a. Digestion and Absorption

ISC 12>CONTENT>STRUCTURE AND FUNCTION OF ANIMALS>1. DIGESTION AND ABSORPTION

SCOPE OF SYLLABUS
Calorific value of carbohydrates, proteins and fats per gram;
Structure and functions of the digestive organs and their associated glands,
Types of dentition (thecodont, heterodont, diphyodont) and dental formula of human;
Diagram of the digestive system with correct position of the organs and the associated glands;
Diagrammatic representation of T.S. of gut showing the four layers - histology of individual organs not required;
Physiology of digestion and absorption of food;
definition of bolus, peristalsis, deglutition, emulsification; assimilation of digested food;
disorders of the digestive system – Protein Energy Malnutrition ( PEM), indigestion, constipation, vomiting, jaundice,diarrhoea.

NUTRITION

PROCESS OF OBTAINING FOOD BY LIVING BEINGS, ITS DIGESTION AND UTILIZATION FOR ENERGY.

AUTOTROPHS

Organisms that synthesize organic substances from inorganic substances.

phototrophs
chemotrophs

HETEROTROPHS

Organisms that use chemical energy of organic compounds synthesized by other organisms.

holozoic
saprozoic
parasitic

Intracellular digestion

Food is digested inside the cell- eg. Amoeba, paramoecium.

Extracellular digestion

Food is digested in the alimentary canal- outside the cells.eg. earthworm, fishes, man

Watch the video and answer the following questions-

Name the important organs involved in digestion.
Mention the glands associated with digestion.
Why are enzymes important for digestion?
What according to you is the most important part of the digestive system?
If you had to change something in the digestive system to improve its working what would you change and why?
What is the mesentry and why is it important?

THE HUMAN DIGESTIVE SYSTEM

Diagram of the digestive system with correct position of the organs and the associated glands;

HOW TO DRAW THE DIAGRAM

THE DIAGRAM

PARTS OF THE DIGESTIVE SYSTEM AND THEIR FUNCTIONS

Structure and functions of the digestive organs and their associated glands,

1. MOUTH AND BUCCAL CAVITY

The mouth is a transverse slit like opening bounded by two soft movable lips.

Buccal cavity is bound by-
1. Above- Palate

roof of the buccal cavity has two parts - hard palate with rugae and posterior part the soft palate that makes swallowing easier.
small flap the uvula or velum palati closes the internal nares during swallowing of food bolus.

2. Below- throat
3. Sides- jaws

Inside the buccal cavity is present a muscular tongue and teeth arranged on the jaws.

TONGUE

Is a skeletal muscle, helps to moves food in mouth, and to taste.
Taste buds- have papillae

Fungiform - mushroom shaped
Filliform - thread like
Circumvalate - inverted V at the posterior

Taste regions

Sweet-tip of the tongue
Salt- on the sides
Bitter- on the posterior part

Functions-

Helps in ingestion and tasting food
For swallowing
Helps in speech

Types of dentition (thecodont, heterodont, diphyodont) and dental formula of human;

TEETH

http://www.student.loretto.org/humanbiology/BioLinks/chp5/media/c236f1_0.gif

FOUR types of teeth- incisors, canines, premolars, molars
The human teeth is

Heterodont: Humans have four types present. Incisors, canines, premolars and molars
Thecodont: The neck and root are held in a bony socket.
Diphyodont: There are two sets of teeth. The milk teeth are replaced by permanent teeth.

L.S.of molar tooth

Draw the diagram

Competitive focus-Dental formula

Representation of the arrangement of human teeth.

http://www.merriam-webster.com/art/med/dental.gif

dentalformulae
dentalanatomy

http://media.tiscali.co.uk/images/feeds/hutchinson/ency/c00764.jpg

2. PHARYNX

It is a common passageway for air and food.
It participates in swallowing
It has

Two nasal openings
Two openings for Eustachian tubes
Gullet- the opening of the oesophagus
Glottis opening of the larynx or trachea
Opening of buccal cavity into the pharynx.

