A&P 2, Unit 4 Test, (Digestive system)
Gastrointestinal tract
"digestive tract or alimentary canal" Essentially, forms a continuous tube that includes: -the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestines, and ends at the anus.
Inferior esophageal sphincter
"gastroesophageal or cardiac sphincter" -is a contracted ring of circular smooth muscle at inferior end of esophagus -is not strong enough alone to stop materials from refluxing back into esophagus -instead muscles of diaphragm at esophageal opening contract to prevent this from happening (material coming from stomach back into esophagus)
Pacemaker cells
"interstitial cells or cajal) -in stomach wall spontaneously depolarize less than 4 time per min. and establish its basic rhythm of muscle contraction in this organ
Large intestine
"large bowel" -is a relatively wide tube that is significantly shorter than small intestine
Superior esophageal sphincter
"pharyngoesophageal sphincter" -is a contracted ring of circular skeletal muscle at superior end of esophagus -it is the area where the esophagus and pharynx meet -closed during inhalation, so air enters larynx and trachea not esophagus
Chief cells
"zymogenic cells or peptic cells" -are the most numerous secretory cells within gastric glands -produce and secrete packets of zymogen granules mainly containing pepsinogen
Exocrine cells of pancreas
(acinar cells) produce pancreatic juice to assist with digestive activities
Mechanical digestion (mastication)
(chewing) Requires coordinated activities of the: -teeth, skeletal muscle of lips, tongue, cheeks, and jaw, that are controlled by nuclei withing medulla oblongata and pons called mastication center.
Gastroileal reflex
(have both short and long reflexes that involve the medulla oblongata) -is initiated by food entering the stomach
Oral cavity in divided into quadrants, each would have:
-2 incisors -1 canine -2 premolars -3 molars
Six general function of digestive system
-Ingestion (solid and liquid nutrients in mouth, 1st step) -Motility (voluntary and involuntary muscular contraction, for moving materials in GI tract) -Secretion (produce and release digestive enzymes, acid, bile, etc. in GI tract) -Digestion (breakdown of food into smaller structures to be absorbed in GI tract) -Absorption (involves membrane transport of vitamins, water, etc. from GI tract to blood and lymph. -Elimination (expulsion of indigestible components that are not absorbed)
Nerve signals relayed along motor neurons to effector, cause the following to occur:
-bolus enters oropharynx -elevation of soft palate and uvula block passageway (from oropharynx to nasopharynx) causing epiglottis to cover laryngeal opening (preventing entry to trachea) -also nerve signals sent to respiratory center in medulla oblongata to assure a breath is not taken during swallowing.
Chemical digestion of carbohydrates, consists of
-breakdown of starch into individual glucose molecules -breakdown of disaccharides into individual monosaccharides that compose them
Carbohydrate digestion
-carbohydrates are organized based upon the number of repeating units of simple sugars Classified as: -monosacchardies (glucose, fructose, and galactose) -disaccharids (sucrose, maltose, and lactose_ -polysaccharides (starch and cellulose)
We have 3 phases of secretory activity, which include:
-cephalic phase -gastric phase (both involves events before and during a meal) -intestinal phase (involves events after a meal, ingested food being digested)
HCl has several function in digestive process
-converts inactive enzyme pepsinogen into active pepsin and provides optimal pH environment -kills most microorganisms that enter stomach, due to low pH -contributes to breakdown of plant cell walls and animal CT -denatures proteins, causing them to unfold, thus facilitating chemical digestion by enzymes
Carbohydrate breakdown in oral cavity
-digestion of starch begins in oral cavity It's catalyzed by salivary amylase -that's synthesized and released from salivary glands
Small intestine has 3 specific segments
-duodenum -jejunum -ileum
Individual mesenteries include:
-greater omentum -lesser omentum -falciform ligament -mesentery proper "mesentery" -mesocolon
Upper gastrointestinal tract
-is where initial processing by both mechanical and chemical means takes place Consist of: -oral cavity and salivary glands -pharynx -esophagus -stomach -duodenum
The mucosa of the stomach has three significant features, which include:
-lined by simple columnar epithelium supported by lamina propria -lining indented by numerous depressions called gastric pits -several gastric glands extend deep into mucosa from the base of each gastric pit The muscularis mucosa helps expel gastric gland secretions when it contracts.
Oral cavity and salivary glands
-mechanical digestion (mastication) begins here -saliva secreted from salivary glands in response to food being present in oral cavity. -mixed with ingested materials to form wet mass called a bolus
These components, salivary amylase, mucin, and lysozyme permit saliva to participate in various functions:
-moistens ingested food as it forms a bolus (easy swallowing) -initiates chemical breakdown of starch in oral cavity (salivary amylase) -acts as watery medium, so taste receptors may be stimulated -cleanses the oral cavity structures -helps inhibit bacterial growth because it contains antibacterial substances (lysozyme and antibodies (IgA)).
Voluntary reflex
-of feces from body is learned sometime after 3 years. -conscious decision to defecate involves both the valsalva maneuver and relaxation of the external anal sphincter
Fauces
-represent openings between oral cavity and oropharynx Bounded by paired muscular folds -palatoglossal arch (anterior fold) -palatopharyngeal arch (posterior fold) Tonsil are housed in these folds -known as early line of defense
Accessory digestive glands produce secretions that empty into the GI tract and include:
-the salivary gland -the liver -the pancreas Others beside glands, include: -the teeth and tongue (chewing and swallowing food) -the gallbladder, which concentrates and stores the secretions of the liver
Organization of digestive system, has 2 separate categories of organs
-those composing the GI tract AND -the accessory digestive organs
Accessory organs and ducts
3 accessory digestive organs release secretion into duodenum: -the liver, gallbladder, and pancreas
Pharynx is formed by
3 skeletal muscle pairs called the superior, middle, and inferior pharyngeal constrictors
Gastric secretions
5 types of secretory cells of gastric epithelium are integral contributors to the process of digestion -first 4, produce 3L/day of gastric juice, associated with the stomach -last one, secretes a hormone into the blood
An infant has 20 deciduous teeth (milk teeth) erupt between
6 months and 30 months after birth -these teeth are eventually lost and replaced by 32 permanent teeth
Esophageal phase
Also involuntary -time when bolus passes through esophagus into stomach (5-8 sec.) -peristaltic waves of muscle contracts to assist in propelling bolus toward the stomach
Hard palate
Anterior 2/3 portion of palate -formed by the palatine processes of maxillae and the horizontal plates of the palatine bones -exhibits prominent transverse palatine folds "friction ridges" that assist the tongue in manipulating ingested materials prior to swallowing.
