The Digestive System Flashcards
The nutrients obtained from the food we eat are used for which processes?
-Building new tissues and remaining damaged ones
-Chemical energy
-Electrolyte balance
The digestive system is heavily reliant on which system?
The cardiovascular system to circulate the nutrients it obtains during the process of food breakdown
What are the organs of the GI tract?
-Mouth
-Pharynx
-Esophagus
-Stomach
-Small intestine
-Large intestine
What are the accessory digestive organs?
-Teeth
-Tongue
-Salivary glands
-Liver
-Gallbladder
-Pancreas
What are the functions of the digestive system?
-Ingestion
-Secretion
-Motility
-Digestion
-Absorption
-Defecation
What is ingestion?
taking foods and liquids into the mouth (eating)
What is secretion?
release of water, acid, buffers and enzymes into the lumen of the GI tract
What is motility?
alternating contractions and relaxations of smooth muscle in the walls of the GI tract mix food and secretions and move them towards the anus
What is digestion?
the process of breaking down ingested food into small molecules that can be used by body cells
What is absorption?
movement of the products of digestion from the GI tract into blood or lymph
What is defecation?
wastes, indigestible/unabsorbable substances, bacteria, damaged GI cells, leave the body through the anus as feces or stool
What is mechanical digestion?
teeth cut and grind food, stomach and small intestine churn the food
What is chemical digestion?
carbohydrates, proteins and lipids are broken down by hydrolysis with the aid of digestive enzymes
What is hydrolysis?
a chemical reaction between chemicals and water, leading to the decomposition of both the substance and water
What is the mouth/oral cavity composed of?
cheeks, hard and soft palates, uvula, teeth, tongue and salivary gland
What do the cheeks and lips contain?
contain a mucosal membrane and several muscles that aid in the mechanical breakdown of food (chewing)
What do the hard and soft palate form a barrier between?
form a barrier between the nasopharynx and oropharynx - this allows us to breathe while chewing
What closes off the nasopharynx during swallowing?
The uvula
Where are the palatine and lingual tonsils located?
in the oral cavity
What exocrine gland secretes saliva into the mouth?
The salivary glands
What is saliva?
a watery medium for chemical digestion to begin
What does saliva contain?
-contains digestive enzymes, antibodies, buffers, mucous and ions
-99.5% water
What is the function of saliva?
-normally, just enough saliva is secreted to keep the mouth and esophagus moist
-when food enters the mouth salivation increases to aid in lubrication and dissolution of food, chemical digestion begins
What is the tongue?
An accessory organ composed of skeletal muscle coated in a mucous membrane
What is the tongue attached to?
to the hyoid bone, temporal bones and mandible
What are the functions of the tongue?
-contains muscles that maneuver the tongue for chewing and swallowing and others that alter the shape/size of the tongue for speech and swallowing
-secretes some digestive enzymes and contains sensory receptors for both touch and taste
What are teeth?
accessory organs found in the sockets of the gums (gingivae)
What are the three major external regions of the teeth?
crown, neck, root
What makes up the majority of the tooth?
the dentin (found internally)
What gives teeth its shape and rigidity?
calcified connective tissue
What is the hardest substance in the body?
Enamel, which externally covers dentin
What does the pulp cavity contain?
The pulp cavity contains blood/lymph vessels and nerves and extends through the root canals
What happens in the pharynx (throat)?
-When food exits the mouth it enters the oropharynx and the laryngopharynx
-Muscular contractions help propel the food into the esophagus
What is the nasopharynx?
a passage for respiration
What are the 4 layers of the GI tract?
mucosa, submucosa , muscularis, serosa (listed from superficial to deep)
What is the mucosa?
inner lining, mucous membrane composed of: inner epithelium, connective tissue and thin smooth muscle
What is the epithelium?
-for secretion and absorption
-replaced every 5-7 days
What is the Lamina Propria?
connective tissue containing blood vessels and lymph vessels. Also contains lymphatic nodules involved in immunity
What is the submucosa?
-Connective tissue that binds the mucosa to the muscularis
-Contains more blood vessels, lymph vessels and a network of neurons (submucosa plexus)
What is the muscularis?
-Primarily smooth muscle.
-Breaks down and mixes food with digestive secretions, propels it along the tract.
