Unit 2 - Digestive System

8/10/2019 Unit 2 - Digestive System

1/51


2/51

In digestion, the macromolecules or biopolymers of foodare hydrolyzed to yield their corresponding monomers.

This process is facilitated by enzymes.

Thus the digestive system comprises the alimentary

,

food.

The digestive tract comprises various organs from mouth

to anus.


3/51

The functions of the digestive system include:

Motility

This refers to the movement of food through the digestive

tract through the processes of

Ingestion: Taking food into the mouth.

Mastication: Chewing the food and mixing it with saliva.

Deglutition: Swallowing food.

Peristalsis: Rhythmic, wavelike contractions that move food

through the gastrointestinal tract.


4/51

Secretion

This includes both exocrine and endocrine secretions.

Exocrine secretions:

Water, hydrochloric acid, bicarbonate, and many digestive

enzymes are secreted into the lumen of the gastrointestinal tract.

, ,

juice a day.

Endocrine secretions:

The stomach and small intestine secrete a number of hormonesthat help to regulate the digestive system.


5/51

Digestion

This refers to the breakdown of food molecules into their

smaller subunits, which can be absorbed.

Absorption

blood or lymph.

Storage and elimination

This refers to the temporary storage and subsequent

elimination of indigestible food molecules.


6/51


7/51

Mouth or Buccal cavity The opening of the oral cavity is bounded by the lips.

The lips are muscular folds covered internally by mucosa.

.

The inner walls of the cheeks are lined by moist stratified

squamous epithelium.

The lips and cheeks are useful in the process of

mastication and speech.


8/51


9/51

Tongue

It is a large muscular organ.

It is attached to the floor of the oral cavity.

The anterior part of the tongue is free.

A thin fold of tissue called the frenulum attaches the free end to thefloor of the mouth.

The tongue is divided into two parts by a groove called the terminal

sulcus.

About two thirds of the anterior surface is covered by papillae.

Some of them contain taste buds.


10/51


11/51


12/51

Teeth There are 32 teeth in the mouth of a human adult. These are

called as permanent teeth.

There are 4 different types of permanent teeth seen. This natureis known as heterodontism.

The types of teeth are incisors(8), canines(4), premolars(8)and molars(12).

Since the teeth in the right and left side of the mouth are mirrorimages of each other, the dental arrangement is represented asfollows.

( i 2/2 : c 1/1 : pm 2/2 : m 3/3 ) X 2


13/51


14/51


15/51

The dental formula is a shorthand way of indicating thenumbers and relative positions of the different types of

teeth.

The primary dentition consists of two incisors (I), one

canine (C), and two molars (M) on each side of each jaw,

and its dental formula is written as

Similarly, the permanent dentition [two incisors, one

canine, two premolars (PM), and three molars] is


16/51

Each toothconsists of

three regions.

Upper

crown

Middle neck

Basal root


17/51

The crown region has one or more cusps.

The tooth is made up of a calcified tissue called dentine.

substance called enamel.

The surface of the dentine in the root is covered with abonelike substance called cementum.

It helps to anchor the tooth in the jaw.


18/51

In the centre of the tooth there is a pulp cavity.

This cavity is also called as the root canal.

This canal contains blood vessels and nerves.

.

The teeth are set in sockets along the edges of the upper

and lower jaws.

This region of the jaw is covered by dense fibrous

connective tissue and stratified squamous epithelium. It is

called as the gingiva.


19/51


20/51

Salivary glands

These are scattered throughout the oral cavity.

Three pairs of glands are larger.

The Parotid glands are the largest. They are located just

an er or o e ear on eac s e o e ea .

The submandibular glands are found on the inferior borders of

the mandible.

The sublingual glands are the smallest. They lie immediately

below the mucous membrane in the floor of the mouth.


21/51

There are other numerous small, coiled, tubular glands in

the mouth.

They are

Lingual (tongue) gland

Palatine (palate) gland

Buccal gland

Labial (lips) gland


22/51


23/51

Functions

Tongue

Maneuvers food for mastication, shapes food into a bolus,

maneuvers food for deglutition, detects sensations for taste,

and initiates digestion of triglycerides

Salivary

glandsSaliva produced by these glands softens, moistens, anddissolves foods; cleanses mouth and teeth; initiates the

digestion of starch

Teeth Cut, tear, and pulverize food to reduce solids to smaller

particles for swallowing

Mouth

The functions of the tongue, salivary glands, and teeth, all

happen in the mouth. Additionally, the lips and cheeks keep

food between the teeth during mastication, and buccal

glands lining the mouth produce saliva

PharynxReceives a bolus from the oral cavity and passes it into the

esophagus


24/51

Oesophagus

This part of the digestive tube extends between the

pharynx and the stomach.

It is about 25 cm long.

It lies in the mediastinum of the thorax, anterior to the

vertebra and posterior to the trachea.

