Head and neck nerves 2

1. The Gastrointestinal System

2. Functions of the GI System
Digestion, absorption, secretion and Motility.
 digestion where large molecules in food in order
to be transported to the blood stream must be
chemically broken down to smaller molecules by
enzymes and mechanical action.
 And Absorption happens when these small
molecules are transported into the blood stream

3.  and secretion of enzymes and other substances
into the lumen of the tract will help digestion
and absorption
 and motility due to the contractile activity of
muscle located in the wall of the tract will mix
and propel the content from one end to the
other end of the tract.

4. The GI consists of :
• GI tract and ,
• accessory glands.

5. four layers make up the wall of the tract:
( 1 ) the mucosa which lines the lumen,
is composed of 3 layers : the mucous membrane, the
lamina propria ‫المخصوصة‬ ‫المخاطية‬ ‫الصفيحة‬, the muscularis
mucosae ‫العضلية‬ ‫المخاطية‬
the GI tract
A tube that propels a substance from one end
to the other

6. ( 1 ) the mucosa which lines the lumen,
is composed of 3 layers : the mucous membrane,
the lamina propria ‫المخصوصة‬ ‫المخاطية‬ ‫الصفيحة‬, the
muscularis mucosae ‫العضلية‬ ‫المخاطية‬
( 2 ) the submucosa an underlying layer of
connective tissue containing numerous nerves and
blood vessels,
( 3 ) the muscularis externa which contains circular
and longitudinal smooth muscles, and
( 4 ) the serosa ‫المصلية‬ composed of connective
tissue and an outermost layer the mesothelium
‫المتوسطة‬

7. The mucosa contains :
- the mucous membrane, an epithelial layer
containing enterocytes .
-some of them are absorptive cells,
-others are exocrine cells because they secrete
materials such as fluids and enzymes into the
lumen,
-among these cells are goblet cells which secrete
protecting mucus
-Other enterocytes are endocrine cells which
secrete hormones into the bloodstream.

8. •The lamina propria is a layer of connective tissue
underlying the mucous membrane,
•that contains small blood vessels, nerves, and
lymphatic vessels that communicate with larger
ones in deeper tissues.
•it also contains lymph nodules and Peyer′s
patches to defend against bacteria.
•The muscularis mucosae is made of longitudinal
and circular muscle fibers

9. The Submucosa is :
a thick, elastic connective tissue that enables the GI to
tolerate a large degree of stretch.
• it contains a network of nerve cells known as the
submucosal plexus
( Meissner′s plexus ) that communicate with another
one existing in the muscularis externa called the
myenteric plexus ‫المعوي‬ ‫العضلي‬ ‫المعقد‬
( Auerbach′s )
together they make up what is called the enteric
nervous system ( intrinsic nervous system )
• The enteric nervous system is located within the wall
of the GI tract, that plays an important role in the
control of digestive function.

10. The Muscularis Externa: contain :
• an inner layer of circular muscle that consists of
single-unit smooth muscle capable of generating
slow-wave potentials and its contractions decrease
the diameter of the lumen of the GI tract.
• The outer layer of longitudinal muscle consists of
multi-unit smooth muscle that depends on neural
input for contraction these contractions shortens
the GI tract.

11. • Coordinated contractions of the circular and
longitudinal muscles :
- propels the lumenal contents through the GI tract and ,
- mixes the contents with secretions that help digest
food particles and increase the absorption efficiency.
The Serosa: the outermost layer of the GI wall consists
of :
• an inner layer of fibrous connective tissue which
provides structural support and
• an outer layer of epithelial tissue called the
mesothelium ‫المتوسطة‬ Which secretes a lubricating
fluid that makes it easier for organs to slide past one
another.

12. • The mesothelium with an underlying connective
tissue is continuous with the mesenteries,
membranes that interconnects most of the
abdominal organs and houses nerves and blood
vessels running to them.
• The mesenteries help to anchor the organs in
place and are continuous with the peritoneum,
a membrane lining the inside of the abdominal
cavity.

13. Functional anatomy of GI Tract organs
- it includes the mouth , esophagus ( which
conducts food to the stomach) and is composed of
skeletal and smooth muscles
 there are two sphincters: an upper esophageal
sphincter (skeletal muscle ) and ,
 a lower esophageal sphincter (smooth muscle )
- that prevents the contents of the stomach which
are acidic from entering the esophagus.
- the stomach wall , differs anatomically and
functionally in 3 regions:
 the fundus ‫القاع‬, the body, the antrum ‫غار‬.

