The Urinary System Physiology Flashcards
What do kidneys regulate ?
- plasma ionic composition
- plasma volume
- plasma pH and osmolarity
- removal of metabolic wastes
- the number of red blood cells
- vitamin D production
Which structures compose the nephron ?
- renal corpuscle
- renal tubule
What are the structures composing the renal corpuscle ?
- glomerulus
- Bowman’s capsule
Which structures compose the renal tubule ?
- proximal tubule
- loop of henle
- distal convoluted tubule
- collecting duct
In the kidney what structure regulates blood pressure ?
Juxtaglomerular apparatus composed of :
- macula dansa
- granular cells secreting renin
Which structures of the nephron are found in the renal cortex ?
Renal corpuscle
The proximal tubule
The distal convoluted tubule
Which structures of the nephron are found in the renal medulla
Descending and ascending limbs of henle loops
What are the 2 types of nephron ?
Cortical nephrons
Juxtamedullary nephrons
What is the blood supply of nephrons ?
The efferent arteriole forms a second capillary bed around the renal tubule
In cortical nephron : peritubular capillaries
In juxtamedullary nephron : vasa recta
What are the functions of the nephron allowing the regulation of the composition of plasma
- filtration
- reabsorption
- secretion
What is the role of bowman’s capsule in the nephron ?
It surrounds the glomerulus to form a lumen and captures and directs the filtrate to the proximal tubule. It is composed of a parietal layer and a visceral layer.
What is the proportion of plasma entering the Bowman’s capsule ?
10-20% of plasma enters
Explain how glomerular filtration takes place ?
Glomerular capillaries are fenestrated. The only thing separating the blood from the filtrate is the shared basement membrane. This system ensures a filtration based on size : blood cells and large proteins cannot pass but most other constituents go through.
Proteins associated with fenestration are negatively charged which allows positively charged proteins to pass through more readily. This leads to the creation of a filtrate with a composition very similar to plasma but with a slight predominance of positively charged substances.
What is the glomerular filtration rate ?
The volume of filtrate formed by both kidneys per minute
Which factors can affect the glomerular filtration rate ?
- hydrostatic pressure (pressure produced by a fluid against a surface)
- osmotic pressure
What means an osmotic pressure near to zero ?
Absence of proteins in the filtrate
In the glomerular filtration what are the pressures in favor of filtration ?
- glomerular capillary hydrostatic pressure (60 mmHg)
- Bowman’s capsule osmotic pressure (0 mmHg)
In the glomerular filtration what are the pressures opposing to filtration ?
Bowman’s hydrostatic pressure (15 mmHg)
Glomerular capillary osmotic pressure (30 mmHg)
What is the glomerular filtration rate ?
125 ml/min which equals to 180L of filtrate a date
What is the renal plasma flow ?
The volume of plasma flowing through the kidneys and which equals to 625 ml/min
What is the filtration fraction
The filtration rate divided by the plasma flow rate which equals to 20%
From the 625 ml of plasma arriving per minute to the kidney only 20% arrives to renal tubule
Which factor influences the glomerular capillary hydrostatic pressure ?
The mean arterial pressure
If it rises then the glomerular capillary hydrostatic pressure rises too and favors filtration
At which mean arterial pressure is the glomerular filtration rate kept constant ?
80 mmHg < MAP < 180 mmHg
How is glomerular filtration rate controlled ?
- myogenic regulation
- glomerulotubular feedback
Explain the myogenic regulation of GFR
Mean Arterial Pressure stretches smooth muscles in afferent arteriole Vasoconstriction Higher resistance Less blood flow Lesser pressure in glomerulus
And vice versa
Explain the tubuloglomerular feedback
Change in glomerular filtration rate affect the flow of tubular fluid
Cells of macula dansa sense this flow
Secretion of paracrine signals
Smooth muscle contraction / dilatation in afferent arteriole
If GFR rises : vasoconstriction takes place
If GFR drops : vasodilatation takes place
When does the extrinsic regulation of GFR take place ?
When the mean arterial pressure is < 80 mmHg
Describe the extrinsic regulation of GFR
Sympathetic activation through baroreceptor reflex
Vasoconstriction in afferent and efferent arteriole
Higher resistance
Less blood flow
Less urine output to minimize the diminution of blood volume