Questions - Answers
Very Short Answer Type Questions
1. Give dental formula of adult human beings.
A: 
2. Bile juice contains no enzymes. Yet it is important for digestion. How?
A: a) Bile salts present in bile juice emulsify the fats.
b) Moreover, bile enhances the activity of enzymes of pancreatic and intestinal juices.
3. Describe the role of chymotrypsin. Name two other enzymes of same category and secreted by same gland.
A: a) Chymotrypsin digests the proteins, proteoses and peptones into polypeptides.
b) Trypsin and Carboxypeptidase.
4. What would happen it, HCl was not secreted in the stomach?
A: a) Microbes that enter the stomach along with food cause health problems.
b) Pepsinogen and prorennin are not activated. Hence protein digestion will not occur in stomach.
5. Explain the terms thecodont and diphiodont dentitions.
A: a) If the teeth are embedded in sockets of jaw bone (= thecae), the dentition is described as thecodont dentition.
b) If two sets of teeth are formed in life time (first set is milk teeth, which are replaced by permanent teeth), the dentition is described as diphiodont dentition.
6. What is autocatalysis? Give two examples.
A: a) If a product is obtained in the reaction functions as catalyst in the same reaction, the product is called autocatalyst and the process is called autocatalysis.
7. What is chyme?
A: Food entered the stomach is thoroughly mixed with gastric juice by churning movements and thus it becomes a dense acidic fluid known as chyme.
8. Name the different types of salivary glands and their locations in man.
A: a) Parotid glands - Located below the bases of pinnae.
b) Submaxillary glands - Angles of lower jaw.
c) Sublingual glands - Below the tongue.
9. Name different types of papillae present on tongue of man.
A: a) Fungiform papillae
b) Filiform papillae
c) Circumvellate papillae
10. What is the hardest substance in human body? What is its origin?
A: a) Enamel
b) Ectodermal cells called ameloblasts
11. Name the structure of gut which is vestigial in human beings, but well developed in herbivores and mention the type of tissue with which it is mostly formed.
A: a) Vermiform appendix
b) Lymphoid tissues
12. Distinguish between deglutition and mastication.
A: a) Mastication is the chewing of food among teeth, tongue mix saliva with the food during mastication.
b) The process of swallowing of food through oesophagus is known as deglutition.
13. Distinguish between diarrhoea and constipation.
A: a) Abnormal frequency of bowel movement and increased liquidity of faecal discharge is known as diarrhoea.
b) Retention of faeces within the rectum (as it is hard due to low water content) is known as constipation.
14. Name two hormones secreted by duodenal mucosa.
A: a) Enterocrinin
b) Villikinin
Short Answer Type Questions
1. Draw neat labeled diagram of L.S. of a tooth.
A:
2. Describe the process of digestion of proteins in stomach.
A: Food remains in stomach for hours. Here the gastric juice is secreted and by churning movements of stomach, it is mixed with the food. Mucus protects the mucosa of stomach from excoriation by HCl and also play important role in lubrication. HCl kills the harmful microbes that reached the stomach along with food and also activates the proenzymes pepsinosen and prorennin into pepsin and rennin respectively. Rennin is found in infants. It acts on milk protein, Casein and converts into calcium paracaseinate (curd) in presence of Ca++. Pepsin digests the proteins including curd into proteoses and peptones. Action of gastric lipase is insignificant.
Thus this partially digested food becomes a semi fluid mass in the stomach due to its churning movements known as chyme. It little by little reaches the small intestine.
3. Explain the role of pancreatic juice in the digestion of proteins.
A: The proteolytic enzymes in pancreatic juice are trypsinogen, chymotrypsinogen, carboxypeptidase. Trypsinogen is activated by the enterokinase of intestinal juice into trypsin. Chymotrypsinogen is activated by trypsin. Trypsin and chymotrypsin digests the proteins, proteoses and peptones into polypeptides. Carboxypeptidase digest them into tripeptides and dipeptides.
4. How Polysaccharides and disaccharides are digested?
A: Pancreatic amylase digests the carbohydrates into disaccharides (like maltose, sucrose, lactose etc). They are digested into monosccharides by monosaccharidases (like maltase, sucrase, lactase etc).
Thus after digestion corbohydrates become monosaccharides.
