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Biosciences 2 > Gastrointestinal System > Flashcards

Gastrointestinal System Flashcards

1
Q

What is the gastrointestinal system?

A

The organs that food and liquids travel through when they are swallowed, digested, absorbed, and leave the body as faeces

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2
Q

What is the function of the GI system?

A

Breaks down food into nutrients, which the body uses for energy, growth and cell repair
Food and drink must be changed into smaller molecules of nutrients before the blood absorbs them and carries them to the cells throughout the body
The body breaks down food and drink into carbohydrates, proteins, fats and vitamins

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3
Q

What are the organs of digestion?

A 
Mouth
Oesophagus
Stomach
Small intestine
Large intestine
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4
Q

What are the GI accessory organs?

A

Liver
Gall bladder
Pancreas

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5
Q

Describe the process of digestion

A
  1. Begins in the mouth; chewing breaks down food
  2. Food mixes with digestive juices; breaking down molecules
  3. Small molecules absorbed through wall of small intestine into bloodstream
  4. Bloodstream delivers molecules to the body
  5. Water passes through large intestine and out of the body as solid matter
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6
Q

Describe the digestive process in the mouth

A

Movement= chewing, Digestive Juices= saliva

Food Particles Broken Down= starches

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7
Q

Describe the digestive process in the oesophagus

A

Movement= swallowing
Digestive Juices= none
Food Particles Broken Down= none

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8
Q

Describe the digestive process in the stomach

A

Movement= upper muscle in the stomach relaxes to let food enter and lower muscle mixes food with digestive juices
Digestive Juices= stomach (hydrochloric) acid
Food Particles Broken Down= Protein

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9
Q

Describe the digestive process in the small intestine

A

Movement= peristalsis
Digestive Juices= small intestine digestive juice
Food Particles Broken Down= starches protein and carbohydrates

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10
Q

Describe the digestive process in the pancreas

A

Movement= none
Digestive Juices= pancreatic juice
Food Particles Broken Down= starches, fat and protein

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11
Q

Describe the digestive process in the liver

A

Movement= none
Digestive Juices= bile acids
Food Particles Broken Down= fats

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12
Q

Where do carbohydrates come from in the diet?

A

Mostly from plants
Lactose from milk
Small amount from glycogen from meat
Sugar from fruits, can sugar and milk

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13
Q

Describe the breakdown of carbohydrates

A

Begins in the mouth; salivary amylase (POLYSACCHARIDES (starch) to DISACCHARIDES (sucrose, lactose, maltose)

Ceases in the stomach due to low pH (too acidic)

Pancreatic amylase restarts breakdown in the small intestine
(POLYSACCHARIDES (starch) to DISACCHARIDES (sucrose, lactose, maltose)

Brush border enzymes (maltase, lactase and sucrase) in small intestine breakdown DISACCHARIDES to very small MONOSACCHARIDES (glucose, fructose, galactose)

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14
Q

Where do lipids (fats) come from in the diet?

A

Saturated fats= animal fat and some plants (coconut)
Unsaturated fats= seeds, nuts and vegetable oil
Cholesterol= egg yolks and milk products

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15
Q

Describe the breakdown of lipids- fats

A

Starts in the stomach but action is limited

Lipase in stomach starts the digestion of triglycerides

Limited activity, works best at a pH of 5-6 (most occurs in the small intestine)
- Bile and pancreatic juice rich in bicarbonate ions which increase alkalinity of acid chyme from the stomach (increases the pH)

Bile emulsifies fats which increases surface area (enabling enzymes to work)

The enzyme lipase is released from pancreas and brush border
-Triglycerides to fatty acids and glycerol

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16
Q

Where does protein come from in the diet?

