Ch. 24: Digestive System Flashcards
(241 cards)
1
Q
Accessory digestive organs.
A
Teeth, tongue, salivary glands, liver, gallbladder, pancreas.
2
Q
What are the 6 basic processes of the gastrointestinal tract?
A
1) Ingestion.
2) Secretion.
3) Motility.
4) Digestion.
5) Absorption.
6) Defecation.
3
Q
Which molecules can be absorbed without digestion?
A
Vitamins, ions, cholesterol, water.
4
Q
Mechanical digestion.
A
Molecules are dissolved and mixed with digestive enzymes by teeth and smooth muscles of stomach and small intestine.
5
Q
Chemical digestion.
A
Largo CHO, lipid, protein and nucleic acid molecules are split into smaller molecules by hydrolysis, which is catalyzed by digestive enzymes produced by salivary glands, tongue, stomach, pancreas and small intestine.
6
Q
Mucosa of GI tract.
A
Mucous membrane composed of a layer of epithelium, lamina propria, and muscularis mucosa.
Epithelium: In direct contact with GI contents. Nonkeratinized stratified squamous epithelium in mouth, pharynx, esophagus and anal canal serves a protective function. Simple columnar epithelium in stomach and intestines function in secretion and absorption. Tight junctions between columnar epithelial cells.
Lamina Propria: Areolar connective tissue. Contains blood and lymphatic vessels, which are routes for nutrients absorbed into the GI to reach other tissues. Supports the epithelium and binds to it by the muscular mucosa. Contains the majority of the cells of the MALT.
Muscular mucosa: Thin layer of smooth muscle. Creates many small folds of the mucous membrane of the stomach and small intestine. Movements from this layer ensure that all absorptive cells are fully exposed to the contents of the GI tract.
7
Q
What is the rate of renewal of GI epithelial cells?
A
5-7 days
8
Q
Exocrine cells.
A
Located among epithelial cells in mucosa of GI tract. Secrete mucous and fluid into GI tract.
9
Q
Enteroendocrine cells.
A
Located among epithelial cells in mucosa of GI tract. Secrete hormones.
10
Q
Submucosa of GI tract.
A
Areolar connective tissue. Binds the mucosa to the muscularis. Contains blood and lymphatic vessels, glands, and lymphatic tissue. Contains the submucosal plexus (neuronal network).
11
Q
Muscularis of GI tract.
A
Muscularis of mouth, pharynx, and superior and middle parts of esophagus contains skeletal muscle that produces voluntary swallowing. Skeletal muscle also forms the external anal sphinter.
Throughout the rest of the GI tract, the muscularis consists of smooth muscle that is organized into an inner sheet of circular fibres and an outer sheet of longitudinal fibres. Involuntary contractions of smooth muscle aid in breaking down food.
12
Q
What lies in between the layers of the muscularis?
A
Myenteric plexus.
13
Q
Serosa of GI tract.
A
Covers parts of the GI tract suspended in the abdominal cavity. Serous membrane composed of areolar connective tissue and simple squamous epithelium.
14
Q
Which part of the GI tract lacks a serosa?
A
Esophagus. Instead, only a single layer of areolar connective tissue forms the superficial layer, and it is called the adventitia. This structure attaches the esophagus to surrounding structures.
15
Q
Neurons of the enteric nervous system are arranged in…
A
Myenteric plexus and submucosa plexus.
16
Q
Myenteric plexus.
A
Located between longitudinal and circular smooth muscle layers of the muscularis. Motor neurons supply longitudinal and circular smooth muscle layers of muscularis. Controls GI tract motility, and frequency and strength of contraction of muscularis.
17
Q
Submucosal plexus.
A
Plexus of Meissner. Located within submucosa. Motor neurons supply secretory cells of mucosal epithelium. Controls secretions of organs of GI tract.
18
Q
Describe the role of interneurons and sensory neurons of the enteric nervous system.
A
Interneurons: interconnect neurons of myenteric and submucosal plexuses.
Sensory neurons: supply mucosal epithelium and contain receptors that detect stimuli in GI lumen.
19
Q
The neurons of the ___ can function independently, but they are subject to regulation by neurons of the ___ .
A
ENS, ANS.
20
Q
Which nerve supplies parasympathetic fibres to most of the GI tract?
A
Vagus nerve.
The last half of the large intestine is supplied by sacral spinal cord.
21
Q
Stimulation of parasympathetic nerves…
A
Increases GI secretion and motility by increasing the activity of ENS neurons.
22
Q
Sympathetic nerves that supply the GI tract arise from…
A
Thoracic and upper lumbar regions of the spinal cord.
23
Q
Stimulation of sympathetic nerves…
A
Decreases GI secretion and motility by inhibiting ENS neurons. Emotions like anger, fear and anxiety may slow digestion because they stimulate the sympathetic nerves.
24
Q
Gastrointestinal reflex pathways.
A
Regulate GI secretion and motility in response to stimuli in the GI lumen.
25
Peritoenum.
Largest serous membrane of the body. Consists of a layer of simple squamous epithelium with an underlying supporting layer of areolar connective tissue. Divided into the parietal peritoneum and visceral peritoneum.
26
Parietal peritoneum.
Lines abdominal cavity.
27
Visceral peritoneum.
Covers some organs in the abdominal cavity and is their serosa.
28
Peritoneal cavity.
Slim space containing lubricating serous fluid that is between the parietal and visceral layers.
29
Ascites.
When the peritoneal cavity becomes distended by the accumulation of fluid. Occurs in some diseases.
30
Retroperitoneal organs.
Lie on the posterior abdominal wall. Covered by peritoneum only on their anterior surfaces. Kidneys, ascending and descending colons, duodenum.
31
Describe the peritoneal folds.
