The Digestive System

Purpose: to convert foods into simpler

molecules that can be absorbed and

used by the cells of the body

Sudheerkumar kamarapu

Assistant Professor

Sri Shivani college of pharmacy

Why is Digestion Important?

• When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nourishment.

• Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

• Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.

Let’s Break It Down…

• The digestive system it is a tube running from mouth to anus.

• This tube is like an assembly line, or more properly, a disassembly line.

• Its chief goal is to break down huge macromolecules (proteins, fats and starch), which cannot be absorbed intact, into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed across the wall of the tube, and into the circulatory system for dissemination around your body.

Components of the Digestive

System

The Major Players

• Mouth

• Pharynx

• Esophagus

• Stomach

• Small Intestine

• Large Intestine

The Accessory Structures

• Salivary Glands

• Pancreas

• Liver

• Teeth

• Tongue

All of these organs work together to carry out…

3 Fundamental Processes:

• Secretion: Delivery of enzymes, mucus, ions and the like into the lumen, and hormones into blood.

• Absorption: Transport of water, ions and nutrients from the lumen, across the epithelium and into blood.

• Motility: Contractions of smooth muscle in the wall of the tube that crush, mix and propel its contents.

The Path of Digestion

• Digestion begins in the mouth (oral cavity)

– Food is broken down by chewing (mechanical) and enzymes in the saliva (chemical)

– Teeth coated with enamel cut and tear food

– Saliva contains the enzyme salivary amylase (breaks down starch)

– Food is turned into a soft ball called a bolus

– Bolus travels from the mouth to the pharynx (throat)

The Path of Digestion • Swallowing is a result of the combined

effort of the tongue and throat muscles

• Epiglottis (small flap of connective tissue), prevents food from going into the trachea (airway)

• Next, food travels Into the esophagus

• Peristalsis squeezes

food along into the

stomach

Peristalsis

The Path of Digestion

• A ring of muscles called the cardiac sphincter

closes the esophagus after food passes into the

stomach

• Stomach continues chemical and mechanical

digestion

– Chemical: Glands release mucous, HCl,

pepsin (enzyme that breaks down protein)

– Mechanical: Muscles contact and churn

contents into chyme (a thin watery liquid)

Anatomy and function of

digestive organs

• GIT-PERITONEUM – peritoneum is a serous membrane which lines

the abdomen cavity and covers the abdominal organs.

– It consists of two layers

1) Parietal peritoneum-lines the walls of abdominal cavity.

2) Visceral peritoneum-which covers the abdominal organs.

The space between these two layers is called as peritoneal space.

• Organs completely covered by peritoneum are – stomach, liver and intestines.

• Organs partly covered by peritoneum – kidneys.

Folds of peritoneum

omenta : the folds of peritoneum connected to the stomach are called omenta.

They divided into Greater omentum – which hangs from the lower

border of stomach to the front surface of small intestine.

Lesser omentum – which extends from the lower border of liver to the lesser curvature of stomach.

Mesentry : it is the fold of peritoneum which attaches the different parts of small intestine to the posterior abdominal wall.

Blood vessels, nerves and lymphatics enter the intestine only through mesentry.

Peritoneal ligaments : they are folds of peritoneum which connect organs like liver and uterus to the posterior abdominal wall.

Pelvic peritoneum : it is the part of peritoneum present in the pelvic region.

The pelvic peritoneum is actually the continuation of peritoneum in the abdominal cavity.

The arrangement is different in males and females due to the presence of uterus and fallopian tubes in females.

Functions of peritoneum

• It forms a complete or partial covering for abdominal organs.

• It forms the smooth lining which enables the abdominal organs to move over each other without friction.

• The ligaments and mesentries of peritoneum hold the abdominal organs in position.

• Omentum and mesentry serve as store house for fat.

• The fats of peritoneum prevents infections being carried to abdominal organs.

• The peritoneum itself can absorb large quantities of fluids.

WALL STRUCTURE

• SEROSA:- THE OUTERMOST LAYER MADE

OF A SEROUS MEMBRANE & CONNECTIVE

TISSUES. ALSO CALLED THE PERITONIUM.

• MUSCULAR LAYER:- MADE OF TWO

CIRCULAR & LONGITUDINAL SMOOTH

MUSCLE LAYERS.

• SUBMUCOSA:- MADE OF LOOSE

CONNECTIVE TISSUE CONTAINING NERVES,

GLANDS, BLOOD AND LYMPHATIC VESSELS.

• MUCOSA:- MADE OF EPITHELIUM,

CONNECTIVE TISSUE AND SOME SMOOTH

MUSCLE FIBERS.

