Digestion in large intestine.

Ileo-caecal sphincter begins its opening in 1-4 minutes after feeding and content in small amounts (up to 15 ml) passes in large intestine. About 1,5-2,0 l of chimus comes there for 24 hours. Digestion in large intestine has some distinguishing features.

• Digestive juice has pH 8,5-9,0.

• Juice solid part contains many epitheliocytes and mucus.

• Juice contains enzymes (lipases, peptidases, amylases) in little amounts.

• Large intestine secretion increases in 8-10 times after mechanical tension.

Intestinal microflora – is a constant attribute of this alimentary tract part. It:

• stimulates natural immunity maturation,

• inhibits pathogenic microorganisms growth,

• destroys small intestine enzymes,

• decomposes biliary acids,

• synthesizes vitamines “K”, “E”, “B₆”, “B₁₂”: vit K is especially essential in new-borns when blood coagulation vit-K-dependent factors synthesis is sharply reduced (as it was mentionned above). Until this large intestine function in new-born is not enough activated (due to flora passage) he may have bleedings (haemorrhagia of new-borns);

• unchanged aminoacids synthesis;

• fermentizes carbohydrates and

• causes rotten proteins bacterial decomposition with indole, skatole, sulfuric gas and methane formation. Some of them absorbing in blood are detoxicated in liver (indole, skatole, phenole).

Normal microflora inhibiting (in course of antibiotics treatment) causes staphylococci, yeasts, Esherichia coli and other organisms multiplication.

Excrement (faeces) coloured with biliary pigments is formed in large intestine. At faecal masses formation process intestinal juice solid substances are of great importance namely mucus pieces which glue ungested food residues particles. Faeces content:

• mucus;

• mucosal dead epithelium residues;

• cholesterine;

• salts;

• bacterias;

• proteins, fats and carbohydrates (at digestion disorders).

Large intestine motor function - is quite different. Movements types:

• tonic – one depending on intestine filling and releasing degree;

• pendulum-like - ones directed on content mixture;

• peristaltic – provide intestine content passage;

• antiperistaltic – improve intestinal content utilization and encourage more dense faecal masses formation.

All intestinal motor movements types are regulated by intramural (metasympathetic) nervous system. Sympathetic nervous fibres from superior and inferior mesenterial plexi send inhibitory impulses but parasympathetic – activating. Another large intestine motor activity inhibitors are following:

• adrenaline;

• noradrenaline;

• serotonine;

• glucagon.

Stimulators:

• acethylcholine;

• cortisone.

Final result of large intestine motor activity is defecation act. This process is developed according to the following scheme. Rectum mucosa sensitive nerves irritation leads to external and internal sphincters relaxation; rectum exit is opened and excrement is pushed out by large intestine and rectum peristalsis. It is triggered by making an effort (straining oneself), i.e. abdominal wall muscles, diaphragm and muscles anal sphincter elevators contraction. Defecation reflex center is in spine sacral part. Inarbitrary influencings which retard defecation come from brain cortex. Inarbitrary sphincter relaxation and defecation may occur at some emotional states for instance at fear.

In first hours after birth baby’s intestine is released from primary excrement - meconium. Meconium is sterile in course of 3-5 hours, then microorganisms appear in it. It is delt with feeding. Excrements are connected to meconium at first 2-3 days. Meconium disappears on 4-5^th days. Children have during 1^st month defecation after every feeding. It becomes more seldom since the 2-nd month. It remains 1-2 times a day till 1 year.

Absorbtion. It is substances transfer through semipermeable membrane in blood or lymph, tissular liquid. Due to it approximately 8-9 l of liquid is reabsorbed in digestive tract every day. Absorbtion is performed in all gastro-intestinal tract parts. In oral cavity – water, medicines. In stomach – water, mineral juices, vitamines, alcohol, drugs, hydrolysis products. But main absorbtion place is small intestine. Practically all substances useful for organism are absorbed here.

Absorbtion mechanism is rather complicated, it is physiological process as a result of which filtraction (it depends on hydrostatic pressure), diffusion and osmosis take place.

Different substances take their own absorbtion place. Proteins are absorbed as aminoacids in small intestine in blood. Fats – as monoglycerides and fat acids with biliary acids participation in lymph. Carbohydrates – as glucose (in children – it is possible as fructose and galactose). Water is absorbed in large intestine.