Lecture Reproductive Part 1 (Male)
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What are the male and female primary sex organs and what are their primary functions?
Gonads: testes and ovaries
Produce sex cells (gametes)-exocrine function
- Secrete steroid sex hormones-endocrine function
- -Male: androgens
- -Female: Estrogens and progesterone
Accessory reproductive organs: ducts, glands, and external genitalia
What roles do sex hormones play?
Development and function of the reproductive organs
sexual behavior and drives
growth and development of many other organs and tissues
What is the male reproductive system composed of?
Testes (within the scrotum) that produce sperm
- Sperm are delivered to the exterior through a system of ducts
- epididymis-->ductus deferens-->ejaculatory duct-->and the urethra
- accessory sex glands: seminal vesicles, prostate, and bulbourethral glands
- -empty secretions into the ducts during ejaculation
What is the scrotum?
- Sac of skin and superifical fascia
- -hangs outside the abdominopelvic cavity
- -contains paired testes
- *3 degrees C lower than core body temperature (temp necessary for sperm production)
- Tempterature is kept constant by two sets of muscles
- 1. smooth muscle that wrinkles scrotal skin (dartos muscle)
- 2. bands of skeletal muscle that elevate the testes (Cremaster muscle)
What are the tunics of the testes?
- outter: Tunica Vaginalis (Derived from the peritoneum)
- inner: Tunica Albuginea, the fibrous capsule
Septa (deriving from the tunica albginea) divides the testes into 250-300 lobules, each containing 1-4 seminiferous tubules (site of sperm production)
How is sperm conveyed through the testes?
- seminiferous tubules-->
- tubulus rectus-->rete testes-->efferent ductules-->
What is the spermaticord?
contains blood vessels, nerves, lymph vessels, and vas deferens from testes to body
blood supply comes from the testicular arteries and testicular veins
What produces the androgens in the testes?
The intersitial (Leydig) cells outside the seminiferous tubules produce androgens
What is the Penis and what does it consist of?
External genetalia are the scrotum and the penis
The penis the male copulatory corgan
- Penis consists of:
- -root and shaft that ends in glans penis
- -prepuce, or foreskin-the cuff of loose skin that covered the glans (removed during circumcision)
- *the proximal end surrounded by the ishiocavernosus muscle, anchors the penis to the punic arch
- Spongey urethra and 3 cylindrical bodies of erectile tissue (spongey network of connective tissue and smooth muscle with vascular spaces)
- -corpus spongiosum surround the urethra and expands to form the glands distally and the bulk proximally
- -corpus cavernosa are pased dorsal bodies superior to the corpus spongiosum
- Erection: erectile tissue fills with blood, causing the penis to enlarge and become rigid
What makes up the male duct system?
- (in order of proximal to distal)
- ductus deferens
- ejaculatory duct
What is the epididymis?
sits on top/around back of testes
Head: contains the efferent ductules
- Duct of the epididymis
- -microvilli (sterocilia) absorb testicular fluid and pass nutrients to stored sperm in lumen
- Non motile sperm enter, pass slowly through (about 20 days), and become motile
- * site of sperm maturation
During ejaculation the epididymis contracts, expelling sperm into the ductus deferns
If sperm is not used in a few months, it is phagocytized by epithlial cells of the epididymis
What is the ductus deferins and the ejaculatory duct?
- ductus deferins: passes through the inguinal canal as part of the spermatocords
- -expands to form the ampulla and then joins the duct of the seminal vesicle to form the ejaculatory duct (empty into prostate)
propels sperm from the epididymus to the urethra
Vasectomy: cutting and ligating the ductus deferns, which is a nearly 100% effective form of birth control
What are the three regions of the male urethra?
Male urethra conveys both sperm and urine
- 1. Prostatic urethra
- 2. Membranous urethra
- 3. Spongey urethra
What do the seminal vesicles produce?
Located near the ampulla of the ductus deferens
produces viscous alkaline seminal fluid
fructose, ascorbic acid, coagulating enzyme (vesiculase) and prostaglandins (enhance sperm motility and fertility)
70% of volume of seminal fluid
duct of the sminal vesicle joins the ductus deferens to form the ejaculatory duct
What is the role of the prostate as an accessory gland?
Encircles part of the urethra inferios to the bladder
- Secretes milk, slightly acid fluid
- -contains citrite, enzymes, and prostate-specific antigen (PSA)
- -plays a role in the activation of sperm
- -enters the prostatic urethra during ejaculation
- -makes up to 30% of seminal fluid volume
What are the bulbourethral (cowper's) glands and what are their roles?
pea-sized glands inferior to the prostate
- Prior to ejaculation, produce thick, clear mucus
- -lubricates the glands penis
- -neutralizis traces of acidic urine in the urethra
What is semen?
mixture of sperm and accessory gland secretions
contains nutrients (fructose), protects and activates sperm, and facilitates their movment
- Prostaglandins in semen
- -decrease the viscosity of mucus in the cervix
- -stimulate reverse peristalsis in the uterus to help sperm reach ovum
sperm's alkalinity (pH 7.3-7.7) neutralizes the acid in the male urehra and female vagina
antibiotic chemicals destroy certain bacteria
clotting afctors goagulate semen just as ejaculation, then fibrinolysin liquifies it
only 2-5ml of semen are ejaculated, containing 20-150 million sperm/ml!
