The absorption of amino acids from the mammalian intestine

THE ABSORPTION OF AMINO ACIDS FROM THE MAMMALIAN INTESTINE

John Basil Wilson

A Thesis Submitted for the Degree of PhD at the

University of St Andrews

1949

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- s

•The I n v e s ti a t loDs o f r*ooent year j d e a lin g w ith the su b je c t o f i n t e s t i n a l aboorptlon Imve* on th e w îiole, tended to confirm th e view ttm t tlio

membrane o f th e ;u t, lirovlded th a t i t s n o m a l co n d itio n la igerved^ la n o t to bo c la a se d a s a

oasolvo diap!ira in between blood on th e one a id e and s o lu tio n In the g;ut on tbx) other* r e v e r tlie le a s . I f th e Gonolusiwi tlm t tlie ep ith eliu m o f the v l l l l In some way a c ts a s an a c t iv e au ;ent In a b sorp tion be admitted 9 we are s u l l l very 1 'norent renardIn^ th e

ex ten t to which I t s a c tio ; la m odified by cihan ea In th e p h y sica l and chem ical environment o f the c e l l s w ith in th e lim it s o f Snterferenoo w ith bloplasm lo p ro cesses 9 l i m it s soon outstepped «lion concentrated

s o lu tio n s or s o l u t i œ s o f d e le te : Icua »u )stances a r e

# p

used by th e in vostln ator" *

( aymouth e ld (19)2)^

5

e n tr a i I n t i ^ u o t i o n »

I# General imbure o f problem#

II* stn '.o tu re and h: e t o lo r y o f tîx? [^ t* I I I * H lsto r lo fd review *

IV* Lîodem work*

V# A bsorption o f our ara*

VI* Absorption o f f a t s *

V II. i^ a o r p tlo n o f amlno a c ld s# V III* P ren ait p o s itio n *

:.9oUoD P.40

"^ates o f A bsorption o f to ln o a o iâ a froQ upper and low er lo o p s o f th e sm all I n t e s t in e o f a ts *

I# Intrcx&iotion#

II* l a s t work* I I I . fr e se n t work#

a ) method*

b ) r e s u lt s . o ) 1 la o u sslo n #

IV. Simoary.

o o tla n *4*. f # l 3 l

4

-Cats anâ o f -Cats vbdôov l ret!jane AnaoetW ala*

I# In tr o d u c tio n .

I I . r%st work.

I I I . Preaont w r k .

a ) Method.

b ) l o s u l t s .

. o ) D ism issio n .

IV.' umaa!?y#

. .

i%i9ral I Is o u s o lo o . P.1S6

V

en era l ummar^. p .176

• s «*

G ^ B ^ R A L I B T R G P U C 2 I 0 B

I# r>8nor&l nature o f pt*o.>laa»

II# SGruoturo and hlatoloi^ÿ^ o f übo t# t#

I I I # I s t o r lo a l ~*3vlw?#

IV , üodw o ®oHt#

V# AUaorptlcm o f su g a r s .

VI# Abao2*:JGÎon o f fa ta #

VII* Absorption o f aain o aoida#

w ô «

IK ''oi/ ■a s t i n

.

a ) r-'Operal im turo of

ÂDsorptlan i s th a term a p p lied t o tbe paoaa o o f aubstanooa in to the blood stroan# ohothor from tbo body aurfaoo» I'roa tbo body c e v l t i o a , th o lym ^i

□poooa, o r from any ornana o f tbo body. Tîü» ab sorp tion

o f foodotraffa tokoo p la o o , in vortobratoo* tbrouf^h tho a lia o n ta r y oanal# Food la d i^ostod in order that i t

rîioy be absorbed. The dlQoated food thas d in ln ia h e s

in q u a n tity as i t paasoa t b i w ^ th e allm ontary o a n a l, and th e fa o o es con tain tho u ndinested or I n d ig e s t ib le r e s id u e .

Th? aXimsntary canal shows oonelderabl e d iffe r e n o e a in atru otu re aJoiic i t s le?ir’tih| th o se d iffe r e n c e s de end on the fu n c tio n s o f tho v a rio u s p arts# In tho mouth end oosophejus a b so lu tio n I s a t a minlEiun inertly bocouao o f th e tliio lîn e ss o f tho e p ith o llu a and p a r tly booauso o f tho rap id passa o o f tbo food throu'^h th o se p o r t s . Abaorptlcm ta k es p la c e to a sm a ll ex ten t only Ir the stomach# I t i s e n e r a lly tau ht tlia t water i s n o t absorbcKi irom the sto o a o h

7

-AlooboX Is eb3ort)#d to aorao o z te n t# Also* do

n o t soAQ to bo ao30Xt>oci tm lesa prooent in tsuoh QpAAtor ooooentr At ion g tlian o o o j f in no!%ml d i e t s f ougmr . la

Absorbed o l t h d l f f l e n i t y . OolXoldAl im torlA la auoh A3 p rotein * fa t* and otarch* nhioh arm th o im ln food jt^ ata n o os apart fi*gq smtor and a lta * are b ^ lte n doan in th e I n to o tln a l ooim l by h y d r o ly tic onzyaes in to

so lu b le* d if f a a ib lo .robstonoea (C itarllnc# 1896) • Thus p rotoin a ero broken doon in to azalno acid a o r p o ly p e p tid es * in so lu b le f a t a are broken dom In to f b t t y aoida* uhioh re a o t -aith b i l e a c id s to Ibra vater^ a olu b lo * d i f f u s i b l e oozg^lo&ea* and otaroh I s broken doan in to sunara.

T his forcm tlon o f water - s o lu b le d i f f u s i b l e aubatanoea i s not* however* th e o n ly a l j n i f i o a n t r e s u l t o f tbo breakln ; do «an o f fc^ od stu ffa. I t l a e s s e n t i a l th a t the breakdoan products should bo non* a p e o ific s u b sta n c e s . The importance o f t h i s can b e aeen w ith p r o te in s . r o to ln a o f one s p e c ie s o f an In a l e r e t o x ic I f in je c te d In to the c ir c u la t io n o f another 3i>ooie:j* b u t the same p r o te in taken in to th e i n t e s t i n e i s s p l i t up in to n o n -a p e o ific and n o n -to x ic amino a c id s or p o ly p e p tid e s.

Tlaero are u cid ition al ad van ta e s in th e

• B ■»

end t b ia l a only p o sa lb lo I f tha food aubatanoea d w lv o d from p lan ta or anlimila ei*o f i r s t bTXJkan

doan t o r o la t l v o î y alciplo saol^^culos* ^ona sQbatacoaa suoh aa wôt'ir» and aolubXo s a i t a l l k o sod ln o c h lo r id e oro absorbed unohanced#

Tho sm all i n t e s t i n e , # i l o h posaossoa a very la p fo int(n*nal aurfaoo on asoount o f I t s f o ld s and v l l l l , l a th e T?seln orr;an fo r absor^A lon. AbsorptloD beglna In the duodenum^ m â tho prodtiota o f d ig e s tio n have la r g e ly disappeared by the time the I n t e s t in a l co n te n ts reach th e lleo co X io v a lv e a t t h e ooomonoeoont o f tho larr e In t i s t l n e ; e a te r la absorbed In the la r g e I n t e s t in e but I t s powers o f ab sorp tion o f oth er m a te r ia l 0 are very sm all# A bsorption ta k e s p la c e

o h le fly In th e upper part o f Wae sm all I n te s tin e # /vfter tho food m a te r ia ls p ass through th e I n t e s t i n a l

ep ith eliu m th ey reach e it h e r th e blood v e s s e l s (p o r ta l t r ib u t a r ie s ) o r t2ie lym phatlo v e s s e l s or la o t o a ls # In gen eral te r n s , th e p ro te in s ard oarbohydrateo pass in t o the blood v e s s e l s , and th e f a t s p a r tly in to tho blood v e s s e l s end p o r tly in to th e la c t e a ls *

