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What is the main purpose of the GI system?
Digestion & Absorption - to break down food into molecules and then absorb them.
What is the alimentary canal?
- The GI tract - it runs from mouth to anus
- 30 feet long
List the primary and seconday organs of the digestive system (tract).
- 1. Oral cavity
- 2. pharynx - naso, oro, hypo
- 3. Esophagus
- 4. Stomach
- 5. Intestines - small & large bowel
- - - small = duodenum, jejunum, ileum
- - - large = cecum, ascending, transverse, descending colon, sigmoid colon, rectum
- 6. anus
- Accessory Organs:
- 1. teeth, tongue, salivary glands
- 2. liver
- 3. gallbladder
- 4. pancreas
What is motility?
What is peristalsis?
How does the GI tract "mix"?
- Motility - mixing and moving of substances
- Peristalsis - alternating contracting & relaxing of smooth muscle
- The GI tract mixes and propels through churning and peristalsis.
What are the 2 types of digestion?
Wha is absorption?
- 1. Mechanical digestion - physical chewing & chruning
- 2. Chemical digestion - enzymes, HCl
Absorption - absorb products of digestion (nutrients, drugs) at the molecular level (a.a. not proteins)
Name the 4 layers of the GI tract.
- M = Mucosa
- S = Submucosa
- M = Muscularis
- S = Serosa
Describe the mucosa.
Where does absoprtion occur?
- Mucosa is the innermost layer - surrounds the lumen
- Has 3 regions (layers)
- 1. Epithelium - stratified squamous (upper) - simple columnar (lower) (absorption)
- 2. Lamina Propria - loose areolar CT - some absorption occurs here
- 3. Muscularis mucosa -smooth muscle layer - ridges (folds) for more SA so above absorbs better.
Absorption occurs in the epithelium & lamina propria regions
Describe the submucosa.
What nerve plexus enters here & what does it do?
- Submucosa = CT layer (blood vessels, lymph, & nerves)
- - some absorption occurs here
- Submucosal nerve plexus called the Plexus of Meissner that controls movement of the muscularis mucosa & gastrointestional secretions.
Describe the muscle types.
What is the myenteric plexus?
- Muscularis has two types of tissue layers:
- 1. Voluntary - single layer of skeletal muscle - occurs from oral cavity to upper esophagus & also at the external anal sphincter.
- 2. Involumtary - double layer of smooth muscle - from lower espohagus to internal anal sphincter. Arranged in two sheets:
- a. longitudinal (outer)
- b. circular (inner)
- - The myenteric pleus called the Plexus of Auerbach (ANS) is between the two muscle layers and controls muscularis contraction/ relaxation
What is the serosa?
What is adventitia?
- Serosa is also known as the visceral peritoneum
- - it attaches areas of the lower GI to the surrounding structures
- - it is simple squamous epithelium (outer) + CT (inner)
- - it is found in the abdominopelvic cavity
- in the esophagus
it is called the adventitia
and is only CT (no epithelium)
What is the ENS - Enteric Nervous System?
The ENS is the brain of the gut - it is part of the ANS (sym & para) but the ENS can function independantly
Where are the plesuses of Auerbach & Meissner located?
1. Plexus of Auerbach - Myerteric plexus = motor (GI motility) - located in the muscularis between the muscle layers
2. Plexus of Meissner - in the Submucosal layer - controls movement of secretions
What does parasympathetic stimulation do to the GI tract? What neurotransmitter does it use?
- Parasympathetic tells the GI to rest & digest
- Vagel nerve innervates the top half → ACh
- Sacral never innervates botton half → ACh
Why is sympathetic output "thoraco/ lumbar"?
What is the sympathetic neurotransmitter?
- Sympathetic nerves that innervate the GI tract arise from the thoracic and upper lumbar area of the spinal cord.
- Sympathetic = GI inhibition (fight or flight) → NOR
What type of sensory receptors are found in the ENS?
Chemoreceptors = activated by the presence of chemicals found in food
stretch receptors = activated by food pushing against the walls of the GI organ
Where in the brain is the ENS input integrated?
Peritoneum - layers & functions
- Peritoneum - 2 layers
- 1. Perietal layer - lines abdominal wall
- 2. Visceral layer - on organs
- Paritoneal cavity is between them
- - Made of simple squamous epithelial with loose CT underneath (mesothelial tissue)
The peritoneum has large folds that weave between the visera and hold the organs together.
