Chapter 24: The Digestive System Flashcards
1
Q
List the accessory digestive organs
A
teeth tongue salivary glands liver gallbladder pancreas
2
Q
What are the 6 basic functions of the digestive system?
A
Ingestion - taking food into mouth
Secretion - release of water, acid, buffers, and enzymes into lumen of GI tract
Mixing & propulsion - churning and movement
Digestion - mechanical and chemical breakdown
Absorption - passage of digested products from GI tract into blood and lymph
Defecation - elimination of faces
3
Q
Define motility
A
Capacity of GI tract to mix and move material along its length
4
Q
What is the difference between mechanical and chemical digestion?
A
Mechanical - teeth cut and grind food, smooth muscles churn the food
Chemical - large carbs, lipids, proteins, and nucleic acid molecules are split into smaller molecules by hydrolysis
5
Q
List the 4 layers of the GI tract from deep to superficial
A
Mucosa
Submuscosa
Muscular
Serosa/adventita
6
Q
Describe the 3 layers of the mucosa tissue
A
- Epithelium - in direct contact with the contents of the of GI tract; are sloughed off every 5-7 days and have exocrine glands (release secretions) and enteroendocrine cells (secrete hormones)
- Lamina propria is areolar connective tissues containing many blood and lymphatic vessels, which are the routes by which nutrients are absorbed; containing the majority of mucosa-associated lymphatic tissue (MALT) that contain immune cells that protect against disease
- Muscular mucosal - thin layer of smooth muscles that throws the mucous membrane of stomach and small I into many small folds, increasing the SA
7
Q
Describe the submucosa
A
Areolar connective tissue that binds mucous to the muscularis
Located in the submucosa is the submucosa plexus which is an extensive network of neurons
8
Q
Describe the muscularis layer
A
In the mouth, pharynx, and superior and middle esophagus (and anal sphincter) the muscularis contains skeletal muscle that produces voluntary swallowing (and defecation)
Throughout the rest is smooth muscle that allows for involuntary contracts to help bread down food and proper it along the GI tract
9
Q
`Describe function of the serosa layer
A
The most superficial layer which is a serous membrane composed of areolar connective tissue and simple squamous epithelium
aka the visceral peritoneum because it forms a portion of the peritoneum
10
Q
Which part of a GI tract does not have a serosa layer?
A
The esophagus
Has only a single layer of areolar connective tissue called the adventitia
11
Q
Describe the two plexuses of the enteric nervous system
A
Myenteric plexus - located between the longitudinal and circual smooth muscle layers of muscularis; mostly controls GI tract motility particularly strength of contraction of muscularis
Submucosal plexus - found within the submucosa; controls the secretions of the organs that supply the GI tract
12
Q
How is the enteric nervous system regulated by the autonomic nervous system?
A
The vagus nerve (X) supply parasympathetic fibers to most parts of the GI tract, except the last half of large I which is supplied by the sacral spinal cord
Stimulation of the parasympathetic nerves that innervate the GI tract causes an increase in GI secretion and motility by increasing the activity of ENS neurons
Sympathetic nerves that supply the GI arise from the thoracic and upper lumbar regions of spinal cord and in general cause a decrease in GI secretion and motility by inhibiting activity of ENS neurons
13
Q
What is a gastrointestinal reflex pathway?
A
Initial components are sensory receptors (chemoreceptors and baroreceptors) that are associated with the sensory neurons of ENS
They synapse with other neurons located in the ENS, CNS, or ANS and subsequently activate or inhibit GI glands and smooth muscle, altering GI secretions and motility
14
Q
Describe the peritoneum and its subdivisions
A
Peritoneum is the largest serous membrane that consists of a layer of simple squamous epithelium with underlying supporting layer of connective tissue
14
Q
Describe the peritoneum and its subdivisions
A
Peritoneum is the largest serous membrane that consists of a layer of simple squamous epithelium with underlying supporting layer of connective tissue
Divided into the parietal peritoneum which lines the wall of the abdominal cavity and the visceral peritoneum which covers some of the organs in the cavity and is their serosa
Between these two subdivisions is the peritoneal cavity
15
Q
What does it mean when organs are retroperitoneal?
