Colon anatomy

colon anatomy, anatomy of large intestine, anatomy of large bowel, histology of large intestine, large intestine, histology, colon, appendices epiploica, taenia coli, haustrautions, ilio caecal valve

1. Anatomy of Colon by, dr . m. gowri Shankar, DEPARTMENT OF SURGERY For suggestions mail me at [email protected]

2. Objectives., Embryology Gross anatomy Features of colon, facts, relations and its attachments Blood supply ( Arterial and Venous ) Lymphatic drainage of colon Nerve supply Histology

3. Colon Introduction., Large bowel extends from ileocaecal junction to the Anus 1.5m long Large intestine = caecum + colon + rectum Colon is Divided into., Ascending colon Transverse colon Descending colon Sigmoid colon

4. Embryology of colon

5. Embryology Of Gut.., Blastocyst has, Outer cell mass ( trophoblast ) & Inner cell mass ( embryoblast ) N ow coming to Embryoblast .,which divides into, Epiblast & Hypoblast And here comes the process of gastrulation, which results in division of epiblast into., Ectoderm Mesoderm & Endoderm

6. Embryology Of Gut.., And we know that entire gut is formed from endoderm Now coming to endoderm which replaces hypoblast and covers entire yolk sac…. Now imagine that entire surface of yolk sac is covered with endoderm Yaa ..finally precursor for GUT tube is formed successfully

7. Embryology Of Gut.., Now the yolk sac which is covered by endoderm forms head and tail fold After formation of head and tail fold, Part of Yolk sac goes into embryo and forms primitive Gut

8. Embryology Of Gut.., Primitive GUT has 3 parts Foregut Midgut and Hindgut

9. Embryology Of Gut.., For colon, midgut and hindgut are the precursors Midgut initially is a blunt wide tube which later forms a loop along the axis of vitelline artery (later forms the Superior Mesenteric Artery) After loop formation midgut is divided into prearterial and postarterial parts

10. Embryology Of Gut.., ( M idgut ) After loop formation midgut is divided into prearterial and postarterial parts Derivatives of prearterial midgut includes, Half of D2, D3, D4 Jejunum Ileum Derivatives of postarterial midgut includes , Terminal ileum Caecum and Appendix Ascending colon Right 2/3 rd of transverse colon

11. Embryology Of Gut.., (Hindgut) Now coming to hindgut.. Hindgut is divided by allantoic diverticulum into Pre allantoic part and Post allantoic part Derivatives of Pre allantoic HindGut Left 1/3 rd of transverse colon, descending colon and sigmoid colon Derivatives of post allantoic Hindgut Forms dilated cloaca which again divides into ventral urogenital sinus and dorsal Rectum and A nal Canal

12. Anatomical features, Relations and Attachments of colon

13. Colon Introduction., Large bowel extends from ileocaecal junction to the Anus 1.5m long Large intestine = caecum + colon + rectum Colon is Divided into., Ascending colon Transverse colon Descending colon Sigmoid colon

14. Anatomical features of colon Large intestine is wider at caecum (7.5cm) and narrower at sigmoid colon (2.5cm) Greater part of colon is fixed ( i.e , Reteroperitoneal ) except at the Appendix Tranverse colon Sigmoid colon Longitudinal muscle plays some important roles in colon Major role is to form 3 ribbon like bands termed Taenia Coli Minor role in forming a thin layer of muscle coat in colon

15. Anatomical features of colon ( Taenia coli) Now let us see about TAENIA COLI ., They are 3 in nos 1 anterior (t. libera ) 1 posteromedial (t. mesocolia ) 1 posterolateral (t. omentalis ) Location of these taenia is not same in the entire large bowel… bcoz large bowel is not a pvc pipe but flexible fire service pipe Taenia converge @ appendix and helps in identification of appendix It diverges @ distal part and continues with long. Muscles of rectum

16. Anatomical features of colon contd.,

17. Anatomical features of colon ( Haustrations ) As discussed already longitudinal muscle layer is very thin in colon But circular muscle layer of colon is very thick This leads to formation of sacculations (termed HAUSTRATIONS)

