• The duodenum forms a 'C' shape around the head of the pancreas. Its main function is to neutralise the acidic gastric contents (called 'chyme') and to initiate further digestion; Brunner's glands in the submucosa secrete an alkaline mucus which neutralises the chyme and protects the surface of the duodenum.

• The jejunum

• The ileum. The jejunum and the ileum are the greatly coiled parts of the small intestine, and together are about 4-6 metres long; the junction between the two sections is not well-defined. The mucosa of these sections is highly folded (the folds are called plicae), increasing the surface area available for absorption dramatically.

• The Pancreas

• The pancreas consists mainly of exocrine glands that secrete enzymes to aid in the digestion of food in the small intestine. the main enzymes produced are lipases, peptidases and amylases for fats, proteins and carbohydrates respectively. These are released into the duodenum via the duodenal ampulla, the same place that bile from the liver drains into.  Pancreatic exocrine secretion is hormonally regulated, and the same hormone that encourages secretion (cholesystokinin) also encourages discharge of the gall bladder's store of bile. As bile is essentially an emulsifying agent, it makes fats water soluble and gives the pancreatic enzymes lots of surface area to work on.  structurally, the pancreas has four sections; head, neck, body and tail; the tail stretches back to just in front of the spleen. 

The Large Intestine

• By the time digestive products reach the large intestine, almost all of the nutritionally useful products have been removed. The large intestine removes water from the remainder, passing semi-solid faeces into the rectum to be expelled from the body through the anus. The mucosa (M) is arranged into tightly-packed straight tubular glands (G) which consist of cells specialised for water absorption and mucus-secreting goblet cells to aid the passage of faeces. The large intestine also contains areas of lymphoid tissue (L); these can be found in the ileum too (called Peyer's patches), and they provide local immunological protection of potential weak-spots in the body's defences. As the gut is teeming with bacteria, reinforcement of the standard surface defences seems only sensible... 

41. Describe the general ways in which antimicrobial agents may kill microorg or inhibit their growth

. Microbicidal agents are chemicals that will kill or destroy microorganisms. There are several factors that will influence the effectiveness of antimicrobial agents. When attempting to sterilize, disinfect or sanitize a surface and in the application of aseptic technique, these factors must be taken into consideration. 1. Organic solvents and strong surfactants both act by dissolving the phospholipid bilayer. This destroys the barrier that usually limits movement of ions and other chemicals into or out of the cell. 2. Agents that alter transmembrane proteins destroy the ability of a cell to selectively import or export substances and, in the bacterial cell, can lead to the inactivation of cytochromes and ATP synthase. Inactivation of these proteins destroys the ability of the cell to generate ATP. Damage to a cell’s DNA will inhibit that cell from properly reproducing and stop the use of the DNA as a guide to make RNA. Bombardment of cells with radiation will lead to DNA damage. Certain drugs bind to the enzymes needed to make DNA or RNA and interfere with the functioning of these enzymes. Nucleotide analogs are chemicals that have considerable similarities to the nucleotides used in the synthesis of DNA. When the analog is added to a growing DNA strand during replication, the synthesis of the DNA strand immediately stops. 3. Many antimicrobials work solely or in part by altering the tertiary structure (shape) of a protein or by blocking the active site of an enzyme. Reactive chemicals will often covalently bind to proteins. This changes the shape of a protein in ways that leave it unable to function properly. Many antimicrobial drugs bind to the ribosome or active site of RNA polymerase. By blocking the action of these two enzymes protein synthesis can be effectively shut down. 4. Chemical agents do not have equal levels of disinfection. Halogens react with proteins in such a way that secondary and tertiary structure is altered. Alcohols At 50-95% concentration are effective in disrupting membranes and alter protein tertiary structure. At 95-100% concentrations alcohols mainly serve to dehydrate cells. Hydrogen peroxide produces reactive hydroxyl radicals that oxidize proteins and other organic molecules. Detergents mainly disrupt membranes. 5. Several types of radiation are commonly used to kill contaminating organisms. 1. Ionizing radiation penetrates organic matter very easily and when it strikes a molecule it will often cause the molecule to breakdown into highly reactive ions. 2. Ultraviolet radiation (UV light) reacts with the pyrimidine bases of DNA (thymine and cytosine) - pyrimidine dimer. These dimers interfere with the ability of the effected pyrimidines to complementary base pair. This destroys the ability of the damaged DNA to carry out transcription or replication.