BIOLOGY 2 Marks Questions

The bile released into the duodenum contains bile pigments (bilirubin and biliverdin), bile salts, cholesterol and phospholipids but no enzymes. Bile helps in emulsification of fats, i.e. breaking down of fats into small micelles. It also activates lipases which carry out the digestion of fats.

The proenzyme pepsinogen, on exposure to hydrochloric acid, gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Pepsin converts proteins into proteoses and peptones (peptides). Pepsinogen → Pepsin + Protein → Proteose + Peptone.

Gastric glands include three major types of cells. These are as follows:

S.No.
1.	Mucus (neck) cells	Secrete mucus
2.	Peptic or chief cells	Secrete pepsinogen
3.	Parietal or oxyntic cells.	Secrete hydrochloric acid and intrinsic factor.

As the digestive waste reaches the rectum, it gets accumulated in rectum. If it is not excreted out through egestion process, it will intoxicate the whole body.

1. Absorption of water, minerals and certain drugs.
2. Secretion of mucus that helps in adhering the undigested wastes into coherent faeces and lubricating it for easy passage.

The maximum absorption of digested food occurs in the small intestine of alimentary canal. The absorbed form of different food materials are:

S.No.	Food Material	Absorbed Form
1.	Carbohydrate	Glucose
2.	Protein	Amino acid
3.	Fat	Fatty acid

Causes of Kwashiorkar: Protein deficiency unaccompanied by calorie deficiency can lead to kwashiorkar. It results from the replacement of mother's milk by a high calorie low protein diet in child more than one year in age.

Bile juice has no digestive enzymes, yet, it performs the following functions to facilitate digestion of fats in the food:

1. Bile emulsifies fats and increases the surface area for action of lipases.
2. Bile activates lipases, the enzymes which digest fats.

• Nucleases present in the pancreatic juice convert the nucleic acids into nucleotides.
• Nucleotidases present in the intestinal juice convert the nucleotides into nucleosides and phosphates.
• Nucleosidases present in the intestinal juice convert the nucleosides into nitrogen bases and sugars.

The lining of the oesophagus, stomach and intestine is muscular, these help in pushing food through it easily by its own by peristalsis movements. These movements of muscles help the food to pass through along the whole alimentary canal.

The sight, smell and/ or presence of food in the oral cavity can stimulate the secretion of saliva. Gastric and intestinal secretions are also stimulated by similar neural signals. Muscular activities of alimentary canal is coordinated by both local and CNS neural mechanisms. Hormonal control of secretion of digestive enzymes is carried out by local hormones.

1. Gall bladder.
2. Stomach.
3. Pancreas.
4. Deuodenum.

Tongue helps in mixing the food properly with salivary enzymes. Moreover, tongue has tastebuds which give the sense of different tastes. Eating is a complex process which needs involvement of olfactory and visual senses as well. Alongwith tongue all these senses help in picking the right food.

1. Fibrous food material expands the gut and softens the stool volume (faecal matter), stimulates peristalsis and also prevents constipation.
2. Indigestible fibrous food material is known as roughage.
3. Raspberries, avocado, apple, peach and green leafy vegetables are good sources of the fibre.
4. Lalit, is a good and obedient student, patient listener and a good learner.

After digestion and absorption of food is over, the residue left makes the digestive waste. The digestive wastes, solidified into coherent faeces in the rectum initiate a neural reflex causing an urge or desire for its removal. 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.

2. The person may suffer from poor bowel movement; leading to constipation. Constipation is a condition in which the patient does not passes stool at regular intervals. It can lead to accumulation of waste products in the large intestine. As we know; removal of waste products is necessary for the body because such substances can prove very harmful for the body. Moreover, constipation can also lead to overall discomfort in the body. The person may lose his appetite. Too much strain during passing the stool can put extra workload on the heart. Constipation can also result in aggravation of piles. One should drink lot of water and take lot of fibre in food to avoid constipation.

