BIOL102 NOTES TEST 5

-- 4/23/10

Digestive System

- Gastrointestinal (GI) Tract

- 2 layers of smooth muscle (except in stomach which has 3)

- structure - common layers throughout system

- mucosa - innermost layer, nutrients pass through

- submucosa - connect tissue, lymph and blood vessels, nerves

- muscularis - 2 or 3 layers of smooth muscle responsible for motility in GI tract

- serosa - outermost later, connective tissue sheath

Digestive system processes

- 5 processes

- mechanical processing and movement - chewing, mixing

- secretion - fluid, digestive enzymes and hormones, bile, acid, alkali, mucus

- digestion - breaking down food to smallest absorbable units (not complete

breakdown)

- absorption - throughout mucosa, into blood or lymph vessels

- elimination - undigested material eliminated

Motility - peristalsis - like eating go-gurt - most obvious in esophagus

Motility - segmentation - most common in small intestine

The mouth - begins digestion

- teeth - incisors & canines - chopping; premolars & molars - grinding

- structure - crown, root

- tongue - skeletal muscle, moves food in mouth, taste

- saliva

- source - parotid, submandibular, sublingual salivary glands

- composition - mucin, salivary amylase (begins breakdowns of complex carbs in

mouth; hungrier = more salivary amylase), bicarbonate, lysozyme

swallowing - delivers food to stomach

- voluntary phase - tongue pushes bolus of food into pharynx

- involuntary phase/swallowing reflex - receptors in pharynx stimulated by presence of

food

- soft palate rises

- larynx rises slightly

- epiglottis closes opening to trachea

- tongue pushes food further

- good enters esophagus

pharynx

- common passageway for air and food

- participates in swallowing

esophagus

- structure - mix of skeletal and smooth muscle

- mucus-secreting cells - assist passage of food (by decreasing friction)

- food motility - gravity and peristalsis

stomach function

- functions - food storage, digestion, regulation of delivery

- gastric juice - specific cells secrete

- HCl (hydrochloric acid) - produces a pH of about 2, breaks down large bits of

food

- Intrinsic factor - made by same cells making acid, needed to absorb vitamin

B12

- mucus - protects stomach lining from acid

- pepsinogen - with acid, begins protein break-down - inactive until the production

of stomach acid

- stomach contraction - stomach contractions - blend food and propel forward

- structural adaptation - third muscularis layer

- direction - from lower esophageal sphincter to pyloric sphincter

- chyme - result of mixing, affects hormone secretions regulation peristalsis and

emptying of stomach

--4/26/10

small intestine - 10’10” long. most digestion occurs in 1st 10”; most absorption occurs in

last 10’

small intestine

- functions

- digestion - neutralize acid from stomach, add digestive enzymes and bile, break

proteins, carbohydrates, lipids, and nucleic acids to absorb materials

- absorption - 95% of food absorbed here

- structure

- regions - duodenum (1st 10”), jejunum & ileum (last 10’)

- mucosa adaptations - villi (& microvilli - increase absorption and digestion

surface area by 500x) containing blood capillaries (break down everything but

lipids) and lacteal capillaries

Enzymes - generally end with “-ase” - made in pancreas

- carbohydrases - break down carbs

- proteases - break down proteins

- nucleases - break down nucleic acids

- lipases - break down lipids

* enzymes break down food under a basic pH (> 10)

Accessory organs - aid digestion and absorption

- pancreas - exocrine functions

- secretes digestive enzymes and sodium bicarbonate

- also endocrine gland - helps control blood-sugar level (via insulin)

- liver

- produces bile - bile helps water and oil “mix” by