Digestive system Flashcards
(121 cards)
1
Q
What are the functional segments of the GI tract (alimentary canal) ?
A
Mouth, pharynx, esophagus, stomach, small intestine, large intestine
2
Q
What are the accessory structures of the GI tract?
A
Teeth, tongue, salivary glands, liver, gallblader, pancreas
3
Q
What is the function of the alimentary canal?
A
Nourish the body
4
Q
What is the function of the accessory structures ?
A
Aid in the breakdown of food
5
Q
What are the six basic processes of digestion?
A
- Ingestion : taking food into the mouth
- Secretion: release by cells within the walls of the GI tract and accessory organs– of water, acid, buffers, and enzymes into the lumen of the tract
- Mixing and propulsion: cause by the alternating contraction and relaxation of the smooth muscles within the walls of the GI tract
- Digestion: mechanical and chemical breakdown of food into small molecules
- Absorption: passage of the end products of digestion from the GI tract into blood or lymph for distribution to cells
- Defecation: emptying of the rectum, which eliminates indigestible substancecs from the GI tract
6
Q
What movements compose propulsion and where does it occur?
A
- Swallowing (oropharynx)
- Peristalsis (esophagus, stomach, small intestine, large intestine)
7
Q
What muscles can peristalsis be done with?
A
Smooth muscles only
8
Q
What movements compose mechanical digestion and where does it occur?
A
- Chewing (mouth)
- Churning (stomach)
- Segmentation (small intestine)
9
Q
How does the lymphatic system support the digestive system?
A
MALT and other tissue defend entry of pathogens, lacteals absorb lipids and lymphatic vessels transport lipids into the bloodstream
10
Q
What is the basic arrangement of layers of the GI tract ?
A
Mucosa, submucosa, muscularis and serosa
11
Q
What is another name for serosa?
A
Visceral peritoneum
12
Q
What are the three layers of the mucosa?
A
Epithelium, lamina propria, and muscularis mucosa
13
Q
What kinds of cells are in the epithelium of the mucosa?
A
- Protective layer of non keratinized stratified squamous cells (except in stomach and intestine, then columnar)
- Simple cells for secretion and absorption)
- Goblet cells (mucus secreting cells )
- Enteroendocrine cells (excrete hormones that help to regulate the digestive process)
14
Q
What is in the lamina propria of the mucosa ?
A
Lymphatic nodules (mucous associated lymphatic tissue) and Peyer’s patched in the distal ileum
15
Q
What is the role of the muscularis mucosa?
A
To cause the local folding on the mucosal layer to increase the surface area for digestion and absorption
16
Q
What type of tissue is the submucosa made of ?
A
areolar connective tissue
17
Q
What is the submucosa composed of ?
A
- Blood vessels
- Plexus of Meissner (submucosal plexus)
- lymphatic glands and tissues
- Enteric nervous system
18
Q
What is the role of the plexus of Meissneir?
A
Regulate digestive secretions and react to presence of food
19
Q
What is the muscularis composed of?
A
- In the mouth, pharynx and superior part of the esophagus, skeletal muscles to rpoduce voluntary swallowing
- In the rest of the GI tract, smooth muscles with inner circular fibers and outer longitudinal fibers
- Major nerve supply (myenteric plexus or plexus of Auerbach)
20
Q
What is the role of the plexus of Aeuerbach and what division of the nervous system controls it ?
A
Controls GIT mobility and it is controlled by both divisions of the autonomous nervous system
21
Q
Where is the serosa located, and what is its function?
A
In the portions of the GIT that are suspended in the abdominopelvic cavity. It holds the alimentary canal in place near the surface of the veretebral column
22
Q
What are the two layers of the serosa?
A
Epithelium and connective tissue
23
Q
What is the other name of the serosa?
A
The visceral peritoneum
24
Q
What is the largest serous membrane of the body?
A
The peritoneum
25
Differentiate between the parietal and the visceral peritoneum
- The parietal lines the wall of the abdominal cavity
- The visceral is the outer later of the GIT
26
Describe the peritoneal cavity
A potential space between parietal and visceral portions of the peritoneum, containing serous fluid
27
What does retroperitoneal organs means, give examples
Organs that lie on the posterior abdominal wall behind the peritoneum. Pancreas and kidneys are examples of it.
28
Name the five major peritoneal folds
Greater omemtum, falciform ligament, lesser omentum, mesentery and mesocolon
29
What is the mesentery?
An extension of the peritoneum that attaches the small intestine to the posterior abdominal wall.
