B5: Cell Bio Exam 1

cephalic phase

Which phase of digestion:

-the taste, smell, or thought of food or tactile sensations of food in the mouth stimulate the medulla oblongata

-CN X carries parasympathetic action potentials to the stomach, where enteric plexus neurons are activated

-post-ganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells

-gastrin is carried through the circulation back to the stomach, where, along with histamine, it stimulates secretion

oral phase

Which phase of digestion:

-pH 5-7, enzymes, salts, 5s-2min

-food lubrication

-mastication

-bolus formation

-initiation of swallowing

-preparation of GI tract for digestion

esophageal phase

Which phase of digestion:

-propel food from the mouth to the stomach

-sphincters protect the airway during swallowing and protect the esophagus from acidic gastric secretions

cephalic phase

Which phase of digestion:

-Purpose = prepare the body for a meal before food is consumed

-Stimulated by thoughts of food, hunger cues, sight/smell of food, sound of a sizzling grill, emotional states (e.g., can be positive or negative)

-Results in increased parasympathetic outflow (e.g., increased salivation via CN IX and VII as well as activation of the dorsal vagal complex (DVC) resulting in increased gastric acid and pancreatic enzyme secretion, gallbladder contraction, and sphincter of Oddi relaxation

parasympathetic

The cephalic phase of digestion results in increased (parasympathetic/sympathetic) outflow

1.5L

How much saliva is secreted per day (approximately) at a rate of 1 mL/min/g?

saliva

What is a watery liquid secreted into the mouth by glands and functions to:

-break down starch via salivary amylase (chemical digestion)

-lubricate the mouth for speech and swallowing

-neutralize acids (important for reflux + vomiting)

-initiate starch and lipid digestion

-fight microbes

-maintain tooth homeostasis

-enhance taste

both sympathetics and parasympathetics

What provides stimulation for saliva secretion?

CN VII and CN IX

What cranial nerves are involved in the parasympathetic stimulation of saliva secretion?

sleep, dehydration, and anticholinergic drugs (atropine)

What inhibits saliva secretion?

xerostomia

What disorder:

-dryness in the mouth, which may be associated with a change in the composition of saliva, or reduced salivary flow, or may have no identifiable cause

-can be due to side effects of medication, dehydration, radiation, chemotherapy

-results in dental caries, oral candidiasis, dysguesia, dysphagia, fissured tongue with atrophy of the filiform papillae and erythematous appearance of tongue

-a symptom of Sjogren syndrome, a long-term autoimmune disease that affects lacrimal and salivary glands and is detectable by anti-Ro/SSa and/or anti-La/SSb Abs

parotid, submandibular, sublingual

what are the 3 major salivary glands?

Hint: Responsible for 90% secretion via ducts into the oral cavity

complex tubuloacinar

What type of glands are the salivary glands?

acinar cells

What cells of the salivary glands:

-produce primary saliva via serous cells and mucous cells

-blind end of each duct

-serous cells secrete fluid of water, ions, and enzymes

-mucous cells secrete mucin glycoproteins

ductal cells

What cells of the salivary glands:

-modify salivary composition by altering the concentrations of electrolytes, producing final saliva

-intercalated and striated ducts due to high content of mitochondria to support high metabolism

myoepithelial cells

What cells of the salivary glands:

-facilitate secretion in the acini and intercalated ducts

serous

(serous/mucous) cells secrete fluid of water, ions and enzymes (e.g. alpha amylase). Parotid glands secrete almost entirely this type of secretion

mucous

(serous/mucous) cells secrete mucin glycoproteins for lubrication and for surface protection purposes. Submandibular and sublingual glands secrete this type and the serous type (so both types)

acinar

Which mechanism of salivary secretion:

-saliva is isotonic, similar to plasma

-includes organics like IgA, alpha amylase, lipase, lactoferrin, kallikrein

-leaky cells that allow for paracellular transport

ductal

Which mechanism of salivary secretion:

-Net secretion of K+ and bicarb

-Net absorption of Na+ and Cl-

-saliva is hypotonic because these cells have TIGHT JUNCTIONS, therefore impermeable to water moving out (e.g., water cannot escape saliva)

-3 transporters in luminal membrane: Na+/H+ exchange, Cl-/HCO3- exchange, and H+/K+ exchange

-on the basolateral membrane, there is a Na+/K+ pump and a Cl- channel & the combined action of these is absorption of Na+ and Cl- with secretion of K+ and bicarb

K+ and bicarb

ductal cells have a net secretion of what ions?

