Urinary System

What is the functional unit of the kidney?

The nephron

What is the main job of a nephron?

To filter blood, reabsorb needed substances, secrete wastes, and produce urine

What are the three main processes performed by nephrons?

Filtration, Reabsorption, Secretion

Besides making urine, what three additional functions do nephrons perform?

Help regulate blood pressure by producing renin, Stimulate red blood cell production through erythropoietin (EPO), Activate vitamin D (calcitriol) to increase calcium absorption

What two structures make up the renal corpuscle?

Glomerulus, Bowman's (glomerular) capsule

What is the glomerulus?

A tuft of high-pressure capillaries where blood filtration begins

What is Bowman's capsule?

A cup-shaped structure that surrounds the glomerulus and collects the filtrate

Where does the filtrate go after Bowman's capsule?

Into the proximal convoluted tubule (PCT)

What are podocytes?

Specialized cells that wrap around glomerular capillaries

What are pedicels?

Finger-like extensions of podocytes

What are filtration slits?

Small openings between pedicels that allow filtration

What three structures make up the filtration membrane?

Fenestrated capillary endothelium, Basement membrane, Podocyte filtration slits

What can pass through the filtration membrane?

Water, ions, glucose, amino acids, and small molecules

What cannot pass through the filtration membrane?

Blood cells and large proteins

Why are negatively charged proteins usually not filtered?

The filtration membrane is negatively charged and repels them

What are mesangial cells?

Cells that contract to help regulate the glomerular filtration rate (GFR)

What is the juxtaglomerular apparatus (JGA)?

A structure that helps regulate kidney filtration and blood pressure

Which two cell types make up the JGA?

Macula densa cells, Juxtaglomerular cells

Where is the macula densa located?

In the wall of the distal convoluted tubule (DCT)

What does the macula densa monitor?

Sodium concentration and fluid flow in the DCT

What chemicals are released by the macula densa?

ATP and adenosine

Where are juxtaglomerular cells found?

In the wall of the afferent arteriole

What hormone do juxtaglomerular cells release?

Renin

What enzyme is released by juxtaglomerular cells?

Renin

What does renin convert?

Angiotensinogen into angiotensin I

Which enzyme converts angiotensin I into angiotensin II?

Angiotensin-converting enzyme (ACE)

Where is ACE mainly found?

In the lungs

What does angiotensin II do?

Constricts blood vessels, Raises blood pressure, Stimulates aldosterone release

What hormone is released from the adrenal cortex because of angiotensin II?

Aldosterone

What does aldosterone do in the kidneys?

Increases sodium reabsorption, causing more water retention and increasing blood pressure

What type of cells line the PCT?

Simple cuboidal epithelial cells with microvilli

Why does the PCT have microvilli?

To increase surface area for absorption

Why do PCT cells contain many mitochondria?

They need ATP for active transport

What are the two major parts of the loop of Henle?

Descending limb, Ascending limb

What type of epithelium lines the thin portions of the loop of Henle?

Simple squamous epithelium

What type of epithelium lines the thick portions of the loop of Henle?

Simple cuboidal epithelium

How does the DCT compare to the PCT?

It is shorter, has fewer microvilli, but still contains many mitochondria for active transport

Are collecting ducts technically part of the nephron?

No. They collect filtrate from several nephrons

What hormone acts on the collecting ducts?

Antidiuretic hormone (ADH)

What are aquaporins?

Water channel proteins that allow water to move through cell membranes

What happens when ADH is present?

Aquaporins are inserted into collecting duct cells, increasing water reabsorption and producing concentrated urine

What happens when ADH is absent?

Fewer aquaporins are present, so less water is reabsorbed and more dilute urine is produced