Chapter 11 Flashcards
What are the two roles of the testes?
(1) Synthesis of sperm (spermatogenesis) (2) Secretion of male sex hormones into the blood stream
Site of spermatogenesis within the testes
Seminiferous tubules;
Sustentacular cells
Walls of the seminiferous tubules are formed by cellls called sustentacular clues They protect and nurture the developing sperm, both physically and chemically
What are important cells found in the testicular interstitium?
Interstitial cells (also known as Leydig cells); They are responsible for androgen (testosterone) synthesis
Where does the seminiferous tubule empty into?
Epididymis; a long coiled tube located on the posterior of each testicle
Where does the epididymis from each testicle empty?
Into a duct deferens which leads to the urethra
What path does the duct deferens travel to get to the urethra?
It enters the inguinal canal –>joins the duct of the seminal versicle to form the ejaculatory duct –> joins the urethra
Seminal vesicles
A pair of glands located on the posterior surface of the bladder that nourish sperm They secrete about 60 percent of the total volume of the semen into the ejaculatory duct
What are the three glands that produce semen?
The seminal vesicles, the prostrate and the bulbourethral glands Collectively called accessory glands
Prostate gland
Nourishment, allows semen to coagulate after ejaculation
Bulbourethral glands
Lubricate urethra, neutralize acids in the male urethra and female vagina
Erectile tissue
Composed of modified veins and capillaries surrounded by a connective tissue sheath Blood accumulates at high pressures
Three compartments contain erectile tissue
The corpora cavernosa (two of these) and the Corpus spongiosum (one of these)
Three stages of the male sexual act
Arousal, orgasm and resolution
The sexual act events are controlled by an integrating center in the spinal chord, how is it activated/inactivated?
The cerebral cortex can activate this integrating center (in sexual arousal during sleep) or inhibit it (anxiety with sexual function)
What is arousal dependent on?
The parasympathetic nervous input and can be subdivided into two stages: erection and lubrication
Erection
Involves dilation of arteries supplying the erectile tissue. This results in swelling which obstructs venous outflow and causes the erectile tissue to become pressurized with blood
Lubrication
Function of the parasympathetic system. Bulbourethral glands secrete a viscous mucous which serves as a lubricant
What is required for an orgasm?
Stimulation by the sympathetic nervous system which can be divided into two stages: emission and ejaculation
Emission
Propulsion of semen into the urethra by contraction of smooth muscles
Ejaculation
Semen is propelled out of the urethra by rhythmic contractions of muscles surrounding the base of the penis
Resolution (2-3 minutes)
Or “returning to normal”, unstimulated state, is also controlled by the sympathetic nervous system Caused by a constriction of erectile arteries which results in decreased blood flow to the erectile tissue and allows veins to carry away trapped blood
Gametogenesis
Process by which diploid germ cells undergo meiotic division to produce haploid gametes
Syngamy
Fusion of sperm with the egg. The gametes produced by males and females differ dramatically in structure but contribute equally to the genome of the zygote
Spermatogenesis
Sperm synthesis. It begins at puberty and occurs in the testes throughout adult life
What is the site of spermatogenesis?
In the seminiferous tubule Spermatogenesis occurs with the aid of the specialized sustentacular cells found in the walls of the seminiferous tubule
Where are immature sperm precursors found?
The outer wall of the tubule
Where are nearly-mature spermatozoa’s deposited?
In the lumen and the they are transported into the epididymis
Germ cells
Give rise to male and female spermagonia Can germinate and give rise to full organisms
Spermatogonium Job
(1) Mitotically reproduce prior to meiosis (2) Replicate DNA in S phase of meiosis “SpermatoGONium is GONNA become a sperm”
Primary spermatocyte job
Meiosis I “Any gamete precursor (male or female) with “cyte” undergoes a meiotic division”
Secondary spermatocyte job
Meiosis II “The secondary spermatoCYTE undergoes the second meiotic division”
Spermatic Job
Turn into a spermatozoan “The spermatid’s a kid, almost mature”
Spermatozoan Job
Finish maturing: (1) in seminiferous tubule (2) in epididymis “Just remember that a mature sperm is called a spermatozoan”
Where do the final stages of sperm maturation occur?
