UNC BIOL252 Final Exam Study Guide

Urinary system, digestive system, reproductive system

Kidney Functions

Excretory:

• Filter blood and remove wastes

• Regulate osmolarity of fluids

• Regulate acid-base balance

Cardiovascular:

• Regulate blood volume and blood pressure

Endocrine:

• EPO: stimulates RBC production

• Vitamin D: stimulates Ca²⁺ uptake by the intestines

• Renin: regulates systemic BP and renal blood flow

Nephron

The functional unit of the kidney made of tubules that carry “filtrate”

Nephron Tubules

1. Renal corpuscle

2. Proximal tubule

3. Nephron loop // Loop of Henle (descending & ascending)

4. Distal tubule

5. Collecting duct

Blood Vessels of the Nephron Tubules

1. Afferent arteriole

2. Glomerulus

3. Efferent Arteriole

4. Peritubular capillaries

5. Venule

Afferent arteriole

Supplies blood to the renal corpuscle

Overview of Urinary System:

Filtration: blood plasma (excluding proteins and cells) moves into tubules

Reabsorption: solutes and water are transported out of the tubule, back into the peritubular capillaries

Secretion: solutes are transported into the tubule, removing substances from peritubular capillaries

Urine

the excreted product remaining after filtration, reabsorption, and secretion

Under normal conditions, glucose is filtered and fully reabsorbed. What is the result?

No glucose is found in the urine

If proteins are not filtered, which of the following is false?

Proteins would be abundant in the filtrate

Renal corpuscle

Bowman’s capsule + Glomerulus

Podocyte

highly specialized cells in the kidney's glomerulus that form the inner layer of Bowman's capsule, wrapping around the capillaries to form a critical part of the blood filtration barrier

Glomerulus

a cluster of nerve endings, spores, or small blood vessels, in particular a cluster of capillaries around the end of a kidney tubule, where waste products are filtered from the blood.

Layers of Bowman’s Capsule

1. Parietal layer

2. Capsular space

3. Visceral layer (podocytes)

Filtration slits

narrow gaps between the foot processes of podocytes, which are specialized cells in the kidney's glomerulus. These slits act as a crucial filter that allows water and small molecules like glucose and amino acids to pass from the blood into the Bowman's capsule, while blocking larger molecules such as proteins from leaving the bloodstream

Foot process

a small, foot-like projection from a specialized cell in the kidney called a podocyte. These processes wrap around the glomerular capillaries and, with the spaces between them, create a filtration barrier that allows fluid to pass while blocking larger proteins from entering the urine. 

Filtration membrane

Keeps out large particles (proteins and larger). About 20% of the blood plasma leaves the blood and becomes filtrate.

Proximal tubule

A major site for reabsorption. It has a brush border to enhance the surface area.

Juxtaglomerular apparatus

a specialized structure in the kidney, located where the distal convoluted tubule meets the afferent arteriole of the glomerulus. It is crucial for regulating blood pressure and the rate of glomerular filtration. 

• Macula densa

• “JG” cells

Macula densa

These cells act as sensors, monitoring the sodium chloride concentration in the tubular fluid and playing a crucial role in regulating glomerular filtration rate and blood pressure through a process called the tubuloglomerular feedback mechanism

Juxtaglomerular cells

specialized smooth muscle cells in the walls of the afferent arterioles of the kidney that synthesize and secrete the enzyme renin

Renin

an enzyme secreted by and stored in the kidneys which promotes the production of the protein angiotensin

Net filtration pressure (NFP)

the driving force that determines how much fluid is filtered out of the blood into the Bowman's capsule in the kidney. It is the balance between forces that push fluid out (promoting filtration) and forces that pull fluid back in (opposing filtration).

• glomerular hydrostatic pressure - (capsular hydrostatic pressure + blood colloid osmotic pressure)

• = 10 mm Hg → if it’s reduced, filtration could stop

Normal GFR

125 ml/min or 180 L/day

Normal urine output

1-2 L/day

Glomerular hydrostatic pressure (GHP)

the blood pressure within the glomerular capillaries of the kidneys that pushes fluid and small solutes out of the blood and into the Bowman's capsule, driving the filtration process. This is the main force that opposes capsular hydrostatic pressure and blood colloid osmotic pressure, leading to a net filtration pressure that determines how much fluid is filtered from the blood to form urine

• FAVORS FILTRATION

• = 50 mm Hg

• higher than other two capillaries

Capsular hydrostatic pressure (CHP)

the pressure exerted by the fluid already in the glomerular (Bowman's) capsule that pushes back against the filtration membrane

• OPPOSES FILTRATION

• = 30 mm Hg

Colloid osmotic pressure (COP)

the osmotic pressure exerted by macromolecules, particularly proteins in the blood, that draws water into the capillaries

• OPPOSES FILTRATION

• = 10 mm Hg