-Histology of the small intestine- (from the previous slide show)

The gastrointestinal tract (from the esophagus to the anal canal) is composed: (from the inside

to the outside)

Mucosa: epithelium+ the inside structures.

Submucosa: (loose connective tissue).

Smooth muscle layer: (muscular mucosa).

The muscular layer is composed of, A. Inner layer (muscularis interna) -> circular muscle

B. outer layer (muscularis externa) -> longitudinal muscle.

Then comes the serosa layer.

(.a mucosa, a submucosa, a muscularis interna, a muscularis externa, and a serosa) :يعني

The mucosal membrane of the small intestine (duodenum, jejunum, and ileum) is thrown

into folds called Villi. The cells covering the surface are columnar cells with microvilli. In

addition, this membrane contains depressions called Glands, (glands of the intestine), which

are called crypt of Lieberkühn.

Crypt of Lieberkühn contains many types of cells such as, -Enterocytes. –goblet cells (mucus

secreting). –stem cells. –paneth cells (secretes digestive enzymes, they exist mostly in the

jejunum and less in the ilium. Paneth cells are eosinophils).

Some differences between the parts of the large intestine:

Villi: -in the jejunum, they are tall and cylindrical in shape.

-in the ileum, they are short and cylindrical in shape.

Lymphoid tissue: -exists in the submucosa of the ileum only. (it is called peyer's

patches).

-it does not exist in the duodenum or the jejunum.

Glands: there are glands called Brunner’s glands exist only in the duodenum

(they are mucus-secreting glands).

The villus contains a vein, an artery, and a lymph vessel (called lacteal).

Carbohydrates, proteins, and short chain fatty acids are absorbed to the blood, in the veins,

and then transferred to the liver where they are broken and converted to glucose, amyl acids,

or fatty acids. While, the fat (glycerate, triglyceride) are absorbed in the lymph vessels, it is

absorbed in the lacteal and unites with a protein forming chylomicrons ( نيتبروال مالتحا ), they

move through the lymphatic duct, then the thoracic duct, ending up in the subclavian vein. This

fat then goes to the heart and the muscles, breaks there by the lipase. The fatty acids finally

absorbed by the tissues.

So, the fat moves from the intestine to -> adipose tissue. (Adipose tissue is the store of the

heart and skeletal muscle, where the components of triglycerides are hydrolyzed by the activity

of a lipoprotein (lipase). The tissue absorbs fatty acids then.

-Anatomy of the large intestine-

Large intestine is a part of the gastrointestinal tract, 1.5 meters long, starting from the ileocecal

(the end of the ileum).

Cecum-> ascending colon-> transverse colon-> descending colon-> sigmoid colon-> rectum->

anal canal.

Main differences between large and small intestine, are the large intestine is 1) Wider 2) Saculated.

It also differs with the stomach because it has two layers when the stomach has three.

(Large intestine is saculated because it has two muscular layers; longitudinal and circular, and the

longitudinal one is shorter than the actual length).

The longitudinal layer (the outer one) does not cover the intestine all around; it is gathered

into three bands, called Tinea Coli. Those three bands are (posteromedial, posterolateral, and

anterior).

Those bands meet at the base of the appendix (the site of the attachment of the base to the

cecum).

of base ال نالكه نوكي ىلخرأا حزملا عم اهئقاتال عضومو هاتيهانل coli tinea ال بعتتن appendixال ديجاإ ةبوعص دنع*

appendix. لا داجيإ نانكمي هنمو appendix the

1. The cecum:

The beginning of the colon is called cecum, which is located in the right ileac fossa; it is

surrounded by the peritoneum, having no mesentery. Therefore, we can call the cecum an

intraperitoneal organ.

The cecum is 8 cm long, 8 cm wide.

It lye on the posteromedial surface, and attaches to the appendix. 3 cm above it is attached to

the ileum. Cecum and ileum are separated by the ileocecal orifice, which is surrounded by a

circular layer of muscle, we can consider it a horizontal valve. (this circular muscle refers to

the ileum)

Relations with cecum:

- Superiorly: the ascending colon.

- Anteriorly: anterior abdominal wall/ coils of ileum (small intestine).

