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Gastrointestinal System > Alimentary Canal Physiology > Flashcards

Alimentary Canal Physiology Flashcards

(80 cards)

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1
Q

What are are the main functions of the digestive system?

A

Digestion
Secretion
Absorption
Motility

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2
Q

What is the role of the mouth in the process of digestion?

A

Chews foodstuffs until they are broken down, uses saliva as a lubricant.

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3
Q

What are the 3 pairs of salivary glands called and where are they located?

A

Parotid - front of your ear on the inside of your cheeks.
Submandibular - on the floor of your mouth.
Sublingual - under the tongue

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4
Q

What is the role of the oesophagus?

A

Conduit between mouth and stomach. Ensures foodstuffs gets to the correct place. (rubble shoot)

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5
Q

What is the role of the stomach?

A

Site of digestion proteins, foodstuffs are reduced to liquid form.
Storage of food and regulates its release into the duodenum. Sterilises food as a defensive mechanism.

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6
Q

What is the role of the pancreas?

A

Secretes digestive enzymes - pancreatic lipase- for digestion of fats, carbs and proteins.

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7
Q

What is the role of the liver?

A

Produces bile salts that are essential for digestion and the absorption of fats in the small intestine.

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8
Q

What is the role of the Gallbladder?

A

Stores and concentrates bile

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9
Q

What is the role of the small intestine?

A

Site of the final stages of chemical digestion and site if 95% of nutrient absorption.

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10
Q

What is the role of the large intestine?

A

Site of water absorption, bacterial fermentation and formation of faeces.

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11
Q

What are the methods of control of chewing?

A

Somatic nervous control - somatic nerves supply skeletal muscle of mouth and jaw.

Reflexes - mechanoreceptors in tongue and hard palate are activated when food is pushed against them. The mechanoreceptors then fire signals to inhibit jaw muscles and the pressure reduces. Continuous cycle throughout chewing.

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12
Q

What is saliva made of?

A

Water - softens, moistens and dilutes particles which controls osmolarity.

Mucins - protein component that form smucus when mixed with water, lubricates mouth.

Alpha- amylase - enzyme tjat breaksdown alpha 1,4- glycosidic bonds found in polysaccharides.

Electrolytes - control the tonicity and pH within mouth e.g sodium, potassium.

Lysozyme - bactericidal that cleaves the polysaccharide component of bacterial cell walls. Defensive.

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13
Q

What cells secrete saliva?

A

Alveolar cells secrete saliva, duct cells mediate its flow.

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14
Q

What nerves are involved in the parasympathetic control of saliva secretion?

A

Cranial nerves VII facial and IX glossopharyngeal.

Produces large volume of watery saliva.

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15
Q

How does the sympathetic nervous system control saliva secretion?

A

Also stimulatory.

alpha-1-adrenoceptors are stimulated and produce a high mucus content.

beta-2-adrenoeceptors are stimulated and cause a high amylase content.

Very viscous saliva that clogs mouth.

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16
Q

How do reflexes control the secretion of saliva?

A

Food in the mouth stimulates chemoreceptors and mechanoreceptors to secrete saliva.

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17
Q

What type of cells make up the oesophageal mucosa?

A

Stratified squamous epithelium (non keratinised) - robust as it is still dealing with solid food.

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18
Q

What type of muscle cells make up the muscular externa?

A

Upper section of oesophagus = skeletal.

Lower section of oesophagus = smooth.

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19
Q

How is food movement regulated between the mouth and the stomach?

A

Oesophageal sphincters at the top and bottom regulate the movement of material in and out controlling when it can move from the mouth or into the stomach.

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20
Q

What stimulates the swallowing reflex?

A

Bolus at the back of the throat.

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21
Q

What are the functions of the stomach?

A

Temporary store of ingested material.

Dissolve food particles and initiate digestive process.

Controls delivery of contents to small intestine.

Sterilisation of ingested material.

Produces intrinsic factor for vitamin b12 absorption.

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22
Q

What is the serosa?

