1
Q
steroid hormones: where are they secreted, what are they derived from, key characteristics
A
- secreted by 3 steroid glands: adrenal cortex, testes and ovaries
- derived from cholesterol
- lipid-soluble
- transported through blood stream
2
Q
how do steroid hormones work?
A
- pass through the cell membrane of the target cell —> lipid-soluble so can diffuse directly through the phospholipid bilayer
- binds with receptor in the cytoplasm, forming a receptor-hormone complex
- complex enters nucleus and triggers gene transcription
- transcribed mRNA is translated into proteins
3
Q
peptide hormones: what are they made of, where are the made, key characteristics
A
- made of amino acids
- made by specialised endocrine glands
- water-soluble therefore cannot pass through cell membranes
- short half life so break apart easily (used to direct processes quickly and efficiently)
4
Q
how do peptide hormones work?
A
- bind to receptor on cell’s surface
- the hormone-receptor complex triggers a series of biochemical reactions that produces the second messenger
- the second messenger triggers a series of reactions that leads to altered cell functions
5
Q
name 3 steroid hormones and 3 peptide hormones
A
steroid —> androgens, progesterone, oestrogen
peptide —> insulin, FSH, LH
6
Q
FSH: origin, endocrine target, function, regulation
A
- origin: anterior pituitary
- endocrine target: testes and ovaries
- function: promotes follicle development in females, and with LH stimulates the secretion of estrogens by ovarian cells
- regulation: inhibited by inhibin, regulated by GnRH.
7
Q
what is GnRH?
A
gonadotropin-releasing hormone
- pulsatile
- released by hypothalamus
- binds to receptors in the anterior pituitary gland
8
Q
LH: origin, endocrine target, function, regulation
A
- origin: anterior pituitary
- endocrine target: ovaries and testes
- function: induces ovulation. promotes the secretion of estrogens and the progestins by the ovaries. FORMATION OF CORPUS LUTEUM
- regulation: regulated by GnRH
9
Q
what is the effect of a mid-cycle surge of LH?
A
triggers the rupture of the mature follicle with release of the oocyte
10
Q
progesterone: origin, function, regulation and how is it formed
A
- origin: ovary (corpus luteum), placenta
- function: preparation of uterus for pregnancy, maintenance of pregnancy, inhibit LH secretion
- regulation: corpus luteum is formed under LH stimulation and the lipids contained within it are used to from progesterone. Placenta produces sufficient amounts of progesterone to maintain the endometrial lining and continue pregnancy.
11
Q
oestrogen: origin, function, regulation (what’s it stimulated by?)
A
- origin: ovary, testes, placenta
- function: stimulates bone and muscle growth, development of secondary female sexual characteristics. initiates growth and repair of endometrium during the menstrual cycle
- regulation: FSH and LH stimulate
12
Q
inhibin: origin, endocrine target, function, regulation (what is it stimulated by?)
A
- origin: follicular cells of the ovaries (F = granulosa cells, M = sertoli cells)
- endocrine target: anterior pituitary gland
- function: inhibits secretion of FSH
- regulation: stimulated by FSH from anterior pituitary gland (negative feedback)
13
Q
hCG: origin, endocrine target, function, regulation (when does it stop being secreted?)
A
- origin: syncytiotrophoblasts (placental barrier between maternal and foetal blood)
- endocrine target: corpus luteum
- function: maintains the integrity if the corpus luteum and promotes continued secretion of progesterone. appears in blood soon after implantation. the presence of hCG reduces after 3-4 months, but by now the placenta actively secretes both estrogen and progesterone.
- regulation: once placental secretion is sufficient, the cells stop secreting hCG
14
Q
relaxin: origin, function
A
- origin: corpus luteum and placenta
- function: increase the flexibility of the pubic symphysis, permitting the pelvis to expand during delivery. causes dilation of the cervix and suppresses the release of oxytocin by the hypothalamus - delaying onset of labour contractions
15
Q
what is the role of leptin and where is it found?
