I. Alimentary Canal (Gastrointestinal Tract): 9 m long.

    A. Mouth.
    B. Pharynx.
    C. Esophagus.
    D. Stomach.
    E. Small intestine.
    F. Colon (Large Intestine).
    G. Rectum.
    H. Peristalsis: wave-like muscular contractions that move food.

II. Accessory Organs.

    A. Teeth.
    B. Tongue.
    C. Salivary Glands.
    D. Liver.
    E. Gallbladder.
    F. Pancreas.

III. Mouth.

    A. Teeth: reduce size of food particles.
    B. Saliva.
        1. From salivary glands.
        2. Moisten and lubricate food for swallowing.
        3. Contains salivary amylase: breaks starch into maltose.
    C. Tongue: churns food and pushes down into the esophagus.

IV. Neck.

    A. Uvula rises, closing the nasal cavity.
    B. Epiglottis lowers, covering the glottis to keep food out of the trachea.
    C. Peristaltic muscular contractions force food down the esophagus.

V. Stomach.

    A. Cardiac sphincter.
    B. Holding chamber: 2 l capacity.
    C. Glands release acid and enzymes for protein digestion.
    D. These enzymes would digest the stomach wall if not covered by a thick mucus layer.
    E. Thick muscular walls churn contents.
    F. Absorbs water, alcohol, certain drugs, but little food.
    G. Pyloric sphincter.

VI. Small Intestine.

    A. 3 m long (not 7 m).

    B. Duodenum.
        1. 25 cm long.
        2. Acidity of food stimulates intestinal lining to secrete hormones.
        3. These hormones stimulate the intestinal lining, gallbladder, and pancreas to release digestive enzymes.

    C. Liver.
        1. Largest organ in the body.
        2. Composed of soft tissue with many sinusoids: microscopic spaces.
        3. Blood from all the digestive organs flows through the sinusoids.
        4. Each liver cell performs over 500 separate functions.
            a. Engulf bacteria and worn-out red blood cells.
            b. Remove many drugs and poisons from the blood.
            c. Convert excess glucose into glycogen and store it.
            d. Absorb amino acids from blood and use them to make blood protein.
            e. Store fat-soluble vitamins, iron, copper.
        5. Produces bile.
            a. .5 l per day.
            b. Used in breakdown and absorption of fat.

    D. Gallbladder.
        1. Reservoir for bile.
        2. When fat enters the duodenum, the gallbladder contracts and sends bile to the intestine.

    E. Pancreas.
        1. Soft, pinkish-white gland 15-25 cm long.
        2. Produces enzymes for digesting carbohydrates, fats, and proteins.
        3. 3% of cells produce hormones involved in regulating the amount of sugar in the blood.

    F. Jejunum and Ileum.
        1. Lining has folds 8-10 mm high.
        2. Folds have villi 1 mm high.
        3. Villi have microvilli 1 µm high
        4. These are extensions of the membrane of the cells lining the intestine.
        5. These three levels of folding increases the surface area 600x.
        6. Nutrients absorbed by the cells lining the intestine through the membrane of the microvilli.
        7. Nutrients are then passed to capillaries directly beneath the lining cells.

VII. Colon.

    A. 1.5 - 2 m long.
    B. Cecum.
        1. A pouch 6 cm long.
        2. Vermiform appendix is at the narrow end.
            a. Secretes mucus.
            b. Contains microorganisms that digest cellulose.
    C. Absorbs water, minerals, vitamin K.
    D. Contains millions of bacteria which produce vitamin K.
    E. Pushes waste into the rectum for storage until defecation.

VIII. Digestive Enzymes.

    A. All are hydrolases: break down large molecules by adding water to the bond.
    B. All are found only in the small intestine except amylase and pepsin.

    C. Glycosidases break carbohydrates into monosaccharides.
        1. Amylase.
            a. Starch to disaccharides.
            b. Secreted by salivary glands and pancreas.
        2. Maltase.
            a. Maltose to glucose.
            b. Secreted by intestinal lining.
        3. Sucrase.
            a. Sucrose to glucose and fructose.
            b. Secreted by intestinal lining.
        4. Lactase.
            a. Lactose to glucose and galactose.
            b. Secreted by intestinal lining.

    D. Lipases.
        1. Lipids to fatty acid + glycerol.
        2. Secreted by pancreas.

    E. Proteases.
        1. Pepsin.
            a. Protein tissue to protein fragments.
            b. Secreted by and found in the stomach.
        2. Trypsin.
            a. Protein fragments to polypeptides.
            b. Secreted by pancreas.
        3. Chymotrypsin.
            a. Protein fragments to polypeptides.
            b. Secreted by pancreas.
        4. Peptidase.
            a. Polypeptides to amino acids.
            b. Secreted by intestinal lining.

IV. Ruminants.

    A. Saliva.
        1. Alkaline: pH 8.5.
        2. 10 to 15 l produced per day.

    B. Food enters the rumen and reticulum.
        1. Food is mixed to a pulp.
        2. Fermented by anaerobic bacteria and protozoans.
            a. Microorganisms use sugars from the breakdown of carbohydrates in the food.
            b. Host absorbs fatty acids produced by the microorganisms during fermentation..
        3. Food regurgitated as cud.

