Chapter 22: The Digestive System
What critical functions does bile serve?
(1) It is required for the digestion and absorption of lipids; and (2) it is the mechanism by which the liver excretes wastes and other substances that the kidneys cannot excrete.
What are the three portions of the pancreas?
(1) a wide head that contacts the duodenum (2) a middle body (3) a thinner tail that tapers off toward the spleen
Describe Propulsion
**The movement of a substance through a hollow organ via peristaltic contractions of smooth muscle layers** -This is how ingested food and liquids pass from one digestive organ to the next -accomplished largely by rhythmic contractions of the smooth muscle of the alimentary canal called peristalsis (pehr-uh-STAL-sis) and is aided by mucus secreted by multiple organs.
Give an example of acetylcholine receptors being blocked
-A number of medications such as antihistamines for allergies have anticholinergic properties that block the effects of ACh around the body. -Anticholinergic drugs bind to the ACh receptors on the salivary glands and decrease saliva secretion, leading to the common side effect of a dry mouth.
What is found between villi? Function?
-Between villi, the mucosa indents to form intestinal crypts, which house glands that also contain enteroendocrine cells (which secrete a variety of hormones).
Describe Defecation Process
-Certain ingested materials are not digestible or usable by the body. -Such materials continue their transit through the alimentary canal until they exit the body as feces through defecation. -Defecation also provides the body with a way to eliminate certain metabolic wastes. **Note that defecation is simply a specialized form of propulsion.
Describe the Voluntary Phase of Swallowing
-During the voluntary phase, the tongue pushes the bolus superiorly against the hard palate and posteriorly toward the oropharynx. The voluntary phase is the only stage of swallowing under conscious control.
Describe the H+/K+ pump
-The H+/K+ pump drives a hydrogen ion out of the cell and into the lumen of the gland while taking a potassium ion into the cytosol. -The chloride ion follows the hydrogen ion via passive diffusion through a membrane channel.
Describe the soft palate
-The arch-shaped soft palate consists of stratified squamous epithelium overlying skeletal muscle. -Extending inferiorly from the soft palate is a projection called the uvula
Describe the Pharyngeal Phase of Swallowing
-The bolus passes from the pharynx to the esophagus during the pharyngeal phase. -This phase involves the involuntary contraction of skeletal muscles such as the pharyngeal constrictor muscles, and is controlled by the swallowing reflex, a reflex initiated by the medulla oblongata. -The reflex arc is initiated when the bolus contacts sensory receptors in the oropharynx. -This triggers the elevation of the uvula and soft palate, which prevents the bolus from going into the nasopharynx. It also triggers the elevation of the larynx. **Notice in Figure 22.9 that the bolus pushes the epiglottis down. This, together with the elevation of the larynx, prevents aspiration, or the entry of food into the larynx**
Describe the Mucous Neck Cells Difference between goblet cells and mucous neck cells? Importance?
-The cells located near the top, or "neck," of the gland -As their name implies, these cells secrete mucus much like goblet cells. However, goblet cells secrete alkaline mucus, whereas mucous neck cells secrete acidic mucus. This prevents their mucus from neutralizing the acid produced by other cells known as parietal cells.
Describe Incisors
-The incisors are the central teeth that are broad and flat with a narrow crown. -They are specialized for cutting off pieces of food. -The middle two incisors are the central incisors, and those to either side are the lateral incisors
Describe the serous or adventitia layer of the alimentary canal
-The outer connective tissue layer is the serosa in the organs within the peritoneal cavity and the adventitia in organs outside the cavity. -The serosa, also called the visceral peritoneum, is composed of simple squamous epithelial tissue and loose connective tissue, whereas the adventitia is composed of dense irregular connective tissue. -Both structures support digestive organs and anchor them to surrounding structures.
Describe Cardia of the Stomach
-The region where the esophagus empties into the stomach is the cardia (KAR-dee-ah). -The cardia receives the bolus when the gastroesophageal sphincter relaxes.
Describe Submandibular glands
-The smaller submandibular glands are located just medial to the inferior portion of the body of the mandible. -They secrete saliva through the submandibular duct, which empties into the floor of the oral cavity. -In spite of their smaller size, the submandibular glands are very active, and secrete 65-70% of total saliva.
Describe Molars
-The teeth posterior and lateral to the canines are the premolars and the molars. -Both types of molars have broad crowns with rounded projections called cusps that are specialized for grinding.
Describe the hepatic arteriole found in the portal triad
-a branch of the hepatic artery
Describe the Muscularis externa layer of the alimentary canal
-a thick muscular layer composed of smooth muscle in most of the alimentary canal. -We generally find two layers of smooth muscle that are arranged in the same manner as in the muscularis mucosae, with inner circular and outer longitudinal layers. -The motility of the muscularis externa is regulated by groups of nerves of the enteric nervous system called the myenteric plexus (my- = "muscle," enter- = "intestine"), or Auerbach's plexus.
What is the porta hepatis?
-an indentation found on the liver's posterior side -Numerous blood vessels enter and exit the liver at the porta hepatis
Describe Parotid glands
-are large glands located over the masseter muscle just anterior to the ear. -These glands secrete saliva through the parotid duct, which passes over the masseter muscle and pierces the buccinator muscle to open into the oral cavity near the second molar. -The parotid glands secrete 25-30% of total saliva.
Describe secondary dentition
-are situated above the primary dentition in the maxilla and below it in the mandible. -When the child is about 6 years of age, these teeth enlarge and begin to press on the deciduous teeth. -This causes the root to gradually dissolve and the deciduous tooth falls out of the bone. -The permanent tooth then erupts and takes its place. -There are 32 permanent teeth, with 4 incisors, 2 canines, 4 premolars, and 6 molars in both the mandible and maxilla. -Generally by age 12 all of the deciduous teeth have fallen out and all but the third set of secondary molars have erupted.
How does bile flow through the liver lobule?
-bile flows through the liver lobule in the opposite direction, from the hepatocytes into tiny ducts called bile canaliculi (kah′-nah-LIK-yoo-lye; singular, canaliculus), which eventually drain into a bile duct.
Describe Lysozyme
-catalyzes the perforation of bacterial plasma membranes. -This allows bacteria-killing substances in the saliva to enter and kill the bacteria.
What do the extrinsic muscles control?
-control the position of the tongue. -Extrinsic muscles, involved during the ingestion phase of digestion, move the tongue during chewing and help turn the food into a bolus.
What do the intrinsic muscles control?
-control the shape and size of the tongue. -Intrinsic muscles push the food against the hard palate during chewing, which assists in mechanical digestion, and also push the bolus posteriorly during swallowing.
What is rugae (ROO-ghee)?
-folds found in the interior of the stomach -Rugae allow the stomach to expand considerably
What are the functions of the liver?
-has both endocrine and exocrine secretions -converts harmful chemicals into nontoxic substances that the body can eliminate
What 3 components make up the porta hepatis?
-hepatic artery -hepatic portal vein -hepatic veins
Describe the lesser omentum
-is a smaller mesentery that extends from the medial surface of the stomach to the liver.
Describe the submucosa layer of the alimentary canal
-is composed of dense irregular connective tissue with blood and lymphatic vessels and submucosal glands. -A cluster of nerves is called a plexus, and here we find nerve clusters of the enteric nervous system referred to as the submucosal plexus , or Meissner's plexus. -Each plexus regulates secretion from and blood flow to its area of the alimentary canal.
Describe the inner pulp
-is composed of loose connective tissue and housed within the central pulp cavity. -Pulp contains blood vessels and nerves that supply the other tissues of the tooth with nutrients and innervation. -The pulp cavity extends into the root via the thin root canal. **Occasionally, the pulp becomes infected, which results in inflammation and generally a great deal of pain. When the infection risks the health of the tooth, a root canal procedure may be performed to remove the pulp from the pulp cavity and root canal, and fill the newly hollow space with an inert material**
Describe the Serous cells
-secrete a water-based fluid with enzymes and other solutes -The secretions from serous cells are involved in digestive processes, and are generally released just before or during eating
Describe Parietal Cells
-secrete the hydrochloric acid (HCl) that is responsible for the acidic pH of gastric juice. -In addition, parietal cells produce the chemical intrinsic factor, which is required for intestinal absorption of vitamin B12, found in various foods.
Describe Chief Cells
-secrete the inactive precursor enzyme pepsinogen.
Describe the hard palate
-the anterior two-thirds -consists of stratified squamous epithelium and connective tissue covering the palatine processes of the maxillary bones and the palatine bones. -The surface of the hard palate is slightly rough, which assists in mechanical digestion.
Describe Mucous cells
-which secrete mucus -secretions from mucous cells are primarily involved in keeping the oral mucosa moist, and so are released continually.
Why must the chyme be thoroughly mixed before it moves to the rest of the small intestine?
1) Chyme is acidic, and the duodenum must mix it with bicarbonate ions to avoid damaging the intestinal mucosa; and (2) chyme is generally very concentrated and must be diluted with water from pancreatic juice to prevent the chyme from drawing water into the intestinal lumen by osmosis.
What are the steps in the absorption in the alimentary canal?
1. A molecule crosses the apical side of the enterocyte plasma membrane via a channel or transport protein 2. The molecule travels through the cytosol 3. The molecule exits from the basal side of the plasma membrane and enters the interstitial fluid 4. The molecule passes through or between endothelial cells of an intestinal capillary and enters the blood
What are the steps in carbohydrate digestion and absorption in the small intestine?
1. Polysaccharides are broken into oligo- and disaccharides in reactions catalyzed by pancreatic amylase 2. Brush border enzymes catalyze the breakdown of disaccharides into monosaccharides 3. The Na+/K+ pump creates a gradient for Na+ absorption from the fluid in the lumen 4. This gradient drives the secondary active transport of glucose and galactose via the Na+/glucose co-transporter 5. Fructose is absorbed by facilitated diffusion 6. All three monosaccharides cross the basal side of the enterocyte membrane and then diffuse into the blood
What are the three phases of secretion?
1. cephalic phase 2. gastric phase 3. intestinal phase
What is cementum?
A different kind of mineralized bone-like tissue found on the outer portion of the root of the tooth -is composed of about half calcium hydroxyapatite crystals and half organic molecules such as collagen fibers. -This is approximately the same composition that bone has, and for this reason cementum is about as hard as bone.
Define chyme (KYME)
A liquid mixture that results from the stomach churning a bolus and mixing it with gastric juice.
Define bolus
A moistened, partially digested ball of ingested food that is swallowed and transported to the stomach via the pharynx and esophagus.
What is the labial frenulum
A narrow band of mucosa that attaches the internal surfaces of the upper and lower lips to the gums on the midline.
What is the uvula?
A portion of the soft palate suspended in the posterior oral cavity; seals off the nasopharynx during swallowing to prevent food and liquid from entering the nasal cavity.
What is the basic secretory cell of the salivary glands?
Acinar cell (ASS-uh-nahr)
What is the hepatopancreatic ampulla?
An enlarged area at the base of each semicircular duct in the ear that contains receptor cells that detect rotation of the head.
Define vitamins
An organic compound required in small amounts for specific functions within the body.
What other factor allows the stomach to fill?
Another factor that allows the stomach to fill is the inherent ability of smooth muscle to relax when it is stretched.
Describe the flow of blood through the sinusoids
Blood flows slowly through the sinusoids as materials are exchanged between the blood and hepatocytes, eventually draining into the central vein.
The cephalic phase is directed by what?
CNS
What are gastric pits?
Deep structures that are formed by the mucosa of the stomach being heavily indented
What happens to the skeletal and smooth muscle during swallowing?
During swallowing, the skeletal muscle and smooth muscle of the muscularis undergo peristalsis, which pushes the bolus inferiorly.
How are water soluble vitamins absorbed?
Fat-soluble vitamins are packaged into micelles with fats and other lipids and are absorbed with them. The fat-soluble vitamins include A, D, E, and K.
How are nucleotides further digested?
Further digestion occurs via brush border enzymes, which remove the phosphate group and the sugar from the nucleotide to leave a phosphate ion, ribose or deoxyribose, and a nitrogenous base. These three molecules are absorbed via primary and secondary active transport mechanisms into capillaries in the villi. The hepatic portal system then takes them via the blood to the liver to be metabolized.
What can be found at the base of the gastric pits?
Gastric glands
Describe Secretory IgA
IgA binds specific antigens on pathogens and mediates their destruction.
What is chemical digestion?
In chemical digestion, enzymes secreted by digestive organs catalyze reactions that break the chemical bonds within food particles until only small molecules remain.
What structures rely their motility on smooth muscle?
In the rest of the alimentary canal, motility is the work of smooth muscle.
What is the final component of tooth?
Inner pulp
What is the final phase of gastric acid secretion?
Intestinal phase
How is gastric and pancreatic secretion similar?
Like gastric secretion, pancreatic secretion occurs at a basal rate between meals.
What do the cardia and pylorus have in common?
Like the cardia, the pylorus contains a sphincter that controls the flow of ingested food.
Describe liquids passing through the pyloric sphincter
Liquids such as water and saline move rapidly from the stomach to the duodenum with essentially no delay.
Are the accessory organs part of the alimentary canal?
NO
Does the ANS directly control swallowing?
NO, The ANS does not directly control any phase of swallowing, BUT it does influence the esophageal phase—the parasympathetic division stimulates peristalsis, and the sympathetic division inhibits it.
Where is the gallbladder found?
On the posterior side of the liver *a small sac
What is the function of pepsin?
Pepsin catalyzes the beginning of the chemical digestion of proteins and the stomach's churning actions begin mechanical digestion -it comes from the inactive form of pepsin (pepsinogen) encountering an acidic pH
What does swallowing rely on?
Swallowing relies on the coordinated action of the upper alimentary canal, including the soft palate, pharynx, and esophagus
Define the enteric nervous system, or ENS
The ENS is a self-contained branch of the autonomic nervous system that extends from the esophagus to the anus (the terminal portion of the large intestine)
What is the stomach?
The J-shaped organ in the abdominopelvic cavity that is responsible for chemical and mechanical digestion and propulsion of ingested food.
What surrounds the hepatopancreatic ampulla?
The ampulla is surrounded by a ring of smooth muscle called the hepatopancreatic sphincter
What is the function of the distal intestine?
The distal large intestine performs a small amount of absorption, primarily of water, but its main role is to store fecal material until it is ready to be expelled during defecation.
How are Hydrogen ions secreted?
The hydrogen ions are secreted by an ATP-consuming pump in the plasma membrane, called the H+/K+ pump, or proton pump
When is the importance of ACh in salivation evident?
The importance of ACh in salivation is evident any time ACh receptors are blocked.
What triggers the intestinal phase?
The intestinal phase is triggered by the presence of partially digested proteins in the fluid entering the duodenum. -As in the stomach, these partially digested proteins trigger enteroendocrine cells to release intestinal gastrin. -This hormone has the same effect as gastrin produced by the stomach, and stimulates hydrogen ion secretion from parietal cells.
How do keratinized cells make our tongue feel? Why is this important?
The keratinized cells make the surface of the tongue rough, which assists in mechanical digestion. -Human tongues have a limited number of keratinized cells, so our tongues do not feel rough to the touch.
Does the large intestine host bacteria?
The large intestine hosts a staggering number of bacteria; indeed, there are about 10 times more bacteria in the large intestine than cells in the human body, and bacteria make up as much as 60% of the dry mass of feces.
What may cause the motility of the large intestine to decrease?
The large intestine's motility may be slowed by drugs such as opiate narcotics or those that block the effects of acetylcholine (ACh).
What are circular folds? What structures does it involve? Purpose of it
The largest type of folds, which are visible with the naked eye as ridges in the wall -Circular folds involve both the mucosa and submucosa of the small intestine. -These folds not only increase surface area but also slow down the transit of chyme through the small intestine, which gives the nutrients more time to be digested, and the small intestine cells, called enterocytes (EN-tehr-oh-sytz), more time to absorb nutrients.
What are the lateral walls of the oral cavity?
The lateral walls of the oral cavity are formed by the cheeks, which are composed largely of the buccinator muscles and lined internally by stratified squamous nonkeratinized epithelium.
Describe how the liver functions in detoxification
The liver detoxifies substances produced by the body, such as the previously mentioned bilirubin. In addition, the liver processes substances that we eat or drink, some of which are toxins harmful to the body (such as alcohol). These substances are generally delivered to the liver first via the hepatic portal vein, where the liver converts them into less harmful materials that can be excreted in bile or in urine. The liver also metabolizes many drugs, such as antibiotics. Individuals with impaired liver function metabolize drugs more slowly than those with normal liver function, and the drugs remain in their systems much longer.
What is the liver covered with?
The liver is wrapped in a thin connective tissue capsule, and most of it is covered by the visceral peritoneum.
Describe how the liver functions in nutrient metabolism Example?
The liver processes nutrients obtained from the diet. Carbohydrates and proteins absorbed from the alimentary canal are delivered to the liver by the hepatic portal vein, and lipids by the hepatic arteries. Within the liver, some of these nutrients are stored for later use, modified into another form, or used to synthesize other molecules. -For example, some of the glucose taken in by the liver is stored in the form of glycogen, and many of the dietary amino acids are used to synthesize plasma proteins such as albumin and clotting proteins.
Does liver produce and secrete bile at basal rate?
The liver produces bile continually but generally does not secrete it at a basal rate, the way pancreatic and gastric juices are released.
What is the mesocolon?
The mesentery attached to the much of the large intestine
What is the mouth's inferior wall composed of?
The mouth's inferior wall is composed of muscles of the tongue and muscles that attach to the hyoid bone.
What does the mucosa of the large intestine lack? What does this highlight?
The mucosa of the large intestine lacks villi and its cells lack microvilli. -These structural adaptations reflect the fact that nutrient absorption is not the large intestine's primary function.
What makes the muscularis externa of the large intestine unique?
The muscularis externa of the large intestine is unique in that its longitudinal layer is not continuous throughout most of its length. -Instead, this layer is gathered into three bands or ribbons of muscle called taeniae coli
What is the Vestibule?
The narrow space between the teeth and gums and the internal surfaces of the lips and cheeks
Describe the Peritoneal Cavity
The narrow space between the visceral and parietal peritoneal membranes that is filled with serous fluid. -This fluid lubricates organs as they slide past one another. Note that the peritoneal cavity is much larger than the pleural or pericardial cavity. -Abdominal trauma or infection can inflame the peritoneum
How does the gut flora deter the growth of harmful bacteria?
The normal flora prevent the growth of pathogenic, or disease-causing, microorganisms by competing for nutrients and producing chemicals that kill certain harmful bacterial species.
What does the oral cavity house?
The oral cavity houses hundreds of different bacterial species, collectively called the normal flora. -causes no issues in individuals with healthy immune system and good oral hygiene, but can set the stage for tooth decay in people with damaged enamel sets!!
What helps "cement" the tooth in place?
The periodontal ligament extends collagen fibers into the cementum, which helps this substance "cement" the tooth in place.
What is the gastric pacemaker responsible for?
The peristaltic waves are initiated and controlled by a group of specialized cells collectively called the gastric pacemaker. -The pacemaker controls the rate of the waves, which remains relatively constant at about three per minute.
What happens to the bolus after it has been created by the teeth, tongue, and salivary glands?
The posterior oral cavity, pharynx, and esophagus then deliver the bolus to the stomach through the process of swallowing.
Define Vomiting
The process during which stomach contents move backward and are expelled from the mouth.
Describe the receptors located in walls of the alimentary canal organs
The sensory component of the reflex arcs is provided by receptors located in the walls of the alimentary canal organs. These receptors respond to stimuli such as stretch, the concentration and pH of the fluids the organs contain, and the presence of certain products of digestion. When these receptors are stimulated, their axons contact neurons in the ANS or ENS, which then initiate the appropriate response such as triggering peristalsis or secretion from certain glands.
What is the gallbladder?
The small, hollow organ on the posterior side of the liver that stores and releases bile.
Describe Descending colon
The splenic flexure gives rise to the retroperitoneal descending colon, which passes along the left side of the abdominal cavity.
What is the greater curvature?
The stomach's convex left side
What is the lesser curvature?
The stomach's convex right side
What is the palate?
The superior boundary, or "roof," of the mouth
What are the functions of the large intestine?
The tasks of the large intestine also include: -secretion (primarily in the form of mucus) -propulsion -defecation -it houses numerous bacteria that perform important functions such as synthesizing vitamins.
Describe the Pylorus of the Stomach
The terminal portion of the stomach is the pylorus (pylor- = "gatekeeper"), which abuts (has a common boundary with or is close to) the first portion of the small intestine, the duodenum. -In the pylorus, a thick ring of smooth muscle called the pyloric sphincter regulates the flow of materials between the stomach and the small intestine.
How do the three salivary glands differentiate?
The three main types of salivary glands differ in the proportion of mucous and serous cells they contain.
Does the tongue play a role in swallowing?
The tongue also plays a role in this process, and is the ONLY accessory organ to directly participate in motility
What is the composition of the tongue?
The tongue consists of skeletal muscle covered with a layer of stratified squamous epithelium.
What is the function of the tonsils?
The tonsils perform defensive functions and help protect the remainder of the alimentary canal from any pathogens that enter the body via the oral and nasal cavities.
Describe Stimulation of histamine secretion
The vagus nerve stimulates a specific type of enteroendocrine cell to release the hormone histamine. Like gastrin, histamine triggers hydrogen ion secretion.
Describe Direct stimulation of hydrogen ion release
The vagus nerves release ACh onto parietal cells, which directly stimulates them to release hydrogen ions.
Describe the taeniae coli
Their constant tension bunches the colon into pockets referred to as haustra
Describe the primary dentition, or deciduous
There are 20 deciduous teeth, with 4 incisors, 2 canines, and 4 molars in both the mandible and maxilla (Figure 22.5b). -The first deciduous teeth to erupt are generally the lower central incisors at about 6 months of age. -Deciduous teeth continue to erupt at a rate of about one pair of teeth per month until the age of 24 months, at which time all 20 teeth are usually present.
What is teeth masticate?
This is when we chew
Describe the rectum
This portion of the large intestine runs anterior to the sacrum and is retroperitoneal. -The walls of the rectum feature horizontal folds called rectal valves, which allow the passage of flatus (gas) without risking the simultaneous passage of feces.
What are mesenteries?
This the structure formed when the visceral peritoneum folds over on itself around certain organs, particularly the small intestine
Describe Stimulation of gastrin secretion
Vagal nerve stimulation triggers the release of a peptide that stimulates G cells to release the hormone gastrin. Gastrin triggers hydrogen ion secretion.
What regulates both peristalsis and segmentation?
Vagus nerve
What is another another name for the serosa of the large intestine?
Visceral Peritoneum
What is receptive relaxation?
When food or liquid is swallowed, the gastroesophageal sphincter and smooth muscle of the fundus and body of the stomach relax to allow the stomach to fill.
What happens when motility in the large intestine increases? What is produced as a result?
When motility increases, the large intestine does not have enough time to absorb water from fecal material. -This produces watery feces, a condition known as diarrhea (dy-ah-REE-ah).
What happens when pepsinogen encounters an acidic pH?
When pepsinogen encounters an acidic pH, it becomes the active enzyme pepsin, which begins protein digestion in the stomach.
What factors trigger a negative feedback loop that delays gastric emptying?
When sensory receptors in the wall of the duodenum detect a high degree of stretch, a low pH, a high lipid composition, and/or a high solute concentration in the chyme
What is impaction?
When teeth remain embedded in the bone, especially wisdom teeth. -wisdom teeth become impacted more often than any other teeth because of their position at the back of the jaw. -Impacted teeth can be removed surgically.
Are the organs of the digestive system supplied with nerves?
YES, The organs of the digestive system are extensively supplied with nerves, most of which are branches from the autonomic nervous system.
Can an organ be both, intraperitoneal and retroperitoneal?
YES, the pancreas is an example
What is a gastric ulcer?
acid and enzymes eat away at the mucosa and expose the underlying tissues. -Ulcers are often associated with the presence of certain bacteria and/or excessive production of acid.
Describe the control of swallowing
almost entirely neural
What is found between anal columns? What is the responsibility of the structure?
anal sinuses -secrete mucus when feces pass through the anal canal during defecation.
What is the function of the hepatic portal vein?
brings nutrient-rich, de-oxygenated blood to the liver from multiple abdominal organs
What is the function of the hepatic artery?
brings oxygen- rich blood to the liver
How does saliva function regarding mechanical digestion?
by moistening and helping to mix ingested food into a bolus so it can be swallowed
What other factors influence bile secretion?
including the hormone secretin, which stimulates bile production and release by hepatocytes.
What is swallowing, or deglutition?
is a specialized type of propulsion that pushes a bolus of food from the oral cavity through the pharynx and esophagus to the stomach.
Where is the liver located?
is located in the right upper quadrant nestled against the inferior surface of the diaphragm **one of the largest organs in the body, and pyramid shaped
What mediates the cephalic phase?
is mediated by the sight, smell, taste, or even thought of food.
What is found at the brush border?
numerous digestive enzymes produced and secreted by enterocytes, such as sucrase, maltase, and lactase, which catalyze the reactions that break down disaccharides, and peptidases, which catalyze reactions that break down peptides.
Of the three divisions, which two are part of the alimentary canal?
only the oropharynx and laryngopharynx are part of the alimentary canal
What is the function of the upper esophageal sphincter?
ontrols the passage of the bolus into the esophagus
Which enzymes catalyze reactions that digest nucleic acids?
pancreatic enzymes called nucleases, these enzymes catalyze the reactions that break nucleic acids into individual nucleotides.
What are the primary functions of the esophagus?
propulsion and a small amount of secretion of mostly mucus.
What is the enamel covering?
pulp
What is the function of the hepatic veins?
receive blood from the sinusoids fed by both the hepatic arteries and the hepatic portal vein, and drain into the inferior vena cava.
Where is the large intestine located?
runs along the border of the abdominal cavity, surrounding the small intestine and other abdominal organs like a frame
What are the three primary functions of the stomach?
secretion, propulsion, and digestion
What is the only acinar cell found in the parotid glands? What does this mean?
serous cells -the parotid glands secrete mainly water and enzymes
What is primary dentition, or deciduous teeth?
set of "Baby teeth"
What is the secondary dentition?
set of "permanent teeth"
What is the pulp?
soft, inner gelatinous substance
What is filiform covered with?
stratified squamous keratinized epithelium
What is a key factor in determining the rate of gastric emptying?
the amount and composition of chyme in the duodenum
What structures join to form the common bile duct?
the cystic duct joins the common hepatic duct to form the common bile duct.
Which of the two segments of the large intestine is less motile?
the distal large intestine is much less motile than the proximal large intestine.
How is epithelium of the tongue arranged?
the epithelium of the tongue is arranged into small projections called papillae
What is dentin?
the inner layer of mineralized tissue in both the root and crown - is composed of about 70% calcium hydroxyapatite crystals. This makes dentin the second hardest material in the body. However, dentin also has some degree of elasticity, which is critical for preventing the overlying enamel from fracturing when chewing hard substances. -Unlike enamel, dentin is formed throughout life by cells called odontoblasts that line its inner surface.
Describe the Body of the Stomach
the largest portion of the stomach
What does the abdominopelvic cavity house?
the largest serous membrane in the body, the peritoneal membrane (pehr′-uh-toh-NEE-uhl), or peritoneum
What three muscles surround the pharynx?
the pharynx is surrounded by three pairs of skeletal muscles: the upper, middle, and lower pharyngeal constrictor muscles These muscles contract sequentially during swallowing and propel the bolus inferiorly.
Describe the red margin
the portion near the mouth, called the red margin, contains less keratin than the surrounding skin. As a result, the red margin is fairly translucent and the blood in the vessels of the dermis is more visible, giving the lips a slight reddish tint.
What comes after the sigmoid colon?
the rectum
What are pharyngeal and esophageal phases of swallowing both controlled by?
the remaining two phases are regulated by the medulla and the enteric nervous system
Describe small intestinal motility during fasting
the small intestine exhibits slow, rhythmic contractions along its length in a pattern called the migrating motor complex. These contractions clear any remaining material from the small intestine, including leftover food and secretions. The migrating motor complex requires about 2 hours to push digesting food from the duodenum to the ileocecal valve. This movement is controlled by both the ENS and a hormone called motilin, which is produced by cells in the duodenal mucosa.
Describe the Ileum
the small intestine's final segment, is also intraperitoneal. -About 3.6 meters (10.8 feet) in length, it terminates at the portion of the large intestine called the cecum (SEE-kum). -A sphincter known as the ileocecal valve (ill′-ee-oh-SEE-kuhl) controls the movement of materials from the ileum into the cecum. This sphincter also prevents materials in the large intestine from flowing backward into the ileum. This function is key because, as we discuss shortly, the large intestine houses a great number of bacteria that could cause illness if they entered the ileum
Where is the stomach located?
the stomach sits primarily in the left upper quadrant just inferior to the diaphragm
What is the composition of acinar cells found in the sublingual glands? What does this mean?
the sublingual glands contain mostly mucous cells -sublingual glands secrete mainly mucus with a small amount of enzymes
What is the compostion of acinar cells in the submandibular glands? What does this mean?
the submandibular glands have mostly serous cells and a small number of mucous cells -submandibular glands secrete enzymes mixed with some mucus
Describe the walls of the sinusoids
their walls are not continuous, which allows large substances to enter and exit
Describe the Autononomic Nervous System
there are two branches of the ANS: 1. the sympathetic nervous system 2. the parasympathetic nervous system (see Chapter 14).
What happens after the nutrients are digested chemically?
they are absorbed across the enterocytes into either the blood or the lymph, along with water, vitamins, and other substances.
What are gastric glands?
they contain both endocrine cells that secrete hormones into the bloodstream and exocrine cells that secrete an acidic, enzyme-containing fluid called gastric juice into the lumen of the stomach.
What does the stomach's motility enable it to perform?
three actions (1) receive food from the esophagus (2) churn the incoming bolus into chyme (3) control the rate at which chyme empties into the small intestine.
What is the final function of gastric motility?
to control the movement of chyme into the duodenum
What is the liver's main digestive function?
to produce bile
When does the gastric phase begin?
when food enters the stomach, and continues the stimulation provided during the cephalic phase.
What happens when motility in the large intestine decreases?
when motility decreases, the large intestine absorbs too much water and the fecal material becomes hard, -a condition called constipation.
Define fat-soluble vitamins
which are lipid-based and mostly nonpolar
Define water-soluble vitamins
which are polar molecules
What is the esophageal mucosa is lined with...?
with stratified squamous nonkeratinized epithelium
Describe the large intestine
-About 1.5 meters (5 feet) long, -it is so named because it has a larger diameter than the small intestine. -The large intestine receives material from the small intestine that was not digested or absorbed. -the large intestine is simply a passageway for the leftovers, known as feces , or fecal matter. -is very active in absorbing water and electrolytes.
Describe Sublingual glands
-As implied by their name, the sublingual glands (sub-LING-gwuhl) are situated inferior to the tongue. -The sublingual glands secrete saliva through several small sublingual ducts that empty into the oral cavity just under the tongue. - These are the smallest salivary glands and secrete only about 5% of total saliva.
What is the pancreas? Describe both types of secretions
-a gland with both endocrine and exocrine functions -Its endocrine secretions, the hormones insulin and glucagon, are released from pancreatic islets into the blood and affect most cells in the body. -Its exocrine secretions are enzymes secreted primarily by clusters of acinar cells. These enzymes are released into ducts of the pancreas that empty into the alimentary canal, where they help with digestion.
Describe Salivary amylase
-is the first digestive enzyme that ingested food encounters. -It catalyzes the beginning of carbohydrate digestion, breaking down large polysaccharides into smaller polysaccharides.
Describe the Greater Omentum
-is unique among the mesenteries in that it consists of four layers of folded visceral peritoneum, -is named for the fact that it covers the abdominal organs like an apron (Figure 22.3c). -The greater omentum, which is the first structure visible when the abdominal cavity is opened, extends from the base of the stomach down into the pelvis.
What 3 other structures are found entering and exiting the porta hepatis?
-nerves, lymphatic vessels, and the common hepatic duct
Describe the cecum
-the first portion of the large intestine a blind pouch (cecum- = "blind") that is intraperitoneal and located in the right lower quadrant of the abdomen. The cecum features a smaller blind-ended pouch extended from its posteroinferior end, called the vermiform appendix (VER-muh-form uh-PEN-diks; "wormlike appendage"), which is generally shortened to simply appendix
Describe the mucosa layer of the alimentary canal
-the innermost layer if the alimentary canal. -Made up three components: 1. First is a layer of epithelium facing the lumen 2. followed by a thin layer of loose connective tissue called the lamina propria 3. finally two thin layers of smooth muscle together known as the muscularis mucosae. -The epithelium from the stomach to the end of the large intestine is simple columnar epithelium with copious goblet cells that secrete an alkaline mucus. -This mucus coats the epithelium and protects it and the underlying tissues from ingested food and chemicals secreted by digestive organs. -The mucosa also houses regenerative epithelial cells that have a high rate of mitosis. These cells allow the mucosa to replace epithelial cells as they are damaged or sloughed off in the alimentary canal. -The lamina propria houses blood and lymphatic vessels, glands, and mucosa-associated lymphatic tissue (MALT; see Chapter 20). -The two layers of the muscularis mucosae are arranged in different directions—the inner layer is circular and the outer layer is longitudinal. As discussed later, this arrangement allows motility as the two layers contract alternately.
What are the four portions of the colon?
1. Ascending colon 2. Transverse colon 3. Descending colon 4. Sigmoid Colon
The stomach have five anatomical regions. What are they?
1. Cardia 2. Fundus 3. Body 4. Pyloric Antrum 5. Pylorus
What are two hormonal mediators of pancreatic secretion?
1. Cholecystokinin, or CCK 2. Secretin
What are the four physiological effects resulting from the cephalic phase?
1. Direct stimulation of hydrogen ion release 2. Stimulation of gastrin secretion 3. Stimulation of histamine secretion 4. Inhibition of somatostatin secretion
What are the four types of paipllae?
1. Filiform 2. Fungiform 3. Circumvallate 4. Foliate papillae
Describe the digestion process (generalized)
1. Food is ingested at the mouth 2. propelled through the canal from one organ to another as it is digested mechanically and chemically. 3. The nutrients are absorbed into the bloodstream 4. the indigestible substances are removed from the body by defecation. *** Substances secreted by various digestive organs aid each of these processes.
What are the two prominent mesenteries?
1. Greater Omentum 2. Lesser Omentum
What two portions make up the palate?
1. Hard palate 2. Soft palate
What are the 3 types of teeth?
1. Incisors 2. Canines 3. Molars
What are the four processes that take place in the oral cavity, or mouth?
1. Ingestion 2. Secretion 3. Chemical and mechanical digestion 4. Propulsion
How does the digestive system complete its tasks?
1. Ingestion 2. Secretion 3. Propulsion 4. Digestion 5. Absorption 6. Defecation
What are the steps in the digestion of lipids?
1. Lipids are broken apart by stomach churning and broken down in reactions catalyzed by gastric lipase 2. Lipids enter the small intestine and are emulsified by bile salts 3. Pancreatic lipase catalyzes reactions that digest the lipids into free fatty acids and mono glycerides 4. Bile salts remain associated with the digested lipids to form micelles
Liquid absorption in the small intestine (STEPS)
1. Micelles escort lipids to th enterocyte plasma membrane 2. Lipids diffuse through the phospholipid bilayer and enter the cytosol 3. Lipids are reassembled into triglycerides and packaged into chylomicrons 4. Chylomicrons are released into the interstitial fluid by exocytosis and then enter a lacteal
What is the basic tissue organization of most of the alimentary canal?
1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa or adventitia
What are the four main types of cells in or near gastric glands?
1. Mucous Neck Cells 2. Parietal Cells 3. Chief Cells 4. Enteroendocrine Cells
What are other liver functions?
1. Nutrient metabolism 2. Detoxification 3. Excretion
What are the steps in amino acid digestion and absorption in the small intestine?
1. Oligopeptides are broken down into free amino acids in reactions catalyzed by pancreatic and brush border enzymes 2. The Na+/K+ pump creates a Na+ gradient 3. This gradient drives the secondary active transport of certain amino acids into the enterocyte 4. Amino acids cross the basal enterocyte membrane by facilitated diffusion and enter the blood
What are two layers of the peritoneal membrane?
1. Parietal peritoneum 2. Visceral peritoneum
What are the three salivary glands?
1. Parotid Glands 2. Submandibular Glands 3. Sublingual Glands
What functions do the normal flora, or gut flora, contribute to?
1. Produce vitamins 2. Metabolize undigested materials 3. Deter the growth of harmful bacteria 4. Stimulate the immune system
What are the two functional segments of the large intestine?
1. Proximal 2. Distal
What four lobes make up the liver? -where is each located?
1. Right lobe-right side of the liver 2. Left lobe-left side of the liver 3. Caudate Lobe 4. Quadrate Lobe-located on the posterior side of the liver's right lobe.
What are 4 more components that make up saliva?
1. Salivary amylase 2. Lysozyme 3. Secretory IgA 4. Bicarbonate ions
What four main processes occur in the small intestine?
1. Secretion 2. digestion 3. Absorption 4. Propulsion
What are the two main types of acinar cells in salivary glands?
1. Serous Cells 2. Mucous Cells
What are the steps in the defelcation reflex process?
1. Stretch receptors transmit the sensation of rectal distention to the spinal cord. 2. Parasympathetic neurons cause smooth muscle in the sigmoid colon and rectum to contract, and the internal anal sphincter to relax. 3. Impulses from the cerebral cortex trigger relaxation of the external anal sphincter and contraction of the levator ani muscle, allowing feces to pass out of the body.
How the reflex arc works
1. The arc begins with sensory stimuli such as the smell or taste of food, which communicate this information to the salivatory nucleus in the brainstem 2. Parasympathetic fibers from the brainstem exit via the facial nerve (cranial nerve VII) to innervate the submandibular and sublingual glands, and via the glossopharyngeal nerve (cranial nerve IX) to innervate the parotid glands. 3. Neurons from these nerves release acetylcholine (ACh) onto the acinar cells, which triggers the acinar cells to secrete saliva. **Even the mere smell of food can trigger this reflex, which is why you find yourself drooling when you smell your favorite food cooking.
Describe the process of digestive organs draining drains the digestive organs?
1. The digestive organs are drained by a set of veins that drain into the hepatic portal vein. 2. The hepatic portal vein then delivers the blood to the liver for processing. 3. Blood drains from the liver by a set of hepatic veins, which in turn deliver blood to the inferior vena cava.
What are the two main types of motility exhibited by the primary large intestine? Describe each
1. The first is a type of segmentation, or churning, similar to what we saw in the small intestine, in which the circular muscle of each haustrum contracts repeatedly. This swirls the material around in the haustrum, which aids in water and electrolyte absorption. These contractions are controlled primarily by local neurons of the ENS and are triggered by stretch. 2. The other type of motility in the proximal large intestine is a propulsive motion known as a mass movement, or mass peristalsis.During a mass movement, multiple haustra undergo peristalsis, which propels their contents toward the distal large intestine. Mass movements occur three to four times per day, and appear to be triggered by food consumption, which initiates reflexes controlled by the ENS.
What are the two sphincter located in the terminal portion of the anal canal?
1. The first is the involuntary internal anal sphincter, which is simply the thickened circular layer of the muscularis externa. The internal anal sphincter is supplied by parasympathetic motor neurons. 2. The second is the voluntary external anal sphincter, which is composed of skeletal muscle. As this sphincter is voluntary, it is innervated by somatic motor neurons controlled by the cerebral cortex.
What two stimuli trigger acid secretion during the gastric phase?
1. The first is the simple presence of food in the stomach. 2. The second stimulus is the presence of partially digested proteins in gastric juice.
What is the function of the mesenteries? Why is it important?
1. The mesenteries support and bind these organs together and keep the small intestine in a particular shape that fits within the abdominopelvic cavity. -This function is key, as we don't want loops of intestine wandering around our abdominopelvic cavities. 2. The mesenteries also house blood vessels, nerves, and lymphatic vessels, anchoring them in place
What are the two types of vitamins?
1. Water-soluble 2. Fat-soluble
What are the three main clusters of nerves from the sympathetic and parasympathetic that serve the digestive organs?
1. celiac plexus 2. superior mesenteric plexus 3. inferior mesenteric plexus *Notice that these clusters have the same names as the arteries that supply the digestive organs.
What are the two structures that make up a tooth?
1. crown 2. root
What are the steps in bile secretion?
1. duodenal cells secrete cholecystokinin (CCK) and secretin into the blood. 2. CCK triggers contraction of the gallbladder, which releases bile. 3. Bile salts and secretin trigger the release of more bile, an example of positive feedback
What are the three divisions of the small intestine?
1. duodenum 2. jejunum 3. ileum
What three structures (referred to as the portal triad) are found at each of the six corners of the liver lobule?
1. hepatic arteriole 2. portal venule 3. bile duct
What are the two groups of skeletal muscles that control tongue movement?
1. intrinsic 2. extrinsic
What is the composition of the muscularis externa of the esophagus?
1. its superior third is composed of skeletal muscle 2. its middle third is a mixture of skeletal and smooth muscle 3. its inferior third is composed of smooth muscle.
What are the three divisions of the pharynx?
1. nasopharynx 2. oropharynx 3. laryngopharynx.
Humans develop two sets of teeth. Describe both
1. one set of "baby teeth" and 2. one set of "permanent teeth."
What two structures does the oropharynx house?
1. palatine tonsils 2. lingual tonsils
What are the final three organs of the digestive system?
1. pancreas 2. liver 3. gallbladder
What are the two types of movement exhibited by the small intestine during eating?
1. peristalsis and 2. segmentation
What accessory organs are housed in the oral cavity? What do these three accessory organs create?
1. teeth 2. tongue 3. salivary glands Together, these organs turn ingested food into a moist, chewed mass called a bolus.
What three segments make up the large intestine?
1. the cecum 2. the colon 3. the rectum
The digestive system consists of what two organs?
1. the organs of the alimentary canal, also known as the gastrointestinal (GI) tract or digestive tract ; 2. and the accessory organs
What are the three steps in churning?
1. the stomach's smooth muscle produces peristaltic contractions that propel a small amount of chyme through the pyloric sphincter into the duodenum. The rest of the chyme is pushed backward into the stomach. 2. The peristaltic waves then churn and mix the remaining chyme, and 3. the process repeats.
What are three phases of swallowing?
1. voluntary 2. pharyngeal 3. esophageal
How many sphincters can be found at the terminal portion of the anal canal?
2
What is the stomach volume at resting state? How much can it expand to?
50 ml, can expand to 1500 ml when filled with food and liquid
What is the falciform ligament?
A fold of visceral peritoneum that separates the right and left lobes. -it also anchors the liver to the anterior abdominal wall.
Define chylomicrons
A large molecule composed of triglycerides packaged with cholesterol, other dietary lipids, phospholipids, and lipid-binding apoproteins that delivers dietary lipids to cells.
What is Pancreatic juice?
A liquid consisting of water, bicarbonate ions, and enzymes produced by pancreatic acinar cells and released into the small intestine during digestion.
What is the composition of the liver lobule?
A liver lobule is composed of flattened plates of cells, called hepatocytes (heh-PAH-toh-sytz), arranged in the shape of a hexagon and stacked on one another.
Define emulsification
A process in which an amphiphilic compound physically breaks lipids into smaller clusters through polar and nonpolar interactions.
Define the Pyloric Sphincter
A ring of smooth muscle between the stomach and duodenum that controls the flow of chyme between the two organs.
What is the alimentary canal?
A series of hollow digestive organs through which food passes as it is ingested, digested, and absorbed; also carries out defecation.
What are salivary glands?
A set of three pairs of glands around the oral cavity that secrete saliva into it.
Define micelles
A small vesicle composed of an outer layer of bile salts surrounding an inner core of chemically digested lipids.
Why is absorption in the large intestine critical?
Absorption in the large intestine is critical for maintaining fluid, electrolyte, and acid-base homeostasis.
Why is acid important in gastric juice?
Acid is an important component of gastric juice because it is required to activate a precursor enzyme called pepsinogen (pep-SIN-oh-jen) and also because it destroys most disease-causing organisms we ingest.
What are acinar cells?
Acinar cells are modified simple cuboidal epithelial cells.
What happens after a meal?
After a meal, the smooth muscle layers of the stomach begin to produce waves of peristalsis for churning
What do fungiform, circumvallate, and foliate papillae contain?
All papillae except filiform contain epithelium with sensory receptors called taste buds, which detect chemicals associated with different taste sensations.
Describe the normal flora
Also known as the gut flora, is the bacteria found in the gut -consist of about 500 different bacterial species that coexist with humans in a symbiotic (mutually beneficial) relationship. -Humans provide the bacteria with the environment they need to survive, and the bacteria perform a number of useful functions for humans
What is the gastroesophageal sphincter?
Also known as the lower esophageal sphincter, that regulates the passage of the bolus into the stomach. This sphincter also prevents the contents of the stomach from re-entering the esophagus.
Where is the pharynx located?
Also referred to as the throat, sits posterior to the nasal and oral cavities
Where does the rectum end?
At the anal canal, which is the last portion of the large intestine
Where is the gastroesophageal sphincter located?
At the esophagus' inferior end
Describe Transverse colon
At the hepatic flexure, the ascending colon becomes the intraperitoneal transverse colon, so named because it passes transversely across the superior abdominal cavity. -At the spleen, it takes a sharp turn inferiorly at a junction called the splenic flexure , also known as the left colic flexure.
