Bahan Kuliah Pencernaan

Outline

Overview of GI Tract Movement of GI Tract Nutritional requirements Exocrine GI secretions Digestion, absorption, assimilation Endocrine control

Sekilas saluran

pencernaan• Menerima• Menyalurkan (Conducting)

dan menyimpan• Digesti, absorpsi• Absorbsi air, defekasi

Proses dasar1. Sekresi : menghasilkan & menyalurkan enzym, mucus, ions

dan sejenisnya ke lumen saluran pencernaan, and hormones ke aliran darah.

2. Absorpsi: Transport air, ion dan nutrient dari lumen melewati epithel kemudian masuk aliran darah.

3. Motilitas: Kontraksi otot polos dlm dinding saluran pencernaan untuk memotong, mencampur dan mengaduk isi saluran pencernaan.

peristaltik segmentasi

Pengaturan Ekstrinsik

Sistim Syaraf Pusat Sistim Endokrin

Intrinsik Saraf intrinsik Endokrin intrinsik

DISTRIBUSI SARAF OTONOM KE SALURAN PENCERNAAN

The autonomic nervous system Sympathetic system:

Noradrenaline

Gut secretions (+) e.g acid, enzymes & electrolytes

Sp

inal co

rd

Pons/medulla

Midbrain

Gut sphincters (-) reflex relaxation

Pancreas (+) exocrine & endocrine secretion

ACTION

Rectum (+) defaecation

ACTION

Gut wall (+) increased motility and tone

adrenaline

EFFECTSEFFECTS

Salivary glands (+) secretion of saliva

X IX

VII

Cranial nerves

Parasympathetic system:

Acetylcholine (Ach)

(+) secretion of saliva salivary glands

(+) vasoconstriction gut blood 2 (-) vasodilation vessels

1/2 (-) decrease motility gut wall, (+) contraction sphincters

(+) secretion

Adrenal medulla

The enteric nervous system

Deep muscular plexus

Submucosal artery

Muscularis mucosa

Submucosalplexus

MUCOSA

Myenteric plexus

Longitudinal muscle

Circular muscle

CNS to gut connections

SPINAL CORD

dorsal root ganglion

Spinal afferent

Vagalafferent

Vagal efferent

nodose ganglion

BRAIN STEM

The brain-gut axis

Gut- to- brain (afferent neurons)

Brain- to- gut (efferent neurons)

• autonomic reflexes

• e.g. vago-vagal reflex control of gastric tone

• Pain

• discomfort, bloating etc.

• cyto-protection

• reflex control of blood flow

• “Cephalic phase”

• thought, smell, taste stimulate H+

• autonomic reflexes

• e.g. vago-vagal reflex control of gastric tone

Receptive relaxation of the body of the stomach (corpus) in response to a meal

nodose g.

BRAIN STEM

Vagal efferent fibres

Vagal afferent

CCK & DISTENSION

VIP Ach

AchAch

- +

Relaxation of corpus to

accommodate food

Satiety effects

CCK receptors

I-cell

circulation

CCK

Cholecystokinin (CCK) cell physiology

Fatty acidProtein? Other

+

Small intestine lumen

-

-food intake

gastric emptying

pancreas

gallbladder

CNS

+

+

Apical

basolateral

+

Vagus nerve

CCK: integrator of brain and gut

Cholecystokinin (CCK)

regulates digestion in the small intestine by:

• stimulating secretion of pancreatic juice• stimulating gallbladder contraction• inhibiting gastric emptying and food intake

CCK acts directly on pancreas and gallbladder, and modifies CNS function via the vagus nerve

Kelenjar Ludah

Gas can’t escape(Animal dies from suffocation because

of distended rumen )

• Tongue – Used more by cattle and goats (also

use lips)• Teeth

– No upper incisors – Used more by sheep (use lips to “sort”

feed)• Saliva

– Continual production – Cattle: 12 gal/d vs Sheep: 2 gal/d – No enzymes; High pH

