Digestive System

does digestion occur in accessory organs?

no

Name the part of the alimentary tube in which MOST absorption takes place

small intestine

ingestion

food taken in

digestion

food modified chemically or mechanically

Motility or propulsion

food moved along

absorption

useful nutrients moved into internal environment via passive/active transport or diffusion

why is mechanical digestion important

creates a larger surface area for digestive enzymes

what organs aid in mechanical digestion

mouth (chewing) stomach (churning) small intestine (segmentation)

Chemical digestion

Process by which enzymes break down food into small molecules that the body can use

what nutrients need to be chemically digested in order to be absorbed?

carbs fats and proteins

The alimentary tube consists of..

oral cavity, pharynx, esophagus ,stomach, small intestine, large intestine, rectum, anal canal

accessory organs consist of...

salivary glands, liver, tongue, teeth, gallbladder, pancreas, vermiform appendix

Mechanoreceptors and chemoreceptors located in walls of GI tract respond to

stretching, osmolarity , PH level of contents and presence of end products of digestion

Mechanoreceptors respond to

touch, pressure, vibration, stretch

Hormones in the alimentary tube distribute via..

blood and interstitial fluid

sympathetic influence on digestive system

decreased activity of glands and muscles, constriction of sphincters to reduce movement

parasympathetic influence on digestive system

increased secretory activity, enhanced mobility, relaxation of sphincters to allow movement

visceral peritoneum

covers organs

parietal peritoneum

lines the body wall

mucosa anatomy

stratified squamous, simple columnar, lamina propria (loose areolar), muscularis mucosae

Mucosa Physiology

protection against abrasions and infections, secretes digestive enzymes and hormones, absorption, muscularis twitches to loosen food

submucosa anatomy

areolar ct with embedded blood, nerve and lymph vessels, rich supply of elastic fibers

submucosa physiology

provides second line of defense, regulates glands autonomically, allows stomach to regain shape after large meal

muscularis exterior anatomy

2 layers of smooth mm (in stomach 3)
inner layer - circular
outer layer - longitudinal
stomach only - oblique

muscularis exterior physiology

responsible for moving food through tube and segmentation, churning mechanically breaks down food

how are sphincters formed?

circular muscularis exterior layer thickens to prevent backflow

serosa anatomy

adventina- in thoracic cavity, holds esophagus in place
visceral peritoneum - abdominopelvic cavity, covers digestive organs

serosa physiology

secretes serous fluid to prevent friction during contractions, peritoneum's extensions (mesentery) bind organs together to prevent intestine strangulation

oral cavity physiology

ingestions, starts mechanical digestion (chewing), starts chemical digestion (starches)

the uvula dangles from what palate?

soft palate

soft palate is made of mostly...

skeletal muscle

tongue anatomy

intrinsic - confined in tongue, speech/swallow
extrinsic - extend from tongue to points of origin on bones of skull/soft palate

tongue physiology

speech, swallowing, mixed food with saliva to form bolus, taste

swallowing times (liquid and solid)

liquid - 1-2 seconds
solid- 8 seconds

buccal phase

voluntary, forces bolus into oropharnyx

pharyngeal esophageal phase

involuntary, bolus continues down alimentary tube

teeth anatomy

crown - covered with enamel
dentin - forms bulk of tooth, adentoblasts
pulp cavity - contains nerves and blood vessels
neck - area surrounded by gums
root - in socket, covered by cementum that cements teeth to gums

primary teeth and permanent teeth numbers

20, 32

by what age have 2 sets of teeth formed?

21

3 molars aka wisdom teeth appear at what age range?

17-25

Incisors

chisel shape, cut and rip

canines

conical, fang-like

premolar

two-point shape, grinding

molar

broad crown with rounded crusps, grinding and crushing

salivary glands: exocrine or endocrine?

exocrine (mouth is ailmentary tube is considered exterior)

salivary glands are composed of

serous cells and mucous cells

intrinsic salivary glands:

parotid, submandibular, sublingual

parotid gland

serous cells only, just in front of ear, empties into vestibule

submandibular gland

50/50 serous and mucous, below mandibular angle, empties into mouth on either side of lingual frenulum

sublingual gland

mostly mucous, smallest gland, empties into floor of mouth

secretion of gastric juice may begin with sight or smell of food. this is a _________ nervous system response

parasympathetic

composition of saliva

slightly acidic, 97-99.5% water to liquify food, digestive enzymes

lower esophageal sphincter

located in region of cardiac orifice, relaxes to let food through then contracts to prevent backup of stomach content

esophageal layers:

has all 4 basic alimentary layers
mucosa: stratified squamous epithelium changes to simple columnar at esophagus/stomach junction

muscular layer: skel mm 1/3, mixed 1/3 and smooth 3/3

how much of the esophagus is voluntary?

