Gastrointestinal Tract Flashcards
Describe Digestion
Break down of food into molecules small enough to be absorbed
Describe Absorbtion
The passage of molecules through the plasma membranes of the cells lining the stomach and intestines into the blood and lymph
Structures of the Gastrointestinal System
- GI Tract
2. Accessory Digestive Organs
GI Tract A.k.a
Alimentary Canal
Describe the GI tract
Continuous tube from the mouth to the anus
What are the accessory Digestive Organs?
- Teeth
- Tongue
- Salivary Glands
- Liver
- Gallbladder
- Pancreas
Functions of the GI system
- Ingestion
- Secretion (breakdown)
- Mixing and propulsion
- Digestion
- Absorption
- Elimination
Ingestion
Eating
What is Secretion?
Cells in the walls of the GI tract and accessory organs secrete water, acid, buffers, and enzymes into the lumen of the tract
What is Mixing and Propulsion ?
- Muscles in the organ wall rhythmically contract and relax to mix the food and secretions together
- Move mixture through the system
What are the 2 types of Digestion?
- Mechanical
2. Chemical
Describe Mechanical Digestion
- Tongue mixes food
- Teeth grind and cut food
- Stomach and small intestines churn/mix food
Describe Chemical Digestion
- Enzymes help break larger nutrients into smaller ones (which are then absorbed)
- Enzymes are secreted by salivary glands, tongue, stomach, pancreas and small intestine
Describe Absorption
- Taken in through the membranes of cells lining the stomach and small intestines
- Enters blood or lymphatics
- Circulated through the body
Elimination A.k.a
Defecation
Describe Elimination
Feces: wastes, undigested substances, unabsorbed substances, bacteria, cells sloughed off from the GI tract lining
Chewing
Mastication
Swallowing
Degluitition
Vomiting
Emesis
Taste
Gustation
What do teeth do?
- Cut/grind food
- Mix food with saliva
- Food more manageable to swallow
What is the tongue?
A skeletal muscle covered in mucous membrane
What are the 3 major salivary glands?
- Parotid
- Submandibular
- Sublingual Glands
Salivary gland inferior and anterior to the ear, between skin and masseter
Parotid Gland
Salivary gland located the floor of the mouth
Submandibular Glands
Salivary gland beneath the tongue
Sublingual Glands
Lingual refers to ____
The Tongue
What is saliva?
Water, solutes, and enzymes
Soft, flexible mass that is swallowed
Bolus
Pharynx A.k.a
Throat
Structure of pharynx
Skeletal muscle lined with mucous membrane
What happens through the pharynx?
Muscle contractions move bolus from the mouth through the pharynx to the esophagus
Structure of the esophagus (where located)
- Skeletal and smooth muscle
- Collapsible muscular tube posterior to trachea
- Lowest segment of pharynx through diaphragm to superior aspect of the stomach.
How does the esophagus go through the diagram?
Esophageal Hiatus
Functions of the Esophagus
- Secrete mucous
2. Transport bolus to stomach
Wave-like contractions of smooth muscle lining the walls of the GI tract that move the bolus along the tract
Peristalsis
What is the passage of food from the pharynx into the esophagus controlled by?
Upper esophageal sphincter
What is the passage of food from the esophagus into the stomach controlled by?
Lower esophageal sphincter
What does the Lower Esophageal Sphincter prevent?
Acid from the stomach back into the esophagus Heartburn
The wall of the GI tract from the lower esophagus to the anal canal has the same 4 layered arrangement. What is it from superficial to deep?
- Mucosa
- Submucosa
- Muscularis
- Serosa
What is the reference point of the 4 layered arrangement of the GI tract wall?
The Lumen
Mucosa consists of:
- Epithelium
- Lamina Propria
- Muscularis Mucosa
Cells of the epithelium element of mucosa
- Epithelial cells
- Exocrine Cells
- Enteroendocrine Cells
What do the exocrine cells secrete?
Mucous, liquid
What do the enteroendocrine cells secrete?
Hormones
Describe the Lamina Propria
- CT areolar
- Blood and lymphatic vessels (absorption)
- Mucosa-asscociated lymphatic tissue (MALT) (immune)
Describe Muscularis Mucosa
Smooth muscle layer that created folds in the mucosa for increasing surface area for absorption
Describe Submucosa
- CT layer binds mucosa to muscularis layer
- Contains blood and lymphatic vessels (nutrient transport)
- Contains neurons of the ENS for GI control
What type of muscle is the Muscularis layer?
