Ch. 50: male reproduction

Asexual reproduction

many invertebrates, including sponges, cnidarians, rotifers, flatworms, and annelids

some vertebrates reproduce asexually under certain conditions

Advantages of asexual reproduction

sessile animals have difficulty finding mater (can exchange gametes)

rapid increase in number in favorable environment

disadvantages of asexual reproduction

genetically identical to parent

difficult to evolve

types of asexual reproduction

fission, budding, fragmentation, parthenogenesis

fission

cell divides in either the longitudinal or transverse plane

Example: protists

budding

when new individual forms and then buds off parent

Example: sponges and cnidarians

fragmentation

when body is broken into smaller parts with each peace developing into a new

individual

Regenerates missing parts to develop whole animal

Example: some flatworms, annelids

parthenogenesis

occurs when unfertilized egg develops into adult [no partner]

most species alternate with sexual reproduction

Example: insects and crustaceans, some nematodes gastropods, fishes, amphibians, reptiles

sexual reproduction

Requires a mate - production and fusion of two haploid gametes

Sperms (motile) and small

Ovum (nonmotile)

advantages of sexual reproduction

promotes genetic variety

Favorable for evolution in changing environments

disadvantages of sexual reproduction

less efficiency (mate required)

Requires more energy than asexual

external fertilization

often simultaneous release eggs and sperm into water

Internal fertilization

sperm deposited into or enter female's reproductive tract

male development

Sex determination occurs due to presence or absence of masculinizing factors during critical period of

embryonic development

genotypic sex

XX or XY

Results in gondola sex

phenotypic sex

involves sex-determining region on Y short arm (SRY gene) that codes for testes

determining factor (TDF)

Activated addition genes

Combined production leads to

AMH (antimullerian hormone)

Gene on chromosome 19 codes for secretion of AMH

stimulates degeneration of Mullerian ducts, so no oviducts formed

Ducts become oviducts in female

testicular cells involved in development

sertoli cells, interstitial cells of leydig (endocrinocytes)

sertoil cells

secrete AMH

Interstitial cells of Leydig [endocrinocytes]

secrete testosterone and dihydrotestosterone

Stimulated differentiate of wolffish ducts into contests structures in males (vas deferens, seminal vesicles, prostate glands)

testosterone

drives movement of testes into scrotum

seminal vesicles

secretes fructose (energy source) ascorbic acid, prostaglandins, fibrinogen

contribute to ~60-70% if semen volume

prostate

secretes alkaline fluid, enzyme, components to activate sperm prostaglandins, clotting enzymes, prostate specific antigens (PSA)

bulbourethral glands

paired glands at base of penis

secrete thick alkaline mucus-like fluid, neutralize acid

"pre-ejacultatory" fluid

epididymis

sperm storage, maturation, transport

testis

site of sperm synthesis

vas deferens

sperm storage and maturation, smooth muscles expel sperm

Accessory reproductive organs

prostate gland, seminal vesicles, bulbourethral glands, penis

duct system

Carries sperm in semen secreted by accessory organs (nourishment and support)

Involved in expelling sperm from reproductive tract

Spermatic cord

vas deferens, blood and lymphatic vessels, nerves

Inguinal hernia

protrusion of abdominal visceral tissues into inguinal canal

scrotum

saclike structure

Smooth muscle (dartos and cremaster muscle - temp regulation)

Seminiferous tubules

will come together forming ductus epididymis

Beginning of tubular network

Tightly coiled branched in lobules

Actual site of sperm production in wall of tubule

Spermatogenic cells

sperm forming cells

Sustentacular (Sertoli, nurse cells)

support sperm production

Blocks immune cells from reaching developing spermatids

from blood-testis barrier

sustentacular cells produce/secrete

Secrete testicular fluid [has nutrients for developing spermatids]

Helps move sperm toward tubular lumen

Produce: Androgen binding protein (ABP) - binds testosterone

Inhibin - regulates sperm production (turns down abp productions)

