L 40, 41, 42

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Questions and Answers

What percentage of sperm is typically found in a single ejaculation of semen?

25 to 30%

5 to 10% (correct)

50 to 60%

15 to 20%

Which component of sperm is responsible for providing energy to propel its tail?

Tail

Head

Acrosome

Midpiece (correct)

How long does it typically take for sperm to mature in the seminiferous tubules?

Two months (correct)

One month

Three months

One week

What enzyme is contained in the acrosome of a sperm cell?

Penetrating enzymes Signup and view all the answers

During a single human ejaculation, how many sperm are typically present?

200 to 500 million Signup and view all the answers

What is the primary function of fructose within semen?

To nourish the sperm Signup and view all the answers

Which phase of sperm development follows the primary spermatocyte stage?

Secondary spermatocytes Signup and view all the answers

What is the total number of sperm a man produces approximately over his lifetime?

525 billion Signup and view all the answers

During which phase of the menstrual cycle does the uterus lining break down?

Menstruation Phase Signup and view all the answers

Which hormonal changes are primarily responsible for the repair of the uterus lining?

Increased levels of Oestrogen and Progesterone Signup and view all the answers

What event is marked on day 14 of the menstrual cycle?

The ovulation event Signup and view all the answers

Which of the following hormones is NOT involved in the menstrual cycle?

Adrenaline Signup and view all the answers

What is the primary role of the Sertoli cells in the epididymis?

Secrete nutrient fluid essential for sperm maturation Signup and view all the answers

Which of the following denotes the period during which blood and cells are lost from the uterus?

Menstruation Signup and view all the answers

Under which conditions do mature sperm show optimal motility?

In a neutral to slightly alkaline medium Signup and view all the answers

What is the effect of sperm count below 20 million/ml?

Leads to infertility Signup and view all the answers

Which substance secreted by the seminal vesicles plays a crucial role in providing energy for sperm?

Fructose Signup and view all the answers

What is the primary hormonal effect of luteinizing hormone (LH) in the male reproductive system?

Triggers testosterone secretion from Leydig cells Signup and view all the answers

What is the maximum duration that sperm can maintain their fertility in the epididymis?

Up to 1 month Signup and view all the answers

How does the prostate gland contribute to the fertilization process?

By producing an alkaline fluid that enhances sperm viability Signup and view all the answers

Which factors can render sperm with a normal count infertile?

Abnormal sperm shape or poor motility Signup and view all the answers

What must occur for normal sexual function in males?

Intact libido and the ability to achieve penile erection Signup and view all the answers

During which phase of the sexual response cycle does heightened sexual awareness occur?

Excitement phase Signup and view all the answers

What primarily mediates the emission phase of ejaculation?

Sympathetic nervous system impulses Signup and view all the answers

What leads to the flaccid state during detumescence?

Contraction of smooth muscle in the corpus cavernosa Signup and view all the answers

What role does the pudendal nerve play during ejaculation?

Coordinates the expulsion of semen Signup and view all the answers

What is the primary vessel involved in the vascular phenomenon of erection?

Corpora cavernosa Signup and view all the answers

Which structure mediates the tactile stimulation that contributes to sexual arousal?

Dorsal nerve of the penis Signup and view all the answers

Which neurotransmitter is crucial for the induction of vascular smooth muscle relaxation during erection?

Nitric oxide Signup and view all the answers

What is the result of increased blood flow during erection?

Compression of the emissary veins Signup and view all the answers

Where do sperm undergo maturation after formation in the seminiferous tubules?

Epididymis Signup and view all the answers

What role does follicle stimulating hormone (FSH) play in the male reproductive system?

Stimulates Sertoli cells to convert spermatids to sperm Signup and view all the answers

How is estrogen formed in the male reproductive system?

From testosterone by Sertoli cells under FSH stimulation Signup and view all the answers

Which process initiates emission during the male sexual act?

Contraction of the vas deferens and ampulla Signup and view all the answers

What is the primary function of testosterone in the male body?

