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Questions and Answers
What is the normal range for sperm count in mL of semen?
What is the normal range for sperm count in mL of semen?
Semen is composed of 60% prostatic fluid, 30% sperm, and 10% seminal vesicle fluid.
Semen is composed of 60% prostatic fluid, 30% sperm, and 10% seminal vesicle fluid.
False
What is the role of prostatic fluid in semen?
What is the role of prostatic fluid in semen?
To buffer vaginal acidity and provide enzymes for sperm motility.
The fluid expelled during orgasm is known as __________.
The fluid expelled during orgasm is known as __________.
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Match the components of semen with their respective percentages:
Match the components of semen with their respective percentages:
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Which chromosome pair determines the male sex?
Which chromosome pair determines the male sex?
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Females produce half Y-carrying eggs and half X-carrying eggs.
Females produce half Y-carrying eggs and half X-carrying eggs.
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What initiates the development of testes in male embryos?
What initiates the development of testes in male embryos?
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The paramesonephric ducts develop into the __________ reproductive tract.
The paramesonephric ducts develop into the __________ reproductive tract.
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Match the hormone to its primary function in sexual development:
Match the hormone to its primary function in sexual development:
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At what week do testosterone secretion and the development of male anatomy begin?
At what week do testosterone secretion and the development of male anatomy begin?
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Hormones like estrogens are only involved in female sexual development.
Hormones like estrogens are only involved in female sexual development.
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What hormone initiates development of the mesonephric ducts in males?
What hormone initiates development of the mesonephric ducts in males?
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Which component is NOT part of semen composition?
Which component is NOT part of semen composition?
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The primary sex organs are responsible for producing gametes only.
The primary sex organs are responsible for producing gametes only.
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What is the name of the process by which sperm cells mature?
What is the name of the process by which sperm cells mature?
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Semen is primarily composed of ____ and sperm cells.
Semen is primarily composed of ____ and sperm cells.
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Match the following phases of male sexual response with their descriptions:
Match the following phases of male sexual response with their descriptions:
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What role does the Y chromosome play in male sexual development?
What role does the Y chromosome play in male sexual development?
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The female reproductive system typically has a penis for introducing gametes.
The female reproductive system typically has a penis for introducing gametes.
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What is one secondary sex characteristic commonly associated with males?
What is one secondary sex characteristic commonly associated with males?
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The ____ serves as the copulatory organ in males.
The ____ serves as the copulatory organ in males.
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What type of muscle is primarily involved in the innervation of the penis?
What type of muscle is primarily involved in the innervation of the penis?
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Study Notes
Chapter 26: Sexual Reproduction and the Male Reproductive System
- Sexual reproduction involves the combination of male and female gametes (sex cells) to form a zygote (fertilized egg).
- The male gamete is sperm (spermatozoon), which has motility; the female gamete is an egg (ovum), which contains nutrients.
- The sex of a child is determined by the sex chromosome in the sperm that fertilizes the egg.
- Males have XY chromosomes; females have XX chromosomes.
- Males produce half Y-carrying sperm and half X-carrying sperm.
- All eggs carry an X chromosome.
Anatomy Terminology
- The following are anatomical terms, often used in professional settings:
- Penis
- Testicles
- Scrotum
- Sperm
- Semen
- Vagina
- Labia Major
- Clitoris
- Ovaries
- Uterus
- Femur
- Nasal cavity
- Blood
- Plasma
- Artery
- Vein
- Ulna
- Smooth muscle
- Lymph
- Aorta
Expected Learning Outcomes (Sexual Reproduction and Development)
- Identify the fundamental biological distinction between males and females.
- Define primary sex organs, secondary sex organs, and secondary sex characteristics.
- Explain the role of sex chromosomes in determining sex.
- Describe how the Y chromosome influences fetal gonad response to prenatal hormones.
- Identify homologous male and female external genitalia.
- Describe the descent of gonads and its importance.
The Two Sexes
- Male and female gametes combine their genes to form a zygote.
- One gamete (sperm) has motility; the other (egg) nourishes the developing embryo.
- A parent producing sperm is considered male.
- A parent with a Y chromosome is male.
- A parent lacking a Y chromosome is female (in mammals).
- The female provides a sheltered internal environment and prenatal nutrition.
Overview of the Reproductive System
- The male reproductive system produces sperm and introduces them into the female body.
- Males have a penis for introducing gametes.
- The female reproductive system produces eggs, receives sperm, enables fertilization, harbors the fetus, and nourishes the offspring.
