The Digestive System
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The Digestive System B. Pimentel, M.D. University of Makati College of Nursing
Overview There are 2 major groups of organs in the digestive system: Alimentary Canal - Organs thru which food actually passes (in order they are the: oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine). Accessory Organs - They assist in digestion, but no food actually passes through them. Includes the teeth, tongue, salivary glands, pancreas, liver, and gallbladder.
Overview
Functions
Ingestion Mastication Propulsion Mixing Secretion Digestion Absorption Elimination
The Abdominal Cavity
The majority of digestive organs are located Peritoneum
Visceral peritoneum Parietal peritoneum Peritoneal cavity Mesenteries
Retroperitonium Duodenum
Pancreas Colon
The Abdominal Cavity
Histology
1. Mucosa - innermost tunic, consists of three layers. Mucosa epithelium, stratified squamous epithelium Lamina propria, loose connective tissue. Muscularis mucosae, outer thin smooth muscle.
Histology
2. Submucosa – thick connective tissue layer containing nerves blood vessels and small glands. 3. Muscularis – inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Exceptions superior esophagus has striated muscle, and the stomach has three muscular layers. 4. Serosa or Adventitia – connective tissue.
Histology
Histology
Histology
The Oral Cavity Boundaries Anteriorly by the lips Laterally by the cheeks Superiorly by the hard and soft palates Inferiorly by the tongue
Epithelial lining: nonkeratinized stratified squamous epithelium
The Oral Cavity STRUCTURE Lips Frenula
Cheeks
FUNCTION Mastication, speech, & entrance Mucosal folds attach upper lip to alveolar process of the maxilla, and from the alveolar process of the mandible to lower lip. Mastication ,speech, & facial expression
The Oral Cavity Palate (hard & soft)
Tongue
Intrinsic muscles
Mastication, soft palate prevents food from entering nasal cavity. Movement of food in mouth for mastication, swallowing, taste, speech. Flattening and elevating tongue for swallowing.
The Oral Cavity Extrinsic muscles
Teeth Incisors Canines Premolars Molars
Protrude and retract, side to side, and shape change. Mastication and speech Cutting or nipping off food Tear and pierce Grinding and crushing Grinding and crushing
The Oral Cavity
The Oral Cavity
Salivary Glands Structure
Location
Parotid glands
Just anterior to the ear, bilaterally.
Submandibular glands
Inferior border of the posterior mandible
Sublingual glands
Immediately below the mucus membrane in the floor of the mouth
Salivary Glands
Salivary Glands Saliva
Secretion rate 1 to 1.5L/day Salivary amylase – serous saliva breaks down apart glucose molecules in starch and other polysaccharides into disaccharides. Prevents bacterial infection together with lysozyme Mucin – proteoglycan that gives saliva a lubricating quality. Stimulated primarily by the parasympathetics and less by sympathetics.
Esophagus (Gross Anatomy)
Approx. 25 cm.
Between pharynx and stomach
Located in the mediastinum anterior to vertebrae and posterior to trachea.
Esophagus (Gross Anatomy)
Esophageal hiatus – opening in diaphragm and ends at stomach.
Upper esophageal and Lower esophageal sphincter – regulate the movement of materials into and out of esophagus.
Esophagus (Histology)
Mucosa stratified squamous epithelium with mucous glands that secret a thick lubricating mucus. 4 tunics: mucosa, submucosa, muscularis, and adventitia.
Deglutition
Deglutition
Stomach (Gross Anatomy)
Enlarged segment in left superior part of abdomen.
Gastroesophageal opening (cardiac) – opening of stomach from esophagus.
Cardiac region – located around the cardiac opening where food enters from the esophagus
Stomach (Gross Anatomy)
Fundus – left and superior to the cardiac region.
Body – largest part of stomach curves to the right forming the greater and lesser curvature.
Greater curvature
lateral surface of the stomach anchors the greater omentum
Lesser Omentum
medial surface
anchors the lesser omentum
Stomach (Gross Anatomy)
Stomach (Gross Anatomy)
Pyloric region – region where body narrows
Pyloric opening - joins to the small intestine.
Pyloric sphincter – thick smooth muscle surrounding the pyloric opening.
Stomach (Gross Anatomy)
Stomach (Histology)
Serosa – visceral peritoneum, outer most layer.
Muscularis – three layers, longitudinal layer, circular layer, and an inner oblique layer.
Rugae – large folds of submucosa and mucosa, allows stomach to stretch.
Stomach (Histology)
Stomach is lined with simple columnar cells, with tube like gastric pits, which are openings for the gastric glands.
Surface mucous cells – produce mucus on the surface and lines the gastric pit.
Stomach (Histology)
Stomach (Histology) Gastric gland cells Mucous neck cells – produce mucus.
Parietal cells – produce hydrochloric acid and intrinsic factor.
Chief cells – produce pepsinogen.
Endocrine cells –produce regulatory hormones.
Stomach Secretions Chyme – food and stomach secretions mixed SECRETION
SOURCE
FUNCTION
Mucus
Surface and neck mucus cells .
Lubricates, protects
Intrinsic factor
Parietal cells in gastric glands of the pyloric region.
Binds with and makes more readily absorbed in the ilium VITAMIN B12
Hydrochloric acid Parietal cells
Pepsinogen
Chief cells
Low pH bactericidal, denature proteins, provides proper pH for pepsin.to pepsin, catalyzes Converts the cleavage of peptide bonds in proteins.
Phase of Secretion
Phase of Secretion
Phase of Secretion
Functions of Gastrointestinal Hormones Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Gastrin
Stomach & duodenum
Distention, partially digested proteins, autonomic stim., alcohol & caffeine
Increases gastric secretions
Increased gastric emptying by increasing motility and relaxing pyloric sphincter.
Functions of Gastrointestinal Hormones Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Secretin
Duodenum
Acidity of chyme
Inhibits gastric secretions, stimulates pancreatic secretions, Decreases increases the rate of gastric motility bile and increases intestinal secretions; mucus secretion
Functions of Gastrointestinal Hormones Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Cholycystokinin
Intestines
Fatty acids and other lipids
Slightly inhibits gastric secretions, stimulates pancreatic Decreases secretions, gastric motility contraction of gall bladder, relaxation of hepatopancreatic ampular sphincter.
Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Gastric Inhibitory Polypeptide Duodenum & Jejunum
Fatty acids and other lipids
Inhibits gastric secretions
Decreases gastric motility
Gastric Movements Mixing of Stomach Contents
Gentle mixing waves which are peristalsis like contractions proceed from the body toward the pyloric sphincter. 80%
Peristaltic waves occur less frequently, significantly more powerful, force chyme near the periphery of the stomach toward the pyloric sphincter. 20%
Gastric Movements Stomach Emptying
Fluids remain in the stomach approx. 1.5 to 2.5 hours, food approx. 3 to 4 hours.
Each peristaltic contraction is strong enough to force a small amount of chyme through the pyloric sphincter and into the duodenum, this is referred to as Pyloric Pump.
Gastric Movements Regulation of stomach emptying
Hormonal – Gastrin
CNS - distention of stomach wall and local reflexes
All promote increased in stomach emptying.
Small Intestines
Consists of three parts:
Duodenum Jejunum ilium
Length approx. 4.6 to 9 meters (14 to 29 feet). Site of greatest amount of digestion and absorption. 8 to 8.5 liters of water enter the small intestine per day.
Small Intestines (Duodenum)
Begins with a short superior end, which is where it exits the pylorus of the stomach, and ends in a sharp bend, where it joins the jejunum.
Major duodenal papilla & lesser duodenal papilla - two small mounds 2/3 of the down the descending part. At the major papilla the common bile duct and pancreatic duct join to form the hepatopancreatic ampular sphincter which empties into the duodenum.
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Hepatopancreatic sphincter - regulates the opening of the ampular.
