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DIGESTION AND
ABSORPTION
•1•HSE Zoology blog
MAJOR COMPONENTS OF FOOD
• Carbohydrates
• Proteins
• Fats
• Vitamins
• Minerals
• Water
•2•HSE Zoology blog
DIGESTION
• The process of conversion of complex food substances to simple absorbable form is called digestion.
•3•HSE Zoology blog
HUMAN DIGESTIVE SYSTEM
Alimentary canal
Associated glands•4•HSE Zoology blog
DIGESTIVE
SYSTEM OF MAN
•5•HSE Zoology blog
ORAL CAVITY (BUCCAL CAVITY)
• Teeth
• Tongue
• Palate(roof)
•6•HSE Zoology blog
DentitionRefers the number, kinds and
arrangement of teeth
Thecodont
Heterodont
Diphyodont
TEETH
•7•HSE Zoology blog
THECODONT
• Teeth are placed in jaw sockets
•8•HSE Zoology blog
HETERODONT
• Teeth are different types or dissimilar
Incisors
Canine
Premolars
Molars
•9•HSE Zoology blog
DIPHYODONT
• Teeth appear twice in the whole life
• Milk teeth
• Permanent teeth
•10•HSE Zoology blog
The kind and number of teeth are explained in the form of formula is called dental formula.
• Adult 32 permanent teeth
• Incisors 2/2
• Canine 1/1
• Premolars 2/2
• Molars 3/3
• Child 20 milk teeth
• Incisors 2/2
• Canine 1/1
• Premolars 0/0
• Molars 2/2
DENTAL FORMULA
•11•HSE Zoology blog
WISDOM TEETH
• Third molar appears after the age of 20 years and hence is called wisdom teeth.
•12•HSE Zoology blog
OdontoblastFound in the dental
pulp secrete dentine
Crown
Neck
Root
STRUCTURE OF TOOTH
•13•HSE Zoology blog
TONGUE
• Freely movable muscular organ attached to the floor of the buccal cavity by frenulum.
•14•HSE Zoology blog
TONGUE
• The upper surface of the tongue has small projections called papillae, some of which bear taste buds.
•15•HSE Zoology blog
PHARYNX
• Common passage for digestive and respiratory system.
• Opening of oesophagus
• Opening of larynx -Glottis
•16•HSE Zoology blog
GLOTTIS
• Glottis is guarded by a flap of tissue called epiglottis.
• When food materials pass through the pharynx the epiglottis closes the glottis.
•17•HSE Zoology blog
OESOPHAGUS
• Narrow muscular tube
• 30 cm long
• Leads to stomach
• Pass through the diaphragm (a muscular partition that separates thorax from abdomen).
•18•HSE Zoology blog
OESOPHAGEAL SPHINCTER(GASTRO OESOPHAGIAL SPHINCTER)
• Posterior region of the oesophagus there is a ring of muscle called oesophagial sphincter.
• It controls the opening of the oesophagus into the stomach.
•19•HSE Zoology blog
PERISTALSIS
• The movement of food materials in the esophagus is effected by the wave like contraction and relaxation of longitudinal and circular muscles of the esophagus is known as peristalsis.
•20•HSE Zoology blog
STOMACH
• Large muscular ‘J’ shaped sac.
• Lying just below the diaphragm in the abdominal cavity.
• Three major parts
– Cardiac
– Fundic
– Pyloric
•21•HSE Zoology blog
PYLORIC SPHINCTER
• The opening of the stomach into the duodenum is guarded by pyloric sphincter.
• Controls the flow of food to the intestine.
•22•HSE Zoology blog
SMALL INTESTINE
• Long, highly coiled, narrow tube
• Seven metres long
• 2.5 cm diametre
• Divided in to duodenum, jejunum & ileum.
•23•HSE Zoology blog
DUODENUM
• First part of SI
• ‘U’ shaped
• Area of digestion
• Receives common opening of the bile and pancreatic duct.
•24•HSE Zoology blog
JEJUNUM
• Coiled and longer
•25•HSE Zoology blog
ILEUM
• Highly coiled
• Opens into the large intestine
• Area of absorption
•26•HSE Zoology blog
LARGE INTESTINE
• 1.5 metres long
• Differentiated into Caecum , Colon &Rectum
•27•HSE Zoology blog
CAECUM
• Small blind sac (at the junction of SI &LI)
• Plays no role in Nutrient absorption.
