Urinary System

Which kidney is lower? Why?

Right kidney sits lower, because of the liver.

What are the four main organs of the excretory system?

Skin, Lungs, Large Intestine, and urinary system (Kidneys, ureters, bladder, and urethra)

Which kidney is lower? Why?

Right kidney sits lower, because of the liver.

What are the four main organs of the excretory system?

Skin, Lungs, Large Intestine, and urinary system (Kidneys, ureters, bladder, and urethra)

Four major structures of urinary system

Kidneys, Ureters, Bladder, and Urethra

5 functions of the urinary system

1. Filtration of blood to remove waste

2. Regulation of blood volume and pressure

3. Regulation of electrolytes and metabolites

4. Regulation of blood pH levels

5. Production of hormones like erythropoietin and renin

Order these from superficial to deep: renal fascia, adipose capsule, renal capsule.

Renal fascia, adipose capsule, renal capsule.

What is the function of the renal fascia?

Anchors the kidney and helps maintain its position.

What does the adipose capsule do?

Provides cushioning and protection for the kidney.

Describe the function of the renal capsule.

Protects the kidney from infections and holds its shape.

What happens at the renal hilum?

Entry and exit point for the renal artery and vein, ureter, nerves, and lymphatics; coordinates blood supply and urine drainage.

What is the renal corpuscle?

Includes the glomerulus and Bowman's capsule; filters blood to initiate urine formation.

What is the renal tubule?

Comprises the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct; modifies filtrate through reabsorption and secretion.

What two structures make up the renal corpuscle?

Glomerulus (filters blood) and Bowman's capsule (collects filtrate).

What is another name for the capsular space?

Bowman's space (collects filtrate from the glomerulus).

Afferent Arteriole

Larger diameter; brings blood into glomerulus.

Efferent Arteriole

Smaller diameter; carries blood away from the glomerulus.

Significance of Arteriole Diameters

Size difference increases pressure in the glomerulus, aiding in filtration.

Juxtaglomerular Apparatus (JGA) Overview

structure in the kidney that checks and regulates blood pressure and filtration rate of the glomerulus

Macula Densa

Senses sodium chloride concentration in the distal tubule and signals to adjust blood flow and filtration rate.

Juxtaglomerular Cells

in the afferent arteriole, these cells release renin in response to low blood pressure.

Renin

enzyme that initiates the renin-angiotensin-aldosterone system (RAAS) to increase blood pressure.

Extraglomerular Mesangial Cells

Support communication between macula densa and juxtaglomerular cells to help maintain blood pressure

Force Driving Glomerular Filtration

High blood pressure in glomerular capillaries pushes plasma into Bowman's capsule.

Hydrostatic Pressure

Main force exerted by blood pressure to move fluid into the nephron.

Filtrate

Fluid from blood containing water, ions, and small molecules.

Components of Filtrate

Includes water, glucose, ions, and urea; excludes large proteins and cells.

Proximal Convoluted Tubule (PCT)

(Main region of reabsorption) of nutrients, water, ions; returns them to blood.

Loop of Henle

Concentrates filtrate; reabsorbs water and salts.

Distal Convoluted Tubule (DCT)

Further reabsorption of ions and water; some secretion.

Collecting Duct

Final water reabsorption; urine formed and sent to bladder.

Filtrate Fate

Becomes urine if not reabsorbed; excreted through the bladder.

Location of:

Proximal Convoluted Tubule (PCT)

Distal Convoluted Tubule (DCT)

Located in the renal cortex.

Loop of Henle location

Extends into the medulla, then returns to cortex.

Location of Collecting Duct

Passes through the medulla

What drains urine from nephrons through the medulla.

Collecting Ducts

What collects urine from collecting ducts; funnels to ureter.

Renal Pelvis

What transports urine to the bladder.

Ureter

What stores urine prior to excretion.

Bladder

What is the final pathway for urine excretion.

Urethra

Cortical vs. Juxtamedullary Nephrons

• Cortical: Located in cortex, short loops, 85% of nephrons.

• Juxtamedullary: Near cortex-medulla junction, long loops, concentrate urine.

Common Functions of Nephrons

Both perform filtration, reabsorption, and secretion.

Glomerular Hydrostatic Pressure (GHP)

Blood pressure in glomerular capillaries; pushes water and solutes OUT of blood.

CsHP (Capsular Hydrostatic Pressure)

Pressure from fluid in Bowman's capsule; opposes filtration (back in)

BCOP (Blood Colloid Osmotic Pressure)

Pressure from blood proteins; pulls water back into capillaries.

Capsular Colloid Osmotic Pressure

Generally negligible; would pull water into capsule if present.

