Urinary System

Explain the blood flow of the kidneys. (Simple)

1. Arteries carry blood away from the heart 2. Blood arrives via the renal artery. 3. Branching vessels carry blood through medullar into cortex 4. Blood is filtered 5. Branching vessels carry filtered blood down and out the renal vein 6.Urine drains into the renal pelvis 7.Urine exits via ureter.

What are the other mechanisms of urine filtration besides filtering? Why are these other steps needed? COMPLICATED

1. Filtration- solutes and fluids are forced out of the glomerulus (globe-shaped capillary bed in the renal corpuscle) and into the glomerular (Bowman's capsule). Bowman's capsule is a sac that captures the fluid, which we now call filtrate (no longer blood, but not yet urine). Together, the glomerulus and the capsule are called the Renal Corpuscle. 2. Reabsorption (happens in Renal Tubule) - 99% of the filtrate is reabsorbed, including water, salts, sugar, plasma proteins from blood. Reabsorption occurs in these structures: Proximal convoluted tubule (PCT), Loop of Henle (nephron loop), Distal convoluted tubule (DCT), collecting duct. Reabosrbed substances go back to where they came from (the blood). Capillaries originate from the efferent arteriole, peritubular capillaries reabsorb throughout most of the nephron, vasa recta reabsorbs in the Loop of Henle, capillaries drain into venules. 3. Secretion-despite the filtration process, there are still wastes in the blood that must be removed. This occurs primarily in the Distral Convoluted Tubule (DCT). Ammonia, drugs, acids, and other solutes exit the capillaries and move into the filtrate.

Why do we say "filtering blood is more than just filtering"? (What are the other mechanisms of urine filtration besides filtering? Why are these other steps needed?) SIMPLY

1.Filtration- The capillaries in the kidneys filter the blood. (They keep large items in the blood (RBC), they let out the metabolic wastes, they also let out good stuff like water, salts, and sugar). 2.Reabsorption-Because of inefficient filtration process, we not must reabsorb all the good stuff that was lost. (Downstream capillaries wrap around the renal tubule, good stuff moves back into the blood). 3.Secretion- Surprisingly, the overzealous filtration process missed some of the wastes. (While reabsorption occurs, the downstream capillaries are in a convenient position to secrete more wastes into the renal tubule.)

What is a nephron? Where are they found in the kidney? What are the two kinds of nephron? What are the two main parts of a nephron?

A nephron is the functional unit of the kidney. Each kidney contains 1 million. Nephrone is made up of renal corpuscle ("Little Body") and renal tubule. There are two types Cortical: Mainly in cortex and Juxta-medullary: Extend deep into medulla.

Describe the gross anatomy of the kidneys.

Bean-shaped, reddish-brown, paired organs. They are retroperitoneal (behind serous membrane) in superior lumbar region. Right kidney is lower than left cause liver takes up tons of space. 3 coverings: Renal Capsule, Adipose Capsule, Renal Fascia.

Why are females more prone to UTI's?

Because their urethra is shorter then men.

Describe the urethra.

Carriers urine from bladder to urethral orifice. Has mucosa lining made up of transitional epithelium at superior end of tube, but at the hole/inferior end there is stratified squamous epithelium to keep out bacteria and debris.

What does the hypothalamus have to do with the collecting ducts of the kidney?

It responds to Antidiuretic Hormone (ADH). In the presence of ADH it opens aquaporins to release (reabsorb) water. Aquaporins may close, if: you are well hydrated, ADH secretion is inhibited by diuretics.

Describe the structure and function of the "JGA".

Juxtaglomerular Complex/Apparatus (JGA). This region between the DCT and the afferent arteriole. It regulates the rate of filtration and blood pressure. Juxtaglomerular cells: are smooth muscle cells along the afferent arteriole that monitor blood pressure. Macula Densa: ("dense spot") cluster of cells made of columnar cells in the DCT that monitor solute concentration of filtrate. Mesangial Cells: occupy space between afferent and efferent arteriole, the function if unclear.

Describe the difference in urethra's between men and women.

Men Three regions: Prostatic urethra, membranous urethra, spongy(penile) urethra. About 20cm when penis is not erect, carries both urine and sperm. Women No separate regions, only 4cm long, more prone to bacterial infection. (More prone to UTI's!!!!)

Explain the Distal Convoluted tubule (DCT).

No microvilli, some reabsorption, primarily involved in secretion.

What is filtrate? Where is it formed? When and where does it become urine?

Once the filtrate drips from the renal papilla into the minor calyx, we have made urine. -You start with "dirty blood". -You filter blood to make filtrate. 99% of filtrate shouldn't be in there. You need to push more waste product into filtrate. -Once you modify filtrate through reabsorption and secretion processes then it's called urine. -Blood is not clean and can exit the kidney.

What is pee? What primary waste product is in pee? Also, what is poop?

Pee is metabolic wastes excreted by the kidneys. Consists of Urea and Uric Acid. Urea is a primary by-product of protein catabolism in humans. Ammonia (very toxic) combines with carbon dioxide and water to produce non-toxic urea. Uric Acid is another by-product that is more energetically-expensive to synthesize. Humans don't make much but Birds do!

Describe the bladder.

Stores urine, has three layers: Mucosa (made of transitional epithelium), detrusor muscle, adventitia). Rugae and transitional epithelium allow expansion. There are stretch receptors in trigone area that sense stretch. They are stimulated at about 8 oz of urine. At 2-5 years a reflex action occurs and bladder will start to push and sphincters will open without your control, but can be controlled with potty training. Detrusor and internal sphincter is involuntary, when we're "ready". External urinary sphincter (in urethra) is voluntary.

Explain the Loop of Henle.

The Loop Of Henle (aka nephron loop), is composed of descending limb and ascending limb, supports the PCT's efforts, especially reabsorbing water and salt.

Explain The Proximal Convoluted Tubule.

The Proximal Convoluted Tubule (PCT) has simple cuboidal epithelium, is lined with microvilli (reabsorption), and is the primary reabsorption center especially for organic nutrients like water, salt, glucose.

Why is there a difference size between the afferent and efferent arteriole?

There's a lot of blood coming in. So the high pressure keeps the blood moving, causing water, salts, sugars, vitamins, and urea, to pour out of capillary bed.

Describe the ureter.

They drain urine from renal pelvises in the kidney. The ureter was three layers: mucosa (made of transitional epithelium), muscularis, and adventitia). Peristalsis and gravity moves urine down the ureter. They drain into the back of bladder.

What is the function of the urinary system? What is a major organ?

To remove nitrogenous wastes created by cellular metabolism from the body. Kidneys are the primary urinary organs, they filter the blood to produce urine. The urinary system also has homeostatic effects and other effects (cause eyrthropoiesis, activate vitamin D)

Explain the collecting duct.

not part of the nephron, the collecting duct transports filtrate from many nephrons to the renal papillae. It responds to Antidiuretic Hormone (ADH). In the presence of ADH it opens aquaporins to release (reabsorb) water. Aquaporins may close, if: you are well hydrated, ADH secretion is inhibited by diuretics.