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Human Physiology Module > GI tract Flashcards > Flashcards

GI tract Flashcards

1
Q

What organs does the GI tract flow through?

A

Mouth
Pharynx
Oesophagus
Stomach
Small intestine: Duodenum ? Jejunum
? Ileum
Large intestine: Cecum ? Ascending ?
Transverse ? Descending ? Sigmoid
Rectum ? Anus

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2
Q

What are accessory digestive organs?

A

Supply secretions contributing to
the breakdown of food

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3
Q

Name some accessory digestive organs.

A

Teeth & tongue
Salivary glands
Gallbladder
Liver
Pancreas

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4
Q

What are the 4 layers in the walls of the GI tract?

A

Mucosa, Submucosa, Muscularis Externa and Serosa.

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5
Q

\What are the three layers in the mucosa?

A

Mucous membrane, Lamina propria and muscularis mucosae.

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6
Q

What are the cells called that makes up the mucous membrane? These cells can be classified differently depending on their function- what are these functions?

A

The cells in the mucous membrane (in the mucosa) are enterocytes. These enterocytes can be absorptive cells, exocrine cells or endocrine cells. If the cells are absorptive, they are specialized with the absorption of nutrients through the whole GI tract. If the cells are exocrine, they are specialized to secreting substances into the GI tract and spaces surrounding the GI tract. For example, there may be goblet cells that secrete mucous to create a coating in the GI tract to protect against abrasion and substances in the lumen. If the cells are endocrine, they are releasing hormones to bring about a function.

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7
Q

What does the submucosa layer contain?

A

A lot of elastic tissue, to tolerate stretching of the GI tract if larger substances are passing through. This layer also contains large blood vessels and lymphatic vessels. On the outside of this layer are nerve cells called the submucosal plexus. These nerves are part of the enteric nervous system.

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8
Q

What is the enteric nervous system?

A

The enteric nervous system is a system, independent of the autonomic and sympathetic nervous system. The enteric nervous system runs along the gastrointestinal tract, and is capable of regulating the functions of the GI tract.

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9
Q

What are the two important neurons in the GI tract?

A

Submucosal plexus and myenteric plexus.

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10
Q

What is peristalsis?

A

Peristalsis is a process of the contraction and relaxation of muscles to allow the movement of food down the GI tract.

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11
Q

What muscles in the GI tract allows propulsion activity to occur during peristalsis?

A

The inner circular layer and the outer longitudinal layer in the muscularis externa.

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12
Q

Give a brief description of what occurs during peristalsis.

A

During peristalsis, the muscle action occurs in segments. In the proximal segment, the circular muscle contracts and the longitudinal muscle relaxes. This decreases the diameter of the lumen of the GI tract, that food is forced down.

Simultaneously, in the distal segment, the circular muscle relaxes and the longitudinal muscle contracts. This causes an increase in the diameter of the lumen. Hence, this allows an easier flow of the food that was just forced down.

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13
Q

Where does peristalsis normally occur?

A

The oesophagus and small intestine.

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14
Q

What is segmentation?

A

Segmentation is a non-propulsive action. It is so that when a part of the GI tract relaxes, the segments on BOTH sides contract. This ensures the direction of travel of food goes both ways, and is not uni-lateral.

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15
Q

How is segmentation in the GI tract useful?

A

It aids in digestion because it allows the mixing of food and it brings digestive products in close contact with epithelium.

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16
Q

Where does segmentation dominantly occur along the GI tract?

A

In the small intestine.

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17
Q

What are sphincters?

A

Sphincters are muscles that are able to open and close passages in the body to regulate the flow of substances such as bile, urine, and feces.

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18
Q

What is the role of the myenteric plexus neurons?

A

Controls the mutability and contraction of sphincters.

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19
Q

What is the role of submucosal plexus neurons?

A

Senses environment and regulates GI function like absorption, secretions and digestion.

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20
Q

What three main regions can the stomach be separated into?

A

The fundus (stores food), the corpus and the antrum.

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21
Q

What is the migrating motor complexes?

A

MMc is a process that occurs between meals. The process initiates in an empty stomach and travels along the whole of the small intestine in order to remove undigested material. This process normally removes larger undigested material and old cell debris, to prevent the production of any bacteria colonies. As well as this, there is an increase in secretions from accessory glands. MMC is inhibited when food is ingested again, resulting in normal digestive motility.