Peritoneum contains large folds that weave between the viscera, and bind the organs to one another and to the walls of the abdominal cavity. These folds also contain blood vessels, lymphatic vessels, and nerves that supply the abdominal organs.
32
What are the 5 major peritoneal folds?
1) Greater omentum.
2) Falciform ligament.
3) Lesser omentum.
4) Mesentery.
5) Mesocolon.
33
Greater omentum.
Longest fold. Drapes over transverse colon and small intestinal coils, and folds back on itself to give it a total of 4 layers. Contains adipose tissue and lymph nodes, which contribute macrophages and antibody-producing plasma cells that fight against GI infections.
34
Falciform ligament.
Attaches the liver to the anterior abdominal wall and diaphragm.
35
Which is the only digestive organ attached to the anterior abdominal wall?
Liver.
36
Lesser omentum.
Arises as an anterior fold in the serosa of the stomach and duodenum. Connects stomach and duodenum to liver. Pathway for blood vessels entering the liver. Contains hepatic portal vein, common hepatic artery, common bile duct, and lymph nodes.
37
Mesentery.
Largest fold. Fan-shaped. Binds jejunum and ileum of small intestine to posterior abdominal wall. Contributes to large abdominal in obese individuals as it is laden with fat. Extends from posterior abdominal wall to wrap around small intestine and return to its origin to form a double-layered structure. Between the 2 layers are blood vessels, lymphatic vessels and lymph nodes.
38
Mesocolon.
2 separate folds (transverse mesocolon, sigmoid mesocolon).
Bind transverse colon and sigmoid colon of large intestine to posterior abdominal wall. Carries blood and lymphatic vessels to intestines.
39
How do the mesentery and mesocolon folds work together?
They hold intestines loosely in place to allow movements of muscular contractions.
40
Mouth.
Oral cavity. Cheeks, hard palate, soft palate, tongue.
41
What lies in between the skin and mucous membrane of the cheeks?
Buccinator muscles and connective tissue.
42
Labial frenulum.
A midline fold of mucous membrane that attaches the inner surface of the lips to the gingiva.
43
Oral vestibule.
The space bounded externally by the cheeks and lips and internally by the gums and teeth.
44
Oral cavity proper.
The space that extends from gums and teeth to the fauces.
45
Fauces.
Openings between the oral cavity and oropharynx.
46
Palate.
Wall/septum that separates the oral cavity from the nasal cavity. Forms the roof of the mouth.
Hard palate: Anterior roof of the mouth. Formed by maxillae and palatine bones. Covered by mucous membrane.
Soft palate: Posterior roof of the mouth. Arch-shaped muscular partition between the oropharynx and nasopharynx. Covered by mucous membrane.
47
Uvula.
Muscular structure. Hangs from free border of soft palate.
48
Lateral to the base of the uvula, there are 2 muscular folds that run down the lateral sides of the soft palate.
Palatoglossal arch: Anterior. Extends to the side of the base of the tongue.
Palatopharyngeal arch: Posterior. Extends to the side of the pharynx.
Palatine tonsils are located between these arches.
Lingual tonsils are located at the base of the tongue.
49
What are the salivary glands in the mouth and tongue?
Labial glands in lips.
Buccal glands in cheeks.
Palatal glands in palate.
Lingual glands in tongue.
50
3 pairs of major salivary glands.
Parotid: Inferior and anterior to ears. Between the skin and masseter muscle. Secrete saliva into oral cavity via a parotid duct.
Submandibular: In the floor of the mouth medial and inferior to the mandible. Submandibular ducts run under the mucosa on either side of the midline of the floor of the mouth and enter the oral cavity proper lateral to the lingual frenulum.
Sublingual: Beneath the tongue. Superior to the submandibular glands. Lesser sublingual ducts open into the floor of the mouth in the oral cavity proper.
51
Saliva.
99.5% water, 0.5% solutes.
52
Describe the liquids secreted by parotid, submandibular and sublingual glands.
Parotid: Watery. Contains salivary amylase.
Submandibular: Thickened with mucus. Contains salivary amylase.
Sublingual: Much thicker. Contains a small amount of salivary amylase.
53
Describe water in saliva.
Provides a medium for dissolving fluids, so that they can be tasted by gustatory receptors.
54
Describe Cl- ions in saliva.
Activate salivary amylase.
55
Salivary amylase.
Enzyme that starts the breakdown of starch to maltose, maltotriose, and alpha-dextrin. Inactivated by stomach acids.
56
Describe HCO3- and phosphate ions in saliva.
Buffer acidic foods.
57
Describe IgA in saliva.
Prevents attachment of microbes so they cannot penetrate the epithelium.
58
Describe how salivation is controlled by the ANS.
Parasympathetic stimulation promotes continuous secretion of a moderate amount of saliva, which keeps the mucous membrane moist and lubricates the movements of the tongue and lips during speech. Saliva is then swallowed and helps moisten the esophagus.
Sympathetic stimulation causes dryness of the mouth. Also, if you are dehydrated, the salivary glands will stop secreting saliva to conserve water.
59
How much saliva is release per day?
1,000 to 1,500 mL
60
Describe how salivation is controlled by food.
Chemicals in food stimulate receptors in taste buds on tongue --> impulses are conveyed to superior and inferior salivary nuclei in brainstem --> returning parasympathetic impulses in fibres of facial and glossopharyngeal nerves stimulate salivation.
61
Tongue.
Skeletal muscle covered in mucous membrane. Divided into lateral halves by a median septum. Attached inferiorly to the hyoid bone, styloid process of temporal bone, and mandible. Each half of the tongue consists of an identical arrangement of extrinsic and intrinsic muscles.
62
Extrinsic muscles of the tongue.
Originate outside the tongue. Insert into connective tissues in the tongue. Move the tongue from side to side, and in and out. Form the floor of the mouth. Hold the tongue in position.
63
Intrinsic muscles of the tongue.
