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Male Repro Phys Flashcards

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1
Q

How is puberty initiated?

A

Pulsatile secretion GnRH
Which drive pulsatile secretion of FSH and LH
Which stimulates secretion of gonadal steroid hormones, testosterone, and estradiol
Increased circulating levels of sex hormones responsible for appearance of secondary sex characteristics at puberty

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2
Q

What may be a natural inhibitor of GnRH release? Describe

A

Melatonin
Secreted by pineal gland
Levels are highest during childhood and decline in adulthood
Removal of pineal gland precipitates early puberty

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3
Q

What are the main functions of testes?

A

Spermatogenesis

Secretion of testosterone

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4
Q

Describe function of scrotum

A

Lower temperature essential for spermatogenesis (1-2 degrees C below body temp)

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5
Q

Describe function of epididymis

A

Primary location for maturation and storage of sperm

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6
Q

Describe function of vas deferens

A

Another storage area (ampulla) for sperm

Secretes fluid rich in citrate and fructose

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7
Q

Describe function of seminal vesicles

A

Secretes fluid rich in citrate, fructose, prostaglandins, and fibrinogen

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8
Q

Describe function of prostate gland

A

Secretes milky aqueous solution rich in citrate, calcium, and enzymes, phosphate ion, clotting enzyme, profibrinolysin

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9
Q

Describe epithelium of seminiferous tubules

A

Formed by Sertoli cells with interspersed germ cells

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10
Q

Describe spermatogonia

A

Most immature germ cells

Located near periphery of tubule

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11
Q

Describe spermatozoa

A

Mature germ cells

Located near lumen of tubule

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12
Q

Where are Leydig cells?

A

Interstitial cells that lie between tubules

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13
Q

What are the functions of Sertoli cells?

A

Provide nutrients for differentiating sperm
Form tight junctions with each other, creating a barrier between testes and bloodstream
Secrete aqueous fluid into lumen into seminiferous tubules to help transport sperm through tubules into epididymis

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14
Q

What cells provide nutrients to differentiating sperm, form tight junctions (blood-testes barrier), and secrete aqueous fluid into lumen of seminiferous tubules?

A

Sertoli cells

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15
Q

Describe the blood-testes barrier

A

Formed by tight junctions by Sertoli cells
Imparts selective permeability
Admits certain substances to cross (testosterone) but prohibits noxious substances

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16
Q

What are the main functions of Leydig cells?

A

Synthesis and secretion of testosterone

Main steroidogenic cells

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17
Q

What cells synthesize and secrete testosterone?

A

Leydig cells

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18
Q

Describe fetal Leydig cells

A

Responsible for masculinizing male urogenital tract and inducing testis descent
Cells atrophy shortly after birth and do not contribute to adult Leydig cell population

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19
Q

Describe adult Leydig cells

A

Derived from undifferentiated precursors present after birth and become fully steroidogenic at puberty

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20
Q

How do Leydig cells acquire cholesterol, and what does it convert cholesterol to?

A

Acquire cholesterol from circulation, through low-density lipoprotein (LDL) receptors
To a lesser extent, through high-density lipoprotein (HDL) receptors
Cholesterol is converted to pregnenolone

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21
Q

How do Leydig cells store and transfer cholesterol?

A

Store cholesterol as cholesterol esters
Free testosterone is generated within Leydig cells by cholesterol hormone-sensitive lipase (HSL)
HSL converts cholesterol esters to free cholesterol for androgen production
Cholesterol is then transferred within mitochondrial membranes via steroidogenic acute regulatory protein (StAR)

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22
Q

What enzyme do testes lack?

A

21 beta-hydroxylase
11 beta-hydroxylase
So not glucocorticoids or mineralocorticoids are synthesized

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23
Q

What enzyme does testes have?

A

17 beta-hydroxysteroid dehydrogenase

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24
Q

What does 17 beta-hydroxysteroid dehydrogenase do?

