The Renal System

Question 1

What is the general function of the kidneys?

Answer 1

-maintenance of homeostasis; manages fluid levels, electrolyte balance= to ensure internal environment of the body function as it should

Question 2

What do major excretory organs eliminate?

Answer 2

-excess fluid
-excess ions
-metabolic waste
-soluble toxins, drugs + their metabolites

Question 3

Reabsorption of nutrients- to maintain homeostasis:

Answer 3

-glucose
-amino acids
-bicarbonate
-water
-phosphate
-chloride, sodium, magnesium, potassium

Question 4

What is the general function of the kidneys?

Answer 4

-maintenance of pH
-osmolality regulation; measure of the body’s electrolyte balance
-regulation of blood pressure and volume; through the release of vasoconstrictors (hormones) + blood composition
-secretion of active compounds

Question 5

Urinary system:

Answer 5

Kidney cross-section: 2 layers (outer) renal cortex and (inner) renal medulla
Renal pyramids= composed of many nephrons (smallest functional unit of the kidney)
-striated in appearence
Nephrons- tubular structures + numerous nephrons occur together orientated in the same direction.

Question 6

Structure of the nephron:

Answer 6

*glomerulus= network of small blood vessels (capillaries) called a tuft
-distal and proximal convoluted tubule in (outer) renal cortex
*loops of henle= give the renal pyramids their striated appearance

Question 7

What are the 2 types of nephron?

Answer 7

*juxtamedullary nephrons (20%);
-long, looped and important in maintaining water balance
*cortical nephrons are the most abundant (80%);
-perform the excretory and regulatory functions of the kidney

Question 8

Nephron functioning:

Answer 8

-blood supply is fed into the bowman’s capsule= forming the glomerulus- where blood filtration takes place
-did,enter of blood vessels entering the bowman’s capsule is much wider than those that carry out filtered blood
-collecting duct has many other branches; nephrons are attached
-every nephron in the kidneys = work to filter the blood

Question 9

Kidney;

Answer 9

*afferent arteriole: feeds the incoming blood supply to the capillary bed inside the bowman’s capsule
*glomerulus ultrafiltration: occurs at a normal glomerular filtration rate
*bowmans /glomerular capsule: cup-like sack that holds the glomerulus

Question 10

Mechanisms of urine formation:

Answer 10

*glomerulus filtration;
-fluid is filtered from the glomerulus into golmerular capsule
*tubular reabsorption;
-involves the transfer of substances from tubular lumen into peritubular capillaries
*tubular secretion;
-transfer of substances from peritubular capillaries into the tubular lumen

Question 11

Ultra-filtration membrane of the kidney;

Answer 11

Ultra-filtration membrane; 3 layers
1) capillary wall; fenestrations (little windows); WBC’s and RBC’s are too big to pass through
2) basement membrane; capillary secretor layer (blue)
-podocyte secretor layer (red) -layer of glycoproteins (have a slight negative charge; repels large proteins)
3) filtration slits of podocyte cells

Question 12

Ultrafiltration membrane of the kidney; a cross-section

Answer 12

-fenestrated endothelium of glomerular capillaries; permeable to all plasma components except blood cells
-basement membrane; component glycoproteins have negative charge- repel negatively charged plasma proteins hindering their passage through membrane
-filtration slits; have thin membrane called slit diaphragms

Question 13

What forces determine glomerular filtration and filtration pressure?

Answer 13

-by the time blood reaches kidneys, pressure has dropped to 55mm Hg
-forces are acting in the opposite direction;
1) blood proteins remaining in the blood exhibit attractive forces- termed the blood colloid osmotic pressure (30mm Hg)
2) pressure in the capsule itself 15 mm Hg

Question 14

Net filtration pressure:

Answer 14

-is a glomerular capillary blood pressure

Glomerular filtration rate is 120-125 mL/min
-depends on;
*net filtration pressure
*how much glomerular surface area is available for penetration
*how permeable the glomerular membrane is

Question 15

How is filtration regulated?