A
leptin (in fats) facilitates the production of kisspeptin (the main GnRH generator in females) which pushes the pulsatile secretion of GnRH from the hypothalamus
16
Q
the menstrual cycle: what are the 4 phases, key days
A
4 phases = menstruation, follicular phase, ovulation, luteal phase
cycle usually lasts 28 days. cycle begins on 1st day of menstruation and ovulation occurs on approx day 14
orchestrated by the endocrine system via the hypothalamus, pituitary and gonads
17
Q
what is the result of rising FSH levels at the beginning of the menstrual cycle?
A
causes stimulation of a few ovarian follicles
18
Q
as the follicles develop they compete for dominance. how is the dominant follicle selected?
A
the 1st follicle to fully mature starts to produce large amounts of oestrogen. This causes negative feedback on both the pituitary and hypothalamus which sense the increasing levels of oestrogen and thus hinder the production of FSH and LH —> ensures only one follicle develops to a sufficient level as humans are monofollicular (other follicles become erratic and die off)
19
Q
what is the single follicle that reaches full maturity called?
A
the Graafian follicle
20
Q
the Graafian follicle continues to secrete large amounts of oestrogen. what is the result of this increasing amount of circulating oestrogen?
A
- endometrial thickening
- thinning of cervical mucus to allow easier passage of sperm
- inhibition of LH production by the pituitary gland
21
Q
what does the graafian follicle begin to release and what is the consequence of this?
A
progesterone and inhibin - inhibin inhibits the release of FSH so oestrogen levels continue to rise and soon reaches a threshold at which point negative feedbacks turns into positive feedback —> leads to a surge in LH and FSH (although FSH is much less due to the inhibin)
22
Q
what does the high amounts of LH cause?
A
causes the membrane of the Graafian follicle to become thinner so within 24-48 hours of the surge, the follicle ruptures releasing a secondary oocyte.
23
Q
what does the secondary oocyte develop into?
A
quickly matures into an ootid and then into a mature ovum
24
Q
what happens to the mature ovum?
A
it is released into the peritoneal space and is taken into the uterine tube via fimbriae (ovulation)
25
what do you need for successful implantation?
synchronisation of ovulation with endometrial preparation
26
once ovulation has occurred, what do LH and FSH stimulate?
stimulate the remaining Graafian follicle to develop into the corpus luteum (yellow body)
27
what does the newly formed corpus luteum begin to do?
begins to produce progesterone. as it is no longer a follicle, it stops releasing oestrogen
28
what do increased levels of progesterone released from the corpus luteum result in?
- the endometrium becoming receptive to implantation of blastocyst
- negative feedback causing decreased FSH and LH (both needed to maintain the corpus luteum)
- an increase in the woman’s basal body temperature
29
what happens as a result of falling LH and FSH levels?
the corpus luteum degenerates as it needs both FSH and LH to survive
30
what does the degeneration of the corpus luteum result in?
the loss of progesterone production —> menstruation = superficial stratum functionalis is shed due to constriction of spiral arteries
31
what happens if fertilisation occurs?
- fertilised ovum produces hCG
- hCG prevents the degeneration of the corpus luteum —> continued production of progesterone
- the continued progesterone prevents mentruation
- the placenta eventually takes over the role of the corpus luteum (from 8 weeks gestation)
32
what is menstruation and how does reduced progesterone result in menstruation?
- the degeneration of the endometrial lining as a result lowered progesterone
- lowered progesterone levels causes the contraction of spiral arteries (progesterone keeps the arteries dilated)
- constricted arteries = reduced blood flow to the endometrium
- doesn’t receive oxygen or nutrients
- stratum functionalis becomes necrotic and degenerates
- blood fills the uterine cavity from the broken vessels
33
what are theca cells?
found in the ovary, stimulated by LH: make androgens — androstenedione
34
what are granulosa cells?
form a single layer around the oocyte, many layers around the Graafian follicle. stimulated by FSH
35
what is atresia?
the degeneration of those ovarian follicles which do not ovulate during the menstrual cycle.