It has three parts-

Nasopharynx – nasal chamber
Oropharynx – behind buccal cavity
Laryngopharynx- lowest part with two openings- glottis and gullet.

3. OESOPHAGUS

Oesophagus is a long tube starting from the pharynx to the stomach.
The opening of the oesophagus from the pharynx is called the gullet.
It has a sphincter- upper oesophageal sphincter.
The opening of the oesophagus to the stomach is guarded by lower oesophageal sphincter or the cardiac sphincter.

Structure: mix of skeletal and smooth muscle
Mucus secreting cells: assist passage of food
Food motility: gravity and peristalsis

Peristalsis- contraction and relaxation of muscles which propagates in a wave down the muscular tube.

4. STOMACH

Large, muscular, somewhat J shaped sac, occupying the upper left part of the abdominal cavity.
Two regions- Cardiac and Pyloric.
Shows the presence of longitudinal folds called rugae.
Functions:
Food storage, digestion, regulation of delivery.
Produces gastric juice for digestion.

Hydrochloric acid: produces a pH of about 2, breaks down large bits of food.
Intrinsic factor; needed to absorb Vitamin B12
Mucus: protects stomach lining from acid.
Pepsinogen: with acid, begins protein breakdown.

Gastrin: hormone secreted for stimulating digestion.

Layers of the stomach wall

http://www.daviddarling.info/images/stomach.jpg

http://www.rivm.nl/interspeciesinfo/Images/stomach-figure-2_tcm75-26457.gif

Stomach-innerlayers

What is heartburn or acidity?

Heartburn or pyrosis

When the cardiac sphincter fails to close fully, the acidic chyme squeezes into the oesophagus.
This irritates the lining of oesophagus and causes heartburn.

CARDIAC SPHINCTER
It is less effective in infants hence regurgitation is more common among infants.

SMALL INTESTINE

Small intestine consists of

Duodenum- 10 inches
Jejunum- 8 feet
Ileum- 12 feet

Duodenum- complete digestion takes place here.

Receives enzymes from the pancreas and bile from the liver.

Jejunum- No digestion takes place here.
Ileum- absorption of digested food takes place here.

Has villi and microvilli for increasing the surface area

Functions of the small intestine:
Digestion:
Neutralize acid from stomach,
Add digestive enzymes and bile,
breaks down proteins, carbohydrates and lipids to absorbable materials
Absorption: 95% of food is absorbed here.
Structure
Mucosa adaptations: villi containing blood capillaries and lacteal.
Cells of villi have small projections - microvilli.

Villi in the small intestine

Small Intestine as principle site for absorption

5-6m long- enough time for digestion and absorption.
Inner wall thrown into folds - increases the surface area for absorption.
Villi and microvilli- further increase the surface area.
Lacteals and blood vessels- facilitates easy absorption and transportation.
Single layered epithelium- for easy diffusion of digested substances.

LARGE INTESTINE

About 5-6 feet long and 6 cm diameter
Divided into caecum, colon and rectum
Opening of the small intestine inoto caecum has valve- ileocaecal valve

Functions-

Absorption of water in the food
Secretion of mucus
Egestion of undigested waste

ASSOCIATED GLANDS

Salivary glands

Secretion-Saliva
Source: Parotid, sub-maxillary, sub-lingual
Composition: mucin, salivary amylase, bicarbonate, lysozyme.

Functions:

Ptyalin- starch splitting enzyme
Mucus- mixes with food and makes it soft for easy digestion.
Polysaccharidase- dissolves the bacterial cell wall.

Gastric glands

Simple or branched tubular glands are present in the mucosa of the stomach.-
Gastric juice.
Cardiac glands- secrete mucus
Pyloric glands- secrete mucus
Fundic glands four types of cells

Chief cells or peptic cells- pepsinogen, prorennin and gastric lipase.
Oxyntic cells- HCl
Goblet cells- mucus
Argentaffin cell- serotonin
Endocrine cells- gastric hormone

Gastric enzymes- pepsinogen, prorennin and gastric lipase

Intestinal glands

Microscopic glands present in the mucosa of small intestine.

