Test 3 Flashcards
Urinary structures
Ureter is a tube that transports
using from the kidney to the urinary bladder, which is a holding structure
for urine
In females, the bladder is anterior to the
uterus and posterior to the pubic bone and anterior to the rectum. In
males, there is a connection of the bladder to the prostate, which is
inferior to the bladder.
Close in proximity
or share location
with reproductive
system
Urinary bladder
Urinary bladder
- peritoneum
- detrusor
muscles
- ureteral
openings
- internal &
external
sphincters
- urethra
The bladder is very distensible organ -
distention is made possible by smooth muscle bands that make up the
detrusor muscle. Volumes of fluid in the bladder in adults can go up to
500–600 mL. Uretal openings connect the urinary bladder to the urethra
(urethra empties into bladder here). This leads into the base of the
bladder where urethra starts, which is empties urine into the external
environment (micturition). There are two sphincters (ring of muscles) that
control the passageway using from the bladder to urethra. These are
controlled by reflexes (too much volume will open up the sprinters) but
you have cortical control of the external sphincter as well to control
micturition
What’s in the kidneys
Renal cortex
• Renal medulla:
renal column &
pyramid
• Renal papilla
• Minor & major calyx
• Renal pelvis
• Renal hilum: renal
vein, artery, nerve
and pelvis
The key to urine production are kidneys, which are positioned more
superiorly in comparison to ureter and urinary bladder (vertebrae T12-L3).
Note that the right kidney is slightly lower then left as it is slightly
“displaced” by the liver on the right.
The major function of the kidneys is to filter the blood and this is done in
the functional units of the kidney, the nephron’s and specifically, the
glomerulus of the nephron. Each nephron is supported by several
structures in the kidney, the more superficial, renal cortex and the less
superficial, renal medulla. The medulla is made up of renal pyramids,
which are separated by the renal columns and the base of each pyramid
is referred to the papilla. Nephrons are embedded in the cortex and
medulla and they drain filtrate (urine) into the minor calyx, just below the
papillae, then major calyx, then renal pelvis and then ureter. Note that
renal nerve, renal artery and renal vein are all present in the kidneys and
all make up a section of the kidney called the renal hilum along wit the
renal pelvis.
Nephron
Nephron
• glomerulus
• proximal
convoluted tubule
(PCT)
• distal convoluted
tubule (DCT)
• nephron loop
• collecting duc Nephrons are the functional units of the kidney and can be of varying
sizes and can extend into just the medulla or both the medulla and cortex
(longer nephron loop). Each nephron is composed of the following
sections: glomerulus (filtering), and renal tubule. Renal tubule in the
nephron is composed of the proximal and distal convoluted tubule
(secretion and reabsorption), the nephron loop (secretion and
reabsorption) and collecting duct which drains into the minor calyx.
how blood is supplied
to the kidneys
Renal artery —>
segmental artery
—> interlobar
artery —>
arcuate artery —
> cortical radiate
artery —>
afferent arteriole
—> glomerulus
afferent arteriole
—> Glomerulus
(podocytes) —>
efferent arteriole
• Filtrate into the
renal capsule
space and then
into tubule space
Efferent arteriole
—> peritubular
capillaries (vasa
recta)
Peritubular
capillaries —>
cortical radiate
veins —>
arcuate veins —
> interlobar vein
—> renal vein
To understand kidney function, let’s first focus on how blood is supplied
to the kidneys and how it lives the kidneys. Blood arrived to the kidneys
via the renal artery at the renal hilum. The blood from the renal artery
flows into the segmental artery around the boundary of cortex and
medulla and then into the interlobar artery around each pyramid and then
into the cortical artery which reaches the glomerulus via the afferent
arterioles.
This is the site of bood filtration - blood from the afferent arterioles is
arriving at the glomerulus at high pressures and is surrounded by the
glomerulus filled with podocytes or opening through which the fluid from
the blood is filtered into the renal capsule/corpuscle and starts flowing
through the tubule in the nephron.
The filtered blood then exits the glomerulus via the efferent arteriole and
drains into peritubular capillaries which is a network that surrounds all of
the sections of the tubule of the nephron, with vasa recta being specific
part of the capillaries around the nephron loop. Remember that the
fenestration properties of capillaries (fenestrated capillaries) are the key to
further exchange of water and salts between the tubule of the nephron
and blood (this will determine how much water or salts is in the urine
eventually From peritubular capillaries, the blood then leaves the kidneys vi the
cortical radiate veins, arcuate veins, interlobar veins and then renal vein.
So overall, the blood was filtered at the glomerulus and exchange of
water and ions can take place through the peritubular capillaries as filtrate
(fluids filtered from the blood in glomerulus) flows through the tubule
space in the nephron and blood flows through the tubule for the final
exchange of water and salts before using is formed when filtrate collects
in the collecting duct and drains into the minor calyx. Peritubular
capillaries flow
around distal
(DCT) and
proximal
convoluted tubule
(PCT) and
between loop of
henle & collecting
tubule the blood in the capillaries ends up flowing in the direction opposite to the
filtrate in the tubule. This opposite direction of flow between the blood
and filtrate in the tubule is called the countercurrent flow and is the key to
efficient exchange of salts and water between blood in the capillaries and
filtrate in the tubule of the nephron.
overall outward pressure
in the glomerulus
Due to positive overall outward pressure
in the glomerulus - the fluids can leave the blood through podocytes of
the glomerulus and “drain” or filter in the recap capsule. Renal capsule
leads into proximal convoluted tubule, then the nephron loop and then
the distal convoluted tubule and then the collecting duct. As the filter
travels through the renal tubule further exchange of ions and water takes
place, which determines the final concentration of water and wasted in
the urine that will eventually leave the body.
