DMH-A Flashcards
Anterior abdominal wall muscles:
innervation
external oblique
internal oblique
rectus abdominus
transverse abdominus
innervated by T7-T11 intercostal nerves, subcostal, iliohypogastric, and ilioinguinal nerve.
Posterior abdominal wall muscles:
innervation
Iliacus - femoral nerve
psoas major - lumar ventral rami
quadratus lumborum - T12-L3
What arteries supply the anterior abdominal wall?
superior and inferior epigastric arteries
(branches of the internal thoracic and external iliac arteries; supply the rectus abdominus).
The deep circumflex iliac artery, superficial circumflex iliac artery, and the superficial epigastric artery also supply the anterior abdominal wall.
What arteries supply the posterior abdominal wall and diaphragm?
branches off of the abdominal aorta. The iliolumbar artery, which is a branch of the internal iliac artery, moves superiorly and splits to form the iliac and lumbar branches.
innervation of posterior abdominal muscles
The posterior abdominal wall is innervated by lumbar ventral rami (direct muscular branches)
femoral nerve (iliopsoas)
innervation of anterior abdominal muscles
T7 to T11 intercostal nerves and subcostal nerves (the four main muscles).
All muscles except rectus abdominus are also innervated by the iliohypogastric nerve and ilioinguinal nerve.
Cutaneous innervation is supplied by the iliohypogastric (hypogastric region), ilioinguinal (scrotum or labium majus), genitofemoral (cremaster muscle, scrotum), and by anterior and lateral cutaneous branches of the intercostal nerves (mostly terminal branches of the lumbar plexus).
subcostal nerve innervates______
terminal branches of lumbar plexus
The subcostal nerve is the ventral ramus of T12
innervates the the anterior abdominal muscles as well as some cutanous innervation of the abdomen.
iliohypogastric nerve innervates______
innervates the anterior abdominal muscles and the suprapubic area.
the ilioinguinal nerve innervates_____
ilioinguinal nerve innervates the anterior abdominal muscles and the inguinal area.
the genitofemoral nerve innervates the_____
the inguinal area.
position, input/output of abdominal sympathetic chain
The abdominal sympathetic chain lies between the lumbar vertebral bodies and the psoas major muscle. The upper chain receives presynaptic fibers from the spinal cord via white rami communicanes, and gray rami communicantes along the chain deliver postsynaptic fibers to the ventral rami of the subcostal and lumbar plexus nerves. Some presynaptic fibers arise as lumbar splanchnic nerves, and will synapse in ganglion near the pelvic viscera they innervate.
position, input/output of aorta
The aorta rests on vertebral bodies T12–L4, at which point it splits into the common iliac arteries. It enters the abdomen through the aortic hiatus at the level of T12. The lumbar arteries are branches off of the aorta posteriorly
position, input/output of Inferior Vena Cava
The inferior vena cava receives blood from the lumbar and iliolumbar veins. It begins at L5 when the right and left common iliac veins converge. It ascends between the right psoas major and the aorta and exits through the caval opening in the diaphragm at the level of T8.
Relate the structure of the rectus sheath to the derivation of each layer
what is the arcuate line
components of anterior and posterior; above arcuate line
Anteriorly, the rectus sheath is continuous. Posteriorly, the rectus sheath ends about midway between the pubic symphysis and the umbilicus (the arcuate line).
Anteriorly, above the arcuate line, the sheath has components from the external oblique and the internal oblique muscles. Below the arcuate line, the sheath has components from the external oblique, internal oblique, and transversus abdominus,
Posteriorly, above the arcuate line, the sheath has components from the internal oblique and the transversus abdominus muscles. Below the arcuate line, there is no sheath.
Characterize the location and structure of the inguinal canal including its boundaries and contents and compare based on gender
-passageway between the scrotum/labia majora and the abdominal cavity.
It is bounded by the inguinal ligament, the lacunar ligament, the pectineal ligament, and the conjoint ligament. The canal is bounded by the internal ring and the external ring (deep and superficial). It is surrounded by fascia and contains the spermatic cord (this structure passes anterior (over) the inguinal ligament), which contains blood supply, muscle, the vas deferens, ilioinguinal and genitofemoral nerves, and lymphatics. The scrotal ligament attaches the testes to the scrotum and pulls them down during development (from the abdomen).
