1
Q
Urinary System
A
- consists of the kidneys, ureters, urinary bladder, and urethra
- urine flows from each kidney, down its ureter to the bladder and to the outside via the urethra
- kidneys filter the blood of wastes and return most of water and solutes to the bloodstream
2
Q
Kidney Functions
A
- reg. of blood ionic composition
- reg. of blood pH and osmolarity
- reg. of blood glucose (via glycogenesis)
- reg. of blood volume
- reg. of blood pressure
- release of erythropoietin and calcitriol
- excretion of wastes and forge in substances
3
Q
How much blood plasma is filtered every minute?
A
~125 mL
4
Q
How much blood plasma is filtered every day?
A
~180 L
5
Q
Three major physiological functions kidneys perform on blood
A
- filtration
- reabsorption
- secretion
6
Q
Reabsorption
A
~99% of the nutrients, electrolytes, etc. in filtered blood plasma is returned to blood
7
Q
Renal Threshold
A
if the concentration of any component of blood plasma exceeds its renal threshold, only some of the component will be returned to blood
the rest will be lost in urine
8
Q
Daily Renal Turnover in Adult
A
look at chart
9
Q
How many nephrons does a kidney have?
A
1 million
the number remains constant from birth
10
Q
Why does the size of the kidney increase?
A
the size increase of individual nephrons
11
Q
What happens if kidneys are injured?
A
there is no nephron replacement
12
Q
When is dysfunction in the kidney evident?
A
- until function declines to less than 25% of normal
- remaining nephrons have the capacity to handle larger work loads when necessary
- if one kidney is removed, remaining kidney nephrons will enlarge to handle additional work (remaining kidney will be able to filter at 80% of the normal rate of two kidneys)
13
Q
What are nephrons composed of?
A
corpuscle and tubule
14
Q
Renal Corpuscle
A
- site of plasma filtrate
- glomerulus is a knot of capillaries where filtration occurs
- glomerular (Bowman’s) capsule is a double walled epithelial cup that collects filtrate
15
Q
Renal Tubule
A
-site of reabsorption from filtrate and secretion into filtrate
Contains:
- proximal convoluted tubule (PCT)
- loop of Henle
- distal convoluted tubule (DCT)
16
Q
Where do DCTs drain?
A
collecting duct > papillary duct > renal pelvis > ureter
17
Q
Where are glomerular capillaries formed?
A
between afferent and efferent arterioles
18
Q
What do efferent arterioles give rise to?
A
The peritubular capillaries and vasa recta
19
Q
Renal Blood Flow
A
renal artery segmental arteries interlobar arteries arcuate arteries cortical radiate arteries afferent arterioles glomerular capillaries efferent arterioles peritubular capillaries cortical radiate veins arcuate veins interlobar veins renal veins
20
Q
Cortical Nephrons
A
- 80-85% of nephrons are cortical nephrons
- renal corpuscles are in outer cortex and loops of Henle lie mainly in cortex but can dip into the medulla
21
Q
Flow of fluid through a cortical nephron
A
- glomerular (Bowman’s) capsule
- proximal convoluted tubule
- descending limb of the loop of Henle
- ascending limb of the loop of Henle
- distal convoluted tubule (drains into collecting duct)
22
Q
Flow of fluid through a juxtamedullary nephron
A
- glomerular (Bowman’s) capsule
- proximal convoluted tubule
- descending limb of the loop of Henle
- thin ascending limb of the loop of Henle
- thick ascending limb of the loop of Henle
- distal convoluted tubule (drains into collecting duct)
23
Q
Juxtamedullary Nephrons
A
- 15-20% of nephrons are juxtamedullary nephrons
- renal corpuscles close to medulla and long loops of Henle extend into deepest medulla enabling excretion of dilute or concentrated urine
24
Q
How much blood does the kidney receive through it’s blood vessels?
