protection
pH regulation
Dilution
Breakdown
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20
Q

Describe the vascular supply in the microvilli

A

Rich blood capillary network at tip supplied by arteriole and venule.
Lacteal lymph vessel for collection and reassembly of fat digestion products to take to circulation of thoracic duct

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21
Q

Why does blood supply increase when going from fasted to fed state?

A

Increases to allow increased nutrient uptake and removal of metabolic components

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22
Q

What are the two types of hormonal control in the GI tract?

A

Endocrine and paracrine

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23
Q

What is the role of gastrin?

A

Regulate gastric secretion and motility

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24
Q

What is the role of CCK?

A

Regulate gall bladder contraction for expelling bile acids, pancreatic secretion of enzymes, blood flow and motor activity in GI tract

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25
Q

What is role of GIP?

A

Stimulates insulin release from the pancreas

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26
Q

What innervates the GI system?

A

Intrinsic/enteric nervous system

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27
Q

Describe the phases of GI control

A

Cephalic- sight, smell, taste and chewing
Gastric- distension and acidity in stomach
Intestinal- distension, acidity and osmolarity in intestines

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28
Q

Describe the types of contraction in the GI tract

A

Phasic- lasts seconds, non-propulsive and peristalsis movement
Tonic- Lasts minutes to hours to keep reservoir

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29
Q

Describe the functions of the GI tract musculature

A

Segmentation- non-propulsive movement to allow churning
Peristalsis- moving along contents
Reservoir- sphincter contraction to prevent movement along tract

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30
Q

How do muscle fibres act as a single functional unit?

A

Innervated by varicosities, single fibres connected by gap junctions

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31
Q

Describe the resting membrane potential of GI tract smooth muscle

A

More depolarised by skeletal muscle, oscillates in slow waves

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32
Q

How is GI tract smooth muscle contraction regulated?

A

Hormones and nerves regulate the release of acetylcholine which causes action potentials at the peak of slow waves and force generation

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33
Q

Describe the functions of sphincters

A

Mediate reservoirs- tonic contraction of sphincters
Maintain positive resting pressure- prevent backwards movement
Regulate coordination between compartments with smooth muscle contraction

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34
Q

Name the sphincters of the GI tract

A

Upper oesophageal
Lower oesophageal- prevents acid reflux
Pyloric/bottom of stomach- allows stomach to act as reservoir
Sphincter of Oddi- around liver and pancreatic ducts on entry to duodenum
Ileocecal
Internal anal
External anal- skeletal muscle

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35
Q

What is the difference between the physiological and anatomical sphicters?

A

Physiological in only mucosa changes and anatomical is change in musculature

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36
Q

Describe the motility in the stomach

A

Peristalsis from corpus to pylorus, pyloric sphincter stays closed to allow breakdown of foodstuffs mainly in the antrum until is small enough to pass though sphincter (2mm or less)

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37
Q

Describe the motility in the small intestine

A

Non-propulsive movement from rhythmic contractions of muscularis externa to mix chyme and bring digestion products to the villi

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38
Q

Is the swallowing reflex voluntary or involuntary?

A

Oral phase is voluntary and then is under reflex control

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39
Q

Describe the stages of the swallowing reflex

A

Oral- tongue pushes food to hard palette and into pharynx stimulating touch receptors
Pharyngeal- soft palette raises to close sinuses and nasal cavity, epiglottis lowers over trachea. Upper oesophageal sphincter is open.
Oesophageal- upper oesophageal sphincter closes

40
Q

Describe the process of vomiting

A

Reverse peristalsis from small intestine
Pyloric sphincter and stomach relax
Forced inspiration against closed oesophagus lowers diaphragm and intrathoracic pressure
Elevated intraabdominal pressure forces abdominal contraction
Upper oesophageal sphincter relaxes

41
Q

How does digestion products move through the large intestine?

A

Colonic contractions mix chyme and improve water absorption as contents are moved to anus
Mass peristalsis a few times a day is main movement of waste

42
Q

What initiates large intestine contractions?

A

Gastrocolic reflex from stomach distension

43
Q

What innervates internal anal sphincter?

A

Pelvic nerve

44
Q

What innervates external anal sphincter?

A

Pudendal nerve

45
Q

What are the functions of saliva?

