Chapter 23: The Digestive System

Question 1

The Two Groups of Organs in the Digestive System:

Answer 1

o 1) Alimentary canal ( = gastrointestinal or GI tract):
o Digests and absorbs food
o Consists of the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
o 2) The Digestive System also consists of Accessory digestive organs:
o Teeth, tongue, gallbladder
o Digestive glands
• Salivary glands
• Liver
• Pancreas

Question 2

Digestive Processes:

The Six Essential Activities for the Digestive Process

Answer 2

o 1. Ingestion
o 2. Mechanical Digestion (mixing with saliva) chewing or mastication.
o 3. Propulsion (swallowing = deglutition, peristalsis, mass movement.
o 4. Secretion and chemical digestion (water, mucus, bile, enzymes, hormones) which breaks down nutrients down into small pieces.
o 5. Absorption (small intestine).
o 6. Defecation (removal of waste products).

Question 3

GI Tract Regulatory Mechanisms:

Answer 3

o Mechanoreceptors and chemoreceptors within the GI tract:
o Neuronal control (through reflexes) through enteric nerve plexus (ENS): respond to: stretch, changes in osmolarity and pH, and the presence of digesting food and end products of digestion.
o Enteric motor neurons that:
• Activate or inhibit digestive glands.
• Stimulate smooth muscle to mix and move lumen contents.
o Intrinsic and extrinsic controls:
o Enteric nerve plexuses (gut brain) initiate short reflexes in response to stimuli (pH, stretch) in the GI tract.
o Long reflexes activate in response to stimuli inside or outside the GI tract
• Involves the ANS (sympathetic / parasympathetic).
• Involves the CNS regarding conscious sight, smell, taste and motor from the precentral gyrus.
o Hormones (called paracrines) from cells in the stomach and small intestine stimulate target cells in the same or different organs.

Question 4

Peritoneum and Peritoneal Cavity:

Answer 4

o Peritoneum: serous membrane of the abdominal cavity =
o Visceral peritoneum on external surface of most digestive organs.
o Parietal peritoneum lines the body wall.
o Peritoneal cavity
o Between the two peritoneums.
o Serous fluid lubricates mobile organs.
o Mesentery is a double layer of peritoneum:
o Routes for blood vessels, lymphatics, and nerves.
o Holds organs in place and stores fat.
o Retroperitoneal organs lie posterior to the peritoneum = kidneys, pancreas, duodenum, ascending and descending colon, rectum.
o Intraperitoneal (peritoneal) organs are surrounded by the peritoneum.

Question 5

Blood Supply:

Splanchic Circulation

Answer 5

o Arteries:
o Celiac Trunk, Splenic, Inferior and Superior mesenteric.
o Hepatic portal circulation = veins from the pancreas, gall bladder, spleen, small and large intestines.
o Drains nutrient-rich blood from digestive organs.
o Delivers it to the liver for processing.

Question 6

Histology of the Alimentary Canal:

Answer 6

o Four basic layers (tunics) = deep to superficial:
o 1) Mucosa = epithelium, lamina propria, muscularis mucosa.
o 2) Submucosa.
o 3) Muscularis externa = circular muscle, longitudinal muscle.
o 4) Serosa = epithelium and connective tissue.

Question 7

Submucosa and Muscularis Externa:

Answer 7

o Submucosa
o Dense, thick connective tissue
o Larger blood and lymphatic vessels, lymphoid follicles
o Contains Submucosal nerve plexus or (Meissner’s plexus)
o Regulates surface of the lumen (through the muscularis mucosa), glandular secretions, and local blood.
o Muscularis externa:
o Responsible for segmentation and peristalsis.
o Inner circular and outer longitudinal layers.
o Innervated by the Myenteric Nerve Plexus (also called Auerbach plexus or “gut brain”) regulates peristalsis.