A

In testes

Converts androstenedione to testosterone

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25
In testes, what converts androstenedione to testosterone?
17 beta-hydroxysteroid dehydrogenase
26
Where and how is testosterone concentrated?
In lumen of seminiferous tubules | Concentrated by binding to androgen-binding protein (ABP)
27
What does androgen-binding protein (ABP) in seminiferous tubules do?
Concentrate testosterone
28
In peripheral tissue, what converts testosterone to dihydrotestosterone (DHT)?
5alpha-reductase
29
In peripheral tissues, what does 5alpha-reductase do?
Converts testosterone to dihydrotesosterone
30
What is most circulating testosterone bound to?
Sex hormone-binding globulins (SHBG) | Albumin
31
What do sex hormone-binding globulin (SHBG) and albumin do?
Binds circulating testosterone
32
Most estrogen in males is produced by liver. What else might be a source of estrogen?
Sertoli cells | Conversion of testosterone to estradiol mediated by aromatase
33
Describe the mitochondrial pathway for testosterone synthesis
Cytochrome P450 side-chain cleavage enzyme removes side-chain from carbon at position 20 of cholesterol AKA cholesterol desomolase
34
What is the rate-limiting step in synthesis of testosterone?
Conversion of cholesterol to pregnenolone
35
What does steroidogenic acute regulatory protein (StAR) do?
Transfer cholesterol from inner to outer mitochondrial membrane
36
What stimulates conversion of cholesterol to pregnenolone and regulates overall rate of testosterone synthesis by Leydig cell?
LH
37
What does LH do to Leydig cell?
Stimulates conversion of cholesterol to pregnenolone | Regulates overall rate of testosterone synthesis
38
How does LH promote pregnenolone synthesis?
Increase affinity of P450scc (cholesterol desmolase) enzyme for cholesterol Long-term action in which it stimulates synthesis of P450scc enzyme
39
What increases synthesis of and affinity of P450scc (cholesterol desmolase) for cholesterol?
LH
40
What does aromatase do?
Converts testosterone to estradiol
41
What converts testosterone to estradiol?
Aromatase
42
What are the actions of testosterone during fetal development?
Penis and scrotum Differentiation of internal male genital tract (epididymis, vas deferens, and seminal vesicles) Causes descent of testes into scrotum during last 2-3 months
43
What are the actions of testosterone during puberty?
``` Increased muscle mass Pubertal growth spurt Closure of epiphyseal plates Growth of penis and seminal vesciles Deepening of voice Spermatogenesis Libido ```
44
What are the actions of DHT?
Fetal differentiation of external male genitalia (penis, scrotum, and prostate) Male hair distribution and male pattern baldness Sebaceous gland activity Growth of prostate
45
What can be used as treatment for benign prostatic hypertrophy and hair loss in males?
5alpha-reductase inhibitors
46
Describe the androgenic actions of androgens
Regulation of differentiation of male internal and external genitalia in fetus Stimulation of growth, development of secondary sexual characteristics at puberty Maintenance of reproductive tract and production of sperm Initiation and maintenance of spermatogenesis
47
Describe the anabolic actions of androgens
Stimulation erythropoietin synthesis (stimulates red blood cell production) Stimulation of sebaceous gland secretion Control of protein anabolic effect (nitrogen retention) Stimulation of linear body growth, bone growth, and closure of epiphyses Stimulation of androgen binding protein synthesis Maintenance of secretions of sex glands Regulation of behavioral effects, including libido
48
What is the LH receptor pathway coupled to?
CAMP-PKA pathway | Results in steroidogenesis and testosterone production
49
What is FSH receptor coupled to?
CAMP-PKA pathway | Involved in protein synthesis and production of inhibin, which inhibits FSH release
50
What stimulates Sertoli cells to secrete ABP into lumen of seminiferous tubules?
FSH
51
What cells does FSH stimulate?
Sertoli cells
52
Describe the supportive function of Sertoli cells
Maintain blood-testis barrier Phagocytosis Transfer nutrients from blood to sperm (transferrin, Fe, lactate) Receptors for hormones and paracrines
53
Describe exocrine function of Sertoli cells
Production of fluid Production of ABP Determination of release of sperm from seminiferous tubule
54
Describe endocrine function of Sertoli cells
Expression of testosterone, ABP, and FSH receptors Production of AMH Aromatization of testosterone to estradiol-17beta Production of inhibin to regulate FSH levels
55
What is the histology of Sertoli cells?
Tall, simple columnar cells
56
What are the phases of spermatogenesis?
Mitotic divisions Meiotic divisions Spermiogenesis
57
Describe spermatocytogenesis (mitotic divisions of spermatogenesis)
Proliferate phase At puberty, mitotic cycles increase Spermatogonia (stem cells) divide to produce daughter spermatogonia After last division, resulting cells are called primary spermatocytes
58
Describe meiosis of spermatogenesis
Production of haploid gamete Primary spermatocytes undergo two meiotic divisions First division produces two secondary spermatocytes (haploid of duplicated chromosomes) Secondary spermatocytes enter second meiotic division, producing two spermatids (haploid of unduplicated chromosomes)
