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AUTHOR:-

M HUMAYYUN JAMIL

REFERENCE:-

ESSENTIALS OF MEDICAL

PHYSIOLOGY

Introduction to digestive system

Mouth and salivary glands

Stomach

Pancreas

Liver

Large intestine

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Process by which food is broken down into

simple chemical subctances that can be

absorbrd and used by the body

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Digestive Syestum is accomplished by

mechanical and enzymatic breakdown of

food particles into smaller food particles

A normal young healthy consumes about

1kg of solid diet and 1-2 L of liquid daily

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Intake of food

Breaking them into smaller particles

Transport of smaller particles to all parts of

body

Secretion of necessary enzymes

Digestion of food particles

Absorption of digestive products

Removal of unwanted substances from

body

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GIT consist of 4 major layers

1.mucus or mucosa layer

2.submucus layer

3.muslar layer

4.serous layer

GIT consist of 4 major layers

1.mucus or mucosa layer

2.submucus layer

3.muslar layer

4.serous layer

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Tubular structure extending from oral cavity to anus is called GIT

It is about 30 feet

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It is innermost layer of GIT

It consist of further 3 layers

EPITHELIAL LAYER

It is made up of connective tissues

Epithilial layer of lips,oral cavity,pharyunx

and esophagus has squamous epithelial

cells

Epithelial layer of remaining part of GIT

has collomunar epithelial cells

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It is also made up of connective tisssues

It consist of

lymphocytes,macrophages,fibroblasts,esino

phills

MUSCULAR MUCOSA• IT CONSIST OF SMOOTH MUSCLES

• IT IS ABSENT IN MOUTH AND PHARYNX

• IT IS PRESENT FROM ESOPHAGUS TO ONWARD

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IT IS ALSO ABSENT IN MOUTH AND PHYRYNX

IT IS PRESENT FROM ESOPHAGUS TO ONWARD

IT CONSIST OF CONNECTIVE TISSUES

IT HAS SMOOTH MUSCLE FIBERS AND OTHER LOOSE COLLEGEN FIBERS

IT HAS BLOOD VESSELS,L YMPHATIC VESSEL AND NERVE PLEXUS

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Muscular layer of lips,tounge,mouth and

pharynx has skeltal muscle fibers

Muscular layer of esophagus has both

skeltal and smooth muscle fiers

Muscular layer of small intestine and

stomach has smoth muscle fibers

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Serous layer is outermost layer

Serous layer also consist of connective

tissues

It is found in small intestine and stomach

While fibrous layer is found in esophagus

and pharynx

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PRIMARY ORGANS SECONDARY ORGANS

Esophagus

Pharynx

Small intestine

Large intestine

stomach

Oral cavity

Tounge

Teeth

Glands

Liver

Gall bladder

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Oral cavity is starting point of GIT

Oral cavity consist of;

Mouth

Toung

Lips

Teeth

Palate

Oral cavity opens both anteriorly and

posteriorly

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Taking in food

Griding of food

Lubrication of food

Mixing of food with saliva to form bolus

Transport of food particles to all parts of

body

Role in speech

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SALIVA IS SECRETED MAINLY BY FOLLOWING MAJOR GLANDS

SALIVA IS SECRETED

MINORLY BY

PAROTID GLANDS

SUBMANDIBULAR

GLANDS

SUBLINGUAL GLANDS

LABIAL GLAND

LINGUAL SEROUS GLAND

Lingual mucous gland

Palatal gland

Buccal gland

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It is larges gland

Its wight is 20-30 gm

It is located on side of face below and

infront of ear

Its secretion is poured into mouth against

the upper second molar teeth through

STENSON DUCT which is 35-40 mm long

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Its wight is 8-10 gm

It is located in submaxillary triangle medial

to mandible

Saliva from these glands is emptied into

the oral cavity by Wharton duct, which is

about 40 mm long. The duct opens at the

side of frenulum of tongue, by means of a

small opening on the summit of papilla

called caruncula sublingualis.