• Esofagus– No sphincter valve– Opens into reticulum and rumen– Muscle contractions move in both

directions

Sistem pencernaan ruminansiaPrimarily herbivores Cattle, sheep, goats, deer, elk Camelidsare “pseodu” ruminants60-75% of ingesta fermented by microbes before exposed to gastric juice

Stomach Compartment:

•Reticulum •Rumen •Omasum •Abomasum

Reticulum characteristics– Located next to heart – Honeycomb appearance

• Catches metal and hardware

– Pathways • Esophagus • Rumen • Omasum

– No enzymes secreted

Rumen Characteristics :– Left side of abdomen – Papillae lining – Muscular pillars – Fermentation vat

• Primarily anaerobic • Some aerobic microbes

– Not functional at birth Rumen Functions :

– Storage – Soaking – Physical mixing and

breakdown – Fermentation

• Synthesizes some vitamins

• Synthesizes AA and protein

• Breaks down fibrous feeds into VFAs

Omasum :– “Manyplies” – No enzymes from walls – Function

• Reduce particle size • Absorb some water

Abomasum :• “True stomach”

that secretes enzymes from walls

• Glandular stomach like monogastric fundic region – HCL, Mucin – Pepsinogen,

Rennin and Lipase

Ruminant Differences: • Esophageal Groove

– By passes reticulum and rumen in young animals

• Rumination – Chew their cud (food bolus) – Up to 8 hours/day

• Decrease particle size for microbes

• Increases saliva production to buffer rumen

– About 30 times/day – Eructation (belching) – CO2and Methane – Produced by microbial population

in rumen – Rumen contracts and forces gas

out – Bloat can result if ruminant

doesn’t belch

Rumen ActivitiesPembentukan VFA di

Rumen

Volatile Fatty Acids (VFAs) Acetic Acid (Acetate)

Most comes from cellulose Important to milk fat in dairy cows

Propionic Acid (Propionate) Most comes from starch

Butyric Acid (Butyrate) Derived from Acetic acid

End Products of Ruminant Digestion

1. VFAs (Main energy source for cows)2. CO2 3. CH4(Methane) 4. NH3(Ammonia) 5. Microbes

Parietal cells: HCl and intrinsic factor

Chief cells: pepsinogen (converted to active enzyme, pepsin)

Sistim Saraf Intrinsik Gastrointestinal

Mengandung banyak neuron Sistim syaraf intrisik mengandung badan sel dan

perlengkapannya Di dalam dinding usus badan sel tersusun dalam 2

ganglia: Pleksus Auerbach (mienterik), terletak antara otot

sirkuler dan longitudinal Pleksus Meissner (submukosal), terletak di lapisan

submukosa

The Pharynx- receiving

Mechanical breakdown of food. Lubrication of food. Initial digestion of polysaccharides

(complex sugars). Salivary glands:

parotid (par= ear, otid=ear) submandibular submaxillary

Kelenjar Ludah dan ludah

Saliva disekresikan oleh kelenjar ludah (salivary gland).

Unit sekretoris kelenjar ludah adalah acini. Sel ini mensekresikan cairan yang

mengandung: air, electrolytes, lendir (mucus) and enzymes.

Ada tipe sel epitel acinar: Serous cells, mensekresi a cairan banyak air

sedikit mucus (lendir) Mucous cells, memproduksi sekreta yg kaya

mucus Cairan disalurkan ke rongga mulut melalui saluran

lanjutan

Didalam saluran cairan mengalami perubahan komposisi Natrium secara aktif diabsorbsi kembali, potassium disekresikan sejumlah besar bikarbonat disekresikan.

