renal physio

• Gives an overview of various components and functions in the urinary (renal) system
• Kidneys are highly vascular organs with functional units called nephrons
• Identifies nephron functions including glomerular filtration, tubular reabsorption, tubular secretion, and excretion
• Includes transport maximum (Tm) and renal threshold using glucose as an example
• Describes specific segments of the renal tubule and collecting duct that reabsorb water and solutes and secrete solutes into urine

Kidney Functions

• Regulates blood ionic composition, like sodium (Na+), potassium (K+), calcium (Ca2+), chloride (Cl-), and phosphate ions (HPO42-)
• Regulates blood volume by conserving or eliminating water in urine, altering blood pressure
• Regulates blood pH by excreting hydrogen ions (H+) and conserving bicarbonate ions (HCO3¯)
• Regulates blood pressure via renin secretion, activating the renin-angiotensin-aldosterone (RAAS) pathway
• Maintains blood osmolarity at approximately 300 milliosmoles per liter (mOsm/liter) through water and solute regulation
• Produces calcitriol (vitamin D active form) for calcium homeostasis and erythropoietin for red blood cell production
• Excretes waste products and foreign substances with metabolic origins (ammonia, urea, bilirubin) or external sources (drugs, toxins)

Urinary System Overview

• Kidney cross-section shows outer cortex and inner medulla
• Urine from nephrons flows into the renal pelvis and then through the ureter into the bladder

Nephron and Collecting System

• The nephron is composed of the renal corpuscle, proximal convoluted tubule, nephron loop, and distal convoluted tubule
• The collecting system is composed of connecting tubules, collecting ducts, and papillary ducts
• Proximal Convoluted Tubule: water, ions, and organic nutrients are reabsorbed
• Distal Convoluted Tubule: ions, acids, drugs, and toxins are secreted and water, sodium and calcium ions are variably reabsorbed
• Collecting Ducts: variable reabsorption of water and secretion of ions, hydrogen, potassium etc

Basic Renal Processes

• Glomerular filtration: Water and small solutes move from blood plasma across glomerular capillaries into Bowman's capsule
• Tubular reabsorption: Tubule cells reabsorb about 99% of filtered water and useful solutes back into the blood
• Tubular secretion: Renal tubule and duct cells secrete wastes, drugs, and excess ions from the blood into the fluid
• Glomerular filtration filters 20% of the plasma, and less than <1% of the filtered fluid is excreted

Glomerular (Bowman's) Capsule

• The outer wall is lined with simple squamous capsular epithelium
• Visceral epithelium consists of podocytes that wrap glomerular capillaries
• Filtration slits aid in filtering small materials from the blood

Glomerular Filtration

• Glomerular blood hydrostatic pressure (55 mmHg) is a major filtration force
• Bowman's capsular hydrostatic pressure (15 mmHg) opposes filtration
• Blood colloid osmotic pressure (30 mmHg) due to plasma proteins also inhibits filtration

Glomerular Filtration Rate (GFR)

• Net filtration pressure, or hydrostatic pressure minus colloid osmotic pressure plus fluid pressure, influences GFR
• Filtration coefficient factors include surface area of glomerular capillaries and interface permeability
• GFR regulation includes autoregulation, autonomic regulation (sympathetic division of ANS), and hormonal control (kidneys)

Autoregulation of GFR

• GFR is maintained by controlling the changes in afferent arterioles, efferent arterioles, and glomerular capillaries
• Reduced blood flow will trigger the dilation of afferent arteriole/glomerular capillaries to decrease GFR, and the constriction of efferent arterioles
• Increased blood flow means less filtration

Tubuloglomerular Feedback

• Involves the juxtaglomerular apparatus and detects salt level changes in the fluid
• Higher levels of salt increase secretions of ATP/adenosine and constrict blood flow into the glomerulus/reduce GFR

Hormonal Regulation of the the GFR

• Renin-angiotensin-aldosterone system (RAAS) and Atrial Natriuretic Peptide (ANP) regulate GFR
• Three stimuli that will cause the juxtaglomerular complex (JGC) to release renin: decline in pressure, sympathetic innervation, and concentration
• All of these ultimately cause an increase in reabsorption of Na+/Cl- and water, and a loss of potassium

Angiotensin II

• Angiotensin II constricts glomerular (efferent) arterioles to maintain GFR.
• It increases arteriolar resistance, raising systemic arterial blood pressure.

Dual Aldosterone Secreation

• Aldosterone is a K+ secretion stimulant, and it is a stimulant that drives principal tubular cells
• Rise in plasma K+ stimulates adrenal cortex to increase aldosterone output for secretion, which in turn promotes excretion
• Decline in conc will conversely lower the secretions as well

Plasma K+Regulation

• Dysregulation will result in hyper/hypokalemia
• Hyperkalemia can be corrected by increased aldosterone release
• Hypokalemia caused by kidney disease/diarrhea can be corrected by no K+ secreation

Atrial Natriuretic Peptide (ANP)

• The hormone atrial natriuretic peptide (ANP) is secreted by cardiac atria
• It increases the diameter of the afferent arterioles and decreases sodium reabsorption

Tubular Reabsorption

• All plasma except plasma proteins are filtered through the capillaries
• Essential materials are brought back: this process is efficient and selectable
• Occurs through transepithelial transport, where reabsorption has to pass through certain layers, and can be either passive or active

Na+ Reaborption

• The basolateral Na-K actively transports Na from tubular into fluid, which creates a good passive way for water + Na to go in
• In the PCT, cells transport by crossing luminal and basolateral, and can cross intrercellular jusctions

Na+

• All of the Na+ is reabsorbed actively
• All of the gradient will drive the anion reabsorption
• Water goes through by osmosis, in the lumen

Glucose Tubular Regulation

• Na and glucose are transported from high levels to low levels by membrane proteins
• Glucose moving down will push it into the cell by the SGLT protein

Reabsorption

• Goverened by hydrostatic and colloid pressure levels.
• Lower levels create more absorption

Tubular Secreation

• Happens by transfering molecules into the extracellular
• Penicillin is excreated

PCT

• H+ is secreted depending on the acidity of the body
• Has a high water reabsorption rate

DCT

• Distal tubule fluid increases the amount of released aldosterone
• Water is moved by means of increased vasporessin

Vasopressin

• It is transported along the basolateral membrane, which activates the cyclic AMP secondary messenger pathway
• After that, it opens the membrane

Electrolyte Homeostasis

• Na regulates ECF
• K regulates cardiac function
• Ca regulates muscle contraction
• body weight is regulated through excretion

Countercurrent multiplication system

• Allows tubules to reach max osmolality
• Descending loops permeable to water, non permeable to Na
• Ascending loops is reverse

Steps of function

• Corpuscle makes filtrate same as blood plasma
• The proximal tubule produces osmotic water flow from tubular fluid + reduces volume of filtrate
• descending water into peritubular fluids: reduction in volume
• asending loop transport: na and cl out of tubule
• The collecting ducts adjust concentration
• The restic absords the ducts

Urine makeup

• Mostly filtration and secretion
• Glucose is reabsorbed
• Has colour due to urobiligens created by kindeys
• Dipstick can be used to analyse
• Normal urine has a defined value of characteristics and compoents
• Creatinine determines GFR flow

Explore kidney function, urine formation, and waste excretion. Understand the processes of glomerular filtration, tubular reabsorption, and the kidney's role in maintaining homeostasis. Learn about the regulation of blood pressure, ionic composition, and pH balance.