Physiology II
Gastroinstestinal System
Lecture 1
Dr Than Kyaw
23 May 2012
Introduction
Gastroinstestinal System
(Alimentary system, Digestive system)
• Living things – the most important = to live
• Need to
– eat food
– digest it
– use digested materials for body building, maintenance,
production
• Without food
– survive for a few days/month
– use body stores and tissues
Introduction
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Know the order of principle parts of Alimentary (GI) tract
Carnivorous – flesh eating
Herbivorous – plant eating
Omnivorous – eat both flesh and plants
Digestive systems develop differently in different spp.
e.g. Cecum of horse (large) but of dog (very small) (why?)
- functional need/amount of fermentation required
Functional
Anatomy of
GI Tract
1. Oral cavity (Mouth)
Teeth
Tongue
Pharynx
2. Stomach
Esophagus
Simple & compound stomach
3. Intestines
Small
Large
4. Accessory organs
Salivary glands
Pancreas
Liver
Oral cavity
- Most cranial part
- Food is first received
- Teeth and tongue - assist digestion
Teeth
- cutting
- reduce the size of ingested food particles by grinding
- increase surface areas
– chemical + microbiologic degradation
Types of teeth
• Incisors (nippers): most forward teeth;
for cutting
• Canine teeth (tasks, fangs, eye teeth)
- tearing and separation of food
• Premolars
- caudal to the canines
- grinding
• Molars
- grinding
• Premolars & molars = cheek teeth
TEETH (INCISORS)
Carnivore
Herbivore
Omnivore
Human
Short and pointed
Broad, flattened and spade shaped
Short and pointed
Broad, flattened and spade shaped
TEETH (CANINES)
Carnivore
Herbivore
Omnivore
Human
Long, sharp and curved
Dull and short or long, or none
Long, sharp and curved
Short and blunt
TEETH (MOLARS)
Carnivore
Herbivore
Omnivore
Human
Sharp, jagged and blade shaped
Flattened with cusps, complex surface
Sharp blades and/or flattened
Flattened with nodular cusps
Dental formulas
Dental formulas: domestic animals (permanent teeth)
-One side of the jaw
- Numerator = upper jaw
- Denominator = lower jaw
(A) Cow*
(B) Horse
*Note: Cow, sheep and goats have no upper incisors;
but a dental pad
(C) Sheep
(D) Pig
(E) Dog
- Upper cheek teeth – slightly wider apart than lower
arcade
– also has wider table (grinding
surface) than lower teeth
- In horse
- uneven wear (hooks) - points are formed
- cause injury to the bucal or lingual membranes
- painful, unable to eat
- filing off the points with a dental rasp (floating of
the teeth)
Horse: formation of points
Reece (2009)
Eruption of teeth and age
• Age of animal estimated by the stage of eruption
• E.g: cow (permanent teeth eruption)
Tooth
I1
I2
I3
I4
Age
1½ - 2 y
2 - 2½ y
3y
Tooth
P1
P2
P3
Age
2 - 2½ y
1½ - 2½ y
2½ - 3 y
Tooth
M1
M2
M3
Age
5 – 6 mth
1½ y
2 - 2½ y
3½ - 4 y
• Search and observe dentition for other animals
• Muscles related to chewing
Tongue
Muscular organ
- longitudinal
- Circular
- transverse
Extremely mobile
What does a tongue can do?
- Maneuver food mass
- seize
- bring into the mouth
- move food to the table surfaces of teeth
- swallowing
- gustation (taste)
- clean the fur and body
- remove oil and parasites
- catching the prey
- heat regulation
Taste buds on the tongue
• Numerous projections – k/s papillae
- for traction of food
- grooming of the offspring
• Types of Papillae
- Vallate: Large circular projections
surrounded by a deep groove
- Fungiform: like tiny mushroom
- Filliform: pointed projection
- Folliate: like leaf
- Conical: cone shaped
Nerve supply
- Facial nerve (VII)
- Glossopharyngeal nerve (XI)
Taste buds
- Chemical senses
- Important for feed intake of man and animals
• Abundant in - Vallate, folliate and fungiform
papillae
- Soft palate
- Parts of pharynx
- Epiglottis
- Larynx
Taste Buds, Taste Receptor Cells, and Taste Nerves
The sense of taste - mediated by taste receptor cells
which are bundled in clusters called taste buds.
