Digestive System Flashcards
Two Groups of Digestive Organs
Alimentary Canal (GI Tract):
- mouth, pharynx and esophagus
- Stomach, Small Intestine, Large Intestine
Accessory Digestive Organs:
- teeth and tongue
- salivary glands, liver, gallbladder, pancreas
Functions of Digestive System
- Ingestion
- Mechanical Processing
- Chemical Digestion
- Secretion
- Absorption
- Excretion
What is the major means of propulsion of food through the alimentary canal?
Peristalsis
- alternate waves of contraction and relaxation of circular and longituginal smooth muscle
How is foods mechanically digested within the alimentary canal once it is past the mouth?
Segmentation
- rhythmic local constrictions of intestine
- mixes food with digestive juices
- increases absorption efficiency
What is the serous membrane that lines the abdominal cavity?
What are its two layers?
And the space within it?
- Peritoneum
- Visceral Peritoneum - sits on digestive organs
- Parietal peritoneum - lines body wall
- Peritoneal Cavity - filled with serous fluid
What is an organ behind the peritoneum called?
And which organs are?
Retroperitoneal
- duodenum, pancreas and parts of the large intestine
What are organs within the peritoneum called?
Intraperitoneal
What holds intraperitoneal organs in place?
What’s it made of?
What else does it do?
Mesentery
- a double layer of fused peritoneum which extends to the organs from the body wall
- serves as a site of fat storage as well as a route for circulatory vessels and nerves
What are the two kinds of mesenteries and where do they attach?
Dorsal and Ventral
- Dorsal mesenteries (most) attach to the rear of the peritoneal cavity, closer to the spine
- Ventral mesenteries attach to the front of the peritoneal cavity
What is this structure covering the abdominal organs?
And where does it attach?
Greater Omentum
- Attaches greater curvature of stomach to dorsal body wall, covers spleen, pancreas, transverse colon and much of the small intestine
- covers small intestines like an apron
What does the blue arrow indicate?
Lesser Omentum
- between lesser curvature of stomach and liver, attaching the two
What structure anchors the large intestine to the interior abdominal wall?
Mesocolon
- anchors to posterior of abdominal cavity
What are the four tunics of the alimentary canal wall?
- Mucosa (epithelium, lamina propria, muscularis mucosae)\
- Submucosa (dense CT, glands, elastic fibers, blood/lymph vessels, nerves)
- Muscularis Externa (inner circular and outer longitudinal smooth muscle layers)
- Serosa (visceral peritoneum)
2, #3 and #4 together
what is it?
where is it?
what does it do?
what are its layers?
what kinds of cells are present?
Mucosa
- shown here in esophagus (present throughout GI tract)
- moist surface of lumen
- absorbs nutrients, produces secretions
- Surface Epithelium (non-keratinized stratified squamous in esophagus, simple columnar from stomach to large intestine)
- Lamina Propria (thin layer loose areolar or reticular CT with glands & lymphoid tissue)
- Muscularis Mucosae (longitudinal smooth muscle)
5
- what is it?
- where is it?
- what does it contain?
Submucosa
- dense irregular CT with submucosal glands and elastic fibers
- lies just outside mucosa
- contains blood/lymph vessels and nerve fibers
6
What is it?
What are its two layers (6a and 6b)?
And their functions?
What is special about this layer when shown here in the esophagus?
Muscularis Externa
- two layers of smooth muscle external to submucosa
- Inner (6a) Circular Layer - constricts alimentary canal
- Outer (6b) Longitudinal Layer - shortens alimentary canal
- esophageal muscularis externa also contains skeletal muscle because part of swallowing is voluntary
7
- what is it called here? and on GI organs within the peritoneal cavity?
- what is it made of here? and inside the peritoneum?
Adventitia (Serosa within peritoneum)
- Adventitia is fibrous connective tissue
- Serosa is simple squamous epithelium and loose CT
GI Innervation
- what are the nerve networks called?
- what are the two different ones and their functions?
- what is the entire GI nervous system called?
- Nerve Plexuses
- Submucosal Plexus - controls glandular secretions of mucosa and contractions of muscularis mucosae
- Myenteric Plexus - controls peristalsis via contractions of muscularis externa
- all known as the Enteric Nervous System
What are these?
What do they do?
What muscle controls them?
Lips, AKA Labia
- protect anterior opening to oral cavity
- orbicularis oris muscle
What is the entire space shown here?
- What parts of digestion takes place here and how?
Oral Cavity
- Mechanical digestion occur here via the movement of the tongue and teeth
- enzymatic digestion begins with amylase breaking down starches
- food is moistened and mixed
What is the blue highlighted space shown?
Oral Cavity Proper
- all of the oral cavity posterior to the teeth
Vestibule
- space between cheeks/lips and gums/teeth
Opening indicated by pen
Fauces
- opening between oral cavity and oropharynx
What’s this and what’s it made of?
Cheek
- lateral wall of oral cavity
- has a core of skeletal muscle
what is the highlighted green structure?
what bones make it up?
where is it?
