Tortora - Chapter 24: The Digestive System

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composed of two groups of organs: the gastrointestinal (GI) tract and the accessory digestive organs

- break down food into smaller molecules that can be used by cells

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245 Terms

1

composed of two groups of organs: the gastrointestinal (GI) tract and the accessory digestive organs

- break down food into smaller molecules that can be used by cells

digestive system

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a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities

Organs:

- mouth, pharynx, esophagus, stomach, small intestine, and large intestine

gastrointestinal tract

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include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas

accesory digestive organs

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6 Functions of the Digestive System

1. Ingestion:

- eating

2. Secretion:

- water, acid, buffers, and enzymes into the lumen of GI tract

3. Mixing and Propulsion:

- contraction and relaxation of GI tract smooth muscle (motility)

4. Digestion:

- mechanical digestion

- chemical digestion

5. Absorption:

- passage of digested products through epithelial cells of GI tract into blood and lymph

6. Defacation:

- elimination of waste through the anus

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4 Layers of the GI Tract

(1) Mucosa

(2) Submucosa

(3) Muscularis

(4) Serosa/ Adventitia

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innermost layer of GI tract

- mucous membrane

Composed of:

- epithelial layer

- lamina propria (areolar c.t.)

- muscularis mucosae

mucosa

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Nonkeratinized stratified squamous epithelium:

- mouth, pharynx, esophagus, and anal canal

Simple columnar epithelium:

- stomach and intestines

Epithelium of the GI Tract

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endocrine cells that secrete hormones into GI tract

enteroendocrine cells

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an areolar connective tissue layer containing many blood and lymphatic vessels

- carry the nutrients

- contains MALTs

- supports epithelium and binds it to muscularis mucosae

lamina propria

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mount immune responses against microbes in GI tract

mucosa-associated lymphatic tissue (MALT)

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a thin layer of smooth muscle fibers

- forms folds for increased surface area

- small movements to expose all absorptive cells to GI tract contents

- helps move lymph in lacteals (lipid transport)

muscularis mucosae

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a thin meshwork that contains collagen fibers, nerves, and blood vessels

- areolar c.t. that binds mucosa to muscularis

- contains submucosal plexus of enteric nervous system

submucosa

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Skeletal Muscle:

- mouth, pharynx, superior/middle esophagus

2 Sheets of Smooth Muscle:

(circular and longitudinal)

- rest of GI tract

3rd sheet of smooth Muscle:

(oblique, innermost layer)

- stomach

Muscularis of the GI Tract

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controls GI tract motility (movement)

- found in muscularis

myenteric plexus

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a serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium)

- epithelial portion of the serosa is also called the visceral peritoneum

serosa

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double-layered membrane surrounding the abdominal organs

- consists of a layer of simple squamous epithelium (mesothelium) with an underlying supporting layer of connective tissue

peritoneum

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2 Layers of Peritoneum

(1) visceral peritoneum (serosa)

(2) parietal peritoneum

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lines the wall of the abdominal cavity

parietal peritoneum

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also serosa;

covers /some/ organs in the abdominal cavity

visceral peritoneum

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contains lubricating serous fluid

peritoneal cavity

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retroperitoneal organs

organs outside the peritoneum

Examples:

- ascending/ descending colon

- duodenum

- pancreas

- kidneys/ adrenal glands

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(1) greater omentum

(2) falciform ligament

(3) lesser omentum

(4) mesentery

(5) transverse mesocolon

(6) sigmoid mesocolon

6 Major Peritoneal Folds

(1) greater omentum

(2) falciform ligament

(3) lesser omentum

(4) mesentery

(5) transverse mesocolon

(6) sigmoid mesocolon

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part of the peritoneum attached to the greater curvature of the stomach and to the transverse colon

- fatty apron covering the intestines

greater omentum

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attaches the liver to the anterior abdominal wall and diaphragm

- remnant of umbilical vein

falciform ligament

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attached to the lesser curvature of the stomach

- connects the stomach and duodenum to the liver

lesser omentum

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binds the jejunum and ileum of the small intestine to the posterior abdominal wall

mesentery

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binds transverse colon and sigmoid colon to the posterior abdominal wall

mesocolon

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also "oral cavity";

formed by the cheeks, hard and soft palates, and tongue

- digestion of starch and triglycerides begins

mouth

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form the lateral walls of the oral cavity

- external skin

- internal mucous membrane (nonkeratinized stratified squamous epithelium)

cheeks

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fleshy folds surrounding the opening of the mouth

- external skin

- internal mucous membrane

lips

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median fold of mucous membrane that joins the internal surface of each lip to the gum

labial frenulum

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space between teeth and cheeks

oral vestibule

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the space that extends from the gums and teeth to the fauces;

area contained by the teeeth

oral cavity proper

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the opening between the oral cavity and the oropharynx

fauces

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a wall or septum that separates the oral cavity from the nasal cavity

- forms the roof of the mouth

palate

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bony anterior of the palate formed by the maxillae and palatine bones

- covered by a mucous membrane

hard palate

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muscular posterior portion of the palate

- partition between the oropharynx and nasopharynx

- lined with mucous membrane

soft palate

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small muscular projection hanging from the back of the soft palate

uvula

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What is the function of the soft palate and uvula?

The soft palate and uvula prevent food from entering the nasal cavity by closing off the nasopharynx during swallowing.

