Chapter 22 - Digestive System Flashcards
Take in food, breaks it down into nutrient molecules, absorbs these molecules into the bloodstream, and then rids the body of the indigestible remains.
The digestive system
Two groups of the digestive system:
- Alimentary Canal
2. The accessory organs
The continuous muscular tube that winds through the body from the mouth to the anus
The Alimentary Canal; The Gastrointestinal (GI) Tract
Breaks down food into smaller fragments
Digests
Assimilates digested fragments through it’s lining into the blood
Absorbs
Organs of the Alimentary Canal
Esophagus
Stomach
Small Intestine
Large Intestine
The large intestine leads to the terminal opening or the _____.
Anus
Food in the alimentary canal is technically _____ the body.
Outside
Organs of the Accessory Digestive Organs
Teeth Tongue Gallbladder Salivary Glands Liver Pancreas
We can view the digestive tract as a ______ ______ in which food becomes less complex at each step of processing and its nutrients become available to the body.
Disassembly line
We can view the digestive tract as a ______ ______ in which food becomes less complex at each step of processing and its nutrients become available to the body.
Disassembly line
Six essential activities:
Ingestion Propulsion Mechanical breakdown Digestion Absorption Defecation
Taking food into the digestive tract (eating)
Ingestion
Moves food through the alimentary canal, includes swallowing, which is initiated voluntarily, and peristalsis, an involuntary process.
Propulsion
The major means of propulsion, involves alternate waves of contraction and relaxation of muscles in the organ walls.
Main effect is to squeeze food along the tract, but some mixing occurs as well.
Peristalsis
Page 762 (Figure 22.2)
Increases the surface area of ingested food and physically preparing it for digestion by enzymes.
Chewing, mixing food with saliva by the tongue, churning food in the stomach and segmentation.
Mechanical breakdown
Rhythmic local constrictions of the small intestine.
Mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall.
Segmentation
Involves a series of steps in which enzymes secreted into the lumen (cavity) of the alimentary canal break down complex food molecules to their chemical building blocks.
Catabolic process.
Digestion
The passage of digested end products (plus vitamins, minerals, and water) from the lumen of the GI tract through mucosal cells by active or passive transport into the blood or lymph.
Absorption
Eliminates indigestible substances from the body via the anus in the form of feces.
Defecation
The most extensive serous membrane in the abdominopelvic cavity.
Peritoneum
Covers the the external surfaces of most of the digestive organs
Visceral Peritoneum
Lines the body wall
Parietal Peritoneum
Between the two peritoneum is the slit like potential space containing a slippery fluid secreted by the serous membranes.
Peritoneal cavity
A double layer of peritoneum - a sheet of two serous membranes fused back to back - that extends to the digestive organs from the body wall.
Following functions:
- Proved routes for blood vessels, lymphatics and nerves to reach the digestive viscera.
- Hold organs in place
- Store fat.
Mesentery
In most places the mesentery is _____ and attaches to the posterior abdominal wall.
However, there are _______ mesenteries too.
Dorsal; Ventral
Have peritoneum on the anterior side.
Retroperitoneal organs
Digestive organs that keep their mesentery and remain in the peritoneal cavity are called _________.
Intraperitoneal
Inflammation of the peritoneum.
Can arise from a piercing abdominal wound, a perforating ulcer that leaks stomach juices in the peritoneal cavity or poor sterile technique during abdominal surgery.
Most commonly a burst appendix that sprays bacteria containing feces all over the peritoneum.
Peritoneal coverings tend to stick together around the infection site, localizing the infection.
Peritonitis
Four basic layers of the digestive organs in the alimentary canal:
Mucosa
Submucosa
Muscularis Externa
The Serosa
Four basic layers of the digestive organs in the alimentary canal:
Mucosa
Submucosa
Muscularis Externa
The Serosa
- Innermost layer.
- Moist epithelial membrane that lines the alimentary canal lumen from mouth to anus.
- Major Functions:
1. Secrete mucus, digestive enzymes, and hormones
2. Absorb the end products of digestion into the blood
3. Protect against infectious disease
Mucosa or Mucous Membrane
Three sublayers of the mucosa
- Lining Epithelium
- Lamina Propria
- Muscularis mucosae
Except for the mouth, esophagus and anus where it is _______ _______ _______, the epithelium of the mucosa is a _______ _______ _________ rich in mucus secreting cells..
Stratified squamous epithelium; simple columnar epithelium
The slippery mucus that the mucosa produces protects certain digestive organs from being digested by enzymes working within their cavities and cases, food passage along the tract.
The mucosa also contains both enzyme-synthesizing and hormone-secreting cells.
- Underlies the epithelium.
- Loose areolar connective tissue
- Capillaries nourish the epithelium and absorb digested nutrients.
- Isolated lymphoid follicles, part of MALT, help defend us against bacteria and other pathogens, which have rather free access to our digestive tracts.
Lamina Propria
- External to the lamina propria.
- Scant layer of smooth muscle cells that produces local movements of the mucosa that can enhance absorption and secretion.
Muscularis Mucosae
- Just external to the mucosa.
- Areolar connective tissue.
- Rich supply of blood and lymphatic vessels, lymphatic follicles, and nerve fibers that supply the surrounding tissues of the GI tract wall.
- Abundant elastic fibers enable the stomach to regain its normal shape after temporarily storing a large meal.
Submucosa
- Surrounding the submucosa
- Responsible for segmentation and peristalsis.
- Inner circular layer and outer longitudinal layer of smooth muscle cells.
- Forms sphincters that act as valves to control food passage from one organ to the next and prevent bakflow.
Muscularis Externa
- The outermost layer of the intraperitoneal organs.
- Formed of areolar connective tissue covered with mesothelium, a single layer of squamous epithelial cells.
Serosa
Can also be the visceral peritoneum.
Ordinary dense connective tissue in the esophagus that replaces the serosa that binds to surrounding structures.
Retroperitoneal organs have both an ______ and a serosa.
Adventitia
Includes those arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation.
Splanchnic circulation
The ____ ______ ______ collects nutrient rich venous blood draining from the digestive viscera and delivers it to the liver.
Hepatic Portal Circulation
All digestive tract regulatory mechanisms control _______ conditions so that food breakdown and absorption can occur there as effectively as possible.
Luminal
- In-house nerve supply of the alimentary canal.
- Consists over 100 million neurons.
Enteric Nervous System (Gut Brain)
Communicate widely with one another to regulate digestive system activity.
Provide the major nerve supply to the GI tract wall and control GI tract motility.
Enteric Neurons
_____ nerve plexus occupies the submucosa.
Submucosal
The large ______ nerve plexus lies between the circular and longitudinal muscle layers of the muscularis externa.
Myenteric
- Mediated by enteric nervous system plexuses in response to stimuli within the GI tract.
- Control patterns of segmentation and peristalsis is largely automatic, involving pacemaker cells and reflex arcs between enteric neurons in the same or different organs.
Short Reflexes
- Involve CNS integration centers and extrinsic autonomic nerves.
- The enteric nervous system sends information to the CNS via visceral sensory fibers.
- Receives parasympathetic and sympathetic motor fibers from the autonomic nervous system, which enter the intestinal wall to synapse with neurons in the intrinsic plexuses.
Long Reflexes
Three key concepts govern regulation of digestive activity:
- Digestive activity is provoked by a range of mechanical and chemical stimuli.
Stretching of the organ by food in the lumen, changes in osmolarity (solute concentration), pH of the contents, and the presence of substrates and end products of digestion.
- Effectors of digestive activity are smooth muscle and glands.
Receptors in the GI tract stimulate smooth muscle of the GI tract to mix lumen contents and move them along the tract.
Short or long reflexes can also activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood.
- Neurons (intrinsic and extrinsic) and hormones control digestive activity.
Intrinsic = Short reflexes Extrinsic = Long reflexes
Stomach and small intestine also contain hormone producing cells. These cells release their products into the interstitial fluid in the extracellular space. Blood and interstitial fluid distribute these hormones to their target cells in the same or different digestive tract organs, where they affect secretion or contraction.
Boundaries are the lips anteriorly, cheeks laterally, palate superiorly, and tongue inferiorly.
Mouth (Oral Cavity)
Anterior opening to the mouth
Oral orifice
Posteriorly, the oral cavity is continuous with the _______.
Oropharynx
The walls of the mouth are lined with thick ______ _____ epithelium.