- Posteriorly: iliacus muscle/ psoas muscle/ lateral cutaneous nerve of the thigh

- Medially: femoral nerve/ external iliac artery.

The appendix:

Thin, short intestine. Covered with peritoneum, 8 cm long. It has a mesentery that is attached to

the end of small intestine (mesoappendix), inside of it there is an artery suppling the appendix,

called appendicular.

The appendix varies in size and position, it could be :-preilial –postilail –pelvic –subcecal –

paracolic -paracecal.

2. Ascending colon:

15 cm long, starts from the entrance of the ileum, lying on the lateral side of the abdomen,

setting on the posterior abdominal wall.

Relations of the ascending colon:

- Posteriorly: iliacus muscle/ quadratus lumborum muscle/ the right kidney.

- Anteriorly: the peritoneum (it surrounds it from the front and the sides, so it is fixed to

the posterior wall, retroperitoneal)/ the coils of the small intestine.

- Laterally: a depression called paracolic sulcus. (this depression ends at the subphrenic

space under the diaphragm). *if there was pus around the diaphragm it will gather on the

paracolic sulcus.

3. Lateral cutaneous nerve of thigh

3. Transverse colon:

50 cm long, starts from the hepatic flexure, underneath the liver -> ends at the splenic

flexure.

It is fixed to the diaphragm by a fibrous tissue called phrenicolic ligament.

.طقف حيضوتلل صورةلا*

The transverse colon is intraperitoneal and has a mesentery that is attached to the posterior

abdominal wall. (the greater omentum comes in front of it, so the mesentery attaches to it)

(SLIDE 9) if we left the greater omentum and looked behind it, we can see what’s left of the

mesentery and the transverse colon.

The splenic flexure is located in a higher level than the hepatic flexure, which means that the

transverse colon goes to the left upper side.

Relations of the transverse colon:

- Posteriorly: descending part of the duodenum/ head of the pancreas/ body of the pancreas/ left

kidney.

- Anteriorly: right lobe of liver/ gall bladder/ stomach/ spleen.

(The anterior relation with the transverse colon, from right to left: liver-> gall bladder -> stomach-

> spleen).

- Inferiorly: coils of the small intestine.

4. Descending colon:

30 cm long, covered with peritoneum from the front and both sides (retroperitoneal).

The descending colon extends from the splenic flexure to the pelvic brim. (the pelvic brim is a line

extends from the top of the pubic symphysis, passing through pubic crest, iliopectineal line, then the

promontory of the sacrum)

.طقف حيضوتلل ةيافضإ صورةلا*

It has a depression on the left side of the colon called paracolic sulcus.

Relations of the descending colon:

- Posteriorly: right kidney/ quadratus lumborum muscle/ psoas muscle/ iliacus muscle.

- Anteriorly: coils of the small intestine.

5. Sigmoid colon:

S shaped organ, 40 cm long, and starts from the pelvic brim to the true pelvis and inside the pelvis.

It is an intraperitoneal organ (covered with peritoneum from all sides).

The mesentery

fixes it to the posterior abdominal wall.

(SLIDE 11) if we cut the mesentery of the sigmoid colon and kept the site of the attachment with it, we

will see the site of that attachment appears as an (Inverted V shape), located in front of the left

ureter.

Relations of the sigmoid colon:

- Posteriorly: left ureter/ left common iliac artery/ sacroiliac joint.

- Superiorly: coils of the small intestine.

*(at females, it is lying above the uterus and the urinary bladder.

At males, it is lying above the urinary bladder.)

40cm

*Appendices epiploicae are sacs of fat, fixed to the large intestine (we can distinguish large

intestine from them).

*Haustrations: saculation in the large intestine.

.طقف حيضوتلل صورةلا*

6. Rectum:

30 cm long, located in front of the sacrum.

The sigmoid colon ends at the end of the 2nd sacral piece, and from there starts the rectum

(the 3rd sacral piece).

It is in front of the coccyx and curves with those bones, passing to the lower end of them.

It is directed downward backward creating the anal canal.

Located below the peritoneum, having no mesentery.

The upper third of it is covered with the peritoneum from the front and the sides, the middle

part is covered with peritoneum only from the front, and the lower third has no peritoneum

(devoid of peritoneum).

