Gastrointestinal System

By.Aveen M1st sem MtechBMSP&IRVCE

Introduction• GI System is the route through which the food enters the body.

• Normal young healthy adult consumes 1 kg of solid diet and 1-2 L of liquid diet every day.

• The food consumed cannot be utilized by the body directly.

• The process of conversion of complex food substances into simple food substances that can be absorbed by the body is known as Digestion.

Parts of Digestive System

• Made up of:- GI Tract and the accessory organs

• GI Tract:Mouth-Pharynx-Esophagus-Stomach-Small Intestine-Large Intestine

• Accessory Organs:

Teeth,Tongue,Salivary Glands,Exocrine part of the Pancreas,Liver,Gall Bladder.

Wall Of GI Tract

Made of 4 layers:

Mucous Layer

Submucous Layer

Muscular layer

Serous or Fibrous layer

Nerve Supply to the GI Tract• Two types of nerve Supply- Intrinsic Nerve supply- Extrinsic nerve supply1). Intrinsic nerve supply:- Present within the wall of GI Tract- Fibers are interconnected and form a network called nerve

plexus. Two types :Auerbach’s Plexus and Meissner’s Plexus2) Extrinsic Nerve Supply. :- It is from the Autonomic Nerve System- Both sympathetic and the parasympathetic division of the

ANS

STOMACH

Introduction

• Stomach is a hollow organ situated just below the diaphragm on the left side of the abdominal cavity.

• Specialized for accumulation of food▫Capable of considerable expansion (can hold 2-3L)

• Gastric juice converts food into semi solid material called chyme

• 4 Parts of stomach:▫Cardia▫Fundus▫Body▫Pylorus

Stomach• Gastric glands are the glands of the stomach.

• Gastric mucosa has numerous openings called gastric pits• Gastric glands empty into bottom of pits

• The gastric glands are of three types:-Fundic gland-pyloric gland-cardiac gland.

• Different cells of Fundic glands are:▫Mucous cells▫Chief cells▫Parietal cells▫Enteroendocrine cells

Functions of stomach1).Mechanical Function:-Storage Function: Food is stores in stomach for 3-4 hrs-Formation of chyme: Peristalic movement of stomach mixes the bolus with the gastric juice and forms a semislid material called chyme.

2).Digestive Function:-Gastric juice mainly acts on proteins.-Proteolytic enzymes –pepsin and renin

• Pepsin:-Major proteolytic enzyme .-secreted as pepsinogen which is inactive

-Products: Proteoses,Peptones,Polypeptides.

• Gastric Lipase:- Weak lipatic enzyme- Hydrolyses fats into fatty acids and glycerols

• Others are:-urase(acts on urea,produces ammonia)

-Rennin(curdles milk)- Gelatinase-(converts gelatin to peptides)

-Gastric Amylase(Digestion of carbohydrates)

Functions

3).Hemopoietic Function:

- Intrinsic factor of castle present in gastric juice helps in erythropoeisis.- Necessary for the absorption

of Vitamin B12.- Deficiency leads to

pernecious anaemia

4)Protective Function:

-Thick mucus is responsible for protection of the gastric wall from injury,irritation.-prevents the digestive action of pepsin on the stomach wall.-Alkaline in nature due to which it protects the gastric mucosa from Hcl of the gastric juice

Functions

5).Excretory Function:

- Substances like Toxins, alkaloids and metals are excreted through gastric juice

6).Secretory Function:

Hcl present in the gastric juice :- Activated the pepsinogen

to pepsin- Bacteriolytic action- Provides the acid medium

for the actions of hormones.

PANCREAS

Introduction

• Pancreas is a glandular organ in digestive system

• Pancreas is an organ having Dual functions:

- Endocrine function (Islets of Langerhans)-production of Hormones, secretion of insulin and glucagon onto the blood.

- Exocrine function(Acinar cells)-secretion of digestive juice called as pancreatic juice

- Most cells make up pancreatic acini, which produce pancreatic juice

• Secretes pancreatic juice into a pancreatic duct; pancreatic duct leads to duodenum (small intestine).