Kebanyakan hewan mempunyai 3 pasang kelenjar ludah utama yg berbeda pada jenis sekreta yg diproduksi: Kel. Parotid menghasilkan ludah yg serous (banyak

air) Kel. Submaxillary (mandibular) menghasilkan suatu

campuran serous and mucous Kel. Sublingual glands menghasilkan air liur yang

berlendir

Fungsi saliva: Lubrikasi and pengikat: makanan yg dikunyah

menjadi bolus shg mudah ditelan dan tidak merusak mukosa esofagus. Saliva juga melapisi rongga mulut dan esofagus shg makanan tdk dapat bersinggungan langsung dg epitel. Melarutkan makanan kering.

Kesehatan mulut: Rongga mulut selalu dibasuh dengan air liur sehingga menjaga mulut tetap bersih. Sekresi saliva menurun bertahap selama tidur & membiarkan pertumbuhan populasi bakteri mulut sehingga mulut menjadi bau. Saliva juga mengandung lysozyme, suatu enzim melisis bacteria dan mencegah overgrowth populasi microbial.

lanjutan Inisiasi pencernaan karbohidrat: pd

kebanyakan species, the sel acinar serous men-sekresi alpha-amylase yg dpt memulai pencernaan karbohidrat menjadi maltosa. Amylase tdk terdapat, atau sangat sedikit, di saliva carnivora atau sapi.

Menyediakan buffer alkali and cairan: ini sangat penting bagi ruminansia, memiliki lambung sepan yang tdk bersifat sekretoris.

Pendinginan secara evaporasi: penting pd anjing, yg kel. Keringat tdk berkembang dg baik.

Histologi Kel. Ludah anjing

Acini pada kel. parotid hampir seluruhnya sel epitel serous, sedang kel. sublingual yang dominan adalah sel epitel mucus. Pada kel. submaxillary, acini tersusun dari sel epitel serous and mucus.

Initial carbohydrate digestion Parotid gland -large exocrine gland,

releases water, mucous, and -amylase.

Esophagus- conducting and storage. Muscular, skeletal muscle in anterior part, smooth muscle as near stomach.

Crop is a pouch off of the esophagus, acts as a storage organ in birds.

Stomach- protein digestion Stomach- cardiac region, fundus, pylorus Big washing machine, mechanically breaks up food 3 exocrine cell types

chief cells- secrete pepsinogen (inactive form pepsin)

parietal cells, secrete HCl, causes very low pH(~2 in adult)

Also produce a protein called intrinsic factor, which helps vitamin B12 absorption.

mucous cells Very acidic, aids in protein digestion Therefore both chemical and mechanical digestion

GASTRIN

histamine

Parietal cell

ECL cell

Chief cell

D-cell

somatostatin -

+

noradrenaline,

CCK, VIP & CGRP

Ach

H+

-

+

+

Gland lumen+

Pengaturan Sekresi Asam

Corpus“acid-secreting”

Pepsinogen

Sel G

GASTRINcirculation

Gastrinreleasing peptide (GRP)

somatostatin

Pengaturan Fungsi sel-G

Protein/peptides/ amino acids

+ +

+ -

Sel D

H+

ECL cell & parietal cell

Corpus

Antrum“muscular pump” -

H.pylori

Vagus nerve fibres

Attack and defence in the stomach

HCO3-

Tight junctions between cells

slow H+

diffusion

Blood supply carries H+ away, helps antioxidant function

Mucus-HCO3-

barrier slows H+

diffusion

Acid & pepsin

MUCUS

Mucosal blood flow

Mucosal prostaglandins

Cell migration and regeneration

pH 2

pH 7

H+

Cell surface phospholipids

Refleks Muntah

Efferent fibres: phrenic & vagus

nerve

Afferent fibres: pain, bloating, inflammation, irritants, toxins....

Vomit

Contraction of duodenum, pylorus and

antrum

Vomiting centremedulla oblongata

Diaphragm fixed for inspiration

LOS, UOS & pharynx relaxed

Intercostal muscles contracted…

High abdominal muscular pressure

Receptive relaxation of the body of the stomach (corpus) in response to a meal

nodose g.

