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Urinary System Review
Urinary System Overview
Excretion: The process of removing waste products from the body.
Organs of Excretion: Include sweat glands, intestines, lungs, and kidneys.
Main Organs of the Urinary System
Kidneys: Most important excretory organs; function to make, store, and eliminate urine.
Ureters: Muscular tubes that transport urine from kidneys to the bladder.
Bladder: Temporary reservoir for urine.
Urethra: Conducts urine from the bladder to the outside.
Kidneys
Structure: Bean-shaped, red-brown in color, enclosed in a fibrous capsule.
Dimensions: Approximately 4 inches long, 2 inches wide, and 1 inch thick.
Location: Found in the posterior abdominal cavity, behind the peritoneum.
Functionality:
Forms urine from blood, regulating blood pressure by producing erythropoietin.
Excretes water, electrolytes, nitrogen wastes (urea, uric acid, ammonia, creatinine), and toxins/drugs.
Kidney Regions
Renal Cortex: Outer region containing renal columns.
Renal Medulla: Darker, triangular area that contains renal pyramids.
Renal Pelvis: Basin area collecting urine from renal calyces.
Nephron - The Functional Unit
Structures:
Bowman's Capsule: Encloses the glomerulus, where the filtration process begins.
Renal Tubules: Pathway through which the liquid moves and where reabsorption occurs.
Blood Flow:
Blood enters via the renal artery, enters afferent arterioles into the glomerulus, filtered by the nephron, and exits via efferent arterioles and renal veins.
Urine Formation Processes
Glomerular Filtration:
Occurs in the glomerulus and Bowman's capsule, where approximately 20% of blood is filtered.
Factors affecting filtration: pressure differences in the glomerulus; size of molecules (larger molecules like RBCs and proteins are not filtered).
Filtration Rate: Approximately 125 ext{mL/min}, totaling 180 ext{L/day}.
Tubular Reabsorption:
Process where substances pass from the tubular fluid back into the blood (peritubular capillaries).
Major reabsorptions include glucose (100%), water (approximately 99%), and urea (50%).
Substances not reabsorbed: creatinine and certain diuretics.
Tubular Secretion:
Involves substances (e.g., potassium ions, hydrogen ions) moving from blood back into the tubular fluid for excretion.
Hormonal Regulation
Aldosterone:
Increases sodium and water reabsorption; excretes potassium.
Released upon low blood pressure by the juxtaglomerular apparatus.
Antidiuretic Hormone (ADH):
Increases water reabsorption in the collecting ducts, thus concentrating urine.
Secretion is stimulated by low blood volume or concentrated plasma.
Natriuretic Peptides:
Secreted by the heart; acts to decrease blood pressure by promoting sodium excretion.
Parathyroid Hormone & Calcitonin:
Regulate calcium and phosphate reabsorption excretion and affect electrolyte balance, but not fluid.
Composition of Urine
Components:
Approximately 95% water, nitrogen wastes (urea, uric acid, creatinine), and electrolytes.
Normal urine output: approximately 1,500 ext{mL/day}.
Oliguria defined as less than 400 ext{mL/day}.
Urinary Tract Anatomy
Ureters:
Transport urine from kidneys; can experience obstructions leading to hydronephrosis.
Bladder Structure:
Contains four layers: mucous membrane, submucosa, muscle, and serosa.
Rugae: Folds allowing bladder expansion, with urge to urinate typically sensed at 200 ext{mL}.
Urethra:
Short in females (1.5" or 3.8cm), longer in males (8" or 20cm), serving both urinary and reproductive functions.
Urination Process (Micturition)
Mechanism:
As the bladder fills, stretch receptors activate signals that eventually lead to bladder contraction and sphincter relaxation, allowing urine to exit the body.
Excretion: The process of removing waste products from the body, critical for maintaining homeostasis and overall health.
Organs of Excretion: Include sweat glands, intestines, lungs, and kidneys, with varying functions in waste removal, such as CO₂ from lungs and urea from kidneys.
Main Organs of the Urinary System
Kidneys: The most vital excretory organs, functioning to make, store, and eliminate urine. They are integral in regulating fluid balance, electrolytes, and blood pressure.
Ureters: Muscular tubes approximately 10-12 inches long that transport urine from the kidneys to the bladder through peristaltic movement.
Bladder: A temporary reservoir for urine with the capacity to hold approximately 400-600 mL. Its structure allows for expansion and contraction as it fills and empties.
Urethra: A tube that conducts urine from the bladder to the outside; it is approximately 1.5 inches long in females and 8 inches long in males, playing dual roles in urinary and reproductive systems in males.
