Spermatogenesis

what species have inguinal testis?

bull, ram, stallion, camel

what species have perineal testis?

boar, dog, tomcat

what are the reproductive components in the scrotum?

testes, epididymmis, vas deferens

T/F: testis develop outside the body

false, inside

cryptorchidism

failure of testes to descend into scrotum

phases of testicular descent

1. transabdominal phase- attached to gubernaculum. Cells of peritoneum infiltrate gubernaculum so it becomes fused. Which then tells gubernaculum to grow through inguinal ring into vaginal cavity of scrotum

2. inguinal scrotal phase:

testis enters scrotum and gubernaculum regresses which pulls testis down to bottom of vaginal cavity. Gubernaculum keeps testis attached to bottom of scrotum

where are testis typically retained if they fail to descend?

abdomen or inguinal canal

Dogs with cryptorchidism are 9-14x more likely to develop testicular cancer. Why?

testosterone and growth factors are aberrant = irregularity driving cancer

T/F: spermatogenesis occurs at the same temp of the body

false, needs temps 4-6 degrees cooler than body

What are the three structures that help achieve a cooler temperature of the testes?

pampiniform plexus

cremaster muscle

scrotal skin

function of pampiniform plexus

warm arterial blood from body is cooled on way to testis because surrounding veins are returning cooler blood from testis

function of cremaster muscle

contracts and relaxes to promote venous return of testicular blood

-cannot facilitate long term contractions

how does the scrotal skin help keep the temperature of the testis lower than the body?

1. sweat glands innervated with sympathetic nerves

2. thermosensitive nerves that tell body to increase RR to induce panting

How does heat stress effect sperm production and motility?

decrease drastically

which species have retroperitoneal testis ?

birds, elephants, sloths, armadillos, whales, dolphins

________ is the primary reproductive organ in the male. They produce what?

testes

spermatozoa, hormones and proteins, fluids

what is contained within the testicular parenchyma?

seminiferous tubules

leydig cells

capillaries

lymphatic vessels

Ct

where does spermatogenesis occur?

seminiferous tubules

T/F: the compartments of the seminiferous tubules are basal, adluminal, and interstitial

false, only basal and adluminal

What is housed in the:

a. basal compartment

b. adluminal compartment

spermatogonia, primary spermatocytes

maturing spermatocytes/ spermatids

what separates the basal and adluminal compartments? aka blood testis barrier

tight junctions of sertoli cells

What is the purpose of separating the basal and adluminal compartment?

creates immune-privileged site in testicular epithelium to allow for meiosis of spermatocytes

ALSO protects post-meiotic germ cells from cytotoxic agents

OVERALL: protection from male immune system and toxins

goals of spermatogenesis

1. Provide continual supply of male gametes through stem cell renewal.

2. Provide genetic diversity.

3. Provide billions of sperm daily for maximum reproductive ability.

4. Provide an immunological site for developing germ cells so they are not destroyed by males immune system

what are the phases of spermatogenesis?

Where does each phase occur?

proliferation- basal

meiosis- adluminal

differentiation- adluminal

proliferation phase aka _____________________

a. what occurs during this phase?

b. when does it begin?

c. What is produced from this phase and where do 'they' go?

spermatocytogenesis

mitotic divisions

puberty

spermatogonia B

cross BTB

T/F: all species undergo 5 rounds of mitosis in the proliferation phase

false

Meiotic phase

a. what occurs during this phase?

b. when does it begin?

c. What is produced from this phase and where do 'they' go?

meiosis I

when primary spermatocytes enter adluminal compartment

Differentiation phase aka _____________ has an end result of?

spermiogenesis

creating a sperm cell potentially capable of traveling to and fertilizing an egg.

what are the phases of differentiaiton

golgi

cap

acromoal

maturation

The golgi phase begins with a golgi apparatus. what else is occuring?

vesicles of golgi fuse and create pro-acrosomic granules until a large acrosomic vesicle is formed

Cap phase is where the _________ forms a distinct cap over the nucleus. What happens to the golgi? what is the end result?

acrosome

disappears

primitive flagellum begins to project

What occurs during the acrosomal phase?

acrosome spread across nucleus and eventually forms neck filled with proteinsq

The maturation phase forms the middle piece of sperm. How?

mitochondria accumulate around flagellum

Mature sperm is composed of a head and tail. What is found in the head? the tail?

