Male Reproduction Flashcards
Reproduction in Humans overview
- Essential to the survival of our species
- Primary reproductive organs (gonads) consist of:
- Pair of testes (male)
- Pair of ovaries (female)
- Reproduction is dependent on the union of male and female gametes
- Half set of chromosomes from each
Primary Reproductive Organs (gonads)
In both sexes mature gonads perform dual function:
1) Producing gametes (gametogenesis)
* Spermatozoa (male)
* Ova (female)
2) Secrete sex hormones
* Testosterone (male)
* Oestrogen and progesterone (female)
The Y Chromosome
- Much shorter than the X chromosome – 1/3 the size and contains about 55 genes vs 900!
- Variation in number of sex chromosomes is common (e.g. XXY)
- Contains the sex-determining region Y gene (SRY) involved in male sex organ development
- Male cells lose the Y chromosome as they age
- Some genes thought to be lost from Y have relocated to other chromosomes
How do sex chromosomes determine sex characteristics at 6 weeks gestation?
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IF FEMALE:
- Gonadal cortex forms the ovary.
- Gonadal medulla regresses.
- Wolffian duct regresses (testosterone absent).
- Müllerian duct develops into the Fallopian tube, uterus, cervix, and upper half of the vagina (AMH absent).
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IF MALE:
- Presence of the Y chromosome and SRY gene directs development towards male characteristics.
- Wolffian duct develops into male internal reproductive structures.
- Müllerian duct regresses due to the presence of anti-Müllerian hormone (AMH).
How does the SRY protein influence male development during gestation?
At 10 weeks gestation:
- SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testes.
- Anti-Müllerian hormone from the testes causes the Müllerian ducts to disappear.
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At birth:
- Testosterone from the testes converts the Wolffian duct into seminal vesicles, vas deferens, and epididymis.
- Dihydrotestosterone (DHT) controls the development of the prostate.
Q: What are the reproductive functions of male sex organs?
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Produce sperm (spermatogenesis):
- Testes are the sperm-producing organs suspended outside the abdominal cavity in the scrotum.
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Delivery of sperm (semen):
- Major accessory sex glands include seminal vesicles, prostate, and bulbourethral glands.
- Penis delivers the semen.
Q: What are the components of the male reproductive system?
- Testes: Site of sperm and hormone production.
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Internal genitalia: Accessory glands and ducts, including:
- Seminal vesicle
- Prostate gland
- Bulbourethral gland
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External genitalia:
- Penis
- Scrotum
Additional structures:
- Epididymis: Stores and matures sperm.
- Vas deferens: Transports sperm from the epididymis.
- Ejaculatory duct: Pathway through which sperm mixes with seminal fluid.
- Urethra: Conduit for semen expulsion through the penis.
Q: What are the main parts and functions of the penis and scrotum?
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Penis: Consists of two main parts:
- Root: The midline bulb and the left and right crura.
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Body: Consists of three cylindrical masses of erectile tissue:
- Corpus spongiosum
- Corpora cavernosa on either side.
- Glans: The tip of the penis, covered in foreskin.
- Scrotum: An external sac that testes migrate into during development.
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Functions:
- Penis: Delivers semen and allows for vaginal penetration during intercourse.
- Scrotum: Holds the testes outside the abdominal cavity to keep them below body core temperature, which is essential for sperm production.
Q: What are the structures and functions of the testes in sperm and hormone production?
- Testes: Have a tough outer fibrous capsule.
- Seminiferous tubules: Coiled and clustered tubules that make up about 80% of the testes tissue; they are the site of spermatogenesis.
- Epididymis: A single duct of tightly coiled ‘cord’ connected to the seminiferous tubules. It stores and matures sperm.
- Vas deferens (ductus deferens): Transports sperm from the epididymis into the abdominal cavity and empties into the urethra.
Function:
- Sperm Production: Occurs in the seminiferous tubules.
- Hormone Production: The testes produce testosterone.
Q: What are the key structures and functions of the seminiferous tubules?
- Site of sperm production.
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Contain spermatogonia at all stages of differentiation and Sertoli cells, which:
- Form tight junctions, creating the blood-testes barrier.
