Colon, Cecum, and Appendix: Anatomy

Development

The large intestines develop from the primitive midgut Midgut Development of the Abdominal Organs and hindgut Hindgut Development of the Abdominal Organs:

• Midgut Midgut Development of the Abdominal Organs: cecum to distal transverse colon
• Hindgut Hindgut Development of the Abdominal Organs: distal transverse colon to dentate line Dentate line Rectum and Anal Canal: Anatomy in anorectum
• The primitive gut tube grows and develops:
  • Connected to the posterior abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen by the dorsal mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy
  • Blood supply located within mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy

Gross Anatomy

Parts of the large intestine

• Cecum
• Vermiform appendix
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus colon
• Rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy
• Anal canal

Mesenteries and intraperitoneal Intraperitoneal Peritoneum: Anatomy versus retroperitoneal Retroperitoneal Peritoneum: Anatomy location

• Intestinal mesenteries are folds of peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum: Anatomy that connect these organs to the posterior abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen.
• Some parts of the large intestine have a mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy → intraperitoneal Intraperitoneal Peritoneum: Anatomy
• Some parts do not have a mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy and are located beneath parietal Parietal One of a pair of irregularly shaped quadrilateral bones situated between the frontal bone and occipital bone, which together form the sides of the cranium. Skull: Anatomy peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum: Anatomy → retroperitoneal Retroperitoneal Peritoneum: Anatomy
• Secondarily retroperitoneal Retroperitoneal Peritoneum: Anatomy: organs that had a mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy in utero and that regressed early in development, leaving the organ retroperitoneal Retroperitoneal Peritoneum: Anatomy in its mature position

General characteristics of the colon

• Forms an inverted U shape in the abdomen
• About 1.5–2 m long
• At the inferior margins of stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy and liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
• Surrounds the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy
• Begins at the ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy
• Receives chyme Chyme Small Intestine: Anatomy from the ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy through the ileocecal valves
• Ends at the anus
• Greater omentum Omentum Peritoneum: Anatomy hangs over the transverse colon.
• Includes ascending, transverse, descending, and sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus parts

Cecum

• 1st part of the large intestine
• Approximately 7.5–9 cm in length and breadth
• Intestinal pouch between the terminal ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy (at the ileocecal junction) and the ascending colon
• Located in the iliac fossa of the RLQ of the abdomen
• Covered on all sides by peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum: Anatomy (= intraperitoneal Intraperitoneal Peritoneum: Anatomy), though has no mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy (↓ mobility)
• Contains the opening into the appendix (appendiceal orifice)

Appendix

• Appendix: blind intestinal diverticulum Diverticulum A pouch or sac opening from the colon. Diverticular Disease off the cecum
• Approximately 6–10 cm in length
• Contains significant lymphoid tissue
• Base arises from the posteromedial aspect of the cecum, inferior to the ileocecal junction.
• Location of tail may be:
  • Retrocecal (65%)
  • Pelvic (30%)
  • Subcecal (2%)
  • Preileal (2%)
  • Postileal (1%)
• Mesoappendix:
  • Short triangular mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy that contains the appendicular vessels
  • Mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy: intraperitoneal Intraperitoneal Peritoneum: Anatomy and higher mobility
• McBurney point McBurney point Appendicitis: 
  • Surface projection of the base of the appendix 
  • About ⅓ of the way between the anterior superior iliac spine Anterior Superior Iliac Spine Chronic Apophyseal Injury and the umbilicus (closer to the anterior superior iliac spine Anterior Superior Iliac Spine Chronic Apophyseal Injury)

Ascending colon

• 2nd part of the large intestine
• Narrower than the cecum
• Passes superiorly from the cecum to the right lobe of the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy 
• Right colic flexure (also known as the hepatic flexure): end of the ascending colon where it makes a 90-degree turn toward the midline and becomes the transverse colon
• Secondarily retroperitoneal Retroperitoneal Peritoneum: Anatomy organ → no mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy → less mobility

