HISTOLOGY - BIOL 4000 - LECTURE NOTES
SYSTEM TEXT - POWERPOINT
I. Urinary system
- General information
- semetrically paired organs that form the urine.
- carry urine to bladder, one from each kidney.
- site where urine is collected and stored until urination
- carries urine from bladder to external environment
to site concerned with kidney anatomy, function, disease and treament.
A. General external characteristics
1. Bean shaped => concave on
one side, convex on the other
2. Kidney is surrounded by a
dense connective tissue capsule.
3. An indentation in the concave
side is called hilus
where nerves, blood vessels and lymph vessels enter and leave.
Renal pelvis -
expanded end of the ureter that connects to the hilus. A region where urine
from the kidney collects and drains into ureter.
B. The Kidney can be divided into a
cortex and a
a. Upper portions of
b. Upper portions of
the collecting ducts
a. Parts of nephrons
called loops of Henle
b. The major portions
of the collecting ducts
that tranport urine to the calyces.
and minor calyces
that carry the urine to the renal pelvis
3. Cortex and Medulla in humans
a. The medulla can be
subdivided into structures called the medullary
or Malpighian pyramids
(also called renal
b. These pyramids of
tissue have there vertice (pointed end) at a renal calyx and their base at the
border of the cortex.
c. The pyramid
tissues consist of
that transfer urine from the nephrons in the cortex to the minor calyces
Portions of the nephron's loops of
side of the pyramid that extends toward the cortex is bordered by an
d. Where the
medullary pyramid tissue meets the cortex their are large arched blood vessels
e. Portions of the
medullary tissues called medullary rays
radiata) project into the cortical regions
subdividing it into regions called cortical
f. The cortical
labyrinths consist of many bowman's capsules, and proximal and distal
convoluted tubules and have a "tortuous appearance.
g. Note that in
addition to the cortical areas between the capsule and the bases of the
pyramids, cortical tissue also extends between the pyramids. These areas are
called the renal columns of
nephron - the
nephron is the functional unit of the kidney. There are approximately one
million nephrons in each human kidney - consists of 2 components
- 4 parts
* Can be
considered to be the expanded and invaginated end of the proximal convoluted
surface - parietal layer
surface - visceral layer
Composed of cells called podocytes
that have many processes
The smallest processes
intimately surround the capillaries of the glomerulus.
These pedicel interdigitate with each other and attach to the basal lamina of
Spaces betwen the interdigitating pedicels are called
slit diaphrgms or filtration slits
Filtrate that composes the urine enters Bowman's capsule through the filtration
The function of the podocytes is probably mechanical. They probably act to
prevent the rupture of the glomerular capillaries due to blood pressure and at
the same time allow filtration to proceed.
between the two layers called the subcapsular
parietal layer is composed of simple squamous epithelium
Bowman's capsule intimately surrounds the glomerulus
Composed of a tuft of tortuous capillary loops that arise from the afferent
arteriole and connect to the efferent arteriole.
capillary walls are highly fenestrated and completely encircled by a continuous
basal lamina (formed from fusion of endothelial cell and podocyte basal lamina,
arangement acts to form a selective filter that will allow certain components
of the blood plasma (including excretory wastes) to pass into Bowman's capsule.
arteriole except for the portion close to the glomerulus
In this are it looses it's internal elastic lamina
Smooth muscle cells of tunica medi become enlarged and glandular
These are the juxtaglomerular cells that secrete the enzyme
renin that is
involved in the control of blood pressure.
Function of renin
Converts plasma protein angiotensinogin
The angiotensin I is carried to the lungs by the circulatory system and it
there is converted to angiotensin II
by an enzyme in lung tissue.
Angiotensin II is a powerful vasoconstrictor that causes contraction of smooth
muscle in the tunica media of arteries and a resultant increase in systemic
The angiotensin II also causes an increase in secretion of the hormone
the adrenyl medulla.
Aldosterone acts on cells of renal tubules causing increased reabsorption of
sodium from the filtrate.
