hi let's talk about the structure and function of the urinary system
in this video we'll discuss the major structures and functions of the urinary system we'll also
discuss the gross features of the kidney now when we think of the functions of the urinary system
we can think of what the kidneys do aka the renal functions versus what the ureters the urinary
bladder and the urethra do here in this video we'll focus on the renal functions now when we
think of the physiology of the cardiovascular system you know we have materials coming in
and out of metabolically active cells that are surrounded by interstitial fluid and so there's an
exchange of materials between these areas we also have an exchange of materials in and out of the
cardiovascular system which is going to interplay with various other bodily systems so the digestive
system the respiratory system the urinary system and it's the urinary system which is
of particular interest to us here the kidneys are amazing dynamic filters of the blood and
so we see how the kidneys are very important with respect to the maintenance of extracellular volume
and osmolarity so what we mean by that is all of the fluids which are not found within the cells
the kidneys are going to have some control over now within that fluid are dissolved items that
are very important to physiology things like various ions sodium potassium calcium chloride
phosphate etc all of these things the kidneys can choose to either keep within the body or
excrete as urine now in the process of dynamically deciding whether or not we keep or excrete ions
the kidneys are going to have a profound impact on the maintenance of ph homeostasis
so in particular in a region of the nephron called the distal convoluted tubule
there are opportunities to secrete protons or conserve i hold on to bicarbonate ions and these
are going to be very important in the context of carbonic acid bicarbonate ion buffer system
for ph homeostasis in the blood also extracellular fluid is predominantly water and so the kidneys
in serving as dynamic filters can decide how much water stays and how much water goes
and then finally the kidneys are going to be able to impact glucose homeostasis
so um there are two ways in which they may choose to uh to do this if we were to assign any
leological bases to this one is through the process of gluconeogenesis so
we the kidneys are able to build glucose through glutamine or um they can
reabsorb glucose which they typically do as as part of their uh de facto processes
or if levels of blood glucose are too high they can even excrete it
into the urine the kidneys also serve an endocrine function so there are three hormones
that the kidneys secrete that are important to our body so the the first is calcitriol calcitriol
is an activated form of vitamin d it's secreted by cells of the proximal convoluted tubule
and it is an important cofactor for the absorption of calcium from the gut lumen and so
calcitriol has the impact of increasing plasma concentrations of calcium
there are also peritubular cells that are capable of secreting erythropoietin or epo erythropoietin
as you may recall from the cardiovascular lectures is the hormone that's responsible for
the initiation of erythropoiesis or the creation of red blood cells the kidneys
also secrete renin so there are juxtaglomerular cells as part of the juxtaglomerular apparatus
nestled between the renal corpuscle and the distal convoluted tubule and here depending on
conditions we have a fantastic ability of intrinsically regulating
renal processes but we also have the ability of secreting renin a hormone which
is the beginning of the raa pathway raa stands for renin angiotensin aldosterone which is a pathway
whose ultimately ultimate effect on the body is to increase blood pressure
and then finally and probably most obvious among all of the renal functions is the excretory role
so as part of serving as these dynamic filters the kidneys are able to pull any of the
wastes of catabolism away any biologically active substances drugs etc and excreted as urine
now the basic anatomy of the urinary system is pretty simple there are
bilaterally paired although not bilaterally symmetrical kidneys these kidneys are
very well vascularized by renal arteries and veins as we can see here so they directly
communicate through either the abdominal aorta or the inferior vena cava through these vessels
there are also and this is a mistake bilaterally paired ureters these ureters transport urine
produced by the kidneys down to the urinary bladder and then not seen here is a midline
tube called the urethra that drains the urinary bladder to the outside world
an individual kidney will have two borders and two poles so there is a convex lateral
border the convex lateral border is directed posterior laterally there is also a concave
medial border the concave medial border is directed antero medially and it's at
that medial border that we have the hilum so the hilum is the region which receives the
neurovasculature as well as transmits the renal pelvis so that hilum once we pass that plane
goes into a renal sinus so the renal sinus is the space that's surrounded by
the parenchyma of the kidney there are also superior poles and inferior poles
to kidneys as well and from time to time there can be a special type of accessory renal
arteries called polar arteries which can be directed to either of these poles
so the hilum of the kidney is where everything enters or exits the kidney there are a couple of
major structures here to include so renal arteries enter at the at the hilum here we
can see the renal artery and we can also see the renal plexus associated with that renal artery
so that's going in through the hilum as well that renal artery is going to divide up into segmental
arteries which enter at the hilum and from time to time we may also see an accessory renal artery
entering in the hilum although we don't see that here renal veins also enter at the at the hilah
and the renal pelvis which is contiguous with the ureter is at the hilum as well
the physiologically active portion of the tissues of the kidney or the parenchyma of the kidney is
divided into two types of tissue there is cortex and deep to the cortex or surrounded by the cortex
medulla so the medulla is organized into pyramids it's probably a really
poor choice of of nomenclature here because if you were to dissect away all of the cortex
from the medulla we would actually see that these are more cone-shaped than they are pure middle but
when we look at them through dissected planes they appear to be pyramids and so
that's what they're named so the the base of these pyramids is superficial the apices
are deep and it's right at the apex of the pyramid that we have the renal papilla
the renal papilla is the point of no return for urine so all throughout the cortex and a medulla
blood is converted into filtrate and then there's a process of secretion and reabsorption so the
movement of materials between the blood and the filtrate and it's only at that renal papilla that
there is no more exchange happening so we can see how that renal papilla is surrounded here by
this structure here which is a minor calyx now the cortex which surrounds the medulla is organized in
two regions so there are cortical arches cortical arches are the regions of cortex that
are superficial to the medulla so all of these are cortical arches and then there are renal columns
the columns are the spaces between the cortical arches and the pyramids so i'm filling in the
the cortical columns here and we'll see how nephrons which are the functional units of kidneys
are going to be situated between both the cortex and the medulla
and that leads us to the assessment question of the video and that is
which parts of the renal parenchyma are found between the pyramids is it the cortical arches
no those are found superficial to the pyramids is it the medulla nope those
are the pyramids is it the papillae nope the papillae are the apices of the pyramids
correct answer renal columns are found in between the pyramids thank you very much for your time