6.2 6.2 The Human Digestive SystemThe Human Digestive SystemIn this section, you will: In this section, you will:

identify identify the main structures and functions the main structures and functions of the digestive systemof the digestive system

describe describe the physical and chemical the physical and chemical processing of food through the digestive processing of food through the digestive system and into the bloodstreamsystem and into the bloodstream

explain explain the action of enzymes in chemical the action of enzymes in chemical digestiondigestion

identify identify and and describedescribe, in general terms, , in general terms, how digested molecules enter the how digested molecules enter the bloodstreambloodstream

Digestive SystemDigestive SystemThe Vertebrate Digestive SystemThe Vertebrate Digestive System

the digestive system functions to break the digestive system functions to break down the macromolecules found in the down the macromolecules found in the diet into usable forms for the bodydiet into usable forms for the body

digestion is the process by which large digestion is the process by which large chunks of food are broken down into chunks of food are broken down into molecule-sized piecesmolecule-sized pieces

products of digestion are used for energy, products of digestion are used for energy, building blocks, and as enzymes and/or building blocks, and as enzymes and/or coenzymescoenzymes

the digestive system is a long tube that extends the digestive system is a long tube that extends from the mouth to the anus, and functions to from the mouth to the anus, and functions to perform four functions:perform four functions:– ingestion (eating)ingestion (eating)

movement of the food through the tract, which is movement of the food through the tract, which is accomplished by peristalsis (smooth muscle contractions)accomplished by peristalsis (smooth muscle contractions)

– digestion – the breakdown of food by both digestion – the breakdown of food by both mechanical (chewing and scrunching) and chemical mechanical (chewing and scrunching) and chemical (enzymatic) means(enzymatic) means

– absorption – the nutrients are absorbed from the absorption – the nutrients are absorbed from the digestive system into the blood and lymph from the digestive system into the blood and lymph from the small and large intestinessmall and large intestines

– elimination – defecation – the elimination of elimination – defecation – the elimination of indigestible/unabsorbed materials from the bodyindigestible/unabsorbed materials from the body

the digestive system consists of two basic the digestive system consists of two basic groups – the GI tract (the tube) and the groups – the GI tract (the tube) and the accessory structuresaccessory structures– the GI tract is a tube from 6.5 to 9 m long in the GI tract is a tube from 6.5 to 9 m long in

adultsadults

Digestive TractDigestive Tract

Secretions of the Digestive TractSecretions of the Digestive TractSecretionSecretion Site of productionSite of production FunctionFunction

salivasaliva mouth mouth contributes to starch digestion via salivary contributes to starch digestion via salivary amylase; lubricates the inside of the mouth to amylase; lubricates the inside of the mouth to assist in swallowingassist in swallowing

mucusmucus mouth, stomach, small mouth, stomach, small intestine, and large intestineintestine, and large intestine

protects the cells lining the innermost portion of protects the cells lining the innermost portion of the digestive tract; lubricates food as it travels the digestive tract; lubricates food as it travels through the digestive tractthrough the digestive tract

enzymesenzymes mouth, stomach, small mouth, stomach, small intestine, and pancreasintestine, and pancreas

promote digestion of food masses into particles promote digestion of food masses into particles small enough for absorption into the small enough for absorption into the bloodstreambloodstream

acidacid stomachstomach promotes digestion of proteinpromotes digestion of protein

bilebile liver (stored in gall bladder)liver (stored in gall bladder) suspends fat in water, using bile salts, suspends fat in water, using bile salts, cholesterol, and lecithin to aid digestion of fats in cholesterol, and lecithin to aid digestion of fats in small intestinesmall intestine

bicarbonatebicarbonate pancreas and small intestinepancreas and small intestine neutralizes stomach acid when it reaches the neutralizes stomach acid when it reaches the small intestinesmall intestine

hormoneshormones stomach, small intestine, and stomach, small intestine, and pancreaspancreas

stimulate production and/or release of acid, stimulate production and/or release of acid, enzymes, bile, and bicarbonate; help to regulate enzymes, bile, and bicarbonate; help to regulate peristalsisperistalsis

