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PCAT: BIOLOGY > Reproductive System > Flashcards

Reproductive System Flashcards

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1
Q

what does sexual reproduction require

A
  • production of functionalized sex cells or gametes by adult organisms
  • union of these cells (fertilization or conjugation) to form a zygote
  • development of the zygote into another adult, completing the cycle
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2
Q

what are gonads

A
  • the gametes produced in specialized organs are called gonads
  • the male gonads, called testes produce sperm in tightly coiled seminiferous tubules
  • femal gonads called ovaries produce oocytes (eggs)
  • some species are hermaphrodites and have both functional male and female gonads (ex: hydra and earthworm)
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3
Q

What is Gametogenesis

A
  • production of functionalized sex cells is called gametogenesis
  • in males called spermatogenesis (sperm production) occurs iin seminiferous tubules of the testes
  • in females called oogenesis (egg productino) occuring in the ovaries
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4
Q

desribe fertilization

A
  • union of the egg and sperm nuclei to form a zygote with a diploid number of chromosomes
  • internal fertilization is practiced by terrestrial vertebrates providing a direct route for sperm to reach the egg cell: inc chance of fertilization -> female produce fewer eggs
  • if early development of the offspring occurs outside mothers body more eggs will be laid to inc chance of offspring survival
  • the amount of parental care after birth is also related to the number of eggs produced

*species that care for young produce fewer eggs

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5
Q

describe the male reproductive system

A
  • testes are located in an external pouch called scrotum that maintains the testes’ temp at 2-4 deg lower than body temp for sperm survival
  • sperm pass from testes to vas deferens to ejaculatory duct and then to the urethra
  • urethra passes through the penis and opens to the outside at its tip
  • in males urethra is a common passageway for both reproductive and excretory systems
  • testes are sites for testosterone production which reg secondary male sex characterisics (facial and pubic hair, voice changes)
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6
Q
A
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7
Q

explain spermatogensis

A
  • occurs in seminiferous tubules
  • diploid cells called spermatogonia differentiate into diploid cells called primary spermatocytes
  • undergo 1st meiotic division forming 2 haploid secondary spermatocytes of equal size
  • second meotic division produces 4 haploid spermatids which undergo a series of changes leading to mature sperm (spermatozoa)
  • these are specialized for transporting the sperm nucleus tot he egg or ovum
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8
Q

describe strucutre of a sperm cell

A
  • elongated cell with a head, neck, body and tail
  • head consists almost entirely of the nucleus, the tail (flagellum) propels the sperm while mitochondria in the neck and body provide energy for locomotion
  • a caplike structure called acrosome derived from the Glogi apparatus develops over the anterior half of the head
  • acrosoe contains enzymes needed to penetrate through the tough outer covering of the ovum
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9
Q

descibe the female

A
  • ovaries are found in the abdominal cavity below the digetive system, consists of thousands of follicles
  • follicle = multilayered sac of cells that contains nourishes and protects an immature ovum
  • follicle cell produces estrogen

~ 1/month immature ovum is released from the ovary into abdominal cavity and drawn by cilia into nearby ovictduct (fallopian tubes)

  • each fallopian tube opens into the upper end of the uterus -> the site of fetal development
  • lower narrow part of uterus is called the cervix which connects wth the vaginal canal: site of sperm deposition and passageway through which abby is expelled during birth
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10
Q

describe oogenesis

A
  • production of female gametes occuring in ovarian follicles
  • at birth most of immature ova (primary oocytes) that female will produce are already in ovaries
  • primary oocytes are diploid cells that form by mitosis in ovary
  • after menarche (1st tiem female menstrates) one primary oocyte completes meiosis 1 yeilding 2 daughter cells of unequal size (secondary oocyte and polar body)
  • secondary oocyte is expelled from the follicle during ovulation