What are the 5 major peritoneal folds?
- 1. Greater omentum - fat apron - colon ↔ stomach
- 2. Falciform ligament - liver ↔ anterior abdominal wall 3. Lesser omentum - liver ↔ stomach
- 4. Mesentray - small intestine ↔ abdominal wall
- 5. Mesocolon - large intestine ↔ abdominal wall
Is a perforated viscus a surgical emergency?
Yes. A perforated viscus can reslt in an acute life-threatening form of peritonitis because bacteria gain access to the peritoneal cavity.
What organs are located in the retroperitoneal space?
Pancreas & Kidneys - they are covered anteriorly with parietal peritoneum
Also the ascending & decending colons (large intestine) and the duodenum of the small intestine are retroperitoneal.
What is the purpose of the oral cavity?
What are the structures of the mouth and their funcitons?
Oral cavity - beginning of digestion -enzymes + mastication (chewing and tearing to produce a "bolus")
- 1. Lips - speech, hold food as you eat
- 2. Cheeks - hold food as you eat
- 3. Vestibule - space between the lips & gums
- 4. Hard/ Soft palate - keeps food out of nasal cavity
- 5. Uvula - Flips up when swallowing to keep food out of nasopharynx.
3 salivary glands & function
What is the compostion of salvia?
- 1. parotid
- 2. sublingual
- 3. submandibular
- - produce 1 - 1.5 L of saliva/ day - provides lubrication and starts chemical breakdown.
- a. Salivary amylase - carbs
- b. lysosyme - anti- bac ; dissolves cell wall
- c. buffers - HCO3- & PO4-
- d. mucus - lubricant
- e. H2O - dissolve food into molecules
- f. IgA - immune to eliminate invaders
- - small amt of waste- urea, uric acid
Tongue - What enzyme does it secrete?
What are the physical features of the tongue?
Secretes lingual lipase - breaks down triglycerides - must be activated by HCl in the stomach.
- 1. Mucous membrane lining
- 2. Skeletal muscle
- - extrinsic - manuaver food in mouth
- - intrinsic - changes the tongue shape
- 3. Papillae - cevered with taste buds
- 4. Septum - midline - lingual glands
- 5. Lingula frenulum - connects tongue to floor
Draw a picture of a tooth & label layers.
What are the layers of the tooth?
- 1. Crown - above the gum line
- 2. Neck - below gum - hard to see
- 3. Root - below gum line
- 1. Enamel - hardest substance in man - made of calcium salts.
- 2. Dentin - majory of tooth - calcium salts - harder than bone
- 3. Pulp cavity - CT w/ vessels & nerves
- 4. Root Canal - extension of pulp cavity
- 5. Cementum - connects root to periodontal ligament
Why are baby teeth called desiduous teeth?
How many adult teeth?
- 20 deciduous "baby" teeth - 6 mos → 6 years
- desiduous means "falling out at maturuty"
- 32 adult teeth
- - Incisors - bite
- - cuspids (canines) - tearing
- - molars - chew & grind
What are the parts of the gum?
What is gingivitis?
- 1. alveolar processes (gomphosis) - sockets in bone
- 2. gingiva - gums
- 3. periodontal ligament - dense CT - connects tooth to socket
Gingivitis - inflamation of the gingiva - caused by plaque (biofilm)
Periodontal disease - bacteria gets past gum line and is able to affect underlying structures - cementum
What is the 3rd molar called?
- Thrid molars are called wisdom teeth - erupt after age 17 or not at all.
- If there is not room for them to erupt they may become impacted and have to be surgically.
What are dental caries?
- Dental caries are cavities - tooth decay caused by various bacteria (strep mutans & viridans, lactobacilli)
- that disolve enamel
Name the 3 regions of the pharynx:
- 1. Nasopharynx
- 2. Oropharynx
- 3. Larygopharynx (hypopharynx)
Skeletal muscle - passage from oral cavity to esophagus - also used by respiratory system
Aids in mechanical (mastication) & chemical digestion (amylase & lipase)
What is the function of the esophagus?
What are the 4 muscle layers?
What type of muscle is in the Muscularis layer?
