BAI GIANG HE TIEU HOA

Gastrointestinal/digestive systemObjectives: - Functions of the digestive system -Basics of food digestion process: hydrolysis reactions of food molecules -Structures and components of d

Gastrointestinal/digestive system

Objectives:

- Functions of the digestive system

-Basics of food digestion process: hydrolysis reactions of food molecules

-Structures and components of digestive system

-General structure of the wall of gastrointestinal tract

-Digestion in the mouth

-Digestion and absorption in the stomach

-Digestion and absorption in the small intestine

- Secretion and motility of the GI tracts

Why we need a digestive system ?

• Cells need nutrients for its structure and energy for it activities

• Foods are macromolecules which can not be directly absorbed by cells

Digestion Biosynthesis

Digestion is a process containing

hydrolysis reactions of food molecules

• Polysaccharide +H2O > monosaccharides

• Protein + H2O -–> amino acids

• Triglyceride + H2O > Glycerol + fatty acids

enzyme

enzyme

enzyme

Factors and activities occurring in the digestive system

accelerate hydrolysis reactions of food molecules

• Mechanical activities: mastication/chewing,

mixing, motility of intestines and stomach

Components of human digestive system

• gastrointestinal (GI) tract:

- Billiary system (liver and gallbladder)

Fundamental Physiology 4 e Sherwood, 2012

General structure of the gastrointestinal wall:

• Serosa/adventitia

http://www.easynotecards.com/uploads/358/22/593ab409_13673075871 8000_00000007.jpg

Digestive and absorption processes in the

Digestion in the mouth is minimal; no absorption

of nutrients occurs.

• Mechanical digestion: chewing by teeth and movement of tongue to grind and break food into smaller pieces to facilitate swallowing and to increase the food surface area on which

salivary enzymes will act

• Chemical digestion occurs only with polysaccharides:

amylase

polysaccharides + H2O  disaccharides

• Saliva contents : 99.5% H2O’ 0.5% electrolytes and

protein: amylase, and lysozyme, mucus

• facilitates swallowing by moistening food particles

• Keeps the mouth and teeth clean

• Saliva is rich in bicarbonate buffers, which neutralize acids in food

(tuyến mang tai)

(tuyến dưới hàm)

(Tuyến dưới lưỡi)

Swallowing: the process of moving food from the mouth through the esophagus into the stomach - oropharyngeal stage

1 sec.

Human Physiology 12e, S.Fox, 2011

Swallowing - esophageal stage

• Peristaltic waves push

food through the esophagus to the stomach: 5-9 sec.

• Peristalsis: ringlike

contractions of the circular smooth muscle

of the esophagus

5 to 9 seconds Human Physiology 12e, S.Fox, 2011

• The pharyngoesophageal sphincter keeps air from entering the digestive tract during breathing.

• Cardia Fundus, body, antrum, pylorus

•Lesser and greater

curvatures

• 3 layers of smooth

muscles:

longitudinal/circular/oblique muscle layers

•Gastric mucosa and gastric

rugae (gastric folds)

Gastric mucosa and gastric pits

• Gastric mucosa is folded and covered by mucus and gastric juice

• Food -> gastric wall/mucosa (G-cell) -> Gastrin -> blood -> Gastric gland

-> gastric juice

(Tuyến vị)

(hốc dạ dày)

(Gastrin)

Functions of the stomach

• stores ingested food until it can be emptied into the small

intestine at a rate appropriate for optimal digestion and

absorption

• secretes hydrochloric acid (HCl) and enzymes to begin

protein digestion

• Convert ingested food into chyme by mixing movements

and gastric secretions

• Gastric motility:

(1) filling, (2) storage,(3) mixing, and (4) emptying

Gastric secretion

• 2 liters of gastric juice are secreted per day

• Gastric juice containing watery mucus, HCl, pepsin,

pH=2

• Gastric secretion is controlled by neuronal and hormonal pathways:

– Vagal activity increases gastric secretion

– Gastrin (G cell), Acetylcholine (Ach) ↑ HCl, pepsinogen

secretion, histamin (enterochromaffin –like cells): ↑ HCl

– Somatostatin (D cell): ↓HCl secretion

Human Physiology 12e, S.Fox, 2011

Gastric motility and gastric emptying

• Receptive relaxation triggered by eating action facilitates gastric filling

• peristaltic waves (3/min) : over the fundus -> body -> the antrum -> pyloric

sphincter

• peristaltic contractions in the fundus and the body are weak -> Gastric storage

takes place in the body of the stomach

• Gastric mixing takes place

in the antrum of the stomach

Human Physiology 12e, S.Fox, 2011

Factors in the duodenum and others

control gastric emptying

• fat, acid, hypertonicity, and distension in

the duodenum can slow the rate of gastric emptying by neural or hormonal responses

