Digestion.ppt

Essentials of Human Anatomy & Physiology
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Seventh Edition
Elaine N. Marieb
Chapter 15
The Digestive System
and Body Metabolism

Functions of the Digestive System
Slide 14.1
 Digestion
Breakdown of ingested food
 Absorption
Passage of nutrients into the blood
 Metabolism
Production of cellular energy (ATP)

Gastrointestinal (GI) Tract
• A continuous, hollow coiled tube that
digests food, breaks it down, and absorbs
the fragments through its lining into the
blood

Organs of the Digestive System
Slide
Figure 14.1

Mouth (Oral Cavity) Anatomy
Slide 14.4
 Lips (labia) – protect
the anterior opening
 Cheeks – form the
lateral walls
 Hard palate – forms
the anterior roof
 Soft palate – forms
the posterior roof
 Uvula – fleshy
projection of the
soft palate
Figure 14.2a

Slide 14.5
 Vestibule – space
between lips externally
and teeth and gums
internally
 Tongue – attached at hyoid
& styloid processes, and
by the lingual frenulum
 Frenulum- mem-brane
that secures the tongue
to the floor of the mouth;
limits movement
Figure 14.2a

Slide 14.6
 Tonsils
Palatine tonsils
Lingual tonsil
Figure 14.2a

Processes of the Mouth
Slide 14.7
 Mastication (chewing) of food
(mechanical digestion)
 Mixing masticated food with saliva
(chemical digestion)
 Initiation of swallowing by the tongue
 Allowing for the sense of taste

Pharynx Function
Slide 14.9
 Serves as a passageway for air and
food
 Food is propelled to the esophagus by
two muscle layers
 Food movement is by alternating
contractions of the muscle layers
(peristalsis)

Esophagus
Slide
 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)

Figure 24.10 The Esophagus
Figure 24.10a-c

The Swallowing Process
Figure 24.11a-h

Stomach Anatomy
Slide
 Located on the left side of the
abdominal cavity (~10 in long)
 When full holds about 1 gallon of food
 Food enters at the cardioesophageal
sphincter
 Food exits at the pyloric sphincter
(valve) btwn stomach & small intestine

Stomach Anatomy
Slide
Figure 14.4a

Structure of the Stomach Mucosa
Slide
Figure 14.4b, c

Stomach Functions
Slide
 Acts as a storage tank for food
 Site of food breakdown
 Chemical breakdown of protein begins
 Delivers chyme (processed food) to the
small intestine
 Produces 2-3L/day of gastric juice (HCl,
enzymes, & mucus)
 Regulated by neural & hormonal factors

Diseases and Disorders
• Heartburn – occurs when the cardio-esophageal
sphincter fails to close tightly and gastric juice
backs up into the esophagus
• Hiatal hernia – superior part of the stomach
protrudes above the diaphragm allowing juices to
go into the esopahgus
• Vomiting – reverse movement of food, brought
about by a signal from the medulla

• It takes 4 hours for the stomach
to empty after a well-balanced
meal and 6 hours for a fatty
meal

Small Intestine
(4-8 hrs)
Slide
 The body’s major digestive organ
 Site of nutrient absorption into the blood
 Muscular tube extending from the
pyloric sphincter to the ileocecal valve
 Suspended from the posterior
abdominal wall by the mesentery

Subdivisions of the Small Intestine
“Dogs Just Itch!
Slide
 Duodenum
Attached to the stomach
Curves around the pancreas (10 in)
 Jejunum
Attaches to the duodenum (8 ft long)
 Ileum
Extends from jejunum to ileocecal valve of
large intestine (12 ft long)

Figure 24.16a
Regions of the Small Intestine

Chemical Digestion in the Small
Intestine
Slide
 Source of enzymes that are mixed with
chyme
Intestinal cells
Pancreas
 Bile enters from the gall bladder

Chemical Digestion in the Small
Intestine
Slide
Figure 14.6

Villi of the Small Intestine
Slide
 Fingerlike
structures formed
by the mucosa
 Give the small
intestine more
surface area
Figure 14.7a

Microvilli of the Small Intestine
Slide
 Small projections of the
plasma membrane
 Found on absorptive cells
Figure 14.7c

Structures Involved in Absorption of
Nutrients
Slide
 Absorptive cells
 Blood capillaries
Figure 14.7b

Digestion in the Small Intestine
Slide
 Break double sugars into simple sugars
Complete some protein digestion
 Help complete digestion of starch
Carry out about half of all protein digestion

