Kidney Functions and Filtration Quiz

Renal System Overview

• The renal system consists of kidneys, ureters, urinary bladder, and urethra.
• Its function includes removing nitrogenous wastes from the body and regulating water, electrolyte, and pH balance of the blood.

Learning Outcomes

• Identify the gross structure of the urinary system and relate structure to function.
• Describe the gross anatomy of the kidneys and nephrons.
• Explain the process of urine formation.
• Describe the hormonal control of urine formation, relating it to blood pressure, diuretics, etc.
• Describe the micturition reflex.
• Explain the importance of urinalysis and the interpretation of basic abnormal markers.

Session Overview

• The kidneys and nephrons are discussed, along with their purpose.
• The steps involved in urine production within the nephrons are detailed.
• Factors controlling urine production, including hormonal control, are examined.
• The processes of excreting and analyzing urine, including the bladder and micturition reflex, are covered.
• The significance of urinalysis is highlighted.

Human Body Fluid Composition

• The human body is primarily composed of water (50-70%).
• Intracellular fluid is found inside cells, while extracellular fluid is outside cells in interstitial spaces and plasma.
• The precise regulation of the surrounding fluid is critical for cell function.

Water Balance in the Body

• Water gain occurs through ingestion, metabolic synthesis, and absorption (from the digestive tract).
• Water is lost through urine, sweat, breathing, and feces.
• Factors like hyperventilation, vomiting, and fever can impact fluid balance.

Regulating Water and Solute Loss

• The primary method of water and solute elimination is through urine.
• Hormonal regulation plays a crucial role in sodium and chloride reabsorption within the kidneys.
• Osmosis is a passive process, where water moves from an area of lower solute concentration to higher solute concentration across a semipermeable membrane.

Urinary System Organs

• Kidneys: Filter blood and produce urine.
• Ureters: Transport urine toward the urinary bladder.
• Bladder: Temporarily stores urine before elimination.
• Urethra: Conducts urine to the exterior.
• Adrenal glands are also part of the system

Kidney Structure and Function

• Kidneys are retroperitoneal organs, typically 10-12cm long, 5-7cm wide, and 3cm thick.
• They're protected by connective tissue and adipose tissue (fatty layers).
• Kidney structure includes the cortex, medulla, renal pelvis, calyces, and renal papilla.
• Nephrons are the functional units within kidneys, responsible for filtering blood.

Nephron Structure and Function

• Approximately 1 million nephrons exist per kidney.
• The nephron filters substances from the blood.
• Processes like filtration, reabsorption, and secretion occur within the nephrons.
• The nephron is comprised of Bowman's capsule, renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

Renal Blood Supply

• Approximately 1200ml of blood passes through the kidneys every minute.
• Renal arteries deliver blood to the kidneys.
• Renal veins carry filtered blood away from the kidneys.

Urine Formation Overview

• Three major processes characterize urine formation: glomerular filtration, tubular reabsorption, and tubular secretion.

Plasma, Glomerular Filtrate, and Urine Comparison

• Plasma contains various substances, including proteins, glucose, electrolytes (such as sodium and potassium), urea, creatinine, and other molecules.
• Glomerular filtrate and urine differ in their composition, as useful substances are reabsorbed and wastes are secreted along the nephron, leading to a significant difference in composition of substances found in plasma compared to urine that will be excreted from the body.

Regulation of GFR

• GFR refers to glomerular filtration rate.
• Factors affect glomerular filtration rate, including blood pressure, blood volume, and hormones.

Tubular Reabsorption and Secretion

• Re-absorption and secretion occur in the renal tubules, adjusting the composition of the urine.
• Processes are influenced by various factors like the permeability of the tubules, and countercurrent circulation.

Proximal Convoluted Tubules (PCT)

• PCT cells are significant for reabsorbing essential solutes and water, and secreting waste products from the glomerular filtrate back into the circulatory system.

Loop of Henle

• The loop of Henle plays a crucial role in establishing a concentration gradient within the kidney to efficiently reabsorb water.
• Counter current mechanism takes place here to facilitate water reabsorption.

Distal Convoluted Tubules (DCT)

• DCT cells play a vital role in regulating the reabsorption of water and maintaining the electrolyte balance.
• Hormonal control is crucial in adjusting the DCT's activity.
• Drugs, toxins, and ions are secreted here.

