Gastroinstestinal SystemLecture 2

Dr Than Kyaw

30 April 2012

Physiology II

• Ruminant digestion• Monogastric digestion• Enzymes and hormones• Digestion products• Absorption and utilization

Ruminant and monogastric Digestion

Compound stomach(multichambered , polygastric, ruminant stomach)

• Consume fibrous foods

- forages (grasses)

- roughages

- other fibrous food sources

• Plant materials other simple stoach animals are unable to digest.

• Fermented in the rumen with the help of microbes (microflora)

Cellulose and semicellose

To valuable products

Rumen (paunch)- Bacterial and chemical breakdown of fiber (anaerobic)- Occupy most of the left-side of the abdomen- Has thick, muscular wall- Papillae on walls: up to 1 cm. in length, bacteria more

concentrated- Rumen capacity - 50 to 65 gallons (dairy cattle) - 5 to 10 gallons (sheep)

4 compartments

Dorsal sac

Ventral sac

Posterior Dorsal blind sac

Posterior ventral blind sac

Right longitudinal

grove

Dorsal coronary groove

Ventral coronary groove

Papillae in Rumen Papillae in Rumen

Interior surface of rumen - numerous papillae - vary in shape and size - short and pointed to long and

foliate.

Reticulum (honey combs)

- interior surface – looks like honeycomb- helps to remove foreign matter from the food material.

4 compartments

Reticulum - full Reticulum - cleaned

Epithelium of reticulum - thrown into folds that form

polygonal cells - honey-comb appearance - Numerous small papillae

4 compartments

Omasum (book stomach)- round and muscular- “Grinds” the food material and prepares the food material for chemical breakdown.

Omasum - full

- Broad longitudinal folds or leaves (lay term - 'book').

- Omasal folds - packed with finely ground ingesta

- Estimated to be 1/3 of the total surface area of the forestomachs.

Inner surface of omasum

Abomasum (true stomach)• very similar to the stomach of non-ruminants• the majority of chemical breakdown of food material

occurs.• mixes in digestive enzymes (pepsin)

4 compartments

Abomasum – inside view

Size of young and adult ruminants

Important to know the development of ruminantstomach for feeding young and adult

% of Total Stomach

Newborn Calf Adult Cow

Rumen 25% 80%

Reticulum 25% 6%

Omasum 10% 3%

Abomasum 40% 11%

Compartment size of young and adult ruminants

 Capacities of digestive tract of mature sheep

 Compartment Capacity

 Reticulum Rumen Omasum Abomasum

1.2 to 2.0 quarts5.0 to 10.0 gallons0.5 to 1.0 quarts2.0 to 3.0 gallons

 Small intestines 2.0 to 2.5 gallons (80 ft)

 Large intestines 1.5 to 2.0 quarts

- Bacteria: Over 60 spp - digest sugars, starch, fiber, and protein for the cow.

- Protozoa: About 35 spp (size: 20 – 200 μ) - some spp swallow and digest bacteria, starch

granules, and some fiber.

- Bacteria and protozoa – differ greatly in size, shape, and structure

Rumen microbes (micro flora)

- Fungi

- very small fraction

- important in splitting plant fibers open to provide

easy digestion by bacteria

Rumen microbes (micro flora)

A Protist found in rumen

A Protozoan dividing into two

A Protozoan A fungal spore

Bacteria attaching under side of the protozoan

Protozoa of rumen

Protozoan covered with chains of bacteria

Some protozoan and bacteria have symbotic

relationship

Bacteria attacking a strand of Fiber taken from a cow’s rumen.

- One trilion microbes/oz of ruminal fluid

- multiply in double in 11 minutes

- Almost all rumen microbes – anaerobic

- 2/3 of feed digestion

- 90% of fiber digestion

Rumen microbes (micro flora)

In rumen

- Rumen bacteria – good source of protein for the host

- Microbes - 55% of protein and may provide up to half of total

dietary need

- Urea – can be utilized by microbes (synthesis of microbial protein)

- Vitmins K and B-complex synthesis

- adapted to a pH between roughly 5.5 and 6.5

- Abomasum pH: 2 to 4

Rumen microbes (micro flora)

- 3 primary zones based on their specific gravity

- Gas rises to fill the upper regions

- Grain and fluid-saturated roughage ("yesterday's hay")

sink to the bottom

- Newly arrived roughage floats in a middle layer.