What is GFR?

rate at which glomeruli filter blood in one minute (mL/min)

What three factors affect kidney filtration pressure?

1. Glomerular Blood Pressure: Promotes filtration.

2. Colloid Osmotic Pressure: Opposes filtration.

3. Capsular Hydrostatic Pressure: Opposes filtration.

What is the purpose of GFR autoregulation?

To maintain consistent kidney filtration rates despite blood pressure changes.

What are the two main mechanisms of GFR autoregulation?

1. Myogenic Mechanism

2. Tubuloglomerular Feedback

Describe the Myogenic Mechanism for autoregulation of GFR

Smooth muscle contraction or relaxation in afferent arterioles in response to blood pressure changes.

Describe Tubuloglomerular Feedback for autoregulation of GFR

Macula densa detects flow/Na+ changes and adjusts the afferent arteriole diameter to stabilize GFR

How does the autonomic nervous system regulate GFR?

Through sympathetic nerve activity affecting arteriole constriction and renal blood flow.

What happens to GFR during exercise?

(conserve water and maintain blood pressure)

- sympathetic stimulation increases

-afferent arterioles constrict

-reducing GFR

What happens to GFR at rest?

normal blood flow and GFR due to low sympathetic activity

What is the role of epithelial microvilli in the PCT?

increase surface area for better reabsorption of water, ions, and nutrients.

What happens to substances in the tubular fluid during reabsorption?

Substances move from the tubular fluid into the peritubular fluid (interstitial space).

What is peritubular fluid?

Fluid surrounding the nephron, where reabsorbed substances first enter before the bloodstream.

What is tubular fluid?

Fluid inside the nephron containing waste and substances for reabsorption.

How do substances reach the peritubular capillary?

Substances diffuse from peritubular fluid into the peritubular capillaries, entering the bloodstream

Descending Limb (loop of henle)

Water leaves, no salt leaves. The liquid becomes salty.

Thin Ascending Limb (loop of henle)

No water leaves, salt leaves passively. The liquid becomes less salty.

Thick Ascending Limb

No water leaves, salt leaves actively with help of Na+ pumps. The liquid is even less salty.

Distal Convoluted Tubule

Adjusts salt balance, influenced by hormones (lots of hormone receptors). Prepares urine for excretion.

What is Countercurrent Multiplication?

A process in the loop of Henle that creates a concentration gradient of solutes (salt exiting and H2O following in medulla) in the kidney medulla for urine concentration

Why is the concentration gradient important?

It allows for enhanced water reabsorption in the collecting ducts, concentrating urine and conserving water.

How does countercurrent multiplication benefit desert mammals?

By enabling the production of highly concentrated urine, it helps conserve water in arid environments.

Why don't DCT epithelial cells have microvilli?

The DCT specializes in selective ion regulation rather than bulk reabsorption, so extensive surface area from microvilli isn't necessary.

What are the three main processes of the DCT?

1. Selective Reabsorption: Sodium and calcium reabsorption.

2. Secretion: Potassium and hydrogen ion secretion.

3. Water Reabsorption: Limited reabsorption influenced by ADH.

What is the primary role of the Na+/K+ pump in the DCT?

It maintains sodium and potassium balance by transporting Na+ out and K+ into the cell, aiding sodium reabsorption.

How does aldosterone affect the Na+/K+ pump?

It increases the pump's activity, enhancing sodium reabsorption and promoting potassium secretion.

Why is aldosterone's effect on the Na+/K+ pump important?

It's crucial for blood pressure regulation by controlling sodium and fluid balance.

Which ion is "lost" in the urine due to aldosterone?

Potassium (K+) is secreted and lost in the urine due to aldosterone.

What happens to ADH in a well-hydrated person?

• ADH Levels: Low

• Effect: More urine, less concentrated

What happens to ADH in a dehydrated person?

• ADH Levels: High

• Effect: Less urine, more concentrated

What regulates urine production?

The kidneys filter blood, remove waste, and maintain fluid balance.

What is urea and where does it come from?

Protein metabolism

Main nitrogenous waste product in urine

What is creatinine and where does it come from?

Muscle metabolism

Waste product excreted in urine

What is uric acid and where does it come from?

Breakdown of purines (found in DNA)

Waste product found in urine

What is the transport maximum (Tm)?

The maximum rate at which carrier proteins can reabsorb a substance

( When exceeded, the excess is excreted in urine)

What is the renal threshold?

the concentration of a substance in the blood above which the kidneys start to excrete it into the urine

How does diabetes mellitus relate to Tm (transport maximum) ?

High blood glucose exceeds Tm, glucose spills into urine.

Why does diabetes cause polyuria? (lots of urine)

Excess glucose in urine draws more water, increasing urine volume.