A
25% of resting cardiac output via renal arteries
25
Glomerular Capillaries Function
where filtration of blood occurs
26
Peritubular Capillaries and Vasa Recta Function
carry away substances reabsorbed from filtrate
27
Sympathetic Vasomotor nerves
regulate blood flow and renal resistance by altering diameter of arterioles
28
Vasoconstriction and vasodilation of afferent and efferent arterioles
produces large changes in renal filtration
29
Histology of the Nephron and Collecting Duct
- single layer of epithelial cells forms walls of the entire tube
- distinctive features due to function of each region
30
Distinctive Regions of Nephrons and Collecting Duct
- microvilli
- cuboidal versus squamous
- hormone receptors
31
Microvilli are found on:
- PCT cells
| - intercalated cells of the CD
32
Cuboidal is more common; Squamous cells are found in:
- parietal layer of glomerular capsule
- loop of Henle descending limb
- loop of Henle thin ascending limb
33
Hormone receptors are found on:
- DCT cells
| - principal cells of the CD
34
Excretion
the process of eliminating waste products from body, or product(s) excreted from the body
35
Rate of excretion
rate of filtration plus rate of secretion minus rate of reabsorption
36
Glomerular Filtration
- blood pressure produces glomerular filtrate
- filtration fraction is 20% of plasma
- 180 liters/day of filtrate is reabsorbed to form 1-2 liters/day of urine
37
Filtering capacity is enhanced by:
1. thinness of membrane
2. large surface area of glomerular capillaries
3. high glomerular capillary blood pressure (due to smaller size of efferent arteriole)
38
Filtration Barrier is composed of:
1. fenestration pore
2. basal lamina
3. slit membrane between pedicels
39
Fenestration (pore) of glomerular endothelial cell
prevents filtration of blood cells but allows all components of blood plasma to pass through
40
Basal lamina of glomerulus
prevents filtration of larger proteins
41
Slit membrane between pedicels
prevents filtration of medium-sized proteins
42
Renal Corpuscle and ascending loop of Henle interaction
top of ascending limb contains macula densa cells which interact with cells lining the afferent arteriole (called juxtaglomerular cells)
43
Juxtaglomerular Apparatus
structure where afferent arteriole makes contact with ascending limb of loop of Henle
- macula densa is thickened part of ascending limb
- juxtaglomerular cells are modified muscle cells in arteriole
44
NFP
net filtration pressure
total pressure that promotes filtration
45
GBHP
glomerular blood hydrostatic pressure
46
CHP
capsular hydrostatic pressure
47
BCOP
blood colloid osmotic pressure
48
NFP equation
GBHP- (CHP+ BCOP) = 10mmHg
49
Glomerular Filtration Rate (GFR)
amount of filtrate formed in all renal corpuscles of both kidneys per minute
average adult rate is 125 mL/min
50
Why does homeostasis require a GFR that is constant?
- if GFR is too high, useful substances are lost due to the speed of fluid passage through a nephron
- if GFR is too low, sufficient waste products may not be removed from the body
51
What does NFP depend most heavily on?
glomerular blood hydrostatic pressure (GBHP)
52
How do changes in net filtration pressure affect GFR?
- filtration stops if GBHP drops from 55 mmHg to 45 mmHg
- GBHP is determined by mean arterial pressure (MAP)
- kidney functions normally with MAP between 80 mmHg and 180 mmHg because of GFP regulation
53
Autoregulation of GFR
Mechanisms that maintain a constant GFR despite changes in arterial blood pressure:
- myogenic mechanism
- tubuloglomerular feedback
54
Myogenic mechanism
(FAST)
- system increases in blood pressure stretch the afferent arteriole
- smooth muscle contraction reduces the diameter of the afferent arteriole returning the GFR to its previous level in seconds
55
Tubuloglomerular feedback
(SLOW)
- elevated systemic blood pressure raises the GFR so that fluid flows too rapidly through the renal tubule: Na+ and Cl- and water are not reabsorbed
- macula densa in ascending limb of loop of Henle detects increased Na+ and Cl-: inhibit release of Nitric Oxide (a vasodilator) from the juxtaglomerular apparatus
- afferent arterioles constrict: reduce GFR
56
Neural Regulation of GFR
-blood vessels of the kidney are supplied by sympathetic fibers that cause vasoconstriction of afferent arterioles
(norepinephrine release from sympathetic postganglionic neurons binds to alpha 1 adrenergic receptors and causes vasoconstriction of afferent arterioles)
-SNS will override renal autoregulation
-SNS will also stimulate renin release from the juxtaglomerular cells (see hormonal regulation)
-at rest, renal blood vessels are maximally dilated (sympathetic activity is minimal): renal autoregulation prevails
-with moderate sympathetic stimulation, both afferent and efferent arterioles constrict equally (GFR decreases slightly)
-with extreme sympathetic stimulation (exercise/hemorrhage), vasoconstriction of afferent arterioles predominates
(-GFR decreases substantially
-lowers uric output to maintain blood volume
-permits greater blood flow to other tissues ie. muscle)
57
Hormonal Regulation of GFR
two hormones contribute to the regulation of GFR:
1. atrial natriuretic peptide (ANP)
2. angiotensin II
58
Atrial natriuretic peptide (ANP)
- increases GFR
- stretching of the atria that occurs with an increase in blood volume causes hormonal release
- relaxes glomerular mesangial cells increasing glomerular capillary surface area and increasing GFR
59
Angiotensin II
- reduces GFR
- activated by ACE in the lungs following the release of renin from juxtaglomerular cells
- potent vasoconstrictor that narrows both afferent and efferent arterioles reducing GFR
60
Glomerular filtration rate in the Renal Corpuscle
105-125 mL/min of fluid that is isotonic to blood
61
Filtered substances in Renal Corpuscle
water and all solutes present in blood (except proteins) including ions, glucose, amino acids, creatine, urea, uric acid, etc.
62
Fluid in glomerular capsule is:
isotonic to blood 300 mOsm/liter
63
Tubular Reabsorption and Secretion
- nephron must absorb 99% of the filtrate
| - tubular secretion transfers materials from blood into tubular fluid
64
What does the most reabsorption?
proximal convoluted tubule (PCT)
65
Fine-Tuning Functions of Nephron
- solutes reabsorbed by active and passive processes
- water follows solutes by osmosis
- small proteins move across into the blood by pinocytosis
66
Tubular Secretion
- transfers materials from blood into tubular fluid
- helps control blood pH through the secretion of H+
- help eliminate certain substances (NH4+, creatinine, K+)
67
Paracellular Reabsorption
50% of reabsorbed material moves between cells by diffusion in some parts of the tubule
68
Transcellular Reabsorption
material moves through both the apical and basal membranes of the tubules cell by active transport
69
Which membranes of tubule cells have different types of transport proteins?
apical and basolateral
70
Reabsorption of Na+
- several transport systems exist to reabsorb Na+
| - Na+/K- ATPase pumps sodium from tubule cell cytosol through the basolateral membrane only
71
Obligatory Water Reabsorption
occurs when water is "obliged" to follow the solutes being reabsorbed
72
Facultative Water Reabsorption
occurs in collecting duct under the control of antidiuretic hormone (ADH)
73
What is reabsorbed in the PCT?
```
Water
Na+
K+
Glucose
Amino Acids
```
74
How does reabsorption in the PCT work?
- Na+ symporters help reabsorb materials from the tubular filtrate (glucose, amino acids, lactic acid, water soluble vitamins)
- intracellular sodium levels are kept low due to Na+/K+ pumps on the basolateral side
isosmotic reabsorption (water follows solutes)
75
What is the renal threshold for glucose and what happens when that level is reached?
200 mg/mL
Renal symporters cannot reabsorb glucose fast enough if blood glucose levels exceed 200 mg/mL
(some glucose remains in the urine: glycosuria)
76
What is a common cause for glycosuria?
Diabetes mellitus where in insulin activity is deficient and blood glucose cannot enter cells as readily as it does for unaffected individuals
77
What is reabsorbed in the Loop of Henle?
Water
Na+
K+
Cl-
78
What is secreted in the Loop of Henle?
Urea
79
Symporters in the Loop of Henle
Thick ascending limb of loop of Henle has Na+/K+/2Cl- symporters that reabsorb these ions
- K+ moves back into filtrate through K+ leak channels
- Na+ is pumped out on basolateral side
- Cl- diffuses across cell
Cations passively move to the vasa recta
-drawn to negative charge in capillary
In juxtamedullary nephrons the thick ascending limb is impermeable to water
80
What is reabsorbed in the early DCT?
Water
Na+
Cl-
81
Reabsorption of Na+ and Cl- in Early DCT
- like thick ascending limb, early DCT reabsorbs ions but it is more permeable to water
- Na+ and Cl- are reabsorbed by different symporters than those in the loop of Henle
- fluid entering the early DCT is hypotonic (~150 mOsm/L) and becomes more hypotonic until it reaches the late DCT
- all water reabsorption until late DCT is obligatory (always permitted) This is obligatory reabsorption of water
82
What is reabsorbed in the late DCT and CD?
Water
Na+
Urea
83
What is secreted in the late DCT and CD?
