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Urinary System Anatomy – outline notes

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Urinary System Anatomy

The urinary system consists of two kidneys, two ureters, one bladder, and one urethra.  The kidneys process blood to produce urine.  Urine contains water, nitrogenous wastes, foreign substances, excess ions, etc.  The urine is carried from the kidneys to the bladder via the ureters.  Urine is stored in the bladder until discharged to the external world by the urethra.  The components of urine reflect how the kidneys function in water and electrolyte balance, pH balance, and excretion.  Other functions of the kidneys include the production of renin, the production of erythropoietin, and the formation of active vitamin D.

I. Gross Anatomy of the Urinary System
A. Abdominal Cavity
1. Two Kidneys
2. Two Ureters
B. Pelvic Cavity
1. One Urinary Bladder
2. One Urethra

II. Kidney – Location and External Anatomy
A. Retroperitoneal @ T-12 thru L-3
B. Surrounded by three layers of tissue
1.  Renal capsule (fibrous tunic) – fibrous C.T.
2.  Adipose capsule – adipose tissue
3.  Renal fascia – collagenous fibers anchoring kidney to
surrounding structures
C. Shape – “bean-like”
1. convex on lateral surface
2. concave on medial surface
3. Hilus – prominent medial indentation
a) Renal artery and renal nerves enter
b) Vascular – Renal vein and ureter exits

III. Kidney Internal Anatomy
A. Renal Sinus – centrally located space within the kidney through which all
the “plumbing” runs
B. Renal Cortex
1. outer region of flesh
2. reddish brown, granular appearance

C. Renal Medulla
1. inner region of flesh
2. striped appearance due to urine collecting ducts
3. Renal (Medullary) Pyramids – cone shaped structures
a) Papilla – apex of pyramid
b) Calyx – cup-like structures that receive urine
1) Minor and Major Calyces    D. Renal columns – granular tissue separating pyramids
E. Lobe = Renal pyramid + (its “cap” of cortical tissue + adjacent tissue
of the renal columns)

IV. Nephron = Renal Corpuscle + Renal Tubule
A. One million / kidney
B. functional units of kidney
C. processes blood to produce a filtrate; modifies filtrate to produce urine
D. Renal Corpuscle
1. Glomerulus – ball of capillaries
2. Bowman’s Capsule
a) visceral layer – specialized epithelial cells, podocytes,
cling tightly to glomerular capillaries
b) parietal layer – simple squamous epithelium that lines
E. Renal Tubule
1. Proximal Convoluted Tubule
2. Loop of Henle
3. Distal Convoluted Tubule

F. Collecting Ducts
1. Receives tubular fluid from many nephrons
2. Descend into medulla – give medulla striped appearance

V. Flow of Filtrate / Tubular fluid / Urine
The first step of urine formation, which occurs at the renal corpuscle, produces a solution known as filtrate.  The filtrate becomes known as tubular fluid as it travels through the tubules within the kidney.  Finally, urine is delivered to the minor calyx via the renal papilla.  Trace the flow through the urinary system.

Bowman’s Capsule — proximal convoluted tubule — loop of Henle — distal convoluted tubule — collecting duct — renal papilla — minor calyx — major calyx — renal pelvis — ureter — urinary bladder — urethra

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VI. Blood Supply to Kidney
The kidneys are highly vascularized organs.  They receive about 25% of the cardiac output from the heart.  Urine formation involves the processing of blood by nephrons.  Trace the following sequence of vessels through the kidneys to the nephrons.  Note the specialized vessels that are actively involved with the processing of blood.  Then trace the vessels that carry processed blood away from the nephrons and out of the kidneys.

Abdominal Aorta — renal artery — segmental arteries — interlobar arteries — arcuate arteries — interlobular arteries — afferent arterioles — **glomerulus — efferent arterioles — **peritubular capillaries — interlobular veins — arcuate veins — interlobar veins — segmental veins — renal vein — inferior vena cava
** vessels where EXCHANGE occurs

VII. Kidney – Histology
A. Cortex
1. Renal Corpuscle
a) Bowman’s Capsule
1) parietal layer – simple squamous epithelium
b) Glomerulus
2) covered with visceral layer epithelium (podocytes)
2. Proximal Convoluted Tubules (PCT) and Distal Convoluted
Tubules (DCT)
a) Simple Cuboidal Epithelium
b) DCT differs from PCT in sectional view
1) DCT has a smaller diameter
2) Epithelial cells of DCT lack microvilli (gives DCT a
cleaner border and lumen)
B. Medulla
1. Collecting ducts – simple cuboidal epithelium

VIII. Bladder – Anatomy and Histology
A. Three Tissue layers
1. Mucosa
a) transitional epithelium
b) lamina propria – loose connective tissue
2. Muscular – smooth muscle
a) detrusor muscle
3. Adventitia – fibrous connective tissue
a) Serosa (mesothelium) present on superior surface
B. Empty bladder exhibits rugae
C. Two sphincter muscles
1. internal – smooth muscle; Autonomic Nervous System control
2. external – skeletal muscle; voluntary control

D. Trigone – triangular region bounded by ureteral openings and the entrance of the urethra

IX. Urethra – Anatomy
A. Three regions of a male urethra
1. prostatic urethra
2. membranous urethra
3. penile or spongy urethra

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