NUTRITION AND DIGESTION

CHAPTER 30

KEY CONCEPTS

• Cells require many different nutrients• Six types of nutrients help to maintain

homeostasis.• Meeting nutritional needs supports good health.

• The digestive system breaks down food into simpler molecules.

• Nutrients are absorbed and solid wastes eliminated after digestion

Six type of nutrients help to maintain homeostasis

• Water• Carbohydrates• Proteins• Fats• Minerals• Vitamins

Carbohydrates

Carbohydrates

Functions of Carbohydrates• 1. Energy source for plants and animals • 2. Source of carbon in metabolic processes • 3. Storage form of energy • 4. Structural elements of cells and tissues• Simplest carbohydrate (monosaccharide) –glucose• Disaccharide – sucrose • Complex carbohydrate called polysaccharide –

sstarch, glycogen, cellulose.

Functions of proteins

• They transport molecules (hemoglobin transports oxygen)• Proteins are the raw materials used for the growth and repair of the body’s cells

and tissues.• Proteins make up enzymes and many hormones that are vital for cell metabolism. • They are used in movement (proteins are the major component of muscles); • They are needed for mechanical support (skin and bone contain collagen-a

fibrous protein);

• Antibody proteins are needed for immune protection;

A Good One!!!!!

Source of Proteins

milk, meat, fish, egg, and vegetables are a rich source of proteins. Beans is a rich source of proteins.

Essential Amino Acids

• Proteins are composed of chains of amino acids. Your body can make only 12 of the 20 amino acids it needs to build proteins. The other 8, called essential amino acids, must come from the food you eat.

• Food such as meat, cheese, and eggs contain all eight essential amino acids. However, most plant proteins lack at least one essential amino acid.

• Vegans-people who do not eat meat, dairy products, or eggs-must eat plant foods in combinations to get all the amino acids they need.

• For example, red beans and rice together contain all 20 amino acid.

Deficiency of Proteins

• It leads to a breakdown of muscle tissue, as your body will try to pull protein from muscles to keep things running.

• Stunted growth and poor mental development• Edema -collection of fluid• Hair loss• Kwashiorkar and Marasmus

Protein Deficiency

Kwashiorkar Marasmus

Fats

• Provide energy • Key component in cell membranes, myelin

sheaths for neurons, and certain hormones.• Fat consists of fatty acids and glycerol

molecules.• Your body can make some fatty acids, but you

must obtain all of the essential fatty acids from the food you eat.

• Example –linoleic acid.

Saturated and unsaturated fats

• Fats are classified as saturated and unsaturated, depending on the structure of their fatty acid chains.

• Saturated fats are solid at room temperature and are found in animal products.

• Most unsaturated fats are liquid at room temperature and are found in plant oils, such as corn or olive oils, and in some fish such as cod or salmon.

• Which one of the two fats is better for us and why do you think it is better for us?

Role of Vitamins and MineralsReading Tool Box

• Refer to page numbers 588-590 and also learn the Functions of minerals and Vitamins from the Tables 30-2, 30-3.

• Use a Two-column notes about different nutrients and their functions

• http://teacherweb.com/MD/OxonHillMS/FatFacts/index.html

• Useful link on Obesity

The Food Guide Pyramid

This chart shows the daily servings suggested by the U.S. Department of Agriculture

Dietary Changes Advocated By the U.S. Government

• Increase consumption of fruits, vegetables, and whole grains.• Decrease consumption of refined sugars.• Decrease consumption of fats, replace saturated with

unsaturated fats, and minimize intake of tans fats.• Decrease consumption of animal fats by selecting lean meats,

poultry and fish.• Decrease consumption of salt and foods high in salt content.• Decrease caloric intake to maintain desirable weight.• Engage in a total of 1 hour of moderate physical activity such

as brisk walking daily

Digestion

• Digestion is the process by which the large complex molecules in food are broken down into smaller molecules that can be used by the body.

• The digestive system is a collection of organs that breaks down food into energy that can be used in cells. It includes the alimentary canal and the associated glands.

Steps involved in the process of digestion

• Ingestion: the process of taking in food into the digestive tract through an opening, usually called a mouth is known as ingestion.

