SistemPencernaan_2007

FISIOLOGI SISTEM PENCERNAAN MAKANAN

AQSA SJUHADA

Graduate School of Medicine- Dept of Oral Biology- Dept of PhysiologyAirlangga University

1. Menelan makanan

2. Memecah makanan secara kimia dan mekanik

menjadi molekul nutrien yang mudah diserap

3. Menyerap molekul tersebut menuju aliran darah

4. Membuang bahan-bahan yang tidak diserap

FUNGSI UMUM

DIBAGI MENJADI 2 KELOMPOK

ALIMENTARY CANAL :

Organ yang dilalui makanan (berupa saluran panjang)

ACCESSORY ORGANS :

Membantu proses pencernaan tetapi tidak

benar-benar dilalui olah makan

ALIMENTARY CANAL * rongga mulut * faring * esofagus * lambung * usus halus * usus besar

ACCESSORY ORGANS * gigi-geligi * lidah * kelenjar saliva * pankreas * hati * kandung empedu

Ingestion

Propulsion

Mechanical Digestion

Chemical Digestion

Absorption

Defecation

TERDIRI DARI 6 AKTIVITAS

Ingestion : memasukkan makanan ke dalam tubuh

Propulsion : pergerakan makanan sepanjang the

alimentary canal. Terjadi karena adanya gerakan

peristaltik dinding saluran cerna

Mechanical digestion : Pemecahan makanan

menjadi molekul kecil secara fisik (mekanik),

menjadikan permukaan makanan lebih luas

sehingga enzim bisa bekerja optimal

Chemical digestion : Pemecahan makanan secara kimia

(enzimatik) menjadi bentukan yang dapat diabsorbsi dengan

baik, misalnya monosakarida, asam amino, asam lemak dll

Absorption : Penyerapan dari produk akhir sistem cerna,

misalnya vitamin, mineral dan air dari lumen GI tract menuju

pembuluh darah. Sebagian besar terjadi di usus halus.

Defecation : eliminasi dari bahan-bahan yang tidak dapat

dicerna, sebagai feses.

RONGGA MULUT

1. Gigi sulung (20)

    2. Gigi permanen (32)

    3. Lidah

       a. otot skelet

       b. menggerakkan massa makanan “bolus”

STRUKTUR RONGGA MULUT

    4. Kelenjar saliva (3 pasang)        a. parotis - sebelah anterior to the ear dekat mm. masseter. - muara saliva dekat molar kedua atas - inflamasi parotis: mumps      b. submandibularis - terletak pada medial dari mandibula. - muara saliva pada dasar frenulum lingualis.        c. sublingual - sebelah anterior kelenjar submandibular dan bawah lidah. - muara saliva sebanyak 10-12 pada dasar mulut d. rangsangan parasimpatis: sekresi saliva

STRUKTUR RONGGA MULUT (Cont’d)

ORAL CAVITY STRUCTURES

5. saliva

99% air

membersihkan, melembabkan, membasahi dan melarutkan makanan

mengandung enzim :

* lysozyme

* salivary amylase – mencerna pati (awal, tidak signifikan)

* lingual lipase – mencerna lipid (awal, tidak signifikan)

* garam

* mucin

* antibodi.

masih terdapat beberapa kelenjar saliva minor yang tersebar sekresi saliva : reflex & parasympathetic makanan dan minuman mengaktifkan kemoreseptor dalam rongga

mulut ---- mengaktifkan pusat penelanan pada pons---- signal menuju kelenjar saliva (via n. facialis and n. glossopharyngeal) dan terjadilah proses salivasi

higher brain centers juga dapat menyebabkan salivasi: misal melihat, membau dan memikirkan

    1. orofaring

    2. esofagus :

menghubungkan faring dan lambung

    3. peristaltik - gerakan ritmis otot polos

FARING

"food tube" yang menghubungkan faring dan

lambung

Berhubungan denga lambung pada bagian cardia

lambung.

Diregulasi oleh sphincter cardia atau

gastroesophageal.

