Class Notes

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Function of digestive system

break down larger chemicals into usable levels

absorb the smaller biochemicals

Alimentary/Accessory

Alimentary canal: "tube" that runs from the mouth to anus

Layers of tissue (alimentary canal)

Lumen: hallow space in tube

Mucosa: Inner most layer, physically in contact with particle being digested

mucus

traps bacteria

lubricates what is being eaten

Submucosa: layer behind the mucosa

highly vascularized and innervated (lots of nerves)

used in absorption

Go directly into the blood stream (water soluble nutrients)

Lacteals: Lipids are absorbed here

nerve endings sense and respond to what is being eaten

Muscularis

has 2 layers

one is perpendicular to lumen, one is parallel

job is to move along

is smooth muscle

Adventitia

outer most layer

high in collagen (membrane material called serosa)

stretches, but more encases the canal

is smooth (decreases friction between organs)

Accessory organs: contribute to digestion, but not part of canal

what is broken down, how is broken down, what is absorbed

Mouth

Teeth

crudest way to break down

Rub between tongue and roof of mouth breaks it down

roof has ridges that help break down

Chewing mixes food with saliva and mucus

Saliva returns pH to needed levels

Salivary glands

Parodids

Sublingual

submandibular

Salivary amilase

breaks starches into individual sugars

Salivary lipase

breaks down lipids

much more active at low pH

most of job done in stomach

slightly acidic

Bacteria that cause cavities are pH tolerant

Dental caries (cavities)

Acid eats through the enamel

bacteria give off acid as a byproduct when disgusting food, which causes cavities

Another job not involved in digestion

natural aversion to tastes

protects us from bacteria and fungi in the food

physically sense the food (like bones in fish)

Densest concentration of tactile nerves in our lips

Absorption: no significant absorption

Pharynx/Swallow

Respiratory and digestive tracts cross

top of larynx is extremely sensitive

Coughing pushes out blockage

"Ever bite you take is dangerous" LOL

Epiglottis seals off the respiratory track

muscles lift larynx to the epiglottis

no digestion, no absorption

Why is epiglottis more common in children than adults?

Esophagus

job is to move the food

no digestion, no absorption

have peristalsis

may have developed due to typical eating horizontal

Stomach

Parietal Cells

produce HCl

In mucosa

pH, without food in there, gets down to less than 1

With food, is about 2

Chief Cells

release pepsinogen

pepsinogen is put in contact with acid→turns into pepsin

pepsin: digests proteins, especially collagen

mucosa protects it from being eaten

layer absorbs

water

some sugar

alcohol

mucosa prevents much other absorption

Gastrin

anticipation of food triggers release

stretching of stomach triggers it

caffeine, ETOH both trigger it

stimulates the chief and parietal cells

not made by gastric glands (chief and parietal cells)

Where is it made?

Ulcer

break in the mucosa

ETOH and caffeine triggers more acid, which causes pain to site

Chyme: partially digested food

leaves at a rate of 200 cal/hour

usually takes about 4 hours to empty

leaves through pyloric sphincter

HCl

kills most bacteria

breaks many chemical bonds

Pepsinogen→pepsin

Small intestine

where most of digestion takes place

Duodenum is first part

Jejunum

Ileum

long narrow tube more opportunity for absorption

has folds to increase the surface area

Villi

vastly increase surface area

microvilli on villi

blood vessels (water soluble)

lacteals (fat soluble)

Secretin and CCK

Liver

produces Bile

breakdown products from red blood cells

periferin ring: removed from rbi (bilirubins?)

way to get those out of body

gets cholesterol out of body

Cholesterol salts: help emulsify fat

get at interacting with water and fat due to hydrophilic head and hydrophobic tail

neutralizes the acidity

Removes a variety of nutrients from blood and stores

stores sugar as glycogen

stores iron and vitamins

neutralizes nitrogenous waste to urea

makes blood proteins which draws water back into blood stream

detoxifies many toxins

have enzymes that can reorganize nutrients

amino acids

fatty acids

Why does liver have trouble regenerating from cirrhosis?

Gallbladder

holds the bile

mixes with fatty meals

if high in cholesterol bile and high calcium, either or both can precipitate out (gallstone)

pain with fatty meals (gallbladder)

Fat, fertile, and forty

if remove gallbladder, have serious distress because cannot dump bile

lower intestines digest the fat, causing cramps and digestion distress

Pancreas

different version that break down nutrients

Releases enzymes

help further chemically digest the food

Secretin and CCK

secretin

stimulates pancreas to release enzymes

stimulates liver to let down bile

released by duodenum mucosa cells

low pH triggers release into blood stream

bile helps neutralize acid and emulsify fats

has a negative feedback when pH is raised

CCK

fat stimulates release (only)

released from the duodenuma

stimulates the pancreas

stimulates the gallbladder to contract

Colon

prevents dehydration

retrieves water from chyme

mucosa pulls salt out of chyme, and water follows salt

chymes forms into feces

if mucosa is irritated, will not absorb salt and water (diarrhea)

bacteria produce vitamin k (blood clotting)

vitamin d absorbed

after antibiotic, have digestive upset

if too much water is absorbed, from dehydration, (constipation)

more time sits in colon, more absorbed, so is harder (not physically active) (constipation)

Diarrhea/Constipation

Digestion Notes