Human Biology: Reproductive System

Lesson 2:Functional Inter-relationships of the Male Reproductive Sytem

(Inquiry into Life pg. 419-421)

Today’s Objectives Analyse the functional inter-relationships of

the structures of the male reproductive system, including: Describe the path of sperm from the seminiferous

tubules to the urethral opening List the components of seminal fluid (as contributed

by the Cowper’s glands, prostate gland, and seminal vesicles), and describe the functions of each component

Identify the tail (flagellum), midpiece, head, and acrosome of a mature sperm and state their functions

Describe the functions of testosterone Describe the homeostatic regulation of testosterone

levels by the hypothalamus, anterior pituitary, and testes

Spermatogenesis (Sperm Development) Sperm cells are derived from undifferentiated

cells called spermatogonia (sing. Spermatogonium)

Lie just on the outside wall of a tubule Divide mitotically (dividing into copies) Constantly producing new spermatogonia

Spermatogenesis Some of the newly formed spermatogonia

move away from the walls to increase in size and become primary spermatocytes

These then undergo meiosis, a type of cell division

Primary spermatocytes, with 46 chromosomes, divide to give 2 secondary spermatocytes, each with 23 chromosomes

Secondary spermatocytes divide to produce 4 spermatids, also with 23 chromosomes.(see video)

Spermatids then differentiate into sperm (spermatozoa).

Also present in the tubules are the sertoli, which support, nourish and regulate the spermatogenic cells.

Parts of Sperm Head: 23 chromosomes

Acrosome: attached type of lysosome Contains hydrolytic enzymes Digests in outer layer of egg so sperm can

penetrate Middle piece: contains mitochondria for

energy Tail: flagellum used for locomotion

Path of Sperm 1) Formed in the seminiferous tubules of

the testes 2) Mature and stored in the epididymus 3) Stored in and conducted through the Vas

Deferens 4) Enters the urethra just prior to

ejaculation 5) Accessory glands (prostate, Cowper’s

glands, and seminal vesicles add secretions to semen

6) Semen and sperm exit through the penis

Seminal Fluid

SOURCES: 1. Seminal Vesicle 2. Prostate Gland 3. Cowper’s Gland

Functions of Seminal Fluid 1) Seminal fluid produces slightly basic pH

7.5 preferred pH of sperm (basic) to counteract the acidity level of the vagina

2) Provides fructose for energy for sperm 3) Contains prostaglandins – chemicals which

cause the uterus to contract 4) Aids in the movement of the sperm to the

egg 5) Lubrication

Functions of Testosterone 1) Essential for development of primary sex

organs 2) Essential for the development of sperm

Spermatogenic cells take up testosterone which stimulate their activity

3) Increased testosterone concentration at puberty causes maturation of penis and testes

Functions of Testosterone 4) Secondary sex characteristics

Facial hair Body hair – armpit, chest, legs, etc Pubic hair Oil and sweat glands secrete (smelly!) Larynx expands (voice changes) Increased muscular strength Aggression Sex drive

Hormonal Control of Testosterone

Hypothalamus releases GnRH

(Gonadotropic releasing hormone)

GnRH causes anterior pituitary to release 2

gonadotropic hormones:

Hormonal Control of Testosterone FSH (Folicle stimulating hormone)

Promotes spermatogenesis in the seminiferous tubules

LH (Leutenizing hormone) Promotes production of testosterone in interstitial

cells Produced in the Anterior Pituitary gland

Negative Feedback Increased testosterone concentration in the blood causes the

anterior pituitary to make less LH, therefore less testosterone is produced.

Decreased testosterone concentration in the blood causes the anterior pituitary to make more LH and therefore more testosterone is produced.

 

Negative Feedback

Increased concentration of stored sperm causes an increase in production of inhibin and decreases production of FSH, therefore production of sperm decreases.

Decreased concentration of stored sperm causes a decrease in production of inhibin and more FSH, therefore more sperm is produced.