Gastrointestinal System

Question 1

define digestion

Answer 1

• breaking down large insoluble molecules into components that can be absorbed into the blood

Question 2

broad process of digestion

Answer 2

• obtain food from environment -> sensory, hunting, some foods are indigestible
• broken down chemically and mechanically
• absorption across body surface or tubes

Question 3

define nurient

Answer 3

substance used in organsism’s metabolism or physiology
- nutrients can be oxidised -> bonds broken to provide energy

Question 4

what are the major classes of nutrients

Answer 4

• carbohydrates, proteins, lipids
• also need vitamins and minerals

Question 5

what are vitamins vs minerals

Answer 5

• 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

Question 6

what are carbohydrates, how much energy used, how is it stored, how is it broken down?

Answer 6

• 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

Question 7

what are proteins, how much energy used, how is it stored, how is it broken down?

Answer 7

• 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

Question 8

what are lipids, how much energy used, how is it stored, how is it broken down?

Answer 8

• 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

Question 9

major functions of GI tract

Answer 9

1. digestion -> chemical and mechanical breakdown
2. motility -> movement of substances through gastro tract due to muscle contractions
3. secretion -> substances from cells to lumen or ECF
4. absorption -> movement of substances from lumen into ECF

Question 10

where do the major functions occur

Answer 10

1. mechanical breakdown of food -> mouth, pharynx, oesophagus
2. acidic compartment -> stomach (ATP pumps)
3. chemical digestion and absorption -> upper or small intestine
4. water reabsorption -> lower or large intestine
5. release of indigestible material -> anus

Question 11

wall structure of mucosa

Answer 11

• mucous membrane -> epithelium
• lamina propria -> connective tissue, nerves, blood vessels
• muscularis mucosae

Question 12

wall structure of submucosa

Answer 12

• connective tissue
• submucosal plexus -> enteric nervous system

Question 13

wall structure of muscularis externa

Answer 13

• circular smooth muscle -> myenteric plexus
• longitudinal smooth muscle

Question 14

structure of serosa

Answer 14

*answer later from lab

Question 15

what does the enteric nervous system do in the gastro system?

Answer 15

• sense, integrate and respond to gut stimuli without CNS input
• Parasympathetic nerves stimulate and sympathetic nerves inhibit intestine motility, secretion and hormone release

Question 16

what does the submucosal plexus do

Answer 16

• regulates secretion and absorption

Question 17

what does myenteric plexus do

Answer 17

primarily regulates motility
- allows contraction of cells as a unit

Question 18

what do muscle layers do in gastro

Answer 18

• longitudinal control length
• circular control radius
• slow contraction is peristalsis (spontaneous contractions) -> contraction moves due to pacemaker cells in gut wall

Question 19

what occurs in the mouth

Answer 19

• 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)

Question 20

what occurs in the oesophagus

Answer 20

• conducts food to stomach
• upper portion innervated by somatic nerves -> voluntary control (reduce choking), lower innervated by autonomic

Question 21

what occurs in the stomach

Answer 21

• 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

Question 22

What occurs in the small intestine

Answer 22

• 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

Question 23

explain process of lipid transport/absorption

Answer 23

• 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

Question 24

what occurs in large intestine

Answer 24

• reabsorbs water and ions from chyme
• strong waves of muscle contractions for defecation