Urinary System Part 2 Flashcards
Learn the Urinary System
What are the three processes involved in urine formation and adjustment of blood composition?
- Glomerular filtration
- tubular reabsorption
- Tubular secretion
Glomerular filtration
produces cell and protein-free filtrate
Tubular Reabsorption
selectively returns 99% of substances from filtrate to blood
Tubular Secretion
selectively moves substances from blood to filtrate
What is the first step of urine formation?
Filtration
What are the layers of the filtration barrier?
- capillary endothelium
- basement membrane
- podocytes of glomerular capsule
Capillary endothelium (filtration)
- fenestrated; very permeable
- allows passage of anything smaller than a cell
Basement membrane (filtration)
- not as permeable
- blocks all but small proteins
Podocytes of glomerular capsule (filtration)
creates filtration slits for flow into capsular space
Glomerular filtration is a ________ _____. This means that there is no ________ _________ required
passive process,
no metabolic energy
In glomerular filtration what molecules are able to pass?
allows molecules smaller than 3 nanometers to pass
water, glucose, amino acids, nitrogenous wastes
What happens to the plasma proteins in the blood during glomerular filtration?
- plasma proteins remain in the blood
- prevents a loss of all water to capsular space
- proteins in filtrate may indicate filtration membrane problem
Pressures that affect filtration: outward pressures
- forces that promote filtrate formation
- hydrostatic pressure in glomerular capillaries is essential glomerular blood pressure
- chief force pushing water and solutes out of the blood
Pressures that affect filtration: inward pressures
- forces inhibiting filtrate formation
- hydrostatic pressure in capsular space: filtrate pressure in capsule
- osmotic pressure in capillaries: pull of proteins in blood
What is the golerular filtration rate equal to?
the total volume of filtrate formed by all of the glomeruli of both kidneys each minute
The magnitude of NFP is directly proportional to ___
GFR (glomerular filtration rate)
Net filtration pressure (NFP)
sum of forces, pressure responsible for filtrate formation
Glomerular filtration rate (GFR)
volume of filtrate formed per minute by both kidneys
primary pressure is glomerular hydrostatic pressure
Constant glomerular filtration rate is important as it allows the kidneys to make and filtrate and maintain……
extracellular homeostasis.
How does glomerular filtration rate affect systemic blood pressure?
- increased GFR causes increased urine output, lowers blood volume, and thus blood pressure
What is the goal of extrinsic controls?
to maintain systemic blood pressure
- nervous system and endocrine mechanisms are main extrinsic controls that override intrinsic controls
Intrinsic autoregulatory controls of glomerular filtration?
- maintinas the GFR when arterial blood pressure is 80-180 mmHg
what are the two types of renal autoregulation of glomerular filtration?
- Myogenic mechanism
- tubuloglomerular feedback mechanism
What is the Myogenic Mechanism?
- Afferent arteriole smooth muscle contracts when stretched
- the increased blood pressure causes muscle contraction and constriction of afferent arterioles –>restricts blood flow into glomerulus (decrease hydrostatic pressure) —> decreased BP causes dialtion of afferent arterioles
- both help maintain normal GFR despite normal fluctuations in blood pressure
Tubuloglomerular feedback mechanism
- flow-dependent mechanism directed by macula densa cells (respond to filtrate’s NaCl concentration)
- if GR increases, filtrate flow rate increases causing high NaCl levels in filtrate (constriction of afferent arteriole, which lowers NFP and GFR, allowing more time for NaCl reabsorption).
- opposite mechanism for decreased GFR
Juxtaglomerular complex (JCG)
- each nephron has one
- involves modified portions of distal portion of ascending limb of nephron loop
- important in regulating GFR and blood pressure
What are the 2 cell populations seen in JGC?
- macula densa
- granular cells
Macula Densa
- tall closely packed cells of ascending limb
- contain chemoreceptors that sense NaCl content of filtrate
Granular cells (JG cells)
- enlarged smooth muscle cells of arteriole
- act as mechanoreceptors to sense blood pressure in afferent arteriole
- contain secretory granules that contain enzyme renin
Extrinsic controls: Neural and Hormonal Mechanisms
- regulate GFR to maintain systemic blood pressure
- override renal intrinsic controls if blood volume and pressure need to be increased
How do the extrinsic controls of GFR preserve blood volume and pressure?
- through the sympathetic nervous system
- norepinephrine is released by sympathetic nervous system and epinephrine is released by the adrenal medulla causing:
- sytemic vasoconstriction (increasing BP)
- afferent arteriole contriction, decrease GFR,
less urine
- blood volume and pressure increases
What are the sympathetic effects?
- constricts afferent arteriole
- helps maintain BP and shunts blood to heart and muscles
What is the main mechanism for increasing blood pressure?
the renin-angiotensin-aldosterone mechanism
What are the three pathways to renin release by granular cells of afferent arterioles when blood pressure drops significantly?
- Direct stimulation of granular cells by sympathetic nervous system
- Stimulation by activated macula densa cells when filtrate NaCl concentration is low
- Reduced stretch of afferent arteriole
Study the renin-angiotensine-aldosterone system
Proximal convolute tubule (PCT) mainly functions in__________. (Renal Tubule)
reabsorption
What are the cells of the Proximal convoluted tubule?
cuboidal cells with dense microvilli that form brush border (increase surface area).
Nephron loop allows us to produce a _________ ________.
hypertonic urine
(aka the loop of Henle)
Describe the major aspects of the nephron loop
- U shaped structure
- descending limb: permeable to water
- ascending limb: impremeable to water, actively transports (pumps) solute into interstitial fluid
The nephron loop produces high osmolarity of the _______ ______ deep in the medulla that is 4X that of cortex and plasma.
interstitial fluid
What does the distal convoluted tubule (DCT) mainly function in?
secretion
what are the cells found in the distal convoluted tubule?
- cuboidal cells with very few microvilli
- confined to cortex
What are the collecting ducts?
- recieve filtrate from many nephrons
- run through the medullar pyramids and igve them their striped appreaance
- ducts fuse together to deliver urine into minor calyces and toward major calyces
- maintain water and Na+ balance
- ADH works here
