The Digestive Systemkborsari.blogs.ccps.us/files/2017/11/A-digestive-system... · 2017. 11. 27. · Processes of the Digestive System Ingestion Intake of food into the mouth Mechanical

Chapter 14The Digestive System

Processes of the Digestive System Digestive tract is a

‘disassembly line’ Food becomes less

complex at each step of processing and its nutrients become available to the body

Six digestive processes Ingestion Mechanical digestion Propulsion Chemical digestion Absorption Defecation

Processes of the Digestive System Ingestion

Intake of food into the mouth Mechanical digestion (physical)

Physically prepares food for chemical digestion by enzymes

Chewing and mixing of food with saliva by the mouth

Churning food in the stomach

Propulsion Smooth muscle contractions that move

food through the alimentary canal Swallowing and peristalsis

Processes of the Digestive System Chemical Digestion

Complex food molecules are broken down to their chemical building blocks by enzymes

Begins in the mouth and is completed by the small intestines

Each major food group uses different enzymes

Carbohydrates are broken to simple sugars

Proteins are broken to amino acids Fats are broken to fatty acids and

alcohols

Processes of the Digestive System

Absorption Movement of small organic molecules,

waters, electrolytes and vitamins from the digestive tract to the blood stream (mainly occurs in the small intestines)

Defecation Formation and removal of indigestible

substances in the form of feces

Organs of the Digestive System Two main groups of organs Alimentary canal or gastrointestinal

(GI) tract Continuous, muscular digestive

tube Digests food and absorbs the

building blocks Mouth, pharynx, esophagus,

stomach, small intestine, large intestine, and anus

Accessory digestive organs Teeth, tongue, gallbladder,

salivary glands, liver and pancreas

Contribute to the breakdown of foodstuffs

Mouth (Oral Cavity) Anatomy

Mouth is a mucosa-lined cavity called the oral cavity

Boundaries Lips anteriorly Cheeks laterally Palate superiorly Tongue inferiorly

Anterior opening is called the oral orifice

Walls of mouth are lined with a thick stratified squamous epithelium

Mouth (Oral Cavity) Anatomy Lips (labia) and cheeks

Helps keep food between the teeth when we chew

Composed of a core of skeletal muscle covered externally by skin

Orbicularis oris forms the fleshy lips Buccinators forms the cheeks

Palates Forms the roof of the mouth Two distinct parts

Hard palate (anterior) Soft palate (posterior) Uvula projects downward from

the free edge of the soft palate

Mouth (Oral Cavity) Anatomy Tongue

Occupies the floor of the mouth Fills most of the oral cavity when

the mouth is closed During chewing, it grips the food

and repositions the food between the teeth

Mixes the food with saliva and forms a compact mass called a bolus

Initiates swallowing by pushing the bolus posteriorly into the pharynx

Helps us form consonants when we speak

Mouth (Oral Cavity) Anatomy Salivary Glands

Parotid gland (par = near; otid = ear) Lies anterior to the ear Mumps - inflammation of the

parotid glands caused by the myxovirus which spreads from person to person in saliva

Submandibular gland Lies along the medial aspect of

the mandibular body

Sublingual gland Lies under the tongue and opens

into the floor of the mouth

Mouth (Oral Cavity) Anatomy Salivary Glands

Function is to secrete saliva Cleanse the mouth Dissolves food chemicals so they can be tasted Moistens the food and aids in compacting it into a bolus Contains amylase, an enzyme, that begins the chemical

breakdown of carbohydrates

Mouth (Oral Cavity) Anatomy Teeth

Masticate (chew) food into smaller pieces

Humans have two sets of teeth Deciduous (baby or milk) teeth

20 teeth are fully formed by age two

Permanent teeth Replace deciduous teeth

beginning between the ages of 6 to 12

A full set is 32 teeth, but some people do not have wisdom teeth

Pharynx Anatomy Nasopharynx

Posterior to nasal cavity Oropharynx

Posterior to oral cavity Laryngopharynx

Below the oropharynx and connected to the esophagus

Serves as a passageway for both food and air

Epiglottis, a flap of cartilage Prevents food from entering

trachea (windpipe)

