Ch 27 Biology

What 2 important purposes does the acid in our stomachs serve?

1. 1. It helps with chemical digestion because the stomach contains gastric juices made of strong hydrochloric acid (HCl), digestive enzyme pepsin, and mucus. HCl gives the stomach a pH of 1 which activates pepsin. Pepsin causes proteins to lose their 3D shape, turning them into linear chains of amino acids, making it easier to chemically break down proteins. 2. Stomach acid destroys harmful bacteria and protects us against food-borne diseases.

Describe how bariatric surgery changes the structure of the stomach and small intestine. How does this lead to weight loss?

1. Bariatric surgeries include sleeve gastrectomy and gastric bypass. Sleeve gastrectomy dramatically reduces the size of the stomach but does not redirect the flow of food and chyme through the digestive tract. The stomach is reduced in size up to 80% as its small size limits the amount of food that can be consumed. Stomach contents are still released into the upper small intestine for further processing. Gastric bypass reduces the size of the stomach and redirects the food from the supper stomach pouch to the lower small intestine. The stomach is reduced to the size of a golf ball, diminishing drastically the amount of food it can hold. Also, the stomach contents bypass the upper part of the small intestine, reducing the amount of nutrients that can be absorbed.

Describe the 4 basic steps of food processing.

1. Ingestion- the act of taking food into the mouth. 2. Digestion- mechanical digestion-chewing in the mouth, churning in the stomach; chemical digestion- saliva in the mouth, acid and pepsin in stomach, hydrolases in small intestine. 3. Absorption- nutrients and water in small intestine, water in large intestine. 4. Elimination- feces formed in large intestine, elimination from anus.

Why should anyone considering bariatric surgery not take the decision lightly? What are some benefits and risks?

After 10 years after gastric bypass surgery, patients weighed 25% less than they did before surgery. It costs a lot of money, $11,000- $26,000. There are behavioral changes that come with it, 1 in 200 people die from surgery. They would have a liquid diet, eat extremely small portions otherwise get gastric dumping. Pain and scar tissue, and nutrition deficiency or even malnutrition. The long term effects are unknown and it may stop working for some and they can gain the weight back.

What are some disorders of the large intestine and why do they occur?

Appendicitis- a bacterial infection of appendix causes it to swell like a balloon, producing extreme pain. It's possible to live without your appendix but could give immune support. If it bursts, the bacteria could spread everywhere in your body, causing serious issues. It is very common and people just get it surgically removed if it gets swollen. Diarrhea- increases peristalsis and water is not reabsorbed due to either an infection or nervous stimulation; process is sped up. Constipation- condition when feces are dry and hard that may be controlled with water and fiber; opposite of diarrhea and the process of is slowed down. Hemorrhoids- enlarged and inflamed blood vessels of the anus due to chromic constipation, pregnancy, or aging.

Why is having "good" bacteria in our large intestine important? What do they feed on and what benefits do they provide to us?

Bacteria in the large intestine breaks down indigestible material like cellulose (fiber) and produces B complex vitamins and vitamin K. 1 out of 10 bacteria in your large intestine are good bacteria, the rest are the bacteria in your cells. Bacteria chemically breaks down some fiber to produce nutrients for their own survival and also to provide valuable vitamins, which is one reason fiber is an important dietary nutrient.

How do we ensure food goes "down the right pipe" when we swallow?

During swallowing of a Bolus (ball of chewed up food), a reflex tip the epiglottis to close the windpipe (trachea) entrance. Also, during swallowing, the uvula keeps food out of the naval cavities; the epiglottis closes like a lid and prevents good from entering the trachea or the wrong pipe.

What is an FMT and why might someone have one?

Fecal Microbiota Transplant is a procedure in which fecal matter is collected, mixed with saline, strained, and placed in a patient through colonoscopy, endoscopy, sigmoidoscopy, or enema. The purpose of this is to replace good bacteria that has been killed, usually by the use of antibiotics, causing bad bacteria, specifically C diff, to overpopulate the colon.

How do fungi digest food?

Fungi digest food externally, as they do not have digestive tracts. To obtain nutrients, they extend hyphae (microscopic filaments) into food, then the hyphae release digestive enzymes directly into the food and absorb the digested nutrients directly.

How does shortening the small intestine (as occurs with gastric bypass) lead to weight loss?

