Title: Chapter 12: Digestive System and Nutrition
1Chapter 12 Digestive System and Nutrition
2The Digestive Tract
- The human digestive tract is a tube with
specialized regions and organs between the mouth
and the anus. - Food is ingested, mechanically processed, and
chemically digested to small molecules that are
absorbed indigestible remains are eliminated. - Parts of the digestive tract produce digestive
enzymes.
3Digestive system
4The Mouth
- Lips and cheeks enclose the mouth.
- Taste buds on the tongue provide the sense of
taste skeletal muscle in the tongue allows it to
move. - The roof of the mouth is formed by the hard and
soft palates that separate it from the nasal
cavities. - The soft palate ends in a finger-shaped
projection called the uvula.
5- Tonsils at the back sides of the mouth protect
against infections. - Tonsillitis results when the tonsils become
inflamed the infection can spread to the middle
ears. - Three pairs of salivary glands send saliva
(containing salivary amylase for digestion of
starch to maltose) into the mouth.
6The Teeth
- Twenty deciduous (baby) teeth are replaced by 32
adult teeth. - Each tooth has a crown and a root.
- The crown has a layer of enamel, dentin, and an
inner pulp with nerves and blood vessels that
extend into the root. - The tongue mixes the chewed food with saliva and
then forms the mixture into a mass called a bolus
in preparation for swallowing.
7Adult mouth
8Longitudinal section of a tooth
9The Pharynx
- The air passage and food passage cross in the
pharynx because the trachea is ventral to the
esophagus. - Swallowing occurs in the pharynx and is a reflex
action. - During swallowing, the air passage is usually
blocked off by the soft palate and uvula, and the
trachea moves under the epiglottis to cover the
glottis opening to the windpipe.
10Swallowing
11The Esophagus
- The esophagus is a muscular tube that conducts
food through the thoracic cavity and diaphragm
into the stomach. - Peristalsis begins in the esophagus this
collapsed tube moves the bolus of food downward
after swallowing occurs. - Heartburn is a burning pain when acidic stomach
contents enter the esophagus.
12- No chemical digestion occurs in the esophagus.
- The entrance of the esophagus to the stomach is
marked by a constriction, called a sphincter the
sphincter must relax in order for food to enter
the stomach. - The sphincter prevents food from backing up into
the esophagus.
13The Wall of the Digestive Tract
- The digestive tract wall has four layers
- Mucosa (mucous membrane secretes digestive
enzymes and mucus), - Submucosa (loose connective tissue houses blood
and lymph vessels), - Muscularis (two layers of smooth muscle - for
peristalsis), and - Serosa (serous membrane secretes serous fluid
to prevent sticking).
14Wall of the digestive tract
15The Stomach
- The stomach expands to store food.
- Food in the stomach is churned, mixing the food
with gastric juices containing hydrochloric acid
and pepsin for the digestion of protein to
peptides. - Alcohol, but not food, is absorbed here.
- In 26 hours, the soupy chyme leaves the stomach.
- Ulcers are usually caused by a bacterial
infection.
16Anatomy and histology of the stomach
17Ulcer
18The Small Intestine
- The small intestine, averaging about 6 meters in
length, is small in diameter. - The first 25 cm is the duodenum that receives
bile from the gallbladder and pancreatic juice
containing pancreatic lipase and trypsin for
digestion of protein to peptides, as well as
lipase for digestion of fat to glycerol and fatty
acids. - Pancreatic juice contains NaHCO3 that is basic
and neutralizes the acidic chyme.
19- Enzymes that finish the process of digestion are
produced by the intestinal wall. - Walls of the small intestine have finger-like
projections called villi where nutrient molecules
are absorbed into the cardiovascular and
lymphatic systems. - Villi have microvilli that increase the surface
area available for absorption. - The small lymphatic capillary in a villus is
called a lacteal.
20Anatomy of the small intestine
21Regulation of Gastric Secretions
- Both the nervous system and chemicals called
hormones regulate digestive juice secretion. - In response to eating protein foods, the hormone
gastrin is produced by the lower part of the
stomach and flows through the bloodstream to
stimulate the stomach to produce digestive juice.
22- The duodenal wall produces gastric inhibitory
peptide (GIP) to inhibit gastric gland secretion.
- The hormones secretin and cholecystokinin (CCK)
are produced by the duodenal wall and stimulate
the pancreas to secrete digestive juice and the
gallbladder to release bile. - Acidic chyme stimulates the secretion of
secretin, while fatty chyme with protein triggers
CCK release.
23Hormonal control of digestive gland secretions
24The Large Intestine
- The large intestine consists of the cecum, colon,
rectum and anal canal. - The large intestine does not produce digestive
enzymes but does absorb water, salts, and some
vitamins. - The colon includes the ascending colon, the
transverse colon, the descending colon, and the
sigmoid colon.