How is blood filtered & urine formed?
reabsorption
Urine formation
continues with
reabsorption from
renal tubule into the
body (interstitial
space and blood)
- nutrients and water
reabsorbed into the
blood stream In different sections of the tubule, reabsorption of some elements can
take place - seen as purple boxes and an arrow pointing away from the
tubule. This means that nutrients and water can be taken further from the
filtrate as it passes through the nephron - last change for the body to take
claim of more water and nutrients before they leave the body.
Reabsorbed back into the blood (or interstitial space and then blood)
How is blood filtered & urine formed? Secretions
Urine formation
continues with secretion
from blood into tubule
- waste products and
hydrogen secreted into the
renal tubule
- If all in balance, urine is at
ideal concentration, water
and pH balance is
maintained and wastes are
removed Additionally, in other sections of the tubule, secretion of some elements
can take place - seen as beige boxes here and an arrow pointing towards
the tubule. This means that wastes that have not beed filtered out in the
glomerulus can be added later along the tubule so that they leave the
body as they are not needed. Overall this complex interplay or
reabsorption and secretion of wastes and other components will
determine the composition of the urine. Note that at times, your urine may
be darker in colour, meaning that your body was conserving water and
not adding too much of water to the filtrate (less water was leaving the
body as it is needed for other metabolic and physiological processes -
conserving water when dehydrated, for example). This also plays a role in
how your urinary system plays a role in helping balance a pH of the body
- more hydrogen ions can be secreted and reabsorbed in the renal tubule
space to make adjustments to the blood pH.
Note that orange in the diagrams on the right represents renal tubule cells
and the hello is the space insides the tubule (effectively external
environment). Blue is the body (interstitial space) and red is the blood. Movement towards yellow is secretion and movement towards the blood is
reabsorption. Reabsorption
& secretion in
the nephron
loop
Most specific reabsorption and secretion in the nephron happens in the
nephron loop. This structure is the key to how much water can be
reabsorbed because of three important features:
- descending loop is permeable to water
- ascending loop is permeable to salts
- filtrate moves in the opposite direction to blood flow in the nephron loop
Because of this feature, water can be reabsorbed effectively in the
nephron loop as there is always a favourable concentration gradients of
salts around the loop - the water moves from the filtrate to the blood
(reabsorption); this is referred to countercurrent multiplier.
Why should fluids be balanced?
Fluids in the body
- in cells (intracellular
fluid- ICF)
- outside of cells
(extracellular fluid -
ECF)
- between cells
(interstistial fluid - IF)
- in blood plasma &
other vessels the key to kidney function is driven
by the overall fluid balance in your body. Your body is essentially
composed of these secretions of fluids spaces: fluids inside of your cells
and fluids outside of your cells. Fluids outside of your cells are fluids in
plasma in spaces between cells and blood and in lymph for example.
How are fluids balanced?
Reabsorption &
secretion in the
Loop of Henle and
along the
PCT/DCT
Reabsorption - increase in ECF
Reabsorption in
collecting tubule
with the help of
special channe
Secretion - decrease in ECF Whenever your cells are dehydrated, for ICF goes down for example, the
fluids from ECF will compensate for this loss - fluids will move from ECF
to ICF to hydrate cells. This also means that the overall volume of ECF will
change and this is the signal for example for kidneys to reabsorb more
fluids or more water - your body is always trying to maintain same volume
of ICF to ECF.
Urine formation
starts with filtration in glomerulus
- then reabsorption of nutrients and water from renal tubule back to
interstitial space and ultimately blood
- and secretion of wastes and ions into the renal tubule from
blood/interstitial space
Most specific reabsorption and secretion of salts and water in the
nephron or renal tubule happens in the nephron loop or the Loop of
Henle. This structure is the key to how much water can be reabsorbed
because of three important features:
- descending loop is permeable to water
- ascending loop is permeable to salts
- filtrate moves in the opposite direction to blood flow in the nephron loop
Because of this feature, salts can first be reabsorbed to the blood of vasa
recta around the ascending loop because the blood around the
ascending loop has lower concentration of salts. The highest
concentration of salts in the nephron is at the loop itself, which is where
salt reabsorption starts and water reabsorption from the descending loop stops.
As the blood moves towards the descending loop, it is highly concentrated in
salts and has less water than the filtrate in the descending nephron loop. Since
the descending loop is permeable to water, additional water can further be
reabsorbed in the nephron loop (remember that filtrate already passed through
this area but because of the countercurrent flow arrangement between the blood
and the filtrate flow in the nephron, even more water can be reabsorbed back
into the body from the filtrate that the blood runs passed (this is in addition to
PCT and DCT and collecting duct reabsorbing water).
How are fluids balanced?
Whenever your cells are dehydrated, ICF goes down. The fluids from ECF
will compensate for this loss - water will move from higher concentration
from ECF to lower concentration to ICF to hydrate cells. This also means
that the overall volume of ECF will change or decrease and this is the
signal for example for kidneys to reabsorb more water in order to equalize
ICF and ECF volumes in your body.