In females, the inguinal canal contains only the round ligament, which attaches to the labia majora, and the ilioinguinal nerve.
Relate the layers of the abdominal wall to the layers of the spermatic cord, testes, and scrotum
As the testes descend, they must pass through the layers of the abdominal wall; these include the transversalis fascia, the internal oblique muscle, the external oblique fascia, Scarpa’s fascia (membranous), Camper’s fascia (fat), and the skin (no transversus abdominus because the muscle is not continuous in the area of the inguinal canal).
The skin correlates to the scrotum.
The superficial fascia (Scarpa’s fascia) becomes the Dartos muscle.
The external oblique fascia becomes the external spermadic fascia.
The internal oblique muscle becomes the cremaster muscle.
The transversalis fascia becomes the internal spermadic fascia.
The peritoneum also is pulled in with the testes, forming the tunica vaginalis (visceral and parietal layers).
Compare and contrast the anatomical basis of direct and indirect inguinal hernias and explain their likelihood of incidence in adults vs. children and males vs. females
Direct inguinal hernias: bulge directly through the abdominal wall (medial to the inguinal canal and inferior epigastric artery). More common in adult or elderly males.
Indirect inguinal hernias: do not bulge directly through the abdominal wall. Instead, they bulge through the deep inguinal ring into the scrotum or labia majora, lateral to the inferior epigastric artery. More common in males.
Femoral hernia
where do they bulge through?
most common in who?
Femoral hernia: bulge through the femoral canal into the thigh. More common in adult to elderly females. (Most medial compartment of femoral sheath containing fat and lymphatics.)
Identify the borders of the foregut, midgut and hindgut
head folding –> foregut (superior to anterior intestinal portal)
tail folding –> hindgut (inferior to posterior intestinal portal)
midgut in b/w remains open to yolk sac
respiratory diverticulum turns into what adult structures?
The respiratory diverticulum branches off of the foregut to divide the esophagus and trachea, and will develop into the airways of the lung.
What is formed by the diverticula of the foregut
Glands of the pharynx, respiratory tract, liver, gall bladder, and pancreas
Differentiate the rectum from the urogenital sinus
The rectum is the distal portion of the GI tube. The urogenital sinus is the distal portion of the urinary system and will eventually form the urethra
Identify the regions of the embryonic gut supplied by:
a) the celiac trunk
b) the superior mesenteric artery
c) the inferior mesenteric artery
The celiac trunk supplies the structures of the foregut (from distal esophagus to the upper duodenum).
The superior mesenteric artery supplies the structures of the midgut (from the distal duodenum to the proximal transverse colon).
The inferior mesenteric artery supplies the structures of the hindgut (from the distal transverse colon to the superior part of the anal canal).
Summarize the molecular regulation of gut, liver, and pancreas development
In the midgut and hindgut, sonic hedgehog (Shh) is secreted by the embryonic endoderm, which induces HOX expression in the mesoderm. In general, differentiation is regulated by reciprocal inductions between the endoderm and mesoderm.
The entire gut has the capability to differentiate into liver; however, surrounding tissues secrete factors that repress this growth. However, the cardiac mesoderm secretes fibroblast growth factors (FGFs) and the septum transversum secretes bone morphogenetic protein (BMP) which block the inhibiting factors, allowing for the endoderm to differentiate into hepatocytes and biliary cells. The sinusoids and stroma are derived from cells of the septum transversum (mesoderm).
The notochord secretes FGF and activin, which represses Sonic Hedgehog expression in the neighboring endoderm, allowing for activation of pancreas-specific transcription factors and genes (the homeobox 1 PDX gene). This allows for the dorsal pancreatic bud to form; how the ventral pancreatic bud is induced is still not completely understood.
Distinguish between parietal and visceral peritoneum and describe the differences in their innervation
The parietal peritoneum is associated with the body wall. It is innervated by somatic nerves that supply the body wall and muscles. Thus, pain to the parietal peritoneum is felt as sharp, localized pain.
The visceral peritoneum is associated with the abdominal organs. It is innervated by visceral nerves that supply the underlying organ. Thus, pain to the visceral peritoneum is felt as dull, diffuse pain.