Ingesta flow

• Digestion

Ruminal motility

- mix the ingesta - aid in eructation of gas - propel fluid and fermented foodstuffs into the omasum

- Supression of motility - ruminal impaction - Cycles of contraction - 1 to 3 times/min- During feeding - highest frequency- During resting - lowest

Compound stomach

Ruminal motility

Two types of contractions

Primary contractions - Originate in the reticulum - Pass caudally around the rumen - Involves a wave of contraction followed by a wave of

relaxation, so as parts of the rumen are contracting, other sacs are dilating

Secondary contractions - occur in only parts of the rumen - usually associated with eructation.

RuminationRumination (cud chewing)

- regurgitation of ingesta from the reticulum- remastication - resalivation and - redeglutition (reswallowing)

Provides - effective mechanical breakdown of roughage - increases substrate surface area to fermentative microbes.

Rumination

Rumination time = about 8 h/d1 circle of rumination = 1 min

- Contraction of reticulum- Relaxation esophageal sphincter- Inspiratory movement with closed glottis- Negative pressure in the thorax- Dilation of thoracic esophagus and cardia- Reverse peristalsis

Sequences

Roughage+

Fluid to mouth

Result

Flow of ingesta

– Enormous quantity of gas by fermentation

– About 30-50 liters/h in adult cattle

5 l/h in a sheep or goat

- Eructation or belching

- continually get rid of fermentation gases

- eructation is associated with almost every secondary

ruminal contraction

- Eructated gas travels up the esophagus at 160 to 225 cm/s

Eructation

- Any interferences with eructation – life threatening

- Expanding rumen rapidly interferes with breathing

- Animals suffering ruminal tympany (bloat) die from asphyxiation.

Eructation

Fermentation in the rumen

Carbohydrate fermentation• Fibrous feed (cellulose, hemicellulose, xylans)• Readily fermentable CHO (starch, sugars)

• Principle end products- VFAs Volatile fatty acids- CO2

- CH4

- Heat

Volatile Fatty Acids

Glucose

Microbial Fermentation

- Rumen, cecum, colon

Acetic acid (2c)

CH3 CO

O–CH2 C

O

O–CH3 CH2 C

O

O–CH2CH3

Propionic acid (3c) Butyric acid (4c)

Carbohydrates VFA’s×

VFA Formation

2 acetate + CO2 + CH4 + heat

2 propionate + water

1 butyrate + CO2 + CH4

1 Glucose

- VFAs absorbed passively from rumen to portal blood- Provide 70-80% of ruminant’s energy needs

Uses of VFA

• Acetate– Energy– Fatty acid synthesis

• Propionate– Energy– Gluconeogenic – glucose synthesis

• Butyrate– Energy– Rumen epithelial cells convert to ketone

Proportions produced depends on diet - Fibrous feed – less propionic/a - carbohydrate feed – more propionic/a

Absorption of VFAs

• No evidence for active transport • VFA metabolism in the rumen wall

– Cells use most of the butyrate for their own energy needs

– Acetate and propionate are ‘exported’ to blood

Fermentation of plant protein

Proteolytic organisms

Plant proteins Amino/aAmmoniaOrganic acids

Resynthesized to different microbial

proteins

Rumen microbes – also able to utilze non-protein nitrogens - urea, biurets, amines

Fermentation of lipids

• Plant contains limited amount of lipids

• Lipids found in most plant = galactosyl diglycerides

• Microbes do not alter lipids very much

• Can synthesize some lipids

• Cannot tolerate if dietary fat contains 5 – 7% of total diet

Digestion in simple stomach

Discussed in Lecture (1)

Stomach produces:

- HCl (stomach pH about 2, pareitel cell)

- pepsinogen (pepsin, Chief cell)

- gastric lipase (fat digestion)

- mucus (protect the stomach epithelium)

- gastrin (hormone – G-cell; stimulate gastric secrretions - signals S/I to prepare for arrival of food)

- Liquids - removed quickly (about 30 m)- Solid portion (chyme) - takes hours

Digestion in simple stomach

- Digest mainly protein to polypeptides- Kill pathogens

Pepsinogen pepsin

Protein in bolus

Peptide

HCl

(Pro-enzyme/Precursor of

pepsin)

Small intestine

3 parts- Duodenum- Jejunum- Ileum.

