Gastrointestinal System Flashcards
1
Q
define digestion
A
- breaking down large insoluble molecules into components that can be absorbed into the blood
2
Q
broad process of digestion
A
- obtain food from environment -> sensory, hunting, some foods are indigestible
- broken down chemically and mechanically
- absorption across body surface or tubes
3
Q
define nurient
A
substance used in organsism’s metabolism or physiology
- nutrients can be oxidised -> bonds broken to provide energy
4
Q
what are the major classes of nutrients
A
- carbohydrates, proteins, lipids
- also need vitamins and minerals
5
Q
what are vitamins vs minerals
A
- vitamins -> chemically unrelated molecules with diverse functions, water-soluble ones are excreted in urine, lipid-soluble vitamins are stored in fat (can be dangerous if over used)
- minerals -> metallic elements involved in protein structure, enzymes, bone health, nerve and muscles, transported via channels, carriers and pumps
6
Q
what are carbohydrates, how much energy used, how is it stored, how is it broken down?
A
- 55-60% of total energy intake
- glycogen is how carb is stored = polysaccharides (plants store as starch)
- all complex carbs are broken down into monosaccharides (glucose) to be absorbed -> releases energy
- amylases convert complex sugars to poly then disaccharides = saliva and pancreas (duodenum)
- sucrase, maltase and lactase convert disaccharides into monosaccharides = small intestine
7
Q
what are proteins, how much energy used, how is it stored, how is it broken down?
A
- made of amino acids – broken down into acids, then rebuilt into needed proteins for cells
- 10-20% energy intake
- starts in stomach
- proteases break protein into shorter polypeptides
- peptidases cleave amino acids from polypeptides
8
Q
what are lipids, how much energy used, how is it stored, how is it broken down?
A
- 25-35% total energy intake
- break into fatty acids
- form of energy store (triglycerides n muscle and liver)
- involved in formation of barriers (cell membranes)
- most occurs in small intestine
- lipases release fatty acids from triglycerides and phospholipids
- GI tract secretes chemicals (bile) that emulsify lipids into droplets (micelles) = high SA
- tarbsported by lipoproteins (cholesterol) if highly hydrophobic
- stored in the liver and body tissues when energy intake exceeds requirements
9
Q
major functions of GI tract
A
- digestion -> chemical and mechanical breakdown
- motility -> movement of substances through gastro tract due to muscle contractions
- secretion -> substances from cells to lumen or ECF
- absorption -> movement of substances from lumen into ECF
10
Q
where do the major functions occur
A
- mechanical breakdown of food -> mouth, pharynx, oesophagus
- acidic compartment -> stomach (ATP pumps)
- chemical digestion and absorption -> upper or small intestine
- water reabsorption -> lower or large intestine
- release of indigestible material -> anus
11
Q
wall structure of mucosa
A
- mucous membrane -> epithelium
- lamina propria -> connective tissue, nerves, blood vessels
- muscularis mucosae
12
Q
wall structure of submucosa
A
- connective tissue
- submucosal plexus -> enteric nervous system
13
Q
wall structure of muscularis externa
A
- circular smooth muscle -> myenteric plexus
- longitudinal smooth muscle
14
Q
structure of serosa
A
*answer later from lab
15
Q
what does the enteric nervous system do in the gastro system?
A
- sense, integrate and respond to gut stimuli without CNS input
- Parasympathetic nerves stimulate and sympathetic nerves inhibit intestine motility, secretion and hormone release
16
Q
what does the submucosal plexus do
A
- regulates secretion and absorption
17
Q
what does myenteric plexus do
A
primarily regulates motility
- allows contraction of cells as a unit
18
Q
what do muscle layers do in gastro
A
- longitudinal control length
- circular control radius
- slow contraction is peristalsis (spontaneous contractions) -> contraction moves due to pacemaker cells in gut wall
19
Q
what occurs in the mouth
A
- Functions: start of mechanical breakdown (teeth and jaw), start of carb dig (amylase), defence against pathogens (isozyme) -> kill bacteria
- salivary glands lubricate, dissolve food so can bind to gustatory receptors (for taste), cleanses mouth, digests food (amylase)
20
Q
what occurs in the oesophagus
A
- conducts food to stomach
- upper portion innervated by somatic nerves -> voluntary control (reduce choking), lower innervated by autonomic
21
Q
what occurs in the stomach
A
- food storage, defence against pathogens (acidic), starts digestion of lipids and proteins (acidic and enzymes, mechanical digestion)
- parietal cells secrete acid HCl
- tight junctions reduce leakage
- mucous neck cells = secrete alkaline mucus
- chief cells = pepsin
- smooth muscle = mechanical digestion
- mucus layer is viscous and alkaline -> physical barrier to acid and cells lining stomach (contains bicarb) -> neutralises acid too
22
Q
What occurs in the small intestine
A
- absorption
- duct from pancreas -> delivers pancreatic juice (bicarb, amylase, lipase, protases)
- duct from liver = bile (bicarb, bile salts)
- villi = increase absorption 10x
- microvilli = 20 x increase -> these have embedded enzymes and transport proteins
- lacteals = open lymphatic vessels required for absorption of fat
23
Q
explain process of lipid transport/absorption
A
- bile breaks down fat into micelles = emulsification, now lipase can act faster on high SA
- some fatty acids are small enough and polar enough to diffuse through membrane and into blood vessel
- others (bigger) are taken into cell smooth ER, formed into lipoproteins/chylomicrons, linked with transport vesicle and exocytosis into lacteal (lymph vessel) and enters blood when lymph vessel drains into vena cava
24
Q
what occurs in large intestine
A
- reabsorbs water and ions from chyme
- strong waves of muscle contractions for defecation
