GENERAL CHARACTERISTICS GENERAL CHARACTERISTICS OF DIGESTIVE SYSTEM. OF DIGESTIVE SYSTEM. FEEDING OF BEHAVIORFEEDING OF BEHAVIOR

Components of the Digestive SystemComponents of the Digestive System

Gastrointestinal tractGastrointestinal tract (GI) (GI) is is a continuous tube that a continuous tube that consists of the mouth, consists of the mouth, pharynx, esophagus, pharynx, esophagus, stomach, small intestine, large stomach, small intestine, large intestine, and anus.intestine, and anus.

The lumen of this tube is The lumen of this tube is continuous with the external continuous with the external environment. environment.

The The accessory organsaccessory organs are are the salivary glands, exocrine the salivary glands, exocrine glands, and biliary system glands, and biliary system (liver and gallbladder).(liver and gallbladder).

Food ProcessingFood Processing

Feeding behaviorFeeding behavior

Lack of food Reduction of level of nutrients

Excitation chemoreceptors of

vessels

Lateral nucleus of the hypothalamus

(hunger center)

Feeling of hunger (preventive motivation)

Stimulates appetite Find food (food reaction)

Saturation Saturation Sensory

Stretch receptors of the

stomach

Ventromedial hypothalamic nuclei (center of saturation)

Lateral nuclei of hypothalamus

(hunger center)

Metabolic

Chemoreceptorsof vessels

Ventromedial hypothalamic nuclei (center of saturation)

Lateral nuclei of hypothalamus

(hunger center)

““The feeding center”The feeding center”

Hunger Center Hunger Center - lateral nuclei of the hypothalamus;- lateral nuclei of the hypothalamus; Center saturation Center saturation - ventromedial nuclei of the hypothalamus;- ventromedial nuclei of the hypothalamus; Brain stem centers Brain stem centers that provide chewing, swallowing, that provide chewing, swallowing,

salivation, the allocation of digestive juices, motility;salivation, the allocation of digestive juices, motility; Vegetative centers of the spinal cord Vegetative centers of the spinal cord (lateral horns of (lateral horns of

segments T1-T4);segments T1-T4); Limbic system Limbic system (regulates emotions impact on hunger and (regulates emotions impact on hunger and

satiety, anger, rage - stimulate hunger, longing, sadness - satiety, anger, rage - stimulate hunger, longing, sadness - inhibit hunger);inhibit hunger);

Cerebral cоrtех Cerebral cоrtех are regulates behavioral responses meet of are regulates behavioral responses meet of nutritional dominant.nutritional dominant.

Functions of the digestive systemFunctions of the digestive system

1. 1. MOTILITY.MOTILITY. This refers to the movement of This refers to the movement of food through the digestive tract through the food through the digestive tract through the processes of processes of

IngestionIngestion:: taking food into the mouth taking food into the mouth Mastication:Mastication: chewing the food and mixing it chewing the food and mixing it

with salivawith saliva Deglutition:Deglutition: swallowing food swallowing food Peristalsis:Peristalsis: rhythmic, wavelike contractions rhythmic, wavelike contractions

that move food through the gastrointestinal tractthat move food through the gastrointestinal tract

Primary:

Functions of the digestive systemFunctions of the digestive system

2. 2. SECRETION.SECRETION. This includes both exocrine and This includes both exocrine and endocrine secretions.endocrine secretions.

Exocrine secretions:Exocrine secretions: Water, hydrochloric acid, Water, hydrochloric acid, bicarbonate, and many digestive enzymes are bicarbonate, and many digestive enzymes are secreted into the lumen of the GI tract. The stomach secreted into the lumen of the GI tract. The stomach alone, for example, secretes 2 to 3 liters of gastric alone, for example, secretes 2 to 3 liters of gastric juice a day.juice a day.

Endocrine secretions:Endocrine secretions: The stomach and small The stomach and small intestine secretes a number of hormones that helps to intestine secretes a number of hormones that helps to regulate the digestive system.regulate the digestive system.

Functions of the digestive systemFunctions of the digestive system

3.3. Digestion.Digestion. This refers to the breakdown of This refers to the breakdown of food molecules into their smaller subunits, food molecules into their smaller subunits, which can be absorbed.which can be absorbed.

4.4. Absorption.Absorption. This refers to the passage of This refers to the passage of digested end products into the blood or lymph.digested end products into the blood or lymph.

5.5. Storage and elimination.Storage and elimination. This refers to the This refers to the temporary storage and subsequent elimination temporary storage and subsequent elimination of indigestible food molecules.of indigestible food molecules.

Functions of the digestive systemFunctions of the digestive system

HomeostaticHomeostatic. . GaGastrointestinal tract is involved strointestinal tract is involved in maintaining the sustainability of water, the in maintaining the sustainability of water, the concentrations of ions, glucose, amino acids, concentrations of ions, glucose, amino acids, fatty acids and others.fatty acids and others.

ExcretoryExcretory – – expelling certain products of expelling certain products of metabolism (e.g. bile pigments), and the salt of metabolism (e.g. bile pigments), and the salt of heavy metals, from organism.heavy metals, from organism.

Hemodynamic. Hemodynamic. venous plexus of the venous plexus of the abdominal cavity is played role as depot of abdominal cavity is played role as depot of blood.blood.

