Renal Revision (Wk: 2) Flashcards
What are the kidneys located and at what level in the verebral column?
- retroperitoneal space, just behind the abdominal peritoneum.
- each side of vertebral column between T12 and L3.
- They are surrounded by a layer of adipose tissue, termed a capsule, and held in place by the renal fascia.
- R) kidney sits lower than L) due to position of liver.
Estimate the general size of the kidney
- 12cm long, 6cm wide and 2.5cm thick
Weight: 125-170 grams in men, 115-155 grams in women
Recall the three major section of the kidney and their respective function?
- Cortex
- contains the majority of nephrons (functional units), glomeruli, convoluted tubules and the collection ducts. - Medulla
- inner part comprised of columns, pyramids and calyces which together receive urine from the entry into the renal pelvis. - Renal pelvis
- collects the ureters for urine to flow into the bladder.
Describe the nephron and its components
= a tubular structure containing a funnel-shaped unit called the glomerular capsule (Bowman’s capsule). The capsule has two layers - parietal and visceral.
- The space between the layers is referred to as the glomerular space.
What are the three layers the glomerular filtration membrane is comprised of? and describe the process though it
- endothelium of the capillary
- visceral layer of the glomerular capsule (contains podocytes)
- holds the glomerulus, where blood enters the nephron to start the filtration process - basement membrane between the 2 layers
- Fluid moves from capillaries into the capsule for filtration
Describe the path of filtration through the nephron
- The glomerular capsule holds the glomerulus, where blood enters the nephron to start the filtration process. - Fluid moves from capillaries into the capsule for filtration.
- From there, fluid moves through the proximal convoluted tubule, loop of Henle (nephron loop), and the distal convoluted tubule.
- The distal convoluted tubule then drains into the collecting duct, which contributes to urine formation.
Describe the blood supply to the kidney
- mimics the structure of the nephrons.
- Renal arteries divide into interlobar arteries and then into arcuate arteries, including the afferent and efferent arterioles which enter and exit the glomerulus.
- Glomerular capillaries carry blood to the peritubular capillaries which reabsorb fluid and solutes from the tubules which drain into the renal vein.
What is the primary function of the kidney?
= maintain a stable internal environment for optimal cell and tissue metabolism by balancing outputs (solutes and water) with inputs, resulting in excreting metabolic waste products, conserving nutrients, and regulating acid and bases.
What are some of the primary purposes of the kidney?
- Regulate body fluid volume and osmolality
- Regulate electrolyte balance
- Regulate acid-base balance (in conjunction with body buffer systems and respiratory system)
- Remove metabolic wastes such as urea, creatinine, uric acid, and more
- Regulate blood pressure
- Produce erythropoietin hormone (to regulate bone marrow production of red blood cells)
- Activate Vitamin D to its physiologically active form
- Perform gluconeogenesis (synthesis of glucose)
- Synthesise hormones, such as prostaglandins, endothlein, and nitric oxide,
- Excrete drugs and toxins from body fluids
What hormones does the kidney help produce as a part of its endocrine involvement?
- renin for regulation of blood pressure
- erythropoietin for erythrocyte production
- activate Vitamin D for calcium and phosphate metabolism
Summaries the RASS system
= initiates fluid balance.
Triggers: renal afferent arteriole pressure drops, or an decrease in serum sodium concentration is detected by the distal convoluted tubules.
- renin is released from the juxtaglomerular cells
- Renin is used to convert angiotensinogen to angiotensin I, which is then converted to Angiotensin II via the Angiotensin converting enzyme (ACE) produced in the lungs
- Angiotensin II is a potent vasoconstrictor, raising blood pressure. Angiotensin II also stimulates the release of aldosterone, which acts to increase water and sodium reabsorption in the kidneys to increase intravascular circulating volume. Figure 7 outlines the renin-angiotensin-aldosterone system.
How does ADH influence fluid balance and why?
Antidiuretic hormone (ADH)
aka vasopressin
- produced in the hypothalamus and stored in the pituitary
- released by posterior pit gland
- released in response to
- hyperosmolarity/increased serum osmolality (increase in solute concentrations/decreased water concentration)
- decreased blood pressure
- volume depletion
- noxious stimuli
- hypovolaemia
- pyrexia
- medications
- emotional/physical stress
= ADH in the blood causes the distal convoluted tubules and the collecting ducts to become more permeable to water, increasing water reabsorption, reducing urine output, and improving overall circulating volume.
Summary
- Osmoreceptors (water) located in hypothalamus detecting serum osmolality levels greater than 285mOsm/kg
- ADH released and carried to nephrons
- Kidney distal tubules, connecting tubules and collecting ducts alter permeability to water by action of ‘aquaporins
\What does aldosterone do and why?