A

Molecules of amino acid polymers

Eggs, milk and most meat proteins are complete proteins so provide all the bodies amino acid requirements for tissue maintenance and growth

Legumes, nuts and cereals are incomplete because they lack one or more type of amino acid

Cereals and legumes when combines together provide all the essential amino acids

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17
Q

Describe the breakdown of protein

A

Begins in the stomach: pepsin breaks down large polypeptides

Continues in the small intestine: enzyme chymotrypsin/trypsin in pancreatic juice breaks down smaller polypeptides into even smaller peptides

Brush border enzymes (peptidases) breakdown smaller peptides into amino acids

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18
Q

Where do vitamins come from in the diet?

A

Organic nutrients required in small amounts. No one food provides all the required vitamins

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19
Q

How are vitamins broken down?

A

Most vitamins function as coenzymes. They work with an enzyme to produce a particular type of catalyst

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20
Q

Where are minerals found in the diet

A

Body requires adequate supply of 7 minerals: calcium, potassium, phosphorus, sulphur, sodium, chloride, magnesium and trace of others

Fats and sugars- practically no minerals

Cereals and grains- poor source

Mineral rich- vegetables, legumes, milk and some meat

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21
Q

Explain the process of absorption

A

Nutrients, once they are broken down to smaller molecules, can be absorbed through the wall of the villi and enter the blood

  • Protein as amino acids
  • Carbohydrates as simple sugars: glucose, fructose and galactose
  • Fat as glycerol

Some of the digested fat is absorbed into the lymphatic capillaries
-Fat as fatty acids

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22
Q

What happens to digested food molecules?

A
  • The small intestine absorbs most digested food molecules, as well as water and minerals and passes them on to other parts of the body for storage or further chemical change
  • Specialised cells help absorbed materials cross the intestinal lining into the blood stream
  • The bloodstream carries simple sugars, amino acids, glycerol and some vitamins and salts to the liver
  • The lymphatic system; a network of vessels that carry white blood cells and a fluid called lymph throughout the body, absorbs fatty acids and vitamins
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23
Q

What is the order of movement through the GI tract?

A
  1. Oesophagus
  2. Stomach
  3. Liver
  4. Gall Bladder
  5. Pancreas
  6. Small Intestine
  7. Ileum
  8. Large Intestine (colon)
  9. Rectum
  10. Anus
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24
Q

Describe what happens in the mouth

A

Food enters the mouth and is ground down by the teeth (mechanical digestion) and mixed with saliva containing the enzyme: salivary amylase (chemical digestion) before being swallowed

25
Q

What are the 3 stages of swallowing?

A

Oral (voluntary)
Pharyngeal (involuntary)
Oesophageal (involuntary)

26
Q

Describe the properties of saliva

A
  • Aids digestion
  • Breakdown of food
  • Keeps mouth clean by washing away bacteria and food particles. Controls the amount of good and bad bacteria in the mouth
  • When saliva doesn’t travel freely in the mouth, this may lead to infection, also increase in dental carries. Reduced saliva also causes mouth soreness and reduces ability to taste
27
Q

Describe how saliva is produced

A

Parotid gland- in front of and beneath the ear; secretes saliva through the parotid duct into the mouth

Sublingual gland- under the tongue, in the floor of the mouth

Submandibular gland- situated both superiorly and inferiorly to the posterior aspect of the mandible

28
Q

Describe the properties of taste

A
  • Very limited
  • Taste buds only detect bitter salty sour and sweet
  • It is the sense of olfaction (smell) that allows us to discern subtle differences in the flavour of food
29
Q

Describe the function of the pharynx

A
  • Short section of tube
  • Extends from back of mouth to oesophagus
  • Food passes from mouth into oropharynx and laryngopaharynx
  • Muscles in wall of pharynx contract propelling food
  • The epiglottis closes the larynx protecting the trachea, so food is routed into the oesophagus, not the trachea
30
Q

Describe the function of the oesophagus

A
  • The oesophagus is a muscular tube from to the stomach 25cm long
  • Oesophagus goes through the diaphragm
  • Food and liquid travel aided by involuntary muscles
  • The oesophageal sphincter controls passage of food and liquid to the stomach. Where it joins the stomach is surrounded by the cardiac sphincter
  • As food approaches the sphincter, it relaxes to allow food and liquid to pass
  • Food passes from oropharynx, down the oesophagus to the stomach by peristalsis. Mucus is secreted lubricating the food
  • Peristalsis: waves of muscular contraction and relaxation in the walls of the tract which squeezes food along and mixes it
31
Q