MouthMouth– the mouth is where mechanical and chemical the mouth is where mechanical and chemical

digestion beginsdigestion begins– the food is moistened by saliva produced by the food is moistened by saliva produced by

the salivary glands (we produce 1.7 L per the salivary glands (we produce 1.7 L per day), which moistens the food to make it day), which moistens the food to make it easier to swallow, and also contains the first easier to swallow, and also contains the first digestive enzymes:digestive enzymes:

amylaseamylase which begins the breakdown of starch which begins the breakdown of starch into maltose (a disaccharide) and dextrin's (short into maltose (a disaccharide) and dextrin's (short glucose chains)glucose chains)

SwallowingSwallowing– the tongue is used to push the food to the back of the the tongue is used to push the food to the back of the

mouth – this area is called the pharynx, the presence mouth – this area is called the pharynx, the presence of the food initiates the swallowing reflexof the food initiates the swallowing reflex

– the epiglottis, a small flap of tissue will close over the the epiglottis, a small flap of tissue will close over the trachea, preventing food from entering the lungstrachea, preventing food from entering the lungs

– the bolus of food is then swallowed, and travels down the bolus of food is then swallowed, and travels down the 25 cm esophagus to the stomach, helped by the 25 cm esophagus to the stomach, helped by peristalsis (you can swallow while standing on your peristalsis (you can swallow while standing on your head!)head!)

– at the bottom of the esophagus is the lower at the bottom of the esophagus is the lower esophageal sphincter (or cardiac sphincter) – a small esophageal sphincter (or cardiac sphincter) – a small ring of smooth muscle that keeps food in the stomachring of smooth muscle that keeps food in the stomach

PeristalsisPeristalsis

StomachStomach– the stomach holds up to 2L (the stomach holds up to 2L (4L) of food, and will hold food 4L) of food, and will hold food

for from 3 to 6 hours while it is broken downfor from 3 to 6 hours while it is broken down– There are three important chemicals in the stomach involved There are three important chemicals in the stomach involved

in digestion:in digestion:

HCl(aq)HCl(aq) – secreted by the parietal cells of the stomach, – secreted by the parietal cells of the stomach, lowers the pH of the stomach to 2.0, allowing the lowers the pH of the stomach to 2.0, allowing the activation of pepsin from pepsinogenactivation of pepsin from pepsinogen

Pepsin Pepsin – secreted as an inactive precursor, pepsinogen – secreted as an inactive precursor, pepsinogen (cannot be active or it would digest cellular proteins) by (cannot be active or it would digest cellular proteins) by the peptic (chief) cells. It is activated by the lowered pH the peptic (chief) cells. It is activated by the lowered pH in the stomach (which changes the shape of the enzyme)in the stomach (which changes the shape of the enzyme)

mucousmucous – secreted by the mucous (goblet) cells, protects – secreted by the mucous (goblet) cells, protects the stomach endothelium from the acid and enzymesthe stomach endothelium from the acid and enzymes

Two other secretions:Two other secretions:– gastringastrin – a hormone that stimulates gastric – a hormone that stimulates gastric

secretions (which is stimulated by the secretions (which is stimulated by the presence of proteins in the stomach), and presence of proteins in the stomach), and relaxes the pyloric sphincter to allow stomach relaxes the pyloric sphincter to allow stomach emptyingemptying

– renninrennin – found principally in children, it is – found principally in children, it is involved in the digestion of milk – slowing its involved in the digestion of milk – slowing its emptying from the stomachemptying from the stomach

physical digestionphysical digestion - the acid along with the - the acid along with the peristaltic motions of the stomach contents helps peristaltic motions of the stomach contents helps to break up tissues to break up tissues the pepsin will break up proteins into smaller the pepsin will break up proteins into smaller polypeptides called peptones (protein digestion polypeptides called peptones (protein digestion will be completed in the small intestine)will be completed in the small intestine)most materials are not absorbed in the stomach, most materials are not absorbed in the stomach, but some drugs (notably aspirin), some water, but some drugs (notably aspirin), some water, electrolytes, alcohol and absorbed in the electrolytes, alcohol and absorbed in the stomachstomachthe highly acidic stomach contents, called the highly acidic stomach contents, called chymechyme is emptied into the small intestine a bit at is emptied into the small intestine a bit at a time through the pyloric sphinctera time through the pyloric sphincter

