Urinary system

Week 8

What are the main organs of the urinary system and their general functions?  

Kidneys: Filter blood and produce urine 

Ureters: Carry urine to the bladder   

Bladder: Stores urine 

Urethra: Carries urine out of the body   

What is osmoregulation and why is it important?

• Definition: The active biological process that maintains the balance of water and dissolved salts (electrolytes) in body fluids

• Importance: It maintains homeostasis, preventing cells from swelling and bursting (if too much water enters) or shriveling and dying (if too much water leaves).

3 Body Processes That Require Water

• Cellular Respiration: Water acts as a medium for biochemical reactions and is a byproduct of energy production.

• Thermoregulation: The body uses water in sweat to cool down and maintain a safe internal temperature.

• Waste Excretion: Water is necessary for the kidneys to filter blood and flush out toxins through urine.

What is Nitrogenous waste?

• The Waste Product: Urea is the primary nitrogenous waste product of mammals.

• Where It Is Produced: It is produced in the liver through the urea cycle, which converts highly toxic ammonia (from broken-down proteins) into less toxic urea. It is then transported through the blood to the kidneys to be excreted.

What are the main functions of the kidneys beyond urine production?  

Remove waste products (e.g., urea)  

Control water and electrolyte balance  

Help regulate blood pressure  

Produce erythropoietin (EPO)  

Activate vitamin D  

What are the 5 compartments of the kidney?

Fibrous capsule – tough outer layer that
protects the kidney

Cortex – outer region where blood filtration
begins

Medulla – inner region where urine is
concentrated

Renal pelvis – collects urine from the kidney

Ureter – carries urine to the bladder

What are the roles of the renal artery and renal vein regarding blood supply to the kidney? 

Renal artery: Carries blood to the kidneys  (More urea, co2 , glucose

 

Renal vein: Carries blood away from the kidneys  

What differences are found in the blood inside the renal vein after passing through the kidney?  

Less urea (large amounts removed via nephrons)  

 

Less water and solutes/ions (depending on hydration status)  

 

Less glucose and oxygen (used by the kidney for energy/metabolism)  

 

More carbon dioxide (produced as a metabolic by-product)  

What is the pathway of urine from production to storage?  

Nephrons produce urine 

Urine enters collecting ducts  

 

Collected in the renal pelvis  

 

Travels down the ureter  

 

Stored in the bladder  

What are the primary internal structural regions of the kidney and their functions?  

Fibrous capsule: Tough outer layer that protects the kidney  

 

Cortex: Outer region where blood filtration begins  

 

Medulla: Inner region where urine is concentrated  

 

Renal pelvis: Collects urine from the kidney  

 

Ureter: Carries urine to the bladder  

What is a nephron and what are the main parts that make up its structure?  

The functional unit of the kidney  

Bowman's capsule, Proximal Convoluted Tubule (PCT), Loop of Henle, Distal Convoluted Tubule (DCT), and Collecting duct  

What are the functions of each component of the nephron?  

Bowman's capsule: Filters blood  

 

Proximal Convoluted Tubule (PCT): Reabsorbs glucose, amino acids, and water  

 

Loop of Henle: Concentrates urine and establishes a salt gradient  

 

Distal Convoluted Tubule (DCT): Reabsorbs ions and water (fine-tuning)  

Collecting duct: Carries urine to the renal pelvis and helps with water retention  

What is the precise blood flow pathway through the nephron and associated vessels?  

→ Renal artery

→ Afferent arteriole (brings blood to nephron)

→ Glomerulus (ultrafiltration)

→ Efferent arteriole - Carries blood away from glomerulus

→ Peritubular capillaries & vasa recta (reabsorb useful substances)

→ Renal vein (returns blood to circulation)  

What’s ultrafiltration?

It uses hydrostatic pressure to force water and small solutes through a semipermeable membrane while blocking larger particles (like proteins, cells, or large solids).

