Week 2- Renal Flashcards
(84 cards)
Kidney physiology
Kidneys are retroperitoneal organs located behind abdominal peritoneum, surrounded by adipose tissue capsule and renal fascia. They are on vertebral column sides, with right kidney being lower due to liver position.
Anatomy of the kidneys
The cortex, the outermost region of the kidney, contains nephrons, glomeruli, tubules, and collecting ducts. The medulla, the inner part, consists of renal columns, pyramids, and calyces, receiving urine and connecting to the renal pelvis.
The Nephron
The nephron is a tubular structure, and each nephron contains 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.
The glomerular filtration membrane is comprised of 3 layers:
- endothelium of the capillary
- visceral layer of the glomerular capsule (contains podocytes)
- basement membrane between the 2 layers
Function of the kidneys
The cortex, the outermost region of the kidney, contains nephrons, glomeruli, tubules, and collecting ducts. The medulla, the inner part, consists of renal columns, pyramids, and calyces, receiving urine and connecting to the renal pelvis.
Primary Purpose 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
Maintain fluid balance
The Renin- Angiotensin- Aldosterone System
The kidneys maintain fluid balance by releasing renin when pressure drops, converting angiotensinogen to angiotensin I and Angiotensin II, and stimulating aldosterone release. Antidiuretic hormone (ADH) influences fluid balance by increasing water reabsorption and reducing urine output.
Anti-Diuretic Hormone
- Also know has ‘vasopressin’
- Secreted by posterior pituitary gland
- 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’
Maintain electrolyte balance- 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!
Factors affecting absorption and secretion of potassium:
1. Sodium deficit = potassium loss
2. Acidosis: Hydrogen into cell and potassium out to be excreted
3. Diuretics: Increased loss of potassium in the distal tubule
4. Insulin: Promotes movement if potassium into cell
5. Adrenaline: Enhances potassium resorption (this is not a typo!) from proximal tubule
Maintain electrolyte balance- Sodium
Sodium balance regulated by kidneys, adrenal glands (aldosterone secretion) and posterior pituitary gland (ADH). Most sodium reabsorption occurs in the 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.
Maintain electrolyte balance- Phosphorus
90% of phosphorus in plasma is filtered by glomerulus and 80% is reabsorbed by the proximal tubules. This resorption is increased when phosphorus levels are low.
Maintain electrolyte balance- Chloride
is actively transported out of tubules into interstitium with sodium to help maintain the high tubular interstitial osmolality and the mechanism for concentrating the urine.
Maintain electrolyte balance- Bicarbonate
major ECF acid base buffer. 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.
More bicarbonate is reabsorbed when large numbers of hydrogen ions are present, and more bicarbonate is excreted when fewer hydrogen ions are present.
Regulation of acid-base balance
The kidneys, alongside the lungs, have a crucial role in maintaining the serum pH within a very narrow margin (7.35-7.45). It does this through a buffering process, altering the reabsorption and secretion of acids (H+ ions) and bases (HCO3-) when changes to pH are detected.
Removal of waste products
The kidneys play a crucial role in maintaining homeostasis by removing waste products such as urea, creatinine, uric acid, metabolic acids, bilirubin, and medications/metabolites. These waste products are influenced by the amount of protein in the diet.
Regulate blood pressure
The renin-angiotensin system regulates blood pressure and water balance. When blood volume is low, kidneys excrete renin, which stimulates the production of angiotensin I and angiotensin II. Angiotensin II increases blood pressure due to its vasoconstrictive properties. The system is influenced by blood viscosity and can be disrupted by drugs to control high blood pressure, heart failure, kidney failure, and diabetes.
Vitamin D activation
Kidneys convert Vitamin D into active form, calcitriol, which stimulates calcium absorption and resorption. Kidney failure results in lost ability to activate Vitamin D, leading to poorly absorbed calcium, bone disease, and immunological issues. PTH, secreted by parathyroid glands, overcompensates.
Synthesise prostaglandin
Kidneys produce 2 vasodilatory prostaglandins - PGE1 and PGI2.
Prostaglandins are produced in all nucleated cells.
Both vasodilators act on afferent arterioles to maintain blood flow and glomerular filtration and perfusion.
PGF2 - not produced by kidney, but acting on the kidney, contributes to vasoconstriction in times of volume depletion
mechanisms maintain renal blood flow and GFR:
- renal autoregulation (vasoconstriction or vasodilation of renal artery)
- tubuloglomerular feedback (afferent arteriole vasoconstriction or vasodilation based on Na+ levels)
- sympathetic nervous system (decreased blood pressure detected by carotid sinus and baroreceptors of aortic arch leading to vasoconstriction afferent arterioles)
- Renin-Angiotensin-Aldosterone system
Glomerular filtration and urine formation
The glomerulus filters blood to excrete waste and form urine through passive processes. The filtration membrane, lining arterioles, is fenestrated with small holes for solutes and small proteins. Filtrate, collected in Bowman’s capsule, flows through renal tubules to form urine. Reabsorption occurs passively or actively, with proximal and distal convoluted tubules and loop of Henle reabsorbing different substances.
Acute Kidney Injury
AKI is a sudden, severe impairment of renal function causing a build-up of toxins in the blood.
AKI are categorised as:
- Pre-renal: factors external to the kidneys that reduce renal blood flow and lead to decreased glomerular perfusion and filtration. Examples of pre-renal causes of AKI include: hypovolaemia (e.g. dehydration, haemorrhage, excessive diuresis), decreased cardiac output (cardiac arrhythmias, AMI), decreased renovascular blood flow (renal thrombosis / embolus).
- Intra-renal: conditions that result in direct damage to the renal parenchyma, causing impairment to nephron function. Examples include Acute Tubular Necrosis, renal ischaemia, nephrotoxic injury from drugs, contrast, trauma.
- Post-renal: causes involve mechanical obstruction of urinary outflow. As the flow is obstructed, urine refluxes into the renal pelvis, impairing renal function. Examples of post-renal causes of kidney injury include: renal calculi, renal or bladder tumours, strictures of the urethra, direct trauma.
CKD develops as a complication of systemic diseases such as:
- diabetes,
- glomerulonephritis,
- hypertension,
- cardiovascular disease,
- urinary tract obstruction/infection,
- hereditary defects of the kidneys, or
as a complication of renal diseases (e.g. failure to resolve AKI).
Stage 1 CKD
Kidney damage with normal or increased GFR
>90 GFR mL/min
Diagnosis and treatment
Treatment of co existing conditions
CVD risk reduction
