Renal System 1 Lecture 23

Question 1

External anatomy of a kidney

Answer 1

Size: 150 grams, size of a bar of soap.
Location: One kidney on each side, embedded in fat for protection.

Question 2

What are the three layers of protection?

Answer 2

Renal Capsule: Outermost layer, providing physical protection and maintaining kidney shape.
Adipose Capsule: Fat layer providing padding and positioning.
Renal Fascia: Anchors kidneys to surrounding structures.

Question 3

Renal Capsule

Answer 3

The outermost protective layer of the kidney, providing structural integrity.

Question 4

Renal Cortex

Answer 4

The outer region of the kidney, lighter in color, containing many nephrons.

Question 5

Blood Vessels

Answer 5

These are crucial for the kidney’s function in filtering blood.

Question 6

Renal Columns

Answer 6

Extensions of the cortex that go deeper into the medulla, separating the renal pyramids.

Question 7

Medullary Pyramid

Answer 7

These pyramid-like structures contain parts of the nephron and are involved in collecting urine.

Question 8

Lobules

Answer 8

Subdivisions within each lobe of the kidney.

Question 9

Interlobar

Answer 9

The regions or structures located between two lobes.

Question 10

Lobe

Answer 10

Each kidney has multiple lobes, usually around 8-12 in humans, made up of a pyramid, surrounding cortex, and renal columns.

Question 11

Nephron

Answer 11

The functional unit of the kidney, where filtration occurs. Each kidney contains about 1 million nephrons.

Question 12

Collecting Duct

Answer 12

Many nephrons feed into each collecting duct, which gathers filtrate (soon to become urine).

Question 13

Papillary Duct

Answer 13

Collecting ducts drain into these ducts at the tip of each renal pyramid.

Question 14

Calyx (Calyces)

Answer 14

Small cup-like structures that collect urine from the papillary ducts. Minor calyces converge into major calyces.

Question 15

Renal Pelvis

Answer 15

A flattened, basin-like region that collects urine from the calyces and leads into the ureter, which transports urine to the bladder.

Question 16

Ureter

Answer 16

Muscular tube that transports urine from the kidney’s renal pelvis to the urinary bladder.

Question 17

Urinary bladder

Answer 17

A hollow, expandable organ that stores urine until it is excreted.

Question 18

Key components of a nephron

Answer 18

Question 19

Renal Corpuscle

Answer 19

This includes the glomerulus (a network of capillaries) and Bowman’s capsule where the filtration of blood begins.

Question 20

Proximal Convoluted Tubule (PCT)

Answer 20

After filtration, the filtrate enters the proximal tubule, where most of the reabsorption of water, ions, and nutrients occurs.

Question 21

Thick Descending Loop of Henle

Answer 21

Part of the nephron that dips into the medulla. It is involved in water reabsorption.

Question 22

Thin Descending Loop of Henle

Answer 22

This segment continues reabsorbing water, helping to concentrate the filtrate.

Question 23

Thick Ascending Loop of Henle

Answer 23

Further reabsorption of salts occurs here without water reabsorption, continuing to dilute the filtrate.

Question 24

Distal Convoluted Tubule (DCT)

Answer 24

This area further adjusts the filtrate by reabsorbing sodium and calcium and is regulated by hormones such as aldosterone and parathyroid hormone.

Question 25

Collecting Duct

Answer 25

This duct collects urine from multiple nephrons, and its permeability to water is regulated by the hormone ADH (antidiuretic hormone). It plays a critical role in determining the final concentration of urine.

Question 26

Blood supply to the nephron

Answer 26

Blood Flow Through the Kidney:
Afferent Arteriole: Brings oxygenated blood into the glomerulus for filtration.
Glomerulus (glomerular capillaries): A network of capillaries where blood is filtered, with larger particles remaining in the blood and smaller substances passing into the nephron.
Efferent Arteriole: Carries blood away from the glomerulus. Unlike most capillary beds, blood in the efferent arteriole remains oxygenated.
Interlobular Artery: Small artery that supplies blood to the nephron.
Arcuate Artery: Supplies blood to the nephron and other structures within the kidney.

After Filtration - Blood Flow in the Nephron:
Peritubular Capillaries (of the cortex): These capillaries surround the proximal and distal convoluted tubules in the cortex. They play a key role in the reabsorption of water, ions, and nutrients from the filtrate back into the blood.
Descending Vasa Recta (arterial): Descends into the medulla, bringing oxygenated blood (relatively O₂-rich) to the deep parts of the kidney.
Peritubular Capillaries (of the medulla): Surrounds the loop of Henle in the medulla, responsible for gas exchange (arterial to venous transition) and further reabsorption of water and salts.
Ascending Vasa Recta (venous): Carries deoxygenated blood (relatively O₂-poor) back towards the cortex and eventually to the interlobular vein.
Arcuate Vein: Collects blood from the nephron and surrounding capillaries, leading to the renal vein.
Interlobular Vein: Receives venous blood from the peritubular capillaries and vasa recta, draining into the arcuate vein.