Small intestine secretions
Between intestinal villi are invaginations of the mucosa called intestinal glands (intestinal crypts of lie berkiihn) -they secrete intestinal juice -extend to base of mucosa and resemble anatomy of gastric glands of the stomach
Stomach
Bolus is mixed with gastric secretions as smooth M. contracts
Pharynx
Bolus moves into pharynx, where swallowing occurs -mucous secreted here provided lubrication to facilitate swallowing
Esophagus
Bolus transported from pharynx through esophagus into stomach -mucus secretion here lubricate passages for bolus
Trypsin and chymotrypsin
Break bonds between specific amino acids within the protein to produce smaller strands amino acids called peptides
Bacterial action (in large intestine) produce
CO2, H+, hydrogen sulfide, methane, indoles, and skatoles (some of these account for the odor of feces) ALSO -produce vitamins B and K from bacterial flora, which then are absorbed from large intestine into blood
Stomach is composed of
Cardia (entryway into stomach lumen from esophagus) -where cardia meets esophagus is called the cardiac orifice, located at the cardiac sphincter Fundus (dome-shaped region lateral and superior to esphageal connection to stomach) -weaker contractions and higher pH Body (largest region of stomach) -extends to pylorus Pylorus (funnel-shaped terminal region of stomach) -opening to duodenum of small intestine is called the pyloric orifice, which is surrounded by pyloric sphincter (circular smooth M)
Within the right lobe there are two lobes
Caudate lobe -adjacent to IVC Quadate lobe -adjacent to gallbladder
Intestinal phase involves intestinal reflex and release of two significant hormones, which include:
Cholecystokinin (CCK) and secretin
Lamina propria
Consists of a layer of areolar tissue that contains small blood vessels and nerves -substances are absorbed in blood and lymphatic capillaries located here.
Two sets of teeth develop and erupt during a normal lifetime, they are called
Deciduous and permanent teeth
Brush border enzymes
Dipeptidase -breaks the final bond between 2 amino acids of a dipeptide, so they both may be absorbed Aminopeptidase -generates free amino acids from amino end of peptides
Histology of oral cavity
Epithelial lining is stratified squamous epithelium that protects against abrasion activities associated with mechanical digestion. Nonkeratinized type -lines most of mouth Keratinized type -lines lips, portions of tongue and small region of hard palate
__________ is the final product ___________ and eliminated from ________ tract
Feces Formed GI
Epithelium
For stomach, small intestine, and large intestine it is simple columnar epithelium -allows for secretion and absorption The esophagus that must withstand abrasions has nonkeratinized, stratified squamous epithelium
Duodenum
Forms the first segment of small intestine -originates at pyloric sphincter It's arched into a c-shape around the head of the pancreas and becomes continuous with jejunum at duodenojejunal flexure -most is retroperitoneal, except initial portion
In last portion of ileum bile salts are recovered from
GI tract back into blood by active transport and recycled to liver for reuse -new bile salts are synthesized by hepatocytes to replace those lost during elimination of feces
Hormonal control: three primary hormones participate in regulation of the processes of digestion:
Gastrin -released from stomach Secretion and Cholecystokinin -released from small intestine
Two major reflexes associated with motility
Gastrocolic reflex -initiated by stomach distension to cause mass movement Defecation reflex (elimination of feces through GI tract by process of defection) -filling of the rectum initiates urge to defecate -which causes transmission of nerve signals from receptors to spinal cord In response: -increased nerve signals are along cells of salivary glands called parasympathetic motor neurons Which causes both sigmoid colon and rectum to contract and the internal (involuntary) anal sphincter to relax
Serous membrane (two types)
Greater omentum -extends inferiorly from greater curvature of stomach, forming the fatty apron that covers anterior surface of abdominal organs Lesser omentum -extends superiorly from lesser curvature of stomach and duodenum to the liver
Secretions produced by epithelial cells of stomach mucosa include:
HCl, digestive enzymes, and mucin -the mixing continues as acidic "puree" called chyme is formed.
Pancreas has three parts
Has a wide head -adjacent to the curvature of the duodenum Center, elongated body -projecting toward the left lateral abdominal wall A tail -that tapers as it approaches the spleen
Muscularis has 2 layers, which include:
Inner circular layer -inner layer of smooth M., oriented circumferential within GI tract wall Outer longitudinal layer -outer layer of smooth M., oriented lengthwise within GI tract wall
Gastric phase
Involves processes following the bolus reaching the stomach -regulated by both the nervous system via gastric reflex and endocrine system through release of gastrin hormone
Intestinal phase
Involves the processes following the chyme reaching the small intestine -a phase regulated by both nervous system and endocrine system
Descending colon
Is retroperitoneal and located along the left side of abdominal cavity and slightly posterior -originates at left colic flexure and descends vertically to sigmoid colon
Gross anatomy of pancreas
It's a retroperitoneal organ that extends horizontally from duodenum towards the left side of abdominal cavity, where it has contact with the spleen
Lipid digestion
Lipids are highly variable structures that contain different arrangements of their building blocks -they are NOT water-soluble
The areolar CT of lamina propria in mucosa and submucosa house...
MALT -prevents ingested microbes from crossing GI tract wall and entering body
Digestion has two types:
Mechanical -occurs when ingested material is physically broken down into smaller units by chewing and mixing without changing their chemical structure. Chemical -involves activity of specific enzymes to break chemical bonds to change larger complex molecules into smaller molecules that can be absorbed.
Segmentation
Mixes chyme with accessory gland secretions through a "backward-and-forward" motion
GI tract wall tunics, from innermost to outermost, include:
Mucosa -composed of epithelium, lamina propria, and muscularis mucosae Submucosa -composed of areolar and dense irregular CT Muscularis -contains 2 layers of smooth muscle Adventitia or serosa -composed of areolar CT OR visceral peritoneum
Two types of secretory cells are housed within salivary glands, which include:
Mucous cells -secrete mucin, which forms mucous upon hydration Serous cells -secrete a watery fluid containing electrolytes and salivary amylase
Gross anatomy of stomach
Muscular J-shaped organ Has both a -greater curvature (large convex inferolateral surface) -lesser curvature (small convex superomedial surface)
No _____ enzymes for ______________ digestion are introduced in the _________.
New Carbohydrate Stomach
Carbohydrate breakdown in small intestine
Pancreatic amylase -is synthesized and released by the pancreas as a component of pancreatic juice into small intestine through main or accessory pancreatic duct This enzyme continues digestion of starch into shorter strands of glucose (oligosaccharides), maltose (disaccharide) and individual glucose molecules.
Serous membrane of abdominal cavity, has two membranes:
Parietal peritoneum -the serous membrane that lines the inner surface of the abdominal wall Visceral peritoneum -the portion of serous membrane that reflects over and covers the surface of the internal organs
The portion of mucous and serous cells varies among the 3 types of salivary glands..
Parotid glands only produce serous secretions Submandibular and sublingual glands produce both types of secretions
Motility and regulation (several types of movement in large intestine)
Peristalsis -is usually weak and sluggish Haustral churning -occurs after a relaxed haustrum fills with digested or feces until its distension stimulates reflex contraction in muscularis -contraction, increases churning and move material to more distal haustra Mass movement -are powerful, peristaltic-like contractions involving teniae coli, which propel feces toward rectum -generally, occurs 2 to 3 times a day, often during or right after a meal
Two primary types of motility
Peristalsis -propel ingested material through GI tract Mixing -blends ingested material with secretions within GI tract
Soft palate
Posterior 1/3 portion of palate -uvula extends off here, interiorly
Cephalic phase
Primarily involves the cephalic reflex -which is a nervous system reflex initiated by thought, smell, sight, or taste of food
Mesentery
Refers to the double layer of peritoneum that supports, suspends, and stabilizes the intraperitoneal GI tract organs. -blood and lymph vessels and nerves that supply GI tract are sandwiched between the 2 folds.