Question 8

Mucosa:

Answer 8

o Lines the lumen
o Functions:
o Secretes mucus, digestive enzymes and hormones.
o Absorbs end products of digestion.
o Protects against infectious disease
o Three sublayers: epithelium, lamina propria, and muscularis mucosae.
o Epithelium
o Simple columnar epithelium and mucus-secreting cells: Mucus secretion:
o Protects digestive organs from enzymes.
o Eases food passage.
o Corrals bacteria.
o Secretes enzymes and hormones in the stomach and small intestine.
o Lamina propria:
o Loose areolar connective tissue under the epithelium.
o Lots of capillaries for nourishment and absorption.
o Lymphoid follicles.
o Muscularis mucosae: smooth muscle under the lamina propria that produces movements of mucosa.

Question 9

Serosa:

Answer 9

o Visceral peritoneum
o Replaced by the fibrous adventitia in the esophagus.
o Peritoneal organs have serosa = peritoneum.

Question 10

Enteric Nervous System:

Answer 10

o Intrinsic nerve supply of the alimentary canal. Submucosal nerve plexus:
o Regulates glands and muscularis mucosae in the mucosa.
o Myenteric nerve plexus:
o Controls GI tract movement by innervating the muscularis externa (circular and longitudinal muscle) = peristalsis.

Question 11

Mouth (Oral/Buccal) Cavity:

Answer 11

o Bounded by lips, cheeks, palate, and tongue.
o Oral orifice is the anterior opening.
o Lined with stratified squamous epithelium.

Question 12

Lips and Cheeks:

Answer 12

o Contain orbicularis oris and buccinator muscles.
o Vestibule: trough which is internal to lips and cheeks, external to teeth and gums.
o Labial frenulum: median attachment of each lip to the gingiva.

Question 13

Palates of the Mouth:

Answer 13

o Hard palate: a combination of the palatine bones (facial bones) and palatine or maxillary processes of the two maxillary bones.
o Slightly corrugated to help create friction against the tongue.
o Soft palate: fold formed mostly of skeletal muscle.
o Closes off the nasopharynx during swallowing.
o Uvula projects downward from its free edge.

Question 14

Tongue:

Answer 14

o Functions include:
o Repositioning foods on occlusal plane and the mixing of food during chewing.
o Responsible for the initial formation of the bolus.
o Responsible for the initiation of swallowing, speech, and taste.
o Intrinsic muscles change the shape of the tongue.
o Extrinsic muscles alter the tongue’s position.
o Lingual frenulum: attachment of tongue to the floor of the mouth.
o Surface bears papillae:
o 1. Filiform—whitish, give the tongue roughness and provide friction = highly keratinized.
o 2. Fungiform—reddish, scattered over the tongue. Have a few receptors for taste.
o 3. Circumvallate (vallate)—V-shaped row in back of tongue (12), contains most of the taste receptors.
o 4. Foliate—on the lateral aspects of the posterior tongue.
o Terminal sulcus marks the division between.
o Body: anterior 2/3 residing in the oral cavity.
o Root: posterior third residing in the oropharynx.

Question 15

Composition of Saliva:

Answer 15

o Secreted by serous and mucous cells.
o 97–99.5% water, slightly acidic solution containing:
o Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3–
o Salivary amylase and lingual lipase.
o Metabolic wastes—urea and uric acid.
o Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms.

Question 16

Salivary Glands:

Answer 16

o Extrinsic salivary glands (parotid, submandibular, and sublingual).
o Intrinsic (buccal) salivary glands are scattered in the oral mucosa = minor salivary glands.
o Secretion (saliva) = 1 to 1.5 qts. per day.
o Cleanses the mouth, buffers, and protects (lysozyme enzyme).
o Moistens and dissolves food chemicals.
o Aids in bolus formation for swallowing (deglutition).
o Contains enzymes that begin the breakdown of starch (amylase).
o Parotid gland.
o Anterior to the ear external to the masseter muscle
o Parotid duct opens into the vestibule next to the first/second upper molar.
o Mumps = Myxovirus attacks the parotid gland with swelling/possible sterility (vaccine available).
o Submandibular gland.
o Medial to the body of the mandible.
o Duct opens at the base of the lingual frenulum.
o Sublingual gland:
o Anterior to the sublingual gland under the tongue.
o Opens via 10–12 ducts into the floor of the mouth.

