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Anatomy of Digestive System:- PDF/PPT

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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)

mouthpharynxesophagusstomachsmall intestinelarge
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

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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

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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
Subject:
Digestive System
Semester:
1st
Cource:
B.Pharma

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