ESOFAGUS

Kolaps bila kosong

Mempunyai 4 lapisan histologis

Mokosanya dilapisi oleh non-keratinized stratified

squamous epithelium

Lapisan submukosa mengandung kelenjar mukus

yang membantu pelumasan

ESOFAGUS (Cont’d)

1/3 bagian atas adalah otot skelet

1/3 bagian bawah adalah otot polos

1/3 bagian tengah adalah campuran

ESOFAGUS (Cont’d)

ESOFAGUS (Cont’d)

PENELANAN

(DEGLUTITION / SWALLOWING)

masticated food + saliva = BOLUS

Proses penelanan reflex

1. Stadium volunter

2. Stadium involunter

- Stadium pharyngeal

- Stadium oesophageal

PROSES MENELAN

STADIUM VOLUNTER(Stadium Bukal)

Bolus diletakkan di atas lidah

Didorong ke atas dan belakang pada palatum

Masuk faring

dapat dipengaruhi oleh kemauan

STADIUM PHARYNGEALBolus pada mulut – pharynx merangsang reseptor

TIMBUL REFLEKS-REFLEKS :

Palatum molle ditarik ke atas menutup nasopharynx

Epiglottis bergerak ke belakang menutup larynx

Larynx bergerak ke atas depan membuka oesephagus (sphincter pharyngo-oesephageal relaksasi)

Terjadi gelombang peristaltik dari otot-otot konstriktor pharynx

Nafas berhenti sejenak

Proses sekitar 1-2 detiktidak dipengaruhi oleh kemauan

STADIUM OESOPHAGEAL

Gelombang peristaltik primer; lanjutan dari gelombang peristaltik faring

Gelombang peristaltik sekunder; berasal dari dinding osophagus sendiri karena regangan dinding vagal reflex

proses sekitar 5 - 10 detiktidak dipengaruhi oleh kemauan

PENGATURAN PROSES MENELANPENGATURAN PROSES MENELAN

rangsangan taktil pada reseptor mulut – pharynx

melalui N. V; N. IX

medulla oblongata

(jalur: tr. Solitarius , formatio reticularis)

melalui

N. V, IX, X, XII

menelanmenelan

AEROPHAGIAAEROPHAGIAudara yg ikut tertelan pd saat menelanudara yg ikut tertelan pd saat menelan

RUCTUSRUCTUS FLATUSFLATUSdikeluarkan kembalidikeluarkan kembali diabsorbsidiabsorbsi

diteruskan ke diteruskan ke coloncolon

dikeluarkandikeluarkan

LAMBUNG

FUNGSI LAMBUNG

Penyimpanan makananPencampuran makanan dg gastric juice menjadi CHYMEPengosongan makanan periodikPencegahan masuknya kumanAbsorbsi obat-obatan

CORPUS

Tonus dinding relatif rendah, mampu membesar (s/d 1-1.5 l)

Storage makanan; tekanan lambung tetap rendah

Sebab:

1. Sifat PLASTICITY

2. LAW OF LAPLACE

3. VAGAL REFLEX

LAW OF LAPLACE

Bertambah besar diameter lambung karena isi bertambah

Bertambah besar curvatura minor

Tekanan tidak meningkat atau meningkat sedikit

GERAKAN LAMBUNG

- MIXING CONTRACTION

dimulai dari bag tengah

ke antrum (terkuat)

freq setiap 20 detik

- PERISTALTIC MOVEMENT

lebih kuat dari mixing contr.

pyloric pump

Tidak terjadi regurgitasi dari duodenum ke lambung karena:Kontraksi segmen pylorus berakhir lebih lama daripada segmen duodenum

GASTRIC JUICEDisekresi oleh:1. Kel. Cardia

sekr mukus, pelindung mukosa2. Kel. Fundus

mengandung 4 macam sel- chief cell, sekresi pepsinogen- parietal cell, sekr HCl +fact intrinsic- mucous cell, sekr mukus- argentaffin, sekr 5-OH- tryptamine

3. Kel Pylorussekr mukus + gastrin (oleh G cell)

GASTRIC JUICE

- Volume 1.5-2 liter / hari- pH 1,8 – 3.5- Osmolaritas isotonis- Kandungan:1. Elektrolit2. Pepsin3. Mukoprotein4. Lipase5. Rennin6. Intrinsic factor7. Histamin8. Gelatinase

PEPSIN : suatu enzim proteolitik

PEPSINOGEN PEPSINHCl

PROTEIN POLIPEPTIDApepsin, pH 1,8-3,5

RANGSANGAN SEKRESI- N. Vagus- Histamin- Gastrin

MUKOPROTEIN

sekresi sel mukus

alkalis

melindungi dinding lambung gel

rangs sekresi:

