Lecture 44 - Urinary System Overview

Question 1

What is the urinary system responsible for and what are the 3 pathways of the urinary system?

Answer 1

It is responsible for the production, storage, and elimination of urine

1. The kidneys filter blood, producing urine
2. Urine is moved through the urinary system and is temporarily stored in the bladder
3. Urine is excreted by urination/micturition

Question 2

Where is urine produced and where is it stored?

Answer 2

Urine is produced in the kidneys and is stored in the bladder before elimination

Question 3

What does urine contain?

Answer 3

Mostly water, ions, and wastes (especially nitrogenous compounds)

Question 4

What is the typical range of daily urine production for a healthy adult?

Answer 4

~1.4L in a typical day

Question 5

What coordination is required for micturition (urination)?

Answer 5

It relies on the coordination of bladder and urethral sphincter muscles through the autonomic and somatic nervous systems

Question 6

What is the capacity of the bladder and how does it empty?

Answer 6

The typical capacity is around 0.5L. The urge to urinate occurs when the bladder is ~50% full

To empty the bladder, the 2 urethral sphincters must relax and the detrusor must contract, expelling urine through the urethra

Question 7

Name 4 functions of the kidney

Answer 7

1. Removing wastes and toxins from blood (without removing nutrients)
2. Regulating plasma ion concentrations
3. Regulating blood pH
4. Regulating blood volume and blood pressure

These functions are meant for body fluid homeostasis

Question 8

Is the kidney a primary or secondary endocrine organ?

Answer 8

Secondary

Question 9

How does the kidney act as a target of other endocrine organs?

Answer 9

Hormones made by the kidney can act on the kidney and/or on other organ systems to regulate ion and fluid homeostasis in the body

The kidney also responds to hormones made by other organs

Question 10

Name the 3 hormones that the kidney produces

Answer 10

1. Calcitriol
2. Erythropoietin (EPO)
3. Renin

Question 11

What is the function of calcitriol? Where is it secreted and where does it act on?

Answer 11

It regulates calcium intake and retention.

It’s secreted from the proximal tubule cells in response to the parathyroid hormone (PTH) signalling when plasma [Ca2+] is low

It acts through receptors in both the digestive tract and kidney to promote the absorption (and reabsorption) of Ca2+

Question 12

What is the function of erythropoietin (EPO)? Where is it secreted and where does it act on?

Answer 12

Stimulates RBC production

It’s secreted by intertubular fibroblasts (EPCs; EPO-producing cells) within kidney tissue in response to tissue hypoxia

EPO acts on bone marrow to enhance erythrocyte (RBC) production, leading to increases in blood volume (and hematocrit)

Question 13

What is the function of renin? Where is it secreted and what does it activate?

Answer 13

It regulates other hormones which control blood pressure and plasma volume

It’s secreted by cells within the juxtaglomerular apparatus (JGA) in response to decreased pressure in kidney arterioles

It activates the RAAS, leading to increased blood pressure (through vasoconstriction) and increased blood volume (through intake and reabsorption)

Question 14

What is the functional unit of the kidney? Describe where it’s located in the kidney and its structure

Answer 14

Nephron; it begins at the glomerulus within the renal cortex. Each one has a glomerulus, where blood is initially filtered, and a complex renal tubule where the filtrate is processed

Question 15

Name the specific location where blood is filtered and explain the process

Answer 15

Blood is filtered at glomerular capillaries to create filtrate, which then enters the nephron and flows through its lumen and into the collecting duct

Question 16

What happens to remaining (unfiltered) blood?

Answer 16

It flows through capillaries around the nephron

Question 17

What is filtration?

Answer 17

It refers to the movement of fluid through small pores in response to pressure differences

If higher pressure is inside the vessel, fluid is pushed out the vessel (bulk flow), along with any solutes small enough to filter through the available gaps

Question 18

What affects the composition of urine?

Answer 18

The interactions between renal tubules, interstitial fluid, and peritubular capillaries. The complex patterns of reabsorption of water and solutes (and extra secretion of certain solutes) that occur throughout the nephron and ultimately sculpt the filtrate into the final product (urine)

Question 19

What makes the composition of urine highly variable? Name the 2 processes

Answer 19

It is because some aspects of nephron function are under hormonal regulation

1. Obligatory processes - always present; cannot be modified
2. Facultative processes - not always present; regulated by hormones (especially ADH and aldosterone). Facultative reabsorption means urine can vary in volume and composition, depending on homeostatic requirements

Question 20

What is renal failure? Name 3 symptoms

Answer 20

A life-threatening condition that occurs when kidney function is compromised. Some symptoms are:

1. Reduced urine production
2. Oedema
3. Fatigue

Question 21

Name 4 possible triggers for renal failure

Answer 21

1. Clot in a renal artery or vein
2. Physical damage to kidney tissue
3. (Nephro-)toxins (from certain drugs or breakdown of other body tissues)
4. Kidney stones blocking a ureter

Question 22

What happens when kidney filtration slows, stops, or reabsorption processes are disrupted?

Answer 22

Metabolic wastes, excess ions, and water will be retained in the plasma

Question 23

How can kidney failure be managed?

Answer 23

Using haemodialysis. It allows waste products and excess ions to be removed from the patient’s blood. This process typically takes 3-4 hours and must be repeated 3x per week

Question 24

How does dialysis work?

Answer 24

It relies on passive diffusion across a selectively permeable membrane. The membrane permits ions and small organic molecules to pass, but restricts the movement of large molecules, especially plasma proteins

Question 25

What is the composition of dialysis fluid designed to do?

Answer 25

It’s meant to prevent the loss of nutrients and key ions from plasma. Its adjusted to meet each individual patient’s specific needs