Reproductive Lecture 1 S23 PDF

Chapter 28 Male Reproductive System June 2023 Dr. Kevin Tipper, ND VCMT Male Reproductive System Overview Functions of the male reproductive system 1. gonads produce gametes male gametes are sperm 2. gonads produce hormones Male reproductive struct...

Chapter 28 Male Reproductive System June 2023 Dr. Kevin Tipper, ND VCMT Male Reproductive System Overview Functions of the male reproductive system 1. gonads produce gametes male gametes are sperm 2. gonads produce hormones Male reproductive structures include the external genitalia and internal genitalia © 2018 Pearson Education, Inc. Male Reproductive System Anatomy Overview External Genitalia 1. Penis contains erectile tissue, deposits sperm into vagina 2. Urethra conducts semen to exterior 3. Scrotum Surrounds and supports testes © 2018 Pearson Education, Inc. Male Reproductive System Anatomy Overview Internal Genitalia 1. Testes produce sperm and hormones 2. Epididymis the site of sperm maturation 3. Ductus deferens (vas deferens) conduct sperm between epididymis and prostate 4. Seminal gland (seminal vesicles) secretes fluid making up much volume of semen 5. Prostate secretes fluid and enzymes 6. Bulbo-urethral glands secretes fluids that lubricate tip of penis Male Reproductive System Anatomy Overview Path of sperm Made in the testes Moved to the epididymis Then along the ductus deferens Then along the ejaculatory duct to the urethra Accessory organs secrete various fluids into the reproductive tract along the way Seminal glands, prostate, and bulbourethral glands secrete various fluids into ejaculatory duct and urethra © 2018 Pearson Education, Inc. Male Reproductive System Scrotum and Associated Structures Scrotum Cutaneous outpouching of the abdomen that houses and supports the testes Scrotal septum separates right and left cavities Marked by a raised thickening (raphe of scrotum) in the scrotal surface © 2018 Pearson Education, Inc. Male Reproductive System Scrotum and Associated Structures Dartos muscle Smooth muscle in the skin of the scrotum Elevates testes and contracts the scrotum (reduces heat loss) Cremaster muscle Contracts to pull testes closer to body during sexual arousal or when exposed to cold temperature © 2018 Pearson Education, Inc. Male Reproductive System Scrotum and associated structures Spermatic cords Extend through the inguinal canals between testes and abdominopelvic cavity Each contains layers of fascia and muscle enclosing: ductus deferens blood vessels (testicular artery and veins) Nerves lymphatic vessels Superficial inguinal ring Entrance to the inguinal canal © 2018 Pearson Education, Inc. Male Reproductive System: Structures © 2018 Pearson Education, Inc. Male Reproductive System The testes (testicles) 5 cm long; 3 cm wide; 2.5 cm thick Each weighs 10 – 15 g Form inside the body cavity adjacent to the kidneys Late in fetal development (~ 7 months), connective tissue band contracts Pulls each testis through abdominal musculature into the scrotum © 2018 Pearson Education, Inc. Male Reproductive System The testes (testicles) Tunica vaginalis serous membrane derived from peritoneum partially covers testes Just like other serous membrances, fluid can collect here Called a hydrocele Male Reproductive System The testes (testicles) Tunica albuginea dense, white, irregular CT capsule, deep to tunica vaginalis Extends inward to form many septa, which form 200-300 lobules Each lobule filled with 2 or 3 seminiferous tubules This is where spermatogenesis happens Male Reproductive System The testes (testicles) Male Reproductive System The testes (testicles) Cells of the seminiferous tubules Spaces between tubules contain: Areolar tissue Blood vessels Large interstitial endocrine cells (Leydig cells) Produce androgens, such as testosterone and androstenedione (dominant sex hormones in males) © 2018 Pearson Education, Inc. Male Reproductive System The testes (testicles) Cells of the seminiferous tubules Sustentacular cells (Sertoli cells or nurse cells) extend from basement membrane to lumen of seminiferous tubule protect, support, nourish developing sperm phagocytize excess spermatid cytoplasm produce fluid for sperm transport release sperm into lumen release inhibin (hormone) form blood-testis