THE DIGESTIVE SYSTEM PART II

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MEDICAL PHYSIOLOGY DEPARTMENT – FACULTY OF MEDICINE – MINIA UNIVERSITY DEFINITIONS

❑ Steatorrhea: means passing of greasy bulky pale stools due to deficient bile (i.e. required for fat digestion). ❑ Choleretic: it is a substance that increases the bile secretion from the liver (e.g. bile salts, vagal stimulation and secretin hormone). ❑ Cholagugue: it is a substance that helps the evacuation of the gall bladder (e.g. Cholecystokinin hormone (CKK). JAUNDICE

DEFINITION

It is a yellowish discoloration of the skin, sclera and mucous membranes due to increased serum bilirubin level ≥ 2 mg/dl. JAUNDICE TYPES AND CAUSES OF JAUNDICE

Points Haemolytic Jaundice Obstructive Jaundice Hepatocellular Jaundice • Incompatible blood • Stones in the common • Liver diseases (e.g. transfusion. bile duct (CBD). hepatitis, cancer, liver • All causes of • Cancer head of cirrhosis, bilharzias… Cause haemolytic anaemia pancreas. (e.g. hereditary spherocytosis, sickle cell anaemia, poisons…

Blood Anaemia Present Absent Absent Bilirubin Haemobilirubin Cholebilirubin both

Urine Colour Normal Dark brown brown

Stool Colour Darker than normal Very pale pale Gastrointestinal Motility I. MASTICATION (CHEWING) I. MASTICATION (CHEWING) DEFINITION: The chewing movements break the food into small pieces and stimulate the secretion of saliva to make a suitable food bolus ready for swallowing. The act of chewing is partly voluntary and partly reflex in nature. Functions of Mastication: 1. Break down of food into small particles to increase the surface area of food exposed to the action of digestive enzymes. 2. It stimulates salivary, gastric pancreatic and bile secretions. 3. Reduce mechanical damage of GIT. 4. Development of satiety through stimulation of smell and taste receptors. II. DEGLUTITION (SWALLOWING) Definition: It is the passage of food from mouth to stomach. Stages (Phases) of Deglutition: 1. Buccal Stage: In which food passes from mouth to pharynx. It is the voluntary phase.

2. Pharyngeal Stage: In which food passes from the pharynx to the esophagus. It is involuntary. This phase is sometimes called the Deglutition Reflex:

• Stimulus: touching the pharynx (swallowing receptors) by food. • Afferent: trigeminal nerve. • Center: swallowing center in medulla oblongata. • Efferent: glossopharyngeal and vagus nerve. • Responses: as follows; a. Protective Reflexes: ➢ Elevation of soft palate to close posterior nasal opening to prevent regurgitation of food to nose. ➢ Elevation of the larynx to be covered by epiglottis to prevent entry of food to the trachea. ➢ Approximation of the vocal cords. ➢ Temporary apnea as swallowing center inhibits respiratory center few seconds. b. Pharyngeal Peristalsis: Contraction of pharyngeal muscles and relaxation of upper part of esophagus (upper esophageal sphincter) to push the food bolus to the esophagus. N.B. In anesthesia, cough and swallowing center are depressed and the protective reflexes don't occur so secretion or vomitus may accumulate in pharynx and enter the trachea → choking (i.e. inability to breathe). 3. Esophageal stage: • In which food passes from esophagus to stomach. • It is involuntary.

Stages of Deglutition (i.e. Swallowing). III. GASTRIC MOTILITY Three types; 1. Receptive Relaxation: • A reflex relaxation of stomach wall initiated by the movements of the pharynx and esophagus and increases when food enters the stomach especially in the proximal unit of the stomach (i.e. fundus and body). • Function; it allows the stomach to accommodate up to 1.5 liters of fluids without marked increase in intragastric pressure (i.e. plasticity). 2. Gastric Peristalsis: • Peristaltic waves occur in the distal motor unit of the stomach (i.e. antrum and pylorus) shortly after food intake. • Function; it helps in mixing the food with gastric juice and pushing it to the duodenum.

3. Hunger Contractions: • Strong peristaltic contractions that occur in the body of the stomach when it is empty for long time (e.g. prolonged fasting). Mechanism: • Prolonged fasting ….. Causes hypoglycemia ….. Activates the feeding center which in turn ….. Activates vagal nucleus in medulla oblongata ….. Hunger contractions. • That is why insulin stimulates hunger contractions while glucose inhibits it VOMITING

• Definition: It is a reflex evacuation of upper GIT contents (mainly stomach) through the mouth. • It is preceded by salivation, sweating, rapid heart rate and sensation of nausea. Causes of Vomiting: 1.Reflex vomiting; as a result of smell, taste, vision, severe pain, motion sickness … 2.Central vomiting; as a result of hypoxia, head trauma, drugs, ketosis … Effects of Persistent Vomiting: 1.Dehydration (i.e. water loss). 2.Alkalosis (due to loss of gastric HCl). 3.Potassium depletion. 4.Tetany. Treatment of Vomiting: 1.Treat the cause. 2.Anti-emetic drugs. 3.Correct the complications by giving I.V. fluids, electrolytes (K+) and acidifying salts. IV. INTESTINAL MOTILITY Two types; Segmenting Points Peristaltic movement movement A wave of deep Ring like contractions; circular contraction appear at regular Definition followed by a wave interval along the of relaxation. intestine.

Mechanism Neurogenic. Myogenic. Not abolished by Function Abolished by cocaine. cocaine. Effect of local Help digestion and anaesthetic Push intestinal contents. absorption. (e.g. cocaine)

DEFECATION

Definition: It is evacuation of the colon through the anus. Mechanism: • It is pure automatic reflex in animals and infants of human. • It is under voluntary control in adult human. Defecation Reflex: • Stimulus: distension of rectum by stools. • Receptors: stretch receptors in rectal wall. • Afferent: pelvic nerve. • Center: defecation center in spinal cord (S 2, 3 and 4). • Efferent: pelvic nerve. • Response; either: ➢ If conditions are favorable → contraction of the rectal wall and relaxation of internal anal sphincter → Defection. ➢ If the conditions are not favorable → the cerebral cortex sends inhibitory impulses to the defecation center in the spinal cord → Temporary inhibition of defecation. DISORDERS OF DEFECATION

1. CONSTIPATION

Definition: In normal persons, the frequency of defecation ranges from several times per day to once every 2-3 days. Constipation is an abnormal condition characterized by prolonged interval between defecation associated with difficulty in performing the act.

Causes of Constipation: 1. Repeated voluntary inhibition of the act. This leads to overstay of stool in the colon, resulting in more water reabsorption from it. 2. Decreased motility of the colon as occurs in prolonged ingestion of food with little residue, thus the bulk of stool becomes ineffective to initiate defecation reflex, e.g. old age, lack of muscular exercise, debilitating disease and emotional stress (i.e. spastic colon).

Effects of Constipation: 1. Abdominal discomfort and distension. 2. Nausea and anorexia. 3. Headache. 2. DIARRHEA

• DEFINITION: Abnormal condition characterized by increased frequency of defecation with excretion of watery stool. Causes of Diarrhea: • Hypermotility of the small intestine due to Intestinal infection either viral or bacterial Effects of Diarrhea: Diarrhea is much more dangerous than constipation especially in infants, because it may lead to loss of water (dehydration), electrolytes and bicarbonate (i.e. metabolic acidosis). THANK YOU