A

Lubrication
Protection
Starch digestion by alpha amylase
Fat digestion by lipase

46
Q

What are the salivary glands and their secretions?

A

Parotid- serous, amylase rich
Submandibular and sublingual- seromucous
Minor salivary- mucus, mucin glycoprotein rich

47
Q

Describe the pathway of salivary gland drainage

A

Acinar/ductal epithelial cell
Intercalated duct
Excretory duct

48
Q

Which nervous systems stimulate salivary gland secretion?

A

Parasympathetic and sympathetic neurones both stimulate secretion

49
Q

What is the effect of acetylcholine and noradrenaline on acinar cells?

A

Acetylcholine- stimulates isotonic NaCl and enzyme secretion
Noradrenaline- stimulates enzyme secretion

50
Q

What is the effect of acetylcholine and noradrenaline on duct cells?

A

Acetylcholine- decreases NaCl absorbtion

Noradrenaline- stimulates HCO3- secretion

51
Q

What cells control the composition of saliva?

A

Acinar and duct epithelial cells

52
Q

What is the composition of primary secretions of salvia?

A

Isotonic NaCl accompanied by salt and water secretion

53
Q

How does movement across leaky and tight epithelia differ?

A

Leaky- transcellular and paracellular movement

Tight- only transcellular movement

54
Q

How is salivas composition modified by duct lining epithelial cells?

A

Removes Cl- and Na+

Secretes HCO3- and K+

55
Q

Describe the functions of the stomach

A

Reservoir- accomodate food
Digestion- proteins
Vitamin B12 absorption- protection

56
Q

What is the composition of gastric secretions?

A 
HCl
Pepsin
Intrinsic factors 
Mucus
HCO3-
57
Q

What is the purpose of the cardia stomach region (small region past lower oesophageal sphincter)?

A

Secrete mucus to protect the sphincter

58
Q

What are the 2 regions of gastric mucosa?

A

Antrum- mainly regulatory of g cells for gastrin secretion

Corpus- mucosa contains gastric pits

59
Q

Describe the cells found in gastric pits

A

Surface epithelial cells that produce HCO3-
Mucous neck cells- secrete mucus
Parietal cells- secrete HCl and intrinsic factor
Chief cells- secrete pepsinogen
Endocrine cells- reglatory, ECL or D cell

60
Q

Explain the process of pepsin release and activation from the chief cells into the stomach

A

Chief cells secrete inactive pepsinogen by exocytosis into lumen, stimulated by increased intracellular Ca2+
Pepsinogen spontaneous converts to pepsin, faster in low pH. Pepsin itself activates pepsinogen.

61
Q

Why is it important for HCl to be secreted into the stomach?

A

Activates and promotes activity of pepsins
Kills microorganisms
Stimulates small intestine secretions

62
Q

How do parietal cells morphology change for HCl secretion?

A

Tubulovesicles carrying transport proteins needed for acid secretion move to line apical membrane forming canaliculus with high surface area. Contains more H+ pumps, K+ and Cl- channel

63
Q

How is mucus secreted in the stomach?

A

Exocytosis by surface epithelial cells and mucous neck cells

64
Q

How is bicarbonate secreted into the stomach?

A

Move into epithelial cell through basolateral cotransporter carrying in bicarbonate with Na+. Bicarbonate then leaves via channel

65
Q

What regulates mucus and bicarbonate secretion into the stomach

A

Acetylcholine and prostaglandins

66
Q

How is the lining of the stomach protected from acid and pepsin damage?

A

Thick mucus and HCO3- lines the surface epithelial cells
Tight junctions between epithelial cells prevent H+ penetrating
Apical membrane is impermeable to H+
Viscous fingering so muscularis mucosa squeezes gastric glands so HCl moves directly into the lumen

67
Q

List the order food stuff types leave the stomach

A

Carbohydrates
Proteins
Fats
Indigestible solids (fasting state only when sphincter opens wider)

68
Q

What controls the rate of gastric emptying

A

Rate acid can be neutralised
Rate of fat emulsion
Rate small intestine can process chyme

69
Q

List the pathway pancreatic secretions take

A

Acinar/ductal epithelial cells
Intercalated duct
Interlobular duct
Main collecting duct

70
Q

What regulates pancreatic secretions?