* meiosis II does not occur until fertilization

  • the oocyte cell membrane is surrounded by two layers inner is zona pellucida and outer is corona rediata
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11
Q

what triggers meiosis II

A
  • two surrounding layers of oocyte membrane zona pellucida and corona radiata are penetrated by a sperm cell yeilding two haploid cells: mature ovum and another polar body
  • first generated polar body from meiosis I can also undergo meiosis II, but polar bodies will degenerate
  • mature ovum is a large cell containing cytoplasm, RNA, organelles, and nutrients needed by the developing embryo
  • when polar bodies are formed they lack these resources having given them to the developing oocyte
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12
Q

what are the female sex hormones and what are they regualted y

A
  • ovaries synthesize and secrete female sex hormones: estrogens and progeterone
  • secretion is regulated by luteinizing hormone and follicle stimulating hormone whivh are regulated by gonadotropin releasing hormone (GnRH)
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13
Q

what are estrogens

A
  • steroid hormones necessary for normal female maturation
  • they stimulate the development of the female reproductive tract and contribute to the developmeny of seondary sexual characterisics and sex drive
  • estrogens are responsible for the thickening of the endometrium
  • estrogens are secreted by the ovarian follicles and the corpus luteum
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14
Q

what is progesterone

A
  • steroid hormone secreted by the corpus luteum durign the luteal phase of menstrual cycle
  • progesterone stimulates the development and maintenance of the endometrial walls in preparation for implantation
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15
Q

what plays important roles in the menstrual cycle and its phases

A

hormonal secretions of the ovaries, hypothalamus and anterior pituitary play important roles in menstrual cycle

  • divided into follicular phase, ovulation, luteal phase and menstruation
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16
Q

describe the follicular phase

A
  • begins with the cessation of the menstrual flow from the previous cycle
  • during this phase FSH from the anterior pituitary promotes the development of the follicle which grows and begins to secrete estrogen
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17
Q

describe ovulation

A
  • midway through the cycle ovulation occurs
  • mature follicle bursts and releases an ovum
  • ovulation is caused by a surge in LH thta is preceded and in part caused by a peak estrogen level
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18
Q

describe the luteal phase

A
  • after ovulation, LH induces the ruptured follicle to develop into the corpus luteum
  • corpus luteum secretes estrogen and progesterone
  • progesterone causes the glands of the endometrium to mature and produce secretions that prepare it for the implantation of an embryo
  • progesterone and estrogen are essential for the maintenance of the endometrium
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19
Q

describe menstruation

A
  • if the ovum is not fertilized the corpus luteum atrophies
  • causes a drop in progesterone and estrogen levels causing the endometrium to slough off causing menstrual flow
  • if fertilization occurs the developing placenta produces hCG (human chorionic gonadotropin) maintaining the corpus luteum and thus the supply of estrogen and progesterone that maintains the uterus
  • eventually the placents takes voer production of these hormones and hCG is no longer produced
20
Q

how does fertilization occur

A
  • egg can be fertilizaed 12-24 hours after ovulation
  • occurs in the lateral, widest portion of the fallopian tube
  • sperm must travel throguh the vaginal canal, cervix, uterus and into the fallopian tubes to reach the ovum
  • sperm remains viable and capable of fertilization 1-2 days after intercourse
21
Q

what is the first barrier to sperm how does it overcome

A
  • corona radiata
  • enzymes secreted by the sperm aid in penetration of the corona radiata
  • the acrosome is responsible for penetrating the zona pellucida: it releases enzymes that digest this layer thereby allowing the pserm to come into direct contact with the ovm cell membrane
  • sperm then forms a tubelike structure called asrosomal process which extends to the cell membrane and penetrates it
  • fuses the sperm cell membrane with that of the ovum
  • sperm nucleus enters ovums cytoplasm
  • fertilization causes ovum to compelte meiosis II
22
Q