Thus, In tho i n t e s t i n e , th e fo o d s tu ffs are

•* Q ’ •»

thô oï»ryBnl^ or o f ro a o tln - to fo r a th o o>i^rttotorl3tio

auhstanooa o f tho body. Tho Ibra In ^ l o h tbo

3u*03tanoo la prosont In th e I n to a tin o la o f d e o la lv o Iraportônoa f o r th o q u o a tlo - o f ab ab rp tlc • D iffu sio n i s on ly p o s s ib le In aqueouo o r lip o id s o lu t io n . C ertain o f th e a ij 0 3 t l v e p r o c e sse s produoe e a i l l j d lT fu s lb le

sob 3 tances* e .; > onlno a c id s In p ro te in 01 r e s t ion#

I t has been supposed th a t th er e o u st be prooeaaoe idiloh re r e la t e th e liat ire and ocio^int o f su b stan ces

absorbed* In r e la t io n t o th e r.eeda o f th n orf'snism#

Dut t h i s has n ever been proved . S ta r lln r emphasised

th e f a c t th at tho r*oraal I n t e s t in e absorbs overythln^ th a t I s ccaTverted in to a d i f f u s i b l e foiro In I t s lumen* lo d ep en d ertly o f th e needs o f the b od y.

I t I s very d i f f i c u l t to fin d a tr u ly p h ysiolof^ leal raethod f o r ab sorp tion experim ents* The I n t e s t in a l

cRiOosa I s extrem ely s e n s i t i v e t o a lt e r a t io n s o f

tem perature end blood flo w . For example* the

ab sorp tion o f olicjbvq from on s o la te d lob p o f tSb» sm all

i n t e s t i n e o f th e r a b b it d ecrea ses i f the teoperaW re

f a l l s below 25^0 (AuchlnaoFile* ilaoleod and 1 9 3 0 ).

- 1 0

-InoroAüQd s t a s i s ^ a h l h I n t r a - I n t s s t I n a l

p ressu re dus t o i n j s o t i n • a b lu tio n s in to a 11 atursd lo o p o f Wi@ in t o s t ln o w i l l cisaso alanoromlly rap id

a b so rp tio n <iioDour;all and Vorsar# 1956)» üovsQoiita

o f th e v i l l i coas^ i f tbo blood flo w bsooaso Inadegm te# and :]P@at s tr u o tu r o i ohan os^ J n o lu d ln ^ b leed Inc or

Uosqoaoatlun o f th o ssuooaa» oay ooour In resp o n se to d istu fb a n oea in th e b lood flow #

The problaa undertai:(Ri in th e p resen t vortc la th e oeeaurecient o f tho ^mte o f o b so rp tio n o f omlno 'a c id s from th e sm all i n t e s t i n e and tlie c o r r e la tio n o f tW s e r e s u l t s w ith t ! » c o r n s ponding o o le c u la ^ welf h ts and

apparent m olal voltases» i or th o study th e two speolas^

r a t and o a t , have been ohoaen»

b ) >truoture and h is t o lo r y o f the n u ti

The acm ll I n t e s t in e i s e s p e o ia lly

• 11 •

otruob TP#* aXthc^^-h sh o # ia 0 0 2m dlffmrmioQm* 1# .

#vop^^h#p^ t)n an# In p rln o lp l# * ao «bat on# doaoPips tioei a p p ll# 3 to t i l l o f tiy%a# ?bo taaln fu n ctlon a o f tho acm ll in te a tin # a re (a ) the forim rd ln g o f th#

I

oJiÿsxta ûlonr i t o oo'jpae* (b ) th e oont^nued «lîgaatlon

o f tho ohyae by means o f s p e c ia l J u ic e s 3 0 0 '#t#d by

i t s walk's end by th e aooeasory glands* and (c ) àbaorps

t lo n o f th e liq u e f ie d n u t r i t i v e m t e r i a l in to th e blood and 1 oph v e s s e l s ;

:>urfao# o f th e muooua ciectoraaai

Ttxi uurfaoe o f the mueooa m3mb:»@no in th e jtooaoh* in v ^ c h ab sorp tion la In a l n ifio o n t * d oes n o t show any o u tir o c th a j In tb o iz sa ll in te s tin e ^

fpoQ udiich th e orranism r e o e lv e s alm ost a l l o f i t s food o a t e r i a l ; th e su rfa ce i s enortaoaaly Inoreasod through

th e format ion o f o ir c u la r fo ld s * and the v i l l i (P is* 1)#

The fo ld s are co n stan t s tr u c tu r e s m û do n o t disappear even uftion th ) in te n t In a l «m il i s d isten d ed # T l ^ b egin about 2 em; from th e pyloru s and rea ch th e ir maximal development in th e d i s t a l Im lf o f th e duodenum and th e

Ijpoxioal imrt o f th e jejunum ). In tho ileum tîiey 000000

F If: a. 1 and 13.

I' l n . I la a atero o n lo ro a o o p io vlow o f

the Intoütlxi& l S o h o n a tio . X 17

O penings o f th e in te s tin a l glands L a m in a p ro p ria —

M u scu la ris m u c o s a e L iim p h o id n o d -rtr i n th e la m in a —

p r o p ria S u b m u c o s a —

iL'ith v e s s e ls ) C irc u la r m u s c le —

L o n g itu d i n a l i

m u s c le I

S e r o s a

-L ym p h o id nodule in th e subm ucosa

Villi

Value o f \ K srh rin g L y m p h o id n o d u le

P o r tio n of w ail of «niai! intCHtino; d raw n w ith b in o c u la r m icro sco p e a n d sectio n s. 17 X

after Braus, 1924.

Figure I.

-■i I

S e c t i o n o f a v i l l c s ( c a t ) , . s h o w i n g t h e c l o . s e r e l a t i o n . s h i p o f t h e b l o o d - C A P IL L A B IE S TO T H E E P I T H E L I I M. X 4 0 0 .

r , l o liim n a re p ith p iiia m sse U * , w itli so m e leuoocjft*-» U lw ec n t l a m ; c, b lo o < t-capillary c u t Ic n g th w aj-s ; /, laclpiil. N iim e ro iu s leu c o cT lrs a r c a ls o »<■. ii in tlic t i « « - o l t b e viliu» a n d in t l ie la c te a l,

after Sharpey-Shafer, 1934.

12 •»

Tho v l l l l arm outf^ow ths o f th o ouoous modhrone ocvQTln ; th o ontlrm stirfaoo o f tho au oosa on the aSdo and croate o f tho f o ld a , a s v o l l a s tho spaoas betwaon

tbam* They ^Ivo too surfaoo a t y ^ lo a l v o lv o ty oppoaranoe^ In th o a d u lt rat thoy aro l o # , f l a t and lo a f-sM p o d ;

In tho o a t thoy a re more o o n lo a l o r f l n - o r - l l k e ( I'lgs#

5# 4 , 0 and 7 )* ih o Inoaaarahlo oponln @ o f th e

I n t e s t i n a l ^lands or o ry p ts o f LiebeMmtn may bo seen between tlie b ases o f th e v i l l i ( P i g . 7 ) .

T M _oi^ltholiqqi

The e p i t h e l i u n , to io h co v e rs th e fr e e su rfo o e o f th e taooouj aortorano* to e su rfaoo o f the v i l l i and s o a l l a re a s beto^on t h e ir b a s e s , i s sim ple oolucmar# ih r e e tyi^es o f c e l l s can bo d io tin -^ ia h e d lii i t * - (a ) sim p le ooluonar e p i t h e l i a l c e l l s )aith a s t r i a t e d , c u tio u la r border I (b ) r o b le t o e l l a ; (o ) olirocaaffine c e l l s .

F1p:3, 5 and 4.

