Digestion

Question 1

What is digestion?

Answer 1

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

Question 2

What does the digestive system consist of?

Answer 2

• 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)

Question 3

What is our food composed off?

Answer 3

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)

Question 4

What are the 6 processes of digestion consist of?

Answer 4

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

Question 5

What is the structure of the GI tract?

Answer 5

4 layers

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

Question 6

What does mucosa contain of?

Answer 6

• 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

Question 7

What is a lamina propria in the mucosa?

Answer 7

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

Question 8

What is the submucosa?

Answer 8

• 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.

Question 9

What is in the muscular layer of the GI tract?

Answer 9

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

Question 10

What is the function of this muscular layer?

Answer 10

• 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.

Question 11

What is the main function of the mouth?

Answer 11

-responsible for ingestion

Question 12

What is the structure of the mouth?

Answer 12

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

Question 13

What are the 3 salivary glands properties?

Answer 13

• exocrine- into ducts

- contain both mucous and serious secreting cells

Question 14

What are the 3 salivary glands?

Answer 14

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

Question 15

What do these secretions of saliva serve to?

Answer 15

• 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.

Question 16

Where does the food end up once gone through mouth?

Answer 16

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

Question 17

What is the Pharynx?

Answer 17

Where the food, fluids and air leave the mouth

Question 18

What is the epiglottis?

Answer 18

allows air to pass down the trachea and is normally open

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

Question 19

What happens when swallowing?

Answer 19

• The epiglottis closes

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

Question 20

What is the oesophagus?

Answer 20

a 25cm tube connecting the mouth to the stomach

Question 21

What does the oesophagus consist of?

Answer 21

4 layers (previous layers stated)

Question 22

What does the submucosa contain in the oesophagus?

Answer 22

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

Question 23

What is bolus in the oesophagus?

Answer 23

propelled by peristalsis ( about 8 seconds)

- drinks take 2 seconds

Question 24

What does the stomach serve to do?

Answer 24

• 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

Question 25

Whats the stomach structure?

Answer 25

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

Question 26

What is on the surface on the stomach?

Answer 26

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

Question 27

What does the gastric glands secrete?

Answer 27

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

Question 28

What does the smooth muscle of the stomach have?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

What does the sympathetic activity do?

Answer 30

is decreased in digestion

Question 31

What does the parasympathetic activity?

Answer 31

-increases digestion

Question 32

What does the longitudinal muscle layer contain ?

Answer 32

enteric pacemaker cells

Question 33

What do the enteric pacemaker cells do?

Answer 33

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

Question 34

What are the PACEMAKERs connected to?

Answer 34

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

Question 35

Where is the basic rhythm of contraction?

Answer 35

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

Question 36

What is the small intestine?

Answer 36

where food leaves the stomach and enters in the small intestine

Question 37

What does the small intestine consist of?

Answer 37

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

Question 38

What does the small intestine do?

Answer 38

- 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.

Question 39

What is emulsification

Answer 39

breaking fats into small bits via bile salts

Question 40

What is the small intestine for?

Answer 40

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

Question 41

What is the structure of the small intestine?

Answer 41

- 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

Question 42

What is the large intestine?

Answer 42

it frames the small intestine on 3 sides

Question 43

What is the size of the large intestine?

Answer 43

-it is wide (7cm) -larger in diameter but shorter than the small intestine (1.5m) height -

Question 44

What is the main function of the large intestine?

Answer 44

To remove water from the food and store solid faces - retain water in body - little digestion occurs here

Question 45

What else does the large intestine contain?

Answer 45

bacteria that ferment any remaining carbs - carb digestion - involved in synthesis of vitamins B and K

Question 46

What is the structure of the large intestine?

Answer 46

- 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

Question 47

What is the digestion of carbohydrates?

Answer 47

- either monosaccharides, disaccharides or polysacchruides. | - NEED to be broken down into monosaccharides to be absorbed in the vascular system

Question 48

Process of digestion of carbs?

Answer 48

- 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.

Question 49

What is the digestion of proteins?

Answer 49

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

Question 50

Process of digestion of amino acids

Answer 50

- 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.

Question 51

What is the digestion of fats?

Answer 51

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

Question 52

Process of digestion of fats?

Answer 52

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.

Question 53

What is different about the digestion of fats?

Answer 53

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)

Question 54

What is a lacteal?

Answer 54

villi in small intestine that contains lymphatic vessels