Originate inside the tongue. Insert into connective tissue within the tongue. Alter the shape and size of the tongue for speech and swallowing.
64
Lingual frenulum.
Fold of mucous membrane in the midline of the undersurface of the tongue. Attached to the floor of the mouth. Limits the posterior movements of the tongue.
65
Papillae of tongue.
Projections of lamina propria covered with stratified squamous epithelium. Located on the dorsum and lateral surfaces of the tongue. May contain taste buds or touch receptors. Increase friction between tongue and food.
66
Lingual lipase.
Acts on 30% of dietary triglycerides and converts them to simpler FAs and diglycerides. Secreted by lingual glands in lamina propria of tongue. Becomes activated in the acidic environment of the stomach.
67
Where are teeth located?
Located in sockets of the alveolar processes of the mandible and maxillae. The sockets are lined by the periodontal ligament, which consists of dense fibrous connective tissue that anchors the teeth to the socket walls and acts as a shock absorber during chewing.
68
Dentin.
Forms the majority of the tooth. Consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. Harder than bone because of its higher content of hydroxyapatite.
69
Enamel.
The dentin of the crown is covered in enamel. Consists of calcium phosphate and calcium carbonate. Harder than bone because of its even higher content of hydroxyapatite. Hardest substance in the body. Protects the tooth from wear and tear, and from acids.
70
Cementum.
The dentin of the root is covered in cementum. Attaches the root to the periodontal ligament.
71
Pulp cavity.
Space inside the crown enclosed by dentin. Filled with pulp, which is a connective tissue containing blood vessels, nerves, and lymphatic vessels.
72
Root canals.
Narrow extensions of the pulp cavity that run through the root of the tooth.
73
Apical foramen.
Opening at the base of each root canal. Blood vessels, lymphatic vessels and nerves enter into the tooth through this opening.
74
Describe the blood vessels, lymphatic vessels and nerves of a tooth.
Blood vessels: nourishment
Lymphatic vessels: protection
Nerves: sensation
75
Endodontics.
Prevention, diagnosis and treatment of diseases that affect the pulp, root, periodontal ligament, and alveolar bone.
76
Periodontics.
Treatment of abnormal conditions of the tissues immediately surrounding the teeth.
77
Describe the 2 dentitions of humans.
Deciduous: Primary teeth. Milk teeth. Begin to erupt at 6 months, and two teeth appear each month thereafter. Lost between 6 and 12 years of age. 20 teeth total.
Permanent: Erupt between age 6 and adulthood. 32 teeth total.
78
Incisors.
Closest to midline. Chisel-shaped. Adapted for cutting into food. Central or lateral incisors. Have 1 root each.
79
Canines.
Pointed surface. Tear and shred food. Have 1 root each.
80
First and second deciduous molars.
4 cusps each. Maxillary molars have 3 roots. Mandibular molars have 2 roots. Crush and grind food.
81
Which 2 substances are involved in chemical digestion?
Salivary amylase, and lingual lipase.
82
Pharynx.
Skeletal muscle lined with mucous membrane. Divided into 3 parts (nasopharynx, oropharynx, laryngopharynx).
83
Esophagus.
Collapsible muscular tube posterior to trachea.
84
Describe the path of the esophagus.
Begins at inferior end of laryngopharynx --> inferior part of neck --> mediastinum --> pierces diaphragm through esophageal hiatus --> superior part of stomach.
85
Mucosa of esophagus.
Nonkeratinized stratified squamous epithelium. Contains lamina propria and muscularis mucosa. Contains mucous glands near the stomach.
86
Submucosa of esophagus.
Areolar connective tissue. Blood vessels. Mucous glands.
87
Muscularis of esophagus.
Skeletal muscle in superior 1/3rd of esophagus. Skeletal and smooth muscle in intermediate 1/3rd of esophagus. Smooth muscle in inferior 1/3rd of esophagus.
At each end, the muscularis becomes more prominent and forms two sphincters.
88
Upper esophageal sphincter (UES).
Skeletal muscle. Regulates movement of food from the pharynx into the esophagus.
89
Lower esophageal sphincter (LES).
Smooth muscle. Near the heart. Regulates movement of food from the esophagus into the stomach.
90
Deglutition.
Movement of food from mouth to stomach. Involves mouth, pharynx, esophagus, and saliva and mucus.
91
What are the 3 stages of swallowing?
1) Voluntary stage: Bolus is forced into the back of the oral cavity via the tongue --> oropharynx.
2) Pharyngeal stage: Bolus stimulates receptors in oropharynx --> send impulses to deglutition center in medulla oblongata and lower pons --> returning impulses cause soft palate and uvula to move upward and close off nasopharynx --> epiglottis also closes off the larynx opening --> bolus moves through oropharynx --> laryngopharynx --> UES --> esophagus.
3) Esophageal stage: Esophageal circular muscle fibres contract to constrict esophageal wall --> squeeze bolus towards stomach --> longitudinal fibres inferior to bolus also contract --> bolus reaches LES --> stomach.
92
Peristalsis.
Progression of coordinated contractions and relaxations of circular and longitudinal layers of the muscularis.
93
What does the esophagus secrete?
Mucus only.
94
Passage of solid/semi-solid food from the mouth to the stomach takes ___ .
Passage of very soft foods/liquids from the mouth to the stomach takes ___ .
4-8 seconds, 1 second.
95
Stomach.
Mixing chamber and holding reservoir. Continues digestion of starch and triglycerides. Begins digestion of protein. Semisolid bolus is converted to a liquid, and certain substances are absorbed.
95
Stomach.
Mixing chamber and holding reservoir. Continues digestion of starch and triglycerides. Begins digestion of protein. Semisolid bolus is converted to a liquid, and certain substances are absorbed.
96
What are the 4 main regions of the stomach?