Components of saliva
Salivary amylase, enzyme that initiates chemical digestion of starch (amylase)
Overview of lower GI tract organs:
Small intestine -is divided into 3 continuous regions (duodenum, jejunum, and ileum) -receives chyme from stomach that is mixed with accessory organ secretions -most chemical digestion and absorption occur here Accessory organs (secretions) -include bile and pancreatic juice Large intestine -continues absorption, primarily of water, electrolytes, and vitamins (B and K produced by bacteria here)
Motility of small intestine
Smooth M. activity in small intestine wall has 3 functions: -mixing chyme with accessory gland secretions -moving chyme continually against new areas of brush border -propelling the contents through small intestine toward large intestine All of these function facilitate chemical digestion and absorption, employing processes of segmentation and peristalsis
muscularis mucosae
Thin layer of smooth muscle deep to lamina propria -gently shakes things up
Two major ingested lipids are
Triglycerides (neutral fats) -composed of glycerol molecule and 3 fatty acids bonded to the glycerol -enzymes are required to break the bond between the glycerol and fatty acids Cholesterol -digestion of this is NOT required for its absorption
Gross anatomy of oral cavity: has two distinct spatial regions
Vestibule (buccal cavity) -which is the space between gums, lips, and cheeks Oral cavity proper -which lies central to teeth
Saliva
Volume secreted daily ranges between 1 and 1.5 L -composed of 99.5% water and a mixture of solutes
Gross anatomy of pharynx
a funnel-shaped, muscular passageway with distensible lateral walls that serves as the passageway for both air and food
Lacteal
a type of lymphatic capillary within villus -responsible for absorbing lipids and lipid-soluble vitamins that are too large to be absorbed by blood capillary
Only the last 1.5cm of esophagus is located in the
abdominal cavity -rest is in the thoracic cage
Free amino acids are
absorbed across small intestine epithelial lining and enter into the blood
Intestinal reflex is initiated with entry of
acidic chyme in the duodenum -which causes a decrease in nerve signals relayed to medulla oblongata -results in a decrease of vagal stimulation which decreases motility and secretory activity of stomach
The mucous neck cells produce an
acidic mucin -that helps maintain the acidic conditions resulting from secretions of HCl by parietal cells
Trypsin
activates additional molecules of trypsinogen to trypsin, as well as, chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase
Enteropeptidase
activates trypsinogen to trypsin
Outermost tunic is the
adventitia or the serosa
Gross anatomy of small intestine
also called the small bowel -extends from the pylorus of the stomach to cecum of large intestine -occupying a significant portion of abdominal cavity
Bile salts are
amphipathic molecules composed of a polar head and a nonpolar tail -the nonpolar tail position themselves around the fat of polar heads next to aqueous fluid in lumen -this structure is called a micelle
Submucosa layer of small intestine
another gland housed here and found only in the proximal duodenum is called a submucosal or duodenal gland (Brunner gland) -produces viscous, alkaline mucous secretion that protects the duodenum from the acidic chyme
Blood vessels and nerves housed in the pulp pass through the...
apical foreman
Submandibular gland
are both infereior to the floor of oral cavity and medial to body of mandible -produces most saliva (60-70%)
Gingivae (gums)
are composed of dense irregular CT -with overlying nonkertinized stratified squamous epithelium that covers the alveolar processes of upper and lower jaws and surrounds neck of teeth
Microvilli
are extensions of the plasma membrane of the simple columnar epithelial cells lining the small intestine -further increases SA of small intestine -appear as a fuzzy edge of the simple columnar cells called the brush border
Sublingual salivary gland
are inferior to the tongue, and medial and anterior to submandibular salivary glands -each one extends multiple tiny sublingual ducts that open onto inferior surface of oral cavity, posterior to submandibular duct papilla -contribute only 3-5% of total saliva
Villi
are larger and most numerous in the jejunum -the epithelium and lamina propria of each villus appears analogous to a glove (epithelium) covering a finger (lamina propria) -each one contains an arteriole, rich capillary network and a venule (capillary absorbs most nutrients)
Mucous neck cells
are located immediately deep to the base of gastric pits and interspersed among the parietal cells
Parietal cells (oxyntic cells)
are responsible for two substances in the lumen of the stomach
Parotid salivary glands
are the largest salivary glands -each one is located anterior and inferior to the ear, overlying massester muscle. -produce 20-25% of saliva, which is transported through parotid duct to oral cavity -infection in parotid glands causes mumps
Molars
are the thickest and most posterioly placed teeth -have large, broad, flat crowns with distinctive cusps and 3 or more roots -adapted for grinding and crushing ingested materials
Teniae coli
are thin, distinct, longitudinal bundles of smooth muscle -act like elastic in a waistband -they can bunch up the large intestine into many sacs, collectively called haustra
Hepatic sinusoids
are thin-walled capillaries with large gaps between these cells, which make the sinusoids more permeable than other capillaries
Mucosal and submucosal tunics of small intestine
are thrown into internal circular folds "plicae circlares" -that extend inward toward the lumen -they help increase the SA through which nutrients are absorbed
Chylomicrons
are too large to pass through blood capillary walls, so they enter the lacteals, the lymphatic capillaries of the small intestine
Intrinsic salivary glands
are unicellular glands that continuously release small amounts of secretions independent of presence of food -only secretions from here contain lingual lipase, an enzyme that begins the digestion of triglycerides.
Hepatic portal vein
as part of the hepatic portal system -transports deoxygenated and nutrient-rich blood from the capillary beds of the GI tract, spllen and pancreas (brings about 75% of blood volume to the liver)
Accessory digestive organs
assist in the breakdown of food
The hepatopancreatic sphincter is
associated with hepatopancreatic ampulla that regulates movement of bile (liver/gallbladder) and pancreatic juice (pancreas) into duodenum
The gallbladder is
attached to the inferior surface of the liver -also called the cholecyst
If we eat spoiled food
bacterial toxins send sensory nerve signals to salivary nuclei
Protein breakdown in stomach
begins with enzyme pepsin
Tactile sensory receptors are simulated by the
bolus and sends nerve signals along sensory neurons to swallowing center in medulla oblongata
After food and saliva mix, a..
bolus is formed from chewing and manipulated and mixed by the tongue (pushed superiorly against hard palate) -transverse palatine folds help direct bolus posteriorly towards the oropharynx.