A

CCK and acetylcholine to increase intracellular Ca2+

71
Q

Name the endocrine pancreatic secretions

A

Insulin

Glycogen

72
Q

Name the exocrine secretions of the pancreas

A

Salt, water, HCO3-

Proteases, alpha amylase and lipases

73
Q

What releases enzymes in the exocrine pancreas?

A

Acinar cells

74
Q

What are trypsinogen, chymotrypsinogen and procarboxypeptidases?

A

Zymogens, inactive forms of the enzyme

75
Q

What is the regulation of exocytosis of zymogens in the pancreas?

A

Secretin- acts on cAMP to fuse granules to apical membrane for exocytosis
Parasympathetic nerves- acetylcholine acts on Ca2+ causing granules to fuse and exocytosis
CCK- acts on Ca2+ causing granules to fuse for exocytosis

76
Q

How do zymogens get activated?

A

Enteropeptidase brush border bound enzyme on apical membrane of epithelial cells and also on bile salts activates zymogens.
Active enzymes activate zymogens.
Inhibitors released in activation prevent early activation in pancreas

77
Q

Which process is NaCl secretion in the pancreas the same as?

A

Salivary NaCl secretion

78
Q

What is the composition of liver and biliary secretions?

A

Bile salts
Cholesterol
Phospholipids

79
Q

What is the composition of small intestine secretions?

A

Mucus Enteropeptidases
Salt
Water

80
Q

What happens to bile between meal?

A

Concentrated and stores in the gall bladder

81
Q

What are mixed micelles made of?

A

Fatty acid and monoglycerides surrounded by cholesterol and bile salts

82
Q

What is the enterohepatic circulation?

A

How bile acid is recycled back to the liver

83
Q

Explain the process of bile acid recycling

A

Slow reabsorption of bile along the small intestine actively driven by sodium from the ileum
Return to liver in splanchnic circulation and portal vein into hepatocytes

84
Q

What happens to crypt cells as they migrate up the villi pits?

A

Become absorptive epithelial cells

85
Q

What is the difference in crypts in small and large intestine?

A

Small- secrete salt and water

Large- secrete mucus

86
Q

How are foodstuffs absorbed that are fully digested in the GI lumen?

A

Diffuse across epithelial cell into the blood

87
Q

Explain brush border hydrolysis of dimer to monomer eg. sucrose

A

Sucrase sits on apical membrane to break down sucrose into its monomers which diffuse into blood through epithelial cell

88
Q

Explain luminal hydrolysis of polymer to monomer eg. protein

A

Pancreatic enzymes digest polymer fully in lumen of small intestine. Amino acids diffuse across epithelial cell into blood

89
Q

Explain intracellular hydrolysis of polymers in the small intestine eg. protein

A

Partially digested protein diffuses into epithelial cell where enzymes complete digestion and amino acids diffuse out into blood

90
Q

Explain the process of luminal hydrolysis followed by intracellular resynthesis eg. triglycerides

A

Broken down fully in the lumen of small intestine as monoglyceride and fatty acid
Recombined in cell to triglyceride and diffuses out of cell into the blood

91
Q

What are the transporters for glucose?

A

GLUT5- fructose, glucose transporter 5
GLUT2- glucose, galactose and fructose, glucose transporter 2
SGLT1- glucose and galactose, Na+ coupled glucose transporter

92
Q

Which glucose transporters are in the apical membrane and which in the basolateral membrane?

A

Apical- SGLT1 and GLUT5

Basolateral- GLUT2

93
Q

Why is emulsion of fats important in fat digestion?

A

Reduces size of lipid droplets to increase interface area as lipase is only active at interface

94
Q

How do mixed micelles release fat digestion products into the epithelial cells?

A

Diffuse to unstirred layer releasing contents to diffuse into epithelial cell

95
Q

Name the hormones that act within the GI tract

A 
Gastrin
Secretin
Cholecystokinin/CCK
Glucose dependent insulinotrophic peptide/GIP
Somatostatin (also paracrine)
96
Q

When is an alkaline tide created in the blood?

A

In fed state when parietal cells are stimulated to produce acid

97
Q

What are alpha limit dextrins?

A

Intermediate digestion products that cant be absorbed by epithelial cells

Physiology 1B (4 decks)

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