5. If you take butter in your food, how does it get digested and absorbed in the body? Explain.
A: Butter is a fatty substance. When it is eaten, in intestine, the bile salts emulsify these fats. Then Pancreatic and intestinal lipases digest them into fatty acids and glycerol.
6. What are the functions of liver?
A: * Bile juice secreated by liver contains bile salts (glycocholate and taurocholate of Sodium and Potossium) and they emulsify fats during digestion.
* Liver plays an important role in carbohydrate metabolism (glycogenesis, glycogenolysis, gluconeogenesis, lipogenesis), fat metabolism (formation of cholesterol, triglycerides) etc.,
* Deamination of proteins and conversion of ammonia into urea via ornithine cycle takesplace in liver.
* The lactic acid formed in muscle contraction is converted to glycogen in liver (Cori cycle).
* Liver acts a detoxifying organ.
* Liver acts as a thermoregulatory organ.
* In embryonic state, liver acts as a haemopoitic organ.
* Liver synthesises the plasma proteins (albumins, globulins); blood clotting factors (fibrinogen, prothrombin), anticoagulant (heparin) etc.,
* Kupfer cells acts as macrophases and engulf harmful microbes by phagocytosis.
7. Explain the process of inspiration and expiration under normal conditions.
A: Breathing is the act of taking air into lungs and sending it out of lungs. A healthy man breaths 12 - 16 times per minute. Breathing involves two phases, viz., inspiration and expiration. The muscles of diaphragm (phrenic muscles) intercostal muscles (external and internal) among ribs play an important role in breathing movements.
Inspiration: Intake of atmospheric air into lung is known as inspiration and is an active process. In this process, muscles of diaphragm contract and thus it becomes flat. As a result, volume of thoracic cavity increases antero posteriorly. At the same time, external inter costal muscles contract. Hence, the rib cage and sternum. And hence, volume of thoracic cavity increases further dorso ventrally. As the volume of thoracic cavity increases, similar increase results in pulmonary volume also. Hence, pressure in lungs reduced (intra pulmonary pressure reduces). Hence, air moves into lungs from outside.
Expiration: Elimination of air from alveoli is known as expiration. It is a passive process. During expiration, muscles of diaphragm and external inter costal muscles relax. Thus, diaphragm and ribcage along with sternum reach their original places. Hence, volume of thoracic cavity reduces, there by the pulmonary volume. Hence, pressure in lungs (intra pulmonary pressure) increases, causing expulsion of air from lungs.
Long Answer Type Questions
1. Describe the physiology of digestion of various types of food in human digestive system.
A: In man, digestion is extracellular and it involves two activities, viz., mechanical digestion (cutting and chewing of food and churning in stomach etc.,) and chemical digestion (involves many biochemical reactions catalysed by enzymes.)
1. Digestion in buccal cavity: In the buccal cavity, food is thoroughly masticated among teeth. While chewing, food is mixed with saliva. Tongue play an important role in mixing. Mucus of saliva makes the food into bolus. Ptyalin acts on starch (carbohydrate) and about 30% of starch is hydrolysed into maltose. Lysozyme of saliva check the harmful microbes. Then the bolus is swallowed through pharynx, oesophagus and reaches the stomach. This process is called deglutition.
2. Digestion in stomach: Food remains in stomach for hours. Here the gastric juice is secreted and by churning movements of stomach, it is mixed with the food. Mucus protects the mucosa of stomach from excoriation by HCl and also play important role in lubrication. HCl kills the harmful microbes that reached the stomach along with food and also activates the proenzymes pepsinosen and prorennin into pepsin and rennin respectively. Rennin is found in infants.
It acts on milk protein, Casein and converts into Calcium paracaseinate (curd) in presence of Ca++. Pepsin digests the proteins including curd into proteoses and peptones. Action of gastric lipase is insignificant.
* Thus this partially digested food becomes a semi fluid mass in the stomach due to its churning movements known as chyme. It little by little reaches the small intestine.
3. Digestion in small intestine: In the duodenum the chyme is mixed with bile juice, pancreatic juice and intestinal juice. Mucus protects the mucosa small intestine. Bile makes the chyme (acidic) into alkaline material, because pancreatic and intestinal enzymes work in alkaline medium only.