F in , 3 shows tb s hlatoloG loaX Appearanoe o f

tho uppor loop of tho sm a ll in t o s t l n o o f tho oat In transvorao s e c tio n a f t e r im lf Isosm otlc I'lyoino bad boon l e f t in tho lumen o f th e gut fo r 43 m in u tes. The v l l l l are long^ f in g e r -l ik e p r o o o sso s. There la no apijoront In ju ry to th e Qplt e l l a l o e l l s o f th e v l l l l , X 0 ,

I 'lr . 4 shows tho h l s t o l o r l o a l api^ooranoo o f the upper loop o f tho sm a ll I n t e s t i n e o f the oat a f t e r h a lf Isosm otlc l y o l n e had been l e f t In th e lumen o f the r u t f o r 40 m in u tes. The ep ith eliu m o f the v l l l l l a a b s o lu t e ly

Figure 3

/ / ■ i

8 a 6 .

r i n . s ohowa tiia h la to Io X ^ rlo a l appoarj tonoo o f a tranavorso s e o t io n o f a t y p ic a l ra c îo n o f the upper loop o f the jm a ll

i n t e s t i n e o f the r a t a f t e r h a l f iaoom otlo g ly c in e had been l o f t in th e lumen o f the ju t f o r 1 b ow # iJSnoe tlio v l l l l o f th e r a t are l e a f shaped # In tr a n s v e r s e s o o t ion s they a r e r a th e r lik e mounds than lo n g p rocesses#

X 14#

i If^# 6 aho\98 th e v i l l u s o f th e r a t w ith

•g ajnSij

M:6I li3;D i^ 3S-/2idjD L |S j 3 y D

U l r

•< iM .i.> :ii\i >’iH > ^;iA -ii'M p-i;r t i . i . t u i.\ ;i m ' l ' n i \

Fl<:8# 7 end 0.

I""!/;» 7 ahnwa a X on ritu d liial s o o tlo n o f the jejunum o f th e o a t (aecai dla^Twamatio) d e p ic t in g th e varlou o ooeto o f th e omaXl

in t e o t in o * X 4D#

i.ithi ikuhu musruUtri» muiO'-it

IIP

inltTTt UMUluT

\ , r . SK C TIO N O F T H K SM .M.L IS T K S T IN K ' ' 'O " ''

after Shorpey-Schofer, 1934.

Figure 7.

after Mottram, 1922.

• IS

-oXod9 ocxm^otlOF] o f %h^ e p ith e lltm w ith t h9 oorm aotlve

t is s u e * In the l i v i n g o o a â ltlo n * G ibbet end 8 Lmoo@@$fully th e Sitm .tr airigln^ from the movenfmt o f th e ^ 1 1 1 m â th@ tBOohanlaal e o tio n o f th e p arsin g food m te^ lo X * In

'oath* homv^Vp th e o o m o o tlo n l e ea s! l y d ootroyod and I t I s e s t r e c n ly d l f f l o u l t to p rosorve the t? u o I n t r a v lt a l c o n d itio n s In f ix e d n m torlai# 6 f t o r f i x a t i o n th e o p lth i e llu m , a s a r u le * appears detaohod from th e stroma on

th e yuamlt o f tlio v l l l l In e oontlnuoua la y e r and ft

sm a lle r or la r g e r oavlb y I s aeon jotooon t h e two t i s s u o a .

io h lo t o a l l a »

G oblet o e l l a a r e so a tto r o d between t h e o y lln c ir lo ftl e p i t h e l i a l o e l l i * They Ovicwr on the f r e e su rfa o o aa

w a ll 03 In th e orypta# They are s i n g l e c e l l s and bhoir s id e s are convex by reascm o f th e proaauro o f th e r^ clg a n s and push away th e neighbouring ooltm nar o e l l s *

Crypta o f bleborUuhnt

The e p ith e liu m o o v o r ln i the v i l l i c o n tin u e s

In so the glands o f ^ leberkdtn* iV^ove t h e bottom o f

th e cryp t t b e l r w a lls a re lin e d w ith an u n d iffe r e n tia te d * low oolujanar e p ith e liu m whlc^ oon taln o nxaaerous m ito se s# tîero r s veneration ta k e s p la c e and the new c e l l s taovlng upwaN g rad u a lly d i f f e r e n t i a t e In to ^ o b le t c e l l s and

„*» 14 •

In tho botî&oa o f ube rlan d j o f Li^b^rlsiU» in t h i sm a ll i n t io a t in i, tbQ ./^ o u lia r, l&a», @ o o l l o o f PanOuh occur r o j u 3 o r lj # T bolr n u o lo i ay* l a r j e and

roundod; tsliolr fr*)3 odi,:a ojuo^ilaso I j f u l l o f lurj® cp iio rio al a ^ ld o u lilllc :j?an u lo j, and t*hoir proxizaal

oy^oplaaa c o n ta in s b a s o p h illo ircxa - o o n ta ln ln g

o îiro a ld ta l oubsta. 0 9 *

;i:;,^ooarrin9 c o l l a i

Jhrosaafflno oolXa a r e th e raroau* They w o

aoro abundant In ttio diiodontan than oltîaei* tho jojun^sa or iloum ond a ro found botw eon tbo o a lla l i n i n g Uho

zlandu o f Lloborkulzi*

In th e m iddle o f v i l l u s la a ly a p b a tio v e s a e l» knoon ao th e c e n tr a l l a s t e a l « « i l loh nay be

on lark ed n ear I t s coaom oem ont; tbm en lar, oaent i s

roplaoad Ir 30s» a: Ixaals by a network o f æ m ll v o a s e la . SfirroundInr th e l a o t o a l are f i n e b un d les o f p la in

m uscular t i s s u e prolon^^^od from th s csusoularia aucoaae# À netwoi^c o f b lood c a p i l l a r i e s (F ig s* 2 and G) l i e s

- 15 •

o f tho v l l l u a .

*ho lüzalntt i^ o p p îa o f t?ho muooua aDsabrano f i l l s a l l tiho 3^41093 a o t 'joon uho land a o f î^loborklili and f o m a Uba ooro o f tjho v i l l i #

0 Qat;ü o f th o m i l *

Tho 9uiX3ucou3 la ^ o r oonalst^o o f lo o a o o o m o c tiv o

ülaaua# In thn ’UodoauQ it» la ocouplod by a t»hlok

la y or o f d a - landa f ^ m n o r ^ h lo h send ù b oir

duo tu to tk 4 In iisr ou rfa o o o f tbo oaoouo raoiabrono botvioon tb s cr y p ta o f Llsberkdlm o r In to tUoa»

The e x t n m a l lo n g it u d in a l scid th o I n te r n a l o ir o a la r la y or a o f tba au scu l.jrt.3 e x te r n a (F ig # 7 ) a r e m i l devolopod In th e em a il I n te o tla e # The e x te r n a l o o a t o o n a ia te o f a la y e r o f œ a o t h e l î a i o e l l o r e a t ln g on l o o s e e o n n e o tiv e tlse m e # th e se r o sa # A t th e a tta o h s ment o f th e m esentery^ t î » serou a la y e r o f th e I n t e s t ln o a

cm itin u ea on to th e s u r fa c e o f th e m ea en tery .

;vb3Qgotlvo a c t i v i t i e g i

The c o lo2 2r>ar o e l l a b ear t h e burfion o f th e

•» X O '

co n ten ta # Tbo 'îpîth^lltjra o f tho m aall Intoatîîno

ôdsaXfcn TiatïTP aiul m in era l a a l t s , tâvi pro<3uot3 o f dlreutlO D

o f oa^)obydra^Ao ond ^ata#

^h@ Gmisio a o ld a , nbXoh are a p l l t p ro d u its o f th e p r o t e in s , a r e b l diffuai'oX e^ e n te r (^Alokl^ mid cannot be observed in t r a n s i t beoauao onr caiorooheniaaX te a ta

are n ot a u ffio le n tX y d e l i o a t e ; a lt e r a t lw io in c o l l duruotare

h a v e, ho s e v e r , been rep orted # éiaoklln and (1986)

!Ave 3ho«n v& ouolatlon end aveXXlnc o f tlie oelXa a t the t lp 3 o f th e v lX ll durtuG p r o te in abaorption to be an a -o n a l o r earXy p o s t mortoo plionomenon.