36
name the 4 steps leading to fertilisation
1. sperm binding = sperm binds to zona pellucida
2. acrosome reaction = acrosomes leak out and digest the zona pellucida
3. cortical reaction = cortical granules modify zona pellucida so it can function as a block to polyspermy (it becomes impenetrable to other sperm)
4. genetic material of sperm released into egg
5. when genetic material meets, fertilisation occurs
37
when does the acrosomal head of a sperm rupture?
when a spermatozoon binds to a sperm receptor on the zona pellucida
38
what is the importance of the cortical reaction?
ensures that only one sperm’s DNA can get in
39
what is conception?
the fertilisation of an ovum by a spermatozoon
40
what helps accelerate sperm to its destination and what is this stimulated by?
uterine contractions of uterine musculature, stimulated by prostaglandins in seminal fluid and oxytocin secreted from woman’s posterior pituitary gland during her orgasm.
41
what is cleavage in embryogenesis?
- a series of cell divisions that sub-divides the cytoplasm of the zygote
- splitting without growth — stays within the zona pellucida
42
what is a zygote?
the single cell formed when an egg and a sperm cell fuse
43
how long does cleavage last?
12-24 hours
44
morula —> blastula —> blastocyst: what are they?
- morula = (mulberry) consists of 8 blastomeres
- blastula = a hollow sphere of blastomeres, surrounding a fluid-filled cavity called the blastocoele
- blastocyst = a blastula with an inner cell mass called the embryoblast
45
what does the embryoblast/inner cell mass contain?
pluripotent stem cells
46
how many cells are there roughly in a blastocyst?
roughly 32 cells
47
what is the trophoblast and what is it role?
the outer layer of a blastocyst - the insulator and supplier of nutrients which will give rise to the placenta
48
what happens in the second week of embryogenesis?
- embryo is partly planted in endometrium
- bilaminar disc forms = the point where the epiblast and hypoblast press up against each other
- yolk sac and amniotic cavity (above epiblast) are formed
- chorionic cavity forms
- by the end of the second week, the syncytiotrophoblast produces hCG
49
in blastulation, what happens to the blastocyst?
the inner cell mass differentiates into a line of hypo blasts with the epiblasts on top, containing the newly formed amniotic cavity. there is no zona pellucida remaining
50
what is the bilaminar disc?
the point where the epiblast and hypoblast press up against each other. what splits the sphere to make 2 cavities
51
what forms the lining of the primary yolk sac?
hypoblast and Heuser’s membrane
52
what is the role of the fluid in the yolk sac?
source of nutrition for the embryo before the placenta is fully formed and functional
53
what happens in the 3rd week of embryogenesis?
gastrulation
54
at the start of gastrulation, there are already 2 layers. what are they and what do they become?
epiblast —> ectoderm
| hypoblast —> endoderm
55
what are the 3 germ layers called?
ectoderm, mesoderm, endoderm
56
in general, each germ layer gives rise to what?
- ectoderm = forms epidermis, nervous system
- mesoderm = skeletal, connective and muscle tissues, heart, cardiovascular and renal systems
- endoderm = lining of the GI and respiratory systems
57
what does gastrulation begin with?
the formation of the primitive streak on the surface of the epiblast (base of amniotic cavity)
58
what happens after the primitive streak forms?
- cells of the epiblast migrate towards the streak and slip beneath it
- inward movement = invagination
- invagination leads to 3 germ layers
- more and more cells move between the hypoblast and epiblast. cells begin to spread laterally and superiorly
- gradually they migrate beyond the margin of the disc and establish contact with the extraembryonic mesoderm covering the yolk sac and amnion.
59
what are the 4 extraembryonic membranes the germ layers participate in the formation of?
1. yolk sac — nutrition and blood cell generation
2. the amnion — the amniotic cavity contains amniotic fluid and completely surrounds the embryo
3. the allantois — vascular connection between the embryo and the placenta
4. the chorion — functional placenta
60
what happens in the embryonic period (3rd-8th week) ?
