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THE DIGESTIVE

SYSTEM

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Digestion

Difficult physiological process in

which course the food which

has arrived in a digestive tube,

is exposed to mechanical and

chemical transformations, and

nutrients containing in it after a

depolymerization are soaked

up in a blood and a lymph.

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Digestive System

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Digestive System

Provides processes physical and a chemical food

processing and its transformation into such products which

can be soaked up by vascular system for carrying over and

the further mastering by an organism.

The processes occurring in a

gastroenteric tract

(GASTROINTESTINAL TRACT)

Physical processing of nutrition

(making smaller, a ramollissement, mixing)

Nutrition chemical processing

(splitting of complex proteins, fats,

carbohydrates into monomers by the

digestive juice)

Absorption of nutrients, water, salts,

vitamins in various departments

GASTROINTESTINAL TRACT with their

subsequent entering in a blood and a lymph

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DIGESTION IN THE ORAL

CAVITY

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The Mouth

• Lips and cheeks enclose the

mouth.

• Taste buds on the tongue

provide the sense of taste;

skeletal muscle in the tongue

allows it to move.

• The roof of the mouth is

formed by the hard and soft

palates that separate it from

the nasal cavities.

• The soft palate ends in a

finger-shaped projection called

the uvula.

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• Tonsils at the back sides of the

mouth protect against

infections.

• Tonsillitis results when the

tonsils become inflamed; the

infection can spread to the

middle ears.

• Three pairs of salivary glands

send saliva (containing salivary

amylase for digestion of starch

to maltose) into the mouth.

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The Teeth

• Twenty deciduous (baby) teethare replaced by 32 adult teeth.

• Each tooth has a crown and a root.

• The crown has a layer of enamel, dentin, and an inner pulp with nerves and blood vessels that extend into the root.

• The tongue mixes the chewed food with saliva and then forms the mixture into a mass called a bolus in preparation for swallowing.

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Adult mouth

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Longitudinal section of

a tooth

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TONGUETongue is an organ consisting of muscles, which

difficult movements play an essential role in such

processes, as conversation, chewing, swallowing. Its

top surface is covered by the special tissue containing

sensitive elements (papillae), distinguishing taste.

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Taste

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DIGESTION PROCESSES IN

THE ORAL CAVITY

1. Making smaller of a food

2. Wetting by a saliva

3. Formation of an food bolus

4. Occurrence of gustatory

sensations

The mouth, or oral cavity, is the first part of

the digestive tract. It is adapted to receive

food by ingestion, break it into small

particles by mastication, and mix it with

saliva. The lips, cheeks, and tongue form

the food bolus. The oral cavity contains the

teeth and tongue and receives the

secretions from the salivary glands.

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Mastication

It is made by reflex

1. Irritation of receptors

2. Mastication phases:

• Rest.

• Nutrition introduction in a

mouth

• The rough

• The basic

• Formation of a food bolus

• Swallowing

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SALIVARY GLANDS

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SALIVARY GLANDS

• The glands are found in and around your

mouth and throat. We call the major

salivary glands the parotid,

submandibular, and sublingual glands.

• They all secrete saliva into your mouth,

the parotid through tubes that drain

saliva, called salivary ducts, near your

upper teeth, submandibular under your

tongue, and the sublingual through many

ducts in the floor of your mouth.

• Besides these glands, there are many

tiny glands called minor salivary glands

located in your lips, inner cheek area

(buccal mucosa), and extensively in other

linings of your mouth and throat. Salivary

glands produce the saliva used to

moisten your mouth, initiate digestion,

and help protect your teeth from decay.

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SALIVARY GLANDS

Parotid (cosecrete a serous saliva, a liquid secret, doesn't contain a mucin)

Submandibular (Cosecrete an admixed saliva,

Serous-mucous secret)

Sublingual (Cosecrete an admixed saliva,

Serous-mucous secret)

A lot of tiny salivary glands that cosecreting the admixed and mucous secret rich Mucin

Water(95-99%)

The dense

rest

Mucin;

Enzyme -amylase (starch

hydrolysis);

Enzyme a maltose (maltose

hydrolysis);

Globulins;

Amino acids;

Urea;

Salts К+, Са2+.

lysocime,

IgA,

growth factors,

рН 5,8-7,4

0,5-2 l

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SALIVA FUNCTIONS

• Digestive (hydrolysis of carbohydrates at the expense of amylase and maltose enzymes)

• Promotes occurrence of gustatory sensations (the alimentary substances dissolved by a saliva, provide nutrition influence on gustatory receptors)