K+
84
Reabsorption of Na+ and secretion of K+ in the late DCT and collecting duct
Two types of cells are in the late DCT and collecting duct
1. principal cells
2. intercalated cells
- Principal cells reabsorb Na_ (and water if ADH present) and secrete K+
- intercalated cells reabsorb K+ and HCO3- and secrete H+
85
Formation of dilute urine
- remove excess fluid from blood by producing dilute urine
- blood plasma has 300 mOsm/L concentration
- filtrate osmolarity increases as it moves down descending loop of henle
- filtrate osmolarity decreases as it moves up ascending loop of henle
- filtrate osmolarity decreases in collecting duct and leads to dilute urine
86
What happens to the DCT and CD without ADH?
they are impermeable to water
throughout the journey, the volume of tubular fluid is constantly decreasing
87
Countercurrent Mechanism in descending limb of loop of Henle
- very permeable to water
- higher osmolarity of interstitial fluid outside the descending limb causes water to move out of the tubule by osmosis (at hairpin turn, filtrate osmolarity can reach 1200 mOsm/liter)
- less filtrate is left in the tubule (the volume of tubular fluid decreases)
88
Countercurrent Mechanism in ascending limb of loop of Henle
- impermeable to water, but symporters remove Na+ and Cl- so osmolarity of filtrate drops to 100 mOsm/liter
- for dilute urine, low ADH= water not recovered by DCT/CD
89
Formation of concentrated urine
to prevent water loss by excreting only concentrated urine
90
Facultative Reabsorption of water in the late DCT and CD
- as the concentration of ADH increases, more aquaporin channels (water channels) are inserted into apical membranes of principal cells
- results in loss of water in tubular fluid as CD dives deep into renal medulla, resulting in concentrated urine
- water reabsorption in late DCT and CD is optional (only when needed) This is facultative reabsorption of water
91
ADH actions leading to the formation of concentrated urine
1. stimulates Na+/K+/2Cl- symporters in thick limb of ascending loop of Henle- this builds osmotic gradient in interstitial fluid
2. stimulates facultative water reabsorption in upper and lower collecting ducts
3. stimulates urea recycling in lower collecting ducts- this also builds osmotic gradient in interstitial fluid
4. end result: concentrated urine
92
Countercurrent Mechanisms involve (two things):
1. countercurrent flow through a tube
| 2. an osmotic gradient in fluid surrounding the tube
93
Countercurrent Multiplication
process which produces a progressively-increasing osmotic gradient in interstitial fluid of renal medulla
94
Countercurrent Exchange
process which enables oxygen to cells of renal medulla without loss of the osmotic gradient in interstitial fluid of renal medulla
95
Two main factors that contribute to building and maintaining the required osmotic gradient
1. permeability differences in different sections of loop of Henle and collecting duct
2. countercurrent flow of tubular fluid through the descending and ascending limbs of the loop of henle
96
Permeability of descending loop of henle
- very permeable to water
- higher osmolarity of interstitial fluid outside the descending limb causes water to move out of the tubule by osmosis
- less and less water remains in tubule as hairpin turn approaches
97
Permeability of thick ascending limb of loop of henle
- impermeable to water but permeable to solutes
- symporters reabsorb solutes (Na+, K+, and Cl-) as soon as thick ascending loop is reached
- less and less solute remains in tubule as DCT approaches
98
Permeability of late distal convoluted tubule and collecting duct
only permeable to water in the presence of ADH
99
Countercurrent flow of descending and ascending limbs of the loop of henle
carry tubular fluid in opposite directions (countercurrent flow)
100
Counter current flow and permeability differences in loop of Henle (juxtamedullary)
constant differences in solute concentration (osmolarity) in extracellular fluid of renal medulla
effects build on (multiply) each other, so long loop of Henle functions as a countercurrent multiplier
101
ADH effects on Osmotic Gradient
1. ADH stimulates Na+/K+/2Cl- symporter activity in thick ascending limb of loop of henle (builds osmotic gradient)
2. ADH stimulates facultative reabsorption of water in upper collecting duct
3. ADH stimulates water reabsorption and urea recycling in lower collecting ducts (builds osmotic gradient)
102
Why does ASH require an osmotic gradient
Ability of ADH to cause excretion of concentrated urine requires an osmotic gradient of solutes in the interstitial fluid of the renal medulla
103
