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USC BISC 307L - Exam 3 Study Guide
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BISC 307L 2nd EditionExam 3 Study GuideCalcium Balance in the BodyCalcium in the Body1% of the Ca in the body exists infree ionic form. The other 99%exists as hydroxyapatite, whichforms the mineral portion ofbones. Calcium in bones acts as astorage reservoir formaintenance of Ca in the body atappropriate levels. Ca 2+ Balance in the Body:The small intestine is the onlyplace new Ca comes into thebody, from our diet. This Ca willbe pooped out, or go into theECF. From here, it can bedeposited into bones throughcells called osteoblasts(buildingnew bone), or be filtered into thekidney where it can bereabsorbed or excreted. Regulation of Body CalciumThe 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 calcitriol2. 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 resorption3. Calcitonin – opposes the effect of PTH, reduces blood calcium- stimulates bone deposition- is important in children for growth and in pregnant women to fight osteoporosisReproductive SystemOverview of SexualDifferentiation Step 1: Differentiation ofGonads Humans have 22 pairs ofautosomal chromosomesand one pair of sexchromosomes – genderdepends on whether thefertilized egg bears an Xor Y chromosome.Undifferentiated gonads have germ cells, the coelomic epithelium, and the mesenchyme. Underthe 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 thereproductive tractSo the gonads havedifferentiated. The next stepis shown to the right. At an early stage, embryos ofboth sexes have two primitiveduct systems: Wolffian andMullerian. Under theinfluence of testosterone inmales, Wolffian ductsbecome the malereproductive tract. Leydigcells secrete testosterone,while sertoli cells secreteantimullerian hormones thatkill the mullerian duct cells. In females you have thedefault condition. Theca cellsdon’t secrete testosterone. The Wolffian ducts aretestosterone dependent, sothey die. The granulosa cells don’t release antimullerian hormone, so the mullerian ducts don’t die. Step 3: Development of External Genitalia6 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 RegulationHypothalamus 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 secreteprogesterone andestradiol, which feedsback and inhibits theGnRH and FSH and LHsecretion. In males,testes secretetestosterone, whichsimilarly feeds back andinhibits FSH and LH andGnRH. And both of themsecrete inhibins andactivins, which stimulateor inhibit secretion ofFSH(don’t affect LHsecretion). Other things Herrera mentioned:-Testes secrete testosterone during fetal life in order to develop the male pathway, then stop for10-14 years until puberty occurs, allowing time for the body to grow to a certain stature to allowreproduction 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. MALESMale Reproductive AnatomyTestes and the wolffian ducts start in the abdomen and travel all the way down tothe scrotum, going through an inguinal canal, which closes up. Sperm can only exist at certain temperatures, so there are mechanisms tomaintain temperature in the scrotum:1.) Temp. sensitive nerves in the scrotum cause the levator muscles to contract orrelax, causing the testes to be closer or further from the warm body. 2.) Countercurrent heat exchanger (seen to the right). Blood temp. blood comingin to the testes through the red artery is cooled by transfer of heat from theartery to the veins. The returning, cool venous blood is conversely warmed by theheat transfer as it travels back to the body. Evolutionary considerations:Chimpanzees havelarge testes andproduce a lot ofsperm, and gorillashave small testes andproduce less sperm.Chimpanzees arehigh promiscuous,and gorillas are loyal.So there is acorrelation. Humansare somewhere inbetween.Structure of theTestesTestes consist mostlyof seminiferoustubules. 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  spermA sperm has 3 parts, as seen on the right. The acrosome is a vesicle that containsenzymes and carbs that are necessary topenetrate the layers of granulosa cellssurrounding the oocyte for fertilization. Endocrine Control of Testicular FunctionGnRH secreted from hypothalamus acts on FSH and LH cells in the AP. -Target of the FSH


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