In the epididymis
Where do spermatids develop?
Spermatids develop into spermatozoa in the seminiferous tubules with the aid of sustentacular cells
Acrosome
Contains lytic enzymes needed for penetration of the ovums protective layers
Bindin
Protein that allows for attachment to receptors on the zone pecullia surrounding the ovum
Process by which spermatids develop into spermatozoa?
(1) DNA condenses and cytoplasm shrinks to from a head (contains haploid nucleus) (2) Flagellum forms tail (3) Neck region carries mitochondria
Testosterone
Plays the essential role of stimulating division of spermatogonia
Luteinizing hormone (LH)
Stimulates the interstitial cells to secrete testosterone Secreted by anterior pituitary gland and uses systematic circulation to reach its target
Follicle stimulating hormone (FSH)
Stimulates the sustenacular cells which support and nourish sperm in seminiferous tube
Inhibin
Is secreted by sustenacular cells; its role is to inhibit FSH release
Wolffian ducts
Can develop into male internal genitalia (epididymis, seminal vesicles, and ductus deferens) Can develop into either genitalia
Müllerian ducts
That can develop into female internal genitalia (uterine tubes, uterus and vagina) Müllerian ducts are the default
Although external genitalia is also default, it is not
Derived from the Müllerian ducts
Genetic information on Y chromosomes leads to the development of
Testes, which cause male internal and external genitalia to develop by producing testosterone and Müllerian inhibiting factor (MIF)
Müllerian inhibiting factor (MIF)
Causes regression of Müllerian ducts
Dihydrotesterone
Testosterone enters the systemic circulation and is converted into dihydrotestosterone in target tissues in order to exert its effects.
Three main fetal precursors of the reproductive organs are
Wolffian ducts, Müllerian ducts and the gonads Structures arising from these ducts tend to have the same function
Analogous structures
Wolffian ducts and Müllerian ducts arise from different precursors
Homologous structures
Derived from the same underdeveloped structure i.e. Gonads
Androgens
All hormones involved in the development and maintenance of male characteristics
Estrogens
All hormones involved in development and maintenance of female characteristics
What happens to testosterone after birth
levels of testosterone fall to negligible levels until puberty, at which time increases and remains high for the remainder of adult life
Secondary sexual characteristics
Maturation of the geneticist,male distribution of facial and body hair, deepening of the voice and increased muscle mass. Pubertal growth spurt and fusion of the epiphyseal also results
Why is estrogen required at the beginning of puberty?
Required to regulate the uterine cycle and for the development and maintenance of female secondary sexual characteristics Maturation of the genitalia, breast development, wider hips and public hair
Gonadotropin releasing hormone (GnRH)
From the hypothalamus stimulates the pituitary to release the gonadotropins. Stimulates release of FSH and LH
What is the role of FSH and LH in females
FSH stimulates the granulosa cells to secrete estrogen and LH stimulates the formation of the corpus luteum and progesterone secretion
Labioscrotal swellings
Testosterone causes a pair of skin folds to grow and fuse, forming the scrotum In women they form the labia majora of the vagina
Urethral opening
Where urine exits the body
Labia minora
Surrounding the urethral opening is another pair of skin folds
Where is the opening o the vagina?
Between the labia minora
Endometrium
The inter most lining of the uterus (closest to the lumen) Role is to nourish a developing embryo and if pregnancy does not occur it is shed once a month
Myometrium
Surrounds the endometrium. Thick layer of smooth muscle compromising the wall of the uterus
Uterine tubes
The uterus ends here and then extends into the pelvis on either side
Fimbriae
Uterine tube ends at this bunch of finger like structures
Cervix
Separates vagina and uterus
Female stages of the sexual act
Arousal, orgasm and resolution
Arousal stage
Erection and lubrication
Lubrication in females
Controlled by the parasympathetic nervous system, the clitoris and labia minora become encouraged in blood
What is lubrication in females provided by
Lubrication is provided by mucus secreted by greater vestibular glands and by the vaginal epithelium
Orgasm in the female
controlled by the sympathetic nervous system and involves muscle contraction
What is different between the female sexual act and the male?