What are the two steps of the male sexual response?
What is an erection? How does an erection take place?
An enlargment and stiffening of the penis from engorgement of erectile tissue with blood
- initiated by sexual stimuli including: touch and mechanical stimulation of the penis, erotic sights, sounds, smells
- *can be induced or inhibited by emotions or higher mental activity
- -parasymphatic reflex promotes the release of Nitric Oxide (NO)
- -NO causes the arterioles in the erectile tissue to dialate and fill with blood
- -expansion of the corpus cavernosa
- *compresses drainage veins and maintains engorgement
- -corpus spongiosum keeps the urethra open
impotence: the inabililty to attain erection
What is ejaculation and how does it take place?
propulsion of semesn from the male duct system
- Sympathetic spinal reflex causes
- 1. Bladder sphincter muscles to constrict, preventing the expulsion of urine
- 2. ducts and accessory glands to contract and empty their contents
- 3. Bulbospongiosus muscles to undergo a rapid serious of contractions (orgasm)
What is spermatogensis?
sequence of events that produces sperm in the seminiferous tubules of the testes
- Most body cells are diploid (2n) and contain
- - two sets of chomosomes (one maternal, one paternal)
- -23 pairs of homologous chromosomes
- GAMETES are haploid (n) and contain
- -23 unpaired chromosomes
- -gamete formation involves meiosis
What is the basic process of spermatogenesis?
Spermatic cells give rise to spterm
- -spermatogonia (sperm stem cells) form spermatocytes
- -spermatocytes form spermatids
- -spermatids become sperm
What is the mitosis of spermatogonia?
Begins at puberty
- -stem cells in contact with the epithlial basal lamina
- -Each mitotic division-->type A daughter cell and a type B daughter cell
- Type A Daughter Cell: maintain the germ cell line at the basal lamina
- Type B Daughter Cell: move toward the lumen and develop into primary spermatocytes
How does meiosis turn spermatocytes into spermatids?
- Meiosis I
- -primary spermatocytes (2n)--> two secondary spermatocytes (n)
- Meiosis II
- -each secondary spermatocyte (n)--> two spermatids (n)
- -Spermatid: small nonmotile cells close to the lumen of the tubule
How does spermiogenesis turn a spermatid into sperm?
- spermatids lose excess cytoplasm and form a tail, becoming spermatozoa (sperm)
What are the major regions of a sperm?
Head: genetic region; nucleus and helmetlike acrosome containing hydrolytic enzymes (lysozyme) that enable the sperm to penetrate an egg
Midpiece: metabolic region, contains mitochondria
Tail: locomotor region; flagellum
What are sustentacular cells?
Large supporting cells (sertoli cells) that extend through the wall of the tubule and surround the developing cells
provudes nutrients and signals to dividing cells
dispose of excess cytoplasm sloughed off during spermiogensis
secrete testicular fluid into the lumen for transport of sperm
How do the sustentacular cells split up the seminiferous tubules?
- Tight junctions divide the wall into two compartments
- 1. Basal compartment: spermatogonia and primary spermatocytes
- 2. Adluminal compartment: meiotically active cells and the tubule lumen
- These tight junctions also form a blood-testes barrier
- -prevents the sperm antigens from escaping into the blood where they would activate the immune system
- -because sperm are not formed until puberty, they are absent during immune system development and would be recognized as "self"
How are hormones regulated for male reproductive function?
A sequence of hormonal regulatory events involving the hypothalamus, anterior pituitary gland, and the testes
THE HYPOTHALAMIC-PITUITARY-GONDAL AXIS (HPG)
What are the steps for the HPG axis?
- 1. Hypothalamus releases gonadotropin-releasing hormone (GnRH)
- 2. GnRH stimulates the anterior pituitary to secrete FSH (follicle stimulating hormone) and LH (luteinizing hormone)
- 3. FSH causes sustenacular cells to release androgen-binding protein (ABP), which makes spermatogenic cells receptive to testosterone
- 4. LH stimulates interstitial cells to release testosterone
- 5. Testosterone is the final trigger for spermatogenesis
- 6. Feedback inhibition on the hypothalamus and pituitary result from
- -rising levels of testosterone
- -inhibin (released when sperm count is high)
What are the mechanisms and the effects of testosterone?
synthesized from cholesterol
- transformed to exert its effects on some target cells
- -dihydrotestosterone (DHT) in the prostate
- -Estrogen in some neurons in the brain
targets all accessory organs; deficiency leads to atrophy
has multiple anabolic effects throughout the body (Such as growth of the ducts, glans, and penis)
is the basis of the sex drive (libido) in males
What are the Secondary Sex Characteristics for Men?
Features that are induced in the nonreproducive organs by male sex hormones (mainly testosterone)
- -Appearance of pubic, axillary, and fascial hair
- -enhanced growth of the chest and deepening of the voice
- -skin thickens and becomes oily
- -bones grow and increase in density
- -skeletal muscles increase in size and mass
- (last two are somatic effects)
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