Lecture 14- Reproduction I Flashcards
Asexual Reproduction overview
Single parent-> 2+ offspring
Identical
Clones
No meiosis
No gamete fusion
Types of Asexual Reproduction
Budding
Fission
Fragmentation & regeneration
Parthenogenesis
Advantages of Asexual Reproduction
Rapid- many offspring in short time
Don’t need to find a mate (Great if sessile, low population density)
Sexual Reproduction Overview
Reproduction involving production and fusion of gametes= crossing
Sperm: Small, motile, flagellated
Egg (ovum): Large, nonmotile, contains nutrients for embryo
Involves fertilization: Fusion of sperm + egg -> zygote (2n)
Sexual Reproduction (explain where n, where 2n)
Person (2n) -> meiosis-> n + n -> fertilization -> 2n -> mitosis -> n (embryo)
Disadvantage of Sexual Reproduction
“Reproductive cost”- Only 1/2 of population can actually reproduce
In Asexual reproduction, females can reproduce but in sexual reproduction, males cannot.
Advantage of Sexual Reproduction
Promotes genetic diversity
New combinations of alleles
-> Get rid of harmful alleles or combinations of alleles
-> Offspring may be more fit than parents
-> More likely that some of population can survive environmental changes
2 Functions of Male Reproductive System
Produce sperm (spermatogenesis)
Deliver sperm to female reproductive tract
Testes
Singular= testis
Male gonads (reproductive organs)
Contains
Seminiferous tubules: Site of spermatogenesis (production of sperm). Long hollow tube, very small diameter.
Leydig cells: Produce testosterone, other male sex hormones. Scattered between seminiferous tubules.
Seminiferous tubules
Site of spermatogenesis (production of sperm)
Long hollow tube, very small diameter
Located in testes
Leydig cells
Produce testosterone, other male sex hormones. Scattered between seminiferous tubules.
Located in testes.
Epididymis
Located above testes
Coiled tube, several functions
Transport sperm- takes ~3 weeks
Maturation of sperm
Storage of sperm
Scrotum
Skin-covered sac, contains testes and epididymis
External- Suspended from groin -> cooler than body temp
Sperm cannot develop at body temp
Temperature affects sperm production, longevity
Outside body in most mammals, few exceptions
Penis (basics)
Copulatory organ
Delivers sperm into female reproductive tract
Urethra down middle of penis
Penis Anatomy
Erectile tissue: 3 parallel columns of tissue
During sexual stimulation- NO released -> smooth muscle relaxes -> more blood flow
-> tissue swells, veins compressed
-> blood enters faster than it leaves- hydrostatic skeleton
Glans: Tip of penis, contains most sensory nerves
Prepuce (foreskin): Cuff of loose-fitting skin, often removed
Seminal vesicles
In a pair
Produce fluid rich in:
Fructose- Energy for sperm after ejaculation
Prostaglandins- stimulate contractions of uterus
~ 60% of semen volume- has yellow pigment
Fluoresces- forensically important
Prostate Gland
Contains anticoagulant enzymes and citrate (nutrient)
Secretes into urethra
Common site of cancer in men over 50
1/2 of men over 40 have enlarged prostate
3% of men die of prostate cancer
Bulbourethral Gland
2 small round glands on either side of urethra
1st gland to secrete into urethra during arousal (Bulbourethral fluid)
Mucus- neutralizes any acidic urine
Some sperm released before ejaculation
What are the 3 accessory glands that sperm mixes with to become semen?
Seminal vesicles
Prostate gland
Bulbourethral gland
Semen
Mixture of sperm and fluids from accessory glands
Sperm moves through conducting tubes
-> Mixed with secretions from the 3 accessory glands
-> Semen
Sperm Path
- Created in testes (spermatogenesis)
- Travels through/stored in epididymis (site of growth + maturation)
- Travels through vas deferens- sperm ducts (1 from each epididymis)
- Vas deferens extends from scrotum to pelvic cavity
- Ejaculatory duct: Passes through prostate gland, joins urethra
- Urethra: Carries urine and semen through penis
So
Epididymis
Vas deferens
Ejaculatory duct
Urethra
Exit
Spermatogenesis
Production of mature sperm cells
Takes 7 weeks, occurs continuously
Spermatogenesis steps
Primordial germ cells divide, differentiate into spermatogonial stem cells.
Spermatogonial stem cells divide via mitosis and form spermatogonia. Spermatogonia are undifferentiated cells in walls of seminiferous tubules. Supply of spermatogonia is maintained via mitotic divisions. Some become primary spermatocytes (2n). Primary spermatocytes divide via meiosis. After meiosis 1, they are secondary spermatocytes (n). After meiosis 2, they are spermatids (n). Then they differentiate into mature sperm cells (n).
3 parts of mature sperm cell
Head, mid piece, tail
Tail is plasma membrane
Head has nucleus and acrosome
Midpiece has mitochondria
Androgens
Principle sex hormone in males
Testosterone most important
Signaling Pathway Male Endocrinology
Hypothalamus secretes gonadotropin-releasing hormone (GnRH)
-> Anterior pituitary releases 2 gonadotropins- luteinizing hormone, follicle stimulating hormone
Luteinizing Hormone (LH)
Released by anterior pituitary
Targets Leydig cells
-> Leydig cells produce/secrete testosterone, other androgens
Purpose of testosterone in testes
High levels of testosterone in testes required for spermatogenesis
15-200 million sperm/mL semen- healthy
Less than 15 million/mL- low sperm count
What does testosterone stimulate?
