Digestive and Urinary System Notes

Digestive Tract and Accessory Organs

• Digestive tract (blue in the diagram) and accessory organs (right side).
• Mouth: Food and drink enter here.
  • Chewing: Begins the breakdown process.
  • Accessory Organs:
    • Teeth: Macerate food.
    • Tongue: Propels food towards the pharynx.
    • Salivary Glands: Release enzymes to initiate chemical digestion.
• Pharynx: A passageway that propels food to the esophagus.
• Esophagus:
  • A long tube extending past the sternum.
  • Transports food to the stomach.
• Stomach: Receives food from the esophagus.
• Liver:
  • A large accessory organ in the upper abdomen.
  • Produces bile to aid digestion.
• Gallbladder: Stores bile produced by the liver and releases it as food passes through the stomach.
• Pancreas:
  • Located behind the large bowel and stomach.
  • Releases digestive enzymes and insulin to aid digestion and absorption.
• Small Intestine:
  • Long and coiled; the primary site for nutrient absorption.
• Large Intestine:
  • The final passageway; primarily involved in water absorption and waste elimination.

Types of Digestion

• Mechanical Digestion:
  • Physical breakdown of food (e.g., chewing).
• Chemical Digestion:
  • Enzymatic breakdown of food.
  • Salivary glands release enzymes at the beginning of the digestive process.

Tissue Layers of the Digestive Tract

• Mucosa:
  • Innermost layer; a membrane that produces mucus to facilitate the movement of digesting material.
• Submucosa:
  • Contains blood supply, glands, and lymph vessels.
• Mucularis:
  • Muscle layer responsible for peristalsis.
  • Contractions propel food through the intestinal tract.
• Serosa:
  • Outermost layer; a thin membrane.

Enteric Nervous System

• Extensive network of neurons within the bowel.
• Myenteric Plexus: Located between muscle layers; aids in muscle movement.
• Submucosal Nerve Plexus: Helps regulate movement within the submucosa.
• These plexuses coordinate peristalsis.
• Embedded blood vessels facilitate nutrient absorption into the bloodstream.

Peritoneum

• The abdominal area containing the digestive organs.
• Mesocolon: Fat tissue supporting the transverse colon; contains blood vessels.
• Mesentery: Supports the small bowel, preventing it from packing together.
• Omentum: A fatty apron covering the intestines for protection.
  • Greater Omentum: The fatty apron part.
  • Lesser Omentum: Located behind the stomach.
• Peritoneal Cavity: The hollow space around the intestines.
  • Fluid accumulation (ascites) may occur in this cavity due to conditions like liver damage or cirrhosis.

Oral Cavity

• Accessory Organs:
  • Palate, uvula, tongue.
• Sublingual Area: Area under the tongue; contains salivary ducts and numerous blood vessels.
  • Allows for rapid absorption of medication (e.g., nitroglycerin for angina).
• Parotid Glands: Release digestive substances into the mouth.

Tooth Structure

• Enamel: The hard outer layer covering the crown (visible part) of the tooth.
• Dentin: Softer, cushy layer beneath the enamel.
  • Contains blood vessels and nerve endings (pulp cavity).
• Roots: Anchor the tooth in the jawline. Contain nerves and blood vessels, making tooth pain potentially widespread.
• Infected teeth can easily spread bacteria to other parts of the body due to the vascular structure.

Swallowing

• Bolus: Chewed food formed into a mass.
• Process:
  • Tongue propels the bolus through the pharynx.
  • Epiglottis covers the larynx to prevent food from entering the trachea.
  • Bolus enters the esophagus.
• Sphincters in the Stomach:
  • Lower Esophageal Sphincter: Prevents backflow of food, gases, and gastric acids into the esophagus. Malfunction can cause GERD (gastroesophageal reflux disease).
  • Pyloric Sphincter: Controls the amount of food (chyme) entering the duodenum.

Stomach Structure and Function

• Parts: Fundus, body, pylorus.
• Capacity:
  • Empty: Approximately 50 ml (size of an egg).
  • Expanded: Up to 1.5 liters.
• Rugae: Folds that allow the stomach to expand.
• Chyme: Digested food.
• Pyloric Sphincter: Regulates the release of small amounts of chyme into the duodenum.
• Gastric Mucosa:
  • Contains mucus cells (secrete mucus).
  • Parietal cells (secrete hydrochloric acid HCl, necessary for vitamin B12 absorption for healthy red blood cell production; also kills ingested microbes).
  • Cheek cells (release pepsinogen for digestion).
  • Enteroendocrine cells (release ghrelin to stimulate appetite by signaling the hypothalamus; also release gastrin for digestion).

Stomach Emptying

• Liquids: Empty in less than 4 hours.
• High-fat content: May take up to 6 hours.
• Frequent small meals are recommended for certain conditions such as COPD or diabetes.

Chyme Movement

• The stomach churns the digested food into chyme.
• Peristalsis: Muscle contractions around the stomach and duodenum.
• The pyloric sphincter releases approximately 30 ml of chyme into the duodenum at a time.

Stimulation of Gastric Secretions

• Cephalic Phase:
  • Triggered by the brain (e.g., smelling food).
  • Initiates enzyme release.
• Gastric Phase:
  • Food enters the stomach, causing it to stretch.
  • Gastric juices are released, creating chyme.
• Duodenal Phase:
  • Chyme enters the duodenum.
  • Signals the body that it's full, stopping enzyme production.

