HUMAN DIGESTIVE SYSTEM
Digestion is the mechanical and
chemical break down of food in which
complex and non-diffusible food are converted into diffusible and simple.
1.Digestion is a mechanical and chemical break down of large food contents
in to smaller particles that are easy to be absorbed. Absorption is
transferring the digested molecules across the gastrointestinal tract to the
blood stream.2.Digestion starts from the mouth, but the absorption starts from the stomach.
3.Digestion takes place inside the intestinal tract, but the absorption happens in the line of the intestine.
4.Digestion needs enzymes, but absorption does not need enzymes.
5.Digestion is always an active process and needs energy, but some of the absorption mechanisms do not need energy.
6.Digestion changes the chemical and the mechanical structure of the food, whereas absorption does not.
7.Absorption relates with blood, while digestion does not.
8.Most of the digestion takes place at duodenum, whereas absorption occurs mainly at ileum and jejunum.
2.State the function of liver.
Ans: Functions of liver:
1.Liver is main organ of Bile production. Bile contains bile pigment and salts. Bile pigments are Bilirubin(yellow) and biliverdin(green) used in coloration of bile and faeces. Salts of Sodium and Potassium bicarbonate neutralize acids. Sodium glycocholate and taurocholate help in emulsification.
2.Deamination: NH2 amino group is removed from amino acid resulting in the production of ammonia. Ammonia is converted into urea.
3.Glycogenesis: it is conversion of excess glucose into glycogen with the help of insulin.
4.Glycogenolysis: conversion of glycogen into glucose by liver cells with the help of glucagon.
5.Lipogenesis: conversion of excess glucose and amino acid into fats.
6.Gluconeogenesis: formation of glucose or glycogen from non carbohydrate sources( amino acid, fatty acid and glycerol). It also occurs in kidney and muscle.
7.Detoxification: converts toxic substance into harmless substance eg harmful prussic acid is neutralized and rendered harmless.
3.Discuss the role of bile in the digestion of fat.
Ans: Bile are bio-surfactants present in the gastrointestinal tract that play a crucial role in the digestion and absorption of nutrients. The importance of Bile for controlled release and transport of lipid soluble nutrients and drugs has recently stimulated scientific interest in these physiological compounds. Bile is so-called facial amphiphiles showing a molecular structure that is very distinct from classical surfactants. This peculiar molecular structure facilitates the formation of dynamic aggregates able to solubilise and transport lipid soluble compounds. Bile adsorbs onto fat droplets and can remove other materials such as proteins, emulsifiers and lipolysis products from the lipid surface.
4.Mentain the function of bile juice.
5.Mentain the function of food?
Ans: Food provides our bodies with what they need to:
1.Stay alive, be active, move and work;
2.Build new cells and tissues for growth;
3.Stay healthy and heal themselves;
4.Prevent and fight infections.
6.Name the different types of teeth and give their function.
Ans: Human beings and most of other mammals are heterodont. They have different types of teeth with different functions.
1.incisors -help to cut large piece into small pieces
2.canines - help in tearing flesh
3.premolars – help in mastication
4.molars – help in mastication
7.What are the function of the stomach?
Ans: The stomach receives food from the esophagus. As food reaches the end of the esophagus, it enters the stomach through a muscular valve called the lower esophageal sphincter. The stomach secretes acid and enzymes that digest food. Ridges of muscle tissue called rugae line the stomach. The stomach muscles contract periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.
Ans: Saliva is a clear, watery liquid made by several glands in your mouth area.
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Saliva is important because it,
1.Keeps your mouth moist and comfortable
2.Helps you chew, taste, and swallow
3.Fights germs in your mouth and prevents bad breath
4.Has proteins and minerals that protect tooth enamel and prevent tooth decay and gum disease
5.Helps keep dentures securely in place
9.How does the coagulation of milk take place in the stomach?
Ans: The enzyme rennin is a milk coagulating enzyme. It hydrolysis milk protein casein in to insoluble calcium paracaseinate in the presence of Ca++ ions. This is the curd of milk which can be retained in the stomach for a long time and which is later acted upon by pepsin converting it in to amino acids. Renin is important to infants in which the milk is the main diet. It is said to be into amino acid.
Long-
1.Explain the process of digestion in man.
Ans: The main objective of digestion is to convert complex food molecules in to simple. Which can easily absorbed by the body cells. This process include ingestion, digestion, absorption, assimilation and egestion or defaecation.
Digestion in mouth:
In mouth, the food is mixed with the saliva from salivary gland. Saliva contains the enzyme called salivary amylase. Salivary amylase acts on carbohydrate and changes some of carbohydrate into maltose, isomaltose and limit dextrine. Food remains in mouth for a short time so digestion is not complete.
Enzyme substrate products
Salivary amylase + starch ------------- maltose + isomaltase+ limit dextrine
Digestion in stomach:
In the stomach, the gastric juice is secreted by gastric gland. Gastric juice contains pepsiongen, HCl and water. Peptic cells or zymogenic cells secrete pepsinogen. Parietal cells secrete HCl. Prorenin is found in infants.
Functions of HCl:
1.converts inactive pepsinogen into active pepsin
2.provides acidic medium
3 stops growth of Bacteria
Pepsin changes inactive prorenin into active rennin. Pepsin acts on protein and changes it into peptones and proteoses. Rennin acts on milk casein. Milk casein is changed into paracasein. Paracasein combines with Calcium ion to form Calcium paracaseinate. It is then acted by pepsin and changed into peptones and proteoses. In the stomach, gastric lipase is also secreted. It acts on fats to change into fatty acids and glycerol.
Enzyme substrate products
Pepsin + protein --------- peptones + proteoses
Rennin + milk casein ------- paracasein
Paracasein + Ca ++ -- --- Calcium paracaseinate
Pepsin + Calcium paracaseinate --- peptones + proteoses
Lipase + fats -------------------- fatty acids and glycerol
Digestion in duodenum:
The partially digested food called chime is passed on to the duodenum slowly. It is mixed with bile juice and pancreatic juice. The bile juice contains bile pigments and bile salts. The pancreatic juice contains enzymes like trypsinogen, amylase and lipase etc. The inactive trypsinogen is converted into active trypsin by enterokinase. Trypsin then acts on protein, peptones and proteoses and change into polypeptides. Amylase acts on starch and changes into maltose. Lipase acts on emulsified fat and change into fatty acids and glycerol.
The functions of bile:
1.It neutralizes acids
2. It provides alkaline medium
3. It emulsifies fats
Enzyme substrate products
Trypsin + protein, proteoses, peptones ------ polypeptides
Amylase + starch ----------------------------- maltose
Lipase + emulsified fat ---------------------- fatty acids, glycerol
Digestion in jejunum and ileum:
Here, intestinal juice is produced by crypts of Lieberkuhn. The intestinal juice contains amino peptidase, dipeptidase, maltase, lactase, sucrase etc. the amino peptidase acts on polypeptides and changes into smaller peptides. Dipeptidase acts on dipeptides and changes into amino acids. Maltase acts on maltose. It is changed into glucose. Lactase acts on lactose to change that into galactose and glucose. Sucrase acts on sucrose and changed into fructose and glucose.
Enzyme substrate products
Amino peptidase + polypeptides -------------------- smaller peptides
Dipeptidase + smaller peptides --------------- amino acid
Maltase + maltose ------------------------- glucose
Lactose + lactose --------------------------- glucose and galactose
Sucrase + sucrose -------------------------- glucose and fructose
Absorption :
Absorption takes place in the ileum mainly. For this, the internal lining of ileum is provided with large no. of finger like projections called villi. The villi increase the absorptive surface. These are provided with blood vessels and lymph. Glucose, amino acid etc are absorbed into the blood vessel. Blood takes them to liver for storage of glucose. The fatty acids and glycerol come into the lymph which is taken into adipose tissue for storage.
Assimilation:
Glucose, fatty acids and glycerol are used for the liberation of energy in the body. Amino acids are used to produce protoplasm in the body for growth and repair of damaged tissue.
Egestion:
Undigested materials are passed into large intestine. Water is absorbed here. Then these are carried down. Lastly undigested materials are discharged out from anus. It is called egestion.
2.What is absorption? Discuss the absorptive processes of the digested foodstuff.
Ans: The two primary roles of the digestive process are absorption and secretion. The role of absorption in the digestive system is vital to the body because without it, the vitamins, minerals, carbohydrates and other nutrients we consume could not be used. Absorption is the process by which the nutrients in food are passed on to the blood. The majority of absorption occurs in the small intestine, the digestive tract’s primary organ.
After food passes through the stomach to the small intestines, it is turned into energy for the body to use. Absorption is made possible by the villi, small bristle-like protrusions in the mucosa. The mucosa is the moist tissue lining certain parts of the body’s passages and organs. The villi act as channels through which the nutrients derived from digested foods can pass into the bloodstream and be carried to the rest of the body. The actual absorption process is slightly different for each type of nutrient.
Absorption takes place in the ileum mainly. For this, the internal lining of ileum is provided with large no. of finger like projections called villi. The villi increase the absorptive surface. These are provided with blood vessels and lymph. Glucose, amino acid etc are absorbed into the blood vessel. Blood takes them to liver for storage of glucose. The fatty acids and glycerol come into the lymph which is taken into adipose tissue for storage.
3.Discuss the structure of digestive organs of man with the help of labelled diagram.
Ans: The digestive system consists of alimentary canal and digestive glands. Alimentary canal is complete and has well defined regions. It is concerned with ingestion, digestion, absorption and egestion of waste material.
Alimentary canal:
Fig: parts of alimentary canal of human.
It is a long coiled tube of about 8 to 10 meters long. It is of various diameters at various parts. It starts from mouth and ends in anus. It consists of following parts they are as;
Mouth:
It is a transverse slit like opening bounded by movable upper and lower lip. It opens into a small gap called vestibule. Vestibule is a space between lips and jaw. It opens not buccal cavity.
Buccal cavity:
It is known as oral cavity or mouth cavity also. It is bounded by upper and lower jaws. The upper jaw is fixed and lower jaw is only movable up and down and sidewise. The jaws are provided with teeth in a row. At the floor, there is tongue. The roof of buccal cavity is made by palate.
Pharynx:
It is wide opining at back of mouth cavity. It leads to two openings : gullet and glottis. There is a muscular flap called epiglottis which closes glottis when food is swallowed. There are 2 openings of internal nares above and two openings of Eustachian tubes at the sides. It is the only part common to digestive and respiratory system.
Oesophagus:
It is a long narrow muscular tube which connect mouth to stomach. It is about 25 cm long. It pierces diaphragm to open into stomach. It undergoes peristalsis to carry down food and water or fluid.
Stomach:
It is a large muscular elastic bag situated below diaphragm on left side. It has four parts
1.Cardiac: it is so called because it lies near heart. In between oesophagus and cardiac part of stomach there is cardiac sphincter.
2.Fundus: it extends superiorly from the cardiac part. It is usually filled with air.
3.Body: it is main part of stomach.
4.Pyloric part: it is distal part of stomach. it opens into duodenum. It opens and closes several times. At the time of opening, a small amount of partially digested food(chime) is passed into duodenum.
Gastric gland secretes gastric juice.
Small intestine:
It is divisible into 3 parts.
1.Duodenum – it is c shaped and about 25 cm long. It receives bile juice and pancreatic juice through common bile duct.
2.Jejunum - it is about 2.5 meter in length. It is coiled part.
3.Ileum – it is about 3.5 meter long. It is highly coiled part. Both jejunum and ileum are suspended by mesenteries. The inner wall of ileum has number of folds called villi. It is mainly for digestion and absorption.
large intestine
It is about 1.5 meter long and divisible into following parts;
1.Caecum: It is pouch like structure about 6 cm long. There is ileocaecal valve preventing back flow. Attached to caecum is a slender vermiform appendix of about 10 cm long. It is vestigial in man but functional in herbivores. The inflammation of appendix is called appendicitis at the time of infection.
2.Colon: It is inverted U shaped and divisible into
Ascending colon: It is the first part on right side. It moves upward from caecum.
Transverse colon: It is horizontal part.
Descending colon: It moves down at left side. It descends down
Pelvic colon: It is s shaped or sigmoid. Undigested material can remain in colon for about 36 hours.
Colon is for absorption of water mainly.
Rectum: small muscular region, straight, about 15 cm long. It opens to the exterior through anus. Undigested material remains here for a short time. The anus is guarded by 2 sphincters Throughout the alimentary canal, mucous glands secrete mucus.
Digestive glands:
Associated with digestion, there are following digestive glands which secrete enzymes serving the chemical digestion of food.
1.Salivary glands:
There are three pairs of salivary glands. There is one pair of Parotid gland. It is the largest of the salivary glands. It is situated near the ears. Stenson’s duct of Parotid gland opens near the upper 2nd molar. One pair of sublingual glands is small and situated beneath tongue.
2.Liver:
It is the largest gland. It lies in the upper right side of abdominal cavity just below diaphragm. It is reddish brown and weighs about 1.4 to 1.5 Kg. It has two lobes right and left separated by falciform ligament. The right lobe is further divisible into right lobe proper, quadrate lobe and caudate lobe. Gall bladder is a pear shaped sac like structure. It stores bile juice.
3.Pancreas:
It is soft, lobulated, greenish pink gland. It weighs about 60 grams, 2.5 cm wide and 12 to 15 cm long. It located posterior to stomach. It comprises head, body and tail. Head lies in the curve of duodenum, body behind the stomach and tail reaches the spleen near left kidney. The main pancreatic duct is formed by smaller ducts within pancreas. The main pancreatic duct open into hepatopancreatic ampulla.
Absorption :
Absorption takes place in the ileum mainly. For this, the internal lining of ileum is provided with large no. of finger like projections called villi. The villi increase the absorptive surface. These are provided with blood vessels and lymph. Glucose, amino acid etc are absorbed into the blood vessel. Blood takes them to liver for storage of glucose. The fatty acids and glycerol come into the lymph which is taken into adipose tissue for storage.
Assimilation:
Glucose, fatty acids and glycerol are used for the liberation of energy in the body. Amino acids are used to produce protoplasm in the body for growth and repair of damaged tissue.