Females do not experience ejaculation
Oogenesis
Begins prenatally. In the female ovary, germ cells divide mitotically to produce many orgo is and enter the first phase of meiosis and stops at prophase I (primary oocytes) Male mitotic division occurs in adult stage not in the womb
1st mitotic division after puberty
results in a larger 2nd locution containing all the cytoplasm and organelles. Followed by a polar body (cell is haploid)
2nd mitotic division
Occurs only if the primary oocyte is fertilized by sperm. Unequal division resulting in a large ovum and small 2nd polar body
What happens if fertilization occurs?
The nuclei from the sperm and egg do not fuse immediately. They must wait for the secondary oocyte to release the second polar body and finish maturing to an ootid and then ovum Finally, the two nuclei fuse and the diploid (2n) zygote is formed
Primary Oocyte
Not an isolated cell. Found in a clump of supporting cells called granulosa cells and the entire structure is known as a follicle
Granulosa cells
Assist in maturation. Surrounds an immature primary oocyte and forms primordial follicle
Zone pellucida
Oocyte itself forms a protective later of mucopolysaccharides
Fate of the follicle
Insert picture
Estrogen
Made and secreted by the granulosa cells (with help from the thecal cells) during the first half of the menstrual cycle
Steroid hormones in females
Estrogen and Progesterone
Progesterone
is involved in the hormonal regulation of the menstral cycle and pregnancy
Stages in the ovarian cycle
Follicular phase, ovulatory phase, luteal phase
Follicular phase
Primary follicle matures and secrets estrogen controlled by FSH
Ovulatory phase
2nd oocyte is released from the ovary due to LH and what is left of the follicle becomes the corpus lutem
Luteal phase
Full formation of the corpus luteum. Secrets both estrogen and progesterone
Uterine Cycle
Preparation of the endometrium for potential implantation of a fertilized egg Menstruation, proliferative phase and secretory phase
Mensturation
Degeneration of the corpus luteum and drop in estrogen and progesterone. The lining then sloughed out “bleeding”
Proliferative phase
Follicle produces estrogen which causes production of a new endometrium LH levels peak
Secretory phase
Development of endometrium increases
GnRH from the hypothalamus
Stimulates the release of FSH and LH from the anterior pituitary
What happens when estrogen reaches its threshold?
It’s effects on LH become positive
Stimulation of LH
Causes ovulation and turns the follicle into the corpus luteum which. Secrets estrogen and progesterone and marks the start of the secretory phase
What happens if pregnancy does not occur
High levels of estrogen and progesterone feedback to inhibit FSH, LH and GnRH
What happens when LH secretions drop
The corpus luteum regresses and mesntration occurs
How is ovulation prevented during pregnancy?
Constant high levels of estrogen and progesterone seen during pregnancy to inhibit secretion of LH by the pituitary No LH surge no ovulation
If fertilization occurs
The embryo implants itself in the endometrium and the placenta begins to develop
Chorion
Portion of the placenta derived from the zygote takes LH’s place and secrets HCG which maintains the corpus luteum
When the secondary oocyte is ovulated and enters the uterine tube
Is it surrounded by the corona radiation and the zone pellucida. The oocyte will remain fertile for about a day. When intercourse occurs sperm becomes capacitance and survive 2-3 days to swim to the 2nd oocyte
Sperm capacitation
Involved the dilution of inhibitory substances present in semen
Fertilization
Occurs in the uterine tube usually. The fusion of spermatozoan with the secondary oocyte
Acrosome
Large vesicles in the sperm head contains hydrolytic enzyme which are release by exocytosis.
Once the corona radiation is penetrated
the acrosomal process containing actin elongates towards the zone pellucida
Embryogenesis
Begins within hours of fertilization, but proceeds slowly in humans. 1st stage is cleavage: Zygote undergoes many cell divisions to produce a morula (ball of cells)
Morula
Same size as the zygote: dividing cells spend most of their time in S phase and M phase they skip G1 & G2
When division continues the morula is transformed into
The blastocyst through blastulation
Tropohblast
Secrets protease that lyses the endometrium cells and allows the blastocyst to burrow into the endometrium and become engulfed in it. Absorbs nutrients through trophoblast into the inner cell mass Gives rise to chorion which gives rise to the placenta
Blastocyst
Travels to uterus and implants a week after fertilization
Inner cell mass
Will become the embryo
Where does cleavage occur in animals?
