The Digestive System Flashcards
1
Q
How long is the human digestive tract?
A
The human digestive tract is about 21 - 30 ft long?
2
Q
What is the lumen facing tissue of the digestive tract made up of?
A
The lumen facing tissue of the digestive tract is made up of mucus coated epithelium. The mucus aids in diffusion
3
Q
What are the functions of the digestive tract?
A
The functions of the digestive tract include:
- Getting the food
- Storing the food
- Transporting the food
- Breaking down the food
- Absorbing nutrients from the food
- Evacuation of wastes
4
Q
What is a heterodont?
A
A heterodont has more than one tooth morphology.
Humans are heterodonts, having teeth for tearing into meat, but also crushing seeds.
5
Q
What is a homodont?
A
A homodont is an animal with only one tooth morphology
Reptiles, fish, and amphibians are homodonts
6
Q
How many permanent teeth do adult humans have?
A
Adult humans have 32 permanent teeth
7
Q
What are the parts of the tooth?
A
The parts of the teeth are:
- The crown: The visible part of the tooth
- The root: the portion that is embedded into a gum socket
- The periodontal ligament: Connective tissue that connects the tooth to the alveolar bone of the tooth socket
8
Q
What type of receptors does the tongue have?
A
The tongue has:
- sensory (taste) sensors
- Touch sensors
- Pressure sensors
9
Q
What are Von Ebner’s glands
A
Von Ebner’s glands are exocrine glands (they have ducts) that secrete salivary lipase
10
Q
What is salivary lipase?
A
Salivary lipase is secreted from the Von Ebner’s salivary glands.
- It begins the process of lipid hydrolysis in the mouth
11
Q
What are the salivary glands?
A
The salivary glands include:
- Parotid: largest of the glands
- Submandibular: Produces 70% of Saliva
- Sublingual: Produces mainly mucus
12
Q
What gland does mumps trigger?
A
Mumps triggers the parotid gland through a viral infection
13
Q
What enzyme does saliva contain that allows it to break down carbohydrates?
A
Saliva contains amylase enzyme that allows it to break down carbohydrates into glucose or maltose, depending on the carbohydrate.
- This enzyme is a protein
14
Q
What is the pH of saliva?
A
The pH of saliva is about 7.2
- Alkaline pH can lead to gingivitis
- Acidic pH can lead to periodontitis (The progressive loss of alveolar bone around the teeth)
15
Q
What are the functions of saliva?
A
Saliva has multiple functions:
- helps us taste food
- helps us swallow food
- initiates the digestive process
- initiates protection against foreign bodies
16
Q
What antibacterial agents do saliva contain?
A
Saliva contains:
- IgA: A large protein that works with the immune system
- Lysozyme: Attacks cell wall of many gram positive bacteria (also found in tears)
- Lactoferrin: part of the innate defense (has antibacterial, antiviral, antiparasitic properties
17
Q
What is IgA?
A
IgA is a large protein found in saliva that works with the immune system
18
Q
What is a lysozyme?
A
A lysozyme is a protein found in saliva, tears, small intestine and stomach acid that attacks the cell wall of many gram positive bacteria
- Made in the stomach pylorus, salivary glands, Paneth Cells in the Crypts of Lieberkhun, and tear ducts
19
Q
What is lactoferrin?
A
Lactoferrin is a protein found in saliva that is part of the innate defense of the body
- Has antibacterial, antiviral, and anitparasitic properties
20
Q
What is mucin?
A
Mucin is a glycoprotein that is present in the mouth, that protects the lining of the mouth from abrasions, and lubricates the food so we can swallow easily
21
Q
What is a bolus?
A
A bolus is the lubricated ball of food that is pushed back toward the pharynx.
22
Q
What prevents food from being pushed into the trachea?
A
The epiglottis is a flap of cartilage tissue that covers the glottis when swallowing, preventing food from entering into the trachea.
23
Q
What is the esophagus?
A
The esophagus connects the stomach to the pharynx
- It is a muscular tube that pushes food from the pharynx down into the stomach
- Contains glands that secrete mucus which facilitate the transport of foodstuffs
- The esophageal mucosa is composed of stratified squamous epithelium
- Contains langerhans cells that help in phagocytosis
24
Q
What is the cardiac sphincter?
