Urine Formation Flashcards
(40 cards)
What is the primary function of the kidneys?
To rid the body of waste materials and control the volume and composition of body fluids.
This includes balancing intake and output to maintain a stable environment for cellular activities.
What substances do kidneys excrete?
- Urea
- Creatinine
- Uric acid
- End products of hemoglobin breakdown
- Metabolites of various hormones
These substances include metabolic waste products and foreign chemicals.
What is the functional unit of the kidney?
The nephron.
Nephrons vary in number among species but remain relatively constant within species.
What are the two main regions of the kidney?
- Outer cortex
- Inner medulla
These regions are essential for the kidney’s function.
What is the glomerular capsule also known as?
Bowman’s capsule.
It is the dilated blind end of the nephron that contains the glomerulus.
What is the role of the loop of Henle?
It consists of descending and ascending limbs that play a crucial role in urine concentration.
Cortical nephrons lack a thin ascending limb.
What are the two principal types of nephrons in mammals?
- Cortical nephrons
- Juxtamedullary nephrons
They are classified based on the location of their glomeruli and the depth of their loops of Henle.
What percentage of cardiac output is normally directed to the kidneys?
22%.
This blood flow is crucial for kidney function.
What is the glomerular filtration rate (GFR) in humans?
About 125 ml/min.
Total GFR formed per day is approximately 180 L.
What is the filtration fraction?
The percentage of renal plasma flow that becomes glomerular filtrate.
Normal GFR is 125 ml/min with a plasma flow of 650 ml/min, resulting in an average filtration fraction of 19%.
What factors determine the filtration pressure in the kidneys?
- Glomerular pressure
- Plasma colloidal osmotic pressure (COP)
- Bowman’s capsular pressure
These factors influence the rate of filtration.
True or False: Afferent arteriolar constriction increases GFR.
False.
Afferent arteriolar constriction decreases blood flow into the glomerulus and reduces GFR.
What effect does sympathetic stimulation have on GFR?
Mild to moderate stimulation decreases GFR; strong stimulation can reduce it to zero.
This occurs through vasoconstriction of afferent arterioles.
What is autoregulation of RBF and GFR?
The ability of RBF and GFR to remain relatively constant despite changes in systemic arterial pressure.
It is an intrinsic mechanism independent of nerve supply.
What does the myogenic theory explain?
The response of arterioles to changes in blood pressure, where increased BP causes contraction and decreased BP causes dilation.
This helps maintain normal RBF and GFR.
What is the juxtaglomerular apparatus (JGA)?
A structure that helps regulate renal blood flow and GFR, containing macula densa and juxtaglomerular cells.
JGA cells release renin in response to reduced GFR or blood pressure.
What are the three processes involved in urine formation?
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
These processes occur within the nephrons.
What type of fluid is glomerular filtrate?
Essentially protein-free and devoid of cellular elements.
It is filtered through the glomerular membrane.
What is the significance of the vasa recta?
They play an essential role in the formation of concentrated urine.
Vasa recta are associated with long looped nephrons.
What is the fluid that is filtered through the glomerular membrane into the Bowman’s capsule?
Glomerular Filtrate (GF)
Glomerular fluid is essentially protein-free and devoid of cellular elements.
What are the three layers of the glomerular capillary membrane?
- Endothelium of the capillary
- Basement membrane
- Podocytes (epithelial cells)
Podocytes surround the outer surface of the capillary basement membrane.
What are fenestrae?
Small holes in the endothelial cells lining the glomerulus
Fenestrae allow for increased permeability of the glomerular capillary membrane.
What is the composition of the basement membrane surrounding the endothelium?
A meshwork of collagen and proteoglycan fibrillae
This composition allows the basement membrane to filter large amounts of water and small solutes.
What do podocytes do?
Form slit pores through which glomerular filtrate filters
Lining The outer surface of the Glomerulus
Podocytes have finger-like projections that are not continuous.
