Urinary S1 - Introduction

Question 0

How much ultra filtrate do kidneys produce daily?

Answer 0

~180L

Question 1

The kidneys produce ultra-filtrate. What is ultra filtrate?

Answer 1

Plasma after blood cells and large proteins have been removed.

Question 2

How efficient are kidneys at filtering plasma?

Answer 2

They filter ~20% of plasma volume at each pass through the kidneys

Question 3

What are the names and order of kidney areas?

Answer 3

Glomerulus
Proximal convoluted tubule (PCT)
Loop of Henle (intermediate tubule)
Distal convoluted tubule (DCT)
Collecting duct

Question 4

Where does filtration occur?

Answer 4

In the glomeruli of the nephron, in the cortex

Question 5

Describe the glomeruli

Answer 5

Specialised circulation maintains filtration pressure
Afferent and efferent arterioles
Determines glomerular filtration rate

Question 6

Describe the PCT

Answer 6

Major reabsorption site
Filtrate remains isotonic
Reabsorbed materials leave by peritubular tubules

Question 7

What is re absorbed from ultrafiltrate in the PCT?

Answer 7

~60-70% of Na and H2O
~80-90% of K
~90% of bicarbonate
100% of glucose and amino acids

Question 8

Why does filtrate remain isotonic after the PCT?

Answer 8

Water follows ions so only so much water leaves as ions are reabsorbed

Question 9

In what circumstance would <100% of glucose be reabsorbed?

Answer 9

In patients with diabetes, blood glucose may be high so some glucose may not be re absorbed from the ultrafiltrate, resulting in polydipsia and polyuria

Question 10

What does it mean when we say a cell is polarised?

Answer 10

The membranes of opposite poles (ie basolateral vs luminal membranes) of that cell may have different properties
This allows transport across an epithelium

Question 11

How is sodium transport involved in reabsorption in the PCT?

Answer 11

Na is pumped out from the basolateral membrane
Na enters cell through luminal membrane down concentration gradient
Energy from this drives reabsorption of other substances eg glucose
Water follows electrolytes osmotically

Question 12

Describe the loop of Henle

Answer 12

Site of further salt reabsorption which dips into and out of the medulla
Uses counter current multiplication to create a gradient of increasing osmolarity in the medulla
This allows formation of concentrated urine if water needs to be conserved

Question 13

Describe the DCT

Answer 13

Major site of variable reabsorption of electrolytes and water in cortex
Actively secretes hydrogen ions to maintain pH balance

Question 14

What is diuresis and how does it occur?

Answer 14

It is large volumes of dilute urine

Occurs when water does not follow reabsorption of electrolytes in the DCT

Question 15

Describe the collecting duct

Answer 15

Passes through the high osmolarity environment of the medulla (created by the loop of Henle) to the renal pelvis
Water moves down its osmotic gradient to produce a low volume of concentrated urine if possible
If now, urine remains dilute

Question 16

Describe the variable reabsorption of Na

Answer 16

Occurs in the distal nephron
Controlled by a hormone system: the renin-angiotensin system
This controls ECF volume

Question 17

Describe the variable reabsorption of water

Answer 17

Occurs in the distal nephron
Controlled by hormone system: ADH
ADH controls permeability of DCT and collecting duct to water
His controls ECF osmolarity

Question 18

Describe and explain the metabolic demands of the kidney

Answer 18

Very high O2 and glucose demand
Require 4ml/min/g
Use 25% of cardiac output at rest
Due to kidney function being highly metabolically demanding (>99% of filtered plasma is reabsorbed)

Question 19

Describe kidney locations

Answer 19

Between T12-L3

Right kidney slightly lower due to liver

Question 20

Describe kidney size

Answer 20

~11-12cm long
~5-7.5cm wide
~2.5-3cm thick

Question 21

Describe the blood vessels of the kidney

Answer 21

Renal veins and arteries come directly off the IVC and aorta and enter the kidney in the hilar region
NB it’s not unusual for there to be extra accessory arteries supplying the kidney

Question 22

What is the cause and the common sites of renal colic?

Answer 22

Caused by kidney stones becoming lodged in the ureter

Common locations are: the pelviuretic junction, the pelvic brim and the entry through the bladder wall

Question 23

During what surgery are the ureters particularly vulnerable?

Answer 23

Hysterectomy

Question 24

What is formed by the entrance of the ureters and the exit of the urethra?

Answer 24

The trigone: a triangle shaped area defined by these openings

Question 25

Describe the bladder

Answer 25

Transitional epithelium folded into rugae except for in the trigone
Bag to collect urine until the urination

Question 26

Describe the entrance of the ureters to the bladder and explain the relevance

Answer 26

They enter posteriorly and inferiorly

This prevents back flow

Question 27

Describe the muscle layer of the bladder

Answer 27

Called the detrusor muscle
Circular involuntary internal sphincter
Smooth muscle running longitudinally, transversely and obliquely