Na+ and Cl-

ductal cells have a net absorption of what ions?

low

At (low/high) salivary flow rates:

-saliva is HYPOTONIC

-very different from plasma due to increased time in ducts

high

At (low/high) salivary flow rates:

-saliva is less hypotonic

-composition more similar to plasma from decreased contact time in ducts

-exception = bicarb is selectively secreted at high flow rates

autonomic

saliva secretion is almost exclusively neural by the ______ nervous system

parasympathetics

_______ have a much greater effect on saliva secretion, therefore its interruption will greatly reduce salivation

parasympathetic

(sympathetic/parasympathetic) control of salivary secretion involves:

-via CN VII and CN IX

-ACh used as the transmitter which stimulates muscarinic receptor on acinar or ductal cells to release IP3 and Ca2+

-increases blood flow to meet huge metabolic demand

-stimuli = cephalic phase stimuli or presence of food in oral cavity

-inhibition via dehydration, fear, sleep, medication (atropine and other anti-cholinergics)

sympathetic

(sympathetic/parasympathetic) control of salivary secretion involves:

-from thoracic cord via superior cervical ganglia

-uses NE as transmitter --> stimulates beta receptors which increase cAMP in acinar or ductal cells

oral phase

Which phase of digestion:

-Purpose = lubrication, formation of bolus, and propulsion to esophagus

-Stimulated by taste and mechanical stimuli from food in mouth

-Results in increased salivation via CN VII and IX, chewing, swallowing, and a continuation of preparation of GI tract for a meal through the activation of the dorsal vagal complex which will result in increased gastric acid and pancreatic enzyme secretion, gallbladder contraction, and sphincter of Oddi relaxation

chewing

What result of the oral phase:

-mixes food with saliva to increase taste and begin carb digestion

-reduces particle size to facilitate swallowing and prevent choking

-may assist with satiety

-involves the mm. of mastication (innervated by CN V3) --> temporalis, masseter, medial and lateral pterygoid mm.

-has voluntary and involuntary components in which the involuntary component involves reflexes initiated by food in the mouth which sends sensory information to the brainstem to orchestrate a reflex oscillatory pattern of this activity to the masticatory muscles

-much of the process is caused by a reflex. The presence of a bolus of food in the mouth at first initiates reflex inhibition of the muscles of mastication, which allows the lower jaw to drop. This drop in turn initiates a stretch reflex of the jaw muscles that leads to rebound contraction. This action automatically raises the jaw to cause closure of the teeth, but it also compresses the bolus again against the linings of the mouth, which inhibits the jaw muscles once again, allowing the jaw to drop and rebound another time; this process is repeated again and again

swallowing

What result of the oral phase:

-a highly coordinated action with a rigid order of events

-has 2 functional components; 1) propulsive and 2) protective (e.g., covering via epiglottis to protect the airway)

-3 phases:

1. oral (voluntary) which initiates the process

2. pharyngeal (involuntary) which constitutes passage of food through the pharynx into the esophagus

3. esophageal (involuntary) which transports food from the esophagus into the stomach

-this phase is initiated when the tongue forces a bolus of food back toward the pharynx by pressure of the tongue upward and backward against the palate which will stimulate epithelial swallowing receptor areas all around the opening of the pharynx, especially on the tonsillar pillars, and impulses from these areas pass to the brainstem to initiate a series of automatic pharyngeal muscle contractions

swallowing

What result of the oral phase:

-airway and foodway must be coordinated

-important anatomy for swallowing and protecting airway includes the tongue, hard and soft palates, pharynx, upper esophageal sphincter, and the esophagus

-innervation:

1. Coordinated by the swallowing center in the medulla & pons

2. Trigeminal (V3): motor to soft palate, muscles of mastication

3. Glossopharyngeal (CN IX): Sensory in pharynx

4. Vagus (CN X): motor to pharynx, sensory and motor to esophagus

Oral Phase (voluntary)

1. Tongue presses up against hard palate and propels food to pharynx

2. Swallowing reflex initiated by sensors within the pharynx b/c bolus pushes on sensory receptors (mechanical AND chemical) in the pharynx

Pharyngeal Phase (involuntary)

1. Soft palate moves upward and protects nasal cavity from food reflux

2. Larynx moved forward and up. Epiglottis deflected down to protect the airway.

3. UES (upper esophageal sphincter) relaxes

4. Superior constrictor contracts to propel bolus and initiate peristaltic wave

5.Bolus travels through UES into esophagus

Esophageal Phase (involuntary)

1. UES constricts

2. Primary peristaltic wave to propel bolus down down down

Describe the swallowing sequence.

Need to know this!

swallowing center

What is found in the brainstem and is critical for coordinating the sequence and timing of swallowing?

dysphagia

What disorder:

-difficulty swallowing

-due to disruption of the innervation, neuromuscular junction, musculature, or swallowing center (an obstructive proccess)

-can be caused by/associated with peripheral neuropathy, MS, cerebrovascular accident, brainstem tumor, neuromuscular diseases (e.g., ALS), muscular dystrophy, obstructive processes (e.g., tumor, diverticulum)

-swallowing study important for diagnosis as well as H + P

esophageal phase

Which phase of digestion:

-Purpose = transport food from oral cavity to stomach

-Stimuli = initiated by swallowing and distension of the esophagus

-Result = food bolus is propelled down esophagus via peristalsis

esophagus

What is a muscular tube made up of inner and longitudinal tubes lined with stratified squamous epithelium and has upper, lower, and middle portions which contain striated, smooth, and mixed striated and smooth m., respectively?

sphincters

what part of the esophagus have propulsive and protective roles (as well as regulatory roles)?

swallowing center in medulla and local reflexes

What controls esophageal motility?

CN XI and CN X

afferent signals to the esophagus travel via which nerves?

somatic nerves (CN X)

What innervates the skeletal muscle of the esophagus?

Hint: striated muscle (upper esophagus + UES)

enteric nerves (CN X)

What innervates the smooth muscle of the esophagus?

Hint: lower 2/3 of esophagus

manometry

What measures the pressures along the esophagus and is used to diagnose esophageal motility disorders?

in order to keep them closed, preventing air from entering the esophagus and contents from refluxing

Why are the UES and LES (upper and lower esophageal sphincters) under higher pressures?

1. During swallowing – pharynx constricts, UES opens to allow for bolus to pass, and LES and proximal stomach relax via Ganglionic neurons release VIP and NO to induce relaxation of the sphincters

2. UES constricts

3. Primary peristalsis – a progressive wave of distension and contraction passes through the esophageal body

4. LES closes after bolus passes to proximal stomach

5. If all food does not clear in primary peristalsis, a “second wave” (secondary peristalsis) – completely driven by enteric NS

Describe the sequence of esophageal motility.

Need to know this!!!

primary

(primary/secondary) peristalsis:

-Stimulus = triggered mechanically from swallowing, propagated by stretch from bolus

-Afferent limb: Vagal afferents relay information to dorsal vagal complex

-Efferent limb:

1. Vagal efferents from DVC synapse on enteric nerves.

2. Acetylcholine release by enteric nerves causes contraction proximal to bolus

3. Nitric oxide and VIP release causes relaxation distal to bolus so the bolus can move down.

-Sequential distension and contraction propels bolus toward the stomach.

-Peristaltic wave down the esophagus takes ~10 seconds

secondary

(primary/secondary) peristalsis:

-occurs if bolus is not completely cleared

-completely under enteric nervous system control (local reflexes)

-Occurs only in smooth muscle (lower 2/3)

-Stimulus: distension at a particular site by remaining food bolus

-Afferent and efferent limbs within ENS result in contraction and distention propulsing the bolus toward the stomach

5

If two swallows are initiated in __ seconds, peristalsis stops until the bolus "catches up" and then peristalsis continues (mediated by reflexes)

rapid swallowing ("guzzling")

Peristalsis is inhibited in ___________ in which the LES remains open, and, when it stops, peristalsis resumes

scleroderma

What disorder:

-smooth muscle becomes rigid (cannot move well), thus the esophagus cannot generate peristaltic waves

-chronic connective tissue disease. causes smooth muscle atrophy and fibrosis of the distal two-thirds of the esophagus. Reduced-amplitude or absent peristaltic contractions in this region and normal or decreased lower esophageal sphincter pressure

achalasia

What disorder:

-impaired ability of LES to relax from loss of inhibitory enteric neurons in this region – inc. pressure over baseline of LES

-LES fails to open up during swallowing. LES pressure is elevated and remains so

diffuse esophageal spasm

What disorder:

-uncoordinated smooth muscle activity leading to simultaneous contractions rather than peristalsis

-a condition characterized by uncoordinated contractions of the esophagus

pharyngeal paralysis

What disorder:

-Skeletal muscle disorder lacking in sufficient pharyngeal constriction and an incompetent UES

-Rabies can cause this. Lack of pharyngeal constriction and an incompetent UES

absorb nutrients, electrolytes, and fluid while also eliminating waste

what are the two ultimate functions of digestion?

cephalic

which phase of digestion:

-occurs before food enters the stomach, especially while it is being eaten

-results from the sight, smell, thought, or taste of food; and the greater the appetite, the more intense is the stimulation

esophageal

which phase of digestion:

-bolus is propelled downward by a peristaltic movement

-lower esophageal sphincter relaxes at initiation of the swallow, and this relaxation persists until the food bolus has been propelled into the stomach

gastric

which phase of digestion:

-a period in which swallowed food and semi-digested protein (peptides and amino acids) activate gastric activity

-2/3 of gastric secretion occurs during this phase

-Ingested food stimulates gastric activity in two ways: by stretching the stomach and by raising the pH of its contents

intestinal

which phase of digestion:

-occurs in the duodenum as a response to the arriving chyme, and it moderates gastric activity via hormones and nervous reflexes. The duodenum initially enhances gastric secretion, but soon inhibits it

colonic

which phase of digestion:

-is material that is not absorbed in the small intestines

-The contents of the large intestine are called feces and destined for excretion

digestion

What begins in the mouth with the secretion of saliva and its digestive enzymes, forming food into a bolus via mechanical mastication and swallowed into the esophagus form where it enters the stomach through the action of peristalsis?

motility

Which physiologic process of the GI tract:

-Function:

1. propulsion throughout the GI tract and beyond, mixing w/ digestive jjuice

2. grinding and fragmenting

3. storage (stomach and colon)

-Mechanisms:

1. local affects

2. hormonal control

3. neural control (reflexes)

-Motility patterns vary from region to region in different phases:

1. Oropharyngeal: swallowing

2. Esophageal: peristalsis (primary and secondary)

3. Gastric: propulsion and retropulsion

4. Small intestinal: peristalsis

5. Large intestinal: mass movements, defection

6. Interdigestive phase: migrating motor complex

secretion

Which physiologic process of the GI tract:

-Function:

1. Facilitate digestion and absorption

2. Lubrication

3. Protection

4. Excretion (7L daily)

-Sources:

1. Accessory organs

2. Cells lining GI tract

3. Glands in GI tract wall

-Secretory Products:

1. Fluid and electrolytes

2. Digestive enzymes

3. Protective molecules

-Mechanisms:

1. Local affects

2. Autonomic stimulation

3. Hormonal stimulation

digestion

Which physiologic process of the GI tract:

-Function:

1. Most food we eat is unabsorbable

2. Digestion breaks down particles to absorbable components

-Mechanisms:

1. Mechanical digestion

2. Enzymatic digestion

-Requires motility and secretions

-Sites of Digestion:

1. Oral cavity (minimal)

2. Stomach

3. Small intestine

4. Large intestine (minimal)

absorption

Which physiologic process of the GI tract:

-Function: To transfer nutrients and fluid into the bloodstream for processing and use

-Mechanisms

1. Diffusion

2. Active transport

-What gets absorbed?