describe the cortical reaction in the ovum

A
  • triggered by acrosomal reaction
  • causes calcium ions to be released into the cytoplasm
  • this initiates a series of reactions that result in the formation of the fertilization membrane
  • this is a hard layer that surrounds the ovum cell membrane and prevents multiple fertilizations
  • release of Ca2+ also stimualtes metabolic changes within the ovum greatly inc metabolic rate
  • this is followed by fusion of the pserm nucleus with the ovum nucelus forming a diploid zygote
  • frist mitotic division of zygote soon follows
23
Q

explain how monozygotic twins are formed

A
  • result when a single zygote splits into two embryos
  • if the splitting occurs at th two-cell stage of development, the embryos will have separate chorions an separate placentas
  • if occurs as blastula stage embryos will only have one chorionic sac and will share the same placenta and possible an amion
  • occasionally when division is incomplete results in conjoined twins (will liekly share some organs)
  • monozygotic twins are genetically identical bc they develop from the same zygote

*wll be same sex and blood type

24
Q

explain dizygotic twins

A
  • result when two ova are released in one ovarian cycle and are fertilized by two different sperm
  • the two emryos implant in the uterine wall individually and each develops its own placenta, amnion and chorion
  • faternal twins share no more charcteristics than siblings bc they develop from two distinct zygotes
25
Q

what is embryology

A
  • study of the development of a unicellular organism into a complete multicellular organism
  • over nine months a unicellular human zygote undergoes cell division, cellular differentiation and morphogensis in preparation for life outside uterous
26
Q

explain fertilization in terms of early developmental stages

A
  • egg can be fertilized 12-24 hours after ovulation
  • fertilziation occurs in the widest portion of the oviduct where the sperm traveling from the vagina encounter an egg
  • if more than one egg is fertilized faternal (dizygotic) twins may be convieved
  • idential (monozygotic) twins occur when zygote divides into two separate embroyes
27
Q

what deos cleavage refer to

A
  • early embryonic development is characterized by a series of rapid mitotic divisions called cleavage
  • lead to an inc in cell number w/o corresponding growth in cell protoplasm (total volume of cytoplasm remains constant)
  • cleavage results in progressively smaller cells with an inc ratio of nuceli to cytoplasm
  • also inc surface-to-volume ratio of each cell thereby improving gas and nnutrient exchange
28
Q

when do the initial cleavages occur?

A
  • first complete cleavage ocurs approx 32 hours after fertilization, 2nd after 60 hours and 3rd aftre 72 hours
  • at this point 8 celled embryo reaches the uternus
  • as cell division continues a solid ball of embryonic cells known as the morula is formed
29
Q

describe blastulation

A
  • begins when the morula develops a fluid-filled cavity called the blastocoel
  • by the fourth day becomes a hollow sphere of cells called the blastula
  • blastula is the stage of embryo that implants in the uterus
  • emergency contraception works partially by inhibiting inplantation of the blastula in the uterus (why its most effective if taken within 72 hours of time of potential fertilization)
30
Q

what is an ectopic pregnancy

A
  • embryo implants outside the uterus (ex in fallopian tube)
  • embryo cannot be maintained for long outside the uterus, it will abort spontaneously and hemorraging will follow
  • ectopic pregnancies can be fatal is not caught in time and managed properly
31
Q

what is gastrulation

A
  • after second week the embryo is fully implanted in the uterus and cell migrations transform the sincle cell layer of blastula into three layered structure called gastrula
  • these 3 primary germ layers are responsible for differential development of the tissues, organs and systems of the body at later stages of growth
    layers: ectroderm, endoderm and mesoderm
32
Q

describe the ectoderm

A
  • gives rise to the integument (including epidermis, hair, nails and epithelium of the nose, mouth and anal canal)
  • also lens of eye, retina and the nervous system
33
Q

describe the endoderm

A
  • gives rise to epithelial linings of the digestive and respiratory tracts (including the lungs) and parts of the liver, pancreas, thyorid and the bladder lining
34
Q

describe the mesoderm

A
  • gives rise to the musculoskeletal system, circulatroy system, excretory system, gonads, connective itssue throughout the body and portions of digestive and respiratory organs
35
Q