Smooth m/s

- circular (segmental contraction)

- longitudinal (contract a wave-like action – peristalsis)

- further digestion and absorption of nutrients

- micro villi on the epithelium

Digesta pH Functions

Duodenum 2.7 - 4 Enzymes pH change Flow rate regulation

very little absorption

Jejunum 4 – 7 Enzymes Absorption

Ileum 7 - 8 Absorption Limited fermentation

• Rate of pH increase through small intestine is faster in monogastrics.

Small intestine

Enhanced Surface Area for Increased Nutrient Absorption

Intestinal villi

Note: provision of Large surface areas by the micro villi for absorption

Gastrointestinal Hormones

• Gastrin– Origin: stomach, abomasum– Stimulus: food in stomach– Function: stimulates HCl & pepsinogen secretion,

increases stomach motility• Secretin

– Origin: duodenum– Stimulus: acid– Function: stimulates pancreatic secretions; slows

stomach motility and acid production

• Cholecystokinin (CCK)– Origin: duodenum– Stimulus: fat & protein in duodenum– Function: stimulates bile and pancreatic secretions

• Also regulates appetite and feed intake

• Gastric Inhibitory Protein (GIP)– Origin: duodenum– Stimulus: fats and bile– Function: inhibit stomach motility and secretion of acid

and enzymes

Gastrointestinal Hormones

- long, thin delicate organ - pinkish gray, glandular

Secretions of pancreas- Exocrine

- enzymes and carbonates

- Endocrine- hormones

Pancreas and its secretions

Enzymes1. Amylase: -- carbohydrate digestion (starch, dextrin)

mainly to disaccharides (maltose) -- amylase low in ruminants

2. Lipase: fat digestion - triglycerides to monoglycerides and free fatty

acids

Pancreas and its secretions

3. Proteases*: protein digestionTrypsinogen - converted to trypsin (by enterokinase)Chymotrypsinogen - converted to chymotrypsin (by trypsin)Procarboxypeptidase - converted to carboxypeptidase (by trypsin)

4. Nucleases Digest nucleic acids and nucleotides

5. Lecithinase Lecithin to lysolecithin

Inorganic compoundNaH2CO3 – neutralize acids

Secretion - pH is 7.2-7.8

Pancreas and its secretions

* Enzymes are ususally released in inactive forms in the source organs. Why? - They are capable of doing autodigestion.

Endocrine

- islets of Langerhans - insulin ( beta cells) - glucagon (alpha cells) - somatostatin (delta cells)

Pancreas and its secretions

Blood Glucose

uptake of glucose Muscle, Liver

(Stored as glycogen)Insulin

Amino acids

uptake of amino/a Used for protein

synthesis by all cellsInsulin

- All essential amino/a (balanced ration) are needed for protein synthesis

1. Insulin

Main functions

-- Fat Break down inhibited

-- promote fat deposition and glycogenesis

-- enhance glucose transport across cell

membrane and facilitate diffusion

Glycogen

Glycogenolysis Blood glucoseglucagon

Opposite effect of insulin

Fat

(Lipolysis) Blood glucoseglucagon

2. Glucagon

3. Somatostatin

-- Act as a moderator to the metabolic effect s of insulin, glucagon and growth hormone.