Digestion in the Small Intestine
(help from the pancreas)
Slide
 Pancreatic enzymes play the major
digestive function
Responsible for fat digestion (lipase)
Digest nucleic acids (nucleases)
Alkaline content neutralizes acidic chyme
Produce insulin

Absorption in the Small Intestine
Slide
 Water is absorbed along the length of
the small intestine

Propulsion in the Small Intestine
Slide
 Peristalsis is the major means of
moving food
 Segmental movements
Mix chyme with digestive juices
Aid in propelling food

Figure 24.4 Peristalsis
Figure 24.4

Large Intestine (12-24 hrs.)
Slide
 Larger in diameter, but shorter than the
small intestine
 Frames the internal abdomen

Large Intestine
Slide
Figure 14.8

Functions of the Large Intestine
Slide
 Absorption of water
 Eliminates indigestible food from the
body as feces
 Does not participate in digestion of food

Structures of the Large Intestine
Slide
 Ileocecal valve – btwn small & large
intestine
 Cecum – saclike 1st part of the large
intestine
 Appendix
Accumulation of lymphatic tissue that
sometimes becomes inflamed
(appendicitis)
Hangs from the cecum

Structures of the Large Intestine
Slide
 Colon
Ascending – travels up the right side
Transverse – travel across abdomin
Descending – travels down the left side
Sigmoidal colon (aka pelvic colon)
 Rectum – holding area before release of
fecal material
 Anus – external body opening

Food Breakdown and Absorption in
the Large Intestine
Slide
 No digestive enzymes are produced
 Resident bacteria digest remaining
nutrients
Produce some vitamin K and B
Release gases
 Water and vitamins K and B are absorbed
 Remaining materials are eliminated via
feces

Propulsion in the Large Intestine
Slide
 Sluggish peristalsis
 Mass movements
Slow, powerful movements
Occur three to four times per day
 Presence of feces in the rectum causes
a defecation reflex
Internal anal sphincter is relaxed
Defecation occurs with relaxation of the
voluntary (external) anal sphincter

Digestive Secretion and Absorption of Water

• Diarrhea – results when water is not
sufficiently absorbed by large intestine (can
be due to bacteria)
• Constipation – results when too much water
is absorbed by the large intestine

Accessory Digestive Organs
Slide
 Salivary glands
 Teeth
 Pancreas
 Liver
 Gall bladder

Salivary Glands
Slide
 Saliva-producing glands
Parotid glands – located anterior to ears
(mumps is inflammation of the parotis
glands)
Submandibular glands
Sublingual glands

Saliva
Slide
 Aids in chemical digestion
 Mixture of mucus and serous fluids
 Contains salivary amylase to begin
starch digestion
 Dissolves chemicals so they can be
tasted

Teeth
Slide
 The role is to masticate (chew) food
 Aids in mechanical digestion
 Humans have two sets of teeth
Deciduous (baby or milk) teeth
20 teeth are fully formed by age two

Teeth
Slide
 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
Teech are named according to their main
function

Classification of Teeth
Slide
 Incisors
 Canines
 Premolars
 Molars

Classification of Teeth
Slide
Figure 14.9

Regions of a Tooth
Slide
 Crown – exposed part
(hardest substance in
the body)
 Outer enamel
 Dentin
 Pulp cavity
 Neck
 Region in contact with
the gum
 Connects crown to
root
Figure 14.10

Regions of a Tooth
Slide
 Root
Periodontal
membrane
attached to the
bone
Root canal carrying
blood vessels and
nerves
Figure 14.10

Pancreas
Slide
 Produces a wide spectrum of digestive
enzymes that break down all categories of food
 Enzymes are secreted into the duodenum
 Alkaline fluid introduced with enzymes
neutralizes acidic chyme
 Endocrine products of pancreas
Insulin

Figure 24.18a-c
Figure 24.18 The Pancreas

Liver
Slide
 Largest gland in the body
 Located on the right side of the body
under the diaphragm
 Consists of four lobes suspended from
the diaphragm and abdominal wall by
the falciform ligament
 Connected to the gall bladder via the
common hepatic duct

Figure 24.19a
The Anatomy of the Liver

Bile
Slide
 Produced by cells in the liver
 Composition
Bile salts
Bile pigment (mostly bilirubin from the
breakdown of hemoglobin)
Cholesterol
Phospholipids
Electrolytes

Role of the Liver in Metabolism
Slide
 Several roles in digestion
 Detoxifies drugs and alcohol
 Degrades hormones
 Produce cholesterol, blood proteins
(clotting proteins)
 Plays a central role in metabolism

Metabolism
• Metabolism – chemical reactions that are
necessary to maintain life
– Catabolism – substances are broken down,
energy released and captured to make ATP
– Anabolism – small molecules come together to
form larger molecules

How to maintain blood glucose
(sugar) levels…
• Blood circulates through the liver and
glucose is removed. If the body has an
abundance, glucose is made into gycogen.
This is called glycogenesis.
• If the body is low on sugar, the liver will
break down the glycogen into sugar. This is
called glycogenolysis.