14. -Both the fundus and body contain gastric pits
‫المعدة‬ ‫وهدات‬ which contain cells that secrete the
products found in gastric juice.
-contractile activity of smooth muscle in the
stomach′s wall pulverizes food into smaller particles
-and mixes it with gastric juice forming a mixture
called chyme ‫الكيموس‬

15. • Gastric pits contain a variety of secretory cells,
- the neck cells secrete mucus,
- deeper in the pits are gastric glands, which contain
the following cells:
( 1 ) chief cells ‫الرئيسة‬ ‫الخاليا‬ which
secrete pepsinogen, the
precursor for a proteolytic
enzyme called pepsin,
( 2 ) parietal cells ‫الجدارية‬ ‫الخاليا‬,
which secrete both hydrogen
ions( as HCL ) to acidify the
stomach contents . and
intrinsic factor ‫العامل‬
‫الداخلي‬ ,
which is necessary for the
absorption of vitamin B12 and

16. ( 3 ) G cells which secrete the hormone
gastrin ‫غاسترين‬.
the acidity is necessary for converting
pepsinogen into its active form,pepsin, it
denatures proteins also and kills bacteria
• The stomach′s lining is protected against the
harmful effects of acid and pepsin by
gastric mucosal barrier.
• Neck cells in gastric pits secrete mucus,
whereas surface epithelial cells secrete both
mucus and bicarbonate.

17. The small intestine
-is the primary site of digestion and absorption,
in the duodenum ( 30 cm ).
- chyme is mixed with pancreatic juice,( rich in
bicarbonate and digestive enzymes ) that does not
work at an acidic pH.
-In addition to pancreatic juice , the duodenum also
receives bile secreted by the liver, and contains
bicarbonate and bile salts , which aid in the digestion
of fats.

18. • These processes of digestion and absorption begin in the
duodenum ‫العفج‬ and continue in the remainder of the small
intestine: jejunum and ileum (
‫الصائم‬
‫و‬
‫اللفائفي‬
)
• absorption is typically completed within the first 20% of the
small intestine length.
• This highly absorptive efficiency is attributable to the fact
that the mucosal surface is highly folded ( x 10 ) these folds
are called villi.

19. • The brush border and villi are more prominent in
the proximal portions of the small intestine.
• Brush border enzymes and carrier proteins are
located on the tips of villi ( designed for digestion
and absorption )
• while in other areas crypts of lieberkÜhn ‫خبايا‬
‫لوبركون‬ contain secretory cells ( designed for
secretion )

20. -these cells secrete bicarbonate-rich fluid called
succus entericus ‫المعوية‬ ‫العصارة‬
- which is also secreted in the proximal portion of
the small intestine
- and is absorbed before the chyme reaches the
colon.

21. -Materials that are absorbed from the intestines are
carried by the bloodsream to the liver,
• Blood from intestinal capillaries drains into the
mesenteric veins ‫المساريقية‬ ‫األوردة‬ and is carried to
the liver by the hepatic portal vein,

22. • blood delivered by the hepatic portal vein is
deoxygenated, but
• a supply of oxygenated blood, which is necessary
for the liver′s proper function is delivered to the
liver by the hepatic artery.
-Blood is carried from the liver to the general
circulation by the hepatic vein,
-which drains into the inferior vena cava.

23. -Blood is carried from the liver to the
general circulation by the hepatic vein,
-which drains into the inferior vena cava.

24. The Colon is divided
into:
-the ascending colon,
-transverse ,
-descending,
-sigmoid colon,
leading to the rectum.
-The first three
segments are
specialized for
absorbing water and
ions from the chyme,
• The sigmoid colon serves as a storage depot

25. - The longitudinal muscle layer
of the muscularis externa is
not continuous but instead
compressed into narrow
bands called taeniae coli
‫الكولونية‬ ‫الشرائط‬ which run the
colon ′s length.
- At the junction between the
ileum ‫اللفائفي‬ and colon, the
flow of material is regulated
by a ring of smooth muscle
called the ileocecal
sphincter ‫اللفائفية‬ ‫المصرة‬
‫األعورية‬
-Below this junction is a blind-ended bulb called the
cecum ‫األعور‬ to which is attached the vermiform
appendix ‫الدودية‬ ‫الزائدة‬,

26. -The colon′s primary function is to reduce the
volume of the chyme by absorbing most of the water
remaining in it ,
- thereby transforming it into a semisolid material
called feces.
• Together, the cecum, colon, and rectum constitute
the large intestine.
• Relaxation of both sphincters :
- internal anal sphincter ( smooth muscle)
- and external anal sphincter(skeletal muscle)
which are normally closed,
allows fecal material to be eliminated from the body ,
a process called defecation. ‫التبرز‬

27. The Accessory Glands are
- the salivary glands which
secrete saliva,
- the pancreas which secrete
pancreatic juice and
- the liver which secretes bile.
Secretion of these glands are
carried to the GI tract via ducts
lined by epithelial cells, in the
salivary glands and pancreas
these epithelial cells are
arranged in ball-like clusters
called acini ‫عنيبات‬.