In the body (kidneys): Filters waste, water, and ions out of the blood into the Bowman's capsule, leaving blood cells and proteins behind.

In water treatment: Separation of bacteria, viruses, and suspended solids from water while allowing dissolved minerals to pass through.

What are the 4 main stages of urine formation?  

Ultrafiltration at the Bowman's capsule  

Reabsorption of glucose, amino acids, and water in the PCT  

Concentration of urine in the Loop of Henle  

Final water and ion balance in the DCT and collecting duct  

Explain Stage 1: Ultrafiltration at the Bowman's capsule / Glomerulus.  

• Blood enters the glomerulus via the afferent arteriole under high pressure.  

• Fenestrations (pores) in glomerular capillaries force small molecules (water, urea, glucose, amino acids, ions) into Bowman's capsule to form glomerular filtrate.  

• Note: Blood cells and plasma proteins are too large to pass through. Ultrafiltration is not selective. 

Explain Stage 2: Selective Reabsorption at the Proximal Convoluted Tubule (PCT).  

Useful substances entering the filtrate during ultrafiltration are reabsorbed back into the blood.  

 

The PCT reabsorbs: glucose, amino acids, most water, and many ions.  

Reabsorption is selective (unlike ultrafiltration).  

How does the Loop of Henle function to conserve water?  

It creates a salt concentration gradient in the medulla.  

 

Descending limb: Water leaves the filtrate by osmosis into the high-salt medulla.  

Ascending limb: Salts (NaCl) are pumped out into the medulla.  

 

This creates concentrated urine and helps the body conserve water.  

What role does the Distal Convoluted Tubule (DCT) play in urine formation?  

• Makes final adjustments/fine-tunes the composition of the filtrate.  

• Reabsorbs water and ions back into the blood to maintain blood pH and electrolyte balance.  

• Controlled by hormones such as ADH (Helps conserve water, produced in hypothalamus)  

How does the Collecting Duct handle osmoregulation?  

Reabsorbs water back into the blood to maintain water and electrolyte balance.  

 

Water reabsorption here is strictly controlled by ADH (antidiuretic hormone).  

 

Carries the final urine towards the renal pelvis.  

How does the length of the Loop of Henle relate to an animal's environment?  

Animals living in dry environments tend to have longer Loops of Henle to maximize water conservation (e.g., camels).  

 

Animals living in freshwater environments tend to have shorter Loops of Henle because water is readily available.  

Osmoregelution and ADH 9SLIDE 24)

ADHD helps regulat wate rbalance. Relaesed from puitary gland

slide 25 and 26

How is nitrogenous waste (such as urea) formed and processed in the body?  

Excess amino acids from protein breakdown cannot be stored by the body.

 

They undergo deamination in the liver, where the amino group (NH2) is removed and converted into ammonia, which is rapidly converted into urea (a less toxic nitrogenous waste).

 

Urea is then transported in the blood to the kidneys, where it is filtered out during ultrafiltration and excreted in urine.  

What is the role and mechanism of ADH (antidiuretic hormone) in osmoregulation?  

Source: Released from the posterior pituitary gland.  

VMC006 Urinary System - SC.pptx

 

Target: Acts on the DCT and collecting duct to increase water permeability.  

VMC006 Urinary System - SC.pptx

 

Effect: More ADH

→ More water reabsorbed

→ Small volume of concentrated urine. 

 Less

ADH

→ Less water reabsorbed

→ Large volume of dilute urine.  

VMC006 Urinary System - SC.pptx

What happens in the body when water levels fall (e.g., dehydration, sweating)?  

Blood water content drops / solute concentration rises. 

 

Osmoreceptors in the hypothalamus detect the change and trigger thirst.  

Hypothalamus signals the posterior pituitary gland to release more ADH.  

DCT and collecting ducts become more permeable, reabsorbing more water into the blood.  

Urine becomes more concentrated, returning blood water levels to normal (homeostasis).