Digestion :

Absorption:

Organs of digestion:
            G.I. Tract or alimentary canal

                        Tube-within-a-tube

                        mouth to anus

                        contents outside body

            Accessory organs
                    the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

Layers of the G.I. Tract:
    1. Mucosa
                epithelium
                        In mouth, esophagus and anal canal-

                         In the stomach and intestines -

                lamina propria

                        MALT

                muscularis mucosae.

   2. Submucosa

                    many blood vessels

                    submucosal plexus

    3. Muscularis or Muscular layer

                    two muscle layers allow for peristalsis.

                    myenteric plexus- controls the motility of the GI tract -

    4. Serosa -serous membrane

MOUTH

The mouth is formed by :

It aids mechanical digestion in the process:

   The oral cavity

    The vestibule

    Cheeks

    Lips

    Tongue
                frenulum.

                the root - covered with masses of lymphatic tissue called :

    Palate

            Hard

            Soft

                        Uvula

    Teeth

            Structure

            2 dentitions

            types & functions

    Salivary glands

            Function

            parotid

                        mumps

            submandibular

            sublingual glands

The Pharynx

        1. nasopharynx

        2. The oropharynx

        3. The laryngopharynx

Digestion in the mouth

        Deglutition

Esophagus

        esophageal hiatus - hiatal hernia

        peristalsis

        lower esophageal sphincter - prevents reflux

Stomach

        regions:-

        rugae

        3 muscle layers

        Function

        Histology:
                gastric pits

                gastric glands
                            mucous cells (goblet cells) produce mucus.

                            The chief cells secrete: pepsinogen and gastric lipase.

                            The parietal cells secrete HCl and intrinsic factor

            The enteroendocrine cells or G cells in the pyloric antrum

                        secrete the hormone gastrin

Secretion and motility:
            Cephalic phase

            Gastric phase

            Intestinal phase

Gastric absorption

Emptying

Vomiting

Pancreas:

        Anatomy

        Histology

                Islets of Langerhans -endocrine

                Acini - exocrine

        Pancreatic juice

                sodium bicarbonate

                contains enzymes to digest: 

                            pancreatic amylase

                            trypsin, chymotrypsin, elastase, and carboxypeptidase

                            pancreatic lipase

                            ribonuclease and deoxyribonuclease

Regulation of secretion

                neural - parasympathetic

                hormonal - cholecystokinin (CCK) and secretin

LIVER

    Anatomy

    left and right lobes separated by the: 

     Associated with the right lobe are the caudate and quadrate lobes.

Histology

        The lobes of the liver are made up of lobules

        contain specialized epithelial cells called hepatocytes arranged in plates around a central vein.

        Contains sinusoids with stellate reticuloendothelial (Kupffer's) cells-

        Produces bile -stored in gall bladder

        Ducts

        Blood Supply
                the hepatic artery it obtains oxygenated blood

                the hepatic portal vein

                the hepatic vein

Bile
        role in digestion is the emulsification of dietary lipids

Regulation of Bile Secretion
        neural

        CCK

Functions of the Liver:
        Carbohydrate metabolism

        Lipid metabolism

        Protein metabolism

        Removal of drugs and hormones

        Excretion of bilirubin and synthesis of bile salts.

        Storage   

        Phagocytosis

Gall bladder
        Anatomy

        Location:

    Physiology:
            stores and concentrates bile

Small Intestine- The major events of digestion and absorption occur in the small intestine
        Anatomy

            the pyloric sphincter to the ileocecal sphincter

            divided into duodenum, jejunum, and ileum

        Histology
                villi

                microvilli- the brush boarder
                        further increase surface area.
                        contains several digestive enzymes in cell membranes

            intestinal glands or the crypts of Lieberkuhn
                    secrete intestinal juice

                    Paneth cells -secrete lysozyme and are phagocytes

                    enteroendocrine cells

                    duodenal glands which secrete an alkaline mucus.

            MALT -Peyer’s patches

Movement:
            segmentation

            peristalsis

Digestion and absorption:
        Carbohydrates are broken down into:

        Proteins are broken down into:

            Lipids are broken down into:

            Nucleic acids are broken down into:

Regulation of Intestinal Secretion and Motility:
        local reflexes that respond to the presence of :

            Segmentation movements - intestinal distention.

            Peristalsis

            Autonomic innervation

Physiology of Absorption in the Small Intestine
            Absorption occurs by:

            Carbohydrates are absorbed by 

            Proteins are absorbed by

            Lipids are absorbed by

                    micelles - tiny spheres with bile salts on the outside

                    chylomicrons

                    taken up into the:

        Water is reabsorbed by:

Vitamins :
        fat soluble vitamins are included in micelles

        Most water soluble vitamins are absorbed by simple diffusion.

        B12 is actively reabsorbed.

Peritoneum:
        This is the largest serous membrane of the body

                parietal peritoneum

                visceral peritoneum

                peritoneal cavity

                            ascites

                the mesentery

                The mesocolon

                The lesser omentum

                The greater omentum - the fatty apron, or lace apron.

                 peritonitis

LARGE INTESTINE
        The functions:

                completion of absorption

                the manufacture of certain vitamins

                the formation of feces and the expulsion of feces

            Anatomy:
                    ileocecal sphincter

                    divisions : the cecum, colon, rectum, and anal canal.

Histology:
        has no villi or permanent circular folds

        taeniae coli - bands of longitudinal muscle

            gathers the colon into a series of pouches called haustra

Physiology

            gastroileal reflex

            Mechanical movements

                    haustral churning.

                    Peristalsis

                    mass peristalsis.

                                gastrocolic reflex

The last stages of chemical digestion occur through bacterial action

No enzymes are secreted by the colon

Some vitamins are synthesized by bacteria

Absorption and Feces Formation in the Large Intestine

The large intestine absorbs:

Physiology of Defecation: