pencernaan (farmasi)

8/11/2019 Pencernaan (farmasi)

1/95

Physiology ofDigestion

Department of Physiology

School of Medicine

University of North Sumatra


2/95

Food

Nutrient

Non Nutrient

Assimilated

Eliminated

Digestive

system


3/95

Motility;Movement of food through tract ,includes ingestion,

mastication (chewing food and mixing with saliva),

deglutition (swallowing) and peristalsis (rhythmic

contractions along GI tract that propel food)

muscular contraction.

Secretion;Endocrine (secretion of hormones that regulate digestiveprocess)

Exocrine (secretion of water, enzymes, acid, bicarbonate,

into GI tractenzyme & other digestive juices.

Primary Functions of Digestive SystemActivity necessary:


4/95

Digestion;Hydrolysis reactions that break ingested polymers

(large molecules) into their smaller subunits(monomers)breakdown of substances.

proteins into amino acids

fats into glycerol and free fatty acids

complex sugars into monosaccharides

Absorption;

Transfer of monomer subunits across wall of smallintestine into blood or lymph

transport modified nutrients.


5/95

Regulation;

There are two nerve nets (plexuses) in GI tractthat contain neurons and interneurons

sub mucosal (Meissner)

Myenteric (Auerbach)

Plexuses = brain of the gut

stimulated by stretch (bolus of food), chemicals,

and stomach content (local stimuli) Activity of plexuses can be modified by central

nervous system and the autonomic nervous

system

Neural:


6/95

Neural regulation via autonomic nervous system

GI tract receives bothsympatheticandparasympatheticinnervations

Parasympathetic via vagus nerve and spinal nerves

in sacral region (to lower portion of large intestine) stimulates motility and secretion; favors digestion

Sympathetic

reduces motility and secretory activity andstimulates sphincter contraction


7/95

Paracrine regulation

production of hormone-like molecules that are

produced in one cell and travel through

interstitial fluid (not bloodstream) to affect

activity of nearby cells Hormone regulation

production of hormones that are released into

the bloodstream and carried to target tissueswithin digestive system where they affect

digestive activity

Hormonal.


8/95


9/95


10/95


11/95


12/95

Salivary glands(parotid, submaxillary, sublingual)

secrete saliva

lubricates and softens food; aids in

swallowingcontains amylase = enzyme that begins

breakdown of carbohydrates


13/95

OropharynxTo convey food into the esophagus.

Important role in swallowing.


14/95

Cavity at back of mouth opening toboth esophagus (digestive tract)

and trachea (windpipe)

Voluntary raising of larynx to close

(epi)glottis and prevent food entry

into windpipe

Pharynx = throat


15/95

Esophagus.

Hollow muscular tube connecting pharynx and

stomach.

Bounded by sphincters.

Lined w/ stratified squamous epithelium.Lower esophageal (gastroesophageal) sphincter ;

transtition from low pressure ( intrathoracic )

high pressure (intra-abdominal).Dissorder o/t LES tonemajor cause esophageal

refluxheart burn.


16/95


17/95


18/95

stomach


19/95


20/95


21/95


22/95

Stomach:

Temporary stores ingested food.sphinctersprevent backward flow of materials intoesophagus and regulate release of stomachcontents into small intestine

Churn, mixes food with gastric juice.

Mechanical and chemical breakdown of ingestedmaterial

Produces, mucus, HCl and pepsinogen.

HCl converts pepsinogen into pepsin. Sterilization of stomach contents by acid

Pepsin digests proteins into peptide fragments.

Absorbs some water, alkohol, glucose.

Binds vit. B12allows abs. in ileum

Secretion/Digestion


23/95

Pepsinogen

HCl

Gastrin

Histamine

Stomach:

lower region of stomach(antrum) secretes the

hormone gastrin.

Additional secretions: histamine (ECL cell)

Somatostatin


24/95

Mucous cell, secrete mucousprotects

mucosa from acid & pepsin.

Chief cells, secrete :

- Gastric lipase.

- Pepsinogen PepsinHCl

Prietal (oxyntic) cells, secrete :

- HCl .