Small IntestineSmall Intestinemeasures up to 7m in length, but only 2.5 cm in measures up to 7m in length, but only 2.5 cm in diameter, divided into three sectionsdiameter, divided into three sections– duodenum ~25 cm long, where most digestion duodenum ~25 cm long, where most digestion

occursoccurs– jejunum ~2.3 m longjejunum ~2.3 m long– ileum ~ 3.5 m longileum ~ 3.5 m longthe majority of digestion and absorption (90%) the majority of digestion and absorption (90%) takes place here – lipid digestion, continuation of takes place here – lipid digestion, continuation of carbohydrate and protein digestioncarbohydrate and protein digestionthe accessory organs of digestion, the pancreas, the accessory organs of digestion, the pancreas, gall bladder and the liver secrete their juices into gall bladder and the liver secrete their juices into the duodenum to aid in digestionthe duodenum to aid in digestion

focusing on absorption

the small intestine, in order to better digest and the small intestine, in order to better digest and absorb digested materials is highly folded to absorb digested materials is highly folded to increase surface area (by 600x); the folds are increase surface area (by 600x); the folds are called villi, which are covered in small called villi, which are covered in small cytoplasmic projections called microvillicytoplasmic projections called microvillithe structure of the small intestine (from the the structure of the small intestine (from the outer surface in) includes:outer surface in) includes:– villi/microvillivilli/microvilli – surface (epithelial) cells – surface (epithelial) cells

designed for absorptiondesigned for absorption– lacteal lacteal – vessel projection of the lymphatic – vessel projection of the lymphatic

system, designed to absorb fatssystem, designed to absorb fats– capillariescapillaries – vessels of the circulatory – vessels of the circulatory

system, for absorption of all other nutrients for system, for absorption of all other nutrients for immediate transport to the liver for processingimmediate transport to the liver for processing

Villi in the Small IntestineVilli in the Small Intestine

as the chyme enters the duodenum, its acidity as the chyme enters the duodenum, its acidity and contents stimulates a number of hormones and contents stimulates a number of hormones to be released, which in turn stimulate the to be released, which in turn stimulate the secretion of digestive and protective chemicals secretion of digestive and protective chemicals from accessory organs and the intestinal from accessory organs and the intestinal epithelium itselfepithelium itselfthe small intestine produces enzymes to aid in the small intestine produces enzymes to aid in digestions:digestions:– carbohydrases: carbohydrases: sucrase, maltase and lactase which sucrase, maltase and lactase which

break down sucrose, maltose and lactose, break down sucrose, maltose and lactose, respectively, into simple sugarsrespectively, into simple sugars

– peptidases: peptidases: peptides peptides smaller peptides and amino smaller peptides and amino acidsacids

– nucleosidases:nucleosidases: nucleotides nucleotides bases, sugars, and bases, sugars, and phosphatesphosphates

HormonesHormones– GastrinGastrin: stimulated by proteins in food causing the : stimulated by proteins in food causing the

secretion of HCl and pepsinogensecretion of HCl and pepsinogen– cholecystokinin (CCK):cholecystokinin (CCK): stimulated by partially stimulated by partially

digested proteins and irritants in the chyme, digested proteins and irritants in the chyme, stimulates pancreatic enzyme release and bile from stimulates pancreatic enzyme release and bile from the gallbladderthe gallbladder

– Secretin:Secretin: in response to acidic chyme in the in response to acidic chyme in the duodenum, inhibits the secretion of gastric juice, duodenum, inhibits the secretion of gastric juice, stimulates bicarbonate release by the pancreas to stimulates bicarbonate release by the pancreas to neutralize acidic chymeneutralize acidic chyme

– GIP (gastric inhibitory peptide)GIP (gastric inhibitory peptide)

Chemical DigestionChemical Digestion

Hormone Secretions Hormone Secretions at workat work

Selected Enzymes of the Digestive SystemSelected Enzymes of the Digestive SystemEnzymeEnzyme Where enzyme Where enzyme

acts/pHacts/pHSubstrate (food) Substrate (food)

digesteddigestedProducts of digestionProducts of digestion Origin of enzymesOrigin of enzymes

salivary salivary amylaseamylase

mouth/7mouth/7 starch, glycogenstarch, glycogen maltose (disaccharide)maltose (disaccharide) salivary glandssalivary glands

pancreatic pancreatic amylaseamylase

small intestine/8small intestine/8 starch, glycogenstarch, glycogen maltosemaltose pancreaspancreas

carbohydrasescarbohydrases• • sucrasesucrase• • maltasemaltase• • lactaselactase

small intestine/8small intestine/8sucrosesucrosemaltosemaltoselactoselactose

glucose + fructoseglucose + fructoseglucoseglucoseglucose + galactoseglucose + galactose