It is responsible for the characteristic masculine body Signup and view all the answers

What occurs in the absence of growth hormone (GH) during spermatogenesis?

Absence of spermatogenesis and potential infertility Signup and view all the answers

Which hormone is pivotal during fetal life for initiating testosterone production?

Placental chorionic gonadotropin Signup and view all the answers

Which statement about the secretion of androgens in males is correct?

Androgens include testosterone, dihydrotestosterone, and androstenedione Signup and view all the answers

At what stage of life does testosterone production cease until puberty?

During childhood Signup and view all the answers

What primary role does testosterone play during fetal development?

Formation of male body characteristics and suppression of female structures Signup and view all the answers

During which period do the testes typically descend into the scrotum due to testosterone secretion?

Last 2 to 3 months of gestation Signup and view all the answers

Which of the following is NOT a secondary sexual characteristic influenced by testosterone?

Increased body fat distribution Signup and view all the answers

Which effect of testosterone on hair growth is described in the content?

Inhibits growth of hair on the top of the head while promoting it elsewhere Signup and view all the answers

What influence does testosterone have on the structure of the pelvis?

Narrowing and lengthening of the pelvic outlet Signup and view all the answers

Which of the following statements is true regarding testosterone's effect on muscle development?

Testosterone increases muscle mass by up to 50% after puberty. Signup and view all the answers

Which of the following aspects does testosterone influence concerning bone density?

Enhances bone thickness and promotes calcium retention Signup and view all the answers

How does testosterone affect skin characteristics during development?

Increases skin thickness and sebaceous gland activity Signup and view all the answers

Study Notes

Reproductive System Overview

The lecture covers the reproductive systems of males and females.
Learning objectives include describing semen composition, ejaculation physiology, male sex hormones (testosterone), the female reproductive cycle, female sex hormones (estrogen and progesterone), sperm production, and the physiology of erection and ejaculation.

Sperm Production

Each testis contains seminiferous tubules (over 800 tightly looped vessels).
Sperm development starts as blob-like cells (spermatogonia) lining the inner wall of the tubules.
These cells mature through stages (primary spermatocytes, secondary spermatocytes, spermatids) to become sperm with tails.
Thousands of sperm are produced every second, taking about two months to mature.

Semen Composition

Semen is more than just sperm; it consists of approximately 5-10% sperm.
The remaining 90-95% is composed of fructose, fatty acids, and proteins that nourish the sperm during their journey.
A healthy man produces roughly 525 billion sperm over his lifetime, with close to 1 billion per month.
An average ejaculation contains 200-500 million sperm.

Sperm Structure

Sperm consists of a head, midpiece, and tail.
The head contains the nucleus (with chromosomes) and the acrosome (containing enzymes for penetrating the female egg).
The midpiece has mitochondria for energy to power the tail's movement.
The tail propels the sperm forward.

Physiology of Erection and Ejaculation

Normal male sexual function needs an intact libido, ability to achieve and maintain erection, ejaculation, and detumescence (return to flaccid state).
Erection is mediated by both central (psychogenic) and peripheral (reflexogenic) innervation.
Central innervation involves CNS stimulation or antagonism of spinal pathways for erection and ejaculation.
Peripheral innervation involves tactile stimulation reflexively triggering parasympathetic (PSNS) vasodilation, stimulating endothelium to release NO to induce vascular smooth muscle relaxation and blood flow. Prostaglandins aid SMC relaxation causing the erection.
The response is regulated by sympathetic nervous system (SNS) inhibition.

Sexual Response Cycle

The sexual response cycle consists of excitement, plateau, orgasmic, and resolution phases.
Excitement phase: erection and heightened sexual awareness.
Plateau phase: intensification and body responses (increased heart rate, blood pressure, breathing rate, muscle tension).
Orgasmic phase: ejaculation and other responses that culminate in sexual excitement.
Resolution phase: return to pre-arousal state.

