The Renal System Flashcards
What is the function of the kidneys?
The primary function of the kidneys is homeostasis. This is achieved through regulation of the volume and conc of urine excreted. Urine production is a by-product of homeostasis
- The homeostatic functions of the kidney include
- Osmoregulation. Volume regulation
- Acid-base balance
- Electrolyte regulation
- Removal of metabolic waste and foreign chemicals (eg drugs) from the blood
- Endocrine functions (eg erythropoietin production)
The urinary tract is important for temporary storage and transport or urine out of the body
Describe the nephron
The nephron is the functional unit of the kidney. It contains tiny tubes and interrelated blood capillaries
Urine production begins here with the help of many structures:-blood vessels, the glomerulus, bowman capsule, the renal tubule
How does blood flow through the kidneys?
The whole kidney is supplied by the renal artery. This subdivides many times into tiny afferent arterioles that supply each nephron
The blood is drained by renal vein. This is supplied by venules coming away from each nephron which which merge to eventually form the renal vein
In between these arteries and veins hay complex capillary networks
State the four basic processes of renal function. of water and solutes in the urine
- 1.Glomerular Filtration
- 2.Tubular Reabsorption
- 3.Tubular Secretion
- 4.Excretion
Every few mins our entire plasma volume is filtered thru the Bowman’s capsule. Useful solutes are reabsorbed from the filtrate, unnecessary solutes are excreted in urine.
Describe glomerular filtration
Glomerular filtration is the first step in urine production
Blood form the renal artery enters afferent arterioles, which carry it into the glomerulus. Fluid/solute filtration occurs here. Blood is then carried away by the efferent arterioles
Efferent= smaller than afferent arterioles, which creates a high hydrostatic pa in the glomerulus. This drives fluid and solute filtration through pores in the capillary membrane, into Bowman’s capsule
Ultra-filtrate moves from B.capsule into the tubule.
Describe glomerular filtration rate (GFR)
GFR measures renal function – it is usually ~125mL/min. Reduced GFR indicates reduced renal function
We use plasma creatinine levels as an index of GFR.
It is used because it is freely filtered at the glomerulus, therefore the rate of creatinine filtration is equal to GFR
GFR decreases w age and w kidney damage
Describe tubular reabsorption
Following gf, the ultrafiltrate passes along the rest of the nephron (the proximal convoluted tubule, loop of Henle, the distal convoluted tubule, collecting duct). Useful substances are reabsorbed by the peritubular capillaries
The epithelial cells in the wall of the tubule have microvilli on their surface – this ⇡ SA for reabsorption
Reabsorption is selective for only useful substances (eg water, glucose Na, HCO3-, Cl, Ca). Reabsorption= via active transport and facilitated dif.
Describe tubular secretion
Tubular secretion: transfer of material from the peritubular capillaries to the lumen of the tubule (op of reabsorption)
Mainly driven by active transport and facilitated diffusion. V few, mostly waste substances are secreted back into the tubule.
Tubular secretion is important bc it removes substances not filtered at the glomerulus. It eliminates undesirable substances like urea + uric acid, excess K and H+ (which controls plasma pH)
Using a diagram, explain the excretion of water and solutes in the urine
Amount filtered–amount reabsorbed+ amount secreted = amount excreted in urine
Describe the total body water balance
The input of water= output of water
Balance must equal zero, or otherwise habra change in osmolality. It is renal excretion regulation that maintains 0 balance
Imagine you have exercised for 30 mins but there is no water to drink. How does the body respond?
Plasma osmolality rises, which triggers the thirst response
Response is increased secretion of hormone, ADH (antidiuretic hormone, also known as vasopressin)
This results in decreased urine volume, with increased urine osmolality/conc
What is the body’s response to drinking lots of water/fluids?
There is an increase in water absorption through GIT. Plasma osmolality falls, so in response hay reduced ADH secretion.
This results in increased urine volume with less urine osmolality.
Alcohol reduces ADH, so urine volume increases when you drink a lot of alcohol.
Measuring osmolarity indicates ADH function
Why can drinking so much water actually be bad for you?
If you drink so much that the kidneys cant excrete the excess, then you will dilute the ECFV, and get osmotic damage. Water moves into the cell and can burst/damage the cell
How is ECF volume regulated and determined?
ECF volume is determined by the amount of sodium in the compartment. Na is the major electrolyte in the ECF
Sodium intake and excretion must be balanced to maintain constant ECF volume, so Na balance is vital
Main volume sensors are in the cardiovascular system. A fall in blood volume is opposed by hormonal signals promoting sodium retention; water follows osmotically, restoring volume.
Regulated Renal Excretion is based on which two systems?
Sodium retaining systems: renin-angiotensin-aldosterone system (RAAS)
Sodium eliminating pathways: cardiac natriuretic peptides (ANP)