-Contains another plexus of neurons (myenteric plexus)
What is the serosa?
-Serous membrane anchors to surrounding structure, aka the visceral peritoneum
-Esophagus has an adventitia layer instead of serosa
What is the enteric nervous system?
neurons arranged into the myenteric plexus (muscularis layer) and the submucosa plexus (submucosa layer) and connected by interneurons
What does the myenteric plexus regulate?
regulates motility
What does the submucosa plexus regulate?
regulates digestive secretions
Sensory neurons of the ENS contain which two types of receptors?
-Chemoreceptors (chemical composition of food)
-Mechanoreceptors (stretch receptors)
What is the function of the Vagus (x) nerve for the GI system?
Regulates GI secretions and motility by stimulating or inhibiting ENS neurons
What is the largest serous membrane in the body?
The peritoneum
What is the parietal peritoneum?
lines the wall of the abdominal cavity
What is the visceral peritoneum?
covers many of the organs in the cavity
What is the peritoneal cavity?
The slim space between the two layers, contains serous fluid
What are the retroperitoneal organs?
Organs that lie on the posterior abdominal wall and are only covered by peritoneum on their anterior surface
What does the peritoneum contain that binds organs together?
large folds that weave between the viscera and bind the organs together and to the walls of the abdominal cavity
What is the esophagus?
-A collapsible muscular tube approximately 25cm long that lies posterior to the trachea
-Connects from the laryngopharynx all the way down to the stomach, passes through the diaphragm in an opening called the esophageal hiatus
What is a hiatus hernia?
When the stomach protrudes through the esophageal hiatus
What is the upper esophageal sphincter?
-skeletal muscle
-regulates food passing from the pharynx into the esophagus
What is the lower esophageal (cardiac) sphincter
-smooth muscle
-regulates food passing from the esophagus to the stomach
-secretes mucous for lubrication (no digestive enzymes) and transports food into the stomach, no chemical digestion or absorption occurs
What are the stages of swallowing (deglutition)?
-Voluntary Stage
-Pharyngeal Stage
-Esophageal Stage
What occurs in the voluntary stage?
-bolus of food is moved to the oropharynx by the tongue
What occurs in the pharyngeal stage?
-uvula and soft palate cover the nasopharynx, epiglottis covers the larynx, bolus moves from the oropharynx to the laryngopharynx
-upper esophageal sphincter relaxes, and the food enters the esophagus
What occurs in the esophageal stage?
peristalsis pushes the food through the esophagus, the cardiac sphincter relaxes, and the food enters the stomach
What is peristalsis?
involuntary progression of coordinated contractions and relaxations of the muscularis
What is Gastroesophageal reflux disease (GERD)?
-If the lower esophageal sphincter fails to close adequately after food has entered the stomach, the stomach contents can reflux (back up) into the esophagus
-HCl can irritate the esophageal wall causing a burning sensation (heartburn)
-Certain foods and drinks can increase stomach acid secretion, worsening this problem - coffee, chocolate, fatty foods, acidic foods, etc)
-Drinking alcohol and smoking can cause relaxation of the cardiac sphincter
Where is the stomach located?
Located directly inferior to the diaphragm, the stomach connects the esophagus to the duodenum
What is the function of the stomach?
Functions to continue the chemical digestion of food as well as provides a reservoir for food to sit while room is made in the intestines for more food
What is gastroenterology
the study of the structure, function, diagnosis and treatment of the stomach and intestines
What are the four main regions of the stomach?
-Cardia: surrounds the opening of the esophagus into the stomach
-Fundus: the rounded portion superior and lateral to the cardia -Body: inferior to the fundus, the largest portion of the stomach
-Pyloric Part: inferior to the body, connects to the duodenum via the pyloric sphincter
What are rugae?
Large mucosal folds on the interior wall of the stomach
What are the secretory cells within the folds of the stomach?
Gastric glands
What is gastric juice?
The combination of the various substances secreted by the gastric glands. Contains Mucous, pepsinogen, gastric lipase, and hydrochloride acid (HCl)
What is propulsion?
Waves of peristalsis move gastric contents towards the pyloric sphincter
What is retropulsion?