A
They lie on the posterior abdominal wall and are covered by peritoneum only on their anterior surfaces; they are no in the peritoneal cavity
16
Q
List and describe the 5 major peritoneal folds
A
Greater omentum - largest folds, drapes over transverse colon and coils with small intestine; double layer that folds back on itself giving a total of 4 layers; comprised of a lot of adipose tissue
Falciform ligament - attaches liver to anterior wall and diagrpham
Lesser omentum - arises as anterior fold in the serosa of the stomach and duodenum to the liver; pathway for blood vessels eating the liver and contains hepatic portal vein
Mesentery - fan-shaped fold of peritoneum that binds the jejunum and ileum of small intestine to the posterior abdo wall
Mesocolon - binds transverse colon and sigmoid colon of large I to the posterior abdo wall ; carries blood and lymphatic vessels to intestines
17
Q
What structures form the mouth?
A
Cheeks - covered internally by a mucous membrane, forms the lateral walls
Hard palate - (bony) forms most of the roof of the mouth, formed by maxillae and palatine bones
Soft palate (muscular) forms the rest of the roof of the mouth
Tongue
18
Q
The inner surface of the lips are attached to a gum by a midline fold of mucous membrane called _______
A
labial frenulum
19
Q
Describe the following components of the mouth: oral vestibule, oral cavity proper, fauces
A
Oral vestibule - the space bounded externally by the cheeks and lips and internally by the gums and teeth
Oral cavity proper - the space that extends from the gums and teeth to the faces, the opening between the oral cavity and the oropharynx
20
Q
Describe the function of the uvula during swallowing
A
It is drawn superiorly, closing off the nasopharynx and preventing swallowed food and liquids from entering the nasal cavity
21
Q
Define salivary glands and discuss 3 pairs of major salivary glands and their associated ducts
A
A salivary gland is a gland that release a secretion called saliva into the oral cavity - the major salivary glands lie beyond the oral mucosa, into ducts that lead into the oral cavity
Parotid glands - located inferior and anterior to the ears, between the skin and the masseter muscle; secrete into cavity via parotid duct that pierces the buccinator muscle to open into the vestibule opposite the 2nd maxillary molar tooth
Submandibular glands - found in floor of mouth, medial and partly inferior to the body of the mandible; submandibular ducts run under the mucosa on either side of the midline of the floor of the mouth after enter cavity proper lateral to lingual frenulum
Sublingual glands - beneath the tongue and superior to the submandibular glands; the lesser sublingual ducts open into the floor of the mouth in the oral cavity proper
22
Q
Differentiate between the saliva secretions from each gland
A
Parotid - watery (serous) liquid containing salivary amylase
Submandibular - thickened mucous with salivary amylase
Sublingual - a much thicker fluid that only has small amount of salivary amylase
Salivary amylase is an enzyme that starts the breakdown of starch in the mouth into maltose, malotrisose, and a-dextrin
23
Q
How is salivation controlled by the ANS?
A
Parasympathetic stimulation promotes continuous secretion and sympathetic stimulations decreases salivation causing dry mouth (during stress)
24
Describe the structure and function extrinsic muscles and intrinsic muscles of the tongue
Extrinsic mucles - originate outside the tongue (attach to bones in the area) and insert into connective tissues of the tongue and include the hypoglossus, genioglossus, and styloglossus muscles that move the tongue side to side and in and out
Intrinsic muscles - originate in and insert into connective tissue within the tongue; alter the shape and side of tongue for speech and swallowing and include the longitudinalis superior, longitudinalis inferior, transversus linguae, and verticalis linguae muscles
25
What is the lingual frenulum
A fold of mucous membrane in the midline of the undersurface of the tongue that is attached to the floor of the mouth and aids in limiting the movement of the tongue posteriorly
26
What are lingual glands?