• It hosts some symbiotic microorganisms.
• Caecum bears a finger like out growth of unknown function known as Vermiform Appendix.
•28•HSE Zoology blog
COLON
( Pelvic colon)
•29•HSE Zoology blog
RECTUM
• Temporary storage of faeces
• Rectum opens out by Anus.
•30•HSE Zoology blog
HISTOLOGY OF HUMAN GUT
( Outer most )
forms a fibrous coat
(Inner most)-made of
secretary & absorptive cells
Loose connective tissue layer
with blood & lymph vessels
Smooth muscle
•31•HSE Zoology blog
RUGAE
• Mucosal layer forms irregular fold in the stomach called rugae.
•32•HSE Zoology blog
VILLI
• (Sing:- Villus)
• Mucosal layer forms small finger like folding in the small intestine called Villi
• A villus is about 0.5 to 1 mm long
Villus
•33•HSE Zoology blog
VILLI
•34•HSE Zoology blog
VILLI
•35•HSE Zoology blog
VILLI
•36•HSE Zoology blog
•37•HSE Zoology blog
MICROVILLI
• Each villus has numerous electron microscopic evaginations called microvilli.
• Both villi & micro villi increases the surface area for digestion and absorption of food
•38•HSE Zoology blog
DIGESTIVE GLANDS
• Salivary glands
• Pancreas
• Liver
• Gastric glands
• Intestinal glands
•39•HSE Zoology blog
DIGESTIVE ENZYMES
• Hydrolyses
Group of enzymes released from the cells digestive system play a major role in the extra cellular digestion in human
• Carbohydrase ( amylase ) carbohydrate digesting
E.g.: ptyalin, maltose etc
• Proteases (protein digesting)
Eg: amino peptidase, dipeptidase
. Lipase (lipid digesting)
•40•HSE Zoology blog
SALIVARY GLANDS
• Secrete saliva
• Found in buccal cavity
• Three pairs of salivary glands
1.Parotid glands
(largest)
2.Sub lingual glands
3.Sub maxillary(Sub mandibular)
•41•HSE Zoology blog
SALIVA
• Derived from blood plasma
• Secrete 1.5 liters of saliva per day
• Slightly alkaline
• Contain water & electrolyte (Na+, K+, Cl-, HCO3
-)
• Mucin, ptyalin, lyzozyme & inorganic salts
• Ptyalin digest starch in to maltose
•42•HSE Zoology blog
LIVER
• Largest gland in the human body
• Weighs about 1.5 kg in adult man
• Bi lobed
• Secrete bile
•43•HSE Zoology blog
• Each lobe is separated into numerous tiny hepatic lobules, which are the functional units.
• A lobule is formed of numerous hepatic cells –bile is secreted by hepatic cells
• Each lobule is covered by a thin connective tissue sheath called Glisson’scapsule
Glisson’s
capsule
LIVER
•44•HSE Zoology blog
HEPATIC LOBULES
•45•HSE Zoology blog
GALL BLADDER
• Bile is stored and Concentrated in a thin muscular sac called gall bladder.
• Capacity- 40 – 60 ml
• Absent in whale, horses, rats etc.
•46•HSE Zoology blog
BILE
• Golden yellow or greenish fluid• Alkaline nature• Bile pigments (product of dead RBC) (biliverdin & bilirubin)• Bile salts,• cholesterol, • phospholipids• Bile salts play a very important role in the emulsification of fat
•47•HSE Zoology blog
GALL BLADDER
• The duct of gall bladder (cystic duct) along with hepatic duct from the liver forms a common bile duct.
•48•HSE Zoology blog
GALL BLADDER
• The bile duct and pancreatic duct opens together into the duodenum as common hepato - pancreatic duct, which is guarded by a sphincter called sphincter of Oddi.
Hepato - Pancreatic duct•49•HSE Zoology blog
PANCREAS
• Located between stomach & duodenum
• Second largest glands
• Heterocrine gland (both exocrine &endocrine)
• Pancreatic duct opens into the duodenum along with bile duct
• Secrete pancreatic juice.
•50•HSE Zoology blog
PANCREATIC JUICE
• Alkaline nature
• Trypsinogen , Chymotrypsinogen Proarboxypeptidase, Amylopsin (p. amylase)
• Steapsin (pancreatic lipase)
• Nuclease (Nucleic acid digesting enzyme)
•51•HSE Zoology blog
GASTRIC GLANDS
• Found on the wall of stomach
• Formed of three kinds of cells
1. Mucous cells
2. Chief cells or Zymogen cells
3. Oxyntic cells
or Parital cells
•52•HSE Zoology blog
mucus secreting
GASTRIC GLANDS
•53•HSE Zoology blog
GASTRIC GLANDS
•54•HSE Zoology blog
GASTRIC SECRETIONS
Name of Cell Function
Mucous cells (Goblet cells) Secrete mucous
Oxyntic cells or Parital cellsSecretion of HCl and intrensic factor (factor essential for the absorption of vitamin B12)
Chief cells or Zymogen cellsSecretion of enzymes such as pepsin , rennin, lipase etc.
•55•HSE Zoology blog
• Inactivate the secretion of salivary amylase.
• Kills micro organism
• Lowers the pH of the stomach (1.5 to 2.5)
• Activate proenzyme pepsinogen to active pepsin.
HCl
•56•HSE Zoology blog
INTESTINAL GLANDS
• Simple tubular glands found throughout SI
• Two types
Crypts of Lieberkuhn
Glands of Brunner
•57•HSE Zoology blog
CRYPTS OF LIEBERKUHN
• Goblet cells – Mucous secreting
• Paneth cells – Enzyme secreting
Many surface area of gastro intestinal tract are
lined by evaginations of the epithelium in to sub
mucosa similar to pits. These pits of the
intestine are called Crypts of Lieberkuhn
Paneth cellsGoblet cells
villus
crypt
•58•HSE Zoology blog
GLANDS OF BRUNNER ( DUODENAL GLANDS)
• Confined to the sub mucosa of the duodenum and secrete mucus only
•59•HSE Zoology blog
INTESTINAL JUICE (SUCCUS ENTERICUS)
• Collective secretions of intestinal glands
• Alkaline nature
• Contain enzymes , mucous & inorganic salts.
• Proteases Aminopeptidase, Dipeptidase
• Amylase Maltase, Isomaltase Lactase, Surcease
• Lipase
• Enterokinase
•60•HSE Zoology blog
DIGESTION
• The teeth and tongue with the help of saliva masticate and mix up the food into bolus.
• The bolus is conveyed to pharynx and then to oesophagus by swallowing or deglutition.
•61•HSE Zoology blog
DIGESTION
• The stomach stores the food 4-5 hrs. The food mixes thoroughly with acidic gastric juice to form paste.- Chyme
chyme•62•HSE Zoology blog
• Starch
Maltose
Buccal cavity
Starch Maltose
Salivary amylase
CARBOHYDRATE
DIGESTION
Stomach
No carbohydrate
digestion Small Intestine
Starch Maltose
Maltose 2 Glucose
Lactose Glucose +
Galactose
Sucrose Glucose +
Fructose
P. amylase
Maltase
Lactase
Sucrase
•63•HSE Zoology blog
Buccal cavity
No protein digestion
Stomach
Pepsinogen PepsinHCl
Protein Pepsin Peptones +
Proteoses
Peptones = larger peptides
Proteoses = smaller peptides
Small intestine
Trypsinogen Enterokinase Trypsin
Chymotrypsinogen Chymotrypsin
Procarboxy
peptidase
Carboxy
peptidase
Proteins
Peptones
Proteoses
Dipeptides
Dipeptides Amino acidsDipeptidase
Trypsin / Chymotrypsin
Carboxy peptidase
PROTEIN DIGESTION
•64•HSE Zoology blog
Buccal cavity
No protein digestion
Stomach
Gastric lipase hydrolyses
only a small amount of
fat Small intestine
Fat Fat dropletsBile
Emulsification
Fat Pancreatic lipase
Fatty acids & Glycerol
Diglyceride
Monoglycerides
FAT DIGESTION
•65•HSE Zoology blog
Small Intestine
Nucleic acids Nucleotides Nucleosides Sugar + Bases
NUCLEIC ACID DIGESTION
•66•HSE Zoology blog
END PRODUCTS OF DIGESTION
CarbohydratesGlucose
Fructose
Galactose
ProteinsAmino acids
Fats Fatty acids
glycerol
•67•HSE Zoology blog
• Complete digestion of food take place in the duodenum. The fully digested food is semi fluid in nature and is known as Chyle
DIGESTION
•68•HSE Zoology blog
ABSORPTION OF DIGESTED PRODUCTS
• Absorption is the process by which the end products of digestion pass through the intestinal mucosa ( transported through the intestinal mucosa) into the blood or lymph
• The end products of digestion are absorbed in the jejunum and ileum regions of small intestine.
