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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

2

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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4

6

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

9

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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5 gallons) of food, liquids and
GI secretions enter tract/day
~1000 ml reaches the large intestine
150 ml is expelled as feces

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aspirin)

some digestion occurs here due to bacteria
!esp in caecum

Small Intestine

absorb ~90% of materials
absorbs virtually all foodstuffs
absorbs 80% of electrolytes
absorbs most water

as feces enters rectum, stretch receptors trigger
the awareness of need for defecation
defecation proceeds by coordinated activity of
smooth and skeletal muscles in the
defecation reflex
Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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Large Intestine

Ileum

reclaims some additional bile salts

additional water if body needs it

Small intestine is greatly modified for
absorption

some Vit K and B’s made by bacteria there
Mechanisms of Absorption

1
...
surface area is greatly increased for
more efficient absorption of nutrients:
1” diameter x 10’ long
! if smooth tube

1
...
glucose
amino acids
some minerals
2
...
large molecules are absorbed by pinocytosis

= 0
...
a few large fats and proteins; fats passed to lacteals
with other fats

4
...
4

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Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014
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stores iron, vitamin A, B12 & D

tiny hexagonal cylinders (~2mm x 1mm)

2
...
carries out most of body’s fat synthesis
including cholesterol and phospholipids

sinusoid spaces lined with hepatic cells extend outward
from central vein

4
...
phagocytes remove old/damaged blood cells
and pathogens

! arterial blood brings oxygen to liver cells

6

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