We mention that reabsorption of water happens in DCT and PCT and the
descending loop of Henle. The reabsorption of water along the renal
tubule happens with the help of aquaporins in the collecting tubule and
this is represented on the figure on the right.
Yellow represents the inside of the collecting tubule - the space inside the
tube that is filled with filtrate or pre-urine that eventually becomes using as
it passes through the kidneys. The orange cells represent the wall of the
collecting tubule section of the renal tubule. These cells help special
channels aquaporins, that help transport water into the cells of the
collecting duct wall. They exist on the basolateral (close to the
body/blood) and apical side (close to the lumen/outside of the body) of
the renal tubule wall. As the water concentration in the cells of the wall
increases, the aquporins on the basolateral side also help transport the water
across the interstitial space into the blood/plasma of the blood, therefore
increasing the concentration of the water in the body. This effectively increases
ECF and in the cases where the body needs to balance out ICF and ECF (where
ECF was lost to ICF), the extra water that is reabsorbed in the collecting tubule
can help increase ECF volume and equalize ECF and ICF. This is one solution
but there is also other things that your body can do, like stimulate thirst (see next
slide)
connect changes in ICF and therefore ICF back to blood volume
and cardiovascular system
Increase or
decrease in ICF
volume affects
ECF volume
• ECF volume
connected with
blood pressure
(affecting blood
volume!) When ECF volume is lower (ECF was lost to the ICF because cells are
dehydrated), the body blood volume was decreased and the blood
osmolality is increased (higher concentration of ions/particles dissolved in
the blood/given volume of fluids due to lower concentration of water in
that fluid).
Because there is decreased volume of blood, there is less blood returning
to the heart (the venous return is lower), which is detected by the
baroreceptors in the blood (detect pressure changes in the blood). At the
same the higher osmolality is detected by the osmoreceptors in the
hypothalamus. To ensure increase in ECF thirst is stimulated through
these homeostatic mechanisms: Angiotensin II secretion increases due to
lower blood volume and pressure - angiotensin II causes the muscular
walls of small arteries (arterioles) to constrict (narrow), increasing blood
pressure. At the same time, thirst centers are activated due to detection
of high osmolality and dry mouth feeling. Once thirst is increased and
water is taken in, this overall increases water in ECF (increases blood volume or
venous return) and this decreases blood osmolality overall.
So this is how the water can be balances in the body - and how urinary and
cardiovascular homeostatic loops are involved in this.
How are electrolytes balanced?
waste products &
hydrogen secreted
into the renal tubule
- If all in balance,
urine is at ideal
concentration,
water and pH
balance is
maintained and
wastes are
removed sodium is reabsorbed from the proximal convoluted section of
the renal tubule though several co-transporters, including, sodium-
hydrogen pumps but also many other co-transporters on the apical side
of the wall. The sodium-potassium pump is also active on the basolateral
side of the renal wall of the proximal convoluted tubule. As a result of
apical co-transporter work, the net concentration of sodium increases
inside the cells of the renal tubule wall, which can then move down the
concentration gradient towards the blood (note that this also pulls in
some water - water will follow ions/salts to decrease blood osmolality).
Similar arrangement is needed for the balance of hydrogen ions and the
balance of hydrogen ions is of course critical for maintaining pH balance
in the body and ensure that acidosis/alkalosis is avoided if possible.
Carbonic anhydrase helps break down the carbonic acid both in the
lumen of the proximal convoluted tubule and the cell walls of the tubule
as well. The balance of hydrogens in the lumen and the blood is balanced
through the sodium hydrogen pumps on both the apical side of the cell making
up the renal tubule wall as well as the basolateral side. If there is a build up of
hydrogen ions in the cell of the wall and less hydrogen in the blood, the extra
hydrogen ions would be reabsorbed. If there is more hope hydrogen ions in the
plasma, more would be secreted into the cell of the tubule and then to the lumen
of the tubule. What governs how the direction of hydrogen ion movements is
related to the pH homeostatic mechanisms in the body.
Aldosterone role in electrolyte balance
Decrease
electrolytes
connected to
aldosterone
release
• Aldosterone
targets kidneys to
balance sodium decreasing levels of sodium in the blood (which
also implies higher potassium concentration in the blood - why is this
true?), aldosterone is released from the adrenal cortex. Aldosterone
stimulated reabsorption of sodium by the kidneys, in which case
sodium/potassium levels normalize. Let’s look at the example when both
sodium and blood volume is low next.
renin-angiotensin-
aldosterone system, which balances the blood pressure in the body and
is connected to both electrolyte and fluid balance in the kidneys,
specifically, the nephron.
Cells of the renal tubule wall in the distal convoluted tubule detect low
fluid flow or low sodium concentration in fluids. In response renin is
secreted. Renin helps stimulate aldosterone but it is not the only required
enzyme. Liver also releases angiotensinogen which helps in a series of
enzyme reactions that convert angiotensin I to angiotensin II, which
stimulates adrenal cortex of the adrenal gland just superior to the kidney
to release more aldosterone. Another step that is needed here is from the
respiratory system - pulmonary blood contains more angiotensin-
converting-enzyme, which is an enzyme that helps make angiotensin II
and angiotensin II helps vasoconstriction all vessels in the body (if there is
not enough fluid, this is a signal for all the body to retire less of it locally
but also a signal for the respiratory and cardiovascular centres that overall
more blood and blood at higher pressure is needed to balance the
homeostatic blood volume loop).