18. Barium enema…,

19. Anatomical features of colon (Appendices Epiploicae ) Small bags of filled with fat (termed APPENDICES EPIPLOICAE) Present all over colon ( not all over large bowel – bcoz absent in caecum, rectum) It’s looking like makeup or artwork for colon, but usually it’s too dangerous. Bcoz it’s rich in anastomosis If peeled up by extra traction bleeding and antimesenteric border ischemia occurs

20. Anatomical features of colon ( Appendices Epiploicae ) It’s looking like makeup or artwork for colon, but usually it’s too dangerous. Bcoz it’s rich in anastomosis If peeled up by extra traction bleeding and antimesenteric border ischemia occurs

21. Anatomical features of colon (diverticulosis) Large bowel wall is weakened at region where vessels pierce the wall and Attachment of appendices epiploica So, mucosa may herniate at these areas and will lead to diverticulosis, which may later bcom diverticulitis, fibrosis and stricture

22. Iliocaecal valve Ilium opens into the posteromedial aspect of the caecum, which is guarded by cone shaped ileocaecal valve. The valve has two lips and two frenula. L ips- upper lip – horizontal lower lip- concave

23. Iliocaecal valve – function mechanism., The valve is actively closed by The sympathetic tone and Mechanically by distention of caecum Function is to prevent reflux from caecum to ileum. Thus large bowel obstruction becomes close loop obstruction which is a surgical emergency . Add image of two rubber band

24. Parts of colon., Ascending colon (5 ”) Transverse colon (20”) Descending colon (10”) Sigmoid colon (15”)

25. Ascending colon., The ascending colon is 15cm in length. Extends from iliocaecal junction to the hepatic flexure. Its posterior surface is fixed against the retroperitoneum and the anterior, medial and lateral surfaces are covered by peritoneum (i.e., covered by peritoneum on three sides)

26. Anteriorly, Coils of small intestine Right edge of greater omentum Anterior abdominal wall Posteriorly, Back muscles (quad lumb , transverse abdominis ) Nerves ( ilioinguinal , iliohypogastric and lateral cutaneous) Right kidney Laterally, Right paracolic gutter Ascending colon relations.,

27. Right paracolic gutter., It is a sulcus present laterally to the colon . Fluid and pus transverse along this gutter either from appendicular region to the hepatorenal pouch or from liver and epigastrium to the pelvis

28. Right colic flexure., Hepatic flexure supported by Hepatocolic ligament

29. Transverse Colon Passes from right hypochondriac region into left hypochondriac region. Extends from right colic flexure to left colic flexure below the spleen. The left colic flexure is higher and more posterior than the right colic flexure ,and is attached to the diaphragm by the phrenicocolic ligament. T ransverse mesocolon , the mesentery of transverse colon suspends the transverse colon from the anterior border of pancreas.

30. Anterior relations: Greater omentum anterior abdominal wall Posterior relations: Descending part of the duodenum Head of the pancreas Coils of jejunum and ileum superior relations Liver Gall-bladder Greater curvature of stomach Lower end of spleen Inferior relations – Small intestine Relations of transverse colon:

31. Descending Colon It is 10inch in length Runs vertically down from the splenic flexure up to iliac crest and then inclines medially iliacus and psoas major and then continues with sigmoid colon Descending colon is narrower than the ascending colon

32. Relations of descending colon: Anterior relations: -Coils of small intestine -Greater omentum -Anterior abdominal wall Posterior relations: -Lateral border of left kidney -Origin of transversus abdominis muscle -Quadratus lumborum muscle -Iliac crest -Iliacus muscle -Left psoas muscle -Iliohypogastric and Ilioginuinal nerves -Lateral cutaneous nerve of thigh -Femoral nerve

33. Sigmoid Colon Sigmoid colon starts as descending colon passes in front of the pelvic brim. Below , it becomes continuous with the rectum at the level of S3. Completely surrounded by peritoneum. Sigmoid colon is mobile It hangs down into the pelvic cavity in the form of a loop. It is attached to the posterior wall of the pelvis by a fan shaped fold of peritoneum , known as sigmoid mesocolon . 2-transverse mesocolon 3-small bowel mesentery 4-sigmoid mesentery 1-lesser omentum

