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GASTROINTESTINAL FUNCTIONS

DR JEREMIAH ONUBI MSc, FMCPath

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  • Consists- oral cavity, pharynx, oesophagus, stomach, duodenum, Jejunum, ileum, colon- ascending, transcending and descending sigmoid, Rectum and anus.
  • Others are cecum and appendix at the junction of ileum and ascending colon.

INTRODUCTION

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  • Exterior to GIT are appendages:

Liver, gall bladder, pancreas and secretory glands in the oral cavity.

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Oral cavity

  • permanent teeth- mechanical Function
  • The tongue propels for proper action of the teeth on food.
  • salivary glands- parotid, submandibular, sublingual
  • chemical disintegration of food items.
  • Alcohol, alkaloids, saline, H20 can be absorbed in the oral cavity.

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FUNCTIONS

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Saliva

  • 1.5litres of saliva produced daily.
  • Colourless
  • SG 1002-1008
  • PH 6.6-7.4
  • Constituents – Salivary amylase (ptyalin)

- Squamous epithelial cells

- Dead leucocytes

- Elements like Hg, Pb,

- Na+, K+, Ca2+

- H20

- Agglutinogen.

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Functions of Saliva

  • Digestion of food
  • Enhance the sensation of taste buds
  • Lubrication of food
  • Antibacteria because of lysozymes
  • Excretion of certain substances e.g Pb, Hg and iodides

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Oesophagus

  • The oesophagus – is the tube linking the pharynx with the stomach.
  • It allows for the transportation of any food material in the oral cavity to the stomach.

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Stomach

  • Fundus, Body, Antrum and Pyloric region
  • Receptacle for food from eosophagus
  • Mixing of food
  • Digestion and secretions
  • Gastric juice

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Principal stimulants:

  • Vagus nerve - smell, sight, taste.
  • Hormone gastrin is the most potent stimulus to gastric secretion. It is secreted by G cells in the gastric mucosa and the duodenum in response to vagal stimulation and contact with secretagogues.
  • Distention of the stomach with food or fluid
  • Contact of protein breakdown products, secretagogues with the gastric mucosa

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Gastric juice

  • The pariental cells secrete the hydrochloric acid (HCL) and the Intrinsic factor. PH is from 1 – 1.5
  • The Chief cells secret pepsinogens and other enzymes. Pepsinogens converted to pepsin
  • 2 to 3 L of gastric juice is produced in 24hrs, could be more with food.
  • Concentration of H+ = 70mmol/L, Na+ = 70mmol/L, K+ =10mmol/L, CL- =140mmol/L

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  • Haemopoetic organs(IF)
  • Cyanocobalamin from food reacts with this IF (only produced from stomach) to form co-enzymes which is important for the maturation of erythrocytes. Without it no absorption of cynocobalamin.
  • Pernicious anemia
  • Megaloblastic anemia caused by vitamin B-12 deficiency is referred to as pernicious anaemia.

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Endocrine organs

  • Gastrin- produced by G cell in pyloric antrium
  • Food stays in the stomach from 11/2- 2hrs. by 3hrs everything might have left the stomachAbsorption- absorption of some food substances, glucose, alkaloids, alcohol, saline, H20.

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  • Upper part and lower part; Upper part generates more heat than any other organ in the body.
  • Lower Part- pancreas and bile duct opening as ampula of verta.
  • Secretions -Enterogastron- decreases production of acid
  • Enterokinase enzymes acts on trypsinogen to trypsin.

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Duodenum

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  • Secretin
  • Pancreozymin
  • Cholecystokinin
  • Trypsin- dipeptides to aas.
  • Nuclease- nucleic acid to nucleotides
  • Nucleotidases-nucleotides to purines and pyrimidines
  • Fructase-fructose to glucose

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Duodenum

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  • Motilin- Upper small intestine
  • Glucagon- Pancreatic and intestinal mucosa
  • Gastric Inhibitory Polypeptide(GIP)- Duodenal Mucosa
  • Vasoactive Intestinal Polypeptide (VIP)- Gut
  • Bile Salt, Bicarbonate, Amylase, Lipase.

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Duodenum

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  • Fats are emulsified by the detergent action of bile thereby allowing lipase to hydrolyse it to diglycerides, then monoglycerides then fatty acid and glycerol.
  • Fat Diglycerides Monoglycerides

Fatty acid Glycerol

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Duodenum

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  • About 4m long
  • Absorptive capacity enhanced by its microvillus structure.
  • Succus entericus- produced by acini in the mucosa and it is stimulated by presence of partly digested food. This juice complete digestive process in the GIT.