Three major solutes involved in the osmotic gradient
Na+
Cl-
Urea
104
Countercurrent Multiplication
1. symporters in thick ascending limb cells of the loop of Henle cause a buildup of Na+ and Cl- in the renal medulla (water not absorbed because walls are impermeable to water. Na+ and Cl- ions build up in interstitial fluid)
2. countercurrent flow through the descending and ascending limbs of the loop of Henle establishes an osmotic gradient in the renal medulla (descending limb is very impermeable to water but impermeable to solutes except urea)
3. cells in the collecting duct reabsorb more water and urea
4. Urea recycling causes a buildup of urea in the renal medulla
105
Countercurrent flow through the descending and ascending limbs of the loop of Henle establishes an osmotic gradient in the renal medulla: extra
- osmolarity of interstitial fluid outside the descending limb is higher than the tubular fluid inside
- therefore water moves out of descending limb into interstitial fluid via osmosis
- ascending limb cells are impermeable to water. however, cells have symporters which reabsorb Na+ and Cl- from tubular fluid into interstitial fluid of the medulla
106
Cells in the collecting duct reabsorb more water and urea: extra
- ADH increases water permeability of the principal cells. Water quickly moves via osmosis out of the collecting duct tubular fluid to interstitial fluid to vasa recta
- with loss of tubule water, urea becomes more concentrated. however, because duct cells deep the medulla are urea permeable, urea diffuses into he interstitial fluid of the medulla
107
Urea recycling causes a buildup of urea in the renal medulla: extra
- as urea accumulates in interstitial fluid, some of it diffuses into tubular fluid in the descending and thin ascending limbs (which are urea permeable)
- however, when tubule fluid flows through thick ascending limb, DCT, and cortical portion of collecting ducts, urea remains in tubule fluid because cells in these areas are urea impermeable
- as tubule fluid passes through collecting ducts (where ADH is present) water reabsorption continues via osmosis
- this reabsorption further increases urea concentration in tubular fluid, more urea diffuses into interstitial fluid of inner medulla, and the cycle repeats
108
Countercurrent Exchange
- process by which solutes and water are exchanged between blood of vasa recta and interstitial fluid of renal medulla
- vasa recta has descending and ascending loops parallel to each other and to the loops of Henle
- countercurrent flow through limbs allows for passive exchange of solutes and water between vasa recta blood and interstitial fluid in medulla
- thus, vasa recta is said to function as a countercurrent exchanger
- vasa recta provides oxygen and nutrients to renal medulla without washing out the osmotic gradient
- long loop of henle establishes osmotic gradient in renal medulla via concurrent multiplication WHILE vasa recta maintains the gradient to the best extent possible as it delivers nutrients to nephron cells via concurrent exchange
109
Reabsorption and Secretion in the collecting duct
- by end of distal convoluted tubule 90-95% of solutes and water have been reabsorbed and returned t the bloodstream
- cells in the collecting duct make the final adjustments
110
Principal cells
reabsorb Na+, secrete K+ (aldosterone effect) and reabsorb water (ADH effect)
111
Intercalated Cells
reabsorb K+ and bicarbonate ions and secrete H+
help regulate pH of body fluids by secretion of H+ and absorption of HCO3-
112
Actions of Principal cells
-Na+ enters principal cells through leakage channels
-Na+ pumps keep the concentration of Na+ in the cytosol low
-Cells secrete variable amounts of K+ to adjust for dietary changes in K+ intake
(down concentration gradient due to Na+/K+ pump)
113
Effects of Aldosterone on Principal Cells
aldosterone increases Na+ and water reabsorption and K+ secretion by principal cells by stimulating the synthesis of new pumps and channels
114
Effects of Antidiuretic Hormone (ADH) on Principle cells
increases water permeability of principal cells in collecting duct by triggering the insertion of aquaporin-2 channels into the apical membrane
water molecules will move more rapidly from tubular fluid into interstitial fluid to blood
115
Actions of intercalated cells
1. Secretion of H+ into tubular fluid via proton pumps (ATPases)
2. Absorption of Bicarbonate (HCO3-) via Cl-/HCO3- anti porters
116
Secretion of H+ into tubular fluid via proton pumps (ATPases)
- can pump against [H+] gradient 1000 times higher than blood (urine can be 1000 times are acidic than blood)