• Formation of an alimentary lump (the mucin binds separate particles of nutrition)

• Excretory (as a part of a saliva metabolism products can be allocated)

• Protective (washes the irritating substances which have got to an oral cavity)

• Bactericidal action (lysocime presence)

• Stimulation of secretion a gastric juice

• Participation in the swallowing act

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SECRETION OF THE

SALIVARY GLANDS

• Instinctive reflexes (stimuli the substances operating on receptors of an oral cavity)

• The parasympathetic department –raises secretion (a considerable quantity of a liquid saliva)

• Sympathetic – a small amount of a dense saliva

• Conditioned reflexes (stimuli the factors operating on visual, acoustical, olfactory and other receptors)

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ESOPHAGUS

The esophagus is a muscular tube about ten inches

(25 cm.) long, extending from the hypopharynx to the

stomach. The esophagus lies posterior to the trachea

and the heart and passes through the mediastinum

and the hiatus, an opening in the diaphragm, in its

descent from the thoracic to the abdominal cavity. The

esophagus does not have serous layer; tissue around

the esophagus is called adventitia. It is used

exclusively as passage for nutrition and doesn't accept

participation in digestion and absorption process.

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The esophagus consists of four principle layers:

• the mucosa,

• submucosa

• muscularis.

• serosa (The outermost connective tissue covering of esophagus is adventitia and it form an integral part of such organ or structure.)

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The Wall of the

Digestive Tract

• The digestive tract wall has four

layers:

• Mucosa (mucous membrane –

secretes digestive enzymes and

mucus),

• Submucosa (loose connective

tissue – houses blood and lymph

vessels),

• Muscularis (two layers of smooth

muscle - for peristalsis), and

• Serosa (serous membrane –

secretes serous fluid to prevent

sticking).

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• The esophagus consists of three principle layers: the

mucosa, submucosa and muscularis.

• The mucosa consists of non-keratinized stratified

squamous epithelium, lamina propria (areolar

connective tissue) and muscularis mucosa (smooth

muscle). Near the stomach the mucosa also contains

mucus glands. This provides a protective layer to the

esophagus.

• The submucosa consists of areolar connective tissue,

blood vessels and mucus glands. This provides a

loose connection between the mucosa and

muscularis.

• The muscularis consists of two layers: internal

circular muscles and external longitudinal fibers. This

provides propulsion. It should be noted that

muscularis is covered by the adventitia, an areolar

connective tissue that merges with the connective

tissue of surrounding tissues, as opposed to serosa

like the stomach, small and large intestines.

• Musculature

• The muscularis of the upper third of the esophagus is

skeletal muscle. The middle is mixed skeletal and

smooth muscle and distal is smooth muscle.

Movement is by primary peristalsis. If a food bolus

becomes lodged in the esophagus stretch receptors

stimulate secondary peristalsis causing an increase

of impulses form the swallowing center in the brain.

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The Esophagus

• The esophagus is a muscular

tube that conducts food

through the thoracic cavity and

diaphragm into the stomach.

• Peristalsis begins in the

esophagus; this collapsed tube

moves the bolus of food

downward after swallowing

occurs.

• Heartburn is a burning pain

when acidic stomach contents

enter the esophagus.

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• No chemical digestion occurs

in the esophagus.

• The entrance of the esophagus

to the stomach is marked by a

constriction, called a sphincter;

the sphincter must relax in

order for food to enter the

stomach.

• The sphincter prevents food

from backing up into the

esophagus.

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Swallowing

• The air passage and food passage cross in the pharynx because the trachea is ventral to the esophagus.

• Swallowing occurs in the pharynx and is a reflex action.

• During swallowing, the air passage is usually blocked off by the soft palate and uvula, and the trachea moves under the epiglottis to cover the glottis opening to

the windpipe.

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Swallowing

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SWALLOWING

(or deglutition)

• Passes in 3 phases:

1. Buccal (voluntary)

2. Pharyngeal (fast involuntary)

3. The esophageal (slow involuntary)

• Regulation occurs at the expense of sympathetic and parasympathetic influences and metasympathetic nervous formations

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Planes and stomach

areas

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STOMACHThe stomach, which receives food from the esophagus, is

located in the upper left quadrant of the abdomen. The

stomach is divided into the fundic, cardiac, body, and pyloric

regions. The lesser and greater curvatures are on the right and

left sides, respectively, of the stomach.

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STOMACH COVERINGS

Mucosa – the internal cover, produces

slime that protects from action of

digestive enzymes.