Skeletal muscle and smooth muscle
Where is skeletal muscle found? Where is smooth muscle?
Mouth, pharynx, upper 2/3rds of esophagus, external anal sphincter Everywhere else (Smooth)
What are the two layers of muscle in Muscularis?
- Circular Fibres
2. Longitudinal Fibres
Contractions of muscularis help:
- Break down food
- Mix food with secretions
- Move food through GI tract
Which NS controls the frequency and strength of contractions?
Enteric
Serosa A.k.a
Visceral Peritoneum
Describe the Serosa
- Serous membrane (2 layer peritoneum)
2. Outermost layer of the organs in the abdominal cavity
2 Layers of the peritoneum
1 .Visceral Peritoneum (serosa)
2. Parietal Peritoneum
Where is the peritoneum found?
Between two layers of peritoneal cavity
Some organs are covered by the peritoneum on their anterior side only
Rertoperitoneal
Examples of Retroperitoneals
Kidneys, Ascending/descending colons, duodenum, pancreas
The peritoneum contains large folds that _____…
Bind organs to one another and to the walls of the abdominal cavity
J-shaped enlargement in the GI tract
Stomach
Stomach location
- Immediately below the diaphragm
- Runs from the esophagus to small intestines
How does food enter the stomach?
Through the lower esophageal sphincter
What is the stomach for the GI system?
Storage tank
Allows catch up for the GI tract
Stomach mixes food for 2-4hrs, soupy mix called ___
Chyme
What is absorbed in the stomach?
Little (water, ions, some fats, medications, alcohol)
Once food particles are small enough, where do they go?
To the small intestine through the pyloric sphincter
How is the wall of the stomach arranged?
Same 4 layered structure as GI tract
(Mucosa, Submucosa, Muscularis, Serosa)
+specialized cells
+additional smooth muscle layer
What are the specialized cells in the stomach?
- Mucous Neck Cells
- Parietal Cells
- Chief Cells
- G Cells
What are the specialized cells in the stomach secrete?
- Mucous (mucous neck cells)
- Intrinsic Factor and HCl- (parietal cells)
- Pepsinogen and gastric lipase (chief cells)
- Gastrin (hormone by G cells)
How does pepsinogen activate, what does it do?
- As is, is not active
- HCl- (from parietal cells) becomes active
- Breaks down protein ONLY in chyme
- -Mucous lining of stomach protects proteins making it up
Role of gastric lipase
Breaks down fats in the stomach
Roles of Gastrin
(ENDOCRINE, BLOODSTREAM)
- stimulates gastric juice production
- strengthens LES contraction
- increases stomach peristalsis
- relaxes pyloric sphincter
Collective secretions of mucous, parietal, and chief cells (no G cells)
Gastric Juices
What does the additional layer of smooth muscle do for the stomach?
Facilitate mixing
How large is the small intestine?
~3m long and 2.5cm in diameter
Why does the small intestine have a large surface area?
Digestion and Absorption
3 Regions of the Small Intestines
- Duodenum
- Jejunum
- Ileum
What increases the surface area of the small intestines?
- Circular Folds: ridges in mucosa/submucosa
2. Villi (mucosal layer)
Each villi is covered in..
Epithelium
Epithelial cells of the small intestine
- Absorptive Cells (digestion/absorption)
- Goblet Cells (mucous)
- Paneth Cells (kill bacteria)
- Enteroendocrine Cells (secrete hormones)
What is the brush border?
Name for absorptive Cells have microvilli
Each villus has:
arteriole, venule, lacteal
What is a lacteal
Lymphatic Supply vessel
What is chyme mixed with in the small intestine?
Intestinal and pancreatic juices
In the small intestine, absorbed nutrients pass into either:
- Blood stream and go to the liver
- The lymphatics via a lacteal
- Remaining passes into large intestine
What nutrients are absorbed into the blood?
Carbs, proteins, water, electrolytes, water-soluble vitamins
What nutrients are absorbed into the lymphatics?
Lipids
How does food pass through the small intestine to the large?
Through the ileocecal valve/sphincter
Where does the pancreas sit?
Posterior to the stomach
Functions of the pancreas
Endocrine and exocrine
Exocrine function of the pancreas
Secretes pancreatic juice (water, salts, sodiumbicarbonate, enzymes) into the duodenal lumen
Pancreatic juices are secreted into the proximal duodenum via 2 main ducts..
- Common duct: formed by pancreatic duct joining common bile duct from the liver/gall bladder
- Accessory duct
Liver location
Inferior to the diaphragm in the right superior region of the abdominal cavity
Structure of Liver
Two Lobes:
Larger right, smaller left
How does the liver receive its blood?
