Processes of Digestion:
- 1. Food ingested: by mouth
- 2. Mechanical digestion: chewing
- 3. Chemical digestion: Salivary amylase begins chemical breakdown of starch
- 4. Propulsion: initiated by swallowing
- 5. Pharynx and Esophagus: pass food from mouth to stomach
- passes food and fluids to esophagus and gives air to trachea
- -lined with stratified squamous epithelium and mucus glands
- -two skeletal muscle layers for swallowing
- 1. inner longitudinal
- 2. outer pharyngeal constricters
Swallowing: involving 22 seperate muscle groups and involves 3 phases
- (within deglutition)
- bolus is forced into oropharynx
- (within deglutition)
- -controlled by medulla and lower pons
- routes sealed off except into digestive tract (probably so we don't choke)
- (within deglutition)
- moves food through pharynx and esophagus
- muscular tube going from laryngopharynx to stomach
- travels through mediastinum and pierces diaphragm
- joins stomach at cardiac orifice
nonkeratinized stratified squamous epithelium
What happens when the esophagus is empty?
its folder longitudinally and flattened
The muscle changes from what to what in the esophagus?
skeletal (superiorly) to smooth muscle (inferiorly)
When does a Hiatal Hernia occur?
- when the cardiac (gastroesophageal) Sphyncter does not close when food is in stomach
- -causes pregnancy, obesity, weak sphyncter
- -superior stomach can move into thoracic cavity
Gastro Esophageal Reflux Disease (GERD)
- is a result with acid irritating the esophagus
- -if chronic then esophageal cancer can result
What does the salivary gland secrete?
- Amylase: carbs-glucose
- Lingual Lipase: fats-fatty acids
What does the Stomach secrete?
- Pepsin: proteins-polypeptides
- HCl: pepsinogen-pepsin, destroys pathogens
What does the Liver secrete?
Bile Salts: fats-fatty acids
What does the Pancreas secrete?
- Amylase: carbs-glucose
- Trypsin: polypeptides-peptides
- Lipase: fats-fatty acids
What do the small intestines secrete?
- peptidase: peptides-amino acids
- sucrase: sucrose-glucose
- maltase: maltose-glucose
- lactase: lactose-glucose
What happens when bolus goes into stomach?
chemical breakdown of proteins and food is converted into chyme
surrounds cardiac orifice and cardic sphincter
dome shaped region beneath diaphragm
- made of antrum and canal whih terminates at pylorus
- -pylorus extends to duodenum
What does the greater omentum help with?
holding the small intestines in place
What is the Nerve Supply like in the Stomach?
sympathetic and parasympathetic fibers of autonomic nervous system
Blood Supply in the stomach comes from where?
- celiac trunk (gastric artery
- corresponding veins (gastric veins)
part of hepatic portal system
What does the Muscularis layer do in the Stomach?
- allows stomach to churn, mix, and pummel food physically
- breaks down food into smaller fragments
What is the Epithelial lining in the Stomach composed of?
Goblet cells: produce double layer coat of alkaline insoluble mucus with bicarbonate in between
contain gastric glands that secrete gastric juice, mucus, and gastrin
Mucous Neck Cells (Gastric Pit)
secrete acid mucus
Parietal Cells (Gastric Pit)
secrete HCl and intrinsic factor needed for Vitamin B12 (nucleic acid metabolism and RBC maturation) absorption in small intestines
Chief Cells (Gastric Pit)
(pepsinogen activated to pepsin by HCl in stomach and pepsin breaks down proteins to polypeptides)
Enteroendocrine cells (Gastric Pit):
- -Gastrin: stimulates gastric glands to increase there secretion, stimulates gastric emptying
- -Histamine: activates parietal cells to release HCl
- -Serotonin: stimulates gastric muscle contractions
- -Cholecystokinin (CCK): allows pancreatic and bile enzymes to be released
- -Ghrelin: release when stomach is empty stimulating hunger and appetite
To Keep the stomach from digesting itself, its mucosal barrier has what?
- thick coat of bicarbonate-rich mucus on wall
- epithelial cells joined by tight junctions (damaged cells are replaced quickly)
- gastric glands that have cells impermeable to HCl
What are Stomach ulcers caused by?
- bacteria Helicobacter pylori (H. pylori)
- burrs a hole through the mucusa and allows HCl to further irritate the lining
How does Helicobacter Pylori work to create a stomach ulcer?
- 1. bacteria secretes ammonia, neutralized the HCl
- 2. secretes cytotoxin that damages mucosal cells
- 3. produces proteins that sepertate cells tight junctions
What are the 5 things the stomach does?
- 1. holds food
- 2. degrades food physcially and chemically
- 3. delivers chyme to small intestine
- 4. Enzymatically digests proteins to polypeptides to pepsin
- 5. secretes intrinsic factor required for absorption of vitamin B12 (needed for DNA synthesis and erythropoeisis)
How many phases are there in Gastric Secretion and what are they?