1) Cardia: surrounds opening of esophagus into the stomach.
2) Fundus: rounded part superior to and left of cardia, storage function, not much peristalsis.
3) Body: large central part inferior to fungus.
4) Pyloric: pyloric antrum connects to the body of the stomach, pyloric canal leads to pylorus, and pylorus connects to the duodenum.
97
How do the pylorus and duodenum communicate with one another?
Pyloric sphincter (smooth muscle).
98
Lesser curvature of the stomach.
The concave medial border of the stomach.
99
Greater curvature of the stomach.
The convex lateral border of the stomach.
100
Mucosa of the stomach.
Simple columnar epithelial cells (surface mucous cells). Contains lamina propria and muscular mucosa. Epithelial cells extend down into the lamina propria to form columns of secretory cells, which are gastric glands. Several gastric glands open into the bottom of gastric pits. Secretions from gastric glands flow into each gastric pit and then into the lumen of the stomach.
101
Gastric glands contain 3 types of exocrine gland cells that secrete their products into the lumen of the stomach.
Mucous neck cells: secrete mucous along with surface mucous cells.
Chief cells: secrete pepsinogen and gastric lipase.
Parietal cells: produce intrinsic factor and HCl.
The secretions from these cells form gastric juice.
*intrinsic factor is needed for vitamin B12 absorption*
102
How much gastric juice is produced each day?
2,000 to 3,000 mL
103
G-cell.
A type of enteroendocrine cell in gastric glands. Located in pyloric antrum. Secretes gastrin into the bloodstream.
104
Submucosa of the stomach.
Areolar connective tissue.
105
Muscularis of the stomach.
3 layers of smooth muscle; outer longitudinal, middle circular, and inner oblique.
106
Oblique layer of the stomach.
Limited to the body of the stomach.
107
Serosa of the stomach.
Simple squamous epithelium and areolar connective tissue. The part of the serosa covering the stomach is part of the visceral peritoneum.
108
Peristaltic waves of the stomach.
Minutes after food enters the stomach, peristaltic waves pass over the stomach every 15-25 seconds. Waves begin at the body of the stomach, and intensify as they reach the antrum.
109
Retropulsion.
Because most food particles are initially too large to fit through the pyloric sphincter, they are forced back into the body of the stomach. Another round of propulsion occurs
110
Chyme.
After the bolus has been converted into a liquid, and mixed with gastric juices.
111
Gastric emptying.
Food particles in chyme leave the stomach through the pyloric sphincter.
112
How much chyme moves through the pyloric sphincter at a time?
3 mL
113
How exactly is salivary amylase inactivated in the stomach?
Food particles may remain in the fundus for about an hour without becoming mixed with gastric juices, and during this time, digestion by salivary amylase continues. Churning mixes chyme with acidic gastric juice, inactivating salivary amylase and activating lingual lipase.
114
How exactly is salivary amylase inactivated in the stomach?
Food particles may remain in the fundus for about an hour without becoming mixed with gastric juices, and during this time, digestion by salivary amylase continues. Churning mixes chyme with acidic gastric juice, inactivating salivary amylase and activating lingual lipase.
115
Describe the ions in the stomach.
Parietal cells secrete H+ and Cl- into the lumen of the stomach. Proton pumps powered by H+-K+ ATPases actively transport H+ into the lumen, and K+ into cells.
At the same time, Cl- and K+ diffuse into the lumen through Cl- and K+ channels in the apical membrane.
Carbonic anhydrase catalyzes the formation of carbonic acid from water and CO2. As carbonic acid dissociates, it provides a ready source of H+ for the proton pumps, and also generates HCO3-. As HCO3- builds up in the cytosol, it exits in parietal cells in exchange for Cl- via Cl-HCO3- anti porters in the basolateral membrane. HCO2- diffuses into nearby blood capillaries, elevates blood pH, and makes urine more alkaline.
116
What stimulates HCl secretion from parietal cells?
ACh released by parasympathetic neurons. Gastrin secreted by G-cells. Histamine released by mast cells in lamina propria.
*ACh and gastrin stimulate parietal cells to secrete more HCl in the presence of histamine, which enhances the effects of ACh and gastrin*
117
What is the action of HCl in the stomach?
It denatures/unfolds proteins in food particles, and stimulates the secretion of hormones that promote the flow of bile and pancreatic juice.
118
Pepsin.
The only proteolytic enzyme in the stomach. Secreted by chief cells. Breaks peptide bonds between amino acids. Most effective in the very acidic environment of the stomach. Inactivates at pH > 2.
119
How does pepsin not break down proteins in the stomach lining?
Pepsin is secreted in an inactive form, as pepsinogen, so it cannot digest the proteins in the chief cells that produce it. Pepsinogen is not converted into active pepsin until it comes into contact with HCl or active pepsin molecules. Stomach epithelial cells are protected from gastric juices by a layer of 1-3 mm of alkaline mucous secreted by surface mucous cells and mucous neck cells.
120
Gastric lipase.
Secreted by chief cells. Stomach enzyme that splits triglycerides into FAs and monoglycerides. Limited role in adult stomach. Operates best at pH 5-6.
121
Pancreatic lipase.
Pancreatic enzyme secreted into small intestine.
122
What molecules do mucous cells of the stomach absorb?
Water, ions, short-chain FAs, drugs, alcohol.
123
Within ____ after eating a meal, the stomach has emptied its contents into the duodenum.
2-4 hours.
124
Which foods spend the least amount of time in the stomach, and which foods spend the most amount of time in the stomach?
Least: high CHO.
Most: high protein, high fat.
125
Pancreas.
Retroperitoneal gland. Posterior to greater curvature of the stomach. Connected to the duodenum by two ducts. Consists of a head, body and tail.
126
Pancreatic juices.
Secreted by exocrine cells into small ducts that unite to form two larger ducts (pancreatic duct and accessory duct).