It is covered with a mucus membrane, projecting inside, forming three layers (2 on the left, 1

on the right), they are called transverse folds of the rectum. They form shelves-like

projections holds the feces before defecation.

Relations of the rectum:

- Posteriorly: sacrum/ front tip of the coccyx/ sacral plexus/ levator ani muscle/ piriformis

muscle.

- Anteriorly: coils of the small intestine/ in the upper third there is a pouch.

*(In females: it is called pouch of Douglas, uterorectal pouch, it is located between the

rectum and the uterus. Usually when there is pus in the abdominal cavity it gathers in the

pouch because of the gravity.

In males: it is located between the bladder and the rectum, called rectovesical pouch.)

- In front of the middle and lower third:

*in females: the uterus and vagina.

*in males: posterior surface of the urinary bladder, behind it the seminal vesicle, the vas

deference, and the prostate gland.

The venous drainage:

- Superior rectal vein goes to the portal circulation.

- Middle and inferior rectal veins go to the systemic circulation.

*this is considered as a connection point between the portal and systemic circulations.

The rectum is sensitive to stretch only.

Muscles of the rectum: there are not three bands such as in large intestine. There is only two

bands one is a frontal and the other one is in the back (anterior and posterior bands), and

they are longitudinal muscles.

Blood supply of the rectum: 1. superior rectal artery: it is a branch of the inferior mesenteric

artery.

Runs behind the rectum, enters the wall of the rectum (the mucus

membrane) then goes to the anal canal.

2. Middle rectal artery: supplies the muscles of the rectum.

Branches from the internal iliac artery.

3. Inferior rectal artery: branches from the internal iliac artery.

7. Anal canal:

“The junction between the upper 2/3 (Endodermal in origin) and lower third (Ectodermal in origin) of

Anal Canal is delineated by the Pectinate line ( a remnant of the proctodeum). At this line the

Endothelial lining changes from Simple columnar to a Stratified Squamous Epithelium.

On top of this line are the Anal Columns (Endodermal in origin).”

4 cm long. The upper 2 cm are the origin of it, endodermal, composed of folds and columns at

the end of them there is an anal valve, those cells are columnar cells. The lower 2 cm,

ectoderm, and the cells are stratified-squamous.

The direction of the anal canal: downward backward.

The anal canal has two types of muscles: 1. Thick inner circular (forming an involuntary

sphincter called anal sphincter, composed of three layers; deep, subcutaneous, and

superficial).

2. Longitudinal.

There is a muscle at the end of the anal canal is called puborectalis muscle.

The three rings forming the anal sphincter:

1. Deep ring: voluntary, circular, and attaches to nothing.

2. Superficial ring: involuntary, attaches posteriorly and anteriorly, perineal body and

anococcyx body. (Anorectal ring).

3. Subcutaneous ring: surrounds the anal canal, having no attachment.

ىلع رداق ريغ ضيرمال حبصي لحالتا هذهل ىذأ وأ عقط راحجال ماق اذإ هانم ةبيالقر اطقنمال يف يراحالج لدختال لتااح يف*

.ةمهمو ةحساس ةقطنمال ذهه عدت كلذل لك،ذ حيلصت بعصيو اإلخراج، ىعل طرةيالس

Histology of the colon The large intestine completes absorption of water and sodium from the

luminal contents which become fecal residue. It secretes large amounts of mucus, and some hormones, but no digestive

enzymes. It has thick mucosa with deep crypts, but there are no villi. The

epithelium is formed of columnar absorptive cells with many goblet cells, endocrine cells and basal stem cells, but no Paneth cells. The surface epithelial cells are sloughed into the lumen, and have to be

replaced around every 6 days. The lamina propria and submucosa are similar to the small intestine.

The longitudinal smooth muscle in the muscularis externa is arranged in three longitudinal bands called taenia coli. At the anus, the circular

muscle forms the internal anal sphincter.

Histology of the appendix The arrangement of the layers in its walls is similar to that seen

elsewhere in the large intestine. However, the outer layer of muscle fibres in the muscularis externa forms a continuous layer.

The most characteristic property of the appendix is the presence of masses of lymphoid tissue in the mucosa and submucosa. There are

often follicles containing paler germinal centres similar to the follicles of Peyers patches in the small intestine.

Thank you..