Oral cavity and oesophagus Flashcards
what are Accessory digestive organs?
- Salivary glands
Biliary system – - Liver
- Gallbladder
- Exocrine pancreas
Exocrine organs lie outside the
digrestive tract
Exocrine organs lie outside the digestive tract and empty their
secretions through the ducts into the digestive tract lumen
primary function of digestion ?
makes nutrients absirbable
function of digestion mechanically?
Large foodstuffs broken down into smaller pieces to increase surface area for enzymes
function of digestion biochemically?
Broken down into small, simple compounds and molecules that can be absorbed from the digestive tract
energy source of digestion?
- ATP
- predominantly glucose
- Alternative = amino acids/fatty acids
building supplies of digestion?
Renewal and synthesis of body tissues
- Fatty acids
- Amino acids
Four Basic Digestive Processes
Motility
Secretion
Digestion
Absorption
what is motility ?
Muscular contractions that mix and move forward the contents of the digestive tract
what are the voluntary contractions of skeletal muscle?
Mastication (chewing)
Deglutition (swallowing)
smooth muscle is for
involuntary movement
smooth muscle walls maintain a
constant low level of contraction known as tone
what is the function of tone?
maintains a steady pressure on the contents of the digestive tract and prevents the walls from becoming permanently stretched following distension.
what is peristalsis ?
radial contractions that propel food along the intestinal tract.
what is secretion?
A number of digestive juices are secreted into the digestive tract lumen by exocrine glands
function of secretory cells?
Extract large volumes of water and raw materials from the blood plasma to produce their particular secretion
secretions are reabsorbed back into the…
blood after digestion.
function of endocrine cells in the digestive tract?
Endocrine cells within the digestive tract secrete gastrointestinal hormones into the blood that control digestive motility and exocrine gland secretion.
what kinds of things are secreted in the digestive tract?
Water
Electrolytes: : Na+, K+, Ca2+, Mg2+, HCO3 −, etc…
Specific organic constituents
- Enzymes, bile salts, or mucus
Large molecules cannot be absorbed across …
… plasma membrane of the cells lining the digestive tract
define digestion
biochemical breakdown of structurally complex foodstuffs into smaller, absorbable units.
Humans consume three energy-rich foodstuffs:
carbohydrates
protein
fats
Digestion is accomplished by
hydrolysis by enzymes within the Gastro-Intestinal (GI) tract
what breaks down starch and glycogen
salivary amylase
whart breaks down Short chain polysaccharides and disaccharides (maltose, lactose, sucrose) ?
pancreatic amylase
what breaks down Short chain polysaccharides and disaccharides (maltose, lactose, sucrose, α-Limit Dextrins) ?
Maltase, lactase, sucrase, α-limit dextrinase
what absorbs monosaccharised (glucose, fructose, galactose)?
Intestinal capillaries and hepatic portal system to liver
polysaccharides are a …
… glucose polymer
polysachharides linked by …
… O-glycosidic bonds
what enzyme digests proteins in the stomach?
pepsin (stomach)
what activates pepsinogen to pepsin?
HCl activates pepsinogen to pepsin
pepsin breaks down proteins into
peptone and proteoses
what breaks down peptone and proteoses in the pancreas?
Trypsin and chymotrypsin (pancreas)
what activates trypsinogen to trypsin?
Enteropeptidase, enterokinase (duodenum/small intestine)
what brekas down peptone and proteoses in the small intestines?
Carboxypeptidases (pancrease) and Amonipeptidases (small intestine)
Carboxypeptidases (pancrease) and Amonipeptidases (small intestine) break peptone and proteoses into what?
Dipeptides
Dipeptides are then broken down into
amino acids
what happens to the amino acids?
absorbed by intestinal capillaries and hepatic portal system to liver
whats hydrolysis
break down by water
water is added. a covalent bond between monomers is broken
Complex macromolecular foodstuffs are broken down by
enzymatic digestion
Hydrolysis adds
water across the covalent bonds holding the units together, freeing them for absorption.
Digestive enzymes are specific in
the bonds that they hydrolyse.
As food passes through the digestive tract, it is subjected to
various enzymes, which break down the food molecules into smaller absorbable units in a progressive step wise fashion.
