Urinary System

Question 1

What are the functions of the urinary system?

Answer 1

1. Filter waste from the blood and excrete it as urine
2. Maintain the ECF balance in the body
3. Balance nutrients e.g. minerals
4. Produce the hormone erythropoietin which stimulates the bone marrow to produce red blood cells

Question 2

What lines the abdominal cavity and where are the kidneys found with respect to it?

Answer 2

Parietal peritoneum
- kidneys lie just underneath it and are said to be retroperitoneal

The left kidney is more caudal than the right and is more loosely attached to the wall

Question 3

What attaches the kidney to the wall?

Answer 3

Strong, fibrous, irregular dense connective tissue

Question 4

What its the hilus?

Answer 4

Area of the kidney where blood vessels enter and leave and when urine leaves

Question 5

Describe the structure of the kidney?

Answer 5

Has an outer cortex, an inner medulla and a renal pelvis (collecting area)

Question 6

What are the functions of the kidney?

Answer 6

1. To produce urine
   - excrete some waste materials e.g. urea and some substances that are in excess in the body e.g. water or sodium
2. Erythropoietin production
   - secrete this hormone when blood oxygen levels are low - stimulates the production of RBCs
3. Converts inactive Vit D to the active form in kidney.
   - active Vit D is involved in Calcium reabsorption from the small intestine. (Allows the animal to utilise the calcium in its diet)
4. Produces the hormone Renin
   - in response to fallen blood pressure which alters the pressure via the RAA system
5. Acid-base balance
   - blood pH regulator
   - kidney varies the amount oh H ions in the blood

Question 7

What are nephrons?

Answer 7

Functional part of the renal tissue
Very numerous in the renal tissue
Found partly in the cortex and partly in the medulla (the loop of henle)

Question 8

What supplies the kidneys and how much blood do the kidneys receive in terms of cardiac output?

Answer 8

Renal artery

20-25% of every heart beat

Question 9

Describe the travel of blood from renal artery to the nephron

Answer 9

Renal artery breaks into arterioles.
Arterioles divide into afferent arterioles which form glomerular tufts in the glomerular capsule.
The blood is forced through the renal corpuscle and most substances and water is forced out the blood and into the glomerulus and becomes ‘filtrate’.
The capillaries then reform into the efferent arterioles which then go on to supply the kidney tissue

Question 10

What is the renal corpuscle?

Answer 10

The glomerulus and the glomerular capsule together

Question 11

Describe the location and structure of the proximal convoluted tubule and what happens here?

Answer 11

The PCT is still in the cortex.
Lined by simple cuboidal or columnar epithelium which is lined with microvilli to increase surface area for absorption.
Active reabsorption of Na and Cl. Reabsorption of water by osmosis in response to the movement of Na ions.
Some secretion of drugs which are actively pushed from the capillaries into the filtrate.
Reabsorption of glucose into blood- up to renal threshold

Question 12

Describe the location and structure of the Loop of Henle and what happens here?

Answer 12

Starts in cortex, dips into medulla and returns to the cortex.
Lined by simple squamous epithelium
Main function is to adjust the volume (concentration remains the same) and each side is permeable to a different substance.
In the descending loop, water is reabsorbed by osmosis (no movement of Na). Urine is at its most concentrated at the apex of the loop.
In the ascending loop Na is drawn out and water cannot follow.
The urine entering and leaving the loop of henle has the same concentration but a different volume.

Question 13

Describe the location and structure of the Distal convoluted tubule and what happens here?

Answer 13

In cortex.
Lined by cuboidal epithelium but lacks a brush border.
Fine tunes Na/K balance - Na is reabsorbed and K is secreted to replace to Na ions.
The pH is regulated here by regulating the excretion of H ions into the urine.

Water can also be reabsorbed at this point if needed under the control of Aldosterone.

Question 14

Describe the location and structure of the Collecting Duct and what happens here?

Answer 14

Runs from cortex to medulla.
Lined by columnar epithelium.
Has several collecting tubes and then will drain into the final collecting duct i.e. it receives urine from several nephrons and drains into the renal pelvis.

The permeability of the collecting duct is altered by ADH:
- if the animal is dehydrated, ADH increases the permeability of the collecting duct to water and therefore more water is drawn out of the urine and back into the ECF of the kidney.

Question 15

Describe the Renin-Angiotensin-Aldosterone (RAA) system

Answer 15

High blood pressure is required for the adequate filtration of blood in the renal corpuscle. If there is a drop in BP, Renin is released from the glomerulus. Renin is an enzyme that converts the inactive plasma protein Angiotensinogen to Angiotensin 1 which is then converted to Angiotensin 2.

Angiotensin 2 causes vasoconstriction of blood vessels which diverts blood to where it is needed and increases the pressure in the capillaries that are left.
Angiotensin 2 also stimulates the adrenal gland to produced aldosterone. Aldosterone increases the reabsorption of Na in the DCT and thus water follows.
An increase in water reabsorption increases the blood volume and therefore blood pressure.

Question 16

Where is ADH produced and what is its function?

Answer 16

Produced in the posterior pituitary gland.
Influences the volume of urine produced.
Kidneys sense the drop in blood pressure or increase in osmotic pressure in the blood and tissues. This triggers the release of ADH from posterior pituitary. It travels in the blood and acts on the collecting duct, increasing its permeability. Increasing the reabsorption of water and less is lost in the urine.

Question 17

What buffers H ions in the PCT? and in the DCT?

Answer 17

PCT: H ions are buffered by bicarbonate ions
DCT: H ions are buffered by phosphate and ammonia ions

Question 18

Describe the clinical implication for the kidney and the systems associated?

Answer 18

Shock
- senses BP drop and RAA system starts
Blood Loss
- tells kidney need more blood cells, releases erythropoietin
Dehydration
- Releases ADH
Diabetes insipidus
- ADH not available so urine dilute
Diabetes Mellitus
-excess glucose in urine because it exceeds the renal threshold for reabsorption
- excess glucose in blood

Question 19

Describe the structure of the ureters?

Answer 19

Narrow, smooth muscular tubes.
Has a thick wall with a narrow lumen.
The tube narrows at the renal pelvis of the kidney and also at the trigone.

Lined by transitional epithelium (allows stretch)
Each ureter is suspended in its own little pouch of peritoneum called the mesoureter.
Each then burrows into the bladder wall at the Trigone.

Question 20

Name and describe two clinical problems that involve the ureter

Answer 20

1. Renal calculi (kidney stones)
   - mineral deposits that form large crystals which can lodge in the ureter and cause blockage.
2. Ectopic ureter
   - when during development the ureter ends up in the wrong place.

Question 21

Describe the structure and location of the bladder

Answer 21

Empty it lies in the pelvic cavity; full it extends into the abdominal cavity.

Cranially the bladder is covered by peritoneum in the abdominal cavity.
Made up of smooth muscle and elastic tissue and is lined by transitional epithelium to allow some stretch.

Has 2 sphincters - internal (involuntary) and external (voluntary)

Question 22

Describe the structure of the urethra in females

Answer 22

Fibromuscular tube
Short and wide tube
Carries only urine
Less likely to block, but more likely to catch infection in bladder.
Opens into vestibule

Question 23

Describe the structure of the urethra in males

Answer 23

Fibromuscular tube
Long and narrow tube
Carries urine and sperm
More likely to get blocked, but less likely for infection to reach the bladder.
Runs through prostate gland and joins with the vas deferens near the junction with the bladder.

In cats, the urethra also receives a duct from the bulbo-urethral gland.

Question 24

Define Micturition

Answer 24

Passing urine

Question 25

Define Oliguria

Answer 25

Reduced urination

Question 26

Describe the process of Micturition

Answer 26

When bladder is full, stretch receptors in the wall send sensory messages to the spinal cord and brain. Motor nerve impulses then cause the bladder to contract and the internal sphincter to relax. The release of urine by relaxing the external sphincter is voluntary when In a correct place to urinate.

Question 27

What affects the composition of urine?

Answer 27

1. Hydration status of the patient
2. Animals diet
3. Animals general health
4. Presence/absence of urinary tract disease, calculi etc
5. Environmental conditions

Question 28

What are the rates of normal urine production for Cats and dogs?

Answer 28

Dog = 20-100mls/kg/day
Cat = 10-12mls /kg/day

Question 29

What is the normal pH of urine and normal values for USG for dogs and cats?

Answer 29

pH= 5-7

USG (dog) = 1.016-1.060
USG (cat) = 1.020-1.040

Question 30

What shouldn’t be present in urine that sometimes is?

Answer 30

1. Blood
2. Protein
3. Glucose
4. Ketones
5. Bile
6. Deposits e.g. crystals
7. WBCs