Digestive system
Std IX
Dr. Pramila Kudva
Phases of Digestion
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Ingestion
Movement
Digestion
Absorption
Egestion
1. Parotid
2. Sub-mandibular
3. Sub-lingual
Ptyalin [Salivary Amylase]
Starch
Maltose
Enzymes
They are proteins
Act on Specific product and the end product is
also specific
Speeds up the rate of chemical reaction
Can be used repeatedly
Acts best at a particular temperature
Acts best at a particular acidity or alkalinity
Mechanism of Swallowing
• Swallowing is a coordinated activity of the
tongue, soft palate, pharynx and esophagus.
• Phases
– Food is pushed into the pharynx [throat] by
the tongue. (voluntary)
– Tongue blocks the mouth
– Soft palate closes off the nose
– Larynx (Adam’s Apple) rises so the Epiglottis (a
flap of tissue) can close the opening of the
trachea.
Peristalsis
Stomach
Rugae
Stomach
• J-shaped muscular sac
• Has inner folds (rugae) that increases the
surface area of the stomach.
• Churns and grinds together the bolus into
smaller pieces.
• Food is mixed with gastric juices (hydrochloric
acid and enzymes) secreted by the stomach
walls.
• HCL helps break down food and kills bacteria
that came along with the food.
Stomach
• Pepsin – major enzyme; converts proteins
into peptides in the presence of HCL.
• Renin – acts on Milk proteins
• Mucus – lubricates food and protects the
gastric lining from strong digestive juices.
• Converts the bolus into a liquid (chyme) after
4 hrs of mechanical and chemical digestion
• Chyme passes through the pyloric sphincter
into the small intestine.
Gastric juice contains water, Salts, HCl and
Pepsin
Function of Acid – Kill germs, activates Pepsin
HCl
Pepsinogen
Inactive
Pepsin
Active
Pepsin
Proteins
Enzyme
Prorennin
Inactive
Casein
Soluble
HCl
Peptides
Renin
Active
Renin
Enzyme
Paracasein
A Peptide Insoluble
Calcium Paracaseinate
Soluble
Acted upon by Pepsin
Small Intestine
• Site of greatest amount of digestion and absorption
Small Intestine
• Long (20 ft), coiled tube beneath the stomach.
• Has three parts:
• Duodenum – upper part; about 10 in;
connected to the stomach where the
digestive juices from the pancreas and
the liver combine with chyme making it
thin and watery.
• Jejunum – about 8 ft
• Ileum – about 12 ft
Liver
– Largest gland of the body
– Stores vitamins A,D,E,K
– Stores sugar and glycogen
– Produces bile (watery, greenish substance)
which goes through hepatic duct and cystic
duct join to form the bile duct.
– Bile may directly go to the duodenum or
may get stored in the gall bladder.
– Colour of the bile is due to biliverdin or
bilirubin – formed by the breakdwn of dead
or worn out RBCs.
•Bile contains lot of sodium bicarbonate
which neutralises the acid content
•Bile is an emulsifier NOT an enzyme.
•Emulsifier – dissolves fat into the watery
contents of the intestine.
Fat
Bile
Acidic chyme
Emulsion / Emulsified Fat
Bile
NaHCO3
Alkaline Chyme
Pancreas
– Produces a juice that contains
enzymes (amylase and insulin) to
break down carbohydrates, fats and
protein.
– Secretes the juice into the duodenum
through the pancreatic duct.
Trypsinogen
Enterokinase
Inactive
Proteins &
Peptides
Trypsin
Trypsin
Active
Smaller Peptides + Amino Acids
Left over Amylopsin
Maltose
Starch Pancreatic amylase
Emulsified Fat
Steapsin
Fatty acids + Glycerol
Small Intestine
• Has folded inner walls covered with fingerlike
projections (villi; sing. – villus)
• Each villus has tinier projections called
microvilli that absorbs digested food.
• Villi and microvilli increases the surface area
of the small intestine for greater absorption.
• Each villus is covered by single cell thick
epithelium
• Inside the villus are an artery, A vein, Blood
capillaries and a lymph vessel called Lacteal.
Small Intestine
• Takes about 4 – 8 hrs to complete its journey.
• Mucosa (inner wall) – secretes several enzymes that
acts on the food.
• The Bile and pancreatic enzymes act on the food
• Digested nutrients are absorbed through intestinal
walls.
Intestinal juice converts the remaining peptides
into amino acids, complex carbohydrates into
simple sugars.
Action of Intestinal Juice
Erepsin / Peptidase
Peptides
Amino acids
Maltase
Maltose
Glucose
Sucrase
Sucrose
Glucose + Fructose
Lactase
Lactose
Emulsified Fat
Glucose + Galactose
Lipase
Fatty acids + Glycerol
Large Intestine
Large Intestine
• Caecum, Colon and rectum
• Colon - larger diameter, but shorter (5 ft)
• Water is absorbed from the undigested
food making the waste harder until it
becomes solid.
• Waste stays for 10 – 12 hours.
Large Intestine
• Waste is pushed into the expanded
portion (rectum) of the large intestine.
• Solid waste stays in the rectum until it is
excreted through the anus as faeces. Defecation
• Faeces consists of 75% water, 20% solid
matter - dead bacteria, undigested fat &
proteins and roughage
Assimilation of Food
Carbohydrates & amino acids
Blood stream surrounding
the small intestine
Hepatic Portal
Vein
Liver
Fatty acids & glycerol
Intestinal Villi & lymphatic system
Fats used in the synthesis of compunds in the
body cells
Excess is deposited as subcutaneous fat or
around certain visceral organs