They are glands in the lamina proprietor of the tongue that secrete both mucous and a watery fluid that contains the enzyme lingual lipase which acts on as much as 30% of dietary triglycerides and coverts them to simply fatty acids
27
Teeth are anchored in sockets of the alveolar processes of the mandible and maxillae. Discuss the following components of teeth:
```
Gingivae
Periodontal ligament
Dentin
Enamel
Cementum
```
Gingivae - gums
Periodontal ligament - dense fibrous connective tissue that anchors the teeth to the socket walls and acts as a shock absorber during chewing
Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity
Enamel - primarily calcium phosphate and calcium carbonate which covers the dentin of the crown; hardest substance in the body
Cementum - bonelike subance which covers the dentin of the root and attaches root to periodontal ligament
28
What are the 3 major external regions of a tooth?
Crown - visible portion Avon the levels of the gym
Root(s) - embedded in the socket are 1-3 roots
Neck - constricted junction of the crown and root near the gum line
29
What is the pulp cavity in the tooth?
A space enclosed by dentin that is filled with pulp, a connective tissue containing blood vessels, nerves, and lymphatic vessels
Root canals, narrow extensions of the pulp cavity, run though the root of the tooth; each has an opening at its base called the apical foramen, through which blood vessels, lymphatic vessels, and nerves enter a tooth
30
What are the two dentitions of teeth?
Deciduous - first set aka primary teeth that begin to erupt at about 6m (20 teeth)
Permanent - deciduous teeth are replaced by permanent teeth between 6-12 years (32 teeth)
31
What functions fo the incisors, cuspids, premolars and molars perform?
Incisors - closest to the midline (central or lateral) and are chisel-shaped and adapted for cutting into food
Cuspids (aka canine) have a pointed surface called a cusp that are used to tear snd shred food
Premolars replace deciduous molars and each has 2 cusps crush and grind food to prepare it for swallowing
Molars do not replace any teeth and erupt in 3 waves; the first (6years), second (12 years), and third permanent molars (wisdom teeth ~17 years)
32
Describe the mechanical and chemical digestion processes that occur in the mouth
Mechanical digestion in the mouth results from mastication in which food is manipulated by tongue, ground by teeth, and mixed with saliva - food is reduced to a swallowable mass called a bolus
Salivary amylase and lingual lipase contributes to chemical digestion in the mouth
- salivary amylase imitates the breakdown of starch into monosaccharides, the only form that can absorbed by the blood stream
- lingual lipase (secreted by lingual glands in tongue) becomes activated in the acidic environment of the stomach and thus starts to work after food is swallowed; breaks down dietary triglycerides into fatty acids and diglyceries
33
Describe the function of pharynx in digestion
Both the oropharynx and laryngophrynx have digestive as well as respiratory functions
Food passes from mouth into oropharynx and laryngophrynx and the muscular contractions help propel food into esophagus and then into the stomach
34
Describe the location of the esophagus
Esophagus is a collapsible muscular tube that lies posterior to the trachea - beings at the inferior end of the laryngopharynz and enters the mediastinum anterior to the vertebral column
It pierces the diaphragm through an opening called the esophageal hiatus and ends in the stomach
35
Describe the histology of the esophagus
The mucosa of the esophagus cosnsits of a nonkeratinized squamous epithelium, lamina proprietor (connective tissue), and a muscular mucosa (skeletal - top 2/3; and smooth muscle - bottom)
At each end of the esophagus there is a sphincter: upper esophageal sphincter (UES) and lower esophageal sphincter (LES)
36
What are the functions of the upper and lower esophageal sphincters?
UES - consists of skeletal muscle, regulates the movement of food from the pharynx into esophagus
LES - consists of smooth muscle, reegulates the movement of food from the esophagus into the stomach
37
What is the superficial layer of the esophagus called?
