reproductive system study guide part b

how is spermatogenesis temp sensitive? how is the temperature of the testes regulated so as to ensure healthy spermatogenesis and survival?

cannot occur at 98.6 degrees (body temp)

the position of the scrotum in relation to the abdominal cavity can be varied by a spinal reflex mechanism that plays an important role in regulating testicular temp (contracts scrotal myo in exposure to cold, relax in heat exposure)

where does spermatogenesis take place?

seminiferous tubules (highly coiled, 80% of testicular mass)

where are leydig cells found? what function do they serve?

endocrine cells that produce T. lie in the conn tissue between the seminiferous tubules

where does the T go once produced by leydig cells?

once produced, some of the T is secreted into the blood… BUT a substantial portion goes into the lumen of the seminiferous tubules where it plays an imp role in sperm production

when do leydig cells typically begin making T after birth?

short neonatal surge, then surge again during puberty

define puberty

a period of arousal and maturation of the previously non functional reproductive system. culminating in sexual maturity and the ability to reproduce

when does puberty typically occur? how long does it last? does it timing differ between the sexes?

ages 10-14 on avg, begins 2 years earlier in girls than boys. last 3-5 years

three effects of testosterone unrelated to reproduction

1. has a general protein synthesis effect and promotes bone growth → masculine physique during pubertal growth spurt

2. T stimulates oil secretion by the sebaceous glands

3. in animals T induces aggressive behavior… humans is an unresolved issue

the effects of T on the reproductive system before birth

T masculinizes the reproductive tract and external genitalia and promotes descent of the testes into the scrotum

do males produce/secrete estrogen? is so where is it produced?

a small about by the adrenal cortex and adipose tissue

what is aromatase?

an enzyme that converts T secreted by the testes into estrogen outside the testes

state and summarize the roles of the 2 functionally significant cell types found in the seminiferous tubules

1. germ cells: found in various stages of sperm development

2. sertoli cells: provide crucial support for spermatogenesis

list the 5 cell types created in the formation of sperm

1. spermatogonia

2. primary spermatocytes

3. secondary spermatocytes

4. spermatids

5. spermatozoa

describe spermatogonia (in terms of sperm formation)

stage: mitotic proliferation

undifferentiated primordial diploid germ cells

describe primary spermatocytes (in terms of sperm formation)

stage: mitotic proliferation

diploid spermatogonia divide mitotically and their daughter cells then divide mitotically twice more to form 4 identical diploid primary spermatocytes

define secondary spermatocytes (in terms of sperm formation)

stage: meiosis

each diploid primary spermatocytes forms 2 haploid secondary spermatocytes during first meiotic division

describe spermatids (in terms of sperm formation)

stage: meiosis

result of 2nd meiotic division formed by secondary spermatocytes

describe spermatozoa (in terms of sperm formation)

stage: packaging

remodeled spermatids

list the 3 major stages of spermatogenesis

1. mitotic proliferation

2. meiosis

3. packaging

describe mitotic proliferation (in terms of sperm formation)

diploid spermatogonia divide mitotically; daughter cells form primary spermatocytes

describes meiosis (in terms of sperm formation)

diploid primary spermatocytes form 2 haploid secondary spermatocytes during first meiotic division

2nd meiotic division yields 4 haploid spermatids

describe packaging (in terms of sperm formation)

production of spermatozoa from spermatids; requires remodeling aka spermatogenesis

list and describe the 4 major parts of a spermatozoon

1. head with nucleus

2. acrosome: enzyme filled vesicle that caps the tip of the head (helps to penetrate ovum)

3. tail

4. mid piece: large concentration of mitochondria to power tail

where are sertoli cells located?

seminiferous tubules

list and describe the 6 essiental functions of sertoli cells for spermatogenesis

1. the tight junctions between adjacent cells form a blood-testes barrier

2. sertoli cells provide nourishment for developing sperm

3. sertoli cells have an imp phagocytosis function. engulf the cytoplasm extruded from spermatids during remodeling. destroys defective germ cells,

4. sertoli cells secrete seminiferous tubules fluid into the lumen, which flushes the released sperm from the tubule into the epididymis for storage and further processing

