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COT pt. 2 > Lecture: Urinary System > Flashcards

Lecture: Urinary System Flashcards

1
Q

Le Milieu Intérieur

A

Internal environment
Coined by Claude Bernard

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2
Q

Major functions of the urinary system

A

-Excretion of toxins and metabolic by-products
-Homeostasis of major ions
-Homeostasis of blood volume and osmolarity
-Acid-base balance
-Stimulation of erythrocyte production
-Synthesis of vitamin D

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3
Q

What are the functional compartments of the kidney?

A

The medulla (renal pyramid) and the cortex

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4
Q

Renal papilla

A

Where filtrate is collected in channels at the end of the renal medulla

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5
Q

Minor calyx

A

Located at the tip of the renal papilla. Each pyramid corresponds to one minor calyx. They join to form the major calyx

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6
Q

Renal column of Bertin

A

portion between the pyramids

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7
Q

Hilum of the kidney

A

Middle of the kidney where the major renal artery enters and renal vein leaves

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8
Q

What is the functional unit of the kidney? What is it composed of?

A

The nephron is the kidney functional unit. It is composed of a glomerulus and a kidney tubule

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9
Q

Juxtamedullary nephron

A
  • Very long loop of Henle
  • Important for concentrating urine
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10
Q

Cortical nephron

A

Located higher up in cortex

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11
Q

What are the subdivisions of the kidney tubule?

A

Bowman’s capsule, Proximal convoluted, Thick descending, Thin descending and ascending, Thick ascending, Distal convoluted, Collecting duct

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12
Q

Bowman’s capsule

A

receptacle where the network of capillaries of the glomerulus is found.
Like a glove that completely covers the network of capillaries.

Bowman’s capsule is composed of a visceral and a parietal layer
- Visceral layer is composed of epithelial cells known as podocytes
- Parietal layer is composed of squamous epithelial cells (continuous with proximal convoluted)

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13
Q

Proximal convoluted tubule

A
  • Exclusively found in the cortex
  • Similar morphology to the thick descending limb
  • Permeable to: glucose, ions, water, and amino acids
  • Reabsorbs the molecules and sends them back to into the circulatory system

The proximal tubule plays a key role in the reabsorption of key nutrients (e.g. glucose; amino-acids, vitamins) and ions. Its brush border (microvilli) increases the surface and absorption area. Cells contain many mitochondria to sustain active transport. The proximal convoluted tubule is very long and is responsible for much of the reabsorption.

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14
Q

Thick descending limb

A
  • Crosses the junction between medulla and cortex
  • Part of the Loop of Henle
  • Similar morphology to the proximal convoluted tubule
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15
Q

Thin ascending limb

A
  • Thin ascending limb is NOT permeable to water
  • No aquaporin channels
  • It has specialized transporters to take out Na+ and Cl-
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16
Q

Thick ascending limb

A
  • Crosses the junction between medulla and cortex
  • Similar morphology to the distal convoluted tubule
  • Part of the Loop of Henle

Contains a large number mitochondria and Na+/K+ ATPases and regulate ion transport (i.e. Na+, Cl-, Ca++)

Morphological feature
* No brush border
Properties
* Impermeable to water
* Permeable to Na+/K+

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17
Q

Distal convoluted tubule

A
  • Only in the cortex
  • Similar morphology to the thick ascending limb
  • Permeable to Ca2+, Na+, and Cl- which flow out

Contains a large number mitochondria and Na+/K+ ATPases and regulate ion transport (i.e. Na+, Cl-, Ca++)

Morphological feature
* No brush border
Properties
* Impermeable to water
* Permeable to Na+/K+

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18
Q

Collecting duct

A
  • Has specialized channels, some of which are permeable to water, others are permeable to ions
  • At this level, transport is regulated by hormones
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19
Q

Why is the tubule very long and convoluted?

