Download Chemical Digestion

THE DIGESTIVE
SYSTEM
BASICS
 Digestion
Breakdown of ingested food
 Absorption of nutrients into the blood

 Metabolism
Production of cellular energy (ATP)
 Constructive and degradative cellular
activities

A.DIGESTIVE ORGANS
 Two

main groups
Alimentary canal – continuous coiled
hollow, muscular tube (aka gastrointestinal
[GI] tract) open at both ends
Performs all digestive functions
Ingest, digest, absorb, defecate
 Accessory

digestive organs
Assist process of digestion
If it’s where
food goes through,
it’s the GI tract
If it’s attached
to GI tract, it’s an
accessory organ
Figure 14.1
ALIMENTARY (GI) ORGANS
Organ
Function
1. Mouth
Physical: break food into smaller particles;
Chemical: breakdown starches with amylase
2. Pharynx
Passageway from mouth to esophagus;
contractions
3. Esophagus
AKA gullet, long passageway linking pharynx &
stomach; contractions
4. Stomach
Physical: break food into smaller fragments;
Chemical: breakdown of proteins with gastric
juice; contractions
5. Small intestine
Chemical digestion of food, absorption of
nutrients; contractions
6. Large intestine
Absorption of water ; contractions
7. Anus
End of GI tract, expulsion of waste
1. MOUTH (ORAL CAVITY)




Mechanical breakdown
 Food is physically broken down by mastication (chewing)
Chemical digestion
 Food is mixed with saliva which breaking of starch into maltose
by enzyme salivary amylase
Initiation of deglutition (swallowing ) by the tongue
Allowing for the sense of taste
 5 tastes:
 Sweet Sour
Salty Bitter Umami (savory/tasty)
ANATOMY OF MOUTH
 Lips
(labia)
 Cheeks
 Hard palate – forms
the anterior roof
 Soft palate – forms
the posterior roof
 Uvula – fleshy
projection of the
soft palate; no function
 Vestibule – space
between lips and teeth
and gums
Figure 14.2a
 Oral
cavity – behind
the teeth
 Tongue – attached at
hyoid and styloid, and
by lingual frenulum
 Tonsils
 Palatine tonsils
 Lingual tonsil
Part of lymphatic
(immune) system
Figure 14.2a
2. PHARYNX
 Serves as a passageway for air and food
 Food movement via alternating
contractions of the muscle layers
(peristalsis)
PHARYNX ANATOMY
 Nasopharynx
– not part of the digestive
system; up to the nose
 Oropharynx – posterior to oral cavity; back of
throat
 Laryngopharynx – below the oropharynx and
connected to the esophagus
3. ESOPHAGUS
 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)
 Timeline: 5-8 seconds!
4. STOMACH
 Acts
as a storage tank for food
 Can hold 4 L (1 gal) of food!!
 Site of physical food breakdown
 Chemical breakdown of protein begins
 Lined with columnar epithelium with …
Mucus neck cells– mucus
 Chief cells – pepsinogen (digest protein)
 Parietal cells – HCl (hydrochloric acid, pH~1.5)
 Enteroendocrine cells – gastrin
 Gastric cells – gastrin juice

 Delivers
intestine
chyme (processed food) to the small
PEPSI & PEPSIN
DO NOT COPY
Caleb Bradham of North Carolina was a pharmacist.
 His most popular beverage was something he called
"Brad's drink" made of carbonated water, sugar,
vanilla, rare oils, pepsin and kola nuts.
 He later on renamed his beverage Pepsi Cola and it
advertised it as “Exhilarating, invigorating, aids
digestion.”

STOMACH ANATOMY
Located on the left side of the abdominal cavity
 Food enters at the cardioesophageal sphincter – circular
muscle that acts as “gatekeeper”
 Food empties into the small intestine at the pyloric
sphincter


Timeline: 2-6 hours
Contains rugae – internal folds of the mucosa
 Layers of peritoneum attached to the stomach
 Lesser omentum – attaches the liver to the lesser
curvature
 Greater omentum – attaches the greater curvature to
the posterior body wall
 Contains fat to insulate, cushion, and protect
abdominal organs (see Dr. Oz on Oprah)

OPRAH AND OMENTUM
Figure 14.4a
STRUCTURE OF THE STOMACH MUCOSA
Figure 14.4b–c
5. SMALL INTESTINE
 body’s
major digestive organ – averages 7m
(>23 feet) long!
 Site of nutrient absorption into the blood

Timeline: 3-5 hours
 Muscular
tube extending from the pyloric
sphincter to the ileocecal valve
 Suspended from the posterior abdominal wall
by the mesentery

Double-layer of peritoneum
 Divided
up into three
sections:
 Duodenum
Attached to the
stomach
 Curves around the
head of the pancreas