the head consists of nucleus, acrosome, and post-nuclear cap

the tail consists of a middle piece, principle piece, and terminal piece

______ is the release of spermatozoa from _________ cells into lumen of seminiferous tubules

spermiation

sertoli

T/F: after spermatozoa is release it can fertilize an egg

FALSE, chromatin is compacted meaning transcription and translation of DNA have been stopped

what compacts chromatin in the nucleus of spermatozoa?

keratin, disulfide bonds

what is the acrosome filled with? why?

hydrolytic enzymes to penetrate oocyte

T/F: mitochondria is rapidly degraded after fertilizaiton

true

Even though spermatozoa are continually released spermatogenesis occurs in cycles. Explain

many stages are occurring at different locations

T/F: length of spermatogenesis varies by species

true

What hormones does spermatogenesis require?

GnRH -> LH, FSH -> gonadal steroid (testosterone and estrogen)

Is GnRH secretion pulsatile or continous? what is the effect on LH and FSH?

pulsatile

LH pulses immediately after GnRH but has a short half life which allow for periodic testosterone production

FSH also follows but at lower concentration for longer periods

LH acts on __________ cells which convert progesterone to ________________ which is then transported to _______ cells to do what?

leydig

testosterone

sertoli

maintain spermatogenesis

_________ tells sertoli cells to initiate spermatogenesis but eventually theses cells become less responsive

FSH

When sertoli cells are still responsive to FSH what do they do after initiating spermatogenesis?

convert testosterone to estradiol for negative feedback

What else do sertoli cells secrete?

inhibin, to suppress FSH secretion

What is the effect of using exogenous testosterone/ anabolic steroids on the HPT axis?

GnRH decreases -> decreases LH and FSH -> less testosterone produced by leydig cells = inability to maintain spermatogenesis

T/F: when spermatogenesis is over and spermatozoa are secreted into the lumen of seminiferous tubules they are now able to fertilize an egg

FALSE

Explain passageway of spermatozoa from lumen of seminiferous tubules to head of epididymis

rete testis -> efferent duct -> epididymal duct

What are the 3 sections of the epididymis

caput (head)

corpus (body)

cauda (tail)

How does sperm concentration change when they enter the caput as compared to when they move further through the epididymis?

originally have low concentration due to high levels of rete fluid which is then absorbed by efferent ducts and caput to concentrate sperm number

The location of __________ _______ can help identify sperm maturation issues

cytoplasmic droplet

T/F: when sperm reach the tail of the epididymis they are mature

true

Why is contraction decreased in tail compared to body and head of epididymis?

conserve sperm until sexual excitation and ejaculation

what occurs to the old sperm if no sexual release occurs?

periodic contractions to move old sperm to ductus deferens and urethra to be flushed out during urination

Purpose of accessory sex glands

nourish spermatozoa

activate spermatozoa

clear female repro tract

produce secretions that assist in transport

plug to help retain spermatozoa in female repro tract (some species)

_________ is the enlargement of the ductus deferens that open into pelvic urethra

ampulla

which glands empty directly into pelvic urethra?

vesicular

Prostate gland location varies based on species. It can be corpus or disseminate. Explain

corpus is outside urethralis muscle and disseminate is along walls of pelvic urethra

which glands produce the viscous secretion that causes seminal plasma to coagulate following ejaculation?

bulbourethral

what do the vesicular glands secrete? why?

what does the prostate gland secrete? why?

what does the bulbourethral glands produce? why?

what are the two types of penises?

musculocavernosus

fibroelastic

T/F: the musculocavernous penis have limited erectile tissue so it is encased in tunica albuginea

false, fibroelastic

parts of the penis

glans

shaft

base

the dog has two distinct regions: bulbus glandis and pars longa glandis. what runs through these structures?

os penis

mechanisms of erection

1. erotogenic stimuli

2. activate repro behavior center in hypo

3. stimulate parasym nerves

4. which also release NO

5. NO initiates cascade that causes erection

what is the role of nonadrenergic noncholingeric parasympathetic neurons in erection?

when stimulate they fire and release NO leading to vasodilation

Musculocavernous has a (slow/fast) erection compared to fibroelastic penis

slow

mechanism of ejaculation

intromission

sensory stimulation of glans penis

vontraction of muscles and accessory glands

expulsion of semen

what is a good estimator of sperm producing ability?

scrotal circumference