Adventitia (rather than serosa) because the alveolar tissue is not covered by mesothelium and because the connective tissue merges with the connective tissue of surrounding structures of the mediastinum
38
The esophagus functions to produce digestive enzymes and carry on absorption
True or False
False
It secretes mucous and transports food into stomach
39
Define deglutition and describe its 3 phases
Deglutition is the act of swallowing and it occurs in 3 phases:
1. Voluntary stage - the bolus is passed into the oropharynx
2. Pharyngeal stage - the involuntary passage of the bolus through the pharynx into the esophagus; bolus stimulates receptors in the oropharynx which sends impulses to the deglutition center in the medulla and lower pons which causes the soft palate and uvula to close off the nasopharynx and epiglottis closes off the larynx
3. Esophageal stage - the involuntary passage of the bolus through the esophagus into the stomach; peristalsis the progression of coordinated contractions and relaxations of the circular and longtitutdal layers of the muscularis occurs which pushes the bolus onward
40
What are the 4 main regions of the stomach?
The stomach connects the esophagus to the duodenum, the first part of the small I, but has 4 main regions:
1. Cardia - surrounds the opening of the esophagus into the stomach
2. Fundus - the rounded portion superior to and left of the caridia
3. Body - inferior to the fundus and is the large central portion
4. Pyloric part - divisible into 3 regions: 1) pyloric antrum (connects to body); 2) pyloric canal; and 3) pylorus (connects to duodenum)
41
Where is the pyloric sphincter located?
Between the pylorus and duodenum
42
Define rugae
Large folds that the mucosa lies in when the stomach is empty
43
Differentiate between the lesser and greater curvature of the stomach
Lesser - concave medial border
| Greater - convex lateral border
44
What type of enteroendocrine cell is found in gastric glands?
G cells - secrete gastrin which stimulates parietal cells to secrete HCL, chief cells to secrete pepsinogen, contracts lower esophageal sphincter, increase motility, and relaxes pyloric sphincter
45
Describe the layers of the stomach
1. The mucosa layer has outer layer of surface mucous cells and contains a lamina proprietor (areolar connective tissue) and muscularis mucosa (smooth muscle)
Epithelial cells extend down into the lamina proprietor, where they form columns of secretory cells called gastric glands that open into gastric pits where they then exit into the lumen
2. The submucosa layer is composed of areolar connective tissue
3. The muscularis layer has 3 layers of smooth muscle: an outer longitudinal layer, a middle circulatory layer, and an inner oblique layer (only in body)
4. Serous layer is composed of simple squamous epithelium and areolar connective tissue
46
Describe the 3 types of exocrine gland cells that are found in gastric glands
mucous neck cells - secrete mucous and forms a protective barrier that prevents digestion of stomach wall
parietal cells - secrete intrinsic factors needed for absorption of vit B12 and secrete hydrochloric acid that kills microbes in food, denatures proteins, and converts pepsingoen into pepsin
chief cells - secrete pepsinogen (pepsin breaks down proteins into peptides), secrete gastric lipase which splits triglycerides into fatty acids and monoglycerides
*The overall secretions form gastric juice (2000-3000mL/day)
47
Describe propulsion and retropulsion
Propulsion - each peristaltic wave moves gastric contents from the body of the stomach down into the antrum
Retropulsion - when food particles are too large to fit through the narrow pyloric sphincter they are forced back into the body of the stomach
*These processes occur in a cycle until food becomes a soupy liquid called chyme and can pass through the sphincter, known as gastric emptying
48
Decribe the pancreas and its anatomic subdivisions (3)
Pancreas is a retroperitoneal glands that lies posterior to the great curvature of the stomach; It consists of a:
head - expanded portion of the organ near the curve of the duodenum
body - superior to and to the left of the head
tail - tapering end
49
What are the 2 major ducts in the pancreas?
1. Pancreatic duct (larger) - joins the common bile duct from the liver and gallbladder and enters the duodenum as a dilated common duct called the hepatopancreatic ampulla
2. Accessory duct - leads from the pancreas and empties into the duodenum superior to the hepatopancreatic ampulla
50
What is the major duodenal papilla?
