Kidney Function PDF

Chapter 19 -- kidneys **[19.1 Functions of the Kidneys]** 1. [List and describe the six functions of the kidney] - Regulation of extracellular fluid volume - Regulation of blood pressure - Regulation of osmolarity - Maintenance of ion balance - Excretion of waste - Production of...

Chapter 19 -- kidneys **[19.1 Functions of the Kidneys]** 1. [List and describe the six functions of the kidney] - Regulation of extracellular fluid volume - Regulation of blood pressure - Regulation of osmolarity - Maintenance of ion balance - Excretion of waste - Production of hormones 2. Trace the anatomic path of water from Bowman's capsule to urine leaving the body a. **Bowman's Capsule**: Filtration occurs here. Plasma is filtered from the glomerulus into Bowman's capsule, forming the filtrate that contains water and small molecules. b. **Proximal Convoluted Tubule**: Most water, salts, and nutrients are reabsorbed here. However, a portion of water continues along the nephron. c. **Loop of Henle**: a. **Descending Limb**: Water is reabsorbed due to the medulla\'s high osmolarity, concentrating the filtrate. b. **Ascending Limb**: Water is retained while salts are actively transported out, diluting the filtrate. d. **Distal Convoluted Tubule**: Further adjustments occur. Hormones like aldosterone regulate water and salt reabsorption here. e. **Collecting Duct**: Water reabsorption is controlled by antidiuretic hormone (ADH), fine-tuning urine concentration. The remaining water and solutes form urine. f. **Renal Pelvis**: Urine from multiple nephrons drains into the renal pelvis through the collecting ducts. g. **Ureters**: Urine travels down the ureters through peristalsis to the urinary bladder. h. **Urinary Bladder**: Urine is temporarily stored here until voided. i. **Urethra**: During micturition, urine exits the bladder through the urethra and leaves the body. A diagram of a urinary system Description automatically generated 3. SKIP 4. **Know the anatomic relationship between the vascular and tubular elements of the nephron** 1. **Glomerulus and Bowman's Capsule**: - The **glomerulus**, a tuft of capillaries, is encased by **Bowman's capsule**. Blood enters the glomerulus via the **afferent arteriole** and exits through the **efferent arteriole**. - The close association between the glomerulus and Bowman's capsule facilitates the filtration of plasma into the nephron's tubular system. 2. **Peritubular Capillaries and Tubules**: - After leaving the glomerulus, blood in the efferent arteriole flows into the **peritubular capillaries** (in cortical nephrons) or **vasa recta** (in juxtamedullary nephrons). - These capillaries surround the **proximal tubule**, **Loop of Henle**, **distal tubule**, and **collecting duct**. This proximity enables efficient exchange of substances, including the reabsorption of water, ions, and nutrients into the bloodstream, as well as the secretion of waste into the tubule. 3. **Loop of Henle and Vasa Recta**: - In juxtamedullary nephrons, the **vasa recta** closely follows the descending and ascending limbs of the **Loop of Henle**. This anatomical arrangement helps maintain the medullary osmotic gradient essential for concentrating urine. 4. **Distal Tubule and Collecting Duct**: - The peritubular capillaries around the **distal tubule** and **collecting duct** allow for further reabsorption of water and solutes (regulated by hormones like aldosterone and ADH) and secretion of substances like hydrogen and potassium ions into the tubular system. **Summary of Relationships:** - **Filtration**: Occurs between the glomerulus (vascular) and Bowman's capsule (tubular). - **Reabsorption and Secretion**: Occur along the nephron tubules and are facilitated by the surrounding peritubular capillaries and vasa recta. - **Exchange Efficiency**: The close proximity of vascular and tubular elements ensures efficient filtration, reabsorption, and secretion to regulate fluid and electrolyte balance. **Know Efferent & Afferent arterioles, peritubular capillaries, glomerulus, and vasa recta**  **Afferent Arteriole:** - **Role**: The afferent arteriole brings blood into the glomerulus. It is a branch of the renal artery and regulates blood flow into the nephron. - **Significance**: Its diameter can change to adjust blood pressure in the glomerulus, which affects filtration rates. For example, vasoconstriction reduces filtration pressure, while vasodilation increases it. **Glomerulus (Capillaries):** - **Role**: The glomerulus is a network of capillaries where the initial filtration of blood occurs. Plasma and small solutes pass through its walls into Bowman's capsule, forming the filtrate. - **Significance**: The glomerulus is uniquely specialized for filtration due to: - High hydrostatic pressure, maintained by the afferent and efferent arterioles. - Its fenestrated (porous) endothelium, which allows water and small molecules to pass but retains blood cells and large proteins. **Efferent Arteriole:** - **Role**: The efferent arteriole carries blood away from the glomerulus after filtration. It has