Gastrointesinal anatomy and physiology based on abdominal exam Flashcards
What is the alimentary canal?
Tubular structure makes direct contact with food & has a typical set of histological layers that surround a lumen.
What is the alimentary canal composed of?
-Oral cavity and pharynx
-Esophagus
-Stomach
-Small intestine
-Large intestine
Name the structures associated with the small intestine:
Duodenum, jejunum, ileum
Name the structures associated with the large intestine:
Cecum, appendix, ascending, traverse, descending colon, rectum
What are the accessory digestive organs?
-All of these organs are derived embryologically as “outgrowths” of the early alimentary canal
-All function as glands that secrete substances into the alimentary canal
-Salivary glands
-Liver & Gallbladder
-Pancreas
Which two accessory organs have additional very important functions that impact the rest of the body?
Liver & Pancreas
What, in general, does the alimentary canal do?
Propulsion: food is moved along the “tube” as it’s digested
Secretion(two types):
-Hormonal (impact digestion, secretion, and metabolism)
-Fluid or mucous (aid in propulsion & digestion)
Digestion:
-Chemical- enzymes and acid break chemical bonds in food material or substances facilitate enzymatic interactions
-Mechanical-movements of the canal mix food, break it apart, and increase the SA: volume ratio of food
Absorption (movement from lumen-> bloodstream):
-Water- we ingest over 1L of water per day & secrete 4-6L of water into the canal
-Macro-and micronutrients
Immune function:
-Protection from ingested microbes that are harmful
-Aiding microbes that are useful
-Educating the immune system about whether something that has been ingested is harmful or harmless
What are the layers of the alimentary system?
Mucosa- Epithelial lining, lamina propria, muscularis mucosa
Columnar w/ villi have what function the in the alimentary canal?
absorption/secretion
Cuboidal or squamous has what function in the alimentary canal?
Protection from abrasion
Goblet cells are usually located where? And what is their function?
Epithelial layer; mucous secretion
Neuroendocrine cells are found where, and what is their function?
Cells are interspersed among the epithelium & release signals in response to different nutrients or chemical conditions in the lumen
Lamina propria is the sight of:
-Blood and lymphatic vessels
-Immune tissue (resembles loosely-structured lymphatic nodules, known as MALT)
Describe the muscular mucosa:
Alters the shape of the mucosa to optimize mixing and exposure of the epithelial cells to lumen contents
Loose connective tissue w/ larger blood vessels and lymphatics
Submucosa
What’s found in the submucosa?
-Larger glands
-Large lymph nodes
-A plexus of neurons
What is the neuron plexus of the submucosa known as, and what does it regulate?
Meissner’s(submucosal) plexus: regulates secretions and convey sensory information about whats in the lumen
Name the layer of the alimentary canal:
Usually just an inner and outer layer
Muscularis
Inner layer of the muscularis:
“circular layer” smooth muscle fibers concentrically surround the lumen
Outer layer of the muscularis:
“Longitudinal layer” smooth muscle fibers run along the length of the canal
(when this contracts: the canal shortens)
What plexus regulates the movements of the Inner and Outer layer of the Muscularis layer of the alimentary canal?
Auerbach’s or myenteric plexus
(found between the inner and outer layers)
What is the connective tissue that anchors the esophagus in the chest cavity, and what type of tissue is it?
Adventitia; connective tissue
What is the loose connective tissue that is covered by a simple squamous mesothelium?
Serosa
What does the mesothelium do?
Secretes fluid that collects in the abdominal (peritoneal) cavity
-Source of peritoneal fluid
(continuous with the visceral peritoneum)
Fluid-filled gap between the wall of the abdomen and the organs contained within the abdomen
Peritoneal cavity
The Visceral is formed by what?
Serosa of alimentary canal & the capsule of the liver.
What is the inner lining of the abdominal wall?
Parietal peritoneum: extremely sensitive to inflammation & other chemical irritants
Tube that extends from the pharynx to the stomach, only role is propulsion of food to the stomach.
Esophagus
How long is the esophagus & where is located?
25cm; located retrosternally
When this sphincter closes, it pushes food from the pharynx to the esophagus:
Upper esophageal sphincter
This sphincter limits the movement of stomach acid into the esophagus-> relaxes to receive swallowed food
Lower esophageal sphincter
A sack that can expand to receive and store ingested food
Stomach
What movements accomplish mechanical digestion, and propulsion into the small intestine?
Muscular movements: Churning & breaking up food into acidic chyme
What is the role of chemical digestion in the stomach?
-Denatures proteins and kills ingested bacteria
-Secreted enzymes help to digest protein (collagen in particular)
Stomach doesn’t tell you when your full. (True/False)
False: this is a step of regulating food intake by the stomach
Mucosa has low columnar cells that have a wide range of functions, what are they?
Parietal cells: Secrete acid and intrinsic factor (if needed to absorb B12)
Other cells secrete mucous to protect the lining or digestive enzymes specialized for digesting proteins
Muscularis has how many layers?
