Lecture 25: Urinary System

Question 1

Be able to label slide 4

Answer 1

Do it!

Question 2

What is the function of the kidney

Briefly describe the kidneys anatomy

Answer 2

Kidney functions:

• removal of toxins, metabolic wastes, and excess ions from the blood
• regulation of blood volume, chemical composition, and pH

Kidney anatomy:

• Retoperitoneal, in the superior lumbar region
• right kidney is found lower than the left
• renal hilum leads to the renal sinus
• ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilum

Question 3

Describe the internal anatomy of the kidney

Answer 3

Renal cortex: a granular superficial region
Renal medulla: the cone-shaped medullary pyramids separated by renal columns
Lobe: a medullary pyramid and its surrounding cortical tissue
Papilla: tip of pyramid; releases urine into minor calyx
Renal pelvis: the funnel shaped tube within the renal sinus
Major calyces: the branching channels of the renal pelvis that
-collect urine from minor calyces
-empty urine into the pelvis
Urine flows from the pelvis to ureter

Question 4

Be able to label the diagram own slide 8

Answer 4

Do it!

Question 5

What is the kidneys blood supply and nerve supply come from?

Answer 5

• Renal arteries deliver 1/4 of cardiac output to the kidneys each minute
• nerve supply is via sympathetic fibres from renal plexus

Question 6

List the pathway of blood through the renal blood vessels

Answer 6

Aorta- renal artery- afferent arteriole- glomerulus- efferent arteriole- peritubular capillaries and vasa recta- renal vein -inferior vena cava

Question 7

What are the nephrons?

Answer 7

The structural and functional units that form urine
Has two main parts:
1. Glomerulus: a tuft of capillaries
2. Renal tubule: begins as cup-shaped glomerular (bowmans) capsule surrounding the glomerulus
Renal corpuscle
-glomerulus + its glomerular capsule
Fenestrated glomerular endothelium
-allows filtrate to pass from plasma into the glomerular capsule

Question 8

Nephron capillary beds

Answer 8

1. Glomerulus
   - blood pressure is high because afferent arterioles are smaller in diameter than efferent arterioles.
2. Peritubular capillaries
   - low-pressure, porous capillaries adapted for absorption
   - arise from efferent arterioles
   - empty into venules
3. Vasa recta
   - long vessels parallel to long loops of Henle
   - arise from efferent arterioles of juxtamedullary nephrons
   - function information of concentrated urine

Question 9

What are the extrinsic controls of the urinary system?

Answer 9

The sympathetic nervous system
Under normal conditions at rest
-renal blood vessels are dilated
Under extreme stress
-norepinephrine is released by the sympathetic nervous system
-epinephrine is released by the adrenal medulla
-both cause constriction of afferent arterioles, inhibiting filtration

Question 10

What are the physical characteristics of urine?

Answer 10

Colour and transparency
-clear, pale to deep yellow (due to urochrome)
-drugs, vitamins supplements, and diet alter the colour
-cloudy urine may indicate a urinary tract infection
Odor:
-slightly aromatic when fresh
-develops ammonia odor upon standing
-may be altered by some drugs and vegetables

pH
-slightly acidic (ranges from 4.5-8)
-diet, prolonged vomiting, or urinary tract infections may alter pH
95% water and 5%,solutes
Nitrogenous wastes: urea, uric acid, and creatinine

Question 11

Ureters

Answer 11

Brings urine from kidneys to bladder
Retroperitoneal
Enter the base of the bladder through the posterior wall at the trigone
-as bladder pressure increases, distal ends of the ureters close, preventing backfow of urine
Three layers of wall of ureter:
1. Lining of transitional epithelium
2. Smooth muscle muscularis
-contracts in response to stretch
3. Outer adventits of fibrous connective tissue

Question 12

Urinary bladder

Answer 12

Muscular sac for temporary storage of urine
Retoperitoneal, on pelvic floor posterior to pubic symphysis
Males-prostate gland surrounds the neck inferiorly
Females- anterior to the vagina and uterus
Trigone
-smooth rectangular area outlines by the openings for the ureters and the urethra
-infections tend to persist in this region
Layers of the bladder wall:
1. Transitional epithelial mucosa
2. Thick detrusor muscle (3 layers of smooth muscle)
3. Fibrous adventitia (peritoneum on superior face only)
Collapses when empty
Expands and rises superiorly during filling without significant rise in internal pressure

Question 13

Urethra

Answer 13

Muscular tube
Sphincters
Internal urethral sphincter
-involuntary (smooth muscle) at bladder-urethra junction
-contracts to open
External urethral sphincter
-voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor
Female urethra: (3-4cm)
-tightly bound t the anterior vaginal wall
-external urethral orifice is anterior to the vaginal opening, postior to the clitoris
Male urethra:
-carries semen and urine
Three named regions:
1. Prostatic urethra (2.5cm)-within prostate gland
2. Membranous urethra (2cm)-passes through the urogenital diaphragm
3. Spongy urethra (15cm) -passes through the lens and opens via the external urethral orifice
Be able to label both female and male!

Question 14

Micturition

Answer 14

Urinating or voiding
Three simultaneous events
1. Contraction of detrusor muscle by ANS
2. Opening of internal urethral sphincter by ANS
3. Opening of external urethral sphincter by somatic nervous system
Reflexive urination (urination in infants)
-distension of bladder activates stretch receptors
-excitation of parasympathetic neurons in reflex center in sacral region of spinal cord
-contraction of the detrusor muscle
-contraction (opening) of internal sphincter
-inhibition of somatic pathways to external sphincter, allowing its relaxation (opening)

Question 15

Micturition

Pontine control centres nature between ages 2 and 3

Answer 15

1. Pontid storage centre inhibits micturition:
   - inhibits parasympathetic pathways
   - excites sympathetic and somatic efferent pathways
2. Pontine micturition centre promotes micturition:
   - excites parasympathetic pathways
   - inhibits sympathetic and somatic efferent pathways