Since the food particles are still too large to fit through the pyloric sphincter, the contents are forced back towards the body
What occurs in mechanical and chemical digestion in the stomach?
-Propulsion
-Retropulsion
-Process continues, mixing the gastric contents and gastric juice until the food liquifies into chyme
-Once the food particles in chyme are small enough, they can pass through the pyloric sphincter, gastric emptying
-H+ and Cl- are pumped into the stomach separately but unite to create the HCL in gastric juice
-Different enzymes are responsible for digesting different types of food
What is HCL secretion stimulated by?
-Acetylcholine (ACh): released by parasympathetic neurons
-Gastrin: released by cells within the stomach
-Histamine: paracrine hormone released by mast cells in the stomach, acts synergistically with gastrin and ACh
What is the pancreas made up of?
-Made up of small clusters of glandular epithelial cells
-The majority of these cells (99%) are exocrine and called acini cells
-The remaining cells (1%) are the endocrine islet cells that secrete insulin and glucagon
What do acini cells do?
Secrete pancreatic juices (digestive enzymes) into ducts that empty into the duodenum of the small intestine
What are pancreatic juices composed of?
-Composed mostly of water, salts, sodium bicarbonate and several digestive enzymes
-Bicarb helps to buffer the acidity in chyme and helps adjust the pH in the small intestine
What do the enzymes of the pancreas do?
-Heavily involved in the digestion of proteins, triglycerides and starches within the small intestine
-Inactive and must be activated in the GI tract in order to carry out their functions, or they would cause damage to the pancreas itself
What is the second largest organ?
The liver
Where is the liver located?
Inferior to the diaphragm, occupies the entire URQ of the abdomen
Where is the gallbladder located?
Pear-shaped sac located in a depression of the posterior surface of the liver
What are the functions of the liver and gallbladder combined?
-Secretion of bile
-Regulating glucose metabolism
-Lipid and protein metabolism
-Processing drugs and hormones
-Excreting bilirubin
-Storage of many substances
-Phagocytosis
-Activation of Vit D
What are hepatocytes?
-Main functional cells of the liver and perform a wide variety of functions including the secretion of bile
-Arrange into single layers that are bordered by highly permeable blood capillaries called hepatic sinusoids
What are hepatic sinusoids?
Hepatocytes arrange into single layers that are bordered by these highly permeable blood capillaries
What are hepatic macrophages?
Within the hepatic sinusoids, phagocytize worn out RBCs/WBCs and foreign substances
What is the common hepatic duct?
Between the hepatocytes are tiny ducts that collect bile and carry it to this duct
What is the common bile duct?
The common hepatic duct merges with the cystic duct from the gallbladder to form this duct - which delivers bile to the duodenum
What is the portal triad?
-Branch of hepatic artery
-Branch of hepatic portal vein
-Bile duct
What does the hepatic artery do?
Supplies oxygenated blood from the heart
What does the hepatic portal vein do?
Brings deoxygenated blood rich in newly absorbed nutrients, drugs, microbes and toxins from the GI tract to the liver
How does the liver and gallbladder get blood supply?
-Hepatic artery and hepatic portal vein supply blood to the hepatic sinusoids where oxygen, nutrients and certain toxic substances are taken by the hepatocytes
-Products manufactured by the hepatocytes, and nutrients needed by other cells are returned to the blood, which eventually drains into the central vein and then the hepatic vein
What is bile?
an olive-green liquid with an alkaline pH that is composed mostly of water, bile salts, cholesterol, phospholipid, bile pigments and ions
-when hepatic macrophages phagocytize RBCs, it releases iron, globin and bilirubin (from the heme ring) - the iron and globin are recycled, and the bilirubin is secreted into bile (yellow in color)
-more bile is secreted while digestion is occurring
-between meals, when the entrance to the duodenum closes, excess bile is rerouted and stored in the gallbladder for future use
What are the functions of the liver and gallbladder?
-Lipid Metabolism
-Protein Metabolism
-Processing of Drugs and Hormones
-Excretion of Bilirubin
-Synthesis of Bile Salts
-Storage: glycogen, many vitamins and minerals
-Phagocytosis: aged RBCs/WBCs and some antigens
-Activation of Vitamin D
What is lipid metabloism?