127
Pancreatic duct.
Larger duct. Joins the common bile duct from the liver and gallbladder, and enters the duodenum as a dilated common duct (hepatopancreatic ampulla). Ampulla opens on the major duodenal papilla. The passage of pancreatic juice and bile through the hepatopancreatic ampulla into the duodenum of the small intestine is regulated by a mass of smooth muscle surrounding the ampulla (sphincter of hepatopancreatic ampulla).
128
Accessory duct.
Major duct of pancreas. Leads from the pancreas to the duodenum.
129
Describe the acini and pancreatic islets of the pancreas.
The pancreas is made up of small clusters of glandular epithelial cells. 99% of these clusters are acini, and make up the exocrine part of the pancreas that secretes pancreatic juice. 1% of these clusters are pancreatic islets, and make up the endocrine part of the pancreas that secretes glucagon, insulin, somatostatin, and pancreatic polypeptide.
130
How much pancreatic juice is produced each day?
1,200 to 1,500 mL
131
Describe the action of sodium bicarbonate in pancreatic juice.
Buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine.
132
What are the enzymes in pancreatic juice?
Starch-digesting enzyme: pancreatic amylase.
Protein-digesting enzymes: trypsin, chymotrypsin, carboxypeptidase, elastase.
Princiap triglyceride-digesting enzyme: pancreatic lipase (in adults).
Nucleic acid-digesting enzymes: ribonuclease, deoxyribonuclease.
133
Describe protein-digesting enzymes in pancreatic juice.
They are produced in an inactive form.
Trypsin is secreted as trypsinogen --> pancreatic acinar cells secrete trypsin inhibitor which combines with any trypsin formed accidentally in the pancreas or in pancreatic juice and blocks its enzymatic activity --> when trypsinogen reaches the lumen of the small intestine it encounters an activating enzyme (enterokinase) which splits off part of the trypsinogen to form trypsin --> trypsin acts on inactive precursors (chymotrypsinogen, procarboxypeptidase, proelastase) to produce chymotrypsin, carboxypeptidase and elastase.
134
What is the heaviest gland of the body?
Liver.
135
Where is the liver located?
Inferior to the diaphragm. Occupies most of the right hypochondriac and part of the epigastric region of the abdominopelvic cavity.
136
Where is the gallbladder located?
In a depression of the posterior surface of the liver.
137
The liver is almost completely covered by ____ , and is completely covered by a ____ .
Visceral peritoneum, dense irregular connective tissue layer that lies deep to the peritoneum.
138
Falciform ligament.
Divides the liver into a large right lobe and a small left lobe. Helps suspend the liver in the abdominal cavity.
139
Ligamentum teres.
In the free border of the falciform ligament. Remnant of the umbilical vein of the fetus which extends from the liver to the umbilicus.
140
Right and left coronary ligaments.
Narrow extensions of the parietal peritoneum that suspend to the liver from the diaphragm.
141
What are the parts of the gallbladder?
Fundus: projects inferiorly beyond the inferior border of the liver.
Body: central.
Neck: tapered.
142
Hepatocytes.
Major functional cells of the liver. Specialized epithelial cells. 5-12 sides. Make up 80% of liver volume. Grooves in the cell membranes between neighbouring hepatocytes provide spaces for canaliculi into which the hepatocytes secrete bile.
143
Hepatic laminae.
Plates of hepatocytes bordered on either side of the endothelial-lined vascular space (hepatic sinusoids). Highly branched. Irregular structures.
144
Bile.
Excretory product. Consists of water, bile salts, cholesterol, lecithin, bile pigments, and ions. pH = 7.6-8.6. Aids in the digestion and absorption of fats.
145
Bile canaliculi.
Small ducts between hepatocytes that collect bile produced by the hepatocytes. Bile passes from bile canaliculi --> bile ductules --> bile ducts --> right and left hepatic ducts --> unite and exit the liver via common hepatic duct --> joins the cystic duct from gallbladder --> forms the common bile duct --> duodenum of small intestine --> participates in digestion.
146
Hepatic sinusoids.
Highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery, and nutrient-rich deoxygenated blood from branches of the hepatic portal vein. Converge and deliver blood into a central vein. Blood flows from central veins --> hepatic veins --> inferior vena cava. Bile flows in the opposite direction of blood.
147
Stellate reticuloendothelial cells.
Hepatic macrophages. Present in hepatic sinusoids. Fixed phagocytes. Destroy worn-out WBCs, RBCs, bacteria, foreign material in venous blood draining from GI tract.
148
Portal triad.
A bile duct, a branch of the hepatic artery, and a branch of the hepatic portal vein.
149
In what 3 ways can hepatocytes, bile duct system, and hepatic sinusoids be organized?
1) Hepatic lobule
2) Portal lobule
3) Hepatic acinus
150
Hepatic lobule.
Functional unit of the liver. Hexagon-shaped. At its center is a central vein and radiating out from it are rows of hepatocytes and hepatic sinusoids. Located at 3 corners of the hexagon is a portal triad. Surrounded by thick layers of connective tissue.
151
Portal lobule.
Bile duct of a portal triad is at the center. Triangular-shaped. Defined by 3 imaginary straight lines that connect 3 central veins that are closest to the portal triad.
152
Hepatic acinus.
Preferred model of the liver. Smallest structural and functional unit of the liver. Provides a logical description and interpretation of patterns of glycogen storage and release and toxic effects, degeneration, and regeneration fo the proximity of the acinus zones to branches of the portal triad. Oval mass that includes portions of 2 neighbouring hepatic lobules. The short axis is defined by branches of the portal triad that run along the border of the hepatic lobules. The long axis is defined by 2 imaginary curved lines which connect the 2 central veins closest to the short axis. Hepatocytes in the hepatic acinus are arranged in 3 zones around the short axis.
153
Describe the cells in zones 1, 2 and 3 of the hepatic acinus.
Zone 1: Cells are closest to the branches of the portal triad, and the first to receive incoming oxygen, nutrients, and toxins from incoming blood. Also the first ones to take up glucose and store it as glycogen after a meal, and breakdown glycogen to glucose during fasting. Also the first to show morphological changes following bile duct obstruction or exposure to toxins. Last to die if circulation is impaired. First to regenerate.
Zone 2: Have structural and functional characteristics intermediate between the cells in zone 1 and 3.
Zone 3: Farthest from branches of the portal triad. Last to show the effects of bile obstruction of exposure to toxins. First to show the effects of impaired circulation. Last to regenerate. First to show evidence of fat accumulation.
154
Mucosa of the gallbladder.
Simple columnar epithelium arranged in rugae.
155
Which accessory digestive organ lacks a submucosa?
Gallbladder.
156
Describe the middle layer of the wall of the gallbladder.
Smooth muscle fibres. Contraction ejects the contents of the gallbladder into the cystic duct.
157
The gallbladder's outer layer is the ___ .
Visceral peritoneum.
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Functions of the gallbladder.
Store and concentrate bile produced by the liver until it is needed in the duodenum. Water and ions are absorbed by the gallbladder mucosa.
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Liver receives blood from the ____ .
Hepatic artery and hepatic portal vein. Branches of these blood vessels carry blood into hepatic sinusoids, where oxygen, nutrients and toxins are taken up by hepatocytes. Products manufactured by the hepatocytes and nutrients needed by other cells are secreted back into the blood, which then drains into the central vein and eventually passes into a hepatic vein.
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Why would the liver be a site for metastasis of cancer that originates in the GI tract?
Since blood from the GI tract passes through the liver as part of the hepatic portal circulation.
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The phagocytosis of aged RBCs liberates...
Iron, globin and bilirubin. The iron and globin are recycled. The bilirubin is secreted into the bile and is broken down in the small intestine. Stercobilin is one of its breakdown products.
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Bile salts.
Na+ and K+ salts of bile acids. Play a role in emulsification, which is the breakdown of large lipid globules into a suspension of small lipid globules. The small lipid globules present a large SA that allows pancreatic lipase to more rapidly accomplish triglyceride digestion. Bile salts also aid in the absorption of lipids following digestion.
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When do hepatocytes release bile?
Continuously. They increase production and secretion when the portal blood contains more bile acids. As digestion and absorption continue in the small intestine, bile release increases.
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What happens to bile between meals?
It flows into the gallbladder for storage because the sphincter of the hepatopancreatic ampulla closes off the entrance to the duodenum.
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How does the liver maintain a normal blood glucose level?
By metabolizing CHOs. When blood glucose is low, the liver can break down glycogen to glucose, and also convert amino acids, lactic acid and sugars to glucose. When blood glucose is high, the liver converts glucose to glycogen and triglycerides.
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How does the liver metabolize proteins?
Hepatocytes deaminate amino acids and plasma proteins so they can be used for ATP production or converted to CHO/fats. The resulting toxic ammonia is then converted into less toxic urea which is excreted in urine.
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Duodenum.
First part of the small intestine. Shortest. Retroperitoneal. Starts at pyloric sphincter of stomach. C-shaped. Merges with jejunum. Means "twelve" because it is as long as the width of 12 fingers.
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Jejunum.
Middle part of the small intestine. Merges with ileum. Means "empty" which is how it is found at death.
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Ileum.
Last part of the small intestine. Longest. Joins the large intestine at the ileocecal sphincter.
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Mucosa of the small intestine.
Contains many deep crevices from the intestinal glands that secrete intestinal juice.
Epithelium: Simple columnar epithelium. Absorptive cells produce brush border enzymes that digest food and possess microvilli that absorb nutrients. Goblet cells secrete mucous. Paneth cells secrete lysozyme and are capable of phagocytosis. S-cells secrete secretin. CCK-cells secrete CCK. K-cells secrete GIP.
Lamina propria: Areolar connective tissue. Abundance of MALT.
Muscularis mucosa: Smooth muscle.
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Enteroendocrine cells.
S-cells. CCK-cells. K-cells.
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Lymphatic nodules in the small intestine.
Solitary lymphatic nodules are most numerous in the distal part of the ileum. Groups of lymphatic nodules (Peyer's patches) are also present in the ileum.
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Submucosa of the small intestine.
Duodenum contains duodenal glands which secrete an alkaline mucus that helps neutralize gastric acid in chyme.
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Muscularis of the small intestine.
Outer thin layer of longitudinal muscle fibres. Inner thick layer of circular muscle fibres.
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Serosa of the small intestine.
Completely surrounds the small intestine, except for a major part of the duodenum which is retroperitoneal.
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Plicae circulares.
Circular folds of mucosa and submucosa of small intestine. Enhance absorption by increasing SA and causing the chyme to spiral.
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Each villus of the small intestine is covered by...
Epithelium and has a core of lamina propria. Embedded in the connective tissue of the lamina propria are an arteriole, venule, blood capillary network, and lacteal.
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Nutrients absorbed by the epithelial cells covering the villus pass through the...
Wall of a capillary or lacteal to enter blood of lymph.
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Microvilli.
Projections of apical membrane of absorptive cells. Each one contains a bundle of 20-30 actin filaments. Form a brush border extending into the lumen of the small intestine.
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The small intestine completes digestion of...
CHO, proteins, lipids.
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The small intestine begins and completes digestion of...
Nucleic acids.
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The small intestine absorbs ____ of nutrients and water that pass through the digestive system.
90%
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How much intestinal juice is secreted every day?
1-2 L
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Brush border enzymes.
Secreted by absorptive cells in small intestine.