Muscular contraction by stomach wall are regulated by
both nervous reflexes and hormones -which alter force, not rate of contraction, which is constant -secretory activity of gastric glands is also altered
Salivary amylase
breaks chemical bonds between glucose molecules within the start molecule -to partially digest starch It's inactivated by the low pH of the stomach when the bolus is swallowed -typically, occurs within 15 to 20min after bolus enters stomach (larger meals means longer salivary amylase remains active).
With the GI tract food is..
broken down into smaller components that can then be absorbed along its lenth.
Lactase and sucrase are
brush border enzymes
Completion of starch breakdown is accomplished by
brush border enzymes embedded within epithelial lining of small intestine These enzymes include: Dextrinase and glucoamylase -breaks bonds between glucose subunits of oligosaccharides Maltase -breaks bonds between 2 glucose molecules that compose maltose.
All nucleic acid components
building blocks are absorbed across the epithelium of small intestine into the blood These include: -phosphate, the sugar (ribose or deoxyribose) and the nitrogenous bases (thymine, adenine, guanine, cytosine, and uracil).
Amino acids can be used as
building blocks of new protein cells OR converted to glucose or deminated and used as fuel for cellular respiration.
Bile is produced
by the liver and then stored, concentrated and released by the gallbladder
Glucose
can become part of blood glucose -be taken up by any cell to be oxidized, through cellular respiration -can be taken up liver cells and muscle cells and synthesized into glycogen and stored, or converted into fat (triglycerides) and stored in adipose CT
Oral cavity and small intestine are the mains sites of
carbohydrate digestion
Chyme enter ________ for ileum
cecum
Each root of a tooth in ensheathed within hardened material called
cementum
Pulp cavity
center of tooth -contains connective tissue called pulp
Bacteria (in large intestine) is responsible for
chemical breakdown of complex carbohydrates, proteins, and lipids that remain in chyme after passing small intestine
Pepsin
chemically digests denatured proteins in stomach into smaller peptide fragments Also produce gastric lipase -an enzyme that has a limited role in fate digestion (10-15%)
Input to salivary nuclei is received from..
chemoreceptors or mechanoreceptors in upper GI tract -these receptors detect various types of stimuli -introduces substances in oral cavity (acidic- lemons) and arrival of foods into stomach lumen (spicy or acidic)
Tongue helps mix ingested materials during
chewing and assists in the development of mechanical digestion -also swallowing and speech production
The golgi apparatus packages
chylomicrons into secretory vesicles -these vesicles then merge with plasma membrane of epithelial cells to release chylomicrons by exocytosis
Superior and inferior esophageal sphincters are normally..
closed at rest -when bolus is swallowed, they relax to allow bolus through esophagus -then the inferior sphincter contracts after bolus is through, to prevent reflux of material from stomach back into esophagus.
External anal sphincter generally..
closes off the opening to the anal canal
Teeth
collectively known as dentition
The mesocolon, attaches each section of the..
colon to the posterior abdominal wall
Union of cystic duct from gallbladder and common hepatic duct forms the
common bile duct -that extends inferiorly through pancreas to open into duodenum
The watery chyme that first enters large intestine, soon solidifies and is...
compacted into feces (all the undigested materials) -large intestine then stores this fecal material until it's eliminated through defecation.
Muscularis of stomach
composed of 3 smooth M. layers (instead of 2) -an inner oblique layer -middle circular layer -an outer longitudinal layer (presence of this layer helps the churning and blending of the bolus to help mechanically digest the food).
Adventitia
composed of areolar CT with dispersed collagen and elastic fibers -associated with portion of GI tract outside peritoneal cavity
At periphery of each lobule are several portal triads
composed of bile ductule and branches of both hepatic portal vein and hepatic artery
Pharynx and esophagus
connect the oral cavity to the stomach
Lesser omentum
connects superomedial surface of stomach and proximal end of duodenum to the liver
Absorption from stomach is limited to small, nonpolar substances that are in..
contact with the mucosa of the stomach Ex.) -aspirin and alcohol are absorbed from the stomach
Internal lining of anal canal
contains thin longitudinal ridges called anal columns between which are small depressions called anal sinuses
Lower gastrointestinal tract
continues the processes of digestion and importantly functions in the absorption of nutrients -material that cannot be digested and absorbed is then eliminated
The result of the autonomic motor output is
coordinated secretory and smooth muscle contraction involved in digestive responses. -known as long reflexes
A tooth has an exposed..
crown, a constricted neck and one or more roots that anchor it to the jaw
Swallowing is called
deglutition -it is the process of moving ingested materials from the oral cavity to the stomach 3 phases: -voluntary phase -pharyngeal phase -esophageal phase
Baroreceptors
detect either stretch or pressure of a particular region of GI tract as content moves through.
Chemoreceptors
detect the pressure of specific substances (H+, fatty acids) of the passing contents within the lumen.
Lipid absorption
digested triglycerides (monosaccharide and free fatty acids), cholesterol, other lipids (lecithin) and fat-soluble vitamins are contained within micelles
Pancreatic lipase
digests each triglyceride into a monoglyceride and 2 fatty acids -because triglyceride are lipids and don't dissolve in luminal fluids of digestion system, they form large lipid masses
Lactase
digests lactose to glucose and galactose
Sucrase
digests sucrose to glucose and fructose
At the center of each lobule is a central veins that
drains the blood flood from the lobule
When we shallow the soft palate and uvula....
elevate to close of posterior entrance to nasopharynx and prevent ingested materials from entering nasal region.
External surface of dentin is a tough, durable layer of..
enamel that forms the crown of the tooth
G cells are
enteroendocrine cells -that are widely distributed in the gastric glands of the stomach -secrete gastrin hormone into blood
Embedded in the brush border are various
enzymes that complete the chemical digestion of most nutrients right before absorption -collectively, these are called brush border enzymes
Parotid ducts
extends from gland, across massester muscle and opening in vestibule near the second upper molar.
Greater omentum
extends inferiorly like an apron from inferolateral surface of stomach and covers most abdominal organs -accumulates large amounts of adipose CT (fatty apron)
Process of emulsification is
facilitated by lecithin -a phospholipid molecule in bile
So, cellulose with other indigestible substances is
fiber that adds "bulk" to the contents of the lumen and facilitates it's moving through the GI tract
Submucosal nerve plexus (meissner plexus) are
fine branches of nerves that extend into mucosa and along with their associated autonomic ganglia. -innervated both by smooth muscle and glands of mucosa and submucosa
The more anteriorly placed permanent teeth tend to appear..
first, followed by posterior ones (exception is the first molar- 6 years old)
Roots
fit tightly into dental alveoli, which are sockets within alveolar processes of both the maxillae and mandible
Cheeks terminate at the..
fleshy lips (or labia) that are formed primarily by orbicularis oris muscle -reddish color due to superficial blood vessels.
Inferior surface of the tongue attaches to the
floor of the oral cavity by a thin vertical mucous membrane, the lingual frenulum.
At the neck of the gallbladder, a sphincter valve controls the
flow of bile into and out of gallbladder -bile enters gallbladder when hepatopancreatic sphincter is closed
Mesocolon
fold of peritoneum that attaches parts of the large intestine to the posterior abdominal wall -several distinct sections and names
Mesentery proper "mesentery"
fold of peritoneum that suspends most of small intestine (jejunum and ileum) from the internal surface of the posterior abdominal wall.