A. Digestion of Proteins: Trypsinogen is activated by the enterokinase into trypsin. Thus trypsin further activates the trypsinogen (autocatalysis). Trypsin also activates the chymotrypsinogen into chymotrypsin.
Proteins, proteoses, peptones present in chyme are digested into tripeptides and dipeptides by trypsin, chymotrypsin, carboxypeptidase and aminopeptidase. Tripeptides and dipeptides are digested into amino acids by tripeptidase and dipeptidase. Thus, after digestion, proteins are converted into aminoacids.
B. Digestion of Fats: Bile salts of bile juice emulsify the fats (tryglycerides) (Breakdown of large fat globules into smaller, uniformly distributed particles is known as emulsification.) Lipases of pancreatic juice (= steapsin) and intestinal juice digest the fats (triglycerides) into fatty acids and glycerol. Thus after digestion, fats (triglycerides) become fatty acids and glycerol.
C. Digestion of Carbohydrates: Pancreatic amylase digests the carbohydrates into disaccharides (like maltose, sucrose, lactose etc). They are digested into monosacharides by monosaccharidases (like maltase, sucrase, lactase etc).
* Thus after digestion Corbohydrates become monosaccharides
D. Digestion of nucleic acids:
Nucleases of pancreatic juice digests the nucleic acids in the following way
2. Explain digestive system of man with neat labelled diagrams.
A: Digestive system of human beings consists of an alimentary canal and the digestive glands associated with it.
1. Alimentary Canal: It is a long and coiled tube like structure that begins with mouth and ends with anus.
A. Mouth: Mouth is bound by movable and muscular upper and lower lips (labia). Mouth leads into buccal cavity (oral cavity).
B. Buccal cavity: The roof of buccal cavity is formed by a palate, which separates the dorsal nasal chambers and ventral food passage and it facilitates breathing and chewing at a time. The anterior part of palate is bony and is called hard palate (lined by ectodermal membrane, which is thrown into folds called palatine rugae) and posterior part is known as soft palate. Soft palate hangs down into pharynx asuvula. The jaw bones contains teeth and floor of buccal cavity bears tongue.
A) Teeth: In man, teeth are embedded in sockets on jaw bones. Hence they are described as the codont teeth. Two sets of teeth are formed in life time - first set is called milk teeth (deciduous teeth), which are replaced by the second set called permanent teeth. Hence, the dentition is also called diphiodont dentition. Four different types of teeth are present in adult, viz., incisors (i), canines(c), premolars (pm) and molars (m). Hence, the type of dentition is heterodont dentition. An adult man has 32 teeth in total the arrangement of different teeth in each half of upper and lower jaws is represented by the dental formula.
* Third molars comes out at an age of about 21 years. They are described as wisdom teeth.
* Canines (chisel shaped) are for cutting; canines (dagger shaped) are for tearing; premolars and molars (cheek teeth) help in grinding and chewing.
Structure of a tooth:
* A typical tooth has three parts, namely, root (embedded in the socket of jaw bone), neck and crown (visible part).
* Tooth is formed by a hard material called dentine (mesodermal).
* A cavity is present inside the tooth (called pulp cavity), which is filled with pulp. Pulp cavity is lined by odontoblasts, which secrete the dentine.
* The dentine of root and socket of jaw bone are firmly attached by periodontal membrane (surrounds root) and cementum.
* The attachment is further strengthen by the gums (gingiva).
* The crown is covered by a white, shiny material called enamel. It is the hardest substance in the body and is secreted by ectodermal cells called ameloblasts.
B) Tongue: It is a flat, semi circular muscular structure that is attached behind to the floor of buccal cavity with a tissue called frenulum. The upper surface of tongue has small projections called papillae, which are of three types:
i. Fungiform papillae - Anterior margin and tip of tongue.
ii. Filiform papillae - On the surface of tongue.
iii. Circumvallate papillae - Posterior part and base of tongue.
* Papillae contain taste buds.
* Tongue helps in mixing the food with saliva, detecting taste, deglutition and speaking.
* Tongue acts as universal tooth brush.
