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Anatomy and Physiology 2 > Study Guide 25 > Flashcards

Study Guide 25 Flashcards

1
Q

Renal Cortex and Renal Medulla

A

The cortex contains the nephron’s components, including the glomerulus and convoluted tubules, where initial filtration and reabsorption take place.

The medulla contains structures that help concentrate urine, including the nephron loop and collecting ducts.

Together, these areas allow the kidney to produce and adjust urine concentration based on body needs.

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2
Q

Renal Corpuscle:

A

Located in the cortex, the renal corpuscle is where blood filtration begins.

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3
Q

Glomerulus

A

A bundle of capillaries that allows small molecules, water, and waste to pass through while retaining larger molecules (like proteins).

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4
Q

Nephron Tubules

A

The filtered fluid, or filtrate, passes through different tubules within the nephron:

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5
Q

Proximal Convoluted Tubule (PCT):

A

Reabsorbs nutrients, ions, and water back into the bloodstream.

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6
Q

Nephron Loop (Loop of Henle)

A

Extends into the medulla and has descending and ascending limbs. The descending limb allows water to leave, concentrating the filtrate, while the ascending limb is impermeable to water but allows salts to exit, maintaining a concentration gradient.

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7
Q

Distal Convoluted Tubule (DCT):

A

Further adjusts the composition of the filtrate, primarily by secreting ions and reabsorbing water, influenced by hormones like aldosterone and ADH.

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8
Q

Collecting Ducts:

A

Multiple nephrons feed into collecting ducts, which concentrate the urine by reabsorbing water as it travels toward the renal pelvis. ADH controls water reabsorption here, helping to produce concentrated urine when necessary.

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9
Q

Renal Blood Supply:

A

Renal artery → Segmental artery → Interlobar artery → Arcuate artery → Cortical radiate artery → Afferent arteriole → Glomerulus (capillaries) → Efferent arteriole → Peritubular capillaries or vasa recta

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10
Q

Know urine flow from filtration in glomerular corpuscle to urine excretion from urethra

A

Filtration begins in the glomerular corpuscle and proceeds as follows: Renal tubules → Collecting duct → Papilla of pyramid → Minor calyx → Major calyx → Renal pelvis → Ureter → Bladder → Urethra

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11
Q

Structure of the Nephron

A

the kidney’s functional unit, consists of two main parts—the renal corpuscle and the renal tubule—each with specific segments for filtration, reabsorption, and secretion.

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12
Q

Glomerulus

A

A network of capillaries where filtration begins. Blood enters via the afferent arteriole and leaves via the efferent arteriole. The glomerulus has fenestrated (porous) capillaries that allow water and small solutes to pass through.

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13
Q

Bowman’s (Glomerular) Capsule

A

Surrounds the glomerulus and collects the filtrate that exits the glomerulus

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14
Q

Parietal Layer

A

Simple squamous epithelium for structural support.

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15
Q

Visceral Layer

A

Contains specialized cells called podocytes with foot processes that form filtration slits, adding selectivity to the filtration process.

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16
Q

Descending Limb

A

Permeable to water, allowing it to exit into the surrounding medulla, which concentrates the filtrate.

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16
Q

Proximal Convoluted Tubule (PCT):

A

Lined with cells that have microvilli, increasing surface area for reabsorption of water, ions, glucose, and amino acids back into the blood.

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17
Q

Ascending Limb

A

Impermeable to water but permeable to ions (Na+ and Cl-), which are actively transported out, helping to maintain the concentration gradient in the medulla.

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18
Q

Distal Convoluted Tubule (DCT):

A

Involved in further reabsorption and secretion, regulated by hormones (like aldosterone and parathyroid hormone) for ion balance.

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19
Q

Peritubular Capillaries:

A

Surround the PCT and DCT in cortical nephrons, allowing reabsorption of essential nutrients and water back into the bloodstream.

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19
Q

Collecting Duct:

A

Collects filtrate from multiple nephrons and adjusts urine concentration in response to ADH (antidiuretic hormone), which promotes water reabsorption.

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20
Q

Vasa Recta:

A

Specialized capillaries in juxtamedullary nephrons that maintain the osmotic gradient, critical for urine concentration.

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21
Q

Glomerular Filtration Rate

A

is the rate at which the glomeruli filter blood, producing filtrate in the nephron.

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22
Q

Normal GFR

A

is approximately 120-125 mL/min. GFR depends on blood pressure within the glomerulus and is crucial for removing waste while conserving essential nutrients and water. Maintaining a stable GFR is vital for homeostasis,

23
Q

Juxtaglomerular Apparatus (JGA):

A

contains macula densa, granular, and extraglomerular Mesangial cells

24
Q

Macula Densa Cells

A

Found in the wall of the distal tubule, these cells act as chemoreceptors, detecting NaCl concentration in the filtrate. High NaCl concentration suggests an elevated GFR, while low NaCl indicates a decreased GFR.