Aldosterone stimulates updake of sodium on the apical membrane of the cells
from the lumen of the renal tubule to the cells of the wall and once more sodium
is delivered to the cells, more of it can move down its concentration gradient
from the cells of the wall to the interstitial space and blood. This may seem
counterintuitive, but remember that there was low fluid, fluid moving at low
pressures so the goal here is to increase blood volume first. Because sodium is
reabsorbed, the blood is less concentrated in sodium so that the water can then
be reabsorbed into the blood around the DCT and collecting tubule. Additionally,
aquaporins in the collecting duct increase water reabsorption and this is
stimulated by the increase in secretion of the anti-diuretic hormone (hormone
that increases water reabsorptions- remember that the you take diuretics, you
are increasing how much water you are eliminating from the body, so this would
be the opposite of that or the opposite to secretion).
For those of you who were interested in the digestive system, let’s highlight at
least the role of the liver here. Liver is the key organ to help digestion, to help
make blood clotting factors, to help eliminate wastes and as you have seen here
to help the blood flow effectively. We already mentioned the hepatic portal
system and this system as well as the bile ducts is the key to sending different
enzymes to the digestive system that help digest different elements of the food in
the stomach and moving down the intestine.
How is pH maintained?
Secretion of
hydrogen from
renal tubule key
to what the pH is
in the tissues
outside of the
renal system would take place in the case of pH being too low (too many
hydrogen ions (metabolic or respiratory acidosis)
To help with lowering hydrogen ions in the body, proximal convoluted
tubule can help by secreting more hydrogen ions.
Step 1: Sodium ions are reabsorbed from the filtrate in exchange for H+
by an antiport mechanism in the apical membranes of cells lining the renal
tubule.
Step 2: The cells produce bicarbonate ions that can be shunted to
peritubular capillaries.
Step 3: When CO2 is available, the reaction is driven to the formation of
carbonic acid, which dissociates to form a bicarbonate ion and a
hydrogen ion.
Step 4: The bicarbonate ion passes into the peritubular capillaries and
returns to the blood. The hydrogen ion is secreted into the filtrate, where
it can become part of new water molecules and be reabsorbed as such,
or removed in the urine
Egg conducting & gestation structures
Labia majora
• Vagina
• Labia minora
• Clitoris
• Uterus
- cervix
- uterine tube (oviduct)
- fimbriae
• Ovary
- ovarian ligament Labia majora: folds of hair-covered skin that protect the inner
reproductive structures
Labia minora: medial to the labia majora; protect urethra and the
entrance to the reproductive tract
Clitoris: superior and anterior portions of the labia minora come together
to encircle the clitoris, an organ that originates from the same cells as the
glans penis (in sperm producing individuals); abundant nerves important
in sexual arousal, sensation, and orgasm.
Vagina: a muscular canal, the entrance to the reproductive tract
Uterus: important for support of potential embryo
Uterine tube: important for egg conduction from ovary to uterus
Ovary: sites of production and development of oocytes or eggs
Major structures of uterus
Uterus
- cervix
- perimetrium
- myometrium
- endometrium
- uterine tube
(isthmus,
ampulla,
infundubulum)
- fimbriae Ovary
- ovarian
ligament
- suspensory
ligament Cervix: entry point into uterus from vagina
Endometrium: key structure for developing embryo and where embryo
embeds during pregnancy; surrounded by myometrium and then
perimetric superficially; has two strata or layers: basal and functional layer
- basal layer is attached to the myometrium and does not shed during
menses, the functional layer does and it is the layer that both sheds and
thickens in response to increase estrogen and progesterone. Spiral
arteries are part of the functional layer and they both shed during menses
and rebuild during proliferative phase of the uterine cycle.
Ovaries are supported by ovarian, suspensory and broad ligament just
lateral to the uterus and medial to the start of the uterine tube.
Fimbriae of the uterine tube connect to the ovary to pick up the oocyte,
which then travels to uterine tube (infundibulum, ampulla and then
isthmus) to reach the uterus.
Sperm-producing & conducting structures
Penis
- glans penis
- corpus cavernosum
- corpus spongiosum
- urethra
• Prostate
- prostatic urethra
- ejaculatory duct
• Testis
- scrotum
- epididymis
- ductus deferens
Glans penis, corpus cavernous and spongiosum: reproductive organ
structures that support sexual arousal, sensation and orgasm.
Note the shared placement of urethra in the penis
Tests: site of sperm production and development
Scrotum: skin covered muscular sac that protect sperm developing
structures and maintains temperature within testis
Epididymis: site important for the start of physical maturation of sperm
Ductus deferens: sperm conducting site connecting testis with seminal
vesicles and guiding the semen with spermatozoa to urethra
Prostate: excretes an alkaline, milky fluid to the passing seminal fluid from
the seminal vessicle (together forming semen, which ensures that semen
is first coagulated and then decoagulated following ejaculation).
Major structures of testis
Testis
- scrotum
- seminiferous
tubules
- rete testis
- epididymis
- ductus deferens Tests: site of sperm production and development
Scrotum: skin covered muscular sac that protect sperm developing
structures and maintains temperature within testis
Seminiferous tubules: sperm production starts
Rete testis and epididymis: sites important for the start of physical
maturation of sperm
Ductus deferens: delivers physically maturing sperm towards prostatthic
urethra where if combines with semen, starts functional maturation
(becomes fully motile)
oogenesis
Oogenesis
- oogonia to primary
oocytes in fetal ovary
prior to birth
- suspended in meiosis I
until puberty
- secondary oocyte
development cycles
- oocyte meiosis
completes (mature
ovum) if sperm present The process of oogenesis begins with ovarian stem cell or oogonia, which
are formed during fetal development. They divide via mitosis to form
primary oocytes in the fetal ovary prior to birth (this is not true for sperm).
These primary oocytes are arrested in meiosis I and resume it years later,
beginning in puberty and continuing until near menopause or cessation of
reproductive function in egg-producing individuals). Therefore, the
number of primary oocyte present in the ovaries declines from 1-2 million
in an infant to approximately 400,000 at puberty to zero at the end of
menopause.
The initiation of ovulation or release of an oocyte from an ovary is a
transition from puberty to reproductive maturity and from this point
ovulation occurs approximately monthly. Just prior to the ovulation a
surge of a luteinizing hormone triggers resumption of meiosis I in a
primary oocyte. This causes a transition from primary to secondary
oocyte but the division forms a different looking polar body and a secondary
oocyte (one daughter cell is much larger and this larger cell eventually leaves the
ovary as a secondary oocyte, while the smaller cell may or may not complete
meiosis and eventually disintegrates (so up to four cells may be produced from
primary oocyte, but only one survives as the secondary oocyte!). The single
haploid secondly oocyte inly completes meiosis II is a sperm succeeds in
penetrating barriers and reaching it - it is only then that meiosis II resumes
producing one haploid ovum (mature egg) that at the instant of fertilization by the
haploid sperm becomes the first diploid cell of a new offspring (zygote).
folliculogenesis
Oogenesis
supported by
ovarian follicles
- primordial follicles
recruited in cycles
beginning in puberty
- develop into
primary—
>secondary—
>tertiary follicles
- ovulation This is another look at the process of oogenesis from the perspective of
primary oocyte and follicle development in the ovary - this process of
follicular development is referred to as folliculogenesis or the maturation of
a follicle, which happens monthly approximately. Follicles are key to
support of the developing oocyte and when they stop developing, the
oocytes cannot be supported and released from the ovary.
The process begins with small primordial follicles in newborns and they
can stay in resting state until recruited after puberty (a few recruited every
day to join a pool of immature follicles called primary follicles). Primary
follicles then start transitioning to a different type of tissue (grow) and
become secondary follicles, increasing in diameter. The process
continues and hormones like FSH help stimulates the growth of the
tertiary follicle, while LH stimulateds the production of estrogen by
granulosa and theca cells. Once the follicle is mature, it raptures and
releases the secondary oocyte. The cells remaining in the follicle then
develop into the corpus luteum, which becomes important for
progesterone secretion. Keep in mind that most of the recruited
primordial follicles degenerate in this process (undergo atresia) but a small
percentage is needed to support this growth and development of tertiary follicle)
uterine cycle
oogenesis,
changes happen
to the uterine wall
to support
ovulation of
secondary oocyte
- follicular phase
prior to ovulation
- luteal phase
after ovulation Uterine cycle
- menses (shedding of
the endometrium) and
proliferative phase
(rebuilding of
endometrium) overlaps
with follicular phase
- secretory phase
(support of released
oocyte) during luteal
phase The process
of development of the secondary oocyte and tertiary follicles are part of
the ovarian cycle as this process happens in the ovaries.
While this process is happening in the ovaries, another important cycle,
uterine cycle happens simultaneously and is driven by the hormones
released from the developing follicles and corpus luteum. The first phase
of the ovarian cycle is the follicular phase and once the secondary oocyte
is released and ovulation took place and corpus luteum is developed the
ovaries enter the luteal phase. Development of the corpus luteum is
triggered by the surge in LH secreted by the follicles and cells in the
follicles. It also secretes estrogen, which helps rebuild endometrium of the
uterus.
Once corpus luteum is formed, it also secretes hormones like the
progesterone, which helps maintain endometrium of the uterus. If the
released secondary oocyte is not fertilized and does not complete meiosis
II, it will not form the zygote and it does not need the support of the
endometrium (helps support the developing zygote divisions) another look at the process of oogenesis from the perspective of primary oocyte
and follicle development in the ovary - this process of follicular development is
referred to as folliculogenesis or the maturation of a follicle, which happens
monthly approximately. Follicles are key to support of the developing oocyte and
when they stop developing, the oocytes cannot be supported and released from
the ovary.