- Females have a vagina for receiving sperm.
Overview of the Reproductive System (Primary and Secondary Sex Organs)
- The reproductive system includes primary and secondary sex organs.
- Primary sex organs (gonads) produce gametes (testes in males, ovaries in females).
- Secondary sex organs (other than the gonads) are necessary for reproduction.
- Male - ducts, glands, penis
- Female - uterine tubes, uterus, vagina
Overview of the Reproductive System (Secondary Sex Characteristics)
- Secondary sex characteristics develop at puberty and further distinguish the sexes. These traits attract potential mates.
- Both sexes: pubic and axillary hair, scent glands, voice pitch
- Male: facial hair, coarse hair on torso/limbs, muscular physique
- Female: body fat distribution, breast enlargement, hairless skin.
Chromosomal Sex Determination
- Humans have 23 pairs of chromosomes; 22 pairs are autosomes, and 1 pair are sex chromosomes (XY in males; XX in females).
- Males produce half X-carrying and half Y-carrying sperm.
- All eggs carry an X chromosome.
- The sex of the child is determined by the type of sperm that fertilizes the egg. X-carrying sperm results in a female; Y-carrying sperm results in a male.
Prenatal Hormones and Sexual Differentiation
- Fetuses are sexually undifferentiated for the first 7 weeks.
- Gonads begin developing at 5–6 weeks.
- Two sets of ducts exist: mesonephric (wolffian) and paramesonephric (müllerian)
- The SRY gene (on the Y chromosome) initiates testes development.
- Testes secrete testosterone to develop the male reproductive system and müllerian-inhibiting factor to cause degeneration of the female reproductive tract.
- Absence of SRY causes the paramesonephric ducts to develop into the female reproductive tract and mesonephric ducts to degenerate.
Prenatal Hormones and Sexual Differentiation (SRY gene)
- The SRY gene, found on the Y chromosome, codes for a protein called the testes-determining factor (TDF).
- TDF initiates testes development, which begins secreting testosterone at 8-9 weeks.
- Simultaneously, the testes secrete müllerian-inhibiting factor (MIF). MIF causes the degeneration of the paramesonephric (müllerian) ducts.
Development of External Genitalia
- External genitalia are initially similar in both sexes. They become distinct by week 12.
- Genital tubercle becomes the glans of the penis or clitoris, urogenital folds form the penis or labia minora.
- Labioscrotal folds become the scrotum or labia majora.
Descent of the Gonads
- Both male and female gonads (testes and ovaries) initially develop high in the abdomen.
- They then migrate to the pelvic cavity (ovaries) or scrotum (testes).
- The gubernaculum (a connective tissue cord) guides the gonads' migration.
Descent of the Testis
- Testes descend through the inguinal canal around the 7th month of gestation.
- The position of the testes is critical to spermatogenesis.
- Testes are accompanied during descent by blood vessels, nerves, ducts, and portions of the internal abdominal muscles.
Male Reproductive Anatomy (Learning Outcomes)
- Describe temperature regulation in the scrotum.
- Describe the structure and functions of the male reproductive system.
- Describe the pathway a sperm cell takes from its formation to ejaculation.
- List the names, locations, and basic functions of male accessory reproductive glands.
The Scrotum (Temperature Regulation)
- The scrotum regulates testicular temperature (35°C), which is lower than core body temperature (37°C), necessary for sperm production.
- Mechanisms involve the cremaster muscle, dartos muscle, and pampiniform plexus.
- These muscles contract or relax to move the testes closer to or farther from the body, regulating heat loss or retention.
- The pampiniform plexus is a network of veins that acts like a countercurrent heat exchanger, cooling the arterial blood before it reaches the testes.
Pathway of a Sperm
- Spermatozoa travel through the following structures to the urethra: seminiferous tubules, rete testis, efferent ductules, epididymis (head, body, tail), ductus deferens, ampulla, ejaculatory duct, and urethra.
Accessory Glands
- Seminal vesicles, prostate, and bulbourethral glands produce seminal fluid.
- Seminal fluid contains substances like fructose and prostaglandins to support sperm motility and viability.
- These glands secrete fluids that make up most of the semen.
Sperm and Semen (Learning Outcomes)
- Understand meiosis and the outcome of this cell division.
- Describe the sequence of cell types in spermatogenesis.
- Describe the composition of semen and functions of its components.
Spermatogenesis
- Process of sperm production in seminiferous tubules.
- Involves: remodeling of germ cells; reduction of chromosome number by one-half; shuffling of genes.
