BISC 307L 2nd Edition Exam 3 Study Guide Calcium Balance in the Body Calcium in the Body 1 of the Ca in the body exists in free ionic form The other 99 exists as hydroxyapatite which forms the mineral portion of bones Calcium in bones acts as a storage reservoir for maintenance of Ca in the body at appropriate levels Ca2 Balance in the Body The small intestine is the only place new Ca comes into the body from our diet This Ca will be pooped out or go into the ECF From here it can be deposited into bones through cells called osteoblasts building new bone or be filtered into the kidney where it can be reabsorbed or excreted Regulation of Body Calcium The 1 of plasma Ca in the body is regulated by 3 hormones from the thyroid and parathyroid glands 1 Parathyroid hormone is essential for life it raises plasma calcium stimulates bone resorption of calcium through osteoblasts stimulates reabsorption from kidney tubule back to ECF stimulates calcitriol 2 Calcitriol is a steroid hormone made from Vitamin D it raises plasma calcium stimulates Ca absorption from small intestine it brings new Ca into the body prolactin also has this effect also stimulates bone resorption 3 Calcitonin opposes the effect of PTH reduces blood calcium stimulates bone deposition is important in children for growth and in pregnant women to fight osteoporosis Reproductive System Overview of Sexual Differentiation Step 1 Differentiation of Gonads Humans have 22 pairs of autosomal chromosomes and one pair of sex chromosomes gender depends on whether the fertilized egg bears an X or Y chromosome Undifferentiated gonads have germ cells the coelomic epithelium and the mesenchyme Under the influence of the male chromosome the differentiation on the left occurs In the absence of the sex determining Y chromosome the gonads follow their default pattern for female differentiation as seen on the right above Step 2 Development of the reproductive tract So the gonads have differentiated The next step is shown to the right At an early stage embryos of both sexes have two primitive duct systems Wolffian and Mullerian Under the influence of testosterone in males Wolffian ducts become the male reproductive tract Leydig cells secrete testosterone while sertoli cells secrete antimullerian hormones that kill the mullerian duct cells In females you have the default condition Theca cells don t secrete testosterone The Wolffian ducts are testosterone dependent so they die The granulosa cells don t release antimullerian hormone so the mullerian ducts don t die Step 3 Development of External Genitalia 6 weeks in you see the undifferentiated end of the fetus can t tell if it will be a male or female On the right under the influence of testosterone we have development of male external genitalia The genital tubercle grows and becomes the head of the penis The urethral folds fuse toward the midline and enclose the urethral groove now we have a closed channel which becomes part of the urethra and a is hole created in the head of the penis which is made to be the urethral opening The labia scrotal swellings fuses to form the scrotum and the foreskin of the penis In females the genital tubercle becomes the clitoris the urethral folds become the labia minora and the labia scrotal swellings become the labia major and the foreskin of the clitoris General Gonadotropin Regulation Hypothalamus releases GnRH gonadotropin releasing hormone which stimulates the release FSH and LH which stimulate the growth and hormone secretion development of the gonads testes and ovaries The hormones the gonads secrete are responsible for reproductive function and gender specific secondary sex characteristics Ovaries secrete progesterone and estradiol which feeds back and inhibits the GnRH and FSH and LH secretion In males testes secrete testosterone which similarly feeds back and inhibits FSH and LH and GnRH And both of them secrete inhibins and activins which stimulate or inhibit secretion of FSH don t affect LH secretion Other things Herrera mentioned Testes secrete testosterone during fetal life in order to develop the male pathway then stop for 10 14 years until puberty occurs allowing time for the body to grow to a certain stature to allow reproduction to occur Climacteric cessation of sexual activity in women vs men Women reach menopause can t have children Men reach climacteric around 50 cessation of sperm production but it is a progressive decline such that men in there 90 s technically could still reproduce Older increased likelihood of mutation in sperm egg chromosomes because they divide by mitosis MALES Male Reproductive Anatomy Testes and the wolffian ducts start in the abdomen and travel all the way down to the scrotum going through an inguinal canal which closes up Sperm can only exist at certain temperatures so there are mechanisms to maintain temperature in the scrotum 1 Temp sensitive nerves in the scrotum cause the levator muscles to contract or relax causing the testes to be closer or further from the warm body 2 Countercurrent heat exchanger seen to the right Blood temp blood coming in to the testes through the red artery is cooled by transfer of heat from the artery to the veins The returning cool venous blood is conversely warmed by the heat transfer as it travels back to the body Evolutionary considerations Chimpanzees have large testes and produce a lot of sperm and gorillas have small testes and produce less sperm Chimpanzees are high promiscuous and gorillas are loyal So there is a correlation Humans are somewhere in between Structure of the Testes Testes consist mostly of seminiferous tubules These tubules are made up of sertoli cells surround and nourish the developing sperm and stem cells divide by mitosis to give rise to sperm precursors called spermatagonia Spermatagonia divide into spermatagonium one remains for the next generation of sperm production and the other begins to differentiate into a sperm takes 70 days Spermatagonium primary diploid spermatocyte secondary spermatocyte haploid spermatids sperm A sperm has 3 parts as seen on the right The acrosome is a vesicle that contains enzymes and carbs that are necessary to penetrate the layers of granulosa cells surrounding the oocyte for fertilization Endocrine Control of Testicular Function GnRH secreted from hypothalamus acts on FSH and LH cells in the AP Target of the FSH secreting cells are the sertoli cells in the testes surrounding the developing sperm Targets of the LH cells