Role of large intestine in digestion - class-VII

• The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system.Water is absorbed here from the undigested food and the remaining waste material is stored as feces before being removed by defecation.
  
• Hence water from the undigested food is absorbed mainly in the large intestine.
• So,the correct answer is 'Large intestine'.

The large intestine, also called as the colon or the large bowel, is the last part of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored as feces before being removed by defecation.

The colon is the last part of the digestive system in most vertebrates. It extracts water and salt from solid wastes before they are eliminated from the body and is the site in which large bacterial fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a major role in absorption of foods and nutrients. 

The vermiform appendix is also referred to as the vermix or the cecal appendix. It is a blind ended tube connected to the cecum, at the junction of large and small intestine. The appendix is usually located in the right lower quadrant of the abdomen, near the right hip bone.

The vermiform appendix is also referred to as the cecal appendix. It is a blind ended tube connected to the cecum. The appendix is usually located in the right lower quadrant of the abdomen, near the right hip bone. Its position within the abdomen corresponds to a point on the surface known as McBurney's point.

The completely digested food in small intestine is liquid in physical state, so that, absorption of nutrients can be easily carried out but the faeces are reduced in volume and a semi-solid coherent mass because most of the water is absorbed in large intestine.

After the digestion of carbohydrates in the mouth, food is passed on from mouth to stomach through the oesophagus where the digestion of proteins takes place. The food enters the small intestine for the digestion of proteins, carbohydrates and fats. Finally, it moves to the large intestine which is the last part of the alimentary canal where water is absorbed and undigested/ unabsorbed food is converted into a coherent mass of faeces and ejected from the body through a muscular anus.

The caecum is an intraperitoneal pouch which is considered to be the beginning of the large intestine. It receives chyme from ileum and connects to the ascending colon of the large intestine. The caecum is called blind sac because caecum looks like a sac which has sphincter at the ileocaecal junction and it remains closed and is invisible. Hence, it is called a blind sac.

• The large intestine is the final section of the gastrointestinal tract that performs the vital task of absorbing water and vitamins while converting digested food into feces.
•  Although shorter than the small intestine in length, the large intestine is considerably thicker in diameter, thus giving it its name. 
• The large intestine is about 5 feet (1.5 m) in length and 2.5 inches (6-7 cm) in diameter.

The chyle entering the large intestine consists of about 75% water and some fatty and proteinaceous substances. Water is absorbed into the blood as the waste materials move through the colon. The symbiotic bacteria E. coli and Streptococcus faecalis normally residing in the human healthy colon, feed on protein contents of chyle, breaking them into amino acids which are absorbed into the blood. The colon bacteria also synthesize vitamin B1, B2, biotin, folic acid and K which are absorbed. They convert bile pigments into brown pigments that give colour to faeces. Intestinal bacteria also produce foul-smelling compounds and gases (methane. hydrogen sulphide) which give the characteristic odour to intestinal gas and faeces. The intestinal bacteria also help prevent pathogenic microorganisms from establishing in the intestine. 

Bartholin glands are present on both sides of vaginal opening in mammals like human females. Secretions of bartholin glands act as lubricant during sexual intercourse. Adrenal glands are important endocrine glands present over kidneys. These glands secrete adrenaline, noradrenaline hormones. Prostate is an accessory gland present in male mammals. In human males a single prostrate gland is present. The urethra runs through the center of the prostate, from the bladder to the penis, letting urine flow out of the body. In some carnivores and herbivores scent glands are present in anus. These glands secrete pheromones which act as signals to mark territory and attract possible mates.

Taenia coli are  three bands of smooth muscles which runs in the length of large intestine. Taenia coli contract lengthwise to produce the haustra, the bulges in the colon.

Large intestine is differentiated into three parts cecum, colon and rectum. Cecum continues into colon. Colon is the middle part of large intestine. The longitudinal muscle coat forms three ribbon like bands called teniae coli. Due to the presence of teniae, pouch like structure develops in lumen of colon called as haustra. The colon then continues in a uniform tube called rectum, which is the storage chamber for faeces.

Appendicitis is an inflammation of the appendix, a finger-shaped pouch that projects from the colon on the lower right of the abdomen.
Therefore, the correct answer is option B.

The inferior region of the large intestine forms a short dead-end
segment known as the cecum that terminates in the vermiform appendix.
The superior region forms a hollow tube known as the ascending colon
that climbs along the right side of the abdomen. Just inferior to the
diaphragm, the ascending colon turns about 90 degrees toward the middle
of the body at the hepatic flexure and continues across the abdomen as
the transverse colon. At the left side of the abdomen, the transverse
colon turns about 90 degrees at the splenic flexure and runs down the
left side of the abdomen as the descending colon. At the end of the
descending colon, the large intestine bends slightly medially at the
sigmoid flexure to form the S-shaped sigmoid colon before straightening
into the rectum. The rectum is the enlarged final segment of the large
intestine that terminates at the anus.

