Anatomy and physiology of human digestive system

1. DIGESTIVE SYSTEM
Mr. Sayantan Dutta
Assistant Professor
Faculty of Pharmaceutical Sciences
Rama University, Mandhana, Kanpur, Uttar Pradesh.

2. DIGESTION is defined as the process by which food is broken down in to simple
chemical substances that can be absorbed and used as nutrients by the body.
Digestive system plays the major role in the digestion and absorption of food
substances.
Functions:
• Ingestion or consumption of food substances
• Breaking them into small particles
• Transport of small particles to different areas of the digestive tract
• Secretion of necessary enzymes and other substances for digestion
• Digestion of the food particles
• Absorption of the digestive products
• Removal of unwanted substances from the body
INTRODUCTION

3. • A digestive system is a group of organs consisting of the gastrointestinal
(GI) tract and its associated accessory organs that break down food into
smaller components .
• GI tract is a tubular structure extending from the mouth
up to anus (30feet)
• GI tract is formed by two types of organs:
• Primary digestive organs- Actual digestion takes place
• Mouth , pharynx , Esophagus, Stomach, Small intestine,
• large intestine
• Accessory digestive organs- These organs help primary
digestive organs in the process of digestion
• Teeth, Tongue, Salivary glands, Exocrine part of pancreas, liver, Gal
bladder
FUNCTIONAL ANATOMY OF DIGESTIVE SYSTEM

4. WALL OF GASTROINTESTINAL TRACT
Innermost layer which faces the cavity of the GIT
It has three layered structures
Epithelial lining: inner surface of mouth, surface of tongue,
inner surface of pharynx , esophagus have stratified
squamous epithelial cells.
Stomach, small intestine and large intestine has columnar
epithelial cells
Lamina propria is formed by connective tissue
Muscularis mucosa layer consists of thin layer of smooth
muscle fibers
It is absent in mouth and pharynx
Submucosa layer is absent in mouth and pharynx.
It consists of loose collagen, elastic, reticular fibers and
few cells of connective tissue.
BV, LV , Nerve plexus are present in this layer
Lips , cheeks, pharynx-skeletal muscle fibers
Esophagus has both skeletal and smooth
Stomach and intestine smooth muscle fibers
Anal sphincter consists of both smooth and skeletal
muscle fibers

5. • Outermost layer of the wall of GIT is serosa or fibrous in nature.
• It is formed by connective tissue and mesoepithelial cells
• It covers stomach, small intestine, large intestine
• Fibrous layer covers the pharynx and esophagus
• Auerbach’s plexus is present in between the
Circular and longitudinal muscle fibers of
muscular layer

6. NERVE SUPPLY TO GIT TRACT
GIT Tract has two types of nerve supply
1. Intrinsic nerve supply
2. Extrinsic nerve supply
Intrinsic nerve supply – Enteric Nervous system
These intrinsic nerves control the movements and secretions of GI tract.
Enteric nervous system is present within the wall of the GIT from esophagus to
anus.
Nerve fibers from this system are interconnected and form two major networks
Called
1.Auerbach plexus
2.Meissener plexus
These nerve plexus consists of nerve cells or neurons and receptors. The
receptors in the GIT are stretch Receptors and chemoreceptors. Enteric nervous
system is controlled by extrinsic nerves.

7. NERVE SUPPLY TO GIT TRACT
Sympathetic nerve fibers
inhibit the movements of GIT
tract and decrease the
secretions of GI by releasing
the NT noradrenaline. It
causes constriction of
sphincters
Parasympathetic Nerve fibers
accelerate the movements and
increase the secretions of GI by
releasing Acetylcholine
Facial and glossopharyngeal
nerves - mouth and salivary
glands
Vagus nerve- esophagus,
stomach, small intestine , upper
part of large intestine
Pelvic nerve –lower part of
large intestine

8. DIGESTIVE SYSTEM
01.03.2023
Dr.Sagarika Deepthy T
Assistant Professor
Department of Pharmacology
Dr.B.C.Roy college of pharmacy and AHS