Transverse colon

• The 3rd, longest, and most mobile part of the large intestine
• Runs transversely across the mid-upper abdomen
• Begins at the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy/right colic flexure (hepatic flexure) 
• Ends at the spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen: Anatomy/left colic flexure (also known as the splenic flexure Splenic flexure Small Intestine: Anatomy), where it makes a 90-degree turn inferiorly and becomes the descending colon
• Covered by the greater omentum Omentum Peritoneum: Anatomy
• Divides the greater sac of the peritoneal cavity Peritoneal Cavity The space enclosed by the peritoneum. It is divided into two portions, the greater sac and the lesser sac or omental bursa, which lies behind the stomach. The two sacs are connected by the foramen of winslow, or epiploic foramen. Peritoneum: Anatomy into supracolic and infracolic compartments
• Transverse mesocolon:
  • Mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy for the transverse colon 
  • Mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy: intraperitoneal Intraperitoneal Peritoneum: Anatomy structure, ↑ mobility

Descending colon

• Runs between the left colic (splenic) flexure and the left iliac fossa, where it is continuous with the sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus colon 
• Secondarily retroperitoneal Retroperitoneal Peritoneum: Anatomy organ → no mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy → less mobility

Sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus colon

• S-shaped loop of variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables lengths 
• Runs between the descending colon and the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy
• Sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus mesocolon:
  • Mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy of the sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus colon 
  • Mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy: intraperitoneal Intraperitoneal Peritoneum: Anatomy structure, ↑ mobility

Gross anatomic features unique to the colon

Several anatomic features distinguish the large intestine from the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy and rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy, including:

• Taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli:
  • 3 discrete bands of longitudinal muscle in the colonic wall (rather than a continuous longitudinal layer in the muscularis as seen in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy):
    • Omental taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis: attaches to the greater omentum Omentum Peritoneum: Anatomy
    • Mesocolic taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis: attaches to the transverse mesocolon (which anchors the transverse colon to the posterior abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen)
    • Free taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli: not attached to other structures
  • Contract to form the haustra
• Haustra:
  • Sacculations in the colon created by contraction of the longitudinal taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli 
  • Internally, these sacculations are separated by semilunar folds (protrusions of mucosa into the lumen)
• Omental appendices (also called epiploic appendages): small, fatty, omentum-like projections

Microscopic Anatomy

Overview of the wall structure

• The walls of the large intestine are thinner than those of the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy.
• The general layers are the same: mucosa → submucosa → muscularis propria → serosa

Mucosa

• 3 sublayers:
  • Columnar epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology
  • Lamina propria Lamina propria Whipple’s Disease
  • Muscularis mucosae
• Villi are absent.
• Microvilli (also known as the brush border Brush border Tubular System): present, but less abundant than in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy 
• Intestinal glands (also called intestinal crypts):
  • Pores in the wall, which open into tube-like glands.
  • Contain a large number of goblet cells Goblet cells A glandular epithelial cell or a unicellular gland. Goblet cells secrete mucus. They are scattered in the epithelial linings of many organs, especially the small intestine and the respiratory tract. Glandular Epithelium: Histology:
    • Mucin-producing epithelial cells
    • More prominent in large intestine than in small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy
  • Produce copious amounts of mucus for lubrication of feces
• MALT:
  • Significant lymphoid tissue present in the lamina propria Lamina propria Whipple’s Disease 
  • Most abundant in the appendix

Submucosa

• Loose connective tissue Loose connective tissue Connective Tissue: Histology
• Contains:
  • Larger vessels
  • Meissner nerve plexus (ganglia of the ANS ANS The ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System: Anatomy): controls the muscularis mucosa (independent of the muscularis propria)

Muscularis propria

The primary muscular layer of the colon wall.

• Inner circular layer
• Outer longitudinal muscles:
  • Not a continuous layer
  • Present in only the 3 bands of tissue, known as taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli:
    • Omental taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli
    • Mesocolic taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli
    • Free taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis coli
• Contains the myenteric (Auerbach) plexus:
  • Ganglia of the ANS ANS The ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System: Anatomy, which controls the muscular layer.
  • Located between 2 layers of smooth muscle

Serosa

• Made up of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology
• Continuous with visceral peritoneum Visceral peritoneum Peritoneum: Anatomy 
• Connected to mesentery Mesentery A layer of the peritoneum which attaches the abdominal viscera to the abdominal wall and conveys their blood vessels and nerves. Peritoneum: Anatomy or peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum: Anatomy

Neurovasculature

Arterial supply

The arterial supply is via the superior mesenteric artery Superior mesenteric artery A large vessel supplying the whole length of the small intestine except the superior part of the duodenum. It also supplies the cecum and the ascending part of the colon and about half the transverse part of the colon. It arises from the anterior surface of the aorta below the celiac artery at the level of the first lumbar vertebra. Small Intestine: Anatomy (SMA) and the inferior mesenteric artery Inferior mesenteric artery The artery supplying nearly all the left half of the transverse colon, the whole of the descending colon, the sigmoid colon, and the greater part of the rectum. It is smaller than the superior mesenteric artery and arises from the aorta above its bifurcation into the common iliac arteries. Small Intestine: Anatomy (IMA).