• The pancreatic juice contains amylase, for digestion of starch and lipases for digestion of fats.
• Since these enzymes cannot reach the duodenum, the digestion of these nutrients, will be impaired.

Causes of marasmus: Simultaneous deficiency of proteins and calories can lead to marasmus. In infants less than a year in age, if mother's milk is replaced too early by other foods which are poor in both proteins and calorific value; marasmus can be prevalent. This can happen if the mother has second pregnancy or childbirth when the older infant is still too young.

Starch is not digested in the stomach, because the enzyme ptyalin (salivary amylase) that is used in its digestion cannot survive in the acidic (low) pH of the stomach due to the presence of HCI.

1. Caesin.
2. Lacteal.
3. Micelle.
4. Villi.

Difference between small and large intestine:

S.No.	Small intestine	Large intestine
1.	Longer in length.	Shorter in length.
2.	Major part of digestion take place here.	No digestion happens.
3.	Absorption of food substances taken place.	Absorption of some water takes place.

Major absorption of digested food takes place in the small intestine. This happens in jejunum and ileum which are parts of small intestine and lined by finger like projections called villi. Carbohydrate is absorbed in the form of glucose. Proteins are absorbed in the form of amino acids. Fats are absorbed in the form of fatty acids and glycerol.

In the labelled part A (i.e., the stomach,) the enzyme responsible for first stage of protein digestion is produced. A-stomach, B-pancrease, C-small intestine, D-gall bladder.

Various causative factors for indigestion are:

1. Inadequate secretion of digestive enzymes and gastrointestinal hormones.
2. Anxiety.
3. Food poisoning.
4. Overeating and spicy food.

1. Inactive form of pepsinogen is activated by the action of HCl.
2. Bile salts help in emulsification of lipids and activate the lipases.

The local digestive hormones are produced by gastric and intestinal mucosa e.g., secretin, cholesyctokinine, etc. The hormones stimulate the activity of enzymes. If these are not produced, the process of digestion will be hindered and digestive system will not work properly.

Amylase acts on starch which is not a constituent of any tissue lining the gut, so, there is no need for it to be secreted in an inactive form. Whereas, the trypsin is a protease that can hydrolyse the cellular and intercellular proteins of the gut wall in the absence of food. So, it has to be secreted in an inactive form.

• Kwashiorkar is a form of protein-energy malnutrition (PEM), that arises due to dietary deficiency of proteins in children below the age of five.
• Its symptoms include:

1. Extensive oedema and swelling of body parts.
2. Wasting of muscles.
3. Thinning of limbs.
4. Failure of growth and brain development.

1. Starch.
2. Pepsin.
3. Duodenum.
4. Fatty acids + Glycerol.
5. Nucleases.
6. Lactose.

Organs of human alimentary canal are mouth, oesophagus, stomach, small intestine and large intestine and anus. The major digestive glands and their location are as follows.

S.No.	Digestive Gland	Location
1.	Salivary glands	Mouth cavity
2.	Liver	In abdominal cavity, just below the diaphragm.
3.	Pancreas	Between the limbs of U-shaped duodenum.

Differences between chylomicrons and micelles are:

Chylomicrons	Micelles
Protein coated water soluble tat droplets of about 150mm released into the lymph.	It is formed by combination of fatty acids, monoacylglycerols and the bile salts.
In this form fats/ lipids are put into circulation.	In this form, digested fats are absorbed in intestinal cells in alimentary canal.

S.No.	Micelles	Chylomicrons
1.	The products of fat digestion are incorporated into small, spherical, watersoluble molecules called micelles with the help of bile salts and phospholipids.	The products of fat digestion are used for synthesising new fats, which are released by the intestinal cells into the lymph, in the form of droplets, called chylomicrons.
2.	This is the form in which digested fats are absorbed into the intestinal cells.	This is the form in which the synthesised fats are liberated from the intestinal cells.

The buccal cavity performs the following major functions.

1. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly.
2. Mucus in saliva helps in lubricating and adhering the masticated food particles into bolus.
3. The bolus is then passed into the pharynx and then into oesophagus for further digestion.

After digestion and absorption of food is over the residue left makes the digestive waste. The digestive wastes, solidified into coherent faces in the rectum initiate a neural reflex causing an urge or desire for its removal. The egestion of faces to the outside through the anal opening (defaecation) is a voluntary process and is carried out by a mass peristaltic movement.

Pancreas contributes in following functions in the body:

1. It contributes to the digestion of different components of food.
2. The absorption of food breaken down products from the digestive tract start taking place here.
3. The metabolism of blood sugar is regulated.

Hence, if any malfunctioning happens to pancreas, it fails to perform these functions properly.

1. Any irregularity in bowel movement leads to a condition when person is not able to defecate. Faeces remain inside the digestive septem. It is called constipation.
2. Elimination of excreta out of rectum is called defaecation.

Absorption of water in the small intestine occurs by osmosis. The water passes the lumen of the small intestine through epithelial cells and then to blood capillaries in the villi. Water absorption in general is accompanied with the absorption of electrolytes and digested food in order to maintain an osmotic balance with the blood.

Functions of large intestine:

1. Absorption of some water, minerals and certain drugs.
2. Secretion of mucus. Mucus helps in adhering the waste particles together and lubricates it for easy passage.

The HCl produced in the stomach is not as strong as used for industrial purposes. However, acidic behaviour of HCl does not corrode the stomach walls, because the gastric epithelium of stomach is secretory in nature, i.e., it produces mucus, which covers the stomach wall preventing it from corrosive action of gastric juice.

The Brunner's gland secretes mucoid fluid. It has the following characteristics:

1. It is viscous and enzyme-free.
2. It is alkaline in nature and enables duodenum to withstand the acid chyme.
3. It also protects its wall from getting digested.

• Amylase acts on starch which is not a constituent of any tissue that lines the gut, so there is no need de for it to be secreted in an inactive form.
• Trypsin is a protease that can hydrolyse the cellular and intercellular proteins of the gut wall in the absence of food; so it has to be secreted in an inactive form.

The mucosa is secreted by the goblet cells. It also mixes with the bicarbonates from the pancreas. These protect the intestinal mucosa from acid food. It also provides an alkaline medium (pH-7.8) for pancreatic enzyme activities. Submucosal glands (Brunner's glands) also help in this action.

The mucosa is folded into finger-like projections called villi. The cells lining the villi bear microvilli giving it a brush-bordered appearance. These two features increase the surface area of intestine for absorption. The villi are richly supplied with a network of blood capillaries and a large lymph vessel, lacteal, for easy absorption of nutrients.

Symptoms of marasmus:

• Thinning of limbs.
• Dry and wrinkled skin.
• Very low body weight.
• Growth retardation.
• Impaired development of brain and mental faculty.

Absorption of fat takes place in the following ways:

1. Digested fat is absorbed in the small intestine.
2. Bile salts break up bigger molecules of fat into small droplets called micelles that move into intestinal mucosa.
3. They are reformed into small protein coated fat globules called chylomicrons.
4. These are transported to lymph vessels (lacteales) in this villi.
5. These lymph vessels ultimately release the absorbed substances into bloodstream.

• The alkaline pH is provided by:

1. Secretion of Brunner's glands.
2. The bicarbonates from the pancreas.
3. bile.

• Trypsin:

1. Activates other proteases.
2. Acts on the proteins, proteoses and peptones.

Gut lining is protected from its own secretion of proteases as:

1. Proteases are secreted in its inactive form called proenzymes so, that they do not act on gut lining.
2. Gut secretes mucus which thereby inactivates the proteases and protects the gut lining.

Symptoms of Kwashiorkar:

• Wasting of muscles.
• Thinning of limbs.
• Impaired physical growth.
• Impaired brain development.
• Extensive oedema and swelling of body parts.