- urine is buffered by HPO4-2 and NH3, both of which can combine irreversibly with H_ (as pH drops), and in this way carry away excess H+ ions
117
Absorption of Bicarbonate (HCO3-) via Cl-/HCO3- anti porters
- HCO3- is generated when carbonic acid (generated rapidly by carbonic anhydrase [CA] in intercalated cells) dissociates (into H+ and HCO3-)
- Cl-/HCO3- antiporters exchange chloride in interstitial fluid for bicarbonate in the intercalated cells
- HCO3- enters blood and pH rises
118
Intercalated cells actions when blood pH is low
1. form more carbonic acid from CO2 and H2O
2. secrete more H+ into tubular fluid
3. exchange more Cl- for HCO3-
more HCO3- enters blood, raising blood pH
119
Nonvolatile acids
cannot be "blown off"
the only way to eliminate this acid load is to excrete H+ in urine
120
Diuretics
Substances that slow renal reabsorption of water and cause diuresis (increased urine flow rate)
121
Caffeine as a diuretic
inhibits Na+ reabsorption (inhibits obligatory water reabsorption)
122
Alcohol as a diuretic
inhibits secretion of ADH (inhibits facultative water reabsorption)
123
Prescription medicines as diuretics
can act on the PCT, loop of Henle or DCT
124
Anatomy of Urinary Bladder
- hollow, distensible muscular organ with capacity of 700-800 mL
- trigone is smooth flat area bordered by 2 ureteral openings and one urethral opening
125
The Micturition Reflex
- urination or voiding
| - stretch receptor signal spinal cord and brain when volume exceeds 200-400 mL
126
Impulses of Micturition Reflex
- sent to micturition center in sacral spinal cord (S2 and S3)
- parasympathetic fibers cause detrusor muscle to contract, external and internal sphincter muscles to relax
127
Filling during Micturition Reflex
- causes a sensation of fullness that initiates a desire to urinate before the reflex actually occurs
- conscious control of external sphincter
- cerebral cortex can initiate micturition or defat its occurrence for a limited period of time
128
Testes
produce male gametes (sperm)
129
System of Ducts
for storage and transport of sperm
130
Organs and Supporting Structures of the Male Reproductive System
```
ejaculatory duct
prostatic urethra
ductus (vas) deferens
erectile tissue of penis
spongy (penile) urethra
glans penis
prepuce
seminal vesicle
ampulla of ductus deferens
prostate
membranous urethra
bulbourethral gland
epididymis
testis
scrotum
```
131
Ducts of the Male Reproductive System
```
ejaculatory duct
prostatic urethra
ductus (vas) deferens
spongy (penile) urethra
ampulla of ductus deferens
membranous urethra
epididymis
```
132
Accessory Glands of Male Reproductive System
seminal vesicle
prostate
bulbourethral gland
133
Seminal vesicles secretion
contribute ~60% semen volume
Viscous seminal fluid
- fructose
- prostaglandins
- fibrinogen
134
Fructose
fuel for glycolysis for ATP production
135
Prostaglandins
contribute to sperm viability, motility and transport
136
Fibrinogen
aids coagulation of semen in female reproductive tract
137
Prostate secretion
contribute ~25% semen volume
Thin seminal fluid
- slightly acidic pH (due to citric acid and used for ATP production)
- Proteolytic enzymes
- seminalplasmin
138
Proteolytic enzymes
break down clotting proteins from seminal vesicles
139
Seminalplasmin
an antibiotic that destroys bacteria
140
Bulbourethral (Cowper's) gland secretion
- mucous-like fluid (to minimize damage to sperm during ejaculation)
- alkaline (protects sperm from acids in urine)
141
Sertoli cells
- "nurse cells"
- support sperm-production
- support sperm development within densely packed seminiferous tubules
142
Leydig cells
- testosterone-producing portion of testis
- located in connective (interstitial) tissue
- between loops of seminiferous tubules
143
Spermatogenesis
the conversion of undifferentiated germ cells (spermatogonia) into specialized, motile sperm (spermatozoa)
144
Order of spermatogenesis
```
spermatogonia
primary spermatocyte
secondary spermatocyte
spermatid
sperm cell
```
145
Sertoli cells
- columnar with adjoining lateral processes
| - extend from basal lamina to lumen
146
Mitosis
performed by all replicating cells in the human body, including spermatogonia and oogonia
147
Meiosis
only done by spermatogonia and oogonia
148
Three unique events of meiosis (all in meiosis I):
1. tetra formation (synapsis)
2. crossing over
3. movement of pairs of chromatids towards poles
149
Spermatogonia
sperm stem cells maintaining their number through mitosis
150
What happens with excess spermatogonia?
enter meiosis and become spermatocytes then spermatids then (though differentiation) become spermatozoa (sperm)
151
What does sperm meiosis yield?
