Digestive System and Nutritional Processes

Pancreatic Secretions

• Pancreatic Juice Composition

  • Aqueous Portion: Produced by columnar epithelium of smaller ducts, contains Na⁺, K⁺, HCO₃^-, and water.

  • Function: Bicarbonate aids in lowering pH to inhibit pepsin and provide optimal pH for enzymatic activity.

  • Enzymatic Portion: Contains several inactive precursor enzymes and active enzymes:

  • Trypsinogen → activated by enterokinase to Trypsin.

  • Chymotrypsinogen → activated by Trypsin to Chymotrypsin.

  • Procarboxypeptidase → activated by Trypsin to Carboxypeptidase.

  • Pancreatic Amylase: Breaks down carbohydrates.

  • Pancreatic Lipase: Digests lipids.

  • Deoxyribonucleases and Ribonucleases: Digest nucleic acids.

Regulation of Pancreatic Secretion

• Neural Regulation

  • Parasympathetic Stimulation (Vagus Nerve): Stimulates release of enzyme-rich pancreatic juice.

  • Sympathetic Stimulation: Inhibits secretion.

• Hormonal Regulation

  • Secretin: Released from the duodenum in response to acidic chyme. Stimulates secretion of aqueous pancreatic juice rich in HCO₃^-.

  • Cholecystokinin (CCK): Released in response to fatty acids and lipids in the duodenum. Stimulates secretion of enzyme-rich pancreatic juice.

Digestive Enzymes by Location

• Mouth: Amylase

• Stomach: Pepsinogen → Pepsin

• Pancreas (into duodenum):

  • Trypsinogen → Trypsin

  • Procarboxypeptidase → Carboxypeptidase ‘

  • Chymotrypsinogen → Chymotrypsin

  • Amylase

  • Lipase

  • Nuclease (for nucleic acids)

Large Intestine Anatomy and Functions

• Sections:

  • Cecum, colon, rectum, anal canal.

  • Movements: Sluggish (18-24 hours); chyme converted to feces.

  • Absorption: Water and salts; Mucus secretion for protection.

• Digestion: Microorganisms play a significant role.

  • Water Absorption: 90% of 1500 mL chyme enters cecum, producing 80-150 mL of feces.

Movement and Control in Large Intestine

• Mass Movements: Initiated by stomach and duodenum distention.

• Defecation:

  • Coordinated contractions of large intestine with relaxation of sphincters.

  • Involves parasympathetic reflexes and conscious control.

  • Valsalva Maneuver can initiate defecation by increasing intra-abdominal pressure.

Digestion and Absorption Overview

• Digestion Types:

  • Mechanical: Breakdown of food into smaller particles.

  • Chemical: Covalent bond breaking by digestive enzymes.

• Absorption Techniques: Molecules transported across intestinal walls to circulation, utilizing both diffusion and transport mechanisms.

Nutritional Components and Metabolism

• Carbohydrates:

  • Digested into monosaccharides like glucose for energy or stored as glycogen.

  • Transport via Na⁺ symport and facilitated diffusion.

• Proteins:

  • Broken down into amino acids, transported with varying mechanisms (Na+ co-transport, facilitated diffusion).

• Lipids:

  • Digested into fatty acids and glycerol, absorbed and transported via chylomicrons through lymphatic pathways.

Vitamins and Minerals

• Vitamins: Essential for various metabolic processes, can be fat-soluble (A, D, E, K) or water-soluble (C and B complex).

• Minerals: Inorganic nutrients needed for various bodily functions, some required in larger amounts (major minerals) while others are trace minerals.

Common Digestive Disorders

• Peptic Ulcers: Lesions caused by Helicobacter pylori; treated with antibiotics.

• Hepatitis: Inflammation of the liver, symptoms include nausea and jaundice.

• Inflammatory Bowel Disease (IBD): Causes inflammation along digestive tract, treatment can include anti-inflammatory medications.

• Diarrhea: Can result from infections, loss of fluids, and electrolytes; treatment focuses on rehydration and restoring normal function.

Aging Effects on Digestive System

• Increased susceptibility to infections, decreased mucus production, increased incidence of

Minerals

• Iron: Essential for hemoglobin formation; involved in oxygen transport. Deficiency can lead to anemia.

• Iodine: Crucial for thyroid hormone synthesis; deficiency can result in goiter and various metabolic issues.

• Cobalt: Part of vitamin B12; important for red blood cell formation and neurological function.

• Chlorine: Vital for maintaining fluid balance and preventing dehydration; also important for digestive functions as a component of hydrochloric acid in gastric juice.

• Calcium: Necessary for bone health, muscle function, hormonal secretion, and vascular contraction.

Vitamins

• Vitamin K: Important for blood clotting and bone metabolism. Deficiency can lead to increased bleeding and osteoporosis.

• Vitamin D: Plays a role in calcium absorption and bone health; deficiency can lead to rickets in children and osteomalacia in adults.

• Vitamin C: Essential for collagen synthesis, antioxidant protection, and enhancing iron absorption; deficiency can lead to scurvy.

• Vitamin B12: Vital for nerve function and red blood cell production; deficiency can result in pernicious anemia and neurological issues.

• Folate (Vitamin B9): Necessary for DNA synthesis and repair; important during pregnancy for fetal development. Deficiency can lead to neural tube defects.

• Vitamin B3 (Niacin): Supports metabolism and the production of steroid hormones; deficiency can result in pellagra, characterized by diarrhea, dermatitis, and dementia.

• Vitamin B2 (Riboflavin): Important for energy production and cellular function; plays a role in Fatty acid oxidation and the metabolism of amino acids.

• Vitamin A: Essential for vision, immune function, and cellular communication; deficiency can cause night blindness and increase susceptibility to infections.

Pancreatic Juice Composition

1. Aqueous Portion:

   • Produced by columnar epithelium of smaller ducts.

   • Contains electrolytes including Na⁺, K⁺, HCO₃^-, along with water.

   • Function: Bicarbonate (HCO₃^-) plays a crucial role in neutralizing the gastric acid entering the small intestine, lowering the pH, inhibiting pepsin activity, and creating an optimal pH environment for enzymatic reactions to proceed efficiently.

2. Enzymatic Portion:

   • Comprises several inactive precursor enzymes and active enzymes:

     • Trypsinogen: Inactive precursor activated by enterokinase to become Trypsin, which further activates other enzymes.

     • Chymotrypsinogen: Activated by Trypsin to form Chymotrypsin, essential for protein digestion.

     • Procarboxypeptidase: Activated by Trypsin to produce Carboxypeptidase, facilitating the breakdown of peptide bonds in proteins.

     • Pancreatic Amylase: Breaks down carbohydrates specifically into maltose and dextrin.

     • Pancreatic Lipase: Efficiently digests fats down into fatty acids and glycerol.

     • Deoxyribonucleases and Ribonucleases: Digest nucleic acids, breaking down DNA and RNA into smaller nucleotides for absorption.

Regulation of Pancreatic Secretion

1. Neural Regulation:

   • Parasympathetic Stimulation (Vagus Nerve):

     • Promotes the release of enzyme-rich pancreatic juice in response to the sight or smell of food, enhancing digestive efficiency.

   • Sympathetic Stimulation:

     • Inhibits pancreatic secretion during stress responses to prioritize blood flow away from the digestive system.

2. Hormonal Regulation:

   • Secretin:

     • Secreted from the duodenum upon contact with acidic chyme; stimulates secretion of aqueous pancreatic juice rich in HCO₃^- to neutralize acid.

   • Cholecystokinin (CCK):

     • Released in response to fatty acids and lipids; enhances secretion of enzyme-rich pancreatic juice, coordinating with gallbladder contraction to release bile for fat emulsification.

Digestive Enzymes by Location

• Mouth:

  • Amylase (from saliva) begins carbohydrate digestion.

• Stomach:

  • Pepsinogen is activated into Pepsin by acidic pH, initiating protein digestion.

• Pancreas (Into Duodenum):

  • Trypsinogen → Trypsin

  • Procarboxypeptidase → Carboxypeptidase

  • Chymotrypsinogen → Chymotrypsin

  • Amylase

  • Lipase

  • Nuclease (for nucleic acids)

Large Intestine Anatomy and Functions

1. Sections:

   • Consists of the Cecum, Colon, Rectum, and Anal Canal.

2. Movements:

   • Sluggish movements (18-24 hours) with the conversion of chyme to feces through peristalsis and segmentation.

   • Absorption of remaining water and salts occurs to form solid waste.

   • Mucus secretion provides protection and aids in the passage of fecal matter.

3. Digestion:

   • Microorganisms (gut flora) play a significant role in fermenting residual carbohydrates and synthesizing certain vitamins (e.g., Vitamin K).

   • 90% of the chyme that enters the cecum is absorbed, producing 80-150 mL of feces.

Movement and Control in Large Intestine

1. Mass Movements:

   • Initiated by the distention of the stomach and duodenum; helps propel feces towards the rectum.

2. Defecation:

   • Coordinated contractions of the large intestine paired with the relaxation of anal sphincters.

   • Involves parasympathetic reflexes and conscious control to facilitate bowel movements, with the Valsalva Maneuver potentially aiding by increasing intra-abdominal pressure.

Digestion and Absorption Overview

1. Digestion Types:

   • Mechanical: Physical breakdown of food into smaller particles through chewing and peristalsis.

   • Chemical: Breaking of covalent bonds by digestive enzymes, transforming complex molecules into absorbable units.

2. Absorption Techniques:

   • Nutrients are transported across intestinal epithelial cells into circulation via diffusion and various transport mechanisms such as:

     • Primary Active Transport (e.g., Na+/K+ ATPase pumps, enabling secondary transport of nutrients).

     • Facilitated Diffusion (specific carriers for certain nutrients).

Nutritional Components and Metabolism

1. Carbohydrates:

   • Digested into monosaccharides (e.g., glucose, fructose) for immediate energy or stored as glycogen in liver and muscles.

   • Transport occurs via Na⁺ symporters and facilitated diffusion through GLUT transporters.

2. Proteins:

   • Broken down into amino acids, absorbed through various mechanisms (including Na⁺ co-transport and facilitated diffusion) to be used in protein synthesis or energy production.

3. Lipids:

   • Digested into fatty acids and glycerol for absorption; transported via chylomicrons into lymphatic pathways before entering the bloodstream.

Vitamins and Minerals

1. Vitamins:

   • Fat-soluble: A, D, E, K (stored in fatty tissues).

   • Water-soluble: C and B complex (generally not stored; require regular intake).

2. Minerals:

   • Inorganic nutrients required for various bodily functions; some are required in larger amounts (major minerals) while others are trace minerals, needed in smaller quantities, yet are essential for health.

Common Digestive Disorders

1. **Peptic Ulcers:

   • Caused by Helicobacter pylori infection, leading to lesions in the stomach or duodenum; management typically involves antibiotics and proton pump inhibitors.

2. Hepatitis:

   • Inflammation of the liver characterized by nausea, vomiting, jaundice, and potential liver dysfunction; various types caused by viruses, alcohol use, or autoimmune issues.

3. Inflammatory Bowel Disease (IBD):

   • Conditions such as Crohn's disease or ulcerative colitis; characterized by chronic inflammation in parts of the digestive tract; treatment includes anti-inflammatory medications and lifestyle changes.

4. Diarrhea:

   • Caused by infections, malabsorption, or excessive fluid loss; critical to restore fluids and electrolytes through rehydration strategies.

Aging Effects on Digestive System

• Increased susceptibility to infections, higher occurrence of gastrointestinal disorders, decreased production of digestive enzymes and mucus resulting in altered digestion and absorption efficiency, leading to nutrient