- Genetic variation amongst offspring is a result of spermatogenesis.
Spermiogenesis
- Transformation of spermatids into mature sperm.
- Includes packaging of enzymes, formation of the acrosome, and development of the tail.
- The maturation process takes about 70 days.
Hormonal Control of Male Reproduction
- The hypothalamus releases GnRH, which stimulates the anterior pituitary to release FSH and LH.
- FSH stimulates sustentacular cells to release ABP; LH stimulates interstitial cells to produce testosterone.
- Testosterone regulates spermatogenesis and secondary sex characteristics, etc.
Semen
- Semen is a fluid mixture of sperm and secretions from various glands.
- Typical ejaculation volume is 2–5 mL.
- Normal sperm count ranges from 50 to 120 million sperm/mL.
- Low sperm counts can indicate infertility.
Semen (Cont.)
- Semen's stickiness facilitates fertilization.
- Enzymes in prostatic fluid convert semenogelin to a sticky substance (fibrinlike).
- Sticky substance adheres to the cervix and inner wall of the vagina.
- Sperm motility is facilitated by fluids with proper pH and energy sources.
Semen (Motility Requirements)
- Prostatic fluid buffers vaginal acidity (pH 3.5–7.5) to a suitable pH for sperm motility.
- Seminal vesicle secretions provide fructose and other sugars as an energy source for sperm mitochondria.
Male Sexual Response (Learning Outcomes)
- Describe the blood and nerve supply to the penis.
- Explain how blood and nerve supply govern erection and ejaculation.
Male Sexual Response (Phases)
- Masters and Johnson divided sexual intercourse into four phases: excitement, plateau, orgasm, and resolution.
- The four phases are described for a comprehensive understanding of the male sexual response.
Anatomical Foundations (Male)
- Internal pudendal (penile) artery divides to supply blood to the penis, with dorsal artery supplying skin and fascia of the penis.
- Deep artery supplies the core of the corpus cavernosum, causing its dilation during erection, resulting in blood flow between the arteries.
- When erect, blood flows through the deep and dorsal arteries; during relaxation, blood is drained from the penis.
Anatomical Foundations (Nerves)
- The penis' glans has tactile, pressure, and temperature receptors; sensory information travels through the dorsal nerve of penis and internal pudendal nerves to the spinal cord.
- Autonomic and somatic motor fibers carry response signals back to the penis, controlling erection/ejaculation.
Excitement and Plateau
- The excitement phase is characterized by vasocongestion (swelling), myotonia (muscle tension), and increased bodily functions.
- Bulbourethral glands release pre-ejaculate.
- Parasympathetic stimulation leads to erection.
- Erection begins with nitric oxide secretion which dilates arteries, causes blood to engorge the penis and causes erection.
Excitement and Plateau (Cont.)
- Marked vasocongestion and myotonia
- Phase lasts for a few seconds or a few minutes before orgasm.
Orgasm and Ejaculation
- Orgasm is a short, intense reaction; it occurs after the excitement and plateau phases and is marked by semen discharge.
- Heart rate and blood pressure elevate.
- Ejaculation occurs in two stages: emission (sympathetic stimulation leading to peristalsis and addition of fluid to sperm) and expulsion (somatic stimulation causing muscle contractions releasing semen).
Resolution
- Body functions return to pre-excitement levels.
- Internal pudendal artery constricts; blood is reduced, causing detumescence (penis becomes flaccid).
- Cardiovascular and respiratory responses return to normal.
Refractory Period
- Period after resolution where it's practically impossible to achieve another erection or orgasm.
- Duration varies from 10 minutes to several hours.
Neural Control of Male Sexual Response (Visually Driven)
- Visual, mental, emotional stimulation triggers signals relayed from the brain through the spinal cord (sacral spinal cord).
- Parasympathetic signals stimulate blood flow to the genital area, initiating the erection.
Neural Control of Male Sexual Response (Orgasm/Ejaculation)
- Sympathetic signals cause emission (peristalsis in ducts adding gland secretions).
- Somatic signals stimulate ejaculation (muscle contractions).
Neural Control of Male Sexual Response (Resolution)
- Sympathetic signals constrict internal pudendal arteries, decreasing blood flow to penis, and causing the penis to become flaccid.
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Test your knowledge on human reproductive anatomy and functions. This quiz covers topics such as sperm count, semen composition, and hormonal influences on sexual development. Challenge yourself with matching questions and fill-in-the-blank prompts!