- Intrinsic factorbinds vit. B12

Prietal (oxyntic) cells, secrete :

- HCl .

- Intrinsic factorbinds vit. B12

Pyloric glandAlkaline mucus.


25/95


26/95

Digestion in the stomach

CHO digestion is halted because acidic pH of thestomach inactivates salivary amylase

Little fat digestion occurs in the stomach

Protein digestion begins in the stomach

Involves mechanical breakdown of proteins by thechurning actions of the stomach

Involves the chemical digestion of proteins by acid andhormones Gastric (stomach) acid = hydrochloric acid (HCl)

pepsin


27/95

Protein Digestion in the Stomach

Parietal cells

secrete acid (hydrochloric acid = HCL)

stimulated to produce acid by gastrin

Chief cells

secrete pepsinogen

Pepsinogen = inactive hormone Pepsinogen converted to pepsin (active hormone) by

acidic pH of the stomach

Pepsin breaks large proteins down into smaller peptides


28/95

G cells

Secrete gastrin

Gastrin = hormone

target tissues = chief cells and parietal cells in stomachstimulates gastric juice production

HCL from parietal cells

Pepsinogen from chief cells

Increases pH of stomach Promotes conversion of pepsinogen to pepsin

Protein Digestion in the Stomach


29/95

It also activates gastroileal reflex which moveschyme from ileum to colon

Parasympathetic stimulation releases gastrinreleasing peptide, which stimulates G cell releaseof gastrin

Mucus cells - secretes mucus to protect againstacid and digestive enzymes


30/95

Absorption in the Stomach

Almost all products of digestion areabsorbed in the intestine

Notable exceptions

alcohol and aspirin can be absorbed directlythrough stomach wall

due to their lipid solubility

absorption of aspirin through stomach wall

associated with bleeding, may be related topeptic ulcers in people taking large dosages


31/95

Chyme

Food in stomach is liquified

mixed with stomach juices to form pasty liquid

material = chyme

Chyme = material passed from stomach to

small intestine


32/95

Small Intestine

Functions in digestion CHO digestion resumes and is completed here

Protein digestion continues and completes here

Fat digestion is initiated and completed here

Also functions to absorb nutrients, fluids, andelectrolytes

Divisions (@ 12 feet long total length)

duodenum = upper portion (@ 1 foot long) closest to

stomach

jejunum = middle section

ileum = lower section closest to large intestine


33/95

Anatomy

3 segments (12 ft long, 22 ft in cadaver)

Duodenum

Jejunum Ileum


34/95

Anatomy

Features that increase surface area Circular folds (valvulae conniventes, kerckrings

folds, plicae circularis) Project into lumen 3-10 mm Prominent in duodenum and jejunum and disappear near

mid ileum

Responsible for feathery appearance on bariumradiographs

Villi 4-5 million in entire length

0.5-1.5 mm long

Account for velvet-like appearance


35/95

Anatomy

Microvilli

1.0 um long

Brush border


36/95

Anatomy Structure of the villus

Lacteal

A


37/95

Anatomy Goblet cells and absorptive cells

A t


38/95

Anatomy Brush border enzymes

A t


39/95

Anatomy Crypts of Lieberkuhn


40/95

Physiology

Two primary function Digestion

Absorption of nutrients and water

Digestion

Mainly in duodenumsmall intestine andpancreatic enzymes

Bicarbonate from pancreas neutralizes acids

Mucous protects from acids

Bile emulsifies fats


41/95

Hormones Important in Sm.