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It is smallest gland Its weight is 2-8 gm It is located in mucosa on the flour of mouth It pours its saliva into mouth through 5-15

smaller ducts called duct of ravinus which open on small papilla beneath tounge

One of the larger duct is BARTHOLIN duct

It drains the anterior part of the gland and opens on caruncula sublingualis near the opening of submaxillary duct.

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Volume of saliva; 1000-1500mL/Day

PH of saliva; 6.35-6.85

Gravity of PH; 1.002-1.012

Tonicity; hypotonic to plasma

Reaction; acidic

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Parotid glands; 25%

Submandibular gland; 70%

Sublingual gland; 5%

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Prepration of food for swallowing

Appreciation of taste

Digestive function

Cleaning and protective function

Excretory function

Water ragulation

Maintinance of temperature

Social functions

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STOMACH AND GASTRIC GLANDS

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Stomach is a muscular, hollow organ

located in the upper left abdominal quadrant,

immediately below the diaphragm.

located between the esophagus and small

intestine

Volume of empty; 5o ml but capable of

extending upto 4 L

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Outer serous layer; Formed by peritoniunMuscular layer; divided into

oblique,circular and longitudinal layerSubmuscus layer; formed by blood

vessels, lymphatic vessels and messienernerve plexus

Inner muscular layer; it has small gastric pits where gastric glands open. Lined by mucussecreting columnar epithelial cells.

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Cardiac; upper part where esophagus ends

and has a sphincter called cardiac sphincter

Fundic region; a small domeshaped structure.

It is elevated above the level of esophageal

opening.

Body; Centeral region which encloses 80%

volume

Pyloric region; lower ending region that opens

to duedenum.It is further divided to

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Antrum; where body ends

Pyloric canal; lower tube like portion

Point where fusion of antrum and pyloric

canal takes place is called incisura

angularis

Pyloric region also has a sphincter called

pyloric sphincter

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Fundic glands; glands found in fundic

region

Cardiac glands; found in cardiac region

Pyloric glands; found in pyloric region

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It is long tubular gland It has following cells

chief cellsparietal cellsmucus cellsEC cellsECL cells

It is diff. from other glands due to parietelcells because they pour their secretion into lumen through their canaliculus

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It is short and tortous

It has following cells

mucus cells

goblet cells

EC cells

ECL cells

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It is also short and tortous

It has following cells

chief cells

mucus cells

EC cells

ECL cells

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99.5 % WATER .5 % SOLID

Organic substances

Inorganic subctances;

mucus

intrinsic factor

Enzymes;

pepsin

renin

urase

gelatinin

gastric lipase

Inorganic substances

sodium

calcium

potasium

bicorbonates

phosphate

sulphur

HCL

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.5

further

consist

of

Ph; 0.9-1.2

Volume; 1200-1500 ml/day

Specific gravity; 1.002-1.004

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Mechanical function

Digestive function

Hemopoitic function

Protective function

Excretory function

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i.Storage Function; Food is stored in the stomach for a long period, i.e. for 3 to 4 hours and emptied into the intestine slowly. The maximum capacity of stomach is up to 1.5 L. Slow emptying of stomach provides enough time for proper digestion and absorption of food substances in the small intestine.

ii.Formation of Chyme; Peristaltic movements of stomach mix the bolus with gastric juice and convert it into the semisolid material known as chyme.

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EXCRETORY FUNCTION:Many substances like toxins, alkaloids and metals are excreted through gastric juice. HEMOPOIETIC FUNCTION:Intrinsic factor of Castle, secreted by parietal cells of gastric glands plays an important role in erythropoiesis. It is necessary for the absorption of vitamin B12 (which is called extrinsic factor) from GI tract into the blood.

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Gastric juice acts mainly on proteins. Proteolytic enzymes of the gastric juice are pepsin and rennin Gastric juice also contains some other enzymes like gastric lipase, gelatinase, urase and gastric amylase.

