Renal Physiology Lecture 1-2

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Questions and Answers

Which of the following best describes the primary role of the kidneys in maintaining homeostasis?

Regulating blood sugar levels by secreting insulin

Stabilizing the volume and ion concentrations of the extracellular fluid (correct)

Controlling the body’s immune response to infections

Producing hormones that regulate muscle contractions

List the urinary system components.

Urinary system components include the kidneys, ureters, urinary bladder and the urethra

Out of the urinary system components, which one is physiologically relevant?

Urethra

Urinary bladder

Kidney (correct)

Ureters

List the important functions of the kidney (hint 7)

It aids in urine production, blood filtration, metabolic waste and xenobiotics excretion, retrieves needed metabolic substances, responds to water, electrolyte and acid-base disturbances, gluconeogenesis and hormone production associated with systemic blood pressure, red blood cell production and calcium metabolism Signup and view all the answers

Which of the following is not a function of the kidneys in the body?

Producing insulin to regulate blood sugar levels Signup and view all the answers

What does “endocrine functions of the kidney” refer to?

It refers to the production and secretion of hormones into circulation Signup and view all the answers

What are the three important hormones produced by the kidney?

The three hormones are calcitriol, renin and erythropoietin Signup and view all the answers

What is the primary role of calcitriol in response to Hypocalcemia?

Increasing calcium absorption by the intestinal epithielium Signup and view all the answers

Which organ is primarily responsible for Vitamin D3 into its active form, calcitriol??

Kidney Signup and view all the answers

What’s the function of the liver in the synthesis of calcitriol?

It converts Vitamin D3 to 25(OH)-Vitamin D3 Signup and view all the answers

What is the primary function of erythropoietin in the body?

Regulating erythropoiesis by promoting the proliferation and maturation of erythroid precursor cells Signup and view all the answers

Where are erythropoietin receptors primarily expressed?

On the plasma membrane of erythroid precursor cells Signup and view all the answers

What are the two types of nephrons in the kidney?

Cortical nephrons and juxtamedullary nephrons Signup and view all the answers

Which of the following statements accurately describes a key difference between cortical and juxtamedullary nephrons?

Juxtamedullary nephrons have extremely long loops of Henle critical for urine concentration, while cortical nephrons have short loops of Henle Signup and view all the answers

The glomerulus of the juxtamedullary nephron aer closer to the renal capsule, whereas the glomerulus of the cortical nephrons aer located near the cortex/medulla junction

False Signup and view all the answers

What are the five structures of the nephron?

The five structures aer the renal corpuscle, proximal tubule, loop of henle, distal tubule and the collecting ducts Signup and view all the answers

Nephrons can’t be replaces, and are partially regenerated

True Signup and view all the answers

The (juxtamedullary/cortical) nephron’s blood supply is through the PERITUBULAR CAPILLARIES

The cortical nephron’s blood supply is through the peritubular capillaries Signup and view all the answers

The (juxtamedullary/cortical) nephrons blood supply is from the efferent arterioles giving rise to the vasa recta.

The juxtamedullary nephrons blood supply is from the efferent arterioles giving rise to the vasa recta Signup and view all the answers

What is the primary function of the glomerulus in the nephron?

Filtering the blood and allowing passage of water, urea, and small solutes Signup and view all the answers

Which of the following is the main function of the proximal tubule?

Reabsorbing most filtered water and solutes like Na+, K+, and glucose Signup and view all the answers

What is the primary role of the thin limbs of Henle's loop in the nephron?

Maintaining medullary hypertonicity Signup and view all the answers

Which of the following best describes the function of the thick ascending limb of Henle’s loop?

Reabsorbing Na+, K+, Cl- and generating medullary hypertonicity, while keeping water in the tubule fluid Signup and view all the answers

What is the main function of the distal convoluted tubule?

Diluting the tubule fluid and reabsorbing Na+, Cl-, and divalent cations like Ca2+ and Mg2+ Signup and view all the answers

Which of the following is a key function of the collecting duct in the nephron?

Dividing into cortical, outer medullary, and inner medullary sections that regulate final urine composition Signup and view all the answers

What percent of the cardiac output goes to the kidney?

20-25% Signup and view all the answers

Describe the flow of the cardiac output to the kidney.

Abdominal aorta, renal artery, interlobar arteries, arcuate artery, interlobar arteries, afferent arterioles, glomerular capillaries, efferent arterioles then peritubular capillaries/vasa recta Signup and view all the answers

What is ischemia?

ischemia is the interruption of blood supply to a tissue Signup and view all the answers

What is reperfusion?

It is the re-establishment of the blood flow in the tissue Signup and view all the answers

Which of the following medical scenarios is least likely to involve ischemia-reperfusion injury?

Chronic hypertension Signup and view all the answers

What’s a common outcome of both ischemia and reperfusion at the cellular level?

Progression to necrosis and apoptosis Signup and view all the answers

Why is renal ischemia-reperfusion injury particularly concerning compared to other tissues?