Compare the major divisions of the peritoneal cavity: greater sac, lesser sac, omental (epiploic) foramen
The greater peritoneal sac is the space entered after opening the anterior abdominal wall.
The omental bursa, or lesser sac, is the space that lies behind the stomach as a result of the clockwise rotation of the stomach.
The omental foramen is the opening from the greater sac into the lesser sac (it passes underneath the lesser omentum above the duodenum).
Name the structures of the abdomen that are peritoneal and retroperitoneal
Peritoneal organs are encased in and suspended by peritoneum. Organs include the stomach, liver, small intestine, transverse colon, sigmoid colon, and spleen.
The retroperitoneal organs have peritoneum only on their anteror surface. Organs include the duodenum, pancreas, ascending and descending colon, and the kidneys.
Identify the peritoneal membranes that suspend the abdominal organs and identify their embryological origins
Dorsal mesentery (embryologic structure) forms the following adult structures:
Foregut (The greater omentum, which suspends the transverse colon, spleen, and diaphragm from the stomach (gastrosplenic ligament, gastrocolic ligament, gastrophrenic ligament, splenorenal ligament)
Midgut: The suspensory ligament of the duodenum, the mesentery, and the transverse mesocolon
Hindgut: The transverse mesocolon and sigmoid mesocolon
Ventral Mesentary (embryologic structure) forms the following adult structures:
The lesser omentum, which extends from the stomach to the liver. (hepatogastric ligament, hepatoduodenal ligament)
The falciform ligament, coronary ligament, and left and right triangular ligaments of the liver
Relate stomach rotation to the position of the vagus nerve
The stomach rotates clockwise. As a result, the left vagal trunk becomes the anterior vagal trunk, and the right vagal trunk becomes the posterior vagal trunk
Regarding stomach and intestinal rotation:
a) describe the process
b) indicate when they rotate
c) discuss what forms the axis of rotation
The stomach rotates along the long axis (craniocaudal) in a clockwise direction at about the 4th-5th week. Thus, the left vagal trunk becomes the anterior vagal trunk, and the right vagal trunk becomes the posterior vagal trunk.
- The rotation of the stomach drags the dorsal mesentery and will eventually form the greater omentum.
In addition, the caudal (pyloric) end of the stomach rotates cranially at about the 8th week, tipping the stomach into its characteristic backwards “C” shape.
The intestines rotate along the axis of the vitelline duct (umbilical cord); at the 6th week, the rapid growth of the intestines causes a physiologic herniation into the umbilical cord. The cranial limb of the loop will form the jejunum and ileum; the caudal limb of the loop will form the the ascending colon and proximal part of the transverse colon. As the loop returns to the abdominal cavity, there is a total of 270 degrees of counterclockwise rotation (when looking at the embryo). The first 90 degrees occurs during week 6 and herniation; during weeks 10–12, the rest of the rotation is seen with the return. This causes the transverse colon to be anterior to the duodenum.
types of teeth
components of the adult tooth
The adult tooth contains the crown, which is above the gums, and the root, which is below the gums. The pulp cavity contains the nerves and blood supply of the tooth and is surrounded by dentin, a calcified living tissue that is maintained (and secreted) by odontoblast cells. Cementum holds the root of the tooth to the periodontal ligament and is secreted by cementocytes. The crown of the tooth is covered with enamel.
Enamel is secreted by an ameloblast cell layer during tooth development. Once the tooth erupts, the ameloblasts are lost, and enamel cannot be regenerated. If enamel is lost, it must be repaired by a dentist using artificial mediums.
A dead tooth appears grey and becomes brittle. On the other hand, cavities are patchy areas where enamel is lost, showing the underlying dentin.
Describe the structure of the tongue including lingual papillae and taste buds and explain the contributions of the tongue to normal functioning of the oral cavity
Lingual papillae
- Filiform papillae are located all over the tongue, and are keratinized projections of the epithelial layer that increase friction.
- Interspersed all over the tongue are fungiform papillae, which contain taste buds.
- Circumvallate papillae are located at the junction of the anterior 2/3 of the tongue and the posterior third of the tongue. They lie in a posterior V and are large projections, surrounded by a moat-like sulcus. Taste buds are located in the epithelium along both sides of the sulcus.
- Foliate papillae are elongated taste bud-bearing ridges along the lateral aspects of the tongue
Taste buds are collections of cells that converge on a taste pore that opens to the surface of the tongue.