barrier isolate developing gametes from blood prevents immune response from developing against spermatogenic cells’ surface antigens b/c they are “foreign” Male Reproductive System The testes (testicles) Cells of the seminiferous tubules The walls of the seminiferous tubules also contains the developing sperm cell at different stages of development: Spermatogonia (stem cells) Spermatocytes (undergoing meiosis) Spermatids (undergoing spermiogenesis) Develop into mature sperm Spermiation Process in which a sperm loses attachment to the nurse cell and enters the tubule lumen Male Reproductive System Spermatogenesis The development of sperm Complete maturation takes 65-75 days Millions of sperm produced per day 4 basic steps include: 1. Creation of many spermatogonium through mitosis 2. Meiosis to create gametes 3. Spermiogenesis to create functional sperm 4. Spermiation Male Reproductive System Spermatogenesis 1. Creation of many spermatogonium through mitosis Primordial germ cells migrate from yolk sac to testes in 5th week gestation (fetus) Differentiate into spermatogonia & remain dormant until puberty At puberty, spermatogonium undergo mitosis Male Reproductive System Spermatogenesis 1. Creation of many spermatogonium through mitosis Spermatogonium diploid cells stem cells that undergo mitosis some stay near basement membrane of seminiferous tubule for future cell divisions and sperm production some squeeze through tight junctions to other side of blood-testes border and differentiate into primary spermatocytes Male Reproductive System Spermatogenesis 2. Meiosis Primary spermatocytes Diploid Undergo meiosis I Results in 2 secondary spermatocytes Secondary spermatocytes Haploid Undergo meiosis II Results in 4 spermatids Male Reproductive System Spermatogenesis 2. Meiosis Male Reproductive System Spermatogenesis 2. Meiosis Male Reproductive System Spermatogenesis 3. Spermiogenesis Spermatids undergo spermiogenesis no cell division, spermatid changes into sperm cell changes shape from spherical to elongated forms acrosome (cap) & flagellum (tail) mitochondria multiply sustentacular cells dispose of excess cytoplasm Takes 24 days for spermatids to mature Male Reproductive System Spermatogenesis 4. Spermiation Spermiation is when sperm cells are released from sustentacular cell connections into the lumen of seminiferous tubules sperm are not yet able to swim, so fluid in tubule pushes them toward ducts of testes Male Reproductive System Spermatogenesis Structure of Sperm 60µm (micrometres) Specialized to deliver chromosomes to female gamete Lacks most organelles and intracellular structures in order to reduce size and mass Head 4-5µm long nucleus with 23 chromosomes Acrosome cap filled w proteins (hyaluronidase & proteases) to penetrate ovum Male Reproductive System Spermatogenesis Structure of Sperm Neck Contains both centrioles of the original spermatid Microtubules of distal centriole are continuous with those of the middle piece and tail Middle piece Contains mitochondria to provide ATP for tail movement Tail (flagellum) Whiplike organelle that moves the sperm Male Reproductive System Spermatogenesis Capacitation Sperm released from testes are physically mature But immobile and incapable of fertilizing an oocyte Other parts of male reproductive system are responsible for functional maturation, nourishment, storage, and transport of spermatozoa Capacitation is the process enabling sperm to become motile and fully functional Usually occurs in two steps 1. Sperm become motile when mixed with seminal gland secretions 2. Sperm become capable of fertilization when exposed to the female reproductive tract Male Reproductive Tract Recap Sperm moves to the penis through the reproductive tract 1. Epididymis 2. Ductus deferens 3. Ejaculatory duct 4. Urethra Along the way, three glands add to moving sperm 1. Seminal glands (vesicles) 2. Prostate gland 3. Bulbo-urethral glands Male Reproductive Tract Epididymis Start of the male reproductive tract Coiled tube bound to posterior border of each testis Lined with pseudostratified columnar epithelium Has long stereocilia that increase surface area branching microvilli that increase surface area for reabsorption of degenerated sperm that were stored & not ejaculated