Lecture 1: Kidney Structure and Function I Flashcards
What is the function of the renal system?
Contributes to homeostasis by controlling →
- Blood ionic composition
- Blood pH
- Blood volume
- Blood pressure
- Blood osmolarity
- Excretion of waste
- Hormone production
- Glucose levels
Describe the anatomical location of the kidney
- Kidney is posterior to the perineum (membrane that covers the abdominal cavity)
- Partially protected by the 11-12th rib
What are the signs and symptoms of hypovolemia (dehydrated)?
- Symptoms: thirst, dizziness on standing, confusion
- Signs: low JVP, postural hypotension, weight loss, dry mucous membranes, reduced skin turgor, reduced urine output
Hypovolemia cause
Too little regulation of body fluid volume
Hypervolemia cause
Too much regulation of body fluid volume
What are the signs and symptoms of hypervolemia (fluid overload)?
- Symptoms: ankle swelling, breathlessness
- Signs: raised JVP, oedema, weight gain, hypertension
How do the kidneys regulate fluid balance?
- Kidneys regulate body fluid homeostasis
- Regulate both volume n composition
- Altering plasma volume n composition → influences other fluid compartments
- This is mainly done by changing extracellular sodium conc. and water → controls blood pressure
Osmolarity
The measurement of solute concentration or osmotically active solutes
Osmotic pressure
The pressure which needs to be applied to the solution to prevent an inward movement of fluid across a semi permeable membrane
Oncotic pressure
The osmotic pressure exerted by the proteins in the blood plasma or exudate/filtrate which attracts/pulls water into the compartment
Hydrostatic pressure
Force exerted by a fluid against a capillary wall
Hypo-osmotic solution
Osmotic pressure outside > osmotic pressure inside
Isotonic solution
High osmotic pressure outside = high osmotic pressure inside
Hyperosmotic solution
Osmotic pressure outside > osmotic pressure inside
How do the kidneys regulate body fluid homeostasis?
The kidneys play a major role in regulating body fluid homeostasis by:
- Regulating Volume and Composition: They adjust the volume and composition of body fluids, including plasma, interstitial fluid, and intracellular fluid.
- Altering Urine Volume: The kidneys regulate urine volume to control fluid balance in the body.
- Adjusting Ionic Composition: They can change the concentrations of ions such as sodium, potassium, chloride, calcium, protons, bicarbonate, and phosphate ions in the extracellular fluid.
- Influencing Blood Pressure: Regulation of extracellular sodium and water levels by the kidneys helps control blood pressure.
- Linking to Other Fluid Compartments: Changes in plasma volume and composition by the kidneys influence the fluid balance in other compartments, such as interstitial and intracellular fluid.
How does filtration occur in the kidneys?
- Afferent Arteriole: Blood enters the glomerulus through the afferent arteriole.
- High Hydrostatic Pressure: The afferent arteriole has a larger diameter compared to the efferent arteriole, leading to increased blood pressure within the glomerulus. This high hydrostatic pressure facilitates the movement of fluid out of the capillary.
- Osmotic Pressure: The osmotic pressure within the capillary opposes filtration by drawing water back into the blood vessel.
- Filtration: When the hydrostatic pressure (Pc) exceeds the opposing osmotic pressure, fluid is forced out of the capillary into the renal tubule. This process promotes plasma filtration, allowing small molecules and ions to pass through the filtration barrier into the renal tubules while retaining larger molecules like proteins and blood cells in the bloodstream
How do hydrostatic pressure and oncotic pressure influence filtration in the kidneys?
- Hydrostatic pressure: force exerted by fluid against the walls of blood vessels, pushing fluid out of the capillaries.
- In the kidneys, high hydrostatic pressure in the glomerulus facilitates plasma filtration.
- Conversely, oncotic pressure (also known as colloid osmotic pressure) is the osmotic pressure exerted by proteins, such as albumin, in the blood vessel.
- Oncotic pressure draws fluid back into the capillaries. When hydrostatic pressure exceeds oncotic pressure, filtration occurs, allowing small molecules and ions to pass through the filtration barrier. However, if oncotic pressure exceeds hydrostatic pressure, fluid retention occurs, inhibiting filtration of plasma.
Describe the anatomical structures and flow of fluid in the kidney.
- The kidney consists of the cortex, medulla, and renal pyramids.