• SMA branches (starting in the RLQ and moving clockwise):
  • Ileocolic artery:
    • Colic branch → cecum
    • Appendicular artery (off the colic branch) → appendix
    • Ileal branch → terminal ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy
  • Right colic artery → ascending colon
  • Middle colic artery:
    • Supplies the ascending and transverse colons
    • Continuous with the marginal artery
  • Marginal artery (of Drummond):
    • Supplies the transverse colon
    • Forms an important anastomosis between the middle colic artery (off the SMA) and the left colic artery (off the IMA)
  • Jejunal and ileal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology → jejunum Jejunum The middle portion of the small intestine, between duodenum and ileum. It represents about 2/5 of the remaining portion of the small intestine below duodenum. Small Intestine: Anatomy and ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy
• IMA branches (starting in the LUQ and moving clockwise):
  • Left colic artery:
    • Supplies the descending colon
    • Anastomoses with the marginal artery, connecting circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment from the SMA and IMA
  • Sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology → sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus colon
  • Superior rectal artery → upper rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy
• Vasa recta Vasa recta Glomerular Filtration: small vessels off the major vessel that directly supply the bowel wall.

Venous drainage

The cecum, appendix, and colon drain via named veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology that run parallel to their arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology, which ultimately drain into the superior mesenteric vein (SMV) and the inferior mesenteric vein ( IMV IMV Invasive mechanical ventilation (IMV) is an advanced airway modality used for individuals with immediate or impending respiratory failure and/or in preparation for surgery. The IMV technique involves positive pressure ventilation delivered to the lungs through an endotracheal tube via a ventilator. Invasive Mechanical Ventilation).

• SMV:
  • Receives drainage from:
    • Right ½ of the large intestines
    • Via the ileocolic and right and middle colic veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology
  • Joins with the splenic vein to form the hepatic portal Hepatic portal Liver: Anatomy vein
• IMV IMV Invasive mechanical ventilation (IMV) is an advanced airway modality used for individuals with immediate or impending respiratory failure and/or in preparation for surgery. The IMV technique involves positive pressure ventilation delivered to the lungs through an endotracheal tube via a ventilator. Invasive Mechanical Ventilation:
  • Receives drainage from:
    • Left ½ of the large intestines
    • Via the superior rectal, sigmoid Sigmoid A segment of the colon between the rectum and the descending colon. Volvulus, and left colic veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology
  • Drains into the splenic vein → hepatic portal Hepatic portal Liver: Anatomy vein

Lymphatic drainage

Via multiple abdominal lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy:

• Epicolic
• Paracolic
• Ileocolic
• Right, middle, and left colic lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy

Innervation

The colon is innervated by the ANS ANS The ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System: Anatomy, which has parasympathetic and sympathetic divisions.

• Parasympathetic innervation:
  • Stimulatory
  • Via branches of the:
    • Vagus nerve Vagus nerve The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx). Pharynx: Anatomy
    • Pelvic splanchnic nerves
• Sympathetic innervation:
  • Inhibitory
  • Via the superior and inferior mesenteric plexuses

Function

• Water absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption
• Vitamin production by bacterial flora (and absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption):
  • Vitamin K Vitamin K A lipid cofactor that is required for normal blood clotting. Several forms of vitamin K have been identified: vitamin K 1 (phytomenadione) derived from plants, vitamin K 2 (menaquinone) from bacteria, and synthetic naphthoquinone provitamins, vitamin K 3 (menadione). Vitamin k 3 provitamins, after being alkylated in vivo, exhibit the antifibrinolytic activity of vitamin k. Green leafy vegetables, liver, cheese, butter, and egg yolk are good sources of vitamin k. Fat-soluble Vitamins and their Deficiencies
  • Several B vitamins
• Compaction of feces
• Storage of feces
• Moving waste materials toward the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy for expulsion