Intestinal Morphology

Intestinal Villus and Microvilli

Secretory cells

Stem

cells

WALL STRUCTURE

THE MOUTH • FORM THE ORAL CAVITY WHICH IS

INVOLVED IN THE INTAKE OF FOOD, BREAKING IT, MIXING IT WITH SALIVA AND SWALLOWING IT.

• CONTAIN THE TEETH & IS SURROUNDED BY THE CHEEKS, PALATE & TONGUE.

• MECHANICAL DIGESTION BY CHEWING.

• CHEMICAL DIGESTION BY SALIVARY AMYLASE ENZYME.

THE MOUTH

THE TEETH

THE SALIVARY GLANDS

• THEY SECRETE SALIVA THAT CLEAN &

LUBRICATE THE MOUTH, DISSOLVE,

BIND AND DIGEST FOOD PARTICLES.

• PAROTID GLANDS:- IN FRONT OF EAR.

SECRETE AMYLASE ENZYME.

• SUBMANDIBULAR GLANDS:- IN FLOOR

OF THE MOUTH.

• SUBLINGUAL GLANDS:- UNDER

TONGUE.

SALIVARY GLANDS

PHARYNX & ESOPHAGUS

• THE PHARYNX TRANSPORT FOOD

FROM THE MOUTH TO THE

ESOPHAGUS.

• THE ESOPHAGUS IS A MUSCULAR

TUBE THAT CARRY FOOD FROM THE

PHARYNX INTO THE STOMACH.

• HAS AN UPPER ESOPHAGIAL

SPHINCTER AND A LOWER

ESOPHAGIAL SPHINCTER.

PHARYNX & ESOPHAGUS

THE STOMACH

• A POUCHLIKE PART OF THE DIGESTIVE SYSTEM THAT FUNCTION FOR STORAGE, MIXING AND DIGESTION OF FOOD.

MADE OF FOUR REGIONS:-

• CARDIAC – FUNDIC – BODY – PYLORIC

• ENTERANCE IS GUARDED BY THE LOWER ESOPHAGIAL SPHINCTER WHILE EXIT IS GUARDED BY THE PYLORIC SPHINCTER.

THE STOMACH

THE STOMACH

• A THICK FOLDED MEMBRANE COATED WITH MUCUS LINE THE STOMACH.

• GASTRIC GLANDS SECRETE DIGESTIVE ENZYMES & HYDOCHLORIC ACID.

• PEPSIN ENZYME START THE DIGESTION OF PROTEINS TO FORM SMALL PEPTIDES

• HYDROCHLORIC ACID ACTIVATE PEPSIN & KILL ANY MICROORGANISMS IN FOOD.

GASTRIC GLANDS

CONTROL OF GASTRIC

SECRETIONS

Pancreas

• Pancreas is a long, slender gland which lines transversely across the posterior abdominal wall.

• It lies behind the stomach at the level of Ist and 2nd lumbar vertebrae.

• Parts: pancreas consists of head, body and tail.

• Head lies in the C-shaped curve of duodenum

• Body lies in front of the bodies of lumbar vertebrae.

• Tail lies in contact with the hylum of spleen.

The Pancreas

G. Salaru, M.D.

THE PANCREAS

Structure

• The substance of pancreas contains a number

of lobules of secretory cells called “Acini”

• Inbetween the Acini, there are groups of

endocrine cells called “Islets of Langerhans”.

• Small ducts emerge from these lobules, these

ducts unite and reunite to form the “Pancreatic

duct”(duct of Wirsung)

• This duct begins at the tail and emerge from the

head of pancreas it enters the duodenum along

the common bile duct.

Secretions

• The secretions of pancreas can be classified into

– Exocrine secretion – digestive secretion

– Endocrine secretion – hormonal secretion

• THE EXOCRINE PANCREAS SECRETES

PANCREATIC JUICE INTO DUODENUM PART OF

THE SMALL INTESTINE.

• It is an alkaline fluid with a pH of around 8.

• Daily 1200-1500ml. Of pancreatic juice is

secreted.

• Pancreatic juice contains 97-98%wateralong

with the following digestive enzymes.

• PANCREATIC JUICE CONTAIN DIGESTIVE

ENZYMES & A BICARBONATE SOLUTION.

• PANCREATIC AMYLASE:- CARBOHYDRATES

DIGESTION - converts starch into maltose.

• PANCREATIC LIPASE:- FATS DIGESTION -

converts fats into fatty acids and glyserol.

• TRYPSIN:- PROTEINS DIGESTION - converts

proteins into aminoacids.

CONTROL OF PANCREATIC SECRETIONS

THE LIVER

• It IS THE LARGEST GLAND IN THE BODY.

• It lies in the upper part of abdominal cavity below the diaphragm and under the cover of lower ribs.