a smaller diameter than the afferent arteriole, maintaining high pressure within the glomerulus for effective filtration. - **Significance**: The efferent arteriole branches into either: - **Peritubular capillaries** (in cortical nephrons) for reabsorption and secretion. - **Vasa recta** (in juxtamedullary nephrons) to help maintain the medullary osmotic gradient. **Peritubular Capillaries:** - **Role**: These capillaries surround the proximal and distal tubules in cortical nephrons. They allow for the reabsorption of water and solutes (e.g., glucose, ions) from the tubules back into the bloodstream, as well as the secretion of waste products into the tubular fluid. - **Significance**: The close proximity to the nephron tubules facilitates exchange, playing a critical role in maintaining homeostasis and balancing fluid, electrolytes, and pH levels. **Vasa Recta:** - **Role**: Found in juxtamedullary nephrons, the vasa recta are long, straight capillaries that closely follow the Loop of Henle. They help to maintain the medullary osmotic gradient necessary for the concentration of urine. - **Significance**: The vasa recta perform **countercurrent exchange**, allowing for efficient reabsorption of water and solutes without disrupting the osmotic gradient. **Summary of Key Relationships:** 1. **Afferent arteriole** brings blood into the glomerulus for filtration. 2. **Glomerulus** filters plasma to create the filtrate. 3. **Efferent arteriole** carries remaining blood away, dividing into capillary networks for further exchange. 4. **Peritubular capillaries** manage reabsorption and secretion around cortical nephrons. 5. **Vasa recta** maintain the osmotic gradient for water reabsorption in juxtamedullary nephrons. 2. **[Anatomy of the Urinary System]** - Outer cortex & inner medulla - Portal system - Glomerulus = capillary bed within bowman's capsule where filtrate comes out of blood - Renal blood flow: - Afferent arteriole glomerulus efferent arteriole peritubular capillaries vasa recta 3. **[Overview of Kidney Function]** 5. [Describe the three processes of the nephron] - **Filtration** - [Filters blood & enters tubule] - Only filtration occurs at renal corpuscles within bowman's capsule - Filtered plasma = FILTRATE (will be excreted unless reabsorbed) - **Reabsorption** - Certain materials from filtrate are [passed back into blood] - Occurs with peritubular capillaries - **Secretion** - Materials [pass from blood into lumen of tubule] eventually secreted - Occurs with peritubular capillaries A diagram of a urinary system Description automatically generated  **\*don't need to know osmolarity numbers... just know where filtration, reabsorption, and secretion occurs** 6. SKIP 4. **[Filtration]** 7. [Describe the filtration barriers between the blood and the lumen of the nephron, and explain how they can be modified to control filtration] - **Filtration fraction** = % of renal flow that filters into the tubule - About 20% leaves blood and enters tubule - **Filtration occurs in renal corpuscle** - Glomerular capillaries - Fenestrated capillaries - Epithelium of Bowman's capsule - **Podocytes** -- surround capillaries and have slits for filtration - **Mesangial cells** -- contractile capabilities alter blood flow for filtration A diagram of a gastric tube Description automatically generated - **FILTRATION BARRIER: (3 LAYER) -- in renal corpuscle** - glomerular capillary endothelium (fenestrated capillaries & Glycocalyx) - Basement membrane - Epithelium of bowman's capsule (podocytes / slits) - Mesangial cells = NOT RELATED TO BARRIER 8. [Describe the pressures that promote and oppose glomerular filtration] - **Glomerular Capillary blood pressure (hydrostatic)** - [Hydrostatic pressure] that exerts pressure on wall & favors filtration (OUT OF BLOOD AND INTO TUBULE) -- 55mmHg - **Capillary colloid osmotic pressure** - Proteins in plasma pull solutes - Opposes filtration (pulls fluid back [into blood plasma]) -- 30mmHg - **Hydrostatic Capsule fluid pressure** - [Hydrostatic pressure] on walls within Bowman's capsule - Opposes filtration (pulls fluid back [into blood plasma]) -- 15mmHg  A diagram of the human body Description automatically generated 9. [Define glomerular filtration rate, and give averages for GFR] - **GFR = the amount of fluid that filters into Bowman's capsule per unit time.