Types of Nutrients Micronutrients- vitamins, minerals, & water

Macronutrients- proteins, lipids, carbohydrates, etc…

1- Proteins, polysaccharides and lipids are all digests.2- Large molecules cannot be absorbed through the wall of the gut.3- The membranes of the cell are impermeable to large molecules. 4- Digestion is a chemical process.

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There are 9 amino acids that humans must obtain by

digesting proteins in food. Other amino acids can be

made from these nine and all human proteins can be

synthesized.

Essential amino acidstryptophanmethionine

valinehistidinetheorine

phenylalanineleucine

Isoleucinelysine

Digestion of macromoleculesMost food molecules are large polymers and insoluble

They must first be digested to smaller soluble molecules before they can be absorbed into the blood

6.1.2 Enzymes and digestion.Enzymes are biological catalysts that increase the rate of reaction.Digestive enzymes are secreted into the lumen of the gut.

This image illustrates the reduction in activation energy that is achieved by the use of an enzyme.Notice that the normal reaction requires a higher activation energy which would correspond to a high body temperature. This is usually not possible in living organisms.

The enzyme-catalysed reaction has a lower activation energy. This lower activation energy would correspond to body temperature but is only possible in the presence of an enzyme.

6.1.3 Types of digestive enzymeExample 1 Pancreatic amylase:

Conditions:Source the Pancreas Optimal pH 7.5-7.8 Substrate is starch (amylose) End product is the disaccharide maltose Action: hydrolysis of 1-4 glycosidic bonds

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Example 2: Pepsin is a protease produced in the stomach

Conditions:Source is the stomach Optimal pH is 2 Substrate is a polypeptide chains of amino acids End product is small polypeptides Action is the hydrolysis of peptide bonds within the polypeptide chain (endopeptidase).

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Example 3: Pancreatic lipases:Source is the pancreas The optimal pH is 7.2 The substrate is a triglyceride lipid The product is glycerol and fatty acid chains The action of pancreatic amylases also requires the presence of bile salts that emulsify the lipid. This emulsification has two effects: Increases the surface area of the lipid for the digestion of fat Exposes the glycerol 'head' structure to the enzyme Action: hydrolysis of ester bonds between the glycerol molecules and the fatty acid chains.

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The digestive SystemIt consists of the digestive tract,

a tube extending from the mouth to the anus, and its associate accessory organs.

The regions of the digestive tract include the following:

Oral cavity or mouthPharynx or throatEsophagusStomachSmall intestine

Consists of the duodenum, jejunum and ileum, with liver, gallbladder, and pancreas

Large IntestineIncludes cecum, colon, rectun and anal canal

Anus

The part of the human body used for digestion can be described in simple terms as a tube through which food passes from mouth to the anus.

Human digestive system

GI (gastrointestinal) tract = alimentary canal

IngestionMouth

mechanical digestion teeth

breaking up foodchemical digestion

saliva amylase

enzyme digests starch mucin

slippery protein (mucus) protects soft lining of digestive system lubricates food for easier swallowing

buffers neutralizes acid to prevent tooth decay

anti-bacterial chemicals kill bacteria that enter mouth with food

mouthbreak up fooddigest starchkill germsmoisten food

MouthChemical and mechanical digestion.

Food is chewed (masticated) mechanically.

A bolus (lump) is formed with saliva and the tongue.

Swallowing (& not choking)

Epiglottis flap of cartilagecloses trachea (windpipe) when swallowingfood travels down esophagus

Peristalsis involuntary muscle contractions to move food

along

Which type of digestion is the following?

1. Chewing a saltine? -

2. Saliva breaking the saltine down into molecules of glucose? -

3. Your tongue breaking pieces of a hamburger apart?

4. Pepsin (an enzyme) in your stomach breaking the hamburger into amino acids?

PharynxThe back of the throat.

Larynx- passage for air, closes when we swallow.