Gastric reflex initiated as
food enters stomach -baroreceptors in stomach wall detect a stretch in wall -chemoreceptors detect both protein and an increase in pH of gastric contents (protein buffer H+ and increase pH)
Enteric nervous system
formed of both the submucosal and mysenteric nerve plexus -sensory neurons within these plexuses detect both changes in GI tract wall (stretch) and chemical makeup of the contents of the lumen -composed of both motor neurons and visceral sensory neurons.
Tongue
formed primarily from skeletal muscle -both extrinsic and intrinsic muscles move the tongue -numerous small projections called papillae covers superior surface and involved in taste.
Palate
forms superior boundary or "roof" of mouth and acts as a barrier to separate it from the nasal cavity.
Dentin
forms the primary mass of a tooth -comparable to bone but harder
Gastrointestinal tract wall
from esophagus through large intestine, the GI tract is a hollow tube composed of four tunics
Concentrated bile is transported from
gallbladder through cystic duct and then the common bile duct through the hepatopancreatic ampulla into the duodenum
The cystic duct connects the
gallbladder to the common bile duct
Both CCK and secretin inhibit the release of
gastrin -slowing down the emptying of stomach, allowing small intestine to continue digestive processes before more chyme is added (both also influence digestive processes in lower GI tract)
Presence of food (protein) in stomach causes release of
gastrin from enteroendocrine cells
The internal surfaces of both the superior and inferior lips are attached to the..
gingivae (gums) -by thin mucosa folds in the midline called the labial frenulum.
Collectively, the roots, dental ligament, and periodontal liagment that binds the roots to alveolar processes form a..
gomphosis joint
Pancreas
has both endocrine and exocrine functions
Chyme
has consistency of a paste like soup
Inferior surface of liver
has structures that form the letter H -the gallbladder and round ligament of liver form the vertical superior part of the H and the IVC and ligamentum venosum form the vertical inferior parts
Muscularis of cecum and colon
have 2 layers of smooth muscle -but the outer longitudinal layer is discontinuous and instead it forms the teniae coli
The simple cuboidal epithelial cells lining pancreatic ducts
have the important function of secreting alkaline HCO3- fluid
Venous blood of hepatic portal system and arterial blood are mixed within..
hepatic sinusoids and then slowly flow to central vein -nutrients absorbed from here enter hepatocytes
Within hepatic lobules are liver cells called
hepatocytes
The common bile duct becomes the
hepatopancreatic ampulla (ampulla of vater) -which is a swelling either adjacent to or within the posterior duodenal wall
Input is also received by salivary nuclei from..
higher brain centers in response to thought, smell, or sight of food
Nerve signals from higher brain regions of the brain are sent to the
hypothalamus -where it relays signals to medulla oblongata
Absorption of digested materials continues in the
ileum of the small intestine
Canines
immediately, posterolateral to incisors -have a pointed tip for puncturing and tearing food
Medulla oblongata
increased parasympathetic stimulation of the stomach via vagus nerve (vagal stimulation) -which causes both an increase in contractile force in gastric wall (increases motility) and secretory activity of gastric glands (when stomach "growls")
Digestion of protein releases
individual amino acids so that the amino acids may be absorbed into the blood and transported to cells for the synthesis of new proteins
Cheeks are covered externally by the..
integument and contain the buccinator muscles -which compress cheeks against teeth to hold solid materials in place while chewing.
Blood from branches of the hepatic artery and hepatic portal vein mixes as it passes
into and through hepatic lobules
Both jejunum and ileum are
intraperitoneal and suspended within abdomen by the mesentery proper
Cecum and vermiform appendix are
intraperitoneal organs
At base of anal canal are the
involuntary smooth muscle, internal anal sphincter and voluntary skeletal muscle, external anal sphincter -muscles of these sphincters relax and allow them to opening when defecating.
Regulation of digestive system processes
involves receptors that monitor changes associated with the GI tract and its contents -stimulation of these receptors brings about both nervous system and hormonal responses
Cecum
is a blind sac -first portion of large intestine and located in the right lower abdominal quadrant -extends inferiorly from ileocecal valve
Hepatic artery
is a branch of the celiac trunk that extends off the aorta and transports oxygenated blood to the liver
Cellulose
is a carbohydrate that is a component of plant cell walls -it's not chemically digested because we lack the enzymes required to break bonds between its glucose molecules.
Gastric mixing
is a form of mechanical digestion that changes the semi-digested bolus into chyme
Stomach
is a holding sac in the superior left quadrant of the abdomen immediately inferior to the diaphragm -between 3-4L of food, drink, and saliva enter the stomach daily and spend between 2-6 hours there, depending on amount an composition of ingested materials. -mixes and mechanically digests into a semifluid mass called chyme.
Cholecystokinin (CCK)
is a hormone released from small intestine primarily in response to free fatty acids in chyme
Small intestine
is a long tube that is inferior to stomach and located medially within abdominal cavity -finishes chemical digestion and is responsible for absorbing almost all of the nutrients and a large percent of water and electrolytes
Biliary apparatus
is a network of thin ducts that include the left and right hepatic ducts, which drain the left and right lobes of the liver
Gross anatomy of esophagus
is a normally collapsed, tubular passageway -begins at about the level of the cricoid cartilage of the larynx -this tube is directly anterior to the vertebral bodies, unti it passes diaphragm
Gallbladder
is a saclike organ that stores, concentrates, and releases bile that the liver produces
Cholesterol
is also within the micelle -but not chemically digested No brush border enzymes are required in the breakdown of triglycerides
Liver
is an accessory digestive organ -located in the right upper quadrant of abdomen, immediately inferior to diaphragm
Pancreatic juice
is an alkaline fluid containing mostly water, HCO3-, and a versatile mixture of digestive enzymes These enzymes include: -pancreatic amylase to digest starch -pancreatic lipase for digesting triglycerides -inactive proteases that when activated digest proteins -nucleases for the digestion of nucleic acids (DNA/RNA)
Nucleotide monomer
is composed of 3 components: -sugar (deoxyribose or ribose) -a phosphate group -a nitrogenous base They are not essential nutrients but digested by specific enzymes of the digestive system.