1. monosaccharides

2. Amino acids, di-tripeptides

3. Fat

4. Vitamins

5. Minerals

6. Electrolytes

7. Water

8. Xenobiotics (drugs)

-Sites of absorption:

1. Oral cavity (minimal)

2. Stomach (minimal)

3. Small intestine

4. Large intestine

excretion

Which physiologic process of the GI tract:

-The GI tract is a site for excretion

Only 100mL of fluid is excreted from the GI tract, 99% is absorbed!!!

-Excretory products:

1. Cholesterol

2. Bilirubin metabolites

3. Xenobiotics

4. Fiber

5. Water

alimentary tract (hollow tube)

What part of the GI tract is made up of the mouth, esophagus, stomach, small intestine, large intestine, and anus?

accessory organs

What part of the GI tract is made up of the salivary gland, liver, gallbladder, pancreas?

splanchnic circulation

What circulation comprises the gastric, small intestinal, colonic, pancreatic, hepatic, and splenic circulations, which are arranged in parallel and fed by the celiac artery and the superior and inferior mesenteric arteries?

sympathetic

neuronal control of mesenteric circulation is almost entirely (sympathetic/parasympathetic) in origin

increased

during digestion, local GI activity leads to (increased/decreased) blood flow via mediators (GI hormones, kinins)

sympathetic

You can decrease blood flow to the GI tract by stimulating the (sympathetic/parasympathetic) NS, which is active during exercise or circulatory shock by causing vasoconstriction

somatostatin

What is a hormone that inhibits release of growth hormone and insulin but can also cause vasoconstriction of enteric arteries to decrease blood flow to the GI tract?

octreotide

What drug is a somatostatin analog, given to pts with bleeding esophageal varices caused by cirrhosis in order to heed bleeding?

epithelium

What part of the mucosa:

-Specialized cells carrying out functions of GI tract such as secretion and absorption

-Most of the GI tract has simple columnar (exception oral cavity, esophagus and anus, which are stratified squamous)

lamina propria

What part of the mucosa:

-Contains connective tissue, vessels, nerve endings and immune cells

muscularis mucosa

What part of the mucosa:

-thin muscular layer that assists the function of the epithelium

varies

the mucosal layer of the GI tract ____ the most in order to accommodate the different functions of each region of the GI tract

submucosa

Which structure of the GI Tract:

-Connective tissue, larger vessels, glands and the submucosal (Meissner’s) nerve plexus

-consists of loose connective tissue and larger blood vessels

-may also contain glands that secrete material into the GI lumen

muscularis externa

Which structure of the GI Tract:

-Two smooth muscle layers (inner circular, outer longitudinal) responsible for GI motility. Between the two layers is the myenteric nerve plexus

serosa

Which structure of the GI Tract:

-Outer layer of GI tract containing connective tissue, fat, vessels and visceral peritoneum

-an enveloping layer of connective tissue that is covered with squamous epithelial cells

mucosa

Which structure of the GI Tract:

-single layer of epithelial cells (mostly enterocytes) that contain enteroendocrine cells (EEC) and are renewed ~every 3 days

-epithelium linked together via tight junctions

-contains villi to increase the SA

-contain crypts (folds) which house different cell types

-lamina propia is made up of CT, glands, lymph vessels and nodes, capillaries, and nerve fibers

-muscularis mucosae is a thin smooth muscle layer that will contract to cause folds and ridges in the mucosa

enteric

which neural regulation of the GI tract:

-intrinsic innervation

-cell bodies within gut

-multiple plexuses

-myenteric and submucosal are most important

-Complex network located in the wall of GI tract

-Contains as many neurons as the spinal cord (including afferent, efferent and interneurons)

-Cell bodies are clustered in two plexuses: submucosal and myenteric. Fibers travel among layers

-Can function independently but are modulated by parasympathetic and sympathetic systems

-Involved in motility, secretion and endocrine functions

-Uses many neurocrines (slide later to come)