Is approximately 15cm long.

The part of the digestive tract that extends between the pharynx and the stomach. It is about 25 cm long and lies in the mediastrinum, anterior to the vertebrae and posterior to the trachea. The esophagus transports food from the pharynx to the stomach.

Series of involuntary wave-like muscle contractions which move food along the digestive tract

Peristalsis

StomachFood is temporarily stored here.

Gastric juices are secreted.

Has layers of muscle that line the inside.

Mechanically and chemically breaks down food.

Muscular contractions consisting of a wave of relaxation of the circular muscles in front of the bolus, followed by a wave of strong contraction of the circular muscles behind the bolus, which force the bolus along the digestive tube.

1- The wall of the stomach is glandular, secreting mucus, hydrochloric acid and protease.2- Hydrochloric acid creates very acid conditions that kill bacteria in food that has been swallowed. Without this, we would often catch food poisoining or other diseases from the food that we eat.

3- Acid conditions denature proteins and suit protein digestion by hydrolysis. Protease secrete in the stomach, called pepsin, begins the process by breaking up polypeptides into shorter chains of amino acids.

4- The wall of the stomach is elastic, so large meals can be swallowed quickly, stored and then gradually released into the small intestine.5- The wall of the stomach is muscular and contracts rhythmically to squeeze the food, mixing it and breaking it into smaller lumps.

StomachFunctions

food storagecan stretch to fit ~2L food

disinfect foodHCl = pH 2

kills bacteria

chemical digestionpepsin

enzyme breaks down proteins

But the stomach is made out of protein!What stops the stomach from digesting itself?

mucus secreted by stomach cells protects stomach lining

stomachkills germs break up fooddigest proteinsstore food

sphincter

sphincter

mouthbreak up fooddigest starchkill germsmoisten food

Gastric JuicesSecreted by the stomach.

Acidic (pH 1.5-2.5) (HCl).

Pepsin- an enzyme that breaks down large proteins into amino acids.

Food is further broken down into a thin liquid called chyme.

Accessory OrgansPancreasGall BladderSpleen

Gall bladder Pouch structure located near the liver

which concentrates and stores bile

Bile duct – a long tube that carries BILE. The top half of the common bile duct is associated with the liver, while the bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.

BILEBile emulsifies lipids (physically breaks apart

FATS)

Bile is a bitter, greenish-yellow alkaline fluid, stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion.

A complex organ composed of both endocrine and exocrine tissue that perform several functions.The exocrine secretions of the pancreas, called pancreatic juice, have an aqueous component and an enzymatic component. Pancreatic juice is delivered to the small intestine through the pancreatic ducts, where it functions in digestion.

Pancreas An organ which secretes both digestive enzymes

(exocrine) and hormones (endocrine)

** Pancreatic juice digests all major nutrient types.

Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

Pancreas Digestive enzymes

digest proteins trypsin, chymotrypsin

digest starch amylase

Buffers neutralizes

acid from stomach

It performs important digestive and excretory functions, stores and processes nutrients, detoxifies harmful chemicals, and synthesizes new molecules.

Liver Function

produces bile bile stored in gallbladder until needed breaks up fats

act like detergents to breakup fats

bile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown

bile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown

pancreasproduces enzymes to digest proteins & starch

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

liverproduces bile

- stored in gall bladderbreak up fats

It consists of the three parts: the duodenum, the jejunum and the ileum. The entire small intestine is about 6 m long. Two major accessory glands, the liver and the pancreas, are associated with the duodenum.The small intestine is where the greatest amount of digestion and absorption occurs.

a) Villus which increase the surface area for absorption of the products of digestion(b) Microvilli border of the epithelial cell increases the surface are for absorption. (c) Lacteals are connect to the lymphatic system for the transport of lipids.(d) In the wall of the small intestine are the blood vessels to transport absorbed products to the general circulation, There are also the muscle to maintain peristalsis

1- Pancreatic juice is secreted into the small intestine. It contains protease, amylase and lipase, so the three main groups of the macromolecules are all digested here.