** - [Determined by filtration pressure & filtration coefficient] - GFR = volume/time - **Nearly constant** at 180L/day when MAP is between 80-180mmHg  10. [Explain how GFR can be influenced by local and reflex control mechanisms] - **GFR is controlled primarily by regulating blood flow through the renal arterioles** - Increased resistance / vasoconstriction in afferent arteriole = DECREASE GFR - Decreased resistance in afferent arteriole = INCREASE GFR - Increased resistance in efferent arteriole = INCREASE GFR - Decreased resistance in efferent arteriole = DECREASE GFR - **Tubuloglomerular feedback** helps GFR autoregulation - [Paracrine control signaling mechanism] - Paracrine signaling between [nephron and afferent arteriole] influences GFR - **Juxtaglomerular apparatus** - Consists of macula densa (detect NaCl in filtrate) and granular cells (secrete renin) - **Myogenic autoregulation** -- respond to stretch/diameter of vascular smooth muscle in response to **tubuloglomerular feedback** - Also influenced by hormones and autonomic neurons - Changes resistance in arterioles, or alters filtration coefficient A diagram of the human body Description automatically generated 5. **[Reabsorption]** - Most reabsorption takes place in proximal tube - Peritubular capillaries reabsorb fluid along their entire length 11. [Distinguish between transcellular transport and paracellular pathways] - **Transcellular** (transepithelial) = across apical and basolateral membranes of the tubule of epithelial cells - Most reabsorption uses transepithelial - **Paracellular pathway** = pass through cell-cell junctions between adjacent cells  12. [Describe and give examples of active and passive reabsorption in the proximal tubule] - **Active:** Na pumped out creates concentration gradients for passive reabsorption of other solutes like urea - **Passive:** water following high solute concentrations, GLUT diffusion 13. [Using glucose as an example, create graphs to show filtration, transport maximum, and renal threshold of a substance reabsorbed by protein-mediated transport] - **Transport maximum** = Transport rate at saturation - Can't exceed this maximum - **Renal threshold** = Plasma Concentration at which substance first appears in the urine - **Saturation** = max rate of transport that occurs when all carriers are occupied/saturated with substrate A graph with red line and green line Description automatically generated 6. **[Secretion]** 14. [Explain and give examples of the importance of tubular secretion in renal function] - **Secretion** = active movement of molecules from extracellular fluid into the nephron lumen - **Organic anions = good example** - Remove solutes from peritubular capillaries - Important homeostatic regulation of H+ and K+ - **Secretion enhances excretion!** 7. **[Excretion]** **Excretion = filtration -- reabsorption + secretion** \- if clearance of X is greater than GFR X is secreted \*If excretion is greater than filtration NET SECRETION **Explanation**: - If the clearance of substance X is higher than GFR, it means more of X is leaving the body than what was initially filtered. - This happens because the kidney is actively secreting X into the tubules (in addition to filtration), increasing its excretion. \- if clearance of X is less than GFR X is reabsorbed \*if filtration is greater than excretion NET REABSORPTION **Explanation**: - If clearance is lower than GFR, it means less of X is leaving the body than was originally filtered. - This happens because some of X is being reabsorbed back into the blood from the kidney tubules.  Excretion: The amount of X that leaves the body in the urine.  Filtration: How much of a substance is initially filtered from the blood into the kidney tubules.  Reabsorption: How much of the filtered substance is taken back into the blood.  Secretion: How much of the substance is actively transported from the blood into the kidney tubules (in addition to what was filtered). 15. [Explain mathematically and in words the relationship between the excretion of a solute and its renal clearance] **Excretion = filtration -- reabsorption + secretion** - **Clearance** = describes how many milliliters of plasma passing through the kidneys have been totally cleared of a solute in a period of time  16. [Explain how clearance can be used as an indirect indicator of renal handling of a solute] - Increase secretion = increase excretion - **Clearance** = rate at which solute disappears from body via excretion or metabolism - Clearance = noninvasive measure of GFR - Clearance of X = excretion of X / X plasma - Volume of plasma cleared of substance - **Insulin clearance = GFR & creatine is used in clinical settings to measure GFR** - **Perfect because it is neither filtered nor absorbed** - Clearance can be used to determine how the nephron handles a solute filtered into it A diagram of a human body Description automatically generated  8. **[Micturition (urination)]** 17. [Diagram the involuntary micturition reflex and include the voluntary control pathway exerted by higher brain centers] - Micturition reflex = spinal reflex - Subject to conscious and unconscious control IN CLASS: 7 COMPONENTS OF REFLEX 1. STIMULUS = bladder stretch due to filling 2. SENSOR = stretch receptors 3. INPUT SIGNAL = sensory neurons 4. INTEGRATING CENTER = spinal cord 5. OUTPUT SIGNAL = parasympathetic motor neurons (activated) somatic motor neurons are inhibited 6. TARGET = \* 7. RESPONSE = \* \*Output signal is PARASYMPATHETIC motor neurons: \- bladder smooth muscle = **Target tissue** \- [Contraction of smooth muscle] = opens internal sphincter \- Urination = **Response** \* SOMATIC motor neurons are inhibited/stops firing \- relaxation of external sphincter Diagram of a diagram showing the muscles of the human body Description automatically generated