The posterior aspect of the tongue contains the lingual tonsils (which will be described in #4).
The tongue contributes to speaking, tasting, chewing, forming and swallowing a food bolus, and immune protection.
Describe the location, structure and function of lingual and palatine tonsils
Lingual tonsils are located on the posterior third of the tongue. Lingual tonsils consist of a crypt of invaginated stratified squamous epithelium, associated with about half a dozen lymphoid follicles.
Palatine tonsils are located close to the lingual tonsils, on the lateral walls of the oropharynx. Palatine tonsils have a similar structure as lingual tonsils, but they are larger and have multiple deep crypts.
The tonsils serve in immune surveillance, particularly the generation of IgA antibodies (and IgM during first exposure) to transport into the saliva in response to antigens.
Langerhans cells faciliate this by sampling antigens in the saliva, then present them to lymphocytes in the follicle. B cells will then proliferate and differentiate (affinity maturation).
Describe the location and anatomical relationships of the major and minor salivary glands (review from head and neck dissection), as well as the major components of saliva and their functions.
The minor salivary glands are present throughout the oral mucosa. They provide a basal secretion to keep the mouth moist.
Saliva is composed of:
- Digestive enzymes, i.e. amylase, to break down starch
- Mucin and fluid for lubrication of food and to dissolve substances –Immunoglobulins (IgA and IgM) for immune defense
- Lysozyme, the antibacterial enzyme
-Proteins that form a thin protective layer on the teeth (a pellicle)
Serous cells
these cells secrete the enzymes amylase and lysozyme. They also conduct transepithelial transport of immunoglobulins. Pyramid-shaped epithelial cells with basophilic cytoplasm.
Mucous cells
cuboidal to columnar cells with foamy cytoplasm. They secrete mucous.
Myoepithelial cells
they contract to help expel the contents of the acini. Spindle or stellate cells within the basal lamina.
Intercalated duct cells
low cuboidal epithelial cells, lightly staining. Transport secretions without modification
Striated duct cells
high cuboidal to columnar epithelial cells; appear striated on EM due to infolding of basal plasma membrane to facilitate active ion transport. These ducts modify the ion and fluid composition of saliva.
Excretory duct cells
cuboidal to columnar epithelial cells; form stratified epithelium in distal regions. The epithelium changes to stratified squamous near the opening into the oral cavity. Delivers secreted saliva to the oral cavity.
Epithelial cells of salivary glands
Explain the mechanism whereby antibodies are transported from connective tissues into saliva.
Serous cells conduct transepithelial transport of IgM and IgA antibodies.
The antibodies bind the the poly-Ig receptor o the basolateral surface of serous cells. The antibody is endocytosed, transported across the cell, and exocytosed at the apical surface to become a component of saliva.
Filiform papillae: improve friction
Circumvallate papilla
Fungiform paillae
Lingual tonsils histology
What cells secrete enamel?
Ameloblast cells
Function of striated ducts
modify the ionic composition of saliva
*tons of mitochondria for ion transport
Salivary gland - stroma
CT stroma divides the glands into lobes and lobules and carries excretory ducts, vasculature and nerves
Where does the esophagus enter the abdomen
what are 3 potential sites of lodged objects
blood supply/venous drainage
T10
arch of the aorta, left main bronchus, as it passed thru diaphragm
supplied by branches of thoracic aorta and esophageal branch of left gastric artery
Venous drainage of the thoracic esophagus and in abdomen
azygos, hemiazygos, and accessory hemiazygos veins, as well as through intercostal veins.
In the abdomen, esophageal venous drainage occurs into the left gastric vein into the portal vein, then into the hepatic portal system.
What happens w/ portal HTN?
Due to esophageal anastomoses between the superior and inferior esophageal veins, there is a connection between the portal system and the systemic venous circulation. In portal hypertension, these esophageal veins can bulge with blood, allowing more blood to flow past the liver. They can bleed severely.
left gastric artery
The left gastric artery arises from the celiac trunk and supplies the cardial region and down along the lesser curvature
splenic artery branches to…?
The splenic artery arises from the celiac trunk, travels posterior to the stomach, then gives off the left gastroomental branch, which supplies the greater curvature, and short gastric arteries to supply the fundus
common hepatic artery branches….?