Crypts of Lieberkuhn- multicellular, straight, tubular glands present throughout the mucosa. Secrete digestive enzyme and mucus.

Brunner’s glands- compound tubular glands, found in the duodenum. Secrete alkaline watery juice.

Intestinal secretion- the secretions from the intestinal glands is called succus entericus

http://1.bp.blogspot.com/_qW0F6VNbvlM/TS09u0PKvaI/AAAAAAAAACY/RH1zN0JC10Y/s320/Intestinal+gland.png

Intestinal enzymes

Carbohydrate digesting enzymes

Intestinal amylase
Maltase
Sucrase
Isomaltase
Lactase
Limit dextrase

Protein digesting enzymes

Enterokinase
Aminopeptidase
Dipeptidase
Tripeptidase
Nuclease

Fat digesting enzymes

Intestinal lipase

Pancreas

Pancreas is a diffused leaf shaped gland.
It is formed of exocrine part and endocrine part. Exocrine part is made up of lobules or acini.
Acinus is formed of glandular acinous cells.
These cells secrete pancreatic juice.
Enzymes in the pancreatic juice-

Trypsinogen (for proteins)
Chymotrypsinogen (for proteins)
Procarboxypeptidase (for proteins)
Pancreatic amylase (amylopsin) (for carbohydrates)
Pancreatic lipase (steapsin) (for fats)

Endocrine part is represented by patches of cells called islets of Langerhans.
Two main type of cells are seen-
Alpha cells- produces glucagon.
Beta cells- produces insulin.

http://www.gopetsamerica.com/anatomy/illustrations/pancreas.jpg

LIVER

Liver has two main lobes:- large right lobe and small left lobe.
In addition – quadrate lobe and caudate lobe are present.

Liver cells secrete bile, and is stored in gall bladder.
Bile is a yellowish green secretion.
Pigments- bilirubin and biliverdin
Salts- Na glycocholate, Na taurocholate and Na bicarbonate.
Bile is carried from gall bladder to duodenum by bile duct.

The gallbladder is located beneath the right lobe of the liver. The primary function of the gallbladder is to store and concentrate bile.

Liver - Functions

The primary functions of the liver are:

Bile production and excretion
Synthesis of urea
Excretion of bilirubin, cholesterol, hormones, and drugs
Metabolism of fats, proteins, and carbohydrates
Enzyme activation
Storage of glycogen, vitamins, and minerals
Synthesis of plasma proteins, such as albumin, and clotting factors
Blood detoxification and purification

Lipogenesis- excess of glucose is converted to fats

Glucose metabolism in the liver

Glycogenesis
Excess glucose in the blood is converted into glycogen and stored.

Glycogenoglysis
When required glucose is obtained by hydrolysis of glycogen.

Glyconeogenesis
Glucose is synthesized from amino acids or fatty acids and glycerol.

Bilary system

The biliary system consists of the organs and ducts that are involved in the production and transportation of bile.
The liver cells secrete bile, it is collected by a system of ducts that flow from the liver through the right and left hepatic ducts into common hepatic duct.
The common hepatic duct joins the cystic duct from the gallbladder to form the common bile duct, which runs from the liver to the duodenum. About 50 percent of the bile produced by the liver is first stored in the gallbladder, a pear-shaped organ located directly below the liver.
The gallbladder contracts and releases stored bile into the duodenum to help break down the fats when food enters the duodenum.

The opening of the common bile duct is guarded by the sphincter of Boyden, that then joins the hepato-pancreatic duct to open into the duodenum.
This opening is guarded by the sphincter of Oddi.

Bile is the greenish-yellow fluid (consisting of waste products, cholesterol, and bile salts) that is secreted by the liver cells to perform two primary functions:

To carry away waste
To break down fats during digestion

Food by mastication is converted to bolus in the mouth.
It is passed to the stomach where churning and action of enzymes lead to formation of chyme, the partially digested food.
In the duodenum, complete digestion takes place forming the chyle.

Watch the videos showing the process of digestion.

PHYSIOLOGY OF DIGESTION >