Stratified squamous
The _____ and the ______, help keep food between the teeth when we chew and are composed of a core of skeletal muscle covered externally by skin.
Lips; Cheeks
The recess bounded externally by the lips and cheeks and internally by the gums and teeth is the ____ _____.
Oral vestibule
The area between the teeth and gums is the ____ ____ ____.
Oral cavity proper
Median fold that joins the internal aspect of each lip to the gum.
Labial frenulum.
Forming the roof of the mouth and has two distinct parts.
Palate
Anterior; Underlain by the palatine bones and the palatine processes of the maxillae, and it forms a rigid surface against which the tongue forces food during chewing.
Hard Palate
Mobile fold formed mostly of skeletal muscle that rises reflexively to close off the nasopharynx when we swallow.
Soft Palate
Anchored by to the tongue by the palatoglossal arches and to the wall of the oropharynx by the more posterior palatopharyngeal arches.
Arched area of the oropharynx that contains the palatine tonsils
Fauces
Projecting downward from the free edge of the soft palate is the fingerlike
Uvula
- Occupies the floor of the mouth.
- Composed of interlacing bundle of skeletal muscle fibers.
- Grips food and constantly repositions it between the teeth.
- Mixes food with saliva, forming a compact mass called a bolus.
- Initiates swallowing by pushing the bolus posteriorly into the pharynx.
- Has intrinsic and extrinsic muscles.
Tongue
Confined in the tongue and are not attached to the bone.
Allow the tongue to change its shape ( but not its position), becoming thicker, thinner, longer, or shorter as needed for speech and swallowing.
Intrinsic Muscles
Confined in the tongue and are not attached to the bone.
Allow the tongue to change its shape ( but not its position), becoming thicker, thinner, longer, or shorter as needed for speech and swallowing.
Intrinsic Muscles
Extend to the tongue from their points of origin on bones of the skull or the soft palate.
Alter tongues position (protrude it, retract it, and move it from side to side).
Extrinsic Muscles
Roughen the tongue surface, helping us lick semisolid foods and providing friction for manipulating food.
Contain keratin, which stiffens them and gives the tongue its whitish appearance.
Filiform Papillae
Mushroom-shaped and scattered widely over the tongue surface.
Vascular core that gives its a reddish hue.
Fungiform Papillae
Eight to twelve large _____ _____ are located in a V-shaped row at the back of the tongue.
Vallate Papillae
Located on the lateral aspects of the posterior tongue.
Foliate Papillae
House taste buds.
Fungiform, vallate, foliate papillae.
- Immediately posterior to the vallate papillae.
- A groove that distinguishes the portion of the tongue that lies in the oral cavity (its body) from its posterior portion in the oropharynx.
Terminal Sulcus
- Cleanses the mouth
- Dissolves food chemicals so they can be tasted
- Moistens food and helps compact it into a bolus.
- Contains the enzyme amylase.
Saliva
- Produces most saliva.
- Lie outside the oral cavity and empty their secretions into it.
Major or extrinsic salivary glands
Scattered throughout the oral cavity mucosa augment the output slightly of saliva.
Minor or intrinsic salivary glands
- Roughly triangular gland that lies anterior to the ear between the masseter muscle and the skin.
Parotid Gland
Dry mouth; Too little saliva production.
Difficulty chewing, swallowing and oral infections.
Caused by medications, diabetes, HIV/AIDS and Sjogren’s Syndrome.
Xerostomia
The gland that lies along the medial aspect of the mandibular body.
Submandibular gland
Lies anterior to the submandibular gland under the tongue and opens via 10-20 ducts into the floor of the mouth.
Sublingual gland
The salivary glands are comprised of two types of secretory cells:
Serous; Mucous
The salivary glands are comprised of two types of secretory cells:
Serous; Mucous
Produce a watery secretion containing enzymes, ions and a tiny bit of mucin.
Serous Cells
Produce mucus, a stringy, viscous solution.
Mucous Cells
The parotid and the submandibular glands contain mostly _____ cells.
Serous
The buccal glands have approximately equal numbers of ______ and _______ cells
Serous; Mucous
The sublingual glands contain mostly ______ cells.
Mucous
Saliva is slightly ________ (ph).
Acidic - 6.75-7.00
Saliva Solutes:
Electrolytes (Na+, K+, Cl-, PO43-, and HCO3-
Amylase and Lipase
Mucin, Lysozyme and IgA
Metabolic Wastes (Urea and Uric Acid)
When dissolved in water, the glycoprotein _____ forms thick mucus and lubricates the oral cavity and hydrates foodstuffs
Mucin
Saliva protects against microorganisms because it contains:
- IgA antibodies
- Lysozyme
- Defensins
A bactericidal enzyme that inhibits bacterial growth in the mouth and may help prevent tooth decay
Lysozyme
- Act as a local antibiotic.
- Function as cytokines to call defensive cells (lymphocytes, neutrophils, etc..) into the mouth for battle.
Defensins
Salivation is controlled primarily by_______ division of the ANS.
Parasympathetic
When we ingest food, chemoreceptors and mechanoreceptors in the mouth send signals to the _______ _______ in the brain stem
Salivatory Nuclei
This activates the parasympathetic nervous system.
Chemoreceptors are activated by ______ substances.
Mechanoreceptors are activated by ______.
Acidic; Anything that creates chewing.
The sympathetic nervous system causes release of a _____ _____-_____ saliva.
The sympathetic division constricts blood vessels serving the salivary glands and almost completely inhibits saliva release, causing a dry mouth.
Dehydration also limits saliva because low blood volume reduces blood filtration pressure at capillary beds.
thick mucin-rich
Lie in sockets (alveoli) in the gum-covered margins of the mandible and maxilla.
Teeth
Lie in sockets (alveoli) in the gum-covered margins of the mandible and maxilla.
Teeth
- Consist of deciduous or milk/baby teeth.
- First teeth to appear, at about age 6 months, are the lower central incisors.
- Additional pairs of teeth erupt at one- to two-month intervals until about 24 months, when all 20 milk teeth have emerged
Primary teeth
As the deep-lying _______ _______ enlarge and develop, the roots of the milk teeth are reabsorbed from below, causing them to loosen and fall out between ages 6 and 12.
Permanent Teeth
There are ____ permanent teeth in a full set.
32
Chisel-shaped and adapted for cutting or nipping off pieces of food.
Incisors
Conical or fanglike that tear and pierce.
Canines
Chisel-shaped and adapted for cutting or nipping off pieces of food.
Incisors (2)
Conical or fanglike that tear and pierce.
Canines (1)
Have broad crowns with rounded cusps (tips) best suited for grinding and crushing.
Premolars (2) and Molars (3)
During chewing, the upper and lower molars repeatedly lock together, an action that generates tremendous crushing forces.
A shorthand way of indicating the numbers and relative positions of the different types of teeth.
Uppers over lowers, for 1/2 the mouth and then multiplied by two.
Dental Formula
Fucking stupid, this is not how math works! You can’t just make up fucking ratios.
Two major regions of the tooth:
Crown and root
Enamel-covered part of the tooth above the gingiva.
Crown
Surrounds the tooth like a tight collar
Gingiva (gum)
Brittle ceramic-like material thick as a dime, directly bears the force of chewing.
Heavily mineralized with calcium salts, and its densely packed hydroxyapatite crystals are oriented in force-resisting columns perpendicular to the tooth’s surface.
Hardest substance in the body.
Enamel
The portion of the tooth embedded in the jaw-bone.
Root
Constricted tooth region that connects the crown and the root.
Neck
A calcified connective tissue, covers the outer surface of the root and attaches the tooth to the thin periodontal ligament.
Cement
Anchors the tooth in the bony socket (alveolus) of the jaw, forming a fibrous joint called a gomphosis.
Periodontal ligament
A protein-rich bonelike material, underlies the enamel cap and forms the bulk of a tooth.
Acts as a shock absorber during biting and chewing.
Dentin
Dentin surrounds the central ____ _____ containing a number of soft tissue structures (connective tissue, blood vessels, and nerve fibers).
Pulp cavity
Connective tissue, blood vessels and nerve fibers
Pulp
Where the pulp cavity extends into the root, it becomes the ____ _____.
Root Canal
At the proximal end of each root canal is an ______ ______ that allows blood vessels, nerves and other structures to enter the pulp cavity.
Apical Foramen
The cell type that secretes and maintains the dentin.