Internal surface has modifications which increase surface area about 600 fold.
Circular folds - mucosa and submucosa form a series of folds.
Villi- tiny fingerlike projections of the mucosa, simple columnar epithelium, contains blood capillary network and lacteals.
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Microvilli - most of the cells of the surface of the villi have these numerous cytoplasmic projections to further increase surface area.
Brush border - the combined microvilli on the entire epithelial surface.
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Small Intestines (Duodenum) Cells
Function
Absorptive
Microvilli, produce digestive enzymes, absorb digested food
Goblet
Produce a protective mucus
Granular cells
Protect the intestinal epithelium from bacteria
Endocrine
Produce regulatory hormones
Small Intestines (Jejunum & Ileum) Similar in structure to duodenum, EXCEPT 1. 2. 3. 4.
Gradual decrease in the size of the lumen. Decrease in thickness of the intestinal wall Number of circular folds decrease Decrease in number of microvilli
Small Intestines (Jejunum & Ileum)
The duodenum and jejunum are major sites of nutrient absorption.
Lymph nodes called Peyer’s Patches are numerous in the mucosa and submucosa of the ileum.
Small Intestines (Jejunum & Ileum)
Small Intestines (Jejunum & Ileum)
Ileocecal junction – junction between the ileum and the large intestine.
Ileocecal sphincter – ring of smooth muscle.
Ileocecal valve – one way flow.
Small Intestines (Jejunum & Ileum)
Duodenal glands, intestinal glands, and goblet cells secrete large amounts of mucus.
Mucus provides most of the wall with protection from the acidic chyme, and digestive enzymes.
Small Intestines (Jejunum & Ileum)
Secretin & Cholycystokinin are released from the intestinal mucosa and stimulate pancreatic and hepatic secretions.
Enzymes of the intestinal mucosa are bound to the membranes of the absorptive cell microvilli
Small Intestines (Jejunum & Ileum)
1.
Disaccharidase – breaks down disaccharides to monosaccharides.
3.
Peptidase – hydrolyze the peptide bonds of amino acid chains.
5.
Nucleases – break down nucleic acids.
Movements of the Small Intestine
Mixing and propulsion of chyme are the primary mechanical events.
Mechanical movement occurs due to segmental or peristaltic contractions of the smooth muscle wall, only propagated small distances.
Movements of the Small Intestine
Segmental contractions – mix intestinal contents.
Peristaltic contractions – propel the intestinal contents along the entire length of the intestine.
Wave of contraction can begin in the stomach.
Rate of movement 1cm/min
Movements of the Small Intestine Regulation 1.
Distention of intestinal wall
3.
Hypertonic or hypotonic solutions
5.
pH of contents
Large Intestine
Extends from the ileocecal junction to the anus. Consists of:
Cecum Colon Rectum Anal canal
Large Intestine
Large Intestine (Cecum)
Proximal end of the large intestine.
Extends approx. 6cm. Inferiorly past the ileocecal junction to form a blind sac.
Vermis Appendix – a small blind tube extending approx. 9cm from the blind sac. Contains many lymph nodes.
Large Intestine (Cecum)
Large Intestine (Colon)
Consists of four parts:
Ascending colon Transverse colon Descending colon Sigmoid colon
Large Intestine (Colon) The ascending colon travels up the right side of the abdominal cavity and turns medially (the right colic flexure or hepatic flexure) and travels across the abdominal cavity as the transverse colon.
Large Intestine (Colon)
At the spleen the transverse colon turns downward (the left colic flexure or splenic flexure) and descends on the left side as the descending colon
Large Intestine (Colon)
Inferiorly, the decending colon enters the pelvis where it becomes the sigmoid colon
Large Intestine (Colon)
The last segment of the is the anal canal which begins where the rectum penetrates the muscles of the pelvic floor
Large Intestine (Colon)
The external opening is the anus. Controlling this exit are the internal anal sphincter (smooth muscle and involuntary) and the external anal sphincter (skeletal muscle and voluntary (to a point)).