Esophagus Anatomy Runs from pharynx to stomach through the diaphragm Conducts food by peristalsis (slow rhythmic

squeezing) Passageway for food only (respiratory system

branches off after the pharynx) Pharynx and esophagus act as a conduit to pass food

from the mouth to the stomach Digestive function is propulsion

Digestive Processes: Mouth to Esophagus

Food enters the oral cavity (mouth) Mastication (chewing)

Mechanical breakdown begins as food enters the mouth with chewing

Cheeks and closed lips hold food between the teeth Tongue mixes the food with saliva and compacts it into a bolus Teeth cut and grind solid foods into smaller morsels

Starts chemical breakdown of carbohydrates Salivary amylase, main enzyme in saliva, digests starch and

glycogen Essentially no absorption occurs in the mouth

Pharynx and esophagus act as a conduit to pass food from the mouth to the stomach Digestive function is propulsion

Located in the upper left quadrant of the abdominal cavity

Varies between 6-10 inches but its volume depends on how much food it contains

An empty stomach contains about 50 mL and a full one can hold about 4 L of food

Regions Cardiac

Cardioesophageal sphincter Fundus Body Pylorus

Pyloric sphincter

Digestive Processes: Stomach

Lining is a simple columnar epithelium composed entirely of mucous cells

Cells in the stomach secrete hydrochloric acid and pepsin, a protein digesting enzyme

High acidic levels activate pepsin and kills most of the bacteria and other pathogens ingested


Bolus moves through the esophagus by peristalsis through the cardioesophageal sphincter into the stomach

Stomach functions Storage tank for ingested food Mechanically churns the food Chemically breaks down proteins Converts food into a creamy

paste called chyme Only absorption that occurs in the

stomach is of alcohol and aspirin After 1-3 hours, the chyme moves

into the small intestine through the pyloric sphincter


Body’s major digestive organ Average length 7-13 feet Site of nutrient absorption into the blood Chyme is transported for 3-6 hours

through the small intestine Muscular tube extending from the pyloric

sphincter to the ileocecal valve Small intestine (3 subdivisions)

Duodenum Jejunum Ileum

Digestive Processes: Small Intestines

Enzymes from the brush border Break double sugars into simple sugars Complete some protein digestion

Pancreatic enzymes play the major digestive function Help complete digestion of starch

(pancreatic amylase) Carry out about half of all protein

digestion (trypsin, etc.)

Responsible for fat digestion (lipase)

Digest nucleic acids (nucleases)

Alkaline content neutralizes acidic chyme


Highly adapted for nutrient absorption Its length provides a huge surface area Wall has three modifications that amplify its absorptive surface

Circular folds Force chyme to spiral through causing it to slow its movement and allow time

for absorption Villi

Fingerlike projections that are where the absorptive columnar cells are located Microvilli

Give the absorptive cells a brush border


Liver Largest gland in the body Located on the right upper quadrant

under the diaphragm Produces bile to be exported to the

duodenum Bile is a fat emulsifier, breaks up

fats into smaller particles Gall bladder

Rests in the recess on the interior surface of the right liver lobe

Storage organ for bile Bile leaves the liver through the

common hepatic duct which fuses with the cystic duct that drains the gallbladder and to form the bile duct

Digestive Processes: Liver and Gallbladder

Homeostatic imbalances of the liver Hepatitis or inflammation of the liver

Usually due to one of six hepatitis viruses

Nonviral causes include drug toxicity and wild mushroom poisoning

In the US, 40% are due to HVB which is transmitted via blood transfusion, contaminated needles or sexual contact

Cirrhosis is a chronic inflammation of the liver usually resulting from alcoholism or chronic hepatitis

Liver transplants are the only clinically proven effective treatment for patients with end-stage liver disease