Triglyceride storage and breakdown of fatty acids
What is protein metabolism?
metabolize digestive proteins and synthesize many plasma proteins
Excretion of Bilirubin
excreted into bile to be metabolized in the small intestine
What is jaundice?
-a yellowish discoloration of the skin, sclera, and mucous membranes due to an accumulation of bilirubin
-indicates some form of hepatic impairment
What are gallstones (aka cholelithiasis)?
-If the bile composition of bile salts and cholesterol is imbalanced (more cholesterol than bile salts) the cholesterol may crystallize and form gallstones
-Stones may impair or obstruct the flow of bile from the gallbladder to the duodenum
What are the three segments of the small intestine?
Duodenum - shortest section
Jejunum - middle section
Ileum - final and longest section. Connects to the large intestine via the ileocecal sphincter
True or False:
The small intestine plays little to no role in digestion
False:
The majority of chemical digestion and absorption of nutrients occurs in the small intestine
What does the small intestine contain?
-Cells that line the small intestine secrete digestive enzymes, secrete mucous and absorb nutrients
-Walls are arranged in circular folds, villi and microvilli that maximally increase the surface area for digestion and absorption
-Contains an abundance of lymphatic tissues and nodules for immunity
What occurs in mechanical digestion in the small intestine?
Segmentation:
-Churning/mixing of chyme and digestive juices in an isolated and distended region of the small intestine
-This process allows for more contact time between the chyme and the absorption cells
-After sufficient absorption has occurred, peristalsis pushes the chyme onwards in the GI tract
What occurs in chemical digestion in the small intestine?
-Chyme is further broken down in the small intestine with the help of intestinal juices, bile and pancreatic juice
-A wide variety of different enzymes are responsible for the specific breakdowns of different substances (proteins, carbohydrates, lipids)
What occurs in absorption in the small intestine?
-Once the food particles are small enough they are absorbed through the epithelial tissue, this process occurs by diffusion, facilitated diffusion, osmosis and active transport
-Anything that does not get absorbed or has not been digested yet continues to the large intestine
What substances are absorbed by the small intestine?
-monosaccharides
-amino acids
-lipids
-bile salts
-electrolytes
-vitamins
-water
What are the functions on the large intestine?
Responsible for completion of absorption, production of vitamins, and the formation and elimination of feces
Where do the small and large intestine meet?
ileocecal sphincter
The ileocecal sphincter opens up into the first of which 4 major regions of the large intestine?
-Cecum: lies inferior to the ileocecal sphincter (location of appendix)
-Colon: ascending, transverse, descending, sigmoid
-Rectum: small segment at the end of the colon
-Anal canal: terminal 2-3cm, highly vascular (opening of the anal canal to the exterior - anus)
What is the majority of absorption that occurs in the large intestine?
water absorption
What is the appendix?
found just inferior to the secum, purpose isn’t completely understood but it is thought to have once been functional lymphatic tissue
What occurs in mechanical digestion in the large intestine?
-The ileocecal sphincter is normally partially open to allow for slow passage of chyme into the large intestine
-Following a meal, the peristalsis in the ileum forces chyme in to the cecum while hormones relax the sphincter
-The presence of substances in the cecum begin the peristalsis and similar contractions that continue to churn the chyme and progress it along the tract
What occurs in chemical digestion in the large intestine?
-No digestive enzymes are secreted in the large intestine. Instead, mucous and bacteria prepare the chyme by fermenting any remaining substances
-This can produce hydrogen, carbon and methane gas which occupy the large intestine
-The bacteria break down some substances and transport them to the liver, where they are further broken down and eventually excreted in urine
-Certain vitamins are also absorbed in the colon
-Chyme remains in the large intestine for 3-10 hours and has the remaining water absorbed, this solidifies the chyme converting it to feces
What is the defecation reflex?
-Peristaltic movements push feces from the sigmoid colon into the rectum
-The distension of the rectal wall stimulates stretcher receptors that trigger the defecation reflex
-Sensory nerve impulses travel from the stretch receptors to the spinal cord where the reflex is integrated and motor impulses are sent to shorten the rectum (increasing pressure)
-This increased pressure, along with coordination of abdominal muscles and the diaphragm, force open the internal anal sphincter
-The external anal sphincter is under voluntary control