This reabsorption of sodium and its increased concentration in the blood along
with additional retension of fluid causes further increase in the systemic
called a venule because structure is like an arteriole
to afferent arteriole, but fewer juxtaglomerular cells
immediately breaks up into a capillary bed tht surrounds the convoluted
it extends between capillary beds, this may be considered a portal system
Renal tubule -
extends from Bowman's capsule, through cortex, into medulla, back into cortex
where it connects with a papillary collecting duct - 3 parts
Proximal convoluted tubule
Filtrate exits Bowman's capsule through proximal convoluted tubule.
tubule wall is composed of a simple cuboidal epithelium with a microvillar
brush border along the lumen of the tubule.
have many mitochondria located basally, a central, spherical nucleus, and a
well developed basement membrane.
walls of these cells interdigitate with each other.
apical plasmelemma shows very active pinocytosis between microvilli. This is
because these cells are responsible for reabsorption of proteineceous molecules
from the filtrate.
cells also reabsorb 75 - 80% of the water and sodium ions in the filtrate, as
well as certain sugars and amino acids.
Loop of Henle
Composed of the decending and ascending components.
* Each of
these has a thick and thin segment.
Each thick segment is a transition zone: decending thick segment goes from a
simple cuboidal to simple squamous epithelium, ascending thick segment goes
from a simple squamous to a simple cuboidal epithelium.
Thin segment resembles a blood capillary with somewhat thicker walls than
loop of Henle further concentrates the urine by the removal of aditional water
by a osmotic diffusion.
Distal convoluted tubule
by simple cuboidal epithelium in most regions (but see below).
* On your
lab slides these cells will look similar to those that line the proximal
tubule, however they lack a microvillar brush boarder.
* At the
point where the distal tubule is adjacent to the afferent and efferent
arterioles of it`s own renal corpuscle, the structure of its epithelium changes
(called the juxtaglomerular
become more columnar and take on a darker stain.
region is called the macula
Function of the macula densa is not certain, but it's close association with
the juxtglomerular cells suggests that it may provide "information"
to these cells that regulates the secretion of renin.
tubules and ducts
1. The distal convoluted tubules
of the nephrons empty into the collecting
2. The collecting tubules extend
into the renal medulla and merge to form the large
papillary ducts of Bellini
that empty into the calyces.
3. The smaller tubules are lined
with simple cuboidal epithelium. As they penetrate deeper into the medulla and
approach the papillary ducts, the lining becomes columnar.
4. The collecting tubules and
papillary ducts are not areas of reabsorption, but simply act to transfer the
urine to the calyces.
Cardiovascular circulation to the kidney
1. The kidneys receive blood from
2. These enter the kidney through
the connective tissue of the hilus.
3. Within the hilus these
arteries branch to form the interlobar arteries
which extend between the medullary pyramids.
4. As the interlobular arteries
reach the medullary - cortical boundary, they branch to form the
that run parallel to the connective tissue capsule surrounding the kidney at
the level of the cortical-medullary junction.
5. Branches from the arcuate
arteries extend perpendicular into the cortex and give rise to the
of the glomeruli.
6. The capillaries of the
glomerulus recoalesce to form the efferent
arteriole that leaves the glomerulus and then
rebranches to form two capillary networks,
a. one surrounding
the proximal and distal convoluted tubules and
b. the other
extending into the medullary tissue to form a capillary net around the loop of
7. In the case of the
juxtamedullary (next to the medulla) nephrons, one arteriole branch of the
efferent arteriole follows a path into the medulla were it breaks up into
linear capillaries that run parallel to the linear portions of the loops Henle
and the collecting ducts. These linear capillaries then loop back toward the
cortex where they form venules that will join the arcuate vein. These linear
capillaries are called the vasa recta
and provide oxygen and nutrients to the tissues of the medulla.
receive blood from the capillaries and carry it to the
which connect to interlobar veins
that extend parallel to their corresponding interlobar arteries.
9. The interlobar veins connect
to the renal vein
that carries blood out of the kidney.
10. There are also the stellate
veins in the peripheral cortex of the kidney that result from the convergence
of capillaries in this area.
structure is relatively simple. Read about it on pp. 375 - 379 in text.
1. Note there are differences
between male and female urethra.
2. Also note that the walls of
the bladder and the urinary passages leaving the bladder are lined with