Ch. 23 LEC - Digestive System

Lecture Exam 4

the digestive system has [NUMBER] groups of organs: the [FIRST GROUP] and the [SECOND GROUP] digestive organs

2, alimentary canal (gastrointestinal or GI tract), accessory

name the organs that make up the alimentary canal (gastrointestinal or GI tract)

mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus

name the organs that make up the accessory digestive organs

• teeth, tongue, gallbladder

• digestive glands

  • salivary glands

  • liver

  • pancreas

in chronological order, list the 6 essential activities of the digestive process

1. ingestion

2. propulsion

3. mechanical digestion

4. chemical digestion

5. absorption

6. defecation

describe peristalsis, the goal of peristalsis, and the locations where it occurs

segments of alimentary tract organs alternately contract and relax;

GOAL: to move food along the tract distally

LOCATIONS: esophagus, stomach, intestines

describe segmentation, the goal of segmentation, and the locations where it occurs

segments of alimentary tract organs alternately contract and relax;

GOAL: to move food forward and backward so that food mixes together

LOCATIONS: small intestine

list the 2 main GI tract regulatory mechanisms

1. mechanoreceptors and chemoreceptors

2. intrinsic and extrinsic controls

what does the GI tract’s mechanoreceptors and chemoreceptors respond to?

• stretch in the GI tract

• changes in osmolarity

• changes in pH

• the presence of substrate and end products of digestion

what reflexes do the GI tract’s mechanoreceptors and chemoreceptors initiate?

• activate/inhibit digestive glands

• stimulate smooth muscle to mix and move lumen contents

define “enteric nervous system” (enteric nerve plexus)

a network of neurons in the walls of the GI tract; operates semi-autonomously to regulate digestion, local blood flow, and immunity

GI tract regulatory mechanism: intrinsic and extrinsic controls

• [GUT BRAIN] initiate [SHORT/LONG] reflexes in response to stimuli in the [BRAIN/GI TRACT]

• [SHORT/LONG] reflexes in response to stimuli inside or outside the GI tract involve [CNS/PNS] centers and autonomic nerves

• [CHEMICAL MESSENGERS] from cells in the [GI TRACT ORGAN] and small intestine stimulate target cells in the same or different organs

enteric nerve plexuses, short, GI tract, long, CNS, hormones, stomach

define “peritoneal cavity”

fluid-filled space inside the abdomen; the fluid acts as a frictionless lubricant that allows digestive organs to expand, contract, and slide; between the 2 peritoneum

define peritoneum

2-layered serous membrane of the abdominal cavity

[VISCERAL/PARIETAL] peritoneum is on the external surfaces of most digestive organs

visceral

[VISCERAL/PARIETAL] peritoneum lines the body wall

parietal

define mesentery

a double layer of peritoneum that anchors the GI organs (i.e., small and large intestines) to the posterior abdomen; it contains blood vessels, lymphatics, and nerves; stores fat

identify the functions of the hepatic portal circulation

• drains nutrient-rich blood from digestive organs

• delivers it to the liver for processing

histology of the alimentary canal (GI tract):

• 4 basic layers (tunics):

  • [DEEPEST]

  • [ ]

  • [ ]

  • [MOST SUPERFICIAL]

mucosa, submucosa, muscularis externa, serosa

list the functions of the mucosa tunic (of the GI tract)

• secretes mucus, digestive enzymes, hormones

• absorbs end-products of digestion

• protects against infectious disease

name the 3 sublayers of the mucosa tunic

epithelium, lamina propria, and muscularis mucosae

describe the specific histology and functions of the epithelium layer of the mucosa tunic

• HISTOLOGY: simple columnar epithelium

• FUNCTIONS:

  • secretes mucus: protects digestive organs from enzymes and eases food passage

  • sometimes secretes enzymes and hormones (in stomach and small intestine)

describe the specific histology and functions of the lamina propria layer of the mucosa tunic

• HISTOLOGY: connective tissue, capillaries, lymphoid follicles

• FUNCTIONS: supports epithelium, provide nutrients and oxygen, immune defense

describe the specific histology and functions of the muscularis mucosae layer of the mucosa tunic

• HISTOLOGY: smooth muscle

• FUNCTIONS: produces local movements of mucosa to move substances along the tract

describe the specific histology of the submucosa tunic (of the GI tract)

dense connective tissue, blood, lymphatic vessels, lymphoid follicles, and submucosal nerve plexus

muscularis externa tunic of the GI tract:

• responsible for [MOVEMENT AND MIXING OF FOOD] and [MOVEMENT OF FOOD]

• inner circular and outer longitudinal layers

• myenteric nerve plexus

• sphincters in some regions

segmentation, peristalsis

name the 2 nerve plexuses of the enteric nervous system

submucosal and myenteric

identify the function of the submucosal nerve plexus

regulates glands and smooth muscle in the mucosa

identify the function of the myenteric nerve plexus

controls GI tract motility

enteric nervous system:

• linked to the [CNS/PNS] via [EFFERENT/AFFERENT] visceral fibers

• long ANS fibers synapse with enteric plexuses

  • [SYMPATHETIC/PARASYMPATHETIC] impulses inhibit secretion and motility

  • [SYMPATHETIC/PARASYMPATHETIC] impulses stimulate secretion and motility

CNS, afferent, sympathetic, parasympathetic

list the functions of saliva

• cleanse the mouth

• moisten and dissolve food chemicals

• aids in bolus formation

• contains enzymes that begin the breakdown of starch (e.g., amylase, lipase)

name the types of cells that secrete saliva

serous and mucous cells

saliva is [NUMBER RANGE] % water, but is a slightly acidic solution containing [TERM] (Na+, K+, Cl-, PO4 2-, HCO3-), salivary [ENZYME] and lingual [ENZYME], mucin, metabolic wastes (urea and uric acid), and lysozyme (to neutralize some harmful bacteria in the mouth)

97-99.5, electrolytes, amylase, lipase

[INTRINSIC/EXTRINSIC] glands continuously keep the mouth moist with saliva. [INTRINSIC/EXTRINSIC] glands produce secretions when ingested food stimulates [RECEPTOR TYPES] in the mouth

intrinsic, extrinsic, chemoreceptors and mechanoreceptors

true/false: extrinsic salivary glands produce secretions when salivatory nuclei in the brain stem send impulses along sympathetic fibers in cranial nerves VII and IX

false — extrinsic salivary glands produce secretions when salivatory nuclei in the brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX

what results in xerostomia?

strong sympathetic stimulation inhibits salivation

name the class of teeth that best fits this description: chisel-shaped for cutting

incisors

name the class of teeth that best fits this description: fang-like teeth that tear or pierce

canines

name the class of teeth that best fits this description: have broad crowns with round cusps for grinding or crushing

premolars (bicuspids) and molars

name the tooth/gum disease that fits this description:

• gradual demineralization of enamel and dentin

• dental plaque (sugar, bacteria, debris) adheres to teeth

• acid from bacteria dissolves calcium salts

• proteolytic enzymes digest organic matter

dental caries (cavities)

what are the preventative measures against dental caries (cavities)?

daily flossing and brushing

name the tooth/gum disease that fits this description:

• plaque calcifies to form calculus (tartar)

• calculus disrupts the seal between the gingivae (gum) and teeth

• anaerobic bacteria infect gums

• infection is reversible if calculus is removed

gingivitis

name the tooth/gum disease that fits this description:

• immune cells attack intruders and body tissues

  • destroy periodontal ligament

  • activate osteoclasts

• consequences

  • possible tooth loss

  • promotion of atherosclerosis and clot formation in coronary and cerebral arteries

periodontitis

name the digestive processes that occur in the mouth

ingestion, mechanical digestion (mastication), chemical digestion (salivary amylase and lingual lipase), propulsion (deglutition, swallowing)

true/false: deglutition involves the stomach, small intestine, large intestine, and rectum

false — deglutition involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups

there are 2 phases of deglutition: first, the [NAME] phase (the [VOLUNTARY/INVOLUNTARY] contraction of the tongue). second, the [NAME] phase (the [VOLUNTARY/INVOLUNTARY] movement led by the control center in the medulla and lower pons)

buccal, voluntary, pharyngeal-esophageal, involuntary

true/false: the stomach receives innervation from the parasympathetic nervous system only

false — the stomach receives innervation from both the parasympathetic and sympathetic nervous systems

the stomach receives its SYMPATHETIC ANS nerve supply via _

splanchnic nerves and celiac plexus

the stomach receives its PARASYMPATHETIC ANS nerve supply via _

vagus nerve

where does the stomach receive its blood supply from?

the celiac trunk and veins of the hepatic portal system

the stomach is unique out of all the GI organs because it has modified _ and _ tunics

mucosa, mucularis

the stomach’s muscularis externa tunic has [NUMBER] layers of smooth muscle. the [LAYER NAME] allows the stomach to churn, mix, move, and physically break down food

3, inner oblique layer

the stomach’s mucosa tunica is composed of [TYPE] epithelium composed of mucous cells. the layer of mucus traps bicarbonate-rich fluid beneath it. gastric pits lead into gastric glands

simple columnar

name the 4 cell types found in gatric glands

mucous neck cells (secrete thin, acidic mucus), parietal cells, chief cells, enteroendocrine cells (secretes hormones)

name the cell type found in the gastric glands that secrete:

• HCl

  • lowers the pH to 1.5-3.5, which denatures protein in food, activates pepsin, and kills many bacteria

