Urinary system

Question 1

Name the three functions of the urinary system

Answer 1

• Urine excretion
• Endocrine organ
• Homeostatic role (controls blood pressure, tissue osmolality, electrolyte and water balance and plasma pH

Question 2

How can the kidneys affect the pH balance?

Answer 2

• Excreting hydrogen ions in acidosis and bicarbonate ions in alkalosis

Question 3

How can the kidneys indirectly raise the blood pressure and drive red blood cell production?

Answer 3

• They secrete renin which raises blood pressure
• They secret erythropoietin which drives red blood cell production

Question 4

What carries urine from the kidneys to bladder?

Answer 4

• Ureters

Question 5

Describe the position of the kidneys

Answer 5

• They are high up in the abdomen with one on each side.
• They sit inferior to the diaphragm and posterior to the abdominal wall in the retroperitoneal space

Question 6

What protects the kidneys?

Answer 6

• They are encapsulated by layers of fascia and firm renal fat

Question 7

Describe the basic internal structure of the kidney

Answer 7

• The outer portion of the kidney is called the cortex
• The cortex extends down between medullary pyramids
• The pyramids project into a minor calyx (calyces for plural)
• The minor calyces converge into major calyces, which form the renal pelvis at the hilum
• The renal pelvis becomes the ureter

Question 8

What is the functional unit of the kidney?

Where are they located?

Answer 8

• The functional unit of the kidney is called a nephron
• Nephrons are found in the medullary pyramids

Question 9

Describe the basic structure of a nephron?

Answer 9

• The renal corpuscle (glomerulus) is in the bowman’s capsule, and is where the blood supply comes in
• Then it moves into the proximal convoluted tubule
• Then into The loop of Henle, which is closely related to circulation, and is important when determining the concentration of urine.
• This then moves into the distal convoluted tubule which them moves into a collecting duct (where a number of nephrons merge together).

Question 10

How does the structure of the collecting duct change?

Answer 10

• It increases in size

Question 11

Name the two different types of nephrons and describe them

Answer 11

• Juxtamedullary nephron
• Located in the inner cortex
• This is designed to concentrate and dilute urine
• They have long nephron loops
• The superficial nephron
• Located in outer cortex
• They reabsorb a large volume of fluid that is filtered from vasculature
• Short nephron loops

Question 12

Describe the general location of the ureter in females

Answer 12

• Females - posterior to ovary, lateral to cervix and anterior to the womb

Question 13

Describe the general location of the ureter in men

Answer 13

• Superior to the bladder.

Question 14

Describe the basic structure of the ureter

How does it propel urine downwards?

How does it stop urine from refluxing?

Answer 14

• It is muscular and uses peristaltic waves to propel urine downwards
• It also contains a one-way valve to prevent urine reflux into the ureter once in the bladder

Question 15

What is the bladder made from?

How is the bladder filled?

How is the bladder emptied?

What is the bladder lined by?

Answer 15

• It is made of smooth muscle
• It is filled by relaxation of its muscular wall (the detrusor muscle)
• It is emptied by the contraction of the detrusor muscle, which is aided by raising intra-abdominal pressure.
• Lines by urothelium (transition epithelium)

Question 16

What is the glomerulus of the kidney?

Answer 16

• It is a cluster of capillaries where filtration occurs.

Question 17

Where does the filtration process occur?

How does it occur?

What are starlings forces?

Why allows/prevents small/large molecules moving into the bowman’s capsule.

Answer 17

• Blood enters the glomerulus in the bowman’s capsule, where it is filtered
• There is net flow out of filtrate in the glomerulus to the bowman’s capsule, as the hydrostatic pressure is higher than the oncotic pressure in the capillaries of the glomeruli.
• The hydrostatic and oncotic pressure are referred to as Starling’s forces
• The glomerular capillaries have endothelial cells which are fenestrated
• There is a basement membrane, then filtration slits between podocytes
• These filtration slits and fenestrated capillaries allow small molecules, such as glucose, to move out into the bowman’s capsule, while large molecules are kept in the blood.

Question 18

What is osmolality?

How does osmolality change at different parts of the kidney?

Answer 18

• Osmolality refers to the concentration of dissolved particles, such as sodium and electrolytes, present.
• It ranges from relatively low osmolality from the cortex and outer medulla to high osmolality in the inner medulla (where the loops of henle are located)

Question 19

Give an overview of the reabsorption process.

Answer 19

• Sodium/potassium ATPase creates a sodium gradient and provides energy for transportation.
• Ion transport creates a voltage gradient between the nephron tubule lumen and interstitium of the nephron
• This allows for more movement of substances across the membrane to be reabsorbed into peritubular circulation
• Water follows sodium and is reabsorbed by osmosis.
• Solvent drag means solutes are carried along in the water flow.
• A concentration of solutes is left in the lumen after water reabsorption.

Question 20

Describe how water is reabsorbed as it moves through the proximal convoluted tubule of the nephron

Answer 20

• As filtrate comes down from the proximal convoluted tubule, water is exposed to high osmolality, and is driven out due to the osmotic pressure gradient.

Question 21

What prevents water from being absorbed in the nephron?

Why is this the case?

Answer 21

• The impermeability of the ascending limb of the loop prevents water from re-entering and diluting its contents.
• Dilution would collapse the gradient that drives sodium diffusion out of the nephron (generated by Na/K ATPase)

Question 22

What is the type of epithelium that lines the proximal convoluted tubules?

What 2 features does it have and why?

What is the epithelium in the lumen of the loops of henle?

What is the epithelium in the lumen of the distal convoluted tubules?

Answer 22

• it is simple cuboidal epithelium
• They have apical microvilli, which increases surface area
• The tight junctions between cells are leaky, so they maximise free flow of water and dissolved solutes
• the loops of henle contain simple squamous epithelium.
• the distal convoluted tube contains simple cuboidal epithelium, with few microvilli

Question 23

What controls the outflow of urine via the urethra

what are they controlled by?

Answer 23

• Inner and outer sphincters control outflow of the urine from the urethra
• The inner sphincter and bladder contraction is controlled by spinal reflexes and the CNS.
• The outer sphincter is under voluntary control.

Question 24

What does filling of the bladder cause?

Answer 24

• Urine filling the bladder causes the muscular wall to stretch, which initiates a spinal micturition reflex.
• This reflex causes the parasympathetic motor efferents to stimulate bladder contraction

Question 25

What prevents you from urinating?

Answer 25

* The central nervous system prevents urination. * The bladder will only empty when the outer sphincter is voluntarily relaxed