Friday, March 4, 2011

Alimentary system




General structures of viscera


Hollow organ



Parenchymatous organ



The reference lines of the thoracic and abdominal regions:

Anterior median line
Midclavicular line
Midaxillary line
Scapular line
Posterior median line


Abdomen can be divided into 9 regions by four lines:

the horizontal lines

passes through the lowest point of the costal margin

passes through the tubercles of the iliac lines.

the vertical lines ---- midclavicular line




The alimentary canal is a muscular tube, consists Alimentary system

The alimentary system consists of the alimentary canal and its associated organs:

Tongue;
Teeth;
Salivary glands;
Pancreas;
Liver and Gallbladder
The alimentary canal is a muscular tube, consists of the mouth, pharynx, esophagus, stomach, small intestine and large intestine.

The small intestine can be subdivided into three parts: the duodenum, the jejunum and the ileum.

The large intestine consists of five parts: the cecum,appendix, colon, rectum and anal canal.









Food is broken down both physically and chemically as it passes through the GIT.

Absorption occurs chiefly through the walls of the small intestine. Undigested food and other matter are excreted as faeces.

The alimentary mucosa is the surface across which most substances enter the body.

The functions of this mucosa include:

1.Barrier function: barrier to the entry of noxious substances, antigens and pathogenic organisms.

2.Immunologic functions: lymphatic tissue serves as the first line of defence.

3.Secretory function: digestive enzymes, hydrochloric acid, mucin and antibodies.

4.Absorptive function: absorption of metabolic substrates.


Alimentary canal:


The oral cavity


The oral cavity consists of the mouth and its contents.

It is divided into the vestibule and the mouth cavity proper.

The vestibule lies between the lips, cheeks and teeth.

The oral cavity proper lies behind the teeth and is bounded
by the hard and soft palate superiorly, the tongue and floor of the mouth inferiorly and the oropharyngeal isthmus posteriorly.






Tongue

Is attached by muscles to the hyoid bone, mandible,styloid process,palate,and pharynx

Dorsal surface

Is divided in to by a v – shaped sulcus terminalis in to 2 parts, an anterior 2/3 & a posterior 1/3, which differ developmentally structurally and in innervation

Lingual papillae

Are small nipple shaped projections on the anterior 2/3rd of the dorsum of the tongue

The papillae and their associated taste buds constitute the specialised mucosa of the oral cavity.

Are devided in to the filiform,vallate, fungiform, & foliate papilla







Muscles of the tongue:

Intrinsic muscles ---- alter the shape of the tongue
Extrinsic muscles --- change the position ( genioglossus )


Salivary glands


Pharynx

The PHARYNX is a fibro muscular tube which extends from the base of the skull to the lower border of the cricoid cartilage (at which point it becomes the esophagus).
Portions of the pharynx lie posterior to the nasal cavity (nasal pharynx), oral cavity (oral pharynx) and larynx (laryngeal pharynx).

Naso pharynx:

Is situated behind the nasal cavity above the soft palate & communicates with the nasal cavities with the nasal choanae
Contains pharyngeal tonsils in its posterior wall

Is connected with the tympanic cavity through the auditory tube, which equalizes air pressure on both sides of the tympanic membrane


1. Nasopharynx: base of the skull → soft palate

① Tubal torus
② Pharyngeal recess
③ Pharyngeal opening of auditory tube



2. Oropharynx: soft palate → epiglottis

3. Laryngopharynx: epiglottis → 6th CV





Esophagus

extends from end of pharynx → stomach
25cm long

1.. Cervical part:
6th cv → jugular notch of sternum

2. Thoracic part:
in the thoracic cavity

3. Abdominal part:
esophageal hiatus → cardiac orifice




Stomach


Ⅰ. The morphology:

2 openings:cardiac, pyloric orifice
2 walls: anteriror, posterior wall

2 curvatures: greater, lesser curvature

4 divisions:

① Cardiac part
② Fundus of stomach
③ Body of stomach

④ Pyloric part
pyloric antrum
pyloric canal


Ⅱ. Position

lies in the epigastric, umbilical and left hypochondriac region




Small intestine


This is the longest component of the digestive tract, whose main function is absorption, and is comprised of the duodenum, jejunum and ileum.
extends from pylorus → ileocecal valve
5~7m long


Ⅰ. Duodenum
20~25m long

① Superior part
② Decending part
③ Horizontal part
④ Ascending part



The Superior Part

This part is 2.5 (Ashwell) to 5 (Moore) cm long and is the most movable part of the duodenum.
It lies anterolateral to the body of L1 vertebra. It begins at the pylorus and passes to the right, posteriorly, and slightly superiorly toward the neck of the gallbladder and the right kidney.