The common hepatic artery arises from the celiac trunk, and then splits to form the proper hepatic artery and gastroduodenal artery. The right gastric artery is a branch of the proper hepatic, and ascends up the lesser curvature of the stomach. The right gastroomental artery branches from the gastroduodenal artery and ascends up the greater curvature of the stomach.
Venous drainage of the stomach
Venous drainage of the stomach mostly parallels the arteries. The right and left gastric veins drain into the portal vein. The short gastric and left gastroomental veins empty into the splenic vein. The right gastroomental vein drains into the superior mesenteric vein. The splenic and superior mesenteric vein converge to form the hepatic portal vein.
Diagram the orientation of the duodenum and the placement of the major duodenal papilla and accessory pancreatic duct.
The duodenum is a short, fixed part of the small intestine that makes a “C” around the head of the pancreas.
The major duodenal papilla is located in the wall of the descending part of the duodenum. This is where the pancreatic duct and common bile duct converge to empty into the duodenum. It is located in the wall next to the head of the pancreas.
The accessory pancreatic duct is not always present. If it is, it will empty into the duodenum superior to the main pancreatic duct at the minor duodenal papilla.
Describe the blood supply and innervation of the duodenum
The blood supply of the proximal duodenum occurs from the ciliac trunk. The gastroduodenal artery branches to form the anterior and posterior superior pancreaticoduodenal arteries. The distal duodenum is supplied from the superior mesenteric artery, which branches to form the anterior and posterior inferior pancreaticoduodenal arteries.
innervated by the vagus nerve and the celiac and superior mesenteric plexuses, T5-T9 (sympathetic)
Describe the blood supply and innervation of the jejunum and ileum
The blood supply of the rest of the small intestine comes from branches of the superior mesenteric artery. The terminal branch that supplies the ileum is called the iliocolic artery.
The jejunum and ileum are innervated by sympathetic efferents from T9–T10; Thus pain is referred to the periumbilical region of the anterior body wall. Parasympathetic innervation is derived from the posterior vagal trunk
Regarding the large intestine: a) identify its normal orientation in the abdomen, b) describe its innervation and c) discuss to where pain from the large intestine is referred.
The large intestine normally makes an inverted “C” in the abdominal cavity. Much of the large intestine is peritoneal (the sigmoid and transverse colon), so the actual position can vary greatly from person to person.
Innervation of the large intestine is provided by different fibers depending on the location. Up to the left colic flexure, parasympathetic innervation is derived from the vagus nerve and sympathetic innervation is supplied by T10 to L1. Past the left colic flexure to the rectum, parasympathetic innervation is derived from sacral parasympathetics (S2–S4), and sympathetic innervation is supplied from L1 and L2.
Most of the time pain from the colon is felt in the hypogastric region due to the levels of innervation.
Identify the inferior mesenteric artery and the left colic and sigmoid branches
The large intestine is supplied by branches of the superior and inferior mesenteric arteries, as seen in the figure below. Note the location of the left colic and sigmoid arteries.
The rectum is supplied by the superior rectal artery, from the inferior mesenteric, and the middle rectal artery, from the internal iliac, and the inferior rectal artery, from the internal pudendal artery.
Describe the venous drainage of small and large intestine and discuss the clinical consequences of drainage through the hepatic portal system.
The venous drainage of the small and large intestine parallels the arterial blood supply. Most of the venous drainage empties into the hepatic portal vein (except the terminal portion of the anal canal, that drains systemically).
The large intestine is drained by veins that parallel the arterial system.
The rectum is drained by the superior rectal artery, which drains into the portal system, and the middle and inferior rectal arteries, which drain into the systemic circulation.
Essentially all of the blood that is involved in absorbing nutrients is delivered to the liver first. The liver has first exposure to both nutrients and toxins.
Regarding the pancreas:
a) describe its anatomical relations
The pancreas is located retroperitoneally. Its head extends from the “C” of the duodenum to the tail, which is posterior to the stomach and against the omental bursa. The neck of the pancreas passes over the superior mesenteric artery and vein. The body of the pancreas lies posterior to the stomach and is in contact with the aorta, superior mesenteric artery, left suprarenal gland, and the left kidney. The uncinate process extends from the inferior part of the head and passes posterior to the superior mesenteric artery and vein.
