The Department of Human anatomyThe Department of Human anatomy

Splanchnology.

Digestive systemPart - 2

Small intestineSmall intestine is the longest part of is the longest part of

alimentary canal. It extends alimentary canal. It extends from the pylorus of the from the pylorus of the stomach to the junction stomach to the junction between cecum and ileum. between cecum and ileum. Much of digestion and Much of digestion and absorption of food takes place absorption of food takes place in the small intestine. in the small intestine. Ingested nutrients spend at Ingested nutrients spend at least least 1212 hours in the small hours in the small intestine.intestine.

The small intestine is divided into The small intestine is divided into three parts:three parts:

- - Duodenum Duodenum - - Jejunum Jejunum - - Ileum. Ileum.

Duodenum:Duodenum:It is the first part of small It is the first part of small

intestine that joins the intestine that joins the stomach. It is a C-shaped stomach. It is a C-shaped tube, about 10 inches longtube, about 10 inches long (25,4 sm)(25,4 sm). It lies between . It lies between the stomach and jejunum the stomach and jejunum ((begins with the duodenal begins with the duodenal bulb and ends at bulb and ends at the ligament of Treitzthe ligament of Treitz)) and and is very important because is very important because it receives the openings of it receives the openings of the bile and pancreatic the bile and pancreatic ducts. ducts. These 2 ducts unite These 2 ducts unite in the duodenal wall to in the duodenal wall to form the hepatopancreatic form the hepatopancreatic ampulla. The ampulla. The hepatopancreatic hepatopancreatic sphincter controls entry of sphincter controls entry of bile and pancreatic juice bile and pancreatic juice into the intestinal lumen.into the intestinal lumen.

TThe duodenum is divided into four he duodenum is divided into four partsparts::

superiorsuperior descending descending inferior/horizontainferior/horizontall ascending ascending

The organs and structures The organs and structures surrounding the duodenum surrounding the duodenum includes :includes :

Superior (above) – liver and Superior (above) – liver and gallbladdergallbladder

Anterior (in front) – gallbladder Anterior (in front) – gallbladder and transverse colonand transverse colon

Posterior (behind) – inferior Posterior (behind) – inferior vena cava, right psoas major vena cava, right psoas major muscle and aortamuscle and aorta

Lateral – pancreasLateral – pancreas

A A liquid mixtureliquid mixture of food and gastric  of food and gastric secretions enters the superior duodenum secretions enters the superior duodenum from the pylorus of the stomach, triggering from the pylorus of the stomach, triggering the release of pancreas-stimulating the release of pancreas-stimulating hormones from glands in the duodenal wall. hormones from glands in the duodenal wall. Ducts from Ducts from the the pancreaspancreas and  and gallbladdergallbladder enter at  enter at the descending duodenum, bringing the descending duodenum, bringing bicarbonate to neutralize the acid in the bicarbonate to neutralize the acid in the gastric secretions, pancreatic enzymes to gastric secretions, pancreatic enzymes to further digestion, and further digestion, and bile saltsbile salts to emulsify  to emulsify fat. The mucous lining of the last two fat. The mucous lining of the last two segments of the duodenum begins the segments of the duodenum begins the absorption of nutrients, in particular iron and absorption of nutrients, in particular iron and calcium, before the food contents enter the calcium, before the food contents enter the next part of the small intestine, next part of the small intestine, the the jejunumjejunum. .

The Jejunum and IleumThe Jejunum and Ileum The The jejunumjejunum

middle region of the small intestine. middle region of the small intestine. approximately 2.5 meters (7.5 feet)approximately 2.5 meters (7.5 feet) makes up approximately two-fifths of the makes up approximately two-fifths of the

small intestine’s total length. small intestine’s total length. primary region for chemical digestion and primary region for chemical digestion and

nutrient absorption nutrient absorption The The ileumileum

is the last region of the small intestine. is the last region of the small intestine. about 3.6 meters (10.8 feet) in lengthabout 3.6 meters (10.8 feet) in length forms approximately three-fifths of the forms approximately three-fifths of the

small intestine. small intestine. terminates at the ileocecal valveterminates at the ileocecal valve

sphincter that controls the entry of materials sphincter that controls the entry of materials into the large intestine.into the large intestine.