25
Q

Granular (Juxtaglomerular) Cells

A

Located in the afferent arteriole, they are mechanoreceptors that detect blood pressure changes. When blood pressure drops, they release renin, an enzyme that activates the renin-angiotensin-aldosterone system (RAAS) to increase blood pressure and GFR.

26
Q

Extraglomerular Mesangial Cells

A

Positioned between the afferent and efferent arterioles, they facilitate communication between macula densa and granular cells.

27
Q

Myogenic Mechanism

A

When blood pressure rises, the afferent arteriole constricts to reduce blood flow into the glomerulus, maintaining GFR. Conversely, if blood pressure drops, the arteriole dilates to increase blood flow and GFR.

28
Q

Tubuloglomerular Feedback

A

If GFR increases, the filtrate’s flow rate is too fast for adequate reabsorption, leading to high NaCl in the distal tubule. The macula densa cells detect this and signal the afferent arteriole to constrict, lowering GFR. If GFR decreases, the afferent arteriole dilates to increase GFR.

29
Q

Extrinsic Mechanisms

A

Renin-Angiotensin-Aldosterone System (RAAS)

Sympathetic Nervous System

30
Q

Intrinsic mechanisms

A

o Tubuloglomerular Feedback and Myogenic Mechanism

31
Q

Renin-Angiotensin-Aldosterone System (RAAS):

A

When blood pressure drops significantly, granular cells release renin. This activates angiotensin II, which constricts arterioles throughout the body (increasing systemic blood pressure), stimulates aldosterone release (enhancing Na+ reabsorption), and increases GFR.

32
Q

Sympathetic Nervous System

A

Under stress or extreme conditions, sympathetic nerves constrict afferent arterioles, lowering GFR to conserve fluids.

33
Q

Macula Densa Cells function

A

These cells act as chemoreceptors, sensing the concentration of sodium chloride (NaCl) in the filtrate. High NaCl levels in the filtrate suggest a high GFR, while low levels indicate a lower GFR. Based on these concentrations, macula densa cells signal the afferent arteriole to adjust its diameter to regulate GFR.

34
Q

Granular Cells (Juxtaglomerular Cells) function

A

These cells are mechanoreceptors that detect changes in blood pressure within the afferent arteriole. When blood pressure is low, granular cells release renin, an enzyme that activates the renin-angiotensin-aldosterone system (RAAS), which increases blood pressure and GFR by causing vasoconstriction and promoting sodium and water retention.

35
Q

Extraglomerular Mesangial function

A

help transmit signals between the macula densa and granular cells, supporting the communication required for GFR regulation.

36
Q

Proximal Convoluted Tubule (PCT) cell type and function

A
  • Cell Type: Cuboidal epithelial cells with dense microvilli (forming a brush border).
  • Function: These cells increase surface area for maximum reabsorption and are packed with mitochondria to support active transport.
37
Q

Proximal Convoluted Tubule (PCT) reabsorption and secretion

A
  • Reabsorption:
    o 65% of water and sodium (Na+), along with most nutrients (glucose, amino acids).
    o Ions like Cl-, K+, HCO₃⁻, and almost all uric acid.
  • Secretion: Certain drugs, waste products (such as ammonia and creatinine), and hydrogen ions (H+) to help maintain acid-base balance.
38
Q

Nephron Loop (Loop of Henle): descending cell type, function, and reabsorption

A

o Cell Type: Simple squamous epithelium, thin and permeable to water.
o Function: Freely allows water to exit but not solutes, concentrating the filtrate.
o Reabsorption: Water exits the filtrate due to the surrounding hyperosmotic medulla.

39
Q

Nephron Loop (Loop of Henle): ascending cell type, function, and reabsorption

A

o Cell Type: Cuboidal or low columnar cells in the thick ascending limb, impermeable to water.
o Function: Actively reabsorbs Na+, Cl-, and K+, which dilutes the filtrate.
o Reabsorption: Solutes (Na+, Cl-) are reabsorbed actively, helping create the medullary osmotic gradient necessary for water reabsorption in later segments.

40
Q

Distal Convoluted Tubule (DCT): cell type and function

A
  • Cell Type: Cuboidal cells with fewer microvilli compared to the PCT.
  • Function: Primarily responsible for selective reabsorption and secretion.
41
Q

Distal Convoluted Tubule (DCT): reabsorption and secretion

A
  • Reabsorption:
    o Na+, Cl-, and Ca2+ (regulated by parathyroid hormone for calcium).
  • Secretion: Hydrogen ions (H+) and K+, contributing to acid-base and electrolyte balance.
42
Q

Aldosterone affect

A

Promotes Na+ reabsorption (and K+ secretion) by increasing the synthesis of Na+/K+ pumps and channels. This indirectly increases water reabsorption, raising blood volume and pressure.