59
Describe spermiogenesis (maturation in spermatogenesis)
Spermatids mature into spermatozoa Nuclear and cytoplasmic changes Ends in testis with release from Sertoli cells
60
What hormone is essential for growth and division of testicular germinal cells?
Testosterone
61
What stimulation is necessary for spermiogenesis to occur?
FSH stimulating Sertoli cells to nurse and form sperm
62
What promotes early division of sperm?
Growth hormone
63
Describe FSH and LH levels in childhood vs adult reproductive period vs senescence
Childhood: FSH>LH Repro period: LH>FSH Senescence: FSH>LH
64
Where do sperm undergo maturation and decapacitation?
Epididymis
65
How do prostaglandins from seminal vesicles aid in fertilization?
React with female cervical mucus to make to make it more receptive to sperm movement (make cervical mucus less thick) Cause backward, reverse peristaltic contractions in uterus and fallopian tubes to move ejaculated sperm toward ovaries
66
What does alkaline prostatic fluid do?
Helps neutralize acidity of other seminal fluids during ejaculation to enhance motility and fertility of sperm
67
What is semen composed of?
Fluid and sperm from vas deferens (10%) Fluid from seminal vesicles (60) Fluid from prostate (30) Small fluid amounts from mucous glands (bulbourethral gland)
68
What are the 3 erectile bodies in the penis?
2 corpora cavenosa | 1 corpus spongiosum
69
Describe erection of male sexual response
Parasympathetic nerves innervating vascular SM of helicine arteries that supply blood to cavernosus spaces release NO NO activates guanylyl cyclase, activating cGMP, which decreases intracellular Ca2+ and causes relaxation of vascular SM Vasodilation allows blood to flow into spaces, causing engorgement and erection Engorged tissue presses veins against a noncompliant outer fascia, thereby reducing venous drainage Somatic stimulation increases contraction of muscles at base of penis, further promoting erection
70
Describe emission of male sexual response
Movement of semen from epididymis, vas deferens, seminal vesicles, and prostate to ejaculatory ducts Under sympathetic control (adrenergic transmitter) Causes sequential peristaltic contraction of SM of vas deferens, closing internal sphincter of bladder (prevents retrograde ejaculation) (also mediated by sympathetic adrenergic stimulation) Emission normally precedes ejaculation but also continues during ejaculation
71
Describe ejaculation of male sexual response
Propulsion of semen out of male urethra Caused by rhythmic contraction of bulbospongiosus and ischiocavernous muscles (striated muscles), which surround base of penis Innervated by somatic motor nerves
72
Describe capacitation of spermatozoa
Sperm are mature when they leave epididymis, but actions are in check by secretions from genital duct epithelia When sperm come into contact with fluids of female tract, capacitation occurs Changes include: Uterine & uterine tubes wash away inhibitory factors Loss of cholesterol that had built-up on acrosome, so head of sperm becomes weaker Membrane of sperm is much more permeable to Ca2+, increases motility of sperm
73
Describe sperm acrosome reaction
Hyaluronidase and proteolytic enzymes are stored in the acrosomal head of sperm Hyaluronidase depolymerizes hyaluronic acid polymers in intercellular cement that hold ovarian granulosa cells together Proteolytic enzymes digest proteins in structural elements of tissue cells that adhere to ovum
74
What happens if there is testosterone deficiency in males in 2nd-3rd month of gestation?
Varying degrees of ambiguity in male genitalia and male pseudohermaphrodism
75
What happens in males if there is a testosterone deficiency during the 3rd trimester of pregnancy?
Cryptorchidism (undescended testes) | Micropenis
76
What happens in males if there is testosterone deficiency during puberty?
Poor secondary sexual development and overall eunuchoid features
77
Describe eunuchoidism
Persistence of prepubertal characteristics | Often by the presence of characteristics typical of opposite sex
78
What happens in males if there is testosterone deficiency during post-puberty?
Decreased libido, erectile dysfunction, decreased facial and body hair growth, low energy, infertility
79
Describe Kallman's syndrome
Genetic disorder Hypothalamic neurons that are responsible releasing gonadotropin-releasing hormone (GnRH) fail to migrate into hypothalamus during embryonic development Characterized by delayed or absent puberty and impaired sense of smell Form of hypogonadotropic hypogonadism
80
Describe Klinefelter syndrome
Men with extra X chromosome Phenotypically male and appear normal at birth At puberty, increased levels of gonadotropins fail to induce normal testicular growth and spermatogenesis Androgen production is usually low Primary hypogonadism Seminiferous tubules are largely destroyed, resulting in infertility
81
Describe possible andropause
As men age, gonadal sensitivity to LH decreases, and androgen production drops Serum LH and FSH levels rise (FSH>LH) Testosterone decreases and causes decreased bone formation, muscle mass, growth of facial hair, appetite, libido Sperm production declines

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