• Emotions can alter gastric motility by acting through the autonomic nervesHuman Physiology 12e, S.Fox, 2011

Digestion in the stomach

• Carbohydrate digestion continues in the body of the stomach by salivary amylase until amylase is inactivated by HCl

• Protein digestion begins in the antrum

HCl

pepsinogen - pepsin

protein peptide fragments

• Almost no absorption occurs in the stomach (exception to alcohol and aspirin)

pepsin

Fundamental Physiology 4 e Sherwood, 2012

Acidic environment in the stomach and the gastric

mucosal barrier

• HCl activates the enzyme precursor

pepsinogen to an active enzyme, pepsin,

and provides an acid environment optimal for pepsin action

proteins from their highly folded final form,

thus exposing more of the peptide bonds for enzymatic attack

• HCl kills most of the microorganisms

ingested with food.

• The gastric mucosal barrier protects the stomach lining from gastric secretions.

Human Physiology 12e, S.Fox, 2011

Gastritis and Peptic Ulcers

• The layer of mucus containing alkaline bicarbonate (HCO 3

−) protects epithelial surface of the stomach from damage caused by HCl and pepsin

• Excessive gastric acid secretion -> erosions of the mucosa of

the stomach or duodenum (Peptic ulcers)

• Cause of Peptic ulcers:

– Excessive gastric acid secretion (by Excessive gastrin secretion ->ulcers

of the duodenum)

– Reduce the barriers of the gastric mucosa (gastric ulcer)

– Helicobacter pylori infection (2005 Nobel Prize)

– Anti prostaglandin (e.g aspirin, as prostaglandin stimulate mucus and HCO3- secretion of the gastric mucosa)

– Alcohol, coffee (stimulate acid secretion)

Digestion and Absorption in the

small intestine

Small intestine

• The small intestine is the site

where most digestion and

absorption take place

• Bile and pancreatic juice are

secreted into the duodenum facilitating digestion in the small intestine

www.humanillnesses.com/ /Pancreatitis.html

Secretion in the small intestine

• Intestinal juice: mucus, electrolytes,

H2O, enzymes

Emulsification of fat , neutralize acidic chyme from stomach

Small - intestine Mucosa

• circular folds (3x)

• villus-villi (10x)

• Microvilli (20x)

• Absorptive cells

• Goblet cells: mucus

• Paneth cells: antibacterial molecules

(lysozyme and antimicrobial peptides)

• Endocrine cells: hormones

• intestinal crypts (crypts of Lieberkühn)

• stem cells at the base of intestinal

crypts

• intestinal epithelium is renewed every four to five days

Procarboxypeptidase

Chemical digestion in the small

Emulsification of fat by bile salts

Chemical digestion in the small intestine

Maltose maltase Glucose

– Saccharose Glucose + Fructose

– Lactose Glucose + Galactose

Saccharase Lactase

Regulation of secretions in the small

intestine, pancreas, gallblader

HCl

Pancreas: enzymes

liver: bile juice (H2O, HCO3-)

Intestine: intestinal juice

(Pancreozymin)

Pancreas: H2O, NaHCO3

gallbladder: ejection of bile into

the duodenum

intestine: intestinal juice

•Parasympathetic nervous stimulation: increased intestinal, pancreatic, intestinal juices

• Sympathetic stimulation, morphin: inhibit…

Amino acid, fatty acids

Cholecystokinin

Duodenum mucosa

Digestive products of nutrients

Absorption of Fatty acids and monoglycerides

Lipoproteins and plasma cholesterol

Lipoproteins

Phospholipid (%)

Triacylglycerol (%)

Cholesterol (%)

Protein (%)

• lipoproteins are complex of lipids and proteins to transport

lipids in the blood

•Plasma lipoproteins are classified based on the density of

protein contained in them

– Very low density lipoprotein (VLDL) – Low density lipoprotein (LDL) – bad cholesterol –Low density lipoprotein ( HDL)

Absorption of H2O

juices

– 92% H20 is absorbed in the small intestine

– 6-7% is absorbed in the large intestine

• Osmosis

– H20 is absorbed followed the absorption of other nutrients

Absorption of ions

• Na+,K+, Mg2+: active transport