Description
ASHISH BISHNOI
9871050761
The Digestive System
We need food for cellular utilization:
nutrients as building blocks for synthesis
sugars, etc to break down for energy
most food that we eat cannot be directly used by the body
too large and complex to be absorbed
chemical composition must be modified to be useable by cells
Functions of Digestive System:
1. physical and chemical digestion
2. absorption
3. collect & eliminate nonuseable components
Anatomy of Digestive System
organs of digestive system form essentially:
a long continuous tube open at both ends
alimentary canal (gastrointestinal tract)
mouthpharynxesophagusstomachsmall intestinelarge
intestine
attached to this tube are assorted accessory organs
and structures that aid in the digestive processes
salivary glands
teeth
liver
gall bladder
pancreas
mesenteries
The GI tract (digestive system) is located mainly in abdominopelvic cavity
surrounded by serous membrane = visceral peritoneum
1
this serous membrane is continuous with parietal peritoneum and extends
between digestive organs as mesenteries
hold organs in place, prevent tangling
2
The wall of the alimentary canal consists of 4 layers:
outer serosa:
visceral peritoneum,
mainly fibrous and areolar CT
muscularis
several layers of smooth muscle
submucosa
blood vessels, lymphatic vessels, nerves,
connective tissue
inner mucosa:
mucous membrane lining
these layers are modified within various organs
some have muscle layers well developed
some with mucous lining modified for secretion of digestive juices
some with mucous lining modified for absorption
1. Mouth (Buccal Cavity, Oral Cavity)
bordered above by hard and soft palate
forms partition between mouth and nasal passages
fauces
opening of buccal cavity into throat
uvula
is suspended from rear of soft palate
blocks nasal passages when swallowing
tongue
lines ventral border of mouth cavity
is skeletal muscle covered with mucous membrane
rough elevated projections = papillae
types of papillae: fungiform, foliate, vallate
on some are taste buds
frenulum is thin fold of mucous membrane on ventral surface of tongue
that anchors the tongue to the floor of the mouth
3
short frenulum “tongue tied”
Teeth
two sets
deciduous (=baby teeth)
20
begin at 6 months; shed 6-13 yrs
permanent teeth
32
each tooth has a crown (above gum) and a root (below gum)
neck is the line where crown, gum and root meet
imbedded in socket = alveolus
gingivitis = inflammation of gum surrounding teeth; can lead to
periodontal disease
kinds of teeth modified for specific functions
incisors –cut, knip
canines –holding onto prey
premolars –cutting, crushing
molars –chewing, grinding, crushing
each tooth is composed of several layers:
enamel
very hard
outer surface
on upper exposed crown only
not living tissue, noncellular secretion deposited before
tooth erupts from gum
resists bacterial attack
cannot regenerate if damaged
dentin
below enamel
living connective tissue with cells that line pulp cavity
that send processes into the calcified matrix through
tiny parallel tubes
less hard, similar to bone matrix
decays quickly of enamel is penetrated
pulp
living portion of tooth
4
consists of blood vessels, nerves
cementum
on root of tooth only
outer surface
living connective tissue with cells in lacunae
holds root into socket in jaws
Salivary Glands
3 Pairs of salivary glands:
sublingual
submandibular
parotid
largest, below ears
mumps = acute infection of parotid gland
secrete saliva (enzymes and mucous for digestion)
secrete saliva (enzymes and mucous for digestion)
2. Pharynx (throat)
already discussed
3. Esophagus
collapsible tube ~ 10” long
extends from pharynx to stomach
gets food through thorax to abdominal cavity
pierces diaphragm
posterior to trachea and heart
uses peristalsis to move food to stomach
can swallow upsidedown
4. Stomach
muscular sac just below diaphragm and liver
alimentary canal expands to form stomach
divided into regions:
fundus
body
pyloris
5
Muscle layers are very well developed in stomach
circular
longitudinal
oblique
Help to break up food by churning action
results in milky white liquid = chyme
sphincter muscles close both stomach openings
cardioesphageal sphincter
pyloric sphincter
within the mucous lining of stomach are glandular tubes called gastric pits
within gastric pits are numerous microscopic
gastric glands:
epithelial cells secrete mucous for protection
chief cells secretes various digestive enzymes
parietal cells secretes HCl
5. Small Intestine
longest part of alimentary canal:
1” diameter x 10’ long (living) or 20’ long (cadaver)
small intestine fills most of abdominal cavity
held in place by mesenteries (=serous membranes)
subdivided into 3 functional regions:
duodenum
10” long
uppermost
drains pyloric stomach
receives ducts from gall bladder and pancreas
jejunum
8’
central portion
mostly in umbilical region
6
ileum
12’
mainly in hypogastric region
joins to caecum of large intestine
6. Large Intestine
2.5” diameter x 6’ long
valve like sphincter separates small from large intestine = ileocecal valve
subdivided into 3 regions:
cecum
blind ended sac that extends from point of attachment to small
intestine
contains appendix ~3.5” (9cm) long
significant source of lymphocytes
herbivorous primates such as gorillas and orangutans have
an enormous cecum packed with bacteria that digest plant
fiber
colon
subdivided into:
ascending colon
transverse colon
descending colon
sigmoid colon
rectum
last 7-8”
ends at anus
external anal sphincter of skeletal muscle
7. Serous Membranes
body wall and organs of abdomen are lined with peritoneum
parietal peritoneum
visceral peritoneum
most, but not all, of the visceral organs are completely lined with visceral
peritoneum
7
when an organ is lying against the dorsal body wall
and is covered by serosa on the ventral side only = retroperitoneal
eg. duodenum, most of pancreas, parts of large
intestine
these layers are continuous with thin flaps of serous tissues = mesenteries
mesenteries
allow free movement while holding organs in place and prevent
them from tangling
greater omentum
fold of mesentery extending from stomach and duodenum
loosely covers the small intestine like an apron
contains fat deposits
lesser omentum
smaller fold of mesentery between liver and stomach
Accessory Organs of Digestive Tract
A. Liver
is the largest gland in body
lies immediately under the diaphragm
consist of 2 lobes separated by falciform ligament
B. Gall Bladder
lies on undersurface of liver
gall bladder stores and concentrates bile
C. Pancreas
most digestion is carried out by pancreatic enzymes
in curve of duodenum and dorsal to greater curvature of the stomach
composed of 2 kinds of glandular tissue:
endocrine secretes hormones
islets = 2% of total mass of pancreas
their secretions pass into circulatory system
secrete insulin and glucagon
exocrine digestive function
pancreatic digestive secretions are collected in pancreatic duct
8
and usually a smaller accessory pancreatic duct that both drain into the
duodenum