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22
Q

What are the 4 major activities of the GI tract?

A
  1. Motility
    Propels ingested food from mouth to rectumPropels ingested food from mouth to rectum
  2. Secretion
    Aids in the digestion and absorption processAids in the digestion and absorption process
  3. Digestion
    Chemical and mechanical breakdown of foodChemical and mechanical breakdown of food
  4. Absorption
    Active or passive transfer of substances fromActive or passive transfer of substances from
    lumen to the ECFlumen to the ECF
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23
Q

Briefly describe the process of gastric motility and emptying in the stomach.

A

The smooth muscle in the fundus relaxes. Throughout this whole process the pyloric valve is closed (at the end of the pylorus). The corpus has pacemaker cells that generates action potentials and causes the corpus to contract. This contraction and increase in pressure causes the pyloric valve to open slightly, so the digestive products can now leave the pylorus.

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24
Q

What is the role of the colon in the GI tract?

A

1) mix chyme;
2) expose chyme to surface membrane to
facilitate absorption of minerals & water;
3) propel contents towards rectum for storage
and eventually elimination

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25
Q

What processes in the colon contributes to the motility of digested products?

A

Haustration: Segments (haustra) have
pacemaker cells causing smooth muscle
to contract at regular intervals (2 per
hour) similar to segmentation. Slow!
Mass Movement: Like a peristatic wave,
but contraction lasts longer before
relaxation leading to propulsion of formed
faeces to rectum.
Gastrocolic Reflex: Meal in stomach
increases colonic motility and increase the
frequency of mass movement.

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26
Q

What part of the GI tract takes longer to transport digested material?

A

The large inestine- digested material travels through here for around 1-2 days.

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27
Q

What part of the GI tract takes less time to transport digested material?

A

The oesophagus; around 10 seconds.

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28
Q

What can affect the transit time (time for digested products to travel) in different parts of the GI tract?

A

Diet, Stress, congenital abnormality, pathogens

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29
Q

State the stimulus that causes the following hormones to be released: gastrin, somatosatin, cholecystokinin, secretin, GIP.

A

Gastrin- amino acids; Somatostatin-acid; cholecystokinin-fat/protein; secretin-pH; GIP-glucose/fat

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30
Q

What is the role of neurotransmitter Acetylcholine in the GI tract?

A

Smooth muscle contraction, Increase secretion, Sphincter relaxation.

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31
Q

What is the role of the neurotransmitter, nitric oxide, in the GI tract?

A

Smooth muscle relaxation.

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32
Q

What is mechanical digestion?

A

Chewing of food (mastication) creates a bolus of food that can be easily swallowed.

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33
Q

What helps with chemical digestion in the mouth?

A

Saliva.

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34
Q

What enzymes are present in the saliva that aids in chemical digestion? What is the other purpose of saliva?

A

Salivary amylase begins to break down starch. Salivary lipase begins to break down lipids. Another role of saliva is the mucus that lubricates the food to make swallowing easier. Also lysozymes present that kills bacteria.

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35
Q

What are 3 functions of the stomach?

A

Protection
Parietal cells secretes gastric acid (HCl, pH ~1-2). Kills most
microorganisms.
Digestion
Protein digestion (pepsin)
Some lipid digestion (lipase)
Storage
Empty is size of an adult human fist, but can expand to a
capacity of approx. 4 litres

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36
Q

What are the functions of the liver?

A

Metabolic regulation
Storage and systemic release of nutrients and vitamins
Regulation of blood
Plasma protein regulation
Removal of old red blood cells
Production of bile
Required for fat digestion

37
Q

Where is bile produced? Where is bile stored? Where is bile secreted?

A

Bile is a greenish yellow liquid
produced by the liver and stored in
the gallbladder and secreted into
duodenum via the bile duct

38
Q

What are the constituents of bile?

A

HCO3-
Cholesterol, bile salts
Pigments (these are excretory
products formed from the
breakdown of haemoglobin).

39
Q

What does bile help with?

A

Fat digestion.

40
Q

What are the constituents of pancreatic juice?

A

Digestive enzymes, buffer

41
Q

What is the function of the small intestine?

