kidneys

What makes up the Filtration Membrane?

The endothelium and visceral layer of the glomerulus

Describe the endothelium of the glomerulus.

The endothelium of the glomerulus is fenestrated.

What does it mean that the endothelium of the glomerulus is fenestrated?

This means that there are pores in the endothelium that allow smaller substances to be filtered out of the blood, while restricting the passage of larger structures, such as proteins, platelets, and blood cells.

What is the visceral layer of the glomerulus made of?

Podocytes. Podocytes have long foot-like extensions called pedicles that wrap around the glomerular capillaries.

What are pedicles separated by?

Thin slits called filtration slits. These filtration slits restrict the passage of most small proteins.

What must substances pass through to enter the capsular space?

BOTH the fenestrated epithelium and the filtration slits of the visceral layer.

Why is blood entering the glomerulus from the afferent arteriole at high pressure important?

This high pressure will force substances from the blood, through the filtration membrane.

Why is the glomerulus designed to be leaky?

Via the fenestrated endothelium it will allow the passage of some plasma and solutes

What do the filtration slits between the podocytes allow?

Further passage of solutes into the capsular space.

Why is the filtrate require modification to reabsorb the wanted substances and secrete the unwanted substances?

This process is non-specific, thus the filtrate will require modification to reabsorb the wanted substances and secrete the unwanted substances. Modification begins in the proximal convoluted tubule.

Where does the proximal convoluted tubule (PCT) originate?

At the tubular pole of the renal corpuscle. It is made of simple cuboidal cells with tall microvilli.

What is the function of the tall microvilli in the proximal convoluted tubule (PCT)?

To increase surface area, which increases the reabsorption capacity.

What does a PCT look like when observed at 100x using light microscopy?

The lumen appears fuzzy. The cells also stain very brightly because of the high amount of mitochondria in the cells.

What do the cells of the PCT do?

Actively reabsorb and secrete substances to modify the filtrate

Where does the nephron loop originate?

At the sharp turn of the PCT.

What is the main function of the nephron loop?

To reabsorb ions to further modify the filtrate.

Describe the path of the nephron loop.

The nephron loop descends into the medullary pyramid and then ascends back to the cortex as the distal convoluted tubule.

What are the two types of nephrons?

Cortical nephrons and juxtamedullary nephrons.

Describe cortical nephrons.

85% of the nephrons are cortical nephrons, they are called cortical nephrons because the bulk of the nephron lies in the cortex and their short nephron loop barely penetrates the medulla.

Describe juxtamedullary nephrons.

The remaining 15% are called juxtamedullary nephrons because they lie close to the corticomedullary junction and their long nephron loop extends deep into the medulla

What is the function of cortical vs juxtamedullary nephrons?

Cortical nephrons (85% of all nephrons) mainly perform excretory and regulatory functions, while juxtamedullary nephrons (15% of nephrons) concentrate urine.

Where does the distal convoluted tubule (DCT) originate?

In the cortex at the end of the nephron loop.

Describe the distal convoluted tubule (DCT).

The DCT is composed of simple cuboidal cells with sparse microvilli and sparse mitochondria.

What is the primary function of the DCT?

To actively reabsorb and secrete substances to modify the filtrate

Where does the DCT lead?

The tubular fluid will then leave the DCT and enter the collecting tubules.

What do the efferent arterioles leaving the glomerulus branch into?

Capillaries that surround the tubules and loop

What are the capillaries surrounding the tubules and loop responsible for/doing?

absorbing or secreting substances during the modification process.

Where do the peritubular capillaries reside?

With the convoluted tubules and reside with the cortex.

Where does the vasa recta reside?

Associated with the nephron loop and reside within the medulla.

Where does Tubular fluid travel after leaving the DCT?

Through small collecting tubules that empty into collecting ducts.

Where do the collecting tubules and ducts move?

Through the renal medulla toward the renal papilla.

What can still modify the fluid flowing through the collecting tubules and ducts?

At this point under the influence of antidiuretic hormone (ADH) and aldosterone.

What is ADH and what produces it?

Stands for antidiuretic hormone and is produced by the pituitary gland in response to a decrease in blood volume.

What is aldosterone and what produces it?

A hormone secreted by the adrenal gland and will assist in water retention

What happens when ADH and aldosterone are secreted?

Water and sodium will be reabsorbed back into the bloodstream.