Question 27

Filtration Membrane within the nephron

Answer 27

Components of the Filtration Membrane:

Fenestration (Pore) of Glomerular Endothelial Cell:
These pores prevent the filtration of blood cells while allowing all components of blood plasma (smaller particles) to pass through. This is the first barrier in the filtration process.

Basal Lamina of Glomerulus:
This layer prevents larger proteins from passing through the membrane. It is the second barrier that helps ensure that only smaller particles can move into the nephron, while larger proteins remain in the bloodstream.

Slit Membrane Between Pedicels:
The podocytes, which are specialized cells of the visceral layer of the Bowman’s capsule, have extensions called pedicels. The spaces between these pedicels are called filtration slits.
The slit membrane across these gaps prevents medium-sized proteins from passing through, acting as the third barrier in filtration.

Question 28

Two main components of the renal corpuscle: the glomerulus and the glomerular (Bowman’s) capsule

Answer 28

Glomerulus:
Endothelium: Specialized network of capillaries.
Input: Afferent arteriole (brings blood to the glomerulus).
Output: Efferent arteriole (takes blood away from the glomerulus).

Glomerular (Bowman’s) capsule:
Visceral Layer: Consists of podocytes, which are modified epithelial cells that closely surround the capillaries in the glomerulus.
Parietal Layer: Made of simple squamous epithelium and forms the outer wall of the capsule.

Question 29

Structure of a renal corpuscle in the kidney

Answer 29

Podocytes (visceral epithelium): These are specialized cells with foot processes that wrap around the capillaries of the glomerulus, playing a crucial role in filtration by forming part of the filtration barrier.
Proximal convoluted tubule: The next part of the nephron that receives the filtered fluid (filtrate) from the glomerulus. It is involved in reabsorbing water, ions, and nutrients.
Capsular/urinary space: The space between the visceral and parietal layers of Bowman’s capsule, where the filtrate collects after passing through the glomerulus.
Afferent arteriole: The blood vessel that brings blood into the glomerulus for filtration.
Efferent arteriole: The blood vessel that carries blood away from the glomerulus after filtration.
Distal convoluted tubule/Thick ascending loop of Henle: A part of the nephron where further ion exchange and filtration adjustments occur.
Endothelial cell: Lines the blood vessels in the glomerulus and forms another part of the filtration barrier.
Parietal epithelium: The outer layer of the Bowman’s capsule, which forms the outer boundary of the renal corpuscle.

Question 30

Components of the glomerular filtration barrier

Answer 30

Fenestrated endothelium (yellow box): The inner lining of glomerular capillaries, containing pores (fenestrations) that allow small molecules and proteins to pass while blocking cells like red blood cells (RBCs).
Basal lamina (blue box): A thick extracellular matrix layer that acts as a physical and charge barrier, filtering out large proteins while permitting smaller ones.
Slit membrane/diaphragm between podocyte foot processes (pink box): A fine mesh-like structure between the foot processes of podocytes, allowing only small molecules (like small proteins) to pass through.

Question 31

What can pass through each part of the filtration barrier?

Answer 31

Cells (like RBCs): Blocked by all three layers (endothelium, basal lamina, slit diaphragm).
Large proteins: Blocked by all three layers, though some large proteins may be partially filtered by the fenestrated endothelium but are stopped by the basal lamina and slit diaphragm.
Medium proteins: Filtered by the fenestrated endothelium but blocked by the basal lamina and slit diaphragm.
Small proteins: These are able to pass through all three layers (endothelium, basal lamina, and slit diaphragm), reaching the urinary space.

Question 32

Venous drainage system of the kidney

Answer 32

Renal vein: This is the main vein through which deoxygenated blood exits the kidney. It collects blood from smaller veins in the kidney and drains it into the inferior vena cava, which then carries the blood to the heart.

Interlobar veins: These veins are found between the renal pyramids and drain blood from the kidney’s outer regions toward the renal vein.

Arcuate veins: These veins run along the border between the cortex and medulla of the kidney. They collect blood from the interlobar veins and eventually lead to the renal vein.

Inferior vena cava: This large vein receives blood from the renal vein and other structures, returning it to the right atrium of the heart.