Digestion Lecture Flashcards

Objectives

Identify major digestive organs and segments within human anatomy.
Understand how histology relates to function of specific digestive organs.
Describe anatomical features and roles of accessory organs (liver, gallbladder, pancreas).
Learn specific roles for amylase and pepsin enzymes in digesting food substances.

Introduction

Digestive system converts food into small molecules for easy absorption.
Digestion begins with chewing:
- Teeth and muscles of mastication break down food.
- Incisors (central and lateral): Flat, broad surfaces for nipping (e.g., carrot).
- Canine teeth: Pointed edge for piercing and tearing, effective for dismantling meat.
- Premolars (bicuspids): Wide, square-like surface to grind food.
- Molars: Broadest teeth for crushing hard foods like seeds; three molars, with the third set being wisdom teeth.
Saliva production:
- Average person secretes 2 liters daily.
- Generated by parotid, sublingual, and submandibular glands.
- Each gland produces saliva with distinct composition (watery serosal to thicker mucosal).

Parotid glands:
* Mainly serosal cells secreting fluid including salivary amylase.
* Salivary amylase digests starch into smaller disaccharides.
Sublingual glands:
* Located beneath the tongue, secrete mucus-rich secretion to lubricate food bolus for swallowing.
Submandibular glands:
* Located along mandible margins, produce mix of serous and mucus-rich fluid, also includes salivary amylase.
* Mucosal cells appear more translucent.

Bolus compacted by tongue, pressed against mouth roof.
- Triggers swallowing reflex moving food to oropharynx.
- Bolus passes upper esophageal sphincter into esophagus.
- Peristalsis propels food along digestive tract.
Bolus transitions into stomach via cardiac sphincter.
- Cardiac sphincter failure exposes esophageal tissue to gastric juices which damages the tissue.
Stomach:
- Parietal cells in gastric pits produce hydrochloric acid, lowering stomach pH to ~1.
  - Acidic conditions denature proteins, facilitating enzymatic digestion.
- Chief cells in gastric pits secrete pepsinogen (proenzyme).
- Acid converts pepsinogen to pepsin, which cleaves proteins into smaller peptide residues.
- Highly muscular tissue with three smooth muscle layers (longitudinal, circular, internal oblique) for mixing.
- Mixing action dissolves bolus into gastric juices, creating chyme.

Gross Anatomy of Stomach:
* Fundus: Upper region bulging towards lungs.
* Body: Middle majority of the stomach.
* Pylorus: Lower region near small intestine.
* Greater curvature: Lateral contour (left).
* Lesser curvature: Lateral contour (right).

Chyme passes from stomach to small intestine through pyloric sphincter.
- Pyloric sphincter more robust than cardiac sphincter.
Duodenum: First segment of small intestine
- Site where pancreas and gallbladder empty secretions via ampulla of Vater.
- Pancreatic secretions neutralize acidic chyme and provide enzymes (lipase, chymotrypsin, pancreatic amylase) for further hydrolysis.
- Gallbladder secretes bile which emulsifies fats for easier absorption. Accessory organsLiver:
  - Synthesizes bile, delivered to gallbladder for storage.
  - Nutrients absorbed in small intestine are delivered via hepatic portal vein.
  - Liver processes these materials and creates storage forms like glycogen from glucose.
  - Hepatocytes (major liver cells) organized into hexagonally shaped hepatic lobules.
  - Hepatic triad at lobule margins includes branches of bile duct, hepatic portal vein, and hepatic artery.
Small Intestine
* Jejunum: Second segment of the small intestine, ~40% of its length.
* Majority of absorption occurs here, nutrients transported into blood and lacteals (for fats).
* Ileum: Last segment of small intestine
* Longest segment, empties into large intestine (colon) via ileocecal valve.
Large Intestine
* Divided into ascending, transverse, descending, sigmoid colons, and rectum.
* Water and electrolytes reabsorbed, compacting feces.
* Defecation controlled by internal (unconscious) and external (voluntary) sphincters.
* Feces leaves body via anal canal through anus.

Procedures

PART A: Abdominal Cavity and Membranes
* Review abdominal cavity and membranes.
* Abdominopelvic cavity
* Peritoneal cavity
* Visceral peritoneum (serosa)
* Parietal peritoneum
* Mesenteries
* Lesser omentum
* Greater omentum
* Mesentery proper

PART B: Mouth and Esophagus
* Review anatomy of mouth and esophagus.
* Oral cavity
* Hard palate
* Soft palate
* Body of tongue
* Oropharynx
* Parotid salivary gland
* Sublingual salivary gland
* Submandibular salivary gland
* Teeth
* Incisors
* Central incisors (2)
* Lateral incisors (2)
* Cuspids (canines) (2)
* Bicuspids (premolars)
* 1st Premolar (2)
* 2nd Premolar (2)
* Molars
* 1st Molar (2)
* 2nd Molar (2)
* 3rd Molar (Wisdom tooth) (2)

Esophagus
* Upper esophageal sphincter
* Lower esophageal sphincter (cardiac sphincter)
* Microanatomy of salivary glands (parotid, sublingual, submandibular): differentiate based on histological appearance.
* Serous cells
* Mucous cells
* Esophagus microanatomy
* Stratified squamous
* Lamina propria
* Muscularis mucosae

PART C: The Stomach
* Review anatomical features of the human stomach.
* Cardia
* Fundus
* Body
* Pylorus
* Rugae
* Cardiac sphincter
* Pyloric sphincter
* Greater curvature
* Lesser curvature

PART D: The Intestines
* Review small and large intestines.
* Small intestine
* Duodenum
* Hepatopancreatic ampulla (Ampulla of Vater)
* Jejunum
* Ileum
* Large intestine
* Haustrum
* Teniae coli
* Cecum
* Appendix
* Ascending colon
* Descending colon
* Sigmoid colon
* Rectum
* Anal canal
* Internal anal sphincter
* External anal sphincter

PART E: Accessory Structures
* Review anatomy of pancreas.
* Pancreas
* Tail
* Body
* Head
* Pancreatic duct
* Accessory pancreatic duct
Liver
* Right lobe
* Falciform ligament
* Left lobe
* Common hepatic duct
* Hepatic portal vein
Gallbladder
* Gallbladder
* Cystic duct
* Common bile duct
* Pancreas tissue specimen: exocrine structures
* Connective tissue septum
* Pancreatic acini
* Duct
* Liver Tissue Specimen
* Hepatocyte
* Central vein
* Portal triad
* Bile duct branch
* Hepatic portal vein branch
* Hepatic artery branch
* Hepatic sinusoid

PART F: Digestive Physiology
* Review roles of amylase and pepsin in digestive physiology.

*Amylase Digestion of Starch*
    *   Amylase produced in salivary glands and pancreas.
    *   Salivary amylase (mostly from parotid glands) converts starch to di- and tri-saccharides (e.g., starch to maltose).
    *   Factors influencing enzyme activity: temperature, enzyme/substrate concentration, acidity/alkalinity.
    *   Experiment to explore effect of enzyme concentration on enzyme activity.
        *   Solutions A-D of unknown amylase concentration (2, 0.2, 0.02, 0.002 units/mL).
        *   Lugol’s solution (iodine and iodine salt) indicates starch presence (purple/dark blue).

Experiment steps:
* Label 5 test tubes (A, B, C, D, acetate buffer).
* Add 0.5 mL of 0.5% starch to each tube.
* Add 0.5 mL of each enzyme concentration to labeled tube.
* Add acetate buffer to “acetate buffer” tube.
* Incubate at room temperature for 10 minutes.
* Stop reaction by adding 1 mL of hydrochloric acid (0.2 M) to tubes A-D.
* Incubate for 10 minutes.
* Visualize remaining starch by adding 8 drops of Lugol’s solution.
Pepsin Digestion of Protein
* Pepsin produced by chief cells in stomach, breaks down proteins into smaller peptide subunits.
* Secreted as inactive pepsinogen (proenzyme).
* Hydrochloric acid in gastric juices activates pepsinogen to pepsin.
* Experiment to demonstrate pepsin activity using beef jerky.
* Label two test tubes: P + M (pepsin + meat), W + M (water + meat).
* Add 1mL of hydrochloric acid (20 mM) to each tube.
* Add 1mL of water to W + M tube.
* Add 1mL of pepsin enzyme solution (0.8%) to P + M tube.
* Add a 5 mg piece of meat to each tube, stopper, and incubate at 37 degrees Celsius overnight.
* Record observations.