Egestion:
Undigested materials are passed into large intestine. Water is absorbed here. Then these are carried down. Lastly undigested materials are discharged out from anus. It is called egestion.
4.Give an account of the structures and functions of human teeth and tongue.
Ans: Human beings and most of other mammals are heterodont. They have different types of teeth with different functions.
1.incisors -help to cut large piece into small pieces
2.canines - help in tearing flesh
3.premolars – help in mastication
4.molars – help in mastication
They are diphyodont. They have two sets of teeth, milk teeth and permanent teeth.
Dental formula – it is expression of number and type of teeth on right or left side (one side) of jaw.
Dental formula of milk teeth i 2/2 c 1/1 pm 0/0 m2/2 5x2/5x2 = 20
Dental formula of permanent teeth i 2/2 c1/1 pm 2/2 m 3/3 8x2/8x2 = 32
i stands for incisor
c stands for canine
pm stands for premolar
m stands for molar
the numerator is for number of teeth in upper jaw
the denominator is for number of teeth in lower jaw
milk teeth start to drop out at about age of 5 or 6. the 3rd molar teeth are also known as wisdom teeth and appear at about the age of 17 to 21. teeth in females appear earlier than in males.
Structure of tooth:
It has 3 regions.
Fig; L.S. of an incisor and a molar tooth.
1.Crown – part which project above gum
2.Neck - part surrounded by gum
3.Root - part embedded in bone, the incisor and canine and lower premolar have one root, upper premolar and lower molar have 2 roots and upper molar have 3 roots.
Tooth consists of enamel which is the hardest part of human body. It covers the dentine of crown. Dentine has many canaliculi that pass radially from the pulp cavity. Cement covers root of tooth. Periodontal membrane covers cement and fixes tooth in socket (thecodont).
Inside tooth, there is pulp cavity containing mass of cells, blood vessels and nerve constitute pulp. It is for growth of tooth. Dentine forming odontoblast and enamel forming ameloblast cells are also present.
Tongue:
It is highly muscular organ attached at the floor of buccal cavity by a fold called frenulum. The upper surface is provided with numerous papillae containing taste buds. The taste buds are sensitive to taste of food. Types of papillae
1.Filliform- smallest, most numerous, conical, mostly found at center of tongue, white in color.
2.Fungiform - less in no. red and rounded, found at tip and margin of tongue.
3.Vallate papillae- large in size, about 5 to 12 in no. arranged in inverted v shape at the base of tongue.
4.Foliate – leaf like, not developed in man, found at sides of tongue.
Tip of tongue – sweet
Sides of tongue – sour
Posterior end of tongue – bitter.
Functions of tongue:
1.Detects taste
2.Helps in chewing, mix saliva
3.Aids in swallowing
4.Cleans teeth and gum
5.Plays role in speech
5.How do you account pancreas as an endocrine gland? Discuss the function of pancreatic juice.
Ans: : The pancreas is an endocrine organ that lies in the abdomen, specifically the upper left abdomen. It is found behind the stomach, with the head of the pancreas surrounded by the duodenum. The pancreas is about 15cm (6 in) long. Anatomically, the pancreas is divided into a head, which rests within the concavity of the duodenum, a body lying behind the base of the stomach, and a tail, which ends abutting the spleen. The neck of the pancreas lies between the body and head, and is in front of the superior mesenteric artery and vein. The head of the pancreas surrounds these two vessels, and a small uncinate process emerges from the lower part of the head, lying behind the superior mesenteric artery. The pancreas is a secretory structure with a internal hormonal role (endocrine) and an external digestive role (exocrine). It has two main ducts, the main pancreatic duct, and the accessory pancreatic duct. These drain enzymes through the ampulla of Vater into the duodenum.
function of pancreatic juice:
1.Pancreatic fluid or juice contains digestive enzymes that pass to the small intestine where they help to further break down the carbohydrates, proteins, and lipids (fats) in the chyme.
2.Pancreatic fluid is alkaline in nature due to the high concentration of bicarbonate ions that makes it useful in neutralizing the acidic gastric acid, allowing for effective enzymic action.
3.Pancreatic juice secretion is regulated by the hormones secretin and cholecystokinin. It is produced by the walls of the duodenum upon detection of acid food, proteins, fats, and vitamins.
6.Write the basic feature of digestive system in mammals. Draw a well-labelled diagram of the alimentary canal of man.
Ans: The mammalian digestive system consists of the alimentary canal ( complete digestive tract) and various accessory glands that secret digestive juices into the canal through the ducts. The digestive system is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract. The digestive system consists of alimentary canal and digestive glands. Alimentary canal is complete and has well defined regions. It is concerned with ingestion, digestion, absorption and egestion of waste material.
Fig: parts of alimentary canal of human.
