The lower digestive system Flashcards
The large intestine
- Subdivided into: Cecum, appendix, colon, rectum and canal
- Lies around the edges of the abdominal cavity and is supported by the mesocolon
- It forms 4 colons (ascending, transverse, descending, sigmoid)
- Absorbs water and electrolytes from the remaining digested material to solidity into faeces
- Stores faecal material until ready to defecate
Gastroileal reflex: results in the accumulation of more chime in the cecum and ascending colon
Gastrocolic reflex: controls mass movement that propels faecal material towards the rectum
Cecum and Appendix
Cecum
- Receives chyme from ileum through ileocecal valve
- Sphincter prevents faeces from travelling back into ileum
- Mostly intraperitoneal
Appendix
- Blind tube that opens into posterior medial wall of cecum
- Contains lymph nodes, neutralizes pathogens
- Intraperitoneal
- Appendicitis
The colon
Ascending colon
- Origin from cecum
- Retroperitoneal
Transverse colon
- Origin: Hepaitic felxure
- Intraperitoneal
Descending colon
- Origin: Splenic flexure
- Retroperitoneal
Sigmoid colon
- Origin: Sigmoid flexure
- Intraperitoneal
Rectum and Anal Canal
Rectum
- Retroperitoneal muscular tube
- Stores faeces prior to defecation
Anal canal
- Last subdivision of the large intestine
- Approx 3 cm long
- Line with squamous epithelium
- Internal and external anal sphincter regulate the movement of faeces
Diseases of the digestive system
Celiac disease
- Immune reaction to gluten
- Causes inflammatory response of small intestine, leading to inflamed and flattened villi
Crohn’s disease
- Inflammatory bowel disease is a chronic inflammatory condition
- The body’s immune system attacks the bacterial antigens located within the GI tract
- Causes ulcers and fissures along the intestinal tract
Blood supply of GI tract
- Unpaired organs get blood supply from unpaired blood vessels
- Organs located above transverse mesocolon get blood supply from celiac trunk
- Organs located below transverse mesocolon get blood from mesenteric arteries
- Organs located on the right of the mesentery get blood supply from the superior mesenteric artery
- Organs located on the left side of the mesentery get blood supply from inferior mesenteric artery
Blood supply
- The celiac trunk is a branch of the ab aorta and supplies all organs which are located intraperitoneally and above the transverse mesocolon
- It supplies only superior parts the pancreas and duodenum as both these organs are located above and below the transverse mesocolon
Blood supply of lower ab regions
Superior mesenteric artery
Supplies (right side of mesenterium)
- Ascending and transverse colon
- Small intestine
- Parts of pancreas and duodenum
Inferior mesenteric artery
Supplies (left side of mesenterium)
- Descending and sigmoid colon
- Upper parts of rectum
Accessory digestive organs (Liver and pancreas)
- The cholecystokinin (CCK) peptide hormone is secreted by the duodenum and jejunum, in response to food in the alimentary tract
- The main stimulator for the secretion is the release of food-particularly fatty food- from the stomach into the duodenum
- CCK triggers the release of bile and pancreatic enzymes
Liver
- The largest visceral organ
- Sits underneath the diaphragm
- Essential for survival
- Covered by connective tissue capsule and visceral peritoneum
Liver anatomy (inferior)
The lesser omentum - Spans between the liver and the lesser curvature of the stomach
- Contains the veins/ arteries of the liver and stomach as well as the bile duct
- Can be viewed as the mesentery of liver and stomach
The liver function
To remove and add compounds to the blood as it circulates through the lobule
Secretion
- Secretes plasma proteins and bile
- Water and ions dilute and buffer the acids in the chyme as it enters the SI
- Acids in digestion of fats
Hematological regulation
- The largest blood reservoir
- Phagocytes cells remove cellular debris and pathogens from circulation
- Liver cells synthesise plasma protein
Metabolic regulation
- Blood from the GI tract enters the liver via the hepatic portal system
- Liver cells extract nutrients, metabolites, or toxins, from the blood
- Absorption of fat soluble vitamins
Hepatic portal system
- A network of veins that carries blood from the GI tract to the liver
The hepatic portal system carries venous blood from the gastrointestinal tract and spleen to the liver before it returns to the inferior vena cava and the heart: - Capillaries of gastrointestinal organs
- Hepatic portal vein
- Sinusoids of the liver (storage/ metabolic conversion/ extraction)
- The liver receives 2 blood supplies
- The hepatic portal vein contains nutrients rich, O2 poor blood
- The hepatic artery proper contains O2 rich blood
Hepatic Portal branches
- The inferior mesenteric vein: drains the distal part of the large intestine; and receives blood from the superior rectal vein, sigmoid reins, and left colic vein
- The splenic vein: drains the spleen: receives blood from pancreatic veins, short gastric veins, and the right gastroepiploic vein
- The superior mesenteric vein: drains the small intestine and part of the large intestine; and receives blood from the intestinal veins, pancreaticoduodenal veins, ileocolic vein and right and middle colic veins
The liver- blood supply
- Portal veins contribute 15% of the blood volume of the liver (rich in nutrients and poor in O2)
- Hepatic artery contributes 25% of blood volume entering the liver (rich in O2 and poor in nutrients)
- Blood from the portal veins and the hepatic artery mix as it enters and passes through a liver lobule
- Then the blood is collected by the hepatic central vein. The hepatic vein carries 100% of the blood out of the liver and into the inferior vena cava
Bile duct
Blood supply
- Cystic, hepatic, gastroduodenal
Nerve supply
- Parasympathetic: Contraction of the gallbladder, relaxes the sphincter of Oddi
- Sympathetic: relaxes gall bladder