It allows less nutrients to be absorbed so therefore, less Calories are absorbed. The small intestine is where all the absorption happens so if there is less room to absorb nutrients, the body can only take in so many nutrients and Calories.

How are mechanical digestion and chemical digestion different

Mechanical digestion is the physical act of breaking something down into smaller pieces (chewing). Chemical digestion is breaking something down into subunits using digestive enzymes (hydrolases). Salivary glands produce saliva à saliva contains salivary amylase à starch à glucose.

Be able to list in order the path food takes as it moves through the digestive system.

Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine, Rectum, Anus.

List the organs of the upper digestive tract.

Mouth, pharynx, esophagus, stomach.

List the organs of the digestive system and describe their basic functions.

Mouth- oral cavity, functions in ingestions and the preliminary steps of digestion. Teeth mechanically process food. Salivary glands produce salivary amylase, an enzyme that chemically digests carbohydrates. The tongue forms food into a ball and pushes it to the back of the mouth. Pharynx- connects the mouth to the esophagus and also opens to the trachea. During swallowing, a reflex tip the epiglottis to close the windpipe (trachea) entrance. Esophagus- waves of muscle contractions called peristalsis force food alone this long tube into the stomach. A muscular tube which connects the pharynx to the stomach, moves food down by peristalsis (rhythmic waves of muscular contractions that squeeze food) Stomach- can store food for several hours, tucked tight under the diaphragm on the left side of the abdominal cavity. Functions to store food, start digestion of proteins, and control movement of chyme into the small intestine. J-shaped organ with a thick wall. Peristalsis in the stomach mixes food with stomach acid and pepsin, creating a mixture called chyme. Stomach acid destroys harmful bacteria in our food. The acid also denatures food proteins, making them more digestible by the enzyme pepsin present in stomach secretions. Small intestine- 20-21 ft long, 1 inch in diameter, large surface area for majority of digestion and absorption. Duodenum (first part) is 10 inches long, then jejunum is 8 ft long, and ileum is 12 ft long. Major organ that digests the food, all of the absorption and most of the chemical digestion occurs here. Also produces digestive enzymes. It's longer than the large intestine, but diameter is smaller. Only organ that absorbs nutrients. Large intestine- Functions the absorb water to prevent dehydration, absorbs vitamins (B complex and K) produced by intestinal flora, forms stool (solid undigestible waste material) and rides the body of feces through the anus. Includes the cecum, colon, rectum and anal canal. Larger in diameter but shorter than the small intestine (only 4 ½ ft long). The cecum has a projection known as the appendix that may play a role in fighting infections. Rectum-the last section of the colon Anus- anal sphincters hold feces in the rectum until socially acceptable times and places.

What is a sphincter, and what happens to someone experiencing "heartburn"?

Muscles that encircle tubes like the esophagus and act as valves. When lower esophageal sphincter is relaxed and open, food can enter the stomach from the esophagus. Heartburn or acid reflux is when stomach acid leaks up into esophagus because the esophageal sphincter doesn't close fully.

Identify the accessory organs of the digestive system and explain their basic functions.

Pancreas- fish-shaped spongy organ behind the stomach. Secretes enzymes into the small intestine. Trypsin digests proteins, lipase digests fats, pancreatic amylase digests carbohydrates. Secretes bicarbonate into the small intestine to neutralize stomach acids (liquid tums). Makes sure you don't burn a hole in the duodenum from acidity from stomach. Secretes insulin into the blood to keep blood sugar levels under control. Liver- secretes bile (stored in gallbladder), which helps digest fats. Filters blood from the GI tract thus acting to remove poisons and detoxify the blood. Removes iron, vitamins A, D, E, and K, and B12 from the blood and stores them. Stores glucose as glycogen and breaks it down to help retain blood glucose levels. Makes blood proteins and helps regulate cholesterol levels by making bile salts. Makes bile that is then stores in the gallbladder to be secreted into the small intestine to emulsify fats. Breaks down and recycles red blood cells. Gallbladder- stores bile and bile salts, which is made in the liver, and releases them as needed into the small intestine when food enters the duodenum.

Describe peristalsis and compare its function in the esophagus and the stomach.