BRAIN STEM

Vagal efferent fibres

Vagal afferent

CCK & DISTENSION

VIP Ach

AchAch

- +

Relaxation of corpus to

accommodate food

Satiety effects

CCK receptors

I-cell

circulation

CCK

Fisiologi Sel Cholecystokinin (CCK)

Fatty acidProtein? Other

+

Lumen Usus Halus

-

-food intake

gastric emptying

pancreas

gallbladder

CNS

+

+

Apical

basolateral

+

n. Vagus

Small intestine- digestion and absorption

Receives secretory products from pancreas, liver (via gallbladder)

most absorption of nutrients and water takes place here

mostly alkaline digestion of proteins, fats, carbos, because bicarbonate (HCO-3 from pancreas) neutralizes stomach acid

Small intestine- digestion and absorption

duodenum- receives liver and pancreas secretions, secretes digestive enzymes

jejunum and ileum-digestion and absorption secretion- transport away from body;

absorption, transport toward bloodstream

Usus Halus

BRUSH BORDER

Glycocalyx

Protein rich coat that covers microvilli. Contains dipeptidases, enzymes that breakdown disaccharides, mucous.

Intestinal surface area

Usus Besar Most water reabsorbed in small

intestine, but- the principal role of the large

intestine is reabsorption of remaining water- 8 L of water may be secreted by GI tract in the course of a day.

Consolidation of waste.

Gerakan saluran pencernaan

Three main functions for movement translocation of food from point A to B mechanical breakdown of food mix food for enzymatic digestion

3 types of movement

Peristalsis- traveling wave of constriction

segmentation-asynchronous constriction of gut tube- breaks down large food particles

regurgitation- reverse peristalsis

Control of motility

PSNS stimulates SNS inhibits. Exception- irritable

bowel syndrome- SNS stimulates movement of colon

hormonal control gastrin(stomach)- stimulates motility secretin (duodenum) inhibits motility

Cellular basis for motility Smooth muscle throughout GI tract GI smooth muscle is myogenic- contracts

12-3 times per minute GI smooth muscle acts as a functional

syncytium- nexus or gap junctions connect muscle cells

neuronal and hormonal cues are not required for contraction, but are important for changing rate of contraction

Nutritional Requirements

Figure 4.1 The composition of the adult human body

Figure 4.2 Amino acid chemistry (Part 1)

Figure 4.2 Amino acid chemistry (Part 2)

Figure 4.3 Fatty acids and triacylglycerols (Part 1)

Figure 4.3 Fatty acids and triacylglycerols (Part 2)

Figure 4.4 Carbohydrate chemistry

Figure 4.5 Vitamin structures

Exocrine Secretions

Salivary glands Stomach Pancreas Liver and gall bladder Small intestine

Stomach

Chief cells Pepsinogen (inactive) converted to

pepsin (active) form of a proteolytic enzyme.

Parietal cells Intrinsic factor- required for vitamin B12

absorption Hydrochloric acid

Mucous cells

Produksi HCl oleh Sel Parietal

Small intestine

Kel. Brunners glands (duodenal glands)Ditemukan hanya di duodenum, sekresi mucous berair

Crypts of LieberkuhnSekresi banyak air dan bikarbonate

Brush borderMucous and digestive enzymes- peptidases, enterokinase, lipases, disaccharidases

Disaccharide breakdown

Starches broken down into disaccharides by salivary amylase (30%) and pancreatic amylase (70%)

Maltase- breaks down maltose to two glucose molecules.

Lactase- breaks down lactose into galactose and glucose

Sucrase- breaks down sucrose into fructose and glucose.

Peptides and carbohydrates are broken down by enzymatic hydrolysis

PANCREATIC SECRETIONS

Endoproteases Cleave internal peptide bonds Trypsin- trypsinogen converted to

trypsin by enterokinase. Attacks on carboxyl side of arginine or lysine.

