Digestive Processes in the Large Intestine: Defecation

Digestive System

• The digestive system's main functions are to take in food, break it down into nutrient molecules, absorb molecules into the bloodstream, and rid the body of indigestible remains.

Mouth and Associated Organs

• The mouth, also called the oral cavity, is where food is chewed and mixed with enzyme-containing saliva that begins the process of digestion, and swallowing is initiated.
• Associated organs include the mouth, tongue, salivary glands, and teeth.

Structure of the Mouth

• The mouth is bounded by lips, cheeks, palate, and tongue.
• The oral orifice is the anterior opening.
• The walls of the mouth are lined with stratified squamous epithelium, which are tough cells that resist abrasion.
• The cells of the gums, hard palate, and part of the tongue are keratinized for extra protection.

Palate

• The palate forms the roof of the mouth and has two distinct parts: the hard palate (anterior) and the soft palate.
• The hard palate is formed by palatine bones and palatine mucosa, which is slightly corrugated to help create friction against the tongue.
• The soft palate is a fold formed mostly of skeletal muscle that closes off the nasopharynx during swallowing.
• The palatine tonsils are located in the soft palate, and the uvula is a fingerlike projection that faces downward from the free edge of the soft palate.

Digestive Processes in the Large Intestine

• Defecation is assisted by Valsalva's maneuver, which includes closing the glottis, contracting the diaphragm and abdominal wall muscles, and contracting the levator ani muscle to lift the anal canal superiorly and allow feces to leave the body.

Mechanisms of Digestion and Absorption

• Digestion breaks down ingested foods into their chemical building blocks, which are then absorbed across the wall of the small intestine.
• Enzymes carry out hydrolysis, adding water to break chemical bonds.
• Absorption is the process of moving substances from the lumen of the gut into the body.

Processing of Nutrients

• Carbohydrate digestion begins in the mouth with salivary amylase and is further broken down into lactose, maltose, and sucrose in the intestine.
• Proteins are broken down into amino acids, which are then absorbed via active transport with Na+ and/or facilitated diffusion.
• Lipids need pretreatment with bile salts to break large fat globules into smaller ones, aided by a Micelle, and can be absorbed via diffusion or active transport.

Proteins

• Proteins can have a positive nitrogen balance (protein synthesis exceeds breakdown) or a negative nitrogen balance (protein breakdown exceeds synthesis).
• The daily protein requirement is approximately 0.8 g per kg body weight for adults over 19 years old.

Vitamins and Minerals

• Vitamins are organic compounds crucial for the body's use of nutrients, functioning as coenzymes, and must be ingested, except for vitamin D and some B and K vitamins synthesized by intestinal bacteria.
• There are two types of vitamins based on solubility: water-soluble vitamins (B complex and C) and fat-soluble vitamins (A, D, E, and K).
• Vitamin deficiencies can cause health problems, and excessive consumption can also lead to health issues.

This quiz covers the final steps of the digestive process in the large intestine, focusing on defecation. It includes details on how muscles in the rectum contract, the Valsalva's maneuver, and the role of the levator ani muscle in expelling feces from the body.