2- The wall of the small intestine secretes a variety of other enzymes, which digest other substances. Nucleases, for example, are secred to digest DNA and RNA in food eaten. Because of the great length of the small intestine, food spends hours passing thorugh, giving time for digestion to be completed.

3- Digested foods are absorbed by the small intestine. 4- Areas in the wall of the small intestine called Peyer´s patches contain lymphocytes that detect pathogenic organisms in the food in the small intestine and help in the production of antibodies against them.

Small IntestineMost chemical digestion takes place here.

Simple sugars and proteins are absorbed into the inner lining.

Fatty acids and glycerol go to lymphatic system.

Lined with villi, which increase surface area for absorption, one cell thick.

Small intestineFunction

chemical digestionmajor organ of digestion & absorption

absorption through liningover 6 meters! small intestine has huge surface area = 300m2

(~size of tennis court) Structure

3 sectionsduodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

Duodenum 1st section of small intestines

acid food from stomach mixes with digestive juices from:

pancreas

livergall bladder

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

pancreasproduces enzymes to digest proteins & starch

Absorption in the SI Much absorption is thought to occur

directly through the wall without the need for special adaptations

Almost 90% of our daily fluid intake is absorbed in the small intestine.

Villi - increase the surface area of the small intestines, thus providing better absorption of materials

Absorption by Small IntestinesAbsorption through villi & microvilli

finger-like projectionsincrease surface area for absorption

                                  (a) folds increase SA:VOL ration by X 3(b) Villi project into the lumen of the gut increasing the surface area by X 10(c) Microvilli are outward folds of the plasma membrane increasing the surface area another X10

This sequence of light microscope and electron micrograph images show the same sequence as the diagram above.

                                                                                                                                                                                                                                                                                                                                     

This sequence of light microscope and electron micrograph images show the same sequence

as the diagram above.

Histological adaptations within the villus.                                                                                                                            

•Blood supply in the villus which absorb the end products of digestion from the epithelial cells •The lacteals (green) that receive the lipoproteins before transporting them to the circulatory system. •Muscular walls that maintain the movement of chyme by peristalsis.

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The movement of the large intestine are more sluggish than those of the small intestine. While in the colon, chyme is converted to feces. The formation of feces inclives the absorption of water and salts, secretion of mucus and extensive action of microorganisms. The colon stores the feces until they are eliminated by defecation.

Large intestines (colon)Function

re-absorb wateruse ~9 liters of water

every day in digestive juices

> 90% of water reabsorbednot enough water absorbed diarrhea

too much water absorbedconstipation

Large IntestineSolid materials pass through the large intestine.

These are undigestible solids (fibers).

Water is absorbed.Vitamins K and B are reabsorbed with the water.

Rectum- solid wastes exit the body.

You’ve got company!Living in the large intestine is a community of helpful bacteriaEscherichia coli (E. coli)

produce vitamins vitamin K; B vitamins

generate gasesby-product of bacterial metabolism methane, hydrogen sulfide

AppendixVestigial organVestigial organ

Rectum Last section of colon

(large intestines)eliminate feces

undigested materialsextracellular waste

mainly cellulose from plants

roughage or fiber masses of bacteria

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DefecationStretch receptors in rectal wall initiate spinal reflex

Motor through parasympathetic fibersLongitudinal muscles contractAided by voluntary contraction of diaphragm and abdominal muscles and relaxation of external anal sphincter

Insoluble food molecules are digested to soluble products in the lumen of the gut.Absorption:The soluble products are first taken up by various mechanisms into the epithelial cells that line the gut. These epithelial cells then load the various absorbed molecules into the blood stream.

Assimilation:The soluble products of digestion are then transported to the various tissues by the circulatory system. The cells of the tissues then absorb the molecules for use within this tissues