Renal system (wk7) Flashcards
What is the renal system?
-The renal system = Integrative system. It has functions of: excretion of waste, regulate H2O and electrolyte balance and hormones
The main functions of the kidneys:
-Functions:
* Regulation of water, inorganic ion balance, and acid-base balance (in cooperation with the lungs)
* Removal of metabolic waste products from the blood and their excretion in the urine (e.g. Urea, creatinine)
* Removal of foreign chemicals from the blood and their excretion in the urine
* Gluconeogenesis (during prolonged fasting)
* Production of hormones/ enzymes. 1. Erythropoietin (EPO), which controls erythrocyte production, 2. Renin, an enzyme that controls the formation of angiotensin, which influences blood pressure and sodium balance, 3. Conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, which influences calcium balance.
Describe stage 1-8 of the structure and function of the kidney
-From lecture 09/11
The structure and function of the nephron
-Nephrons are the structural and functional units of the kidney. Each kidney has over 1 million of these units. Helps regulate blood pressure in the body. Helps regulate water content.
-Each nephron consists of a renal corpuscle, which contains the glomerulus (which is a tuft of capillaries) and a renal tubule.
-The tubule forms a cup shape around the glomerulus called the glomerular capsule (Bowman’s capsule)
The structure and function of the nephron
-Juxtaglomerular Apparatus
-Juxtaglomerular Apparatus -> The juxtaglomerular cells are mechanoreceptors (they sense blood pressure) in the afferent arteriole. If blood pressure is too high, they can try and manage it through multiple processes. The macula densa cells are chemoreceptors that respond to changes in the NaCl content of the filtrate. Regulate electrolyte content and through nephron absorption and excretion, can manage it.
-Kidney sits in abdominal cavity. Includes the ureter, renal pelvis, nephron, renal cortex + medulla and urinary bladder.
Basic renal processes
-Glomerular filtration and tubular secretion
-Glomerular Filtration -> (Roughly) 20% of plasma entering the Glomerular Capillary (GC) is filtered into BC
-Tubular secretion -> Substances such as hydrogen ion, potassium, and organic anions move from the peritubular capillaries into the tubular lumen. Tubular secretion is an important mechanism for:
* Disposing of drugs and drug metabolites
* Eliminating undesired substances or end products that have reabsorbed by passive processes (urea and uric acid)
* Removing excess K+
* Controlling blood pH
Basic renal processes
-Tubular reabsorption and differential handling in the kidney
-Tubular reabsorption -> Tubular reabsorption begins as soon as filtrate enters the tubule cells. Paracellular transport occurs between cells (even though they have tight junctions) and is seen mainly with ions. Transport can be active (requires ATP) or passive (no ATP).
-Differential handling in the kidney -> The excretion of a substance is equal to the amount filtered plus the amount secreted minus the amount reabsorbed:
* X -> Substance X is an example of handling a foreign substance. Can excrete and remove the chemicals that we don’t need/want.
* Y -> Substance Y is important to retain, but requires maintenance within homeostatic range. As blood goes through nephron, there is a chance to reabsorb some substances.
* Z -> Substance Z is very important for health and therefore completely reabsorbed
Basic renal processes
-Excretion and ‘Divisions of Labour’ in the Tubules
-A substance can gain entry to the tubule and be excreted in the urine by glomerular filtration or tubular secretion, or both. Once in the tubule, however, the substance does not have to be excreted but can be completely reabsorbed. Therefore:
Amount excreted = Amount filtered + Amount secreted – Amount reabsorbed
-‘Division of Labour’ in the Tubules -> The majority of reabsorption is accomplished by the proximal tubule and the loop of Henle. Extensive reabsorption by the proximal tubule and Henle’s loop ensures that the masses of solutes and the volume of water entering the tubular segments beyond Henle’s loop are relatively small. These distal segments then do the fine-tuning for most substances, determining the final amounts excreted in the urine by adjusting their rates of reabsorption and, in a few cases, secretion. Lots of active transport occurs here and is where the majority of reabsorption occurs.
Glomerular Filtration Rate (GFR)
-Basics
-The GFR is the amount of blood filtered by the glomeruli each minute. Factor influencing GFR:
* Capillary permeability (+)
* Surface area (the size of the capillary bed)
* Hydrostatic pressure that drives fluid out of the capillaries, which oppose the exit of fluid
* Osmotic forces within the capillaries, which oppose the exit of fluid
-A normal GFR for a health adult is (roughly) 120ml/min
GFR
-Net filtration pressure
-GFR is governed by Starling’s forces: Hydrostatic pressure difference across capillary wall favouring filtration Vs Protein conc. Difference across the wall that creates an osmotic force. Therefore, GFR is controlled by vascular changes.
GFR
-Kidney glomeruli importance
-The kidney’s glomeruli are a far more efficient filter than other capillary beds in the body because:
* Filtration membrane is a large surface area and very permeable to water and solutes
* Glomerular pressure is higher (roughly 55 mmHg), so they produce 180 L/day vs 3-4L/day formed by other capillary beds.
* That’s 125mL/min of total plasma volume (roughly 3L PV). Thus, kidney’s filter the entire PV (roughly) 60 times in a day
-During filtration, plasma proteins remain in plasma to maintain osmotic pressure. Blood cells or protein in the urine (proteinuria) indicates a problem with the filtration membrane. Filtration is achieved through the large surface area and the capillaries which allow the filtrates through the glomeruli.
GFR
-Concept of renal clearance
The clearance of any substance can be calculated by dividing the mass of the substance excreted per unit time by the plasma concentration of the substance. GFR can be measured experimentally by means of the inulin clearance and estimated clinically by means of the creatinine clearance. RC = (concentration of the substance in the urine x flow rate of urine formation/ concentration of substance in the plasma. If the substance is freely filtered and not reabsorbed or secreted, this ratio allows us to estimate the rate at which fluid is filtered at the glomerulus. To determine RC we use insulin (it’s freely filtered and neither reabsorbed nor secreted_ and creatine can be used but is less accurate.
GFR
-Filtration Fraction
This is the proportion of the plasma that enters the kidneys that is subsequently filtered at the glomerulus and passes into the renal tubules. It is calculated from the ratio GFR/ Renal Plasma Flow (RPF). Filtration fraction is typically 0.16-0.20, meaning 20% of the blood that enters the kidneys is filtered.