Question 17

Control of Salivation:

Answer 17

o Intrinsic glands are scattered throughout the mouth which continually keep the mouth moist.
o Extrinsic salivary glands produce secretions when:
o Ingested food stimulates chemoreceptors and mechanoreceptors in the mouth.
o Salivatory nuclei in the brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX = serous secretion (watery).
o Strong sympathetic stimulation inhibits salivation and results in dry mouth (thick mucus secretion) (xerostomia).

Question 18

Pharynx:

Answer 18

o Oropharynx, and laryngopharynx:
o Allow passage of food, fluids, and air.
o Stratified squamous epithelium lining.
o Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors.
o Deglutition (= swallowing) pushes bolus of food in oropharynx = involuntary reflex.

Question 19

Esophagus:

Answer 19

o Flat muscular tube from laryngopharynx to stomach.
o Esophagus goes through the diaphragm at the esophageal hiatus.
o Esophagus joins the stomach at the cardiac orifice of the stomach.
o Esophageal mucosa contains stratified squamous epithelium. Changes to simple columnar at the stomach.
o Submucosa is comprised of areolar CT and has esophageal glands that secrete mucus to aid in bolus movement
o Muscularis Externa: circular / longitudinal muscle.
o Adventitia is fibrous CT instead of serosa.

Question 20

Digestive Processes of Esophagus:

Answer 20

o 1) Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharanx where the involuntary phase begins.
o 2) The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus.
o 3) The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts after entry.
o 4) Food is moved through the esophagus to the stomach by peristalsis.
o 5) The gastroesophageal sphincter opens, and food enters the stomach.

Question 21

GERD (Gastroesophageal Reflux Disease):

Answer 21

o LES = happens when lower (or gastric) esophygeal sphincter fails to close adequately.
o Stomach contents “reflux” up into esophagus.
o HCl from stomach irritates esophageal lining = heart burn (radiating substernal pain). =acid reducers CaCO3, or Prilosec.

Question 22

Stomach:

Mesentary (Extension of the Serosa)

Answer 22

o Lesser omentum (two visceral mesenteries):
o From the liver to the lesser curvature of the stomach.
o Greater omentum (two visceral mesenteries):
o Drapes from greater curvature of the stomach.
o Drapes anterior to the small intestine.
o Lesser and Greater Omentum both help hold and tie down stomach, intestines and other digestive organs to themselves and to the body walls.
o Has a lot of fat + lymph nodes.

Question 23

Innervations of the Stomach:

Answer 23

o ANS nerve supply:
o Sympathetic via splanchnic nerves and the celiac plexus.
o Parasympathetic via vagus nerve.
o Blood supply:
o Celiac (gastric & splenic) trunk.
o Drains into the veins of the hepatic portal system.

Question 24

Tunics of the Stomach:

Answer 24

o Tunics of the Stomach: (superficial to deep)
o Serosa: fibrous CT
o Muscularis externa:
o Three layers of smooth muscle.
o Longitudinal + circular + oblique controlled by the myenteric nerve plexus.
o Addition of the inner oblique layer allows stomach to churn, mix, move, and physically break down food and propels chyme into the small intestine in duodenum.
o Submucosa = contains blood vessels, diffuse lymph, and nerve plexus for smooth muscle called the submucosal plexus (regulates the muscularis mucosa).
o Mucosa:
o 1) Simple columnar epithelium.
o 2) Lamina propria.
o 3) Muscularis mucosa.

Question 25

Mucosa:

Answer 25

o Simple columnar epithelium which are mucous cells anchored by lamina propria.
o Layer of mucus traps bicarbonate-rich fluid beneath it.
o Rugae = folds in mucosa that allows stomach to expand.
o Millions of Gastric pits lead into gastric glands within gastric pits are gastric glands which secrete gastric juices.

Question 26

Gastric Glands Cell Types:

Answer 26

o Mucous neck cells (secrete thin soluble mucus within the gastric pit areas).
o Parietal cells.
o Chief cells.
o Enteroendocrine cells (G cells).