Esophagus - connects pharynx to stomach - secrets mucus for lubrication - mediastinal, posterior to trachea (10" muscular tube) does not absorb or digest.
- 4 muscle layers: M-S-M-A
- Mucosa, Submucosa, Muscularis, Adventitia (only CT - no epithelium)
- - upper 1/3 = skeletal
- - middle 1/3 = both
- - lower 1/3 = smooth
2 Esophageal sphincters & purpose
What is hiatal hernia?
What is GERD?
- Sphincters - involved in swallowing process
- UES - Upper Esophageal Sphincter - Skeletal
- LES - Lower Esophageal Sphincter - Smooth
Hiatal hernia - stomach herniated (moves upward) through LES = pain & reflux
- GERD = GastroEsophageal Reflux Disease
- Incompetent LES - ↑ abdominal P = gastric acid enters esophagus
- Rx = diet - elevate bed - antacids,
- H2 blockers (zantac - blocks histamine which is an H2 receptor)
- Proton pump inhibitors - (nexium, prilosec, pepcid) protons = H+
3 stages of swallowing
1. Buccal phase- Voluntary -extrinsic muscles - tongue movement - forces food back to pharynx
- 2. Pharyngeal stage - involuntary - medulla & pons control it (Deglutition center = swallowing) - food moves from oropharynx → espohagus
- - swallowing reflex - touch receptors on uvula & soft palate stimulate it
- a. uvual moves up - stop food → nasopharynx
- b. Epiglittis shuts - stop food → trachea
- c. UES - Relaxes
- d. Breathing stops
- e. Food bolus enters esophagus
- 3. Esophageal stage - through esophagus → stomach
- - Bolus is moved by peristalsis (coordinated muscle contraction & relaxation that pushed food forward)
- - LES relaxes
- - food enters stomach
Draw a picture of the stomach
List the 4 regions of the stomach.
In infants - what conditon is caused by a tightened pyloric sphincter?
- 1. Cardia - surrounds superior opening
- 2. Fundus - rounded superior portion
- 3. Body - large central poriton
- 4. Pylorus - where stomach connect to duodenum
- - pyloric atrium - connect to body of stomach
- - pyloric canal - leads into duodenum
- - pyloric sphincter - separates pyloric canal from duodenum
Pyloric stenosis - in infatns pyloric sphincter is too tight - food cant drain properly & backs up in system - Projectile vomit - with force
What are the functions of the stomach?
- 1. Storage
- 2. Mechanical breakdown - mixing
- 3. Chemical breakdown
- 4. Produce IF (intrinsic factor) - for absorption of B125. Turn Bolus in to Chyme - soupy mixture of bolus + gastric juices (vomit) by mixing
- 6. Absorption of alcohol & aspirin ( no nutrients - food particles still to big to be absorbed.
Name all the enzymes involved in chemical digestion
- 1. amylase - from saliva - carbs
- 2. lipase - lingual (tongue) + gastric (cheif cells) - triglycerides
- 3. pepsin - cheif cells makes pepsingoen that turn into pepsin (in presence of HCl) - it is proteolytic - it breaks down proteins into a.a. - proteins
What protects the stomach lining?
What cells does the mucosa in the stomach contain?
What does a parietal cell make?
A Chief Cell?
A G Cell?
1. simple columnar
- Excrine: (secrete products into ducts → external)
- 2. Parietal cells - make HCl & IF
- - - HCl (made by proton pump within the cell) - pH 2
- ACh, gastrin, histamine stimulate parietal cell to make HCl - denatures proteins & kills bacteria
- - - IF - Intrinsic factor - need for B12 absorption
- 2. Chief cells - pepsinogen → pepsin (in presence of HCl - breaks down proteins
- 3. Mucous cells - mucus
- Endocrine (Secrete into blood stream)
- G Cells - Gastrin (Hormone) that stimulates chief & parietal cells
What is parasympathetic innervation of the stomach?
- The vagus nerve supplies the stomach. Vagus nerve originates in the medulla (CN 10 - cranial nerve 10)
- Neurotransmitter is ACh which stimulates cells to secrete their products.
Where is the proton pump? What does it make?
What is the role of histamine in enzyme release?
What is an H2 blocker? Where is it found?
What are the three phases of gastric secretion & motility.