Intestine Digestive Activity

Secretin

Cholecyctokinin (CCK) Enterokinase

Pancreatic enzymes

Lipase, Amylase, Peptidases, Trypsinogen, Trypsin


42/95

Physiology

Digestive enzymes Salivary amylase

Pepsin

Pancreatic enzymes Trypsin

Chymotrypsin

Carboxypeptidase

Nucleases

Pancreatic lipase

Pancreatic amylase

Intestinal enzymes Peptidases

Disaccharidases

Lipase

Nucleotidases


43/95


44/95

Physiology

Absorption

Nutrients broken down into simple sugars, fattyacids and amino acids

Principle sites of absorption

Duodenum: iron, calcium, vitamins, fats, sugars, aminoacids, vitamins

Jejunum: fat, sugar, amino acid (largely complete by mid

jejunum), vitamins Ileum: vitamin B12and bile salts

Most bile salts are absorbed and recirculated to the liverimportant in maintaining bile pool


45/95

Digestion

Most occurs by hydrolysis reactions -

reactions that add water to break chemical

bonds

Enzymes involved:

amylase - breaks complex sugars to

disaccharides

lipases - breaks down lipids

proteases - breaks down proteins


46/95

Hormonal Control of Intestinal

Secretion

S cells secrete secretin

secretin target tissue = pancreatic ducts and liver

induces release of water and HCO3-from pancreatic ductcells and secretion of HCO3

-into bile by liver

HCO3-neutralizes acidic chyme

Stimuli for secretin secretion

acid (pH less than 4.5 stimulates secretion)

secretin = natures antacid


47/95

I cells secrete cholecystokinin (CCK)

CCK target tissues = pancreatic acinar cells and

gall bladder induces secretion of digestive enzymes from

pancreatic acinar cells

induces contraction of gall bladder, which releases

bile into small intestine Stimuli for CCK secretion

presence of protein and/or fat in chyme

Hormonal Control of Intestinal

Secretion (continued)


48/95

CCK and Appetite Control

CCK also thought to act on satiety center inbrain and inhibit appetite

Butabindid = drug that interfers withenzyme responsible for CCK degradation(breakdown)

keeps CCK in system longer

boosts appetite inhibition

used to treat obesity


49/95


50/95

Pancreatic Enzymes (continued) Most pancreatic enzymes are produced as

inactive molecules = zymogens

Are transported to small intestine in zymogen

form

Protects the pancreas from self digestion


51/95

CHO Digestion in Sm. Intestine

Pancreatic amylase secreted into duodenum in

response to secretin

Is active in the intestine because the acidic chymeis neutralized by HCO3

-also secreted from

pancreas in response to secretin

Amylase converts complex CHOs to maltriose,maltose, and short branched sugars


52/95

Small Intestine (continued)

Inner surface (epithelial layer) extensivelyfolded and covered with smaller folds (villi)

and even smaller folds (microvilli) increase

surface area for absorption to occur

Site of absorption of carbohydrates, lipids,

amino acids, calcium and iron in duodenum

and jejunum

Bile salts, Vit B12, water, and electrolytes

mainly in ileum


53/95

CHO Absorption in the Sm. Intestine

Enzymes in the brush border completebreakdown of maltotriose, maltose, and branched

sugars, lactose and sucrose

Lactase converts lactose to glucose and galactose

Sucrase converts sucrose to glucose and fructose

Isomaltase converts branched sugars glucose,

maltose and unbranched short oligosaccharides

Maltase converts maltose to glucose


54/95


55/95

Fat Digestion in Sm. Intestine

Limited fat digestion occurs prior to sm. Intestine Some lipases in saliva and gastric secretions

Lipase = enzyme important in fat digestion

Secreted into sm. intestine from pancreas in response

to secretin breaks down triglycerides to free fatty acids and

monoglycerides

Activity is dependent upon the amount of surface areaon which it can work

Phospholipase A2digests phospholipids

Bile is essential for proper fat digestion

Di ti d Ab ti f Li id i


56/95

Digestion and Absorption of Lipids in

Small Intestine

Fats stimulate I cell release of CCK

CCK triggers release of bile from gallbladder

Bile emulsifies fats breaks large fat globules into smaller globules

does not actually break bonds between glyceroland fatty acids

Increases surface area available for pancreaticlipase to act


57/95

Liver

Largest organ in body Blood supply

hepatic artery delivers oxygenated blood

hepatic portal veinproducts absorbed into capillaries in the intestines

do not directly enter general circulation

this blood is delivered first to the liver by the hepatic

portal vein, and then passed on to the generalcirculation

liver has first crack at absorbed nutrients, except

lipids


58/95


59/95

Non-digestive functions

circulatory functions; destroys aged or abnormal

blood cells and produces clotting factors

converts protein metabolites to urea for

elimination by kidneys

immune function (Kupffer cells)

functions as blood reservoir in regulation of blood

volume

Liver (continued)


