W2: digestive system

Question 1

functions of the digestive system

Answer 1

digestion: chem and mech breakdown of large food particles

absorption: movement of organic molecules and water across digestive epithelium into blood/ lymph

excretion: of waste material

Question 2

features of digestive system

Answer 2

motility: smooth muscle contractions

secretion: water, mucus, acids, enzymes, buffers and salts

Question 3

the teeth

Answer 3

function: cut, tear and grind food
reduce solid material into smaller particle
can be more readily swallowed

Question 4

features of the tooth

Answer 4

enamel: top layer of crown made up of calcium phosphate and calcium carbonate

dentine: next layer underneath made up of calcified connective material

pulp cavity: within dentine and contains CT, vessels, nerves and lymph vessels

nerve root: enters thru root canal

bony material: cementum

Question 5

the tongue

Answer 5

skeletal muscle covered with mucous membrane
anchored to the floor of oral cavity by the lingual frenulum

extrinsic muscle: manoeuvre food around mouth for mastication
intrinsic muscle: enable swallowing and speech

Question 6

pairs of the salivary glands

Answer 6

3 pairs: parotid, submandibular, sublingual

Question 7

composition of saliva

Answer 7

composition: 99.5% water
0.5% solutes

the salivary glands produce saliva that has a slightly different composition

Question 8

types of secretory cells

Answer 8

mucus cells: viscoelastic, nonhomogenous fluid that contains watery matrix, glycoproteins, proteins and lipids

serous cells: secrete mainly water and som proteins such as amylase enzyme

Question 9

functions of saliva

Answer 9

• moisten and lubricates food and mouth
• dissolves food
• initiates the digestion of polysaccharides and lipids
• antibacterial actions

Question 10

the oesophagus

Answer 10

food passage is by peristalsis

sequential contraction of longitudinal and circular sth muscle within wall

Question 11

functions of the stomach

Answer 11

• storage of ingested food
• mech breakdown of ingested food
• disruption of chem bonds in food by acid and enzymes

Question 12

mechanical digestion of stomach

Answer 12

1. peristatic wave in muscularis towards antrum
2. pyloric sphincter opens to allow a small amount of liquid chyme thru
3. majority of chyme and all soldi material returned to stomach for further churning (retropulsion)

Question 13

exocrine glands of the stomach

Answer 13

cardiac glands: situated near the cardiac orifice and they secrete mucus

gastric glands: situated in fundus and body and contain 3 different types of cells:
mucous cells
chief cells (secrete pepsinogen and gastric lipase)
parietal cells (intrinsic factor and HCl acid)

pyloric glands: pyloric antrum (secrete mucous)

Question 14

small intestine

Answer 14

continued digestion and absorption of nutrients
90% of nutrient absorption occurs in small intestine
absorption occurs in the first quarter- duodenum and jejunum

3 sections: duodenum, jejunum and ileum

Question 15

pancreatic juice

Answer 15

pancreas secretes between 1200-1500ml of juice
contains mostly water, salts, sodium bicarbonate and enzymes

bicarbonate: buffers the acidic gastric juice, inactivates pepsin from stomach and provides correct pH for the enzymes to function

enzymes: pancreatic amylase (starch digestion),
trypsin, chymotrypsin, carboxypeptidase and elastase (protein digestion)
pancreatic lipase (triglyceride digestion)
ribonuclease and deoxyribonuclease (nucleic acid disgstion)

Question 16

composition of bile

Answer 16

hepatocytes produce 800-1000ml of bile a day

bile is yellow fluted fluid with a slightly alkaline pH

constituents are water, bile salts, bile pigments and several ions

bilirubin is the main bile pigment - formed from haeme derived from the breakdown of rbc

breakdown of bilirubin in the gut makes shit brown

Question 17

functions of bile salts

Answer 17

• bile salts emulsify and breaks up large lipid globules into smaller globules
• allows the digestive lipases to break the fat down further
• also help the absorption of lipids following digestion

Question 18

small intestine features

Answer 18

plica circulares, villi and microvilli = increases surface area 600 times

microvilli- contains brush border enzymes that complete the job of digesting proteins and carbs prior to absorption across epithelial cells

Question 19

functions of large intestine

Answer 19

• reabsorption of water (10%)
• absorption of important vitamins produced by bacteria
• does not produce enzymes
• provides lubrication for faecal material
• outrage and compaction of faecal material portion to defecation

LACKS VILLI

Question 20

digestive enzymes

Answer 20

carbs- polysaccharides (starch) is broken down onto monosaccharides

protein- broken down into amino acids/ peptides

fats- triglycerides broken down into glycerol and fatty acids

nucleic acids- broken down into nucleotides

Question 21

enzymes

Answer 21

saliva: starts breaking down starch (salivary amylase) and fats (lingual lipase)

stomach: enzymes to break down protein (pepsin) and fats (gastric lipase)

liver: bile salts are secreted into small intestine and emulsifies lipids

pancreas: pancreatic juice- secreted into small intestine
enzymes to break down:
starches- pancreatic amylase
proteins- trypsin and elastase
triglycerides (fats)- pancreatic lipase
RNA/DNA- nucleases

brush border (microvilli):
disaccharides (maltase, lactase and sucrase)
peptides (aminopeptidase and dipeptidase)
nucleotides (nucelosidases)