Odontoblast
Enamel, dentin and cement are all _______.
Avascular
Enamel differs from cement and dentin because it lacks ______ and is almost entirely _______.
Collagen; Mineral
Result from bacterial action that gradually demineralizes enamel and underlying dentin.
Cavities
Begins when sugar, bacteria and other mouth debris adherers to the teeth.
Dental plaque
Begins when sugar, bacteria and other mouth debris adherers to the teeth.
Dental plaque
Bacterial metabolism of the trapped sugars produce acids, which dissolve the calcium salts of the teeth.
Dental plaque that accumulates and calcifies forming ______.
Calculus or tartar
Disrupt the seal between the gingiva and teeth, deepening the sulcus and putting the gums at risk for infection by pathogenic anaerobic bacteria.
Early stage infection where the gums are red, sore and swollen and may bleed.
Gingivitis
Reversible if calculus is removed, but if neglected it will eventually form pockets of infection which become inflamed.
Neutrophils and other immune cells attack not only the intruders but also the body tissues carving deep pockets around the teeth destroying the periodontal ligament and activating osteoclasts which dissolve the bone.
Periodontal disease or periodontitis.
Tooth loss is inevitable. Various treatments can alleviate bacterial infection and encourage the surrounding tissues to reattach to the teeth and bone.
Periodontitis may cause heart disease and stroke in two ways:
- Chronic inflammation promotes atherosclerotic plaque.
- Bacteria entering the blood from infected gums stimulate the formation of clots that clog coronary and cerebral arteries.
Risk factors:
- Smoking
- Diabetes mellitus
- Oral piercing
Mastication is partly _______ and partly ________.
Voluntary; Reflexive
From the mouth, food passes posteriorly into the _______ and then the _______ both common passages for food, fluids and air.
Oropharynx; Laryngopharynx
The histology resembles that of the oral cavity. The mucosa contains a stratified squamous epithelium well supplied with mucus-producing glands. It contains two muscular layers (the inner layer runs longitudinally and the outer layer encircles the wall like three stacked fists).
Muscular tube that is collapse when not involved in food propulsion.
Esophagus
The esophagus takes a fairly straight course through the _______ of the thorax.
It pierces the diaphragm at the end of the ______ ______ to enter the abdomen.
Joins the stomach at the _______ _______ within the abdominal cavity.
Mediastinum; Esophageal hiatus; Cardinal orifice
The cardial orifice is surrounded by the ________, which is a physiological sphincter.
Gastroesophageal sphincter
Acts as a sphincter, but the only structural evidence of this sphincter is a slight thickening of the circular smooth muscle a that point.
The muscular diaphragm keeps the gastroesophageal sphincter closed when food is not being swallowed.
Mucus cells help the esophagus from being swallowed from reflux of stomach acid.
Heartburn is the first symptom of _______.
Burning, radiating substernal pain that occurs when stomach acid regurgitates into the esophagus.
Common in those with a hiatal hernia, a structural abnormality in which the superior part of the stomach protrudes slightly above the diaphragm.
GERD
Histology:
Esophageal mucosa contains:
Nonkeratinized stratified squamous epithelium
At the esophagus-stomach junction, the abrasion-resistance epithelium changes abruptly to simple columnar epithelium of the stomach.
Histology:
The submucosa contains ______-______ esophageal glands.
As a bolus moves through the esophagus, it compresses these glands, causing them to secrete _____ that “greases” the esophageal walls and aids food passage.
Mucus-secreting
Mucus
Histology:
The muscularis externa is _____ ______ in its superior third, a mixture of _____ and _____ ______ in its middle third and _____ ______ in it’s inferior third.
Skeletal Muscle
Skeletal; Smooth Muscle
Smooth Muscle
Histology:
Instead of a serosa, the esophagus has a ______ ______ composed entirely of connective tissue, which blends with surrounding structures along its route.
Fibrous adventita
The single digestive function of the pharynx and the esophagus is ______ ______ accomplished by deglutition, or swallowing.
Food propulsion
The single digestive function of the pharynx and the esophagus is ______ ______ accomplished by deglutition, or swallowing.
Food propulsion
Two major steps in deglutition:
- Buccal Phase
2. Pharyngeal-esophagus Phase
- Occurs in the mouth and is voluntary.
- Ends when a food bolus or a “bit of saliva” leaves the mouth and stimulates tactile receptors in the posterior pharynx, initiating the next phase.
Buccal Phase
Involuntary and is controlled by the swallowing centers in the brain stem (medulla and lower pons).
Vagus nerves transmit motor impulses from the swallowing center to the muscles of the pharynx and esophagus.
Once food enters the pharynx all respiration is momentarily inhibited and all routes except the desired one into the digestive tract are blocked off.
Solid foods pass from the oropharynx to the stomach in about 8 seconds, and fluids, aidedd by gravity, pass in 1 to 2 seconds.
Pharyngeal-Esophageal Phase
A temporary “storage tank”
The stomach
Continues the demolition job begun in the oral cavity by further degrading food both physically and chemically.
As a result, food is converted into a slurry called _____ , which gets delivered to the small intenstine.
Chyme
The stomach is hidden in the _____ _____ quadrant of the peritoneal cavity. It is hidden nearly by the _____ and the ______.
Upper Left
Liver; Diaphragm
The stomach is hidden in the _____ _____ quadrant of the peritoneal cavity. It is hidden nearly by the _____ and the ______.
Upper Left
Liver; Diaphragm
When empty the stomach ______ ______, throwing its mucosa (and submucosa) into large, longitudinal folds called rugae.
Collapses Inward.
The ______ surrounds the cardial orifice through which food enters the stomach from the esophagus.
Cardia
The stomach’s dome-shaped part, tucked beneath the diaphragm bulges superolaterally to the carida.
Fundus
The midportion of the stomach, is continuous inferiorly with the funnel shaped pyloric part.
Body
The wider more superior area of the pyloric part.
Pyloric antrum
Intermediate area of the pyloric part.
Pyloric canal
Inferior area of the pyloric part, where the pyloric part terminates.
Pylorus
Continuous with the duodenum through the _______ ______, which control stomach emptying.
Pyloric Sphincter
Convex lateral surface of the stomach
Greater curvature
Concave medial surface of the stomach
Lesser curvature
Extending from the greater and lesser curvature are two mesenteries called _______ that help tether the stomach to other digestive organs and the body wall.
Omenta
Runs from the liver to the lesser curvature of the stomach.
It becomes continuous with the visceral peritoneum covering the stomach.
Lesser Omentum
Drapes inferiorly from the greater curvature of the stomach to cover the coils of the small intestine.
It runs dorsally and superiorly, wrapping the spleen and the transverse portion of the large intestine before blending with the mesocolon.
Greater Omentum
The greater omentum is riddled with _______ ______. and large collections of ______ _____.
Fat deposits; Lymph nodes
The autonomic nervous system serves the stomach. The sympathetic fibers from the thoracic splanchnic nerves are relayed through the ______ ______ and the parasympathetic fibers are supplied by the ______ ______,
Celiac Ganglion
Vagus Nerve
The arterial supply of the stomach is provided by branches (gastric and splenic) of the ______ ______.
Celiac Trunk
The corresponding veins are part of the ______ _____ ____ and ultimately drain into the ______ _____ _____.
Hepatic Portal System
Hepatic Portal Vein
Besides the circular and longitudinal layers of smooth muscle, the muscularis externa has an incomplete innermost layer of smooth muscle that runs _____.
This allows the stomach to mix, churn and move food along the tract, but also to pummel the food, physically before breaking it down into the small fragments and ramming it into the small intestine.
Obliquely
The lining of the stomach is ______ _______ ______ composed entirely of mucous cells.
Simple columnar epithelium
The lining of the stomach produces a cloudy, protective two-layer coat of alkaline mucus in which the surface layer consists of viscous, insoluble mucus that traps a layer of bicarbonate-rich fluid beneath it.
This otherwise smooth lining is dotted with millions of deep ______ ______, which lead into tubular _____ ______ that produce the stomach secretion _____ _____.
Gastric Pits
Gastric Glands
Gastric Juice
The cells that form the walls of the gastric pits are primarily ______ ______.
Those composing the _____ _____ vary in different stomach regions.
Mucus Cells
Gastric Glands
Glands of the stomach _____ and ______ where most digestion occurs, are substantially larger and produce the majority of the stomach secretions.