Jejunum


Attaches anteriorly to
the duodenum
Ileum

Extends from
jejunum to large
intestine
 Many
chemicals involved in digestion in small
intestine



Enzymes from intestinal cells
Enzymes from pancreas
Bile from gall bladder
 Absorption
is done
through many villi
 Fingerlike structures
formed by the mucosa
 Give the small
intestine more surface
area
 Microvilli on absorptive
cells of villi add for super
absorption
 Small projections of the
plasma membrane
 Found on absorptive
cells
 Absorption
into
bloodstream carried
out by
 Absorptive cells
 Blood capillaries
 Lacteals (specialized
lymphatic
capillaries)
Figure 14.7b
6. LARGE INTESTINE
 Larger
in diameter, but shorter than the small
intestine – 1.5 m long
 Frames the internal abdomen
 Absorption of water
 Eliminates indigestible food from the body as
feces
 Does NOT participate in digestion of food
 Goblet cells produce mucus to act as a
lubricant
 Divided



•
•
up into
Colon
Ascending – up
Transverse – across
Descending – down
S-shaped sigmoidal
Rectum
Anal canal
Cecum – saclike projection, hangs from first
part
Appendix – twisted section that often traps
bacteria & gets infected (appendicitis)
• Timeline: 4-72 hours!
7. ANUS
Ending of anal canal
 Contains two sphincters which work to control
passage of fecal matter
 Internal involuntary sphincter
 Signals us that it’s time to expel feces
 External voluntary sphincter
 Control opening of sphincter until ready

•ACCESSORY DIGESTIVE ORGANS
1.
2.
3.
4.
5.
Salivary glands
Teeth
Pancreas
Liver
Gall bladder
1. SALIVARY GLANDS
 Saliva-producing
glands
Parotid glands –
located anterior to
ears
 Submandibular
glands - under
mandible
 Sublingual glands
– under tongue

 Produce
saliva
Mixture of mucus and serous fluids
 Helps to form a food bolus (ball of
masticated food)
 Contains salivary amylase to begin starch
digestion
 Dissolves chemicals so they can be tasted

2. TEETH
 role
is to masticate (chew)
food
 Humans have two sets of
teeth


Deciduous (baby or milk) teeth
20 teeth fully formed by age two
 Permanent


teeth
Replace deciduous teeth
beginning ages of 6 to 12
full set is 32 teeth, some people
do not have wisdom teeth
3. PANCREAS
 Produces
a wide spectrum of
digestive enzymes that
break down all categories of
food
 Enzymes secreted into
duodenum
 Alkaline fluid introduced
with enzymes neutralizes
acidic chyme
 Endocrine products of
pancreas:
Insulin
 Glucagon

4. LIVER
 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
Produces
bile – highly bitter green
liquid containing:
 Bile
salts
 Bile pigment (mostly green bilirubin
from the breakdown of hemoglobin)
 Cholesterol
 Phospholipids
 Electrolytes
5. GALL BLADDER
 Sac
found in hollow fossa of liver
 Stores bile from the liver by way of the cystic
duct
 Bile is introduced into the duodenum in the
presence of fatty food
 Gallstones can cause blockages
B. SIX PROCESSES OF DIGESTIVE SYSTEM
1. Ingestion – getting food into the mouth
2. Mechanical Digestion – physically
breaking food down
3. Propulsion – moving foods from one
region of the digestive system to another
4. Chemical Digestion – chemically
breaking down food
5. Absorption – getting nutrients/water into
blood stream
6. Defecation – expelling wastes
Figure 14.11
1. Ingestion
•
Voluntary process of getting food
into mouth
2. Mechanical Digestion
Mixing of food in the mouth by the tongue
 Churning of food in the stomach
 Segmentation in the small intestine


Movement of food back & forth serving to mix it
with digestive juices
3. Propulsion
Food is processed by more than one
digestive organ so must be propelled
from one to another. Done via
peristalsis
•
o
Peristalsis – involuntary action where
alternating waves of contraction &
relaxation of smooth muscles squeeze
food along GI tract
PERISTALSIS
 Food
must first be well mixed
 Rippling peristalsis occurs in lower stomach
 pylorus meters out chyme into the small
intestine (30 ml at a time)
 stomach empties in four to six hours
Figure 14.15
4. Chemical Digestion
 Enzymes break down food molecules into their
building blocks
 Each major food group uses different enzymes
Carbohydrates simple sugars
 Proteins amino acids
 Fats fatty acids and alcohols