Digestive Processes: Liver and Gallbladder

Small gland that extends across the abdomen Produces a pancreatic juice that contains a wide spectrum of digestive

enzymes that break down all categories of food Alkaline to help neutralize the acidic chyme

It is secreted into the duodenum via the main pancreatic duct

Digestive Processes: Pancreas

Frames the small intestines on three sides

Extends from the ileocecal valve to the anus

No digestive enzymes are produced

Resident bacteria digest remaining nutrients

Water and vitamins K and B are absorbed

Remaining materials are eliminated via feces

Remains in large intestine for about 12 – 36 hours

Digestive Processes: Large Intestines

Subdivisions Cecum

Appendix Colon Rectum Anal canal


Cecum Lies below the ileocecal valve First part of the large intestine Vermiform appendix is attached to its

posteromedial surface Masses of lymphoid tissue Appendicitis, acute inflammation

of the appendix, results from a blockage that traps infectious bacteria inside

Unable to empty its contents, the appendix swells, which may lead to the appendix rupturing


Regions of the Colon Ascending colon –

travels up the right side of the abdominal cavity

Transverse colon –travels across the abdominal cavity

Descending colon –descends down the left side of the abdominal wall

Sigmoid colon –inferiorly it enters the pelvis and becomes s-shaped


Rectum Anal canal

Last segment of the large intestine and opens to the body exterior at the anus

Indigestible material passes out the anus in a process called defecation

Anal canal has external voluntary (skeletal muscle) sphincter and internal involuntary (smooth muscle) sphincter


Processes of the Digestive System

Nutrition Nutrient

Substance in food used by the body to promote normal growth, maintenance, and repair

Categories of nutrients Major nutrients

Carbohydrates Lipids Proteins

Vitamins Mineral Water

Dietary Sources of Major Nutrients Carbohydrates

Dietary Sources Most are derived from plants Monosaccharides

Glucose, fructose and galactose from fruits, honey, milk, sugar cane

Polysaccharides Starch – from grains, legumes, root vegetables Cellulose – not digested but provides roughage or insoluble

fiber; aids in defecation Function in the body

Glucose is the major body fuel to make ATP Excess glucose is converted into glycogen or fat for storage

Chemical digestion of starch to monosaccharides Begins in mouth with salivary amylase Continues in small intestines with pancreatic amylase

Dietary Sources of Major Nutrients Lipids

Dietary sources Saturated fats (triglycerides) from fatty meats, dairy foods and

hyrdogenated oils such as margarine and solid shortenings Unsaturated fats from nuts, seeds, olive oils and vegetable oils Cholesterol from egg yolk, meats, shellfish and milk products

Functions in the body Component of all cell membranes and myelin sheaths Protective cushion around body organs Insulating layer below skin Easy to store concentrated source of energy fuel Help body absorb fat-soluble vitamins

Chemical digestion of lipids to glycerol and fatty acids Begins in small intestines by the emulsification of bile from the liver Continues with the help of pancreatic lipases in the duodenum

Dietary Sources of Major Nutrients Proteins

Dietary Sources Animal products contain the highest quality proteins Eggs, milk, fish, and meats Complete proteins – contain all essential amino acids

Essential amino acids: isoleucine, leucine, lysine, tryptophan, methionine, phenyalanine, threonine, valine

The body makes the other 12 necessary amino acids Functions in the body

Structural proteins– keratin in skin, tendons, nails, collagen, elastin, muscle proteins, hair

Functional proteins – enzymes, transport, hormones, antibodies Chemical digestion of proteins to amino acids

Begins in the stomach with pepsin Continues in small intestine with pancreatic enzymes

Dietary Sources of Major Nutrients Vitamins

Organic compounds critical in helping the body make functional or energy compounds

Without vitamins carbohydrates, proteins and fats would be useless Most vitamins function as coenzymes and act with enzymes Vitamins made by the body

Vitamin D – from sunshine, skin converts it Vitamin K – synthesized by bacteria in large intestine Vitamin A – made from carotene pigment