small intestinesmall intestine

pancreatic pancreatic lipaselipase

small intestine/8small intestine/8 lipidslipids fatty acids and glycerolfatty acids and glycerol pancreaspancreas

proteasesproteases• • pepsinpepsin• • trypsintrypsin• • chymotrypsinchymotrypsin

stomach/1–2stomach/1–2small intestine/8small intestine/8small intestine/8small intestine/8

proteinproteinpeptidespeptidespeptidespeptides

peptidespeptidessmaller peptidessmaller peptidessmaller peptidessmaller peptides

stomachstomachpancreaspancreaspancreaspancreas

peptidasespeptidases small intestine/8small intestine/8 peptidespeptides smaller peptides and amino smaller peptides and amino acidsacids

pancreas and small pancreas and small intestineintestine

nucleasesnucleases small intestine/8small intestine/8 nucleic acidsnucleic acids nucleotides and nucleotides and componentscomponents

pancreaspancreas

nucleosidasesnucleosidases small intestine/8small intestine/8 nucleotidesnucleotides bases, sugars, and bases, sugars, and phosphatesphosphates

small intestinesmall intestine

Accessory Organs:Accessory Organs:

PancreasPancreas– a soft tubular gland that lies just behind the a soft tubular gland that lies just behind the

stomach, and is connected to the duodenum stomach, and is connected to the duodenum by two ductsby two ducts

– has both a exocrine (secretory) and endocrine has both a exocrine (secretory) and endocrine (hormonal) function(hormonal) function

– its exocrine functions are to secrete digestive its exocrine functions are to secrete digestive enzymes and sodium bicarbonate to enzymes and sodium bicarbonate to neutralize the stomach acid and establish a neutralize the stomach acid and establish a pH of 7.1-8.2 which will not only neutralize the pH of 7.1-8.2 which will not only neutralize the enzyme pepsin, but activate the pancreatic enzyme pepsin, but activate the pancreatic enzymesenzymes

Pancreatic Enzymes:Pancreatic Enzymes:– pancreatic amylase:pancreatic amylase: digest carbohydrates digest carbohydrates

maltosemaltose– trypsin:trypsin: protein digestion: peptides protein digestion: peptides smaller smaller

peptides (activated by enterokinase, secreted by the peptides (activated by enterokinase, secreted by the intestinal wall)intestinal wall)

– chymotrypsin:chymotrypsin: protein digestion: peptides protein digestion: peptides smaller smaller peptides (activated by trypsin)peptides (activated by trypsin)

– peptidase:peptidase: peptides peptides smaller peptides and amino smaller peptides and amino acidsacids

– pancreatic lipase:pancreatic lipase: digests fats into fatty acids and digests fats into fatty acids and glycerolglycerol

– ribonuclease:ribonuclease: digests RNA to nucleotides digests RNA to nucleotides– deoxyribonuclease:deoxyribonuclease: digests DNA to nucleotides digests DNA to nucleotides

LiverLiver

the liver has over 500 functions, four being the liver has over 500 functions, four being fundamental:fundamental:– production of bileproduction of bile– storage of glucose in the form of glycogen (storage of glucose in the form of glycogen ( fat if fat if

glycogen limits exceeded), conversion of galactose glycogen limits exceeded), conversion of galactose and fructose to glucoseand fructose to glucose

– detoxification of the blood (makes enzymes to break detoxification of the blood (makes enzymes to break down toxins; ex: alcohol, caffeine, nicotine, down toxins; ex: alcohol, caffeine, nicotine, barbiturates, poisons, excess hormones)barbiturates, poisons, excess hormones)

– deamination of amino acids – removing nitrogen, deamination of amino acids – removing nitrogen, producing ammonia and eventually urea (excreted by producing ammonia and eventually urea (excreted by the kidneys)the kidneys)

it receives two separate blood suppliesit receives two separate blood supplies– via the portal vein – bringing freshly absorbed via the portal vein – bringing freshly absorbed

nutrients from the small intestinenutrients from the small intestine– via the hepatic artery – bringing oxygenated blood via the hepatic artery – bringing oxygenated blood

from the lungs/heartfrom the lungs/heart

bilebile– each day, the liver secretes between 800 – 1000 mL each day, the liver secretes between 800 – 1000 mL

of bileof bile– bile is stored in the gallbladder for release on demand bile is stored in the gallbladder for release on demand

into the small intestineinto the small intestine– consists of water, bile salts, cholesterol and bile consists of water, bile salts, cholesterol and bile

pigments (made from bilirubin – yellow in colour)pigments (made from bilirubin – yellow in colour)– bile acts as an emulsifier, breaking large fat globules bile acts as an emulsifier, breaking large fat globules

into small ones, allowing lipase more surface area for into small ones, allowing lipase more surface area for digestiondigestion