5. Absorption
 End products of digestion absorbed in blood or
lymph

Food must enter mucosal cells, then into blood or
lymph capillaries
6. Defecation
 Elimination of indigestible substances as feces
CHEMICALS OF DIGESTION
Chemical
Type
Produced
Function
Amylase
Enzyme
Salivary glands,
pancreas
Breakdown starch into maltose
Bile
Compound Liver
Cholecystokinin
(CCK)
hormone
Small intestine Stimulate pancreas to release
Gastrin
Hormone
stomach
Stimulates production of gastric juice
Glucagon
Enzyme
Pancreas
Converts glycogen to glucose
HCl
Acid
Stomach
Activate pepsinogen
Insulin
Hormone
Pancreas
Directs cells to uptake sugar; converts
excess glucose to glycogen
Lipase
Enzyme
Pancreas
Breakdown lipids/fats
Pepsin
Enzyme
Pepsinogen
Breakdown proteins
Pepsinogen
Enzyme
Stomach
Precursor of pepsin
Rennin
Enzyme
Stomach
Breakdown milk protein
Secretin
Hormone
Small intestine Stimulate pancreas & liver to release
Trypsin
Enzyme
Pancreas
Breakdown fats
secretions; gallbladder to release bile
secretions
Breakdown protein
C. CONTROL OF DIGESTIVE ACTIVITY
 Mostly
controlled by reflexes
 Chemical and mechanical receptors are located
in organ walls that trigger reflexes
 Stimuli include:
 Stretch of the organ
 pH of the contents
 Presence of breakdown products
 Reflexes include:
 Activation or inhibition of glandular
secretions
 Smooth muscle activity
D. ACTIVITIES BY GI ORGANS

Mouth-Esophagus (Deglutition = Swallowing)
 Buccal phase
 Voluntary; occurs in mouth; food formed into bolus
 Bolus forced into pharynx by tongue
 Pharyngeal-esophageal phase
 Involuntary transport of bolus
 All passageways blocked
 Tongue blocks off mouth
 Soft palate (uvula) blocks nasopharynx
 Epiglottis blocks larynx
 Cardioesophageal sphincter opened when bolus
presses against it
DEGLUTITION (SWALLOWING)
Figure 14.14
Stomach
Gastric juice regulated by neural and hormonal
factors
 Presence of food and/or falling pH (due to HCl)
causes release of gastrin
Gastrin causes stomach glands to produce
protein-digesting enzymes pepsin & rennin
HCl activates pepsinogen to become pepsin for
protein digestion
HCl provides hostile environment for
microorganisms (except Helicobacter pylori)
 Only absorption occurring stomach is alcohol and
aspirin

 Small
intestine
 Enzymes from brush border break double
sugars (lactose) into simple sugars (galactose
& glucose)
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

Release of pancreatic juice stimulated by:
Vagus nerve
Local hormones
Secretin: causes liver to produce more bile;
pancreas to release more alkaline juice
Cholecystokinin (CCK): stimulates gall
bladder to release more bile; pancreas to
release more enzymes
Figure 14.16
LARGE INTESTINE
 No
digestive enzymes are produced
 Resident bacteria digest remaining
nutrients (Escherichia coli)
 Produce some vitamin K and B
 Release gases
 Water and vitamins K and B are
absorbed
 Remaining materials are eliminated via
feces
 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
E. NUTRITION
 Nutrient
– substance used by the body
for growth, maintenance, and repair
 Categories of nutrients
 Carbohydrates – most from plants
(except lactose)
 Lipids – fats (meat, nuts, oils)
 Proteins – meats, milk, legumes
 Vitamins – act with enzymes
 Mineral – essentials in body (Ca2+)
 Water
F. METABOLISM
 Chemical
reactions necessary to maintain life
 Catabolism – substances broken down to
simpler substances; energy released
 Anabolism – larger molecules built from
smaller ones; energy used
 Fat metabolism (9 cals/g)
 Handled mostly by liver
Use some fats to make ATP
Release breakdown products of fatty acids
to the blood
 Body cells remove fat and cholesterol to build
membranes and steroid hormones
 Carbohydrate

metabolism (4 cals/g)
Carbohydrates are broken down into simple
sugars or monosaccharides
Monosaccharide – one sugar molecule. Only three
are found in our diet that make it into blood
 Fructose (fruit), galactose (milk), glucose
(ubiquitous)
 Disaccharide – two sugar molecules
 Sucrose (table sugar) = glucose + fructose
 lactose (milk) = galactose + glucose
 maltose (malt) = glucose + glucose
 Polysaccharide – many sugar molecules
 Starch (breads), cellulose (plant walls – fiber)

 Protein
metabolism (4 cals/g)
Proteins conserved by body cells as they are
used for most cellular structures
 Ingested proteins broken down to amino acids
 Cells remove amino acids to build proteins
Synthesized proteins are actively
transported across cell membranes
 Amino acids used to make ATP only when
proteins are overabundant or there is a
shortage of other sources

 Cholesterol
metabolism
 Functions of cholesterol
Serves as a structural basis of steroid hormones
(testosterone & estrogen) & vitamin D
 Is a major building block of plasma membranes

