7a Digestive System Organs Flashcards
What are the functions of the digestive system?
Ingestion: intake of food
Digestion: breakdown of food molecules
Absorption: uptake nutrients into blood and lymph
Defecation: elimination of undigested waste
What are the two types of digestion?
Mechanical digestion
Chemical digestion
Describe mechanical digestion.
Physical breakdown of food into smaller pieces
Used accessory organs like teeth
The breaking down is done by teeth as muscular contractions of the intestines
Describe chemical digestion.
Action of enzymes from saliva, stomach, pancreas and intestines
Results in the breakdown of organic molecules
What do enzymes break bigger organic molecules into?
Polysaccharides-> monosaccharides
Proteins-> amino acids
Lipids-> glycerol and fatty acids
Nucleic acids-> nucleotides
What are the monosaccharides our bodies can use?
Glucose, galactose and fructose
What are the types of involuntary contractions in mechanical digestion and their role?
Peristalsis: transport, pushes stuff down, not for breaking food
-alternating waves of contraction and relaxation of the muscle
Segmentation: mixing and breaking food to facilitate chemical breakdown
-mixes it with digestive juices (gastric juice)
-main function is mechanical digestion rather than propulsion
Where does peristalsis occur?
Esophagus, stomach and intestines
Where does segmentation occur?
Intestines (very slow in large intestine)
What is the alimentary canal?
Path extending from mouth to anus
Where organs directly ingest, digest, absorb and defecate
Come into direct contact with food, so not accessory organs
GI tract
What are accessory organs?
Organs that help with digestion but generally do not come into direct contact with teh food
Not a part of the GI tract
What are the organs of the alimentary canal?
Mouth- pharynx- esophagus- stomach- small intestine- large intestine- anus
What are the accessory organs we are responsible for?
Tongue, liver, gallbladder, pancreas, salivary glands
What are the types of salivary glands?
Parotid gland
Sublingual gland
Submandibular gland
Where does the majority of absorption occur?
Small intestine
What is the role of the oral cavity? Describe
Mucous membrane-lines cavity
Mechanical (teeth) and chemical (saliva) breakdown of food
What are the proper terms for chewing and swallowing?
Mastication and deglutition
What are tonsils and the types?
Lymphatic tissues which are part of the body’s défense system
Palatine- posterior end of oral cavity
Lingual- located at the base of the tongue
What is the vestibule?
Space between lips and teeth and gums internally
What is the uvula?
Fleshy projection of the soft palate for saliva production and speech modulation
What are the 3 sections of the pharynx?
Nasopharynx: near nasal cavity
Oropharynx: near oral cavity
Laryngopharynx: meets larynx
What is the role of the pharynx? Describe
Passageway for foods, fluids, air
Has two skeletal muscle layers
Produces peristalsis
What are the two layers of muscle in the pharynx and what do they do?
Longitudinal outer layer and circular inner layer
Produce peristalsis
AND since they are skeletal, provide small voluntary control in the beginning of swallowing
What are the layers of the walls of the alimentary canal?
Mucosa
Submucosa
Muscularis externa
Serosa (visceral peritoneum)
What does the mucosa do?
Innermost layer in the wall of the organs of the alimentary canal
Surface epithelium (stratified squamous or simple columnar)
Laminate propria (areolar connective tissue)
Smooth muscle layer
What does the submucosa do?
Soft connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid tissue and lymphatic vessels
What do lymph vessels do?
Pick up fat
What does the muscularis externa do?
Smooth muscle for peristalsis
-inner circular layer
-outer longitudinal layer
What does the serosa do?
Visceral peritoneum (simple squamous epithelium that produces serous fluid)
Reduces friction
What’s different about the muscularis externa of the stomach?
It has an example muscle layer, an exception
Describe the esophagus.
Runs from pharynx to stomach and through the diaphragm
Conducts food by peristalsis
Food only
What is a sphincter?
A ring/band of muscle that divides organs, even if the tract is continuous
Smooth involuntary muscle, contracts to prevent backflow of food
What are the two phases of deglutition?
Buccal phase
Pharyngeal-esophageal phase
Describe the first phase of swallowing?
Buccal phase
Voluntary
Bolus is forced into pharynx by tongue
Describe the second phase of swallowing.
Pharyngeal-esophageal phase
Involuntary, peristalsis takes it the rest of the way
What are the layers of the muscularis externa in the stomach?
Longitudinal layer
Circular layer
Unique to stomach : oblique layer
What is rugae?
Wrinkles, internal folds of the mucosa that appear when stomach is empty
What sphincters are we responsible for in the stomach?
Cardioesophageal sphincter: where food from the esophagus enters the stomach
Pyloric sphincter: where food moves into the small intestine
What are the regions of the stomach and which must we know?
Cardia, fundus, body, pylorus
We must know: cardia and pylorus
What are the functions of the stomach?
Temporary storage tank for food
Has rugae
Continues mechanical breakdown of food by the inner oblique layer of the muscularis externis
Chemical breakdown of proteins begins
Delivers chyme to the small intestine
Which organic molecule starts breakdown first?
Proteins
What is chyme?
Processed food
What does the stomach lining do?
Produces an acidic environment necessary for the activation of enzymes for protein digestion
Composed of simple columnar epithelium
Majority are mucous producing cells
Gastric pits lead to gastric glands that secrete gastric juice
What do the mucous cells in the stomach lining produce and why?
Bicarbonate-rich alkaline mucus to protect teh stomach from them acidic environment and stop it from digesting itself
What does gastric juice contain?
Protein digesting enzymes (pepsinogens)
Hydrochloric acid
Thin acidic mucous
Hormone gastrin
Intrinsic factor
What cells produce pepsinogens?
Chief cells
What cells produce hydrochloric acid?
Parietal cells
What cells produce the thin acidic mucus?
Mucous neck cells
What cells produce teh local hormone gastrin?
Enteroendocrine cells
What cells produce the intrinsic factor?
Parietal cells
What is pepsin?
Pepsin is the activated form of pepsinogen, and it is activated when pepsinogen meets HCl
Enzyme that breaks down proteins
What process occurs in response to protein needing to be digested?
Enteroendocrine cells release gastrin in response to protein levels
Gastrin stimulates the chief and parietal cells to produce pepsinogen and hydrochloric acid respectively
What are the subdivisions of the small intestine?
Duodenum
Jéjunum
Ileum
What is the role of the small intestine?
Performs all functions except defecation
It digests food and absorbs nutrients
Major digestive organ
What are the structures for nutrient absorption in the small intestine?
Villi: fingerlike projections formed by the mucosa
Microvilli: tiny projections of the plasma membrane
Circular folds: deep folds of mucosa and submucosa to slow the speed of chyme
Describe villi in the small intestine.
Fingerlike projections formed by mucosa
House a capillary bed and lacteal
Allows entry for amino acids, monosaccharides and glycerol/short chain fatty acids into the capillary blood
What are lacteal for?
Part of the lymphatic system, for absorption
Absorption of specifically fatty acids and monoglycerides and enter systemic circulation via the lymphatic system
Note: doesnt enter through blood capillary, rather lymphatic capillary
What do microvilli have that distinguishes them from villi, apart from their size?
Contain enzymes to continue digestion
What is the purpose of all these structures for nutrient absorption?
To maximize the surface area to allow for more efficient absorption
Where molecules do villi absorb and where do they go from there?
Amino acids, monosaccharides, glycerol/ short fatty acid chains
Go to the liver via the hepatic portal vein
What are Peyers patches?
Collections of lymphatic tissue in the small intestine
Located in sub-mucosa
Increase in number towards the end of the small intestine
Why are there more Peyer patches close to the end of the small intestines?
Remaining food residue contains more bacteria for the lymphatic tissue to check
Checks type and quantity
Where does the majority of the chemical digestion occur? Why?
Duodenum
Due to the digestion enzymes produced by intestinal cells of the duodenum + the digestive enzymes of the pancreas that were carried to the duodenum by pancreatic ducts + the bile that enters the duodenum via the bile duct
Where do the main pancreatic duct and the bile duct join?
Hepatopancreatic ampulla
Where is bile made?
Made in liver but stored in gallbladder
On which side of the body is the ascending colon?
Right
Where is the appendix located?
Attached to large intestine, specifically hangs from the cecum
What are the subdivisions of the large intestines?
Cecum
Appendix
Colon
Rectum
Anus
What is the appendix?
Accumulation of lymphoid tissue that sometimes becomes inflammed
What does the large intestine do?
Delivers indigestible food to the exterior
Absorbs water and electrolytes like sodium and chloride
Formation and storage of feces
Microbial fermentation
What are some characteristics of the large intestine?
Larger in diameter but shorter in length relative to small intestine
Extends from the ileocecal valve to the anus
What is the thing that separates the small and large intestines?
Ileocecal valve
What are all the types of colon and where are they generally?
Ascending: right
Descending: left
Transverse: kinda bridge between the two, perpendicular
Sigmoid: bendy part that leads to the rectum, after the descending colon
Where are feces stores and describe the process?
Large intestine
Ingesta/indigestible food is moved through the large intestine, dehydrated, mixed with bacteria and mucous, formed into feces
Where is the microbial life mainly found and what does it do?
Large intestine
Produces enzymes capable of digesting many molecules indigestible to humans such as cellulose
Where does the majority of water/ electrolyte absorption occur?
Large intestine
Sodium and chloride
What role do goblet cells play in the digestive system?
Produce alkaline mucus in the large intestine which contributes to the formation of feces
Lubricates the passage
How many layers are there in the muscularis externa of the large intestine? More or less than typical?
More than typical, 3
What are haustra?
Pocketlike sacs
Slowly move feces through the colon
Bands of muscle that kind of wrinkle
What does it mean to be quiescent?
Inactive
What can stimulate the colon to contract?
Présence of fat in small intestine
Distension/tension in the colon
List the composants of feces.
H2O
Inorganic salts
Epithelial cells (that previously lined digestive tract)
Bacteria (up to 60%)
Products of bacterial decomposition
Unabsorbed/indigestible molecules (like fibre)
Briefly describe the defecation reflex.
Spinal reflex
Stretch receptors pick up distension -> signal to spinal cord->motor nerve responds by relaxing the internal anal sphincter-> voluntary relaxation of the external anal sphincter required to let it out
Briefly, what keeps GI organs in place?
Lesser omentum
Greater omentum
Mesentery
All special extensions of the peritoneum (serous membrane) that still allows organs to expand and contract
What is the lesser omentum?
Double layer of the visceral peritoneum
Extends from liver to the lesser curvature of stomach
Serous membrane
What is the greater omentum and what does it do?
Extension of the visceral peritoneum
Covers the abdominal organs
Fat insulates, cushions, and protects abdominal organs
Fatty cushy outer layers, visible when you cut into it, looks like padding, most superior
What is the peritoneum?
Serous membrane that keep all abdominal organs in place
What is the mesentery and what does it do?
Double layer of parietal peritoneum
Suspends small intestines from posterior abdominal wall
Contains blood and lymphatic vessels and nerves
Why do the lesser omentum and mesentery talk of double layers of peritoneum?
Growth causes folds, and these folds have forces either the parietal sides to touch or the visceral sides to touch, forming the double layer
What are the two intrinsic nerve plexuses in the alimentary canal?
Submucosal nerve plexus
Myenteric nerve plexus
What is a plexus?
Nerve fibre network
