S1 Urinary System

Question 1

What is the role of the urinary system?

Answer 1

The urinary system enables, through filtration and selective reabsorption, precise control of concentration of substances in the ECF; water, Na, CL, HCO3, glucose.

Question 2

Describe the anatomical location of the kidney

Answer 2

Retroperitoneal organ that sits is the abdominal cavity at T12-L3

Question 3

Describe the basic structure of the kidneys

Answer 3

The renal cortex is the outer kidney and contains the Glomerulus and Bowman’s capsule.
Pelvis is the inner kidney.
The renal medulla is split into pyramids.

Question 4

Describe the vertebral levels at which major vessels branch off the aorta

Answer 4

CT - T12
SMA - L1
RA - L1-L2
Gonadal artery - L2
IMA - L3

Question 5

What is the path of the ureters?

Answer 5

Pass over tips of transverse processes, psoas muscle, sacro-iliac joint, bifurcation of common iliac arteries.

NB on a CT, lumbar vertebrae have wide T process and triangle foramen, thoracic has circle.

Question 6

What are the functions of the kidney?

Answer 6

Regulation: control the concentrations of key substances in ECF

Excretion: waste products
Endocrine: synthesis of renin, erythropoietin, prostaglandins

Metabolism: active form of Vitamin D, catabolism of insulin, PTH calcitonin
Control: volume, osmolarity, Ph

Question 7

How does the kidney control plasma volume, pH and osmolarity?

Answer 7

Control plasma volume by filtering and recovering salts

Control plasma pH by filtering and recovering bicarbonate and active secretion of hydrogen ions

Control plasma osmolarity by filtering and recovering water

Question 8

Describe levels of fluid in different compartments

Answer 8

Intracellular fluid – 28L
Extracellular fluid – 14L; 11L interstitial, 3L plasma
Osmolarity – osmoles per litre
Osmolality – osmoles per kg
Plasma osmolality = 280-310 mmol/L
Water moves from low osmolality (many water particles) to high

Question 10

What is the nephron?

Answer 10

Functional unit of the kidney.

Filtration occurs at the glomerulus then passes onto proximal tubule and so on for reabsorption

Question 11

Describe how filtration occurs at the glomerulus

Answer 11

Kidneys produce an ultrafiltrate which is made up of water, ions and small molecules.
Filtration occurs at the glomerulus, where afferent and efferent arterioles maintain a high filtration pressure.

This drives the filtrate out of the plasma at 180 l/day: the GFR.
Once filtered, the ultrafiltrate enters the proximal tubule for reabsorption of substances.

Question 12

How does reabsorption occur in the nephron?

Answer 12

The tubular epithelial cells first absorb the substances across the luminal/apical membrane then the basolateral membrane. This occurs via transport proteins.
The epithelial cells must be polarised, and contain tight junctions.

Question 13

Describe the role of sodium pumps

Answer 13

Sodium enters across luminal membrane down concentration gradient
This drives reabsorption of other substances such as glucose
Water follows electrolytes osmotically

Question 14

Where in the nephron does most reabsorption occur?

Answer 14

Proximal tubule

Question 15

What occurs in the loop of Henle?

Answer 15

Further site of reabsorption of salts.
But main function to create a gradient of increasing osmolarity in the medulla by counter-current multiplication.
This allows formation of concentrated urine if water has to be conserved

Question 16

What occurs in the distal tubule?

Answer 16

Major site of reabsorption of electrolytes and water.

Also actively secretes H+

Question 17

What occurs in the collecting duct?

Answer 17

The CD passes through the high osmolarity environment of medulla created by LoH
If water can cross the epithelium it will leave the urine down the osmotic gradient, producing low volume of concentrated urine. If it cannot urine remains dilute