25- The appendix is an extension of the cecum.
- Indigestible material is stored in the rectum
until the anus allows defecation. - Anaerobic bacteria in the feces break down
indigestible material and produce some vitamins. - Water tests that show the presence of the
bacterium Escherichia coli indicate water is
contaminated.
26Junction of the small intestine and the large
intestine
27- Polyps are small growths arising from the
epithelial lining that may be benign or
cancerous. - Diarrhea and constipation are two common
complaints of the large intestine. - Causes of diarrhea include infection of the lower
tract and nervous stimulation, both moving feces
more rapidly than normal, but also causing
dehydration if prolonged.
28- Water and fiber in the diet can prevent
constipation where the feces become too dry and
hard. - Hemorrhoids are enlarged and inflamed blood
vessels at the anus this condition is associated
with chronic constipation. - Regular elimination reduces the time the colon
wall is exposed to cancer-promoting agents in the
feces and may help prevent cancer.
29Defecation reflex
30Three Accessory Organs
- The pancreas, liver, and gallbladder are
accessory organs of digestion their secretions
assist digestion. - Accessory organs are not part of the digestive
tube but produce enzymes and other substances
that assist digestion. - These three accessory organs send secretions to
the duodenum via ducts.
31The Pancreas
- The pancreas produces pancreatic juice, which
contains digestive enzymes for carbohydrate
(pancreatic amylase), protein (trypsin), and fat
(lipase), along with sodium bicarbonate (NaHCO3)
to neutralize acid in chyme. - The pancreas is also an endocrine gland that
secretes insulin and glucagon, hormones that keep
blood glucose within normal limits.
32The Liver
- The liver produces bile, which is stored in the
gallbladder. - Bile emulsifies fats it is a yellowish-green
substance containing bilirubin from hemoglobin
breakdown and bile salts derived from
cholesterol. - The liver acts as gatekeeper to the blood and
receives blood from the small intestine by way of
the hepatic portal vein.
33Hepatic lobules
34- The functions of the liver are many
- detoxifies blood,
- stores iron and vitamins,
- makes plasma proteins,
- stores glucose as glycogen,
- produces urea from amino acids,
- removes bilirubin after dismantling blood cells,
and - regulates blood cholesterol level when producing
bile salts.
35Hepatic portal system
36Liver Disorders
- When a person has a liver disorder, jaundice may
occur. - Jaundice is a yellowish tint to eyes and skin,
indicating abnormal levels of blood bilirubin. - Hepatitis is inflammation of the liver different
strains of virus cause hepatitis A, B, etc. - Cirrhosis is scar tissue that can form when the
liver is diseased or killed by exposure to
alcohol.
37The Gallbladder
- The gallbladder is a pear-shaped muscular organ
that stores bile until it is sent to the
duodenum. - Water is reabsorbed in the gallbladder making
the bile thick and mucus-like. - Bile enters the duodenum via the common bile
duct. - Gallstones are crystals of cholesterol.
38Digestive Enzymes
- Digestive enzymes are present in digestive juices
and introduce water at specific bonds to break
down food into sugars, amino acids, fatty acids,
and glycerol. - Starches are broken down into simpler sugars by
salivary amylase and pancreatic amylase. - Pepsin in the stomach, and trypsin from the
pancreas break proteins into peptides. -
39- Peptidases and maltase, produced by the small
intestine, complete the digestion of proteins and
starches, respectively. - Glucose and amino acids are absorbed into the
blood capillaries of the villi. - Fatty acids and glycerol rejoin in the villi to
produce lipoprotein droplets which enter the
lacteals. - Digestive enzymes speed specific reactions and
function best at a warm body temperature and
optimum pH.
40Conditions for Digestion
- For digestion to occur the correct enzyme,
optimum pH, optimum temperature, and the correct
substrate must be present. - Exact conditions can be determined during
laboratory experiments. - Most digestive enzymes, aside from pepsin,
require a basic pH.
41Digestion experiment
42Nutrition
- The U.S. Department of Agriculture recommends a
diet high in carbohydrates (whole grains), at
least five servings of fruits and vegetables, and
limited but adequate protein as illustrated in a
food pyramid. - Fats and sweets should be used sparingly.
43Food guide pyramid A guide to daily food choice
44Carbohydrates
- Complex carbohydrates from foods like breads and
pasta can be converted to glucose and used
rapidly. - Body cells can utilize fatty acids as an energy
source, but brain cells require glucose, thus
carbohydrates are an essential part of the diet. - Complex, rather than simple, carbohydrates should
make up the bulk of the diet.
