chapter 24 Flashcards
consists of 2 essential parts
- digestive tract
2. accessory organs
digestive tract
- definition
- known as 2 other names
muscular tube from mouth to anus
-gastrointestinal tract and alimentary canal
the accessory organs
- mostly
- 7
glands
- liver
- gallbladder
- pancreas
- salivary glands
- teeth
- tongue
- gastric and intestinal glands
- liver
functions of the digestive system
- ingestion
- mechanical digestion
- digestion
- secretion
- absorption
- excretion
ingestion
materials entering digestive tract through the mouth
mechanical digestion
crushing and breaking up of ingested material
digestion
chemical breakdown of food into smaller molecules suitable for absorption
secretion
release of H2O acids, enzymes, buffer and salts along the digestive tract
absorption
movement of organic substances, ions, vitamins, and H2O from digestive into interstitial fluids
excretion
removal of waste products
digestive tract
-
- oral cavity (mouth)
- pharynx
- esophagus
- stomach
- small intestine
- large intestine
small intestine
- why is it known as small
- 3 parts
- in diameter
- 1st duodenum (10 in)
- Jejunum (8 ft)
- iliem (12 ft)
- 1st duodenum (10 in)
Large intestine
- why is it known as large
- 4 parts
- in diameter
- cecum
- colon
- rectum
- anus
- cecum
colon
-4 parts
- Ascending
- transverse
- descending
- sigmoid
Histological organization of digestive tract
-4 layers
- mucosa
- submucosa
- muscularis externa
- serosa
mucosa
- innermost or outermost layer
- lines what
- function
- innermost
- lumen
- secretes mucus
mucosa
-3 layers
- muscularis mucosa
- lamina propria
- epithelium
muscularis mucosa
- definition
- function
- thin layer of smooth muscle
- alters lumen shape
lamina propria
-contains
areolar CT, blood vessels and lymphatics
epithelium of the mucosa
- type of epithelium
- contains what
- simple columnar
- goblet cells
submucosa
-contains
CT, blood and lymphatic vessels
muscularis externa
- definition
- controlled by
- double layer of smooth muscle cells
- controlled by the myenteric plexus
serosa
- structure
- does not cover
- peritoneum
- oral cavity, pharynx, esophagus or rectum
submucosal gland
- type of gland
- function
- exocrine gland
- secretes buffers and enzymes
meissner plexus
sensory and autonomic
2 movements of digestive materials
- mixing
2. peristalsis
mixing
- known as
- definition
- where does it occur
- what does it do
- are movements well coordinated
- contractions of
- segmentation
- constricting the tube and dividing its contents
- mostly in the small intestine
- mixes material being digested with intestinal secretions
- no
- muscularis externa and muscularis mucosa
peristalsis
- definition
- depends on
- circular layer
- longitudinal layer
- moves materials toward
- coordinated wave of muscular contraction that propels material through the tube
- coordinated contractions of the muscularis externa
- contracts behind the material while relaxing in front of it
- contracts ahead of the material and shortens the tube
- toward the anus
Oral cavity
- mouth
- lined by
- opens into the oral (buccal) cavity
- oral mucosa
oral mucosa
stratified squamous epithelium
Oral cavity
-4 functions
- sensory analysis of materials before swallowing
- mechanical processing of food begins= formation of bolus
- lubrication of food bolus in preparation for swallowing
- some digestion occurs
Swallowing
- known as
- ___ function of the mouth
- voluntary or involuntary
- controlled
- deglutition
- motor
- voluntary
- subconsciously
steps of digestive tract to stomach
- Buccal phase
- Pharyngeal phase
- Esophageal Phase
- Bolus enters stomach
Buccal phase
-4 steps
- Compression of bolus against the hard palate
- retraction of tongue forces bolus into oropharynx
- soft palate elevates
- Food enters oropharynx
Pharyngeal phase
-5 steps
- bolus in contact with oropharynx
- swallowing reflex
- muscles of pharynx will contract
- larynx elevates and epiglottis folds
- bolus is propelled into esophagus
swallowing reflex
- begins when
- controlled by
- begins when bolus passes uvula
- CN V, IX, X
CN V
- name
- functions
- trygeminal
- sensation to face and controls chewing
CN IX
- name
- functions
- Glossopharyngeal
- sensation to posterior part of the tongue and motor function
CN X
- name
- function
- Vagus
- provide motor to pharynx
Esophagus
- what is it
- lined by
- serosa?