Chymotrypsin- chymotrypsinogen converted to chymotrypsin in small intestine by trypsin. Attacks on carboxyl side of tyrosine, phenylalanine, tryptophan, leucine or methionine.

Pancreatic secretions (con’t) Carboxy- and aminopeptidases- cleave

outside amino acids. Lipases- break down triglycerides into

fatty acids and monoglycerides Trypsin inhibitor- stored in pancreatic

secretory granules. Prevents early intracellular activation of trypsin.

Also lots of water and bicarbonate ions to neutralize and dilute acids in S.I.

Liver and bile Bile is produced in the liver, stored in gall

bladder. Bile salts- one of the most important

components of bile, required for fat digestion.

Bile is very alkaline, neutralizes acid in S.I. Bile transports waste products from liver,

cholesterol, bilirubin, drugs, steroids, and vitamins.

Bile salts

Bile salts are amphipathic, help solubilize fatty acids for uptake.

Fatty acids and monoglycerides have a strong tendency to re-associate after lipolysis- bile salts prevent fatty acids and monoglycerides from reassociating.

Digestion, absorption, and assimilation

Carbohydrate digestion and absorption.

Fat digestion and absorption. Protein digestion and absorption.

SGLT- sodium dependent glucose transporter.

Glut- facilitated diffusion transporter

FAT DIGESTION Emulsification- breaking up large

lipid droplets so that enzymes can digest them.

Enzymatic digestion (hydrolysis) of triglycerides- pancreatic lipase

Micelle formation-hydrolysis products form with bile salts to make micelles.

FAs and glycerol and monogycerides absorbed.

PROTEIN DIGESTION

Pepsin –responsible for about 20% of all protein digestion.

Pancreatic proteases and peptidases- chymotrypsin, trypsin, carboxy- and aminopeptidases.

Virtually all of the water secreted from exocrine glands is reabsorbed in the GI tract.

Hormonal control of digestion

Phases of digestion. Cephalic phase-sensory input from

food. Gastric phase-food enters stomach. Intestinal phase-chyme enters

duodenum.

Cephalic Phase

Increase acid secretion in stomach Increase enzyme secretion, decrease

volume from pancreas. Small increase in bile secretion and

contraction of gall bladder.

Parietal cell

ECL cell

G cell

D cell

HCl

Histamine

Gastrin

Somatostatin

+

++

-

ACh

+

+

-

+

Vagus nerve

Sensory stimuli

ECL, enterochromaffin-like cell

Hormonal and neuronal control of stomach secretions

Gastric hormones

Gastrin-stimulates HCl secretion, stimulates stomach motility

Somatostatin- inhbits HCl secretion and inhibits gastrin secretion

Gastric phase

Identical to cephalic phase, but stimulus is stomach distention

Cerebral cortex

Brain stem

Vagusnerve

Acid secretion

Stomach gastrin

Cephalic phase

Stomachdistention

gastric phase

Intestinal phase

Chyme enters the duodenum-2 subphases

Early intestinal phase pH > 3.0, gastrin from duodenum stimulates

HCl secretion Late intestinal phase

pH < 2, acid stimulates secretin release from the duodenum

Fatty acids, amino acids, stimulate cholecystokinin secretion from duodenum

Ulcer formation

• Acid-rebound theory– Acid and mucous production shuts down during

stress. When recovery occurs, acid starts before mucous production.

• Acid secretion hypothesis• Bacterial hypothesis

– Stress decreases immune system function, allows for an increase in stomach bacteria, specifically Helicobacter pylori, a bacterium that has been associated with ulcer formation.

Reflexes pada Kolon dan Rektum

Mass movements+

+

Food in stomach

Food in

duodenum

Faeces

Defaecation reflex

Colonrectum

anus

Ach

Sp

inal co

rd

IAS

EAS

FAECES

+Distention

-

VIPATP

+

-Pudendal

nerve