How does the gut flora metabolize undigested materials?
Bacteria metabolize carbohydrates such as soluble fibers that the small intestine is unable to digest, converting them into fatty acids and other molecules the body can absorb and use. This also aids in the absorption of certain vitamins and electrolytes. A somewhat unfortunate byproduct of this metabolism is the production of gas within the intestine that is released as flatus.
How does the gut flora produce vitamins?
Bacteria produce vitamins such as vitamin K, which is necessary for blood clotting.
How is secretion divided?
Based on the primary source of regulation
What is found between gastric pits? What do those structures do?
Between the gastric pits we find columnar cells and numerous goblet cells, both of which secrete a thick mucus that lines and protects the cells of the stomach from its own secretions.
What stimulates bile release? What structure does the bile get released into?
Bile release is stimulated by the hormone CCK, which triggers contraction of the smooth muscle in the wall of the gallbladder. This causes the gallbladder to release bile into the cystic duct (SIS-tik).
What is the main organic compound found in bile?
Bile salts
What does it mean that bile salts are amphiphilic?
Bile salts are amphiphilic, meaning they have both polar and nonpolar parts. This allows them to interact with both lipids and the watery environment of the small intestine. When bile is released into the duodenum, the bile salts coat the lipids and physically break them apart into smaller pieces, a process known as emulsification (ee-mul′-sih-fih-KAY-shun). Although emulsification is mechanical digestion, it is necessary for the chemical digestion and absorption of lipids, which we further explore in Module 22.7.
What do the greater omentum and lesser omentum have in common?
Both the greater and lesser omenta generally accumulate adipose tissue between their folds.
Describe Chlolecystokinin
CCK is produced by duodenal enteroendocrine cells in response to the presence of lipids and partially digested proteins in the duodenum. -It acts on acinar cells to trigger the secretion of digestive enzymes and other proteins.
The voluntary phase of swallowing is under control of what system?
Cerebral Cortex
What causes gastric ulcer?
Conditions that decrease the amount of mucus secreted by the columnar cells and numerous goblet cells found between the gastric pits
Describe the arterial supply of the digestive organs?
Consists of branches from the abdominal aorta, including the celiac trunk, superior mesenteric artery, inferior mesenteric artery, and branches from each of these arteries.
Describe Secretion
Digestive organs contain both endocrine and exocrine glands that secrete a variety of substances—such as mucus, enzymes, acid, and hormones—to aid other digestive processes.
Describe Bicarbonate ions
During eating, when flow rates of saliva are high, basic bicarbonate ions (HCO3−) are added to saliva. -Their primary function is to neutralize any acid from the stomach that regurgitates into the esophagus.
How does the gut flora stimulate the immune system? (MALT)
During infancy, the normal flora induce immune tolerance to their own antigens. -At the same time, they stimulate the development of mucosa-associated lymphatic tissue (MALT) and the production of antibodies to pathogens. -This creates a favorable environment for the normal flora while also protecting the host from pathogenic bacteria.
Describe the Esophageal Phase of Swallowing
During the final phase of swallowing, the esophageal phase, the bolus passes through the esophagus to the stomach. -This phase begins as the upper esophageal sphincter relaxes. -Neurons of the enteric nervous system then stimulate the inner circular and outer longitudinal layers of the muscularis externa to undergo peristalsis and "massage" the bolus inferiorly toward the stomach.
What does each acinus surround?
Each acinus surrounds a small duct into which its cells secrete their products.
What is each type of motility regulated by?
Each type of motility is regulated by the nervous system and/or the endocrine system.
What is another word for vomiting?
Emesis
Describe wisdom teeth
Erupt somewhat later between the ages of 17 and 21
What factors may increase motility of the large intestine?
Factors that may increase motility include irritation of the colon due to bacterial or viral infections or drugs that stimulate the parasympathetic nervous system
Describe Ingestion
Food and water are brought into the digestive system by ingestion , which occurs via the mouth under normal conditions.
Does food get in contact with the accessory organs?
Food generally does not come into direct contact with the accessory organs, although the teeth and tongue are exceptions.
Describe gallstones
Gallstones are generally asymptomatic, but occasionally they become lodged in the cystic duct or the common bile duct and block the outflow of bile. This results in abdominal pain, particularly when eating a fatty meal, and the presence of undigested fats in the feces. The feces also take on a clay color due to the lack of bilirubin excretion. Painful gallstones are generally treated by surgically removing the gallbladder, a procedure known as a cholecystectomy (koh′-leh-sis-TEK-toh-mee). The absence of a gallbladder may temporarily reduce the ability of the small intestine to digest fats. However, over time the common hepatic duct enlarges and takes over some of the gallbladder's functions.
Why is the alimentary canal considered external body surface?
However, the lining of the alimentary canal is actually considered an external body surface because it is open to the outside on both ends. Think of it like a paper towel roll—its outer surface is akin to the body's skin, and its inner surface is akin to the alimentary canal. Both its surfaces are in contact with the outside environment and thus are considered "external."
What are the functions stimulated by the ANS called? Why?
In contrast, functions stimulated by the ANS are known as long reflexes because they must travel outside the local digestive neurons to the CNS to function.
What is mechanical digestion?
In mechanical digestion , digestive organs physically break food down into smaller pieces via processes such as chewing and mixing food by movements by the muscles of the alimentary canal
Describe Sigmoid Colon
In the left lower quadrant, the descending colon becomes the S-shaped sigmoid colon (sigmoid = "S-shaped"), which is intraperitoneal and passes toward the sacrum.
What structures rely their motility on skeletal muscle?
In the oral cavity, the pharynx, the superior portion of the esophagus, and the last portion of the large intestine, motility is due to skeletal muscle.
Where does most of the absorption that occurs within the alimentary canal take place?
In the small intestine and the the progressively small folds increase surface area available for absorption
What is Peritonitis? Cause? Symptom? Treatment?
Inflammation of the peritoneum Cause: Peritonitis results when substances such as blood or the contents of an abdominal organ leak into the peritoneal cavity. Usually this is due to abdominal trauma that ruptures a blood vessel or abdominal organ, and often involves a bacterial infection. Symptoms: Abdominal pain is the most universal symptom of peritonitis. Most patients experience rebound tenderness, in which they feel little pain when a hand is placed on their abdomen, but significant pain when the hand is removed. This is caused by the inflamed peritoneal membranes snapping back into place when the hand leaves the abdomen. Treatment: for peritonitis may involve antibiotic therapy and surgery to correct its underlying cause. Most patients recover with appropriate treatment, but it can prove fatal if left untreated
SO when does bile secretion occur?
Instead, bile secretion does not occur until the gallbladder contracts and the sphincter at the hepatopancreatic ampulla relaxes. -is mostly accomplished by cholecystokinin (CCK) and to a small extent by the vagus nerve
What does the alimentary canal consist of?
It consists of the oral cavity (mouth), pharynx, esophagus, stomach, small intestine, and large intestine
Describe the upper esophageal sphincter
It is a a modified sphincter of the muscularis externa at the junction of the pharynx and the esophagus
What initiates defecation reflex?
It is initiated when mass movements force fecal material into the normally empty rectum
What does enzymatic hydrolysis do?
It is when Our digestive enzymes speed up the reactions
What type of organs are the pancreas, liver, and gallbladder?
Like the salivary glands, these accessory organs are exocrine glands that secrete a product through a duct to the outside of the body
How is the small intestine like the stomach?
Like the stomach, the small intestine also mixes and propels its contents along its length and into the large intestine. Let's look at the structure and functions of the small intestine.
What separates liver lobule?
Liver lobules are separated from one another by septa that branch in from the connective tissue capsule of the liver.
Describe Enteroendocrine cells Give an example
Located at the very bottom of the gland -secrete several hormones that influence digestion. --For example, enteroendocrine cells called G cells secrete the hormone gastrin, which stimulates acid secretions from the parietal cells. -enteroendocrine cells are closest to the blood vessels in the underlying submucosa, so their hormones have ready access to the blood.
What can disrupt the normal flora?
Long-term antibiotic therapy, particularly antibiotics taken by mouth, can disrupt these functions by killing large numbers of normal flora. -This can result in multiple problems, particularly infection with antibiotic-resistant pathogenic organisms such as the bacterium Clostridium difficile.
Describe the hormones released by the endocrine system in order to regulate the digestive process
Many of these hormones are actually paracrines that are produced by the digestive organs themselves, particularly the stomach and small intestine. -Each hormone binds to a receptor on or within its target cell and regulates some aspect of its functioning. -Hormones generally either stimulate or inhibit motility of the alimentary canal, often together with one or more neural mechanisms.
How does mastication aid in digestion?
Mastication aids digestion by increasing the overall surface area of the food, giving digestive enzymes more places to catalyze the reactions of chemical digestion
What do most digestive enzymes catalyze?
Most digestive enzymes catalyze hydrolysis reactions—those that use a water molecule to break a bond between two molecules
How are fat soluble vitamins absorbed?
Most of the water-soluble vitamins are absorbed in the small intestine by diffusing through the enterocytes' plasma membranes. One important exception is vitamin B12, which must bind to intrinsic factor—a molecule produced by the parietal cells of the stomach—to be absorbed in the ileum. A shortage of intrinsic factor can impair vitamin B12 absorption
What are the several forms of motility?