• Mechanical breakdown: The process of breaking down food into smaller pieces is accomplished by gizzard or teeth as well as by the churning action of the digestive cavity itself. As a result of breakdown of food, the surface area increases allowing digestive enzymes to attack them more effectively.

• Chemical breakdown: The particles of food are acted upon by enzymes that break them down into simpler subunits.

• Absorption: The small subunits must be transported out of the digestive cavity and into cells.

• Elimination/egestion: Indigestable materials must be expelled from the body.

• What do you think is assimilation?

Digestive System

Animated Biology

• Digestive System• http://

www.youtube.com/watch?v=q3986Yfl5cU&noredirect=1

• http://kitses.com/animation/swfs/digestion.swf

• Animation• http://highered.mcgraw-hill.com/sites/00724

95855/student_view0/chapter26/animation__organs_of_digestion.html

• Organs of Digestion

Intracellular digestion

Intracellular digestion takes place within the cells.Extracellular digestion takes place within the gastrovascular cavity

Digestion in Ruminants

Digestion in ruminants

• The first chamber is the rumen. It is a large fermentation chamber and in cows can hold up to 200litres. Many microorganisms including bacteria and ciliates thrive here. These microorganisms produce cellulase, an enzyme that breaks down cellulose into component sugars.

• The food then enters into the reticulum and the food is formed into masses called cud. The cud is regurgitated, chewed, and swallowed into the rumen. The extra chewing exposes more of the cellulose and cell contents to cellulase and other enzymes of the rumen’s microorganisms for further digestion.

• The food is travels through the narrow omasum and then into the larger abomasums, where protein digestion occurs. Here the cow digests not only plant protein but also the microorganisms from its rumen.

• The cow then absorbs most of the products of digestion through the walls of its small intestine.

Digestion in birds

Digestion in Birds• Birds lack teeth and swallow their food whole. The food then passes

through the muscular tubular esophagus. In seed-eating birds, the food may be stored and softened by water in a large, expandable crop.

• The food then passes into a highly specialized stomach. The first portion of the stomach secretes digestive enzymes, while the next portion is modified into a grinding gizzard- a thick muscular chamber with a hard lining.

• Many bird species swallow small, sharp-edged stones that lodge in the gizzard and act as teeth, crushing, and grinding the food under pressure from the gizzard’s muscular contractions.

• In carnivorous birds gizzard is smaller; bones, hair, and feathers are trapped in the gizzard and regurgitated.

• Further digestion and most absorption takes place in the small intestine.

Digestion in the Mouth• The digestive system of man consists of alimentary canal and its associated glands.• The alimentary canal begins with the mouth. Both mechanical and chemical breakdown of

food takes place here.• The mechanical breakdown is done by teeth. Incisors at the front of the mouth snips off

pieces of food, the pointed canine teeth beside them are useful for tearing the pieces apart, and the premolars and molars at the back of the mouth have flat surfaces for grinding food to a paste. In human adults there are 32 teeth

Digestion in the Mouth

• Teeth help in mechanical digestion of food. Teeth shred and grind the food into smaller pieces. Tongue keeps the pieces positioned between your teeth.

• Chemical digestion is done by the enzymes present in the saliva.

• Saliva is secreted by three pairs of salivary glands present in the mouth. Saliva contains the digestive enzyme amylase (ptyalin) which breaks down starch into maltose.

• amylase• Starch(polysaccharide) --------- maltose(disaccharide)

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• Saliva also contains bacteria-killing enzyme and antibodies that guard against infection. Saliva lubricates the food to facilitate swallowing.

• The tongue rolls the food into a bolus and helps in swallowing. The food then pass into the pharynx, a muscular cavity which connects the mouth with the esophagus.

• Food is prevented from entering into the windpipe by a cartilaginous flap known as epiglottis.

• Waves of alternate contraction and relaxation known as peristalsis enables the food to be passed down the alimentary canal.

• Esophagus leads into the stomach

Peristalsis

Three Major Functions of Stomach• Stomach stores food and releases it gradually into the small intestine at a rate

suitable for digestion and absorption.

• Stomach helps in the mechanical breakdown of food. In addition to peristalsis, its muscular walls undergo a variety of churning contractions that help break apart large pieces of food.