    C. Food then enters the omasum where it is churned again.

    D. Last it enters the abomasum.
        1. Acid and digestive enzymes added.
        2. Many nutrients recaptured by the digestion of the microorganisms.

    E. Advantages of using symbionts in digestion.
        1. Can synthesize amino acids using urea and ammonia (animal cannot).
        2. Can synthesize many vitamins, esp. of the B group.
 

I. Blood.

    A. Plasma.
        1. The liquid portion of blood.
        2. Half the volume of blood.
            a. 90% water.
            b. 8% proteins.
            c. 1% minerals.
            d. 1% misc.: fats, sugars, amino acids, vitamins, hormones, gases, wastes.

    B. Erythrocytes (red blood cells).
        1. Oxygen transport.
        2. Development.
            a. Before birth: formed in spleen, liver, red bone marrow.
            b. After birth: formed only in red bone marrow.
            c. 130 lb. person forms over 1 billion new erythrocytes every day.
            d. Before moving into blood, the nucleus is squeezed out and the amount of hemoglobin is increased.
        3. Structure and function.
            a. Lack a nucleus and most cellular structures: thus not true cells.
            b. Oxygen binds to the iron atom in the heme group of the hemoglobin molecule.
            c. CO₂ binds to the globular proteins of hemoglobin.
        4. Decommissioning.
            a. Four-month life-span.
            b. Broken down in the liver, spleen, and bone marrow.

    C. Leukocytes (white blood cells).
        1. Ameboid.
        2. Fight disease.
        3. Engulf and destroy bacteria, viruses, etc.

    D. Thrombocytes (platelets).
        1. Half the size of an erythrocyte.
        2. Repair broken blood vessels.
            a. Plug the break by sticking to the edges of the vessel.
            b. Release serotonin, which causes the muscles of the vessel wall to contract.
        3. Aid in coagulation.
            a. Stick to rough edges of damaged tissue.
            b. Release a substance which helps form thromboplastin.
            c. Thromboplastin and Ca triggers formation of thrombin.
            d. Thrombin changes fibrinogen into insoluble fibrin.
            e. Fibrin thread form a microscopic mesh which entangles blood cells to form a clot.
            f. A clot takes 5 to 15 min. to form.

II. Heart.

    A. Types.
        1. Fish: 4-chambered linear.
            a. Sinus venosus.
            b. Atrium.
            c. Ventricle.
            d. Conus arteriosus.
        2. Amphibian: 3-chambered.
        3. Reptilian: 3.5-chambered.
        4. Higher vertebrate: 4 chambered.

    B. Structure.
        1. Pericardium.
            a. A fibrous sac that encloses the heart.
            b. Filled with pericardial fluid.
        2. Epicardium.
            a. The outer layer of the heart
            b. Connective tissue.
            c. Prevents pericardial fluid from saturating the heart.
        3. Myocardium.
            a. The middle layer of the heart.
            b. Muscle tissue.
            c. Does the pumping.
        4. Endocardium.
            a. The inner layer of the heart.
            b. Prevents blood from saturating the myocardium.
        5. Septum: a muscular wall that divides the right and left sides.
        6. Atrioventricular valves: between atria and ventricles.
        7. Semilunar valves: at the exits of the ventricles.

    C. Blood Flow.
        1. Right atrium: receives blood from body, passes to ventricle.
        2. Right ventricle: pumps blood to lung.
        3. Left atrium: receives blood from lung, passes to ventricle.
        4. Left ventricle: pumps blood to body.

    D. Regulation of the Heartbeat.
        1. Begun by the sinoatrial node.
            a. Sends an electrical impulse at the default rate of 80 per minute.
            b. This rate can be increased or decreased by the nervous system.
        2. This impulse reaches all the atrial cells simultaneously causing them to contract in unison.
        3. .1 sec. later it reaches the atrioventricular node.
        4. There is a brief pause to allow blood to empty from the atria.
        5. Then this node sends an electrical impulse to all the ventricular cells causing them to contract in unison.

III. Vessels.

    A. Arteries.
        1. Carry blood from heart to body.
        2. Three-layer construction.
            a. Outer elastic layer of connective tissue.
            b. Middle layer of muscle tissue.
            c. Inner layer one cell thick of endothelial cells.
        3. Thick, muscular.

    B. Capillaries.
        1. Carry blood into tissues.
        2. Narrow: erythocytes must pass single file.
        3. Construction: one-cell thick - endothelium.

    C. Veins.
        1. Carry blood from body back to heart.
        2. Same three-layer construction as arteries, but thinner, less elastic, and less muscular.
        3. Valves keep blood flowing in one direction.

IV. Circulation.

    A. Single.
        1. Fish.
        2. One circuit: heart to gills to body.
        3. All blood going to body is oxygenated.
        4. Gill capillaries significantly lower blood pressure.