the digestive systemkborsari.blogs.ccps.us/files/2017/11/a-digestive-system... · 2017. 11. 27. ·...
TRANSCRIPT
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
Digestive Processes: Stomach
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
Digestive Processes: Stomach
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
Digestive Processes: Small Intestines
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
Digestive Processes: Small Intestines
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
Digestive Processes: Large Intestines
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
Digestive Processes: Large Intestines
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
Digestive Processes: Large Intestines
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
Digestive Processes: Large Intestines
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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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
Metabolic Functions of the Liver
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Figure 14.20
Metabolic Functions of the Liver
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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