34. Relations of sigmoid colon: Anterior relations: -Urinary bladder (in males) -Posterior surface of uterus and upper part of vagina (in females ) Posterior relations: - Sacrum -external iliac vessels -left piriformis -left sacral plexus of nerves

35. Arterial supply of colon

36. Both rt. & lt. colic artery has ascending and descending branches

37. Arterial supply of colon From Marginal artery terminal branch arises Divides into vasa longa and vasa brevia Both enter along mesocolic border ( mesocolic taenia ) Blood supply will be less on the side between two amesocolic taenia …..so, here the longitudinal incisions can be given

38. Venous supply of colon Venous supply corresponds to the arterial supply

39. Lymphatic drainage of colon Lymph of colon is being drained via different level of nodes., Epicolic – lying on wall of gut Paracolic – on medial side Intermediate – on main branches Terminal nodes – on IM, SM Vessles If Ca spread occurs till intermediate or terminal nodes, for removing nodes corresponding arteries have to be ligated…so, the corresponding bowel has to be resected eventhough the bowel loop doesn’t contain carcinoma

40. Nerve supply of colon Lymph of colon is being drained via different Gut level Corresponding bowel loops PNS SNS PAIN LEVEL ROUTE OF NERVE SUPPLY CLINICAL IMPORTANCE MIDGUT JUNCN. OF D1/D2 TO RT. 2/3 RD TRANVERSE COLON VAGUS (CN 10) (T11-L1) COELIAC GANGLION AND SUPERIOR MESENTERIC GANGLION AROUND UMBLICUS (T11-L1) DERMATOME VIA SUPERIOR MESENTERIC PLEXUS SO, IN ANY MIDGUT PROBLEM PAIN AROUND UMBLICUS HINDGUT LEFT 1/3 RD TRANSVERSE COLON TO ANAL CANAL NERVI ERIGENTIS (S2, S3, S4) (L1-L2) LUMBAR SYMPATHETIC CHAIN AROUND PUBIC REGION VIA INFERIOR MESENTERIC PLEXUS AND SUPERIOR HYPOGASTRIC PLEXUS SO, IN ANY HINDGUT PROBLEM PAIN AROUND PUBIC REGION

41. Histology of colon

42. Histology of Gut., Histology of gut consists of, Mucosa Epithelium Lamina propria Muscularis mucosa Submucosa Muscularis externa Adventitia / Serosa

43. Histology of colon…, (Mucosa) Mucosa has, Epithelium – Columnar – absorbs water and ions In lamina propria – has 2 glands Goblet cells – secrete mucous for lubrication Entero endocrine cells – secrete various harmones for regulation of secretion and peristalsis muscularis mucosa – has smooth muscles which facilitates secretion No villi, but crypts of lieberkuhn present

44. Histology of colon…, (Sub Mucosa) SubMucosa has, Dense connective tissue Blood vessels and Sub mucosal ( Meissner’s Plexus) – regulates submucosal glands and muscularis mucosa Does not has any glands (but in duodenum submucosa has brunners gland, which secrete mucin and alkalizes acid)

45. Histology of colon…, ( Muscularis Externa ) Muscularis externa has, Inner circular and Myenteric plexus ( auerbach ) Outer Longitudinal layers, which has 2 roles Major role is to form 3 ribbon like bands termed Taenia Coli Minor role in forming a thin layer of muscle coat in colon

46. Histology of colon…, (Serosa / adventitia) Serosa – has serous membrane Made of squamous epithelium Helps in lubrication by secreting serous fluid Present in the bowel loops covered by peritoneum So, in large intestine present in transverse and sigmoid colon Adventitia – Attaches organ to the surrounding tissues It covers retro peritoneal part of large intestine (i.e., except trans. And sigmoid colon)

47. Large Vs Small Intestine M SM ME S E

48. Enteric plexus Enteric plexus are of two types, Submucosal ( meissners ) and Myenteric ( Auerbach ) Myenteric plexus is responsible for peristaltic contraction and relaxation These plexus are derived from neural crest cells

49. Thank you