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What is a characteristic feature of the mucosa in the small intestine
Villi and Crypts
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What increases the surface area of the intestines 3 fold
Plicae circulares
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What increases the intestinal surface area 10 fold
Villus
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Paneth cells are located
Only at the base of the villus (gland area)
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Crypt of lieberkuhn
Base of the villus, the location of the gland (bulbous invagination)
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The small intestines are made of what epithelium with what type of cells present
- Simple columnar
- Enterocytes (absorptive cells)
- Goblet cells (mucus secreting)
- Enteroendocrine cells
- Paneth cells
- Stem cells
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What is the role of Enterocytes in the small intestines
- Absorptive cells with brush boarder microvilli
- Coated with glycocaylx (decrease in frequency toward large intestine)
- Contain lots of mitochondria for active transport
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What are the features of Goblet cells in the small intestine epithelium
- Secrete mucus
- Increase in frequency towards large intestine
- Provides protection from invasive microorganisms
- sIgA present (secretory)
- Tight junctions
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Enteroendocrone (APUD) cells have what features
- Produce hormones modulating various GI activities
- They are found in the crypts
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What are the features of Paneth cells in the small intestine
- Found at the base of crypts
- Produce lysozyme
- Appear as black vesicles with a white ring surrounding them when stained
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Amine Precursor Uptake and Decarboxylate (APUD)
Another name for Enteroendocrine cells
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What are the features of Stem cells in the small intestine
- They are pleuripotent cells
- They can turn into Epithelial cells, Paneth cells, and Enteroendocrine cells
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What are the different cells considered Enteroendocrine cells, and what do they secrete
- G cells - Gastrin
- D cells - Somatostatin "D stat"
- EC cells - Serotonin "Sara is easy (EC)"
- I cells - Cholecytsokinin "ICC"
- S cells - Secretin
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D cells are found where
In the stomach, intestines, and pancreas
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EC cells are found where
Small intestines and Fundus of the stomach
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I cells are found where
Small intestine
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S cells are found where
Small intestine
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What is the effect of Secretin
Stimulate pancreatic, biliary bicarbonate, and water secretion
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What is the effect of Cholecystokinin (CCK)
Stimulates bile production and pancreatic enzyme secretion
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What is the effect of Serotonin in the GI system
- Stimulates smooth muscle contraction
- "Sero-TONE-in"
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What is the effect of Somatostatin in the GI system
- Inhibits parietal cell secretion (acid secretion)
- "SomatoSTATin" stat=stop
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What is the effect of Gastrin
Stimulates parietal and chief cells to secrete HCl and pepsin
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What is Lamina propria
- Loose connective tissue packed with blood vessels, and solitary lymph nodes
- It is located next to the muscularis mucosae proximal to the lumen
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What are the layers in the small intestines from the lumen out
- Villi
- Lamina Propria
- Muscularis mucosae
- Submucosa
- Muscular layer (inner)
- Myenteric plexus
- Muscular layer (outer)
- Serosa
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What is found inside the villus
- Central lacteal
- Lots of capillaries and veins
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How does the blood flow in a villus compare during absorption and quiescent stages
The absorptive stage has an 8 fold increase in blood flow
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What is the difference between transcellular and para
cellular secretion
- Transcellular in through a cell
- Paracellular is between cells
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What is absorbed in the different areas of the small intestine
- Duodenum - Iron, Calcium, Carbs, Fats, Proteins
- Jejunum - Carbs, Fats, Proteins
- Illeum - Fats, Proteins
- End of Small intestine - Bile salts and Vit B12
- "Does from what easiest to absorb to hardest"
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What happens to motility in the Gut upon feeding
- Gastric emptying is delayed
- Motilin decreases
- Peristalsis changes to single short events instead of long forceful found in fasting state
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Where is the highest and lowest rate of peristalsis and segmentation of the intestines
- Highest - Duodenum
- Slowest - Ileum
