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
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- 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
What do these arrows indicate?
What layers of the intestinal wall make them up?
What is their function?
Plicae Circulares
- transverse ridges/folds of mucosa and submucosa
- increase surface area
- cause chyme to move spirally through GI tract
What is this entire strcuture?
What is its function?
What kind of epithelium is it covered by?
Villus (pl: villi)
- finger-like projections of the mucosa
- further increase surface area
- specialized simple columnar epithelium with microvilli
What does the rightmost arrow indicate?
What is it a part of?
What is its function?
Microvilli (AKA Brush Border)
- tiny projections of digestive epithelial cell plasma membranes
- further increases absorptive surface area
- contain enzymes
8
What is it?
What’s its function?
Capillary (within a villus)
- aborbs nutrients into bloodstream
6
Lacteal
- specialized wide lymphatic capillaries in intestinal villi which absorb lipids and lipid-soluble vitamins
9
- what are they?
- what kind of cells do they contain?
Intestinal Crypt
- AKA intestinal glands or crypts of Lieberkuhn
- invaginations of mucosa between villi
- lined by columnar, goblet and enteroendocrine cells
What are the 4 main kinds of cells in intestinal epithelium?
- Absorptive Cells - absorb digested nutrients
- Goblet Cells - secrete mucus that lubricates chyme
- Intestinal Crypts/Glands - secrete intestinal juice
- Enteroendocrine Cells - secrete hormones
8
Submucosa
6
Longitudinal Muscularis Externa
5
Circular Muscularis Externa
1
Muscularis Mucosae
What is the large grey central organ here?
What is its function?
What kind of cells line its lumen?
Large Intestine
- larger diameter, shorter length than small intestine
- reabsorbs water and electrolytes
- eliminates indigestible food residue
- simple columnar epithelium
What is it?
Where is it?
Cecum
- sac-like first part of large intestine
- lower right quadrant (right inguinal region)
- What is this passageway?
Ileocecal Valve
- guards the opening between the ileum and large intestine
What is the green circled structure?
Vermiform Appendix
- blind tube connected to cecum
- may play a role in maintaining digestive flora
What is it?
Ascending Colon
- ascends on right side of adbomen, turns left at inferior surface of liver
What is it?
Transverse Colon
- continuation of colon leftward from the hepatic flexure to the splenic flexure
What is it?
Descending Colon
- continuation of colon downward from splenic flexure to sigmoid colon
Indicated by green line:
Sigmoid Colon
- S-shaped segment of distal colon that projects inward toward the midline
What is it?
Hepatic Flexure
- AKA right colic flexure
- where ascending colon turns 90 degrees leftward just below liver
What is it?
Splenic Flexure
- AKA left colic flexure
- transverse colon bends 90 degrees downward
What is this structure?
Rectum
- final straight portion of large intestine distal to sigmoid colon
What is this?
Anal Canal
- terminal part of the large intestine between the anus and rectum, below the level of the pelvic diaphragm
What does the arrow indicate?
Anus
- opening of the anal canal to the exterior
What does the pencil indicate?
What is it composed of?
What is its function?
Internal Anal Sphincter
- involuntary smooth muscle
- inhibits fecal leakage and defecation during emotional stress
What does the pencil indicate?
What is it composed of?
What is its function?
external anal sphincter
- skeletal muscle
- contracts voluntarily to inhibit defecation
What does the green highlighting indicate?
What is it composed of?
Tenia Coli
- three thin, distinct longitudinal bundles of colonic smooth muscle
- bunches the colon into many sacs called haustra
What does each green circle represent?
A haustrum (pl: haustra)
- sacs formed along large intestine by the effect of the tenia coli
What is the yellow structure indicated by the red arrow?
Epiploic appendix
- small pouches of periotoneum filled with fat along the colon
What does the green arrow indicate?
Anal Columns
- longitudinal folds of the anal canal mucosa
How does large intestine microanatomy compare to that of the small intestine?
large intestine has:
- no villi (no nutrient absorption)
- simple columnar epithelium (same as small intestine)
- more abundant goblet cells
What are the digestive system’s accessory organs?
- Teeth
- Tongue
- Salivary Glands
- Liver
- Gall Bladder
- Pancreas
Teeth
- How many (baby/permament)?
- What kind of joints?
- Attached where?
- 20 Deciduous (milk/baby teeth)
- 32 Permament
- Gomphoses joints
- Attached to alveoli of the mandible and maxilla
What kind of teeth are the blue teeth here?
Their shape? And function?
Incisors
- Chisel shaped, for cutting
What kind of teeth are the green teeth here?
Shape? Function?
Canine
- Cone-shaped, for tearing/piercing
What kind of teeth are blue here?
Premolar
- transitional teeth with both canine and molar characteristics
What kind of teeth are shown here in blue?
Shape? Function?
Molars
- have cusps and valleys, for grinding
6
What main region of the tooth is this?
What is it composed of?
Crown
- exposed part of tooth
- lined by enamel, underlaid with dentin
- internal pulp cavity supplies nutriets
8
- what is it composed of?
- what does it contain?
Root
- part of tooth in socket
- external surface is made of cementum
- contains root canal, part of pulp cavity within root
What is the highlighted green area?
Periodontal Ligament
- modified periosteam that anchors root in socket
What area is circled?
pulp cavity
- contains pulp, loose CT with nerves and blood vessels
-
What is this?
root canal
- the part of the pulp cavity that extends into the root
What is starred here?