30
Desribe the greater and lesser omemtum
- Greater: apron-like structure on top of small intestine and transverse colon
- Lesser: Suspends the stomach from the liver
31
Describe the mesocolon
Attaches transverse and sigmoid colon to the posterior abdominal wall
32
Where is the majority of saliva produced?
By glands outside of the mouth that pour their contents into the oral cavity. The rest comes from buccal glands in the mucous membrane that lines the mouth
33
What are the three pairs of salivary glands?
1. Parotid glands
2. Submandibular (submaxilary)
3. Sublingual glands
34
What are the functions of saliva ?
Lubricate, keep the mucous membranes of mouth and throat moist, dissolve food, and start the digestion of carbohydrates
35
What is the composition of saliva ?
99.5% of water and 0.5% of solutes (salts, dissolved gases, organic substances, enzymes, lysozymes and IgA)
36
How is saliva regulated?
By autonomic nervous system
37
Describe the position of the pharynx
Funnel shaped tube that extends from the internal nares, to the epiglottis
38
What is the pharynx composed of ?
Skeletal muscles and mucous membranes
39
Name the parts of the pharynx
Nasopharynx, oropharynx and laryngopharynx
40
What is the function of the pharynx?
To propel food from the oral cavity to the esophagus
41
What is the distinction between the functions of the different parts of the pharynx?
Nasopharynx serves in respiration only, while oropharynx and laryngopharynx serve in digestion and respiration.
42
Describe the esophagus
Collapsible, muscular tube lying behind the trachea that connects the pharynx to the stomach
43
What type of tissues lines the esophagus?
Stratified squamous epithelium
44
How many spincters does the esophagus have ?
Two, a upper and lower esophageal sphincter
45
Describe the action of swallowing
A bolus moves from the mouth to the stomach. It is facilitated by saliva and mucus. It involes the mouth, the pharynx and the esophagus.
46
Describe the digestive functions of the esophagus
1. Upper esophageal sphincter relaxation: allows the bolus to move from the laryngopharynx to the esophagus
2. Peristalsis: propels the bolus through the esophagus by progressive contractions of the muscularis
3. Lower esophageal sphincter relaxation: allows the bolus to move from the esophagus into the stomach and prevents chyme from entering the esophagus
4. Mucus secretion: lubricates the esophagus and allows easy passage of bolus
47
Describe the muscularis in the esophagus
- First 1/3: skeletal muscle
- 2/3: Mixed smooth and skeletal muscle
- 3/3: smooth muscle
48
How is the most superficial layer of the esophagus called?
The adventia
49
Describe the location of the stomach
Begins at the bottom of the esophagus and end at the pyloric sphincter
50
What is the function of the stomach?
- Mixing and holding area for food.
- Begins digestion of proteins
- Continues digestion of triglycerides
- Converts bolus to chyme
51
What are the gross anatomical subdivisions of the stomach?
- Cardia: point where the esophagus connects to the stomach
- Fundus: upper part
- Body
- Pyloris: connects to duodenum
52
How are the the folds of the mucosa in the stomach called?
Rugae
53
Describe the mucosa of the stomach
- The surface of the mucosa is a layer of simple columnar epithelial cells called surface mucous cells
- The epithelial cells form gastric pits and gastric glands
54
Describe the four types of gastric glands of the stomach
-Mucous neck cells: secrete mucous
- Chief cells: secrete pepsinogen and gastric lipase
- Parietal cells : secrete HCL
- Enteroendocrine cells: secrete hormones, like G cells that secrete gastrin into the blood
55
What is the function of HCl in the stomach?
Activate pepsin and create acidic environment
56
Where are the exocrine glands located in the stomach?
In the mucosa of the fundus and body.
57
What is the submucosa of the stomach made of ?
Areolar connective tissue
58
Describe the muscularis layer in the stomach
Three layers of smooth muscle: longitudinal, circular and inner oblique
59
Describe mechanical digestion in the stomach
Peristaltic movements called mixing waves
60
Describe chemical digestion in the stomach
Conversion of proteins into peptides by pepsin, which is secreted in its inactive form by chief cells in the gastric pits, and activated by HCl, secretes by parietal cells, also located in gastric pits.
61
What is gastric emptying?
Periodic release of chyme in the duodenum, controlled by the pyloric sphincter.
62
How is the pancreas connected to the duodenum?