Describe the function of the stomach

A
  • Stores swallowed food and liquids
  • The muscle of the upper part relaxes to accept food and liquid
  • The muscle of the lower part mixes food with digestive enzymes
  • Digested food (chyme) is slowly emptied into the small intestine through a sphincter
  • Intrinsic factor enables B12 to be absorbed from intestine
  • Absorbs alcohol, alcohol, aspirin and some fat-soluble substances
  • The food is converted to a creamy paste called chyme which is delivered to the duodenum via the pyloric sphincter
32
Q

What are the 5 major functions of the stomach?

A 
Temporary storage of food;
Controls rate of food entering duodenum;
Acid secretion and antibacterial action;
Fluidisation of stomach contents;
Preliminary digestion with pepsin and lipases
33
Q

What are the muscular layers of the stomach?

A

Longitudinal layer
Circular layer
Oblique layer

34
Q

What is the purpose of the muscular layers?

A

Chun, mix and break food into smaller pieces

35
Q

What are the four regions of the stomach

A

-J-shaped organ. Four regions: CARDIA (manufactures digestive juices,)
FUNDUS (collects digestive gases,)
BODY (secreted pepsinogen and hydrochloric acid,)
PYLORUS (secretes gastin, pepsinogen and mucus)

36
Q

What is the lining of the stomach?

A

Mucosa membrane- has many folds, called rugae, enabling expansion when full

37
Q

How many litres of gastric juice are produced daily?

A

2-3 litres (nearly all is reabsorbed in the intestine)

38
Q

What is the pH of gastric juice?

A

1.5-2.0- very acidic (kills most pathogenic organisms)

39
Q

What processes break down stomach contents?

A

Broken down mechanically (muscular activity)

Food is also broken down chemically (enzyme activity)

40
Q

Describe the function of the duodenum?

A
  • First section of the small intestine- 25cm long
  • A duct enters the duodenum delivering bile from the liver and pancreatic juice from the pancreas: the hepatopancreatic ampulla or ampulla of Vater
41
Q

What are the accessory organs to the duodenum?

A

Liver
Gall bladder
Pancreas

42
Q

What are the functions of the liver and gall bladder?

A
  • Liver produces bile
  • Bile is stored and concentrated in the gall bladder
  • The gall bladder releases bile when fatty chyme enters the duodenum
  • Bile emulsifies fat into tiny particles
  • Tiny particles of fat result in an increased surface area for digestive enzymes to work on
  • Bile rich in bicarbonate enzymes
43
Q

What are the functions of the pancreas?

A

-Consists mainly of exocrine glands that secrete enzymes to aid digestion of food in small intestine
-Enzymes produced:
LIPASE (breaks down fats)
PEPTIDASE (breaks down protein)
AMYLASE (breaks down carbohydrates)
-Enzymes from the pancreas are released into duodenum via the duodenal ampulla; the same place that bile from the liver drains into
- Pancreatic juice contains various enzymes that break down all food types
- Pancreatic juice enters the duodenum via the hepatopancreatic ampulla or ampulla of Vater (released with bile)
-Pancreatic juice and bile- rich in bicarbonate ions which is alkaline this neutralises the acid chyme in duodenum
-Amylase and lipase function well in a more alkaline environment

44
Q

What is the pancreatic exocrine secretion?

A

Hormone called cholecystokinin

45
Q

What is the structure of pancreas?

A

Head, neck, body, tail

46
Q

Describe the function of the small intestine

A

The site where most of the chemical and mechanical digestion takes place

  • Lined with absorptive mucosa
  • Smooth muscle wall; rhythmic contractions (peristalsis)
  • Muscles mix food with digestive juices from pancreas, liver and intestine and push food forward to help with further digestion
  • Walls absorb the digested nutrients into bloodstream. Blood delivers these nutrients to the rest of the body
47
Q

What are the three main sections of the small intestine?