Essential vitamins – all other vitamins must be taken in through foods or supplements Fat soluble vitamins – A, D, E, K – bind to ingested lipids and are

absorbed along with their digestion products Water soluble vitamins – B complex and vitamin C – absorbed with

water and excreted in urine if not used

Dietary Sources of Major Nutrients Water-soluble vitamins

Vitamin B1(thiamine) found in lean meats, liver, legumes, peanuts, whole grains; coenzyme used in removing CO2 from organic compounds

Vitamin B2 (riboflavin) found in milk, liver, yeast, meats, vegetables; component of coenzymes FAD and FMN

Vitamin B3 (niacin) found in nuts, poultry, fish, meats and grains; component of coenzyme NAD+

Vitamin B5 (pantothenic acid) found in most foods: meats, dairy products, whole grains, etc; component of coenzyme A; involved in synthesis of steroids and hemoglobin

Vitamin B6 (pyridoxine) found in meats, fish, poultry, vegetables, bananas; coenzyme used in amino acid metabolism and antibody formation

Vitamin B9 (folic acid or folacin) found in liver, oranges, nuts, legumes, whole grains; coenzyme in nucleic acid and amino acid metabolism

Vitamin B12 (cyanocobalamin) found in meats, eggs, dairy products; conezyme in nucleic acid metabolism

Biotin found in legumes, other vegetables, meats, liver, egg yolk; coenzyme in synthesis of fat, glycogen and amino acids

Vitamin C found in fruits and vegetables, especially citrus fruits, strawberries, broccoli, cabbage, tomatoes, green peppers; used in collagen synthesis such as bone, cartilage, gums, etc; antioxidant; aids in detoxification; improves iron absorption

Dietary Sources of Major Nutrients Fat-soluble vitamins

Vitamin A (retinol) In deep green and orange vegetables and fruits; component of visual pigments; maintenance of epithelial tissues; antioxidant

Vitamin D found in dairy products, egg yolk and made in human skin in the presence of sunlight; functionally a hormone; aids in absorption and use of calcium and phosphorus; promotes bone growth

Vitamin E found in wheat germ, vegetable oils, nuts, seeds, dark green leafy vegetables; antioxidant; helps prevent damage to cell membranes

Vitamin K found in green vegetables, tea; important in formation of blood clotting proteins

Dietary Sources of Major Nutrients Minerals

Body requires moderate amounts of seven minerals and trace amounts of about a dozen others

Make up about 4% of the body by weight with calcium and phosphorus making up the most

Play many roles in the body Most mineral-rich foods are vegetables, legumes, milk, and some meats

Dietary Sources of Major Nutrients Seven important minerals

Calcium (Ca) found in dairy products, dark green vegetables, legumes; bone and tooth formation, blood clotting, nerve and muscle function

Phosphorus (P) found in dairy products, meats, whole grains, nuts; bone and tooth formation, acid-base balance, nucleic acid synthesis

Sulfur (S) found in sulfur-containing proteins from many sources (meats, milk, eggs) component of certain amino acids

Sodium (Na) found in table salt, cured meats; osmotic pressure, acid-base balance, water-balance, nerve function, important for pumping glucose and other nutrients

Chloride (Cl) found in table salt, cured meats; osmotic pressure, acid base balance, gastric juice formation

Magnesium (Mg) found in whole grains, green leafy vegetables; component of certain coenzymes in ATP formation

Potassium (K) found in meats, dairy products, many fruits and vegetables, grains; acid-base balance, water balance, nerve function, muscle contraction

Metabolism Nutrient usage

All of the nutrients absorbed into the blood stream are either broken down or built into usable substances

Metabolism Chemical reactions necessary to maintain life

Once inside body cells the nutrients become involved in an incredible variety of reactions known as metabolism

Substances are constantly being built up and torn down Cells use energy to extract more energy from foods Then use some of this energy to drive their activities Catabolism – substances are broken down to simpler substances

such as in cellular respiration; energy is released during catabolism

Anabolism – larger molecules are built from smaller ones such as bonding together of amino acids to make proteins