• intrinsic factor

  • glycoprotein required for absorption of vitamin B12 in small intestine

parietal cell

name the cell type found in the gastric glands that secrete:

• inactive enzyme pepsinogen

• activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism)

chief cell

name the cell type found in the gastric glands that secrete:

• chemical messengers into the lamina propria

  • paracrines: serotonin and histamine

  • hormones: somatostatin and gastrin

enteroendocrine cells

describe the mucosal barrier of the stomach:

• layer of [COMPOUND]-rich mucus

• [STRUCTURE] between epithelial cells

• damaged epithelial cells are [QUICKLY/SLOWLY] replaced by division of stem cells

bicarbonate, tight junctions, quickly

define gastritis

inflammation caused by anything that breaches the stomach’s mucosal barrier

define “peptic/gastric ulcers”

erosion of the stomach wall (mostly caused by H. pylori bacteria)

digestive processes in the stomach:

• physical digestion

• [STRUCTURAL BREAKDOWN] of proteins

• enzymatic digestion of proteins by [ENZYME] (and [ENZYME] in infants)

• secretes [SUBSTANCE] required for absorption of vitamin B12

  • lack of intrinsic factor can cause [DISEASE]

• delivers [BOLUS/CHYME/BILE] to the small intestine

denaturation, pepsin, rennin, intrinsic factor, chyme

define “gastric secretion”

the process by which specialized cells in the stomach lining produce and release gastric juice to prepare for food digestion

name the 3 phases of gastric secretion

1. cephalic (reflex) phase

2. gastric phase

3. intestinal phase

when does the cephalic (reflex) phase of the gastric secretion process take place?

few minutes prior to food entry

when does the gastric phase of the gastric secretion process take place?

3-4 hours after food enters the stomach

describe what occurs during the cephalic phase of the gastric secretion process

the sight, smell, or thought of food signals the vagus nerve to release acetylcholine, which prepares the stomach for incoming food

describe what occurs during the gastric phase of the gastric secretion process

• the moment food arrives in the stomach

• the stomach walls stretch (distension), stimulating:

  • MECHANICAL: local enteric reflexes (stomach motility)

  • CHEMICAL: the production of gastrin, histamine, and ACh (hormones needed for maximum HCl secretion)

describe what occurs during the intestinal phase of the gastric secretion process

• the moment the small intestine’s duodenum fills up with chyme

this phase has both a brief stimulatory and inhibitory component:

• STIMULATORY: partially-digested proteins enter the duodenum, triggering the release of intestinal gastrin → stimulates gastric acid

• INHIBITORY: when small intestine (duodenum) signals stomach to slow down digestion because the duodenum is filled with chyme, stretching, or becomes too acidic

  • MECHANICAL: enterogastric reflex (inhibit stomach muscle contraction)

  • CHEMICAL: enterogastrone hormone secretion (inhibits gastric motility and gastric acid secretion

why is the intestinal phase of the gastric secretion process important?

to protect the small intestine from excessive acidity and allow time for nutrient absorption

name the 3 chemicals that stimulate parietal cells to secrete maximum amounts of HCl

ACh, histamine, gastrin

how does the stomach respond to being filled up with food?

stretch!

describe the stomach’s reflex-mediated receptive relaxation

as you swallow, the swallowing center of the brain stem sends a signal to the stomach to relax the muscle to make room for incoming bolus even before it arrives

describe the stomach’s plasticity (stress-relaxation response)

the stomach’s smooth muscle can be stretched to accommodate a big meal then slowly contracts as it empties

describe the concept of “gastric accommodation”

the stomach has the ability to stretch its walls to fit up to 4L of food while maintaining a relatively constant internal pressure

what are the factors that affect the rate of digestion?

the amount and composition of what was eaten

regulation of gastric emptying:

• as [BILE/CHYME/BOLUS] enters the duodenum…

  • [PROTEIN TYPE] respond to stretch and chemical signals

  • [INHIBITORY] reflex and [INHIBITORY HORMONE] inhibit gastric secretion and duodenal filling

• [MACROMOLECULE]-rich chyme moves [SLOWLY/QUICKLY] through the duodenum

• [MACROMOLECULE] chyme remains in the duodenum 6 hours or more

chyme, receptors, enterogastric, enterogastrones, carbohydrate, fat

true/false: the stomach is the major organ of digestion and absorption

false — the small intestine is the major organ of digestion and absorption

name the structural modifications of the small intestine that allow for increased surface area

circular folds, villi, microvilli

why is a high surface area important for the function of the small intestine?

to maximize nutrient absorption

identify the function of the small intestine’s circular folds

to force the chyme to slowly spiral through lumen

describe the small intestine’s villi

finger-like extensions (1mm high) of the mucosa

describe the small intestine’s microvilli

projections (brush border) of absorptive cells; they bear brush border enzymes

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