Kidneys
Structure: Bean-shaped, red-brown in color, each kidney is surrounded by a fibrous capsule that provides protection and support.
Dimensions: Approximately 4 inches long, 2 inches wide, and 1 inch thick, significantly contributing to its efficiency as an organ of excretion.
Location: Positioned in the posterior abdominal cavity, behind the peritoneum; each kidney is slightly lower due to the liver's presence on the right side.
Functionality:
Forms urine from blood, regulates blood pressure by producing erythropoietin, which stimulates red blood cell production in the bone marrow.
Excretes water, electrolytes (such as sodium and potassium), nitrogenous wastes (urea, uric acid, ammonia, creatinine), and various toxins or drugs, emphasizing their role in detoxification.
Kidney Regions
Renal Cortex: The outer region of the kidney encompassing renal columns; contains the majority of nephrons critical for filtration.
Renal Medulla: A darker, triangular area with renal pyramids, housing structures necessary for urine concentration and storage.
Renal Pelvis: The basin area that collects urine from the renal calyces before it channels into the ureters.
Nephron - The Functional Unit
Structures:
Bowman's Capsule: Encloses the glomerulus, marking the starting point of the filtration process.
Renal Tubules: The pathway through which filtrate passes, allowing for critical reabsorption of water and nutrients.
Blood Flow:
Blood enters the nephron via the renal artery, which branches into afferent arterioles leading to the glomerulus.
The filtration process occurs here, after which filtered blood exits through efferent arterioles and renal veins, maintaining blood supply and pressure.
Urine Formation Processes
Glomerular Filtration:
Takes place in the glomerulus and Bowman's capsule; about 20% of blood volume is filtered during this phase.
Factors affecting filtration include pressure differences within the glomerulus and the size of molecules (e.g., larger molecules like red blood cells and proteins are generally not filtered).
The filtration rate is approximately 125 ext{mL/min}, totaling roughly 180 ext{L/day}, highlighting the kidneys' critical filtration capacity.
Tubular Reabsorption:
A vital process where substances are reabsorbed from tubular fluid back into the bloodstream via peritubular capillaries.
Major reabsorption percentages include glucose (100%), water (approximately 99%), and urea (50%).
Substances not reabsorbed include creatinine and certain diuretics, emphasizing the nephron's selectivity.
Tubular Secretion:
Involves the transfer of substances (e.g., potassium ions, hydrogen ions) from the blood back into the tubular fluid to be excreted, further contributing to fine-tuning the body's chemical balance.
Hormonal Regulation
Aldosterone:
A steroid hormone that promotes sodium and water reabsorption; simultaneously promotes potassium excretion.
Released in response to low blood pressure by the juxtaglomerular apparatus, indicating its role in blood volume regulation.
Antidiuretic Hormone (ADH):
Increases water reabsorption in the collecting ducts, leading to concentrated urine; this mechanism is crucial for preventing dehydration.
ADH secretion is stimulated by conditions like low blood volume or concentrated plasma.
Natriuretic Peptides:
Secreted by the heart; these act to decrease blood pressure by promoting sodium excretion, counteracting the effects of aldosterone.
Parathyroid Hormone & Calcitonin:
Regulate the reabsorption and excretion of calcium and phosphate, affecting electrolyte balance and bone metabolism, but do not directly influence fluid balance.
Composition of Urine
Components:
Urine consists of approximately 95% water, with nitrogenous wastes (urea, uric acid, creatinine), and various electrolytes, which are crucial for diagnosing health conditions.
Normal urine output is about 1,500 ext{mL/day}, with oliguria classified as output less than 400 ext{mL/day}, suggesting possible renal dysfunction.
Urinary Tract Anatomy
Ureters:
Transport urine from the kidneys to the bladder; obstructions can lead to hydronephrosis, a condition where urine backs up into the kidneys.
Bladder Structure:
Composed of four layers: mucous membrane, submucosa, muscle, and serosa; each layer plays a role in function and protection.
Rugae allow for bladder expansion; the urge to urinate commonly occurs when bladder volume reaches approximately 200 ext{mL}.
Urethra:
The short length in females (1.5 inches or 3.8 cm) and longer length in males (8 inches or 20 cm) emphasizes anatomical differences that influence susceptibility to urinary tract infections and other conditions.
Urination Process (Micturition)
Mechanism:
As the bladder fills, stretch receptors send signals to the brain, which eventually leads to bladder contraction and sphincter relaxation, allowing for voluntary or involuntary control over urine expulsion. The process involves neural coordination ensuring effective and timely urination, maintaining bodily function and comfort.