Sperm undergo functional maturation here and storage (up to a month) Male Reproductive Tract Epididymis Regions of the epididymis Head Receives spermatozoa from efferent ductules Body Extends inferiorly along the posterior surface of the testis Tail Starts near the inferior border of the testis Number of coils decreases Connects with the ductus deferens © 2018 Pearson Education, Inc. Male Reproductive Tract Epididymis Histology lined with pseudostratified ciliated columnar epithelium layer of smooth muscle propels sperm onward w peristaltic contractions during sexual arousal Male Reproductive Tract Ductus deferens (vas deferens) Stores sperm and propels them toward the urethra during ejaculation Can store sperm for several months before they degenerate Pathway: ascends along posterior border of epididymis passes up through spermatic cord and inguinal ligament reaches posterior surface of urinary bladder Joins ducts of seminal vesicles to form ejaculatory duct empties into prostatic urethra Male Reproductive Tract Ductus deferens (vas deferens) Histology: lined with pseudostratified columnar epithelium covered with heavy coating of muscle convey sperm through peristaltic contractions Male Reproductive Tract Ejaculatory ducts union of seminal vesicle ducts & ducti deferens eject spermatozoa into the prostatic urethra Male Reproductive Tract Urethra shared terminal duct of the reproductive and urinary systems passageway for semen and urine 3 portions: 1. prostatic 2. membranous 3. spongy (cavernous) Male Reproductive Tract Seminal glands (also called seminal vesicles) Sandwiched between the posterior wall of the urinary bladder and the rectum Secretion ejected by smooth muscle lining gland alkaline: neutralizes vaginal & male urethral acid fructose: sperm ATP production Prostaglandins: motility and viability Stimulates flagellum movement in sperm First step of capacitation Produce ~60 % of semen volume © 2018 Pearson Education, Inc. Male Reproductive Tract Prostate gland Encircles the proximal urethra as it leaves the bladder Roughly the size of a golf ball Secretions contain: seminalplasmin Antibiotic that may help prevent urinary tract infections in males proteolytic enzymes to liquefy semen: prostate-specific antigen (PSA), pepsinogen, lysozyme, amylase, and hyaluronidase citric acid sperm ATP production Produces 20–30 % of semen volume © 2018 Pearson Education, Inc. Male Reproductive Tract Bulbo-urethral glands (Cowper’s glands) Located at the base of the penis Duct of each gland empties into the urethra Secrete thick, alkaline mucus Helps neutralize acids in the urethra Also lubricates the tip of the penis © 2018 Pearson Education, Inc. Semen Semen contains sperm and seminal fluid Seminal fluid is from accessory glands slightly alkaline, milky appearance 2.5 to 5 ml released per ejaculation normal sperm count is 50 to 150 million/ml Once ejaculated, semen coagulates w/in 5 minutes clotting proteins from seminal vesicles after 10-20 mins, semen re-liquifies PSA and proteolytic enzymes from prostate gland This occurs to protect sperm cells from the acidic vaginal environment © 2018 Pearson Education, Inc. The Penis Functions of the penis Two functions 1. Conducts urine to the exterior 2. Introduces semen into the vagina during sexual intercourse © 2018 Pearson Education, Inc. The Penis Regions and structures of the penis Root of the penis Fixed portion that attaches the penis to the body wall just inferior to the pubic symphysis Consists of two parts: Bulb expanded, posterior continuation of corpus spongiosum Crura 2 separated, tapered portions of corpora cavernosa © 2018 Pearson Education, Inc. The Penis Regions and structures of the penis Body (or shaft) of the penis Tubular, movable portion of the organ Glans penis (head) Expanded distal end that surrounds the external urethral orifice Neck of glans Narrow portion between the shaft and the glans © 2018 Pearson Education, Inc. The Penis Erectile tissue The body is composed of three erectile tissue masses: Corpora cavernosa Two cylindrical masses on the dorsal surface of the penis Corpus spongiosum Surrounds the penile urethra Expands at the tip of the penis to form the glans © 2018 Pearson Education, Inc. The Penis Erectile tissue Three-dimensional