Fundus, Body
Glands in these regions contain a variety of secretory cells, including mucous neck, parietal, chief, and enteroendocrine cells.
Found primarily in the “neck” but are also scattered deeper within the glands.
Produce a thin, soluble mucus quite different from that secreted by the mucous cells of the surface epithelium.
Mucous Neck Cells
Scattered among the chief cells, mainly in the more apical (closer to the lumen) region of the glands.
Secrete HCL and intrinsic factor.
Parietal Cells
HCL makes the stomach contents extremely acidic, a condition necessary for activation and optimal activity of the protein-digesting enzyme activity _______.
Pepsin
The acidity of HCL also helps digest food by _________ ________ and breaking down cell walls of plant foods , and its harsh enough to kill many of the bacteria ingested with foods.
Denaturing proteins
_________ _________ is a glycoprotein required for vitamin B12 absorption in the small intestine.
Intrinsic Factor
Occur mainly in the basal regions of the gastric glands and produce pepsinogen, the inactive form of pepsin.
Also secrete lipases (fat-digesting enzymes) that account for about 15% of overall GI lipolysis.
Chief cells
When these cells are stimulated, the first pepsinogen molecules they release are activated by HCL encountered in the apical region of the gland.
Once pepsin is present, it also catalyzes the conversion of pepsinogen to pepsin.
Located deep in the gastric glands and release a variety of chemical messengers directly into the interstitial fluid of the lamina propria.
Some of these, for example histamine and serotonin, act as paracrines.
Others, such as somatostatin, act both as paracrines locally and as hormones that diffuse into the blood capillaries to influence several digestive system target organs.
Enteroendocrine Cells
A hormone that plays an essential role in regulating stomach secretion and motility.
Gastrin
The _______ ______ is exposed to some of the harshest conditions in the entire digestive tract.
Stomach mucosa
The stomach protects itself by producing the _____ _____.
Mucosal barrier
Three factors of the mucosal barrier
- Thick coating of bicarbonate (HCO3-) rich mucus builds up on the stomach wall.
- The epithelial cells of the mucosa are joined together by tight junctions that prevent gastric juice from leaking into underlying tissue layers.
- Damaged epithelial mucosal cells are shed and quickly replace by division of undifferentiated stem cells that reside where the gastric pits join the gastric glands.
The stomach surface epithelium of mucous cells is completely renewed every 3-6 days, but the glandular cells deep within the gastric glands ahve a much longer life span.
Anything that breaches the gel-like mucosal barrier causes inflammation of the stomach wall.
Persistent damage to the underlying tissues can promote peptic ulcers, specifically gastric ulcers when they are erosions of the stomach wall.
The danger posed by ulcers is perforation of the stomach wall, leading to peritonitis and, perhaps massive hemorrhage.
Gastritis
90% of recurrent ulcers are the work of a strain of acid-resistant, corkscrew-shaped _______ _______ bacteria., which burrow like a drill bit throughout the mucus and destroy the protective mucosal layer.
Helicobacter pylori
More than half the population has H. Pylori, however, only 10-20% show symptoms due to the protection of gastric mucin.
A breath test detects H. Pylori and an antibiotic kills the bacteria, promotes healing of the ulcers and prevents recurrence.
Active ulcers may need a H2 Blocker (Histamine) receptors may also help because inhibits HCL secretion by blocking histamines effects.
Digestive processes in the stomach:
Propulsion: The stomach exhibits peristalsis.
Mechanical Breakdown: The stomach exhibits peristalsis.
Digestion: Protein breakdown starts in the stomach and is the main type of enzymatic breakdown that occurs there. HCL denatures dietary proteins in preparation for enzymatic digestion. Pepsin is the most important protein-digesting enzyme produced by the gastric mucosa.
Infants produce renin, an enzyme that acts on milk protein converting it to a curdy substance that looks like soured milk.
The acidic pH of the stomach contribute to the fat digestion from gastric and lingual lipases. The rest occurs in the small intestine.
Absorption: Alcohol and aspirin pass easily through the stomach mucosa into the blood.
The only stomach function essential to life is secretion of _____ _____, which is required for intestinal absorption of vitamin B12, needed to produce mature erythrocytes.
Intrinsic Factor
In its absence is pernicious anemia results.
If vitamin B12 is administered by injection, individuals can survive with minimal digestive problems even after total gastrectomy,
Neural controls of the stomach consist of both long (_____ ______-_____) and short (____ ____) nerve reflexes.
In each case ______ is released stimulating the output of gastric juice.
When the stomach is stimulated by the vagus nerve (parasympathetic) secretory activity of all its glands ______.
When the stomach is stimulated by the sympathetic nerves secretory activity of all its glands _______.
Vagus nerve-mediated; Local enteric
Acetylcholine (ACh)
Increases
Decreases
Hormonal controls of the stomach control of gastric secretion is largely the province of ________. It stimulates secretion of HCL by the stomach and of hormones by the small intestine.
Gastrin
Control of HCL-secretion parietal cells is multifaceted. It is stimulated by three chemicals:
ACh, gastrin and histamine.
Stimuli may affect the head, stomach or small intestine.
Three phases of gastric secretion:
Cephalic (Reflex) Phase
Gastric Phase
Intestinal Phase
Gastric secretion that occurs before food enters the stomach.
Triggered by aroma, taste, sight or thought of food.
Act via the vagus nerve to stimulate gastric glands.
Cephalic (Reflex) Phase
Once the food enters the stomach, local neural and hormonal mechanisms initiate the gastric phase.
This phase lasts 3-4 hours and provides about two-thirds of the gastric juice released.
Gastric Phase
Stimulation of the gastric phase are _______, _______, and _____ ______.
Distensibility, Peptides, Low Acidity
Stomach ________ activates stretch receptors and initiates both short and long reflexes.
In the long reflexes, impulses travel to the ______ and then back to the stomach via vagal fibers.
Distension
Medulla
Chemical stimuli provided by partially digested proteins, caffeine and rising pH directly activate gastrin-secreting enteroendocrine cells called _____ cells in the stomach antrum.
G
During the gastric phase, _____ plays a major role in stimulating parietal cells to secrete HCl in two ways:
Gastrin
- Acting directly on receptors on these cells.
- Stimulating enteroendocrine cells to release histamine.
When proteins are in the stomach, the pH of the gastric contents typically rises because proteins act as buffers to tie up H+. The rise in pH stimulates ____ secretion and subsequently HCl release, which in turn provides t acidic conditions needed to digest proteins.
Gastrin
Highly acidic (pH below 2) gastric contents _____ gastrin secretion - a situation commonly occurs between meals.
Inhibits
Stress, fear, anxiety or anything that triggers fight or flight response inhibits gastric secretion because the sympathetic division overrides parasympathetic (vagal) controls of digestion.
Initial stimulation of the _______ phase is set into motion as partially digested food fills the first part of the small intestine (duodenum).
This stimulates intestinal mucosal cells to release _____ _____, a hormone that encourages the gastric glands to continue their secretory activity.
Intestinal
Intestinal (Enteric) Gastrin
Four main factors of the duodenum cause it to put the “brakes” on gastric secretion:
- Distension of the duodenum.
- Presence of acidic chyme.
- Presence of fatty chyme.
- Presence of hypertonic chyme.
These factors protect the small intestine from too much acidity.
*The same 4 factors decrease gastric emptying.
Inhibition of the intestinal phase occurs in two ways:
- Enterogastric reflex: Duodenum inhibits HCl secretion in the stomach by the enteric (short) and vagus (long) nerves of the sympathetic nervous system.
- Enterogastrones: Released by enteroendocrine cells in the duodenal mucosal epithelium (secretin and cholecystokinin). Inhibit gastric secretion and play other roles.
When parietal cells are appropriately stimulated, _____ is actively pumped into the stomach lumen by H+-K+ ATPases (proton pump)
As acid is pumped into the stomach, ______ is exported to the blood.
This flow of base is called the ______ ______.
H+
HCO3-
Alkaline Tide
Page 782; Figure 22.20
The process of mechanical breakdown and propulsion is _______ in the stomach.
Inseperable
The relatively unchanging pressure in the filling stomach (up to 1.5 L) is due to two factors:
- Receptive relaxation of the smooth muscle in the body and fundus occurs in anticipation and response from food moving through the esophagus and into the stomach; mediated by the vagus nerve.
- Gastric accommodation is the intrinsic ability of visceral smooth muscle to exhibit the stress-relaxation response.