The process begins with small primordial follicles in newborns and they can stay
in resting state until recruited after puberty (a few recruited every day to join a
pool of immature follicles called primary follicles). Primary follicles then start
transitioning to a different type of tissue (grow) and become secondary follicles,
increasing in diameter. The process continues and hormones like FSH help
stimulates the growth of the tertiary follicle, while LH stimulateds the production
of estrogen by granulosa and theca cells. Once the follicle is mature, it raptures
and releases the secondary oocyte. The cells remaining in the follicle then
develop into the corpus luteum, which becomes important for progesterone
secretion. Keep in mind that most of the recruited primordial follicles degenerate
in this process (undergo atresia) but a small percentage is needed to support
this growth and development of tertiary follicle). In other words implementation
does not happen and because of this, endometrium is not needed. If there was
implementation, progesterone levels would remain high as secreted by corpus
albicans, But in this case, progesterone levels drop and corpus albicans
degrades - this degradation happens 14 days post ovulation and at that point
both progesterone and estrogen lower secretion, signalling that the cycle should
start again. This is the onset of the menses phase of the uterine cycle, which
overlaps with a new start of primordial follicle recruitment in the ovarian cycle.
During menses, endometrium is shed and with the shedding of the tissues,
blood vessels are impacted as well. As the follicles are developing, estrogen
secretion increases, which triggers switch from menses to the proliferative phase
in which endometrium is rebuilt and becomes ready for the next ovulation.
Hormones of uterine cycle
follicular phase, hypothalamus increases secretion of
gonadottropin-releasing hormones, which increase secretion of follicle-
stimulating and luteinizing hormone by the anterior pituitary. FSH and LH
both increase follicle development and endometrial rebuilding as well as
increase estrogen secretion. Estrogen will decrease secretion by the
hypothalamus and pituitary to prepare the cycles for the ovulation. At ovulation and at the onset of the luteal phase, the cycle is restarted but
it is the progesterone that triggers a decrease secretion by the
hypothalamus and pituitary to prepare for the next cycle. If corpus luteum
declines so does the progesterone and endometrium maintenance stops
as there is no implantation of the zygote into the endometrium.
Spermatogenesis
Spermatogenesis
• Mitosis of
spermatogonium
• Meiosis of primary
spermatocyte and
secondary
spermatocyte
• Spermatids
• Spermatozoa through
spermiogenesis
During spermatogenesis, a new spermatogonium divides by mitosis
about every 16 days. Primary spermatocytes undergo meiosis I and
secondary spermatocytes meiosis II to form four equally sized spermatids,
which reach physical maturation once they become mobile through
spermatogenesis (become spermatozoa). Spermatogenesis occurs in the
seminiferous tubule and complete physical maturation starts in epididymis
and ductus deferens (note that for spermatogenesis and reaching full
mobility, the sperm must also pass the seminal gland all way around the
prostate). The sperm production process lasts about 64 days and starts
at puberty. No finite number of sperm as the new sperm is procured
every 16 days. (15-200 million sperm per ml of semen)
Regulation of spermatogenesis
• Spermatogenesis
regulated by LH
and FSH (regulated
by GnRH) Release of a hormone called gonadotropin-releasing hormone (GnRH)
from the hypothalamus stimulates the endocrine release of hormones
from the pituitary gland. Binding of GnRH to its receptors on the anterior
pituitary gland stimulates release of the two gonadotropins: luteinizing
hormone (LH) and follicle-stimulating hormone (FSH). FSH binds
predominantly to the Sertoli cells within the seminiferous tubules to
promote spermatogenesis. FSH also stimulates the Sertoli cells to
produce hormones called inhibins, which function to inhibit further FSH
release from the pituitary, thus reducing testosterone secretion. LH binds
to receptors on Leydig cells in the testes and upregulates the production
of testosterone. The system is a also negative feedback loop because the
end products of the pathway, testosterone and inhibin, interact with the
activity of GnRH to inhibit their own production. A negative feedback loop
predominantly controls the synthesis and secretion of both FSH and LH.
When concentrations of testosterone in the blood reach a critical
threshold, testosterone itself will bind to androgen receptors on both the
hypothalamus and the anterior pituitary, inhibiting the synthesis and secretion of GnRH
and LH,
respectively. When
the blood
concentrations of
testosterone once
again decline,
testosterone no longer interacts
with the receptors
to the same
degree and GnRH
and LH are once
again secreted,
stimulating more
testosterone production. This
same process
occurs with FSH
and inhibin to
control
spermatogenesis.”
Trace the
pathway of egg
development and
conduction
Ovary
Uterine tube:
Fimbriae
Infundubulum
Ampula
Isthmus
Uterus (if fertilized stops here - embeds into endometrium; if not fertilized
- degenerates and sheds with endometrium through structures below)
Uterine Isthmus
Cervix
Vagina
Egg conducting structures are ovaries and uterine tube
Gestation structures (development of fertilized egg is uterus)
Structures that lead into uterus are labia and vagina
Trace the pathway of
sperm development
and conduction by
connecting the
structures
Testis
Seminiferous tubules
Rete testis
Epididymis
Ductus deferens
Ampulla
Prostate
Ejaculatory duct
Prostatic urethra
Penis
Urethra Sperm producing structures are testes
Sperm conducting structures are ductus deferens, prostate and urethra
Note that the big difference between production of egg and sperm is that
sperm are continually produced throughout a life time after puberty in a
cycle of about 16 days and this cycle of spermatogenesis or sperm
production takes about 64 days. Sperm are also smaller and mobile when
mature.
Note that the process of spermatogenesis is the process of sperm
development, while last phase, spermiogenesis is the last process of
adding mobility to the sperm tail (this fully completes in external
environment - full mobility, until then although tail developed, it is in
suspended animation (non moving form of tail) until reaches external
environment of the vagina)
Is the following statement true or false?
