Introduction to Urinary System

What is the main function of the Urinary System?

To filter out cellular wastes, toxins and excess water or nutrients from the circulatory system.

What is the urinary system involved in and what are its components?

Involved in: fluid balance, electrolyte balance, and excretion of urine.

Components: kidneys, ureters, urinary bladder and urethra

What are the functions of the 2 kidneys?

The kidneys remove urea from the blood through tiny filtering units called nephrons. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

What are the functions of the 2 ureters?

These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys. If urine backs up, or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.

What are the functions of the bladder?

This triangle-shaped, hollow organ is located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.

What are 2 features of the bladder?

• Two sphincter muscles. These circular muscles help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

• Nerves in the bladder. The nerves alert a person when it is time to urinate, or empty the bladder.

What are the functions of the urethra?

This tube allows urine to pass outside the body. The brain signals the bladder muscles to tighten, which squeezes urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax to let urine exit the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.

Where the kidneys located and what do they do?

• Pair of excretory organs lie on the posterior abdominal wall (retroperitoneal organs), on either side of vertebral column.

• Removes waste products of metabolism and excess of

  water & salts from blood and maintains its pH.

• They extend from upper border of 11th thoracic vertebra to the 3rd lumbar vertebra.

Differentiate between the left and right kidneys.

Right kidney is slightly lower than the left due to the presence of liver.

Left kidney is longer and narrower than the right

Describe the 2 poles of the kidneys.

• Upper pole broader, close contact with adrenal gland

• Lower pole pointed

Describe the 2 borders of the kidneys.

• Lateral border is convex

• Medial border is concave, presents hilum

What is the renal hilum?

deep longtitudinal fissure at the central part of the medial border which transmits the vessels, nerves and lymphatics.

• transmits renal vein, renal artery & renal pelvis

What are the 2 surfaces of the kidneys?

• Anterior surface is irregular and convex

• Posterior surface is flat

What are the anterior relations of the right kidney?

- Liver, duodenum

What are the anterior relations of the left kidney?

- Pancreas, stomach, spleen

What are the posterior relations of both kidneys?

- Diaphragm, psoas major, quadratus lumborum and transversus

abdominis muscles

From deep to superficial, what are th 4 coverings of the kidneys and describe them.

• Fibrous capsule - fibrous membrane closely covering the kidney.

• Perirenal fat - layer of adipose tissue outside the fibrous capsule, thick at the

borders

• Renal fascia – dense elastic connective tissue sheath

o It has anterior and posterior layers

o Anterior layer covers the anterior surface

o Posterior layer covers the posterior surface

o Superiorly 2 layers enclose the suprarenal gland & continue with fascia covering inferior

surface of diaphragm

o Inferiorly 2 layers enclose the ureter

• Pararenal fat – layer of fatty tissue lying outside the renal fascia. Thick at the

posterior aspect and lower pole of kidney

What structures are found in the interior of the kidney?

cortex, medulla and renal sinus

What is the renal sinus and what does it contain?

• Renal sinus is the space that has branches of the renal artery, tributaries of renal vein & renal pelvis.

• Renal sinus also contains 2 to 3 major calyces and 10 to 12 minor calyces.

What is the renal pelvis?

• funnel-shaped structure in each kidney that

  is formed at one end by the expanded upper portion of the

  ureter lying in the renal sinus and at the other end by the

  union of the calyces of the kidney.

What is the medulla composed of?

• pyramid shaped structures called renal pyramids.

• Apex of each renal pyramid projects into the minor calyx

Where is the cortex found in the kidney?

• Cortex lies between the renal pyramids and also covers the base of renal pyramids.

What are the renal columns?

• medullary extensions of the renal cortex that extend between renal pyramids towards the renal sinus.

What is the renal lobe?

• The renal lobe is a portion of the kidney consisting of a renal pyramid

and the adjacent renal cortex above it.

How much nephrons are found in the cortex and medulla?

about one (1) million

What are the 2 parts of the nephron?