= released by adrenal gland cortex and acts on distal tubules to reabsorb sodium from the tubular lumen into the circulation.
When sodium is retained so is water several factors stimulate the release of aldosterone including;
- Thypovolaemia,
- hyponatraemia
hyperkalemia
- stress.
Explain Atrial Natriuretic Peptide Hormone and its effect
= secreted from the atria of the heart in response to hypernatremia, stimulation of stretch receptors due to increased volume and increased pressure on the heart.
- Acts by blocking Aldosterone and ADH production, initiating vasodilation and stimulating increased sodium and water excretion by the collecting ducts.
This produces diuresis, decreased cardiac workload and reduction in cardiac preload and after load.
Where is potassium exchanged and in what way? What are some factors that affect absorption and secretion of potassium?
Potassium is reabsorbed from the filtrate by proximal tubules and secreted back into the filtrate in the distal tubules. It’s all about the filtrate!
- Sodium deficit = potassium loss
- Acidosis: Hydrogen into cell and potassium out to be excreted
- Diuretics: Increased loss of potassium in the distal tubule
- Insulin: Promotes movement if potassium into cell
- Adrenaline: Enhances potassium resorption (this is not a typo!) from proximal tubule.
Where is sodium exchanged and what does this result in?
Sodium balance regulated by kidneys, adrenal glands (aldosterone secretion) and posterior pituitary gland (ADH).
- Most reabsorption in distal tubule under the influence of aldosterone.
- When diuretics are administered, sodium absorption is inhibited and sodium is eliminated in the urine.
- This active process is regulated by site specific sodium transporters.
Where is phosphorous exchanged and in what ways?
- 90% in plasma is filtered by glomerulus and 80% is reabsorbed by the proximal tubules.
- This resorption is increased when phosphorus levels are low.
Where is chloride exchanged and in what ways?
- actively transported out of tubules into interstitium with sodium to help maintain the high tubular interstitial osmolality and the mechanism for concentrating the urine.
Where is bicarbonate exchanged and in what ways?
- Reabsorption of bicarbonate takes place primarily from the proximal tubule into peritubular capillaries.
- Bicarbonate is also produced in the distal tubule and reabsorbed into the blood in response to acid-base balance need.
- Bicarbonate is a major ECF acid base buffer.
- More bicarbonate is reabsorbed when large numbers of hydrogen ions are present, and more bicarbonate is excreted when fewer hydrogen ions are present.
What is normal serum pH?
7.35-7.45
How do the kidneys maintain serum pH?
= a buffering process through altering reabsorption and secretions of acids (H+ ions) and bases (HCO3-) when changes to pH are detected.
carbonic acid- bicarbonate buffering system equation representation
CO2 + H20 ↔ H2CO3- ↔ H+ + HCO3-
- Normally, carbon dioxide is eliminated by the lungs, however, when it remains in the plasma it combines with water to form carbonic acid, a weak acid.
- Carbonic acid then dissociates to form hydrogen ions (an acid) and bicarbonate (a base). In order to maintain normal pH, the kidneys respond by increasing the secretion of H+ and the reabsorption of HCO3-.
- The renal response to changes in blood pH requires several hours to days to take effect.
- During acidosis kidney raises H+ secretion by active transport to combine with ammonia in the renal tube to produce ammonium which is unable to be reabsorbed
- Raised H+ excretion increases the reabsorption of sodium which increases HCO3- resorption
- During alkalosis the resorption of H+ ions is increased
What do the kidneys remove as a part of their waste product removal role?
- By-products of protein metabolism:
- Urea - End product of breakdown of protein, so volume influenced by amount of protein in diet. Urea is filtered in the glomerulus but can also be secreted and reabsorbed in the tubules. Is an indicator of renal function.
- Creatinine - end product of metabolism. Exclusively excreted by kidneys, so indicator of kidney function. Creatinine is filtered in the glomerulus and a small amount is excreted in the tubules.
- Uric acid - Metabolic acids
- Bilirubin
- Medications/metabolites
How do the kidneys regulate blood pressure?
RAAS and the stimulation of angiotensin 2 which
- increases blood pressure via vasoconstriction.
- stimulated adrenal cortex to release aldosterone and cause tubules to increase reabsorption fo sodium and water= increase volume and pressure.
- blood viscosity is modulated by this system
What is the relationship between RASS and high blood pressure?
If the renin-angiotensin-aldosterone system is too active, blood pressure will be too high.
Many drugs interrupt different steps in this system to lower blood pressure.
These drugs are one of the main ways to control high blood pressure (hypertension), heart failure, kidney failure, and the harmful effects of diabetes.