The Descending Part

This part lies to the right of the bodies of L1 to L3 vertebrae.
It extends from the superior duodenal flexure to the inferior duodenal flexure.
The common bile duct and main pancreatic duct enter the posteromedial wall of this part as the hepatopancreatic ampulla

The Horizontal Part

This part is about 10 cm long and runs horizontally at the level of L3 vertebra.

The Ascending Part

This part ascends on the left side of the aorta anterior to the left renal vessels to the level of L2 vertebra.
Here it meets the jejunum at the duodenojejunal flexure.

① Hepatopancreatic ampulla
② Major duodenal papilla
③ Common bile duct
④ Pancreatic duct


Ⅱ. Jejunum and Ileum


How to distinguish the jejunum & ileum in the body?




Large Intestine

Features

Colic bands
Haustra of colon
Epiploic appendices


Cecum

Blind sac, first part of large intestine, with largest diameter and thinnest wall

Lies in right iliac fossa

The ilium enters the cecum obliquely, and partially invaginates into it, forming the ileocecal valve-consists of two folds, probably delays flow of ileal contents into large intestine

Vermiform appendix

Blind worm-like tube, 6-8cm long, about 0.5cm in diameter

Opens into posteromedial aspect of cecum,about 2 cm below ileoceal orifice  

The base at the appendix lies at the point of convergence of three colic bands (used as a guide to find the appendix during operation)


Surface marking of the base is at the so-called McBurney’s point which is at junction of lateral and middle thirds of line joining right anterior superior iliac spine and umbilicus


Tip variable in position

Preileal -28%
Pelvic-26%
Retrocecal -24%
Retroileal-8%
Subcecal-6%


Mesentery of vermiform appendix

Triangular mesentery-extends from terminal part of ileum to appendix
Appendicular a. runs in free margin of the meseoappendix then along wall of appendix



The differences between the large intestine & small intetine:


Ⅰ. Cecum

Ⅱ. Vermiform appendix


Colon

Ascending colon
right colic flexure

Transverse colon
left colic flexure

Descending colon descends almost vertically from left colic flexure to sigmoid colon at left iliac crest.

Sigmoid colon-extends from descending colon to rectum at level of S3.


Rectum

Position: within pelvic cavity, extends from S3 to pelvic diaphragm.

Curves

Sagittal plane

Sacral flexure
convex backward
Perineal flexure
convex forward.

Coronal plane

Upper and lower part-convex to the right.

Middle part-convex to the left.

Lower part of rectum dilated, to from ampulla of rectum

Three transverse folds of rectum



Anal canal


1. Dentate line (pectinate line)

the circular line along which the base of the anal valves and
the lower part of the anal columns

2. White line (Hilton line)

below the lower border of the anal pecten



The Anal Canal

This is about 4 cm long in adults.

The upper half of the anal canal is lined by mucosa, which is plum red due to the internal rectal venous plexus.

The lower half is lined with stratified squamous non-keratinising epithelium (continuous with the skin of the anus).

In this lower half, there are 6 to 7 anal columns. Each column contains a terminal branch of the superior rectal artery and vein,

Enlargement of the venous terminal branches and anastomoses give rise to internal haemorrhoids.

The lower ends of the columns are linked by anal valves, above each of which is an anal sinus.

The anal valves together are known as the pectinate line, which is situated opposite the internal anal sphincter.

The anal canal extends below the pectinate line as the pecten, which is bluish in colour.

The pecten ends inferiorly at the "white line" of Hilton.

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