- pH

- N. Vagus

RENNIN

menggumpalkan susu pada bayi

INTRINSIC FACTOR

suatu glocoprotein

membantu absorbsi vit B-12 di ileum

HISTAMIN

suatu derivat asam amino

reseptor H1 dan H2

H2 perangsang sekr gastric juice

blok H2 receptor: CIMETIDIN

REGULASI PENGOSONGAN LAMBUNG

Pyloric Pump, diatur oleh:1. Lambung

sifat meningkatkan aktivitasregangan merangs N. Vagus/vagal reflex

2. Duodenumsifat menghambat aktivitasenterogastric reflex ok:distensi duodenum, iritasi duodenum, chyme mengandung banyak protein

GASTRITIS- Peradangan mukosa lambung

Sebab:Iritasi alkohol / obat aspirinInfeksi kumanIritasi makanan

Mukosa rusak

Permeabilitas meningkat

Peka thd H + / pepsin

Gastric athropy / tukak atau ulcus

GASTRITIS menimbulkan:- Rasa nyeri- Rasa panas- Sekresi saliva meningkat

ditelan

udara masuk

kembung

HUNGER CONTRACTION

Lambung kosong pd waktu lama: 12-24 jam

Kontraksi ritmik intensive (=tetani)

Berlangsung 1-3 menit, interval 1-2 jam

Sensasi nyeri, lapar : HUNGER PANGS

Intensitas terkuat pada hari ke-3 dan 4, kemudian turun

Lebih hebat pada orang dewasa muda sehat, terutama dengan hipoglikemia

Cephalic Phase of Secretion - Dirangsang oleh pandangan, pembauan, pengecapan.- Sinyalnya direlay menuju feeding center ‘hypothalamus’- Menstrimulasi vagal nuclei pada medulla spinalis- Impuls kemudian dibawa menuju gastric glands via Nn.

vagus

SEKRESI GASTRIC JUICE

SMALL INTESTINE

major organ of both :

digestion and absorption

this convoluted tube extends :

from the pyloric sphincter to the

ileocecal valve

almost 20 feet long!

(what is the importance of this?)

it's divided into 3 regions:

duodenum, jejunum, and ileum.

it’s about 10" long and curves around

the head of the pancreas

much of it is retroperitoneal

the common bile duct :

delivering bile from the liver and gallbladder

main pancreatic duct :

delivering pancreatic juice from the pancreas

DUODENUM

the common bile duct and main pancreatic

duct unite in the wall of the duodenum :

at the hepatopancreatic ampulla

the entry of bile and pancreatic juice

into the duodenum is controlled by :

the hepatopancreatic sphincter.

DUODENUM

it’s extends from the jejunum to

the ileocecal valve

it’s about 12' long.

JEJUNUM

it’s about 8' long

extends between the duodenum

and the ileum

ILEUM

mucosa has intestinal glands (cavities) :

for secretion of intestinal juice

mucosa also has circular folds, villi & microvilli :

for increased surface area

“brush border” has many enzymes

HISTOLOGY

“brush border” has many enzymes

(embedded in plasma membranes) :

    1. several carbohydrate-digesting enzymes

    2. peptidases

    3. nucleosidases

    4. enterokinase is released by :

epithelial cell “shedding”

    important enzyme activator.

HISTOLOGY

the small intestine is built :

for digestion and absorption

it has lots of surface area

it contains 3 main surface area

enhancing adaptations:

Plicae Circulares

Villi

Microvilli

PLICAE CIRCULARES

large deep

permanent folds of the mucosa and

submucosa

they slow the movement of chyme

(more time for digestion/absorption)

they increase the surface

VILLI

fingerlike projections of the mucosa

they also increase the surface area

within the core of each villus is a capillary bed

and a lacteal :

for transport of the absorbed nutrients.

MICROVILLI

tiny projections of the plasma membrane

of the absorptive cells

often called the "brush border" due to their appearance

they further increase the available surface area

and contain membrane-bound enzymes involved in

digestion

the SI epithelium is simple columnar absorptive cells

with goblet cells interspersede

enteroendocrine cells and T lymphocytes are also

interspersed amongst the aborptive cells

between the villi exist pits known as :

intestinal glands or ‘crypts of Lieberkuhn’

the cells lining these pits are epithelial cells :

that secrete intestinal juice (mucus, enzymes, etc.),

lysozyme-secreting cells, and stem cells.