Tubular gastric glands are produced a

gastric juice.

Submucosa – a network of arterial,

venous, lymphatic vessels and

submucous nervous plexuses.

The muscular cover – is formed by

layers of smooth muscles.

The serous cover – an external cover,

frames a smooth surface of an organ.

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Anatomy and histology

of the stomach

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STOMACH FUNCTIONS

Secretory – it is produced of secret by

the chief, parietal and mucous cells.

Absorbtion – promotes entering from a

stomach into an organism of water,

mineral salts, amino acids.

Motor – it is carried out at the expense of

contraction of a stomach muscular wall,

provide mixing and propulsion of chyme.

Excretory – allocation of metabolites of

proteins and carbohydrates (urea, lactic

acid) together with a gastric juice.

Incretory – secretion of some hormones

that cause a specific effect to digestion.

Bactericidal – it is provided by a

hydrochloric acid of gastric juice.

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• Processes occurring in the

stomach:

1) Storage - the stomach allows a meal

to be consumed and the materials

released incrementally into the

duodenum for digestion. It may take

up to four hours for food from a

complete meal to clear the stomach.

2) Chemical digestion - pepsin begins

the process of protein digestion

cleaving large polypeptides into

shorter chains .

3) Mechanical digestion - the churning

action of the muscularis causes

liquefaction and mixing of the contents

to produce acid chyme.

4) Some absorption - water,

electrolytes, monosaccharides, and fat

soluble molecules including alcohol

are all absorbed in the stomach to

some degree.

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GASTRIC GLANDS

• Gastric Secretions

• The mucosal lining of the stomach is simple columnar epithelium with numerous tubular gastric glands. The gastric glands open to the surface of the mucosa through tiny holes called gastric pits. Four different types of cells make up the gastric glands:

• Mucous cells produce mucous

• Parietal cells produce H+ from reaction of CO2 and H20. HCO3 - is sent to blood in exchange for Cl-.

• Chief cells produce pepsinogen

• Endocrine cells - G) cells produce hormones such as gastrin which are secreted into the bloodstream.

• Also present, ECL cells (enterochromaffin-like cells) which produce histamine in response to gastrin and ACh.

• The secretions of the exocrine gastric glands -composed of the mucous, parietal, and chief cells - make up the gastric juice. The products of the endocrine cells are secreted directly into the bloodstream and are not a part of the gastric juice. The endocrine cells secrete the hormone gastrin, which functions in the regulation of gastric activity.

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GASTRIC JUICE

STRUCTURE

• рН 0.9-1.5 2.0-2.5 lEnzymes

• Pepsin splits proteins to polypeptides

• The chemosin provides of transforming of soluble protein caseinogens in insoluble casein

• The gelatinize splits proteins of a connecting tissue gelatin

• The gastric lipase – splits emulsified milk fats

The hydrochloric acid transforms pepsinogens into pepsins, causes a denaturation of proteins and a milk coagulation, bactericidal function, control of intestine secretion.

Mucous protects an internal cover of the stomach from mechanical and chemical destruction

Inorganic substances

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PHASES OF GASTRIC

SECRETION• Complex-reflex (cerebral) is caused by

an appearance and a flavor of food

(conditioned reflexes) and taste of

appetizing nutrition (instinctive

reflexes).

• Gastric begins after nutrition entering

into the stomach. It is regulated by

nervous, chemical and endocrine

influences on mechanoreceptors.

• Intestinal begins after the nutrition

transferring into a small intestine. It is

caused by elimination of enterogastrin

from a duodenum and a stretching of a

small intestine by chyme.

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Regulation of a gastric

secretion

• Parasympathetic department VNS –stimulates secretion

• Sympathetic department VNS – brakes secretion

• Humoral factors:

• Gastrin - stimulates secretion

• The histamine stimulates secretion

• Digestion products - stimulate secretion

• The secretin and cholecystokinin (SIP, VIP, an enteroanthelone, a serotonin, somatostatin, etc.) – brake hydrochloric acid secretion

• Bombesin and mothilin - stimulates secretion

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Motor function of the

stomach

• Nutrition deposition

• Hashing with a gastric juice

• Movement of gastric contents to an exit

• Portions evacuation

• PDVNS – strengthens a motility

• SDVNS – brake a motility

• Hormones:

stimulate: gastrin, motilin, serotonin, insulin;

inhibit: a secretin, cholecystokinin-pancreozymin, SIP, VIP, bulbogastron, an enteroanthelone)