Through the pancreatic duct (duct of Wirsung), and accessory duct (duct of Santorini)
63
Describe the location of the pancreas
Behind the stomach, connected to the duodenum
64
Describe the histology of the pancreas
Islets of Langerhans that secrete hormones, scattered between acinar cells (acinis), which secrete a mixture of fluid and digestive enzymes called pancreatic juice.
65
What is the composition of pancreatic juice?
- Pancreatic amylase for starch, carbohydrates
- Proteases (trypsin, chymotrypsin, carboxypeptidase) for proteins
- Pancreatic lipase for lipids
- Ribonuclease and deoxyribonuclease for nucleic acids
- Sodium bicarbonate to convert the stomach to a slightly alkaline content
66
What is the function of sodium bicarbonate in pancreatic juice?
Convert the stomach to a slightly alkaline content to halt the effect of pepsin and favor the activity of pancreatic enzymes
67
What mechanisms control pancreatic secretion?
Nervous (parasympathetic) and hormonal.
68
What is the function of the pancreas?
- Endocrine function: regulate blood sugar
- Exocrine function: Produce enzymes that help digest food
69
Where is the liver located?
On the right side of the body
70
Is the liver the largest organ in the body?
No, it is the second after the skin, but it is the largest gland.
71
How is the liver split anatomically?
Into right and left lobes, separated by the falciform ligament
72
Describe the histology of the liver
Lobules are structures making up the lobes. They contain:
- Hepatic cells (hepatocytes)
- Sinusoids
- Stellate reticuloendothelial cells (Kupffer's cells)
- Central vein
- Bile canaliculi
73
What are Kupffer's cells?
Phagocytes that remove dead white and red blood cells as well as bacteria
74
What is the function of hepatocytes?
Produce bile, which is transported by a duct system to the gallblader for concentration and temporary storage.
75
Describe bile
Partially an excretory product and partially a digestive secretion. Bile is made of water, bile salts and other substances. It contributes to digestion by emulsification of lipids in the small intestine.
76
How is bile secretion regulated?
By nervous and hormonal mechanism (Cholecystokinin (CCK), volume of hepatic blood flow and concentration of bile salts in the blood)
77
Name the functions of the liver
1. FIltration (using phagocytosis) and storage of blood
2. Metabolism: can regulate the release of chemicals from other tissues, glycogenesis, fat metabolism (storage + utilisation), protein metabolism (stores excess a.a and uses for ammonia + urea conversion, makes important proteins)
3. Detoxification : general detoxification (remove drugs and hormones from blood), red blood cells bilirubin conjugation + excretion to kidneys and intestine)
4. Bile formation: synthesis of bile salts
5. Storage of vitamins and minerals
5. Activation of vitamin D
78
Describe blood flow in the liver
1. Blood flows from the hepatic portal vein and hepatic artery into the sinusoids
2. Epithelial part of the sinusoids filtrate the blood into hepatocytes (as well as with Kupffer's cells)
3. Blood flows out to the interlobular vein, to the hepatic vein, then inferior vena cava
79
Describe the location of the gallblader
In a depression on the posterior surface of the liver
80
Describe the histology of the gallblader
- Mucosa: Simple columnar epithelium arranged in rugae.
- No submucosa
- Smooth muscle in muscularis
- Outer layer is visceral peritoneum
81
Describe the function of the gallblader
Store and concentrate bile until it is needed in the small intestine
82
What are the three parts of the small intestine
Duodenum, jejunum and illeum
83
Describe the shape of the epithelial part of the mucosa of the small intestine
The epithelium is distributed in plicae circulares, then in vili.
84
What is the use of plicae circulares and vili in the mucosa of the small intestine ?
Increase absorption by increasing the surface area, causing chyme to spiral as it passes through the small intestine.
85
What is a lacteal?
It is a lymphatic capillary embedded in the villus of the mucosa of the small intestine, used for fat absorption
86
What are the cells in the mucosal epithelium of the small intestine?
- Absorptive cells: digestion and absorption of nutrients in chyme
- Goblet cells: secretion of mucus
- Endocrine cells: hormone producing
87
What is the brush border?
The microvili at the free surface of the absoprtive cells in the small intestine. It contains several enzymes
88
What are intestinal crypts?
Cavities in the mucosa lined with glandular epithelium, they are also called intestinal glands
89
What is special about the submucosa of the duodenum?
It contains duodenal glands (Brunner's) that secrete alkaline mucus to neutralize gastric acid in chyme
90
What are the phases of digestion?
