The Renal System

Question 1

What are the functions of the renal system?

Answer 1

-Excretion of physiological waste products from body fluids
-Elimination of waste products into the environment
-Homeostatic regulation of volume and solute conc. of blood
-Also regulates BP
-Regulates plasma conc. of Na, K and Cl ions
-Helps stabilise blood pH
-Conserves valuable nutrients
-Assists liver in detoxification

Question 2

What is the anatomy of the kidney?

Answer 2

-Fibrous capsule covering the kidney
-Cortex – superficial portion
-Medulla – composed of renal pyramids
-Renal column – band of cortical tissue which extends between and separates pyramids
-Kidney lobe – renal pyramid, overlying area of cortex and adjacent renal column

Question 3

What is the nephron?

Answer 3

→ Functional unit of the kidney
→ Renal corpuscle – Bowman’s capsule and glomerulus
→ Renal tubule
→ Collecting system

Question 4

What is the PCT

Answer 4

Its the proximal covulated tubule, reabsorption of ions, glucose, amino acids, vitamins, water

Question 5

What is the loop of henle

Answer 5

-Descending limb - reabsorption of water
-Ascending limb - reabsorption of ions
-each limb of the loop has a thick and thin segment, refers to the thickness of the epithelium
-Thick segments have cuboidal epithelium
-Thin segments have squamous epithelium

Question 6

What is the DCT and what is its function?

Answer 6

It is the distal covulated tubule, reabsorption of Na & Ca ions, secretion of acids & ammonia

Question 7

What is the function of the collecting duct?

Answer 7

Reabsorption of water & Na ions, concentration of tubular fluid

Question 8

What are the waste products in urine?

Answer 8

-Urea
-Creatine
-Uric acid

Question 9

How is urea formed?

Answer 9

From breakdown of amino acids, ~21 g produced per day

Question 10

How is creatine formed?

Answer 10

From breakdown of creatine phosphate, ~1.8 g per day

Question 11

How is uric acid formed?

Answer 11

-Formed from recycling of RNA nitrogenous bases, ~480 mg per day

-Dissolved in blood

-Can only be excreted when dissolved– therefore this involves the unavoidable loss of water

Question 12

Urine formation: Filtration

Answer 12

○ Blood pressure forces water & solutes across walls of glomerular capillaries
○ Sieving effect

Question 13

Urine formation: reabsorption

Answer 13

○ Removal of water and solutes across tubular epithelium

○ Reabsorbed substances re-enter the blood

○ can be passive (water) or active (carrier proteins, glucose)

Question 14

Urine formation: secretion

Answer 14

○ Cells produce and then discharge substances directly into the urine
○ creatinine, hormones, some drugs eg penicillin

Question 15

What is hydrostatic pressure?

Answer 15

Fluid pressure

Question 16

What is colloid osmotic pressure?

Answer 16

Pressure due to materials in solution on either side of the capillary walls

Question 17

What conditions monitor filtration pressures?

Answer 17

-Fenestrations are large – even plasma proteins can pass through

-Basement membrane - only small proteins can pass through

-Filtration slits stop nearly all proteins passing

Question 18

What is the glomerular filtration rate?

Answer 18

GFR is the amount of filtrate produced by the kidneys per minute

Question 19

What is used to estimate glomerular filtration rate?

Answer 19

A creatine clearance test
(As creatine is filtered out in the glomerulus and is not reabsorbed it is a good indication of the rate)

Question 20

What is the Renin-angiotensin-aldosterone system

Answer 20

· Signalling pathway responsible for regulating the body’s blood pressure
· Low renal BP causes release of renin from kidneys
· Converts angiotensinogen produced by liver to angiotensin
· Angiotensin converted to angiotensin II by angiotensin converting enzyme (ACE)
· Causes increase in sympathetic activity, resorption of Na and Cl ions and water, excretion of K ions and vasoconstriction
· Induces release of aldosterone from adrenal cortex
· Induces release of ADH from pituitary gland

Question 21

What are the ureters and their function?

Answer 21

· Pair of muscular tubes extending from kidneys to bladder
· Ureters penetrate posterior wall of bladder at an oblique angle
· Ureteral openings are slit-like
Helps prevent backflow of urine towards ureter and kidneys when bladder contracts

Question 22

What is the urinary bladder and its function?

Answer 22

· Hollow, muscular organ which acts as a reservoir for urine
· Urethral entrance is at the neck of the bladder
· Neck contains internal urethral sphincter
○ Involuntary control over release of urine
· When layers of muscle contract the bladder compresses and urine is expelled into the urethra
· Can contain up to 1 litre of urine
· Neck of the bladder is at the bottom of it

Question 23

What is the urethra and its function?

Answer 23

· Extends from neck of bladder to exterior
○ Males 18-20 cm
○ Females 3-5 cm
· External urethral sphincter
· Voluntary control
· Must be relaxed to allow urination

Question 24

What coordinates urination?

Answer 24

· Micturition reflex coordinates urination
· As the bladder fills, stretch receptors in the bladder wall are stimulated
· Results in message being relayed to cerebral cortex
○ Become aware of fluid pressure in bladder
· If volume exceeds 500 ml, bladder contractions may be so great that it forces open the internal urethral sphincter
○ Reflexive relaxation of external urethral sphincter
○ Release of urine despite voluntary opposition
· Urge to urinate usually appears when there is about 200 ml urine

Question 24

What are age related changes in the renal system?

Answer 24

· Decrease in number of functional nephrons
· Reduction in GFR
· Reduced sensitivity to ADH
· Problems with micturition reflex
· Nephrons decrease by 30-40 % between ages 25 and 85
· GFR decrease because of fewer glomeruli, reduced renal blood flow
· With age, distal portions of tubule and collecting duct are less responsive to ADH. Water and Na ions resorbed at a reduced rate so more lost in urine
· Incontinence due to reduced muscle tone in sphincters, CNS problems like Alzheimers and stroke can cause loss of ability to control micturition reflex, in males urinary retention can be caused by enlargement of prostate which compresses the urethra