A

High surface area in order to maximize exchange

20
Q

ADH/Vasopressin

A

Binds to receptor to increase # of aquaporin channels in collecting duct so that H2O flows out

From Google:
Water balance: ADH helps the kidneys reabsorb water, reducing the amount of urine produced. ADH levels are usually higher at night to prevent urination while sleeping.

21
Q

Peritubular capillaries

A

In cortical nephron: capillaries around the convoluted tubules and the Loop of Henle

In juxtamedullary nephron: capillaries only around the convoluted tubules. Going further down, it becomes vasa recta instead.

22
Q

Vasa recta

A

“straight vessel”
capillaries around the Loop on Henle found ONLY in juxtamedullary nephrons

23
Q

How does the osmolarity of the medulla play a role in urine concentration?

A

The concentration of the medulla goes from 300 mOs (close to blood osmolarity) to 1200 mOs. This high osmolarity allows water to flow out and follow its concentration gradient

24
Q

Thin descending limb

A
  • Part of the Loop of Henle
  • Thin descending limb is permeable to water which flows out following its concentration gradient

Morphological features
- Extremely thin
- Few basal or luminal specializations (no microvilli)
- Not many active processes
Functional properties
- Permeable to water
- Little permeability to Na+
- Allows selective reabsorption of H2O

25
Q

Principal cells

A

Cells of the collecting duct that can re-absorb water and Na+ via the action of hormones (ADH and aldosterone respectively), contributing to control blood volume and blood pressure. Cells have only few and short microvilli

Lecture Notes:
The majority cell termed principal cell responsible for ADH-dependent water resorption through aquaporin receptors

26
Q

Intercalated A and B cells

A

Cells in collecting duct that modulate acid/base balance via H+ and HCO3 exchange. Cells are very rich in mitochondria for intense ion transport.

B cells: specialized to transport bicarbonate ions
A cells: H+ exchange

From Lecture Notes
The minority intercalated cell responsible for acid-base adjustment

27
Q

Renal corpuscle

A

Glomerulus + Bowman’s capsule

28
Q

Glomerulus

A

Big network of capillaries
Has fenestrated endothelium

29
Q

Vascular pole

A

The side of the glomerulus where the afferent and efferent arteries are contained

30
Q

Urinary pole

A

The side of the glomerulus where the ultra-filtrate collects

31
Q

Podocytes

A

Epithelial cells that make up the visceral layer of the Bowman’s capsule

32
Q

Pedicels

A

Finger-like structures formed from podocyte processes.

Pedicels cover the surface of capillaries. Pedicels from two podocytes interdigitate to form filtration slits.

This is done to contribute to the filtration of blood because the space (filtration slits) limit the movement of large molecules from the blood vessels to the urinary space.

Podocyte prevents large molecules from leaving the capillaries and reaching the urinary space.

33
Q

Which structures make up the filtration barrier?

A

The filtration barrier involves:
- endothelial pores
- filtration slits
- glomerular basement membrane (GBM)
- endothelial glycocalyx
- glycocalyx of podocytes

34
Q

Glomerular basement membrane (GBM)

A

The GBM is a fusion of the basal lamina of the endothelial cell and the podocyte

35
Q

The filtration barrier is based on which two criteria?

A

The filtration barrier is based on the size and charge of a molecule.

Several molecules of the filtration barrier are negatively charged:
- Sulfated proteoglycans
- Heparan

The charge barrier is due to negatively charged molecules that cover the podocyte and endothelial cells. Negatively charged molecules are less likely to cross the barrier

36
Q

Mesangial cells

A

3rd cell in glomerulus between the capillary and the podocyte

  • Have a phagocytic activity that contributes to remove cellular debris
  • Are specialized contractile pericytes that
    participate in the structural integrity of glomerular capillaries and contribute to modulate filtration
  • Release growth factors that maintain the integrity of the capillary network
  • Produce the glomerular matrix (or mesangial matrix, which is abnormally expanded in diabetic nephropathy)

Functions as resident macrophage, smooth muscle and fibroblast for the glomerulus

37
Q

What are the three components of the juxtaglomerular apparatus (JGA)?