It passes through the diaphragm and ends at the

stomach.


25/51

The oesphagus has thick walls.

The inner wall is lined by a moist stratified squamous

epithelium.

regulate the movements of materials.

Esophagus receives a bolus from the pharynx and moves it

into the stomach; this requires relaxation of the upperesophageal sphincter and secretion of mucus.


26/51

Stomach

It is an enlarged sac like structure.

This sac found in the upper part of the abdomen ishorizontally placed.

It is divisible into two regions namely cardiac and pyloricstomachs.

The cardiac stomach is towards the left of the abdomen.

The oesophagus opens into the cardiac stomach through the

gastroesophageal or cardiac opening.


27/51


28/51

A part of the stomach to the left of the cardiac region is

the fundus.

The largest part of the stomach is the body.

The body narrows to form the pyloric region.

The pyloric opening between the pylorus and intestine is

surrounded by a ring of muscles called the pyloricsphincter.


29/51


30/51

1. Mixes saliva, food, and gastric juice to form chyme.

2. Serves as reservoir for food before release into smallintestine.

3. Secretes Gastric juice, which contains HCl (kills bacteria and

denatures protein)

Pepsin (begins the digestion of proteins)

Intrinsic factor (aids absorption of vitamin B12) Gastric lipase (aids digestion of triglycerides).

4. Secretes gastrin into blood.


31/51

Small intestine

It consists of three parts: the duodenum, thejejunum and

the ileum.

The entire small intestine is about 6m long.

Duodenum

It is about 25 cm long.

It curves within the abdominal cavity and completes nearly

180 degree arc. Liver and pancreas are associated with the duodenum.


32/51


33/51


34/51

Jejunum and ileum

The jejunum and ileum are 2.5m. and 3.5m in lengthrespectively.

These two are similar in structure to the duodenum.

However there is a radual decrease in the diameter of the

small intestine.

The junction between the ileum and the large intestine is theileocaecal junction.

It has a ring of smooth muscles forming a sphincter, and a oneway ileocaecal valve.


35/51


36/51

Functions of the Small Intestine

1. Segmentations mix chyme with digestive juices and

bring food into contact with mucosa for absorption;

peristalsis propels chyme through small intestine.

. , ,

lipids; begins and completes digestion of nucleic acids.

3. Absorbs about 90% of nutrients and water that pass

through digestive system.


37/51

Liver

It is the largest visceral organ.

It weighs about 1.36 Kg.

The liver consists of two major left and right lobes

It consists of two minor lobes caudate and quadrate.


38/51


39/51

The bile secreted by the liver gets collected in the gall

bladder.

There are two hepatic ducts and they unite to form a single

duct.

The common hepatic duct is joined by the cystic duct

from the gall bladder to form the common bile duct.

It empties into the duodenum.


40/51

Gall bladder

It is a sac like structure on the inferior surface of the liver.

t s a out cm ong an cm w e.


41/51

Pancreas

It is a complex organ.

It is composed of both endocrine and exocrine tissues.

The endocrine part of the pancreas consists of pancreatic

islets.

They produce insulin and glucagon.


42/51

The exocrine part of the pancreas consists of acini.

They produce digestive enzymes.

The ancreas consists of several lobules.

The ducts from the lobules unite to form the pancreatic duct.

It joins the common bile duct at the hepatopancreaticampulla.


43/51


44/51

Functions

Pancreas

Pancreatic juice :

Buffers acidic gastric juice in chyme

Stops the action of pepsin from the stomachCreates the proper pH for digestion in the small

intestine

Participates in the digestion of carbohydrates,

proteins, triglycerides, and nucleic acids.

Liver

Produces bile, which is required for the

emulsification and absorption of lipids in the

small intestine.

GallbladderStores and concentrates bile and releases it into

the small intestine.


45/51

Large intestine

Caecum

It is the proximal end of the large intestine.

The caecum is about 6 cm in length.

Attached to the caecum is a small blind tube about 9 cm long.

It is called the vermiform appendix.


46/51

Colon

It is about 1.5 - 1.8 m long.

,

transverse colon, descending colon and sigmoid colon.

The sigmoid colon extends into the pelvis and ends at the

rectum.


47/51


48/51

Functions of the Large Intestine

1. Haustral churning, peristalsis, and mass peristalsis drivecontents of colon into rectum.

2. Bacteria in large intestine convert proteins to amino acids,break down amino acids, and produce some B vitamins andvitamin K.

3. Absorbing some water, ions, and vitamins.

4. Forming feces.

5. Defecating (emptying rectum).


49/51

Rectum

It is a straight, muscular tube that extends from the

sigmoid colon to the anal canal.

Anal canal

It s t e last 2cm o t e gest ve tract.

It ends at the anus.

The canal has two sphincters, namely the internal anal

sphincter and the external anal sphincter.


50/51


51/51

Documents

Unit 2 - Digestive System