Hard Palate
- formed by maxilla and palatine bones
- horizontal partition between the oral and nasal cavities
- forms anterior portion of roof of mouth
What is it? Where is it? What’s it made of?
Soft Palate
- forms posterior portion of roof of mouth
- muscular layer between oro- and nasopharynx
3
what is it?
what does it do?
Uvula
- fleshy projection of soft palate
- elevates during swallowing to close off entrance to nasopharynx, preventing food from entering
What is it?
What’s it made of?
What is its function?
How is it attached?
Tongue
- skeletal muscle
- grips food, repositions it, mixes it with saliva and moves it into pharynx
- attached to skull processes and inferiorly via lingual frenulum
Through what structure is the top piercing?
Lingual Frenulum
- a thin vertical mucus membrane attaching inferior tongue to floor of oral cavity
What is this structure? How many are there in the mouth?
Labial Frenulum
- two: one superior, one inferior
What are #2 and #3 and how are they part of the digestive system?
Why isn’t #1?
What kind of cells line them?
And what is their function in digestion?
Oro- and Laryngopharynx, respectively
- common passageways for air and food
- # 1 is the nasopharynx, which is shut off to incoming food by the uvula during swallowing
- lined by stratified squamous epithelium
- superior, middle and inferior pharyngeal constrictor muscles propel food (known here as bolus) into esophagus
Starred area?
What is it?
Where does it start and lead?
What are its layers?
esophagus
- a muscular tube
- begins as continuation of pharynx, leads to stomach
- has most usual layers : mucosa, submucosa, muscularis externa, adventitia (outermost layer of extraperitoneal GI tract)
esophageal hiatus
- passageway of esophagus into abdomen through diaphragm
What is the perpendicular structure smooth muscle shown here just superior to the stomach?
What is its function?
Lower Esophageal (or Gastroesophageal or Cardiac) Sphincter
- contracts to close entrance to stomach
- prevents regurgitation
What is this portion of the stomach?
Where does it begin?
Cardia or Cardiac Orifice
- where the esophagus joins the stomach
- begins where squamous epithelium of esophagus gives way to columnar epithelium of stomach
What is this?
Where is it?
What is its function?
Stomach
- a J-shaped organ extending from the esophagus to the small intestine
- stores food temporarily
- churns food into chyme
- secretes pepsin and HCL to begin protein digestion
Fundus of stomach
- expanded superior region under diaphragm
Body of stomach
- large midportion inferior to cardia and fundus
Light blue region:
Pyloric Region of stomach
- funnel-shaped pouch at terminal end of stomach
pyloric sphincter
- smooth muscle that regulates passage of chyme from stomach to duodenum
- a thickening of the circular muscularis externa
lesser curvature
- concave curvature on medial side of stomach
greater curvature
- large convex curvature on lateral side of stomach
What are the folds?
Rugae
- folds inside stomach
- allow for expansion of stomach wall
Layer 2
Circular Muscularis Externa
- movement breaks food into smaller pieces
Layer 3
Longitudinal Muscularis Externa of stomach
- movement helps to break food up
layer 1
Oblique Layer of Muscularis Externa of stomach
- extra layer of muscularis externa in stomach
- jacknifes stomach into a v to move chyme into small intestine
blue highlighted regions:
- what are they?
- what do they contain?
gastric pits
- indentations of stomach that enter into gastric glands
highlighted blue area:
- what are they?
- what are their four major cell types and their secretions?
Gastric Glands
- groupings of specialized cells deep to gastric pits that produce various secretions that aid in gastric function
- Enteroendocrine Cells - secrete gastrin which directs HCL secretion and motility
- Parietal (Oxyntic) Cells - secrete HCl
- Chief (Zymogenic) Cells - secrete pepsinogen, a pepsin precursor activated by HCl
- Mucous Neck Cells - secrete mucus
What is the point in this photomicrograph where light purple epithelium meets dark purple epithelium?
esophageal cardiac junction
- point where esophagus meets stomach and epithelium changes from non-keratinized stratified squamous to simple columnar
What organ is indicated by the red blob?
What is its function and from/to where does it extend?
How long is it?
Small Intestine
- the body’s major digestive organ
- site of nutrient absorption into blood
- it extends from the pyloric sphincter to the large intestine
- 18 - 20 feet long
What are the three subdivsions of the small intestine?
Duodenum - shortest (10”), retroperitoneal section just after stomach, curves around head of pancreas
Jejunum - (7.5 ft) superior, middle portion of small intestine
Ileum - (10.5 ft) inferior, distal, longest portion ending at large intestine
Which section of the small intestine receives bile from the liver/gallbladder and enzymes from the pancreas?
Through which ducts?
Duodenum
- Bile Duct and Main Pancreatic Duct
What three structures increase the absorptive surface area of the small intestine?
And by how much
- Plicae Circulares (3x)
- Villi (10x)
- Microvilli (20x)
- Increase total surface area by 600x