A
The cardiac sphincter is the valve that allows food into the stomach from the esophagus, but under normal conditions does not allow backflow back into the esophagus
- Heartburn occurs when the valve relaxes too much allowing stomach contents into the esophagus. Some foods cause the cardiac sphincter to relax more than others
- If you vomit, the valve relaxes to allow vomitus to enter the esophagus and out the mouth.
- Too much exposure to vomitus can cause serious damage to the esophagus and even cancer.
25
What is chyme?
Chyme is the acidic mixture of food and digestive fluid in the stomach
26
What is the pH of the stomach? What does the pH allow the stomach to do?
The pH of the stomach is a very low 1.5 that does two things:
- Destroy pathogens
- Break down proteins - a protease called pepsin is present
27
What is pepsin and how is it formed?
Pepsin is a protease that helps break down proteins. It forms as follows:
- Chief cells release an inactive form (proenzyme or zymogen) of pepsin called pepsinogen
- Pepsinogen mixes with HCl and 44 aa residues are cut off forming the active enzyme pepsin
- Pepsin can also cleave off the 44 aa residues of pepsinogen, causing a positive feedback loop
28
What cells produce HCl
HCl is produced by parietal cells when stimulated by the hormone gastrin.
- Histamine and Acetylcholine also play a role and have receptors on the parietal cell
29
What role does the hormone gastrin play in the stomach?
Gastrin is a peptide hormone that stimulates the secretion of HCl by parietal cells.
- Gastrin is made by G cells in the stomach pylorus (the part that attaches to the small intestine- duodenum)
30
What protects the stomach from the harsh acidic conditions?
The stomach is protected from the harsh acidic conditions by a layer of mucus.
- Cells in the stomach lining replace themselves every 3 or 4 days
31
What two things do parietal cells produce?
Parietal cells produce:
- HCl
- Gastric Intrinsic Factor: A glycoprotein involved with B12 absorption
32
What is Gastric Intrinsic Factor?
Gastric Intrinsic Factor is a glycoprotein involved with B12 absorption
- Produced by Parietal cells in the stomach
33
How does chemotherapy affect the stomach?
Chemotherapy drugs are designed to kill rapidly dividing cells. Since cells in the stomach are rapidly dividing, it kills the cells in the stomach as well. This results in:
- diarrhea
- nausea
- other intestinal and stomach issues
34
What is an ulcer?
An Ulcer is damage to the epithelial layer of the stomach
| - caused by chemicals like aspirin and even microorganisms like Helicobacter Pylori
35
What are enteroendocrine glands?
Enteroendocrine glands are endocrine glands in the digestive system that produce hormones
36
What hormones are produced in the stomach?
The stomach produces the following hormones:
- Glucagon (enteroglucagon)
- Somatostatin
- Serotonin
- Substance P
- Histamine
- Gastrin
37
Where does most digestion occur in the digestive system?
Digestion is where macromolecule hydrolysis occurs.
| - The small intestine is where the most digestion occurs
38
What are the three segments of the small intestine?
The three segments of the small intestine in order of food flow is as follows:
- Duodenum: First segment
- jejunum: Middle segment
- Ileum: Final Segment
39
What controls the flow of chyme from the stomach to the small intestine?
The pyloric sphincter controls the flow of chyme into the duodenum of the small intestine
40
What two ducts carry fluids to the duodenum of the small intestine?
About midway along the duodenum two ducts carry liquids to the small intestine:
- The common bile duct carries bile from gall bladder to the duodenum
- The Pancreatic Duct carries pancreatic juice to the small intestine
41
What are the duodenal hormones produced?
The hormones produced in the duodenum are:
- Gastrin: Triggers secretion of HCl by parietal cells.
- Secretin: Stimulates HCO3- (Bicarbonate) release from the pancreatic fluid
- Cholecystokinin: Stimulates gall bladder contraction
NB these ^ three for the DAT
- VIP (Vasoactive Intestinal Peptide): Hormone that increases peristalsis in the small intestine
42
What is Secretin?