A
  1. Macula densa
  2. Juxtaglomerular cells
  3. Extraglomerular mesangial cells

From Lecture Notes:
The point of close approximation of the returning distal tubule to its originating glomerulus is the location of structures collectively referred to as the juxtaglomerular apparatus. These structures are important in transmitting signals about the efficiency of filtration. The juxtaglomerular apparatus consists of three structures; one epithelial, one a cell of CT, and one a modified smooth muscle cell.

38
Q

Macula densa

A

The macula densa is a specialized region of the distal convoluted tubule near the vascular pole. (The distal convoluted tubule always circles back next to the Bowman’s capsule)

Macula densa cells detect Na+ levels in the lumen of the distal tubule and signal juxtaglomerular cells to release renin when Na+ is low (indicates a low filtration rate)

Cells of the macula densa also contribute to increase prostaglandins levels via the activity of COX-1 and COX-2 enzymes (also in tubules and medullary interstitial fibroblasts)

From Lecture Notes:
a specialization of about 25 (in humans) of the distal tubule epithelial that are closest to its glomerulus of origin. The macula densa senses salt balance in the filtrate at its apical surface & communicates with the below cell types via paracrine signaling.

39
Q

Juxtaglomerular cells

A

Juxtaglomerular cells are specialized smooth muscle cells in the wall of the afferent (or efferent) arteriole.

Juxtaglomerular cells release renin in response to a decrease in Na+. Renin increases the production of angiotensin II, which increase the reabsorption of Na+ and blood volume.

Have granules that contain renin.

From Lecture Notes:
The last and first few smooth muscle cells in the wall of the afferent and efferent arterioles as they transition to the glomerular capillary. These cells are positioned to control the glomerular filtration rate both directly by changing the diameter of their associated vessel, and indirectly by the secretion of renin, which affects the renin-angiotensin-aldosterone system that controls systemic blood volume and vascular resistance.

40
Q

Extraglomerular mesangial cells

A

Extraglomerular mesangial cells are specialized mesangial cells that release signaling molecules contributing to regulate the glomerular filtration rate (and other functions!)

From Lecture Notes:
The nearby cells in the connective tissue compartment that form a cap over the vascular pole of the glomerulus, and thus sit generally between the other two structures. These cells have numerous poorly understood functions including being a resident macrophage, compartmentalizing the glomerulus, and affecting glomerular perfusion in a manner similar to capillary pericytes.

41
Q

What role does the juxtaglomerular apparatus play?

A

The juxtaglomerular apparatus plays a key role in the modulation of glomerular filtration rate by modulating the caliber of AA and EA

The juxtaglomerular apparatus plays a key role in modulating blood volume and osmolarity by activating the renin-angiotensin system and Na+ transport

42
Q

What is the glomerular filtration rate (GFR)?

A

The rate at which blood is filtered

smaller AA diameter = decreased GFR
smaller EA diameter = increased GFR

43
Q

Prostaglandins

A

Acts on afferent arterioles
Can increase GFR by increasing the dilation of afferent arterioles

Kidney PGs are vasodilatory and can increase renal blood flow and glomerular filtration rate (GFR) by dilating afferent arterioles

44
Q

Angiotensin II

A

Acts on efferent arterioles
Can increase GFR by decreasing the dilation of efferent arterioles

45
Q

Erythropoietin

A

Erythropoietin is released by specialized fibroblasts in response to a decrease in oxygen tension in the renal matrix.

The number of erythropoietin-producing cells increase during hypoxia and at high altitude.

46
Q

Peritubular fibroblasts

A

Peritubular fibroblasts can differentiate into myofibroblasts in stress conditions and this can lead to kidney fibrosis.

CT will start occupying more space at the detriment of the normal function of the kidney which is to filter blood.

47
Q

Renal sinus

A

Between the lobes, and continuous with the hilum is a connective tissue space termed the renal sinus, within which are the first branches of the major vessels, and the distal branches of the ureter, the major calyces (calyx s.) and minor calyces.

COT pt. 2 (11 decks)

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