Large Intestine (Colon)
The circular muscular layer of the colon is complete, but the longitudinal layer of muscle is incomplete
The mucosal lining consists of simple columnar epithelium.
Lining is not folded or villi, but has numerous straight tubules glands called crypts.
Large Intestine (Colon)
Crypts are similar to the glands of the small intestine, with absorptive, goblet, and granular cells.
The major difference is goblet cells are the predominate cell type while the others decrease in number.
Large Intestine (Rectum)
Straight muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal
Simple columnar epithelium.
The muscular tunic is relatively thick compared to the rest of the digestive tract.
Large Intestine (Anal Canal)
Last 2 to 3cm of the digestive tract.
Begins at the inferior end of the rectum an ends at the anus.
The smooth muscle layer is even thicker than that of the rectum.
Large Intestine (Anal Canal)
Internal anal sphincter – superior end of anal canal.
External anal sphincter – skeletal muscle, inferior end of the canal.
Simple columnar to stratified squamous from superior to inferior anal canal.
Movement of the Large Intestines
Major secretory product, mucus.
Mucus lubricates and helps fecal matter to stick together
Peristaltic waves are largely responsible for moving chyme along the ascending colon.
Movement of the Large Intestines
Mass Movements – several strong contractions in the transverse and descending colon. This large contraction propels the colon contents a considerable distance toward the anus.
Movement of the Large Intestines
Defecation Reflex – local reflex distention of the rectal wall by feces, weak contractions of the rectum and relaxation of internal and external anal sphincters. Parasympathetic reflexes cause strong contractions of the rectum, normally responsible for most of defecation.
The Liver
The Liver
Largest gland in the body
Occupies most of the right hypochondriac and epigastric regions. Inferior to diaphragm, protected by ribs.
The Liver
Four lobes:
Right lobe – largest Left lobe Caudate lobe – posterior Quadrate lobe – inferior to left lobe
The Liver
The Liver
The Liver
Falciform Ligament separates right and left lobes, suspends liver the liver from the diaphragm.
Porta hepatis – entrance for the hepatic artery and hepatic portal vein, and common hepatic duct.
The Liver
Bile leaves the liver through several bile ducts that form the left and right hepatic ducts which then combine to yield the common hepatic duct
The common hepatic duct will fuse with the cystic duct from the gallbladder to form the common bile duct which empties into the duodenum
The Liver
The Liver (Histology)
Each functional unit is called a liver lobule.
Roughly hexagonal in shape.
The Liver (Histology)
Hepatocytes – liver cells, plates of hepatocytes are arranged around a central vein.
The Liver (Histology)
Portal triad – located at each of the six corners, three basic structures are always present.
Hepatic artery Hepatic portal vein Bile duct
The Liver (Histology)
The Liver (Function)
Detoxification Production of bile
Fat emulsifier Yellow green alkaline solution Contains
Bile salts, Bile pigments, Cholesterol neutral fats , Phospholipids, Electrolytes
The Liver
The Gall Bladder
Storage of bile Concentration of bile. Thin walled, green, muscular sac. Located in a shallow fossae on the ventral surface of the liver. Secretes bile by muscular wall contracting, bile travels out the cystic duct and then flows to the common bile duct.
The Gall Bladder (Biliary Calculi)
The Pancreas
Lies deep to the stomach. Produces a broad spectrum of digestive enzymes.
The Pancreas
Has both exocrine and endocrine functions Pancreatic juice- exocrine product, drains via the Main pancreatic duct. Acini – small clusters of secretory cells.
Secretions
Pancreatic juice, Trypsinogen, Carboxypeptidase, Chymotrypsin, Amylases, Lipases, Nucleases
The Pancreas
The Pancreas
Insulin and glucagon is secreted on its endocrine portion via patches of hormone-secreting cells known as Islets of Langerhans Insulin and glucagon act in antagonistic fashion
The Pancreas
End
Overview There are 2 major groups of organs in the digestive system: Alimentary Canal - Organs thru which food actually passes (in order they are the: oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine). Accessory Organs - They assist in digestion, but no food actually passes through them. Includes the teeth, tongue, salivary glands, pancreas, liver, and gallbladder.
