1. Anatomy and physiology of the urinary system

Question 1

What are functions of the kidneys?

Answer 1

• elimination of waste substances from plasma
• salvage of essential compounds from filtrate
• regulation of ion levels
• maintenance of osmolality
• regulation of plasma volume and hence blood pressure
• production of hormones

Question 2

What are functional properties of the kidneys?

Answer 2

• heavily vascularised
• receive 25% of the cardiac output
• convert approximately 20% of this plasma to filtrate while retaining cells and protein in the circulation
• all but 1% of the filtrate is absorbed
• entire circulatory volume is filtered and reabsorbed every 30 minutes

Question 3

Describe the macroscopic appearance of ox kidneys

Answer 3

Lobed appearance + asymmetry

Question 4

Describe the macroscopic appearance of horse kidneys

Answer 4

Two different shapes

• right is shaped like a heart
• left is shaped like a bean

Question 5

Describe the macroscopic appearance of pig kidneys

Answer 5

Normal bean shaped

Question 6

Describe the macroscopic appearance of sheep kidneys

Answer 6

Normal bean shaped

Question 7

Describe the macroscopic appearance of cat kidneys

Answer 7

Rounder with capsular veins present on the outside of the kidney

Question 8

Describe the general anatomy of the urinary system

Answer 8

• Right kidney more cranial to left
• adrenal glands cranial and medial to kidney
• split into upper and lower urinary tract
• renal arteries are branches of the aorta, receive 25-30% of cardiac output

Question 9

Describe the structure of the deeper renal parenchyma

Answer 9

Medulla - subdivided into renal pyramids that have a base and then a narrow apex

• apex of the medullary pyramid is surrounded by one of the funnels formed by the subdivision of the renal pelvis
• subdivision of the pelvis surrounding the apex of the medulla = papilla

Question 10

What are the renal parenchyma?

Answer 10

Cortex and medulla made up of millions of nephrons (functional units)

Question 11

Where in the nephron is filtrate produced?

Answer 11

Proximal end of nephron in capsule

Question 12

What is the renal corpuscle?

Answer 12

First component of the nephron

- consists of glomerulus (tuft of capillaries) surrounded by the Bowman’s capsule

Question 13

What are podocytes?

Answer 13

Specialised epithelial cells - sit adjacent to epithelium of capillaries (endothelium)

Question 14

What is the function of the efferent arterioles in the renal corpuscle?

Answer 14

Arterial blood perfuses out of the capillary network + drains from glomerulus via efferent arteriole
- capillaries have a fenestrated epithelium = fairly permeable epithelium

Question 15

How is the glomerular filtrate produced?

Answer 15

Some components of plasma are filtered from the glomerulus into the space of the Bowman’s capsule
- this is the glomerular filtrate

Question 16

What is the GFR?

Answer 16

Glomerular Filtrate Rate

• useful measure of glomerular function
• volume of fluid filtered from the glomerular capillaries into the Bowman’s capsule per unit time

Question 17

What is the function of the endothelial cell processes in the Bowman’s capsule?

Answer 17

Single layer of endothelial cells lining glomerular capillaries (contains fenestrations)
- restricts the passage of blood cells

Question 18

What is the function of the glomerular basement membrane in the Bowman’s capsule?

Answer 18

Lies between the endothelium and podocytes (non cellular made up of collagen or collagen like proteins in a glycoprotein matrix)
- main filtration barrier

Question 19

What is the function of the podocytes in the Bowman’s capsule?

Answer 19

Single layer of the visceral epithelial cells lining Bowman’s capsule
- restrict passage of medium sized proteins and phagocytose macromolecules + metabolising macromolecule fragments + returning them to various body compartments

Question 20

What is the net filtration pressure?

Answer 20

Net total of hydrostatic and oncotic pressures

Question 21

What is the hydrostatic pressure?

Answer 21

Capsular pressure

- pressure exerted by a fluid

Question 22

What is the oncotic pressure?

Answer 22

Form of osmotic pressure induced by soluble proteins

Question 23

What do low levels of albumin in circulation cause?

Answer 23

Problems with circulatory balance

Question 24

What are the steps in reabsorption in the proximal convoluted tubule (PCT)?

Answer 24

1. Filtration by glomerulus
2. Obligatory absorption and secretion by proximal tubule
3. Generation of osmotic gradient by loop of Henle
4. Regulated absorption and secretion by distal tubule
5. Regulation of water uptake by collecting ducts

Question 25

Under normal circumstances what solutes are reabsorbed?

Answer 25

All glucose
All amino acids
Most Na+, Cl- and HCO3-

Question 26

What is paracellular reabsorption?

Answer 26

Flux between cells

- largely a result of concentration or electrical gradients

Question 27

What is transcellular reabsorption?

Answer 27

Molecules move across cells

• Largely a result of secondary active transport of solutes by tubular cells
• after initial filtration

Question 28

What is diffusion?

Answer 28

Net movement from high to low concentration

• no competition
• net flux is proportional to concentration difference and permeability
• dissolved substances can cross the membrane
• can occur through tight junctions

Question 29

What is facilitated diffusion?

Answer 29

Proteins act as carriers or pores to permit flux of substances that cannot directly diffuse through a membrane

• still passive from high to low concentration
• saturates due to limit of available carrier protein
• competition
• Tm (transport maximum) = maximum rate of transport i.e., fully saturated

Question 30

What is primary active transport?

Answer 30

Proteins in membrane act as pump

• move ions or small molecules from low concentration to high concentration
• not passive
• e.g., Na-K ATPase, Ca-ATPase, H-ATPase

Question 31

What is secondary active transport?

Answer 31

Couples the movement of several different molecules in each different cycle

• can saturate
• co-transport moves 2 or more molecules in the same direction across the membrane
• counter transport is in opposite directions
  e. g., Na-glucose co-transport