3.6: digestive processes

regulation of digestive activity

hormones: form gastric/ intestinal enteroendocrine cells

-central nervous system regulates small portion of digestion (like hunger)

-enteric nervous sytem: main source of control

→ nervous netweork in esophagus, stomach, intestines
→ regulates digestive tract motility, hormonal secretions, blood flow
> 100 million neurons

-can function independently of CNS but CNS influences activity

neural regulation of digestion

-short (____) reflexes: for ___ control

→

→

long (_____) reflexes: for ___ control

→

→

myenteric, intrinsic

-regulated solely be enteric system in response to local stimuli

-mediated by mechanoreceptors, chemoreceptos, osmoreceptors in wall of digestive tract

vagovagal, extrinsic

-integration of CNS autonomics

-can be irnitially by internal or external stimuli

mastication

-mechanical processing of injested food

→ easier to swallow

→

-partially ___

-teeth: ____

-lips & cheeks function in ____

-tongue focuses in ____

-muscles of mastication: ____

increased surface area

voluntary & partially reflective

cut food

retaining food

manipulating food

masseter & temporalis elevate jaw

pterygoids: lateral excursion

gastric motility

-antral pump:

~3 mL of ___

-overfill of __

-stomach typically ___

-strong contractions mechanically process food to prepare for entering duodenum

-contraction close pyloric sphincter

-chyme passes into duodenum at a time:

→ relaxation of stomach allows sphincter to open

→ provides time to neutralize HCl, digest nutrients

-duodenum inhibits gastric motility

-takes about 4 hrs to empty

vomiting

-controlled by ____

-induced by:

-these help to expel chyme:

emetic center in medulla oblongata

-overstretching of stomach/ duodenum

-chemical irritants

-visceral trauma, intense pain

-psychological/ sensory stimuli

-lower esophageal sphincter relaxing

-intense abdominal contractions

-reverse peristalsis

intestinal motility: segmentation

-stationary ___ form & re-from___

→

→

-transition to ____

contractions, in several locations

-mix chyme with bile & digestive juices

-bring chyme into contact w intestinal mucosa

peristalsis after most nutritents are absorbed

intestinal motility: peristalsis

-____ movement of contents _____

→

→

-refilling of ___

gradual, towrads large intestine

-triggered by duodenal hormones

-moves chyme towards LI over ~2 hrs

-stomach suppresses persistalsis & reactivates segmentation

digestion & absorption: carbohydrates

-enterocytess (absorptive cells) can only absorb ___

-begins with ___

-continued by __

-__ digestion produces ___

monosaccharides: larger sugar molecules must be chemicaly broken down

salivary amylase: optimal pH of 6.9-7.0: salivary amylase inactivated by stomach acid

pancreatic amylase

contact; monosaccharides: pas through enterocytes via facilitated diffusion

digestion & absorption: proteins

-beings in ___

-pancreatic ___

-brush boarder

stomach w pepsin: first 10-15% of protein digestion, optimal pH of 1/5-2.3: inactivated by pancreatic juice
enzymes take over in duodenum

enzymes digest peptides into free amino acids: absorbed by enterocytes

digestion & absorption: lipids

-mechanical digestion:

→

→

-chemical digestion:

→

→

→

-micelles:

-absorbed lipids __

mechanical

-gastric/ intestinal motility produces emulsification droplets (tiny pieces of lipids)

-bile coats droplets to keep from recombining

chemical

-begins in mouth via lingual lipase

-continued by gastric & pancreatic lipase

-produces monoglycerides & free fatty acids

micelles

-made up of bile molecules arranged around lipid center

-carry lipids from chyme to enterocytes

-taken up by lacteal lymph capillaries

-chyle: fat-heavy intestinal lymph

-travels through lymphatic vessels to return too bloodstream

digestion & absorption: vitamins

-fat soluble vitamins:

-water soluble vitamins:

A, D, E, K

-absrobed with other lipids

-not absorbed at all without fat in chyme

B complex & C

-mainly absorbed by diffusion

-B12 requires intrinsic factor (produced by parietal cells in stoamch)

defacation

at rest:

-___ nerve:

-____ nerve:

defacation

1)

2)

3)

hypogastric: sympathetic innervation: relaxes rectum, closes internal anal sphincter

pudendal: somatic motor innervation: closes external sphincter

1) rectum contracts

2) internal sphincter relaxes

3) external sphincter relaxes

reflexive defacation

-controlled by ___

1)

2)

2 defacation reflexes: stimulated by stretching of rectum

1) intrinsic reflex: mediated by myenteric plexus: stretch stimulus activates peristalsis in descending & sigmoid colon

2) spinal reflex: mediated by pelvic splanchnic nerves:

-stretch stimulus carried to sacral spinal cord

parasymphathetic stimulus:

-contracts rectum

-intensifies peristaltic contractions

-reflexes internal anal sphincter

voluntary defacation

-initiated by ___

-___ reflex relaxes ___

-

stretch of rectum

-parasymphathetic, internal anal sphincter

-voluntary relaxation of skeletal mm:

→external anal sphincter (pudendal nerve)

→puborectalis (sacral plexus)

-voluntary suppression

-eternal anal sphincter voluntarily remains closed

-intestinal contractions temporarily cease

-reflexes reoccur when another pass movement moves more feces into rectum