Carbohydrate metabolism
• Cellular respiration – glucose is broken
down, releasing chemical energy to form
ATP
• Glucose + O2 = CO2 + H20 + ATP
• If too much sugar is in the blood, it si
converted to FAT!

Fat metabolism
• Most of it occurs in the liver
• Fat is broken down into acetic acid. Then it
is oxidized and CO2, H2O, and ATP are
formed.
• This occurs when there are low amounts of
sugar in the blood.

Protein metabolism
• Amino acids (make up proteins) are used to
make ATP only when proteins are over
abundant or carbs. and fats are not
available.
• Amino acids are oxidized and ammonia
(NH3) is given off (secreted). The rest if the
amino acids enter the citric acid cycle.

Gall Bladder
Slide
 Sac found in hollow part of the liver
 Stores bile from the liver
 Bile is introduced into the duodenum in
the presence of fatty food
 Gallstones can cause blockages

Figure 24.21a, b
The Gallbladder

• Gallstones occur when bile is stored for too
long and fat crystallizes
• Jaundice – bile enters the blood stream and
tissues become yellow

Processes of the Digestive System
Slide
 1. Ingestion – getting food into the
mouth
 2. Food breakdown –(Propulsion) –
moving foods from one region of the
digestive system to another

Slide
 Mechanical digestion
Mixing of food in the mouth by the tongue
Churning of food in the stomach
Segmentation in the small intestine

Slide
 Chemical Digestion
Enzymes break down food molecules into
their building blocks
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

Slide
3. Food movement
Peristalsis – alternating
waves of contraction
Segmentation – moving
materials back and forth
to aid in mixing
Figure 14.12

Slide
 4. Absorption
End products of digestion are absorbed in
the blood or lymph
Food must enter mucosal cells and then
into blood or lymph capillaries
 5. Defecation
Elimination of indigestible substances as
feces

Slide
Figure 14.11

Nutrition - Take a Class!
Slide
 Nutrient – substance used by the body for
growth, maintenance, and repair
 Categories of nutrients
 Carbohydrates: simple sugars, starches,
fiber (fruit, grain, veggies, some milk &
meat)
 Lipids: triglycerides, phospholipids, fatty
acids
 Proteins: amino acids

Nutrition cont.
• Vitamins: need a balanced diet to obtain
essential vitamins
• Most fxn as a coenzyme (act w/out an enzyme to
complete a rxn)
• Mineral – body requires 7 minerals (Ca, P, K, S,
Na, Cl, Mg)
• Water

What nutrients do for the body
• Carbohydrates – broken down to form ATP
• Lipids – build cell membranes, make
myelin sheath and insulates the body
• Proteins – major structure for building cells

Body Energy Balance
Slide
 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

Metabolic rate
• Basal metabolic rate – the amount of heat
produced by the body per unit of time while at
rest. This represents the energy supply a person
needs to perform essential life activities.
• Ex. 154lb adult has a BMR of 60-72 kcal/hr
• Total metabolic rate – total amount of kilocalories
the body must consume to fuel all ongoing
activities

Factors that influence BMR
• Surface area, gender, age, and thyroid
• Younger people have a high BMR
• Smaller people have a lower BMR
• Hyperthyroidism – excessive metabolic rate
= thin
• Hypothyroidism – slower metabolic rate =
obese

• Frostbite – when the body is exposed to low
temperatures. Capillaries constrict to keep
blood deeper for the internal organs.
• Shivering – occurs when internal body
becomes too cold; this produces heat
• Hypothermia – extremely low body temp.
This results from prolonged exposure to the
cold; vital signs decrease

• If the body is hot, capillaries become flushed with
warm blood, releasing heat. Sweating will occur.
Heat stroke or heat exhaustion can occur.
• Cleft palate – palate does not form properly;
deformities of mouth, nose, and lips
• Cystic fibrosis – excessive mucus impairs activity
of pancreas. Fat and fat-soluble vit. are not
digested

• PKU – inability to use amino acids in food;
can cause brain damage and mental
retardation
• Gastroenteritis – inflammation of the
gastrointestinal tract; can be caused by
contaminated food

• Appendicitis – inflammation of the
appendix
• Ulcer – lesion or erosion of mucus
membrane, exposed to secretions of the
stomach

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