week 7 sem 2

Question 1

MACROscopic internal organisation of the kidney

Answer 1

Cortex – outer zone, granular
Medulla – inner zone made of renal pyramids, divided into lobes
Renal pelvis – funnel-shaped, continuous with ureter

Question 2

MICROscopic internal organisation of the kidney

Answer 2

Cortical nephrons, which lie predominantly in the renal cortex and their Loop of Henle dips into the renal medulla.

Juxtamedullary nephrons, which lie at the cortex-medulla junction and have long nephron loops that are located deep in the medulla.

Question 3

Vascular components

Answer 3

Abdominal aorta
Renal artery
Afferent arteriole
Glomerulus (capillaries)
Efferent arteriole
Peritubular capillaries
Renal vein
Inferior vena cava

Question 4

Tubular components

Answer 4

Renal corpuscle (Glomerulus and Bowman’s capsule)
Proximal convoluted tubule (PCT)
Loop of Henle (nephron loop)
Distal convoluted tubule (DCT)
Collecting duct

Question 5

Ureters

Answer 5

Muscular tubes that transport urine from renal pelvis to urinary bladder by peristalsis.

Question 6

Bladder

Answer 6

Hollow, muscular organ that stores urine before voiding.
It is a powerful detrusor muscle (smooth muscle).
Has internal urethral sphincter (smooth muscle).

Question 7

Urethra

Answer 7

In the female, the urethra serves as a passage for urine.
In the male, there are three parts: prostatic, membranous and penile. It serves for the passage of semen and urine.
In both female and male it has a voluntary external sphincter (striatal muscles).

Question 8

Major function of the kidneys

Answer 8

Maintenance of the composition of the extracellular fluid: ECF volume, electrolyte composition and osmolarity
Therefore, the major function of the kidney is homeostatic regulation

Question 9

Other functions of the kidneys

Answer 9

Primary functions

Excretion (metabolic waste and foreign substances such as drugs)
Acid-base balance (regulate concentration of ions e.g. Hydrogen ions)
Osmoregulation (regulate total volume of water and total concentration of solutes in that water).
Secondary functions

Blood pressure maintenance (regulate water and solute concentration)
Anaemia correction (produce erythropoietin, regulating red blood cell production)
Calcium regulation
Protein catabolism – urea
Detoxification (removes toxins and waste).

Question 10

To calculate GFR:

Answer 10

GFR = U x V /P​

U is the urine creatinine concentration ​

P is the serum creatinine concentration ​

V is the urine flow rate = X mL /min

A normal GFR is 90-120 mL/min

Question 11

1. Glomerular hydrostatic pressure influenced by

Answer 11

Blood pressure in the glomerulus influenced by
* Arterial systemic blood pressure
* Vascular tone of afferent and efferent arterioles
* Hydrostatic pressure in glomerulus is higher than in
other capillaries
* Afferent arteriole has larger diameter than efferent
arteriole
* leads to increases glomerular capillary BP

Question 12

2. Colloid osmotic pressure

Answer 12

30 mmHg
* Aka Plasma oncotic pressure
* Plasma proteins cannot cross glomerular membrane* Water moves by osmosis from low to high protein
concentration (oncotic pressure)

Question 13

3. Capsular hydrostatic pressure

Answer 13

15 mmHg
* Aka Bowman’s capsule hydrostatic pressure
* Pressure exerted by the fluid in this initial part of the tubule

Question 14

Net filtration pressure (NFP)

Answer 14

• Glomerular Hydrostatic pressure – (Colloid osmotic pressure + Capsular hydrostatic pressure)

Question 15

Autoregulation

Answer 15

Changes in hydrostatic glomerular pressure (BP) are detected in the juxtaglomerular apparatus

Question 16

GFR hormone does what to the kidneys

Answer 16

The kidneys need a constant GFR to make filtrate and maintain extracellular homeostasis.

Question 17

2. Hormonal

Answer 17

GFR is hormonally regulated by the renin-angiotensin-aldosterone system (RAAS)

Question 18

Angiotensin II

Answer 18

powerful vasoconstrictor
stimulates aldosterone and ADH production
reabsorption of Na+, water

Question 19

Antidiuretic hormone (ADH)

Answer 19

makes collecting ducts more permeable to water for reabsorption
more concentrated urine
higher blood volume and pressure

Question 20

Aldosterone

Answer 20

activates Na+/K+ pump at DCT and CD
retains more Na+, water follows
increase in blood volume and blood pressure

Question 21

Atrial natriuretic peptide (ANP) / Brain natriuretic peptide (BNP)

Answer 21

stretch receptors in atria and ventricles
inhibits secretion of ADH, aldosterone
increase in excretion of sodium, water
increase in urine volume, decrease in blood volume and blood pressure

Question 22

3. Autonomic sympathetic regulation of GFR

Answer 22

Vasoconstriction of afferent arteriole reduces GFR
Overall effect of SNS is to ↑ fluid retention and ↓ GFR

Question 23

Steps in urine formation

Answer 23

Glomerular filtration: In renal corpuscle (glomerulus to Bowman’s capsule)
Tubular reabsorption: Occurs mostly In PCT (all nutrients) but also in loop of Henle, DCT and CD
Tubular secretion: Some in PCT but mostly in DCT and CD (all waste)

Question 24

Glomerular filtration

Answer 24

Water and most solutes in blood plasma move from
glomerulus into Bowman’s capsule
* Cells and proteins do not get filtered in physiological conditions

Question 25

. Tubular reabsorption

Answer 25

Selective process that moves substances from filtrate into blood
* Takes place in tubules (mainly PCT) and CD* Tubule cells reabsorb:
* Water
* Ions: Na+ K+ Ca ++ Mg++ Cl- HCO3
- HPO4* Nutrients: glucose, amino acids, vitamins
* Returned to venous system via peritubular capillaries

Question 26

Reabsorption of glucose

Answer 26

• Normally 100% reabsorbed
• If carriers proteins saturated, excess stays in urine
• Temporary glycosuria
• Excess glucose lost in urine
• Water follows, thus lose water and glucose

Question 27

Reabsorption of water

Answer 27

Water ‘carried along’ with sodium, during absorption of glucose and other solutes
* Passive (osmosis)
* 90% obligatory (must follow solutes; can’t control)
* By osmosis
* In the PCT and nephron loop (descending part ONLY)
* 10% facultative (adapts to body’s needs; variable)
* Mainly due to hormonal regulation (ADH and indirectly aldosterone)
* In the DCT and CD

Question 28

Tubular secretion

Answer 28

• Selective process that moves substances from the
  peritubular capillaries into renal tubule lumen
• Wastes, H+, ammonium, urea, drugs, etc.
• Provides a second route for substances to enter renal tubules from the blood

Question 29

The micturition reflex coordinates urination

Answer 29

Filling of the bladder is enabled by:

Contraction of internal urethral sphincter
Inhibition of detrusor (bladder) muscle activity.
Emptying of the bladder is enabled by:
contraction of the detrusor (bladder) muscle
relaxation of the internal and external sphincters

Question 30

Urination and ageing

Answer 30

Micturition reflex problems:

Sphincter loses muscle tone which leads to incontinence
Urinary retention if prostate enlarged.
Decreased number of functional nephrons:

↓ GFR due to fewer glomeruli
Deterioration in filtration, reabsorption and endocrine functions
Nephrons become less sensitive to ADH.