Gastrointestinal physciology

1. THE DIGESTIVE
SYSTEM

2. The digestive system consists of:
1- Gastrointestinal tract (GIT)
include:
 -Mouth - pharynx
 - Esophagus - stomach
 -Small intestine - large intestine
 - Rectum - anal canal

6.  2- digestive glands: their secretion
containing digestive enzymes reach
GIT includes:
 a- Salivary glands
 b- Liver.
 c- Pancreas.
 d- Glands of G.I.T.(gastric and
intestine)

7. Functions of the GIT
 (1) Digestion of food.
 (2) Secretion of digestive juices.
 (3) Absorption of the products of
digestion.
 (4) Excretion of the undigested and
nonabsorbed substances in feces.
 (5)motility.

9. Structure of the GIT wall
(1)Mucosa (=mucous membrane)
(2) Submucosa.
(3) Musculosa (muscle coat).
(4) Serosa.

12. The enteric nervous
system (E.N.S):
The enteric nervous system is
made up of two plexuses
which are interconnected by
neurons:

13. 1-The myenteric plexus:
 This is in the musculosa and
concerning with controlling the
motor activity.
2-The submucosal plexus:
This is found in the submucosal
layer and concerning with
controlling the secretory function

15. Innervation (nerve supply)
of the GIT
(1) Parasympathetic nerve.
(2) Sympathetic nerve.

16. a) Sympathetic supply to the
abdomen (greater splanchnic
nerve):
Origin: preganglionic fibers
arise from the L.H.Cs of the
lower 6 thoracic segments.

17. Functions:
 1- V.C of the majority of the arterioles in the
stomach, small intestine, proximal part of the
large intestine, kidney, liver and pancreas.
 2- Relaxation of the walls of the stomach,
small intestine and proximal part of the large
intestine and contraction their corresponding
sphincters

18.  3- Contraction of the smooth muscle in the
capsule of spleen→ squeeze the stored blood
into circulation.
 4- Stimulation of glycogenenolsis in the
liver→ increased blood glucose level.
 5- Stimulation of adrenal medulla to secrete
its hormones (catecholamine).
 6- Inhibits insulin hormone secretion.

19.  B- Parasympathetic supply to the
abdomen (vagus nerve):
 1- The gastrointestinal tract (GIT): Vagus
stimulation causes contraction of the walls of
the esophagus, stomach, small intestine and
proximal part of the large intestine with
relaxation of their corresponding sphincters.
 2- The gallbladder: vagus stimulation helps
gallbladder evacuation by causing contraction
of its wall and relaxation of the sphincter of
Oddi.

20. 3-Glands: secretory to the glands of:
 a) Stomach → gastric juice secretion.
 b) Pancreas → pancreatic juice secretion
and insulin secretion.
 c) Liver → bile secretion.
 d) Duodenum → mucus secretion from
Brunner's glands.
4- V.D of the hepatic blood vessels.

21. Regulation of gastrointestinal
functions:
 1- Nervous regulation:
 This occurs through the following
reflexes:
 A- Local enteric reflexes.
 B- Ganglionic reflexes.
 C- Central nervous reflexes.

22. 2-Hormonal regulation:
The gastrointestinal hormones
are divided into main families:
Gastrin family.
Secretin family.

23. Mastication

24. Mastication is the process
of the breakdown of large food
particles into small pieces and
stimulate the secretion of saliva
to make a suitable food bolus
ready for swallowing.

25. Functions of mastication:
 1-Breakdown of food into small particles.
 2- It helps swallowing.
 3- It helps digestion.
 4- It reduces the mechanical damage to
the GIT mucosa.
 5- It leads to stimulation of the taste and
smell receptors.

26. Salivary secretion

27. The mouth has 3 pairs of
salivary glands:
Submaxillary.
Parotid.
Sublingual.

28. Innervation to the salivary
glands:
Sympathetic
Parasympathetic.

30.  Effect of sympathetic onSalivary
glands:
 a) Trophic secretion (small in volume,
viscous and rich in organic material).
 b) Motor to the myoepithelial cells
surrounding the acini → squeeze saliva.
 c) Vasoconstriction of the salivary blood
vessels.