involves 2 rounds of cell division to yield 4 haploid cells called gametes
152
Sperm gamete
chromosome number is halved (one copy of each human autosome plus one sex chromosome [X or Y] for a total of 23)
153
Spermatogenesis
meiosis and spermiogenesis
results in the release of sperm into the lumen of the seminiferous tubules
154
Meiosis I (spermatogonium)
undergoes differentiation, thereby committing to sperm formation
155
Meiosis II (spermatogonium)
follows immediately after meiosis I, resulting in 4 spermatids
156
Spermatids
differentiate into sperm (spermiogenesis) and are released from Sertoli cells into the lumen of the seminiferous tubules (spermiation)
157
Acrosome of sperm
facilitates penetration of secondary oocyte
158
Nucleus of sperm
contains 23 highly-condensed chromosomes
159
Middle piece or Mitochondrial sheath of sperm
provides ATP for locomotion
160
Tail of sperm
propels sperm through female reproductive tract
161
Spermiation
the release of mature spermatozoa from Sertoli cells into the lumen of the seminiferous tubule
162
Capacitation
final maturation of the sperm occurs within female reproductive tract (triggered by secretions from the uterus)
163
Hyperactivation of tail in capacitation
- required to penetrate the matrix surrounding the oocyte
- triggered by Ca+2 influx, the result of increased progesterone (produced by women) acting on the male sperm in the female reproductive tract
- men deficient in the progesterone binding Ca+2 channel (CATSPER1 null individuals) are infertile
164
Hormonal control of male gamete formation
- increased GnRH triggers increased production of LH and FSH
- LH stimulates testosterone production by Leydig cells (testosterone stimulates final spermatogenesis steps and inhibits LH release)
- FSH acts on Sertoli cells to promote spermatogenesis by stimulating ABP production which helps keep local testosterone high
- Sertoli cells also release Inuit which reduces FSH release
165
Ovaries
produce female gametes (oocytes) which have the potential to develop into mature ova (eggs) if fertilized by a sperm
166
Oocyte development
produced prior to her own birth
- germ cells migrate to the ovary and become oogonia
- oogonia undergo mitosis most degenerate
- some develop into primary oocytes and are inactive until puberty
167
How many oocytes are present at birth?
~200,000 to 2 million
168
How many oocytes remain at puberty?
~40,000
169
How many oocytes will mature and be ovulated during a woman's life?
~400
170
Ovulation
- hormone release causes several follicles (each contains one primary oocyte) to begin maturing
- only one secondary oocyte completes maturation
171
Fertilization
- if released secondary oocyte is penetrated (fertilized) by a sperm, it become a zygote (diploid cell at the 1-cell stage of human development)
- if no fertilization occurs, the released oocyte dies
172
Ovarian follicles
sac-like structures; basic structural unit in ovary
(follicle is also primary endocrine tissue in the ovary during the first half of the ovarian cycle when it synthesizes and secretes estradiol)
consists of:
- oocyte: one immature
- follicular cells: surround the oocyte
173
What is necessary for estradiol synthesis?
theca and granulosa cells (as well as LH and FSH)
174
Theca cell
Cholesterol> (LH) Progesterone> Androstenedione
theca cells cannot convert androstenedione to estradiol
175
Granulosa cell
Androstenedione> Testosterone> (FSH/aromatase) Estradiol
granulosa cells cannot convert cholesterol to androstenedione
176
Where do oocytes mature?
in developing ovarian follicles (primordial> antral> graafian)
177
Three phases of the Ovarian Cycle
1. follicular phase
2. ovulation
3. luteal phase
178
Follicular Phase
1. primary oocyte suspended in first meiotic division at birth
2. cohort of follicles recruited to grow (proliferation of granulosa cells, theca cells)
3. antrum formation (fluid filled space, growth stimulated by FSH & LH)
4. mature follicle (estradiol production requires LH & FSH)
179
Ovulation
1. wall of follicle and vary broken down by proteases, collegenases, and prostaglandins
2. follicle ruptures (oocyte has just completed first meiotic division & ovum released into abdominal cavity)
180
Luteal Phase
- follicular wall left behind will transform into corpus lute under influence of LH
- corpus lute produces progesterone and estrogen
181
Endometrium of uterus
- stratum functionalis (sheds during menstruation)
| - stratum basalis (replaces stratum functionalis each uterine cycle)
182
Myometrium of uterus
3 layers of smooth muscle
183
Perimetrium of uterus
visceral peritoneum
184
3 phases of Uterine Cycle
1. Menses
2. Proliferative phase
3. Secretory phase
185
Menses
degeneration and sloughing off of stratum functionalis (menstruation)
lasts ~5 days (day 1 is defined as the first day of menses)
186
Proliferative phase
regrowth of endometrium
lasts from day 6 until ovulation by an ovary (day 14 on average)
187
Secretory phase
endometrial glands secrete special mucous in response to progesterone and estrogen to prepare for potential implantation of a fertilized ovum
begins after ovulation and continues to day 28
188
Hormone release regulation of Uterine Cycle
- in absence of fertilization, corpus lute will degenerate and the stratum functionalis will be lost with menses
- growing human embryo (8 or more days after fertilization) will produce hCG which will halt the cycle by rescuing the corpus letup from degeneration to support pregnancy (after 3-4 months, placenta takes over hormone production
189
Where do hormones come from in the Female Reproductive Cycle?