Peristalsis is wave-like contraction of muscles that moves food along the digestive tract. The esophagus and the stomach have similar peristaltic conditions. In the esophagus, peristalsis is waves of muscular contractions move food along the long tube of the esophagus to the stomach. In the stomach, peristalsis is mixing food with stomach acid and pepsin (enzyme produced in the stomach to chemically break proteins apart into amino acids), producing a mixture called chyme.

Compare digestion in sea anemones and humans

Sea anemones digest their food internally like humans, but they don't have a digestive track like we do. They have a single multifunctional digestive cavity where digestion and absorption take place. Capture food, shove it in their mouths using tentacles. Cavity has the mouth opening through which food enters and is exited as waste as well.

What are the main differences between sleeve gastrectomy and gastric bypass?

Sleeve gastrectomy removed a part of the stomach but the flow of digestion remains the same, it limits the amount of food that can be consumed. Gastric bypass reduces size of stomach as well, but it redirects food from the gastric pouch right to the lower small intestine. It decreases the amount of food that can be held and bypasses the upper part of the small intestine, reducing the amount of nutrients being absorbed. It calls for other anatomical rearrangements as well.

In which digestive organ does the majority of digestion and all of the absorption of nutrients occur?

Small intestine

What is the duodenum and what happens there?

The duodenum is where food from the stomach is mixed with digestive secretions in the duodenum, the first portion of the small intestine. Mixing of chyme and digestive enzymes occurs here. It is the first 25 cm of the small intestine.

What are the main contributions to digestion of the pancreas, liver and gall bladder?

The pancreas secretes enzymes that help break down organic macromolecules like carbs, proteins, and fats into smaller molecules (lipase) that act in the small intestine. It also secretes bicarbonate that neutralizes acidic chyme like liquid tums. This makes sure that a hole isn't burnt in your stomach from the acidity of it. It secretes insulin into the blood to keep blood sugar levels under control as well. Trypsin digests proteins, lipase digests fats, and pancreatic amylase digests carbohydrates. The liver secretes bible which helps digest fats. It makes bile that is then stored in the gallbladder to be secreted into the small intestine to emulsify fats, breaking them into smaller droplets. This allows lipase to more efficiently break down fat molecules. Lipase is made by the pancreas and secreted into the small intestine. The gallbladder stores bile/bile salts and passes them into the small intestine when food enters the duodenum. When we eat a high-fat meal, bile salts pass from gallbladder into duodenum, where they help emulsify the fats.

What are the adaptations of the small intestine that increase its efficiency in absorbing nutrients?

The small intestine has a large surface area for the majority of digestion and absorption to happen. It is longer than the large intestine because more absorption needs to happen there and it takes the longest time. Villi helps absorption in the small intestine as well. The inner surface of the small intestine is folded into fingerlike projections called villi which are composed of many densely packed epithelial cells. Villi increase the surface area of the small intestine, enabling more nutrients to be absorbed.

lipase

a fat-digesting enzyme active in the small intestine

pepsin

a protein-digesting enzyme that is active in the stomach

stomach

an expandable muscular organ that stores and mechanically breaks down food. Specific enzymes in the stomach digest proteins.

liver

an organ that aids digestion by producing bile salts that emulsify fats.

pancreas

an organ that helps digestion by producing enzymes (such as lipase) that act in the small intestine, and by secreting a juice that neutralizes acidic chyme.

gallbladder

an organ that stores bile salts and releases them as needed into the small intestine.

bile salts

chemicals produced by the liver and stored by the gallbladder that emulsify fats so that they can be chemically digested by enzymes.

peristalsis

coordinated muscular contractions that force food down the digestive tract.

salivary glands

glands that secrete enzymes into the mouth to break down macromolecules in food. One such enzyme in salivary amylase, which digests carbohydrates.

stool

solid waste material eliminated from the digestive tract

chyme

the acidic "soup" of partially digested food that leaves the stomach and enters the small intestine.

duodenum

the first portion of the small intestine, where mixing of chyme and digestive enzymes occurs.

large intestine

the last organ of the digestive tract, in which remaining water is absorbed and solid stool is formed.

digestion

the mechanical and chemical breakdown of food into subunits, enabling the absorption nutrients.

small intestine

the organ in which the bulk of chemical digestion and absorption of food occurs.

digestive system

the organ system that breaks down molecules into smaller subunits, absorbs nutrients, and eliminates wastes; it is composed of the digestive tract and accessory organs.

esophagus

the section of the digestive tract between the mouth and the stomach.