Peristalsis begins near the ________ ________, where it produces gentle rippling movements of the thin stomach wall.
Gastroesophageal Sphincter
Peristalsis waves in the stomach:
- Propulsion - Peristaltic waves move from the fundus toward the pylorus.
- Grinding - The most vigorous peristalsis and mixing action occur close to the pylorus. The pyloric end of the stomach acts as pump that delivers small amounts of chyme into the duodenum.
- Retropulsion - The peristaltic wave (the contraction) closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach and breaking up solids.
The rate of the stomach’s peristaltic waves can be modified, their rate is constant - always around _____ per minute
3
The contractile rhythm is set by ______ _______ cells, muscle-like non contractile cells.
enteric pacemaker
The pacemaker cells depolarize and repolarize spontaneously _____ times each minute, establishing the so-called cyclic slow waves of the stomach, or its ____ _____ _____.
three; basic electrical rhythm
Use gap junctions.
The pacemakers set the maximum frequency of contraction, but they do not initiate contractions or regulate their force.
Instead, they generate subthreshold depolarization waves, which are then “ignited” by neural and hormonal factors.
Distension of the stomach wall and gastrin-secreting cells both stimulate gastric smooth muscle and increase gastric motility.
The more food in the stomach the more vigorous the mixing and emptying movements will be - within certain limits.
The stomach usually empties within _____ hours after a meal.
4
The larger the meal (the greater the stomach distension) and the more liquid its contents, the ______ the stomach empties.
Faster
Fluids pass _____ through the stomach.
Quickly
The gastric emptying also depends as much - and perhaps more - on the contents of the ______ as on what is happening in the ________..
Duodenum; Stomach
As chyme enters the duodenum, receptors in its wall respond to chemical signals and to stretch. This initiates the enterogastric reflex and the hormonal (enterogastrone) mechanisms that inhibit gastric secretion.
These mechanisms also prevent further duodenal filling by reducing the force of pyloric contractions.
A ______-rich meal moves through the duodenum quickly, however _____ form an oily layer at the top of the chyme and are digested more slowly by enzymes acting in the intestine.
Carbohydrate; Fat
Extreme stretching of the stomach or the intestine or irritants such as bacterial toxins, excessive alcohol, spicy foods, and certain drugs.
Vomiting
Produces bile for export to the duodenum
Liver
Fat emulsifier that breaks down fat into tiny particles and make them more readily digestible.
Bile
Chiefly a storage organ for bile.
Gallbladder
Supplies most of the enzymes that digest chyme as well as bicarbonate that neutralizes stomach acid.
Pancreas
Largest gland in the body.
Liver
- Located under the diaphragm and lies within the rib cage.
- Occupies the right hypochondriac and epigastric region.
- Extends farther to the right of the body midline than to the left.
Liver
The liver has ____ primary lobes.
Four
The largest _____ lobe, is visible on all liver surfaces and separated from the smaller ____ lobe by a deep fissure. The posteriormost _____ lobe and the ____ lobe, which lies inferior to the left, are visible in an inferior view of the liver.
Right; Left; Caudate; Quadrate
A mesentery that separates the right and left lobes anteriorly and suspends the liver from the diaphragm and anterior abdominal wall.
Falciform Ligament
A fibrous remnant of the fetal umbilical vein that runs along the falciform ligament.
Round Ligament
Except for the ________ liver area which touches the diaphragm, the entire liver is enclosed by the visceral peritoneum.
Superiormost
The _____ _____ _____ and the _____ _____ _____, which enter the liver at the _____ _____, and common hepatic duct, which runs inferiorly from the liver, all travel through the ______ ______ to reach their destination.
Hepatic Artery Proper; Hepatic Portal Vein; Porta Hepatis
Lesser Omentum
Bile leaves the liver lobes through the _____ and ____ ____ ____. These fuse to form the ____ _____ _____, which travels downward toward the duodenum.
right and left hepatic ducts
Common hepatic duct
The common hepatic duct fuses with the _____ _____ draining the gallbladder to form the ____ ____.
cystic duct; bile duct
Sesame seed-sized structural and functional units that are roughly hexagonal structure consisting of plates of hepatocytes, liver cells, organized like bricks in a garden wall.
Liver lobules
The liver’s main function is to….
process nutrient-rich blood delivered to it.
At each of the six corners of a liver lobule is a _____ _____. Named that because (3) basic structures:
Portal Triad
- Branch of the hepatic artery.
- Branch of the hepatic portal vein (carrying venous blood laden with nutrients from the digestive viscera)
- Bile duct.
Between the hepatocyte plates are enlarged, heavily fenestrated ______ ______.
Liver sinusoids
Blood from both the hepatic portal vein and the hepatic artery proper percolates from the triad regions through these sinusoids and empties into the central vein.
From the central vein the blood eventually enters the hepatic veins, which drain the liver and empties into the _____ ______ ______.
Inferior Vena Cava
Remove debris such as bacteria and worn-out blood cells from the blood as it flows past. They form part of the sinusoid walls.
Hepatic macrophages
Versatile hepatocytes have large amounts of:
Rough ER Smooth ER Golgi Apparatus Peroxisomes Mitochondria
Hepatocytes can:
- Secrete some 900 ml of bile daily.
- Process bloodborne nutrients in various ways (example: store glucose as glycogen and use amino acids to make plasma protein - albumin).
- Store fat-soluble vitamins.
- Play important roles in detoxification such as riding the blood of ammonia by converting it to urea.
Secreted bile flows through tiny canals, called _____ ______ that run between adjacent hepatocytes toward the bile duct branches in the portal triads.
Bile canaliculi
Blood and bile flow in _______ directions in the liver lobule.
Opposite
Bile entering the bile ducts eventually leaves the liver via the common hepatic duct to travel toward the duodenum.
Yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids (lecithin and others), and a variety of electrolytes.
Of these, only bile salts and phospholipids aid in the digestive process.
Bile
Primarily slats of cholic and chenodeoxycholic acids, are cholesterol derivatives.
Bile salts
Many substances secreted in bile leave the body in ______, but bile salts are not among them.
Feces
The enterohepatic circulation conserves bile salts by:
- Bile salts are secreted into the duodenum.
- Bile salts travel through the small intestine, they allow lipid digestion and absorption to occur.
- 95% of bile salts are reabsorbed by the ileum (last part of the small intestine)
- Reabsorbed bile salts travel via the hepatic portal vein back to the liver, where they are recycled. Only 5% of bile salts are newly synthesized each time.
The enterohepatic circulation minimizes the amount of new bile salts that must be synthesized, which is important because they are recirculated ___ to ___ times per day.
4; 12
The chief bile pigment is _______, a yellow waste product of the heme of hemoglobin formed during the breakdown of worn-out erythrocytes.
The ____ and _____ parts of hemoglobin are saved and recycled.
Bilirubin is absorbed from the blood by liver cells, excreted into bile and metabolized in the small intestine by resident bacteria.
Bile
Iron; Globin
Gives feces it’s brown color.
Stercobilin
Inflammation of the liver that has many causes including the toxic effects of alcohol, drugs and wild mushrooms.
Hepatitis
Hepatitis ____ has emerged as the most important infectious liver disease in the United States because it produces persistent or chronic liver infections.
C
The most common liver disease in North America. It affects about 30% of the general population, but 70% of the obese.
Obesity and increased insulin resistance are associated with abnormal lipid metabolism and liver inflammation, .
Non-Alcoholic Fatty Liver Disease (NAFLD)
The last stage of progressive chronic inflammation of the liver.
Results from severe chronic hepatitis due to chronic alcoholism.
Cirrhosis
Damaged hepatocytes can regenerate, the liver’s connective (scar) tissue regenerates faster. Liver activity is depressed and the liver becomes fibrous with scar tissue.
Scar tissue obstructs blood flow throughout the hepatic portal system, causing _____ _____.
Portal hypertension
_______ ________ are only clinically proven effective treatment for patients with end-stage liver disease.
Liver Transplants
The one- and five-year survival rate of such transplants is approximately ____% and _____%.
90; 75
The regenerative capacity of a healthy liver is exceptional. it can regenerate to it’s normal size in ____ -____ months even after surgical removal or loss of 80% of its mass.
6-12
Thin-walled muscular sac that may appear green when filled with bile.
Snuggles in a shallow fossa on the inferior surface of the liver from which its rounded fundus protrudes.
