Reproductive 2 - Spermatogenesis, Regulation, Seminal Fluid

Where does spermatogenesis occur

Occurs in the space between adjacent sertoli cells of the seminiferous tubles

Male teste germ cell

Spematogonium

Are spermatogonia haploid or diploid

diploid

Steps of spermatogenesis

1. Spermatogonium undergoes mitosis, creating 1 cell that will remain spermatogonium (rejoins pool), and one cell that becomes a primary spermatocyte

2. Primary spermatocyte undergoes meiosis I, splitting into a secondary spermatocyte which is haploid with 2 copies of DNA (23 pairs of chromatids)

3. Secondary spermatocyte undergoes meiosis 2 to be come a haploid spermatid

4. Spermatids mature/differentiate into spermatozoa

Are primary spermatocytes haploid or diploid

Diploid (2n x 2) - 2 copies of genetic DNA

Are secondary spermatocytes haploid or diploid?

Haploid (1n x2) - 2 copies of genetic DNA

Are spermatids haploid or diploid

Haploid (1n)

From 1 spermatogonium, how many sperm are made?

4

Location of Spermatogenesis mitosis

Basal compartment of the seminiferous tubule

Location of Spermatogenesis meiosis I

Luminal compartment of the seminiferous tubule

Location of spermatogenesis meiosis II

luminal compartment of seminiferous tubule

How many days does spermatogenesis take?

64 days

How do primary spermatocytes move from the basal compartment to the luminal compartment of the seminiferous tuuble

Tight junctions between sertoli cells open up to permit primary spermatocytes to move

Location of maturing spermatids

Create cavities in the luminal surface of certoli cells

What is spermiogenesis

Maturation of spermatids into spermatozoa

How long does spermiogenesis take

24 days (part of the 64 it takes for spermatogenesis)

What happens during spermiogenesis

Spermatids become sperm: produce a flagellum, an acrosome, and lose most cytoplasm and organelles

What happens to the mitochondria during spermiogenesis

They aggregate and become the neckpiece for spermatozoa

Components of a sperm cell

Head, Midpiece, Tail

Sperm head composition

Nucleus: chromosomes must be passed on to the egg

Acrosome - tip (cap) on the head, contains enzymes necessary for fertilization

Sperm midpiece

location of mitochondria = ATP generation. Required for flagellar motion

Sperm tail composition

Tail made by microtubules - use whip live movements to propel

By the time sperm are moved from the seminiferous tubules to the epididymis, are they mature?

No - they are non-motile

How are sperm moved from the seminiferous tubules to the epididymis

Pressure generated by fluid secreted from Sertoli cells

How long do sperm stay in the epididymis, and what do they do there?

Stay for 6-12 days, and they mature until they acquire motility

What happens to surrounding sperm fluid in the epididymis

Most fluid is reabsorbed (stereocilia), sperm is concentrated

How does sperm move from epididymis to vas deferens

Via peristalsis (remains in vas deferens until ejaculation)

What do Sertoli cells secrete

Androgen binding protein and inhibin

Role of inhibin

Regulates the anterior pituitary do help decrease FSH secretion. Does not work on hypothalamic level

What is inhibin made of

Peptide

How does testosterone regulate male reprodction

Inhibits both the anterior pituitary from releasing LH and from the hypothalamus from releasing GnRH pulses

Role of androgen binding protein

Concentrates testosterone in seminiferous tubules

= enables spermatogenesis

Role of testosterone in sperm production

Stimulates spermatogenesis

Where does sperm move after the vas deferens

Common urethral tract

How does the body prevent urine from entering the semen

Valve in urethral tract closes when sperm moves into urethra

3 functions of seminal fluid

1. Dilution of sperm

2. Provision of energy (fructose)

3. Formation of semen clot

What male reproductive accessory gland secretes the most seminal fluid

Seminal vesicles

Function of seminal vesicles

Secretions - it secretes

- Fructose (energy)

- Enzymes (form semen clot)

- Prostaglandins (causes contraction of female tract for forward movement)

What pH is semen

Alkaline - neutralize the acidic female genital tract

Location of prostate gland

inferior to the bladder

Role of the prostate gland

Secretions = it secretes:

- Citrate (energy): required when sperm are sitting in fluid

- Prostate specific androgen (PSA) - breaks down protein in semenal clot

Use of prostate specific androgen as a biomarker

Works as a biomarker for cancer

- Increased with prostate gland benign growth or cancerous

Role of bulbourethral gland

Secretes viscous fluid with mucus - joints with common urogenital tract that ends up in penile tissue

What are the accessory male reproductive glands

seminal vesicle, prostate gland, bulbourethral glands

What is semen composed of

Sperm + Seminal fluid

What nervous system controls male sexual response

Autonomic nervous system

3 phases of male sexual response

3 E's

- Erection

- Emission

- Ejaculation

What controls an erection

Parasympathetic nervous system

What controls emission

sympathetic nervous system - thoracolumbar region (sacral region is PSNS)

How does the PSNS cause erection

Under mechanical stimulation or neural inputs, PSNS is activated and causes relaxation of the penis arteries for increased blood flow = erection

How does the SNS cause emission

SNS causes smooth muscle contraction of vas deferens, leading to movement of sperm from the vas deferens and mixing of seminal fluid in urogenital tract

How does ejaculation occur

Rapid contraction of skeletal muscle for semen expulsion (somatic control)

How is blood flow increases in an erection

PSNS nerve activation increases nitric oxide, which increases cGMP. cGMP causes vasodilation for increased blood flow = erection

How is cGMP broken down during an erection

Phosphodiesterase breaks down cGMP to stop erection

What enzyme produces cGMP

guanylate cyclase - converts GTP to cGMP

What is erectile dysfunction, and how is it caused

Erectile dysfunction - inability to get an erection. Possible causes include diabetes, alcohol, or depression

How to treat erectile dysfunction

Sildenafil (Viagra)

How does Sildenafil (viagra) cause an erection

Inhibits cGMP breakdown by inhibiting phosphodiesterase

How many sperm are deposited into the vagina during ejaculation, how many get past the cervical area, and how many get past the fallopian tube?

200-300 million sperm are ejaculated, 100 000 get past the cervical area, 100 get past the fallopian tube

What accounts for the low number of sperm to reach fertilization site

Acidic pH of vagina kills sperm

Where does the final stage of sperm maturation occur

Inside the female reproductive tract

What are the final stages of sperm development

Capaciation and the Acrosome reaction

Capaciation

Receptors are made available for removal of ova glycoprotein layer, and sperm become fully motile (whiplash movement instead of gentle wave)

Zona pellucida

A thick coating rich in glycoproteins that surrounds an oocyte.

What causes activation of the acrosome reaction

Binding of sperm to zona pellucida

Acrosome reaction

When sperm binds to zona pellucida, Pores are made in acrosome, and acrosomal contents are released. Acrosomal enzymes digest zona pellucida for sperm to fertilize ova.