GallbladderGallbladder– is lodged in one of the lobes of the liveris lodged in one of the lobes of the liver– a light muscular bag that stores and releases bilea light muscular bag that stores and releases bile– why store bile? We eat large quantities of fats at a why store bile? We eat large quantities of fats at a

time, so having a store of bile is useful but can lead to time, so having a store of bile is useful but can lead to problems – bile salts can crystallize in the gallbladder problems – bile salts can crystallize in the gallbladder forming gallstonesforming gallstones

back to digestion….back to digestion….

– the combination of hormones and the presence of the combination of hormones and the presence of certain foods leads to the secretion of pancreatic certain foods leads to the secretion of pancreatic enzymes, bile, and intestinal enzymes (maltase, enzymes, bile, and intestinal enzymes (maltase, lactase, sucrase and enterokinase), all of which are lactase, sucrase and enterokinase), all of which are active in the slightly basic pH of the duodenumactive in the slightly basic pH of the duodenum

the villi of the small intestine are the villi of the small intestine are specialized to absorb the molecules of specialized to absorb the molecules of digestion:digestion:– large surface arealarge surface area– transport proteins on the epithelial cells move transport proteins on the epithelial cells move

amino acids, glucose, water soluble vitamins, amino acids, glucose, water soluble vitamins, etc. by facilitated diffusion and active etc. by facilitated diffusion and active transport into the capillary system, then on to transport into the capillary system, then on to the liver immediately for processingthe liver immediately for processing

– electrolytes by diffusion, water by osmosiselectrolytes by diffusion, water by osmosis– fatty acids and glycerol are absorbed into the fatty acids and glycerol are absorbed into the

epithelial cells and are repackaged as epithelial cells and are repackaged as triglyceridestriglycerides

– being hydrophobic, they are packaged into being hydrophobic, they are packaged into protein packs to enable their transport through protein packs to enable their transport through the bodythe body

– the packaged fats are absorbed into the the packaged fats are absorbed into the lacteals in the interior of the villi, and are lacteals in the interior of the villi, and are transported through the body’s lymphatic transported through the body’s lymphatic systemsystem

– fat soluble vitamins will move with fats into fat soluble vitamins will move with fats into lacteals for absorption in the bodylacteals for absorption in the body

Absorption of NutrientsAbsorption of Nutrients

Top:Top: Glucose is actively transported Glucose is actively transported into cells of the intestinal wall to into cells of the intestinal wall to move into the bloodstream.move into the bloodstream.

Middle:Middle: Amino acids are actively Amino acids are actively transported into the cells of the transported into the cells of the intestinal wall to move into the intestinal wall to move into the bloodstream. bloodstream.

Bottom:Bottom: Glycerol and fatty acid Glycerol and fatty acid molecules diffuse into the cells of the molecules diffuse into the cells of the intestinal wall where they are intestinal wall where they are resynthesized into fats, coated with resynthesized into fats, coated with proteins, and move into lymph proteins, and move into lymph vessels for eventual transport into vessels for eventual transport into the bloodstream.the bloodstream.

Large IntestineLarge Intestine– about 1.5 m in length, a diameter of 6.5 cm.about 1.5 m in length, a diameter of 6.5 cm.– at the junction of the small and large intestine, at the junction of the small and large intestine,

exists the appendix, which has no real function exists the appendix, which has no real function given our dietgiven our diet

– the large intestine has three main functions:the large intestine has three main functions:absorption of water and electrolytesabsorption of water and electrolytes

production of feces – consisting of water, inorganic production of feces – consisting of water, inorganic salts, cells from the GI tract, bacteria, bacterial salts, cells from the GI tract, bacteria, bacterial decomposition and undigested fooddecomposition and undigested food

housing bacteria, that will use remaining unabsorbed housing bacteria, that will use remaining unabsorbed nutrients or undigested carbohydrates to make vitamin nutrients or undigested carbohydrates to make vitamin K and B vitamins for us to absorb (as well as methane K and B vitamins for us to absorb (as well as methane gas)gas)