Regarding the pancreas:
b) describe its the blood supply and innervation
c) discuss why pancreatic cancer often goes unrecognized.
The pancreas receives blood from the splenic artery, which forms arcades with the gastroduodenal artery and superior mesenteric artery branches. The head receives blood from the anterior and posterior branches of the superior pancreaticuoduodenal and inferior pancreaticoduodenal arteries. Venous drainage parallels the arterial supply.
The pancreatic acinar cells and islets are innervated by thoracic splanchnic nerves (sympathetic) from T5–T9, and from the vagus nerve (parasympathetic, acinar cells only). Parasympathetic innervation by stimulate secretion of pancreatic enzymes.
Pancreatic cancer often does not affect the function of the pancreas; the patient has normal digestive enzyme production. There are just no symptoms of the mass until it invades other structures, such as the posterior body wall, where then somatic nerves can send pain signals. At this point the cancer is late stage and the prognosis is poor.
Regarding the liver:
b) describe its blood flow
c) discuss the functions of the hepatic portal system.
Blood flow to the liver comes from the hepatic portal vein (70%), as well as from the right and left hepatic arteries (30%)
The celiac trunk gives rise to the common hepatic artery, which then branches to form the proper hepatic artery. The proper hepatic artery divides to form the right and left hepatic arteries.
Venous drainage from the liver occurs when blood in the sinusoids (from hepatic arteries and portal vein) empties into the hepatic veins (right, middle, and left). The hepatic veins drain almost immediately into the inferior vena cava.
The liver is innervated from the hepatic nerve plexus. Sympathetic fibers come from T7–T10, and parasympathetic fibers come from the vagus. Pain can be referred to the epigastrium via T7–T10, or up to the shoulder via the phrenic nerve.
The hepatic portal system serves to filter blood of toxins as well as nutrients. The liver can process and metabolize substances in the blood, serving to either activate them (as in the case of prodrugs) or deactivate them (in the case of drugs or toxins).
Describe the lymphatic drainage of the gastrointestinal tract
The foregut structure, i.e. the stomach, proximal duodenum, and pancreas, drain into the celiac nodes, then into the cisterna chili.
For the midgut structures, the distal duodenum, small intestine, and ascending colon and proximal transverse colon, drainage is into the superior mesenteric nodes, then into the cisterna chili.
For the hindgut structures, the distal transverse colon and descending colon, the lymphatic drainage is via the inferior mesenteric nodes.
The rectum is drained by the inferior mesenteric, pararectal, and sacral lymph nodes.
The anal canal is drained to the internal iliac lymph nodes above the pectinate line. Below the pectinate line, drainage is to the superficial inguinal lymph nodes.
Determine the sites of Portal-Systemic anastomoses
Between the paraumbilical vein and the epigastric vein
Esophageal veins: between the left gastric vein and the azygous vein
Retroperitoneal: between veins of the retroperitoneal organs and the abdominal wall veins
Rectal veins: between the superior and middle/inferior rectal veins
Small intestine
histology
functional features
The outer layer is serosa, except for where the duodenum and terminal ileum attach to the posterior abdominal wall; in these areas there is adventitia.
The muscularis propria contains inner circular and outer longitudinal layers. The inner layer thickens to form a sphincter at the ileocecal valve.
The submucosa contains glands in the duodenum (which secrete bicarbonate rich mucous), but not in other areas of the small intestine. This protects the duodenum from acidic stomach contents.
The mucosa has a simple columnar epithelium which is invaginated to form crypts of Lieberkuhn, and evaginated to form villi. The size of the villi decreases as you move distally. Lymphoid follicles are isolated throughout in addition to groups of lymphoid follicles called Peyer’s patches in the ileum.
Large intestine
histology
functional features
The outer layer is serosa in areas and adventitia in others (adventitia at the ascending colon, descending colon, and rectum, while serosa in other areas).
The muscularis propria contains inner circular muscle, and strips of outer longitudinal muscle known as the taeniae coli (3 in total). The circular layer forms an internal anal sphincter at the recto-anal junction, while skeletal muscle forms the external anal sphincter.
The submucosa contains the blood vessels that make up the internal hemorrhoidal plexus at the recto-anal junction.
