Case 6: Urinary System

Question 1

Define circulatory shock

Answer 1

condition when blood pressure has fallen to the point where blood flow to tissue can no longer be maintained

Question 2

Functions of the urinary system

Answer 2

1. excretion - removal of organic wastes from body fluids
2. elimination - discharge of these wastes from the environment
3. homeostatic regulation - volume and solute concentration in blood plasma

Question 3

Outline the homeostatic functions of the urinary system

Answer 3

1. Regulating blood volume and blood pressure: by adjusting volume of water lost in urine, releasing erythropoeitin and renin.
2. Regulating plasma concentrations of sodium, potassium, chloride etc. by influencing the quantities lost in urine.
3. Stabilising blood pH: control the amount of H+ ions and bicarbonate ions lost in urine
4. Conserving valuable nutrients: preventing the loss of nutrients but simultaneously eliminating organic wastes (especially urea and uric acid).
5. Assisting the liver by detoxifying poisons and dominate amino acids during starvation.

Question 4

Anatomical position of kidneys

Answer 4

• either side of the vertebral column
• between the muscles of the posterior body wall and parietal peritoneum in a retroperitoneal position
• between T12 and L3
• left kidney = slightly superior
• right kidney displaced by the right lobe of the liver

Question 5

Outline how the position of the kidneys are stabilised

Answer 5

1. Overlying peritoneum
2. Contact with adjacent visceral organs
3. Supporting connective tissue (3 layers)
   a) fibrous capsule: collagen fibre layer that covers the outer surface of the entire organ.
   b) perinephric fat capsule: thick layer of fat tissue that surrounds the fibrous tissue.
   c) renal fascia: fibrous outer layer that anchors the kidneys to the surrounding organs and structures. Posteriorly, the renal fascia fuses with the deep fascia of muscle, and anteriorly it fuses with the peritoneum.

• essentially, each kidney hangs suspended by collagen fibres from the renal fascia and is packed in a soft cushion of adipose tissue.

Question 6

Blood supply and innervation of the kidneys

Answer 6

• each kidney receives blood supply through a renal artery, originating along the lateral surface of the abdominal aorta near the level of the superior mesentery artery.
• as it enters the renal sinus, renal artery provides blood supply to the segmental arteries
• segmental arteries further divide into interlobar arteries. These arteries radiate outwards through the renal columns between the renal pyramids
• interlobar arteries provide blood supply to the arcuate arteries which give rise to numerous cortical radiate arteries (interlobular arteries) which supply the cortical regions of the adjacent renal lobes.
• numerous affarent arterioles branch off each cortical radiate artery. They deliver blood to the capillaries supplying individual nephrons.
• after passing through the capillaries of the nephrons, blood enters a network of venues and smaller veins that merge on the cortical radiate veins. These then deliver blood to the arcuate veins and then the interlobar veins which drain directly into the renal vein (no segmental veins). The renal veins drain into the inferior vena cava.
• kidneys and ureters are innervated by the renal nerves, most of which are sympathetic postganglionic fibres from the celiac plexus and the inferior splanchnic nerves.
• renal nerves enter the kidneys at the hilum and follows the branches of the arteries and each individual nephron.

Question 7

Briefly describe the structure of a juxtaglomerular apparatus

Answer 7

The DCT inserts between the affarent and efferent arterioles. A specialised region of the DCT called the macula densa senses the NaCl concentration in the tubular fluid. Mesangial cells between the DCT and arterioles help constrict the efferent arterioles when required. On the surface of the affarent arteriole, granular cells (juxtaglomerular cells) produce renin.

Question 8

Types of nephrons and how they differ in structure and function

Answer 8

1. cortical nephrons - most abundant. Located nearly entirely on the surface or cortex of the kidney. Nephron loop relatively short. Efferent arteriole deliver blood to a network of peritubular capillaries which surround the entire renal tubule. These capillaries drain into small venues that carry blood to the cortical radiate veins. Perform most of the reabsorptive and secretive functions.
2. juxtaglomerulary nephrons - have long nephron loops and extend deep into the medulla. Peritubular capillaries connected to the vasa recta. Produce concentrated urine.

Question 9

Functions of the renal system

Answer 9

1. water & solute absorption - in PCT
2. active secretion - PCT and DCT
3. regulate final volume and concentration of urine - nephron loops and collective ducts.
4. urine production - maintain homeostasis by a) regulating volume and composition of blood and b) excretion of metabolic waste products (urea, creatine, uric acid)

Question 10

Process of urine formation

Answer 10

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion