Ch. 17

Digestive System

Alimentary Canal

mouth to anas

What are the 2 parts of each of the digestive organs? Know the function of each part.

What are the functions of the digestive system?

• Ingestion

• Propulsion- move food through the digestive tract

• *Digestion

  • Mechanical digestion breaks large pieces of food into smaller ones without altering their chemical composition. This mechanical breakdown increases the surface area of ingested foods, getting them ready for chemical digestion. Mechanical digestion also involves muscular movements that help mix food molecules and digestive juices

    • BOLUS- mass of chewed food mixed with saliva

  • Chemical digestion involves enzymes that act to chemically break down larger food molecules into simpler chemicals (building blocks), a catabolic process.

• *Absorption

  • Involves the passage of nutrients from the alimentary canal into the blood after food undergoes mechanical and chemical digestion, it is small enough to be absorbed through the microvilli lining the small intestines- glucose, nucleic acids, etc. Considered to be on one of the main function of the digestive system

• Elimination

  • Defecation of unabsorbed material

• MAIN FUNCTIONS ARE DIGESTING AND ABSORPTION

Describe the nervous system’s role for digestion i.e., parasympathetic system

• Activities of digestive system increase when stimulated by parasympathetic impulses

Omentum

• A filmy, double fold of peritoneal membrane called the greater omentum

  • drapes like an apron from the stomach over the transverse colon and the folds of the small intestine (fig. 17.34 below)

  • If the wall of the alimentary canal becomes infected, cells from the omentum may adhere to the inflamed region and help seal it off, lowering the risk that the infection will spread to the peritoneal cavity.

  • Note the location of the gallbladder in Fig 17.34 below

Epiglottis

• The epiglottis usually upright and allows air to enter the larynx.

• During swallowing, muscular contractions raise the larynx, and the base of the tongue presses the epiglottis downward, partially covering the opening into the larynx, helping prevent foods and liquids from entering the air passages.

• The epiglottis is attached to the larynx

The stomach receives food, mixes it with gastric juice, carries on a limited amount of absorption, moves food into the small intestine

Identify the following structures

• Stomach

• Esophagus

• Liver

• Gallbladder

• Small Intestine

• Large Intestine

  • Ascending Colon

  • Transverse Colon

  • Descending Colon

  • Functions

    • Absorb Water

    • Store Feces

    • Digest Proteins

    • Synthesize Vitamin B

  • Appendix- located in lower right quadrant

Parts of the stomach- Be able to identify structures- see image below

• Cardial Notch- is a temporary storage area and sometimes fills with swallowed air.

• Fundus- is a temporary storage area and sometimes fills with swallowed air.

• Body- main part of the stomach

• Pylorus- is the distal portion of the stomach where it approaches the small intestine

  • Pyloric Antrum

• Lesser Curvature

• Greater Curvature

• Longitudinal Layer- refer to 2nd image next page

• The pyloric sphincter serves as a valve between the stomach and the small intestine.

Layers of Stomach Muscle

• Be able to identify longitudinal layer- outer musculature layer- see arrow

The 2 major types of motor processes in the digestive tract are mixing movements and propelling movements

• Peristalsis- A propulsive movement of contents of the lumen from one area to another

• Segmentation

Salivary Glands

• Produce saliva

  • Function of saliva- break down food in mouth into smaller pieces

• Know location of the 3 glads

• Identify the following digestive structures

  • Parotid gland

  • Submandibular gland

  • Sublingual gland

Functions of saliva

• Moistens, binds, dissolves food particle

• Beginning of chemical digestion of carbohydrates

• Cleanses teeth and mouth

Palate of Mouth- know location and identify - hard and soft palate

Pancreas location: See picture below- Be able to identify

Pancreatic Acinar Cells- What do they secrete?

• The cells that produce pancreatic juice, called pancreatic acinar (a′sĭ-nar) cells, make up the bulk of the pancreas

  • These cells form clusters called acini (sing, acinus) around tiny tubes into which they release their secretions.

  • The smaller tubes unite to form larger ones, which join a pancreatic duct that extends the length of the pancreas

  • The pancreatic duct usually connects with the duodenum at the same place where the bile duct from the liver and gallbladder joins the duodenum, although divisions of the pancreatic duct and connections to other parts of the duodenum may be present

Passage of Food

• Passageway of food from pharynx to esophagus to stomach

• From stomach to the 3 parts of the small intestine: the duodenum, the jejunum, and the ileum

Function of Gallbladder

• The liver and gallbladder are accessory glands that function together in the production and storage of bile.

• Bile is a fluid that contains important bile salts, needed for the breakdown of lipids in the small intestine

Teeth

• Function to tear and used food

Differentiate between primary and permanent teeth- how many of each?

• Primary teeth- 20 teeth

• Secondary/Permanent Teeth - 32 teeth

Identify the following

• Maxillary canine teeth

• Pharynx

• Small Intestine

• Stomach- located in left upper art

Tooth Enamel

• The tooth is composed of a crown that sits above the gum line, and the root which sits below the gum line

• The crown is composed of a covering of enamel which is composed of calcium salts, and a deeper layer of dentin which is similar to bone but harder

• Enamel thins from years of brushing, teeth grinding, and eating acidic foods

Tooth Root

• Blood vessels and nerves found in root canal

What are the overall functions of the digestive system?

• The digestive system receives foods, breaks down nutrients into forms that can pass through cell membranes, and eliminated unabsorbed materials

Parietal Cells of Gastric Glands

Secrete Hydrochloric Acid

Amylase

• Produced by pancreas to aids in digestion of carbohydrates

• Salivary amylase breakdown carbohydrates

• Makes Chew bite of bread- gets sweeter bc breakdowns carbs into sugar

Lipase

• Fat Splitting enzyme, gastric lipase

• Gastric juice contains small quantities of this enzyme

Pepsin

• Enzyme that begins the digestion of protein in the stomach

HCL (Hydrochloric Acid)- converts pepsinogen ( inactive form) to pepsin

• Pepsinogen: produced by the chief cells of the gastric glands in an inactive form

• If medication is given to decrease HCL, then this conversion to pepsin doesn’t occur as it should & digestion of protein can be impaired

Gastrin

• is a peptide hormone that acts to increase the secretory activity of gastric glands

Trypsin

• Found in pancreatic juice and digest all types of protein

Secretin

• Stimulates release of pancreatic juice

Cholecystokinin

• Regulates pancreatic secretion of digestive enzymes

What are the layers of walls in order in alimentary canal & which one absorbs nutrients?

• Alimentary canal extends from mouth to anus

• Wall of alimentary canal is composed of 4 layers: from innermost to outermost, the layers are

  • Mucosa- composed of epithelial tissue & may contain folds & mucus-secreting glands

    • Innermost layer, mucous membrane

    • Folded in some areas, to increase surface area

    • Absorbs dietary nutrients, secretes mucus & enzymes

  • Submucosa- Connective tissue layer

    • Nourishes cells, transports absorbed food molecules

  • Muscularis or muscular layer (externa)- Muscle tissue

    • *Contains circular & longitudinal layers

    • Moves tube & food materials

  • Serosa- Outermost layer; serous fluid eliminates friction

    • Visceral peritoneum of organs within abdominal cavity

  • Rugae- The folds of mucosa & submucosa in the stomach are known as rugae

Medulla Oblongata

Sensory Signals from the stomach & small intestine sent to medulla oblongata to trigger a vomiting reflex

What are the macronutrients?

• Nutrients required in large amounts, provide energy, & other specific functions

• Include:

  • Carbohydrates

  • Protein

  • Fat

What are micronutrients?

• Required in small amounts. They don’t directly provide energy, but make possible the biochemical reactions thatt extract energy from macronutrient molecules

  • Vitamins

  • Organic compounds that are required in small amounts for normal metabolic processes

    • Vitamins don’t directly supply energy; they aid in the release of energy from carbohydrates, fats, proteins

  • Essential nutrients; can’t be synthesized by body cells in adequate amounts

  • Classified on the basis of solubility;

    • Fat-soluble vitamins: A, D, E, & K

    • Water-soluble vitamins: B vitamins & vitamin C

      • *B vitamins involved in the oxidation of carbohydrates, lipids, & proteins

  • Minerals

    • Inorganic elements required in metabolism

    • Usually extratced from the soil by plants

    • Obtained from plant foods or animals that have eaten plants

Liver

• Largest internal organ in body

• Located in right upper quadrant of body

• Accessory organ in digestive system

• Function of liver: See chart below

  • Removes toxins such as alcohol & certain drugs from the blood

Common Bile Duct

• The bile duct (common bile duct) is formed by the union of the common hepatic & cystic ducts

What is bile? How does it work? What constituent has digestive function?

• Bile

  • Is a greenish-yellow fluid made by your liver & stored in the gallbladder

  • In addition to bile salts, bile contains cholesterol, water, bile acids, & the pigment bilirubin

• Digestive function of Bile salts:

  • Bile salts promote fat-soluble vitamin absorption A, D, E, K

  • Bile salts aid in digestive of fat

Jaundice

• Jaundice is the abnormal yellowish-tint of tissues, such as the sclera of the eye, skin, mucous membranes

• Due to accumulation of bile pigments

  • FYI Causes: Obstructive jaundice, bile ducts are blocked perhaps by gallstones or tumors

  • Hepatocellular jaundice the liver is diseased, as in cirrhosis or hepatitis

  • Hemolytic jaundice, red blood cells are destroyed too rapidly, as happens with a incompatible blood transfusion or a blood infection

Chylomicrons

• Large molecule of lipoproteins

• Chylomicrons transport dietary fats to muscle & adipose cells

What is heartburn?

• Stomachache results from eating a lot of food too quickly

• Takes up to 20 minutes for hypothalamus to sense full stomach

• Excess fullness leads to abdominal pain & gastric reflux, as stomach contents enter esophagus

• Stomach contents in esophagus cause inflammation, called esophagitis; feels like the pain is derived from the heart, so it is called heartburn

• Antacids can provide some relief

• Prevention: eat small meals, eat slowly, stay upright after eating, & avoid caffeine, nicotine, & alcohol

• Over the counter antacids

  • Sodium, aluminum, calcium, or magnesium