CHO-digesting enzymes: alpha-dextrinase, maltase, sucrase, lactase.
Protein-digesting enzymes: peptidase, aminopeptidase, dipeptidase.
Nucleotide-digesting enzymes: nucleosidase, phosphatase.
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Segmentations and MMC are governed by the...
Myenteric plexus.
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Segmentations.
Localized mixing contractions that occur in parts of the small intestine distended by a large volume of chyme. Mix chyme with the digestive juices and bring food particles into contact with mucosa for absorption. Do not push the intestinal contents along.
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Migrating motility complex (MMC).
A type of peristalsis that begins in the lower stomach and pushes chyme along a short stretch of small intestine before dying out. Slowly migrates down the small intestine to reach the end of the ileum in 90-120 min. Then another MMC begins in the stomach.
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Chyme remains in the small intestine for...
3-5 hours
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A segmentation starts with...
The contraction of circular muscle fibres in a part of the small intestine. This constricts the intestine into segments. Next, muscle fibres that encircle the middle of each segment also contract, dividing each segment again. The fibres that first contracted relax, and each small segment unites with an adjoining small segment. Chyme sloshes back and forth as this sequence repeats.
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The completion of the digestion of CHO, proteins and lipids is a collective effort of which juices in the small intestine?
Pancreatic juice, bile, intestinal juice.
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Describe how CHOs are broken down in the small intestine.
Starches not already broken down are cleaved by pancreatic amylase. Alpha-dextrinase acts on resulting alpha-dextrins to clip off 1 glucose at a time. Sucrase breaks sucrose into glucose and fructose. Lactase breaks lactose into glucose and galactose. Maltase breaks maltose and maltotriose into 2-3 glucose molecules.
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Describe how proteins are broken down in the small intestine.
Enzymes of pancreatic juice continue to break down proteins into peptides. Carboxypeptidase splits off the amino acid at the carboxyl end of a peptide. Aminopeptidase cleaves off the amino acids at the amino end of a peptide. Dipeptidase splits dipeptides into single amino acids.
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Describe how lipids are broken down in the small intestine.
Most lipid digestion occurs in the small intestine by pancreatic lipase. Before a large lipid globule containing triglycerides can be digested, it must undergo emulsification, which is when the globule is broken down into small lipid globules. Bile salts are amphipathic, so they are able to emulsify large lipid globules.
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Describe how nucleic acids are broken down in the small intestine.
Ribonuclease and deoxyribonuclease from pancreatic juice digests RNA and DNA. They are further digested by brush border enzymes into pentoses, phosphates and nitrogenous bases.
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Which substances can be absorbed by epithelial cells in the small intestine?
Monosaccharides, single amino acids, dipeptides, tripeptides, fatty acids, glycerol, monoglycerides.
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How is fructose transported?
Facilitated diffusion.
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How are glucose and galactose transported?
Secondary active transport. Coupled to the active transport of Na2+ (binds 1 glucose, 2 Na; galactose competes).
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How are proteins absorbed?
As amino acids by active transport. About 1/2 of the absorbed amino acids are present in food, and the other 1/2 come from the body itself as proteins in digestive juices and dead cells that slough off the mucosal surface. Some amino acids enter absorptive cells of the villi via Na+-dependent secondary active transport processes, and other amino acids are actively transported by themselves.
At least one symporter brings in dipeptides and tripeptides together with H+, and hydrolyzed to single amino acids inside absorptive cells. Amino acids then move out of the absorptive cells via diffusion and enter capillaries of villi.
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____ of the protein present in the small intestine is digested and absorbed.
95-98%
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Which substances are transported in blood to the liver by way of the hepatic portal system?
Monosaccharides and amino acids. If not removed by hepatocytes, they enter the general circulation.
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All dietary lipids are absorbed via...
Simple diffusion.
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Why would newborns absorb only 85% of the lipids in their small intestine, rather than 95%?
Low production of bile.
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Besides their role in emulsification, bile salts help...
Make large short-chain FAs, long-chain FAs, and monoglycerides more soluble with the use of micelles. Once formed, the micelles move from the interior of the small intestinal lumen to the brush border of the absorptive cells. The substances then diffuse out of the micelles into the absorptive cells, and they recombine to form triglycerides which aggregate into globules, phospholipids and cholesterol, and become coated with proteins. These chylomicrons leave the absorptive cell via exocytosis and cannot enter blood capillaries so they enter lacteals. They are transported via lymphatic vessels to the thoracic duct and enter the blood at the junction of the left internal jugular and left subclavian veins. Lipoprotein lipase breaks down triglycerides in chylomicrons into FAs and glycerol. FAs diffuse into hepatocytes and adipose cells and combine with glycerol during resynthesis of triglycerides.
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How are Na+ ions absorbed?
Moved into absorptive cells via diffusion and secondary active transport. Moved out of absorptive cells by active transport basolateral Na-K pumps. Most are reclaimed and not lost in the faces.
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How are bicarbonate, nitrate, Cl-, I- ions absorbed?
Passively follow Na+, or are actively transported.
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How are Ca2+ ions absorbed?
Active transport stimulated by calcitriol.
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How are Fe, K, Mg, P ions absorbed?
Active transport.
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How are fat-soluble vitamins absorbed?
Included with large lipids in micelles. Absorbed via simple diffusion.
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How are B vitamins and vitamin C absorbed?
Simple diffusion.
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How is vitamin B12 absorbed?
Combines with intrinsic factor produced by stomach. Absorbed in ileum via active transport.
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How much water is excreted in feces each day?
0.1 L
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The absorbed electrolytes, monosaccharides, and amino acids establish a...
Concentration gradient for water that promotes water absorption via osmosis.
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Large intestine.
Extends from ileum to anus. Attached to the posterior abdominal wall by its mesocolon. Completes absorption, the production of certain vitamins, the formation of feces, and the expulsion of feces.