Overview
Functions
Ingestion Mastication Propulsion Mixing Secretion Digestion Absorption Elimination
The Abdominal Cavity
The majority of digestive organs are located Peritoneum
Visceral peritoneum Parietal peritoneum Peritoneal cavity Mesenteries
Retroperitonium Duodenum
Pancreas Colon
The Abdominal Cavity
Histology
1. Mucosa - innermost tunic, consists of three layers. Mucosa epithelium, stratified squamous epithelium Lamina propria, loose connective tissue. Muscularis mucosae, outer thin smooth muscle.
Histology
2. Submucosa – thick connective tissue layer containing nerves blood vessels and small glands. 3. Muscularis – inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Exceptions superior esophagus has striated muscle, and the stomach has three muscular layers. 4. Serosa or Adventitia – connective tissue.
Histology
Histology
Histology
The Oral Cavity Boundaries Anteriorly by the lips Laterally by the cheeks Superiorly by the hard and soft palates Inferiorly by the tongue
Epithelial lining: nonkeratinized stratified squamous epithelium
The Oral Cavity STRUCTURE Lips Frenula
Cheeks
FUNCTION Mastication, speech, & entrance Mucosal folds attach upper lip to alveolar process of the maxilla, and from the alveolar process of the mandible to lower lip. Mastication ,speech, & facial expression
The Oral Cavity Palate (hard & soft)
Tongue
Intrinsic muscles
Mastication, soft palate prevents food from entering nasal cavity. Movement of food in mouth for mastication, swallowing, taste, speech. Flattening and elevating tongue for swallowing.
The Oral Cavity Extrinsic muscles
Teeth Incisors Canines Premolars Molars
Protrude and retract, side to side, and shape change. Mastication and speech Cutting or nipping off food Tear and pierce Grinding and crushing Grinding and crushing
The Oral Cavity
The Oral Cavity
Salivary Glands Structure
Location
Parotid glands
Just anterior to the ear, bilaterally.
Submandibular glands
Inferior border of the posterior mandible
Sublingual glands
Immediately below the mucus membrane in the floor of the mouth
Salivary Glands
Salivary Glands Saliva
Secretion rate 1 to 1.5L/day Salivary amylase – serous saliva breaks down apart glucose molecules in starch and other polysaccharides into disaccharides. Prevents bacterial infection together with lysozyme Mucin – proteoglycan that gives saliva a lubricating quality. Stimulated primarily by the parasympathetics and less by sympathetics.
Esophagus (Gross Anatomy)
Approx. 25 cm.
Between pharynx and stomach
Located in the mediastinum anterior to vertebrae and posterior to trachea.
Esophagus (Gross Anatomy)
Esophageal hiatus – opening in diaphragm and ends at stomach.
Upper esophageal and Lower esophageal sphincter – regulate the movement of materials into and out of esophagus.
Esophagus (Histology)
Mucosa stratified squamous epithelium with mucous glands that secret a thick lubricating mucus. 4 tunics: mucosa, submucosa, muscularis, and adventitia.
Deglutition
Deglutition
Stomach (Gross Anatomy)
Enlarged segment in left superior part of abdomen.
Gastroesophageal opening (cardiac) – opening of stomach from esophagus.
Cardiac region – located around the cardiac opening where food enters from the esophagus
Stomach (Gross Anatomy)
Fundus – left and superior to the cardiac region.
Body – largest part of stomach curves to the right forming the greater and lesser curvature.
Greater curvature
lateral surface of the stomach anchors the greater omentum
Lesser Omentum
medial surface
anchors the lesser omentum
Stomach (Gross Anatomy)
Stomach (Gross Anatomy)
Pyloric region – region where body narrows
Pyloric opening - joins to the small intestine.
