Urinary System

Question 1

What are the functions of the urinary system ?

Answer 1

Urine Excretion
Endocrine organ (kidneys produce erythopoietin and renin which raises BP)
Homeostatic role (control BP, tissue osmolarity, electrolyte and water balance, plasma pH by secreting H+ ions during acidosis or bicarbonate ions during alkalosis )

Question 2

What is the function of the kidneys?

Answer 2

Blood water homeostasis by production of urine

Question 3

Where are the kidneys located ?

Answer 3

Retroperitoneal, on posterior abdominal wall, high up under the diaphragm.
Encapsulated by layers of fascia and renal fat.

Question 4

How wide and long are ureters ?

Answer 4

They are 3-4 mm in diameter, 25-30 cm in length.

Question 5

What is the path of urine ?

Answer 5

Pyramids –> papillae –> minor calyces –> major calyces

–> renal pelvis –> ureter –> bladder

Question 6

When is the last stage at which urine is modified ?

Answer 6

When in the pyramids

Question 7

What are the components of a nephron ?

Answer 7

Glomerulus, distal convoluted tubule, proximal convoluted tubule, loop of Henlé collecting ducts

Question 8

What are the kinda of nephrons which exist ? What are the differences between them ?

Answer 8

Juxtomedullary:

• its deeper (though still in cortex) and has long loop of Henlé sitting in inner medulla
• Receives 10% of renal supply
• Designed to concentrate urine (hence long loop)
• Glomeruli in inner cortical regions. Long nephron loops.
• Associated with vena recta (vascular structure)

Superficial:

• sits higher up in cortical region and does not dip into inner medullar
• Receives 90% of renal supply
• Designed to reabsorb large proportion of fluid filtering from vasculature
• Glomeruli in outer cortical regions. Short nephron loops.

Question 9

What is macula densa ?

Answer 9

Area of closely packed specialised cells lining wall of limb of loop of Henlé at the transition to the DCT.

Question 10

How does the ureter get to the bladder in a female ?

Answer 10

Posterior to the ovary, then lateral to the cervix and vagina, then into bladder.

Question 11

How does the urethra get to the penis in a male ?

Answer 11

Through prostate gland

Question 12

What is the structure of the walls of uterus and bladder ? What is their function

Answer 12

Mainly muscular.

• Peristaltic wave properly urine down the ureter
• Bladder fills by relaxation of detrusor muscle, then empties by contraction of detrusor muscle (+ raised intra-abdominal pressure).

Question 13

What kibd of epithelium resides in the bladder ?

Answer 13

Urothelium, AKA transitional epithelium

Question 14

How is urine regulated ?

Answer 14

Through voluntary control of the external (striated) sphincter around urethra and involuntary contraction of detrusor muscle

Question 15

What is the function of ureters ?

Answer 15

Bringing urine from kidneys to bladder.

Question 16

What does filtration basically consist of ?

Answer 16

Filtering plasma from cells and proteins

Question 17

Where does filtration take place ?

Answer 17

Glomerulus, in network of capillaries

Question 18

What factors allow the process of filtration to happen ?

Answer 18

• Hydrostatic Pressure (60 mmHg) in afferent arteriole forces plasma out of blood
• Fenestrations in glomerular capillaries
• BM (repels proteins)
• Slit diaphragm (podocytes have foot processes wrapping around capillaries and leaving slits between them)

Question 19

Where does the filtrate collect ?

Answer 19

In the Bowman’s capsule

Question 20

What is the filtrate recovery module of the kidney ?

Answer 20

Renal tubule

Question 21

What is the glomerular filtration rate ?

Answer 21

180 L/day (does not all get urinated due to re-absorption)

Question 22

What is the proportion of cardiac output received by the kidney ?

Answer 22

20%

Question 23

What is the proportion of plasma received that the kidney filters ?

Answer 23

20%

Question 24

What are the two routes for reabsorption ?

Answer 24

Transcellular and paracellular

Question 25

What is reabsorption ?

Answer 25

Transfer of most of the plasma filtered to circulation (from lumen to interstitium and blood)

Question 26

What are the main steps of reabsorption ?

Answer 26

1. NA+-K+ ATPase creates a Na+ gradient between outside and inside of cell
2. Ion transport creates voltage gradient between tubule lumen and interstitium
3. Water follows Na+ by osmosis
4. Solutes (ions, small molecules) are carried along the water flow solvent drag
5. Water reabsorption concentrates solutes remaining in the lumen

Question 27

Which factors can influence reabsorption and secretion ?

Answer 27

Hormones (aldosterone, ADH) and situation a person may be in (health, diet, influences glucose, K+, AAs content).

Question 28

What is the final urine made up of ?

Answer 28

What we filtered + some things (waste) we secrete later on.

Question 29

What is the countercurrent multiplication mechanism ?

Answer 29

Filtrate is exposed to increasing osmolarity during passage down the descending thin limb (since as osmolarity increases as you go cortex –> outer medulla outer stripe –> inner medulla outer stripe –> papilla)

Water exits tubule driven by osmotic P gradient (=cortico-papillary osmotic gradient).

In the ascending thick limb (normally, with decreasing cortico-papillary osmotic gradient water just leak back in BUT:) ATL impermeability prevents water from re-entering tubule and diluting its contents.
This drives Na+ diffusion

Question 30

How is reabsorbed fluid returned to the vasculature ?

Answer 30

Visa peritubular network

Question 31

What kinds of modifications are present in the epithelium of the PT ?

Answer 31

Apical microvilli and leaky paracellular junctions.

To maximise free flow of water and dissolved solutes.

Question 32

How does reabsorption of different solutes occur by the PT?

Answer 32

• Almost 100% of filtered glucose and AAs, visa Na+ co-transport
• Na absorption by basolateral Na-K ATPase through co-transport with organic solutes and in exchange for H+
• Cl- in the late PT by paracellular route or by Cl- base exchanger
• Water by osmosis, driven by influx of Na, Cl, and solutes

Question 33

What proportion of the fluid and of the solutes filtered does the PT recover ?

Answer 33

2/3 of the fluid and up to 100% of some solutes

Question 34

What is the process of voiding the bladder ?

Answer 34

Micturition

Question 35

What is the volume capacity of the bladder ?

Answer 35

500 mL

Question 36

What is the process from bladder filling to micturition ?

Answer 36

Bladder filling –> Mechanoreceptor activation –> Spinal chord (parasympathetic motor efferents) –> micturition reflex –> detrusor contraction (bladder contractions) —-> Increased luminal pressure —-> if can’t pee, emptying is prevented by pontine micturition center (CNS) —-> if can pee, outer sphincter relaxes voluntarily (and SNS inhibited)

Question 37

How much water is intaken and how much is output everyday on average ?

Answer 37

Around 1600 mL (through food, metabolism and beverages though beverages can be more, it is the most variable category) and 1600 mL (must lose as much as we take in for homeostasis)