- the embryonic disc (initially flat and round ish) becomes elongated with a broad head and a narrow tail
- 2D embryonic disc becomes a 3D embryo via folding
- expansion of embryonic disc occurs mainly in head region (due to continuous migration of cells from the primitive streak in the cephalon direction)
61
in what direction does the embryo develop?
cephalocaudally (head —> tail)
62
nervous system formation
= ectoderm derivative
- anterior region forms brain
- posterior region forms spinal cord
- begins 19-21 days after fertilisation
- neural tube closure occurs 23-26 days post fertilisation
- the overlying ectoderm thickens and forms the neural plate
63
neuralation
- neural plate forms the neural tube
- the lateral edges of the neural plate become elevated to form neural folds. the depressed mid region forms the neural grove
- the neural folds gradually fuse at the mid region
- fusion begins in the cervical region and proceeds cranially to caudally
- the neural tube forms
- neuralation is complete upon closure of the neural tube
- notochord forms in the middle of the mesoderm (underneath where the primitive streak was, mesoderm cells differentiate into the notochord)
- formation of notochord causes a thickening in the ectoderm to form = neural plate
- neural plate cells dive into mesoderm and form a ring/tube structure called the neural tube
- little cells break off from ectoderm into mesoderm = neural crest tissues. these go off into mesoderm and differentiate into their own tissues
64
formation of the heart
= mesoderm derivative, 1st functional organ
- begins 22/23 days after fertilisation + continues through 8th week of gestation
- in the head end of the embryo, the heart develops from a group of mesodermal cells called the cardiogenic area
- area forms a pair of elongated strands called cardiogenic cords — develop a hollow centre. now called endocardial tubes
- paired endocardial tubes fuse (= primitive heart tube) due to the lateral folding of the embryo
- tube develops into 5 distinct regions
1. sinus venous = develops into right atrium and SAN
2. atrium = develops into right and left atriums
3. ventricle = develops into left ventricle
4. bulbous cordis = develops into right ventricle
5. truncus arteriosus = gives rise to ascending aorta and pulmonary trunk
- day 27 = primitive tube begins to fold as bulbus cordis and ventricle grow faster than other regions — becomes S-shaped
- day 32 primitive heart tube orientation finished + atria and ventricles in final adult position
65
formation of gastrointestinal tract
= endoderm derivative
- initially arises from ectoderm
- mesoderm contribution: mesentry, smooth muscle, blood vessels
- ectoderm contribution: enteric nervous system
- embryonic disc begins to bulge into the amniotic cavity and fold cephalocaudally
- lateral folds also form and move anteriorly to assist in body wall closure
- due to cephalocaudal folding, a continuously larger portion of the endodermal layer is incorporated into the body of the embryo to form the gut tube
- tube divided into 3 parts
1. foregut: oral cavity, oesophagus, trachea, and stomach
2. midgut: small intestine and pancreas
3. hindgut: colon
66
hormonal factors that increase uterine contractility?
1. increased oxytocin (secreted by posterior pituitary gland and aids uterine contractions)
2. increased relaxin
3. increased oestrogen and decreased progesterone (progesterone maintains the decidua and prevents uterine contractibility during pregnancy)
4. increased prostaglandins (from fetal membrane)
67
what is surfactant?
a phospholipid which reduces the surface tension at the air fluid interface in the alveoli which helps the air spaces to inflate
68
describe the change in the lungs after birth
- dramatic and rapid change
- prior to birth there is a large volume of fluid in the lungs — needs to be removed to allow air to pass into the lungs
- large volume of fluid is removed through absorption by the blood capillaries and lymphatics of the lungs
- assisted by the thinning of the epithelium
69
purpose of 12 week ultrasound scan
- checks if pregnancy is in the right place (ectopic?)
- check if the pregnancy is viable - right size and heartbeat
- check the number of foetuses
- give indication of the date of pregnancy
- check for any defects in the CV system
70
purpose of 20 week ultrasound scan
- check for any structural defects
| - to check if the ventral wall has closed properly
71
what 2 cell types does the corpus luteum consist of?