The elevation of the duodenal mucousa where hepatopancreatic ampulla opens on located inferior to the pyloric sphincter of stomach
51
What are acini and pancreatic islets?
99% of the clusters in the pancreas are called acini which constitute the exocrine portion of the organ; the cells within acini secrete a mixture of fluid and digestive enzymes called pancreatic juice
The remaining 1% of clusters are pancreatic islets which form the endocrine portion of the pancreas which secrete hormones
52
List the enzymes in pancreatic juice
Pancreatic amylase - starch digesting enzyme
Trypsin, chymotrypsin, carboxypeptidase, and elastase - digest proteins into peptides
Pancreatic lipase - principal triglyceride-digesting enzyme in adults
Ribonuclease (digests nucleic acid) and deoxyribonuclease (digest RNA and DNA into nucelotides)
53
Why is trypsinogen (inactive) secreted rather than trypsin in the pancreas?
The inactive form of protein-digesting enzyme presents the pancreas being digested itself
Trypsin inhibitor is a protein secreted by pancreatic acing cells that combines with tyrpsin formed accediablly and blocks its enzymatic activity
When trypsinogen reaches the lumen of the small I it encounters an activating enzyme called enterokinase which acts on the inactive precursors of the other protein-digesting enzymes, activating all of them.
54
Define the liver
The heaviest gland in the body and second to skin in size - it is inferior to the diaphragm and occupies most of the right hypochondriac and part of the epigastric regions of the abdopelvic cavity
55
Define the gallbladder
Pear shaped sac that is located in a depression of the posterior surface of the liver
56
Describe the two lobes of the liver
Right lobe (larger) and a smaller left lobe that are divided by a falciform ligament, a fold of the mesentery
The right lobe is covered to include an inferior quadrate lobe and a posterior caudate lobe based on internal morphology, however they more appropriately belong to the left lobe
57
Define ligamentum teres
A remanent of the umbilical vein of the fetus which extends from the liver to the umbilicus - located in the free border to the falciform ligament
58
Describe the anatomic subdivisions of the gallbladder
Fundus - projects inferiorly beyond the inferior border of the liver
Body - central portion
Neck - tapered portion
59
Describe the following components of the liver: hepatocytes, bile canaliculi, and hepatic sinusoids
Hepatocytes - major functional cells of the liver that perform metabolic, secretory, and endocrine functions
Bile canaliculi - small ducts between hepatocytes that collect bile and pass it into bile ductules and then bile ducts which merge and eventually form the larger right and left hepatic ducts, which unite and exit the liver as the common hepatic duct that joins the cystic duct from the gallbladder to form the common bile duct where it enters the duodenum
Hepatic sinusoids - highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery and hepatic portal vein; sinusoids converge and deliver blood into a central vein that then flows into the hepatic veins which drain into the inferior vena cava
60
Define portal triad
Formed by the bile duct, branch of hepatic artery, and branch of hepatic vein
61
Describe the 3 ways the hepatocytes, bile duct system and hepatic sinusoids can be organized into anatomical and functional units (3 ways)
1. Hepatic lobule - each lobule is shaped like a hexagon with a central vein in the centre with rows of hepatocytes and sinusoids radiating out from it; has a portal triad at 3 of its corners
2. Portal lobule - the bile duct is taken as the centre and this lobule is triangular in shape, defined by 3 imaginary straight lines that connect 3 central veins that are closest to the portal triad
3. Hepatic acinus (preferred functional unit) - an oval mass that includes portions of 2 neighbouring hepatic lobules; there are 3 zones:
- zone 1: cells closet to the branes of the portal triad and the first to receive oxygen and nutrients from incoming blood
- zone 2: structural and functional characteristics between cells in zone 1 & 3
- zone 3: farthest from the portal triad and the first to show effects of impaired circulation
62
Describe hepatic blood flow - the path through the liver and back to the heart
The hepatic sinusoids receives oxygnatived blood from the hepatic artery and nutrient rich deoxygenated blood from the hepatic portal vein
