Question

5. You are consuming a food item that contains carbohydrates, lipids, proteins, nucleic acids, and a substance A stipulated to not be digestable by human enzymes, but digestible by bacterial enzymes into substance B. Discuss where and how each of the five nutrient types will be digested (multiple locations may be required), and how their absorbable components (monosaccharides, fatty acids, amino acids, nucleotides, and substance B) will be absorbed by the body. Include in your response a complete review of the entire digestive system (not just the digestive tract), including all physical structures the food item will encounter, all digestive secretions (including a breakdown of all enzymatic and non-enzymatic components, and their functions) the food item will occur, and the tissue/organ structures responsible for generating those secretions.

6. Describe the processes involved for the formation of mature spermatozoa, and a secondary oocyte. Include a review of all hormonal regulation involved in the processes of spermatogenesis and oogenesis, as well as the actual formation and maturation of the sex cells from spermatogonia and primary oocytes. Maturation of the sex cells should discuss the supporting cells for both types of sex cells, as well as a review of the organs and structures hosting the maturation and development. Your response should consider formation, development, and maturation for the two sex cells until the end of the process, to be considered as: 1) fully functional, mobile spermatozoa in the epididymis, and 2) just after ovulation for the secondary oocyte.

Answer 1

B. Carbohydrates

The digestion process begins with chewing the food in the mouth. The enzyme present in the saliva ,ptyalin ( salivary amylase ) starts the digestion of starch in the mouth. It hydrolyses starch to dextrins, isomaltose,and maltose in neutral or alkaline pH in the mouth. The activity of amylase continues from mouth to upper part of the stomach. But as soon as the food comes in contact with the hydrochloric acid in the stomach, this action ceases. Very little digestion of carbohydrate takes place in the stomach as the pH is unfavourable. The food mixed with gastric juice form a semi-fluid mass called chyme.It takes about 3-5 Hrs to form chyme. A small portion of chyme is released through pyloric sphicter into the duodenum, the first part of small intestine

The small intestine which is about 20 ft long. most of the digestive activity takes place in its three compartments namely, the duodenum, jejunum and illeum

Carbohydrate digestion takes place almost completely in the small intestine, especially duodenum.Pancreatic amylase breaks starch into maltose and dextrins. The maltase from mucosal cells breaks down maltose into glucose. The brush border , on the surface of the epithelial cells lining the intestine, is the site of action

The enzymes sucrase, lactase ,maltase and isomaltase found on the outer cell membranes of the intestine, acts on the sucrose,lactose, maltose and isomaltose respectively. The monosacchrides formed - glucose, galactose and fructose - pass through the mucosal cells and via capillary into the blood stream. These are carried to the liver by portal Vein. Some glucose is stored in the liver as glycogen, the rest is transported to tissues to be used for activities. Fructose and galacose are converted to glucose and stored in the liver

Cellulose, Hemicellulose and lignin collectively called as fibers are not digested by enzyme amylase ,and excreted through faeces .

Proteins

Digestion of protein start in the stomach, which serves as a store house , where some protein hydrolysis begins. Milk is clotted by a special enzyme Rennin and acid is added

Gastric juice,which is secreated by the stomach, contains hydrochloric acid,pepsin, rennin and mucin and other substances

Importance of Hydrochloric acid on protein digestion

1. It swells the protein and increases surface area for enzyme action
2. Converts inactive pepsinogen to active pepsin
3. provides the acid medium necessary for the action of pepsin
4. Provides acidic pH for the solution of calcium and iron salts
5. Reduces or destroys action of many harmful/pathogenic bacteria present in the food

Pepsin is the only proteolytic enzyme , which is able to digest collagen, the main protein in connective tissue. they split proteins to polypeptides. It also digest the milk curds formed by the renin. The contribution of the stomach for protein digestion is small, as main digestion takes place in the duodenum

As soon as the chyme enters into the duodenum, it stimulates the intestinal mucosa to release an enzyme enterokinase which converts inactive trypsinogen to active trypsin. Trypsin activates other proteolytic enzymes, chymotrypsin and carboxypolypeptidases. These enzymes with the help of peptidases breakdown the intact proteins into small polypeptides and amino acids

The aminoacids released are absorbed via distinct active transport system. Absorbed  aminoacids and peptides are transported by the portal vein to the liver to be released into the general circulaton

By the time it reaches jejunum almost all the proteins are absorbed and about 1% of digested proteins are excreted through the faeces

Lipids

The stomach lipase does act on emulsified fats in milk, cream, butter and egg yolk. But most of the hydrolysis of fat takes place in the small intestine

As soon as food enters the duodenum, gall bladder releases some bile and pancreas secrete enzyme rich juices. These fluids enter the duodenum via common duct. Bile is a secretion composed of bile acids, bile pigments, cholesterol, lecithin and many other compounds

Function of bile

• Emulsify fat particles which increases surface area for enzyme action
• Neutralize acid chyme and provide alkaline pH necessary for the action of the intestinal enzymes

The pancreatic juice contain trypsin, lipase and amylase, which act upon all components of food . lipase acts on glycerides  and converts it into free fatty acids and glycerol

Micelles, a combination of free fatty acids , monoglycerides and bile salts facillitates the passage of the lipds throught the intestinal wall to the brush border

Chylomicrons are formed by a combination of triglycerides, cholesterol and phospholipids with a beta-lipoprotein coat.They are transported by the lymphatic channels and stored in the liver . the triglycerides are transported to adipose tissue for metabolism and storage

Cholesterol is hydrolysed by pancreatic cholesterol esterase from ester form and absorbed in the same manner as lipids

The fat soluble Vitamins A,D,E and K are absorbed in the similar manner. Some vitamins A,E ,K and carotene do not require bile salts for their digestion

Other Nutrients

Vitamins and water pass unchanged from small intestine into blood by passive diffusion

Mineral absorption is a complex process and appears in 3 stages

• Ist stage: chemical reactions occur in the stomach and intestines , which are affected by the pH of the mix.
• 2nd stage: these are carried across the membrane in to the intestinal mucosal cells
• 3rd stage: Minerals are transported into the blood stream or bound within the cells