In a very small portion of the yolk at the animal pole (the side of the egg with the least amount of yolk)
Meroblastic cleavage
Incomplete division in animals partial part of the yolk
What does the trophoblast secrete?
Protease that lyse the endometrial cells
Secretory phase of endometrial cycle
Occurs so the endometrium can uptake glycogen, lipids and other nutrients
Placenta
Specialized to facilitate exchange of nutrients, gases and even antibodies between the maternal and embryonic bloodstreams
Why is hCG essential?
For maintenance of the endometrium In the 1st 3-months of pregnancy until placenta forms
Placental villi
Chorionic projections extending into the endometrium, into which fetal capillaries will grow This surrounds sinuses which contain maternal blood
A minion
Surrounds fluid-filled cavity which contains the developing embryo
Yolk Sac
Important in reptiles and birds because it contains the nourishing yolk Mammals do not store yolk, our yolk sac is the 1st sire of red blood cell synthesis
Allantois
Develops from the embryonic gut and forms the blood vessels of the umbilical cord, which transport blood between embryo and placenta
Gastrulation
When the three primary germ layers (the ectoderm, the mesoderm and the endoderm) become distinct
Ectoderm
Entire nervous system, pituitary gland (both lobes), adrenal medulla, cornea and lens, epidermis of skin and derivatives (hair, nails, sweat glands, sensory receptors), nasal, oral, anal epithelium
Mesoderm
All muscle, bone and connective tissue Entire cardiovascular and lymphatic system, including blood Urogenital organs (kidneys, uterus, gonads, reproductive ducts) Dermis of skin
Endoderm
GI tract epithelium (except mouth and anus) GI glands (liver, pancreas, etc) Respiratory epithelium Epithelial lining of urogenital organs and ducts Urinary Bladder
Neurulation
Formation of the nervous system. Layer of the ectoderm invaginates and pinches on the back of the embryo to form the dorsal neural groove which leads to neural tube and then leads to the brain and spinal chord
Notochord (mesodermal origin)
Gives instructions for neural tube formation which leads to the vertebral column
Organogenesis
Development of organ systems By the 8th week all organs are present and embryo turns into the fetus
Differentiation
Specialization of cell types during development. Cells become better at performing a particular task, but less adept to other tasks
Totipotent cells
Primitive (stem) cells in an early embryo have the potential to become any cell types Determination comes before differentiation
Determined
Point in development of a cell at which the cell fate becomes fixed
How does determination happen
Determination can be preprogrammed or induced by a cells environment
Parturition
Technical term for birth. Dependent on contraction of muscles in the uterine wall
Labor contractions
Increased pressure on the cervix passes a threshold that makes the anterior pituitary secrete oxytocin
Steps on birth
(1) Dilation of the cervix (2) Birth, involves contractions and movement of body down the cervix and birth canal (3) Expulsion of the placenta
Result of increased levels of estrogen and progesterone secreted by the placenta during pregnancy
Causes further development of glandular and adipose breast tissue. These fall after parturition and allow for prolactin the be released and milk production to begin
What happens when sucking occurs
The pituitary gland is stimulated by the hypothalamus to release a large surge of prolactin. Sucking prolongs secretion of prolactin and production of milk
Oxytocin
Posterior pituitary hormone Necessary for milk-let down Released when suckling occurs
Animalistic is split into
(1) Parazoa: animals that lack true tissue (2) Eumetazoa: radial and bilateral symmetry
How many germ laters do radial animals have?
2 germ layers
Bilateral animals have how many germ layers?
3
Acelomates
Solid bodies; flat worms
Coelomates
Fluid filled body that separates digestive tract
Coelomates can be divided into two distinct lines of evolution
Protostomes: annelids, mollusks and arthropods. Mouth first Deuterostomes: echinoderms and chordates. Anus first
What kind of cleavage do protostomes undergo?
Spiral, determinate cleavage, while deuterostomes undergo radial, indeterminate cleavage
Spiral Cleavage
This results in smaller cells that lie in grooves between larger cells
Radial Cleavage
Cells align on top of one another