- 1. Cephalic Phase
- 2. Gastric Phase
- 3. Intestinal Phase
What is the cephalic phase (phase 1) of gastric secretion & motility?
What is secreted during this phase?
- Cephalic - before food enters the mouth - prepares stomach for food - can be triggered by smell, sight, or thoughs of food.
- - lasts only minutes
- Stimulation is parasympathetic - vagus nerve makes ACh which triggers secretions.
- - histamine - stimulates parietal cells to make HCl
- - Mucous
- - pepsinogen → pepsin (HCl) - (made by chief cells)
- - gastrin - hormone that stimulates chief & parietal cells (Made by G cells)
- - HCl - denatures proteins & kills bacteria (made by parietal cells (proton pumps)
- - Lipase + amylase in saliva
What occurs during the Gastric Phase (phase 2) of gastric secretion & motility?
What is secreted?
Gastric phase = when the food reaches the stomach - mixing + gastric juices - neural & hormonal control
- parasympathetic response
- 1. Stretch receptors - expansion of stomach
- 2. Chemoreceptors - low pH (stomach acid)
- 3. Chemo + stretch receptors = mixing waves
- Negative feetback system
- - mucous, pepsinogen, && HCl continue
- - Gastrin - made by G cells in presence of peptides in chyme - travels in blood stream to stomach to stimulate parietla & chief cells
What occurs during the intestinal phase of Gastric secretion & motility?
What is secreted?
Intestinal Phase - when food reaches small intestine (duodenum) - sympathetic (inhibits gastric motility) - stimulated by duodenal stretch (chyme in)
- Neural - inhibitory reflex -
- Duodenal stretch → medulla →sympathetic output → pyloric sphincter constricts and gastric mixing stops
- CCK - cholecystokinin - made in duodenum (CCK cel)
- Secretin - made by S cells in duodenum in response to low pH.
- - Inhibits chief cells & parietal cells (No HCl)
- - stim pancreas to make buffer HCO3- (neutralize HCl)
- - Stim liver to make bile
How long does food stay in your stomach?
3-4 hours min
What 2 cells do gastrin (hormone) stimulate?
Parietal cell and Chief cells
What does parasympathetic stimulation do in the stomach?
What is the entero/gastric reflex?
Stretch & Chemo receptots stimulate mixing waves for digestion.
Entero/ gastric reflex - sympathetic response that inhibits gastric mixing
Where is CCk made?
- CCK - Cholecystokinin - HORMONE - that is produced in the duodenum.
- - production is stimulated by a.a.'s, FAs, TGs
- CCK =
- - ↑ pancreatic juice
- - sphincter of Oddi opens (controls bile flow)
- - gall bladder contraction - releases bile
- - pyloric sphincter closes - feel full
What is secretin?
Where is it made?
What does it do?
- Secretin =
- - made by S cells in duodenum in response to low pH.
- - Inhibits chief cells & parietal cells (No HCl)
- - stim pancreas to make buffer HCO3- (neutralize HCl) - Stim liver to make bile
How are the exocrine cells of the pancreas arranged?
Two types of cells in the pancreas.
- In clusters called acini that make pancreatic juice.
- 1. islets of langerhans (endocrine)- Alpha cells = glucagon, Beta cells = insulin - 1% of pacreatic cells
- 2. acini - make pancreatic juices:
- - - HCO3- to neutralize HCl
- - - trypsin - protein breakdown
- - - lipase - lipid breakdown
- - - Ribo/ deloxyribo nucleases - break down nucleotides
What is pancreatic juice?
What enzymes are in it?
What stimulates its production?
Pancreatic juice is H2
O, enzymes, and HCO3-
- All enzymes are produces in an inactive form to prevent autodigestion
- Digestive Enzymes:
- 1. Pancreatic amylase - carbs
- 2. Trypsin - proteins - proteolytic
- 3. Pancreatic lipase - TGs
- 4. Ribonuclease & Deoxyribonuclease
Pancreas is stimulated by CCK and Secretin from the duodenum.
Draw the Liver
Liver - largest gland - 2 lobes divided by falciform ligament
What is the functional cell of the liver?
What is a kupffer cell?