Clinical Relevance

• Appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis: acute inflammation Acute Inflammation Inflammation of the appendix caused by obstruction of the lumen, typically due to calcified feces, tumors, or foreign bodies. Appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis is the most common abdominal surgical emergency Surgical Emergency Acute Abdomen worldwide; it classically presents with periumbilical abdominal pain Abdominal Pain Acute Abdomen that migrates to the RLQ, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, anorexia Anorexia The lack or loss of appetite accompanied by an aversion to food and the inability to eat. It is the defining characteristic of the disorder anorexia nervosa. Anorexia Nervosa, nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics, and vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia. Management is usually surgical.
• Diverticulosis Diverticulosis A pathological condition characterized by the presence of a number of colonic diverticula in the colon. Its pathogenesis is multifactorial, including colon aging, motor dysfunction, increases in intraluminal pressure, and lack of dietary fibers. Diverticular Disease: An intestinal diverticulum Diverticulum A pouch or sac opening from the colon. Diverticular Disease is a sac-like bulge of the intestinal wall protruding outward. Diverticula arise because of the increased intestinal pressures associated with a low-fiber diet and when the transport of intestinal content is slower. The condition is typically asymptomatic.
• Diverticulitis Diverticulitis Inflammation of a diverticulum or diverticula. Diverticular Disease: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of diverticula that occurs when the diverticula become occluded. Diverticulitis Diverticulitis Inflammation of a diverticulum or diverticula. Diverticular Disease often presents with lower abdominal pain Abdominal Pain Acute Abdomen and changes in bowel habits and may become complicated by abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease, perforation Perforation A pathological hole in an organ, blood vessel or other soft part of the body, occurring in the absence of external force. Esophagitis, fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula, and bowel obstruction Bowel obstruction Any impairment, arrest, or reversal of the normal flow of intestinal contents toward the anal canal. Ascaris/Ascariasis.
• Ischemic colitis Ischemic colitis Inflammation of the colon due to colonic ischemia resulting from alterations in systemic circulation or local vasculature. Large Bowel Obstruction: ischemia Ischemia A hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation. Ischemic Cell Damage of the colon due to hypoperfusion that may result from vessel occlusion (e.g., arterial thromboembolic events), hypovolemic shock Hypovolemic Shock Types of Shock, sepsis Sepsis Systemic inflammatory response syndrome with a proven or suspected infectious etiology. When sepsis is associated with organ dysfunction distant from the site of infection, it is called severe sepsis. When sepsis is accompanied by hypotension despite adequate fluid infusion, it is called septic shock. Sepsis and Septic Shock, or traumatic vessel laceration Laceration Torn, ragged, mangled wounds. Blunt Chest Trauma. The SMA is most commonly affected. Classically, presentation is with sudden onset of pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways that is out of proportion to physical findings. The primary goal of management is to restore blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure.
• Colon polyps Colon polyps Colon polyps are growths of mucosal tissue in the colon, the most common site of polyps in the GI tract. Polyps can be classified as neoplastic or nonneoplastic and may be associated with genetic syndromes. Hyperplastic polyps are nonneoplastic and are the most common type overall, whereas adenomas are the most common type of neoplastic polyp and have the potential to progress to cancer. Colon Polyps: A polyp is an overgrowth of mucosal tissue in the large intestine. A polyp may be sessile (wide and flat), branched, or pedunculated. Polyps are usually < 1 cm and do not cause any symptoms, though they may cause constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, or blood in the stool. Polyps can be classified as neoplastic or nonneoplastic. Hyperplastic Hyperplastic Colon Polyps polyps are nonneoplastic, while adenomas are the most common type of neoplastic polyp and have the potential to progress to cancer. Polyps may be associated with genetic syndromes.