Circular folds Circular folds ((plicae circularesplicae circulares) ) – deep, circular, – deep, circular, permanent folds of permanent folds of the mucosa and the mucosa and submucosa. They submucosa. They increase surface increase surface area and slow the area and slow the movement of chyme. movement of chyme. This provides more This provides more time for absorption time for absorption and digestion to and digestion to occur. occur.

Villi – Villi – fingerlike fingerlike extensions of the mucosa. extensions of the mucosa. Absorptive epithelial cells Absorptive epithelial cells line the surface. Within line the surface. Within the core of each villus is the core of each villus is the lamina propria, which the lamina propria, which contains blood capillaries contains blood capillaries (for absorption of amino (for absorption of amino acids and acids and monosaccharides) and a monosaccharides) and a lacteal lacteal (for absorption of (for absorption of fatty acids). fatty acids).

Microvilli Microvilli – tiny – tiny projections of the plasma projections of the plasma membrane of each membrane of each absorptive epithelial cell. absorptive epithelial cell. They give the cell’s They give the cell’s luminal surface a fuzzyluminal surface a fuzzy

Ileocecal valve, as the name indicates, is a Ileocecal valve, as the name indicates, is a structure present at the junction of ileum structure present at the junction of ileum and cecum. It is a rudimentary valve and and cecum. It is a rudimentary valve and consists of two horizontal folds of mucous consists of two horizontal folds of mucous membrane that project around the opening membrane that project around the opening of the ileum. Ileocecal valve controlof the ileum. Ileocecal valve controlss the the flow of contents from ileum into the large flow of contents from ileum into the large intestine. intestine.

Large IntestineLarge Intestine approximate length of 1.5 meters approximate length of 1.5 meters

(5 feet)(5 feet) diameter of 6.5 centimeters (2.5 diameter of 6.5 centimeters (2.5

inches).inches). Absorbs most of the waterAbsorbs most of the water and and

electrolytes from the remaining electrolytes from the remaining digested material. digested material.

Watery material that first enters Watery material that first enters the large intestine soon the large intestine soon solidifiessolidifies and becomes and becomes faeces.faeces.

Stores faecal material until the Stores faecal material until the body is ready to body is ready to defaecate.defaecate.

Absorbs a very small percentage Absorbs a very small percentage of of nutrientsnutrients still remaining in the still remaining in the digested material.digested material.

Composed of four segments: Composed of four segments: the the caecumcaecum, , coloncolon, , rectumrectum, , anal anal

canalcanal

        Structures Structures 

       a. cecum with vermiform appendix        a. cecum with vermiform appendix        b. ascending, transverse, descending colon        b. ascending, transverse, descending colon        c. sigmoid colon, rectum        c. sigmoid colon, rectum             

Haustra are pouches in wall of large intestine Haustra are pouches in wall of large intestine                   

Millions of bacteria colonize the large intestine. Millions of bacteria colonize the large intestine. They breakdown indigestible carbohydrate They breakdown indigestible carbohydrate residues and produce many B vitamins as well residues and produce many B vitamins as well as most of the body’s vitamin K supply. as most of the body’s vitamin K supply.

Typically 100 g of feces are produced per day Typically 100 g of feces are produced per day consisting of 75% water and 25% solids. Solids consisting of 75% water and 25% solids. Solids include dead bacteria, fat, inorganic matter, include dead bacteria, fat, inorganic matter, protein, undigested plant fibers, bile pigments, protein, undigested plant fibers, bile pigments, and shed epithelial cells.  and shed epithelial cells.       

The liverThe liver is an accessory digestive organ is an accessory digestive organ that has multiple functions including: that has multiple functions including:

Carbohydrate metabolism – storage and Carbohydrate metabolism – storage and release of glucose release of glucose

Removal of drugs, toxins, and foreign Removal of drugs, toxins, and foreign chemicals from the plasma chemicals from the plasma

Storage of vitamins (A, D, E, and K) and Storage of vitamins (A, D, E, and K) and minerals (iron and copper) minerals (iron and copper)

Protein metabolism Protein metabolism Lipid metabolism Lipid metabolism Synthesis of plasma proteins (e.g., Synthesis of plasma proteins (e.g.,

albumin, fibrin, etc.) albumin, fibrin, etc.) Phagocytosis of old RBCs and of Phagocytosis of old RBCs and of

pathogens. pathogens. Production of bile (0.5-1 L/day). Production of bile (0.5-1 L/day).