Puberty
Puberty
Period of sexual maturation
Adolescent growth spurt
Growth of primary male sex characteristics- sex organs
Growth of secondary male sex characteristics- physical, behavioral differences between males & females, not directly related to reproduction. Facial/body hair, deep voice, muscle development.
Difference between primary and secondary male sex characteristics
Primary male sex characteristics- sex organs
Secondary male sex characteristics- physical, behavioral differences. Facial/body hair, deep voice, muscle development.
Follicle Stimulating Hormone (FSH)
Secreted by anterior pituitary
Stimulates development of seminiferous tubules
Stimulates Sertoli cells to produce, secrete androgen binding protein (ABP)
ABP binds testosterone, helps maintain high testosterone levels, allows testosterone to be sequestered
FSH secretion inhibited by inhibin- peptide hormone secreted by Sertoli cells
This creates a negative feedback loop. The FSH stimulates Sertoli cells to produce and secrete androgen binding protein, but Sertoli cells secrete inhibin (peptide hormone) that will eventually stop FSH secretion.
_____ is a form of asexual reproduction in which growth and development of embryos occur without fertilization by sperm. In animals, _____ means development of an embryo from an unfertilized egg cell.
Parthenogenesis
Inhibin and androgen binding protein (ABP) are secreted by the _____.
Sertoli cells
What are the advantages of asexual reproduction?
No mate needed / Fast
What are the three types of cells found in the seminiferous tubules?
Spermatocytes / Sertoli cells / Leydig cells
A(n) _____ is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics.
Androgen
The prostate gland secretes ____ and ____ into seminal fluid (semen) in the urethra.
Anticoagulant enzymes / Citrate (nutrient)
____ is a type of asexual reproduction in which a new organism develops from an outgrowth due to cell division at one particular site.
Budding
Where does spermatogenesis take place?
Seminiferous tubules in the testicles
What is the main function of the male reproductive system?
Synthesize and deliver sperm
What do spermatogonia produce when they undergo mitosis?
One primary spermatocyte (2n) & one replacement spermatogonia cell
_____ is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original.
Fission
What are the main functions of testosterone?
Facilitates spermatogenesis / Triggers puberty / Secondary sex characteristics
What do the bulbourethral glands add to seminal fluid?
Mucus (which neutralizes the acid in the vagina and residual urine in the urethra) - first gland to secrete during arousal
What are the male gonads?
Testes
How does the anterior pituitary respond to a rise in gonadotropin-releasing hormone (GnRH)?
Secretes follicle-stimulating hormone (FSH) & Luteinizing hormone (LH)
Where does spermatogenesis take place?
Seminiferous tubules
Which part of a sperm cell contains enzymes?
Acrosome
_____ is a form of asexual reproduction in which an organism splits into pieces and each piece develops into a mature clone genetically and morphologically identical to its parent.
Fragmentation
Is nitric oxide (NO) an endocrine, paracrine, or autocrine signal?
Paracrine
What is the function of primary spermatocytes?
Primary spermatocytes (2n) undergo meiosis in the seminiferous tubules to become secondary spermatocytes (n)
Where is testosterone produced?
Leydig cells
True or False: Primary spermatocytes undergo mitosis to form secondary spermatocytes
False; primary spermatocytes undergo MEIOSIS to form 2 haploid secondary spermatocytes
What is/are the advantage(s) of sexual reproduction?
Genetic variation
_____ is released by endothelial cells during sexual stimulation and causes arterial wall smooth muscle to relax, which dilates arteries and compresses veins.
Nitric oxide (NO)
The _____ is a tube that connects a testicle to a vas deferens in the male reproductive system.
Epididymis
The seminal vesicles secrete into the _____.
Vas deferens
True or False: Both sperm and eggs are motile
False; ONLY sperm is motile (flagellated)
Is prostaglandin an endocrine, paracrine, or autocrine signal?
Paracrine
What is the function of the scrotum?
Keeps sperm 1-2 degrees celsius cooler than internal body temperature - increases sperm longevity
How is ploidy restored to diploid if meiosis creates haploid cells?
Fertilization
Why do sperm cells carry enzymes?
To break down the outer membrane of the ovum
What are the functions of the epididymis?
Sperm maturation/storage/transport
Testosterone inhibits the production of _____ and _____.
Luteinizing hormone (LH) and gonadotropin-releasing hormone (GnRH)
The _____ are a pair of two convoluted tubular glands that lie behind the urinary bladder and secrete yellow fluorescent fluid that composes ~60% of semen volume.
Seminal vesicles
How does the brain respond to low levels of testosterone?
Hypothalamus secretes gonadotropin-releasing hormone (GnRH) to anterior pituitary
What is the primary function of the penis?
Deliver sperm to female reproductive system
Where are mitochondria stored in a sperm cell?
Midpiece
What does follicle-stimulating hormone (FSH) do in males?
Stimulates Sertoli cells to secrete inhibin and ABP
Sperm and urine travel through the _____, which runs through the middle of the penis.
Urethra
In the embryonic testes, _______ divide and differentiate into spermatogonial stem cells (2n).
Primordial germ cells (2n)
_____ inhibits follicle-stimulating hormone (FSH) production.
Inhibin
What is erectile tissue and what is its function?
3 parallel columns in penis - engorge with blood during erection
Secondary spermatocytes (n) undergo _____ to form _____.
Meiosis 2 to form 4 spermatids (n)
What are the two external structures of the penis near the tip?
Glans / Prepuce (foreskin)
What is contained in the fluid secreted by seminal vesicles?
Fructose (for energy) / Prostaglandins (lipids that stimulate uterine contraction)
What does luteinizing hormone (LH) do in males?
Causes Leydig cells to produce testosterone which stimulates spermatogenesis