- granulosa lutein cells — produce progesterone
| - theca lutein cells — produce progesterone and androgens
72
what is the corona radiata?
the innermost layer of the cells of the cumulus oophorus and is directly adjacent to the zona pellucida
73
what is the cumulus oophorus?
the cells surrounding the corona radiata. surrounds and supported by the oocyte
74
what floats freely in the antrum right before ovulation?
the oocyte and corona radiata
75
how long does the corpus luteum remain active for in pregnancy?
remains active for 1st 6 months
76
during pregnancy the symphasis pubis and the ligaments of the sacroiliac and sacrococcygeal joints soften. what hormones are responsible?
oestrogen, progesterone, relaxin
77
what is fundal height and what is it used for?
the level at which the fundus can be felt during pregnancy. fundal height measured throughout pregnancy as it gives a good indication of continuing foetal growth and wellbeing.
78
at what week gestation would an obstetrician be able to palpate the fundus at the level of the pubis symphysis?
12 weeks
79
at what week gestation would an obstetrician be able to palpate the fundus at the level of the xiphisternum?
36 weeks
80
what does the drug syntocinon cause?
contraction of the myometrium of the uterus
81
what is pre-eclampsia?
when there is a new high blood pressure after 20 weeks and there is protein present in the urine
82
what hormone stimulates contractions of the uterus? where is this hormone made and stored?
oxytocin — made in the hypothalamus, stored in the posterior pituitary gland
83
by what percentage does blood plasma volume increase during pregnancy and why does this happen?
40-50% — happens because there are large increases in blood flow to organs - extra oxygen requirements + more RBCs
84
what do theca interna cells produce and what are they stimulated by?
produce androstenedione — stimulated by LH
85
during childbirth what is the approx diameter of the cervix when fully dilated?
10cm
86
how does the entry of sperm prevent polysperm?
entry of sperm causes calcium ions to be released causing granules in the oocyte to release an enzyme destroying sperm receptors on the membrane surface — cortical reaction
87
name 3 things oestrogen does
- promotes the development and maintenance of female reproductive structures and secondary sex characteristics
- lowers blood cholesterol
- in moderate levels, it inhibits the release of GnRH and the secretion of LH and FSH
88
what does aromatase break down to make oestrogens?
androstenedione
89
what congenital disorder risk increases with a deficiency of folic acid in pregnancy?
spina bifida
90
in foetal circulation, where is the foramen ovale?
between the left and right atria
91
why is a baby placed on its mother’s chest almost immediately after birth?
to promote bonding
92
approx how many primordial follicles does a female have at birth?
2,000,000
93
what is the ‘zone of polarising activity’?
it directs the outgrowth of limb buds along the proximal-distal axis
94
what is the viability of the corpus luteum maintained by?
human chorionic gonadotropin (hcg) produced by the syncitiotrophoblast
95
what is prolactin?
a protein hormone produced in the pituitary gland — promotes the breasts to grow and produce milk during and after pregnancy
96
what hormone is responsible for the formation of the corpus luteum?
LH
97
a commercially availed family planning kit that identifies the most fertile point of a woman’s menstrual cycle is most likely to detect what?
a rise in the circulating conc of LH
98
what is an organ that forms by the process of branching morphogenesis?
the lungs
99
what are the 3 stages of kidney organogenesis?
pronephros, mesonephros, metanephros
100
what is the foramen ovale?
the opening between the atria that allows blood to bypass the lungs before birth
101
due to its anatomical structure, what structure is most likely to be torn during childbirth?
puborectalis
102
what causes a woman to become constipated and develop gastric reflux during pregnancy?
high levels of progesterone
103
a commercially available family planning kit that identifies the most fertile point of a woman’s menstrual cycle is most likely to detect a rise in what?
a rise in the circulating concentration of LH
104
where is oxytocin produced and secreted and what is its role in parturition?
- produced by the hypothalamus and secreted from the posterior pituitary gland
- contracts the uterus and promotes the progress of labour
105
name 3 maternal changes that occur during pregnancy
1. altered pulmonary function
2. weight gain
3. edema and possible varicose veins
not
- increased stroke volume, cardiac output and heart rate, and decreased blood volume
- increased gastric motility, causing a delay in gastric-emptying time
106
what are 3 rules regarding maternity leave in the UK?
1. if you’re an employee, you can take up to 52 weeks of Statutory maternity leave
2. if you’re an employee, you must take a compulsory maternity leave of 2 weeks
3. if you’re having a child through surrogacy, you won’t qualify for maternity leave
PBL SEM 1
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