Secretin is a hormone produced in the duodenum that stimulates the release of HCO3- (Bicarbonate) from pancreatic fluid
43
What is Cholecystokinin?
Cholecysokinin is a hormone produced in the duodenum that stimulates the gall bladder contraction
44
What is Vasoactive Intestinal Peptide (VIP)?
Vasoactive Intestinal Peptide (VIP) is a hormone produced by the duodenum that increase peristalsis of the duodenum
- Also stimulates the elimination of ions and H2O by the GI tract
45
What are villi?
Villi are fingerlike projections in the small intestine.
- They help increase the surface area of the small intestine by a factor of 10
- On the surface of the villi are microvilli which is sometimes called the brush border
- Each villus contains a lacteal, which is a lymphatic vessel that can absorb fats
- These villi are only one cell thick
46
What are micovilli?
Microvilli are hair like projections that surround the villi, greatly enhancing the surface area of the small intestine.
- These are sometimes called the brush border
- This greatly enhances the nutrient absorbing capability of the small intestine.
47
How are triglycerides transported out of the small intestine?
- Triglycerides are made into water soluble globules called chylomicrons.
- Chylomicrons are taken into the lacteals of the villi and into the lymphatic system
48
What is a chylomicron?
A chylomicron is a fatty acid that has been modified by the small intestine, coating it with proteins, cholesterol, and phospholipds until its a water soluble globule.
- Once in this state, it can travel into the lacteals of the villi and into the lymphatic system
49
What is a lacteal?
A lacteal is a lymphatic vessel located on a villus that can take in chylomicrons from the small intestine into the lymphatic system.
50
What happens to the nutrient rich blood of the villi?
Villi are only one cell thick and are up against the hepatic portal vein.
- Nutrients easily flow into the blood from the villi
- The blood of the hepatic portal vein travels to the Liver where it is screened for toxic substances, and much of the nutritive foodstuff is converted to glycogen
Villi -> Hepatic Portal Vein -> Liver -> Organs
NB for the DAT
51
What are crypts in the small intestine?
Crypts are small invaginations between the villi.
- Also called Crypts of Lieberkuhn
- These crypts are actually glands that contain:
* Goblet Cells: Mucus producing
* Enteroendocrine Cells: Hormone Making
* Regenerative Cells
* Paneth Cells: Lysozyme making
52
What is a goblet cell?
A goblet cell is a cell found in the crypts of lieberkuhn in the small intestine.
- It produces mucus
53
What is a Paneth Cell?
A Paneth cell is a cell found in the crypts of Lieberkhun in the small intestine.
- It produces lysozyme
54
What are Peyer's Patches
Peyer's Patches are an aggregation of lymphoid tissue noted in the ileum wall
- Monitor intestinal bacteria and prevent the growth of pathogenic bacteria
- They look like round balls of lymphatic tissue
- They contain:
* Macrophages
* Dendritic cells
* B-lymphocytes and T-lymphocytes
- Part of GALT (Gut Associated Lymphoid Tissue)
55
What happens if the intestinal mucosa becomes irritated by toxic substances?
If the intestinal mucosa gets irritated by toxic substances, swift peristaltic contractions occur called the peristaltic rush.
- Chyme is propelled much faster than normal (within minutes) for elimination as diarrhea
56
What is the jejunum? What are its distinct characteristics?
The jejunum is the middle portion of the small intestine, between the duodenum and the Ileum.
- Villi are found here, but are longer than those found in the duodenum
- Paneth cells are found in the crypts of lieberkhun, producing lysozymes
- The enzymes that were released into the duodenum are still actively working (pancreatic amylase, pancreatic protease, pancreatic lipase)
57
What is the ileum? What are its distinct characteristics?
The ileum is the last portion of the small intestine, coming from the jejunum and separated from the large intestine by the ileocecal valve
- Peyer's patches occur here
- Amino acid, bile salts, and Vitamin B-12 absorption occurs here
- There's no clear demarcation between the Ileum and the jejunum. They merge gradually
58
What is the ileocecal valve?
