Lecture on anatomy & physiology of GIT for nursing students. Encompasses basic sciences with a dash of clinical applications.

1. Anatomy & Physiology of GIT
Chea Chan Hooi
Surgeon
Department of Surgery
Sibu Hospital

2. Content
• Introduction
• Anatomy
– Parts
• Physiology
– Functions

3. Gastrointestinal tract
• Coiled muscular tube
• 6 - 9 meters long, from mouth to anus
• Each has its own blood supply, lymphatic drainage and
nerves
• The stages involved in breakdown process are:
– Ingestion
– Mechanical digestion (chewing, churning and pulverising)
– Chemical digestion (digestive enzymes)
– Absorption into the blood and lymph, assimilation of useful
components into the body by the liver
– Elimination of non-usable residues via faeces

4. 4 layers of GIT
Protects, secretes substances, absorb
products of digestion.
Folded  provide larger surface area for
digestion and absorption
Loose connective tissue containing blood
vessels, lymphatics, nerves
2 layers of muscle for peristalsis; outer
longitudinal, inner circular
Outermost, protective layer of loose
connective tissue and squamous cells
The 4 layers are found throughout the
GIT, different parts are adapted for different functions

5. Anus

6. • Specialized compartments/parts are:
– Oral Cavity
– Pharynx
– Oesophagus
– Stomach
– Small Intestine
– Large Intestine
– Anus
• Accessory Digestive Organs:
– Salivary Glands
– Pancreas
– Liver & Gall Bladder

7. Mouth & pharynx
• Mechanical breakdown
• Chemical breakdown begins with digestion of starch by salivary
amylase.
• Functions of saliva
– Digestion
– Lubrication of food & oral cavity
– Formation of food bolus
– Swallowing
– Speech
– Taste
– Antiseptic properties
– Control of thirst
– Sensation
– Heat dissipation

8. Oesophagus
• 25 cm long
• 2 sphincters: Superior & Inferior Gastro-
Oesophageal Sphincter.
• Stratified squamous epithelium
• Upper third is surrounded by striated muscles,
lower third by smooth muscles and middle
third by mixed muscles (peristalsis)
• Swallowing
• The normal time for food to pass through is 4-5
seconds

10. Stomach
• Epigastrium & left hypochondrium
• 25cm long
• J shaped
• Can expand up to 4L although empty volume is
50ml
• Interior surface area of the stomach is 800cm2.
• Extra muscle layer in addition to the rest of the GI
tract
– An oblique layer  distend in order to store food
• Collapses on itself when empty  folds or rugae

11. Parts of stomach Rugae

12. Functions of stomach
• Food reservoir
– Ability to expand and hold food
– The contents are released slowly by pyloric sphincter for proper digestion rate in small intestine
• Churning food
– Food that enters the stomach is mixed with and diluted by the
gastric secretions into a thick soup-like (chyme)
– The chyme iscchurned by waves of peristalsis. Each wave lasts about half a minute
and 'flows'
from the top of the stomach to the bottom;
• Mucus secretion
– Prevents the stomach digesting itself (bicarbonate, which helps to neutralise the stomach acids)
– To lubricate food
• Digestion
– Breakdown of protein starts
• Absorption
– Small amount - some water, alcohol, drugs, esp. aspirin and other non-steroidal anti-
inflammatory drugs

13. • Gastric juice secretion
– intrinsic factor (see below) and hydrochloric acid (HCl), pepsinogen
– 2 - 3L of gastric juice a day
– highly acidic (pH 1.2-3.0):
- Stops the proliferation of bacteria in the stomach
- Inactivates salivary amylase, mixed with the food in the mouth
- Curdles milk to prepare it for digestion
- Tenderises proteins (by denaturing them);
- Converts pepsinogen (from stomach) into pepsin, to start digest protein
• Production of intrinsic factor.
– Essential for the absorption of vitamin B12 from ileum in the small intestine
– Vitamin B12 is necessary for the healthy functioning of nerve fibres & formation of
red blood cells
• Immune system
– Acidity and lymph tissues in the wall help prevent bacterial proliferation & invasion

14. Small Intestine
• Coiled tube, over 3 – 6 meters long
• Coils, folds & villi give it a surface area of 500-
600m2
• Final digestion of proteins & carbohydrates
• Absorption process:
– Sugars & amino acids  blood stream
– Glycerols & fatty acids  lymphatic system
• 3 parts:
– Duodenum, jejunum & ileum
– Jejunum & ileum have mesentery

15. Duodenum
fats

16. Duodenum
• C-shaped, 10 inches/25 cm
• 4 parts:
– First part begins at pylorus, covered completely by
peritoneum for first inch
– 2nd – 4th parts are retroperitoneal
• Common bile duct & pancreatic duct enter the
2nd part at ampulla of Vater

17. Jejunum & Ileum
• First two-fifths form jejunum, rest form ileum.
• Main functions
– Emulsifying of fats by bile acids & digestion by
lipase
– Absorb glucose, water, electrolytes, bicarbonate,
chloride

18. Large Intestine
• Begins at ileo-caecal
junction and ends at anus
• Components:
– Caecum
– Appendix
– Ascending Colon
– Hepatic flexure
– Transverse Colon
– Splenic flexure
– Descending Colon
– Sigmoid Colon
– Rectum
– Anal Canal

19. • Ascending & descending colons do not
have mesocolon, i.e. are retro-peritoneal
• Appendix  3 taenia coli fused at its base
• Omentum extends from greater curvature of
stomach to transverse colon, called
“Policeman of abdomen”
• Large Intestine is larger, have haustrations,
taenia coli & appendices epiploicae

20. Functions of large intestine
• 1st half (absorbing half)
– Absorb water, small amount of electrolyte;
<100ml of water in faeces
• 2nd half (storage half)
– Storage of faeces
– Secrete bicarbonate to counter acidity of
bacterial actions on faeces

21. Liver, Gall Bladder & Pancreas

22. Liver & Gall Bladder
• Liver is the largest organ in the body
– Under diaphragm in right hypochonrium.
– Right & left lobes
– Blood from GIT goes thru liver via portal vein before entering systemic
circulation
• i.e function as a sieve to remove bacteria, harmful ions
• Immune cells (Kupffer cells)
• Metabolic functions – carbohydrate, fat, protein metabolisms mainly
– Secrete bile
– Deactivate excess drugs, hormones
• Gall Bladder lies under the liver
– it stores & concentrates bile
– Released when stimulated by cholecystokynin (CCK) from duodenum
• Cystic duct joins with common hepatic duct to form common bile
duct that opens into duodenum via ampulla of Vater

23. Pancreas
• Pancreas is both an exocrine & endocrine gland.
• It lies in the curve of duodenum, under the
stomach
• Forms part of the “Stomach Bed”
• It has a Head, Neck, Body & Tail
• Main pancreatic duct carrying pancreatic juice
joins with common bile duct & opens into
duodenum, maybe an accessory pancreatic duct
• Islets of Langerhans secrete insulin whose
deficiency causes diabetes mellitus.

24. Thank You
Q&A?