Gastroinstestinal SystemLecture 1

Dr Than Kyaw

23 May 2012

Physiology II

Introduction

• 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

Gastroinstestinal System(Alimentary system, Digestive system)

Introduction

• 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

1. Oral cavity (Mouth)TeethTonguePharynx

2. StomachEsophagusSimple & compound stomach

3. IntestinesSmallLarge

4. Accessory organsSalivary glandsPancreasLiver

Functional Anatomy of

GI Tract

- 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

Oral cavity

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 Short and pointedHerbivore Broad, flattened and spade shapedOmnivore Short and pointedHuman Broad, flattened and spade shaped

TEETH (CANINES)

Carnivore Long, sharp and curvedHerbivore Dull and short or long, or noneOmnivore Long, sharp and curvedHuman Short and blunt

TEETH (MOLARS)

Carnivore Sharp, jagged and blade shapedHerbivore Flattened with cusps, complex surfaceOmnivore Sharp blades and/or flattenedHuman Flattened with nodular cusps

Dental formulas

(A) Cow*

(B) Horse

Dental formulas: domestic animals (permanent teeth)

-One side of the jaw- Numerator = upper jaw- Denominator = lower jaw

*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 pointsReece (2009)

Eruption of teeth and age

• Age of animal estimated by the stage of eruption • E.g: cow (permanent teeth eruption)Tooth Age Tooth Age Tooth AgeI1 1½ - 2 y P1 2 - 2½ y M1 5 – 6 mthI2 2 - 2½ y P2 1½ - 2½ y M2 1½ yI3 3 y P3 2½ - 3 y M3 2 - 2½ yI4 3½ - 4 y

• Search and observe dentition for other animals• Muscles related to chewing

Tongue

Muscular organ - longitudinal - Circular - transverseExtremely 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

• 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

Taste buds on the tongue

Nerve supply - Facial nerve (VII) - Glossopharyngeal nerve (XI)

- 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 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 – 25000Pig - 15000Cat - 470Chicken – 30Goat - 15000Man - 8,000 - 10,000Catfish - 100,000 – 175,000

Examples of some human thresholds of taste

Taste Substance Threshold for tasting

Salty NaCl 0.01 MSour HCl 0.0009 M

Sweet Sucrose 0.01 MBitter 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

The sequences of reflexes:1. Respiration inhibited (danger of inhaling food minimized)2. Glottis (opening to larynx) closed3. Larynx - pulled upward and forward4. Root of tongue – fold the epiglottis over the glottis as the

tongue plunges the bolus from mouth to pharynx5. Soft palate – elevated; close the nasal cavity from pharynx6. Peristaltic contraction of pharynx – directs food from

pharynx to esophagus7. Reflex peristaltic wave – initiated, transport bolus to

stomach

Swallowing (deglutition)

Salivary glands and saliva

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)

3 paired, well defined salivary glands

Parotid

Duct of sublingual gland

Mandibular

Salivary glands of dog

Sublingual

Zygomatic

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 of horse

Salivary glands and saliva

Amount of saliva- greatest in herbivores

- 80% of water entering the stomach in cattle is provided by saliva

Saliva contains: waterElectrolytesMucus andEnzymes – amylase (present in pig; absent in

ruminants and dog)

Salivary glands and saliva

Species Secretion ml/hr Total/day

Ox Parotid 800-2400 56 kgCow Mixed - 50 glSheep Parotid 4 to 25Goat Parotid 10 to 60

• 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

Function of saliva

Salivary glands and saliva

Esophagus

• Muscular tube – from pharynx to stomachthrough 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

Circular muscle relaxation

Bolus

• 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.

Antiperistalsis / Reverse peristalsis

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

E = EsophagusC = CardiaF = FundusB = BodyP = Pylorus

C F

BP

?

Simple stomach and digestion• Dilated portion• Store ingesta temporarily• Contract and mix food with gastric juice Chyme

Gastric glands in regions of

CardiaFunduspylorus

WaterMucusHCLPepsinogenrenin

Gastric juice

Pyloric gland (G cells)Parietal cellsChief (peptic) cells

Gastrin (hormone)HCLPepsinogen (proteolytic

enzyme)

Simple stomach

Smell, Sight, taste,Thinking of food

Cephalic phase(stimulatory)

Presence of food in the stomach (stretch)

Gastric phase (stimulatory)

Cholecystokinin and secretin (hormones

released by duodenum)

Intestinal phase (inhibitory)

Regulation of gastric secretion

Simple stomach

1. Smell,

2. Seeing,

3.taste

4. Thinking of food

medulla oblongata

endocrine cells in the stomach

Gastrin

stomach

Cephalic phase

secretes gastric juice

Parasympathetic

(vagal) sti

circulatomry system

Smell, taste, seeing,

thinkingStomach

Circulation Sti gastric juice

secretion

BrainStretch

Brain

Stomach AcidityCarnivore Less than or equal to pH 1 with food in

stomachHerbivore pH 4 to 5 with food in stomachOmnivore Less than or equal to pH 1 with food in

stomachHuman pH 4 to 5 with food in stomach

COW:Bite size >1.5 inches (25,000 to over 40,000 prehensile bites)>1/3 = grazing1/3 = cud chewing<1/3 = idling

Pepsinogen

Simple stomach

pepsin

Protein in bolus

Peptide

Activated by HCl

Pepsinogen - proteolytic enzyme- inactive form

- initial (partial) digestion of proteins

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 2Next week