Question 27

Gastric Gland Secretions:

Answer 27

o Glands that are in the fundus and body produce most of the gastric juice.
o Parietal cell secretions:
o Secrete HCl: pH 1.5–3.5 denatures protein in food, activates pepsin, and kills many bacteria.
o Intrinsic factor: a Glycoprotein required for absorption of vitamin B12 in small intestine which is necessary in the formation of mature RBCs. If intrinsic factor decreased or absent= pernicious anemia.
o Chief cell secretions:
o Secretes the inactive enzyme pepsinogen.
o Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism) which break apart peptide chains into amino acids.
o Also, secretes enzymes (lipases) for fat digestion.
o Enteroendocrine cells (deep into gastric pit)
o Produce and secrete chemical messengers into the interstitial fluid of the lamina propria and blood.
o Paracrines (affect local cells):
o Serotonin = causes gastric smooth muscle contraction
o Histamine = targets parietal cells to produce HCl
o Hormones (local and systemic into blood)
o Somatostatin = inhibits gastric mobility and secretions
o Gastrin from G cells = causes release of more gastric juices: = increases gastric mobility (stimulates the release of paracrines ) Relaxes pyloric sphincter. Constricts gastric LES.

Question 28

Protection of Stomach Mucosa:

Answer 28

o Thick coat (1-3 mm) of alkaline gel-like mucus (layer of bicarbonate-rich mucus) which literally prevents the stomach from digesting itself , comes from surface epithelial cells.
o Tight junctions between epithelial cells, which prevent leakage of gastric juices into underlying tissues.
o Pepsin is secreted in an inactive form (pepsinogen).
o Damaged epithelial cells are quickly replaced by fast division of stem cells (surface epithelium is entirely replaced every 3 to 6 days).

Question 29

Peptic Ulcers:

Answer 29

o Gastritis: chronic inflammation caused by anything that breaches the mucus barrier.
o Peptic or gastric ulcers: erosion of the stomach wall by hypersecretion of HCL, hyposecretion of mucus can perforate stomach wall and/or hemorrhage.

Question 30

Digestive Processes in the Stomach:

Answer 30

o Physical digestion or breakdown by smooth muscle actions
o Chemical Digestion by denaturation (unfolded) of proteins by HCl:
o HCl converting pepsinogen (from chief cells) into pepsin.
o Enzymatic digestion of proteins by pepsin (and rennin in infants that breaks down milk protein) = breaks peptide bonds yielding amino acids.
o Aspirin and alcohol (lipid soluble) easily pass through stomach wall.
o Parietal cells of stomach secretes HCl and intrinsic factor required for absorption of vitamin B12 .
o Lack of intrinsic factor lead to pernicious anemia.
o Delivers chyme (semifluid mass made in stomach) to the small intestines.

Question 31

Regulation of Gastric Secretion:

Answer 31

o Gastric secretion is controlled by both neural and hormonal mechanisms (3 L / day produced).
o Stimulatory and inhibitory events occur in three phases:
o 1. Cephalic (reflex) phase: few minutes prior to food entry.
o 2. Gastric phase: 3–4 hours after food enters the stomach.
o 3. Intestinal phase: Stomach emptying into duodenum.

Question 32

Cephalic Phase:

Answer 32

o Stomach Getting Ready
o Cerebral cortex = sight, smell, taste and thoughts of food (causes a conditioned reflex).
o Stimulates the hypothalamus (hunger center) and medulla oblongata, parasympathetic system is triggered.
o Vagus nerve = (Cranial nerve X) increases stomach and glandular activity.

Question 33

Gastric Phase:

Answer 33

o Stomach Working.
o Nervous control keeps stomach active
o Stretch receptors (distention) and chemoreceptors (pH and food chemicals) provide sensory information to the medulla leads to vagal motor fibers travel from medulla to the stomach.
o Vigorous peristalsis and glanduar secretions continue through action of the myenteric (local ENS) and vagal (long) reflexes ) = causes movement of chyme into the pyloric antrum.
o Chyme is released into the duodenum.
o Endocrine influences over stomach activity:
o Glandular secretion (paracrines), stomach peristalsis, pyloric sphincter relaxation is stimulated by gastrin (from G cells).
o Distention (stretch) and presence of protein (peptides) stimulates G cells to secrete gastrin into blood.