Root canal
is continuous with pulp cavity and opens in the CT surrounding the tooth through an opening called the apical foreman
Sphincter
is formed by inner circular muscle layer thickening at several locations along GI tract -contraction of circular muscle will constrict the lumen -contraction of longitudinal layer will shorten tube (think of it as a hollow tube)
Pepsin
is formed from pepsinogen, an inactive precursor released by chief cells -HCl that's released from parietal cells causes a low pH in stomach that activates pepsinogen into pepsin, and denatures proteins
Breakdown of nucleotide's
is further accomplished by brush border enzymes embedded in epithelial lining of small intestine These enzymes include: Phosphatase -which breaks the bond holding the phosphate to the rest of nucleotide Nucleosidase -which breaks the bond between the sugar and nitrogenous base of the nucleoside (which is a molecule without the phosphate), releasing the sugar and nitrogenous base
Secretin
is released from small intestine primarily in response to an increase in chyme acidity
Carboxypeptidase
is resticted to breaking the bonds only between an amino acid on the carboxyl end and the remaining protein (it releases an amino acids one at a time) -break down products of this are dipeptides and free amino acids
The oral cavity (mouth)
is the entrance of the GI tract -food is ingested and undergoes mechanical and chemical digestion
Enamel
is the hardest substance in the body -primarily composed of calcium phosphate crystals
Pepsinogen
is the inactive precursor of proteolytic enzyme pepsin -pepsin must be produced from inactive form to prevent destroying the chief cell proteins
Rectum
is the third major region of the large intestine -it's a retroperitoneal structure that extends from sigmoid colon -It's a muscular tube that readily expands to store accumulated feces prior to defecation.
Function of bile salts
is to emulsify fats so that pancreatic lipase has greater "access" to triglyceride molecules and may more effectively chemically digest fat molecules
Histology of pancreas
it contains modified simple cuboidal epithelial cells called acinar cells that are arranged in saclike acini -these cells organized in larger clusters are called lobules.
Liver secretes bile..
it's a yellowish green alkaline fluid contain mostly water, bicarbonate ions (HCO3-), bile salts (formed from cholesterol), bile pigments (bilirubin), cholesterol, lecithin (a phospholipid), and mucin
Pepsinogen is activated following
it's release in the stomach -by HCl and other active pepsin molecules
Many lymphatic nodules and lymphatic cells occupy
lamina propria of large intestine
Gross anatomy of large intestine
large intestine originates at the ileocecal junction to it's termination at the anus. 3 major regions -cecum, colon, and rectum
For pancreatic lipase to effectively digest fat, the
large lipid droplets must first be mechanically separated into smaller droplets -this process in known as emulsification
Ileum
last region of small intestine (3/5 of small intestine) -it's distant end terminates at the ileocecal valve, which is a sphincter that controls the entry of materials into the large intestine.
Retroperitoneal organs
lie outside the parietal peritoneum directly against the posterior abdominal wall -so only the anterolateral portions are covered with the parietal peritoneum
Cross section of hepatic lobule
likes like a bicycle wheel -central vein is the hub of the wheel -where tires would be are the portal triads -cords of hepatocytes make up the spokes of the wheel and are bordered by the hepatic sinusoids
Surface mucous cells
line the stomach lumen and extend into the gastric pits -secrete alkaline product containing mucin on gastric surface -once hydrated it is mucous (1-3mm layer thick)
Once, lipids are in the stomach triglycerides undergo digestion by both..
lingual and gastric lipase -these "acidic lipases" digest 30% of triglycerides to diglyceride and a fatty acid Neither of these lipase enzymes require bile salts
Lipid breakdown in stomach
lingual lipase (produced by intrinsic salivary glands in mouth) -is a component of saliva in oral cavity It's not activated until it reaches stomach
Posterioinferior region of the tongue lies the...
lingual tonsils
Duodenum is attached to the
liver by the lesser omentum
Gross anatomy of liver
liver is the largest internal organ (2% of body weight) -covered by a CT capsule except at the porta hepatis -covering this capsule is a layer of visceral peritoneum, except for the small region on the diaphragmatic surface known as the bare area.
Duodenum receives accessory organ secretions from
liver, gallbladder, and pancreas -and chyme from the stomach
Liver is composed of four primarily separated
lobes and is supported by two ligaments
Hanging off external surface of haustra are
lobules of fat called omental appendices (epiploic appendages)
Some digestive reflexes do not involve CNS, instead they are..
local and occur only within neurons of enteric nervous system -housed within the GI tract wall -known as short reflexes
Premolars
located posterolateral to canines and anterior to molars -have flat crowns with prominent ridges called cusps that are used to crush and grind ingested materials -may have 1 to 2 roots
The GI tract is _________ in a cadaver (30ft) and __________ in a living person, due to smooth muscle tone.
longer shorter
HCl is responsible for..
low pH (1.5-2.5) in stomach EX.) -vomiting increases HCl which results in an increase in HCO3- in the blood, which increases blood pH -extensive vomiting leads to metabolic alkalosis
Mucus produced by both mucous cells has
lubricating properties to protect the stomach lining from abrasion or mechanical injury
Lipid breakdown in small intestine
majority of triglyceride digestion occurs in small intestine and is facilitated by pancreatic lipase -an enzyme produced by pancreas and released into duodenum
Anal canal
makes up the terminal few cm of large intestine -lined by stratified squamous epithelium and passed through an opening in the levator ani muscle of pelvic floor and terminates at the anus.
Submucosa
many large blood vessels, lymph vessel, nerves and glands are within the submucosa
Bile salts and lecithin function in the
mechanical digestion of lipids -allowing more efficient chemical digestion of triglycerides.
Primary function of mastication is to
mechanically reduce its bulk of food into smaller particles to facilitate swallowing -chemical digestions and absorption are not affected a whole lot, except that chewing increases SA -which facilitates exposure to and action by digestive enzymes -also promotes salivation to help soften and moisten food to form bolus
Nerve signals relayed along sensory neurons to
medulla oblongata and result in an increase in stomach motility and secretory activity of gastric cells
Jejunum
middle region of small intestine (2/5 of length) -primary region within small intestine for chemical digestion and nutrient absorption
Both the gastrocolic and defecation reflex is an example of a
monosynaptic reflex
The reverse flow known as retropulsion, not only prevents
more chyme moving into small intestine but also contributes to more mixing of stomach content to further reduce size of food particles
Incisors
most anteriorly placed teeth -shaped like chisel and have a single root -for slicing/cutting into food
Retroperitoneal organs include:
most of duodenum (first part of small intestine), pancreas, ascending and descending colon, rectum
Extrinsic salivary glands
most saliva -is produced from multicellular exocrine glands outside oral cavity.
The ileum contracts, ileocecal sphincter relaxes and the cecum (first part of large intestine) relaxes, so contents within GI tract are
moved from ileum through open ileocecal sphincter into cecum -the sphincter contracts to prevent back flow
The intestinal glands of large intestine secrete
mucin to lubricate undigested material and facilitate it's passage through large intestine
Two major receptors are embedded throughout the..
mucosa and submucosa of the GI tract length -baroreceptors and chemoreceptors
Fine branches between the inner circular layer and outer longitudinal layer of muscularis is known as
mysenteric nerve plexus (auerbach plexus) -controls muscle contractions.
