Renal (Urinary) System Flashcards

Renal (Urinary) System

Overview

• The renal system, also known as the urinary system, is crucial for maintaining homeostasis in the body.

Organs of the Renal System

• Kidneys: filter blood and produce urine.
• Ureters: transport urine from kidneys to the bladder.
• Bladder: stores urine.
• Urethra: expels urine from the body.
• Sphincter: controls the release of urine from the bladder through the urethra.

Learning Objectives

• List the functions of the renal (urinary) system.
• Describe the structure & function of the main organs of the renal system (males & females).
• Describe the gross anatomy of the kidney.
• Identify the parts of the nephron & their function (renal corpuscle, sections of the renal tubule & collecting system, blood supply).
• Describe the structure and function of the glomerular filter.

Functions of the Renal System

• Homeostasis: The primary function is to maintain a stable internal environment.
• Waste Disposal:
  • Filters blood and disposes of waste products via urine.
• Blood pH Regulation:
  • Maintains blood pH balance.
• Osmoregulation and Electrolyte Balance:
  • Controls water and electrolyte levels in the body.
• Blood Volume and Pressure Regulation:
  • Helps regulate blood volume and pressure.
• Hormone Production:
  • Produces hormones such as erythropoietin, which stimulates red blood cell production in bone marrow.

Process Overview

• Filtration: Kidneys filter blood.
• Transportation: Ureters transport urine to the bladder.
• Storage: Bladder stores urine.
• Excretion: Urethra expels urine.

Urine Excretion

• Waste materials and water are transported via urine.
• Urine collects in the bladder, which can hold up to a liter.
• The bladder wall consists of smooth muscle called the detrusor muscle.
• To excrete urine, the urethral sphincters relax, and the detrusor muscle contracts.

Male Urinary System Anatomy

• Bladder:
  • Features rugae (folds) and smooth muscle.
  • Ureteral openings and internal urethral sphincter are present.
• Urethra:
  • Prostatic urethra passes through the prostate gland.
  • Membranous urethra is located in the urogenital diaphragm.
  • External urethral sphincter consists of skeletal muscle.
• Prostate Gland:
  • Located near the neck of the bladder.

Urine Storage and Exit - Male

• Ureters transport urine to the bladder.
• The bladder stores urine.
• The urethra, surrounded by the external urethral sphincter, allows urine to exit the body.
• The prostate gland is situated around the prostatic urethra.

Urine Storage and Exit - Female

• Ureters transport urine to the bladder.
• The bladder stores urine.
• The urethra, surrounded by the external urethral sphincter in the urogenital diaphragm, allows urine to exit the body.
• The female anatomy includes the uterus and vagina, which are separate from the urinary pathway.

Urination (Micturition)

• Involves both autonomic and somatic nerve pathways.
• Voluntary control of the external sphincter allows continence.
• Process:
  1. Sensory fibers detect bladder fullness.
  2. Parasympathetic pre-ganglionic fibers are activated.
  3. Parasympathetic post-ganglionic fibers activate detrusor muscle contraction.
  4. Interneurons relay sensation to the thalamus, and then to the cerebral cortex.
  5. Voluntary relaxation of the external sphincter causes relaxation of the internal sphincter.

Bladder Problems and Renal Complications

• Ascending UTI:
  • Can damage the kidney (Pyelonephritis).
• Cystitis:
  • Inflammation of the bladder, often due to stagnant urine encouraging microorganism growth.
• Vesicoureteral Reflux:
  • Urine refluxes up the ureter, leading to ascending infection due to a defective valve.
• Obstruction:
  • Can be caused by prostatic hypertrophy, leading to residual urine in the bladder.
• Other Factors:
  • Immobility and blood-borne organisms can also cause renal complications.

Kidney Anatomy

• Description:
  • Reddish, kidney bean-shaped organs.
  • Approximately the size of a bar of soap.
• Location:
  • Posterior wall of the abdomen.
  • Either side of the spine (vertebral column).
  • Around the level of the twelfth rib (partially protected by the rib cage).
  • Just above the waist.
  • The right kidney is slightly lower due to the position of the liver above it.

Blood Supply to the Kidneys

• Blood Flow:
  • Kidneys receive 20-25% of resting cardiac output.
  • Approximately 1200 ml of blood per minute.
• Vessels:
  • Abdominal aorta supplies blood via the left and right renal arteries.
  • Blood returns to the vena cava via the left and right renal veins.

Kidney Blood Supply and Internal Structure

• Structure:
  • Renal artery enters the kidney.
  • Renal vein exits the kidney.
  • Ureter carries urine away.
  • Cortex and medulla are the two main regions.

Internal Anatomy of the Kidneys

• Key Structures:
  • Capsule: outer covering.
  • Cortex: outer region.
  • Renal Pyramids: located in the medulla.
  • Renal Columns: separate the renal pyramids.
  • Calyces (singular: Calyx): collect urine.
  • Renal Pelvis: where urine collects before entering the ureter.
  • Ureter: transports urine to the bladder.
• Function:
  • Walls of calyces, renal pelvis, and ureter have smooth muscle, which pushes urine along by peristalsis.
  • Kidneys are surrounded by adipose tissue for protection.