-- Inhibit the secretion of insulin and glucagon

-- As a moderator – it also inhibit the secretion of – gastrin, secretin, cholicystokinin, pancreatic exocrine secretion and gastric acid

4. Pancreatic polypepitides-- secretion stimulated by -- ingestion of protein

-- exercise

-- fasting

Control of insulin and glucagon secretion

Insulin sensitivity

Brain

Kidney

Intestine

Erythrocytes

Little response to insulin

Liver

Muscle

Adipose tissue

Leucocytes

readily response to insulin

Normal blood glucose value of animals (mg/dl)

Horse cow sheep Pig dog chicken60-110 40-80 40-80 80-120 70-120 130-270

Blood glucose level lower than other animals

• Absorption o f VFAs• Absorption of ammonia-N

– About 30 to 40% of the net transport of N into body fluid– Absorbed N may be used for:

• Synthesis of nonessential amino acids• Recycling of N to the rumen

– Important on low protein diets– Regulated by:

• Increased by increasing N concentration of diet• Decreased by increasing the amount of carbohydrate fermented

in the large intestine

• Mineral absorption• Water absorption

– 90% of water entering the LI is absorbed

Large Intestine (Colon)

Note: No enzymatic digestion fermenting micro-organisms are not digested; voided with feces.

Passive transport (by concentration gradient) - Diffusion: freely movable through lipid bilayers of cell

membrane - especially smaller molecules e.g. O2, CO2

- Facilitated diffusion – molecule diffusion facilitated by the help of transport protein, e.g glucose, amino acids

Active transport – use of transport protein, – need energy

– e.g. N+-K + pump, glucose and amino acid absorption in GIT

Nutrient absorption

2 types

Nutrient absorption

Transporter protein

Avians Digestive System

Digestive Tract - Poultry

Esophagus

Crop

Proventriculus

Gizzard Liver

Gall bladder

Cecum

Cloaca

Large intestine

Small intestine (jejunum, ileum)

Pancreas

Duodenum

Avians (Poultry)

Mouth• No teeth, rigid tongue• Poorly developed salivary glands

– Saliva contains amylase• Beak - adapted for prehension and

mastication

Avians (Poultry)

Esophagus– Has an enlarged area called crop

• Ingesta holding and moistening• Location for breakdown of carbohydrate by

amylase• Fermentation

Proventriculus (stomach)• Release of HCl and pepsin (gastric juices)• Ingesta passes through very quickly (14 seconds)

Avians (Poultry)

Gizzard (ventriculus)– Muscular area with a hardened lining reduces

particle size• Muscular contractions every 20-30 seconds• Includes action of grit • HCl and pepsin secreted in proventriculus

Small intestine– Similar to other monogastrics

Avians (Poultry)

Ceca and large intestine– Contain two ceca instead of one as in other

monogastrics– Large intestine is very short (2-4 in) and

empties into cloaca where fecal material will be voided via the vent

• Water resorption• Fiber fermentation by bacteria• H2O soluble vitamin synthesis by bacteria

mouth mouth mouth

esop esop esop

reticulumRumen

omasum

crop

abomasum stomach proventriculus

gizard

S/IS/IS/I

cecum cecum cecum

compound Simple Avian

colon colon colon

Salivary glands

Rumen microbesfermentation

Rumen microbes

Gastric secretion

Grinding, mixing

Digestion, absorption

fermentation

Absorption of water

summary

(RUMEN)

Telephone CordWire

Traumatic reticulitis in cow

Sponge taken from digestive system of an animal

End of Lecture

Major Gastrointestinal Hormones

Honnone Production Action Releasestimulus

Gastrin Distal stomach Primary: Stimulates acid secretion from stomach glandsSecondary: Stimulates gastric motility, growth of stomach epithelium

Protein in stomach; high gastric pH;vagal stimulation

Secretin duodenum Primary: Stimulates bicarbonatesecretion from pancreasSecondary: Stimulates biliary bicarbonate secretion

Acid in duodenum

Cholecysto-kinin (CCK)

Duodenum to ileum, with highestconcentration induodenum

Primary: Stimulates enzyme secretion from pancreasSecondary: Inhibits gastric emptying

Proteins and fats in small intestine

Gastric inhibitorypolypeptide (GIP)

Duodenum andupper jejunum

Primary:Inhibits gastric motility andsecretory activitySecondary:Stimulates insulin secretionprovided sufficient glucose ispresent; may be most importantaction in many species

Carbohydrate and fat in small instine

Motilin Duodenum andjejunum

Primary: Probably regulates motilitypattern of the gut in period between mealsSecondary:May regulate tone of lower esophageal sphincter

Acetylcholine

Major Gastrointestinal Hormones