Secondary

Functions of the digestive systemFunctions of the digestive system Regulatory.Regulatory. GIT is secreted by a numbers of GIT is secreted by a numbers of

gastrointestinal hormones (GIH) that are gastrointestinal hormones (GIH) that are participating in the secretory, motor and suction participating in the secretory, motor and suction functions of the alimentary canal;functions of the alimentary canal;

Protective.Protective. Nonspecific protection is provided Nonspecific protection is provided by the bactericidal properties of saliva, gastric by the bactericidal properties of saliva, gastric juice, bile, and antitoxic barrier function of the juice, bile, and antitoxic barrier function of the liver, vomiting. Specific protection is provided in liver, vomiting. Specific protection is provided in immunoglobulins, which are part of the digestive immunoglobulins, which are part of the digestive secrets.secrets.

DigestionDigestion

Digestion:Digestion: is the process of breaking down food is the process of breaking down food into molecules the body can use, the absorption of into molecules the body can use, the absorption of nutrients, & the elimination of waste.nutrients, & the elimination of waste. Carbohydrates are broken down to monosaccharides Carbohydrates are broken down to monosaccharides

(example: glucose)(example: glucose) Proteins are broken down to amino acidsProteins are broken down to amino acids Lipids are broken down to fatty acids and glycerolLipids are broken down to fatty acids and glycerol

Types of digestion:Types of digestion: Mechanical digestion:Mechanical digestion: breaking chunks of food into breaking chunks of food into

smaller piecessmaller pieces Chemical digestion:Chemical digestion: changing food into the subunits changing food into the subunits

listed above by the action of enzymeslisted above by the action of enzymes

Types of digestionTypes of digestion Classification by localizationClassification by localization

DIGESTION

INTRACELLULAR EXTRACELLULAR

Contact Distal (cavity digestion)

Pariental Membrane

Types of NutrientsTypes of Nutrients

MicronutrientsMicronutrients- vitamins, minerals, & water- vitamins, minerals, & water

MacronutrientsMacronutrients- proteins, lipids, - proteins, lipids, carbohydrates, etc…carbohydrates, etc…

The wall of the digestive tract consists of The wall of the digestive tract consists of four layers.four layers.

The The mucosamucosa lines the luminal surface. lines the luminal surface. Its inner epithelial layer has exocrine Its inner epithelial layer has exocrine and endocrine cells. The lamina and endocrine cells. The lamina propria is a middle layer of connective propria is a middle layer of connective tissue. The muscularis mucosa is a tissue. The muscularis mucosa is a sparse layer of smooth muscle.sparse layer of smooth muscle.

The The submucosasubmucosa is under the mucosa is under the mucosa This connective tissue has large blood This connective tissue has large blood and lymph vessels. It contains a and lymph vessels. It contains a submucous plexus.submucous plexus.

The The muscularis externamuscularis externa is the main is the main smooth layer of the digestive tube. It is smooth layer of the digestive tube. It is between the submucosa and outer between the submucosa and outer serosa. The muscularis externa has an serosa. The muscularis externa has an inner circular layer and an outer inner circular layer and an outer longitudinal layer. Their contractions longitudinal layer. Their contractions produce the propulsive and mixing produce the propulsive and mixing movements. movements.

A myenteric plexus is between the two A myenteric plexus is between the two smooth muscle layers.smooth muscle layers.

Autonomous smooth muscle functionAutonomous smooth muscle function

Smooth muscle in GIT shows rhythmic Smooth muscle in GIT shows rhythmic spontaneous variation in it’s resting spontaneous variation in it’s resting membrane potential (slow waves). It is also membrane potential (slow waves). It is also called basic electric rhythm (BER). They do called basic electric rhythm (BER). They do not cause contraction by themselves, but not cause contraction by themselves, but they bring smooth muscle to their thershold they bring smooth muscle to their thershold and action potentials occur and at that time and action potentials occur and at that time contraction developed.contraction developed.

*** Smooth muscle cells is connected to the *** Smooth muscle cells is connected to the adjacent smooth muscle cells by cap junction adjacent smooth muscle cells by cap junction and electrical activity in one muscle can pass and electrical activity in one muscle can pass through these cap junction so the whole through these cap junction so the whole muscle sheet acts as functional syncytium. muscle sheet acts as functional syncytium.

This slow cyclic electrical activity is This slow cyclic electrical activity is originated from pacemaker cell called Cajal originated from pacemaker cell called Cajal cells which found between circular and cells which found between circular and longitudinal layers.longitudinal layers.

BER BER

Characteristic of mechanisms Characteristic of mechanisms regulation digestionregulation digestion

Central nervous mechanismsCentral nervous mechanisms

Inconditioned reflexes Conditioned reflexes (inborn) (depend on experience)

Established by smell, by thought food, by talking about food, and even by sounds by its preparation

Established when food put in mouth

ensure the preparation of the digestive system to eat foods

provide such complex reflex acts as chewing, swallowing, vomiting, and regulation of secretion of saliva and gastric and others. juice

Central nervous mechanisms especially pronounced in the upper part of the alimentary canal, as distance from which their role is reduced.

Central Humoral MechanismsCentral Humoral Mechanisms

almost no effect on secretion and motility almost no effect on secretion and motility GI tract, but have some effect on the GI tract, but have some effect on the absorption of certain substances (calcium, absorption of certain substances (calcium, phosphorus, sodium, etc.)..phosphorus, sodium, etc.)..

Methods of studying the functions of Methods of studying the functions of the alimentary tractthe alimentary tract

Experimental methods:Experimental methods:- Fistula method;Fistula method;- X-raying method;X-raying method;

Clinical methods:Clinical methods:- Method for collecting human saliva by means of the Method for collecting human saliva by means of the

Lashley-Krasnogorsky capsule (small metal funnel);Lashley-Krasnogorsky capsule (small metal funnel);- ElectrogastrographyElectrogastrography;- Х-Х-raying methods;raying methods;- Endoscopy.Endoscopy.