28. - The acinar cells secrete a fluid called the
primary secretion which is modified later by the
secretion of ducts.

29. • Saliva is produced by the parotid glands ‫الغدد‬
‫النكفية‬ , the
sublingual ‫اللسان‬ ‫تحت‬ and submandibular ‫الفك‬ ‫تحت‬ glands.
• Saliva is composed of bicarbonate and mucus, salivary
amylase, and lysozyme.

30. • The Pancreas: is an endocrine ( pancreatic islets) and
an exocrine gland which produce the pancreatic juice
from acini,
• this juice is rich in bicarbonate, pancreatic amylase,
and pancreatic lipases, proteases, nucleases.

31. 31
- The liver is the largest organ in the body,
- The basic functional unit of the liver is the liver lobule,
which is a cylindrical structure
- The human liver contains 50,000 to 100,000 individual
lobules.

32. The Liver has many important functions:
1- Secretion of bile: that contain bicarbonate,
phospholipids, inorganic ions, and bile salts
( derivatives of cholesterol)
2- Metabolic processing of nutrients:
• following a meal , the liver converts some of the
glucose to glycogen and some amino acids to fatty acids,
• it also synthesizes triglycerides and cholesterol
• During periods in which nutrients are not being
absorbed,the liver converts glycogen to glucose and fatty
acids to ketones
• it also produces glucose by gluconeogenesis and
synthesizes urea from ammonia

33. 3- Removal of aged red blood cells from the blood
• the liver contains macrophages that remove old red
blood cells and bacteria from the blood ,
hemoglobin is then broken down by the liver some
components like iron are saved for reuse while others such
as bilirubin are eliminated from the body
4- Elimination of wastes from the body Bilirubin and other
breakdown products of hemoglobin are secreted in the
bile ( bile pigments ) are secreted in the bile and
eliminated from the body in the feces with excess
cholesterol, drugs, or poisons, and trace metals.

34. 5- Synthesis of plasma proteins like albumin,
steroid-binding and thyroid-hormone-binding
proteins clotting proteins and angiotensinogen
6- Secretion and modification of hormones :
the liver participate with the kidney in the
activation of vitamin D, and it secretes
somatomedins also known as insulin-like growth
factors.
• The liver also helps to clear many hormones
by metabolizing them.

35. • Bile is manufactured and secreted by the liver
continually,
• but it is released into the tract only when food
is present .
• between meals the bile is stored in the
gallbladder, during meals the gallbladder is
stimulated to contract , which forces the stored
bile into the common bile duct which carries it
to the duodenum

36. Digestion and absorption of nutrients and water
the digestion or chemical digestion is when
macromolecules are broken down enzymatically
into smaller molecules before absorption.
• Digestion of Carbohydrates to monosaccharides
Salivary amylase can digest polysaccharides for
only a short time , before it is inactivated by
acids in the stomach , pancreatic amylase
continue the digestion of polysaccharides in the
small intestine

37. • Proteins
proteins must be digested to amino acid before
absorption , it requires two type of enzymes :
endopeptidases and exopeptidases.

38. • Digestion of proteins to small peptides and amino
acids
- it begins with the action of pepsin in the stomach
( endopeptidase ) .
- Pepsinogen is secreted by chief cells of the stomach
which is partially activated by HCL secreted by parietal
cells
• Digestion of lipids
dietary fats ( mostly triglycerides ) are digested by
lipases ( lingual- pancreatic ) , efficient digestion of
lipids is made possible by the action of bile , the bile
simply facilitates the action of lipases by breaking
down fat globules into smaller droplets , a process
called emulsification .

39. The action of Pancreatic Lipase
- As fat is being emulsified in the duodenum , it is also
mixed with pancreatic lipase .
- as a result the end products of triglyceride digestion
are2 fatty acids and a monoglyceride .

40. Regulated Absorption of Calcium
The absorption of calcium is regulated based on the
body′s needs. Calcium is actively absorbed in the
duodenum and jejunum via two steps :
( 1 ) Calcium binds to a brush border protein, called a
calcium -binding protein and is then taken into the cell
( 2 ) Calcium is transported out of the cell by a calcium
pump on the basolateral membrane.
• Calcium absorption is increased by the hormone 1,25-
(OH)2D3 which increases the amount of calcium-
binding protein.

41. • Absorption of water
- The absorption of water is passive and driven
by osmotic gradient across the mucosal
epithelium,
- a gradient created by the transport of solutes,
sodium in particular, from the lumen to the
interstitial fluid.
- About 95% of the water that is initially present
in the duodenum is absorbed by the time
chyme reaches the colon.