Gallbladder
Stores bile that is not immediately needed for digestion and concentrates it by absorbing some of its water and ions.
Gallbladder
The gallbladder’s muscular walls contract to expel bile into the ______ _______. From there bile flows into the bile duct.
Covered by visceral peritoneum.
Cystic duct
Major vehicle for excreting cholesterol from the body, and the bile salts keep the cholesterol dissolved within ____.
Bile
Too much cholesterol or too few bile salts allows the cholesterol to crystallize, forming _______.
Gallstones
Gallstones block the flow of bile from the gallbladder.
Cholelithiasis
Treatments for gallstones include:
Dissolving the crystals with drugs, pulverizing them with ultrasound vibration, vaporizing them with lasers, and the classical treatment, surgically removing the gallbladder (cholecystectomy).
When the gallbladder is removed, the _____ _____ enlarges to assume the bile-storing role.
Gallbladder duct
Bile duct blockages prevent both bile salts and bile pigments from entering the intestine. As a result, yellow bile pigments accumulate in blood and eventually are deposited in the skin, causing it to become yellow, or jaundiced.
Jaundice caused by blocked ducts is called ______ ______.
Obstructive jaundice
An important part of the digestive process because it produces enzymes that break down all categories of foodstuffs.
Pancreas
An important part of the digestive process because it produces enzymes that break down all categories of foodstuffs.
Pancreas
Soft, tadpole-shaped gland that extends across the abdomen from its tail to its head.
Retroperitoneal and lies deep to the greater curvature of the stomach.
An important part of the digestive process because it produces enzymes that break down all categories of foodstuffs.
Pancreas
Soft, tadpole-shaped gland that extends across the abdomen from its tail to its head.
Retroperitoneal and lies deep to the greater curvature of the stomach.
The ______ part of the pancreas produces pancreas juice.
Exocrine
Pancreas Juice consists of
- Acini - Clusters of secretory acinar cells that produce the enzyme-rich component of pancreatic juice.
- Ducts - A system of ducts transports the secretions of the acinar cells. The epithelial cells of the smallest ducts secrete the water that makes up the bulk of the pancreatic juice and the bicarbonate that makes this secretion alkaline (pH 8).
Pancreas Juice consists of
- Acini - Clusters of secretory acinar cells that produce the enzyme-rich component of pancreatic juice.
- Ducts - A system of ducts transports the secretions of the acinar cells. The epithelial cells of the smallest ducts secrete the water that makes up the bulk of the pancreatic juice and the bicarbonate that makes this secretion alkaline (pH 8).
Acinar cells are full of ______ _______ and exhibit deeply staining ________ ________. These granules contain digestive enzymes (proenzymes).
Endoplasmic reticulum; Zymogen granules
The endocrine part of the pancreas is a scattering of mini endocrine glands called _______ _______.
Pancreating Islets
Pancreatic Islets release _______ and _______ hormones that play an important role in carbohydrate metabolism.
Glucagon; Insulin
Consists mainly of water, and contains enzymes and electrolytes (primarily bicarbonate ions).
Pancreatic Juice
The high pH of pancreatic juice helps neutralize acidic chyme entering the duodenum and provides the optimal environment for intestinal and pancreatic enzymes.
Pancreatic Enzymes
Proteases
Amylases
Lipases
Nucleases
Like pepsin of the stomach, _______ are produced and released in inactive forms that are activated in the duodenum. This protects the pancreas from digesting itself.
Proteases
Within the duodenum, _________, an enzyme bound to the plasma membrane of duodenal epithelial cells, activates trypsinogen to trypsin.
Trypsin activates more trypsinogen and two other pancreatic proteases to their active forms, carboxypeptidase and chymotrypsin.
Enteropeptidase
The ____ ____, delivering bile from the liver, and the main ______ ______. carrying pancreatic juice from the pancreas, unite in the wall of the duodenum.
They fuse together at a bulblike structure called the ______ ______.
Bile Duct; Pancreatic Duct
Hepatopancreatic ampulla
The ampulla opens into the duodenum via the volcano-shaped _____ ______ ______. A smooth muscle valve called the _______ ________ controls the entry of bile and pancreatic juice.
A smaller accessory pancreatic duct empties directly into the duodenum just proximal to the main duct.
Major Duodenal Papilla
Hepatopancreatic Sphincter
Accessory Pancreatic Duct
________ and _______ stimuli both regulate the secretion of bile and pancreatic juice into the small intestine.
Hormones and neural
Bile salts themselves are the major stimulus for enhanced bile secretion. After a fatty meal, when the _______ _______ is returning large amounts of bile salts to the liver, its output of bile rises dramatically. ______ also stimulates liver cells to secrete bile.
enterohepatic circulation; secretin
When no digestion is occurring, the hepatopancreatic sphincter is _______ and the released bile backs up the _______ _______ into the gallbladder, where it is stored and needed.
closed; cystic duct
The _____ _____ is the body’s major digestive organ. There digestion is completed (with the help of bile and pancreatic enzymes) and virtually all absorption occurs.
Small intestine
The small intestine is a convoluted tube extending from the _______ _______ to the _______ ________ where it joins the large intestine. It is the longest part of the alimentary canal.
Pyloric Sphincter; Ileocecal Valve
Three subdivisions of the small intestine:
- Duodenum
- Jejunum
- Ileum
Three subdivisions of the small intestine:
- Duodenum; Retroperitoneal
- Jejunum; Intraperitoneal
- Ileum; Intraperitoneal
The ileum, the third part of the small intestine, joints the large intestine at the _______ _______.
Ileocecal valve
The arterial supply of the small intestine is primarily from the _____ _____ _____, which branches off the abdominal aorta.
Superior mesenteric artery
The veins parallel the arteries and typically drain into the ______ _______ ______. From there, nutrient-rich venous blood from the small intestine drains into the ______ ______ _____, which carries it to the liver.
Superior mesenteric vein; Hepatic portal vein
Nerve fibers serving the small intestine include parasympathetic from the _____ _____ and sympathetics from the _____-_____ _____, both relayed through the superior mesenteric (and celiac) plexus.
Vagus nerve; Thoracic-splanchnic nerves
The structural modifications of the small intestine for absorption:
- Circular folds
- Villi
- Microvilli
These amplify its absorptive surface enormously (by a factor of more than 600 times). Roughly equal to 200 square meters.
Deep, permanent folds of the mucosa and submucosa. Force chyme to spiral through the lumen, slowing its movement and allowing time for full nutrient absorption.
Circular Folds
Fingerlike projections of the mucosa that give it a velvety texture, much like a soft nap of a towel.
Large and leaf-like in the duodenum (most active absorption) and gradually narrow and shorten along the length of the small intestine.
Villi
In the core of each villus, there is a dense capillary bed and a wide lymphatic capillary called a ______. Digested foodstuffs are absorbed through the enterocytes into both the capillary blood and the ______ (same as above).
Lacteal
_______ are long, densely packed cytoplasmic extensions of the absorptive cells of the mucosa that give the mucosal surface a fuzzy appearance called the _____ _____.
Microvilli; Brush border
The plasma membrane of the microvilli bear enzymes referred to as ______ ______ _______, which complete the digestion of carbohydrates and proteins in the small intestine.
Brush border enzymes.
Between the villi, the small intestine mucosa is studded with tubular glands called ______ ______.
Intestinal crypts
- Form the bulk of the epithelium.
- Simple columnar absorptive cells bound by tight junctions and richly endowed with microvilli.
- Primarily responsible for absorbing nutrients and electrolytes in the villi.
In the crypts:
- Primarily secretory cells that secrete intestinal juice, a watery mixture that contain mucus and serves as a carrier fluid for absorbing nutrients from chyme.
Enterocytes
Mucus-secreting cells found in the epithelia of the villi and crypts.
Goblet Cells
The source of the enterogastrones discussed earlier (secretin and cholecystokinin). Mostly found in the crypts but some are also found in the vili.
Enteroendocrine Cells
- Found deep in the crypts
- Specialized secretory cells that fortify the small intestine’s defenses by releasing antimicrobial agents such as defensins and lysozyme,
- These secretions destroy certain bacteria and help to determine which bacteria colonize the intestinal lumen.
Paneth Cells
- Continuously divide in the depths of the crypts.
- Daughter cells differentiate to become tall of the other cell types.
- Most differentiate as they gradually migrate up the villi.