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muscular fold that extends from the lateral side of the soft palate to the base of the tongue

palatoglossal arch

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muscular fold that extends from the lateral side of the soft palate to the side of the pharynx

palatopharyngeal arch

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a gland that releases saliva into the oral cavity

salivary gland

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3 Major Salivary Glands

(1) parotid glands

(2) submandibular glands

(3) sublingual glands

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large salivary glands at the angle of the jaw which secrete saliva into the oral cavity via a parotid duct

- open into vestibule

- ONLY serous acini

parotid glands

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found in the floor of the oral cavity beneath the base of the tongue

- open into oral cavity proper

- MOSTLY serous acini

submandibular glands

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superior to the submandibular glands

- open into oral cavity proper

- MOSTLY mucous acini

sublingual glands

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digestive juice produced by salivary glands

- contains salivary amylas

saliva

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enzyme that begins starch digestion in the mouth

salivary amylase

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secretion of saliva

- controlled by ANS (sympathetic and parasympathetic)

salivation

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What are the two salivary nuclei in the brain stem?

Impulses from taste buds are sent to superior and inferior salivatory nuclei in brain stem which stimulates salivary gland secretion.

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an accessory digestive organ composed of skeletal muscle covered with mucous membrane

- manipulates food for chewing and swallowing

- provides taste sensation

- assists speech

tongue

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- maneuver food for chewing and swallowing

- form the floor of the mouth

- hold the tongue in position

- assist in speech

extrinsic muscles of the tongue

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alter the shape and size of the tongue for speech and swallowing

intrinsic muscles of the tongue

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anchors tongue to floor of mouth

- limits movement of the tongue posteriorly

lingual frenulum

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"bumps" on the tongue;

projections of the lamina propria covered with stratified squamous epithelium

- contain taste buds (gustatory receptors)

papillae

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mushroom-like elevations on dorsum and margin of tongue

- most contain taste buds

fungiform papillae

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papillae arranged in an inverted V-shape on the posterior surface of the tongue

- ALL contain taste buds

vallate papillae

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located in small trenches on the lateral margins of the tongue

- Adult: DO NOT contain taste buds

foliate papillae

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threadlike elevations that cover most of the anterior tongue

- DO NOT contain taste buds

- receptors for touch

- increase friction of food against tongue

filiform papillae

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enzyme secreted by lingual glands that breaks down lipids; activated in the stomach

lingual lipase

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accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae

teeth

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cover the alveolar processes of the upper and lower jaws and surrounds the necks of the teeth

gingivae (gums)

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space between tooth and gum

gingival sulcus

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dense fibrous connective tissue that lines sockets of teeth

- anchors the teeth in position

- acts as a shock absorber during chewing

periodontal ligament

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3 Regions of a Tooth

(1) crown

(2) root

(3) neck

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the visible portion above the level of the gums

crown

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2 or 3 extensions of the tooth embedded in the socket

root

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the constricted junction of the crown and root near the gum line

neck

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internal calcified connective tissue that gives the tooth its basic shape and rigidity

- beneath the enamel at the crown

- makes up majority of tooth

dentin

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consists primarily of calcium phosphate and calcium carbonate

- covers dentin at the crown

- protects tooth from wear and tear

enamel

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attaches the root of the tooth to the periodontal ligament

cementum

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enclosed space within the dentin of the tooth lying within the crown of the tooth

pulp cavity

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a connective tissue in teeth containing blood vessels, nerves, and lymphatic vessels

pulp

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narrow extensions of the pulp cavity that run through the root of the tooth

root canals

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opening at the base of the root canal through which blood and lymphatic vessels and nerves pass

apical foramen

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sets of teeth

dentitions

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How many sets of teeth do humans have?

Two sets of teeth:

(1) deciduous teeth

(2) permanent teeth

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20 baby teeth that begin to erupt around the age of 6 months

- eventually pushed out by the permanent teeth

deciduous teeth

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teeth closest to the midline between the canines

incisors

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2 Types of Incisors

(1) central incisors

(2) lateral incisors

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front teeth at the midline

central incisors

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teeth adjacent to the central incisors

lateral incisors

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teeth next to the incisors with a pointed cusp

canines

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teeth posterior to the canines having four cusps each

-ONLY in "baby" deciduous teeth

- (replaced by premolars in adults)

first and second deciduous molars

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the 32 teeth of the adult that erupt between age 6 and adulthood

permanent teeth

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replace first and second deciduous teeth

first and second premolars

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do not replace any deciduous teeth

- next to second premolars

- erupt at age 6

first permanent molars

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do not replace any deciduous teeth

- erupt at age 12

second permanent molars

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also "wisdom teeth";

erupt at age 17 or not at all

third permanent molars

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the third molars remain embedded in the alveolar bone and cause pain

- removed surgically

impacted (teeth)

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chewing of food;

tongue manipulates food, teeth grind it, food mixes with saliva

mastication

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soft flexible mass of food;

term used to describe food after it has been chewed and mixed with saliva

bolus

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tube that extends from internal nares to the esophagus (posteriorly) and larynx (anteriorly)

pharynx

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also "deglutition";

a mechanism that moves food from mouth to the stomach

swallowing

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A muscular tube that connects the mouth to the stomach

- lies posterior to the trachea

esophagus

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opening in the diaphragm where esophagus passes through

esophageal hiatus (diaphragm)

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Histology of the Esophagus

(1) Mucosa:

- nonkeratinized stratitified squamous epithelium

- lamina propria (areolar c.t.)

- muscularis mucosae (smooth muscle)

(2) Submucosa:

- areolar connective tissue

(3) Muscularis:

- Superior 1/3: skeletal muscle

- Middle 1/3: skeletal AND smooth muscle

- Inferior 1/3: smooth muscle

(4) Adventitia

- areolar c.t.

- NO mesothelium*

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regulates passage of food from laryngopharynx into the esophagus

- skeletal muscle

upper esophageal sphincter (UES)

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waves of muscle contractions that propel food along the digestive tract

- circular muscles contract

- longitudinal muscles contract

- repeat

paristalsis

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ring of muscles between the esophagus and the stomach

- smooth muscle

lower esophageal sphincter (LES)

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