- Hepatic Artery: oxygenated blood
2. Hepatic Portal Vein: deoxygenated blood
Why would the liver want deoxygenated blood through its ______.
Hepatic Portal Vein: delivers absorbed nutrients, medications, microbes and toxins
What are hepatocytes? What do they do?
Liver cells (glycogen storage)
- Absorb oxygen, nutrients, and toxins
- Release nutrients
- Manufacture and secrete bile (not into blood stream)
When the blood flows past the liver, it enters the ____
Hepatic Vein
Other functions of the liver (7)
- Carb Metabolism
- Lipid Metabolism
- Protein Metabolism
- Drug and Hormone Processing
- Bilirubin Elimination
- Vitamin and Mineral Storage
- Vitamin D Activation
Liver’s affect on Carb Metabolism
- Low Blood Sugar: hepatocytes break down glycogen and release glucose into the blood
- High Blood Sugar: Remove glucose and store as glycogen and fat
- Can convert amino acid, lactic acid and other sugars into glucose
Liver’s affect on Lipid Metabolism
Hepatocytes store fat, break it down (ATP) and make cholesterol
Liver’s affect on Protein Metabolism
- Makes amino acids available for energy
- Convert amino acids into carbs of fats
- Synthesize most plasma proteins
Liver’s affect on Drug and Hormone Processing
Detoxifies/inactivates substances
What is bilirubin?
End product of the break down of RBCs.
Has yellow pigment–Jaundice
Structure and location of gallbladder
Pear shaped, posterior surface of liver
Function of gallbladder
Stores and concetrates bile –break down fats
What is bile? What is its function?
- Yellow/brown/olive liquid
- Made by hepatocytes
- Collects into larger and larger vessels
- Break down of fats
What is the term for breaking down
Emulsification
4 Regions of the large intestine
- Cecum
- Colon
- Rectum
- Anal Canal
Functions of Large Intestine
- Completion of absorption
- Vitamin K production (blood clotting processes)
- Formation/elimination of feces
Small pouch attached to the ileocecal valve
Cecum
What is attached to the Cecum?
Appendix
Contents move from the Cecum to the ____
Colon
4 Divisions of the Colon
- Ascending (to hepatic flexure)
- Transverse (to spleen flexure)
- Descending (to left iliac crest)
- Sigmoid (to the rectum at ~S3)
What happens when food accumulates in the Colon?
- Fills haustra
- Stimulates smooth muscle contraction
- Food moves to next haustra
Mass peristalsis moves meal from the transverse colon to the ______
Rectum
Travels inferiorly to the anal canal
Rectum
Terminal portion of the large intestine
Anal canal
How is elimination controlled?
Internal Anal Sphincter: involuntary
External Anal Sphincter: voluntary
What is the defecation reflex?
Distension of the rectum ultimately gives the urge to go, relaxes internal anal sphincter
Divisions of the GI tract
Upper GI: mouth, pharynx, stomach, duodenum
Lower GI: most of the intestines and the anus
3 Overlapping Phases of Digestion
- Cephalic
- Gastric
- Intestinal
Cephalic Phase of Digestion
Thought, smell, sight, and initial taste of food activates NS
-Salivary glands and gastric glands are stimulated to prepare mouth and stomach for digestion
Once food reaches the stomach, it is the _____ phase of digestion
Gastric Phase
Changes during Gastric Phase of Digestion
- Stretch receptors stimulated by stomach change shape
2. Chemo receptors are stimulated by stomach pH change
What do the changes in the Gastric Phase of Digestion do?
- Increase peristalsis and gastric juice production
- Stimulate gastrin release (G-cells)
Explain the Gastric Phase after the stomach.
- Chyme through pyloric sphincter into duodenum
- Decreases stomach volume–removes stretch receptor stimulus
- Stomach more acidic
- decreased stretch receptors and normalizing pH removes some stimulus for gastrin release
What happens in the Intestinal Phase?
Chyme in duodenum causes enteroendocrine cells to release hormones
What are the hormones secreted in the Intestinal Phase
- Cholecystokinin (CCK)
- Secretin
What are the affects of the hormones secreted in the Intestinal Phase?
- Stimulates gallbladder to eject bile into duodenum (CCK)
- Secretin decrease gastric juice production (CCK/secretin)
- Slow food coming through the pyloric valve (CCK/secretin)
- Increase pancreatic juice secretion (CCK/secretin)