C. Pharynx: Buccal cavity is posteriorly continued as pharynx, which is a common passage for food and air. Soft palate divides the pharynx into nasopharynx (present above the soft palate) oropharynx (middle part) and laryngopharynx (lower part). Trachea and oesophagus open into the laryngopharynx through glottis and gullet respectively. Glottis has a cartilagenous flap called epiglottis, which prevents the entry of food and water into the trachea. Pharyngeal wall contains the tonsils (lymphoid organs), which are of three types, namely, pharyngeal tonsil (adenoids), palatine tonsils and lingual tonsils.
D. Oesophagus: It is a thin walled long muscular tube passing through the neck, thorax, diaphragm and opens into the stomach through cardia. It is surrounded by a cardiac sphinctu (muscle) (which regulates the opening of oesophagus into stomach).
E. Stomach: It is a wide, distensible sac like organ present in the upper part of abdominal cavity towards left side. It is distinguished into cardiac portion (receives oesophagus), fundic portion and pyloric part (opens into the small intestive through pylorus). Pylorus is guarded by a pyloric sphincter (muscle).
F. Small intestine: It is the longest part of the alimentary canal of man. Its anterior part is described as duodenum middle part as jejunum and distal long and coiled ileum. Ileum opens into the large intestine. Major part of digestion, absorption of digested food occurs in small intestine. Inner lining of small intestine has many villi, which increase area of Absorption.
G. Large intestine: It can be distinguished into three parts, namely caecum (contains symbiotic microbes. Vermiform appendix, avestigial organ arises from caecum. Caecum opens into colon), Colon (it is divided into an ascending, a transverse and a discending parts and sigmoid colon). Colon shows external bulged out pouches called haustra. Colon is continued as rectum. It joins the anal canal. Large intestine absorbs water, some minerals and certain drugs.
H. Anus: Anal canal opens out through anus. It is guarded by an internal anal sphincter (formed by smooth muscles) and an external anal sphincter (formed by striped muscles).
2. Digestive glands
A. Salivary glands: Opening into the buccal cavity, there are three pairs of salivary glands. They are
i. Parotid glands - at the bases of pinnae.
ii. Sub-maxillary glands - at angles of lower jaw.
iii. Sub lingual glands - below the tongue.
Salivary glands are formed by serus cells and mucus cells which secrete saliva (pH = 6.8). Saliva contains water, salts, mucin and an enzyme ptyalin (salivary amylase).
Inflammation of parotid glands due to infection ofparamyxovirus is known as Mumps.
B. Gastric glands: These are minute tubular glands present in the wall of stomach. These are of three types, viz., cardiac glands (secrete mucus), pyloric glands (secrete mucus and the hormone gastrin), fundic glands or oxyntic glands. Fundic glands are formed by neck cells (secrete mucus), peptic or chief cells (secrete the proenzymes - pepsinogen, prorennin) and oxyntic cells (secrete HCl and Castle's intrinstic factor)
Gastric glands secrete gastric juice (pH = 0.9 to 1.8), which contains mucus, HCl, pepsinogen, prorennin and Castls intrinsic factor and gastric lipase.
C. Intestinal glands: These are present in the wall of small intestine and are of two types, namely, Brunner's glands and crypts of Leiberkuhn. Secretion of Brunner's glands (that is mucus) along with that crypts of Leiberkuhn is called intestinal juice or succus entericus (pH = 7.5 - 8.0). It contains peptidases (aminopeptidase, tripeptidase, dipeptidase), disaccharidases (sucrase/invertase, maltase, lactase), lipase and enterokinase (enzyme activator).
D. Liver: It is the largest gland in the human body (1.2 kg - 1.5 kg). It is a bilobed gland, that lies in the abdominal cavity below the diaphragm towards right side. Each lobe of the liver is formed by hexagonal hepatic lobules, which are surrounded by
connective tissue sheath, known as Glisson's capsule. They are the structural and functional units of the liver. Each lobule contains a central vein in the middle. Around this vein liver cells (hepatic cells) are arranged in the form of hepatic cords. Liver secretes bile juice (pH = 7.6) which does not contain enzymes. The bile juice secreted by hepatic cells passes through the hepatic ducts and is stored in a thin walled muscular sac called gall bladder. The cystic duct arising from gall bladder and the common hepatic duct are united to form common bile duct. Bile duct and pancreatic duct open into the duodenum through a common duct called hepatopancreatic duct. The opening of this duct into duodenum is guarded by a sphincter of oddi. Bile juice is alkaline (due to presence of bile salts) and it emulsfy the fats.