Ejaculation

Ejaculation is mediated by sympathetic nervous system (SNS) impulses.
Emission is mediated by T11-L2 spinal segments via hypogastric and pelvic plexuses, involving contraction of the epididymis, ductus deferens, seminal vesicles and prostate which prevents semen from entering the bladder.
Expulsion is mediated by somatic motor impulses via the pudendal nerve, characterized by rhythmic contraction of bulbospongiosus and ischiocavernosus muscles, increasing pressure in the penis to expel semen.
The subsequent detumescence phase is mediated by NA from SNS nerves and endothelin from vascular endothelium, causing SMC contractions induced by postsynaptic adrenergic receptors for increased venous outflow, restoring the flaccid state.

Maturation of Sperm in the Epididymis

After sperm formation in the seminiferous tubules, several days are needed to pass through the epididymis (still non-motile).
Motility develops in 18-24 hours in the epididymis.
Inhibitory proteins in the epididymal fluid prevent final motility until after ejaculation.

Storage of Sperm

Adult human testes produce up to 120 million sperm daily.
The majority of sperm are stored in the epididymis, maintaining fertility for at least a month.
Sperm are kept inactive by inhibitory substances.
After ejaculation, sperm become motile and capable of fertilization.

Physiology of Mature Sperm

Mature sperm are motile and capable of fertilization in a neutral to slightly alkaline medium.
Their activity decreases in a mildly acidic medium.
Life expectancy in the female genital tract is only 1-2 days.

Function of Seminal Vesicles and Prostate Gland

Seminal vesicles secrete mucoid material containing fructose, citric acid, nutrients, prostaglandins, and fibrinogen.
The prostate gland secretes a thin, milky fluid containing calcium, citrate, phosphate ions, a clotting enzyme, and profibrinolysin.
The alkaline prostatic fluid is crucial for successful fertilization.

Effect of Sperm Count on Fertility

Normal semen volume during coitus is 3-5 ml.
Normal sperm counts range from 35-200 million sperm per ml.
Sperm counts below 20 million per ml lead to infertility.

Hormonal Factors Stimulating Spermatogenesis

Testosterone (secreted by Leydig cells) is essential for growth and division of germinal cells.
LH (luteinizing hormone) stimulates Leydig cells to secrete testosterone.
FSH (follicle-stimulating hormone) stimulates Sertoli cells, stimulating the conversion of spermatids to sperm.
Estrogen is derived from testosterone by Sertoli cells under FSH stimulation and also essential for spermatogenesis.
Growth hormone is necessary for controlling metabolic functions of the testis

Male Sexual Act

Stages of the male sexual act (Erection, Lubrication, Emission and Ejaculation)

Testosterone and Its Functions

Testosterone is secreted by interstitial Leydig cells within the testes. The testes also secrete other male hormones known as androgens that include dihydrotestosterone and androstenedione.
Testosterone is more abundant but dihydrotestosterone is more active within target cells. Active testosterone requires conversion into dihydrotestosterone.
Testosterone plays a key role in fetal development, stimulating male characteristics and suppressing female ones.
During fetal development and puberty, testosterone stimulates development of primary and secondary sexual characteristics. Specific features involved include:
Enlargement of penis, scrotum, and testes
Distribution of body hair (pubic, facial, chest, etc.)
Baldness
Voice changes (larynx enlargement)
Acne
Increased muscle mass
Increased bone thickness
Ca2+ retention and bone growth.

Cryptorchidism

Cryptorchidism is the failure of the testes to descend into the scrotal sac.
It should be treated before puberty due to a higher incidence of malignant tumors.

Menstrual Cycle

The menstrual cycle is the body's preparation for pregnancy, controlled by hormones.
Hormones involved include follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone.
Key phases include menstruation, proliferation, and ovulation.

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Test your knowledge on human reproductive biology with this quiz. Questions cover sperm production, maturation, and the menstrual cycle, allowing you to explore the fascinating processes of human reproduction. Perfect for students and biology enthusiasts alike!