45- Simple carbohydrates like table sugar (sucrose)
contribute to energy needs and weight gain
without supplying other nutrients. - Insoluble fiber helps regularity and may help
prevent cancer by limiting the time substances
are in contact with the intestinal wall. - Soluble fiber combines with bile acids and
cholesterol in the intestine and prevents them
from being absorbed.
46Complex carbohydrates
47Proteins
- Meat, milk or eggs are complete proteins they
provide all 20 essential amino acids. - Because individual vegetables do not provide all
essential amino acids, vegetarians must be
careful to consume a combination of legumes,
grains, vegetables, seeds and nuts to secure
complementary proteins. - The amino acid pool relies on continual uptake
amino acids are not stored.
48Ancient versus modern diet of native Hawaiians
49Lipids
- Fat and cholesterol are lipids.
- Lipids, found in fats and oils, should be used
sparingly. - Current guidelines suggest that fat should
account for 30 or less of daily calories. - High-density lipoproteins (HDL) carry cholesterol
to the liver and is considered to be good.
50- Low density lipoprotein (LDL) takes cholesterol
to the cells and may contribute to the
development of plaque on blood vessels walls it
is considered to be bad. - Saturated fatty acids lack double bonds and raise
LDL cholesterol levels. - Linoleic acid and linolenic acid are two
essential fatty acids the body cannot make
polyunsaturated fats supply these.
51Fake Fat
- Olestra looks, tastes, and acts like real fat but
the digestive system cannot digest it therefore,
it is called fake fat. - However, fat-soluble vitamins are taken up by
olestra and pass through the digestive system
unabsorbed. - Those who consume olestra have reduced
carotenoids in their blood.
52Vitamins
- Vitamins are organic compounds that the body
cannot produce but needs for metabolic purposes
some are portions of coenzymes. - Vitamins A, E, and C are antioxidants that
protect cell contents from damage due to free
radicals. - Free radicals donate an electron to DNA,
proteins, enzymes, membranes, etc. and can damage
cell structures or cause cancer.
53- Vitamin D
- A precursor molecule in skin is converted to
vitamin D after exposure to ultraviolet (UV)
light. - Vitamin D is modified first in the kidneys and
then the liver until it becomes calcitriol, which
is needed for calcium absorption in intestines. - In the U.S., milk is often fortified by vitamin
D. - Vitamin D is a fat-soluble vitamin.
54Illnesses due to vitamin deficiency
55Minerals
- The body contains more than 5 grams of each major
minerals and less than 5 grams of each trace
minerals. - Calcium and phosphorus are in bones and teeth.
- Potassium and sodium are involved in nerve
conduction. - Trace minerals are critical in various enzymes
and hormones.
56Minerals in the body
57- Calcium
- Calcium is needed to have strong bones.
- Older women in particular are at risk for
osteoporosis, a degenerative bone disease due to
insufficient intake of calcium because bone cells
are constantly building and eroding bone tissue. - Calcium supplement with vitamin D (and also
estrogen for women) can help prevent this bone
loss.
58- Sodium
- Most Americans have too much salt in their diet.
- High sodium intake is linked to hypertension in
some persons. - About one-third of the sodium we consume occurs
naturally in foods another one-third is added
during commercial processing and the final
one-third is added during cooking or at the table
in the form of table salt.
59Eating Disorders
- Obesity is defined as a body weight of more than
20 above the ideal weight for that person. - Obesity can have hormonal, metabolic, and social
causes. - For many, a commitment to a sensible diet and
exercise program can prevent obesity or a harmful
cycle of weight gain-and-loss.
60Recognizing obesity
61- Bulimia nervosa is characterized by a restrictive
diet, binging, and purging. - Psychotherapy and antidepressants may help.
- Anorexia nervosa is characterized by a distorted
body image and feeling fat even when emaciated. - It can be life-threatening and carries the same
risks as starvation.
62Recognizing bulimia nervosa
63Recognizing anorexia nervosa
64Chapter Summary
- The human digestive tract is a tube with
specialized regions and organs between the mouth
and the anus. - Food is ingested, mechanically processed, and
chemically digested to small molecules that are
absorbed indigestible remains are eliminated.
65- The mouth, pharynx, esophagus, stomach, small and
large intestines have distinct functions and
hormones control digestive gland secretions. - The pancreas, liver, and gallbladder are
accessory organs of digestion their secretions
assist digestion. - The products of digestion are small molecules,
such as amino acids and glucose, that can cross
plasma membranes.
66- Digestive enzymes are specific and have an
optimum temperature and pH. - Proper nutrition supplies the body with energy
and nutrients, including essential amino acids
and fatty acids, and all vitamins and minerals. - Anorexia nervosa, bulimia, and obesity are
primary eating disorders in the United States.