Blood flows from the sinusoids through the central vein, though the hepatic vein, drains into the inferior cava, and is returned to the right atrium of the heart
63
Describe the role and composition of bile
Bile is a yellowish, brownish or olive-green liquid that consists of mostly water, bile salts, cholesterol, lecithin, bile pigments, and several ions
The principal bile pigment is bilirubin which is liberated from the phagocytosis of aged RBCs which is secreted into bile and eventually broken down in the intestine
Bile plays a role in emulsification, the breakdown of large lipid globules into a suspension of small lipid lobules
64
Describe the functions of the liver
1. Carbohydrate metabolism - breaks down glycogen to glucose
2. Lipid metabolism - break down fatty acids to produce ATP
3. Protein metabolism - dominate amino acids so they can be used for ATP
4. Processing of drugs and hormones
5. Excretion of bilirubin
6. Synthesis of bile salts - used in small I for emulsification and absorption of lipids
7. Storage - stores glycogen, vitamines, and minerals
8. Phagocytosis
9. Activation of vit D
65
Describe the 3 regions of the small intestine
Duodenum - shortest regions and is retroperitoneal; starts at pyloric sphincter and is C shaped until it merges with jejunum
Jejunum
Ileum - final and longest region that joins the large intestine at a smooth muscle sphincter called the ileocecal sphincter
66
Describe the function of the following epithelial cells of the small intestine:
absorptive cells
goblet cells
intestinal glands
Absorptive cells - release enzymes that digest food and contain microvilli that absorb nutrients in small intestinal chyme
Goblet cells - secrete mucous
Intestinal glands - lines the deep crevices in the epithelium and secretes intestinal juice
67
Beside absorptive and goblet cells, which other cells are found in intestinal glands?
Paneth cells - secrete lysozyme, a bactericidal enzyme, and are capable of phagocytosis
3 types of enteroendocrine cells: S cells, CCK cells, and K cells which secrete the hormones secretin, cholecystokinin (CK), and glucose-dependent insulinotropic peptide (GIP)
68
What are solitary lymphatic nodules?
Most numerous in the distal part of the ileum
Groups of lymphatic nodules are referred to as aggregated lymphatic follies (Peyer's patches)
69
Where are duodenal glands found?
In the submucosa of the duodenum - they secrete an alkaline mucous that helps neutralize gastric acid in the chyme
70
What are the special structural features of the small intestine that facility the process of digestion?
Circular folds - located in mucosa and submucosa; permanent ridges that enhance absorption by increasing SA and causing the chyme to spiral rather than move in a straight line
Villi - fingerlike projections that increases SA of epithelium available for absorption and digestion and gives the intense mucosa a velvety appearance; nutrients wabsnored pass through the wall of a capillary or a lacteal to enter blood or lymph respectively
Microvilli - projections of the apical (free) membrane of the absorptive cells; they form a fuzzy link called the brush border that extends into the lumen of small I; these increase SA of plasma membrane allowing larger amounts of digested nutrients to diffuse into absorptive cells
71
What is the role of intestinal juice and brush-border enzymes?
Intestinal juice (clear yellow fluid) is secreted each day and contains water and mucous with an alkaline pH that provides a liquid medium that aids in the absorption of substances from chyme
Brush border enzymes are inserted into the plasma membrane of the microvilli
- 4 carb-digesting enzymes: a-dextrinase, maltase, sucrase, lactase
- protein-digesting enzymes: peptidases
- 2 nucleotide-digesting enzymes: nucleosidases & phosphateases
72
Describe mechanical digestion in the small intestine
There are 2 types of movements in the small intestine which are both covered by the myenteric plexus:
Segmentations - localized mixing contractions that occur in portions of the intestine distended by a large volume of chyme, they bring participates of food in contact with digestive juices rather than pushing the contents along the tract
Migrating motility complex (MMC) - type of peristalsis that occurs when most of the meal as been absorbed and it pushes chyme forward slowly migrating from the stomach to the end of intestine
73
Which enzymes digest carbohydrates in the small intestine?