“Ovulation takes place at a mid-point of the
ovarian/uterine cycle.”
First of all, uterine and ovarian cycle can be synchronized over a varying
amount of days but your textbook reports an average
To calculate ovulation day, most people assume it is at mid-point of a
cycle. In fact, it is tied into hormone regulation of the cycle.
It should be the length of the cycle minus 14 days that it takes for corpus
luteum to degenerate (if you subtract 14 from total cycle days it will give
you the time that corpus luteum is formed which is what marks ovulation.
Average 13-14 in luteal phase but follicular much more variable: 10-13
days
Key points for uterine cycle: secretory phase overlaps with luteal phase
(supporting potentially fertilized egg); menses and proliferative phase is
aligned with follicular phase; estrogen (estradiol) secretion is the key for
menses and proliferative phase and increase in estrogen increases LH
and FSH just before ovulation and this spike in LH in particular, triggers
ovulation and release of secondary oocyte from the ovary; progesterone
secretion from the corpus lute takes over and is the negative feedback for
inhibition of LH and FSH until it disintegrates.
Compare and contrast the role or LH in
ovulation and sperm production.
LH in oogenesis:
- follicular development
- luteal development
- ovulation (surge in LH needed for ovulation to take place)
LH in spermatogenesis:
- testosterone release (leydig cells) Note that in follicular phase, hypothalamus increases secretion of
gonadotropin-releasing hormones, which increase secretion of follicle-
stimulating and luteinizing hormone by the anterior pituitary. FSH and LH
both increase follicle development and endometrial rebuilding as well as
increase estrogen secretion. Estrogen will decrease secretion by the
hypothalamus and pituitary to prepare the cycles for the ovulation (and
inhibit FSH and LH). At ovulation and at the onset of the luteal phase, the
cycle is restarted but it is the progesterone that triggers a decrease
secretion by the hypothalamus and pituitary to prepare for the next cycle.
If corpus luteum declines so does the progesterone and endometrium
maintenance stops as there is no implantation of the zygote into the
endometrium GnRH (gonadotropin-regulating hormone from hypothalamus) stimulates
secretion of FSH and LH. FSH stimulates secretion of ABP, and this
together with LH secretion stimulates testosterone secretion. Both
increase in FSH and testosterone inhibit FSH (though secretion of inhibin),
LH and GnRH secretio
Anemia and diabetes both have connections
with renal issues. What are the
connections/issues
Anemia is a condition in which there are not sufficient red blood cells
in the blood. EPO increase in the kidney is needed to correct for this.
EPO produced in the peritubular cells specifically in the cortex
(stimulated by partial pressure of oxygen levels). In chronic anemia,
EPO levels in the kidney are low. (EPO gene synthesized by kidney,
secreted into blood, binds to EPO receptor to promote RBC
production in the bone marrow).
In diabetes there is a continually high amount of sugar filtered into the
glomerulus and the nephron in general and this can damage the blood
vessels in the kidney. Usually there is also high blood pressure (build
up of deposits in the blood vessels contracts the blood flow, giving the
signal to the heart to pump more blood and at higher pressures to the
constructed areas - this raises blood pressure), which increases
glomerular pressure. This can lead to both ineffective secretion and
reabsorption in the kidneys and kidney failure.
Why can’t we drink saltwater? What would it
take for our nephrons to be able to handle
salt water?
b. If we were to drink salt water, our blood would absorb too much salt with a
given volume of water - would be too salty. Our kidneys would not be able to
compensate with the volume of salt that needs to be removed. What would
be needed for the kidneys to be able to handle this amount of salt in the
blood? Special salt channels in the kidneys or salt glands (animals living in
marine environments have these!) to remove the extra salt from the blood
before the blood reaches the kidneys.
Explain why you feel thirsty by creating a
concept map for the following words: ECF,
cells, blood volume, blood pressure, and renin.
When ECF volume is lower (ECF was lost to the ICF because cells are
dehydrated), the body blood volume was decreased and the blood
osmolality is increased (higher concentration of ions/particles dissolved in
the blood/given volume of fluids due to lower concentration of water in
that fluid). Because there is decreased volume of blood, there is less
blood returning to the heart (the venous return is lower), which is detected
by the baroreceptors in the blood (detect pressure changes in the blood).
At the same the higher osmolality is detected by the osmoreceptors in the
hypothalamus. To ensure increase in ECF thirst is stimulated through
these homeostatic mechanisms: Angiotensin II secretion increases due to
lower blood volume and pressure - angiotensin II causes the muscular
walls of small arteries (arterioles) to constrict (narrow), increasing blood
pressure. Renin increase helps with angiotensin II increase, which helps in
widespread vasoconstriction. The widespread vasoconstriction is a
stimulus for the cardiovascular system to send more blood to this area as
well. . At the same time, thirst centers are activated due to detection of
high osmolality and dry mouth feeling. Once thirst is increased and water
taken in, this overall increases water in ECF (increases blood volume or
venous return) and this decreases blood osmolality overall. When ECF volume is lower (ECF was lost to the ICF because cells are
dehydrated), the body blood volume was decreased and the blood
osmolality is increased (higher concentration of ions/particles
dissolved in the blood/given volume of fluids due to lower
concentration of water in that fluid). Because there is decreased
volume of blood, there is less blood returning to the heart (the venous
return is lower), which is detected by the baroreceptors in the blood
(detect pressure changes in the blood). At the same the higher
osmolality is detected by the osmoreceptors in the hypothalamus. To
ensure increase in ECF thirst is stimulated through these homeostatic
mechanisms: Angiotensin II secretion increases due to lower blood
volume and pressure - angiotensin II causes the muscular walls of small
arteries (arterioles) to constrict (narrow), increasing blood pressure.
