一、消化的意義·

二、消化系統(tǒng)At

its

simplest,

the

digestive

system

it

is

a

tube

runningfrom

mouth

to

anus.

This

tube

is

like

an

assembly

line,

ormore

properly,

a

dissembly

line.

Its

chief

goal

is

to

breakdown

huge

macromolecules

(proteins,

fats

and

starch),

whichcannot

be

absorbed

intact,

into

smaller

molecules

(amino

acidfatty

acids

and

glucose)

that

can

be

absorbed

across

the

wallof

the

tube,

and

into

the

circulatory

system

for

disseminationaround

your

body.The

breakdown

of

foodstuffs

like

a

Big

Mac

is

accomplished

through

a

combination

of

mechanical

and

enzymatic

processes.

Toaccomplish

this

breakdown,

the

digestive

tube

requires

considerableassistance

from

accessory

digestive

organs

such

as

the

salivaryglands,

liver

and

pancreas,

which

dumptheirsecretions

into

the

tube.The

name

"accessory"

should

not

be

taken

to

mean

dispensible;indeed,

without

pancreatic

enzymes

you

would

starve

to

death

inshort

order.In

many

ways,

the

digestive

system

can

be

thought

of

as

a

well-runfactory

in

which

a

large

number

of

complex

tasks

are

performed.

Thethree

fundamental

processes

that

take

place

are:Secretion:

Delivery

of

enzymes,

mucus,

ions

and

the

like

into

thelumen,

and

hormones

into

bloodAbsorption:

Transport

of

water,

ions

and

nutrients

from

the

lumen,across

the

epithelium

and

into

bloodMotility:

Contractions

of

smooth

muscle

in

the

wall

of

the

tube

thatcrush,

mix

and

propel

its

contents三、口腔內消化四、胃內消化（一）胃運動胃容受性舒張（receptive

relaxation)胃蠕動peristalsis胃排空

(gastric

empty)（二）胃液成分和作用鹽酸胃蛋白酶黏液內因子Gastric

function

is

often

classified

into

three

phases

in

whichsecretory

anactivities

are

tightly

coupled.

Try

identifying

these

phases

in

yourself

orones

around

meal

time:Cephalic

phase

("wake

up

call"):

Seeing,smelling

and

anticipating

food

in

perceived

inthe

brain

and

the

brain

informs

the

stomachthat

it

shouldprepare

for

receipt

of

a

meal.This

communication

is

composed

ofparasympathetic

stimuli

transmitted

thoughtthe

vagus

nerve

to

the

enteric

nervous

system,resulting

in

releaseofacetylcholine

in

thevicinity

of

G

cells

and

parietal

cells.Binding

ofacetylcholine

to

its

receptor

on

G

cells

inducessecretion

of

the

hormone

gastrin,

which,

inconcertwithacetylcholine

and

histamine,stimulates

parietal

cells

to

secrete

smallamounts

of

acid.

Additionally,a

low

level

ofgastric

motility

is

induced.

In

essense,

thegastric

motor

is

turned

on

andbeginsto

idle.Gastric

phase

("full

steam

ahead"):

When

a

meal

entersthe

stomach

several

additional

factors

come

into

playforemost

among

them

distension

and

mucosal

irritationDistension

excites

stretch

receptors

and

irritationactivates

chemoreceptors

in

the

mucosa.

These

eventssensed

by

enteric

neurons,which

secrete

additionalacetylcholine,

further

stimulating

both

G

cells

andparietal

cells;

gastrin

from

the

G

cells

feeds

back

toparietal

cells,

stimulating

it

even

further.

Additionactivation

of

the

enteric

nervous

system

and

release

ogastrin

cause

vigorous

smooth

muscle

contractions.

Thnet

result

is

that

secretory

and

motor

functions

of

thstomach

are

fully

turned

on

-

lots

of

acid

and

pepsinogare

secreted,

pepsinogen

is

converted

into

pepsin

andvigorous

grinding

and

mixing

contractions

take

place.However,

there

is

a

mechanism

in

place

in

the

stomach

tprevent

excessive

acid

secretion

-

if

lumenal

pH

dropsenough

(less

than

about

2),

motility

and

secretion

aretemporarily

suspended.Intestinal

phase

("step

on

the

brakes"):

Asfood

is

liquefied

inthe

stomach,

it

is

emptiedinto

the

small

intestine.

Its

seemsto

beimportant

for

the

small

intestine

to

beable

toslow

down

gastric

emptying,

probablytoallow

it

time

to

neutralize

the

acid

andefficiently

absorb

incoming

nutrients.Hence,

this

phase

of

gastric

function

isdominated

by

the

small

intestine

sendinginhibitory

signals

to

the

stomachto

slowsecretion

and

motility.

Two

types

of

signalsare

used:

nervous

and

endocrine.

Distensionof

the

small

intestine,

as

well

as

chemicaland

osmotic

irritation

of

themucosa

istransduced

into

gastric-inhibitoryimpulsesin

the

enteric

nervous

system

-

thisnervouspathway

is

called

the

enterogastric

reflex.Secondly,

enteric

hormones

such

ascholecystokinin

and

secretin

are

released

from

cells

in

the

small

intestineandcontribute

to

suppression

of

gastric

activity.五、小腸的消化（一）運動形式緊張性收縮分節(jié)運動蠕動二、小腸內化學性消化（一）膽汁的成分、作用水無機鹽：Na

K

Ca

HCO-。中和一部分鹽酸有機成分：膽汁酸+甘氨酸、牛黃酸+

Na+

K+→膽鹽膽色素：膽紅素→膽綠質膽固醇：肝合成卵磷脂：比例適就應溶解態(tài)/沉積、膽石膽鹽、膽固醇、卵磷脂，作為乳化劑微滴3000-10000nm脂肪的消化和吸收 一定濃度膽鹽→微膠粒（水溶性）進而促進脂溶性Vit

A

D

E

K的吸收肝臟的機能：500種以上的主要有糖代謝：血糖穩(wěn)定中心作用，肝糖元占肝重5%-6%蛋白質、脂肪代謝：合成血漿蛋白、防解氨成尿素。

Aa互變，蛋白質→脂肪分泌膽汁：人800-1000ml/d其中膽達1.1g%缺乏食入脂肪40%

不能消化吸收解毒酒精代謝激素失活貯存作用胰島素T

T3（T4）

消除抗原。甘油酯

VB12

用幾年Food

is

processed

in

the

digestive

tract

in

a

very

organizedmanner.

The

mouth

is

responsible

for

moistening

and

physicalbreakdown

of

the

food.

Very

little

enzymatic

digestion

occurs

herThe

highly

acidic

(hydrochloric

acid)

stomach

has

a

number

offunctions,

including

physical

breakdown

of

food,

food

storage,killing

microorganisms,

and

initial

protein

digestion.

The

smallintestine

is

where

most

food

digestion

occurs

includingcarbohydrate,

fat,

and

protein.

Entry

of

acidic

stomach

fluids(=chyme)

into

the

small

intestine

cause

the

release

of

pancreaticjuices.

These

basic

jui