- Enterocytes at the tis of the villi undergo apoptosis and are shed, renewing the villus epithelium ever 3-5 days.
Stem Cells
Mucosa-associated Lymphoid Tissue (MALT) includes both individual lymphoid follicles and aggregated lymphoid nodules, the later called ______ ______, which are primarily located in the lamina propria but occasionally protrude into the submucosa below.
Peyer’s Patches
There increasing abundance towards the end of the small intestine reflects the fact that this region contains huge numbers of bacteria that must be prevented from entering the bloodstream.
The ________ _______ of the mucosa contain large numbers of ________ ___ (____)-secreting plasma cells that help protect against intestinal pathogens.
Lamina Propria
Immunoglobulin A; IgA
The submucosa of the small intestine is typically ____ _____ tissue.
Areolar Connective
Elaborate mucus-secreting ______ _______ in the submucosa of the duodenum produce an alkaline (bicarbonate-rich) mucus that helps neutralize acidic chyme moving in from the stomach.
When protective mucus is inadequate, the intestinal wall erods and duodenal ulcers result.
Duodenal Glands
The muscularis externa in the small intestine is typical and bilayered, except for the duodenum, which is retroperitoneal and has an ________, visceral peritoneum that covers the external intestinal surface.
Adventitia
The major production of intestinal juice comes from the ______ or ______ ______ from the stomach.
Hypertonic; Acidic Chyme
Normally, intestinal juice is slightly alkaline (7.4-7.8) and isotonic with blood plasma.
Intestinal juice is largely ______ , but also contains some _____, which is secreted both by the duodenal glands and by goblet cells of the mucosa.
Water; Mucus
By the time food reaches the small intestine, it is unrecognizable, but far from being digested.
Carbohydrates and proteins are partially degraded, but fat digestion has only begun.
The process of digestion accelerates during the chyme’s tortuous _____- to ______-hour journey through the small intestine, and it is here that most of the water and virtually all nutrients are absorbed.
3- to 6-hour
Most of the substances required for digestion - _______, ______ _______, and ________ _______ (provide proper pH for enzymatic catalysis) - are imported from the liver and pancreas.
Bile
Digestive Enzymes
Bicarbonate Ions
_______ _______ enzymes perform the final digestion of the food into the simple components that can be absorbed by the intestinal cells.
Brush border
_______ _______ enzymes perform the final digestion of the food into the simple components that can be absorbed by the intestinal cells.
Brush border
Chyme entering the duodenum is usually _______.
Hypertonic
_______ _______ enzymes perform the final digestion of the food into the simple components that can be absorbed by the intestinal cells.
Brush border
Chyme entering the duodenum is usually ________.
Hypertonic
If large amounts of chyme rushed into the small intestine, the osmotic water loss from the blood into the intestinal lumen would result in dangerously low blood volume.
Additionally, the low pH of entering chyme must be adjusted upward and the chume must be well mixed with bile and pancreatic juice to continue.
Feedback from the _______ _______ and ________ to the stomach pylorus carefully controls food movement into the small intestine to prevent the duodenum from being overwhelmed.
Enterogastric reflex; Entergastrones
The principal form of motility that ensures chyme is mixed thoroughly with bile and pancreatic intestinal juice.
It can also ensure that the absorbable products of digestion come in contact with the mucosa for absorption.
Segmentation
Unlike the strength of the contraction of the small intestine, the ______ of contraction of each intestinal region is not affected by reflexes or hormones.
rhythm
The intestinal contents are massaged (alternating contractions and relaxation rings of smooth muscle simply move the chyme backward and forward a few centimeters at a time). _______ ________ cells initiate these segmenting movements.
Intrinsic Pacemaker
Unlike the strength of the contraction of the small intestine, the ______ of contraction of each intestinal region is not affected by reflexes or hormones.
rhythm
Most of the time the ______ _______ is closed.
Ileocecal valve
As motilin blood levels rise, peristaltic waves are initiated in the proximal duodenum every 90 to 120 minutes and sweep slowly along the intestine, moving 50-70 cm before dying out.
Each successful wave begins a bit more distally, this pattern is called ______ ____ ______.
A complete trip from the duodenum to the ileum takes about two hours.
The process then repeats itself, sweeping the last remnants of the meal plus bacteria, sloughed-off mucosal cells and other debris into the large intestine.
This keeps bacteria from the large intestine from entering the small intestine.
As food enters the stomach with the next meal, segmentation replaces peristalsis.
Migrating Motor Complex
Two mechanisms that cause the ileocecal valve to open:
- Gastroileal Reflex - a long neural reflex triggered by stomach activity, increases the force of segmentation in the ileum and relaxes the ileocecal valve.
- Gastrin - a hormone released by the stomach, increases the motility of the ileum and relaxes the ileocecal valve.
Once the chyme passes through the ileocecal valve, it closes the valve flaps preventing regurgitation into the ileum.
The ______ ______ frames the small intestine on three sides and extends from the ileocecal valve to the _______.
Large intestine; Anus
Except for its terminal the longitudinal muscle layer of its muscularis is mostly reduced to three bands of smooth muscle called _____ ______.
Teniae Coli
Except for its terminal the longitudinal muscle layer of its muscularis is mostly reduced to three bands of smooth muscle called _____ ______.
Teniae Coli
The teniae coli’s tone puckers the wall of the large intestine into pocketlike sacs called _____.
Haustra
Small fat-filled pouches of visceral peritoneum that hang from the surface of the large intestine.
Epiploic appendages
The twisted structure of the appendix makes it susceptible to _______.
Blockages
__________ results from a blockage of the appendix that traps infectious bacteria in its lumen.
Appendicitis
If the appendix ruptures, feces containing bacteria spray over the abdominal contents causing peritonitis.
The colon elements in order from the ileocecal valve to the anus:
- Ascending Colon
- Right Colic (Hepatic) Flexure
- Transverse Colon
- Left Colin (Splenic) Flexure
- Descending Colon
- Sigmoid Colon
- Rectum
- Anal Canal
The rectum has three lateral curves or ends, represented internally as three transverse folds called _____ _____.
Rectal Valves
These stop feces from being passed along with gas.
The ____ ____ is the last segment of the large intestine and lives in the perineum, entirely external to the abdominopelvic cavity.
Anal canal
Opens to the anus.
The anal canal has two sphincters
Internal anal sphincter (smooth muscle)
External anal sphincter (skeletal muscle)
Act like purse strings to open and close the anus, are ordinarily closed except during defecation.
The colon is retroperitoneal except for its ______ and _____ parts. These parts are anchored to the abdominal wall by mesentrary sheets called _____.
Transverse and sigmoid parts
Mesocolon
The walls of the large intestine differ from the small intestine in several ways:
- There are no circular folds, villi, or brush border because most food is absorbed before reaching the large intestine.
- Its mucosa is thicker, its abundant crypts are deeper, and the crypts contain tremendous numbers of goblet cells.
Mucus produced by the goblet cells eases the passage of feces and protects the intestinal walls from irritation by acids and gases released by resident bacteria.
Like the small intestine, the large intestine mucosa is ______ _______ ______, except in the anal canal.
Simple columnar epithelium
The mucosa of the anal canal, a _______ _______ ______, merges with the true skin surrounding the anus and is quite different from the mucosa in the rest of the colon - reflecting the great abrasion this region recieves.
stratified squamous epithelium
The mucosa of the anal canal hangs in long ridges or folds called _____ _____ and _____ _____ recess between them and exude mucus when compressed by feces, which aids in emptying the anal canal.
Anal columns; Anal sinuses
Superior to the anal sinuses, the area is ________ to pain and inferior the anal sinuses, the area is _______ to pain.
Insensitive; sensitive
When hemorrhoidal veins become dilated and inflamed, they become ________.
Hemorrhoids
Some bacteria colonize the colon via the ______, but other enter from the small intestine still “alive and kicking” after running the gauntlet of antimicrobial defenses, which include:
Anus
Lysozyme, defensins, HCl, protein-digesting enzymes
Gut bacteria help us by recovering energy from otherwise indigestible foods and synthesizing some vitamins:
- Fermentation
2. Vitamin synthesis
Gut bacteria ______ some indigestible carbohydrates and mucin in the gut mucus. The resulting ______-_____ _____ ______ can be absorbed and used for fuel by the body’s cells.
ferment; short-chain fatty acids
_______ produces a mixture of gases (including dimethyl sulfide, H2, N2 CH4, and CO2).
Fermentation
Gut bacteria _______ vitamins.