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Jejunum and Ileum

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  • Content of this juice- H20, Erepsin, Maltase, Lactase, Lipase, Trypsin, Nuclease, Nucleatidase and Enterokinase
  • Erepsin- dipeptides to amino acids
  • Maltase- maltose to monosaccharides
  • Lactase- lactose to glucose, galactose
  • Lipase- fat to fatty acids

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Jejunum and Ileum

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  • The intestinal mucosa contains a highly selected mechanism for the absorption of each nutrients.
  • Carbohydrate absorption
    • Monosacharides – glucose, galactose, fructose are absorbed by Specific active – transport mechanism

Conc

Intestine gradient Blood stream

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Jejunum and Ileum

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  • Disacharides – Split by enzymes to Monodisaccharidase located at the microvilli. Eg milk sugar

Lactase

Lactose Glucose galactose

Sucrase

Sucrose Glucose fructose

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Maltase

Maltose 2 Glucose

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Jejunum and Ileum

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  • Polypeptides, dipeptides and amino acids
  • Proteins are not absorbed directly but specific absorptive mechanisms designed for various types of aas are located in the mucosal surface.

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Jejunum and Ileum

Protein

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  • Micelle- Product of digested fat in the intestine.
  • FAs and monoglycerides- diffusion into the epithelial cells
  • With binding proteins –triglycerides- Chylomicrons- To Lymphatic system then transported to Thoracic duct before entering blood stream.

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Jejunum and Ileum

Fat Absorption

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  • Not water soluble hence absorbed with lipids.

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Water and Sodium Absorption

  • Water goes with Na in the intestine.

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Jejunum and Ileum

Vits ADEK

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  • Colon- large intestine(=5 feet long)Ceacum, vermiform appendix, ascending colon, Transverse Colon, descending colon and anus.
  • Little or no digestion here
  • Two major functions- water resorption i.e the 1.5L of fluid received by the cecum is reduced to about 100-300ml of faeces, and storage of faeces, (Rectum)before defecation.

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Colon

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  • Absorption- H20, glucose, saline and certain metals including calcium and some alkaloids.
  • Motility- parasympathetic- contraction.
  • Sympathetic –relaxes
  • Chyme-end product of digestion enters the caecum- hepatic flexor about 6hrs- splenic flexor in 9hrs. in 24hrs will appear in faeces. 1/3 of what is eaten appear in the faeces.

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Colon

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  • At 36hrs- 50% appear
  • At 72hrs- everything has disappeared from colon.
  • Aromatic smell
  • Composition- water 70-80%
  • Organics & inorganic matters,Na+,ca,cl,po4,mucus

Desquamated epithelial cells, dead leucocytes & lots of dead bacteria

  • Fats < 5%
  • Pigments as a result of bilirubin metabolism.

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Colon

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  • Stomach Ulcers- Genetic- Persons with blood group O (Peptic Ulcers), physcological
  • Deudonal ulcer- Have increased secretion of acid and pepsin

- Mucosal Prostaglandins

- Presence of bacteria ( Helicobacter Pylori)

  • Chronic active gastritis by H. Pylori and Increased serum gastrin

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GIT disorders

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  • Pyloric Obstruction

- Tumour of the head of pancreas

- Presents as projectile vomiting

- loss of HCL

- Leading to severe hypochloremic metabolic alkalosis

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GIT disorders

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  • Zollinger- Ellison Syndrome
  • A peptic ulcer disease caused by a gastrin secreting tumour of the pancreas( Gastrinoma)

Clinical Presentation

  • Recurrent peptic ulceration
  • Steatorrhea
  • Diarrhea
  • Z-E Syndrome is associated with hyperthyrodism in 20% of patients. Other abnormalities are pituitary, Adrenal, Ovarian and Thyroid tumours.

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GIT disorders

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  • Pernicious aneamia
  • Gastric achorhydria, gastric atrophy and failure to secrete IF
  • Cancer- Mostly at the Pylorus and antrum

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GIT disorders

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  • Small Intestine -Mucosal linning generally affected.

- Steatorrhea- Malabsorbtion of dietary fat from Z-E Syndrome.

- Celiac disease- Have abnormal immunological ressponse to presence of gluten in the diet.

- Lactose intolerance

- Carcinoid syndrome- vasculrr flushing, diarrhoea, calcinoid tumour of the bowel, occasional tricuspid insufficiency, rarely pellegra

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GIT disorders

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  • Large Intestine

- Diarrhea- Severe diarrhea causes sodium and water depletion. Potassium is also lost

- Acidosis- Results from increased faeces loss of bicarbonate in Chronic, mild diarrhoea- hypokalemic alkalosis may be found.

- Cancer- of colon and rectum

- Blind loop syndrome

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GIT disorders

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  • Gastric acidity
  • Gastric Stimulation test

- Gastric analysis

- Hollander insulin test.

- Gastrin stimulation test

  • Schilling test
  • Pancreatic challenge test

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Biochemical Tests

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  • Fat absorption test

- Qualitative Feacal fat estimation

- Serum test estimations

- Isotope tests

  • D-xylose test- normally absorbent and found in urine but if there is malabsorption will be found in stool and not urine. D- xylose cannot be metabolized but absorbed in intestine.
  • Lactose tolerance test

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Biochemical Tests

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  • Occult blood
  • Carcinoembrionic antigen (CEA)
  • 5- Hydroxylindoacetic acid (5-HIAA)
  • Serum folate
  • Vit B12
  • Fibrotic endoscopy and improved radiological procedures

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Biochemical Tests

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THANK YOU

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