9. MOUTH & SALIVARY GLANDS
• Mouth - oral cavity or buccal cavity
• It is formed by cheeks ,lips and palate
• It encloses the teeth, tongue, salivary glands
• It opens anteriorly to the exterior through lips and
posteriorly through pharynx
• Digestive juice – saliva
• Functions of mouth:
• ingestion,
• chewing,
• appreciation of taste , transfer of food in to
esophagus, role of speech, social functions like
smiling and other expressions

10. TEETH

11. TONGUE
`Thread shaped ,thin
long, v shaped cones ,
numerous fill entire
surface of the tongue
Mushroom shaped,
scattered, tip and lateral
margins of tongue , help to
identify different tastes

12. SALIVARY GLANDS
• Parotid glands – largest
• At the side of the face Just below and in front of the ear
• Each gland weighs 20-30g in adults
• Secretions are emptied into the oral cavity by stensen
duct which opens inside the cheek against upper second
molar tooth
• Submaxillary or submandibular glands
• Located medial to mandible
• 8-10g
• Saliva is emptied into the oral cavity by Wharton duct
through the small opening caruncula sublingualis
• Sublingual glands are the smallest salivary glands
situated in the mucosa at the floor of the mouth
• 2 to 3g
• Saliva from these glands open into 5to 15 small ducts
called ducts of rivinus
• They open beneath the tongue
• One large duct is called Bartholin duct
In humans, saliva is secreted by 3 pairs of
major salivary glands and several minor
salivary glands
• Parotid glands
• Submaxillary or sub mandibular glands
• Sublingual glands

13. MINOR SALIVARY GLANDS
• Lingual Mucus Glands – behind circumvallate papillae and at tip &margins of
the tongue
• Lingual serous Glands- located near circumvallate and filiform papillae
• Buccal Glands – Located between the mucus membrane and buccinator muscle
• Labial Glands- Located beneath mucus membrane around the orifice of mouth
• Palatal Glands- located beneath the mucus membrane of the soft palate

14. CLASSIFICATION OF SALIVARY GLANDS
Based on the type of secretion:
Serous glands: Made up of serous cells, thin and watery saliva
Eg: Parotid glands, Lingual serous glands
Mucus glands: mucus cells, thick viscous saliva with high mucin content
Eg. Lingual mucus glands, buccal glands , palatal glands
Mixed glands: serous and mucus cells
Eg.Submandibular,sublingual,labial glands

15. STRUCTURE AND DUCT SYSTEM OF SALIVARY GLANDS
• Salivary glands are formed by small cells
called acini or alveoli
• Each acinus is formed by small group of
cells which surround the central globular
cavity
• Central cavity of each acinus is in
continuous with the lumen of the duct
• Fine duct from each acinus is called
intercalated duct. Many intercalated
ducts form intralobular duct
• Many intralobular ducts form interlobular
duct which unite to form main duct of the
gland
• Racemose type (bunch of grapes)

16. PROPERTIES AND COMPOSITION OF SALIVARY GLANDS
• 1000ml to 1500ml of saliva is secreted per day
• Acidic in nature pH 6.35 to 6.85
• Specific gravity: 1.002- 1.012
• Saliva is hypotonic to plasma

17. FUNCTIONS OF SALIVA
• Preparation of food for swallowing
• Appreciation of taste
• Digestive function
• Cleansing and protective functions
• Role in speech
• Excretory in function
• Regulation of body temperature
• Regulation of water balance

18. DIGESTIVE SYSTEM
15.03.2023
Dr.Sagarika Deepthy T
Assistant Professor
Department of Pharmacology
Dr.B.C.Roy college of pharmacy and AHS

19. PHARYNX
The pharynx (throat) is part of the respiratory system
and digestive system.
It carries air, food and fluid down from the nose and
mouth.
The pharynx is the site of common illnesses, including
sore throat and tonsillitis.
Funnel shaped tube
Skeletal muscles lined with mucous membrane
The pharynx anatomy includes:
• Nasopharynx: The top part of the throat connects to
the nasal cavities (nose) and lets air pass through.
• Oropharynx: The middle part of the throat connects to
the oral cavity (mouth). It allows air, food and fluid to
pass through.
• Laryngopharynx (or hypopharynx): The bottom part of
the throat is near the larynx (or voice box). It regulates
the passage of air to the lungs and food and fluid to the
esophagus.