In the small intestine, digestion is
completed and most absorption occurs.
describe absorption in the SI
The small products of digestion together with water, vitamins, and electrolytes are transferred from the digestive tract lumen into the blood or lymph.
is the digesticve tract internal or external?
This is external to the body
The pH of the stomach can reach as low as
pH 2 due to HCl secretion
The pH of the stomach can reach as low as pH 2 due to HCl secretion, yet in the body fluids the range of pH is
6.8 to 8
The digestive enzymes that hydrolyse food molecules could also
destroy the body’s own tissues that produce them.
In the lower part of the intestine live…
billions of bacteria that, if entering the body, may be extremely harmful.
Foodstuffs are complex foreign particles that
would be attacked by the immune system if in contact with the body.
what is the digestive tract?
Essentially a tube, 15 m in length in its normal contractile state (30 m ‘relaxed’)
the digestive tract is continuousfrom
mouth to anus.
Continuous from mouth to anus, therefore the contents of the digestive tract are
technically outside of the body.
Only after a substance has been absorbed across the digestive tract wall is it
considered part of the bodfy
Layers of the digestive tract wall
A cross section of the digestive tract reveals four major tissue layers:
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
The digestive tract wall has the same
general structure throughout most of its length with some local variations characteristic of each region.
layers of the mucosa?
mucus membrane
lamina propria
muscularis mucosa
whats mucus membrane?
Inner epithelial layer, protective surface, modified in particular areas for secretion and absorption.
what are the two types of gland cells in the mucus membrane?
- Exocrine gland cells: secretion into digestive tract lumen
- Endocrine gland cells: secretion of hormones into blood/lymph
what is the lamina propria?
Thin middle layer of connective tissue.
lamina propria function?
It houses the gut-associated lymphoid tissue (GALT) important in the defence against bacterial invasion.
what is Muscularis mucosa?
A sparse layer of smooth muscle.
contractions of Muscularis mucosa causes…
… changes to the surface folding of the mucosa, important in exposing the absorptive surface to the luminal contents.
what are the three layers of mucosa?
1) mucus membrane (outer)
2) lamina propria (middle)
3) muscularis mucosa (inner)
whats submucosa?
Thick layer of connective tissue that provides elasticity and distensibility
what does the submucosa contain?
Contains the larger blood and lymph vessels which send branches inwards to the mucosal layer and outwards to the surrounding thick muscle layer.
what is the submucosa plexus?
Nerve network that has both sensory and motor neurons that regulate the activity of glands in the mucosa and smooth muscle of the muscularis mucosa.
how many neurons in the neteric nervous system?
500 million neurons
Muscularis externa is the major…
… smooth muscle coat of the digestive tract
the Inner circular muscle encircles…
… the digestive tract.
contraction of Inner circular muscle decreases…
… the diameter of the lumen, constricting the tube at the point of contraction.
Outer longitudinal muscle runs
longitudinal along the tract.
Outer longitudinal muscle contractions …
… shortens and dilates the digestive tract.
what is the Myenteric plexus?
Nerve network that lies in between the two muscle layers
what is the function of Myenteric plexus contraction?
Together, contractile activity of these smooth muscles is responsible for the propulsive and mixing movements
what is the serosa?
Outer connective tissue covering of the digestive tract.
what is the function of the serosa?
Secretes a slippery fluid (serous fluid) that lubricates and prevents friction between the digestive organs.
whats the Mesentery?
Double fold peritoneum
Throughout much of the tract, the serosa is continuous with …
… the mesentery
mesentery suspends the
digestive organs from the inner wall of the abdominal cavity like a sling.
what does the oral (buccal) cavity consist of?
Lips
Palate
Uvula
Tongue
lips function
Help procure and contain food in the mouth.
Sound articulation
the lips have an abundance of…
… sensory receptors (pressure, touch, stretch, temperature
the palate forms…
arched roof of mouth
the palate separastes?
mouth from nasal passages
the palate allows…
… simultaneous breathing and chewing/sucking
whats the uvula?
Dangling projection that seals nasal passages during swallowing.
whats the tongue?
- floor of oral cavity
- Voluntary muscle that guides food during chewing and swallowing.
32
what do malocclusion affect?
Affects ability to bite, tear, and chew food
the different malocclusions?
excessive spacing
crowding
open bite
overbite
crossbite (front teeth)
cross bite (back teeth)
underbite
overjet
abnormal
Odontostomatologic anomaly is commonly seen in
congenital genetic disorders such as :
gardners syndrome
cleidocranial dysostosis
cleft lip and palate
functions of chewing?
To grind and break up food into smaller pieces
to mix food with saliva
to stimulate the taste buds
chewing facilitates
swallowing
chewing creates a greater
surface area on which salivary enzymes can act.
To stimulate the taste buds – this reflex increases:
salivary,
gastric,
pancreatic,
bile secretion to prepare for the arrival of food.
act of chewing is voluntary, but most chewing during a meal is…
…a rhythmic reflex
Act of chewing is voluntary, but most chewing during a meal is rhythmic reflex
Activation of the …
… skeletal muscle of the jaws, cheeks, lips, and tongue in response to the pressure of food against oral tissues.
There are 4 types of lingual papillae on the tongue
3 involved in taste
1) foliate papilla
2) filiform papilla
3) Circumvallate (vallate) papilla
4) Fungiform papilla
what do Foliate papilla have?
Vertical folds on edges
Filiform papilla details?
Most numerous/small brush like
Not involved in tasting
how many Circumvallate (vallate) papilla ?
Usually, 8-12 in total
Circumvallate (vallate) papilla size?
Large (1-2 mm) – covered in stratified squamous epithelium
Fungiform papilla is scattered trhough the …
filiform papillae
Chemorecepters for taste are packaged int…
… taste buds
how many taste buds
10,000
the majority of taste buds are on the…
… upper surface of the tongue
tasdte buds contain
around 50 long taste receptors
taste buds are arranged like
orange segments
taste buds each have a small
opening
the small opening in taste buds is the
taste pore
taste buds are also known as
modified epithelial scells
tatse buds are activared by
a taste-provoking chemical (tastant)
Afferent (sensory) fibres take i
impulses via brain stem to thalamus to cortical gustatory area
what are taste receptor cells?
Modified epithelial cells with many surface folds (microvilli) that protrude slightly from the taste pore.
Plasma membrane contains
receptors that bind selectively with chemicals in a solution – a tastant.
a tastant causes…
… ion-channels to open (depolarisation) leading to entry of Ca2+ and neurotransmitter release.
Signals are conveyed to
cortical gustatory area and the brain stem projects fibres to the hypothalamus and limbic system to add affective dimensions (pleasant/unpleasant taste).
The thousands of different taste sensations we can discriminate all come from…
… varying combinations of the five primary tastes:
Receptor cells use different
pathways to bring about a receptor potential in response to each taste category.
40 - 45
saliva produced by…
three major pairs of salivary glands
Exocrine glands - Acini secretory cells that
lie outside of the oral cavity
Discharge via
short ducts into the mouth
what is saliva made up of?
Made up of 99.5% H2O and 0.5% electrolytes (salts) and protein.
Salivary NaCl concentration is…
…one seventh that of blood plasma – important in perceiving salty tastes.
Similarly, glucose is absent from
saliva
Similarly, glucose is absent from saliva – important in
perceiving sweet tastes
important salivary proteins are…
- amylase
- mucus
- lysozyme
- salivary kallikrein (no important role in food digestiion)
saliva begins…
digestion of carbohydrates and lipids
salica begins digestion of carbohydrates and lipids using whch enzymes?
salivary amylase
lingual lipase
salivary amylase function
breaks polysaccharides into maltose (disaccharide)
lingual lipase function
breaks down triglycerides into diglycerides and free fatty acids
salica facillitates…
…. swallowing
saliva facilitates swallowing by
moistening food, lubrication provided by mucus secretion
saliva also has
antibacterial activity
enzymes involved in saliva antibacterial activity
lysozyme
globulin A
lactoferrin
rinsing
lysozyme function
enzyme that destroys bacteria by breaking down their cell walls.
globulin A function
a glycoprotein that binds IgA antibodies.
lactoferrin function
a protein that tightly binds the iron needed by bacteria to multiply.
rinsing away function
Rinsing away material that may serve as a food source for bacteria
saliva is a solvent for…
Rinsing away material that may serve as a food source for bacteria
- Only molecules in solution can react with taste bud receptors
saliva aids
speech by facilitating movement of lips and tongue
what type of hygeine does saliva help with?
oral hygeine
describe oral hygeine by saliva?
