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Biology > Digestion > Flashcards

Digestion Flashcards

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1
Q

What is digestion?

A

the breaking down of ingested food into useable nutrient molecules that can enter the vascular or lymphatic system.

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2
Q

What does the digestive system consist of?

A
  • digestion achieved by gastrointestinal tract (tube from mouth to anus which breaks down food)
  • The accessory structures (digestive organs)- not part of the tract - (e.g. teeth, tongue, liver, pancreas that help by mechanical or chemical means - things which we can absorb into the vascular or lymphatic system)
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3
Q

What is our food composed off?

A

the major nutrients:

  • Carbohydrates
  • Protein
  • Fats (glycerol and fatty acids)

Vitamins- act as co-enzymes.
they can be either fat soluble A,D,E,K) OR wake soluble. (B AND C)

Minerals/trace elements- body requirements of 7 minerals- calcium, phosphorous, potassium, sulphur, sodium, chloride, magnesium) and trace amounts of. about aa dozen others. They serve other functions such as CA: bone, Fe- haemoglobin, Ca/Na/K- nerve/muscle)

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4
Q

What are the 6 processes of digestion consist of?

A

Ingestion- take food in
Propulsion- propel food through gastrointestinal tract
Mechanical Breakdown-in the stomach with teeth (accessory structure)
Digestion- chemically
Absorption- into vascular system
Defecation- get rid off it

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5
Q

What is the structure of the GI tract?

A

4 layers

  • Inner layer known as mucosa
  • Under sub mucosa
  • Layer of muscle
  • Outer serosa - tough outer protective connective tissue
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6
Q

What does mucosa contain of?

A
  • Mucosa usually consists of a simple columnar epithelium
  • layer of mucous which secrete many goblet cells to protect and lubricate the passage of food
  • in stomach and small intestine, the mucosa also contains cells secreting digestive enzymes and hormones
  • epithelial cells (simple columnar epithelium)
  • Lamina propria- contains aereolar connective tissue and containing protective lymphoid follicles
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7
Q

What is a lamina propria in the mucosa?

A

Lies underneath the epithelium which is aerolar connective tissue
-have lymphatic vessels of lymphatic system- protect body.

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8
Q

What is the submucosa?

A
  • loose areolar c.t
  • has layer of lymph and blood vessels
  • abundant nerve supply
  • elastic fibres/tissue due to the gastrointensital needs to be elastic as it needs to expand when we intake food.
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9
Q

What is in the muscular layer of the GI tract?

A

-2 layers of smooth muscle (inverted by autonomic system) : inner circular and outer longitudinal.

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10
Q

What is the function of this muscular layer?

A
  • Shove food along by the process of peristalsis.

- Food turned into a bolus (balls) and that is then pushed through GI tract by contraction of the muscle.

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11
Q

What is the main function of the mouth?

A

-responsible for ingestion

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12
Q

What is the structure of the mouth?

A

lined with stratified squamous epithelium

  • Has tongue which mixes the food with saliva, forming a bolus
  • tongue contains taste buds
  • teeth macerate the food (mastication- crush food)
  • mouth is connected to a number of glands whose secretions form saliva
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13
Q

What are the 3 salivary glands properties?

A
  • exocrine- into ducts

- contain both mucous and serious secreting cells

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14
Q

What are the 3 salivary glands?

A

-Parotid glands
-Submandiular gland
-Sublingual gland
(they produce saliva)

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15
Q

What do these secretions of saliva serve to?

A
  • dissolve the food so we can taste it
  • help form the food into a bolus
  • lubricate the mouth
  • begin digestion of starch and fats by producing amylase and lipase.
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16
Q

Where does the food end up once gone through mouth?

A
  • Back of throat- Pharynx- which can be divided into various regions
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17
Q

What is the Pharynx?

A

Where the food, fluids and air leave the mouth

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18
Q

What is the epiglottis?

A

allows air to pass down the trachea and is normally open

- If food gets stuck it will cause you to choke / lead to death

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19
Q

What happens when swallowing?

A
  • The epiglottis closes

- ensuring food and liquids to not enter the trachea but instead enter the oesophagus

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20
Q

What is the oesophagus?

A

a 25cm tube connecting the mouth to the stomach

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21
Q

What does the oesophagus consist of?

A

4 layers (previous layers stated)

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22
Q

What does the submucosa contain in the oesophagus?

A

contains mucous -secreting oesophageal glands, that aid the passage of the food.- LUBRICATE

23
Q

What is bolus in the oesophagus?

A

propelled by peristalsis ( about 8 seconds)

- drinks take 2 seconds

24
Q

What does the stomach serve to do?

A
  • store food
  • mixed food into’chyme’ (semi fluid)- continually going through contractions and mixed with digestive enzymes
  • begin the digestion of proteins and fats-carbs digestion happens in mouth
25
Q

Whats the stomach structure?

A

15-25cm long
Has a volume of 500ml
- When had a meal a volume can be up to 4L
- Is guarded at either end by a sphincter muscle
-An empty stomach has multiple longitudinal folds (rugae)
-Folds in stomach increases S.A
- Has the usual 4 layersof the GI tract

26
Q

What is on the surface on the stomach?

A

-has gastric pits- these are connected to gastric glands. opening to glands

27
Q

What does the gastric glands secrete?

A

mucous
-produce HCL
-Produce pepsinogen
-Secret Lipases
both HCL and pepsinogen combine to form pepsin which is a digetsive enyme that can digest proteins.
- Lipases digests fats
- Covered in a whole layer of thick mucous so it protects the stomach from acidiy and protein sigesting enzymes

28
Q

What does the smooth muscle of the stomach have?