Kidney Lobes and Nephrons

• Renal artery and vein split into finer vessels that follow routes through the renal columns dividing the kidney into sections or lobes.
• Each lobe contains nephrons, the functional units of the kidney.

Nephrons

• Definition:
  • The functional unit of the kidney.
• Location:
  • The cortex and medulla are made of nephrons.
• Quantity:
  • Each kidney contains approximately 1 million nephrons.

Overview of Nephron Function

1. Glomerular Filtration: Water and small molecules enter the tubule from the blood.
2. Tubular Reabsorption: Water and valuable solutes are returned to the blood.
3. Tubular Secretion: Specific substances are removed from the blood and added to the tubule.
4. Excretion: Urine exits the body.

Nephron - Renal Corpuscle

• Function:
  • Nephrons consist of a renal corpuscle and a renal tubule.
  • The renal corpuscle is where blood is filtered and lies within the renal cortex.
• Components:
  1. Glomerulus: network of blood capillaries.
  2. Bowman's capsule: start of the renal tubule.

Glomerular Filtration

• Process:
  • The first step of urine production.
  • Blood pressure in the glomerulus forces fluids and small dissolved substances through the filtration membrane.
  • Blood cells and plasma proteins are too large to pass through.
  • Filtrate drains into the renal tubule.
• Arterioles:
  • Afferent arteriole has a wider diameter than the efferent arteriole.
  • More blood enters the glomerulus than leaves, forcing blood into Bowman’s capsule.

Renal Corpuscle Details

• Glomerulus:
  • Capillary network.
• Bowman’s Capsule:
  • Double-walled cup of epithelial cells.
  • Inner visceral layer (podocytes) wraps around endothelial cells of glomerular capillaries.
  • Outer parietal layer forms the outer wall of the capsule.
• Capsular Space:
  • Space between the two layers.

Filtration Membrane Layers

1. Endothelium:
   • Thin capillary wall; fenestrated (porous).
2. Basal Lamina:
   • Basement membrane that endothelial cells sit on.
3. Filtration Slit:
   • Space between foot processes (pedicels) of the podocyte cells of Bowman’s capsule.

Filtration Mechanism

• Red cells, white cells, and platelets are too large to pass through the filtration membrane.
• Proteins are mostly prevented from passing through.
• Filtered material includes water, ions, and small organic molecules.

Glomerular Filtrate Composition and Volume

• Composition:
  • Water.
  • Ions (Na+, K+, Cl-, H+ etc.).
  • Glucose, amino acids (i.e., plasma minus plasma proteins).
• Filtrate Production:
  • Approximately 1 million nephrons in both kidneys.
  • A large amount of filtrate is produced daily: ~150 L/day in females and ~180 L/day in males.

Parts of the Renal Tubule

1. Bowman's capsule
2. Proximal Convoluted Tubule (PCT)
3. Loop of Henle
4. Distal Convoluted Tubule (DCT)
5. Collecting Duct

Blood Supply to Nephrons

• Glomerular Capillaries:
  • Afferent arteriole takes blood into the glomerulus.
  • Efferent arteriole takes blood away from the glomerulus.
• Peritubular Capillaries

Tubular Reabsorption

• Occurs in the tubules.
• Substances Reabsorbed:
  • Water.
  • Glucose.
  • Amino acids.
  • Ions.
  • Bicarbonate.
• Mechanisms:
  • Occurs by osmosis, diffusion, and active transport.
• Efficiency:
  • Approximately 99% of filtered fluid is reabsorbed.
  • Only 1% of filtrate leaves the body (1-2 liters/day of urine).

Diffusion and Osmosis

• Diffusion: molecules move from an area of high concentration to an area of lower concentration.
• Osmosis: diffusion of water molecules from an area of high concentration to an area of lower concentration through a partially permeable membrane

Tubular Secretion

• Substances move from peritubular capillaries into tubules.
• Mainly occurs in the PCT, DCT, and collecting ducts.
• Substances Secreted:
  • Ions.
  • Creatinine.
  • Urea.
  • Drugs.
• Mechanisms:
  • Occurs by diffusion and active transport.

Regulation of Blood pH

• Blood pH is tightly controlled between 7.35 and 7.45.
• Kidneys contribute to blood pH regulation by controlling:
  • H+ secretion.
  • Bicarbonate (HCO3-) reabsorption.
• Urine typically has a pH of around 6 due to H+ secretion.

Osmoregulation and Electrolyte Balance

• Controlling osmotic pressure of fluids is crucial to maintain proper functioning of cells.
• Kidneys regulate the amount of water reabsorbed from glomerular filtrate.
• Kidneys maintain electrolyte (ion) concentration by controlling reabsorption and secretion of electrolytes.
• Osmoregulation is the process by which organisms regulate the balance of water and electrolytes to maintain homeostasis.

Summary

• Structure and function of the urinary system.
• Structure and function of the kidney.
• Kidney's role in:
  • Production of urine.
  • Regulation of blood pH.
  • Osmoregulation and electrolyte balance.