- Help keeps the mouth and teeth clean.
- Consistent flow helps flush away food residues, foreign particles and old epithelial cells shed from oral mucosa.
saliva is rich in…
bicarbonate buffers (HCO3-)
saliva is rich in bicarbonate buffers (HCO3-):
neutralise….
… acids in food as well as those produced by bacteria in the mouth.
- kept at pH 6.8
saliva secretion is
continuous
how much saliva secreted per day?
1-2 litres secreted/day
rate of saliva secretion?
Rate of 0.5-5 ml/min, depending on stimulus
Constant basal level maintained by
parasympathetic nerve endings in salivary glands.
Salivary secretion may be increased by two reflexes:
Simple reflex
Conditioned reflex
whats the simple reflex?
Chemoreceptors/pressure receptors respond to the presence of food.
the simple reflex initiates?
impulses in the afferent (sensory) fibres to the salivary centre located in the medulla of the brain stem.
Simple Reflex
- Chemoreceptors/pressure receptors respond to the presence of food.
- Initiate impulses in the afferent (sensory) fibres to the salivary centre located in the medulla of the brain stem.
This sends impulses back to
the salivary glands to increase salivation
Conditioned Reflex
this relfex is a …
…learned response based on previous experience.
in the conditioned reflex, sensory input acts through the …
… cerebral cortex to stimulate the salivary centre in the medulla.
Sympathetic and parasympathetic responses do not
play antagonistic roles.
Parasympathetic regulation has a
dominant role in salivary secretion
Parasympathetic regulation causes
a prompt and abundant flow of watery saliva
Parasympathetic regulation causes the production of Prompt and abundant flow of watery saliva which is …
… rich in enzymes.
Sympathetic regulation causes
Smaller volume of thick saliva
Sympathetic regulation
- Smaller volume of thick saliva
- rich in
… mucus
Sympathetic regulation of saliva is in control in
stress situations
- Why the mouth goes dry before public speaking!
Digestion in the mouth is
minimal
Digestion in the mouth is minimal – most amylase digestion occurs in the
stomach after swallowing
Acidic stomach environment inactivates …
… amylase, but still active in centre of food mass.
Net result of NaCl in Acinar lumen causes
water to follow by osmosis through leaky tight junctions and water channels (aquaporins) in plasma membrane.
Net result of NaCl in Acinar lumen causes water to follow by osmosis through leaky tight junctions and water channels (aquaporins) in plasma membrane.
The final salivary solution is
isotonic
what is deglutition?
swallowing
Swallowing is
the entire practice of moving foodstuffs from the mouth to the stomach
All or none pattern: initiated …
…voluntarily, but once begun cannot be stopped.
swallowing is initiated when …
… a bolus (ball of chewed or liquid food) is voluntarily forced by the tongue to the rear of the mouth into the pharynx
- Initiated when a bolus (ball of chewed or liquid food) is voluntarily forced by the tongue to the rear of the mouth into the pharynx.
- Bolus presses on…
… pharyngeal pressure receptors
- Initiated when a bolus (ball of chewed or liquid food) is voluntarily forced by the tongue to the rear of the mouth into the pharynx.
- Bolus presses on pharyngeal pressure receptors
- This sends…
… afferent impulses to the swallowing centre in the medulla of the brain stem.
Swallowing centre reflexively activates the
…
… appropriate sequence of muscles involved in swallowing – highly complex reflex.
what are the three main stages of swallowing?
