Accessory Digestive Organs and the Urinary System: Structure and Function Unit 4 Week 13 LO's

Accessory Digestive Organs

Liver

The liver is the largest internal organ and plays a central role in metabolism, detoxification, and digestion. It is essential for processing nutrients, producing bile, and maintaining homeostasis.

• Produces bile: Bile is necessary for the emulsification and digestion of fats in the small intestine.

• Detoxifies blood: The liver removes toxins, drugs, and metabolic waste from the bloodstream.

• Stores nutrients: Glycogen, vitamins (A, D, B12), and iron are stored for later use.

• Processes nutrients: Carbohydrates, fats, and proteins absorbed from the digestive tract are metabolized.

• Produces plasma proteins: Such as albumin and clotting factors, which are vital for blood function.

• Breaks down old red blood cells (RBCs): Hemoglobin is processed and bilirubin is excreted in bile.

Structure of the Liver

• Lobes: Right, left, caudate, and quadrate lobes.

• Ligaments:

  • Falciform ligament: Divides right and left lobes.

  • Round ligament (ligamentum teres): Remnant of fetal umbilical vein.

  • Coronary ligament: Attaches liver to diaphragm.

• Porta hepatis: The gateway for hepatic artery, hepatic portal vein, bile ducts, nerves, and lymphatics.

Location

• Right upper quadrant (RUQ) of the abdomen

• Inferior to the diaphragm

• Anterior to the stomach

• Superior to the gallbladder, duodenum, and right kidney

Classic Hepatic Lobule

• Hexagonal structural unit of the liver.

• Contains a central vein, hepatocytes (liver cells), sinusoids (capillary spaces), and portal triads (branch of hepatic artery, portal vein, and bile duct).

• Blood flow: From portal triads toward the central vein.

• Bile flow: From hepatocytes away from the central vein toward bile ducts.

Gallbladder

The gallbladder is a small, muscular sac located beneath the liver. It stores and concentrates bile produced by the liver and releases it into the duodenum to aid in fat digestion.

• Structure: Small sac under the liver.

• Function: Stores and concentrates bile; releases bile during digestion.

• Location: Inferior surface of the liver, right upper quadrant, near the duodenum.

Pancreas

The pancreas is a dual-function gland with both exocrine and endocrine roles. It is crucial for digestion and blood glucose regulation.

• Parts: Head (nestled in the curve of the duodenum), body, and tail (toward the spleen).

• Exocrine function: Secretes digestive enzymes and bicarbonate into the duodenum.

• Endocrine function: Secretes hormones such as insulin and glucagon into the bloodstream.

• Location: Retroperitoneal, posterior to the stomach; head adjacent to duodenum, tail near spleen.

Histology

• Pancreatic acini: Exocrine cells that produce digestive enzymes.

• Islets of Langerhans: Endocrine cells that secrete insulin and glucagon.

Biliary Apparatus

The biliary apparatus is a network of ducts that transport bile from the liver and gallbladder to the duodenum, facilitating fat digestion.

• Functions: Produces, stores, and transports bile; aids in fat digestion.

Component	Description
Right & Left Hepatic Ducts	Drain bile from liver lobes
Common Hepatic Duct	Formed by right and left hepatic ducts
Cystic Duct	Connects gallbladder to common bile duct
Common Bile Duct	Delivers bile to duodenum
Main Pancreatic Duct	Delivers pancreatic juice to duodenum
Hepatopancreatic Ampulla (Ampulla of Vater)	Union of bile and pancreatic ducts
Sphincter of Oddi	Controls flow into duodenum
Major Duodenal Papilla	Opening into duodenum

Flow of Bile and Pancreatic Juice

• Bile: Liver → hepatic ducts → common hepatic duct → (to gallbladder via cystic duct or continue) → common bile duct → ampulla → duodenum

• Pancreatic juice: Pancreas → pancreatic duct → ampulla → duodenum

Urinary System

Kidney vs. Urinary Tract

The urinary system maintains homeostasis by filtering blood, forming urine, and eliminating waste. It consists of the kidneys and the urinary tract (ureters, bladder, urethra).

• Kidneys: Filter blood, produce urine, regulate pH, blood pressure, and electrolytes.