Draw a Lobule
- Hepatocyte - primary liver cell - makes bile
- Kuppffer cells - fixed macrophages (from monocytes) that eat debris
- Lobule = functional unit of the liver (hexagon)
- Portal Triad:
- 1. portal vein
- 2. hepatic artery
- 3. bile duct
Where is bile made? Stored?
What is the composition of bile?
What does it do?
- Bile is made in the liver and stored in the gallbladder.
- Bile is made of :
- - H2O
- - Bilirubin - necessary for heme
- - Bile salts -emulsification of fat
- - realsed from GB by CCK
- - emulsifies fats (break down into tiny pieces so lipase can break it down)
- - pH about 8
- - no food = sphincter of Odi closes and GB fills with bile
Draw the biliary drainage system.
What does hyperbilirubinemia cause?
3 types of Jaundice
Hyperbilirubinemia is a byporduct of brakdown of the heme group of HGb - it presents as jaundice - yellow skin, eyes (sclera), musous membranes.
- 1. prehabitic jaundince - caused by increased production of bilirubin (hemolysis)
- 2. hepatic - liver is diseased and unable to process biliriubin (hepatitis, cirrhosis)
- 3. post hepatic - obstruction (stones, cancer)
What are the functions of the liver?
- 1. Carbohydrate metabolism - insulin (anabolic )& glucagon (cat)
- 2. Lipid metabolism - TG storage - blood fa, TG, & cholesterol levers
- 3. Protine metabolism - break down into a.a = NH3 + urea as byproducts
- 4. Metabolism & detoxification of drugs & hormones
- 5. Excrete bilirubin in bile
- 6. make bile salts - from bile acid
- 7. Make clotting factors - complement, albumin, cholesterol
- 8. Store KADE, B12, iron, copper
- 9. Immune - Kupffer cells
- 10. Vitamin D activation - skin & kidneys
3 regions of the small intestine
- 1. Duodenum (10")
- 2. Jejunum (3 ft)
- 3. Ilium (6 ft)
Regions of the large intestine
- 1. Cecum
- 2. Colon
- 3. Rectum
- 4. Anus
Regions of the colon
- 1. Ascending colon (R) - curve = hepatic flexure
- - retroperitoneal
- 2. Transverse colon (across) - curve = splenic flexure
- 3. Descending colon (Anatomic L) - retro
- 4. Sigmoid colon - s shaped - leads to rectum → anal canal → anus
Where is the appendix?
What does the ileocecal valve do?
- Appendix = located in the cecum
- Ileocecal valve = located between the ilium of the small intestine & cecum of Large Intestine - it regulates entry of chyme into LI
What is the function of the small intestine?
10 feet long - 1" in diameter
- Small intestine - majority of digestion/ absorption occurs here - 90 % off all absorption (food & water)
- - recieves chyme from stomach & secretions from liver & pancreas
- - chemically & mechanically breaks down chyme
What structures in small intestine increase absorption?
Cell types of the small intestine.
- 1. Plica - circular mucosal/submucosal folds - ↑ surface area & causes chyme to spiral
- 2. Villi - fingerlike projections - ↑ surface area - contains lacteals to absorb lipids (in lamina propria of mucosa)
- 3. Microvilli - on villi - brush border - digestive enzymes insterted in cell membrane
- Cells: Has same 4 layers M-S-M-S
- Cells types in muccosa:
- 1. simple columnar for absortion/ digestion
- 2. goblet cells - mucous
- 3. crypts of Lieverkuhn - exocrine = intestinal juice
- 4. endocrine - S cells → secretin → HCO3-
- - CCK cells - pancreatic enzymes
- 5. Paneth cells - immune - regulates flora - lysozyme - phagocytosis
- 6. MALT - Mucosa Associated Lymphoid Tissue
- - Peyers patches & lymphatic follicles - found in lamina propria
- 1. Brunners glands - secrete alkaline mucous to neutralize chyme
- 1. Concentric muscle
- 2. Longitudinal muscle
Serosa - visceral peritoneum
What are the 2 types of intestinal movement?