- Basil lamina: Acts as a barrier, but allows testosterone to easily pass through.
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Outside the tubules:
- Peritubular myoid (PTM) cells: Smooth muscle layer.
- Interstitial tissue.
- Leydig (interstitial) cells: Produce testosterone.
- Blood vessels.
- Smooth muscle cells.
Function:
- Sperm Production: Occurs within the seminiferous tubules.
- Hormone Production: Leydig cells produce testosterone.
Q: What are the key features observed in the cross-section of seminiferous tubules?
- Seminiferous Tubules: Site of sperm production.
- Leydig Cells: Found outside the tubules, responsible for testosterone production.
- Spermatogonia: Located near the basal lamina, at various stages of sperm development.
- Sertoli Cells: Support and nourish the developing sperm cells, forming the blood-testes barrier.
- Lumen: Central cavity where mature spermatozoa tails are seen.
Q: What are the three main stages of spermatogenesis?
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Mitotic Proliferation and Clonal Expansion:
- Mitotic Division: Spermatogonia undergo mitosis to produce primary spermatocytes (diploid).
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Meiotic Division (I and II):
- Meiosis I: Primary spermatocytes (diploid) divide to form secondary spermatocytes (haploid).
- Meiosis II: Secondary spermatocytes divide to produce spermatids (haploid).
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Spermiogenesis (Germ Cell Remodeling):
- Spermatids undergo morphological changes to become mature spermatozoa (sperm cells).
Key Points:
- Diploid Cells: 2 complete sets of chromosomes (46), one from each parent.
- Haploid Cells: Single set of chromosomes (23) in gametes (egg and sperm).
- Sperm: Smaller than primary spermatocytes.
Q: What are the main components and functions of a sperm cell?
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Head:
- Nucleus: Contains the genetic information.
- Acrosome: An enzyme-filled vesicle that caps the tip of the head, used to penetrate the ovum.
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Midpiece:
- Contains mitochondria which provide energy for motility, acting as the “power station.”
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Tail (flagellum):
- Provides motility, enabling the sperm to swim towards the egg.
Components:
- Microtubules: Structural elements within the tail that aid in movement.
- Diagram Labels:
- Head (acrosome and nucleus)
- Midpiece (mitochondria)
- Tail (flagellum with microtubules)
Q: What are the main components and functions of seminiferous tubules?
- Site of Sperm Production.
- Contain Spermatogonia: At all stages of differentiation.
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Sertoli Cells:
- Form tight junctions, creating the blood-testes barrier.
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Basil Lamina:
- Acts as a barrier but allows testosterone to easily pass through.
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Outside the Tubules:
- Peritubular Myoid (PTM) Cells: Smooth muscle layer.
- Interstitial Tissue.
- Leydig (Interstitial) Cells: Produce testosterone.
- Blood Vessels.
- Smooth Muscle Cells.
Diagram Labels:
- Lumen
- Spermatogonium
- Sertoli Cell
- Capillary
- Leydig (Interstitial) Cell
- PTM (Peritubular Myoid Cell)
Q: What are the functions of Sertoli cells in spermatogenesis?
- Sustentacular Cells: Provide environment and sustenance for developing sperm.
- Secrete Growth Factors and Enzymes: Also secrete hormones and provide feedback to the hypothalamus to regulate spermatogenesis.
- Take Up LDLs and HDLs: Use cholesterol for sperm production.
- Separate Columns of Developing Spermatogonia: Ensures organized development of sperm cells.
Diagram Labels:
- Sertoli Cell: Provides structural support.
- Spermatogonia: Developing sperm cells.
- Blood-Testis Barrier: Formed by tight junctions between Sertoli cells.
- Leydig Cells: Produce testosterone.
- Basement Membrane, Vasculature, Macrophages, Peritubular Myoid Cells.
Other Cell Stages:
- Elongated Spermatids, Round Spermatids, Pachytene Spermatocytes, Pre-Leptotene Spermatocytes.
Q: What are the stages and key points of sperm production?
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Spermatogonia:
- Clustered near the basal lamina.
- Undergo mitosis to maintain the germ cell line.
- Undergo meiosis to become spermatocytes.