A

both the normal circular and longitudinal layers as well as a 3rd layer, oblique layer

29
Q

What do these smooth muscle layers serve to do as part of the stomach?

A

to mix, grind and propel the food in the stomach ( constant contractions)

30
Q

What does the sympathetic activity do?

A

is decreased in digestion

31
Q

What does the parasympathetic activity?

A

-increases digestion

32
Q

What does the longitudinal muscle layer contain ?

A

enteric pacemaker cells

33
Q

What do the enteric pacemaker cells do?

A

they depolarise spontaneously, causing 3 slow waves of contraction (causing a.p) in the stomach every minute.

  • generates its own action potential
  • Leaky to Na ions
34
Q

What are the PACEMAKERs connected to?

A

the pacemaker of the stomach are connected to the surrounding smooth muscle by gap junctions, a.p spreads evenly throughout the stomach

35
Q

Where is the basic rhythm of contraction?

A

generated in the stomach
-can be modulated by the autonomic system as wells as by local tissue factors such as stomach stretch receptors and gastric secretions

36
Q

What is the small intestine?

A

where food leaves the stomach and enters in the small intestine

37
Q

What does the small intestine consist of?

A

Duodenum (25cm)
jejunum (2.5m)
ileum (3.6m)

38
Q

What does the small intestine do?

A
  • produces digestive juices
  • linked to liver, gall bladder and pancreas
  • They produce digestive enzymes that break down all categories of foodstuffs (e.g amylase., lipase, nuclease)- Pancreas
  • The liver and gall bladder act together to produce bile and bile emulsifies fat.
39
Q

What is emulsification

A

breaking fats into small bits via bile salts

40
Q

What is the small intestine for?

A

are specialised for absorption

  • surface area increased x600
  • 1cm tall circular folds of the mucosa and submucosa
  • 1mm tall villi(containing blood and lymph vessels)
  • microvilli on the absorptive epithelial cells(brush border)

total absorptive area of the small intestine = 200m2

41
Q

What is the structure of the small intestine?

A
  • same 4 layers as other areas of the GI tract - mucosa, subucosa, muscular layer and outer serosa
  • simple columnar epithelium= specialised for absorption
  • cells in mucosa which produce enzymes involved in carb and protein digestions
  • the epithelium also contains many mucous secreting goblet cells
  • Pits- connected to tubular glands which secrete intestinal juice
  • these contain mucous, antibacterial agents and other protective components of the immune system
42
Q

What is the large intestine?

A

it frames the small intestine on 3 sides

43
Q

What is the size of the large intestine?

A
44
Q

What is the main function of the large intestine?

A

To remove water from the food and store solid faces

  • retain water in body
  • little digestion occurs here
45
Q

What else does the large intestine contain?

A

bacteria that ferment any remaining carbs

  • carb digestion
  • involved in synthesis of vitamins B and K
46
Q

What is the structure of the large intestine?

A
  • Made of the same 4 layers as the GI tract
  • No villi o increase SA
  • Intestinal glands contain goblet cells that produce mucous- to ease the path of the faeces and protect the intestinal wall.
  • Most of the large intestine is lined by simple columnar- however the anal canal has stratified squamous epithelium
47
Q

What is the digestion of carbohydrates?

A
  • either monosaccharides, disaccharides or polysacchruides.

- NEED to be broken down into monosaccharides to be absorbed in the vascular system

48
Q

Process of digestion of carbs?

A
  • Happens in mouth
  • Amylase from the salivary gland begins the breakdown of starch in the mouth, forming shorter oligosaccharides- taste sweet
  • This process is completed by amylase from the pancreas
  • Remaining carbs are digested by amylase from pancreas in small intestine
  • These short chain sugar molecules are then converted to monosaccharides by the brush border enzymes (produced on microvilli) in the small intestine, where they are absorbed.
  • –Glucose and fructose get absorbed by the wall of the small intestine and into vascular system.
49
Q

What is the digestion of proteins?

A

-Proteins are chains of amino aids which need to be converted into dipeptides or single a.a before they can be absorbed.

50
Q

Process of digestion of amino acids

A
  • doesnt occur in mouth, occurs in stomach
  • pepsin (pepsinogen+hcl) in the stomach breaks proteins into polypeptides and free a.a
  • pancreatic enzymes continue this breakdown
  • which is completed by brush border enzymes in the small intestine.
  • individual a.a absorbed in the epithelial cells in the small intestine and end up in the vascular system.
51
Q

What is the digestion of fats?

A

-most ingested fats are triglycerides that need to be broken down into monoglyercides and fatty acids

52
Q

Process of digestion of fats?

A

Limited digestion of fats occurs in mouth and stomach

  • As fat is not soluble in water it would form big globules in water that could not be digested by enzymes
  • It is therefore emulsified (broken into smaller bits) by bile salts
  • These small fat spheres are split into monoglycerides and fatty acids by pancreatic lipases which form ‘micelles’ , that are absorbed.
53
Q

What is different about the digestion of fats?

A

fats absorbed in small intestine BUT put into lymphatic system.
- While the breakdown products of carbs and protein digestion are absorbed into blood capillaries in the villi o the small intestine, monglycerides and fatty acids enter lacteals (lymphatic vessels)

54
Q

What is a lacteal?

A

villi in small intestine that contains lymphatic vessels

Biology (30 decks)

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