Apical Foramen
- hole through which nerves and blood vessels pass into teeth
1
enamel
- hard mineralized tissue of hydroxyapatite on outside of tooth crown
2
Dentin
- underlies enamel
- less hard and mineralized than dentin
What does the green line indicate?
Cementum
- external surface of tooth root
- attaches teeth to alveoli of the mandible and maxilla by anchoring the periodontal ligament
What tissue is indicated?
Gingiva (or gums)
What are the two kinds of salivary glands?
And their function/location?
Intrinsic Salivary Glands - small and scattered in oral mucosa
Extrinsic Salivary Glands - 3 paired glands (6 total) external to oral cavity
- produce saliva
What is this blue structure?
What kind of cells does it contain?
Parotid Gland
- one of the three paired extrinsic salivary glands
- serous cells
What is the blue structure here?
- what kind of cells does it contain?
Submandibular Gland
- one of 3 paired extrinsic salivary glands
- contains both serous and mucus cells
What structure is this?
What kind of cells does it have?
sublingual gland
- one of 3 paired extrinsic salivary glands
- mucus cells only
What organ is this?
What is its main digestive function? And other functions?
Where is it located?
Liver
- largest gland in the body
- produces bile for digestion
- performs many metabolic functions
- located inferior to diaphragm across all three top abdominal regions, but mostly on the right
What are some (5) of the liver’s main metabolic functions?
- Conversion of glucose to glycogen
- Processing fats & amino acids
- Storing vitamins
- Detoxifying drugs & poisons
- Synthesizing clotting factors, transport proteins, bile
What are the liver’s two surfaces?
Diaphragmatic - anterior & superior
Visceral - posterior & inferior
What is part A?
Right Lobe of Liver
What is part B?
Left Lobe of Liver
What is part C?
falciform ligament
- separates left and right lobes
What is indicated by the arrow?
Quadrate Lobe of liver
Caudate Lobe of liver
- superior lobe on inferor side of liver
What is #3?
hepatic portal vein
- carries blood from splenic and mesenteric veins to liver for processing
What is the area of the visceral surface of the liver through which blood vessels and bile ducts enter and exit called?
Porta hepatis
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Bare Area of liver
- no visceral peritoneum, touches diaphragm
What is the red outlined structure?
- how big are they?
- what are their 3 components?
- what is their function?
Liver Lobule
- 2 mm by 1 mm
Components:
- central vein
- triads
- hepatocytes
- blood filters through them and is acted on by hepatocytes which carry out all liver functions
What does the black box indicate?
Central Vein of liver lobule
- sinusoids lead to the central vein and it then drains blood to larger veins leading back to the heart
- what are they?
- what is their function?
Hepatocytes
- specialized epithelial cells which carry out all of the functions of the liver
What are these spaces?
How does blood get from them to hepatocytes?
sinusoids
- vascular spaces within lobules through which blood filters from triads to central vein
- they are lined with fenestrated epithelium which makes it easier for blood to enter and exit
What is this arrangment of several lumens?
What are each of the lumens?
Triad (or portal space)
- largest is branch of hepatic portal vein
- medium sized lumen is a bile ductus (lined by larger cells than blood vessels)
- smallest is a branch of the hepatic artery
What are the tiny ducts through which bile flows from the hepatocytes to the triads?
bile canaliculi
- visible as tiny green dots amongst hepatocytes on lobule models
- keep bile from contacting blood
What is the green organ here?
- Where is it?
- What is its function?
gallbladder
- a muscular sac in a shallow depression in the right liver lobe
- stores and concentrates bile
What is the light yellow, lumpy organ shown here?
Where is it?
What are its two kinds of function?
Pancreas
- sits posteroinferior to stomach
- exocrine function - digestive enzymes
- endocrine function - blood sugar-regulating hormones (insulin and glucagon from islets)
What is the rightmost, rounded portion of the pancreas called?
Head of Pancreas
What does the pen indicate?
body of pancreas
What does the pen indicate?
Tail of Pancreas
Highlighted green structure?
Accessory pancreatic duct
What is the yellow vessel down the middle of the organ here?
main pancreatic duct
What is the path of bloodflow through the liver’s functional units and back towards the heart?
Both oxygenated and de-oxygenated.
- Hepatic Portal Vein and Hepatic Arteries
- Portal Venules and arterioles at triads
- Sinusoids of lobules
- Central Vein of lobules
- Interlobular vein
- Hepatic vein
- Inferior Vena Cava
What is the basic unit of the pancreas’ exocrine function?
What kind of cells make it up?
Acinus (pl: acini)
- clusters of simple cuboidal cells that secrete pancreatic enzymes
What does the yellow line indicate?
Right Hepatic Duct
- branch of common hepatic duct
What does the yellow line indicate?
left hepatic duct
- branch of common hepatic duct
What does the green circle indicate?
common hepatic duct
- where left and right hepatic ducts join before meeting with cystic duct
What does the green circle indicate?
cystic duct
What is this?
Common Bile Duct
- the joining of the cystic duct and common hepatic duct leading to the duodenum
- sphincter right before meeting with main pancreatic duct
What is circled here?
hepatopancreatic ampulla
- common space where common bile duct and pacreatic duct empty into duodenum
- hepatopancreatic sphincter controls the exit of bile/pancreatic juice into the small intestine