A

Connective tissue outer layer

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23
Q

What is the muscularis externae?

A

Muscular second most outer layer. Normally has 2 layers circular muscle on innerside and longitudinal on outside.

In lower section of stomach there is an extra layer - oblique muscle - the innermost layer to help with the grinding of food.

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24
Q

What is rugae?

A

Folds of the mucosa lining the stomach. Increases stomach surface area.

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25
What is the difference between peristaltic waves in the body of the stomach and the antrum?
Body is thin muscle so contractions are weak and there is no mixing. Antrum is thick muscle so contractions are more powerful (oblique muscle) and there is mixing.
26
How does the pyloric sphincter aid digestion?
Upon contraction it closes off the stomach so pushes food back up to be churned and mixed again - comes into contact with acid and secretions.
27
What generates the peristaltic rhythm?
Pacemaker cells located in the longitudinal muscle layer
28
What initiates action potentials that trigger gastric peristaltic waves?
Slow wave depolarisation is sub threshold so needs hormonal or neural input. Gastrin - increase contraction Distension of stomach wall - increased contraction. Signs of stomach emptying appear then motility is inhibited.
29
What is the function of bicarbonate in the duodenum?
Neutralise any acid present to prevent epithelial destruction.
30
What is the mechanism for duodenal bicarbonate secretion?
Acid triggers long vagal and short enteric reflexes which trigger bicarbonate release. Release of secretin from s cells also trigger bicarbonate release from the pancreas and liver.
31
What is the route of the pancreatic enzymes to the duodenum?
Produced in exocrine portion (lobules) Lobules are connected by intercalated ducts that lead to interlobular ducts - pancreatic duct - common bile duct - hepatopancreatic ampulla - duodenum.
32
What is the function of the exocrine pancreas?
Site of acini that’s secrete digestive enzymes. Site of duct cells that secrete bicarbonate.
33
What type of cells are duct cells?
Specialised cuboidal cells
34
What is a zymogen?
Inactive forms of digestive enzymes
35
What is the trigger for digestion?
Enterokinase - located in lumen of the duodenum on the brush border. Converts trypsinogen to trypsin.
36
What is function of trypsin?
Converts all other zymogens into their active forms.
37
What are the categories of pancreatic enzymes?
``` Proteases Nucleases Elastases Phospholipases Lipases Alpha-amylase ```
38
What stimulates zymogen secretion?
Cholecystokinin (CCK)
39
What stimulates the release of CCK?
Fat and amino acids in the duodenum. Vagal and reflex stimulation by the arrival of organic nutrients in the duodenum
40
How many lobes does the liver have?
4 - 2 major lobes with the right being bigger than the left. 2 minor lobes the caudate and the quadrate.
41
What is the aorta?
Defined area of the liver where all the vessels enter and exit. e.g hepatic portal artery/vein, lymphatics, ducts, hepatic nerve plexus. On inferior surface of liver.
42
What is the function of the coronary ligament?
Ligament that attaches liver to the underside of diaphragm.
43
What are lobules?
Hexagonal functional units of the liver separated by septa.
44
What is a portal triad?
Hepatic artery, hepatic portal vein and hepatic duct located at the corner of each lobule.
45
In what direction does flow in a lobule?
Oxygenated blood from hepatic arteries moves from outside into the lobule. out - in.
46
What is a hepatocyte?
Main cell of parenchymal liver tissue.
47
Why is the gut in series with the liver?
To allow the liver to filter blood - it can absorb any nutrients from the hepatic portal vein that just came from gut (food) and get rid of any toxins e.g metals, excess glucose etc.
48
What is Canaliculi?
Fine tubular channels situated throughout the liver parenchyma that join to form bile ductules and eventually the hepatic duct.
49
What are some functions of hepatocytes?
Bile synthesis Nutrient storage Detoxification Nutrient conversion
50
What are the components of bile?
``` Bile acids Lecithin Cholesterol Bile pigments - bilirubin from haemoglobin. Toxic metals Bicarbonate ```
51
What components of bile are produced by hepatocytes?
