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