Pyloric sphincter – thick smooth muscle surrounding the pyloric opening.
Stomach (Gross Anatomy)
Stomach (Histology)
Serosa – visceral peritoneum, outer most layer.
Muscularis – three layers, longitudinal layer, circular layer, and an inner oblique layer.
Rugae – large folds of submucosa and mucosa, allows stomach to stretch.
Stomach (Histology)
Stomach is lined with simple columnar cells, with tube like gastric pits, which are openings for the gastric glands.
Surface mucous cells – produce mucus on the surface and lines the gastric pit.
Stomach (Histology)
Stomach (Histology) Gastric gland cells Mucous neck cells – produce mucus.
Parietal cells – produce hydrochloric acid and intrinsic factor.
Chief cells – produce pepsinogen.
Endocrine cells –produce regulatory hormones.
Stomach Secretions Chyme – food and stomach secretions mixed SECRETION
SOURCE
FUNCTION
Mucus
Surface and neck mucus cells .
Lubricates, protects
Intrinsic factor
Parietal cells in gastric glands of the pyloric region.
Binds with and makes more readily absorbed in the ilium VITAMIN B12
Hydrochloric acid Parietal cells
Pepsinogen
Chief cells
Low pH bactericidal, denature proteins, provides proper pH for pepsin.to pepsin, catalyzes Converts the cleavage of peptide bonds in proteins.
Phase of Secretion
Phase of Secretion
Phase of Secretion
Functions of Gastrointestinal Hormones Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Gastrin
Stomach & duodenum
Distention, partially digested proteins, autonomic stim., alcohol & caffeine
Increases gastric secretions
Increased gastric emptying by increasing motility and relaxing pyloric sphincter.
Functions of Gastrointestinal Hormones Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Secretin
Duodenum
Acidity of chyme
Inhibits gastric secretions, stimulates pancreatic secretions, Decreases increases the rate of gastric motility bile and increases intestinal secretions; mucus secretion
Functions of Gastrointestinal Hormones Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Cholycystokinin
Intestines
Fatty acids and other lipids
Slightly inhibits gastric secretions, stimulates pancreatic Decreases secretions, gastric motility contraction of gall bladder, relaxation of hepatopancreatic ampular sphincter.
Site of Production
Method of Stimulation
Secretory Effects
Motility Effects
Gastric Inhibitory Polypeptide Duodenum & Jejunum
Fatty acids and other lipids
Inhibits gastric secretions
Decreases gastric motility
Gastric Movements Mixing of Stomach Contents
Gentle mixing waves which are peristalsis like contractions proceed from the body toward the pyloric sphincter. 80%
Peristaltic waves occur less frequently, significantly more powerful, force chyme near the periphery of the stomach toward the pyloric sphincter. 20%
Gastric Movements Stomach Emptying
Fluids remain in the stomach approx. 1.5 to 2.5 hours, food approx. 3 to 4 hours.
Each peristaltic contraction is strong enough to force a small amount of chyme through the pyloric sphincter and into the duodenum, this is referred to as Pyloric Pump.
Gastric Movements Regulation of stomach emptying
Hormonal – Gastrin
CNS - distention of stomach wall and local reflexes
All promote increased in stomach emptying.
Small Intestines
Consists of three parts:
Duodenum Jejunum ilium
Length approx. 4.6 to 9 meters (14 to 29 feet). Site of greatest amount of digestion and absorption. 8 to 8.5 liters of water enter the small intestine per day.
Small Intestines (Duodenum)
Begins with a short superior end, which is where it exits the pylorus of the stomach, and ends in a sharp bend, where it joins the jejunum.
Major duodenal papilla & lesser duodenal papilla - two small mounds 2/3 of the down the descending part. At the major papilla the common bile duct and pancreatic duct join to form the hepatopancreatic ampular sphincter which empties into the duodenum.
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Hepatopancreatic sphincter - regulates the opening of the ampular.
Internal surface has modifications which increase surface area about 600 fold.