5. androgen-binding protein (component of sertoli secretion); binds w/ T and maintains increased T in the seminiferous tubules fluid into lumen (essential for sustaining sperm production)

6. sertoli cells also release another hormone, inhibin regulates FSH secretion

describe the location and function of the blood-testes barrier

prevent blood-borne substances from passing between the cells to gain entry to the lumen of the seminiferous tubule

what is the function of seminiferous tubule fluid? where is it produced and by what type of cells?

bathes germ cells which is critical for later stages of sperm development.

produced by sertoli cells in the seminiferous tubule

describe the function of androgen binding protein. where and by what type of cells is it made.

a component of sertoli secretion (in seminiferous tubule) is androgen binding protein; binds w/ T and maintains a high lvl of T w/in seminiferous tubule lumen; T is 100X more concentrated here than in the blood to help sustain sperm production

what are the 2 gonadotropic hormones secreted by the anterior pituitary gland?

LH and FSH

summarize the function of luteinizing hormone (LH) on the development and maintenance of the male reproductive system.

LH acts on Leydig cells to regulate T secretion

summarize the function of follicle-stimulating hormone (FSH) on the development and maintenance of the male reproductive system.

FSH acts on sertoli cells of seminiferous tubules to enhance spermatogenesis

summarize how both LH and FSH are stimulated and how they act on the development and maintenance of the male reproductive system.

both stimulated by a hypothalamic hormone called gonadotropin released hormone (GnRH)

1. T acts in negative feedback fashion to inhibit LH secretion

2. Inhibin secreted by sertoli cells, acts on pituitary to inhibit FSH

discuss the level of GnRH secretion before, during early, and during the later stages of pubertal development

1. pre-pubertal period: LH and FSH are not secreted at adequate levels to stimulate any testicular activity and GnRH is inhibited

2. puberty initiation: via an increase in GnRH activity sometimes between 8-12 years old

3. early puberty: GnRH secretion occurs only at night, causing a brief nocturnal increase in LH secretion and T secretion.

4. as puberty progresses: extent of GnRH secretion gradually increases

describe one hypothesis regarding the factos responsible for initiating puberty in humans.

role of hormone melatonin from pineal gland. in many seasonally breading species the overall decrease in melatonin secretion in connection w/ longer days/shorter nights initiates breeding season, some researchers observed decrease of overall melatonin secretion rate at puberty

what is inhibin? location, function?

a hormone released by sertoli cells; acts in negative feedback to regulate FSH secretion

trace the anatomical path a typical sperm cell as it travels through the reproductive tract of males from its genesis in the testes to when in exits of the body. are they ever stored at some point during their travels? if so where?

seminiferous tubules → epididymis → epididymal ducts → vas deferens → urethra

briefly describe a vasectomy and explain its effect on fertility. are sperm still produced after a vasectomy? if so what happens to them?

common sterilization procedure in males; a segment of each vas deferns is surgically removed after it passes testis but before entering the inguinal canal, blocking the exit of sperm from testes

sperm is still produced but builds up and removed by phagocytosis. does not interfere with T activity

where is defensin found? what is its function?

protein secreted by epididymis that defends sperm from microorganisms

summarize function of epididymis

secretes protein that protects sperm from microorganisms (defensin)

summarize function of vas deferns

storage site for sperm (up to days)

list 3 accessory glands of the male reproductive system

1. pair of saclike seminal vesicles

2. prostate gland

3. bulbureathral glands

describe seminal vesicles and their secretions and function

empty into last portion of 2 ductus deferns, one on each side.

supply:

1. fructose (energy source for sperm)

2. prostaglandins

3. more than half the semen (washes and dilutes sperm)

4. fibrogen

describe the prostate gland and its secretion and functional role

large single gland that completely surrounds ejaculatory duct and urethra

describe the bulbourehtral glands and their secretions and functional roles

drain into the ureathra after it has passed through the prostate just before it enters the penis

where are prostaglandins made in the male reproductive system? what function do they serve?

made in the seminal vesicle; stimulate myo contractions of male and female reproductive tracts

where is fribrogen made in the male reproductive system? what function does it serve?

made in seminal vesicles; combines w/ clotting enzymes from prostate gland to produce fibrin which clots the semen