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.