BSC2086 1st Edition Lecture 23Outline of Last Lecture I. Renal PhysiologyII. Aldosterone and ADHIII. Glomerular FiltrationIV. Reabsorption and SecretionV. Transport, Storage, and Elimination of Urine Outline of Current Lecture I. Introduction to the reproductive systemII. Structures of the reproductive systemIII. Male reproductive functions I. Introduction to the reproductive systema. Reproductive system is the only system not essential to lifeb. Structuresi. Gonads: organs that make gametes and hormones ii. Ducts: receive and transport gametes iii. Accessory glands: secrete fluids into the ducts iv. External genitalia: collective name for perineal structure II. Structures of Reproductive Systema. Male VS. Females i. Functionally different ii. Secrete hormones: play big roles in the maintenance of normal sexual functioniii. Make and store reproductive cells 1. Combine to form new people2. Female makes on gamete per month a. Retains and nurtures zygote3. Male makes large amounts of gametes a. Makes ½ billion sperm per dayb. Male Reproductive Systemi. Testes (male gonads)1. Secrete androgens, or male sex hormones2. Make male gametes, known as spermatozoa or spermii. Accessory organs1. Secrete fluids into the ejaculatory ducts and the urethra2. Seminal glands (vesicles)3. Prostate gland4. Bulbo-urethral glands III. Male Reproductive Functions a. External genitaliai. Penis 1. Erectile organ that houses the distal portion of the urethraii. Scrotum1. Encloses the testes2. Made of 2 chambers or scrotal cavitiesa. Each chamber houses one testis 3. Raphe: raised thickening in scrotal surfacea. Marks the partition between the 2 scrotal chambers b. Dartos musclei. Layer of smooth muscle in the dermis of the scrotum ii. Characteristic wrinkling of the scrotal surface is caused by resting muscle tone 1. Also elevates testesc. Cremaster Muscle i. Layer of skeletal muscle deeper than the dermisii. Can contract or relax scrotum 1. Relax = moves away from pelvic cavity, causing a decrease in temperature2. Contract = moves towards pelvic cavity, causing a rise in temperature a. Occurs with temperature regulation or sexual arousal3. Normal sperm development in the testes requires a temperature that’s 1.1 degrees Celsius or 2 degrees Fahrenheit lower than normal body temperature d. Spermatic Cordsi. Extended between the abdominopelvic cavity and testes ii. Made of layers of fascia and muscle iii. Encloses:1. Ductus deferens 2. Blood vessels 3. Nerves4. Lymphatic vessels of testes iv. They pass through the scrotum through the inguinal cavity 1. Ways of passage between abdominal musculature 2. Forms during development as the testes descend into the scrotum 3. Cryptorchidism: testes don’t enter into the scrotuma. If they remain in the abdominopelvic cavity, the elevated temperature will cause infertility, or even testicular cancer e. Male inguinal hernias i. Protrusions of visceral tissues into the inguinal canal ii. Weak point in the abdominal wall caused by spermatic cord iii. Only common in males due to:1. Abdominal wall is almost intact in females2. Female inguinal canals are very small a. They contains ilioinguinal nerves and round ligaments of the uterus f. Histology of testesi. Subdivided into lobules by septaii. Lobules have about 800 slender and tightly coiled seminiferous tubules1. Make sperm2. About ½ mile of tightly coiled seminiferous tubules in each testesa. Make loop connected to rete testisb. Rete testis: network of passageways connected to epididymis iii. Connected tissue capsules surround the seminiferous tubules 1. Blood vessels and large interstitial cells known as Leydig cells are found in that spacea. Make androgens, which are the dominant male sex hormones i. Testosterone is most important androgen g. Meiosis i. Special form of cell division only seen in producing gametes 1. Spermatozoa in males2. Oocytes in femalesii. Gametes have 23 chromosomes, half of the normal amountiii. Zygote: made of 46 chromosomes, a fusion of the male and female gametesiv. Occurs in seminiferous tubules in males 1. Begins with primary spermatocytes and produces spermatids2. Spermatids: undifferentiated male gametes v. Meiosis I1. Reductional division because chromosome amount goes from 46 to 23 2. Prophase Ia. Chromosomes condense b. Synapsis: tetrad made from combination of maternal and paternal chromosomes i. The exchange of genetic material which increases genetic variation in the offspring occurs, known as crossing over 3. Metaphase I a. Tetrads line up at metaphase plate 4. Anaphase I a. Maternal and paternal chromosomes separateb. Tetrads splitc. Components from mother and father distributed randomly to the daughter cell5. Telophase I a. Ends with formation of 2 daughter cells, each with a unique combination of chromosomes b. Both cells have 23 chromosomes with 2 chromatids each i. Not the same as diploid cell 6. Interphase a. Separates meiosis I and meiosis II b. Very short, DNA not replicatedvi. Meiosis II 1. Equational division, chromosome number not changed2. Proceeds through prophase and metaphase II 3. Anaphase IIa. Duplicate chromatids separate4. Telophase II a. Yields 4 cells, each with 23 chromosomes b. Cytoplasm may not be distributed evenly h. Spermatogenesis i. Process of sperm production 1. Starts at outermost cell layer in the seminiferous tubules 2. Continues towards the lumen of the seminiferous tubules ii. Cells 1. Spermatogonia (stem cells) divide by mitosis to make 2 daughter cells, each with the same information a. One stays as spermatogoniumb. Second differentiates into primary spermatocyte 2. Primary spermatocyte starts meiosis and makes 2 secondary spermatocytes a. Formed be end of meiosis I b. These cells don’t have same genetic information 3. Secondary spermatocytes go through meiosis and make spermatids, or immature gametes, by end of telophase II 4. Spermatids differentiate and mature into spermatozoa 5. Spermatozoa will lose contact with the wall of seminiferous tubule and enter the fluid in the lumen of seminiferous tubule iii. Spermiogenesis is the final step of spermatogenesis 1. Each spermatid matures into one spermatozoon, or sperm a. They are attached to cytoplasm of nurse cells2. At the spermiation, a spermatozoon,a. Loses attachment to the nurse cell and enters the lumen of the seminiferous tubule 3. Spermatogonial division to spermiation takes about 9 weeks i. Contents of seminiferous tubules i. Stem cells, or spermatogonia ii. Spermatocytes at
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