• Chemical breakdown of food. Gastric glands lining the walls of the stomach secrete gastric juice. Gastric juice contains pepsinogen an inactive form of pepsin. Pepsin is a protein digesting enzyme, that helps to break down protein into shorter chains of amino acids called peptides. Pepsin functions best in a very acidic pH of 1 to 3.

HCl• Pepsinogen (inactive)------------- Pepsin Pepsin Proteins ----------------- Peptides.

Functions of HCl

• Activates inactive pepsinogen into active pepsin.

• Kills bacteria.• Makes the medium acidic which is suitable for

pepsin to act on proteins.

What keeps the stomach from digesting itself?

• Pepsin is active only when there is food to digest.• The stomach secretes a layer of mucus to protect

itself from its own acidic environment.• Digested juices and enzymes turn the partly

digested food in the stomach into a semi liquid mixture called chyme. The pyloric sphicter opens slightly, and chyme squirts into the small intestine where digestion continues. It takes six hours to empty the stomach after a meal.

Predict

• What might happen if the digestive sections were not divided by sphincters?

Rings of muscles, called sphicters, separate one section from another. The opening and closing of these sphincters and the contractions of smooth muscle in the walls of the organs keep food moving in one direction.

SMALL INTESTINE

• The small intestine is narrow and has a length of 10feet, it is the largest part of the digestive tract. The main function of small intestine is to digest food and absorb the digested food into the bloodstream.

• The digestion is accomplished with the help of digestive secretions from the liver, pancreas and the cells of the small intestine itself.

The Liver

• Functions of liver• The liver stores fat and carbohydrates for energy.• Regulates blood glucose levels• Synthesizes blood proteins• Stores iron and certain vitamins• Converts toxic ammonia into urea• Detoxifies harmful substances we ingest such as

nicotine and alcohol.

The Role of Liver in Digestion

• Liver secretes bile which is stored in the gall bladder and released when needed through the bile duct.

• Bile helps in emulsification of fats.

Role of Pancreas in Digestion

• Pancreas secretes pancreatic juice, which is released into the small intestine. The pancreatic juice neutralizes the acidic chyme and digests carbohydrates, proteins and lipids.

• Sodium bicarbonate neutralizes the acidic chyme in the small intestine, producing a slightly basic pH.

• Pancreatic amylase breaks down starch into maltose.• Pancreatic proteases(trypsin) break down protein into

peptides.• Pancreatic lipases break down fats into fatty acid and

glycerol.

Enzymes present in intestinal juice

• The walls of the small intestine secrete digestive enzymes to digest food.

• Peptidases to split small peptides into amino acids.• Maltase acts on maltose and converts it into glucose.• Sucrase acts on sucrose and converts it into glucose

and fructose.• Lactase acts on lactose and converts it into glucose and

galactose.• Lipases acts on lipids and convert it into fatty acid and

glycerol.

Structure of Villus

Role of Villus

• Small intestine is the major site of nutrient absorption into the blood. The small intestine has numerous folds and projections that give it an internal surface area that is 600 times that of a smooth tube of the same length.

• Minute finger like projections called villi cover the entire folded surface of the intestinal wall. Each individual cell of the villi bear microscopic projections called microvilli.

• Nutrients absorbed by the small intestine include water, monosaccharides, amino acids and short peptides, fatty acid produced by lipid digestion, vitamins and minerals.

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• Each villus of the small intestine is provided with a rich supply of blood capillaries and a single lymph capillary called a lacteal, to carry off the absorbed nutrients and distribute them throughout the body. Most of the nutrients enter the blood stream through the capillaries through the capillaries, but fat subunits take a different route. After diffusing into the epithelial cells lining the small intestine, they are resynthesized into fats coated with protein, and then released as particles into the interstitial fluid and then enter the lymph vessel and are eventually delivered to the blood stream when the lymph vessel empty into the vein.

Large Intestine

• It is 5 feet long and 3inches in diameter.• It has two parts, colon and rectum.• The large intestine has bacteria which live on unabsorbed food.• The intestinal bacteria can synthesize vitamin B12, thiamin,

riboflavin and Vitamin K.• Cells lining the large intestine absorb these vitamins and water

and salts.• After absorption is complete, any remaining material is

converted into semisolid feces.• •