The Male Reproductive System and Spermatogenesis

Female Reproductive System Overview:
- The endometrium is the structure that decreases over a month during the menstrual cycle.
- Eggs are produced in the ovaries.
Male Reproductive System Overview:
    - Sperm are produced in the testes.
    - The glands contributing to semen include the Cowper's gland (also known as the bulbourethral gland), the prostate gland, and the seminal vesicles.
    - Duct Pathway: The tubes providing the pathway for sperm to exit the body are the ductus deferens (or vas deferens), the ejaculatory duct, and the urethra.
    - Epididymis: This is where sperm mature and become mobile.

The Scrotum:
- The scrotum is the skin sac around the testes that holds them in place.
- Primary function: Ensures that the temperature of the testes is correct for sperm production.
Seminiferous Tubules:
    - These are long, tiny tubes packed within each testis.
    - Total length: There are approximately $250\,m$ of seminiferous tubules in each testis.
    - Etymology: The term "tubule" ends in "-ule" because it refers to a very tiny tube (cylinder).
    - Function: This is the specific location where male sperm cells are manufactured through the process of meiosis.

Internal Geometry:
    - A cross-section of a tubule reveals a hollow center (lumen) and an outer rim.
    - Immature sperm cells are aligned along the outer edges of the tubule.
    - Mature sperm (with tails) are found in the hollow center (lumen) of the tubule.
Cellular Development and Chromosomes:
    - Sperm start as diploid cells: $2n = 46$ .
    - As they undergo meiosis, they become haploid cells: $n = 23$ .
    - Meiosis in males occurs exclusively inside the testes within the seminiferous tubules.

For Biology 30, students must know three specific cell types within the male reproductive system, remembered by the acronym SIST:

S — Sperm Cells:
- These are the gametes produced in the tubules.
S — Sertoli Cells:
    - Found within the seminiferous tubules.
    - Their role is to support, nourish, and help the sperm cells grow.
    - On a diagram, the nucleus of the Sertoli cell and the cell itself are often labeled separately.
I — Interstitial Cells:
    - Found "hanging out" on the outside or in between the seminiferous tubules.
    - Function: They produce testosterone.
    - Often called the "cells of Leydig," named after their discoverer.
    - Memory Aid: The word "interstitial" has three 't's, and the word "testosterone" also contains 't's, linking the cell to the hormone.

Sperm Structure:
    - Head: Contains the genetic material.
    - Acrosome: A cap on the head containing enzymes. These enzymes act as a catalyst to "bore a hole" (dig a hole) through the egg's outer layer.
    - Mid-region: Contains mitochondria to fuel movement.
    - Tail (Flagellum): Provides mobility.
The Fertilization Event:
- Only one sperm can penetrate the egg.
- Once a sperm enters, the egg cell depolarizes, creating a shield to prevent any other sperm from entering.

Polyploidy Warning:
- If two sperm cells ( $n = 23$ each) fertilized one egg ( $n = 23$ ), the resulting zygote would be $3n = 69$ .
- This condition is called polyploid and is not compatible with life.
Fraternal Twins:
- Occur when a female releases two separate eggs in one month, and both are fertilized by two separate sperm.
Identical Twins:
    - Occur when one egg is fertilized by one sperm ( $2n = 46$ ).
    - Early in development (e.g., the 2 to 4 cell stage), the baby/zygote splits into two.
    - These individuals are clones of one another with identical DNA.

Sperm Count Decline:
- Over the past 50 years, there has been a significant decline in male sperm quality and count.
- Potential Cause: Research suggests a link to plastics used in everyday life.

Biological Investment:
- Females make a "big bet" (high investment): One large ovum ( $0.1\,mm$ ), significant tissue support via the uterus, and a 10-month commitment if fertilized.
- Males use the "penny slots" strategy (low investment/high volume): Sperm is $1/100,000$ the mass of an egg; males produce millions to overcome low individual odds of success ( $1,500$ sperm per second).
Thermoregulation:
- The testes are outside the body because sperm are sensitive to temperature.
- Core body temperature ( $7\,degrees$ according to the transcript) is too high for proper spermatogenesis; a lower temperature is required.
Hormone Cascade:
    - GnRH: Released by the hypothalamus at puberty; triggers the anterior pituitary.
    - LH (Luteinizing Hormone): In males, spurs Interstitial/Leydig cells to release testosterone.
    - FSH (Follicle Stimulating Hormone): Triggers Sertoli cells to release ABP (Androgen Binding Protein), which binds testosterone to stimulate sperm production.

Seminal Vesicles:
- Secrete a yellowish, alkaline fluid.
- Contains fructose (energy), coagulating enzymes, and prostaglandins (to decrease cervical mucus viscosity and trigger reverse peristalsis in the uterus).
Prostate Gland:
- Encircles the urethra; secretes citric acid and an enzyme cocktail to keep semen liquefied.
Bulbourethral (Cowper's) Glands:
- Pea-sized; secrete clear mucus into the urethra to clear out acidic urine before ejaculation.

Seminiferous Tubules: Production site (takes about 5 weeks total).
Rete Testis: Posterior testis collection area.
Epididymis: Coiled tube ( $6\,meters$ long if uncoiled) with stereocilia to reabsorb fluid. Sperm spend nearly 20 days here maturing and gaining mitochondria.
Vas Deferens: Travels up behind the bladder.
Ejaculatory Duct: Formed by the union of the vas deferens and seminal gland duct.
Urethra: Runs through the penis to the outside world.

Question: Why does one testis look different from the other in the diagram?
Answer: One is an outside view, and the other is a cross-section showing the internal structures (tubules).
Question: What is the white part in the tubule diagram?
Answer: The lumen (hollow center) where mature sperm swim out, and the spaces between the tubes where interstitial cells reside.
Question: How long does it take for sperm to grow?
Answer: The whole process takes about 5 weeks, though they spend about 20 days specifically maturing in the epididymis.

Worksheet Reference: Use textbook pages $478-481$ for the male reproductive system worksheet.
Preparation for Next Class:
- Read page $483$ for the lab (looking at gametes/gonads under a microscope).
- Complete textbook pages $485$ , numbers $1-8$ .