hypothalamus
anterior pituitary
ovary
190
Ovarian cycle
changes in the ovary during and after maturation of the oocyte
191
Uterine cycle
preparation of the uterus to receive fertilized ovum, and if implantation does not occur, the stratum functionalis is shed during menstruation
192
Menstrual phase in ovary
- ~20 follicles that began to develop 6 days before are now beginning to secrete estrogen
- fluid is filling the antrum from granulosa cells
193
Menstrual phase in uterus
- declining levels of progesterone causes spiral arteries to constrict and glandular tissue degenerates
- stratum functionalis layer is sloughed off along with 50 to 150 mL of blood
194
Preovulatory phase in the ovary
follicular phase
- follicular secretion of estrogen and inhibin has slowed the secretion of FSH
- dominant follicle emerges by day 6
- by day 14, Graafian follicle has enlarged and bulges at surface
- increasing estrogen levels trigger the secretion of LH
195
Preovulatory phase in the uterus
proliferative phase
increasing estrogen levels have repaired and thickened the stratum functionalis to 4-10 mm in thickness
196
At moderate concentrations (preovulatory phase) estrogen:
inhibits release of GnRH
197
At low and high concentrations (preovulatory phase) estrogen:
stimulates release of GnRH
198
Ovulation and hormones
1. high levels of estrogen from almost mature follicle stimulate release of more GnRH and LH
2. GnRH promotes release of FSH and more LH
3. LH surge brings about ovulation
199
Postovulatory phase in the ovary
luteal phase
- if fertilization does not occur, corpus albicans is formed (as hormone levels drop, secretion of GnRH, FSH, & LH rise
- if fertilization occurs, developing embryo secretes human chorionic gonadotropin (hCG) which maintains health of corpus lute and its hormonal secretions
200
Postovulatory phase in the uterus
secretory phase
- hormones from corpus lute promote thickening of endometrium to 12-18 mm (formation of more endometrial glands and vascularization)
- if no fertilization occurs, menstrual phase will begin
201
GnRH role in reproductive cycle
secreted by the hypothalamus controls the female reproductive cycle
stimulates anterior pituitary to secrete FSH and LH
202
FSH role in reproductive cycle
growth of follicles that secrete estrogen
estrogen maintains reproductive organs
203
LH role in reproductive cycle
stimulates ovulation and promotes formation of the corpus lute which secretes estrogens, progesterone, relaxin, and inhibin
- progesterone prepares uterus for implantation and the mammary glands for milk secretion
- relaxin facilitates implantation in the relaxed uterus
- inhibin inhibits the secretion of FSH
204
Hormones of ovarian and uterine cycle
slides 13 and 14 of lecture 39
205
Gestation (prenatal development) stages:
1. germinal stage
2. embryonic stage
3. fetal stage
206
germinal stage
first 2 weeks following fertilization
- zygote> morula> blastocyst which reaches the uterus
- after implantation, the blastocyst is called an embryo
207
embryonic stage
weeks 3-8 of gestation
- embryo develops the 3 primary tissue layers and develops rudiments of every organ and organ system
- embryo becomes a fetus at the end of the 8th week
208
fetal stage
weeks 9-38+ of gestation
lasts until birth
209
Three primary germ layers
ectoderm
mesoderm
endoderm
210
ectoderm
- all nervous tissue
| - epidermis of skin
211
mesoderm
- cartilage, bone, other connective tissues
- skeletal, cardiacs and smooth muscle tissue
- blood vessels and lymphatic vessels
- epithelium of gonads
212
endoderm
- epithelium of digestive tract
- epithelium of respiratory system
- epithelium of thyroid, liver, and pancreas
- epithelium of bladder
213
Development of placenta
- forms during 3rd month
| - develops from embryonic chorion as well as uterine tissue
214
Functions of the placenta
1. site of nutrient, gas and waste exchange
2. secretes hormones that maintain pregnancy
3. barrier to microorganisms, except some viruses (AIDS, measles, chickenpox, polio, encephalitis
not a barrier to drug and alcohol
215
Umbilical cord
- contains two umbilical arteries and one umbilical vein
| - connects the embryo and the placenta
216
Endocrine functions of the placenta
- human chorionic gonadotropin (hCG) is produced by the chorion of embryo
- hCG rescues the corpus luteum from degeneration until the 3rd or 4th month of pregnancy
- after 4 months, the placenta takes over the corpus luteum's production of steroid hormones (estrogens and progesterone)
217
Cortisol function in pregnancy
needed for maturation of the fetal lungs and for production of surfactant in fetal alveoli
PSIO 202
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