what is neurulation

A
  • by the end of gastrulation, regions of the germ layers begin to develop into rudimentary nervous system
  • the process is known as neurulation and starts before 3rd week
  • a rod of mesodermal cells (notochord) develops along the longitudinal axis of the embryo under the doral layer of ectoderm
  • has an inductive effect on overlying ectoderm causing it to bend inwards and form a groove along the dorsal surface
  • fold on either side of groove, folds grow upwards and will fuse to forma closed tube (this is the neural tube, gives rise to the brain and spinal chord)
  • once the neural tube formed it detaches from surface of ectoderm
36
Q

what are cells at the tip of neural fodl called and what will they give rise to

A
  • called neural crest cells
  • migrate laterally and give rise to many components of the peripheral nervous system including: sesory ganglia, autonomic ganglia, adrenal medulla and schann cells
37
Q

what happens if the neural tube does not close properly

A
  • spinal bifida
  • opening can be corrected surgically but most patients will have neurological impairments
  • incidence can be decreased if mother takes folic acid aupplements during pregnancy
38
Q

what are the final stages of the developmental process

A

Organogenesis: the body organs begin to form. in this process cells interact, differentiate and change physical shape, proliferate and migrate

Growth: Organs inc in size, which is a continual process from infancy to childhood to adulthood

Gametogenesis: eggs develop in women and sperm in men, permitting reproduction to occur

39
Q

how does fetus get oxygen

A
  • growing fetus recieves oxygen directly from its mother through specialized circulatory system
  • system not only supplies oxygen and nutrients but removes carbon dioxide and metabolic wastes
  • two components of this sytem are placenta and umbilical cord which both develop in the first few weeks after fertilization
40
Q

what is the placenta and umbilical chord

A
  • outgrowths of the four extra embryonic membranes formed during development: amnion, chorion, allantois and yolk sac

Amnion:

  • thin tough membrane containing a watery fluid called amnionic fluid
  • acts as a shock absorber of external pressure during gestation and localized pressure from uterine contractions during labour

Chiron

  • where placenta formation begins
  • membrane that completely surrounds the amnion
  • assists in transfer of nutrients from mother to fetus

Allantois

  • this membrane, develops as an outpocketing of the gut
  • blood vessels of allantoic wall enlarge and become umbilical vessels which will connect the fetus to developing placenta

Yolk sac

  • site of early developmen of blood vesels, becomes associated with imbilical vessels
41
Q
A
42
Q

what is gestation

A
  • human pregnancy
  • 9 months, 266 days
  • can be divided itno 3 trimesters
43
Q

describe the first trimester

A
  • major organs begin to develop
  • heart begins to heat at 22 days and soon after eyes, gonads, limbs, and liver start to form
  • by five weeks the emrbyo is 10 mm in length, by 6 weeks its 15mm
  • cartilaginous skeleton begins to turn into bone by week 7
  • at end of 8 weeks most organs have formed, brain is fairly developed and embryo is reffered to as fetus
  • at end of 3rd month its 9cm long
44
Q

descibe the second trimester

A
  • fetus grows a lot and begins to move in amniotic fluid
  • face appreas human and toes and finger elongate
  • by end of 6th month its 30-36 cm long
45
Q

describe the third trimester

A
  • seventh of eighth month are charcaterized by continued growth and further brain development
  • during ninth month antibodies are transported by highly selective active transport from mother to fetus for protection against foreign matter
  • growth rate slows and fetus becomes less active bc it has less room to move
46
Q

describe child birth and maturation

A
  • accomplished by labour, series of uterine contraction
  • can be divided into 3 stages- 1st stage; cervix thins and dilates and amniotic sac ruptures releasing its fluids (contractions mild)
  • 2nd stage characterized by rapid contractions resulting in birth of the baby
  • final stage, uterus contracts and placenta is expelled and umbilical chord

PCAT: BIOLOGY (18 decks)

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