Taste receptor cells sample oral concentrations of a
large number of small molecules and report a
sensation of taste to centers in the brainstem.
Number of taste buds
Cattle – 25000
Pig - 15000
Cat - 470
Chicken – 30
Goat - 15000
Man - 8,000 - 10,000
Catfish - 100,000 – 175,000
Examples of some human thresholds of taste
Threshold for
Taste
Substance
tasting
Salty
NaCl
0.01 M
Sour
HCl
0.0009 M
Sweet
Sucrose
0.01 M
Bitter
Quinine
0.000008 M
Umami
Glutamate
0.0007 M
Pharynx
• Common passage to air and food
- Naso-pharynx
- Oro-pharynx
- Laryngo-pharynx
• Responsible for the proper directing of
- air to the air passage
- food and liquid to the esophagus
Mastication and Deglutition
(Chewing and swallowing)
• Mechanical breakdown of food (chewing)
• Fibrous food – require more chewing
• Bolus (round/oval) mixed with saliva
- mucus: adhesion & lubrication for ease of
swallowing
Swallowing (deglutition)
- co-ordinated with swallowing center in the brain
- Mouth – voluntary initiation
- Pharynx – reflex action
- Esophagus - reflex
- Unconsciousness – danger of inhaling vomitus
due to – lack of voluntary control
- depressed reflex centers
Swallowing (deglutition)
The sequences of reflexes:
1. Respiration inhibited (danger of inhaling food minimized)
2. Glottis (opening to larynx) closed
3. Larynx - pulled upward and forward
4. Root of tongue – fold the epiglottis over the glottis as the
tongue plunges the bolus from mouth to pharynx
5. Soft palate – elevated; close the nasal cavity from pharynx
6. Peristaltic contraction of pharynx – directs food from
pharynx to esophagus
7. Reflex peristaltic wave – initiated, transport bolus to
stomach
Salivary glands and saliva
3 paired, well defined salivary glands
1. Parotid - Serous (watery, clear fluid)
2. Sublingual - Mucous (viscid, tenacious and
protective)
3. Mandibular - mixed (serous and mucous)
Autonomic nerve supply (symp- and parasymp)
Salivary glands of dog
Zygomatic
Parotid
Mandibular
Sublingual
Duct of sublingual gland
Salivary glands of horse
1 Parotid gland. 2 Molar glands.
3 Sublingual gland. 4 Parotid Duct.
5 Masseter muscle. 6 Facial nerve.
7 Jugular vein. 8 Submaxillary
vein. 10 Labial glands. 11 Labial
ducts.
1 Submaxillary gland. - - Submaxillary
duet (Wharton's duct). 3 Cluster of
openings of ducts of sublingual
glands. 4 Tongue. 5 Circumvallate
papilla. 6 Fungiform papillae. 7 Jugular
vein. 8 Submaxillary vein.
Salivary glands and saliva
Saliva contains:
water
Electrolytes
Mucus and
Enzymes – amylase (present in pig; absent in
ruminants and dog)
Amount of saliva
- greatest in herbivores
- 80% of water entering the stomach in
cattle is provided by saliva
Salivary glands and saliva
Species
Ox
Cow
Sheep
Goat
Secretion
Parotid
Mixed
Parotid
Parotid
ml/hr
Total/day
800-2400 56 kg
50 gl
4 to 25
10 to 60
Salivary glands and saliva
Function of saliva
• buffering action in ruminants (neutralize acids
produced by fermentation) pH 6.2 – 6.8
• Digestion of carbohydrate by amylase
• evaporation and cooling in panting animals
Esophagus
• Muscular tube – from pharynx to stomach
through thoracic cavity, diaphragm
• Constriction waves of muscular contractions
(peristaltic movement)
Peristalsis
• both longitudinal and circular muscle fibers
propel the ingesta, consisting of a wave of
contraction passing along the tube.
• Increased peristalsis means faster movement
of ingesta through the gut and less absorption
of fluid, both tending to diarrhea.
• Reduced peristalsis means a longer alimentary
sojourn, greater inspiration of ingesta and a
tendency to constipation.