Question 34

Intestinal Phase:

Answer 34

o Stomach Emptying.
o Stretch receptors in duodenum slow stomach activity and increase intestinal activity (through enterogastrins).
o Distension of small intestine, pH decrease, fats, proteins slows things down through the enterogastric reflex:
o Sympathetic nerves slow stomach activity = (pyloric sphincter tightens).
o Parasympthatic activity slows (through vagus nerve).
o Inhibition of the myenteric plexus (local).
o Hormonal influences = Enterogastrins (from duodenum):
o Secretin hormone decreases stomach secretions (acid).
o Cholecystokinin (CCK) decreases stomach emptying.
o Gastric inhibitory peptide (GIP) or incretins decreases stomach secretions, motility, and emptying.

Question 35

Sequence of Events at the Pyloric Valve:

Answer 35

o 1) Propulsion: Peristaltic waves move from fundus toward the pylorus.
o 2) Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus.
o 3) Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chime into the duodenum, simultaneously forcing most of its contained material backward into the stomach.

Question 36

Regulation of Gastric Emptying:

Answer 36

o As chyme enters the duodenum:
o Receptors respond to stretch and chemical signals.
o Enterogastric reflex and enterogastrones from the duodenum inhibit gastric secretion and duodenal filling.
o Carbohydrate-rich chyme moves quickly through the duodenum.
o Fatty chyme remains in the duodenum 6 hours or more.

Question 37

Small Intestine:

Answer 37

o Major organ of digestion and absorption
o Subdivisions:
o Duodenum (retroperitoneal) = 10” long = bile (liver) and pancreatic enzymes are deposited, nutrient absorption begins.
o Jejunum = 2.5’ – 3’ long = greatest number of villi and where most nutrient absorption occurs.
o Ileum = 3’-4’ long = longest and associated with the reabsorption of bile salts and B12.

Question 38

Duodenum:

Answer 38

o The bile duct and main pancreatic duct:
o Join at the hepatopancreatic ampulla.
o Enter the duodenum at the major duodenal papilla.
o Are controlled by the hepatopancreatic sphincter.
o Has Duodenal glands in submucosa which produces alkaline rich mucus to neutralize acid.

Question 39

Circular Folds:

Answer 39

o Increases surface area 2 to 3 fold.
o Permanent ridges (~1 cm deep or high).
o Greatest number in the jejunum.
o Forces chyme to slowly spiral through the lumen rather than a straight line.

Question 40

Villi:

Answer 40

o Motile fingerlike extensions (~1 mm high) of the mucosa
o Villus epithelium: Simple columnar absorptive cells, Goblet cells (produce mucin).
o Core of villus = the lamina propria and has capillaries, lacteals (lymph capillary for fat absorption), and smooth muscle fibers.

Question 41

Microvilli:

Answer 41

o 1 micron tall.
o Microvilli have projections (brush border = look like bristles on a brush microscopically) on top of the intestinal cells…typically there are more than 2500 to 3000 microvilli extending from each intestinal cell!!
o Brush border enzymes fine tune and complete chemical digestion.

Question 42

Surface Area Amplification:

Answer 42

o For Greater Nutrient Intake.
o Circular folds (Plicae circulares)= increases surface area 2 to 3 fold.
o Intestinal villi = increases surface area 8 – 10 fold.
o Microvilli = increases surface area 400 to 600 fold.
o Total surface area = 2200 square feet.

Question 43

Intestinal Crypts:

Answer 43

o Intestinal crypt epithelium (secretion and little absorption) = area between the bases of the intestinal villi and below the surface.
o Secretory cells that produce intestinal juices.
o Enteroendocrine cells = secretin + cholecystokinin (CCK) + GIP (gastroinhibitory peptide) = incretins (causes a release of insulin from pancreas).
o Intraepithelial lymphocytes (IELs):
• Release cytokines (communicating chemicals) that summon immune cells to kill infected cells (e.g. T cells)
o Paneth cells:
• Secrete antimicrobial agents (defensins and lysozyme).
o Stem cells:
• Goblet cells that produce mucin (mucus).

Question 44

Liver:

Answer 44

o Largest gland in the body = and exocrine and an endocrine organ.
o Located just underneath the diaphragm in the upper right quadrant of the abdominal cavity.
o Four lobes—right, left lobes (anterior) and caudate, and quadrate (inferior).
o Enclosed by thin CT capsule, very little CT in rest of liver except for reticular fibers for support.
o Falciform ligament:
o Separates the (larger) right and (smaller) left lobes.
o Suspends liver from the diaphragm and anterior abdominal wall.
o Round ligament (ligamentum teres):
o Remnant of fetal umbilical vein along free edge of falciform ligament.

Question 45

Blood Supply to the Liver:

Answer 45

o Receives blood from two sources:
o 25% of blood comes from the hepatic artery (feeds cells which are called hepatocytes).
o 75% of blood comes from the hepatic portal vein coming from the nutrient rich blood of the intestines, as well as from the spleen and pancreas.
o Venous blood “percolates” through hepatic sinusoids in between plates of liver cells (hepatocytes).
o Sinusoids empty into a central vein at the center of a hepatic lobule.
o Central veins of all hepatic lobules drain eventually into several hepatic veins.
o Hepatic veins drain into the inferior vena cava.

Question 46

Porta Hepatis:

Answer 46

o Found on the inferior surface of liver.
o Where blood vessels, ducts, nerves, lymph vessels enters/exits the liver.
o Beginning here the CT capsule sends a branching network of SEPTA into the liver, dividing liver into hexagonal-shaped lobules.

Question 47

Hepatic Lobules:

Answer 47

o Repeating pattern of hexagonal units within the liver.
o Classic lobule is 2mm X 0.7 mm.
o Portal areas (triads) are found in 3 to 6 corners of the hexagon = Bile duct, portal arteriole, portal venule.
o Blood drains toward the central vein in the center of the lobule.

Question 48

Portal Area (Portal Triad):

Answer 48

o Branch of the hepatic artery: Brings in oxygenated blood from the aorta.
o Branch of the hepatic portal vein: Brings in nutrient rich blood plasma from the intestines, as well as venous blood from the pancreas and spleen.
o Bile Duct receiving bile from canaliculi in liver cells that eventually form either the right or left hepatic duct.
o Lymphatic vessels: Liver produces large amounts of lymph!

Question 49

Specialized Cells of the Liver:

Answer 49

o	Hepatocytes = 80% of cells of the liver
o	Kupffer cells = fixed macrophages
o	Line the hepatic sinusoids
o	Remove and recyle worn out RBCs
o	Attack pathogens and remove debris
o	Endothelial cells line liver sinusoids
o	Ito cells = stellate shaped cells
o	Store Vitamin A and lipids
o	Acquire features of myofibroblasts with liver injury or liver disease which causes fibrosis of liver or scarring of liver = cirrohis.

Question 50

Hepatocytes:

Answer 50

o Polyhedral cells with 6 or more surfaces.
o Form the hepatic plates (in between are hepatic sinusoids).
o Contain glycogen granules, lipid droplets, thousands of mitochondria, peroxisomes, lots of endoplasmic reticulum.
o MAKES BILE and secrete it into tiny ducts called bile canaliculi.

Question 51

Bile:

Answer 51

o Yellow-green, alkaline solution made by the hepatocytes: 500-1000 mL/day produced = empties into duodenum.
o Neutralizes stomach acid and mostly water.
o Bile acids = different acids made in the hepatocytes that are cholesterol derivatives which function in fat emulsification and absorption = becomes Bile Salts when combine with Na+ (breaks fats down into smaller clumps for easier digestion).
o Facilitates fat and cholesterol absorption.
o Contains Bilirubin: pigment formed from heme (from breakdown of hemoglobin in liver).
o Contains cholesterol, neutral fats, phospholipids, and electrolytes, metabolic byproducts of medications.
o Enterohepatic circulation:
o Most bile salts are recycled in the distal ileum (small intestine)
o Bile salts to the duodenum to be reabsorbed from ileum to the hepatic portal vein to the liver sinusoids to the captured by the hepatocytes then resecreted into new bile.