- muscular tube
- stratified squamous epithelium
- no
Espohageal stage
-2 steps
- Bolus is pushed toward stomach by peristaltic waves
2. Lower esophageal sphincter opens and bolus continues into stomach
Bolus enters stomach
chemical digestion of food continues
Stomach
-parts
- Fundus
- Body
- Rugae
- Pylorus
- Cardia
Fundus of the stomach
- contains what
- function
- contains gastric glands
- secretes acids and enzymes for gastric digestion
Body of the stomach
mixing tank for food secretions
Rugae
folds of the mucosa that flatten as the stomach fills with food
pylorus
secretes mucus and digestive hormones
Cardia
produces mucus that helps to protect the esophagus
2 curvatures of the stomach
- lesser curvature (by liver)
2. Greater curvature (by spleen)
4 functions of the stomach
- Storage of ingested foods
- mechanical breakdown of ingested foods
- disruption of chemical bonds in foods through the action of acids and enzymes
- production of intrinsic factor for absorption of vitamin B12
- 1st 3 functions produces chyme
chyme
soupy mixture of partially digested food, highly acidic
factors that iincrease stomach mobility
- increased stomach mobility =
- 2
- increased stomach emptying
1. distention of the stomach
2. gastrin hormone
distention of the stomach
- definition
- stimulates what
- stretching of stomach wall (food enters)
- mechanoreceptors
mechanoreceptors
-function
activates parasympathetic NS which promotes contractions of muscularis externa
Gastrin
- produced by
- secreted by what (1)
- secreted by (2)
- promotes
- endocrine glands
- stomach in response to arrival of food
- duodenum when chyme containing partially digested materials enter
- gastric secretions and contraction of muscularis externa
2 factors that decrease stomach motility
- distention of the duodenum
2. Hormones: cholecytokinin, secretin and gastric inhibitory peptide
distention of the duodenum
- definition
- function
- stretching of the duodenum when chyme enters
- activation of enterogastric reflex
enterogastric reflex
-2 functions
- inhibits contraction of muscularis externa
2. promotes contraction of pyloric sphincter
hormones that decrease stomach motility
- 3
- produced by
- function
- cholecytokinin
- secretin
- gastric inhibitory peptide
- cholecytokinin
- the duodenum
- function to reduce gastric secretions and motility
small intestine
- local
- 2 components
- movements are controlled by myenteric plexus = PNS
- segmentation
- peristalsis
- segmentation
segmentation of the small intestine
- how many times/min
- function
- 11-12 times/min
- mix chyme with intestinal secretions
peristalsis of the small intestine
- movements are
- moves how many cm/sec
- how long does it take chyme to move through the sm intestine
- what does it direct
- very weak propulsive movement
- 0.5-2.0 cm/sec
- 3-5 hours
- coordinated movements
2 reflexes that control movements
-stimulated in response to
- gastroenteric reflex
- gastroileal reflex
- gastroenteric reflex
- to stretch receptors in the stomach
gastroenteric reflex
stimulates motility and secretion along the entire small intestine
gastroileal reflex
triggers relaxation of the ileocecal valve
stimulation of the gastroenteric and gastroileal reflex promotes
the passage of materials from the small intestine to the large intestine
large intestine
- conversion of what
- 3 processes
- chyme into feces
- haustral churning
- mass movements
- defecation
- haustral churning
Haustral churning
-2 steps
- Taenia coli contract and bunch up which produces bulges called haustra
- new contractions produce mixing of colon contents necessary for the production of feces
taenia coli
- location
- definition
- large intestine
- longitudinal bands of smooth muscle
mass movements
- what is this
- feces move as a __ down the colon
- occurs towards the beginning or end
- occurs where
- how many times per day
- function
- peristalsis in the large intestine
- unit
- end
- in the transverse and descending colon
- 1-2 times per day usually right after the gastrocolic reflex
- push feces down into the rectum
what do mass movements initiate
defecation
defecation
elimination of feces from the body
the defecation reflex
- stimulus
- response
- response leads to
- feces in the rectum
- stretch receptors are stimulated
- increase in peristalsis in rectum and action potentials are conducted along afferent neuron
3 consequences of the defecation reflex
- strong contraction of descending sigmoid colon and rectum
- internal anal sphincter relaxes (opens-no control)
- external anal sphincter contracts (closes)
Internal anal sphincter
-type of muscle
smooth
external anal sphincter
-type of muscle
skeletal
socially unacceptable
-2 things
- voluntarily keep external anal sphincter closed
2. feces back up and out of rectum and reflex dies
socially acceptable
-3
- voluntarily relax external anal sphincter
- to initiate defecation take a deep breath
- push feces into anal canal and expel
what does taking a deep breath while defecating do
increase abdominal pressure
Chemical digestion
- definition
- what does this produce
breakdown of food from high molecular weight components to low molecular weight components
-produces a form that can be absorbed
basic strategy of chemical digestion
- proteins ->
- carbs ->
- fat ->
- protein fragments (short polypeptides )-> AA (absorbed)
- small fragments (di and trisacharrides) -> monosaccharrides (absorbed)
- triglycerides -> glycerol and FA (absorbed)
saliva
- produces ___ /day
- pH
- contains 3 things
- 1-1.5 L/day
- ~7.0
- 99% H2O
- salt and mucus
- enzymes
- 99% H2O
enzymes of saliva
- lysozyme
- lingual lipase
- salivary amylase
lysozyme
destroys bacteria
lingual lipase
fat digestion
salivary amylase
carb digestion
4 functions of saliva
- clean mouth (lysozyme kills bacteria)
- dissolves food for taste
- helps to form bolus for swallowing
- beginning stages of digestion
digestion by saliva: salivary amylase
-starch ->
-salivary amylase convert starch to di and trisaccharides
regulation of salivary secretions
- smell, sight, thoughts of food and/or food in the mouth stimulates cranial nerves V, VII, IX, or X
- salivary nuclei in medulla oblogata
- parasympathetic stimulation stimulates increase secretion from salivary glands
3 pairs of salivary glands
- parotid
- submandibular
- sublingual
chemical digestion: stomach
-2 components
- gastric juice
2. gastric pits and glands
gastric juice
- basic or acidic
- pH
- produced by
- highly acidic
- 2
- by the cells of the gastric gland
gastric pits and glands
-4 components
- mucous cells
- parietal cells
- chief cells
- G cells
Mucous cells
- location
- what are they doing
- function
- in the gastric pit
- actively dividing
- secrete thick protective mucus
parietal cells
- cells of the
- function
- gastric gland
- secrete intrinsic factor and hydrochloric acid (HCl)
intrinsic factor of parietal cells
facilitates absorption of vitamin B12 needed for erythropoesis
hydrochloric acid
- explains what
- 3 functions
- acidity
- kills microbes
- softens cell wall of plant material
- helps denature protein
- kills microbes
what is the gastric pit called
the lumen of the stomach