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What causes gas and bloating in those with lactose intolerance
Due to the deficiency of lactate, the undigested lactose is sent to the colon where it is mobilized by bacteria which create the product of Hydrogen and CO2
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What are the methods for diagnosing lactose intolerance
- Hydrogen breath test
- Oral lactose intolerance test
- Therapuetic trial of lactate along with lactose Ingestion of lactate while measuring the effect
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What is the first enzyme used in digestion
Amylase found in saliva
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What is the ultimate product derived form Dextrins, Maltotriose, and Maltose enzymes breaking down Starch
Glucose
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What are the products of Lactose enzyme reactions
Glucose and Galactose
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What are the products of Sucrose enzyme reactions
Glucose and Sucrose
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What is the product of Trehalose enzyme reactions
Glucose
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The majority of glucose uptake and output is via what transport systems
- Carrier mediated transport (Sodium Glucose transporter SGLT1)
- Output of basal end is by GLUT-2
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Fructose is transported into and out of the intestines via what transport
- GLUT-5 (does not require Na+ as a costransport)
- The driving force here is the difference in concentration gradients
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What is the primary active transport that creates an environment in enterocytes for movement of glucose into the cell
K+/Na+ moving Na+ out and K+ in on the basal end of the cell
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What happens to the action of Amylase from saliva when it enters the stomach
The high acid content stops its actions
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What happens to the absorption of glucose if SGLT1 is deficient
- There is a Glucose malabsorption
- SGLT1=Sodium GLucose Transport 1
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What is the effect of Celiac disease on Glucose and Fructose absorption
They both fall dramatically
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Proteins begin digestion where, and by what
Stomach by Pepsin and H+
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What enzymes in the intestines work on proteins, and what is the end product
- Trypsin
- Chymotrypsin
- Carboxypeptidases A & B
- Elastase
- End product is Oligopeptides
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What important Enzymes are found on brush boarder cells specifically for Protein derivatives
Amino-oligopeptidases - Digest 3-8 residue oligopeptides to Di-Tripeptides or amino acids
Amino peptidase - Digest Di-Tripeptides to amino acids
Dipeptidyl aminopeptidase - Digest large Oligopeptides (in prep to be further broken down for transport)
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What are the cytoplasmic peptidases that further break down Di-Tripeptides
- Prolidase
- Dipeptidase
- Tripeptidase
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The primary transporter for Di and Tripeptide uptake into Enterocytes and output of amino acids
- PepT1 (input) = Peptide Transport 1
- SLC's (output)
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What is the mechanism of PepT1
It is a symporter that carries peptides in conjunction with protons (H+) generated by the H/Na pump
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What are the two ways that peptides are transported to the enterocyte
- Na+ Amino acid co-transports utilizing the sodium concentration gradient
- PepT1 which transports amino acids along with H+
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What creates the concentration gradient in Enterocytes allowing Amino acid and Na+ co-transportation
K+/Na+ pump on the basal end of the cell (Na+ out, K+ in)
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Hartnups disease
- Absence of Phenylalanine transporters
- Skin changes of pellagra, cerebellar ataxia, and psychiatric abnormalities
- Oligopeptides are still transported
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Cystinuria
- Absence of Arginine or Cystine transporter
- Associated with kidney stones
- Oligopeptides are still transported
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Calbindin
Calcium binding molecule
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What are the two ways that absorbed calcium leaves the Enterocyte
- Calcium ATPase pump
- Sodium/Calcium exchange
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What drives the absorption of water
Solute transport, water follows the solutes
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What is Chloride transportation like in the crypts
- Intracellular Chloride develops from a Sodium, Chloride, Potassium triporter on the basal side.
- As a result of the build up of Chloride it exits the lumen side through CFTR channels
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Submucosal neurons release ACh and VIP causing what action
Stimulate secretion of water
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Rehydration therapy
Mixtures of salt and glucose powders for consuption. Uptake of Na+ and glucose from these solutions, mediated by SGLT1 drives water back into the body to balance osmotic forces.