Cephalic (reflex), Gastric, and Intestinal phase
Cephalic (reflex) phase: Gastric Secretion
- happens before food enters stomach
- -Excitatory: think, smell, taste, see
- enhanced secretory activity (reflex) only happens when we want or like food we see
- -Inhibitory: loss of appetite/depression, decrease in stimulation of parasympathetic division
Enteric ganglionic neurons stimulate the stomach glands
Gastric phase: (Gastric secretion)
- food enters stomach
- last 3-4 hours
- Excitatory: stomach distension,
- activation of stretch receptors,
- activation of chemoreceptors by peptides caffeine, and lowering pH,
- release of gastrin in blood (stimulates gastric glands to increase secretion=gastric emptying
- Inhibitory: pH lower than 2
- emotional upselt overrides parasympathetic division
- *ACh release, stimulates more gastric juice
- rise in pH stimulates gastrin secretion and HCl release (more acid for protein digestion)
Intestinal Phase: (Gastric Secretion)
low pH; partially digested food enters duodenum and encourages gastric gland activity
- Inhibitory: distension of duodenum, presence of fatty, acidic, hypertonic chyme, and/or irritants in duodenum
- -initiates inhibition of local reflexes
- -closes pyloric sphincter
- -small intestines release enterogastrones (CCK and Secretin), inhibit gastric secretion
HCl secretion is stimulated by...
Antihistamines block___ receptors and decrease ____ release.
Stomach pressure remains constant until ___ of food is ingested.
How much food can the stomach hold?
How long is the stomach when it is empty and how big can it get?
- 6-10 inches
- to the top of the pelvis when filled
Peristaltic waves move toward the pylorus at rate of __ per________.
Gastric Contractile Activity:
The BER is initiated by ________ (________).
- Basic Electrical Rhythm
- pacemaker cells
- Cells of Cajal
Where are the Cells of Cajal (otherwise known as) located?
- pacemaker cells
- longitudinal muscles of stomach
- * these cells are stimulated by the stretch
Where does the most vigorous peristalsis and segmentation occur?
What are the 2 ways Chyme can be delivered?
- -small amounts to duodenum
- -backward into stomach for further mixing
Gastric emptying regulated by:
- -neural enterogastric reflex
- -hormonal (enterogastrone) mechanisms
-they inhibit gastric secretion and duodenal filling
What type of chyme moves quickly through duodenum?
What type of chyme moves slowly through duodenum?
fat-laden chyme, because its digested slower
How long are each of the divisions of the small intestines?
- Duodenum: 10-12 inches
- Jejunum: 8 feet long
- Ileum: 11 feet long
- deep circular folds of the mucosa and submucosa
- forces chyme through and increase time of absorption
fingerlike extensions of mucosa
- brush border cells
- tiny projections of absorptive mucosal cells' plasma membranes
- also secrete digestive enzymes
What are the cells of intestinal cypts?
- Crypts of Lieberkuhn
- secrete intestinal juice
Peyer's patches are found where?
What secretes alkaline mucus within the duodenum?
Brunner's glands which neutralizes acidic chyme from stomach
- seperates right and left lobes of liver
- suspends liver from diaphragm and anterior abdominal wall
- remnant of fetal umbilical vein
- runs along free edge of falciform ligament
When you eat, the Sphincter of Oddi is...
What does the portal triad consist of?
- bile duct
- hepatic artery
- hepatic portal vein
Where are the portal triads found?
each of the 6 corners of each liver lobule
Hexagonal shaped liver lobules are composed of?
hepatocyte (liver cell) plates radiating outward from central vein
- enlarged, leaky capillaries located between hepatic plates
- blood from hepatic portal vein and artery come through here and empties into central vein
- hepatic macrophages found in liver sinusoids
- they remove debris such as bacteria and worn out blood cells from blood
Function of Hepatocytes:
- 1. Production of Bile
- 2. Processing bloodborne nutrients
- 3. Storage of fat-soluble vitamins
- 4. Detoxification
Bile flows between _________ toward ___ ___ in the ____ _____.
- bile ducts
- portal triads
- bile salts
- bile pigments
- neutral fats
- cholesterol derivatives:
- -emulsify fat
- -facilitate fat and cholesterol absorption
- -solubilize cholesterol
Chief bile pigment is?
bilirubin, waste product of heme
What does the Enterohepatic circulation do with bile salts?
- thin walled, green muscular sac on ventral surface of liver
- stores and concentrates bile by absorbing water and ions
- releases bile by cystic duct
Acidic and fatty chyme causes...
- duodenum to release CCK and secretin into bloodstream
- this stimulates liver to produce bile
causes weak contractions of gallbladder
Cholecystokinin (CCK) causes:
- gallbladder to contract
- hepatopancreatic sphincter to relax
- *Result: bile enters duodenum
- produces most digestive enzymes of any organs
- 1200-1500mL per day
- exocrine and endocrine gland
What enzymes does the pancreas secrete?
- 1. Typsin: polypeptides-peptides
- 2. Lipase: fat-fatty acids
- 3. Amylase: Carbs-glucose
- 4. Nucleases: Nucleic acid-nucleotides
- 5. Carboxypeptidase: polypeptides-peptides
*part of Exocrine function
- cluster of secretory cells
- contain zymogen granules with digestive enzymes
- (Beta cells of Islets of Langerhans)
- decreases blood sugar by removing it from blood into cells
- Alpha cells
- increases blood sugar by breaking down glycogen into glucose and fat.
Composition of Pancreatic Juice:
water solution of enzymes and electrolytes
Function of Pancreatic Juice:
- Neutralizes acid chyme
- provides optimal environment for pancreatic enzymes
- enzymes are activated in duodenum
As chyme enters duodenum...
- -carbs and proteins are partially digested
- -no fat digestion takes place
- -chyme release slowly because low pH, mixing required for proper digestion
- -substances needed provided by liver
- -all nutrient absorption take place in small intestine
Motion in small intestine:
- -initiated by pacemaker cell (Cajal cells)
- -Migrating Motility Complex (MMC) peristaltic activity
After nutrients are absorbed by small intestine...
meal remnants, bacteria, mucosal cells, debris are moved into large intestine
How long does it take matter to get through duodenum to ileum?