^ f t e r a b so rp tio n th e aubatanoeo e ü e r th e t la sue f l u i d on th e o th e r s id e and a r e tak en up by th e blood v e s s e l? and lym p iiatioa. The c a p i l la r io a form a vez^ d en se n e t wo in th e lam ina p r o p r ia , o r ->:>re, o f the v i l l u s * The lyiapVatioa h ere se r v e a double f u n o t iw * In a d d itio n t o d r a ln in Wie t i s s u e f l u i d , a s they do e ls e w h e r e , th ey ta k e up th e absorbed f a t ; henoe th e s e s tr u e t u r e s a n k n o w a a tW XaoteaXa* In th e d isten d ed s t a t e th eu e are th e l a r e s t stx^iottures in th e v i l l i *

o ) t i l g ^ o r i o a l r e v i e e t

X7

-two a a în l i b o a . I t nmy

\rt

a'osorptilaT from th a in t o a t in a io a p h y sic a l or

i)hy8ico*«K»c^AT^ioiil ro o a ss or sZiat tîm pro ca s 9 o f

in t » 3 t iim l a oaorp tio n l a , in p a r t , a t cgiy r a t o , &n a c t iv e p h y a lo lo g ic a l funotlcm o f tho a p î t b o l î a l e o lla #

(1308) (potOS Ü p p o o ra to c (B* *403^"3?7)

aad l a l e n (^#L. 13^«200) oo proponndW tlm e a r l i e s t

th e o r ie s oti tho 0 0 chan io n o f ab sorp tion # The l a t t e r

b e lie v e d th a t a b so rp tio n occurred throu ;h o r i f i c e s in th e blood v e s s e l s , p a r t ic u la r ly th e venous blood su p p ly, in th e i n t e s t i n a l o o l l #

Kudo 1 phi (1 3 3 3 ) and i^iapandle (1025) %mre omon^iat th e f i r s t workers to hold th e view th a t p:i^'3ical "iaUib; i t i o n ° was th e ca u se o f a b so rp tio n # A lso e o o iv s t th e e a -* lie st recorded vlm#s on a b so rp tio n was th a t o f

Biedeaiann m ô -molin (1 3 2 )) aho oom;)arod th e ab sorb in g v i l l i to in v erte d seo-^etln : lan ds# - 1 t h th e odvenoe o f knowled ] 0 o o n o em in ; osm otic phenomena, P iso lier ( 1 8 ^ )

and D utrooW t (1326) ex p la in e d th e p ro cess o f i n t e s t i n a l a b so rp tio n by th e th eo r y o f endosmosic# ^rüdko (1351s 1 3 ^ } , boweven, s t i l l upheld fâ» h y p o tlie s ls form ulated by Liebm^kuhc (1745) th a t th e predominant f a c t o r in i n t e s t i n a l &b3orpti<%i u»3 n i t r a t i o n # The tf^iory

18

-o f bkn v i l l i vîh-oncse tbay #-o 'O up oy übo

blood voaaala# Xlyj ao&lon WJ aald to bo o .a o f

f i l t r a t lor of oc»ntont3 of tm ln to 3 tl,io j j

prosauro thi>.->u db tbo gut imXi Izito tM voao^la o f tlB

v l l l l # do til Lloborkulm oxiù 3rüok@ b o lto v o d th at tljoy

had obsirv'^»! oponln^a Into tho v l l l l # tbvlonoly, suoh

o*5ndltlono w o ld load to o b llto r a tio n o f tho o u p llla rlo o

and lo o ta eIs and^ I f f i l t r a t i o n ooouri*od at a l l ,

flu id s oxpt*0330d TDUld ^û33 Into tho :)orltoroal oavlty

and only v^ry s i 3^htly into tho blood or lytaph#

V o lt and iauor (10G9) u#&pld t h i s view fo llo w in g o b se r v a tio n 3 on tho a b so rp tio n o f p v o to ln a o lu tlo n o ,

jem m , and s a l t s fro© th e I n te s tin e # -boy oon d n d ed th a t f i l t r a t i o n brought about b y l n t r a # l n t o s t l n a l o r o o sw e

«aa r e s p o r a îb îo fo r I n to :tI n a l ab sorp tion and m t oaoosla# 'The30 d ed u c tio n s ?oro founded j a r t l j upon th e orrozieoua

id ea th a t the pas aero o f s o lu t io n s through tho in to i t In a l ^%all should im ita te the d i f f u s i o n o f t h e sac^ s o lu t io n s tlirouph a r t i f i c i a l nocD ones# The f a c t th a t an In a l

:coA)ranos may vary in t h e i r p o rm o a b lllty ^ms n o t knoun a t the t io 9 #

X9 •

In f u o t f i t probable from t&o work o f Ludwig

(1351)

ai'td S t iln a c h ( 1 3 ^ ) tibat sotaa s p o o ia l o ^ ll a c tio n vma

c o n o o m ^ In tW proooas o f & Jsorption« ülX^r bad#

liidaod# as o a r ly a s 1041 Jeo larod th at th@ c y l l M e r o o l l s dl30cv4f.»d by H^nlm (1027} axsrtoC in 1^9 pSKJO^as o f ab aorp tlor an ®oï*{anîâbô Analwbmns® (o r g e n lc a tty a o tio m )* !iop 9#'^oyl9T (1£31) waa feh9 f i r a t to raaintain d e f i n i t e l y th a t I n t e s t i n a l ab so rp tion m a a f a r o tlo n o f ttie l i v i n g e p i t h e l i a l c e l l s * The evldeno© taas haaeC upon the

a c t io n o f tW / u t in oh-olera end poison ed by c a p ta in t o x ic 3Ubetanc93* Sl^boe# in th e s e oases» nor^aal

ab sorp tio n did r o t oocur ^loppe^ e y l e r oonaidored ubat the "’v i t a l ” a c t i v i t y o f th e I n t e s t i n a l c e l l s had been impaired* In o b o lw a # «bora th e ^ i t h o l i u n o f th e

i n t e s t i n e i s la r g e ly s:ieJ^ the ah eorp tion I s a t a Jwand* s t i l l a lth o u ^li th in n in g o f th e laec^raoe m ight favour osm otic t r a n s f e r o f the g u t oontcm tJ. * ss^taoufsh ^eld

(1 9 3 0 ) p o in ted out th at th e s e e^pe ^im^Tits d id n o t n eo esss a r l l y prove th a t th e epltbm llum ocG lvoly t ran i f erred th e

• 2) ^

d i f f u s e ovmr Into tbn no th a t tly* volu o o f tb n lr

ozm otlo preaanr 1 aa a f a c t o r in aooorptiorz o f :m tw

Î3 onrajll^td’’.