Pancreatic amylase - splits starch into smaller fragments
a-dextrinase - brush border enzyme that clips of glucose from a-dextrins
3 brush border enzymes that digest disaccharides into monosaccharides: sucrase, lactase, and maltase
74
Which enzymes digest proteins in the small intestine?
protein digestion is completed by two peptidases in the brush border:
aminopeptidase - cleaves off the amino acid at the amino end of a peptide
Dipeptidase - splits dipeptides into single amino acids
75
Which enzymes digest lipids in the small intestine?
Enzymes that split triglycerides and phospholipids are called lipase: lingual lipase, gastric lipase, and pancreatic lipase*
76
Which enzymes digest nucleic acid in the small intestine?
brush-border enzymes celled nucelosidases and phophatases
77
How are monosaccharides absorbed in the small intestine?
Pass from the lumen through the apical membrane via facilitated diffusion or active transport
Fructose is transported via facilitated diffusion and glucose and galactose are transported into absorptive cells of the villi via secondary active transport coupled with Na+
** All digested carbohydrates are absorbed, leaving only indigestible cellulose
Transported in blood to liver by way of hepatic portal system
78
How are amino acids, dipeptides and tripeptides absorbed by the small intestine?
Most proteins are abored as amino acids via active transport (Na+)
At least one symporter brings in dipeptides and tripeptides together with H+; the peptides are hydrolyzed to single amino acids inside the absorptive cell and then move out and into capillaries via diffusion
Transported in blood to liver by way of hepatic portal system
79
How are lipids and bile sats absorbed in the small intensive?
All dietary lipids are absorbed via simple diffusion
Large short-chain fatty acids and long chain fatty acids that are not water-soluble are surrounded by bile salts forming tiny spheres called micelles which move from interior to small I lumen to the brush border to absorptive cells
They then aggregate inside the cell in spherical masses called chylomicrons that leave the absorptive cell via exocytosis where they enter lacteals before they enter the blood
Once in the blood lipoprotein lipase which breaks down triglycerides in chylomicrons removes them
80
Define enterohepatic circulation
The cycle of bile salt secretion by hepatocytes into bile, reabsorption by the ileum, and resection into bile
81
How are vitamins absorbed in the small intestine?
fat-soluble vitamins and most water-soluble vitamins are absorbed via simple diffusion
Vit B12 however combines with intrinsic factor and is absorbed via an active transport mechanism
82
How is water absorbed in the GI tract?
All absorption occurs via osmosis
83
Describe the anatomy of the large intestine
Extends from the ileum to the anus and is attached to the posterior abdominal wall by its mesocolon, which is a double layer of peritoneum
There are 4 major regions:
1. Cecum - inferior to the ileocecal valve; small pouch that is attached to the appendix (vermiform appendix)
2. Colon - long tube which is divided into 4 portions: ascending, transverse, descending, and sigmoid portions
3. Rectum - lies anterior to the sacrum and coccyx
4. Anal canal - terminal end of large intestine that is comprises of anal columns which are longitudinal folds of mucous membrane that contain a network or arteries and veins
84
Describe the 4 portions of the colon
Ascending - ascends on the right side of abdomen, reaches the inferior surface of liver, and turn abruptly to the left to form the right colic fixture
Transverse - continues across the abdomen to the left side
Descending - passes inferiorly to the level of the iliac crest
Sigmoid - projects medially and terminates as the rectum
85
Differentiate between in the internal and external anal sphincter
Internal - smooth muscle (involuntary)
| External - skeletal muscle (voluntary)
86
How does the mucosa and submucosa differ in the large intestine compared to small intestine?
They have the same 4 layers found in the rest of the GI tract but the large I lacks the structural adaptions that increase SA
In the submucosa of the large I the longitudinal muscles are thickened, forming 3 conspicuous bands called teniae coli that gated the colon into a series of pouches called hausfrau, which gives the colon a puckered appearance
87
Describe mechanical digestion in the large intestine
Immediately after a meal, a gastroileal reflex intensifies peristalsis in the ileum and forces any chyme into the cecum
Haustral churning - the haustra remains relaxed and become distending while they fill up and then the walls contract and squeeze the contents into the next haustrum
Mass peristalsis - strong peristaltic wave that beings at middle of transverse colon and quickly drives the contents into the rectum
Because food in stomach inmates this gastrocolic reflex mass peristalsis typically occurs 3-4 times per day, during or immediately after a meal
88
Describe chemical digestion in the large intestine
Mucous (but no enzumes) are secreted and chyme is prepared for elimination by action of bacteria, which ferment any remaining carbs and release H+, CO2, and methane gases
89
Describe the defecation reflex
Distension of the rectal wall stimulates stretch receptors which initiates a defectaton reflex that results in defecation
The receptors send sensory impulses to the sacral spinal cord and motor impulses from the cord travel along the parasympathetic nerves back to the descending colon, sigmoid coli, rectum, and anus resulting in contraction of longitudinal muscles that increases pressure and opens the internal anal sphincter
90
List the 3 phages of digestion
1. Cephalic phase - smell, sight, thought or initial tate of food activates neural centres in the cortex, hypothalamus, and brains stem which stimulates secretion of saliva and gastric juices
2. Gastric phase - neural and hormonal mechanisms regulate the gastric phase to promote gastric secretion and motility
3. Intestinal phase - begins once food enters the small I and has inhibitory effect that slow the exit of chyme from the stomach preventing the overloading of the duodenum
91
Describe how the gastric phase of digestion is regulated by neurons and hormones
Neural regulation - when baroreceptors or chemoreceptors are activated, a neural negative feedback loop is set in motion
- receptors send nerve impulses to submucosal plexus
- parasympathetic nerve impulses are sent that cause partial cells to secreter HCL and smooth muscles to contract more vigorously
- homeostasis returns when receptors are no longer activated
Hormonal regulation - gastrin is released from G cells of the gastric glands where it enters the bloodstream and stimulates gastric glands to secrerare large amounts of gastric juice and strengthens contractions of lower esophageal sphincter and increases motility of stomach
92
Describe how activities of the intestinal phase of digestion are regulated by neural and hormonal mechanisms
Neural regulation - distension of the duodenum by presence of chyme causes the enterogastric reflex to send impsules to medulla where they inhibit parasymapthic stimulation and stimuate the sympathetic nerves to the stomach, inhibiting gastric motility
Hormonal regulation - cholecystokinin (CCK) stimulates secretion of pancreatic juice rich in digestive enzymes, causes ejection of bile from gallbladder and opening of sphincter in hepatpancreatic ampulla; secretin stimulates secretion of pancreatic juice and bile that are which in bicarbonnate ions
93
Define dental caries
aka tooth decay - involves gradual sofenting of the enamel and dentin which can allow microorganisms to invade the pulp, causing inflammation and infection which can cause dead of the pulp
94
Define personal disease
Characterized by inflammation and degeneration of the gingival, alveolar bone, periodontal ligament, and cementum
95
Define peptic ulcer disease
an ulcer is a crater like lesion in a membrane; ulcers that develop in areas of the GI tract exposed to acidic gastric juices are called peptic ulcers
Helicobacter pylori is the most frequent cause of PUD
96
Define diverticulosis
Saclike out pouching of the wall of the colon occur in places where the muscularis has weakened and may become inflamed
97
Define hepatitis
Inflammation of the liver that can be caused by viruses, drugs, and chemicals
97
Define hepatitis
Inflammation of the liver that can be caused by viruses, drugs, and chemicals