- Oral stage (A, B, C)
- Oropharyngeal stage (D, E)
- Oesophageal stage (F)
Bolus of food must move from
mouth through pharynx to oesophagus
Bolus must be prevented from:
- Entering the nasal passages
- Entering the trachea
- Re-entering the mouth
Position of tongue against
the hard palate
- Position of tongue against the hard palate
- Prevents …
… bolus from re-entering the oral cavity
the uvula is
extended
The uvula is extended and lodges against
the back of the throat
- The uvula is extended and lodges against the back of the throat
- Sealing off the…
… nasal passages from the pharynx
Pharynx is the part of the throat below the
nasal passages
Pharynx is the part of the throat below the nasal passages
- Forms part of the …
… respiratory & digestive system
Food is prevented from entering the trachea (wind pipe) by
elevation of the larynx
Food is prevented from entering the trachea (wind pipe) by elevation of the larynx.
With the…
… tight closure of the vocal folds across the glottis
Bolus tilts the …
… small flap of cartilaginous tissue (epiglottis) backward, down over the closed glottis
Pharyngeal muscles contract to
force the bolus into the oesophagus
Pharyngeal muscles contract to force the bolus into the oesophagus
Also known as the…
… gullet
- Pharyngeal muscles contract to force the bolus into the oesophagus
- Also known as the “gullet”.
- Transports …
… food towards the stomach
Upper oesophageal sphincter (UES) …
… closes again
Describe Pavlov’s Dogs and Classical Conditioning
- Dogs learnt to associate see Pavlov’s Assistant (white lab coats) with food and would start to salivate.
- Other stimulus used were metronome, a harmonium, a buzzer, and electric shock.
what is the oesophagus?
Fairly straight, muscular tube between the pharynx and the stomach.
Oesophagus is guarded at
both ends
Oesophagus is guarded at both ends by …
… sphincters: ring-like muscular structures that when closed prevent passage through the tube
what is the upper sphincter of the oesophagus?
Upper: Pharyngoesophageal sphincter.
Pressure gradient exists between the
atmosphere and the oesophagus (as a result of respiratory activity).
sphincters remain
closed
sphincters remain closed except when
swallowing
sphincters remain closed (except when swallowing) prevents …
… large amounts of air from entering oesophagus and stomach during breathing.
sphincters remain closed (except when swallowing) prevents …… large amounts of air from entering oesophagus and stomach during breathing.
Instead, air is directed into the …
… respiratory airways
The swallow triggers a
primary peristaltic wave that sweeps from beginning to end of oesophagus
The swallow triggers a primary peristaltic wave that sweeps from beginning to end of oesophagus
Forces the …
… bolus ahead of it through the oesophagus to the stomach
the primary peristaltic wave takes between…
… 5-9 seconds to reach the lower end of the oesophagus
The wave takes between 5-9 seconds to reach the lower end of the oesophagus and is controlled by
the swallowing centre in the medulla of the brain stem.
If the bolus gets stuck:
- A second more powerful wave is initiated by pressure receptors (secondary peristaltic waves).
- Responding to distension of the oesophagus wall.
Gastroesophageal sphincter (smooth muscle) stays
tonically contracted to maintain a barrier between the stomach and oesophagus
Gastroesophageal sphincter (smooth muscle) stays tonically contracted to maintain a barrier between the stomach and oesophagus.
Reduces the chance of…
… reflux of acidic gastric contents into the oesophagus.
- Gastroesophageal sphincter (smooth muscle) stays tonically contracted to maintain a barrier between the stomach and oesophagus.
- Reduces the chance of reflux of acidic gastric contents into the oesophagus.
If this does occur, the acidity of these contents irritate the…
… oesophagus causing discomfort – heartburn!
As the peristaltic wave sweeps the oesophagus, the gastroesophageal sphincter…
… relaxes so that the bolus can pass into the stomach.
- As the peristaltic wave sweeps the oesophagus, the gastroesophageal sphincter relaxes so that the bolus can pass into the stomach.
- Once entered, the swallow is …
… complete and the lower oesophageal sphincter contracts.
Oesophageal Secretions are entirely…
… mucus for protection and lubrication
Mucus secreting gland cells in the
submucosa
Mucus from Oesophageal Secretions prevents…
1) Damage by sharp edged food.
2) Acidic attack of oesophageal walls.
3) Enzyme attack of oesophageal walls.
Entire time period from the pharynx to the stomach is between…
… 6-10 seconds
Entire time period from the pharynx to the stomach is between 6-10 seconds.
Too slow for
any digestion to take place.