Synthesize
B complex vitamins and some vitamin K of the liver need in order to produce several clotting proteins are synthesized by gut bacteria.
The _______ _______ threatens to destroy any bacteria that threaten to breach the mucosal barrier.
Immune system
The gut bacteria, instruct the immune system to not _______ to their presence in the lumen.
overreact
Potentially harmful bacteria in our large intestine are kept in check in two ways.
- Beneficial bacteria outcompete and actively suppress harmful bacteria, and as a result normally vastly outnumber them.
- Our immune system prevents bacteria from entering the body through the gut epithelium.
_______ cells sample the microbial antigens in the lume. They then migrate to the nearly lymphoid follicles within the gut mucosa (MALT) and trigger an IgA antibody mediated response restricted to the gut lumen.
Dendritic
This prevents bacteria from straying into the tissues deep to the mucosa and causing a much more widespread systemic response.
An anaerobic bacterium, accounting for 14,000 deaths per year.
The most common cause of antibiotic-associated diarrhea.
Colstridium difficile
The type of bacteria present influences the balance between subtypes of ______, in which turn affects the balance between pro- and anti-inflammatory responses.
T Cells
______ results from an abnormal immune and inflammatory response to bacterial antigens that normally occur in the intestine.
Irritable Bowel Disease
Digestion in the large intestine takes about _____-______ hours
12-24
The large intestine harvests vitamins made by the gut bacteria and reclaims most of the remaining water and some of the electrolytes (particularly sodium and chloride).
Primary concerns are propulsive activities that force fecal material toward the anus and eliminate it from the body (defecation).
IF the colon is removed, the terminal ileum can be brought out of the abdominal wall in a procedure called ______.
From there food residues are eliminated into a sac attached to the abdominal wall.
Ileostomy
Slow, segmenting movements that last about one minute and occur every 30 minutes or so.
Haustral contractions
As a _______ fills with food residue, the distension stimulates its muscle to contract. These movements mix the residue, which aids in water absorption.
Haustrum
Long, slow-moving but powerful contractile waves that move over large areas of the colon 3-4 times daily and force contents towards the rectum.
Mass movements
Occur typically during or after just eating.
The presence of food in the stomach activates the gastroileal reflex in the small intestine and the propulsive ______ ______ in the colon.
gastrocolic reflex
Haustral contractions in the descending and sigmoid colon promote the final ______ ____ of the feces.
drying out
______ in the diet strengthens colon contractions and softens the feces, allowing the colon to act like a well- oiled machine.
Fiber
Semisolid feces delivered to the rectum contain:
Undigested food residue
Mucus
Sloughed-off epithelial cells
Millions of bacteria, and just enough water to allow their smooth passage
Of the 500ml or so of food residue that enters the cecum daily, only _____ becomes feces.
150 ml
When the diet lacks fiber and the volume of residues in the colon is small, the colon narrows and its contractions become more powerful, increasing the pressure on its walls. This promotes formation of _______, small herniations of the mucosa through the colon walls.
This condition is called _______, most commonly occurs in the sigmoid colon and affects over half of people over the age of 70.
Diverticula
Diverticulosis
In 4-10% of cases, diverticulosis progresses to ________, which the diverticula become inflamed and may rupture, leaking into the peritoneal cavity, which can be life threatening.
Diverticulitis
`A functional GI disorder not explained by anatomical or biochemical abnormalities.
Recurring (or persistent) abdominal pain that is relieved by defecation.
Changes in consistency and frequency of their stools and varying complaints of bloating, flatulence, nausea and depression.
Stress is a common precipitating factor and stress management is important aspect of treatment.
Irritable Bowel Syndrome
Stretching the rectal walls initiates _______.
Defecation
Defecation reflex:
Page 802; Figure 22.35
Involuntary or automatic defecation occurs in ______ because they have no yet gained control of their external anal sphincter. It also occurs in those with spinal cord transections.
Infants
Result from any condition that rushes food through the large intestine before that organ has had sufficient time to absorb the remaining water.
Diarrhea
When food remains in the colon for extended period of times, too much water is absorbed and the stool becomes hard and difficult to pass.
Constipation
Insufficient fiber, fluid intake, improper bowel habits, lack of exercise or laxative abuse.
Mechanical breakdown only changes _______, digestion breaks down ingested food into their ______ ____ _____, which are very different molecules chemically.
Appearance; Chemical Building Blocks
Only these chemicals are small enough to be absorbed through the small intestine.
Catabolic process that breaks down large food molecules into monomers (chemical building blocks)
Digestion
Accomplished by enzymes secreted into the lumen of the alimentary canal and by intrinsic and accessory glands.
Enzymatic breakdown of any food molecule is _______.
Hydrolysis
Adds a water molecule to each molecular bond to be broken.
_______ _______ break large chemical (usually polymers) into smaller pieces that are broken down into individual components by the intestinal (brush border) enzymes.
Pancreatic Enzymes
Alkaline pancreatic juice neutralizes the acidic chyme that enters the small intestine from the stomach.
_______ _______ break large chemical (usually polymers) into smaller pieces that are broken down into individual components by the intestinal (brush border) enzymes.
Pancreatic Enzymes
Alkaline pancreatic juice neutralizes the acidic chyme that enters the small intestine from the stomach for the operation of enzymes.
________ is the process of moving substances from the lumen of the gut into the belly.
Absorption
Epithelial have a _____ and a _____ side.
______ ______ join the epithelial cells (enterocytes) of the intestinal mucosa at their apical surfaces, substances usually cannot move between cells.
Apical; Basal
Tight Junctions
Food material must pass through ___________. Materials enter through the ______ membrane from the lumen of the gut and exit through the ______ membrane into the interstitial fluid on the other side of the cell.
Enterocytes
Apical
Basolateral
Once substances are in the interstitial fluid they diffuse into the _____ _____.
Blood capillaries.
From the blood capillaries, material is transported in the _______ _______ _______ to the liver.
The exception is some lipid digestion products, which enter the lacteal in the villus to be carried by the lymphatic fluid to the blood.
Hepatic Portal Vein
Most nutrients are absorbed by ______ transport processes driven directly or indirectly by metabolic energy, ATP.
Active
Up to ____ of food, drink, and GI secretions enter the alimentary canal daily, but ____ or less reaches the large intestine.
10L; 1L
Most of absorption occurs in the small intestine and most of that is completed by the time it reaches the _____.
Ileum
The major absorptive role of the ileum is to reclaim _____ _____ and transport back to the liver for resecretion.
Bile Salts
Most digestible carbohydrates are in the form of ____, with smaller amounts of disaccharides and monosaccharides.
Starch
Only three common monosaccharides in our diet:
Glucose, Fructose, Galactose
The more complex carbohydrates that our body is able to break down to monosaccharides are the disaccharides:
Sucrose (Table Sugar), Lactose (Milk Sugar), Maltose (Grain Sugar)
The more complex carbohydrates that our body is able to break down to monosaccharides are the polysaccharides:
Glycogen and Starch
Present in the saliva, splits starch into oligosaccharides, smaller fragments of two to eight linked glucose molecules
Saliva Amylase
Starch digestion continues until salivary amylase is inactivated by HCl and broken apart by the stomach protein-digesting enzymes.
The larger the meal, the longer it takes for salivary amylase to work in the stomach.
Undigested disaccharides (lactose) create osmotic gradients that prevent water from being absorbed in the intestines and also pull water from the interstitial space into the intestines. The result is diarrhea.
Lactose Intolerance
Bacterial metabolism of the undigested solutes produces large amounts of gas that result in bloating, flatulence, and cramping pain.
Proteins digested in the GI tract:
- Dietary Proteins
- Enzyme proteins secreted into the GI tract by various glands
- Protein derived from sloughed and disintegrating mucosal cells.
Protein digestion begins in the stomach when _______ secreted by chief cells is activated to ______.
Pepsinogen; Pepsin
Pepsin functions optimally in acidic pH range from the stomach ____ to _____.
1.5 to 2.5
Pepsin cleaves bonds consisting of the amino acids _______ and _______.
Tyrosine; Phenylalanine
Pepsin is inactivated by high pH of the ________.
Duodenum
Pepsin is inactivated by high pH of the ________.
Duodenum
The _____ _____ is the primary source of lipid digestion because the pancreas is the major source of fat-digesting enzymes, or _______
Small intestine; Lipases