Circular muscle
contraction
Bolus
Circular muscle
relaxation
Antiperistalsis / Reverse peristalsis
• peristalsis directed orally (reverse of going to
stomach)
• Result of intestinal obstruction and acute, significant
distention of the intestinal lumen
• May also rise from mild digestive upsets
• Major contributing mechanism in vomiting.
Vomition (Emesis)
- forceful expulsion of the contents of one's stomach
through the mouth and sometimes the nose
- Protective response to remove potentially harmful
ingesta from the stomach and upper small intestine
- Relaxation of upper and lower esophageal
sphincters, glottis, nasal cavity
- Reflex action through vomiting center in the brain
Regurgitation vs. vomiting
•Rregurgitation:
- passive expulsion of ingested material out of the mouth
- normal component of ruminant digestion for cud chewing
- Cattle and horses vomit rarely
- Dogs and cats vomit easily and frequently,
Stomach
• Simple stomach
• Complex stomach
E
C
F
B
P
?
E = Esophagus
C = Cardia
F = Fundus
B = Body
P = Pylorus
Simple stomach and digestion
• Dilated portion
• Store ingesta temporarily
• Contract and mix food with gastric juice
Chyme
Gastric juice
Gastric
glands in
regions of
Cardia
Fundus
pylorus
Water
Mucus
HCL
Pepsinogen
renin
Simple stomach
Regulation of gastric secretion
Cephalic
phase(stimulatory)
Smell,
Sight,
taste,
Thinking of food
Intestinal phase
(inhibitory)
Gastric phase
(stimulatory)
Presence of food in the
stomach (stretch)
Pyloric gland (G cells)
Parietal cells
Chief (peptic) cells
Cholecystokinin and
secretin (hormones
released by
duodenum)
Gastrin (hormone)
HCL
Pepsinogen (proteolytic
enzyme)
Simple stomach
Cephalic phase
1. Smell,
2. Seeing,
3.taste
Parasympathetic
(vagal) sti
medulla oblongata
4. Thinking of food
endocrine cells in the stomach
Gastrin
secretes gastric juice
stomach
circulatomry system
Circulation
Sti gastric
juice
secretion
Brain
Stretch
Brain
Stomach
Smell, taste,
seeing,
thinking
Stomach Acidity
Carnivore Less than or equal to pH 1 with food in
stomach
Herbivore pH 4 to 5 with food in stomach
Omnivore Less than or equal to pH 1 with food in
stomach
Human
pH 4 to 5 with food in stomach
COW:
Bite size >1.5 inches (25,000 to over 40,000 prehensile bites)
>1/3 = grazing
1/3 = cud chewing
<1/3 = idling
Simple stomach
Pepsinogen
- proteolytic enzyme
- inactive form
- initial (partial) digestion of proteins
Protein in
bolus
Pepsinogen
Activated by
HCl
pepsin
Peptide
Gastric emptying
• Powerful contractions of gastric smooth muscle
- Crushed, ground, mixed and liquefy the ingesta to
form chyme
- chyme is forced through the pyloric canal into the
small intestine (gastric emptying)
- 3 times/min in man; 5 to 6 times/min in dogs
• Neural and hormonal control (enteric and vagus nerve);
receptors present in the duodenum
Stomach of horse
Gastric emptying
• rate of gastric emptying
- strongly influenced by both volume and
composition of gastric contents
• Liquid food faster movement (e.g. water)
- unnecessary to crush or grind
• Solid and large vol. of ingesta - take longer time
• Solid and smaller amount stay long as less gastric reflex
Mechanism of delay in gastric emptying
• Sufficient delay time is necessary for adequate digestion of
ingesta
• This is accomplished by 2 reflexes• Enterogastric reflex (neural)
- osmoreceptors in duodenum respond to hypertonic
contents (products of protein and C/H digestion;
electrolytes)
- H+ receptors in duodenum respond to high H+ conc.
• Enterogastrone reflex (endocrine)
- Cholecystokinin – released from duodenum in response
to lipid entering the duodenum
- GIP (gastric inhibitory peptide) released from jejunum in
response to lipid and C/H
To be continued to lecture 2
Next week