``` Bile acids Lecithin Cholesterol Bile pigments - bilirubin from haemoglobin. Toxic metals ```
52
How are bile acids produced?
Synthesised in liver from cholesterol
53
How are bile salts produced?
Bile acids are conjugated (chemically joined) with glycine or taurine to make a salt. Increases their solubility.
54
How does the gallbladder concentrate bile?
Uses a sodium pump to osmotically remove water. Water follows sodium out of the cell. Uses ATP to drive this process. The longer the time spent in the gallbladder the more concentrated the bile becomes.
55
What structure controls the release of pancreatic juice and bile into the duodenum?
Sphincter of Oddi
56
What is the mechanism of the sphincter of Oddi to control the release of bile?
CCK triggered by fat in stomach causes sphincter to relax and the gallbladder to contact so bile is released. When the sphincter is contracted it is closed and bile is being stored.
57
What is the main role of the jejunum?
Nutrient absorption (95%) Structurally it is ribbon like and pink as it has an extensive vasculature for absorption.
58
What is the main role of the ileum?
Sodium and water absorption to dehydrate chyme - create faeces for excretion.
59
What are some substances villi of the ileum absorb?
``` Sodium chloride Monosaccharides Amino acids Peptides Fats Vitamins Minerals Water ```
60
What do crypts secrete?
Water and chloride
61
Why do crypts secrete water?
Maintain lumenal contents in a liquid state. Promotes mixing of nutrients with digestive enzymes. Aids nutrient presentation to absorbing surface. Dilutes and washes away potentially injurious substances.
62
What is CFTR?
Cystic Fibrosis Transmembrane Conductance Regulator - protein within apical membrane that allows Chloride to leave the cell and subsequently water.
63
What is segmentation?
Pattern of contraction and relaxation within the small intestine to mix chyme and bring it into contact with enzymes and the absorptive surface.
64
What initiates the generation of segmentation contractions?
Depolarisation by pacemaker cells within the longitudinal muscle layer. The intestinal basic electrical rhythm then brings the membrane potential to threshold so an action potential is fired and the intestine segment contracts.
65
How can nerves affect segmentation?
Parasympathetic via vagus increases contraction. Sympathetic decreases contraction.
66
What hormone stimulates the initiation of a migrating motility complex?
Motilin.
67
What is the function of the migrating motility complex?
Move undigested material into the large intestine. | Limit bacterial colonisation of the small intestine.
68
In what direction does the bolus always move?
Into the are of relaxation towards the colon. | Controlled by myenteric plexus.
69
What are the stages of the gastroileal reflex?
Gastric emptying increases segmentation activity in ileum. ileocaecal valve opens. Chyme enters large intestine. Colon distends. reflex contraction of ileocaecal valve prevents back flux into small intestine.
70
What are the 4 parts of the colon?
Ascending Transverse Descending Sigmoid
71
How does the muscularis externa layer of the colon differ from the rest of the gut tube?
It has a complete circular muscle layer but an incomplete longitudinal layer.
72
What is taeniae coli?
3 separate longitudinal ribbons of smooth muscle that sit just below the serosa. Found in all 4 sections of the colon.
73
What causes the haustra of the colon?
Contractions of the taeniae coli create the pouches.
74
Describe the mucosa of the colon?
Large, straight crypts lines with a large number of goblet cells - provides lubrication for the movement of faeces.
75
Describe the rectum?
Straight muscular tube situated between the end of the sigmoid colon and anal canal. Has a simple columnar epithelium and a thick muscularis externa.
76
What is the anal canal?
Part of the gut tube between distal end of rectum and the anus. Thicker muscularis than the rectum due to the internal anal sphincter.
77
What is the external anal sphincter made of?
Skeletal muscle
78
What is the epithelium of the anal canal?
Begins as simple columnar but gradually becomes stratified squamous.
79
What is the nervous nature of the internal anal sphincter?
Autonomic - involuntary
80
What is the nervous nature of the external anal sphincter?
Somatic - voluntary.

Gastrointestinal System (2 decks)

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