Renin increase helps with angiotensin II increase, which helps in
widespread vasoconstriction. The widespread vasoconstriction is a
stimulus for the cardiovascular system to send more blood to this area
as well. . At the same time, thirst centers are activated due to detection of high osmolality and dry mouth feeling. Once thirst is increased
and water is taken in, this overall increases water in ECF (increases blood
volume or venous return) and this decreases blood osmolality overall.
What role does the nephron loop play in
electrolyte balance? In your answer use the
following terms: countercurrent, ascending,
descending, sodium, and water.
nephron loop plays a role in electrolyte reabsorption because of
several features of the nephron loop itself as well as the blood flow in the
vessels around it. Electrolytes are first be reabsorbed to the blood of vasa
recta around the ascending loop because the blood around the
ascending loop has lower concentration of salts and because the
ascending loop is permeable to solutes/electrolytes only. The highest
concentration of salts in the nephron is at the loop itself, which is where
salt reabsorption starts and water reabsorption from the descending loop
stops. As the blood moves towards the descending loop, it is highly
concentrated in salts and has less water than the filtrate in the
descending nephron loop. Since the descending loop is only permeable
to water, additional water can further be reabsorbed in the nephron loop.
The pre-filtrate already passed through this area of the nephron but
because of the countercurrent flow arrangement between the blood
flowing in the vasa recta and the filtrate flow in the nephron, even more
water can be reabsorbed back into the body from the filtrate that the
blood runs passed in addition to reabsorption of electrolytes and water in PCT and DCT.
of these do you think
are most directly regulated by kidneys during
exercise? If you think there is a connection, add
a term that connects the kidney to this
particular variable.
Terms: pH, RBC, 2,3-BPG, EPO, Hemoglobin,
temperature
All of the terms other than temperature have some more or less direct
connection to the kidneys:
pH - Hydrogen ion balance
RBC - connection to EPO available in the kidneys which stimulate RBC
production (this is also a connection with EPO)
Hb - the more RBCs through EPO increase, the more Hb available
BPG biphosphate glycerine is made by RBCs (glycolysis - more RBCS
operating at low oxygen conditions, the more BPG - produced -
promotes dissociation of oxygen from hemoglobin)
To help with lowering hydrogen ions in the body, proximal convoluted
tubule can help by secreting more hydrogen ions.
Step 1: Sodium ions are reabsorbed from the filtrate in exchange for H+
by an antiport mechanism in the apical membranes of cells lining the renal
tubule.
Step 2: The cells produce bicarbonate ions that can be shunted to
peritubular capillaries.
Step 3: When CO2 is available, the reaction is driven to the formation of
carbonic acid, which dissociates to form a bicarbonate ion and a
hydrogen ion.
Step 4: The bicarbonate ion passes into the peritubular capillaries and
returns to the blood. The hydrogen ion is secreted into the filtrate, where
it can become part of new water molecules and be reabsorbed as such,
or removed in the urine.
Keep in mind that aldosterone helps govern another process in which
hydrogen and potassium is also exchanged in distal convoluted tubule
and collecting tubule: when there is too much potassium or too much hydrogen,
it is the aldosterone that governs what should be transported here (low sodium,
potassium exchanged more; why aldosterone activated when thirsty because
water follows high concentration of salts like sodium; aldosterone stimulates
potassium ion exchange instead of hydrogen in DCT and Collecting
tubule/collecting duct)
Blood path of kidneys
Blood arrives to the kidneys via the renal artery at the renal hilum. The
blood from the renal artery flows into the segmental artery around the
boundary of cortex and medulla and then into the interlobar artery around
each pyramid and then into the cortical artery which reaches the
glomerulus via the afferent arterioles. Blood from the afferent arterioles is
arriving at the glomerulus at high pressures and is surrounded by the
glomerulus filled with podocytes or opening through which the fluid from
the blood is filtered into the renal capsule/corpuscle and starts flowing
through the tubule in the nephron. The filtered blood then exits the
glomerulus via the efferent arteriole and drains into peritubular capillaries
which is a network that surrounds all of the sections of the tubule of the
nephron, with vasa recta being specific part of the capillaries around the
nephron loop. Remember that the fenestration properties of capillaries
(fenestrated capillaries) are the key to further exchange of water and salts
between the tubule of the nephron and blood (this will determine how
much water or salts is in the urine eventually). From peritubular capillaries,
the blood then leaves the kidneys vi the cortical radiate veins, arcuate
veins, interlobar veins and then renal vein. So overall, the blood was filtered
at the glomerulus and exchange of water and ions can take place through
the peritubular capillaries as filtrate (fluids filtered from the blood in
glomerulus) flows through the tubule space in the nephron and blood flows
through the tubule for the final exchange of water and salts before using is
formed when filtrate collects in the collecting duct and drains into the minor
calyx.