E. Pancreas: It is the second largest gland in human body. It is a mixed gland formed by acini and Islets of Langerhans and lies in the loop of duodenum. Acini secrete pancreatic juice (pH = 8.4), which contains sodium bicarbonate, trypsinogen chymotrypsinogen, carboxypeptidase, lipase/steapsin, amylase and nucleases (DNAase and RNAase). Islets of Langerhans (endocrine cells) secrete insulin, glucagon etc.)
III. PROCESS OF DIGESTION / PHYSIOLOGY OF DIGESTION
In man, digestion is extracellular and it involves two activities, viz., mechanical digestion (cutting and chewing of food and churning in stomach etc) and chemical digestion (involves many biochemical reactions catalysed by enzymes.)
1. Digestion in buccal cavity: In the buccal cavity, food is thoroughly masticated among teeth. While chewing, food is mixed with saliva. Tongue play an important role in mixing. Mucus of saliva makes the food into bolus. Ptyalin acts on starch (carbohydrate) and about 30% of starch is hydrolysed into maltose. Lysozyme of saliva check the harmful microbes. Then the bolus is swallowed through pharynx, oesophagus and reaches the stomach. This process is called deglutition.
2. Digestion in stomach: Food remains in stomach for hours. Here the gastric juice is secreted and by churning movements of stomach, it is mixed with the food. Mucus protects the mucosa of stomach from excoriation by HCl and also play important role in lubrication. HCl kills the harmful microbes that reached the stomach along with food and also activates the proenzymes pepsinosen and prorennin into pepsin and rennin respectively. Rennin is found in infants. It acts on milk protein, Casein and converts into Calcium paracaseinate (curd) in presence of Ca++. Pepsin digests the proteins including curd into proteoses and peptones. Action of gastric lipase is insignificant.
Thus this partially digested food becomes a semi fluid mass in the stomach due to its churning movements known as chyme. It little by little reaches the small intestine.
3. Digestion in small intestine: In the duodenum the chyme is mixed with bile juice, pancreatic juice and intestinal juice. Mucus protects the mucosa small intestine. Bile makes the chyme (acidic) into alkaline material, because pancreatic and intestinal enzymes work in alkaline medium only.
A. Digestion of Proteins: Trypsinogen is activated by the enterokinase into trypsin. Thus trypsin further activates the trypsinogen (autocatalysis).
Trypsin also activates the chymotrypsinogen into chymotrypsin. Proteins, proteoses, peptones present in chyme are digested into tripeptides and dipeptides by trypsin, chymotrypsin, carboxypeptidase and aminopeptidase. Tripeptides and dipeptides are digested into amino acids by tripeptidase and dipeptidase. Thus, after digestion, proteins are converted in to aminoacids.
B. Digestion of Fats:
Bile salts of bile juice emulsify the fats (tryglycerides) (Breakdown of large fat globules into smaller, uniformly distributed particles is known as emulsification). Lipases of pancreatic juice (= steapsin) and intestinal juice digest the fats (triglycerides) into fatty acids and glycerol.
Thus after digestion, fats (triglycerides) become fatty acids and glycerol.
C. Digestion of Carbohydrates: Pancreatic amylase digests the carbohydrates into disaccharides (like maltose, sucrose, lactose etc). They are digested into monosaccharides by monosaccharidases (like maltase, sucrase, lactase etc).
Thus after digestion corbohydrates become monosaccharides.
D. Digestion of Nucleic acids: Nucleases of pancreatic juice digests the nucleic acids in the following way:
IV. ABSORPTION
Diffusion/ Transport of digested food into the blood/lymph through intestinal mucosa is known as absorption.
i. Little amounts of monosaccharides (glucose, galactose), amino acids, Cl - are absorbed by simple diffusion (based on concentration gradient).
ii. Some substances such as fructose, amino acids etc. are absorbed with the help of carrier ions such as Na+ (facilitated transport)
iii. Water is absorbed on the basis of osmotic gradient.
iv. Glucose, aminoacids and some electrolytes are absorbed by acitve transport.
v. Bile salts combine with long chain fatty acids and glycerol to form micelles. They are absorbed by the cells of intestenal lining. In these cells, they are converted into lipids forming the chylomicrons along with phospholipids and cholesterol and coated with proteins. By exocytosis, they pass into lacteals of villi. When lymph mixes with blood, an enzyme lipoprotein lipase in blood plasma hydrolyses the chylomicrons into fatty acids and glycerol.