3: innermost layer is the oblique layer
Regulates the amount of acidic chyme that enters the duodenum:
Pyloric sphincter
What is the main digestive organ?
Small intestine
(Largest surface area)
The small intestine is the site of what?
Most chemical digestion, absorption, and secretion in the alimentary canal
What are the three separate components of the small intestine?
Duodenum, Jejunum, and Ileum
The short C-shaped tube that receives chyme from the stomach and overlies the head of the pancreas
Duodenum
Both the duodenum and ________ have specialized immune tissue called________
Jejunum; Peyer’s patches
Longest portion of small intestine, main function is reabsorption of bile, salts, micronutrients/vitamins, and water
Ileum
What type of epithelium is in the small intestine?
Highly folded (microvilli), mucosa (villi), and submucosal layers (circular folds) are meant to optimize surface area.
-Columnar epithelium w/ microvilli
-Interspersed with goblet cells and cells that secrete chemical messengers into the blood
-Messengers help regulate propulsion, overall metabolic function, secretions from the pancreas or liver
The main function of this organ is absorption of water from stool, storage of stool, and housing the majority of the microbes in the gut.
Large Intestine
What type of epithelium make up the large intestine?
Low columnar cells with fewer microvilli, plenty of goblet cells
What is the muscular layer of the large intestine?
-Continuous circular muscle layer
-Longitudinal muscle layer is separated into bands that do not completely surround the canal
What organs have ducts that convey their secretions to the lumen of the duodenum?
Pancreas, Liver, Gallbladder, salivary glands
What are the roles of the liver?
-Carbohydrate metabolism
-Protein synthesis and degradation
-Lipid metabolism
-Detoxification of molecules so that they can be secreted into the bile and defecated
-Making hydrophobic molecules water soluble so that they can be eliminated by the kidney
-Storage of vitamins and minerals
-Synthesis of bile-essential for lipid digestion
-Endocrine-secretion of IGF-1, important hormone regulating growth
Where do most of the proteins that are secreted into the bloodstream come from?
Liver
Which accessory organ is in charge of the storage and modification of bile?
Contraction-> bile release into the duodenum
What accessory organ has exocrine and endocrine functions?
Pancreas:
Exocrine-secretes digestive enzymes that are crucial for carbohydrate, protein, and lipid chemical digestion
Endocrine-secretes hormones that impact glucose, protein, and lipid metabolism into the bloodstream
Where do the exocrine secretions from the pancreas go?
Pancreatic duct, which drains into the duodenum
What are some of the hormones that are secreted through the pancreas?
Insulin, Glucagon, & Somatostatin
What do hyperactive bowel sounds probably indicate?
Diarrhea, gastroenteritis, inflammatory bowel disease, laxative issues, gastrointestinal bleed
or
early bowel obstruction (often described as a high pitched tinkling sound)
What do hypoactive bowel sounds typically indicate?
-Often suggests more emergent conditions
-Bowel obstruction, peritonitis, intestinal ischemia
How long do we listen before assuming absence of bowel sounds?
5 min
Tenderness=
pain in the region where you palpate
-Abdominal pain is present regardless of whether you palpate the abdomen
(tender to light or deep palpation)
“Deep” or visceral pain in the abdomen can come from what?
Stretching, ischemia, chemical irritation of a component of the alimentary tract or accessory organ
(Sometimes pathologies in the thorax (heart attack, pneumonia) can also be present as abdominal pain.)
A voluntary contraction of the abdominal musculature due to abdominal discomfort:
Guarding:
-Can be exacerbated by anxiety
-Serious pathology , but often less serious
Involuntary contraction of the abdominal musculature , usually accompanied by severe pain.
Rigidity:
-More serious pathology
-Due to chemical irritation of the parietal peritoneum lining or “rubbing” of an inflamed organ against it:
ex)
-Bile (ruptured cholecystitis), infected material (ruptured or ischemic intestinal wall), Pancreatic secretions (Pancreatitis), gastric or duodenal contents (perforated peptic ulcer)
-Inflamed structure rubbing against the parietal peritoneum-appendicitis, diverticulitis
Abdominal pain in the three areas in the “center” can be:
Visceral pain from the alimentary tract or accessory organs
(can also be due to irritation of the parietal peritoneum)
Abdominal pain in the six regions on the “sides” are often due to what?
Irritation of the parietal peritoneum
(Can also be due to visceral pain from non-GI organs)
Abdominal pain FYI:
Good to know for the future
What is hepatomegaly:
Enlarged Liver:
-A palpable liver does not necessarily indicate hepatomegaly
-Pathological changes in consistency could be noted-from the normal softness to an abnormally firm or hard liver
(pathologies can also cause the liver size to increase)
Liver Cirrhosis:
Large liver with firm, non-tender edge
Hepatocellular carcinoma:
large liver that is firm and in irregular edge (may or may not be tender)