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Spermatids:
- Remain embedded in the apical membrane to complete transformation.
- Lose most of the cytoplasm.
- Develop a tail.
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Timeline:
- Takes approximately 64 days.
- Approximately 200 million sperm are made per day.
- There are 20-300 million sperm per ml of semen.
Diagram Labels:
- Lumen of seminiferous tubule
- Mature spermatozoa
- Spermatids undergoing packaging
- Spermatids
- Secondary spermatocyte
- Primary spermatocyte
- Spermatogonium
- Sertoli cell
- Tight junction
Q: How is sperm production regulated hormonally in the male reproductive system?
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Hypothalamic-Pituitary-Testicular Axis:
- GnRH: Produced in the hypothalamus.
- FSH and LH: Released by the anterior pituitary.
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FSH (Follicle Stimulating Hormone):
- Directly stimulates Sertoli cells to secrete Androgen Binding Protein (ABP).
- ABP: Facilitates testosterone stimulation of spermatogenesis.
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LH (Luteinizing Hormone):
- Directly stimulates Leydig cells to secrete testosterone.
- Testosterone: Stimulates spermatogenesis and has other effects.
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Negative Feedback:
- Inhibin: Secreted by Sertoli cells.
- Testosterone: Provides negative feedback to the hypothalamus to regulate the production of GnRH, FSH, and LH.
Q: What is the pathway of sperm release in the male reproductive system?
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Testes:
- Sperm move into the seminiferous tubules and are free to move within the secreted fluid.
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Epididymis:
- Takes approximately 12 days to transit through the epididymis where full maturation takes place, including the development of the tail.
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Vas Deferens:
- Sperm are expelled here for ejaculation, pushed up over the bladder to the prostate.
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Ejaculatory Duct:
- Joins the seminal vesicles to form the ejaculatory duct, mixing sperm with seminal fluid to form semen.
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Prostate to Urethra:
- Sperm pass through the prostate to the urethra and into the penis for ejaculation.
Diagram Labels:
- Seminal Vesicle
- Ejaculatory Duct
- Prostatic Urethra
- Urethra
- Vas Deferens
- Epididymis
- Testicle
Q: What are the functions of the accessory glands in semen production?
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Semen Composition:
- Semen is 99% seminal fluid, and only 1% sperm.
- Contains water, mucus, buffers for vaginal acidity, nutrients (sugar, vitamin C), enzymes to clot, prostaglandins (smooth muscle contraction/transport), and immunoglobulins (protect from pathogens).
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Seminal Vesicle:
- Contributes about 2/3 of the semen volume.
- Provides sugar, prostaglandins, and enzymes.
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Prostate:
- Adds sperm-activating and clotting enzymes.
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Bulbourethral Glands (Cowper’s Glands):
- Pea-sized glands.
- Add mucus to semen to support the motility of sperm.
Diagram Labels:
- Seminal Vesicle
- Prostate
- Bulbourethral Gland
Q: What are the physiological mechanisms involved in achieving an erection?
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Flaccid Penis:
- Cannot achieve vaginal penetration and insemination.
- Vessels are constricted via norepinephrine (NE) from the sympathetic nervous system (SNS).
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Erect Penis:
- Essential for insemination.
- Vessels are dilated via nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) from the parasympathetic nervous system (PSNS).
Key Points:
- NE (SNS): Constricts vessels, resulting in a flaccid penis.
- NO and cGMP (PSNS): Dilate vessels, resulting in an erect penis.
- An erection is a spinal reflex that can be modulated by higher brain centers following sexual excitement.
Diagram Labels:
- Dorsal Nerve
- Dorsal Artery
- Corpora Cavernosa
- Tunica Albuginea
- Corpora Spongiosum
- Urethra
- Mechanisms of Flaccid vs. Erect Penis
- Higher Brain Centers and Spinal Cord Pathways
Q: What are the two phases of ejaculation and their processes?
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Emission:
- Sperm move from the testes/epididymis to the urethra via surrounding muscle contractions.
- The urethral sphincter closes to prevent return/reflux.
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Ejection Proper:
- Semen/sperm are moved through the urethra and ejected via penile muscle contraction.