Functions of pancreas

1). Digestive Functions of pancreatic juice:

a. Digestion of Proteins : - Proteolytic enzymes: trypsin, chymotrypsin, carboxypeptidase , nucleases , elastase , collagenase

proteins peptides;

• stored and released as inactive form in zymogen granules• trypsinogen is activated to trypsin by enterokinase• trypsin then activates chymotrypsin and carboxypeptidase

b. Digestion of Carbohydrates:•   (Starch and Glycogen) maltose and dextrin With the help of pancreatic amylase . c. Digestion of Fats/Triglycerides :•   Fats/Triglycerides 2 fatty acids + monoglyceride With the help of pancreatic lipase,colipase,cholestrol ester hydrolase, phospholipase A and B,Bile salt-lipase.

d. Digestion of Nucleic Acids:• Nucleic acids nucleotides. With the help of nucleases

3).Endocrine Function:Consists of Islets of langerhans.(alpha cells,Beta cells and delta cells).

2). Neutralizing action of pancreatic Juice:

- Bicarbonate ions are also released to neutralize acidic chyme entering from the stomach.

- This protects the intestine from destructive action of the acidic chyme.

LIVER

Introduction

• Largest internal organ.• Location: below diaphragm / right side • Contains hepatocytes• also contains Kupffer’s cells (macrophages) remove and destroy: -microbes; -foreign matter. -worn platelets and erythrocytes

Functions Of Liver

Metabolism of monosaccharides, lipoproteins, amino acids.

Storage (glycogen, Vitamin A, B12, D, iron), Filtering of blood (worn blood cells and debris), Destruction of toxic chemicals (alcohol and drugs), Production/secretion of bile. Heat Production Hemopoetic Function Inactivation of Hormones and drugs(catabolism) Hemolytic Function (kupffer’s cells) Synthesis of glucose, few proteins

Functions of Liver

Synthetic functions

Metabolic functions

Detoxification Functions

Hormone Inactivation

Storage Functions

Bile secretion

Examples

Plasma proteins

Enzymes

Clotting factors

Urea, cholesterol

Steroid binding proteins

Acute phase proteins

Protein metabolism

CarbohydrateMetabolismFat

Metabolism

Glycogenesis

Steroid Hormones

GlycogenVit A

β oxidation

Urea Synthesis

Drugs , Alcohol

Immunity

Kupffer cells

INTESTINE

Small Intestine

• 3 Parts:

-Duodenum-nearest stomach -Jejunum- mid-region -Ileum- near large intestine

• Mucous membrane of SI is covered by minute projections called as villi

• Primary site for digestion and absorption of nutrients

• Bile duct and pancreatic duct empty into duodenum

Functions of Small Intestine Digestive Functions:• Secretions from SI is called succus entericus.• Enzymes of succes entericus acts on partially digested food

and converts into final digestive products.

Functions Digestive Function:With the help of proteolytic and

Amyloytic ,lipolytic enzyme.Protective Function: Mucus secreted by succus entericus

protects the wall of intestine and paneth cells(secretes defensins)Activator Function: Enterokinase activated trysinogen to

trypsin.Hemopoetic Function(intrinsic factor of castle)Hydrolytic Function(helps in enzymatic reactions)Secretory function(secretes enterokinase,succus entericus)Mechanical FunctionAbsorptive FunctionHormonal Function (secretes GI hormones like secretin)

Large Intestine

• Parts of Large Intestine:  o cecum - nearest ileum of small intestine; (appendix is

a blind pouch in this region);o colon – majority of length;(ascending,transverse,Descending,sigmoid)o rectum - distal region of colon;o anal canal - narrowing of rectum & opening to

outside;

• Reabsorbs water and electrolytes • Eliminates waste• NO Villi• Mucosa contains numerous tubular glands called crypts

▫Responsible for mucus secretion

Functions of Large IntestineSecretion - only mucin and other inorganic substances(cl)

Absorption of water , electrolytes.

Formation of Feces –unwanted substances form feces

Bacterial flora of LI - synthesises vit B12,folic acid,vit K.

Excretory Function-Excretes heavy metals like bismuth,mercury,lead through faeces.

Function Tests- Endoscopies

Endoscope• Endoscopy is a nonsurgical procedure used to examine a

person's digestive tract.

• Using an endoscope, a flexible tube with a light and camera attached to it, your doctor can view pictures of your digestive tract on a color TV monitor.

• An endoscopy is often used to confirm a diagnosis when other devices, such as an MRI , X-ray, or CT scan are considered inappropriate.

- The following conditions and illnesses are most commonly investigated or diagnosed with an endoscopy:

• Breathing disorders• Chronic diarrhea• Incontinence• Internal bleeding• Irritable bowel syndrome

Thank you