60/95

Bile Synthesis

This is the main digestive function of the liver;Approximately 1 liter per day is produced

bile salts are cholesterol derivatives and functionto emulsify fats

bile salts are recycled, not excreted

main bile pigment is bilirubin, derived from RBCheme

bile is synthesized in the liver and stored in thegallbladder

release is stimulated by cholecystokinin andvagus nerve


61/95

Bile

Product of the liver cells bile contains bile pigment, bile salts, phospholipids,

cholesterol, and inorganic ions

bile pigment = bilirubin = breakdown product of hemoglobin

bile salts = derivatives of cholesterol that are combined withtaurine or glycine, form micelles = lipid aggregates with non-

polar parts in central region and polar regions toward water

Essential for absorption of fat from the digestivetract

Emulsifies fat; breaks large fat globules into smaller fatdroplets, provides greater surface area on which lipasecan act


62/95


63/95

Micelles

Aggregates of bile salts, free fatty acids,

monglycerides, lysolecithin, and fat-soluble

vitamins

Arranged with non-polar regions to center, polar,

water-soluble portions to outside

makes lipids more water soluble in lumen of intestine

Micelle is transported to epithelial cells liningsmall intestine


64/95

Importance of Micelle Formation

Intestinal epithelial layer is covered by an unstirred

water layer

Fats are nonpolar, and therefore insoluble in water Micelles are structures whose outer borders are polar,

but whose inner segments are nonpolar

Outer polar portion can dissolve in the unstirred water layer

and be transported to epithelial cell surfaces

Nonpolar contents can then be removed from micelle and

absorbed individually, or in some cases the micelle itself

may be absorbed


65/95

Chylomicrons

Inside epithelial cells, triglycerides and

phospholipids are re-synthesized

Resynthesized triglycerides and phospholipids are

combined with cholesterol and protein inside the

cell to form chylomicrons

Chylomicrons are released into the lymphatic

system - NOT INTO HEPATIC PORTAL VEINliver does not get first crack at lipids


66/95

Protein Digestion in Sm. Intestine

Proteolytic enzymes are released (in inactive,zymogen forms) from the pancreas in response tosecretin

Trypsinogen = inactive precursor that isconverted (by enterokinase) to trypsin in the brushborder of the small intestine

Trypsin converts other zymogens to their activeforms

Collectively, the proteolytic enzymes breakproteins and peptides into single amino acids, ordi- and tripeptides


67/95

Absorption of Amino Acids in Sm.

Intestine Amino acids are absorbed by the epithelial cells of

the small intestine by active co-transport with

sodium

Di- and tripeptides are also absorbed by epithelial

cells of the small intestine and then broken down

into amino acids within the epithelial cells

Epithelial cells release amino acids into portalblood, which is transported first to the liver, then

to rest of the body


68/95


69/95


70/95

Intestinal Contractions and Motility

2 major types ofcontractions occur in thesmall intestine:

Peristalsis: Slow movement.

Pressure at the pyloric endof small intestine is greaterthan at the distal end.

Segmentation: Major contractile activity of

the small intestine.

Contraction of circularsmooth muscle. Mix chyme.

Insert fig. 18.14


71/95

Brush border

enzymes

reassembly

Anatomy and Physiology


72/95

Anatomy and Physiology Anatomy



73/95

Functions (converts chyme to feces)

Absorption of water and electrolytes (mainly onright side) Absorbs 800 ml water/day

Capacity 1500-2000 ml/day (when exceeded results indiarrhea)

Sigmoid colon reservoir for dehydrated fecalmass

~200 g feces/day

Water80-90%

Food residue

Bacteria

Cells

Unabsorbed minerals



74/95

Secretes mucus (no enzymes)

Bacteria produce vitamin K and several Bs

Flatus (NH3, CO2, H2, H2S, CH4) CO2 produced when fatty acids and HCl are neutralized

by bicarbonate

Bacterial fermentation of carbohydrates produces CO2,H2, CH4

~1000 ml expelled each day Excess occurs with aerophagia and diets high in

indigestible carbohydrates

Rectum and anus sites of some of most commondisorders known to humans Constipation Hemorrhoids

Abscesses and fistulas

Colon and rectal cancer

Colon


75/95

Colon

1,51,8 m.