Pancreas is a gland having exocrine and endocrine portions involved in secreting digestive enzymes as well as hormones. Major secretions of pancreas involved in digestion are inactive enzymes listed below:

1. Trypsinogen.
2. Chymotrypsinogen.
3. Procarboxypeptidases.
4. Amylases.
5. Lipases.
6. Nucleases.

The food which has been digested and absorbed by the blood passes through the liver. A person, who consumed some poisonous substance, its traces would naturally go to the liver. Hence, liver cells are chemically examined during postmortem to know the contents of the cells of liver.

The alkaline pH is provided by the following type of secretions:

1. Secretion of Brunner's glands.
2. The bicarbonates from the pancreas.
3. Bile.

Actions of trypsin are as follows:

1. Activates other proteases.
2. Acts on the proteins. proteases and peptones.

The salivary glands present in our mouth produce saliva, which makes our mouth watery. The brain registers, that food is coming and instructs the salivary gland present underneath the tongue to produce saliva, which helps in breakdown of food as we chew it. Thus, making it softer as it enters the gut.

As the pancreatic juice contains amylase, for the digestion of starch and lipases for digestion of fats. Thus, if there is any blockage in the pancreatic duct, these enzymes would not be able to reach the duodenum of small intestine which will ultimately impair the digestion of these nutrients.

Apart from taking part in digestion of starch, saliva also helps to lubricate the food for swallowing.

Liver is the largest gland in human body which is mainly responsible for the digestion of food. Role of liver in digestion of food:

1. Its hepatic cells secrete bile juice which passes through the hepatic duct into the gall bladder.
2. It has its major role in processing of proteins, i.e., formation of urea.
3. Bile secreted by it is mainly responsible for digestion of fats for easy absorption in the body.
4. Also responsible for the removal of toxins from blood.

• Pepsinogen in gastric juice and trypsinogen in pancreatic juice are the proenzymes.
• Pepsinogen is activated by hydrochloric acid into pepsins that acts on proteins and converts them into peptones and proteoses.
• Trypsinogen is activated by enterokinase into trypsin, which acts on proteins, peptones and proteoses and converts them into smaller peptides.

• Enterokinase is secreted by the intestinal mucosa in the succus entericus.
• It activates trypsinogen into active trypsin.

Bile is produced by the liver and pancreatic juice is secreted by pancreas. Liver and pancreas are the two glands of alimentary canal these produce substances (enzymes and bile free) involved in the digestion of fat.

Lysozyme and salivary amylase. Lysozyme kills bacteria and amylase digest carbohydrate, specially starch.

The lacteal absorbs the end products of fat digestion, i.e., fatty acids and glycerol. This, transports them to the lymphatic vessels that eventually empty these products into the blood circulation.

1. Liver secretes bile juice. It is stored in gall bladder.Bile secretion contains no enzymes.
2. Bile contains salts, namely, sodium glycolate and sodium taurocholate. These reduce the surface tension of large fat droplets and break them into many small ones. The process is called emulsification. Bile salts also form a thin coating around tiny fat droplets to keep them free from each other.

1. Gastric glands of stomach mucosa have oxyntic cells which secrete HCl.
2. Saliva contains enzymes that digest starch.

Constipation: Difficult, delayed and infrequent defecation (elimination of solid, semisolid or liquid waste material from the digestive tract via the anus) caused by insufficient water in the feces is called constipation. It is caused by a decrease in intestinal tract motility leading to dry, potentially painful fecal evacuation. It may results from stress, lack of exercise, or insufficient fiber in the diet.Indigestion: Indigestion also known as dyspepsia refers to condition of impaired digestion and uncomfortable sensations which affect the upper abdomen with burning or pain. It can appear with heartburn, belching, bloating, or nausea. The symptoms of indigestion include a feeling of fullness during a meal and bothersome fullness after a meal, burning or pain in the upper abdomen etc. It could be caused by a condition in the digestive tract such as gastro esophageal reflux disease (GERD).