Interstitial cells (Leydig cells)

located between seminiferous tubules

Produce and secrete androgens (mainly testosterone)

Myoid cells [muscle-like cells]

surround seminiferous tubules

contract to push sperm and testicular fluid through tubules

Epididymis (ductus epididymis)

site of sperm maturation and storage

Sperm maturation and sperm

absorb excess testiculare fluid

Provide nutrients to sperm

Complete maturation process of sperm

Ductus deferens

from tail of epididymis and continues to seminal vesicles

Can store sperm for months, reabsorb sperm not ejaculated over time

Muscularis layer (smooth muscle)

contracts during ejaculation moving sperm forward along tract

Three layers of smooth muscle

Ejaculatory duct

is very short section between vas deferens and urethra and passes through prostate

Receives secretion form seminal vesicle

Urethra

runs from bladder through prostate and penis; has dual function

Urinary system and reproductive system

accessory sex glands

exocrine gland that produce liquid portion of semen

seminal vesicles location

paired glands near the bladder

seminal secretion

yellowish and ~60-70% of semen volume

fructose

sperm use for ATP synthesis

prostaglandins

stimulate smooth muscle contraction

increase sperm viability

thin mucus for easier sperm movement - better change for fertilization

enhance sperm motility

coagulating proteins

with enzymes from prostate form temporary clot of semen in female reproductive tract

pH

alkaline to neutralize acid in urethra and female reproductive tract

prostate gland

egg sized - inferior to urinary bladder

produces milky colored fluid

prostate fluid

~20-30% of semen and pH is alkaline

contains: prostaglandins, citrate, prostate specific antigen, and antimicrobial chemicals

citrate

serves as another sugar sperm can utilize for ATP synthesis

prostate specific antigen (PSA)

dissolve semen clot in female reproductive tract

allows sperm to move along female tract

antimicrobial chemicals

inhibit some bacterial growth, decreases infection risk in female reproductive tract

semen composition

glandular secretions: ~95%

sperm: ~5%

semen volume

~2.5-5 ml

semen- sperm count

40-750 million

testes

sperm productions: mitosis, meiosis and differentiation

penis

erection and ejaculation

low count of sperm production

variety of environmental factors

smoking and alcohol abuse

exposure to industrial and environmental toxins

use of anabolic steroids may contribute to low sperm count and sterility

spermatogenesis

Location: in wall of seminiferous tubules

Post puberty: spermatogonia (2N) located next to basement membrane of seminiferous tubules become

fully functional stem cells and divide by mitosis

One daughter cell remains as stem cell

Stays on blood side of blood testis barrier

One becomes diploid primary spermatocyte

primary spermatocyte

pushed through blood-testis barrier toward lumen, undergoes first meiotic division forming two smaller haploid cells

secondary spermatocyte

undergo second meiotic division

produces four haploid spermatids

spermatids

continue to move toward lumen of tubule

continue to lose cytoplasm

spermiogenesis

process of sperm maturation

takes ~65-75 days

spermiogenesis process

1. spermatids elongate and shed excess cytoplasm

2. acrosome develops - organelle in tip of sperm (involved in fertilization)

3. mitochondria increase in number - migrate to base of flagellum (midpiece)

4. mature sperm cell has head, midpiece, tail

contracting fluid

from seminal vesicles

allow for sperm to be motile

capacitation and capable of fertilization

sperm are exposed to secretions in female reproductive tract plus semen secretions

hypothalamus

secretes gonadotropin-releasing hormone (GnRH) that stimulated FSH and LH from anterior pituitary

Follicle-stimulating hormone (FSH)

stimulates sustentacular cells to secrete androgen-binding protein (ABP) and other signaling molecules

luteinizing hormone (LH)

stimulates interstitial cells to secrete testosterone

negative feedback regulation of sperm cell production

sertoli cells also secrete inhibin that reduces FSH secretions - reduced ADP

interstitial cells have been producing testosterone and higher testosterone levels reduces secretion of GnRH, FSH, and LH