Answer 15

2 physiological mechanisms regulate GFR (glomerular filtration rate) in the kidneys;
-intrinsic mechanisms maintain GFR despite changes in bp (80-180mmHg) , if bp remains in this range the kidney can regulate GFR itself
-if bp drops below 80mmHg extrinsic mechanisms that maintain systemic blood pressure come into play and maintain GFR

Question 16

The juxtaglomerulus apparatus comprises of 2 cell types: juxtaglomerulus cells + macula densa cells

Answer 16

Juxtaglomerular cells=
-enlarged smooth muscle cells
-act as mechanoreceptors= sensitive to stretch and to pressure of blood entering the kidney
-release hormone renin

Macula densa cells=
-tall, closely packed DCT (distal convoluted tubule) cells
-function as chemoreceptors; sensing the amount of Na2+ ions in the blood; if Na2+ levels drop= not enough filtrate
-release of vasoactive chemical= inhibited= reduces resistance to blood flow in the afferent arterioles, raises glomerular hydrostatic pressure= increases filtration rate
-stimulates mechanoreceptor juxtaglomerular cells- causes vasodilation of afferent arterioles

Question 17

Summaries; slides 24-28

Question 18

Filtration

Answer 18

Glomerular filtration:
-fluid is filtered from the glomerulus into glomerular (Bowman’s) capsule
Tubular Reabsorption:
-involves the transfer of substances from tubular lumen into peritubular capillaries
Tubular secretion:
-transfer of substances (urea, toxins, drugs + their metabolites) from peritubular capillaries into the tubular lumen

Question 19

Tubular reabsorption can be active or passive:

Answer 19

Passive reabsorption:
-no energy is required for the substances net movement
-occurs down electrochemical or osmotic gradients
Active reabsorption:
-occurs if any one of the steps in transepithelial transport of a substance requires energy
-movement occurs against electrochemical gradient

Question 20

2 routes of tubular reabsorption:
Transcellular and paracellular

Answer 20

Transcellular (across cells):
-transport across the luminal (apical) membrane
-diffusion through the cytosol
-transport across the basolateral membrane
-movement through the interstitial fluid into the capillary
Paracellular route (between cells)
-tight junctions

Question 21

Tubular reabsorption

Answer 21

Slide 11, 12, 13

Question 22

What is the importance of Na+ reabsorption in the kidney?

Answer 22

• An active Na+-K+ ATPase pump in basolateral membrane is essential for Na+ reabsorption
• 80% of energy spent by kidneys is used for Na+ transport
• Water is obliged to follow reabsorbed sodium – this sodium-linked water flow is called obligatory water reabsorption
• Na+ is not reabsorbed in the descending limb of the loop of Henle
• It plays a role in maintaining blood volume and blood pressure

Question 23

Substances removed via tubular secretion

Answer 23

-H+, K+ and organic ions
*H+= important in regulating acid base balance
-secreted in the proximal, distal and collecting tubules
*K+= keeps plasma conc at the appropriate level to maintain normal membrane excitability in muscles and nerves
*organic ions= accomplish more efficient elimination of endogenous and exogenous organic compounds from the body

Question 24

Osmolarity

Answer 24

-osmotic concentration of the blood plasma is kept constant by regulating urine concentration and volume

Question 25

2 types of nephron

Answer 25

juxtamedullary nephrons + cortical nephrons

Question 26

Why does this osmotic gradient exist in the inner medulla of the kidney?

Answer 26

21

Question 27

Role of ADH

Answer 27

• positive water balance= dilute urine, large volume
• negative water balance= concentrated urine, smaller volume
  -ADH controlled, variable water reabsorption occurs in the collecting duct
  -secretion of ADH increases the permeability of the collecting tubule cells to water- inserts aquaporins into the membrane of the collecting duct.
  -it is produced in the hypothalamus and stored in the posterior pituitary
  -works on the distal tubule and collecting duct tubule cells through a cyclic AMP mechanism