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The activation of apical membrane Cl- channels is extremely important in the pathophysiology of many
Secretory diarrheal disorders such as cholera
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In most diarrheal diseases what ion flow is taking place
NaCl and Na+ absorption are down-regulated at the same time that Cl- secretion may be stimulated
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What is the difference in the submucosa of the Ileum, Duodenum, and Jejunum
- Duodenum is occupied by Brunners glands
- Ileum is occupied by Peyers patches (aggregated lymph nodes)
- Jejunum has neither
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Brunners glands
- Tubuloacinar glands found in the submucosa of the Duodenum
- Secretion is clear alkaline mucin providing protection from acid chyme
- Produces optimal pH for pancreatic enzymes
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Submucosa consists of what
- Dense irregular connective tissue
- Blood vessels, nerves, and lymphatics are present
- Meisseners plexus
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Peyers patches
- Aggregated lymph nodules
- More prominent distally (Ileum)
- Covered by M cells (microfold)
- Important in immune response
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Microfold cells
- Cells found in the Peyers patches that are important to immune defenses
- Lymphocytes migrate through the discontinuous lamina below, and through the microfold cell to the lumen of the gut for defenses
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Serosa is present in what regions of the small intestines
Jejunum and Ileum are completely covered by Serosa, Duodenum is only covered on its distal ends
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What is the difference between Serosa and Adventitia
- Serosa is is present in the portions that are not touching the body wall
- Adventitia is found where small intestines are touching the body wall
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What is the basic function of the large intestines
- Reabsorption of water and salts from feces
- Digestion does not occur here
- Flora and fauna are found as extractors of vitamins
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What is not found in the mucosa of the large intestine
- Villi
- Plicae circularis
- (Crypts are present)
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What cells and epithelial type are found in the mucosa layer of the large intestine
- Simple columnar absorptive epithelium
- Goblet cells (most numerous)
- Enteroendocrine cells
- Stem cells
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What are the layers found in the large intestines
- Mucosa
- Lamina propria
- Submucosa
- Muscularis Externa
- Outer longitudinal muscle is found in 3 strips on the outside (Stripes-taeniae coli)
- Serosa/Adventitia
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What is in the appendix
It is filled entirely with both diffuse lymphatic tissue and nodules, all containing plasma cells
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The rectum is much like the colon accept
In lacks taeniae coli
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What are the sections of the anal canal
- Upper 1/2, simple columnar (endoderm)
- - Anal columns
- Pectinate line divides the two halves
- Lower 1/2, stratified squamous non karatinized (ectoderm)
- Anus, Stratified squamous keratinized skin
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What in the alternate name for Anal columns
Columns of Morgagni
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The lamina propria of the anus contains large veins which can contribute to
Hemorrhoids
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What is the difference between the internal and external sphincters on the anus
- Internal - Thickened circular layer of muscularis externa
- External - Skeletal muscle
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Ileocecal valve (sphincter)
One way valve that controls the entry into the colon protecting against reflux (bacteria)
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How do the functions of the ascending, transverse, descending, and anus of the large intestine differ
- Ascending is predominately absorption of water and ions
- Transverse is where Vit K is made by bacteria, bile conversion takes place, and oxidation of bilirubin
- Descending is storage of waste
- Anus eliminates stored feces
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Ileal brake
Undigested nutrients like fats are detected around the Ileocecal valve sending signals like Peptide YY and GLP-1 and 2 to the stomach decreasing the movement of food into the GI tract giving more time for digestion of the undigested nutrients
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Colono-colonic reflex
Distensions in colon relaxes other parts of the colon
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Gastro-ileal reflexes
- Food in stomach increases Ileal motility causing the Ileocecal valve to relax
- This is controlled by PNS (ACh) and gastrin
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Ileo-gastric reflexes
Ileal distension decreases gastric motility
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Gastro-colic reflex
- Gastric distensions increase colonic motility
- PNS (ACh), gastrin, and CCK controlled
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Colono-gastric reflex
- Colonic distensions decrease gastric motility
- Vagal response
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Haustral shuffling vs Mass movement
- These are different movements performed in the colon to advance chyme
- Haustral - Segmentation
- Mass movement - Peristaltic movement
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Hirschprungs disease
- Congenital megacolon
- Relaxation of the internal anal sphincter in response to rectal distension can't be initiated
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In the proximal colon the absorption of short-chain fatty acids occurs by
Na+-dependent symporters known as sodium monocarboxylate transporters (SMCTs).
-
Short chain fatty acids (SCFA) are used by the colonocytes for
Used for energy
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What transporters are found on the proximal colon
- Apical side:
- Sodium/Hydrogen exchange (Na in)
- Chloride/Bicarbonate exchange (Cl in)
- Sodium/SCFA cotransport in
- Basal side:
- Potassium/Sodium exchange (Potassium in)
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On the distal end of the Colon, what cellular transporters are present on the cells
- Apical side:
- Sodium channel in (ENac)
- Potassium channel out
- Basal side:
- Sodium/Potassium exchange (Sodium out)
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ENac
- Sodium channel found in both the kidneys and the distal colonocytes
- These are the last attempt to prevent loss of water in the feces
-
Patients with bowel inflammatory disease show a dramatic loss in
- ENac channels
- This could be the cause of their loose stool
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Aldosterone has what effect on ENac
It causes these channels to be more prevalent in the kidneys and the distal colon increasing water and sodium retention
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What is the Chloride secretion in the small intestines
CFTR Chloride channel pumping into the lumen
Sodium/Chloride/Potassium triport pumping into the cell (basal side)
- Sodium/Potassium exchange (Na out) (basal side)
- All producing a net flow of sodium and water into the lumen
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What are the three types of constipation
- Normal Transit
- Slow-transit
- Defecatory disorder
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What are the three types of Diarrhea (loss of >500mls a day)
- Osmotic (absorption defect)
- Secretory (eg. cAMP increase Cl secretion)
- Hypermotility (decrease colonic transit time)
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