• Urinary tract: Ureters transport urine, bladder stores urine, urethra eliminates urine.

Filtration, Reabsorption, and Secretion

• Filtration: Blood is filtered in the glomerulus, forming filtrate.

• Reabsorption: Useful substances are reabsorbed from filtrate back into the blood.

• Secretion: Additional wastes are secreted from blood into the tubule for excretion.

Kidney Anatomy

External Structure

• Fibrous capsule: Protective outer covering.

• Perirenal fat: Cushions and protects the kidney.

• Renal fascia: Anchors kidney to surrounding structures.

• Renal hilum: Entry/exit for vessels and ureter.

• Renal sinus: Internal cavity containing vessels, nerves, and fat.

Internal Divisions

• Cortex: Outer region containing renal corpuscles and convoluted tubules.

• Medulla: Inner region with renal pyramids and collecting ducts.

• Renal pyramids: Cone-shaped structures in the medulla.

• Renal papillae: Tips of pyramids where urine drains into calyces.

• Minor and major calyces: Collect urine from papillae and funnel it to the renal pelvis.

• Renal pelvis: Central collecting region for urine before it enters the ureter.

Cortex vs. Medulla

• Cortex: Contains renal corpuscles, proximal convoluted tubule (PCT), and distal convoluted tubule (DCT).

• Medulla: Contains loops of Henle and collecting ducts.

Blood Flow Through the Kidney

• Aorta → renal artery → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate arteries → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta → veins → inferior vena cava (IVC)

Nephron Structure

• Renal corpuscle: Glomerulus (capillary tuft) and Bowman's capsule (surrounds glomerulus).

• Tubule: Proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting duct.

Cortical vs. Juxtamedullary Nephrons

• Cortical nephrons: Short loops of Henle; most common type.

• Juxtamedullary nephrons: Long loops of Henle; important for concentrating urine.

Vascular Elements

• Afferent arteriole: Brings blood into the glomerulus.

• Efferent arteriole: Carries blood away from the glomerulus.

• Peritubular capillaries: Surround cortical nephrons.

• Vasa recta: Surround juxtamedullary nephrons in the medulla.

Filtrate Flow

• Bowman's capsule → PCT → loop of Henle → DCT → collecting duct

Urinary Tract

• Ureters: Muscular tubes that transport urine from kidneys to bladder.

• Bladder: Muscular sac that stores urine until elimination.

• Urethra: Tube that carries urine from bladder to outside the body.

Male vs. Female Urethra

• Female: Short, carries urine only.

• Male: Longer, carries urine and semen.

Sphincters

• Internal urethral sphincter: Smooth muscle, involuntary control.

• External urethral sphincter: Skeletal muscle, voluntary control.

Urine Pathway

• Renal papilla → minor calyx → major calyx → renal pelvis → ureter → bladder → urethra

Micturition (Urination)

Micturition is the process of expelling urine from the bladder. It involves both involuntary and voluntary muscle control.

• Bladder fills: Stretch receptors in the bladder wall are activated.

• Parasympathetic stimulation: Detrusor muscle contracts, internal sphincter relaxes, urine moves into urethra.

• Sympathetic stimulation: Relaxes bladder to store urine.

• Somatic (voluntary) control: External sphincter is consciously controlled.

Summary Table: Main Functions and Structures

Organ/System	Main Function	Key Structures
Liver	Metabolism, bile production, detoxification	Lobes, ligaments, porta hepatis, hepatic lobule
Gallbladder	Stores and concentrates bile	Muscular sac, cystic duct
Pancreas	Digestive enzymes, hormones	Head, body, tail, acini, islets
Kidney	Filters blood, forms urine	Cortex, medulla, nephron, hilum
Urinary Tract	Transports, stores, eliminates urine	Ureters, bladder, urethra, sphincters

Example: When a person eats a fatty meal, the liver produces bile, which is stored in the gallbladder. Upon eating, the gallbladder contracts, releasing bile into the duodenum to aid fat digestion. The kidneys filter blood to remove waste, forming urine, which is stored in the bladder until voluntary urination occurs.

Additional info: The coordination of the urinary and digestive accessory organs is essential for maintaining fluid, electrolyte, and metabolic balance in the body.