<2 ) :rM3o Til "forIt;

Holdonliain (1394) and l i i s p u p ils Leubusoher (1 3 3 5 )4, Cumll^'^kl (1S8G) miô ^bl-rmm (1037) oame t o tbo

38130 oonoluslori arj th a t o f -iop:)0^ i j l i r ^ h ot vrlth oao la o d lflo a tlo n * Hoidonbaln b^lavc»3 th a t a o o rta in p o rtio n

o f tho 3olv«mt and a o lu to a^sofbod o siio sla *

Another p ortion imo ahaorbod b y th e p h y a lo lo ^ io a l a o tltr lty o f the llv ln ,'; e p i t h e l i a l o e llo and <343 not obey th e knomx p h y s ic a l la w s , Heldonhain saaiutaiiiod th a t by th e

^ a c t iv it y o f th e liv in g s ooH** th e c e l l oould e x e r t aa iiifl'îô n o o upon i t s p h y sia a l o r oljflEdoal proooaoaa#

Cohribeim (1398 -1933 ) absorbed t h a t th e prooooe

o f a b so rp tio n jaaj a one-way neohanlom# 313 S r m s tlp a tlo n a le d h la to th e d e c l s l o r u hat, undei^ noi^aal 0 0 nd I t i o n s ,

a p p r e c ia b le amounts o f c llfT u s ib le blood o o n a tltiie its d id n o t pass In to th e in t e s t in e # I n t a s t ln a l absorption^ uooordSns to Cohnh''lm*3 th eo r y Involved two f a o t o r c i -( 1 ) or. It^ p e m e a b lllty t o body f l u i d s and d is s o lv e d îTJbatflEicas due to th e a c t i v i t y o f tlie c a p i l l a r y

« 21 4»

( 8 ) an a l l l b y o f m i l t o tolm up th o

o n to n ta fpoa lt»a lumen tli*ou;h th e in to rm o â ia tlo n o f t t o v i t a l G o tiv ity o f th e (^ I W ie lia l c e l l s , a lU n otlon a h a o lu te ly f r e e o f p ljy slo a l Iri'lnonooa# T h is h y p o th e sis* th e p o fo r e , d if f e r e d from th a t o f lioidenhoin in th a t i t r e je c t e d th e Idea o f c e ll u la r a o t i v i t y o f th e ep itliellu B i belnr a f fo o ted by th e osm otic p ressu re o f th e in t e a t In a l oo n ten ts#

ayaouth Held ( 1092*1912) on th e acme ;;;enoral rounds a a . ^eidenhain end Johnheim ooDeluded th a t

i n t e a t l n a l a b sorp tion was due to th e i^ y s io lo Q io a l a c t i v i t y o f th e e p i t h e l i a l o o lla * Ilo sta te d * however* t h a t th e forma o f ener^iy u t i l i s e d in th e c e l l u l a r mechanism ware n o t o th er than th o s e k n o w in th e p h y s ic a l world# Be a so irn ed th e power o f ahaorption e n t i r e l y t o c e l l u l a r a c t i v i t y and oonaequaatly h is th eo r y waa in c lo s e r a

ment w ith ohnheia than w ith uoSdonhain p o stu la te d

th a t osm osis played some p art in th e prooeas o f ab so rp tio n # aymouth e ld (1898 a*b . ) based h ia c o n c lu s io n s on th e

e v id en ce o f a s e r i e s o f experim ents where a b so r p tio n o f serum from th e I n t e s t i n e under c o n d itio n s in wl^lch the p u rely p h y s ic a l fo r o e s o f f i l t r a t i o n * om oosis* and a d so rp tio n wore exclcided# îie showed thut o p e r a tio n s

— 22

e p ith e llo Q 3topp«>â tails a b s o r p tiv e p ro ce ss# In : a o t# any o o n â ltlo n depressJn:; the a c t i v i t y o f tb e c e l l s te id o d to redu ce the a c tio n o f etosorptlran# By ooans o f a

d if f u s io n ap )aratua c a lle d an o s o o o e te r end an I s o la t e d

' r

s u r v iv in g p ie c e o f I n t e s t i n e a s a m^xahraoe aymouth A e ld dosons tr a ted In 1892 t l » t movement o f sv ^ sta n o es took p la c e a c r o s s th e :^ndt>reno# The aovenent took p la c e from th e f l u i d In CK'^ntact a l t h th e mucosa t o th a t bath ln ^ th e o p p o s ite s e r o s a l s id e o f th e In to t in e # Oomotlo p ressu re I n flu e n c e s he ixnaoved by u s in g f l u i d s o f th e 3ome com position on e i t h e r s i d e o f t i e noobrane and In t h i s manner, i t v a s a r u e d , tlie a c t iv e fo r o e o u s t be a v i t a l fu n c tio n Inherent In th e e p i t h e l i a l o e lla # waymouth ffeld (1 9 )1 b ) v e r i f i e d Gohnholra’ s f in d in g t h a t th e p ro cess o f a b so rp tio n was a one««ay meci^anlam* The r e v e r s e p ro ce ss o f raovoment o f su b sta n ces In to th e r u t lumen mas sa id t o r e s u l t from c e l l u l a r In ju ry o n ly , in e h lo h ca se tho o e l l s l o s t t h e i r ^ o r ie n tin g ootion®#

In 1992 wayoouth eld d e v ise d exp erim en ts t o d etm m ln e th e e f f e c t o f Intravenous I n ja a tlo a s o f sodium c h lo r id e

on th e a b so rp tio n o f g lu c o se from th e I n t e s t in e # ïio .

jhowed th a t the de o f ^ a ter ^mssare from th e I n t e s t i n a l s o lu t io n was n ev er Snoi^aaml under c o n d itio n s o f

•• 23 4#

ohlor*îâ03 aoov^ th e n^^naal amount he b e lie v e d th a t th e uptake o f w ater fx*oa a s o lu t io n in th e in t e s t i n e » wliere

th e ep ith eliu m was uninjured» was n ot a sim p le fu:x^tion o f o a o o tlo iv ea o u re o f th e sodium c h lo r id e o f the blood# He oonoluded th a t aa t h i s waa th e c h i e f Dlood s a l t i t was

n ot l i k e l y th a t any o th e r b lo o d c o n a titu e n t could i n f luonoe the a b so rp tio n o f f l u id from tâie in t e s t i n e #

*ho work o f th e s e th r e e a u th o rs provided the b a s i s f o r t4ie theory th a t t î » p h y s io lo n lo a l a c t i v i t y o f th e

i n t e s t i n a l c e l l s was r e s p o n s ib le f o r a b so rp tio n from th e in t e s t in e #

bambur^^ (1000 - 1034) opposed th e tlieo ry t h a t th e a b so rp tio n prooesa was duo t o '’v i t a l ” c e l l a c t i v i t y # From a s e r i e s o f aKperlizi%ts in ten d ed t o e s t a b l i s h th e

e f f e c t o f i n t r a - i n t o s t l n a l proa su re upon a b so rp tio ii he ocxieluded t h a t a ltb o u :h z^hyalologioal end ^ atliolo i e a l changes cou ld a f f o o t th e p h y s ic a l fo r o e o in v o lv e d th ey d id n o t ce a so t o be p u rely læ oîm n ioal# Ue found t h a t

inoreaaed in tra ^ ^ in testin a l i^ressuro f a c i l i t a t e d aboorptlon^ a f a c t a lreo i:y e s ta b lis h e d by Loubusoher (1085)» and

b e lie v e d th a t th e i>itra*in t e s t I n a l p ressu re which would aH o;: o f a b so rp tio n was low er than th a t o f th e i n t e s t i n a l c a p i l l a r i e s » how mu oh low er i t ml h t b e depended on t h e fo r o e o f t i n p ro cess o f ir a b io itio n and th e ”suokinc®

^ 24 •

aX30 ir eluded th e “auotlon'* and p ro a a w o a o tlo n o f the v l l l l a s w e ll aa fo r o ea o f osm osis and f i l t r a t Iwi# lie clai^ned to have im ita ted a l l th o phenomena e x lilb lta d