Most cholesterol is produced in liver and is not
from diet
 Cholesterol & fatty acids can’t freely circulate in
bloodstream
 Are transported by lipoproteins (lipid-protein
complexes)

Low-density lipoproteins (LDLs) transport to body cells
 High-density lipoproteins (HDLs) transport from body
cells to liver (“good”, since it gets stored in liver)

G. ROLE OF LIVER IN METABOLISM
 Several
roles in digestion
Detoxifies drugs & alcohol
 Degrades hormones
 Produce cholesterol, blood proteins (albumin
and clotting proteins)

 Plays
a central role in metabolism
Glucose = useable sugar
 Glycogen = stored sugar

 Glycogenesis:
making glycogen
 Glucose molecules converted to
glycogen when in excess
 Glycogen molecules stored in liver
 Glycogenolysis: breaking glycogen
 Glycogen converted into glucose when
not enough, released from liver
 Gluconeogenesis: making new glucose
 Glucose is produced from fats and
proteins in emergencies
Figure 14.21
Glucose ($)
blood
Glycogen (€)
liver
Fats/protein (£)
Insulin
 Converts
glucose
to glycogen
 Helps cells
absorb glucose
Glucagon
 Converts
glycogen back to
glucose
H. HOMEOSTATIC IMBALANCES (DISEASES)
 Hyperglycemia = diabetes mellitus
 High (hyper) sugar in blood
 Literally from Latin “something sweet
is being siphoned from body”
 High levels of glucose stimulate
release of hormone insulin (produced
by pancreas) to assist all cells in
absorbing glucose  level decreases
 As glucose level decreases, insulin no
longer released
 Normal
fasting glucose level is 70-100
mg/dL
 Diabetes glucose level is > 126 mg/dL
Excess sugar is not being absorbed by
cells for one of two reasons:
Type I Diabetes: insulin is not
produced (genetic)
Type II Diabetes: insulin receptors
unresponsive (adult-onset)
Glucose flushed from body in urine
Body still needs glucose, so pulls it
from fats &/or protein
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 Hypoglycemia
 Low

(hypo) sugar in blood
High levels of glucose stimulate excess
insulin to be released from pancreas
Too much glucose absorbed by cells
 fasting glucose level < 70 mg/dL in blood
May lead to diabetes in future
 Peptic

ulcer
Craterlike erosion in mucosa of any GI tract
organs that gets exposed to gastric juice
Esophagus – esophageal ulcer
 Stomach – gastric ulcer
 Duodenum – duodenal ulcer (most common)

Definitive cause still unknown
 May be triggered by:

Excess HCl and pepsin due to stress, diet
 Acid-resistant bacteria Helicobacter pylori (70-90%
people with ulcers have it)
 Overuse of OTC (over-the-counter) pain killers like
aspirin, naproxen, ibuprofen (acetaminophen ok)

 Diarrhea
Watery stools as a result of any condition that
rushes food residue through large intestine
before it has chance to absorb water
Most commonly result of bacteria (food
poisoning), viruses (cold/flu), food intolerances,
or reaction to medications
 Constipation
 Hardened stools as a result of any condition that
prolongs food residue’s time in large intestine,
leading to excess water being absorbed
Most commonly result of lack of fiber (poor
diet), poor bowel habits (holding it too often),
laxative abuse, not enough water

Appendicitis
 Inflammation
of the appendix due to a
blockage
Usually blocked by stool, but a foreign
body or cancer can prevent proper
draining
As result, bacteria in large intestine
multiply in appendix, causing swelling
If appendix ruptures (pops open),
bacteria in peritoneum (abdominal
cavity) cause peritonitis which can be
fatal
 Symptoms
Pain in lower
right abdomen
 Loss of appetite
 Nausea/vomiting
 Abdominal
swelling
 Fever of 99º F to
102º F

Jaundice
 Not
a disease but a condition signaling
complications in liver and/or gallbladder
as a result of bile salts and bilirubin
pigments entering bloodstream
Blockage of hepatic or bile ducts
prevents bile from entering small
intestine. May be from
Gallstones
Hepatitis (inflammation of liver)
Cirrhosis (scarring of liver)
Diverticulosis
 Diet devoid of fiber will
force colon to contract more
forcefully to move stool
 Too much force causes
pouch-like diverticula to
herniate or pop outward.
 Condition is called
diverticulosis, which may
lead to diverticulitis
 Diverticulitis
 Inflammation of diverticula
 May be fatal if
diverticulum ruptures


Hemorrhoids
 When too much force is needed
to expel feces, veins in anus
bulge causing hemorrhoids
 Can be internal (rectum) or
external (anus)
 May have to be surgically
removed if inflammation
causes defecation to be
painful or impossible
internal
external
FIN