43
Q

Angiotensin II

A

Stimulates aldosterone release and directly increases Na+ reabsorption to help raise blood pressure.

44
Q

Collecting Duct cell types

A

o Principal Cells: Involved in water and Na+ reabsorption; sensitive to hormonal control by ADH and aldosterone.
o Intercalated Cells: Help regulate acid-base balance by secreting H+ and reabsorbing HCO₃⁻ as needed.

45
Q

Collecting Duct : Reabsorption and Secretion:

A

o Water reabsorption (regulated by ADH).
o Na+ reabsorption and K+ secretion (regulated by aldosterone).
o Urea reabsorption in the medullary collecting ducts contributes to the medullary osmotic gradient, essential for urine concentration.

46
Q

Collecting Duct: Hormonal Influence

A

o Antidiuretic Hormone (ADH): Increases water reabsorption by promoting the insertion of aquaporins(water channels) in the cell membranes. This makes the collecting duct more permeable to water, concentrating the urine.
o Aldosterone: Enhances Na+ reabsorption (and K+ secretion), raising blood volume and pressure.
o Angiotensin II: Stimulates Na+ reabsorption and constricts blood vessels, enhancing water and Na+ retention to increase blood pressure.

47
Q
  1. Countercurrent Multiplier (Nephron Loop): o The descending limb
A

the nephron loop is permeable to water but impermeable to solutes. Water exits the filtrate due to the high osmolarity of the surrounding medulla, concentrating the filtrate as it moves deeper into the medulla.

48
Q

Countercurrent Multiplier (Nephron Loop): ascending limb

A

is impermeable to water but actively transports Na+ and Cl- out of the filtrate into the medullary interstitial fluid. This action decreases filtrate osmolarity but increases medullary osmolarity.

48
Q

Countercurrent Multiplier (Nephron Loop): positive feedback loop

A

as more NaCl is pumped out of the ascending limb, the descending limb loses more water, which increases the saltiness of the filtrate entering the ascending limb. This difference in permeability establishes a gradient that increases from the cortex to the inner medulla.

49
Q

Countercurrent Exchanger (Vasa Recta):

A

o The vasa recta, a series of capillaries parallel to the nephron loop, acts as a countercurrent exchanger. It preserves the medullary osmotic gradient by allowing solutes and water to enter and leave freely without washing out the gradient.
o Blood in the vasa recta flows in the opposite direction of filtrate in the nephron loop, allowing for a continuous exchange. Solutes enter the descending vasa recta and leave in the ascending portion, while water reabsorbed from the nephron loop is taken up by the ascending vasa recta, maintaining gradient stability.

50
Q

Result of the Countercurrent Mechanism:

A

o The established osmotic gradient allows the collecting duct to reabsorb water as it passes through the medullary gradient, concentrating the urine.

ADH regulates this water reabsorption by increasing aquaporin channels in the collecting duct, allowing more water to exit into the medulla if the body needs to conserve water.

The countercurrent multiplier and exchanger work together to produce concentrated urine when

51
Q

Micturition Reflex (Urination)

A

is a coordinated process controlled by the nervous system that allows urine to be expelled from the bladder. This process involves both involuntary (autonomic) and voluntary (somatic) control.

52
Q

Bladder Filling and Stretch Receptors:

A

o As urine fills the bladder, the bladder wall stretches, activating stretch receptors in the bladder wall.
o These receptors send signals to the sacral region of the spinal cord, where they activate the micturition reflex pathway.

53
Q

Involuntary Control (Autonomic Nervous System):

A

o The parasympathetic nervous system causes contraction of the detrusor muscle (the smooth muscle layer in the bladder wall), increasing pressure in the bladder.
o The internal urethral sphincter (involuntary smooth muscle) relaxes, allowing urine to move toward the urethra.

54
Q

Voluntary Control (Somatic Nervous System):

A

o The external urethral sphincter is made of skeletal muscle and is under voluntary control.
o When the individual decides to urinate, signals from the cerebral cortex and pontine micturition centerinhibit motor neurons, causing the external sphincter to relax, allowing urine to exit through the urethra.

55
Q

Reflexive Urination in Infants:

A

In infants, the micturition reflex is a simple spinal reflex since voluntary control is not yet developed. As the bladder fills, stretch receptors activate the reflex, leading to automatic contraction and urination.

56
Q
  1. Higher Brain Centers and Micturition:
A

Anatomy and Physiology 2 (7 decks)

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