Various segment.

Columnar epithelium at the surface (few, short),no villi, few folds (except in the distal rectum).

Goblet cells.

Endocrine cells.

Absortive cells.

Anatomi & Histology


76/95

Large Intestine

Larger diameter, shorter length (@ 4 feet)

than small intestine

separated from small intestine by ileocecal

valve

Collects food residue (indigestible) material

Site of final water reabsorption - causes

chyme to become solid (forms feces)

Stores feces until eliminated from body


77/95

Bacteria live in the colon and stimulate theproduction of vitamin K and some of the B

complex vitamins Mucus is produced but no enzymes are

secreted in the large intestine


78/95

Divisions

cecum = section nearest small intestine

(appendix attached in this region)

colon = major portion

ascending

transverse

descendingsigmoid (leads to rectum)

Large Intestine (continued)


79/95

Water Absorption in the Intestine

Majority ( 98%) of water that enters gut is

(re)absorbed

85% (re)absorbed in small intestine 13% in large intestine

Absorption of water is passive process

osmotic gradient created by active transport ofions

water moves according to its gradient

Large Intestine


80/95

Large Intestine


81/95

Large

Intestine


82/95

Colon: Function

Absorb H2O and electrolytes

Secretion of mucus

Formation, propulsion & storage ofunabsorbed material (feces)

Some digestion by bacteria

Mass Peristaltic Movements (2-3x day)

Moves through in 12-24 hours

DIGESTIVE ACTIVITIES OF


83/95

DIGESTIVE ACTIVITIES OFLARGE INTESTINE

STRUCTURE ACTIVITY RESULT

Mucosa Secretes

mucus

Lubricates colon &

protects mucosa

Absorbs water Maintains water

balance; solidifies

feces; absorbs

vitamins & some ions



84/95



Lumen Bacterial

activity

Breaks down

undigested

carbohydrates,protein, & amino

acids into products

that can be expelled

in feces or absorbed& detoxified by liver

Synthesizes certain B

vitamins & vitamin K



85/95



Muscularis Haustral

churning

Contractions move

contents from haustrum

to haustrum

Peristalsis Contractions of circular

& longitudinal muscles

move contents along

length of colon



86/95



Muscularis Mass

peristalsis

Forces contents into

sigmoid colon

Defecation

reflex

Eliminates feces by

contractions in sigmoid

colon & rectum

Large Intestine


87/95

Large IntestineDigestion and Absorption

Fermentation breaks down undigested complexCHO and proteins Produce lactate and short chain fatty acids used by

the colonocytes for energy Bacteria produce absorbable vitamins like K

Gases are produced in the large intestine

Colon is responsible for absorbing most of the

water that enters it in the form of chyme Colonocytes absorb NaCl

Secretion


88/95

Secretion

& H2Oabsorption

2000 ml150 ml = ?

Ion &


89/95

Ion &

Vitaminabsorption

Rectum


90/95

Rectum

The


91/95

Figure 24.25

TheDefecation

Reflex


92/95

Defecation process

Reflex relaxation of internal sphincter

Valsalva maneouvre raising intraabdominal

pressure Relaxation of puborectalis (anorectal

angle)

Voluntary relaxation of external sphincter

Defecation reflex


93/95

f f> 15 mm Hg


94/95

Continence mechanism

Rectum normally empty

Colonic movements distend rectum -

150 mls, 25 cm H2O which activatedefecation reflex

Voluntary inhibition (external sphincter)

movement of faecal material back intocolon


95/95

pencernaan (farmasi)

Documents