The vermiform appendix is attached to its posteromedial surface of the large intestine. It contains masses of lymphoid tissue. It is a part of mucosa-associated lymphoid tissue which gives the appendix an important role in immunity. Appendicitis is the result of a blockage that traps infectious material in the lumen. The appendix can be removed with no damage or consequence to the patient. 

Small intestine is the longest part of alimentary canal. It extends from the pylorus of the stomach to the junction between cecum and ileum. Much of digestion and absorption of food takes place in the small intestine. The small intestine is divided into three parts duodenum, jejunum and ileum

The small intestine in adults is a long and narrow tube about 7 meters (23 feet) long. The large intestine is so called because it is wide in diameter. However, it is shorter than the small intestine, only about 1.5 meters (5 feet) long. 

The small intestine in adults is a long and narrow tube about 7 meters (23 feet) long. The large intestine is so called because it is wide in diameter. However, it is shorter than the small intestine - only about 1.5 meters (5 feet) long. 

The process in which the complex and insoluble contents of food are converted into simpler and soluble substances, suitable for absorption and assimilation is called digestion. The food is digested by the digestive system with the help of digestive enzymes.  The usable materials are absorbed by the small intestine and the unusable food is passed on to the large intestine where the water is absorbed and moves to the anus for removal. Hence, the digestive system processes food into usable and unusable materials. The usable materials are sent to the body's cells as food and unusable material goes into the large intestine to await disposal.

Food is digested in three steps i.e mouth, stomach and small intestine. The undigested food is passed through large intestine. Large intestine larger diameter as compared to small intestine but is smaller in length.

Food is digested in small intestine. No digestion takes place in large intestine. Salt and water is absorbed by the large intestine to maintain Osmo regulation.

Digestion ends in small intestine. Waste products are excreted from our body through large intestine. Excess water and salts are absorbed from intestine through muscular finger like projections called Villi.

Putrefaction is the decomposition of proteins caused due to bacterial or fungal decomposition of organic matter. The bacteria, yeast and other organisms in the fermented food allow colon to produce good bacteria. The fermented foods increase B vitamins such as riboflavin, thiamin and niacin. The activated form of folic acid is increased, which helps in cardiovascular and cancer risks. Choline is increased, which breaks down fat in the body and liver and helps with constipation. In addition, fermentation increases glutathione, an anti aging amino acid, and enzymes needed for digestion and detoxification.

The main function of the colon is absorption of much of the water from undigested food and leaving the solid material as faeces.

Haemorrhoids, commonly known as piles, are swollen and inflamed veins in the rectum and anus that cause discomfort and bleeding.

The digestive system starts with the mouth, followed by the food pipe or oesophagus that opens into the stomach. The stomach secretes acid and powerful enzymes that continue the process of breaking the food down into simpler substances. From there, food moves to the small intestine, which is made up of three segments, i.e., the duodenum, jejunum, and ileum.

• The sigmoid colon is the part of the large intestine that is closest to the rectum and anus
  
• It forms a loop that averages about 35-40 cm in length
• The loop is typically shaped like a Greek letter sigma or Latin letter S

There are many bacteria that live in the large intestine of human. They live in symbiotic association. These are Lactobacillus, Bifidobacterium, Methanogens, Bacteroids, Enterococcus, Escherichia coli. Lactobacillus help in digestion, maintaining the pH balance and replacing the healthy bacteria in the gastrointestinal tract. It acts as a probiotic. Bifidobacterium is also a probiotic. It helps in metabolism of undigested carbohydrates. It also prevents pathogen colonization. Methanogen helps in the fermentation of organic matter to obtain energy. They help in breakdown of complex indigestible carbohydrates. Bacteroids helps in amino acid biosynthesis. Enterococcus helps in digestion of undigested carbohydrates and fibres.

In herbivores, the caecum stores food material where bacteria are able to break down the cellulose. This function no longer occurs in the human caecum, so in humans it is simply a dead-end pouch forming a part of the large intestine.

The major function of the large intestine is to absorb water from the remaining indigestible food matter and transmit the useless waste material from the body.

Colonoscopy is the endoscopic examination of the large intestine and the distal part of the small bowel with a CCD camera or a fibre optic camera on a flexible tube passed through the anus. It can provide a visual diagnosis and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions. 

The large intestine also secretes K+ and Cl-. Chloride secretion increases in cystic fibrosis. Recycling of various nutrients takes place in colon. Examples include fermentation of carbohydrates, short chain fatty acids and urea cycling. 

The wall of the large intestine is lined with simple columnar epithelium. Instead of having the evaginations of the small intestine (villi), the large intestine has invaginations (the intestinal glands). While both the small intestine and the large intestine have goblet cells, they are abundant in the large intestine.