2/3

esophagus physiology

peristalsis - wave-like ripple of smooth mm in response to stretch on GI wall

moves bolus downward despite position person is in

when the stomach is empty, the mucosa/submucosa fold into large folds called

rugae

cardiac orifice is the..

sphincter for lower esophagus

the parts of the stomach that mainly do storage are...

fundus, body

the funnel shaped part of the stomach, most digestion takes place here

pylorus

the lesser omentum connects the ____ to the _____

liver, lesser curvature

greater omentum connects the _______ to the ______, ________ and __________

greater curvature, small intestine, spleen and large intestine

mucous neck cells produce

thin acidic mucus

chief cells produce

pepsinogen

endocrine cells produce

ghrelin gastrin

parietal cells produce

HCl and intrinsic factor

mucous neck cells product physiology

helps secretions of other glands travel through pits of stomach

chief cells product physiology

pepsinogen interacts with HCL acid to form pepsin, digests protein

endocrine cells product physiology

ghrelin - hormone stimulates hypothalamus, increase in appetite

gastrin - stimulates secretion of gastric juices to digest food

parietal cells product physiology

HCL - denatures protein, activates pepsin, stomach turns acidic (3rd line of defense)

Intrinsic factor - binds to vitamin B12 to protect it from digestion

stomach mucosal barrier mods-

2 layers of bicarbonate rich mucus; damaged mucosal cells are replaced quickly, gastric glands

what are the lines of defense in order

mucosa, submucosa, HCL acid, bacterial flora in colon

the stomach produces what hormones

gastrin, ghrelin

small intestine anatomy (superior to inferior)

duodenum, jujenum, ileum

small intestine modifications

1. absorptive cells
2. mucus secretes goblet cells to move things along
3. endocrine cells produce secretin, cholecystokinin (CCK) and gastric inhibitory peptide (don't want stomach acid coming into intestine)
4. paneth cells produce definsins and lysosome

paneth cells provide what defenses?

anti microbial (defensins) and anti-bacterial (lysosome)

plicae circulares are

deep folds in mucosa/submucosa of small intestine, forces chyme to spiral slowly

what produces intestinal juice?

microvilli on brush border

mucosa cells are produced by...

stem cells at base of intestinal crypts dividing

small intestine physiology

completes digestive process, can trigger pyloric sphincter to tighten to prevent further food entry, digestive juices of pancreas liver gallbladder and intestinal mucosa mixed at duodenum/upper jejenum

segmentation (small intestine)

contraction and relaxation of rings of smooth mm, allows bolus to make contact with mm and improve absorption, breaks food down

muscular contraction is regulated by .___ and ____ is released when chyme is present in small intestine

stretch reflexes hormone cck

Where does most absorption of nutrients occur?

jejunum

capillaries absorb ______ soluble products

water

lacteals absorb _____ soluble products

fat

villi contain

capillaries, lymph vessels and lacteals

large intestine modifications

mucosa has large amount of goblet cells, longitudinal muscle layer reduced to three bands, epiploic appendages

The taeniae coli are

three longitudinal bands of smooth muscle located beneath the serosa of the colon.

Haustra occurs when

walls of large intestine pucker into pouches

epiploic appendages

fat storages, part of mesentary

parts of the large intestine

ileocecal calve, ascending colon, tranverse colon, descending colon, sigmoid colon

large intestine physiology

absorbs most of remaining water, eliminates residue from body as semi-solid feces, harvests vitamins made by bacterial flora

bacterial flora make what vitamins and inhibit what? (reminder that while they live in the large intestine, the large intestine itself doesn't make vitamins)

vitamin b and k, inhibit growth of pathogens

what are the differences between haustral contractions and mass movement?

haustral occurs every 30 minutes in walls of iNDIVIDUAL haustra, mass occurs 3-4 times daily ,typically during/after meals, over large areas of colon

haustral contractions

Slow segmenting movements in walls of individual haustra

mass movement

slow moving but powerful contractile waves, move over large areas of colon 3-4 times a day to force contents to rectum, typically occur during/after eating

what increases the strength of mass movement contractions?

bulk/fiber

vermiform appendix anatomy AND physiology

located in vicinity of rectum, contains lymphoid tissue that protects passages open to exterior, twisted structure makes ideal location for intestinal bacteria (ideally for normal flora but can lead to appendicitis)

how many lateral curves does the rectum contain and what are they called?

3 rectal valves

the anus has two sphincters. name them and their muscle type

internal sphincter - smooth mm, involuntary
external sphincter - skeletal, voluntary