The oropharynx and laryngopharynx are lined with
nonkeratinized stratified squamous epithelium -provides protection against abrasion when swallowing food
B12 is needed for
normal production of erythrocytes -decreased or absence of this results in pernicious anemia
hydrocloric acid (HCl)
not formed in the cell for it would destroy it -instead it forms from the H+ and Cl- secreted from the parietal cells surface
Nucleic acid breakdown in small intestine
nuclei acid digestion occurs in small intestine -the nucleases (deoxyribonuclease and ribonuclease) are synthesized and released by pancreas, wich begins digestion of nuclei acids
Nucleic acid digestion
nucleic acids are polymers of nucleotides Two types: -deoxyribonucleic acid and ribonucleic acid (DNA/RNA)
Pancreatic juice contains
numerous enzymes and is produced and released by pancreas.
Internal stomach lining is composed of
numerous gastric folds, or rugae -seen only when stomach is empty -allows for expansion when full
Central veins collect blood and merge throughout liver to form
numerous hepatic viens -that empty into IVC
Bacterial action in large intestine
numerous normal bacteria flora inhabit the large intestine -they are termed the indigenous microbiota
Voluntary phase
occurs after ingestion -controlled by cerebral cortex
Emulsification
occurs by the action of bile salts -which are part of bile
Sympathetic stimulation
occurs during exercise, or when anxious -results in more viscous saliva by decreasing water content of saliva -occurs because sympathetic stimulation constricts capillaries of salivary glands and decreases fluid added to saliva.
The cells of the liver receive blood from 2 sources:
one is oxygenated and the other is deoxygenated
The overlapping epithelial cells of lacteals act like
one-way valves to permit entry of chylomicrons -enters blood and deliver lipids to the liver and other tissues (adipose CT, skeletal M tissue, and cardiac M)
Submandibular duct
opens form each gland through a papilla in floor of cavity on either side of lingual frenulum
Intestinal reflex
opposes cephalic and gastric reflex -it protects the small intestine from being overloaded with chyme
Intraperitoneal organs
organs within the abdomen that are completely surrounded by visceral peritoneum Includes: -stomach, most of small intestine and parts of large intestine.
Ascending colon
originates at ileocecal valve and extends superiorly from edge of cecum along the right lateral border or abdominal cavity -it's retroperitoneal The bend in the colon as it turns from liver to left side is called the right colic flexure (hepatic flexure)
Sigmoid colon
originates at sigmoid flexure and turns inferomedially into pelvic cavity -it's intraperitoneal Terminates at the rectum
Transverse colon
originates at the right colic flexure and curves slightly anteriorly as it projects horizontally to the left across anterior region of abdominal cavity. -it's intraperitoneal The bend here as it's approaching the spleen, turns inferiorly and posterior, and its called the left colic flexure (splenic flexure)
Stimulation of salivary nuclei results in increased nerves signals relayed along..
parasympathetic neurons within both facial and glossopharyngeal nerve (additional saliva is released)
Lactose intolerant
people with reduced amount or lack of lactase enzyme
The space between the parietal and visceral peritoneum is known as the
peritoneal cavity -which produces a lubricating serous fluid -allows abdominal organs to move freely and reduces friction resulting from this movement.
Falciform ligament
peritoneal fold that holds the liver to internal surface of the anterior abdominal wall
Arrival of bolus at the oropharynx initiates the swallowing reflex of the
pharyngeal phase -this phase is involuntary
Each nucleases breaks the
phosphodiester bond between individual nucleotide's of DNA and RNA
Acinar cells
produce and release digestive enzymes -small ducts lead form each acinus into larger ducts that empty into larger pancreatic ducts that leads to duodenum
Endocrine cells of pancreas
produce and secrete hormones such as insulin and glucagon
Goblet cells
produce mucin that when hydrated form mucus -which lubricates and protects the intestinal lining -increases in number from duodenum to ileum, more lubrication needed as digested material absorbed and undigested materials left behind
Salivary glands
produces saliva -located within oral cavity and outside oral cavity
Protein digestion
proteins are polymers composed of amino acid subunits linked by peptide bonds
Located in plasma membrane are the required
proteins for membrane transport of digested molecules
The peristaltic wave creates a greater pressure on the contents in the
pylorus than the pressure exerted by pyloric sphincter to stay closed and prevent movement -causing 3mL of chyme to empty into small intestine -after pyloric wave has moved past pyloric sphincter, the pressure of sphincter is greater than pressure on contents, so pyloric sphincter closes -as this sphincter closes, stomach contents are squeezed back toward the stomach body This reverse flow event is called retropulsion
The bolus passes ____________ and ___________ through pharynx to esophagus.
quickly involuntary (1 second)
Once, inside epithelial cells, the fatty acids are
reattached to monosaccharide to re-form triglyceride -triglyceride, cholesterol, and other lipid molecules are then "wrapped" with proteins to form a chylomicron
The 3 thick transverse folds of the rectum are called
rectal valves -to ensure that feces is retained during the passing of gas
Autonomic motor output is
relayed through the facial, glossopharyngeal, and vagus nerves to different digestive system effectors Such as: -salivary glands, pancreas, and muscularis layers of GI tract wall.
Enteroendocrine cells
release hormones such as: -CCK and secretin
All enzymes that digest proteins are
released from the stomach and pancreas as inactive enzymes -must all be activated This is because the proteolytic enzymes would destroy the proteins with the cells that produce them
The monosaccharides
released from these enzymatic reactions include: -glucose, fructose, and galatose They are absorbed across small intestinal epithelial lining the blood
Secretin
released primarily in response to acidic chyme in small intestine which decreases secretory activity of stomach
Cholecystokinin
released primarily in response to fatty chyme within small intestine causing a decrease in stomach motility
In the inferior free edge of the falciform ligament lies the
round ligament of the liver (ligamentum teres) -which represents the remnant of fetal umbilical vein
Other components of saliva include:
salivary amylase, mucin, and lysozyme
Serosa
same composition as adventitia but completely covered by a serous membrane called visceral peritoneum -associated with portion of GI tract within peritoneal cavity
Colon
second region of large intestine -begins and form an inverted u-shaped arch It is divided into 4 segments -ascending, transverse, descending, and sigmoid colon
Pancreatic secretions
secretions of acinar cells and cells that line pancreatic ducts from pancreatic juice
Nervous control
sensory input from both mechanoreceptors and chemoreceptors is relayed to the CNS in response to stimulation.
Right lobe
separated from smaller left lobe by the falciform ligament, a peritoneal fold that secures the liver to the anterior abdominal wall
Accessory organ ducts
series of ducts deliver secretions to duodenum of small intestine, they include: -the biliary apparatus from the liver and gallbladder, and the pancreatic ducts from pancreas
Left and right hepatic ducts merge to form..
single common hepatic duct
Sandwiched between each cord of hepatocytes is a bile canaliculus, which is a
small channel that transports bile produced by hepatocytes to the bile ductule in the portal triad
The pyloric sphincter regulates material that enters the
small intestine
Motility in the stomach
smooth M. activity in the stomach has 2 primary functions: -mixing the bolus with gastric juice to form chyme -emptying chyme from the stomach into the small intestine
Other enteroendocrine cells produce other hormones, such as
somatostatin -a peptide hormone that modulates the function of nearby enteroendocrine and exocrine cells
Exceptions with the tunic layers include:
some GI organs deviate from typical patterns of tunics Such as: -esophagus has nonkeratinized stratified squamous epithelium in its mucosa to protect lining -stomach has 3 layers of smooth muscle in muscularis
The internal circular folds of the mucosal and submucosal layers also act as
speed bumps -to slow down the movement of chyme and ensure that it remains within the small intestine for maximal nutrient absorption -more numerous in duodenum and jejunum than the ileum
Sinusoids are lined with
stellate (star shaped) cells called reticuloendothelial cells (Kupffer cells) -these cells are macrophages that are responsible for engulfing potentially harmful substances (microbes), as blood is transported through the liver sinusoids
Gastrin
stimulates stomach motility and secretions
Primary function of CCK
stimulation of smooth muscle in gallbladder wall to strongly contract causing the release of concentrated bile Other functions include: -stimulation pancreas to release enzyme-rich pancreatic juice -relaxing smooth M. within hepatopancreatic ampulla, allowing entry of bile and pancreatic juice into small intestine ALSO -inhibits stomach motility and release of gastric secretions
Inferior region of esophagus connects to the
stomach -where it passes through an opening in diaphragm called the esophageal hiatus
Regulation of the digestive processes in the stomach
stomach is a holding bag for partially digested food, until entering small intestine, where digestion is complete
Gastrin enters blood and circulates back to
stomach to further stimulate contractile activity of muscle in gastric wall and to increase release of HCl from parietal cells -it also stimulates contraction of pyloric sphincter to slow stomach emptying -which allows time for completing digestive activities associated with the stomach before chyme moves into small intestine
Peyer patches are located in
submucosa -withing the small intestine (last portion of ileum)
Digestion of other ingested disaccharides
such as lactose (milk sugar) and sucrose (table salt) requires only one enzyme each
Both circular fold and villi help increase
surface area for absorption and secretion
Unicellular gland cells
synthesize enteropeptidase -an enzyme
Proteins broken down into amino acids by enzymes that:
target bonds between specific adjacent amino acids within proteins OR non-specifically release amino acids
All venuous blood from small intestine is transported though:
the hepatic portal vein to liver, where fructose and galactose will convert into glucose
Protein breakdown in small intestine
the high pH of small intestine inhibits further action by pepsin n protein shortly following entry of chyme into small intestine
Porta hepatis
the horizontal cross of the H -is the site at which blood and lymph vessels, bile ducts, and nerves extend from the liver -the hepatic portal vein and branches of hepatic artery proper enter at the porta hepatis
Histology in small intestine
the length of muscularis mucosae is shorter than the two layers internal to it, forcing the two inner layers of mucosa (epithelium and lamina propria) into folds to form small finger-like projections of the mucosa called villi
Histology of liver
the livers CT capsule branches throughout the organ and forms septa that partition the liver into thousands of microscopic polyheldral hepatic lobules -that are the structural and functional units of the liver
Gastric emptying
the movement of acidic chyme from the stomach through the pyloric sphincter into the duodenum -as a wave of peristaltic muscular contraction moves through pylorus towards pyloric sphincter, a pressure gradient is created that drives the stomach content toward the small intestine.
Histology of large intestine
the mucosa is lined by a simple columnar epithelium with numerous goblet cells -but is is smooth M. and lacks intestinal villi (opposite of small intestine) -though it's similar to small intestine because it has epithelial cells and numerous intestinal glands (or crypts) that extend inward toward the muscularis mucosa.
Digestive system includes:
the organs that ingest the food, mix and move the ingested materials, add secretions to facilitate digestion of these materials into smaller usable component, absorb necessary nutrients into blood or lymph, and expel the waste products from the body.,
Main function of the liver in digestion is
the production of bile
Intrinsic factor (of parietal cells )
the production of this glycoprotein is the only essential function performed by the stomach -required for absorption of vitamin B12 in ileum
Secretion primarily causes
the release of an alkaline solution that contains HCO3- from both the liver and ducts of pancreas -upon entering small intestine this alkaline fluid helps neutralize the acidic chyme ALSO -inhibits gastric motility and secretions
Only essential function performed by the stomach is
the release of intrinsic factor -substance required for absorption of vitamin B12, occurs in small intestine.
Regulation of salivary secretion
the salivary nuclei within the brainstem regulate salivation -a basal level of salivation in response to parasympathic stimulation ensures the oral cavity remains moist
Pressure exerted on anal sinuses causes
their cells to release mucin to form mucus -extra mucus lubricates anal canal
Peristalsis
then propels materials within GI lumen by altering contract of the circular and longitudinal muscle layers in small regions -net movement of intestinal contents is toward left intestine
Gross anatomy of salivary glands
there are 3 pairs of multicellular salivary glands, external to the oral cavity -parotid, submandibular, and sublingual glands
The contraction of the stomachs
thick muscularis layer churns and mixes the bolus with gastric secretions -leading to reduction in size of swallowed particles
The muscularis of the stomach progressively gets
thicker as it moves from body to pylorus
Last teeth to erupt are the
third molars "wisdom teeth" -in late teens to early 20s -jaw often isn't big enough to hold these molars, so only grow partially or become impacted
Alternative way for pancreatic juice to enter duodenum is
through an accessory pancreatic duct -this duct penetrates the duodenal wall, forming the minor duodenal papilla
A significant function of the stomach is
to serve as a "holding sac" for controlled release of partially digested materials into the small intestine, where most chemical digestion and absorption occurs
Micelles
transport lipid to the simple columnar epithelial lining of small intestine -here lipids enter epithelial cells, whereas bile salts remain in small intestine lumen to be recycled and reused
3 enzymes that continue digestion of proteins from the pancreas into small intestine in inactive forms are:
trypsinogen chymotrypsinogen procarboxypeptidase Once, these inactive enzymes reach small intestine they are activated by enzyme enteropeptidase -an enzyme previously synthesized by small intestine and released into lumen of small intestine
The mucous layer in the stomach, with the high rate of cell turnover in mucosa helps prevent..
ulceration of stomach lining, with high acidity of gastric fluid and gastric enzymes.
Regulation of accessory structures
vagal stimulation during cephalic and gastric phase, plus stimulating stomach motility and secretion, also activates pancreas to release pancreatic juice.
Projectig inferiorly from cecum is the
vermiform appendix -a thin, hollow, finger like sac lined by lymphocytes, filled with lymphatic nodules
Outermost layer of muscularis is a serosa called
visceral peritoneum because the stomach in intraperitoneal
Small intestines also absorb
vitamins -fat soluble vitamins absorbed with lipids -water soluble vitamins absorbed through various membrane transport mechanisms
The large intestine absorbs..
water and electrolytes (mainly Na+ and Cl- ions) from the digested material that enters into it from small intestine (vitamins B and K)
Saliva is formed as
water and electrolytes are filtered from plasma within capillaries then through cells (acini) of a salivary gland
Major duodenal papilla
within duodenum -is a projection where hepatopancreatic ampulla penetrates the wall and both bile and pancreatic juice enters duodenum