31. Effect of parasympathetic on
Salivary glands:
 1-V.D and secretion at their effector
organs.
 2-True secretion (watery saliva, large
in volume and little in enzymes).

32. Mechanism of salivary secretion
 It is nervous mechanism occurs through:
 1- Conditioned reflex:
 Acquired reflex needs training and
experience.
 Depends on the cerebral cortex.
 Absent during sleep and anesthesia.
 It occurs before the entry of food to mouth.

33. 2-Unconditioned reflex:
 Inherent reflex not needs training.
 Not depends on the cerebral
cortex.
 It occurs when the food enters the
mouth

34. Formation and composition of
saliva
The amount of saliva is about 1.5
L per day.
Its pH is about 7.
It is hypotonic relative to plasma.

35. It contains about 99.5%
water and 0.5 % solids which
include:
Inorganic ions.
Organic substances.

36. 1-Stages of salivary secretion:
 Primary stage(primary secretion in
the acini):
 It is secreted from the acini by filtration
and active process.
 Isotonic with plasma.
 Of high concentration of Na+ and Cl- and
lower concentration of K+.

37. 2- Stage of modification:
In the salivary ducts Na+ and
Cl- are reabsorbed.
K+ is secreted.

39. Function of saliva
 1- Digestion function.
 2- Help in speech (it keeps the mouth
moist).
 3- Help in swallowing (its mucin
content lubricates food).
 4- Help in taste sensation(it serves as
solvent for molecules → stimulate the
taste receptors).

40.  5- Cleaning action(it keeps the mouth and
teeth clean).
 6- Buffering action(HCO3, mucin and
phosphate).
 7- The saliva acts as a dilution medium for
ittitant substances.
 8- It helps heat loss through evaporation.
 9- Regulation of water balance.
 10-Excretory function (urea, mercury and
iodide).

41. Swallowing

42.  It is the passage of food from
mouth to stomach.
The process is divided into 3
stages:
 Buccal stage.
 Pharyngeal stage.
 Esophageal stage.

44. 1-Buccal stage
It is a voluntary stage.
The food passes from mouth
to pharynx.

45. Mechanism:
 Lips and jaws are closed.
 The food bolus collected on the upper
surface of the tongue.
 The bolus of food is moved to the
pharynx by upward and backward
movement of the tongue.

46. 2- Pharyngeal phase:
This is involuntary phase.
The food passes from pharynx
to esophagus.

47. Mechanism:
 Food stimulates the swallowing
receptors around the opening of
the pharynx → afferent nerve (5th
and 9th ) → swallowing center in
medulla oblongata→ efferent nerve
(5th, 9th, 10th and 12th) and this
leading to the following:

49.  A- Protective reflexes:
 1- Elevation of soft palate.
 2- Elevation of larynx against the
epiglottis.
 3- Approximation of the vocal cords.
 4- Temporary apnea.
 5- Approximation of the palate-pharyngeal
folds.
 6- Continued contraction of the mylohyoid
muscles.

50. Pharyngeal peristalsis:
 Contraction of the superior
pharyngeal muscle and relaxation
of the upper part esophagus →
passage of food bolus to the
esophagus.

53. 3-Esophageal stage:
- It is involuntary stage.
- The food passes from the
esophagus to the stomach.
-There are 2 types of esophageal
peristalsis:

54. a-Primary peristalsis:
- This is continuation of
peristaltic wave that begins in the
pharynx.
- Produced by impulses
discharged in efferent vagal
nerve.

55. b-Secondary peristalsis:
 - This occurs if the primary
peristalsis fails to propel all food in
esophagus.
 - It originates in the esophagus due
to distension of its wall by food.
 - Produced by vago-vagal reflex.