The Ileocecal valve separates the ileum from the cecum of the large intestine.
59
What is the pancreas?
The pancreas is a dual organ that has both endocrine and exocrine functionality
- About 5 inches long, lies behind the stomach, and extends transversely the upper abdomen
- As an endocrine gland it produces:
* Insulin
* Glucagon
* Somatostatin (inhibits insulin and glucagon secretion)
- Hormones are produced by the islets of langerhans
- The digestive enzymes are made by the exocrine portion
60
How much pancreatic juice is made per day?
About 2 L of pancreatic juice is made per day
61
What does pancreatic juice contain?
Pancreatic juice contains:
- HCO3-
- Proteases (trypsin, chymotrypsin, procarboxypeptidase)
- Amylases
- Lipases
- Nucleases (Digest DNA and RNA)
- Elastase
62
What proteases are produced by the pancreas for digestion? Why is the method of their transport important?
The proteases produced by the pancreas for digestion are:
- Trypsin
- Chymotrypsin
- Procarboxypeptidase
Trypsin, Chymotrypsin and Procarboxypeptidase are stored as zymogens. Trypsin is cleaved and activated by enterokinase in the intestine. Trypsin then can activate chymotrypsin and procarboxypeptidase through proteolytic cleavages. This is what is known as a cascade and is often seen when enzymes are activated by covalent modification.
The activation of the proteases in the small intestine prevents the pancreas from digesting itself.
NB for the DAT this whole card
63
What is enterokinase?
Enterokinase is an enzyme produced by the Brunner glands in the Duodenum of the small intestine.
- It activates trypsinogen into trypsin. This then allows the cascade of trypsin activating the other proteases and elastase in the pancreatic juices
64
What controls the pancreatic secretions of digestive juices?
The pancreatic secretion of digestive juices is controlled by two hormones:
- CCK (cholecystokinin)
- Secretin
Acid and chyme enters into the duodenum and stimulates the release of CCK and secretin
65
What is the purpose of secretin?
Secretin is a hormone that controls the pH of the duodenum.
- When the duodenum detects a low pH, it releases secretin into the blood stream.
- Secretin causes Bicarbonate and water to be released from the pancreas into the duodenum to raise the pH of the small intestine.
- Without this, damage can occur to the small and large intestine.
- This is needed so that the rest of the digestive enzymes can function at their required pH
66
What is the gall bladder and its purpose?
The Gall bladder stores concentrated bile and delivers it to the duodenum via the common bile duct
- 4 inches in length, 1.5 inches in cross section, and can store about 70 mL of bile. It resembles a sac.
67
What triggers the release of bile from the gall bladder?
The CCK hormone triggers the release of bile from the gall bladder via the common bile duct into the duodenum.
- Acytelcholine released by the parasympathetic fibers of the vagus nerve also stimulate bile release
68
What causes gall stones?
```
Gall stones (cholelithiasis) are 80% cholesterol.
- The people with gallstones have more cholesterol in their bile as it leaves the liver, thus showing that the liver is the likely culprit of gallstones
```
69
What is the largest internal organ?
The largest internal organ is the liver
70
What is compensatory hyperplasia and how does it relate to the liver?
The liver is an organ that can regenerate.
- Hepatocytes (liver cells) begin to divide in response to toxic substances through compensatory hyperplasia
- compensatory hyperplasia is the proliferation of cells while they maintain their differentiated structure.
- Hepatocytes live about 150 days
- New cells are made until the original tissue size is returned to normal
71
What are the main functions of the liver?
The main functions of the liver include:
- Making bile and cholesterol
- Drug detoxification
- Produces plasma proteins (albumin, fibrinogen)
- Vitamin Storage (Vitamin A is stored in the greatest amount)
- Deamination of proteins (Removal of NH2 group)
- Chylomicrons are broken down into glycerol and fatty acids
- Makes 90% of blood proteins
- Stores glycogen and releases glycogen (glycogenolysis) and gives glucose to be transported to the body. Iron storage too!