•69•HSE Zoology blog
Absorption is carried out by
– Passive transport
– Facilitated transport
– Active transport
ABSORPTION
•70•HSE Zoology blog
PASSIVE TRANSPORT
• Small amounts of monosaccharide like glucose, amino acids, and some of electrolytes like chloride ions are generally absorbed by simple diffusion.
•71•HSE Zoology blog
•72•HSE Zoology blog
FACILITATED TRANSPORT
• Fructose and some amino acids are absorbed with the help of carrier ions like sodium. This mechanism is called facilitated transport.
•73•HSE Zoology blog
ACTIVE TRANSPORT
• Requires energy
• Various nutrients like amino acids, monosaccharide like glucose, electrolytes like Na+ are reabsorbed into the blood by active transport.
•74•HSE Zoology blog
•75•HSE Zoology blog
ABSORPTION OF FAT
• Fatty acids and glycerol insoluble in water so they cannot be absorbed directly from the lumen of the intestine.
• With the help of bile salts & phospholipids the fatty acids and glycerol are converted into small spherical water soluble droplets called micelles.
•76•HSE Zoology blog
ABSORPTION OF FAT
Micelles are reformed into very small protein coated fat
globules called chylomicrons. Which are transported in to
the lymph vessels (lactales)in the villi.
•77•HSE Zoology blog
ABSORPTION OF FAT
•78•HSE Zoology blog
LARGE INTESTINE
Functions
Absorption of water, minerals and certain drugs.
Secretion of mucus which helps in adhering waste.
• No significant digestive activity occurs in the large intestine.
•79•HSE Zoology blog
LARGE INTESTINE
• The undigested and unabsorbed substances (faeces) enters into the caecum of the large intestine through the ileo caecal valve, which prevents the back flow of faecal matter.
•80•HSE Zoology blog
EGESTION
• The egestion of faeces to the outside through the anal opening (defaecation) is a voluntary process and is carried out by a mass peristaltic movement.
•81•HSE Zoology blog
THE SUMMARY OF ABSORPTION IN DIFFERENT PARTS OF DIGESTIVE SYSTEM
Oral cavity Stomach Small Intestine Large Intestine
Certain drugs coming in contact with the mucosa of the mouth and lower side of the tongue are absorbed into the blood capillaries lining them.
Water, simple sugars, alcohol
Glucose Fructose
Fatty acids
Glycerol
Amino acids
Water , some minerals, drugs
•82•HSE Zoology blog
DISORDERS OF DIGESTIVE SYSTEM
• Infections of the digestive system are caused by bacteria, virus, parasites like tape worm, thread worm, round worm, hook worm, pinworm etc.
Bacteria
Tape worm
Virus
Pinworm
Thread worm
•83•HSE Zoology blog
VOMITING
• It is the ejection of stomach content through the mouth.
•84•HSE Zoology blog
DIARRHOEA
• The abnormal frequency of bowel movement and increased liquidity of faecal discharge is known as diarrhoea.
• It reduces the absorption of food.
•85•HSE Zoology blog
JAUNDICE
• The liver is affected, skin, eyes turn yellow due to the deposition of bile pigments.
•86•HSE Zoology blog
CONSTIPATION
• The faeces are retained with in the rectum as the bowel movement occur irregularly.
•87•HSE Zoology blog
INDIGESTION
• The food is not properly digested leading to the feeling of fullness.
• The cause of indigestion are inadequate enzyme secretion, anxiety, food poisoning, overeating and spicy food.
•88•HSE Zoology blog