• Colorectal cancer Colorectal cancer Colorectal cancer (CRC) is the 2nd leading cause of cancer-related deaths in the United States. Colorectal cancer is a heterogeneous disease that arises from genetic and epigenetic abnormalities, with influence from environmental factors. Colorectal Cancer (CRC): malignant tumor Tumor Inflammation of the colon and/or rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy. Almost all cases of CRC are adenocarcinoma, and the majority of lesions come from the malignant transformation Transformation Change brought about to an organism’s genetic composition by unidirectional transfer (transfection; transduction, genetic; conjugation, genetic, etc.) and incorporation of foreign DNA into prokaryotic or eukaryotic cells by recombination of part or all of that DNA into the cell’s genome. Bacteriology of an adenomatous polyp Adenomatous polyp Benign neoplasms derived from glandular epithelium. Colon Polyps. Colorectal cancer Colorectal cancer Colorectal cancer (CRC) is the 2nd leading cause of cancer-related deaths in the United States. Colorectal cancer is a heterogeneous disease that arises from genetic and epigenetic abnormalities, with influence from environmental factors. Colorectal Cancer is usually asymptomatic, with symptoms such as occult bleeding typically developing late. The prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas depends on the stage of cancer at discovery.
• Malrotation Malrotation Pediatric Gastrointestinal Abnormalities of the gut: congenital anomaly resulting from abnormal rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays of the primitive gut tube during development. There are a number of variants of this condition, but typically the entire large intestine is located in the left ½ of the abdomen and the small intestines are located in the right ½. Malrotation Malrotation Pediatric Gastrointestinal Abnormalities of the gut may be asymptomatic, or it may result in significant complications, such as midgut Midgut Development of the Abdominal Organs volvulus Volvulus A volvulus is the twisting or axial rotation of a portion of the bowel around its mesentery. The most common site of volvulus in adults is the colon; most frequently the sigmoid volvulus. Patients typically present with symptoms of bowel obstruction such as abdominal pain, distension, vomiting, and constipation/obstipation. Volvulus.
• Large bowel obstruction Bowel obstruction Any impairment, arrest, or reversal of the normal flow of intestinal contents toward the anal canal. Ascaris/Ascariasis: interruption in the normal flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of intestinal contents through the colon and rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy. This obstruction may be mechanical (due to actual physical occlusion of the lumen) or functional (due to a loss of normal peristalsis Peristalsis A movement, caused by sequential muscle contraction, that pushes the contents of the intestines or other tubular organs in one direction. Gastrointestinal Motility, also known as pseudo-obstruction). Malignancy Malignancy Hemothorax and volvulus Volvulus A volvulus is the twisting or axial rotation of a portion of the bowel around its mesentery. The most common site of volvulus in adults is the colon; most frequently the sigmoid volvulus. Patients typically present with symptoms of bowel obstruction such as abdominal pain, distension, vomiting, and constipation/obstipation. Volvulus are the most common causes of mechanical large bowel obstruction Bowel obstruction Any impairment, arrest, or reversal of the normal flow of intestinal contents toward the anal canal. Ascaris/Ascariasis. The typical symptoms include intermittent lower abdominal pain Abdominal Pain Acute Abdomen, abdominal distention Abdominal distention Megacolon, and obstipation Obstipation Large Bowel Obstruction.
• Irritable bowel syndrome Irritable bowel syndrome Irritable bowel syndrome (IBS) is a functional bowel disease characterized by chronic abdominal pain and altered bowel habits without an identifiable organic cause. The etiology and pathophysiology of this disease are not well understood, and there are many factors that may contribute. Irritable Bowel Syndrome ( IBS IBS Irritable bowel syndrome (IBS) is a functional bowel disease characterized by chronic abdominal pain and altered bowel habits without an identifiable organic cause. The etiology and pathophysiology of this disease are not well understood, and there are many factors that may contribute. Irritable Bowel Syndrome): functional bowel disease characterized by chronic abdominal pain Abdominal Pain Acute Abdomen and altered bowel habits without an identifiable organic cause. Symptoms of IBS IBS Irritable bowel syndrome (IBS) is a functional bowel disease characterized by chronic abdominal pain and altered bowel habits without an identifiable organic cause. The etiology and pathophysiology of this disease are not well understood, and there are many factors that may contribute. Irritable Bowel Syndrome may include digestive problems along with abdominal pain Abdominal Pain Acute Abdomen, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, or constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation. This syndrome is associated with gluten Gluten Prolamins in the endosperm of seeds from the triticeae tribe which includes species of wheat; barley; and rye. Celiac Disease sensitivity and psychological factors and is a diagnosis of exclusion.