Lesson 24 Digestive Physiology 2

Functions of Small intesine

Mix chyme with digestive juices

Digestion of carbohydtazes, proteins, lipids, nucleic acids

Absorption of 90% of nutrients and water

What fascilitates large absorption of small intestine

Folds, intestinal villi, microvilli

How is intestinal juice composed?

Water, mucus, pancreatic juice, bile, maltase, sucrase, lactase, peptidase, nucleosidases

What does the presence on nutrients and distension of intestinal wall cause during small intestinal stage

• stimulation of billiary secretion

• Regulation od gastric emptying

• Stimulus pancreatic secretion

• Contraction gallbladder

Pancreatic secretion

Main components of nutrients digested by enzymes

Bile secretion

Bile is produced in liver, stored in gallbladder and released to intestine in presence of remain of food

Contain bile salts for absoprtion of lipids

Factors that increase and decrease pancreatic and bile secretion

Increase: acetylcholine, CCK, secretin

Decrease: Somatostatin

What does secretin do

Increase bile synthesis and increase secretionof bicarbonate from pancreas

Small intestinal phase

1. Chyme entering duodenum causing secretion of CCK and secretin

2. CCCk and secretin enter bloodstream

3. Cck induces enzyme rich pancreatic juice, secretin induces bicarbonate rich pancreatic juice

4. Bile salts and secretin transported to liver to produce bile

5. Cck causes gallbladder to contract and hepatopancreatic duct to contract. Bile enterd duodenum

6. Vagal nerve stimulates gallbaldder to contract weakly

Carbohydrates

Must be broken down into monosaccharides to get broken down.

Salivary amylase and pancreatic amylase produce oligosaccharides

Enzymes of Microvilli of SI cleave down oligosaccharides to mono

Monosaccharides absorption

Absorbed though apicak surface to capillaries through: Secondary active transport and facilitated diffusion

Proteins

Have to be broken down into aminoacids

Pepsin and pancreatic enzymes break down proteins into oligopeptides

Enzymes of brush border break down oligopeptides to amino acids

Aborbed and into blood

Lipids

Must be broken down into monoglycerides

Fat broken down by gastric and salivary lipase and pancreatic enzymes in intestine

Enterocytes

Absorb water and most of ions (Sodium, potssium calcium

How much fluid reaxhes SI and how much goes to large instestine and how much excreted

9 L to small

2 liter to large

250 only secreted

What is the goal of motility in intestine and what are the types of movements

Mixing the content

Peristaltic,m segmental, migrating motor complex

Peristaltic, MMC, Segmental movement

Peristaltic movements

MMC: periszalting movement during fasting regulated by motilin. Cleanses the GI tract of food debris and baczteria

Sgmenral localized contraction

Functions of large intestine

Digest and absorb

Reabsorb remaining liquid

Store waste products

Stool formation

Defecation

Cells of LI

No folds or villi

Lieberkuhn cells

How is food digested in large intestine

Glands of large large intestine secret mucose but not enzymes.

Only way of digestion food debris is fermantation.

Bacteria break down carbohydrates and remaining preoteins

Composioition of stool or faeces

Water 100-200 ml

Inorganic salts

Non digestible part of food

Non absorbed digested material

Function of bacterial flora

Protection of epithelium from infection of pathogemic bacteria

Detoxification

Colon motility

Haustral propulsion

Mass peristalsis

mixing and delaying allowing longer contact with epithelium

Forms of movements in colon

mixing movement = 30 sec duration followed by minurtes of rest

Propulsion movements = mass movements 3-4 times a day

Defecation

Coordinated action of smooth and striated muscle layers in rectum and anus

Sphincter of anal canal

• Internal: smooth muscle fibers, involuntary innervation.

• External: skeletal muscle fibers, voluntary innervation.

Reflexes of anal cavity

• retain rectal contents

• Allow expulsion (also of gases)

Defecation reflex

Mass peristalsis

Strecth receptors → defecation reflex