1. Segmentation - local mixing -moves chyme back & forth slowly - chyme touches wall for absorption of nutrients - does not propel
2. Peristalsis - propels chyme forward slowly - over a period of 3 - 5 hours
Name all the juices & their composition
- 1. Intestinal Juice
- - H2O
- - HCO3- (pH 7.6)
- - Enzymes
- Brush Border Enzymes:
- - Lactase - monosacarides
- - Sucrase - disacarides
- - Maltase -
- - Peptidase - proteins
- - mucleosidase - nucleotides
- Pancreatic juice + bile + intestinal juice = very liquidy for better absorption
- + brush border enzymes
Describe Carbohydrate Digestion
- 1. Starts in mouth - salivary amalaise
- 2. Completed in duodenum - pancreatic amalaise
- 3. Brush border enzymes convert di- to mono-
- a. Maltase - glucose & glucose
- b. Sucrase - fructise & glucose
- c. Lactase - glucose & galactose
Describe Protien digestion
- Starts in stomach - pepsin - breaks into peptides
- Completed in duodenum - pancreatic juice trypsin
- Brush border enzymes - aminopeptidase & dipeptidase - break dipeptides into a.a.
Describe lipid digestion
- Stomach - Lingual lipase & gastric lipase - split TGs
- Duodenum - pancreatic lipase - breaks down TGs - after emulsification
Digestion of Nucleic Acids
- Small Intestine - Pancreatic juices:
- - Ribonuclease - digests RNA
- - Deoxyribonuclease - digests DNA
- Brush border enzymes - nucleosidase & phosphatase
- Nucleic Acids broken down into:
- 1. Nitroginous bases
- 2. Pentose sugar (mono)
- 3. Phosphate
- All are absorbed via active transport
What are the mechanims of absorption?
- 90% absorption in Small Intestine
- 10% in colon
- Absorption - to pass nutrients from GI lumen to blood or lymph
- GI lumen to Cell & Cell to blood stream
- 1. simple dissusion - a.a. to BS
- 2. facilitated diffusion - carbs to cell & BS
- 3. active transport -
- primary - carbs to cell & a.a. to cell
- secondary - carbs to cell & a.a. to cell
- 4. osmosis - all water
How are electrolytes absorbed?
Electrlytes absorbed via simple diffusion and Active transport (for both GI to cell & cell to BS)
- - KADE are absorbed from micelles (bile salts) via simple diffusion
- - Water sol = simple diffusion
- - B12 - must be bound to intrinsic factor (from stomach) them moved by active transport
How is water absorbed?
- In GI tract - water moves by osmotic gradient → higher solute concentrations in cell
- 90% in Small Intestine
- 10% in colon
4 parts of colon
What is the mesocolon?
Why is LI called Large?
- 1. Ascending colon - retroperitoneal
- 2. Transverse colon
- 3. Descending colon - retroparitoneal
- 4. Sigmoid colon - sigmoid shaped
Mesocolon - viseral peritoneum that connects LI to posterior abdominal wall
Large Intestine = 5' long & 2.5" wide
Functions of Large Intestine:
- Completion of absorption - last 10% -
- Completion of digestion - via bacteria
- Absorption/ produciton of some Vitamins - by bacteria
- Formation of Feces - last 10% H2O absorbed
Structure of the Large Intestine:
- 1. lymphatic nodules in lamina propria (mucosa)
- 2. microvilli - no villi
- 3. Teniae coli - longitudinal smooth muscle - midline
- 4. Houstra - pouches
- 5. Epiploic appendages - fat on visceral peritoneum at the teniae coli
Draw a segment of Large Intestine
Draw the anal canal & 2 sphincters
What type of muscle is each shpincter?
- Internal sphincter - smooth - involuntary
- External sphincter - skeletal - voluntary
What is haustral churning? Mass Peristalsis?
Alternating contraction & relaxation that moves chyme into adjascent haustra.
Mass peristalsis = strong wave that move chyme int the rectum (gastrocolic reflex) - peristalsis is usually weaker in LI than SI
What role do bacteria play in digestion?
- Bacteria in Large Intestine - break down any remaining large particles into smaller substances
- - produce Vit K & B
- - gas is a product of bacterial fermemtaion (anerobes) - CH4 (methane) & CO2
How is feces formed?
Chyme in Large Intestine get last 10% of water absorbed from it - becomes solid mass
Diarrhea - ↑ motility - moving too fast for complete absorption of H2O
Constipation - ↓ motility - more time for water to be absorbed
Feces in rectum triggers stretch receptors → parasympathetic motor signal initiates dification
Can also be triggered by mass peristalsis