Renal Physiology Quiz

Lecture Information

• This lecture series covers the anatomy of the kidney and nephron, with emphasis on glomerular filtration.
• The series includes lectures on nephron segments, assessment of renal function, endocrine regulation of water and sodium homeostasis, disorders of water and sodium homeostasis, renal regulation of potassium, and renal pathophysiology.

Learning Objectives (Lecture 1)

• List basic renal functions.
• Describe the gross anatomy of the kidney.
• Name the nephron segments.
• Describe the three basic renal processes.
• Discuss the glomerulus components and their role in filtration.
• Describe autoregulation and explain the mechanism.

Renal Functions

• Removal of metabolic waste products (urea, uric acid, creatinine, urobilin).
• Removal of foreign chemicals and bioactive substances (drugs).
• Regulation of water and electrolyte balance (osmolarity, blood pressure, pH).
• Kidney's role in regulating blood pressure.
• Blood pressure = CO x TPR
• Gluconeogenesis (synthesis of glucose from non-carbohydrate sources).
• Erythropoietin: Red blood cell production.
• Renin: Rate limiting enzyme for Angll production.
• 1,25-dihydroxyvitamin D (Calcitriol): active form of VitD for Ca2+ absorption.

Basic Anatomy of the Kidney

• Paired bean-shaped structures behind the peritoneum, on each side of the vertebral column.
• Extends from the 12th thoracic to the 3rd lumbar vertebrae.
• Combined weight of both kidneys is less than 0.5% of the total body weight.
• Male kidneys typically 125 - 170g; Female 115 - 155 g.
• The hilus is a slit in the concave surface, which serves as the point of entry for the renal artery and nerves, and as the exit point for renal vein, lymphatics, and the ureter.
• Renal sinus contains calices, pelvis, blood vessels, nerves, and fat.

Kidney two basic layers

• Cortex (outer layer): characterized by glomeruli (microscopic capillaries) and numerous tubules.
• Medulla (inner layer): subdivided into 8-18 cone-like shaped renal pyramids.
• Urine escapes into minor calices of the renal sinus through perforations at the tip of the renal pyramids.

Comparison between Cortex and Medulla

• Cortex: glomeruli, high pressure (favors filtration), high O2, lower interstitium osmolarity.
• Medulla: tubules, low pressure (favors reabsorption), low O2, high interstitium osmolarity.

Blood flow through the renal circulation

• High resistance afferent arteriole, followed by
• High pressure glomerular capillary network for filtration
• Second high resistance efferent arteriole
• Low pressure capillary network (peritubular capillaries).

Nephron

• Functional unit of the kidney, with approximately 800,000 to 1,200,000 per kidney.
• Operates independently until merging with collecting ducts.
• Composed of glomerulus and tubules.
• Glomerulus: where filtrates form.
• Tubules: convert blood filtrate into urine.
• Bowman's capsule: The junction of the tubule and glomerulus.

Basic Renal Processes

• Glomerular Filtration: the process by which water and solutes in the blood leave the vascular system and enter Bowman's space (~20% of plasma).
• Tubular Secretion: process of moving substances into the tubular lumen from the peritubular capillaries (also applies to excretion from epithelial cells in tubules).
• Tubular Reabsorption: process of moving substances from the tubular lumen into the peritubular capillaries.

Tubule segments

• Proximal tubule
• Loop of Henle
• Distal convoluted tubule
• Cortical collecting tubule
• Medullary collecting ducts

Major Determinants of Glomerular Filtration

• Arteriole = a small diameter blood vessel in the microcirculation that branches out from an artery and leads to capillaries.
• The kidneys receive about 20% of the cardiac output.
• The filtrate is the portion of blood that is filtered by the glomerulus.
• Hydrostatic pressure forces a liquid against a semipermeable membrane.
• The afferent and efferent arterioles determine the hydrostatic pressure in the glomerular capillaries.
• The vascular tone of the arterioles is controlled by sympathetic innervation.

Neuronal control of renin release

• Sympathetic innervation of granular cells.
• Increased sympathetic nervous activity stimulates renin production from the kidney.

Autoregulation

• Renal blood flow and glomerular filtration rate (GFR) are maintained relatively constant across a wide range of systemic arterial pressures.
• Two basic mechanisms underlie autoregulation: myogenic response, and tubuloglomerular feedback.

Tubuloglomerular Feedback

• Macula densa cells respond to changes in luminal delivery of NaCl.
• Na+-Cl- or Na+-K+-2Cl- co-transporters in the luminal membrane of the Distal Convoluted Tubule or Thick Ascending Loop.
• The activity of this transporter is controlled by NaCl concentration.

Glomerulus

• Composed of two main structural components: the glomerulus (or glomerular capillaries) and a surrounding capsule (called Bowman's capsule).
• Afferent and efferent arterioles and Juxtaglomerular (JGA) cells filter and deliver blood from the renal artery to the glomerulus.

Filtration barrier

• consist of capillary endothelium, glomerular basement membrane, and podocyte foot processes. The size and charge of particles determine filtration.

Test of Knowledge (Lecture 1)

-Correct statement about the nephron is that the glomerular pressure needs to stay high for filtration to occur, rather than reabsorption

Lecture 2 Information

• This lecture covers the specific mechanisms of water and sodium reabsorption in nephron segments.
• Key concepts include the arrangements of the tubule segments, mechanisms of solute transport, the counter-current mechanism, and the interaction of the counter-current mechanism with endocrine signals to regulate urine concentration.

Learning Objectives (Lecture 2)

• Describe the arrangements of tubule segments and their functions.
• Discuss the mechanism of solute transport out of the tubule lumen.
• Describe the counter-current mechanism.
• Discuss the interaction of counter-current mechanisms and endocrine signals to regulate urine concentration.

Basic renal processes

• Glomerular Filtration
• Tubular Secretion
• Tubular Reabsorption

Tubule Segments

• Proximal tubule
• Loop of Henle
• Thin descending limb of Henle
• Thick ascending limb of Henle
• Distal Convoluted Tubule

Functions of Proximal Tubule

• Sodium and glucose reabsorption.
• Acid-base balance.
• Regulation of calcium and hydrogen phosphate.
• Excretion of endogenous and exogenous solutes (drugs).

Water Reabsorption in the Collecting Tubule

• Water reabsorption is hormonally controlled by ADH and other mediators, such as atrial natriuretic peptide (ANP).
• The presence(or absence) of ADH determines the permeability of the collecting tubules to water.

Osmoregulation

• Osmoreceptors in the hypothalamus detect changes in solute concentration in body fluids which stimulates the release or inhibition of ADH (anti-diuretic hormone).

Loop of Henle

• The descending limb is permeable to water but not to ions.
• The ascending limb of the loop is permeable to ions but not to water.
• 20-25% of filtered sodium is reabsorbed in the ascending limb.

Water Reabsorption

• Aquaporins and osmotic gradient promote water reabsorption in the thin descending limb of the loop.

Other important notes from the lecture series

• Normal GFR in an adult ≈ 80-120 ml/min
• The clearance of a solute is the volume of blood totally cleared by the kidney of the solute in a given time.
• GFR is important for excretion of salt and water.
• Estimated Glomerular Filtration Rate (eGFR) can be calculated from serum creatinine and demographic data.
• Renal pathologies can cause disruptions in the kidney's ability to excrete salt and water, leading to various medical conditions.

Test your knowledge on the roles of renin and arginine vasopressin in kidney function. This quiz covers autoregulation of renal blood flow, the impact of arteriolar resistance on glomerular filtration rate, and the mechanisms involved in osmoregulation. Prepare to dive deep into the fascinating world of renal physiology!