-Can initiate many patterns of GI activity (“program library”) in the digestive and interdigestive periods

sympathetic and parasympathetic

which neural regulation of the GI tract:

-extrinsic innervation

-cell bodies outside the gut

-input (efferent) and sensory (afferent)

extrinsic

The (extrinsic/intrinsic) component of the ANS to the GI tract:

-sympathetic and parasympathetic influence enteric nervous system

-enter GI tract within the mesentary (afferent and efferent) and synapse onto ganglia or target cells

intrinsic

The (extrinsic/intrinsic) component of the ANS to the GI tract:

-also known as the enteric nervous systeem

-contained within the wall of the GI tract and can function fairly independently

-nerve cell bodies are in the submucosal and myenteric plexuses

higher brain centers

What innervation of the GI tract involves the limbic system, cortex, and hypothalamus?

true

T/F: Diabetic neuropathy can involve the autonomic nervous system and result in impaired motility such as gastroparesis

parasympathetic

which neural regulation of the GI tract:

-mainly excitatory

-from the medulla and sacral cord (craniosacral) travel to the gut in the vagus and pelvic nerves

-Vagus nerves innervate foregut and midgut contains 75% afferent and 25% efferent fibers. Afferent signals include distension and nausea. Efferents are secretomotor to muscle, glands and endocrine cells. Reflexes contained within vagus nerve are called vagovagal reflexes

-Pelvic nerves innervate the hindgut

-Pre-ganglionic neurons are cholinergic (use ACh) and synapse on post-ganglionic neurons in the myenteric plexus

-Post-ganglionic neurons are cholinergic or peptidergic (use peptides such as VIP and GRP)

-in general, increases motility + secretions while relaxing sphincters

-post-ganglionic NTs = ACh and peptides (e.g., substance P, VIP, GRP)

sympathetic

which neural regulation of the GI tract:

-generally inhibitory

-derived from thoracolumbar cord.

Fibers are 50% afferent, 50% efferent.Afferent signals include pain and nausea.Efferent signals are secretomotor

-really controls sphincter tone

-Pre-ganglionic neurons are cholinergic (use ACh) and synapse on post-ganglionic neurons in the pre-vertebral ganglia

-Post-ganglionic neurons are adrenergic (use NE) and synapse on ENS neurons or target cells

-in general, decreases motility and secretions while contracting sphincters and blood vessels

-post-ganglionic NT = NE!!!

CN X

Which nerve of the parasympathetic NS innervation to the GI tract innervates the esophagus, stomach, gallbladder, pancreas, intestine, cecum, and proximal colon?

pelvic n.

Which nerve of the parasympathetic NS innervation to the GI tract innervates the distal colon and anorectal region?

neurocrines

What are NTs that are synthesized in the cell bodies of GI neurons, released by APs, and interact on post-synaptic cells?

ACh

Which NT of the gut:

-comes from cholinergic neurons

-contracts smooth m. in wall of GI tract

-relaxes sphincters

-increases salivary secretion, gastric secretion, and pancreatic secretion

Norepinephrine

Which NT of the gut:

-comes from adrenergic neurons

-relaxes smooth m. in wall

-contracts sphincters

-increases salivary secretion

Vasoactive intestinal peptide (VIP)

Which NT of the gut:

-comes from neurons of mucosa and smooth m.

-relaxes smooth m.

-increases intestinal, pancreatic, and gastrin secretion

Gastrin-releasing peptide (GRP) or bombesin

Which NT of the gut:

-comes from neurons of gastric mucosa

-increases gastrin secretion

Enkephalins (opiates)

Which NT of the gut:

-comes from neurons of mucosa and smooth m.

-contracts smooth m. and decreases intestinal secretion

Neuropeptide Y

Which NT of the gut:

-comes from neurons of mucosa and smooth m.

-relaxes smooth m. and decreases intestinal secretion

Substance P

Which NT of the gut:

-cosecreted with ACh

-contracts smooth m.

-increases salivary secretion

Nitric Oxide

Which NT of the gut:

-released be neurons of enteric nervous system

-relaxes smooth muscle