Motility takes several forms, including: -swallowing -churning -peristalsis -defecation. **Some of these movements propel food through the canal, whereas others mix it as part of mechanical digestion.
Does filiform papillae play a role in taste?
NO
Can damaged enamel be repaired?
NO, The cells that secrete enamel deteriorate after the tooth erupts, so the body cannot repair damaged enamel
Does the duodenum receive large amounts of chyme?
NO, because it can process incoming chyme only so quickly therefore, must receive small amounts at a time.
Does the stimulatory effect of the intestinal phase last long? Why?
NO, it is brief -As chyme enters the duodenum, the declining pH and presence of lipids trigger the enterogastric reflex, which decreases vagal activity and acid secretion. -The low pH in the duodenum also triggers the production of hormones by the cells of the duodenal mucosa, including secretin and gastric inhibitory peptide (GIP). *Both hormones reduce acid secretion.
What does the main pancreatic duct merge with?
Near the duodenum, the main pancreatic duct merges with the duct from the liver and gallbladder, after which it empties into the duodenum.
How is nervous system regulation of motility accomplished?
Nervous system regulation of motility is accomplished by the nerves of the autonomic nervous system, or ANS.
Do the materials all pass through the sphincter at the same rate?
No, different materials pass through the pyloric sphincter at different rates.
Describe the smaller two folds of the small intestine? What is the structure (central core made of...)?
Not visible to human eye -the mucosa folds into projections called villi (VILL-ahy; singular, villus; -Notice that each villus consists of a layer of enterocytes and occasional mucus-secreting goblet cells surrounding a central core of blood capillaries and a lymphatic vessel called a lacteal.
Describe Absorption
Once food particles are mechanically and chemically digested, nutrients move through the wall of the alimentary canal into blood or lymphatic vessels by a process called absorption . Water, electrolytes, and vitamins are also absorbed into the blood in the same manner.
Does the positive feedback loop continue forever?
Once the acid concentration reaches a certain level—a pH of about 2.0—a negative feedback mechanism is initiated. -Extremely low pH levels trigger somatostatin release, which in turn decreases acid secretion.
What is the space posterior to the teeth and gums?
Oral Cavity proper
Water absorption occurs exclusively by?
Osmosis
What is another name for gastric ulcer?
Peptic ulcer
What is between these two peritoneal layers?
Peritoneal Cavity
What kind of mechanism is present in the stomach?
Positive feedback loop
Where are the gums?
Posterior to the lips and cheeks
What happens during the cephalic phase?
Prepares the stomach to receive food by increasing the release of hydrogen ions into it. These stimuli trigger output from the vagus nerve, the main nerve of the parasympathetic nervous system
Describe how the liver functions in excretion
Recall that the liver directly excretes bilirubin in bile. Several other substances the liver processes are excreted in bile, particularly drugs such as certain antibiotics. The liver also modifies substances so that they can be excreted by the kidneys.
What can we find on the inferior side of the liver?
Round ligament, which is a remnant of the umbilical vein that was present in the fetus
What runs down the middle of the pancreas? What is the function of this structure?
Running down the middle of the pancreas is the main pancreatic duct: -which receives secretions from acinar cells
What does Saliva consist of?
Saliva consists primarily of water; electrolytes such as sodium, chloride, and potassium ions; and variable amounts of mucus, depending on the type of salivary gland
What are the functions of saliva?
Saliva performs several functions in the oral cavity, including: -moistening -lubricating -cleansing the oral mucosa - its lysozyme and IgA deter the growth of pathogenic bacteria in the oral cavity -
What system primarily controls salivation?
Salivation is primarily controlled by the parasympathetic nervous system in a reflex arc
What does salivation refer to?
Salivation refers to the process of secretion from the three pairs of salivary glands
What are gallstones?
Since bile contains calcium salts and cholesterol, and both can precipitate, they end up forming hard lumps, which are gallstones
What is another word for small intestine?
Small bowel
Describe solids passing through the pyloric sphincter
Solids must be converted to a nearly liquid state before they are able to enter the small intestine.
Describe what happens when the sympathetic nervous system innervates the salivary glands and their ducts
Sympathetic nerves innervate the salivary glands and their ducts, triggering increased saliva production and facilitating saliva transport through ducts.
What other system innervates the salivary glands?
Sympathetic nervous system
What structure is a key organ of mechanical digestion?
Teeth
What is the basic unit of the liver?
The basic unit of the liver is the liver lobule
Describe Canines
The canines (KAY-nynz), also known as cuspids, are on either side of the incisors. -Their pointed crowns are specialized for ripping and tearing.
Where do the cheeks terminate? Describe the structure
The cheeks terminate anteriorly as the lips, which are formed by the orbicularis oris muscle and covered with stratified squamous keratinized epithelium. The integument covers most of the lips
What is the Splanchnic circulation
The collection of blood vessels that supplies and drains the digestive organs in the abdominopelvic cavity.
What structures join to form the hepatopancreatic ampulla?
The common bile duct joins the main pancreatic duct near the duodenum to form the hepatopancreatic ampulla (heh-PAH-toh-payn′-kree-at-ik am-POOL-uh).
What is another role the digestive system assumes?
The digestive system also plays a critical role in: -fluid, electrolyte, and acid-base homeostasis by taking in water and electrolytes via the diet and delivering them to the blood. -Other functions of the digestive system include ingesting vitamins and minerals, producing hormones, and excreting metabolic wastes.
Describe the Fundus of the Stomach
The dome-shaped top of the stomach
Describe the duct cells of the small duct that is surrounded by the acinus?
The duct cells also secrete products, discussed shortly. -Most of these small ducts merge and drain into the main pancreatic duct, although some secrete into the smaller accessory pancreatic duct.
Where does the esophagus structure go to next?
The esophagus pierces the diaphragm and passes through the esophageal hiatus (hy-AY-tus) to empty into the J-shaped organ known as the stomach.
What are the functions stimulated by the ENS called? Why?
The functions stimulated by the ENS are often called short reflexes because the reflex pathways are confined to local neurons.
In what 3 ways does the gallbladder handle bile?
The gallbladder stores bile, concentrates it (removing water), and releases it when stimulated.
Describe the gums
The gums are covered with stratified squamous nonkeratinized epithelium overlying connective tissue and the maxilla and mandible, where the teeth are housed
Where do both the hepatic and portal venule drain?
The hepatic arteriole and portal venule both drain into large, leaky capillaries, the hepatic sinusoids, that pass between rows of hepatocytes.
Describe Inhibition of somatostatin secretion
The hormone somatostatin (soh-mah′-toh-STAT-in) is produced by a type of enteroendocrine cell located in the antrum of the stomach. Somatostatin inhibits acid secretion. Vagal nerve stimulation inhibits somatostatin release, which has the effect of increasing hydrogen ion secretion.
Describe the Pyloric Antrum of the Stomach
The inferior portion of the stomach
What does the internal surface of the small intestine contain?
The internal surface of the small intestine contains three progressively smaller types of folds.
Where the digestive system begin?
The oral cavity, or mouth
What carries out all the aforementioned processes?
The organs of the alimentary canal carry out all of these basic processes.
Describe the parietal peritoneum layer
The outer layer is the parietal peritoneum (puh-RY-uh-tal), which lines the inner surface of the body wall. Where the parietal peritoneum meets the abdominal organs, it folds in on itself to become the inner visceral peritoneum, or serosa
Where is the pancreas located?
The pancreas is mostly located in the left upper quadrant of the abdomen, where it extends from the duodenum to the spleen; most of it is retroperitoneal.
What the difference between the parasympathetic and the sympathetic nervous system innervating the salivary glands?
The primary difference is that sympathetic nerves stimulate mostly mucous cells, whereas parasympathetic nerves stimulate mostly serous cells
What is the primary function of the pharynx?
The primary function of the pharynx is propulsion in the form of swallowing, during which the bolus passes through the pharynx and into the esophagus.
Describe Digestion
The process of breaking a substance into smaller sub-units; may be mechanical (physical) or chemical
Describe Ascending colon
The retroperitoneal ascending colon travels superiorly along the right side of the abdomen from the right lower quadrant to the right upper quadrant. -When it reaches the liver, it makes a sharp left-hand turn at a junction called the hepatic flexure, also known as the right colic flexure.
Describe how the sympathetic and the parasympathetic nervous system affects digestion?
These two branches generally have opposite effects on gastrointestinal motility: 1. sympathetic activity inhibits digestive processes 2. parasympathetic activity stimulates them.
The smooth muscle ability and receptive relaxation are important, why?
These two factors, along with the rugae, allow the stomach to receive food and fluid without raising its internal pressure. This is important, as increases in gastric pressure can trigger vomiting, expelling of the stomach contents through the mouth.
Where are acinar cells found?
They are found in clusters known as acini (ASS-uh-nye; singular, acinus)
Where are the accessory organs located? What do they include?
They are located around the alimentary canal and include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
Where are teeth located?
They are located in their bony sockets, called alveoli, within the mandible and maxilla and are held in place by bands of connective tissue known collectively as the periodontal ligament
How do the accessory organs help the alimentary canal?
They assist in digestion in some way.
What mediates that feedback loop?