Pepsin ;Pepsin is secreted as inactive pepsinogen. Pepsinogen is converted into pepsin by hydrochloric acid. Optimum pH for activation of pepsinogen is below 6. Pepsin converts proteins into proteoses, peptones and polypeptides. Pepsin also causes curdling and digestion of milk (casein).

Gastric Lipase ;Gastric lipase is a weak lipolytic enzyme It is active only when the pH is between 4 and 5 and becomes inactive at a pH below 2.5 and hydrolyses tributyrin into faaatyacids and glycerol

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i.Gelatinase: Degrades type I and type V gelat in and

type IV and V collagen (which are proteo glycans in

meat) into peptides

ii.Urase: Acts on urea and produces ammonia

iii.Gastric amylase: Degrades starch (but its action is

insignificant)

iv. Rennin: Curdles milk (present in animals only)

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FUNCTION OF MUCUS Mucus is a mucoprotein, secreted by mucus neck

cells of the gastric glands and surface mucus cells in fundus, body and other parts of stomach. It protects the gastric wall by the following ways:

Mucus: i. Protects the stomach wall from irritation or

mechanical injury, by virtue of its high viscosity. ii.Prevents the digestive action of pepsin on the

wall of the stomach, particularly gastric mucosa.

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According to Davenport theory, hydrochloric acid secretion is an active process that takes place in the canaliculi of parietal cells in gastric glands. The energy for this process is derived from oxidation of glucose. Carbon dioxide is derived from metabolic activities of parietal cell. Some amount of carbon dioxide is obtained from blood also. It combines with water to form carbonic acid in the presence of carbonic anhydrase. This enzyme is present in high concentration in parietal cells. Carbonic acid is the most unstable compound and immediately splits into hydrogen ion and bicarbonate ion. The hydrogen ion is actively pumped into the canaliculus of parietal cell. Simultaneously, the chloride ion is also pumped into canaliculusactively. The chloride is derived from sodium chloride in the blood. Now, the hydrogen ion combines with chloride ion to form hydrochloric acid. To compensate the loss of chloride ion, the bicarbonate ion from parietal cell enters the blood and combines with sodium to form sodium bicarbonate. Thus, the entire process is summarized as (Fig. 38.4): CO2 + H2O + NaCl → HCl + NaHCO3

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Pepsinogen is synthesized from amino acids in the

ribosomes attached to endoplasmic reticulum in chief

cells. Pepsinogen molecules are packed into zymogen

granules by Golgi apparatus. When zymogen granule is

secreted into stomach from chief cells, the granule is

dissolved and pepsinogen is released into gastric juice.

Pepsinogen is activated into pepsin by hydrochloric acid.

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It is a dual organ

It has both endocrine and exocrine

function

Endocrine is to produce harmones

Exocrine is to secrete pancreatic juice

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Volume; 500-800 ml/day

Ph; 8-8.3

Specific gravity; 1.010-1.018

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WATER 99.9% SOLID .5%

Organic subctances

Sodium

Calcium

Potassium

Magnisium

Phosphate

Bicarbonate

OTHER

INORGANIC

SUBSTANCE

S;

Albumin

Glubulin

ENZYMES;

trypsin

Chympotry

psin

Carboxype

ptidase

Elastases

Nucleases

Collagenas

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Digestion of protein

Digestion of lipids

Digestion of carbohydrates

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Lipid is a dual organ having both secretory

and excretory function

Largest gland

Weighs about 1.5 kg

Located in upper right side of abdominal

cavity beneath diaphgram

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Hepatic lobes

Hepatic lobules

Hepatocytes

Hepatic plates

Portal triads

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Biliary syestum is made of;

Gallblader

Extrahepatic bile

duct

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Right +left hepatic duct=common

hepatic duct

Common hepatic duct+cystic duct

=common bile duct

Common bile duct+pancreatic

duct=ampula of vater

Liver recives blood supply of about

1500ml/min. through 2 sources

HEPATIC ARTERY:

It arises fromm aorta

Supplies oxygenated blood

PORTAL VEIN;

