lecture 7 and 8: digestive system Flashcards
1
Q
4 main functions of the GI tract
A
motility
secretion
digestion
absorption
2
Q
motility
A
- smooth muscle maintains constant low level contraction
- peristalsis
- mixing of contents with digestive juices
3
Q
secretion
A
- water, electrolytes, enzymes, buffers
- neural and hormonal control
4
Q
digestion
A
biochemical breakdown by enzymes
5
Q
absorption
A
into blood or lymph
6
Q
mouth
A
mastication and initial stages of CHO digestion
7
Q
stomach
A
initial stages of protein digestion
8
Q
small intestine
A
- protein, CHO, fat and nucleic acid digestion
- main site of absorption of nutrients
9
Q
large intestine
A
- final digestion and absorption of nutrients
- water absorption
- waste concentration
10
Q
general structure of GI tract
A
- serosa
- submucosa
- muscularis externa
- mucosal layers
- lumen
- myenteric plexus
- submucous plexus
- duct of large accessory digestive gland emptying into digestive tract lumen
11
Q
mucosa
A
- highly folded
- modified for secretion and absorption
- secretes digestive juices and blood-borne hormones
12
Q
submucosa
A
- connective tissue for elasticity
- contains nerve network- submucosal plexus (mainly sensory and secretory)
13
Q
serosa
A
lubricates and prevents friction between organs
14
Q
muscularis externa
A
- smooth muscle for contraction- propulsion and mixing
- myenteric plexus nerve network lies between the 2 layers (largely motor in function)
15
Q
regulation of digestion
A
- ensures presence of sufficient secretions when food present
- helps avoid overabundance of secretions in absence of food
2 types of mechanisms : endocine and neural
16
Q
enteric NS
A
- autonomous behaviour of digestive system
- CNS control isn’t required for digestive functioning
17
Q
submucosal nerve plexus
A
- mechano and chemo receptors in mucosa
- controls exo and endocrine secertion of the mucosa
18
Q
myenteric nerve plexus
A
controls contraction and relaxation of smooth muscle
19
Q
regulation of swallowing
A
- chemo and mechanoreceptors respond to food presence
- afferent impulses go to salivary centre in brainstem
- PNS stimulates watery saliva secretion
20
Q
saliva
A
- contains salivary amylase and bicarbonate
- moistens food
- antibacterial effects
- no nutrient absorption
- food bolus forms
21
Q
swallowing reflex
A
bolus stimulates stretch receptors which cause widening of path ahead and narrowing behind
- inhibitory neurons cause area of receptive relaxation of bolus
22
Q
roles of stomach
A
-secretes intrinsic factor, mucus, pepsinogen
-peristaltic contractions start in ‘pacemaker’ region and sweep towards antrum and pyloric sphincter
-small amount forced into duodenum
-contraction of pyloric sphyincter causes gastric mixing
23
Q
what is gastrin and what does it do
A
hormone secreted by stomach- causes release of gastric secretions (gastric acid, intrinsic factor, pepsin)
24
Q
cephalic (head) phase
A
-food in mouth
-thinking about, smelling, tasting, chewing or seeing food
25
gastric phase
-food in stomach
-stretch and presence of proteins increase gastric secretions
26
intestinal phase
- food in SI
- inhibitory phase (helps shut off gastric juices as chyme enters SI)
27
what is the state of the food/fluid mixture in the duodenum as chyme leaves stomach
carbs- partial disaccharides by salivary amylase
proteins- small peptides due to pepsin and HCL action
fats- mainly triglycerides
acidic environment (inactivate bile and gallbladder contraction)
28
what does acid in the duodenum stimulate
- secretin release
- bicarbonate secretion
- buffers acid, increasing pH
- stimulates liver to produce bicarbonate rich bile and gallbladder contraction
29
gallbladder size shape capacity
9cm
long pear shaped
50ml
30
bile salts
bilirubin, cholesterol, phospholipids, proteins, electrolytes and water
31
what secretes bile salts
hepatocytes- bile salts transported down the bile duct to gallbladder
32
gallbladder
stores bile before being emptied into duodenum
33
how much bile produced by liver per day
1000ml
34
what does secretin do
stimulates bile generation, gall bladder contraction and bile secretion into duodenum
35
what does fat and protein in the duodenum do
stimulates CCK (cholecystokinin) release
- stimulates pancreatic release of proteolytic enzymes, lipases, amylase, disaccharides and nucleases
- increases motility and SI and colon (contraction and relaxation)
- gall bladder contraction
36
HCL
- released into stomach (doesn't actually digest any nutrients)
- exhibits antimicrobial activity
- aids in breakdown of connective tissue and muscle fibres
- denatures protein- uncoiled from highly folded state exposing more peptide bonds for enzymatic attack
- activates pepsin- pepsinogen is precursor to active enzyme pepsin
37
intrinsic factor
secreted into stomach
- required for absorption of vitamin b12 at terminal ileum
- vitamin b12 required for RBC synthesis- therefore become anaemic if deficient
38
absorption of vitamin b12
-intrinsic factor is a glycoprotein
-vit b12 combine with intrinsic factor forming complex that resists digestion by GIT enzymes
-complex absorbed at terminal ileum by pinocytosis
-vit b12 transported to liver where it's stored
39
stomach absorption
-alc and aspirin because lipid soluble and diffuses across plasma membrane that lines stomach and enters blood
- not food or water
40
pancreas
elongated gland lies posterior and inferior to stomach and has endo and exocrine tissue
41
what does exocrine pancreas secrete
pancreatic juice of 2 components
1. alkaline solution containing bicarbonate
2. pancreatic enzymes
42
pancreatic enzymes
released into duodenum when stimulated by CCK
-amylase
-lipase
-proteolytic enzymes (e.g. trypsin)
43
what are proteolytic enzymes secreted as
inactive precurosors
44
protein digestion in SI
- microvilli contain enzymes that complete protein digestion
- AA absorbed into cells and then blood via transporter proteins
45
what are AA converted to in the liver
protein, CHO, fat
46
what is the most digestible dietary carb
starch (glucose polysaccharide)
47
where does full digestion of carbs occur
SI
48
what is starch/glycogen converted to
amylase which is converted to maltose, sucrose, lactose
49
disaccharide digestion in SI
maltase, sucrase and lactase breakdown disaccharides into their constituent monosaccharides which are absorbed into cells and then into blood via transporter proteins
50
pancreatic lipase
breaks down triglycerides into FFA and monoglycerides
51
what do bile salts do
-make fat droplets smaller so lipase can have access to all TG's
-act as detergents converting large fat globules into a lipid emulsion
52
fat digestion
intestinal movements break up large fat droplets into smaller ones (mechanical digestion)
- these would quickly re-coalesce if bile salts weren't present