Circular folds - mucosa and submucosa form a series of folds.
Villi- tiny fingerlike projections of the mucosa, simple columnar epithelium, contains blood capillary network and lacteals.
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Microvilli - most of the cells of the surface of the villi have these numerous cytoplasmic projections to further increase surface area.
Brush border - the combined microvilli on the entire epithelial surface.
Small Intestines (Duodenum)
Small Intestines (Duodenum)
Small Intestines (Duodenum) Cells
Function
Absorptive
Microvilli, produce digestive enzymes, absorb digested food
Goblet
Produce a protective mucus
Granular cells
Protect the intestinal epithelium from bacteria
Endocrine
Produce regulatory hormones
Small Intestines (Jejunum & Ileum) Similar in structure to duodenum, EXCEPT 1. 2. 3. 4.
Gradual decrease in the size of the lumen. Decrease in thickness of the intestinal wall Number of circular folds decrease Decrease in number of microvilli
Small Intestines (Jejunum & Ileum)
The duodenum and jejunum are major sites of nutrient absorption.
Lymph nodes called Peyer’s Patches are numerous in the mucosa and submucosa of the ileum.
Small Intestines (Jejunum & Ileum)
Small Intestines (Jejunum & Ileum)
Ileocecal junction – junction between the ileum and the large intestine.
Ileocecal sphincter – ring of smooth muscle.
Ileocecal valve – one way flow.
Small Intestines (Jejunum & Ileum)
Duodenal glands, intestinal glands, and goblet cells secrete large amounts of mucus.
Mucus provides most of the wall with protection from the acidic chyme, and digestive enzymes.
Small Intestines (Jejunum & Ileum)
Secretin & Cholycystokinin are released from the intestinal mucosa and stimulate pancreatic and hepatic secretions.
Enzymes of the intestinal mucosa are bound to the membranes of the absorptive cell microvilli
Small Intestines (Jejunum & Ileum)
1.
Disaccharidase – breaks down disaccharides to monosaccharides.
3.
Peptidase – hydrolyze the peptide bonds of amino acid chains.
5.
Nucleases – break down nucleic acids.
Movements of the Small Intestine
Mixing and propulsion of chyme are the primary mechanical events.
Mechanical movement occurs due to segmental or peristaltic contractions of the smooth muscle wall, only propagated small distances.
Movements of the Small Intestine
Segmental contractions – mix intestinal contents.
Peristaltic contractions – propel the intestinal contents along the entire length of the intestine.
Wave of contraction can begin in the stomach.
Rate of movement 1cm/min
Movements of the Small Intestine Regulation 1.
Distention of intestinal wall
3.
Hypertonic or hypotonic solutions
5.
pH of contents
Large Intestine
Extends from the ileocecal junction to the anus. Consists of:
Cecum Colon Rectum Anal canal
Large Intestine
Large Intestine (Cecum)
Proximal end of the large intestine.
Extends approx. 6cm. Inferiorly past the ileocecal junction to form a blind sac.
Vermis Appendix – a small blind tube extending approx. 9cm from the blind sac. Contains many lymph nodes.
Large Intestine (Cecum)
Large Intestine (Colon)
Consists of four parts:
Ascending colon Transverse colon Descending colon Sigmoid colon
Large Intestine (Colon) The ascending colon travels up the right side of the abdominal cavity and turns medially (the right colic flexure or hepatic flexure) and travels across the abdominal cavity as the transverse colon.
Large Intestine (Colon)
At the spleen the transverse colon turns downward (the left colic flexure or splenic flexure) and descends on the left side as the descending colon
Large Intestine (Colon)
Inferiorly, the decending colon enters the pelvis where it becomes the sigmoid colon
Large Intestine (Colon)
The last segment of the is the anal canal which begins where the rectum penetrates the muscles of the pelvic floor
Large Intestine (Colon)
The external opening is the anus. Controlling this exit are the internal anal sphincter (smooth muscle and involuntary) and the external anal sphincter (skeletal muscle and voluntary (to a point)).