Formed by superior mesenteric vein and

sphlencic vein

Oxygen content is less in portal blood

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WATER---97.6% SOLID---2.4%

Organic subctances;

Bile salts

fatty acids

Bile pigments

Lecithin

Mucin

cholesterol

Inorganic subtances

Sodium

Calcium

Potassium

Chloride

Bicarbonte

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VOLUME; 800-1200ml/day

REACTION; alkaline

PH; 8-8.6

SPECIFIC GRAVITY; 1.010-1.011

CLOUR; golden yellow or green

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Starts from pyloric sphincter upto ileoceacl

valve

About 6 m long

Less in diameter

Small intestine consists of three portions:

1. Proximal part known as duodenum

2. Middle part known as jejunum

3. Distal part known as ileum.

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Intestinal valve has small projections called villi with height 1mm and diameter less than 1mm covered by cells called enterocytes

Each enterocyte has further minute hair like projections called microvilli

Within each villus, there is a central channel called lacteal, which opens into lymphatic vessels. It contains blood vessels also

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simple tubular glands of intestinedo not penetrate the muscularis mucosaopen into the lumen of intestine between the

villi lined by columnar cells.Types of cells interposed between columnar

cells of intestinal glands: 1. Argentaffin cells or enterochromaffin cells, which secrete intrinsic factor of Castle2. Goblet cells, which secrete mucus3. Paneth cells, which secrete the cytokines called defensins.

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Volume : 1800 mL/day

Reaction : Alkaline

pH : 8.3

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„1. DIGESTIVE FUNCTION

2. PROTECTIVE FUNCTION

3. ACTIVATOR FUNCTION

4. HEMOPOIETIC FUNCTION

5. HYDROLYTIC PROCESS

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1. DIGESTIVE FUNCTION

2. ABSORPTIVE FUNCTION

3. ACTIVATOR FUNCTION

4. HEMOPOIETIC FUNCTION

5. HYDROLYTIC PROCESS

6. HORMONAL FUNCTION

7. SECRETORY FUNCTION

8. MECHANICAL FUNCTION

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It extends from ileocecal valve up to intestine

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Cecum with appendix

Ascending colon

Transverse colon

Descending colon

Sigmoid colod

Rectum

Anal colon

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Serous layer; formed by peritonium

Muscular layer; further devided to outer

longitudinal and inner circular layer

Submucus layer: not well defined

Mucus layer; it has crypts of liberkuhn and

mucussecreating glands

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Solid .5%

Inorganic subctances

Albumin

Mucin

Globulin

urea

Organic subctances

Sodium

Calcium

Potassium

Phosphate

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Water - 95.5%

Digestive enzymes

are absent

Neutralization of AcidsStrong acids formed by bacterial action in large intestine

are neutralized by the alkaline nature of large intestinal juice. The alkalinity of this juice is mainly due to the presence of large quantity of bicarbonate. LubricationActivity Mucin present in the secretion of large intestine lub- ricates the mucosa of large intestine and the bowel contents, so that, the movement of bowel is facilitated. Mucin also protects the mucus membrane of large intestine by preventing the damage caused by mechanical injury or chemical substances.

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„1. ABSORPTIVE FUNCTION Large intestine plays an important role in the absorption of various substances such as: i. Water ii. Electrolytes iii. Organic substances like glucose iv. Alcohol v. Drugs like anesthetic agents, sedatives and steroids. „2. FORMATION OF FECESAfter the absorption of nutrients, water and other substances, the unwanted substances in the large intestine form feces. This is excreted out. „3. EXCRETORY FUNCTION Large intestine excretes heavy metals like mercury, lead, bismuth and arsenic through feces.

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4. SECRETORY FUNCTION Large intestine secretes mucin and inorganic substances like chlorides and bicarbonates.5. SYNTHETIC FUNCTION Bacterial flora of large intestine synthesizes folic acid, vitamin B12 and vitamin K. By this function, large intestine contributes in erythropoietic activity and blood clotting mechanism.

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Diarrhea

Constipation

Appendicitis

Ulcerative cilitis

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