This feedback loop is mediated by both the vagus nerve and hormones secreted by the duodenum, including secretin, cholecystokinin, and gastric inhibitory peptide. **Each of these hormones is also involved in secretion from the stomach and other digestive organs
What does it mean for an organ to be intraperitoneal?
This is used to describe organs that are located entirely within the peritoneal cavity
What does it mean for an organ to be retroperitoneal?
This is when abdominal organs are partly or completely outside the peritoneal cavity
Which contents are easy to mix with gastric juice? Which aren't?
This occurs relatively easily with carbohydrates and proteins, which mix with gastric juice with few problems. It may take much longer with lipids, because they require extensive churning due to their nonpolar structure.
What is the most fundamental function of the digestive system?
To take food into the body and break it down into its component nutrients so that they can be used by body cells.
The four physiological changes during the cephalic phase are responsible for...?
Together, the four changes during the cephalic phase are responsible for about 30-40% of total hydrogen ion secretion from parietal cells.
What is the first pancreatic enzyme that is activated?
Trypsinogen, which becomes active enzyme trypsin
What happens when trypsinogen turns into its active form?
When the active form, trypsin, is achieved, catalyzes the reactions that convert the other pancreatic enzymes to their active forms, and activates additional trypsinogen as it is secreted by the pancreas. These enzymes catalyze reactions that digest proteins and polypeptides into oligopeptides and some free amino acids.
What happens when absorption in the large intestine is interrupted?
When this absorption is disrupted, as with bacterial or viral gut infections, dehydration as well as electrolyte and acid-base disturbances may result
What is the third set of molars called?
Wisdom teeth
What 2 muscles help our teeth masticate?
With the assistance of the masseter and temporalis muscles, the teeth masticate, or chew, ingested food, grinding it into smaller pieces.
Describe the portal venule of the portal triad
a branch of the portal vein
Define saliva
a fluid containing water, enzymes, mucus, and other solutes, through a duct into the oral cavity.
What is bile?
a liquid that contains multiple components, including water, electrolytes, and organic compounds.
What is the esophagus?
a muscular tube about 25 cm (10 in.) long found posterior to the trachea. -It transmits the bolus from the pharynx to the stomach.
Describe the bile duct of the portal triad
a small bile duct that carries bile
What is found at the center of the liver lobule?
a small central vein
Describe the gall bladder What does it receive and how?
a small sac that sits on the posterior liver, receives most of the bile from the common hepatic duct
Anything that increases or decreases the motility of the large intestine, also affects what?
affects the amount of water present in feces.
How is the muscularis externa of the alimentary canal different from the stomach?
alimentary canal usually has two layers of smooth muscle: an inner circular layer and an outer longitudinal layer. --there is an ADDITIONAL inner layer of smooth muscle in the stomach's body with its fibers oriented obliquely.
What is the importance of this oblique layer of smooth muscle in the stomach?
allows the stomach to perform churning , a motion that pummels the food into a liquid called chyme (KYME).
Describe Segmentation
also known as intestinal churning, involves contractions of only the circular layer of smooth muscle, which produces a squeezing motion (see Figure 22.16b). The primary functions of segmentation are mechanical digestion and mixing the chyme with intestinal and pancreatic enzymes as well as bile.
Why are the digestive enzymes secreted by the acinar cells important? What four things is it breaking down?
are crucial in chemical digestion and catalyze the reactions that digest carbohydrates, proteins, lipids, and nucleic acids.
Where are the microvilli found?
are found in the plasma membrane of the enterocytes -Each enterocyte has as many as 3000 microvilli, which gives the cell the appearance of a bristle brush, or brush border, on microscopic examination.
What is the oropharynx and laryngopharynx made up of? Importance of their composition
are lined with stratified squamous epithelium to protect them from abrasion by food
Why is the control of gastric emptying critical?
because the duodenum must mix the incoming chyme thoroughly before it moves to the rest of the small intestine.
What is the most potent stimulus for bile production and release?
bile, specifically bile salts
Describe Osmosis regarding the absorption of water
both the cytosol of the enterocytes and the extracellular fluid in the villi must be more concentrated than the fluid in the lumen of the intestine to drive water movement
How does the endocrine system regulate the digestive processes?
by secreting hormones
How does saliva function regarding chemical digestion?
by the actions of salivary amylase
What does the proximal large intestine consist of?
consists of the ascending and transverse colon
What does the serosa, or visceral peritoneum, of the large intestine contain?
contains fat-filled pouches known as epiploic appendages (ep-ih-PLOH-ik; epiploic = "membrane-covered"). -Their function is unknown.
Function of hepatopancreatic sphincter?
controls the emptying of bile and pancreatic fluids into the duodenum. **Recall that the contents of the hepatopancreatic ampulla then empty into the duodenum at the major duodenal papilla.
What does the distal large intestine consist of?
distal large intestine consists of the descending and sigmoid colon, rectum, and anal canal
Where do the central veins drain once they merge?
drain into the hepatic veins, which in turn feed into the inferior vena cava.
What are the cells of the small intestine?
enterocytes
What do the mucosa and submucosa contain?
esophageal glands (eh-sah′-fah-JEE-uhl) that secrete mucus to lubricate the bolus as it passes through the esophagus
Describe the Visceral Peritoneum
forms the outer tissue layer of such organs. formed when the parietal peritoneum folds on itself
Where and how is the tongue attached?
is attached to the floor of the oral cavity by a thin band called the lingual frenulum (LING-gwuhl; lingual = "tongue"), which prevents the tongue from moving too far posteriorly.
Describe the root
is embedded within the alveolus
What mediates the receptive relaxation?
is mediated by both the medulla (as part of the swallowing reflex) and the vagus nerve
What is secretin?
is released by duodenal cells in response to acid and lipids in the duodenum. -Secretin primarily triggers duct cells to secrete bicarbonate ions.
What is the intestinal phase responsible for?
is responsible for the remaining approximately 10% of acid secretion, after which further acid secretion is inhibited
What is the oral cavity? What is bounded by?
is the area posterior to the teeth and bounded by the palate and tongue
Describe the crown
is the visible portion above the gum line
Although the thick epithelium of the esophagus prevents any significant absorption from taking place, what does it accomplish?
it does protect the esophagus from abrasion by food
What mediates defecation reflex?
it is parasympathetic mediated
What is the primary function of the proximal large intestine?
it is the primary site of water and electrolyte absorption and bacterial activity
What is the mucosa of the large intestine rich in?
its mucosa is rich with goblet cells that secrete protective and lubricating mucus.
What are anal columns?
longitudinal grooves on the anal canal
Describe bile salts
main organic compound found in bile -Bile salts are amphiphilic
What are the smallest folds?
microvilli
What group of nerves is also responsible for regulating motility?
motility is regulated by a group of nerves known collectively as the enteric nervous system, or ENS
What is the enamel?
outer layers of hard mineralized substances -is composed almost fully of secreted calcium hydroxyapatite crystals with only a small amount of organic material. -This makes enamel the hardest substance in the body, allowing it to endure the forces that accompany chewing.
What happens to pancreatic secretion during eating? What two stimulations cause this?
pancreatic secretion rises due to parasympathetic and hormonal stimulation
Describe Peristalsis
peristalsis in the small intestine is accomplished by alternating contractions of the longitudinal and circular layers of smooth muscle in the muscularis externa (see Figure 22.16a). Its primary function is to propel chyme toward the ileum and ultimately through the ileocecal valve to the cecum
What do the cells of the small intestine/enterocytes produce?
produce multiple digestive enzymes, hormones, and mucus. These enzymes, along with those released by the pancreas, are responsible for the bulk of chemical digestion
What is the longest portion of the alimentary canal?
small intestine, almost 20ft long ( 6 meters)
What gives the peristaltic waves their strength?
stimulation from the vagus nerve and secretion of certain hormones for example, serotonin, which stimulates gastric motility. -Another hormone with the same effect is intestinal gastrin, which is produced by the duodenum.
What is the longest portion of the large intestine?
the colon, which is divided into four portions
Duct cells secrete bicarbonate ions, what is the function of this?
the duct cells secrete bicarbonate ions, a base, which make pancreatic juice alkaline. This helps to neutralize the acidic chyme that enters the duodenum from the stomach and protects the duodenum from damage by the acid.
Describe the duodenum
the initial segment of the small intestine -begins at the pylorus. The shortest of the three divisions, it is only about 25 cm (10 in.) long. -The duodenum arches into a "C" shape as it curves around the pancreas. Only the proximal portion of the duodenum is within the peritoneum; the remainder sits posterior to the peritoneal cavity and so is retroperitoneal. -Internally, the duodenum houses the major duodenal papilla , which is where secretions from the gallbladder and pancreas enter the small intestine. -The duodenal submucosa contains specialized glands called duodenal (Brunner's) glands, which produce an alkaline mucus to protect the duodenum from the acidic chyme.
Describe the Jejunum
the middle portion of the small intestine, -measures about 2.5 meters (7.5 feet) in length. -It begins at the duodenojejunal flexure and sits within the peritoneal cavity. -It is the most active site for chemical digestion and absorption.
Where do the organs of the alimentary canal receive innervation from?
the organs of the alimentary canal receive innervation from nerve plexuses of the ENS, including the submucosal and myenteric plexuses we introduced earlier in this module. These plexuses work together to control secretion from and motility of the alimentary canal.