THE LAYER OF THE SI

it’s typical with an inner circular and an outer

longitudinal layer of smooth muscle

the majority of the SI is covered by a serosa

the submucosa is rather mundane save for

the proximal duodenum and terminal ileum

in the proximal duodenum :

the submucosa houses Brunner's glands which secrete

an alkaline mucus to help neutralize the acidic chyme

(coming from the stomach)

in the terminal ileum, we find Peyer's patches :

large lymphoid nodules that help prevent colonic

bacteria from entering the SI.

THE LAYER OF THE SI

Here are 3 gross and one microscopic view of Peyer's patches.

INTESTINAL PHASE OF REGULATING DIGESTION

1. chyme enters duodenum

2. three hormones secreted from SI mucosa

3. receptors in SI mucosa sense food

or chemical presence in duodenum

4. neuronal activation of sympathetic NS

or inhibiton of parasympathetic NS

REGULATING ABSORPTION

absorption of C L P, Ca2+, Fe2+ :

duodenum & jejunum

absorption of bile salt,

vit.B12,H2O,electrolite :

ileum

absorption of monosacharide & aa :

secreted into cappilar

absorption of lipid :

secreted into central lacteal

REGULATING ABSORPTION

absorption of H2O within SI:

passive, depend on osmotic gradient

(from ion transport)

mucosa epithelial cell of intestine :

collect to form tubulus is like kidney :

* functions as Na+/K+ pump within basolateral

membrane

* can stimulates absorption of NaCl & H2O

within ileum

THREE HORMONES SECRETED FROM SI MUCOSA    

1. gastric inhibitory peptide (GIP)

    i. fatty acids in chyme induce GIP secretion

    ii. GIP inhibits gastric secretion

    iii. GIP inhibits gastric “churning”

    iv. GIP activates insulin secretion

2. secretin

    secretin inhibits gastric secretion

3. cholecystokinin (CCK)

    i. CCK fatty acids in chyme induce CCK secretion

    ii. CCK slows gastric emptying    

PROBLEM WITHIN SI

Diare

Colitis ulcerative

DIARE

fast movement of fecal matter through colon

etio : enteritis, psychogenic, colitis ulcerative

enteritis :

* etio : virus or bacteria, cholera

* iritation of mucosa

* secretion , motility

* cholera : electrolite & fluid

secretion from crypts Lieberkuhn 10-12 L/hr

reabsorp colon 6-8 L/hr

* Tx : replace fluid & electrolite that lost (saline iv & glucose)

excretion of excess fluid together feces

3 mechanism :

1. cholera : * enterotoxin released by bacteria of cholera

* enterotoxin stimulates active transport of

NaCl followed by osmotic movement of H2O

into lumen

2. celiac sprue : intestinal mucosa rupture

disturb of absorption

by consumption of gluten

3. lactose intolerance

COLITIS ULCERATIVE

etiology : idiophatic, alergy/ destructive

immune effect

secretion

motility

colon wall : inflamation & ulcer

LARGE INTESTINE

the large intestine receives indigestible material

from the small intestine

its major function is :

* to absorb water from the food residues

* then eliminate them as feces

it frames the small intestine on 3 sides

and extends from the ileocecal valve

to the anal canal

compared to the small intestine :

its diameter is bigger but its length is far shorter

(only about 5').

THE LI HAS 3 DISTINCT CHARACTERISTICS

the longitudinal layer of the muscularis

is reduced to 3 bands of smooth muscle

called teniae coli

their tone causes the LI wall to pucker into

pocketlike sacs called ‘haustra’

the cecum

appendix

colon

rectum

and anal canal

the sac-like cecum lies below the ileocecal valve

and is the first part of the LI.

The LI is divided into :

within the large intestine are significant numbers

of bacterial colonies

they enter via both the anal canal and the oral cavity

and colonize the LI

in the LI, they metabolize and ferment indigestible

carbohydrates

they also synthesize B vitamins as well as vitamin K.

water absorption occurs as materials pass thru the LI

haustral contractions move material from

one haustrum to another and aid in mixing

mass movements are slow waves of peristalsis

that move feces en masse into the rectum

it should be noted that one stimulus of colonic mass

movements is the presence of food within the

stomach

this is known as the gastrocolic reflex.

feces enter and stretch the rectal wall :

initiate the defecation reflex

this results in :

* the contraction of the sigmoid colon and rectum

muscularis

* the relaxation of the internal anal sphincter

higher input determines whether the external

sphincter remains :

contracted or relaxes.