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Transcript
DIGESTIVE
SYSTEM
Dr. Manpreet Kaur
Dept of Home Science,
PGGCG-42, Chandigarh.
What is Digestion?
Digestion is a process by which the complex and unabsorbable food materials like carbohydrates, proteins
and fats are broken down by mechanical and chemical
processes to simpler forms i.e. mono saccharides,
amino acids & fatty acids & glycerol that can be
absorbed through the intestines and then utilized by
the cells for various activities.
Organs of Digestive System

Gastrointestinal tract (GIT) –
continuous passageway which
contains the food from the time it
enters the body, until it leaves;
organs include:


mouth (oral cavity), pharynx, esophagus, stomach,
small intestine, large intestine, rectum, anus
Accessory organs - participate in
digestive processes; organs
include:

teeth, tongue, salivary glands, liver, gall bladder,
pancreas
Mouth (Oral Cavity)

Regions include the vestibule & oral cavity proper

Roof comprised of hard & soft palate; floor primarily comprised of tongue

Mucosa of stratified squamous epithelium (non-keratinized)

Joins the pharynx at the fauces
THE TONGUE
Organ of taste
Mastication of food
Swallowing of food
Articulation
Tooth
Crown – dentin
surrounded by enamel,
has hollowed pulp
cavity.
 Neck – at gingival
border
 Root – within mandible
& maxilla, has hollowed
root canal with blood
vessels & nerves.

TEMPORARY & PERMANENT TEETH
Salivary Glands
Are three pairs
which secrete
saliva
 It is clear alkaline
fluid made of H2O,
salts & “salivary
Sublingual
amylase”
gland

Submandibular duct
Parotid
duct
Parotid
gland
Submandibular
gland
PHARYNX



Common passageway for air & food
Oropharynx & laryngopharynx lined with stratified squamous
epithelium
Uvula & epiglottis protect airway when swallowing (“deglutition”) to
avoid choking
Nasopharynx
Uvula
Oropharynx
Epiglottis
Laryngopharynx
ESOPHAGUS

Muscular 10” tube running from pharynx, posterior to trachea, down thoracic cavity, through
“esophageal hiatus” of diaphragm, to lower esophageal (a.k.a. cardiac) sphincter at junction
of stomach

Functions in “deglutition” through action of peristalsis

Mucosa is simple squamous epithelium

Variations in muscles– begins as skeletal voluntary muscle at upper 1/3, mixed skeletal &
smooth muscle in middle, smooth involuntary muscle by lower 1/3
THE STOMACH
Functions of the Stomach




Bulk storage of undigested food
Mechanical breakdown of food
Secretion of gastric juice (water, HCl, mucin, pepsin &
renin) to digest food
Production of intrinsic factor which helps in absorption of
vitamin B12
Liver

Largest gland in the body weighing 1550 gms.

Located on the right side of the body under the diaphragm

Consists of four surfaces suspended from the diaphragm and abdominal wall by the falciform ligament

Hepatic artery and portal vein enter the liver & bile duct leaves the liver.


Liver is built of lobules which have their own blood supply & small bile ducts which unite to form common bile
duct.
Connected to the gall bladder via the common hepatic duct
THE DUODENUM AND RELATED ORGANS
GALLBLADDER
8-10 cm long pouch greenish in colour.
 It has three coats –

 Outer
peritoneal coat is continuous with peritoneum of
liver.
 Muscular coat helps in contraction.
 Inner mucous coat

It stores bile which is released when required for
digestion
FUNCTIONS OF LIVER







Secretion of bile
Storage of glycogen
Formation of urea
Production of plasma proteins
De-saturation of fats
Storage of vitamin B12 and iron
Production of heat
Small Intestine



Connects stomach to large intestine;
15-20’ long; 1” diameter; held together
in abdominal cavity by “mesentery
proper”
Cite for completion of chemical
digestion & absorption of nutrients
comprised of three regions:

Duodenum – 10” in length; receives chyme from
stomach, secretions from liver, gallbladder &
pancreas

Jejunum – 8’ long; most digestion & absorption
occurs here

Ileum – 12’ long; connects to ceacum of large
intestine at ilioceacal valve (sphincter)
Small Intestine

Finger like projections - villi lined with “absorptive cells” - mucosal epithelium of simple
columnar epithelium with microvilli “brush border” which increases the absorptive
surface by 5 times.

Submucosa of each villus contains a capillary network & a “lacteal” (lymphatic capillary)
for absorption of nutrients

Intestinal glands( glands of liberkuhn) within intestinal crypts secrete “intestinal juice” –
provides watery medium to keep enzymes & digestive products in solution for help with
absorption
Intestinal crypts
containing intestinal
glands
Villi
Large Intestine



Absorption of water and salts.
Excretion of faeces which consists of 50%
Dead bacteria and 50% cellulose.
Transverse
colon
Ascending
colon
Ileocecal
sphincter
Ceacum
Vermiform
appendix
Descending
colon
ileum
Rectum
Anus
Sigmoid colon
Digestion, Absorption, Transport

Digestion

Breakdown of food molecules for absorption into
circulation



Mechanical Process: breaks large food particles to small with teeth,
contraction of stomach walls & peristaltic movements.
Chemical Process: breaking of covalent bonds by digestive enzymes
Absorption and transport

Molecules are moved out of digestive tract and into
circulation for distribution throughout body
Ingestion

Mouth

mechanical digestion

teeth


breaking up food by cutting & grinding
chemical digestion

saliva




salivary amylase (ptylin)
 enzyme digests cooked starch
mucin
 slippery protein (mucus) assists in passage of food
 protects soft lining of digestive system
 lubricates food for easier swallowing (bolus)
buffers
 neutralizes acid to prevent tooth decay
anti-bacterial chemicals
 kill bacteria that enter mouth with food
Swallowing (& not choking)

Epiglottis
flap of cartilage
 closes trachea (windpipe) when swallowing
 food travels down oesophagus


Peristalsis

involuntary muscle contractions to move food
along the pharynx & oesophagus.
Stomach

Food Storage
 can
stretch to fit ~2L food
 Gastric
 HCl
Juice
= pH 2
kills bacteria
 Absorbs iron

 Water

Liquifies food
 Intrinsic

factor
Controls absorption of Vit B12
 Mucus
 chemical
digestion
 Pepsinogen
breaks down proteins into peptones &
proteoses
 Renin
 Converts insoluble caseinogen into soluble
casein

Duodenum

1st section of small intestines
 acid
food from stomach
 mixes with digestive juices from:
 pancreas
 liver
 gall bladder
Pancreatic Juice






Non viscous watery fluid. Contains Na, K, HCO3 & water. Bicarbonate lowers
pH inhibiting pepsin and providing proper pH for enzymes
Enzymatic portion:
 Trypsinogen
 Chymotrypsinogen
 Procarboxypeptidase,
 Pancreatic amylase
 Pancreatic lipases (Steapsin)
Interaction of duodenal and pancreatic enzymes.
 Enterokinase from the duodenal mucosa activates trypsinogen to trypsin.
 Trypsin activates chymotrypsinogen to chymotrypsin
 Trypsin activates procarboxypeptidase to carboxypeptidase.
Trypsin, chymotrypsin and carboxypeptidase digest proteins to peptones &
polypeptides.
Pancreatic amylase continues digestion of starch to maltose, dextrins & glucose
Pancreatic lipase digests lipids to fatty acids & glycerol.
Intestinal Juice







Clear yellowish fluid which contains water, salts and enzymes.
Enzymatic portion:
 Aminopeptidase
 Dipeptidase,
 Maltase
 Sucrase
 Lactase
Peptidases digest polypeptides, dipeptides & tripeptides into amino acids
Maltase converts disaccharide maltose into two units of glucose
Sucrase converts disaccharide sucrose into glucose & fructose
Lactase converts milk sugar, lactose into glucose & galactose
All carbohydrates get converted into simple sugars, proteins into amino acids
and fats to fatty acids & glycerol and are absorbed through villi in jejunum &
ileum.
Organs of Digestive System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Large Intestine





Solid materials pass through
the large intestine.
These are undigestible solids
(cellulose).
Water absorbed.
Vitamins K and B are
reabsorbed with the water.
Rectum- solid wastes exit the
body.