Digestion and absorption

DIGESTION AND

ABSORPTION

•1•HSE Zoology blog

MAJOR COMPONENTS OF FOOD

• Carbohydrates

• Proteins

• Fats

• Vitamins

• Minerals

• Water

DIGESTION

• The process of conversion of complex food substances to simple absorbable form is called digestion.

HUMAN DIGESTIVE SYSTEM

Alimentary canal

Associated glands•4•HSE Zoology blog

DIGESTIVE

SYSTEM OF MAN

ORAL CAVITY (BUCCAL CAVITY)

• Teeth

• Tongue

• Palate(roof)

DentitionRefers the number, kinds and

arrangement of teeth

Thecodont

Heterodont

Diphyodont

THECODONT

• Teeth are placed in jaw sockets

HETERODONT

• Teeth are different types or dissimilar

Incisors

Canine

Premolars

Molars

DIPHYODONT

• Teeth appear twice in the whole life

• Milk teeth

• Permanent teeth

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

WISDOM TEETH

• Third molar appears after the age of 20 years and hence is called wisdom teeth.

OdontoblastFound in the dental

pulp secrete dentine

STRUCTURE OF TOOTH

TONGUE

• Freely movable muscular organ attached to the floor of the buccal cavity by frenulum.

TONGUE

• The upper surface of the tongue has small projections called papillae, some of which bear taste buds.

PHARYNX

• Common passage for digestive and respiratory system.

• Opening of oesophagus

• Opening of larynx -Glottis

GLOTTIS

• Glottis is guarded by a flap of tissue called epiglottis.

• When food materials pass through the pharynx the epiglottis closes the glottis.

OESOPHAGUS

• Narrow muscular tube

• 30 cm long

• Leads to stomach

• Pass through the diaphragm (a muscular partition that separates thorax from abdomen).

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.

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.

STOMACH

• Large muscular ‘J’ shaped sac.

• Lying just below the diaphragm in the abdominal cavity.

• Three major parts

– Cardiac

– Fundic

– Pyloric

PYLORIC SPHINCTER

• The opening of the stomach into the duodenum is guarded by pyloric sphincter.

• Controls the flow of food to the intestine.

SMALL INTESTINE

• Long, highly coiled, narrow tube

• Seven metres long

• 2.5 cm diametre

• Divided in to duodenum, jejunum & ileum.

DUODENUM

• First part of SI

• ‘U’ shaped

• Area of digestion

• Receives common opening of the bile and pancreatic duct.

JEJUNUM

• Coiled and longer

• Highly coiled

• Opens into the large intestine

• Area of absorption

LARGE INTESTINE

• 1.5 metres long

• Differentiated into Caecum , Colon &Rectum

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.

( Pelvic colon)

RECTUM

• Temporary storage of faeces

• Rectum opens out by Anus.

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

• Mucosal layer forms irregular fold in the stomach called rugae.

• (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

MICROVILLI

• Each villus has numerous electron microscopic evaginations called microvilli.

• Both villi & micro villi increases the surface area for digestion and absorption of food

DIGESTIVE GLANDS

• Salivary glands

• Pancreas

• Liver

• Gastric glands

• Intestinal glands

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)

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)

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

• Largest gland in the human body

• Weighs about 1.5 kg in adult man

• Bi lobed

• Secrete bile

• 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

HEPATIC LOBULES

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.

• 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

GALL BLADDER

• The duct of gall bladder (cystic duct) along with hepatic duct from the liver forms a common bile duct.

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.

PANCREATIC JUICE

• Alkaline nature

• Trypsinogen , Chymotrypsinogen Proarboxypeptidase, Amylopsin (p. amylase)

• Steapsin (pancreatic lipase)

• Nuclease (Nucleic acid digesting enzyme)

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

mucus secreting

GASTRIC GLANDS

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.

• 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.

INTESTINAL GLANDS

• Simple tubular glands found throughout SI

• Two types

Crypts of Lieberkuhn

Glands of Brunner

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

GLANDS OF BRUNNER ( DUODENAL GLANDS)

• Confined to the sub mucosa of the duodenum and secrete mucus only

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

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.

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

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

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

Small Intestine

Nucleic acids Nucleotides Nucleosides Sugar + Bases

NUCLEIC ACID DIGESTION

END PRODUCTS OF DIGESTION

CarbohydratesGlucose

Fructose

Galactose

ProteinsAmino acids

Fats Fatty acids

glycerol

• Complete digestion of food take place in the duodenum. The fully digested food is semi fluid in nature and is known as Chyle

DIGESTION

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.

Absorption is carried out by

– Passive transport

– Facilitated transport

– Active transport

ABSORPTION

PASSIVE TRANSPORT

• Small amounts of monosaccharide like glucose, amino acids, and some of electrolytes like chloride ions are generally absorbed by simple diffusion.

FACILITATED TRANSPORT

• Fructose and some amino acids are absorbed with the help of carrier ions like sodium. This mechanism is called facilitated transport.

ACTIVE TRANSPORT

• Requires energy

• Various nutrients like amino acids, monosaccharide like glucose, electrolytes like Na+ are reabsorbed into the blood by active transport.

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.

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.

ABSORPTION OF FAT

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.

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.

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.

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

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

Pinworm

Thread worm

VOMITING

• It is the ejection of stomach content through the mouth.

DIARRHOEA

• The abnormal frequency of bowel movement and increased liquidity of faecal discharge is known as diarrhoea.

• It reduces the absorption of food.

JAUNDICE

• The liver is affected, skin, eyes turn yellow due to the deposition of bile pigments.

CONSTIPATION

• The faeces are retained with in the rectum as the bowel movement occur irregularly.

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.

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