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The Digestive System

Anatomy of the
Digestive System

We need food for cellular utilization:

organs of digestive system form essentially a long
continuous tube open at both ends

!nutrients as building blocks for synthesis
!sugars, etc to break down for energy

! alimentary canal (gastrointestinal tract)

most food that we eat cannot be directly used by the
body

mouth! pharynx! esophagus! stomach!
small intestine! large intestine

!too large and complex to be absorbed

attached to this tube are assorted accessory organs
and structures that aid in the digestive processes

!chemical composition must be modified to
be useable by cells
digestive system functions to altered the chemical and
physical composition of food so that it can be
absorbed and used by the body; ie
Functions of Digestive System:

salivary glands
teeth
liver
gall bladder
pancreas
mesenteries
The GI tract (digestive system) is located mainly in
abdominopelvic cavity

1
...
absorption

surrounded by serous membrane
= visceral peritoneum

3
...
4

1

serosa:

tongue
lines ventral border of mouth cavity
is skeletal muscle covered with mucous membrane

visceral peritoneum,
mainly fibrous and areolar CT
with some pockets of adipose CT

muscularis

contains taste buds

several layers of smooth muscle

frenulum is thin fold of mucous membrane on
ventral surface of tongue that anchors the
tongue to the floor of the mouth

submucosa

blood vessels, lymphatic vessels, nerves,
connective tissue

inner

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is suspended from rear of soft palate
blocks nasal passages when swallowing

The wall of the alimentary canal consists of 4 layers:
outer

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Mouth (Buccal Cavity, Oral Cavity)
bordered above by hard and soft palate

imbedded in socket

forms partition between mouth and nasal passages

gingivitis = inflammation of gum surrounding teeth; can lead to

uvula
Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Salivary Glands

periodontal disease

kinds of teeth modified for specific functions

3 Pairs of salivary glands:

incisors – 4+4; cut, knip
canines – 2+2; holding onto prey
premolars – 4+4; cutting, crushing
molars – 6+6; chewing, grinding, crushing

sublingual
submandibular
parotid
largest, below ears
mumps = acute infection of parotid gland

each tooth is composed of several layers:

secrete saliva (enzymes and mucous for
digestion)

enamel
very hard
outer surface
on upper exposed crown only
resists bacterial attack
cannot regenerate if damaged

2
...
Esophagus

below enamel
less hard, similar to bone matrix
decays quickly of enamel is penetrated

collapsible tube ~ 10” long
extends from pharynx to stomach

pulp

!gets food through thorax to abdominal cavity

living portion of tooth
consists of blood vessels, nerves

posterior to trachea and heart

cementum

pierces diaphragm

on root of tooth only
outer surface
holds root into socket in jaws

uses peristalsis to move food to stomach
! can swallow upsidedown
5

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Muscle layers are very well developed in stomach
circular
longitudinal
oblique

4
...
5 L after meal

sphincter muscles close both stomach openings:

Major functions of stomach:

cardioesphageal sphincter
(=lower esophageal sphincter)

1
...
chemical digestion – esp proteins

pyloric sphincter

3
...
4

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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Small Intestine
longest part of alimentary canal:

ileum

! 1” diameter x 10’ long (living) or 20’ long (cadaver)

~5’
mainly in hypogastric region
joins to caecum of large intestine
absorbs and reclaims bile salts and some additional
nutrients

Major functions of small intestine:
1
...
secretes hormones which direct secretion of
digestive juices by stomach, gall bladder,
pancreas

the intestinal mucosa also contains small finger-like
projections = villi

3
...
Large Intestine

jejunum

2
...
4

within this is an arteriole, capillary bed, venule

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valve-like sphincter separates small from large
intestine = ileocecal valve

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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absorb additional water as needed by body
2
...
collects, concentrates and rids body of
undigested wastes

last 7-8”
ends at anus

subdivided into 3 regions:

held shut by two anal sphincters:

cecum

internal anal sphincter of smooth muscle
external anal sphincter of skeletal muscle

blind ended sac that extends from point of
attachment to small intestine

Intestinal Flora

contains appendix ! ~3
...
4

our gut bacteria provide many benefits:
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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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might be able to test for changes in kinds and numbers of
species as an early indication of certain diseases

gut bacteria change and adapt as your foods change

eg
...
fecal transplants: restores bowel flora to a healthy state

gut bacteria affect our mood and behavior:

7
...
100% cure rate for C
...
4

duodenum

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Gall Bladder

lesser omentum

lies on undersurface of liver
3-4” long and 1
...
6 – 1
...
Liver

can hold 30-50 ml of bile

is the largest gland in body

gall bladder stores and concentrates bile

lies immediately under the diaphragm

When needed bile travels down Cystic Duct to
Common bile Duct to the duodenum

consist of 2 lobes separated by falciform
ligament

C
...
4

most digestion is carried out by pancreatic
enzymes

Hepatic Vein

in curve of duodenum and dorsal to greater
curvature of the stomach (retroperitoneal)

Hepatic Bile Duct

6-9 “ long
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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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sphincters

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2
...
Esophagus

digestion = all food changes that occur in the
alimentary canal

wave of reflex contractions = peristalsis

need to convert food into a form that can be absorbed
and used by body cells

4
...
Mouth
food entering mouth is physically broken down
teeth
mixed with saliva
lubricant
enzyme = amylase
! begins carbohydrate digestion
at end of digestion in mouth, food = bolus
Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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physical digestion is completed in stomach
once digestion in stomach is competed have a
white milky liquid = chyme
stomach takes about 2-6 hours to empty after a meal
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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Duodenum

jaundice = bile ducts obstructed
!body cant get rid of bile
!bile is absorbed into blood
!causes yellowing of skin

all physical digestion has been completed
!most chemical digestion occurs here

droplets to speed their digestion

receives digestive juices from pancreas and gall
bladder

95% of bile secreted by gall bladder is
reabsorbed after it is used in digestion

also produces its own set of enzymes

! recycled back to liver

a
...
Pancreatic Juices
pancreas is an endocrine gland (insulin,
glucagon)

most lipids are very insoluble in water
! must be made somewhat soluble before
they can be digested and absorbed
bile is a surfactant

but 98% of its tissues make and secrete
digestive juices through ducts to the
duodenum
c
...
4

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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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phagocytic cells remove toxic compounds
and convert them to nontoxic compounds

7
...
some vitamins and nutrients are removed and stored

8
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secrete bile to aid in digestion (~1pt /day)
Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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synthesis of starches, lipids and proteins for storage

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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Digestive Problems

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Colonic Irrigation
alternative medical practice
potentially harmful
unneccessary
can rupture the intestine

1
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Vomiting

mineral oil
can interfere with absorption of fat soluble vitamins

symptom of many diseases
waves of reverse peristalsis
if severe may empty duodenum as well
rest and drink small amounts of fluids
guard against massive fluid loss

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...
Bulemia

self induced vomiting
may cause damage and infection of esophagus,
pharynx, or salivary glands
erosion of teeth, more dental caries
esophagus may rupture or tear

7
...
Diarrhea

frequent loose watery stool
intestinal contents moving too fast for fluid
absorption to occur
main danger is fluid loss
also upsets acid/base balance

8
...
Constipation

caused by:
lifestyle ! inadequate water input
lack of physical activity
side effect of medication

9
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4

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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eat or drink too much
clothing too tight
cure:
eat small meals
drink liquids 1 hr before or 1 hr after meal
don’t lie down or bend over
lose weight if overweight
don’t smoke
use antacids but sparingly

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Peptic Ulcers

eg
...
Celiac Disease

eg
...
soil eating is common in many traditional societies
! may be instinctive way to get trace minerals like Fe or Zn
pica is also common among people with cognitive or psychiatric
disorders such as autism and schizophrenia

Gall Stones
“calculi” can form in kidney, urinary bladder and
gall bladder
seed becomes surrounded by layers of crystalline
deposits
if large enough can block cystic duct or common
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bile duct and cause jaundice

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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compulsive consumption of ice is often associated with iron
deficiency

eg
...
wheat,
barley, rye, & oats
disease 1st reported in second century by Aretaeus of
Cappadochia
these grains have large amounts of a protein, =gluten,
causes loss of villi & brush border, and increased numbers of
WBC’s
leads to inadequate intestinal absorption
symptoms: diarrhea, weight loss, abdominal distension and
bloating and weakness
due to genetic and environmental factors
patients with such sensitivity must adhere to gluten-free diet
substitute: corn, millet, buckwheat, sorghum & rice

Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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another pregnant woman was eating almost half a kg of
baking soda each day

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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014

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