Large Intestine (Colon)
The circular muscular layer of the colon is complete, but the longitudinal layer of muscle is incomplete
The mucosal lining consists of simple columnar epithelium.
Lining is not folded or villi, but has numerous straight tubules glands called crypts.
Large Intestine (Colon)
Crypts are similar to the glands of the small intestine, with absorptive, goblet, and granular cells.
The major difference is goblet cells are the predominate cell type while the others decrease in number.
Large Intestine (Rectum)
Straight muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal
Simple columnar epithelium.
The muscular tunic is relatively thick compared to the rest of the digestive tract.
Large Intestine (Anal Canal)
Last 2 to 3cm of the digestive tract.
Begins at the inferior end of the rectum an ends at the anus.
The smooth muscle layer is even thicker than that of the rectum.
Large Intestine (Anal Canal)
Internal anal sphincter – superior end of anal canal.
External anal sphincter – skeletal muscle, inferior end of the canal.
Simple columnar to stratified squamous from superior to inferior anal canal.
Movement of the Large Intestines
Major secretory product, mucus.
Mucus lubricates and helps fecal matter to stick together
Peristaltic waves are largely responsible for moving chyme along the ascending colon.
Movement of the Large Intestines
Mass Movements – several strong contractions in the transverse and descending colon. This large contraction propels the colon contents a considerable distance toward the anus.
Movement of the Large Intestines
Defecation Reflex – local reflex distention of the rectal wall by feces, weak contractions of the rectum and relaxation of internal and external anal sphincters. Parasympathetic reflexes cause strong contractions of the rectum, normally responsible for most of defecation.
The Liver
The Liver
Largest gland in the body
Occupies most of the right hypochondriac and epigastric regions. Inferior to diaphragm, protected by ribs.
The Liver
Four lobes:
Right lobe – largest Left lobe Caudate lobe – posterior Quadrate lobe – inferior to left lobe
The Liver
The Liver
The Liver
Falciform Ligament separates right and left lobes, suspends liver the liver from the diaphragm.
Porta hepatis – entrance for the hepatic artery and hepatic portal vein, and common hepatic duct.
The Liver
Bile leaves the liver through several bile ducts that form the left and right hepatic ducts which then combine to yield the common hepatic duct
The common hepatic duct will fuse with the cystic duct from the gallbladder to form the common bile duct which empties into the duodenum
The Liver
The Liver (Histology)
Each functional unit is called a liver lobule.
Roughly hexagonal in shape.
The Liver (Histology)
Hepatocytes – liver cells, plates of hepatocytes are arranged around a central vein.
The Liver (Histology)
Portal triad – located at each of the six corners, three basic structures are always present.
Hepatic artery Hepatic portal vein Bile duct
The Liver (Histology)
The Liver (Function)
Detoxification Production of bile
Fat emulsifier Yellow green alkaline solution Contains
Bile salts, Bile pigments, Cholesterol neutral fats , Phospholipids, Electrolytes
The Liver
The Gall Bladder
Storage of bile Concentration of bile. Thin walled, green, muscular sac. Located in a shallow fossae on the ventral surface of the liver. Secretes bile by muscular wall contracting, bile travels out the cystic duct and then flows to the common bile duct.
The Gall Bladder (Biliary Calculi)
The Pancreas
Lies deep to the stomach. Produces a broad spectrum of digestive enzymes.
The Pancreas
Has both exocrine and endocrine functions Pancreatic juice- exocrine product, drains via the Main pancreatic duct. Acini – small clusters of secretory cells.
Secretions
Pancreatic juice, Trypsinogen, Carboxypeptidase, Chymotrypsin, Amylases, Lipases, Nucleases
The Pancreas
The Pancreas
Insulin and glucagon is secreted on its endocrine portion via patches of hormone-secreting cells known as Islets of Langerhans Insulin and glucagon act in antagonistic fashion
The Pancreas
End
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