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Ileocecal sphincter.
Smooth muscle. Opening of ileum into large intestine.
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4 regions of large intestine.
Cecum, colon, rectum, anal canal.
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Cecum.
Inferior to ileocecal sphincter. Small pouch. Attaches to appendix and colon.
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Colon.
Divided into ascending, transverse, descending and sigmoid parts. Ascending and descending are retroperitoneal.
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Rectum.
Anterior to sacrum and coccyx.
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Anal canal.
Terminal 2-3 cm of large intestine. Mucous membrane is arranged in longitudinal folds (anal columns) that contain a network of arteries and veins.
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Internal anal sphincter.
Smooth muscle.
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External anal sphincter.
Skeletal muscle.
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Mucosa of large intestine.
Epithelium, lamina propria, muscularis mucosa. Simple columnar epithelium. Absorptive cells and goblet cells are located in long straight tubular intestinal glands that extend the full thickness of the mucosa. No circular folds or villi. There are microvilli, and they are present on the absorptive cells.
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Submucosa of large intestine.
Areolar connective tissue.
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Muscularis of large intestine.
External longitudinal smooth muscle. Internal circular smooth muscle. Parts of the longitudinal muscles are thickened, forming 3 teniae coli that run the length of the large intestine. Tonic contractions of these teniae coli gather the colon into a series of haustra which give the colon a puckered appearance. A single layer of circular smooth muscle lies between teniae coli.
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Serosa of large intestine.
Part of the visceral peritoneum. Small pouches of visceral peritoneum filled with fat are attached to teniae coli and are called omental appendices.
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Right after a meal, what happens to the ileocecal sphincter?
A gastroileal reflex intensifies peristalsis in the ileum and forces any chyme into the cecum while gastrin relaxes the sphincter. Whenever the cecum is distended, the degree of contraction of the ileocecal sphincter intensifies.
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Haustral churning.
Haustra in large intestine remain relaxed and become distended while they fill up. When distention reaches a certain point, the walls contract and squeeze the contents into the next haustrum.
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Mass peristalsis.
Strong peristaltic wave that begins at the middle of the transverse colon and quickly drives the contents of the colon into the rectum.
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The final stage of digestion occurs in the ___ through the activity of ____ .
Colon; bacteria.
The bacteria prepare chyme for elimination by fermenting any remaining CHOs and releasing H, CO2 and CH4 gases. Bacteria also convert any remaining proteins to amino acids and break them down into simpler substances. Bacteria also converts bilirubin to simpler pigments like stercobilin.
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Feces.
After 3-10 hours of chyme remaining in the large intestine. Sold or semi-solid due to water reabsorption.
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Defecation reflex.
Mass peristaltic movements push fecal material from sigmoid colon to rectum --> distension of rectal wall --> stretch receptors send sensory nerve impulses to sacral spinal cord --> motor impulses travel along parasympathetic nerves to large intestine --> contraction of longitudinal rectal muscles --> shortens the rectum --> increases rectal pressure --> voluntary contractions of diaphragm and abdominal muscles --> internal anal sphincter opens.
If defecation does not occur, the feces back up into the sigmoid colon until the next wave of mass peristalsis stimulates stretch receptors.
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Phases of digestion.
Cephalic phase, gastric phase, intestinal phase.
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Cephalic phase.
Prepares mouth and stomach for food.
Smell, sight, thought or initial taste of food activates neural centres in cerebral cortex, hypothalamus and brain stem --> brain stem activates facial, glossopharyngeal and vagus nerves --> facial and glossopharyngeal nerves stimulate salivary glands --> vagus nerves stimulate gastric glands.
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Gastric phase.
Begins once food reaches the stomach.
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Neural regulation of gastric phase.
Chemoreceptors or stretch receptors in stomach detect increases in pH or distention --> nerve impulses propagate to submucosal plexus --> activate parasympathetic and enteric neurons --> resulting impulses cause waves of peristalsis and continue to stimulate the flow of gastric juice --> small amounts of chyme undergo gastric emptying --> pH decreases and distention decreases --> suppresses secretion of gastric juice and waves of peristalsis.
*negative feedback*
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Hormonal regulation of gastric phase.
Gastric secretion is regulated by gastrin, which is released from G-cells of gastric glands --> enters blood --> reaches target organs in digestive system --> stimulates gastric glands to secrete gastric juice, strengthens contraction of lower esophageal sphincter to prevent acid reflux, increases stomach motility, and relaxes pyloric sphincter to promote gastric emptying.
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What stimulates gastric glands to release gastrin?
Stomach distension, partially digested proteins in chyme, high pH of chyme, caffeine in chyme, ACh released from parasympathetic neurons.
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Intestinal phase.
Begins once food enters small intestine. Reflexes of this phase slow gastric emptying to prevent the duodenum from being overloaded.
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Neural regulation of intestinal phase.
Distension of duodenum causes enterogastric reflex --> stretch receptors send nerve impulses to medulla oblongata --> inhibit parasympathetic stimulation --> stimulate sympathetic nerves of stomach --> inhibits gastric motility.
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Hormonal regulation of intestinal phase.
CCK is secreted by CCK-cells of intestinal glands in response to chyme containing amino acids from partially digested proteins, and FAs from partially digested triglycerides. CCK stimulates secretion of pancreatic juice, causes contraction of gallbladder wall, causes relaxation of hepatopancreatic ampulla sphincter, allows gastric emptying by promoting contraction of pyloric sphincter, produces satiety by acting on hypothalamus, promotes normal growth and maintenance of pancreas, enhances secretin effects.
Secretin is secreted by S-cells of intestinal glands in response to acidic chyme entering the duodenum. Secretin stimulates the flow of pancreatic juice, inhibits gastric juice secretion, promotes normal growth and maintenance of pancreas, enhances CCK effects.