The mucosa has simple columnar epithelium invaginated to form crypts of Lieberkuhn. No villi are present. At the recto-anal junction, the epithelium switches to stratified squamous; eventually it transitions to keratinized epithelium. Lymphoid follicles are present in the distal colon and rectum especially.
Enterocytes
relate structural features (including organelles) to functions in digestion, absorption, and/or immune defense
function in digestion, absorption, and immune defense. They are located throughout the small and large intestine.
Digestion: large surface area via microvilli to attach brush border enzymes to (produced in the RER and Golgi). This allows for breakdown of food products to amino acids and monosaccharides for absorption.
Absorption: amino acids and monosaccharides diffuse through the large surface area of the apical membrane (microvilli), then move across the basolateral membrane (ignoring mechanism here) and enter fenestrated capillaries in the lamina propria. Fatty acids diffuse into the cell across the apical membrane (microvilli) and are synthesized into triglycerides (smooth ER), then packaged into chylomicrons and vesicles for exocytosis (Golgi), where they enter lacteals in the lamina propria. Electrolytes are moved in through the apical membrane by facilitated diffusion, then are actively pumped through the basolateral membrane by Na+,K+-ATPase (energy supplied by mitochondria); water follows Na+ and enters lymphatic and blood capillaries.
Immune defense: The poly-Ig receptor is expressed at the basolateral membrane, and mediates transport of IgA and IgM from the lamina propria into the lumen of the intestine.
Stem cells
relate structural features (including organelles) to functions in digestion, absorption, and/or immune defense
Stem cells: undifferentiated cells located in the crypts, just above Paneth cells. Provide new cells to replace sloughed off cells.
Distinguish the roles of pancreatic enzymes and brush border enzymes in digestion, and predict what deficiencies would arise with loss of pancreatic and/or brush border function.
Pancreatic enzymes are secreted in an inactive form to prevent digestion of the pancreas itself. They are activated inside the lumen of the duodenum.
One of the brush border enzymes is called enteropeptidase; this cleaves trypsinogen to trypsin. Trypsin goes on to activate other digestive enzyme precursors secreted from the pancreas.
Pancreatic enzymes digest fats and convert proteins to oligopeptides and carbohydrates to oligosaccharides.
Brush border enzymes digest oligopeptides to amino acids and oligosaccharides to monosaccharides.
Examples of brush border enzymes are lactase, sucrase, maltase, etc.
Loss of pancreatic enzymes would prevent large food molecules from being broken down to small molecules. Loss of brush border enzymes would prevent breakdown of small molecules into diffusable nutrients. Loss of either would cause malabsorption and malnutrition, however loss of brush border enzymes would not impact the digestion of fats, electrolytes, or water.
Characterize the cells and tissues participating in immune defense in the intestines and summarize the roles of M cells and enterocytes in immune protection of the GI tract.
Enterocytes participate in immune defense by pumping antibodies across the cell into the lumen of the intestine (via the poly Ig receptor on the basolateral surface). The enterocytes add a secretory component to the antibody to protect it from proteolytic cleavage in the lumen.
Lymphocytes in the epithelial layer also participate in immune defense, possibly by preventing immune response to food antigens.
Lymphoid follicles participate in immune defense, particularly through M cells, which are in the epithelial layer above the lymphoid follicle. The M cells have a scooped out area where macrophages and lymphocytes can enter to get closer to the lumen of the GI tract; across this apical cytoplasmic isthmus, the M cell pumps antigens from the lumen to present to immune cells in the lymphoid follicle.
Stimulated B cells can then differentiate into pre-plasma cells and leave the follicles to enter the lamina propria of other parts of the digestive tract before differentiating into plasma cells to secrete antibodies.
Outline the distribution of normal flora throughout the digestive tract and give examples of the importance of normal flora to colonic health.
In the oral cavity, there are 10^4 bacterial per ml. In the stomach there is almost no bacteria due to the acidity. Bacterial numbers increase slowly throughoout the small intestine, then increase rapidly at the ileocecal valve through the rest of the large intestine.
Bacteria in the colon synthesie vitamin K, ferment plant matter (i.e. fiber), and outcompete potential pathogens (like C. difficile).
There are many lymphocytes in the lamina propria of the colon to deal with the bacterial population.