In th o i n t e s t i n a l a b so rp tio n o f ioôSxm c lilo r ld o and ovQc o f serum w ith a r t l f l o i a l l y o o i^ t n oted ooc&>ran9s#

nober (1800 • 1014)» cson^parinr: th e r a te o o f

d lffu s lo r i o f v a rio u s s o lu t io n s o f s a l t s vAth t h o lr ap^eâ o f ab so rp tio n In th o I n t e s t in e » oonoludod th a t a lth o u g h th e p h y s ic a l fa o to r a p lay a p art In tho ooolianista o f a b so rp tio n they did n ot f u l l y e x p la in th e %Aol@ prooesa* So was ccnvl-noad th a t s a l t s were absorbed In to th e

i n t e s t i n a l c e l l s o n ly I f th e y tn r e l i p id s o lu b le * T h is a T eed w ith the worlc o f O v ertœ (1007; 1 8 9 0 ), # :o postxA t ated th a t lip o id s o l u b i l i t y determ ined o e l l p erm ea b ility * I t was on t h i s b a s is th a t ^icber exp'»alned how t h e

o p l t l i o l l a l o e l l a uohsved towards d is s o lv e d su b ston oes l i k e o th e r o e l l s * l i s s o l v e d substanoeo h avin g a

p a r a l l e l r a t e o f a b so rp tio n and jpeed o f d l f f u i l w i wore l i p o i d I n s o lu b le end passed between tâie c e l l s * 3t!ier ta a te rîô lo liavlng a greater r a te o f a b so rp tio n than o f d if f u s io n were l i p o i d s o lu b le and passeri through th e

c e l l s * 'îôber b e lie v e d t h i s th%xry to be n o t in o o n s l s t m t or oonf n o t i n g w ith any osm otic e x p la n a tio n o f the prooesa* Zhls co n cep tio n r e le g a te d a vory In o i ;n iflo a n t r o l e t o

the e p i t h e l i a l o e l l s In th e l i v i n g anim al and a

• 20

in l i p o i d0 xma33iBted b y any othar* f& otor would# aa

iioora (1921) has statocl# r m sa lt In th a a o w m u la tlo n to s a tu r a tio n p oin t o f tho su h stan oos in q u e stio n in th e l i p o i d s o f tho t i s s u e s and oould n o t accou n t f o r th e ste a d y stro a n o f r lu ld s though tho o p ith ^ litw t th a t ooours durinr ab so rp tio n *

a lla u e and .ushny (1G0B| 1899) o mparod tb s r a t e s o f a b so rp tio n o f a la r c o nuohsr o f eq u i^ o lo o u la r

s a l t s o lu t io n s w ith a 1^ fv ) sodium o h lo r ld e s o lu t io n and found t h a t th e r a t e s o f a b so rp tio n d id n ot oor r e spend w ith th e d if f u s io n r a t e s * S a l t s «h ioil were e a s i l y

d ls s o o ia te d in t o io n s bavir^; threat speed wore n o t a Iway# absorbed f a s t e r than s a l t s l e a s eauil;,' d is s o c ia t e d and whose io n s poaaesood low er sp e e d . a l l a o e end v ehny d ecla red th a t tiieao f a c t s d id n o t n e o e s o u r ily in d ic a t e th a t th<% e p i t l i e l i a l o e l l s opm^atoc; o n ly by a v it a l ^ a c t i v i t y end that i t waa more l iU e l y tâmt tlie p r o c e ss o f a b so rp tio n was due to a c h e o io a l r e la t io n o f c H o ld to

s a l t s o f such a n a tu rs t h a t tlie c m ll mlr.ht ta k e up one s a l t e a s i l y and r e j e c t a n o th e r .

e)

I t was th o c a r e f u l stu d y o f tho a b so rp tio n o f th e asn osaooh arid os e ^ c h le d o v o n tiia lly t o th e s o lu t io n o f tho problem Which 1ms d iv id ed th o cK^ohanlsts and

*■ 26 •»

ttiatp a lth o u h knom p b y a lo a l law s are fi&otors o f (jpoat liqportar^oo lu p roooss o f a b so rp tio n # tb sy oannot e x p la in a l l tho ^^xmoooRa oonoomod w îth

a b so rp tio n » ^ o rl usod i^mnaostb@11 sW r a t s a s hi s oxperixasntal on n a i s . Ilo d s to m ln o d tho r a t o s o f absorption o f nonosaooharldas from tb s sm all I n t e s t in e by fe e d ln r a known anoLint o f a Iv e n sunar in s o lu t io n

throurli a stoo aoh tubs# k i l l i n g th o o n lc m l, end e s tim a tin g th e anouTit o f su^rar remain inn In th e î n t o s t l n e . lie was a b le t o d o te m ine w ith T o a t aooupuoy the esnount o f aucar absorbed in a riven tim e by a r a t of îmoan w e ig h t.

i t h l n f a i r l y wide lim it a # th e amount o f lu o o s e absorbed d id n o t vary w ith th e o o n o a n tra tlo r o f th e s o l u t e . In

o th e r words# th e p ro ce ss o f a b so rp tio n d id n o t o o n fo m to th e law s o f d i l ' f u s l w and o sta b sis. I f absorpticxi was m erely a m atter o f d i f f slo n th e nuaho^ o f Ion s bombard In c th e obaorbii f’ su rfeo e In u n i t tim e would o b v io u s ly be a f a c t o r o f g r e a t Im portance.

- C a r l’ s method o f d etG roin in g tho r a t e o f a b so rp tio n o f aonosaocîm ridea g o ffered frp a one d e fe a ts namely

the n optyin g tim e o f the stomach was v a r i a b l e . To overcome t h l j# V e r a ^ (X 935| 1330) 1 ije o te d tfte auger

s o lu t io n s d i r e c t ly in t o lo o p s o f the s n a i l i n t e s t i n e o f a n a e s th e tis e d r a t s . i l » amount o f sugar remoinia;-

- 27

-end rm a n lta . ^ t h Qo@^mr@ found tlm t

1i9%oeo8 3uoh a s glu co a o and naXaotoao a sort^ad a t

a lauoh fasfcai* r a t a from tho sm all In to ? tln o o f tho r a t than woro pontosos suoh a s x y lo s o end a ra b ln o eo . I t tîas p o stu la to d hy V s r a ^ th a t th s d lffo r o n o o în t?.o r a t e o f a b so rp tio n o f hoxoeos end p o c to so s In tho s : » 11

I n t e s t in s o f tho r a t was duo to a s p o o la l a c t i v i t y o f tho i n t e s t i n a l nsoosa# namoly î^ a p h o r y la t lo n o f tho lioxoaoa*

^vldonco fo r t h i s th eo ry # hswevor# I s n o t

oonolualvo end a p p lie s to ;ho r e t o n ly . end

%lr& (1937) p o stu la te d th a t th e y e f o r e n t l a l ^ s o r p t i o n o f z^luoose d e o r e a se s aa one p rofv easo a towards th e

oaudal end o f th e s m a ll i n t e s t i n e o f t h e r a t and th ere# f o r e th e phosphorylatlnc: iseohanlao was more a c t i v e In

the o r o n la l reg io n o f tho nut# However# la v ld s o n and arry (1 9 4 ) ) found th a t w ith in (Aie oaudal h a l f o f th e sm all i n t e s t i n e o f th e oat th e r e was no evldonoo o f d e o r e a sln a b so r p tiv e power f o r gluooao in th e more d i s t a l region #

f ) a b so rp tio n o f f a t s #

• 28

-ürmnaport d lffo r u fv o n t5 » t o f p r o to in or

(mrbobzyidratf) ùranoport în th a t t l » f&tfcy aolda» tb e elQiainbal o o a s t l t u ^ t j or th o f&t» aro I n s o lu b le in

a to r A3 a e a lo o most o f t h e i r ocvmpoiinda^ it iile th e ooxvespoîiüiîi^ oloQOiita o f /apoteln #L:M3 ^orbohydrate e r o r e a d ily ^ t e r - o o l u b l e #

^‘hare a re ulyeo t h e o r ie s ea to ho*^ f a t * l e I n s o lu b le in iw tar^ osn pass tbo e p ltU o llic i o f th e au ooea, n a r e l y j d ) th a t f a t ol^/bt bo d is s o lv e d in tho l i p o i d s o f

th e o e l l s a f t e r s p l i t tin(^ in to f a t t y a c id s « > ^ ile th e ly o e r o l a i r h t b e absox^bed by i t s e ^ l b i l i t j in ;m tor ( leidonhaln* 1380) • Iloeever* f a t t y a o ld s a re ^ ir a o tlo a lly n o t aasorbad ohon Inti^^duoed alan o in to an ea p ty