1. Cephalic phase: secretion of saliva and gastric juices in response to the sight, smell, sound or thought of food
2. Gastric phase: food enters the stomach. Gastric juice secretion is promoted by gastrin, chyme leaves the stomach
3. Intestinal phase: chyme enters the small intestine, gastric emptying is inhibited. Mechanical and chemical digestion in the small bowel is promoted, acidity of chyme is buffered
91
What are the two types of digestion in the small intestine
Mechanical and chemical
92
Name the two types of mechanical digestion in the small intestine
1. Segmentation: major movement of the small intestine, localized contractions in areas containing food. Does not propel chyme forwards, mixes it with digestive juices and pushes it against mucosa
2. Peristalsis: propels the chyme onwards through the intestinal tract.
93
Describe how chyme is delivered into the small intestine and why
In small amounts from the pylorus. Because it is hypertonic, so we want to prevent low blood volume. Also, alkalinization of chyme, mixing with bile and pancreatic juices takes time.
94
What are the hormones liberated in the small intestine and what is their function?
- Secretin: reacts to acidity in chyme and stimulates the pancreas to liberate bicarbonate ione
- CCK: freed in response to fatty acids and amino acids
95
Describe the chemical digestion of carbohydrtes, proteins, tryglycerides and nucleic acids in the small intestine
- Carbohydrates are broken down to monosaccharides (glucose, galactose and fructose)
- Proteins are broken down to amino acids, even if digestion had already started in the stomach
- Tryglycerides are emulsified by bile salts from globules into droplets.Pancreatic lipase hydrolyses tryglycerides into fatty acids and monoglycerides
- Nucleic acids are broken down into nucleotides
96
Define absorption
Passage of end products of digestion from the GIT into blood or lymph.
97
What types of transport can absorption use?
Simple diffusion, facilitated diffusion, osmosis (water), active transport, endocytosis
98
How much of the absorption occurs in the small intestine ?
90%
99
Which type of transport is used for protein absorption?
Active transport (cotransport with sodium ions) and simple diffusion for exit
100
How is water absorbed in the GIT?
Osmosis from the lumen to the epithelial cells into the blood capillaries
101
What type of transport is used for electrolyte absorption?
Active transport
102
Which type of transport is used for carbohydrate absorption?
Active (cotransport with sodium ions), and facilitated diffusion for exit
103
How are fat-soluble vitamins digested?
They are included along with lipids in micelles and absorbed by simple diffusion
104
How are water soluble vitamins absorbed?
Simple diffusion
105
Which vitamins are fat soluble, and which are water soluble?
- Fat soluble: A, D, E K
- Water soluble: B and C
106
Describe the location of the large intestine
Extends from the ileocecal phincter to the anus
107
What are the subdivisions of the large intestine?
- Cecum
- Colon
- Rectum
- Anal canal
108
What is inferior to the cecum?
The appendix
109
What are the parts of the colon?
- Ascending
- Transverse
- Descending
- Sigmoid
110
Describe the mucosa of the large intestine
It has no vili or permanent circular folds, it has simple columnar epithelium with goblet cells, in deep intestinal glands.
111
Describe the muscularis of the large intestine
It has specialized portions of longitudinal muscles called taeniae coli, which contract and gather the colon into a series of pouches
112
Describe the last stages of digestion in the large intestine
Substances are further broken down, and some vitamins are synthesized, by bacterial action, then absorbed.
113
Which substances are absorbed by the large intestine ?
Water, electrolytes and some vitamins
114
What are the movements of the large intestine?
churning, peristalsis and mass peristalsis
115
Define mass peristalsis
A strong peristaltic wave that moves the contents of the colon into the rectum
116
What creates the defecation reflex ?
Stretching of the rectal wall
117
Describe hepatitis
An inflammation of the liver, most commonly caused by viruses. Autoimmune disorder, drugs, alcohol or other toxic chemicals can also cause it
118
What are hepatitis A, B and C caused by?
Different viruses
119
Describe hepatitis A
Caused by the hepatitis A virus. Highly contagious. Spread by fecal contamination of food and fomites. Symptoms are mild and inflammation is acute (short term).
120
Describe hepatitis B
Caused by hepatitis B virus. Spread by sexual contact, contaminated syringes, razors, toothbrushes, tears and saliva. Hepatitis B can produce chronic (long term) inflammation, liver failure and liver cancer.
121
Describe hepatitis C
Caused by hepatitis C virus. Similar to hepatitis B in spread and severity. Can also be passed by a mother to a child. 25% of people can defeat the virus, 75% are infected for life.