- Fluid drains from the medulla into the calyx and then into the renal pelvis, which connects to the ureter.
- The functional unit of the kidney is the nephron, which is primarily located in the cortical region and has a granular appearance.
- Each nephron consists of a renal corpuscle (glomerulus and Bowman’s capsule) and a renal tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct).
- Blood is filtered in the glomerulus, and the filtrate passes through the renal tubule, where substances are reabsorbed or secreted.
- The vasa recta are capillaries that surround the nephron, helping to maintain the osmotic gradient in the medulla.
- Finally, the collecting ducts drain into the minor calyx, major calyx, renal pelvis, ureter, and bladder.
What are the components of a nephron and their functions?
- Renal corpuscle: Bowman’s capsule and the glomerulus, a tuft of capillaries nestled within Bowman’s capsule. Blood is filtered to produce the initial filtrate.
- Renal tubule:
- PCT: reabsorbs water, ions, and nutrients from the filtrate
- The loop of Henle: establishes a concentration gradient in the medulla
- DCT: involved in further ion reabsorption and secretion, connects to the collecting duct.
- Collecting duct:
- Receives filtrate from multiple nephrons and plays a crucial role in regulating water reabsorption and maintaining electrolyte balance.
What are the two types of nephrons and how do they differ?
- Cortical nephrons:
- Have a short loop of Henle.
- Juxtamedullary nephrons:
- Have a longer loop of Henle.
- Represent about 15% of all nephrons.
- Produce highly concentrated urine due to their longer loop of Henle and the presence of a counter-current multiplier mechanism.
Describe the flow of fluid in a juxtamedullary nephron.
- Fluid begins in the glomerular (Bowman’s) capsule.
- It then moves through the proximal convoluted tubule, descending limb of the nephron loop, thin ascending limb of the nephron loop, thick ascending limb of the nephron loop, and distal convoluted tubule.
- Finally, it drains into the collecting duct.
What are the major processes involved in urine formation in the kidneys?
- Filtration:
- Hydrostatic pressure pushes fluid out of the capillaries into the Bowman’s Capsule, forming the glomerular filtrate.
- Glomerular filtration rate (GFR) is approximately 125 mL/min.
- Tubular reabsorption:
- Occurs mainly in the proximal convoluted tubule (PCT) and loop of Henle.
- About 99% of water, along with many ions, glucose, amino acids, urea, and other substances are reabsorbed back into the bloodstream.
- Tubular secretion:
- Involves the transfer of materials from the blood into the renal tubule and duct cells to be excreted as waste.
- Includes substances like drugs and metabolites.
- Urine excretion:
- Kidneys produce urine containing waste products, excess ions, and other substances.
- Urine exits the kidneys through the collecting ducts, into the calyces, renal pelvis, ureter, and finally out of the urethra.
Describe the structural components and key cells involved in the renal corpuscle.
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Afferent and Efferent Arterioles:
- Afferent: Brings blood toward the glomerulus.
- Efferent: Carries blood away from the glomerulus.
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Bowman’s Capsule:
- Surrounds the capillaries (glomerulus) and is the initial structure of the renal tubule.
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Glomerulus:
- Network of capillaries where blood is filtered.
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Basement Membrane:
- Single membrane around the capillaries.
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Mesangial Cells:
- Contractile cells regulating glomerular filtration rate.
- Unique to the glomerulus.
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Podocytes:
- Epithelial cells of Bowman’s Capsule.
- Have clear gaps crucial for filtration.
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Tubule:
- Hollow tube surrounded by a single layer of epithelial cells.
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Juxtaglomerular Apparatus:
- Sits between the afferent and efferent arterioles.
- Involved in controlling glomerular filtration rate and releasing renin.
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Renin:
- Released by the juxtaglomerular apparatus.
- Important in controlling blood pressure and volume.
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Macula Densa Cells:
- Part of the juxtaglomerular apparatus.
- Sense the level of salt in the bloodstream.
What triggers the secretion of renin by juxtaglomerular (JG) granular cells?
- Juxtaglomerular (JG) granular cells secrete renin in response to falls in extracellular fluid (ECF) volume or low sodium levels.
- Changes are detected by baroreceptors located around the body.
- The aim of this response is to increase sodium reabsorption, and consequently water reabsorption, to restore fluid balance.