I n t e s t lim l lo o p . T heir l i p o i d s o l u b i l i t y i s fa r to o s l i g h t t o a l l o e tliem to d i f f u s e In to Wie e p i t h e l i a l c e l l s in any r e a t q u a n tity # (2 ) th a t f a t s so f i n e l y

e a u l s lf l e d by tlw b i l e th a t tW f a t d \ ) p l 3 t s m ight b e a b le to a s s tlie e p i t h e l i a l <iall and n > u tra l f a t appear a g a in In t h e lyc^T iatios (Wmik# 1 8 ^ ) # A m eohonical fo r c e m 3 onoo su g g ested to e:<plain the eu tranoe o f th o se f i n e d r o p le ts in t o th e e p i t h e l i a l c e l l s b u t improved

h l s t o l o g i o a l tech n iq u e has a/.om # i l s to be q u it e

errim eou s. (3 ) in ID ol P flu g e r opposed t h i s liy p o tW sis# end put forward a new th eory o f f a t a b so rp tio n # lie

- 29 •

Tba f a t a a m w by l i p a s e In o f b i l e

In to f a t t y a c id s and - ly o e r o l# 3 1 y o o ro l l a gater*# s o lu b le and d lf f u o o s m a d lly ^ and. th e f a t t y acld a a re s a p c n lfle d by the 3 odium carb on ate o f tW p o r o r e a tio

and I n t e s t i n a l j lo o s#

i’ho aa ln d lf f io u lt r r fb r tho th eory a m s o «hen th e a o tu a l r o a a tlo n o f tho I n t e s t i n e e a s te ste d # Pfluj^er 3peaâ:3 o f the a llr a lln o r o a o tlo ^ o f the I n te s tin e ^ but as a m atter o f f a c t , a lth ou gh th e p a n o rea tlo Ju lo e îias a pH o f 8 or rjom . I t l e q u la k ly changed b y th o I n t ^ i t l n a l co n te n ts# K oatyal (102 0) s tu d ie d th e o f the I n t e s t in e o f r a t s , d o g s , ju in e a p ig s and p ig e o n s , o ’p e o l a l l y fo r t h i s parposo end found i t to bo so ld o u rroato^ than pB7, and gon-*rally under t h is v a l u o , l# o # In th o a cid pogton# Icb ln so n (1936) fbund a r e a c t io n o f pHG#5 In th e

duodonum o f r a t s , and i)H7#0 „ G a t tho I l e o c o l i c v a lv e * 2h i s ezclu d ed th e p o a c l b l l l t y th a t f a t s tforo aosozW d In th e f o r a o f a l l m l l soaps#

A ccordin'; to V orsar (19 36) th e f a t t y acld a

eoablned e l t h th e p aired b l l o a c id s to forta ocopounds# which ar^ n ot o n ly w ter##8oliib lo and d i f f u s 3ble # b ut a ls o e s p e c i a l l y s t a b le at tlie s l i g h t l y a cid r e a c tio n

• 5)

-adsorbed ooto sraooaal e p ith e liu m ao that th e y ^jore a b le to d ia j o lv o a auoh r e a t e r q u a n tity o f f a t t y aoid:3 than in v itr o #

The f a t t y a cid « îilo h vfao r o e In th e c o l l combined 5 lt h tho tlyooT O l, « îiich tmo ahoorbed a t thD aaao tim e , to reayn tho a ls o n e u tr a l f a t # This c y n th e s ia jasboA

through an I n t o n e d l a t e e ta ^ e o f pboapîm tîdo form ation# The ly o o *ol uao phoopborylatod and o^obîned i7ltb th e

f a t t y a o id s# Thus th e d i f f u s io n .r a d ia it In to th e o e l l s fo r th e f a t t y a o ld s »aa Inoreaaed# s y n t h e s is o f n e u tr a l f a t , v ia th e f o r a a tlo n o f p h o sp h a tid e, uaa

tija refo re art a o o e le r a tln y f a c t o r In the a b so rp tio n o f f a t i Just a s the phesphoryl& tion o f jlu ooa e Q coelerated - th e a u s o r p t lw o f t h i s su^sr#

In th o m ucosal ep ith e liu m th e p liosp h atlâe v a s tronsfermod s - o i n in t o n e u tr a l f a t an d , fo r the most p a r t , appeared as suoh in th e lyoph# S i ^ i f l e a n t hut varyin g amounts escaped tho tr a n a fo n a a tio n , and apiioared in th e lymph aa p hosp h atid e ( l e c i t h i n ) , and so In creased th e l e c i t h i n co n te n t o f th o blood d u rin g f a t abaorptloci#

51

-I t îma shown by wu5f»r anâ (1958)

tb a t a f a t $ su ch a s t r io l e i n ^ ^as o n ly p a r t i a l l y d ig e s te d in th o i n t o i t i r o by tho m n oreatio ju ic e * ?^ydroî/sÎ3

d etoraln od th e path taîter by th o absorbed! f a t t y m a t o r ia l, th e f a t t y acid f r a c tio n pass in ; by th e p o r t a l v ein to th e liv e r ^ and the unliydrolyeeC p o r tio n by th e lym phatic r o u te in t o th e ay3te*T!io blood* and %ienoe to th e f a t depots* î l i l a ccMriaeption la con trary t o th e p r e v io u s ly aooeotec! h yp oth ea la o f Voraar* î^ore r e c e n tly * in a re v ie w o f f a t ohsorpticxi#

r a s e r (1 9 4 )) a rain aen tiosied th a t n o t a l l o f th o f a t in th e I n t e s t in e aosorbod a s f a t t y as id s and ^ ly c e r o l* b u t th a t a t l e a s t soLie o f i t was absorbed a s e ^ su lsifie d fa t^

i . o . a s t in y p a r t i c l e s o f f a t or o i l * He based h i s ovldm'ioe in part on obaorvationa o f tlie f a t p a r t i c l e s p r e se n t in blood# These a r t i c l e s * c a lle d "chylotalorons” can b e oo’snted under darkfleXd illu m in a tio n # An I n t e r e e t ia g argument in fa v o u r o f th e a b so rp tio n o f e m u ls ifie d d r o p le ts o f o i l i s th e f a c t

tlmt

wall

te w a r t, and Schulman, 1942)* I r a s e r eod M s co-w orliers were

a t a l o s s

to

however* lopao (195?; 1943) and ‘Copac and '>hanf)ers (1957)

32

-»6Ss) and f o r p lan t o e l l s th a t I f an o i l y d r o p le t Î3 plaoed

In co n ta c t e l t h tb'3 c e l l rmi>r^un^ tlv5 o i l w i l l ra I d ly e n te r th e c e l l I n t e r i o r . " '^ a ls if lo a tlo n o f f a t s in th e I n t e s t i n e I s favou red by b i l e s a l t s and th e s e s a l t s tend to '-'ako f a t t y o o ld s n ore s o lu b le , lliu s th e b i l e bas an ltar>ortant I n flu e n c e on f a t absorption#

(g ) iw 3or::tior o f main:- a c l d s *-^

r e s e n t v le ^ s on n a tu r i o f aninr; g o ld s In s o lu t io n : S ln o e u a ts r undergoes i o n is a t io n w ith p ro d ro ti :icm o f hydrogen Ion and Ttyd o x y llo n . I t w i l l a c t b o th a s

an a cid and as a a lk a li# T his prorjorty i s a ls o ?iet w ith in the. c a s e o f many o th er oomixwads whsn d is s o lv e d In w a te r , and which are t!:ep ofore six>ken o f a s am photeric e l e c t r o l y t e s or an p b olytes# The amino a c id s a r e s o æ o f tlie moat

Ix ^ w ta n t o f t h e s e .

A c e tic a c id , wh<m d is s o lv e d in w ater under "oes io n is a t io n to a sm a ll extend w ith produo t io n o f hydrogen io n s ; i t th s r e f o r e a c t s a s an a cid # I f tSbo assiao

;;roap ( W Hg) i s Introdtioed in t o m o le c u le , a a in o -a o e tio a c id o r

Glycine,

cjoaiX3unci, in sc lu t i e r , oaixiot o n ly yielx: hydrogen io n , c a t in v ir t u e o f th e p resm o e o f th e group, oan a l s o ,

throu ;h r é a c tio n w ith w ater g iv e

- 55

a lk a lis * m a l aa e oaao ^Rlvin ; rn lta

w ith û c lâ a , o . GHg Cr)3Ü» îîCl)« i^a in th e oaaa o f

a l l a:ip^3olyt‘^:., ^ io n isa tio n Uakea plaoo on ly to a s llr ^ t s& tw t$ an that lyaln o whavoa a s a vopy wsak a lk a li

and a v^ry woak acid*

Acoord Inc ^ cic>2*o v iew s m ;ardlnr a Ida and

b a ses ar ocipholyto I s a su b sta n ce ifihlch om\ a o t b o th a s a

^)Totc^ donor and a s a proton aooep tor* Thus in tlio c a se

o f aqueous s^iXutions o f rl^ oin o* f^Iîg GH^ one may nave

tho r o a o tlo n s :

f i f l r . OHr, CO O H ;;= ± n n C H „ )0 0" h- H*" o r

a ^ a " +

and j.n i ^ BU* dH O i h + J'd op

B a* + OH'

C lyoln e may th oroforo y i e l d b o th a c a tio n o% d an onion#

b ln o e an OQpholyto oiku o o t b o th a s ari u o ld ond a base I t w i l l ha VO an a c id Ic siia u tlo n cons ta n t K _{• a} a s vvoii

0 3 a b a sic I o n is a tio n co n sta n t ( a lk er* 19b4 o^b#) The

oorre:3po d in e moss las? eq u aticu a ore*»

^a * L ”1 s?lxM?o H” i s tl50 Ion BH^OE^,G >9 or

m 34

D

M

_{& ]M}

Î3 t b i o a t Ion )!^# i'be c o n s ta n ts K. mtd K bavo

t- 2 a &)

boon oûlculGt^O rî»02î c io to n a im tio iia o f tljo Jo r@o : f

h yd roiyu la o f tho com pounds o f t2jo ta^pliolyte w ith stroirs a o ld a and w ith atron r m oos, and from maasuromonta o f th o oOk'jJuctlvity o f s a l t s o f th o am oW lyto. *Ito va liiaa so ob tain ed f o r

a o v ir a l o f tlio amino a c id s a ro v o iy s m a ll, b o li : about

XO"^ - 13-1 fr y ana 1)"^^ - 13*12 fpp Sltsoa ttho

amino a c id s may b e r'»oi*dod a s a a b stitu to d d o r iv a t lv e s o f e o o t lo a d d and a-?nonlum \xjÛvoslô^ « h ich Imvo io n is a t io n oo n atan ts ab %3t ocp al to 1«B x 11**^, an aooo ta n c e o f t h e s e low f ir ^ r e s f o r Him amino a d d s ira o llo s a trmcmndous 1 flu e n o e o f the s u b s titu e n t rou p s on e X e o tr o ly tio d is s o c ia t io n *

i t

noticed bg JJerrun ( 1925 ^ that by aa strains

the uncîiarr.ed traction of the colno add to e x ist mostly in

the form of d-uUly

^witterionon or dipolar Ions,

(tb5 %)rd awittor is

eiiua. to m for a liei^mplïTodito),

much mere reas nablo vcluos for th^ oo. star:to cf the aaino

acids

oould

be obt&lred from tho ooao oxperiaentul d ata#

Therofors

x^efers to

dlasocutdon of tho I

-^roup and

the loalaatilon z»olati no are do crlbou by tlio e q u illl^ ia ,

■*'eh,cii, c 53H * ;.;l .;:„C33" + s * w ? ' +

• 35

Hgl + 4- OZ" or jg'

f o r whloh tho nasa l a ’s- o/..Ti@$3 on3 a r o i

-\ * C a i —L z iJ ’t . - b n ' J . L i - J .

^ and

M

I?-]

^ v ld o ^ tl^ 3060Tir=mort3 t^^îoh 7 5 old valtios f o r fÇ, o f ^ alk or»»

th o o rj :^lli iv o v o l' 1 0 8 f o r K o f Shoory end

%3oa3uro30nt3 , Ivin^ w i l l a ls o Iv o Tho tt?o oota o f

conatcT.ts aa’* m l a t od b y I d e n t if y in g ^ and sln o o sa ch r e f e r s bs^o to th^ t o t a l e l e o t r l c a l l y n e u tr a l am pholyte,

i f th e eq u ation s doflnlnr^ . K end Ky^TJ a re s r o lt le lle d to^ etlier*. W a s a n th ose d e f in in g K and K , I t f o llo w s th e t T K. «

^ a &% L)

K,K , These oroduots ere eq u al to th^ lo^ rrfx^^'Ot o f « a te r

' w f 8

s in c e j^Oir^ Y.^+ f o r any s o lu t io n so

d ilu t e th a t th e a c t i v i t y o f u n io n ised m t e r smy b'» taken a s u n its * In th l? end o th er taass la i eq u a tio n s th e b raok eta r e f e r to the TRolnl corcon tratIon ^ and Y to th e a c t i v i t y ODCfî I c lo n t o f th e Ion or m o le o u le . At v er y l o r ooncenj t t r e t l o n e a l l a c t i v i t y c o e f f i o i e n t a ai>proaoh u n it y and a c t i v i t y ten d s to become id e n t l o a l t^îth th e m o l a l i t y .

Tha d e s ir e d r e l a t i o n s oro* th er efo re ^ E Z Eu ©rid i ! r

E . » ,\g . The a d van ta jo o f tho E m itter ion s y s fn n I s th a t I t Iv es reore '^eae n a b le t^alues t o the 0 0 s t in t s ^ # i i o h

- 36

In 3 u f f îcîfn iîsly a c t s 3 0 Î a tio i3 , feho sn în o a old la

p o s i t i v e l y on o l o o t r o l y s l s ml;;pat03 to tho

otithode, ah9?9U3 In s u f f l o l e i t l y a lk a lin e s o lu t io n s I t la

n o,3ativaly obar^^od and nl^Tûtoo to th o on od e. ^b^loxisly

th ere lauat bo a d o f l n l t e hydrogen io n cono ont r a t io n at nî:loh i t n i j r a t o s n o îtb o r to th e anode nor to th e OEithodo. T h is I s oelloci th e I s o o l o c t r lc p o in t . '’^ ch o sln o a c id has a a p a o lfic î a o e lo o t r îc p o in t . -o have a l l p r o t e in s . I t m&a o r ig l: : a lly - hcra^ht th a t a t I t s i s o o l o c t r l o p o in t , an asiirso a cid was n ot d isa n o la to d e i t h e r ao an acid or ca a b a s e ,

i^^kooorjln,: to th e Z w ltto rlo n îiy p o th o sls , th e amino a c id tsoloou lo i s e l o c t r l e a l l y n e u tr a l a t t&io I s o d b o tr lc p o in t , but t h i s

n a a t r a l i t y la due to th e com plété and sltsn lta n eo u s I o n is a t io n o f a c id and b a d e r o u p s.

The fa c t th at ir o te in s c o n sist o f amp^iotorio «usine

a cid s i s o f r e a t Inportanco in iotoria?oting nany o f th o lr

r e la t io n s .

3ober and -iobor

1 37) found anlno acids to

be eboorbod at a hlrtnr rate than could bo onpeotod f*roo

tlioir calculated nkolecular volnmi

oron at a M her rate

oonsidoriii " the voluno of tho swlttorions of t?io ampholytes

b ein g

enlarge

sh e ll

tmtir dlpoleo.

t^ie other