20. PHARYNX
The pharynx also contains:
• Tonsils: There are three sets of tonsils. They are
located at the back of the throat and base of the
tongue. Tonsils are the body’s first defense against
infection.
• Auditory (eustachian) tubes: These two tubes
connect the ears to the throat. They equalize
pressure and help drain fluid.
• FUNCTIONS:
• Passage for air and food
• Taste
• Warming and humidifying of inhaled air
• Hearing
• Protection
• speech

21. Oesophagus
Long muscular tube (10-25cm long
It forms the passage for the food to pass from
pharynx to stomach
It begins from the inferior end of the
laryngopharynx, lies posterior to trachea and is
anteriorly bounded by the trachea
Function: Swallowing

22. STOMACH
• Hollow muscular bag like structure
• Stomach lies in between esophagus and small
intestine
• It is positioned on the left side of the abdominal
cavity between oesophagus and the duodenum
• Anatomically stomach can be divided into 4
regions:
• Cardiac region: continuous with the oesophagus.
Cardiac sphincter
• Fundus: Dome shaped part is formed by upper
curvature of the stomach
• Body: This is central region of the stomach
• Pyloric region or Antrum: Lower region of
stomach which continues into the duodenum.
Pyloric sphincture

24. STOMACH

25. STOMACH
Functions:
It provides highly acidic environment
It secretes about 2-3 l of gastric acid per day
Pepsinogen is secreted by chief cells of
stomach wall and turns into pepsin under
low pH conditions which is helpful in protein
digestion
Help in absorption of Vitamin B12

26. DIGESTIVE SYSTEM
22.03.2023
Dr.Sagarika Deepthy T
Assistant Professor
Department of Pharmacology
Dr.B.C.Roy college of pharmacy and AHS

27. SECRETION OF PEPSINOGEN
• PEPSINOGEN is synthesized by
the ribosomes present on ER in
chief cells.
• Pepsinogen molecules are
packed in Zymogen granules by
golgi apparatus and secrete them
in to the stomach
• The parietal cells of the gastric
glands secrete HCL and the chief
cells secrete pepsinogen, an
inactive enzyme.
• The HCL activates the enzyme
by removing some amino acids
and converting it to pepsin.
• Pepsin digests dietary protein to
shorter peptide chains as well as
converts pepsinogen to pepsin
(autocatalytic effect)

28. SECRETION OF HCl
• HCl secretion is an active process that occurs in the
canaliculi of parietal cells
• Energy required for this process is obtained from
oxidation of glucose.
• CO2 is derived from several metabolic activities of the
parietal cells
• It combines with water and form carbonic acid in
presence of enzyme carbonic anhydrase
• Carbonic acid id unstable and dissociates to form H+
and HCO3-
• H+ is actively pumped into the canaliculus of the
parietal cell
• Cl- is also pumped actively and combine with H+ ion
and forms HCl
• To compensate the loss the HCO3- Ions move enter
the blood and combine with sodium and forms sodium
bicarbonate

29. Entire process can be summarised by this equation:

30. Phases of gastric secretion

31. Peptic Ulcer
• Peptic ulcers are the Open sores that develop
in the inside lining of the oesophagus ,
stomach and upper portion of small intestine
as a result of erosion from stomach acids
• The mucosa of GIT tract in this area is digested
by pepsin (peptic digestion)
• Components of Gastric defence Mechanism:
• A. Gastric mucus and bicarbonate secretion by
gastric mucosal cells
• B. Presence of tight junctions between
epithelial cells of stomach and duodenum

32. • Components of aggressive Mechanism
• Most often caused by Helicobacter pylori infection
• Helicobacter pylori is a gram –ve bacteria found in gastric and duodenal
mucosa .
• It splits the urea into ammonia and elevate the pH and damage the local
area of the mucosa by high alkalinity
• In this way they strongly help the peptic ulcer development (PUD)
• Excess Acid production from gastrinomas or tumors of parietal cells of
stomach increases acid output
• NSAID Aspirin,Naproxen, Ibuprofen
• Stress
• Genetics
• Smoking and alcohol consumption
Peptic Ulcer

33. Pathophysiology
• The normal stomach maintains the balance between the protective factors (mucus
,bicarbonate secretion ,blood flow) and aggressive factors ( Acid secretion & pepsin)
• Gastric ulcers develop when aggressive factors overcome the protective mechanism