V. ASSIMILATION
Utilisation of digested food by the tissues for the production of energy, growth and repair this process is called assimilation.
VI. DEFAECATION
Undigested and unabsorbed substances (called roughase) reach the colon, where water is absorbed along with some minerals and drugs. Mucus hold the undigested matter and also lubricate the passage. Then the matter is temporarily stored in rectum till it is egested through anus (defaecation) they initiate a neural reflex causing an urge for its removal. Egestion is a voluntary process and is carried out by mass peristalsis.
VII. INFLUENCE OF HORMONES ON DIGESTION
Gastro intestinal mucosa contains certain endocrine cells and they secrete hormones that facilitates the digestive process.
|
Hormone |
Secreted by... | Effect(s) |
| Gastrin | Epethelium of stomach | Stimulates the secretion of HCl and pepsinogen |
| Enterogastrone (Gastric Inhibitory Peptide - GIP) | Epithelium of duodenum | Inhibits gastric secretion |
| Secretin | Epithelium of duodenum | Acts on acini of pancreas and stimulates secretion of water, HCO3− |
| Cholecystokinin | Epethelium of duodenum | Makes the gall bladder to contract. Hence bile juice is poured into duodenum |
| Pancreozymin | Epethelium of duodenum | Stimulates the secretion of pancreatic enzymes |
| Enterocrinin | Duodenal mucosa | Stimulates the secretion of succus entericus |
| Villikinin | Intestinal villi | Stimulates movement of villi to increase absorption |
VIII. CALORIFIC VALUES
The energy released by one gram each of carbohydrates, proteins and fats on oxidation is shown in the following table.
Food Material (1g) Energy released on Oxidation (K.cal)
Carbohydrates 4.0
Proteins 4.0
Fats 9.0
IX. DISORDERS OF DIGESTIVE SYSTEM
i. Inflammation of the gut is the most common ailment due to viral and bacterial infections.
ii. Vomiting: It is the expulsion of the contents of the stomach through mouth. This is a reflex action controlled by the vomiting center in medulla oblongata of brain. A feeling of nausea preceeds vomiting.
iii. Diarrhoea: Increased liquidity of the faeces and abnormal bowel frequency are described as diarrhoea. In diarrhoea, dehydration and reduction of absorption of digested food result.
iv. Indigestion: In this condition, food is not properly digested leading to a feeling of fulliness. Spicy foods, over eating etc. are causes for indigestion.
v. Constipation: In this condition, due to low water content in faeces, it becomes hard and is retained in the rectum. Movement bowel occur irregularly.
vi. Jaundice: It is the disease of liver. Anarexia (loss of appettite) is the main symptom. Due to deposition of bile pigments the skin and white parts of eye balls turn yellow.
X. FUNCTIONS OF LIVER
¤ Bile juice secreated by liver contains bile salts (glycocholate and taurocholate of Sodium and Potossium) and they emulsify fats during digestion.
¤ Liver plays an important role in carbohydrate metabolism (glycogenesis, glycogenolysis, gluconeogenesis, lipogenesis), fat metabolism (formation of cholesterol, triglycerides) etc.,
¤ Deamination of proteins and conversion of ammonia into urea via ornithine cycle takesplace in liver.
¤ The lactic acid formed in muscle contraction is converted to glycogen in liver (Cori cycle).
¤ Liver acts a detoxifying organ.
¤ Liver acts as a thermoregulatory organ.
¤ In embryonic state, liver acts as a haemopoitic organ.
¤ Liver synthesises the plasma proteins (albumins, globulins); blood clotting factors (fibrinogen, prothrombin), anticoagulant (heparin) etc.,
¤ Kupfer cells acts as macrophases and engulf harmful microbes by phagocytosis.
¤ Glycogenesis: Formation of glycogen from glucose.
¤ Glycogenolysis: Formation of glucose from glycogen.
¤ Gluconeogenesis: Formation of glucose/ glycogen from non carbohydrates.
¤ Lipogenesis: Formation of lipids.