A

Projection, digestion and dilution

42
Q

What may the small intestine secrete for protection?

A

Mucus, Alkaline solutions

43
Q

What may the small indestine secrete for digestion?

A

Alkaline solutions, secretin and CCK, Bile, enzymes, trypsin and water

44
Q

Some proteins or molecules have the phonetic ending ‘ogen’. What does this normally signify?

A

ogen’ normally signifies that the molecule has no real function until it is activated by another substance.

45
Q

Pepsinogen is secreted into the stomach for the break down of proteins. What molecule activates it and what does it turn into?

A

In the presence of HCl, pepsinogen turns into pepsin. Pepsin then catalyses the breakdown of proteins.

46
Q

From which cells in the stomach is pepsinogen secreted?

A

Chief cells

47
Q

From which cells in the stomach is HCl secreted?

A

Parietal cells

48
Q

Name the 3 different components of the small intestine.

A

Duodenum, Jejunum, Ileum

49
Q

How long is the small intestine?

A

About 6 metres long.

50
Q

What molecule is responsible for the breakdown of proteins in the small inestine?

A

Trypsinogen

51
Q

Where does the trypsinogen in the small intestine come from?

A

The trypsinogen comes from the pancreatic juices that enters the duodenum via the pancreatic duct.

52
Q

Trypsinogen by itself has no function. What activates it and what does it turn into?

A

Trypsinogen is activated by an enterokinase enzyme that is attached to the enertocytes lining the duodenum wall. Trypsinogen turns into trypsin. Two other enzymes comes from the pancreatic duct, chymotrypsinogen and Procarboxypeptidase. They are activated by the trypsin to form chymotrypsin and carboxypeptidase.

53
Q

Why are there multiple enzymes that break down protein in the small intestine?

A

The way they break down the proteins are different to form different products- amino acids, dipeptides, tripeptides.

54
Q

What monomers make up the following disaccharides: Maltose, sucrose, lactose.

A

Maltose- 2x glucose. Sucrose- glucose + fructose. Lactose- glucose and galactose.

55
Q

What does it mean if someone is lactose intolerant?

A

The person does not have the lactase enzyme present in the border of the small intestine and so is unable to breakdown lactose into glucose and galactose.

56
Q

Where does lipid digestion start in the body?

A

It starts in the mouth (lingual lipase), then the stomach (gastric lipase), then the small inestine (pancreatic lipase).

57
Q

Unlike all the other molecules (like proteins and carbohydrates), why can’t lipids be broken by their respective enzyme, lipase?

A

Lipids are a very hydrophobic molecule, so it does not interact with water at all. This especially shows in the stomach, where the lipid molecules join together to form fat lobules on top of the gastric digestive juices. This also means lipase is unable to interact with the lipids because lipase is hydrophilic, like all other enzymes. (It basically means that due to all the non-polar regions on the outside of the lipids, the polar regions of the enzyme is unable to interact with it).

58
Q

What is the solution to the breakdown of lipids?

A

Emulsification, which occurs in the small intestine. This happens due to the bile salts that enters the duodenum from the gallbladder. The bile salts does not have any actual enzymes that digest the lipids. Instead, there is derivatives of cholesterol that had been synthesised in the liver. Cholesterol itself is quite hydrophobic but it has one polar ring (with an -OH), and this region is the part that interacts with the acquiesce pancreatic juices, whilst the rest of the molecule binds onto the fat lobule. The surrounding of the fat lobules in bile salts (and hence cholesterol molecules) initiates the breakdown of triglycerides into smaller emulsified fat droplets (emulsification). This increases the surface area of the lipids that is exposed to water, increasing its susceptibility to enzyme digestion.

59
Q

What happens after emulsification?

A

Lipase finally digests the emulsified fat droplets into free fatty acids and monoglycerides. These then dissolve to form micelles.

60
Q

What is the role of colipase in lipid digestion?

A

Colipase aids in fat digestion by helping lipase attach to fat droplets and as a cofactor for the lipase enzymes.

61
Q

Give a brief outline of glucose absorption into the bloodstream.

A

Sodium ions in the epithelial cells lining the duodenum is actively pumped into the space next to the capillaries (this is antiport because this also causes potassium ions to be pumped into the epithelial cells; so a sodium potassium pump). This decreases the concentration of sodium ions in the epithelial cells, so creates a chemical force sodium ions in the small inestine lumen. Sodium ions travels down the concentration gradient by being co-transported with glucose (symport). The glucose then diffuses into the blood stream.

62
Q

What are exopeptidisases? Give examples.

A

Exopeptidases are enzymes that breaks the peptide bond on the terminal amino acid, or second to last amino acid of the polypeptide chain, which produces one amino acid or a dipeptide. Examples of exopeptidases include aminopeptidases and carboxypeptidases.

63
Q

The amino acids, dipeptides and tripeptides in the small intestine is absorbed into the bloodstream by what processes?

A

Activate transport- The molecules are actively transported into the epithelial cells lining the small intestine. They then passively diffuse into the bloodstream.

64
Q

What are endopeptidases?

A

Enzymes that break peptide bonds on non-terminal amino acids. E.g. trypsin, pepsin and chymotrypsin.

65
Q

Briefly describe the process of absorbing fats.

A

Fatty acids and monoglycerides are emulsified to form micelles. Fatty acids enter the epithelial cells and link to form triglycerides. Triglycerides combine with proteins inside the Golgi body to form chylomicrons. Chylomicrons enters the lacteral and are transported away from the intestine.

66
Q

How does the absorption of water occur in the small inestine?

A

In the duodenum and jejunum of the small inestine is where the absorption of most organic nutrients occur. The absorption creates an osmotic gradient for water absorption, as the water potential in the blood is now lower compared to the small intestine.

67
Q

How much water does the intestines absorb each day?

A

9000 to 10000 ml

68
Q

When nutrients has entered the blood, one of the absoption routes it can take is through the hepatic portal system. What happens when it goes through the system?

A

The nutrients absorbed enters the hepatic portal circulation and is transported to the liver. A few things the liver does is storage of glucose, detoxification. The nutrients then enters the general circulation, travels to the heart, then to the lungs where it picks up oxygen and removes waste. Now the oxygen and nutrient rich blood travels to body cells.

69
Q

Another absorption route is the enterohepatic circuit. What is absorbed here and why?

A

In the enterophepatic system, bile salts are absorbed in the capillary, rather than going through the whole intestines and being excreted. The capillaries goes to the hepatic portal vein, which travels the bile salts to the liver, where it is brought to be stored in the gallbladder,and when needed secreted in the small intestine. The idea is that the bile salts is recycled to be used again, rather than having to make new bile salts due to excretion. In a single meal, bile salts are recycled 2-5 times.

70
Q

If there is a stimulus in the GI tract, what receptors would detect it and to what type of stimulus?

A

Chemoreceptors detected a change in substances. Mechanoreceptors detects distention in the GI wall. Osmoreceptors detects osmolarity of lumen contents.

71
Q

When a stimulus is detected in the GI wall, the body can take a long reflex pathway or a short reflex pathway. What is the difference?

A

If the body takes a short reflex pathway, the signal travels to the enteric nervous system, which is contained in the GI system and is dependent of the autonomic nervous system. Hence, the response brought about by the short reflex pathway gives a quicker response compared to the long reflex pathway, which goes all the way through the CNS.

72
Q

What are some responses that are brought about in the gastrointestinal system?

A

Muscle contraction, exocrine secretion (like enzymes, mucus, acid and bicarbonate) and endocrine secretion.

73
Q

Where is the gastrin formone secreted and in respone to what hormone? What action does it bring about through its secretion?

A

Gastrin is secreted in the stomach in response to proteins and protein digestion products in the stomach, distension in the stomach (stretching of the stomach walls to accommodate food). The release of gastrin stimulates gastric secretion and motility, motility and relaxation of the ileocecal sphincter, and stimulates mass movement in the colon. Essentially it helps with digestion and mortality in the stomach onwards.

74
Q

Where is the cholecystokinin secreted and to what stimulus? Whar response does its secretion bring about?

A

CCK is secreted into the duodenum and jejunum in response to fat or protein digestion in the duodenum. This inhibits gastric secretions and motility because most, if not all, the food has left the stomach (stopping release of gastric secretions prevents an extremely acidic environment). It also stimulates pancreatic enzyme secretion, bile secretion by the liver and gallbladder contraction.