A
  • Duodenum
  • Jejunum
  • Ileum
48
Q

Describe the passage through the jejunum and ileum

A
  • Chyme moves backwards and forwards by muscular contractions in the small intestine; mixing the chyme with bile and pancreatic juices
  • 90% nutrients absorbed in small intestine
  • Villi increase surface area for absorptions
  • Glands between the villi release enzymes (brush border enzymes)
  • Food residues move through the small intestine by peristalsis and into the large intestine via the ileocaecal valve
49
Q

What is peristalsis?

A

The involuntary constriction and relaxation of the muscles creating a wave like movement

50
Q

What are villus?

A
  • Tiny protrusions in the wall of the small intestine, well adapted for absorbing digested food by diffusion
51
Q

Describe the properties of villlus?

A
  • Increase surface area of intestinal wall- more surface area available for absorption of food
  • Thin cell walls allow molecules to pass through to capillaries./ blood quickly
52
Q

What are the functions of the small intestine?

A
  • Completion of chemical digestion
  • Bile emulsifies fat
  • Duodenum receives pancreatic enzymes from pancreas and bile from the liver and gall bladder
  • Pancreatic enzymes and ‘brush border enzymes,’ break large molecules into smaller molecules
  • Major site of absorption of nutrients into blood due to large surface area of small intestine
  • Onward movement of non-digested or absorbed contents to the large intestine via the ileocaecal valve
53
Q

What are the properties of the large intestine?

A
  • Waste products of digestive process include indigested parts of food and older cells from the GI tract lining
  • Muscles push these waste products into large intestine
  • Absorbs water and any remaining nutrients and changes waste from liquid to stool
  • 1.5m long
  • Nutrients have been absorbed before reaching the large intestine so there are no villi or digestive enzymes
  • Bacteria colonise the colon, ferment indigestible carbohydrates and synthesize vitamin B and K
  • Mostly water, some electrolytes and vitamin B and K absorbed into the bloodstream
  • Mass movements: a long slow-moving peristalsis occur 3-4 times a day to move the contents towards the rectum
  • The rectum stores stool until it pushes stool out of the body during a bowel movement
  • Faeces contain undigested food residues, mucus, sloughed off epithelial cells, millions of bacteria, and just enough water to allow smooth passage
54
Q

Describe the process of defecation

A
  • The rectum is normally empty
  • During mass movement faeces is forces into the rectum
  • Stretch receptors in the rectal wall sense the distention of the rectal walls
  • The information is sent to the nerves of the spinal cord and the information is sent back to the walls of the rectum causing them to contract and the anal sphincter to relax
  • Faeces is forced into the anal canal through the internal sphincter, and we can decide whether to relax or tighten the external sphincter (voluntary control)
  • During defecation the muscles in the rectum contract to expel the faeces out of the body via the anus
55
Q

Describe hormone regulation

A

Cells in the lining of the stomach and intestine produce and release hormones, these hormones stimulate production of digestive juices and regulate appetite

56
Q

Describe extrinsic (outside) nerve regulation

A

Extrinsic nerves connect the digestive organs to brain and spinal cord which causes GI tract to contract or relax depending on whether there is food to digest

57
Q

Describe intrinsic (inside) nerve regulation

A

Triggered when food stretches the walls of the GI tract; releases different substances that speed up or delay movement of food and production of digestive juices

58
Q

What are the properties of GI tract?

A 
INGESTS food
PROPELS peristalsis
DIGESTS mechanical digestion (physical)
enzymes (chemical)
ABSORBS nutrients into the bloodstream
ELIMINATES waste material, faeces
59
Q

Describe the use of enzymes in the GI tract

A

Act as catalysts which speed up or bring about a chemical change without itself undergoing alteration

  • PEPSIN starts the breakdown of protein, releases as pepsinogen (inactive)
  • GASTRIC LIPASE starts the breakdown of fat
  • RENIN acts on milk products in children

Biosciences 2 (5 decks)

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