Liver

• Two lobes (right and left).
• Breaks down blood cells into iron and bilirubin.
  • Iron goes to bone marrow for new blood cell creation.
  • Bilirubin goes to the gallbladder to create bile.
• Hepatic Artery: Brings oxygenated blood from the aorta.
• Portal Vein: Carries oxygen-poor, nutrient-rich blood to the organs.
• Lobules: Functional units containing a central vein.
  • Hepatic cells and sinusoids filled with blood.
  • Coniculae carry bile out of the liver to the gallbladder.
• Kupffer Cells: Remove bacteria and worn-out red blood cells from the blood system.

Gallbladder

• Stores bile.
• Releases bile down the common bile duct, through the pancreas, and into the stomach.
• Bile salts can clump together, causing blockages or gallstones.

Pancreas

• Produces pancreatic enzymes and insulin.
• Islets of Langerhans: Contain beta cells that produce insulin.
• Located throughout the pancreas.

Hormones and Pancreatic Juice

• Cholecytokinin: Stimulated when chyme hits the duodenum; tells pancreatic enzymes to be released.
• Gastrin: Produced in the stomach; releases pancreatic enzymes and signals the gallbladder to contract and release bile.
• Secretin: Causes the bile and pancreatic ducts to release bicarbonate, which reduces acid levels in the stomach.

Small Bowel

• Duodenum: First part of the small intestine.
• Jejunum:
  • Approximately 8 feet long (pink box).
  • Major site for nutrient absorption.
• Ileum:
  • Approximately 12 feet long (green box).
  • Contains Peyer's patches (lymph nodes of the lymphatic system).
• Microvilli: Increase the absorption area of the GI tract.

Chemical Digestion

• Carbohydrates:
  • Amylase (secreted in the mouth) starts carbohydrate digestion.
  • Pancreatic amylase is released into the duodenum.
  • Glucose is absorbed.
• Proteins:
  • Pepsin breaks down proteins.
  • Trypsin and chymotrypsin (pancreatic enzymes) break peptide bonds in the duodenum for amino acid absorption.
• Fats:
  • Bile emulsifies fats.
  • Broken down fats are absorbed as triglycerides via the lymph system.

Large Intestine

• Structure:
  • Cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus.
• Water absorption occurs here.
• Appendix: Can become blocked and inflamed (appendicitis).
  • Rupture can cause peritonitis.

Digestive Enzymes

• Key digestive enzymes: Review which organ secretes which enzyme.

Effects of Aging on the Digestive System

• Slowed processes.
• Constipation.
• Weakened sphincters leading to heartburn and GERD.

Urinary System

• Components: Kidneys, bladder, urethra.
• Adrenal Glands: Sit atop the kidneys; secrete cortisol.
• Major Vessels: Inferior vena cava and aorta, renal arteries and veins.
• Ureters: Mini tubes that transport urine from the kidneys to the bladder.
• Kidneys: Sit under the 12th rib.
  • Contain renal pyramids that carry urine.
  • Calyx collects urine for passage through the ureter.
• Renal Circulation: Blood passes through the kidneys at about a liter per minute.
• Nephrons: Functional units.
  • Cortical Nephron: Site of glomeruli filtration of waste products, sodium, potassium, fluids.
  • Juxtamedullary Nephron: Carries filtrate elsewhere.
  • Loop of Henle: Key structure within the nephron.
  • Bowman's Capsule: Surrounds the glomeruli.

Urine Formation

• Process:
  • Blood flows through the glomeruli where waste is filtered into the Bowman's capsule.
  • Blood leaves via capillaries, allowing sodium, potassium, and nutrients to pass through.
• Glomerular Filtration Rate (GFR):
  • Indicates how well the kidneys are filtering.
  • Lower GFR indicates more severe renal disease; a GFR less than 15 often requires dialysis.
• Causes of Renal Disease: Hypertension, diabetes.
• Proteinuria: Protein in the urine, indicated by a foam-like appearance; can be due to kidney damage or excessive exercise.

Hormone Regulation

• Renin-Angiotensin-Aldosterone System:
  • Drop in blood pressure triggers renin release.
  • Renin converts angiotensinogen to angiotensin I.
  • Angiotensin I converts to angiotensin II by angiotensin-converting enzyme (ACE).
  • Angiotensin II signals adrenal glands to secrete aldosterone, increasing fluid retention and raising blood pressure.

Urine Characteristics

• Water is reabsorbed in the loop of Henle, concentrating the urine.
• Urine should be a pale yellow and clear.
• Concentrated urine is darker and may be cloudy.
• Specific Gravity: Higher specific gravity indicates less fluid and potential dehydration.
• Oliguria: Less than 400 ml of urine output per day.
• Anuria: No urine output.

Bladder and Urethra

• Ureters: Bring urine to the bladder.
• Bladder: Contains sensors to indicate the need to urinate.
  • Has rugae to allow expansion.
• Urethra:
  • Micturition: Urination.

Gender Differences

• Proximity of urethra, vagina, and rectum in females:
  • Increases the risk of UTIs due to bacterial transfer from the rectum.
• Male urethra:
  • Passes through the prostate gland.
  • Prostate enlargement in older men can cause frequent urination and difficulty emptying the bladder.

Age-Related Changes

• Weakened bladder walls and sphincters can lead to incontinence.
• Pelvic floor muscles weaken, possibly leading to prolapse.