75
Q

Where is the secretin hormone secreted and in response to what stimulus? What responses does the release of secretin bring about?

A

The secretin hormone is released in the duodenum and jejunum, in response to acid in the duodenum. Its release inhibits gastric secretion and motility, stimulate bicarbonate secretion, increases actio of CCK on pancreatic anxyme secretion and bile secretion by the liver.

76
Q

Where is the hormone glucose-dependent insulintropic peptide secreted and in response to what stimulus? What responses does the release of GIP bring about?

A

GIP is secreted in the duodenum and jejunum, in response to glucose, fats or acid in the duodenum, as well as distention in the duodenum. Its secretion inhibits gastric secretion and motility as well as stimulating insulin secretion in the pancreas.

77
Q

The cephalic phase is a control or regulation phase of the GI function. What is its main function?

A

The cephalic phase prepares the GI system for arrival of a meal.

78
Q

How is the cephalic phase initiated- how does it know when a meal is coming?

A

Via the senses, like the sight, smell, taste and thought of food.

79
Q

In the cephalic phase, what steps actually occur? For example, what is secreted or produced?

A

Salivation occurs, production of gastric juices and gastric contractions.

80
Q

What is the gastric phase?

A

The gastric phase is when our meal is in our stomach, and what our body does in response to this. Here there is the production of gastric secretion and increased gastric motility. This is done via hormone gastrin and if needed somatostatin, to decrease acid secretion.

81
Q

What is the intestinal phase?

A

This phase is when the meal is in the inestine. In this phase, there is the secretion of bicarbonate, digestive enzymes and bile.

82
Q

In what places is carbohydrates broken down: mouth, stomach or small intestine?

What enzymes are present in each of these areas responsible for their breakdown?

A

Carbohydrates are broken down in the mouth and small intestine.
In the mouth, carbs are broken down by the enzyme amylase.
In the small intestine, carbs are broken down by pancreatic amylase and brush border enzymes (enzyme that exist and bound to the epithelial walls of the small enzyme), like lactase and maltase.

83
Q

In what places is proteins broken down: mouth, stomach or small intestine?

What enzymes are present in each of these areas responsible for their breakdown?

A

Proteins are broken down in the stomach and small intestine.

In the stomach, proteins are digested by an enzyme called pepsin.

In the small intestine, proteins are digested by 3 free enzymes: trypsin, chymotrypsinogen and carboxypeptidase. There are also brush border enzymes like enterokinase.

84
Q

In what places is lipids broken down: mouth, stomach or small intestine?

What enzymes are present in each of these areas responsible for their breakdown?

A

Lipids are broken down in the mouth, stomach and liver.
In the mouth, lipids are broken down by lingual lipase.
In the stomach, lipids are broken down by gastric lipase.
In the small intestine, lipids are broken down by pancreatic lipase.

85
Q

What is the brush border?

A

The brush border is one layer of epithelial cells lining the GI tract in the small intestine, that forms a structure called microvilli, specialised for absorption of digested material into the bloodstream.

86
Q

What is the primary site of absorption of: glucose, water and vitamins?

A

Glucose- small intestine (jejunum)
Water- Most in small intestine
Vitamins- Fat soluble absorbed in duodenum and jejunum. Water soluble vitamins absorbed in ileum.

87
Q

State the route of absorption of glucose from the gut to places it is needed around the body.

A

Small intestine, absorbed into the blood, mesenteric veins, hepatica portal vein, liver, hepatic vein, vena cava, heart, lungs, circulated around the body, given to body cells.

88
Q

How is the anatomy of the stomach and small intestine different to serve for their different functions?

A

The stomach has gastric pits (glands) that are packed with secretory cells, as a lot of mechanic digestion takes place in the stomach via the secretion of digestive juices.
Secretion and digestion does occur in the small intestines, but a large part of its function is absorption. It is specialised to do this because the brush border is a one layer thick lining, with a structure called microvilli, specialised for absorption.

89
Q

What ducts leads into the small intestine that helps with digestion?

A

The liver makes digestive juices that is stored in the gallbladder, and a bile duct allows it to be secreted into the small intestine. The pancreas makes pancreatic juices that leaves via the pancreatic duct, and joins with the bile duct to be secreted in the small intestine.

Human Physiology Module (5 decks)

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