BIOL42A Fall 2025 Lectures 29-31

Renal

Renal System

Kidneys

Ureter

Bladder • 400 to 600mL

Urethra

_____ kidney lies superior to _____ kidney

left; right

superior surface capped by _____ gland

adrenal

Position is maintained by

• overlying peritoneum

• contact with adjacent visceral organs

• supporting connective tissues

Renal System Functions

• Remove waste from the blood - Nephrons

• Maintain water balance in the body - Nephrons

• Maintain ion balance in the body - Nephrons

• Produce erythropoietin (stimulates red blood cell formation)

• Produce 1,25-(OH)2Dihydroxycholecalciferol (active hormonal form of vitamin D) in response to PTH, promotes absorption of Ca2+ from intestine

Dehydration: Low Blood Volume Means _____

Low Blood Pressure

Most Oxygen is transported through blood in _____

Erythrocytes (Red Blood Cells)

What are nephrons?

The functional units of the kidney

Where are nephrons located in?

cortex and medulla of kidney

Where do nephrons drain into?

renal pelvis

About how many nephrons are there?

~1 million

What does each nephron consist of?

A renal corpuscle, which contains the glomerulus (which is a tuft of capillaries) and a renal tubule

What does the renal tube (nephron) do?

form a cup shape around the glomerulus called the glomerular capsule (Bowman’s capsule).

Juxtamedullary Nephrons

• Long loop of Henle

• Involved in the concentration of urine

•Found at the border between the cortex and medulla

• About 15% of all nephrons are in this category

Cortical Nephrons

• Most nephrons are in this category

• Short loop of Henle

Three processes leading to urine formation

1. Glomerular filtration

2. Tubular secretion

3. Tubular reabsorption

Blood Filtration at Bowman’s Capsule - A

Blood flows into the glomerulus through the afferent arterioles and leaves the glomerulus through the efferent arterioles. This proximal tube exits Bowman’s capsule.

Blood Filtration at Bowman’s Capsule - B

Podocytes of Bowman’s capsule surround the capillaries. Filtration slits between the podocytes allow fluid to pass into Bowman’s capsule. The glomerulus is composed of capillary endothelium that is fenestrated. Surrounding the endothelial cells is a basement membrane

Blood Filtration at Bowman’s Capsule - C

Substances in the blood are filtered through capillary pores between endothelial cells (single layer). The filtrate then passes along the basement membrane and through filtration slit between the foot processes (also called pedicels) and enters the capsular space. From here, the filtrate is transported to the lumen of the proximal convoluted tubule.

Forces favoring filtration

Glomerular capillary blood pressure (60 mmHg)

Forces opposing filtration

Fluid pressure in Bowman’s Space (15 mmHg) and Osmotic force due to protein in plasma (29 mmHg)