42. General principles of GI regulation
most of the nutrients ingested are absorbed
completely . Many of the control mechanisms
work in the lumen of the GI tract .
Neural and Endocrine pathways of GI control
- influences of the autonomic nervous system are
generally indirect mediated via communication to
the enteric nervous system.
- The function of GI organs is influenced by stimuli
arising from within the GI tract , such as presence
or absence of food , changes in acidity.

43. • Conditions are monitored by three types of
receptor neurons located within the GI wall.
Mechanoreceptors , chemoreceptors ,
osmoreceptors .
• Afferents from these receptors project to both
the enteric nervous system and the CNS .
• Both will send signals via neurons to the smooth
muscle cells or secretory cells ( exocrine-
endocrine ) once endocrine cells are stimulated
the hormones they secrete circulate in the blood
stream and eventually return to the GI system to
exert their effects.
• We have 3 hormones : Gastrin- cholecystokinin
( CCK ) – secretin.

44. • Short and long reflex pathway
- in short reflex pathway signals may travel from
receptors to the intrinsic nerve plexuses and then
directly to the effectors.
- In long reflex pathway signals travel from receptors to
the CNS and then to the intrinsic nerve plexuses which
relay information to the effectors,

45. - the long reflex pathway involve either the sympathetic
nervous system, the parasympathetic , or both.
- Increased parasympathetic activity usually promotes
an increase in GI activity, which is manifested as an
increase in muscle activity or fluid secretion, sympathetic
activity has the opposite effect
• Regulation of food intake :
Eating a meal because you are hungry and then stopping
because your hunger has disappeared is an example of
short-term regulation,
increase in your daily food consumption over the weeks
since you began an exercise program is an example of
long-term regulation

46. • Leptin :
- Hormone secreted by adipose cells is important in long-
term regulation,
- it acts on appetite-control centers in the hypothalamus
to reduce the sensation of hunger.
- It also promotes a general increase in the body s
metabolic rate, which reduces fat storage.
•food intake is also influenced by a number of
other physiological variables that are important in
short-term regulation.

47. •for ex: The absorption of nutrients from a typical meal,
stimulates pancreatic islet cells to release the hormone
insulin which acts on the hypothalamus to reduce the
sensation of hunger
• CCK released in response to the presence of food in
the duodenum is also another hunger-suppressing
hormone,
• signals from mechanoreceptors and
chemreceptors in response to the presence of
food in the wall of the GI tract can also
suppress hunger.
• These signals are called satiety signals.

48. • Gastrointestinal Secretion and its regulation
- Saliva Secretion
is controlled by parasympathetic activity which
stimulates copious watery saliva,
whereas sympathetic activity stimulates minute
secretion of a protein-rich viscous saliva.
• The secretion of CCK is regulated by the
concentration of protein digestion products
and fat that rise as chyme leaves the stomach.

49. • CCK and secretin are also responsible for
regulating the entry of bile into the
duodenum,
• secretin stimulate bile secretion and
• CCK promotes gallbladder contraction and
relaxation of the sphincter of Oddi.
So bile neutralizes acid and emulsify fats.

50. • Chewing and swallowing
1-as the bolus begins to descend from the pharynx, it
presses downward on the epiglottis, causing it to cover
the glottis and preventing the bolus from entering the
larynx and trachea . Closure of the glottis is aided by
muscles of the neck which raise the larynx. Reflex
mechanisms also inhibit inspiratory muscles which
suppresses breathing motions.

51. 2- the upper esophageal sphincter relaxes, enabling
the entry of the bolus into the esophagus, once
the bolus passes through , the sphincter closes
again
• 3- entry of the bolus into the esophagus stimulates
stretch receptors, triggering peristalsis . The peristaltic
wave propels the bolus toward the stomach which it
reaches in about 9 seconds

52. • 4- upon arrival of the bolus at the lower end of
the esophagus , the lower esophageal sphincter
relaxes momentarily to allow the bolus to enter
the stomach

53. • 5- in the event that the initial or primary peristaltic
wave is unsuccessful in delivering the bolus to the
stomach, it is followed by additional secondary
waves initiated by stimulation of mechanoreceptors
in the esophagus

54. • Defecation
the elimination of feces from the body is
controlled both unconsciously by a
defecation reflex and voluntarily.
the defecation reflex is triggered by distention
of the rectum when the pressure increase in
the rectum the internal anal canal relaxes
while the external sphincter contracts if the
pressure continue to increase the external
anal sphincter relaxes allowing defecation to
proceed

55. Absorption of nutrient
Stomach Duodenum Jejunum Ileum
• Iron • Iron • Fat • Bile salt
• Calcium • Calcium • Folate •Vitamin B-12
• Calcium