The liverThe liver composed of four incompletely composed of four incompletely

separated lobes separated lobes supported by two ligamentssupported by two ligaments

Right lobeRight lobe Left lobeLeft lobe Falciform ligamentFalciform ligament Round ligamentRound ligament Caudate lobeCaudate lobe Quadrate lobeQuadrate lobe

The gallbladderThe gallbladder is a thin-walled is a thin-walled green muscular sac found on the green muscular sac found on the ventral surface of the liver. ventral surface of the liver.

It functions primarily in the storage It functions primarily in the storage and concentration of bile. and concentration of bile.

The liver continuously produces The liver continuously produces bile. However the hepatopancreatic bile. However the hepatopancreatic sphincter is normally closed. This sphincter is normally closed. This results in bile backing up into the results in bile backing up into the common bile duct, cystic duct, and common bile duct, cystic duct, and ultimately into the gallbladder. ultimately into the gallbladder.

When fatty chyme arrives in the When fatty chyme arrives in the small intestine, intestinal glands small intestine, intestinal glands secrete the hormone secrete the hormone cholecystokinin. cholecystokinin.

CCK causes gallbladder contraction CCK causes gallbladder contraction and relaxation of the and relaxation of the hepatopancreatic sphincter, letting hepatopancreatic sphincter, letting bile flow into the duodenum. bile flow into the duodenum.

The pancreasThe pancreas Mostly retroperitoneal and deep to the greater Mostly retroperitoneal and deep to the greater

curvature of the stomach. curvature of the stomach. The The head head of the pancreas sits next to the of the pancreas sits next to the

duodenum as it emanates from and loops away duodenum as it emanates from and loops away from the pylorus. The from the pylorus. The body body extends behind the extends behind the stomach and its stomach and its tail tail ends at the spleen. ends at the spleen.

The pancreas primarily consists of The pancreas primarily consists of acini acini – small – small clusters of enzyme secreting cells. These acinar clusters of enzyme secreting cells. These acinar cells empty their secretion into small ducts. cells empty their secretion into small ducts. Small ducts coalesce into larger ducts that Small ducts coalesce into larger ducts that empty into the empty into the main pancreatic ductmain pancreatic duct, which , which runs centrally along the long axis of the pancreas runs centrally along the long axis of the pancreas

The major function of the acinar and duct cells is The major function of the acinar and duct cells is the secretion of the secretion of pancreatic juice pancreatic juice (1.5 L/day). (1.5 L/day).

Acinar cells contribute digestive enzymes to the Acinar cells contribute digestive enzymes to the pancreatic juice including: pancreatic juice including: proteases, proteases, pancreatic lipase, pancreatic amylase.pancreatic lipase, pancreatic amylase.

Scattered amidst the pancreatic acini are the Scattered amidst the pancreatic acini are the hormone-producing hormone-producing islets of Langerhansislets of Langerhans. Their . Their major function is the regulation of blood glucose major function is the regulation of blood glucose levels. levels.

PeritoneumPeritoneum Parietal peritoneumParietal peritoneum Visceral peritoneumVisceral peritoneum Peritoneal cavityPeritoneal cavity

Intraperitoneal organsIntraperitoneal organs Mesoperitoneal organsMesoperitoneal organs Retroperitoneal organsRetroperitoneal organs

MesentariesMesentaries Double layered folds of peritoneumDouble layered folds of peritoneum

Greater omentumGreater omentum Lesser omentumLesser omentum Mesentery properMesentery proper

Suspends small intestine from posterior wall of Suspends small intestine from posterior wall of abdomenabdomen

MesocolonMesocolon Suspends large intestineSuspends large intestine

Peritoneal ligamentPeritoneal ligament Peritoneum that attaches one organ to anotherPeritoneum that attaches one organ to another

ThankThank you for attention!you for attention!