Chapter 26Drastic Measures

Morbidly obese

• How did Amy Jo become obese?• A person is obese when they weigh 20% more

than their ideal body weight– Body mass index about 30

• Morbid obesity is defined as being 100 pounds or more over one’s ideal body weight or BMI of 40 or higher.

• What was Amy’s BMI?

Surgery

• Several types of bariatric, or weight-loss, surgery– Adjustable gastric banding

• Surgeon wraps an adjustable band around the stomach to make it smaller so it holds less food

– Gastric bypass• Stomach is surgically made smaller and small intestine is

rerouted.• Shrinks the size of stomach and alters the digestion and

absorption of food

– Some risk involved with either method. What are limitation to gastric bypass? Why do the surgery?

The Digestive System

• Heterotrophic organism• Digestion, the

mechanical and chemical breakdown of food into subunits so that nutrients can be absorbed, begins immediately after ingestion (the act of taking food into the mouth).

The Digestive System

• The digestive tract is the central pathway of the digestive system that transforms the food we eat into a form our bodies can use and rids the body of the waste left over once usable nutrients and energy are removed from food we have taken in.

The Digestive System

• The digestive tract is a long muscular tube that pushes food between the mouth and the anus.

• As the muscles relax and contract, the tube pushes food along.

• The tube receives inputs from various other organs including the salivary glands, gallbladder, liver, and pancreas.

The Upper Digestive System

• When food enters the mouth, chewing mechanically breaks it down into smaller pieces. Salivary glands secrete enzymes into saliva, which chemically dismantle macromolecules into their subunits.

The Upper Digestive System

• The tongue, a muscular organ in the mouth that aids in swallowing, compresses the food into a ball and works it to the back of the mouth.

The Upper Digestive System

• When we swallow, food is propelled along the esophagus, the section of the digestive tract between the mouth and the stomach, by rhythmic waves of contracting muscles in a process called peristalsis.

The Upper Digestive System

• The stomach is an expandable muscular organ that stores, mechanically breaks down, and digests proteins in food. The stomach contains acid that can inactivate potentially harmful bacteria ingested with our food.

The Upper Digestive System

• Stomach acid has a pH of close to 1, and its action helps protect us against food-borne diseases.

• Stomach acid also denatures proteins in the food, unfolding their three-dimensional structures into linear strands.

• This makes it easier for the enzyme pepsin, which is produced in the stomach, to chemically break proteins apart into individual amino acids.

The Upper Digestive System

• Like the esophagus, the stomach is also muscular, expanding and contracting as it accepts food and churns it.

• Each time it contracts, stomach acid mixes with food, creating a soupy mixture called chyme.

The Upper Digestive System

• While the stomach can absorb some substances, such as water, ethanol, and certain drugs, directly into the bloodstream, most of the chyme is pushed farther into the small intestine, where it is further processed.

The Small Intestine

• The small intestine is the organ in which the bulk of chemical digestion and absorption of food occurs.

The Small Intestine

• The duodenum is the first portion of the small intestine. The duodenum receives chyme from the stomach and mixes it with digestive secretions from other organs.

The Small Intestine

• The pancreas is an organ that helps digestion by producing enzymes that act in the small intestine, and by secreting a juice that neutralizes acidic chyme.

The Small Intestine

• Because fats are hydrophobic, they don’t mix well with the watery solutions in the small intestine, making it difficult for fat-digesting enzymes to break them down.

• The liver aids in digestion by producing bile salts, which are chemically suited to dividing large hydrophobic fat globules into smaller droplets – that is, emulsifying them.

The Small Intestine

• Bile salts pass from the liver into the gallbladder, which in turn stores them for future use.

• Once fats are emulsified, a lipid-digesting enzyme secreted by the pancreas called lipase chemically breaks them down to release their constituent fatty acids and glycerol.

The Small Intestine

• Once digested into their smallest subunits, food molecules are absorbed by epithelial cells lining the small intestine in a stage of digestion known as absorption.

The Small Intestine

• The inner lining of the small intestine is folded into finger-like projections called villi (singular: villus) that are composted of many densely paced epithelial cells.

• The folds greatly increase the surface area through which the intestine can absorb nutrients.

The Small Intestine

• The food molecules then pass into the blood vessels of the circulatory system, which transport them throughout the body,

• They are used as a source of nutrients and energy to build and maintain cells.

The Large Intestine

• After chyme passes through the small intestine, it moves on to the large intestine, where remaining water is absorbed and solid stool is formed.

The Large Intestine

• Within the colon – the first and longest portion of the large intestine – fiber, small amounts of water, vitamins, and other substances mix with mucus and bacteria that normally live in the large intestine.

The Large Intestine

• As waste travels through the colon, most of the water and some vitamins and minerals are reabsorbed into the body through the colon lining.

• Bacteria chemically break down some of the fiber to produce nutrients for their own survival and also to nourish cells lining the colon.

The Large Intestine

• As the large intestine expands and contracts, it pushes what ultimately becomes stool (solid waste material eliminated from the digestive tract) into the rectum, from which is it eliminated through the anus as feces.

Costs and Benefits of Surgery

• In 2007, Swedish researchers published results from a study in which they followed about 2,000 obese patients who had undergone weight-loss surgery – either gastric bypass or surgical banding – over 15 years and compared them to about 2,000 similarly obese people who didn’t have surgery but who were counseled in diet and exercise.

Costs and Benefits of Surgery

• After 10 years, those who had gastric bypass surgery weighed 25% less than their presurgery weight; those who had stomach-banding surgery were down about 15%. Those who got traditional diet advice lost no more than 2% of their weight.

• After 10 years, I’ve lost 15% of my weight eating a traditional diet with light exercise.

Costs and Benefits of Surgery

• There were 129 deaths in the diet-only group, mostly from weight-related heart disease and cancer, and 101 deaths in the surgery group – a large difference statistically.

• Deaths in the surgery group were also mainly from heart disease and cancer, although there were half the number of heart attack deaths in this group compared with the diet group.

How do other organisms process food?

• Fungi do not have digestive tracts. To obtain nutrients, fungi extend hyphae into food sources.

• Individual hypha cells then release digestive enzymes directly onto their food and absorb the released nutrients directly into their cells.

How do other organisms process food?

• Sea anemones digest their food internally, but they don’t have a digestive tract like humans. They have a single, multifunctional digestive cavity called a gastrovascular cavity.

How do other organisms process food?

• Photosynthetic organisms do not need stomachs or a digestive system because they are autotrophs: they make their own food.