• Externally, the liver contains two lobes (a right lobe and a left lobe) and four surfaces-superior surface, inferior surface, anterior surface and posterior surface)

THE LIVER

• Internally the liver consists of a large number of

liver cells called lobules.

• Each lobules has a central vein or intralobular

vein.

• The connective tissue lying in between the

lobules contains the branches of – portal vein,

hepatic artery and bile duct.

• Liver secretes the bile is carried through bile

ducts which are formed by the union of biliary

canaliculi.

• The biliary canaliculi are small biliary channels

present inbeween the lobules of liver.

• The bile ducts from right and left lobes of liver unite to form common hepatic duct.

• The hepatic duct unites with cystic duct of gall bladder to form common bile duct.

• Later, the common bile duct unites with the pancreatic duct in the duodenum at a papilla called ampulla of vater.

FUNCTIONS:-

• CLEANS HARMFUL CHEMICALS, DRUGS AND DEAD CELLS FROM THE BLOOD.

• STORES FATS, GLYCOGEN, MINERALS & VITAMINS.

• SECRETES BILE THAT BREAKS THE LARGE FAT DROPS INTO SMALLER PARTICLES & HELP THEIR ENZYMATIC DIGESTION.

THE GALLBLADDER

• Gall bladder is a pear shaped storage sac for

bile.

• It is situated in the under surface of the right lobe

of liver.

• It consists of a – fundus, body and neck.

• Coats of gall bladder: gall bladder consists of

three coats. • Outer serous or peritoneal coat – which is continuous with

the peritoneum covering the liver.

• Middle muscular layer coat – made of unstriped muscles.

• Inner mucous coat – which is continuous with the lining of

bile ducts.

• Duct of gall bladder:

• The duct through which gall bladder opens

is called cystic duct – arises at neck of gall

bladder.

• The cystic duct unite with common hepatic

duct and forms common bile duct.

common bile duct joins with pancreatic

duct and opens into the duodenum.

• The sphincter present in the bile duct at

this termination in the duodenum is called

sphincter of Oddi.

Function of gall bladder

• BILE IS STORED IN THE

GALLBLADDER.

• WHEN FATTY FOOD ENTER

DUODENUM, CHOLECYTOKININ {CCK}

HORMONE IS SECRETED BY THE

INTESTINAL CELLS.

• {CCK} STIMULATES THE

GALLBLADDER WALLS CONTRACTION

TO EMPTY BILE INTO THE DUODENUM.

THE GALLBLADDER

THE SMALL INTESTINE • A LONG TUBE EXTENDING BETWEEN

THE STOMACH AND THE LARGE

INTESTINE.

• ENTRANCE IS GUARDED BY THE

PYLORIC SPHINCTER WHILE EXIT IS

GUARDED BY THE ILEOCECAL

SPHINCTER.

• CONSIST OF THREE PARTS:-

• DUODENUM – JEJUNUM – ILEUM

• MOST OF DIGESTION & ABSORPTION

OF FOOD OCCUR IN THE SMALL

INTESTINE.

THE SMALL INTESTINE

SMALL INTESTINE

HORMONES • GASTRIN:- STIMULATE GASTRIC

GLANDS SECRETION.

• CHOLECYSTOKININ {CCK}:-

INHIBIT GASTRIC GLANDS

SECRETION, STIMULATE PANCREATIC

SECRETION & GALLBLADDER

CONTRACTION.

• SECRETIN:- INHIBIT GASTRIC GLANDS

SECRETION & STIMULATE

PANCREATIC JUICE SECRETION.

SMALL INTESTINE ENZYMES

• MALTASE DIGEST MALTOSE TO GLUCOSE

• SUCRASE DIGEST SUCROSE TO GLUCOSE AND FRUCTOSE.

• LACTASE DIGEST LACTOSE TO GLUCOSE AND GALACTOSE.

• LIPASE DIGEST FATS TO FATTY ACIDS.

• PEPTIDASE DIGEST SMALL PEPTIDES TO SINGLE AMINO ACIDS.

ABSORPTION

THE LARGE INTESTINE

• EXTEND FROM THE ILEUM TO THE

ANUS AND IS MADE OF THREE

SEGMENTS:-

• CECUM – COLON – RECTUM.

• FUNCTION FOR ABSORPTION OF

WATER, MINERALS AND VITAMINS.

• ENTRANCE GUARDED BY THE

ILEOCECAL SPHINCTER WHILE THE

ANAL EXIST IS GUARDED BY

INTERNAL AND EXTERNAL ANAL

SPHINCTERS.

THE LARGE INTESTINE

THE RECTUM & ANAL CANAL

FOOD ENERGY