L1: Intro To Blood Supply & Filtration

Question 1

LO: Outline the arrangement of the urinary tract

Answer 1

The urinary tract is made up of:

Kidneys - 2, positioned either side of the spine behind caudal rib

Ureters - conveys urine from kidneys to bladder

Bladder - storage of urine prior to evacuation

Urethra - convey urine from bladder to outside world

Question 2

What are the functions of the kidneys? (3)

Answer 2

1. Regulation of fluid volume and electrolyte balance:
   - ECF and blood pressure
   - osmolarity
   - ion balance
   - maintain pH
2. Excretion of waste:
   - metabolic waste e.g. urea
   - foreign substances e.g. medicine
3. Production of hormones:
   - activation of vitamin D3
   - synthesis of erythropoietin
   - synthesis and release of the enzyme renin

Question 3

What are the names and functions of the two main regions in the kidney?

Answer 3

Cortex - outer section, main function is filtration to form filtrate

Medulla - inner section, main function is to collect and excrete urine

Question 4

What is the functional unit of the kidney?

Answer 4

The nephron

Made up of the renal (Bowman’s) capsule, proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), collecting duct and papillary duct

Question 5

What is the function of Bowman’s capsule?

Answer 5

Production of filtrate

Question 6

What is the function of the proximal convoluted tubule?

Answer 6

Bulk reabsorption of water, ions and all organic nutrients
(Mostly unregulated)

Question 7

What is the function of the Loop of Henle?

Answer 7

Further reabsorption of ions and water
Set up of osmotic gradient in the renal medulla

Question 8

What is the function of the distal convoluted tubule?

Answer 8

Variable (often regulated) secretion and reabsorption of water and ions

Question 9

What is the function of the collecting duct?

Answer 9

Variable (often regulated) secretion and reabsorption of water and ions
Collects from several nephrons

Question 10

What is the function of the papillary duct?

Answer 10

Delivery of modified filtrate (urine) to the renal pelvis

Question 11

Describe the blood supply to the nephron

Answer 11

Kidneys have a specialised blood supply - two capillary beds in series called “capillary portal system”

1. Glomerular capillaries: network sandwiched between afferent and efferent arterioles
   - surrounded by Bowman’s capsule
2. Peritubular capillaries: wraps around PCT and drops down into medulla running parallel to the LOH
   - drain into venules

Question 12

What is meant by filtration?

Answer 12

Movement out of a capillary by bulk flow (by pressure)

Question 13

What are the forces responsible for filtration?

Answer 13

1.Hydrostatic pressure
2. Oncotic pressure (protein conc)

The balance of hydrostatic and oncotic pressure determines amount & direction of fluid transported across capillary wall

Question 14

What are some ways to increase filtration across a capillary bed? (4)

Answer 14

1. Higher volume of blood
2. Large surface area across which filtration can occur
3. High level of glomerular capillary blood pressure - afferent arterioles is wide than efferent arteriole
4. Low resistance to movement of fluid - thin, porous nature of filtration membrane

Question 15

What is meant by glomerular filtration rate (GFR)?

Answer 15

Volume of fluid filtered from the glomerular capillaries into Bowman’s capsule per minute
- varies with metabolic mass of animal

Question 16

What is the approx GFR in dogs?

Answer 16

3ml/kg/min