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