network with vascular spaces (sinusoidal spaces) In the resting state, arterial branches are constricted, and muscular partitions are tense (restricts blood flow into the erectile tissue) © 2018 Pearson Education, Inc. The Penis Phases in the male sexual response Arousal Erotic thoughts or stimulation of sensory nerves in the genital region increase parasympathetic stimulation through pelvic nerves Release of nitric oxide causes arterial dilation Blood flow increases, engorging vascular channels veins become compress, and blood is trapped Erection of the penis occurs © 2018 Pearson Education, Inc. The Penis Phases in the male sexual response Emission or ejaculation Caused by sympathetic activation Begins with peristaltic contractions in the ampullae of the ductus deferens Pushes sperm into the prostatic urethra Contractions continue in the seminal glands and prostate Secretions from these glands mix with sperm to form semen © 2018 Pearson Education, Inc. The Penis Impotence, or erectile dysfunction (ED) Inability to achieve or maintain an erection Various causes Vascular changes (e.g., low blood pressure) Interference with neural commands Psychological factors (depression, anxiety) Medications (e.g., Viagra and Cialis) temporarily inactivate enzymes that oppose nitric oxide (NO) Small amounts of NO can then produce erection © 2018 Pearson Education, Inc. Hormones and the Male Reproductive System Hormonal Regulation Hypothalamus Secretes gonadotropin-releasing hormone (GnRH) Released at a steady rate and pace Targets the anterior lobe of the pituitary gland Anterior lobe of the pituitary Responds by producing two gonadotropins Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) © 2018 Pearson Education, Inc. Hormones and the Male Reproductive System Luteinizing hormone (LH) Targets the interstitial cells of the testes (Leydig Cells) Interstitial cells secrete testosterone and other androgens Testosterone levels are regulated by negative feedback High testosterone level inhibits release of GnRH © 2018 Pearson Education, Inc. Hormones and the Male Reproductive System Follicle-stimulating hormone (FSH) Targets nurse cells of seminiferous tubules Nurse cells (Sertoli cells) Promote spermatogenesis and spermiogenesis Secrete androgen-binding protein (ABP) Binds testosterone and keeps in area of developing sperm Stimulates maturation of spermatids Secrete inhibin Inhibits FSH Provides feedback control of spermatogenesis Hormones and the Male Reproductive System Hormonal control of male sexual function © 2018 Pearson Education, Inc. Hormones and the Male Reproductive System Testosterone principal androgen synthesized from cholesterol Released by interstitial cells (Leydig cells) lipid soluble moves from interstitial cells, to interstitial fluid, to blood Controlled by negative feedback suppresses GnRH & LH external genitalia & prostate transform testosterone to DHT (dihydrotestosterone) © 2018 Pearson Education, Inc. Hormones and the Male Reproductive System Effects of Testosterone Prenatally testosterone stimulates development of male reproductive system & descent of testes DHT stimulated development of external genitals in brain testosterone converted to estrogens, which support some parts of brain development Hormones and the Male Reproductive System Effects of Testosterone Puberty enlarge male sex organs, spermatogenesis, sex drive secondary sex characteristics facial & chest hair muscle/bone enlargement increase sebaceous gland secretion laryngeal enlargement anabolic – ie: stimulates protein production Hormones and the Male Reproductive System Effects of Testosterone After puberty Maintains libido (sexual drive) and related behaviors Stimulates bone and muscle growth Maintains male secondary sexual characteristics Maintains accessory glands and organs of the male reproductive system Hormones and the Male Reproductive System Effects of Dihydrotestosterone (DHT) Testosterone is converted to DHT in some tissues Comprises ~10 percent circulating levels of testosterone Can bind to same receptors as testosterone Some tissues respond to DHT instead of testosterone External genitalia Other tissues are more sensitive to DHT than testosterone Prostate and hair follicles © 2018 Pearson Education, Inc.