Nephrons cannot be replaced and can only be partially regenerated Signup and view all the answers

What is the maximum volume of urine that adult dogs can produce in a day, considering the upper end of the glomerular filtration rate?

5,328 mL/kg/day Signup and view all the answers

Which component is primarily retained during the filtration process in the glomerulus?

Cellular components and proteins Signup and view all the answers

Which statement correctly describes glomerular filtrate?

It is produced in large amounts but mostly reabsorbed. Signup and view all the answers

What is a critical feature of the glomerulus functioning in the filtration process?

It operates as a semipermeable membrane. Signup and view all the answers

What is the primary reason that the glomerular filtration barrier is relatively impermeable to large proteins?

Composition of the glomerular basement membrane Signup and view all the answers

Which layer of the glomerular basement membrane is especially rich in glycoproteins?

Lamina densa Signup and view all the answers

How does glomerular filtration rate (GFR) relate to renal blood flow (RPF)?

GFR is 25% of RPF Signup and view all the answers

What molecular property is NOT a factor influencing glomerular filterability?

Shape Signup and view all the answers

Which statement accurately describes the glomerular filtration barrier?

It consists of capillary endothelial cells and specialized podocytes. Signup and view all the answers

Which part of the kidney's filtration system is primarily responsible for the formation of the filtrate?

Glomerulus Signup and view all the answers

What component of the filtration barrier helps provide the overall net negative charge?

Glomerular basement membrane Signup and view all the answers

In the context of glomerular filtration, which type of molecules are filtered most freely?

Electrolytes and small organic compounds Signup and view all the answers

What criteria must indicator substances meet to be used for calculating GFR?

They must be freely filterable and not altered by reabsorption or secretion in the tubule. Signup and view all the answers

Why is it important for indicator substances not to be metabolized in the kidney?

If metabolized, the amount of the substance would decrease, leading to inaccurate GFR calculations. Signup and view all the answers

Explain one reason why indicator substances must not alter renal function.

Altering renal function could change the filtration dynamics, skewing GFR results. Signup and view all the answers

Identify one consequence of using a substance that does not meet the criteria for GFR calculation.

Using such a substance can lead to misleading results about kidney health and function. Signup and view all the answers

What characterizes an ideal indicator substance for GFR measurement?

An ideal substance is freely filterable, not reabsorbed or secreted, and stable in the kidney. Signup and view all the answers

Study Notes

Urine Formation: Glomerular Filtration

Urine formation begins with fluid filtration from glomerular capillaries into Bowman's capsule.
The glomerulus, a capillary network, acts as a semipermeable membrane.
It retains cells and large proteins, preventing their passage.
Glomerular filtrate, initially large in volume (99%+ reabsorbed), is mostly reabsorbed, leaving <1 liter for excretion. The exact amount is highly variable.
Adult dogs: urine production is approximately 20-40 ml/kg body weight/24 hours (1.0-2.0 ml/kg/hour).
Adult cats: average urine production is 28 ml/kg body weight/24 hours (~1.2 ml/kg/hr).
Glomerular Filtration Rate (GFR):
- Dogs: 2.4 – 3.7 mL/min/kg (up to 5,328 mL/kg/day).
- Glomerular filtrate is similar to plasma.
- GFR depends on renal blood (plasma) flow (RPF); about 20% of renal plasma is filtered.
- Example: If RPF = 625 mL/min, then GFR ≈ 125 mL/min (20% of RPF).

Glomerular Structure and Filtration Barrier

Glomerulus: branching, anastomosing capillaries covered by podocytes (epithelial cells) and encased in Bowman's capsule.
Bowman's capsule: lined with parietal epithelium; Bowman's space lies between capillaries and capsule.
Filtration barrier components:
- Capillary endothelial cells (fenestrated).
- Glomerular basement membrane (GBM): primarily glycoproteins, not cells; functions as a filter.
- Visceral epithelium (podocytes).

Glomerular Basement Membrane (GBM) Details

GBM (sometimes incorrectly called basal lamina): three layers (visible via electron microscopy).
- Lamina rara interna
- Lamina densa (electron-dense; contributes to GBM's net negative charge).
- Lamina rara externa
All three layers contain proteins (lamina densa rich in glycoproteins like lamins, type IV collagens, proteoglycans).
The "mesh-like" structure makes the glomerular capillaries relatively impermeable to large proteins; glomerular filtrate is essentially protein-free.

Glomerular Filterability

The glomerular filtration barrier is highly selective. Filterability depends on:
- Size (inversely related to radius and molecular weight).
- Electrical charge.
- Plasma protein binding.
Electrolytes (e.g., sodium) and small organic compounds (e.g., glucose) filter as freely as water.

Glomeruler Filtration Rate (GFR)

GFR can be calculated using indicator substances.
These substances must be freely filterable.
The filtered amount of the substance must not change due to reabsorption or secretion in the tubule.
These test substances must not be metabolized in the kidney.
The indicator substances must not alter renal function.

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Functions of the kidney, hormones it produces, nephrons etc