- Urea production. It converts NH3 into urea. NH3 comes from two sources: Amino acid deamination and bacterial action in the GI tract
- Along with the spleen, it is involved with disposing of red blood cells. It's debated whether the Spleen or Liver does more of this
72
What is bile and its function?
Bile is:
- an emulsifier of lipids
- not an enzyme
- contains cholesterol, bile salts, bilirubin (pigment), phospholipids, water, and even IgA
73
What is bilirubin?
Bilirubin is a yellow-green pigment formed with red blood cells are destroyed by macrophages in the spleen and liver.
74
What are Kupffer cells?
Kupffer cells are macrophages in the liver that destroy red blood cells and pathogens coming from the small intestine.
- When the red blood cells are destroyed it creates a yellow green pigment called bilirubin
- Bilirubin is released into the bloodstream attached to albumin
75
What is jaundice?
jaundice occurs when bilirubin levels are high in the blood. It can be caused by several things:
- liver disease (hepatitis)
- increased hemolysis of RBC's
76
How does the liver defend against pathogens coming from the hepatic portal vein?
Kupffer cells phagocytose about 99% of all pathogens coming from the small intestine through the hepatic portal vein.
77
What are the three main blood vessels of the liver?
The three main blood vessels of the liver are:
- Hepatic Portal Vein: Carries blood from the duodenum to the liver
- Hepatic vein: Transports deoxygenated blood from the liver to the inferior vena cava
- Hepatic Artery: Carries oxygenated blood to the liver
NB for the DAT
78
Where are lipids and amino acids converted into glucose?
Amino acids and lipids are converted into glucose at the liver, thus gluconeogenesis and deamination will occur at the hepatocyte.
79
What is a unique characteristic of a hepatocyte?
Hepatocytes can have two or more nuclei.
- 50% are polyploid with 4,8, or 16 times the haploid chromosome complement.
- Liver cells are also highly aneuploid (having abnormal amounts of chromosomes, not just having another set. Missing chromosome 9 for example). We still aren't sure why.
80
What is chirrosis?
Chirrosis is due to sustained damage to hepatocytes in the liver. The hepatocytes die and are replaced by fibrous tissue.
- Caused by drugs, alcohol, and hepatitis
81
What is the portal triad on the liver?
The portal triad includes the:
- Hepatic Portal Vein (nutrient rich o2 poor blood from the small intestine)
- Hepatic Artery (Oxygenated blood to the liver)
- Bile Duct (bile conducted away from the liver to the gall bladder)
82
What is the function and characteristics of the large intestine?
The large intestine:
- Stores waste
- Absorbs H20
- Produces mucus that lubricates the intestinal surface
- No Villi are present
- contains bacteria that produce vitamin K and biotin
- vitamin K is absorbed here
83
What are the six regions of the large intestine?
The six regions of the large intestine are:
1. Cecum
2. Ascending Colon
3. Transverse Colon
4. Descending Colon
5. Sigmoid Colon
6. Rectum
84
What valve connects the small intestine to the large intestine?
The ileocecal valve connects the ileum of the small intestine to the cecum of the large intestine.
85
Where is the appendix located and what is its perceived purpose?
The appendix is located as an invagination of the cecum next to the ileocecal valve
- It is thought to contain a reservoir of good bacteria.
- There is evidence that the appendix has an immune function during the early years of life, helping with the maturation of B lymphocytes and the production of antibodies
- By age 60, it has virtually no function
86
What is the microorganism composition of the large intestine?
The microbiome of the large intestine is dominated by bacteria, with 99% being obligate anaerobes.
- fungi, protozoa, and viruses are also seen in small numbers
87
What is the composition of feces?
Feces is about 3/4 water and 1/4 solids
88
What percentage of water is absorbed in the small and large intestine?
About 90% of water is absorbed from the small and large intestine under normal conditions.
89
What is a ruminant? How do they do what they do?
A ruminant is an organism that can break down cellulose with the help of their microbiome.
- A microbiome of bacteria, fungi, and protozoa in the large intestine break down the 1,4 -beta linkages in cellulose with the help of enzymes
- The bacteria here are obligate anaerobe in nature and include: clostridia and bacterioidetes