• Renal corpuscle: is the part of the nephron where blood plasma is filtered

• Renal tubule: is the part of nephron into which the glomerular filtrate passes

What structures are found within the renal corpuscle?

• Glomerulus – network of blood capillaries

• Bowman’s capsule

What are the components which make up the renal tubule?

• PCT

• Loop of Henle

• DCT

Where does the DCT open into?

• Distal convoluted tubules open into the collecting tubules which open

into collecting ducts

Describe and state the function of mesangial cells.

• irregular shaped nuclei (darker than podocyte nuclei)

• help regulate blood flow

• immune defense and repair

What type of cells is found in the outer parietal layers and the inner visceral layer of the Glomerular/Bowman’s Capsule?

• outer parietal layer: flat simple squamous epithelium

• inner visceral layer: complex epithelial cells called podocytes which have a large oval nuclei and wrap around each capillary; form narrow slits that filter blood (result; ultrafiltrate)

What substances are allowed to pass through the filtration slits?

• water, glucose & ionic salts

What substances cannot pass filtration slits?

• large proteins & red blood cells

What does the vascular pole of the Renal corpuscle contain?

• afferent and efferent arterioles which enter & exit the glomerulus

What is the importance of the urinary pole of the Renal corpuscle ?

• where the ultrafiltrate is drained from the capsular/ Bowman’s space

What is the function of the PCT? Describe the PCT.

• reabsorbs organic nutrients, proteins, water and electrolytes

• secretes anions and cations e.g. Hydrogen & ammonium

• has long microvilli & the cytoplasm is more eosinophilic then DCT and collecting duct.

• it has a star shaped lumen

Describe the Loop of Henle.

composed of:

• simple cuboidal or columnar epithelial cells

• long microvilli

• dark pink/ eosinophilic cytoplasm

• has thick descending (proximal straight tubule) limb, thick ascending lim (distal straight tubule) & think descending and ascending limbs

Describe the distal straight tubule (thick ascending limb).

• reabsorb electrolytes (e.g. Na+, K+, Cl-)

• simple cuboidal epithelial cells

• indistinct borders between cells

• neutral staining (noticeably lighter stain/ colour)

describe the think descending and ascending limbs.

• simple squamous epithelium (passively reabsorbs water)

What is the macula densa?

• junction between the thick ascending limb & DCT

• tightly packed cells which faces the arterioles

• prominent nuclei & taller cell bodies

• detect NaCl levels within the tubule (trigger autoregulatory responses to maintain normal blood pressure & blood volume)

Describe the DCT.

• lighter stained

• shorter microvilli

• reabsorb Na+ & Cl- (makes urine hypotonic)

• very similar to PCT - has simple cuboidal epithelium, shorter than those of Proximal convoluted tubule.

Describe the collecting ducts.

• drains urine from the nephron into the minor calyx

• simple cuboidal & columnar epithelial cells that have well dfeined borders

• lightly stained

• reabsorbs water

• secrete or absorb various electrolytes

Describe the arterial supply of the kidneys.

• Renal artery from abdominal aorta

• Accessory renal arteries are present in 30% of the individuals.

• At the hilus renal artery divides into anterior & posterior divisions which later divide into segmental arteries.

• The segmental arteries are end arteries and supply vascular segments of the kidney

• Segmental artery divides into lobar arteries

• Lobar artery divides into interlobar arteries

• Interlobar arteries divide into arcuate arteries which give interlobular arteries (cortical radiate arteries)

• Afferent arterioles for glomerulus arise from interlobular arteries (cortical radiate arteries)

What is the venous drainage of the kidneys?

• Renal vein – drain into inferior vena cava

What is the lymphatic drainage of the kidneys?

• Lateral aortic lymph nodes

What is the nerve supply of the kidneys?

• By renal plexus composed of sympathetic & parasympathetic

• Sympathetic fibers are derived from T10-L1 and are vasomotor

• Parasympathetic are derived from vagus

What is the importance of the juxtaglomerular complex & cells?

• sense low sodium & chloride levels

• They secrete renin which increases Na+ reabsorption,

  increases blood volume, increases constriction of blood

  vessels, increases blood pressure