Question 52

General Functions of the Liver:

Answer 52

o Production/secretion of bile = Exocrine.
o Excretion of bilirubin and other wastes.
o Phagocytosis by Kupffer cells (helps spleen filter blood).
o Detoxification of alcohol, meds, hormones.
o Converts NH3 (from breakdown of proteins which is very toxic) to urea (nontoxic).
o Helps activate Vitamin D to calcitriol.
o Makes 80% cholesterol (for making plasma membranes and hormones).
o Makes hormones = EPO (mostly kidney), TPO, Angiotensin.
o Makes proteins = Makes 90% of plasma proteins.

Question 53

Metabolic Functions of the Liver:

Answer 53

o	The liver gets “first dibs” nutrient rich blood coming from the recent absorption in the small intestine
o	The liver processes and metabolizes blood borne nutrients in a multitude of ways:
o	Carbohydrate metabolism = maintains normal blood glucose levels through glycogenolysis and glyconeogenesis = both increase serum glucose.
o	Glycogenesis (glycogen formation) and lipogenesis {converts excess carbs to TG (fat)} = both decreases serum glucose.                       
o	Lipolysis = breakdown TG into fatty acids to make ATP.
o	Alcohol Metabolism = 80% ETOH absorbed in small intestine (20% stomach)—broken down through alcohol dehydrogenase to acetaldehyde (toxic in high levels).

Question 54

Cirrhosis:

Answer 54

o Chronic inflammation of the liver.
o Death of hepatocytes and replacement with fibrous CT.
o Fibrous bands of CT destroy the normal architecture of the liver.
o Necrotic cells replaced by regenerative nodules in between the fibrous CT.
o Causes of cirrhosis:
o Alcoholism.
o Biliary obstruction.
o Chronic and severe hepatitis.

Question 55

The Gallbladder:

Answer 55

o Thin-walled muscular sac (pear shaped) on the ventral surface of the liver.
o Stores and concentrates bile by absorbing its water and ions.
o Can hold 40 – 100mL of fluid.
o Releases bile via the cystic duct, which flows into the bile duct.

Question 56

Pancreas:

Answer 56

o Location:
o Mostly retroperitoneal, deep to the greater curvature of the stomach.
o Head lies within the curve the duodenum; body extends across abdominal wall; tail abuts to the spleen.
o Most of pancreas is posterior to the stomach.
o Exocrine and endocrine gland.
o Endocrine function:
o Pancreatic Islets (or Islets of Langerhans)secrete insulin (from beta cells) and glucagon (from alpha cells) and released into blood.
o Exocrine function:
o Acini (acinar = one cell) which are clusters of secretory cells that secrete pancreatic juice.
o Acini cells have zymogen granules which contain digestive enzymes.

Question 57

Pancreatic Juice:

Answer 57

o Is a watery alkaline solution (pH 8) which neutralizes acidic chime. Electrolytes primarily HCO3– to neutralize acidic chime.
o Released into duodenum.
o Secretes through acinar cells digestive enzymes:
o Pancreatic Amylase (starches; glucose), lipases, nucleases (break down nucleic acids) are secreted in active form but requires bile for optimal activity.
o Proteases secreted in inactive form until released in the duodenum.
o Protease activation in duodenum:
o Trypsinogen is activated to trypsin by brush border enzyme = enteropeptidase (enterokinase). Remember, the brush border are microvilli on top of each villus.
o Trypsin activates procarboxypeptidase and chymotrypsinogen:
• Becomes carboxypeptidase (breaks apart protein).
• Becomes chymotrypsin (breaks apart protein).

Question 58

Regulation of Pancreatic Secretion:

Answer 58

o CCK induces the secretion of enzyme-rich pancreatic juice by acini and gall bladder contraction.
o Secretin is released from intestinal cells when stimulated by acidic chyme from stomach.
o Secretin causes secretion of bicarbonate-rich alkaline juices by the pancreatic duct cells.
o Gastrin = released by the stomach and the duodenum, stimulates pancreatic enzyme secretion and gall bladder contraction.
o Incretins = released by small intestine and stimulate the secretion of insulin (new insulin meds enhance this).
o Vagal stimulation also causes release of pancreatic juice (minor stimulus).

Question 59

Chyme in the Stomach Contains:

Answer 59

o Partially digested carbohydrates and proteins.

o Undigested fats.

Question 60

Requirements for Digestion and Absorption in the Small Intestine:

Answer 60

o Slow delivery of acidic chime.
o Delivery of bile, enzymes, and bicarbonate from the liver and pancreas.
o Mixing.

Question 61

Motility of the Small Intestine:

Answer 61

o Segmentation:
o Initiated by intrinsic pacemaker cells (enteric nervous system).
o Mixes and moves contents slowly and steadily.
o Peristalsis:
o Initiated by motilin (secreted by special cells in the intestinal mucosa into blood = hormone).
o Each wave starts distal to the previous one.
o Meal remnants, bacteria, and debris are moved distally to the large intestine.
o Ileocecal sphincter relaxes and admits chyme into the large intestine from ileum of small intestine.
o Gastroileal reflex enhances the force of segmentation in the ileum.
o Enteric or intestinal Gastrin increases the motility of the ileum.
o Ileocecal valve flaps close when chyme exerts backward pressure.

Question 62

Large Intestine:

Answer 62

o Unique Features:
o Teniae coli: Three bands of longitudinal smooth muscle in the muscularis layer, also has muscularis mucosa and circular muscle with the longitudinal muscle.
o Haustra: Pocketlike sacs caused by the tone of the teniae coli, gives the colon segmented appearance.
o Epiploic appendages: Fat-filled pouches of visceral peritoneum that are situated along colon and rectum (unknown function).
o Regions:
o Cecum = pouch with attached vermiform appendix (lymphoid tissue). First area of large intestine and lies below the ileocecal valve.
o Colon.
o Rectum.
o Anal Canal.

Question 63

Colon:

Answer 63

o Ascending colon and descending colon are retroperitoneal.

o Transverse colon and sigmoid colon are anchored to posterior body wall via mesocolons (mesenteries).

Question 64

Rectum and Anus:

Answer 64

o Rectum:
o Three rectal valves stop feces from being passed with flatus.
o Anal canal:
o The last segment of the large intestine.
o Sphincters:
o Internal anal sphincter—smooth muscle.
o External anal sphincter—skeletal muscle.

Question 65

Bacteria Flora:

Answer 65

o Enter from the small intestine or anus:
o Colonize in the colon.
o Ferment indigestible carbohydrates (cellulose).
o Large intestinal bacteria bilirubin into simpler substances which gives feces its’ color.
o Release irritating acids and gases = dimethyl sulfide, methane, H2, N2,CO2.
o Makes up 30% of dry weight of feces.
o Bacterial flora synthesizes B complex vitamins and vitamin K (for blood coagulation).

Question 66

Functions of the Large Intestine:

Answer 66

o Absorption of important vitamins, water, and electrolytes (Vita K & Biotin = B vitamin).
o Concentration of residual residues into fecal matter.
o Secretion of mucus and bicarbonate ions to minimize damage to intestinal wall.
o No digestive enzymes.
o Major function is propulsion of feces toward the anus.
o Colon is not essential for life.

Question 67

Motility of the Large Intestine:

Answer 67

o Gastroilial reflex = when stomach is full, gastrin hormone relaxes the ileocecal sphincter and small intestine empties into large intestine to make room.
o Haustral contractions:
o Slow segmenting movements = churning.
o Haustra sequential contraction in response to distension.
o Gastrocolic reflex:
o Initiated by presence of food in the stomach.
o Activates three to four slow powerful peristaltic waves per day in the colon (mass movements).
o Moves contents of transverse colon into rectum.

Question 68

Defecation:

Answer 68

o Mass movements force feces into rectum.
o Distension initiates spinal defecation reflex.
o Parasympathetic signals.
o Stimulate contraction of the sigmoid colon and rectum.
o Relax the internal anal sphincter.
o Conscious control allows relaxation of external anal sphincter (skeletal muscle).

Question 69

Sequence of Events for Defecation:

Answer 69

o 1) Distension, or stretch, of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons.
o 2) A spinal reflex is initiated in which parasympathetic motor fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincters.
o 3) If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces may pass.