Juxtaglomerular Apparatus (JGA)

• The JGA is a specialized structure responsible for regulating glomerular filtration rate (GFR) in response to blood pressure. It plays a key role in the renin-angiotensin-aldosterone system (RAAS).

Collecting Duct

• The collecting duct regulates the final composition of urine by controlling the reabsorption of water based on hormonal signals.

How We Produce Urine

• The kidney filters substantial amounts of blood and produces a smaller volume of urine (1-3 Litres per day).
• The process involves several interconnected steps.

Glomerular Filtration

• The glomerulus is a network of capillaries within the kidney, forming the filtration unit of the nephron.
• Filtration through these capillaries creates glomerular filtrate, which passes into Bowman's capsule.
• Substances like water, electrolytes, glucose, and waste products are initially filtered out.

Podocytes and Filtration Membranes

• Podocytes and capillaries form the glomerular filtration membrane.
• These structures create a 'sieve-like' structure filtering out cells and proteins, while allowing smaller substances to pass.

Urine Formation – Summary

• Hydrostatic and oncotic pressure differences in blood capillaries and Bowman's capsule drive the filtration process.

Regulation of Glomerular Filtration Rate (GFR)

• The glomerular filtration rate is controlled by the interplay of pressures inside and outside the capillaries, including hydrostatic and oncotic pressures.

Excretion and Analysis of Urine

• The body excretes metabolic waste and adjusts composition to maintain homeostasis.

Why We Produce Urine

• The kidneys produce urine as a way to maintain homeostasis by regulating blood volume and composition.
• Metabolic waste products like creatinine, urea, and uric acid are excreted through urine.

Bladder

• The bladder is a muscular organ responsible for urine storage and controlled release.
• Its structure includes rugae, internal and external urethral sphincters.

Micturition Reflex

• The micturition reflex controls urination, acting automatically to regulate the process.
• The nervous system coordinates filling, storage, and release of urine in conjunction with the bladder.

Incontinence

• Incontinence is the inability to control urination, a condition that can have several underlying causes.
• Incontinence, more likely to occur in women is a consequence of a variety of etiologies.

Urinalysis

• Urinalysis is the examination of a urine sample used for diagnostic purposes.
• Screening for various conditions, diagnostics, and disease management reasons form the clinical significance of this procedure.

Substances Not Normally Found in Urine

• The presence of certain substances in urine, like protein, glucose, or blood cells, suggests the presence of potentially underlying issues.

Proteinuria

• Protein in urine (proteinuria) indicates damage to the glomerular filtration membrane, and can result from various factors such as injury, high blood pressure, toxins, and certain medical conditions.

Ketonuria

• Ketones in the urine are an indicator of accelerated fat breakdown in the body, often linked to starvation or uncontrolled diabetes.

Glycosuria

• Blood glucose is typically and normally completely reabsorbed into the blood; however, the presence of glucose in the urine (glycosuria) signifies insufficient reabsorption, usually related to diabetes.

Haematuria

• Blood cells in urine (haematuria) are a sign of damage to the urinary tract, requiring further investigation.

Urinary Tract Infections (UTIs)

• UTIs involve infections in the urinary system.
• Women are more susceptible due to factors affecting bacterial access to the bladder (shorter urethra).
• UTIs manifest with various symptoms, such as pain, urgency, and frequency, necessitating medical attention.

Control of Urine Formation - Hormonal Control

• Hormones regulate hydration status through various mechanisms, and influence water retention.

Antidiuretic Hormone (ADH)

• ADH, also known as vasopressin, regulates water reabsorption in the kidneys.
• Its release is triggered by low blood volume or increased blood concentration.
• ADH increases water re-absorption by stimulating the collecting ducts.

Atrial Natriuretic Peptide (ANP)

• ANP is secreted by the heart, and opposes the effects of ADH, and it plays a role in regulating blood pressure and volume.

Aldosterone

• Aldosterone, secreted by the adrenal glands, promotes sodium retention.
• It leads to water reabsorption and the regulation of electrolytes in the body.

Renin-Angiotensin-Aldosterone System (RAAS)

• The RAAS is a series of chemical reactions acting to regulate blood pressure.

Test your knowledge on the essential functions of the kidney, particularly focusing on the glomerulus and its role in filtration. This quiz covers topics such as glomerular filtration rate (GFR) and the mechanisms that prevent blood cells from passing through the filtration membrane.