6.3 Health and the Digestive 6.3 Health and the Digestive SystemSystem

In this section, you will:In this section, you will:

recognize recognize and and appreciate appreciate the relationship the relationship between health and nutritional decisionsbetween health and nutritional decisions

identify identify conditions that adversely affect the health conditions that adversely affect the health of the digestive system and the technologies that of the digestive system and the technologies that are available to treat themare available to treat them

Digestive DisordersDigestive Disorders

Digestive DisordersDigestive Disorders

Disorders of the digestive system and its Disorders of the digestive system and its accessory organs include:accessory organs include:– ulcers, ulcers, – inflammatory bowel disease, inflammatory bowel disease, – hepatitis, hepatitis, – cirrhosis, cirrhosis, – and gallstones. and gallstones.

All disorders that affect digestion, including eating All disorders that affect digestion, including eating disorders, can seriously damage overall health by disorders, can seriously damage overall health by depriving the body cells of the nutrients they need depriving the body cells of the nutrients they need to survive.to survive.

Chapter 6 ReviewChapter 6 ReviewWhy are some amino acids classified as Why are some amino acids classified as essential?essential?

Describe the relationship between the Describe the relationship between the organs in the digestive tract. organs in the digestive tract.

What are the benefits of having stomach What are the benefits of having stomach stapling? What are the risks?stapling? What are the risks?

Summarize chemical digestion of Summarize chemical digestion of macromolecules.macromolecules.

Explain how glucose levels are affected Explain how glucose levels are affected after meals. Include the effects of different after meals. Include the effects of different foods.foods.

Concept OrganizerConcept Organizer

Chapter 6 SummaryChapter 6 Summary

The human body takes in matter from the The human body takes in matter from the environment in the form of food and water. The environment in the form of food and water. The human digestive system processes the food and human digestive system processes the food and water in order to obtain the macromolecules it water in order to obtain the macromolecules it needs for survival.needs for survival.

Making Healthy Food ChoicesMaking Healthy Food Choices

Chapter 6 SummaryChapter 6 SummaryFood passes through the digestive tract—the Food passes through the digestive tract—the mouth, pharynx, esophagus, stomach, small mouth, pharynx, esophagus, stomach, small intestine, and large intestine—during physical intestine, and large intestine—during physical digestion. digestion. The accessory organs—the salivary glands, liver, The accessory organs—the salivary glands, liver, gall bladder, and pancreas—supply chemicals that gall bladder, and pancreas—supply chemicals that also contribute to the digestion of food as it passes also contribute to the digestion of food as it passes through the digestive tract. through the digestive tract. The stomach supplies chemicals to aid digestion as The stomach supplies chemicals to aid digestion as well as generating physical contractions to well as generating physical contractions to physically break down food. physically break down food. The food is eventually liquefied into soluble units The food is eventually liquefied into soluble units that can pass through cell membranes for transport that can pass through cell membranes for transport via the circulatory system to all the cells in the body. via the circulatory system to all the cells in the body. The waste materials from the digestive process The waste materials from the digestive process leave the body via the large intestine.leave the body via the large intestine.

Good Nutrition + Exercise = Good Nutrition + Exercise = HealthHealth

Chapter 6 SummaryChapter 6 SummaryThe nutrients that food supplies include carbohydrates, The nutrients that food supplies include carbohydrates, lipids (fats), protein, and nucleic acids. lipids (fats), protein, and nucleic acids. Carbohydrates and lipids are broken down to supply Carbohydrates and lipids are broken down to supply energy; lipids also supply material for the cell energy; lipids also supply material for the cell membranes. membranes. Proteins are more structurally and functionally diverse Proteins are more structurally and functionally diverse than carbohydrates and lipids. They assist in transport, than carbohydrates and lipids. They assist in transport, immunity, and muscle action and are used to make up immunity, and muscle action and are used to make up most cellular structures. most cellular structures. Nucleic acids direct growth and development. Enzymes Nucleic acids direct growth and development. Enzymes speed up chemical reactions, particularly for the speed up chemical reactions, particularly for the production of energy. production of energy. Vitamins and minerals are organic and inorganic Vitamins and minerals are organic and inorganic substances that enable chemical reactions to occur and substances that enable chemical reactions to occur and aid in tissue development and growth and immunity. aid in tissue development and growth and immunity. These substances are needed for a healthy, functional These substances are needed for a healthy, functional human body.human body.

Chapter 6 SummaryChapter 6 Summary