Metabolism Chemical reactions necessary to maintain life

Once inside body cells the nutrients become involved in an incredible variety of reactions known as metabolism

Substances are constantly being built up and torn down Cells use energy to extract more energy from foods Then use some of this energy to drive their activities Catabolism – substances are broken down to simpler substances

such as in cellular respiration; energy is released during catabolism

Anabolism – larger molecules are built from smaller ones such as bonding together of amino acids to make proteins

Carbohydrate Metabolism The body’s preferred source to produce cellular energy (ATP) Glucose (blood sugar) is the major breakdown product and fuel to

make ATP

Cellular Respiration Oxygen-using events take place within the cell to create ATP Carbon leaves cells as carbon dioxide (CO2) Hydrogen atoms are combined with oxygen to form water Energy produced by these reactions produces ATP ATP can be broken down to release energy for cellular use

Metabolic Pathways in Cellular Respiration Glycolysis – energizes a glucose molecule so that it can be split into

two pyruvic acid molecules and yield ATP Krebs cycle

Produces virtually all the carbon dioxide and water resulting from cell respiration and yields a small amount of ATP

Metabolic Pathways in Cellular Respiration Electron transport chain

Hydrogen atoms removed during glycolysis and the Krebs cycle are delivered to protein carriers

Hydrogen is split into hydrogen ions and electrons in the mitochondria Electrons give off energy in a series of steps to enable the production of

ATP

Role of the Liver in Metabolism

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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Several roles in digestion Detoxifies drugs and alcohol Degrades hormones Produce cholesterol, blood proteins

(albumin and clotting proteins) Plays a central role in metabolism

Metabolic Functions of the Liver

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GlycogenesisGlucose molecules are converted to glycogenGlycogen molecules are stored in the liver

GlycogenolysisGlucose is released from the liver after

conversion from glycogen

GluconeogenesisGlucose is produced from fats and proteins


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Figure 14.20


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Fats and fatty acids are picked up by the liverSome are oxidized to provide energy for liver

cells

The rest are broken down into simpler compounds and released into the blood

Cholesterol Metabolism

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Functions of cholesterolServes as a structural basis of steroid hormones

and vitamin D

Is a major building block of plasma membranes

Most cholesterol is produced in the liver and is not from diet

Cholesterol Transport

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Cholesterol and fatty acids cannot freely circulate in the bloodstream

They are transported by lipoproteins (lipid-protein complexes)Low-density lipoproteins (LDLs) transport to

body cells

High-density lilpoproteins (HDLs) transport from body cells to the liver

Body Energy Balance

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Energy intake = total energy output (heat + work + energy storage)Energy intake is liberated during food oxidation

Energy output

Heat is usually about 60%

Storage energy is in the form of fat or glycogen

Regulation of Food Intake

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Body weight is usually relatively stableEnergy intake and output remain about equal

Mechanisms that may regulate food intakeLevels of nutrients in the bloodHormonesBody temperaturePsychological factors

Metabolic Rate and Body Heat Production

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Basic metabolic rate (BMR) – amount of heat produced by the body per unit of time at rest

Factors that influence BMRSurface area – small body usually has higher

BMR

Gender – males tend to have higher BMR

Metabolic Rate and Body Heat Production

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Factors that influence BMR (continued)Age – children and adolescents have a higher

BMR

The amount of thyroxine produced is the most important control factor

More thyroxine means higher metabolic rate

Total Metabolic Rate (TMR)

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Total amount of kilocalories the body must consume to fuel ongoing activities

TMR increases with an increase in body activity

TMR must equal calories consumed to maintain homeostasis and maintain a constant weight

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The Digestive Systemkborsari.blogs.ccps.us/files/2017/11/A-digestive-system... · 2017. 11. 27. · Processes of the Digestive System Ingestion Intake of food into the mouth Mechanical