Endocrine System

Chapter 39Endocrine SystemEndocrine SystemA system of glands that secrete hormones into the blood that regulate growth, development and metabolic processes.

HypothalamusThe hypothalamus makes hormones that control the pituitary gland. In addition, it makes hormones that are stored in the pituitary gland.Pituitary glandThe pituitary gland produces hormones that regulate many of the other endocrine glands.Parathyroid glandsThese four glands release parathyroid hormone, which regulate the level of calcium in the blood.ThymusDuring childhood, the thymus releases thymosin, which stimulates Tcell development.Adrenal glandsThe adrenal glands release epinephrine and nonepinephrine, which help the body deal with stress.Pineal glandThe pineal gland releases melatonin, which is involved in rhythmic activities, such as daily sleep-wake cycles.ThyroidThe thyroid produces thyroxine, which regulates metabolism.PancreasThe pancreas produces insulin and glucagon, which regulate the level of glucose in the blood.OvaryThe ovaries produce estrogen and progesterone. Estrogen is required for the development of secondary sex characteristics and for the development of eggs. Progesterone prepares the uterus for a fertilized egg.Testis The testes produce testosterone, which is responsible for sperm production and the development of male secondary sex characteristicsSection 39-1The Endocrine GlandsHormonesHormones chemical messengers that travel to remote target tissues.Produce slow responses of long duration.Hormones only affect target tissues that have the correct receptor to fit the hormone.

Steroid HormoneTarget cell membranemRNACytoplasm Protein synthesisAltered cellular functionReceptorHormone-receptor complexNucleusDNANonsteroid hormone (first messenger)Receptor Target cell membranecAMP (second messenger)Enzyme activitiesAltered cellular functionCytoplasm NucleusHormone ActionSection 39-1Negative FeedbackHormone levels in the blood are regulated by a negative feedback mechanism.Hormones secreted into the blood bring about a change. When the change occurs, secretion of the hormone stops.Ex: The pancreas secretes insulin to lower blood sugar levels and glucagon to raise blood sugar levels. Secretion of these hormones stops when sugar levels are correct.Diabetics cannot produce enough insulin to maintain correct sugar levels.

Pancreas releasesinsulin into the bloodBody cells absorb glucoseBlood glucose level decreasesHomeostasis: Normal blood glucose levelBlood glucose level decreasesPancreas releases glucagon into bloodLiver converts glycogen to glucoseBlood glucose level increasesBlood glucose level increasesLiver converts excess glucose to glycogen for storageActions of Insulin and GlucagonSection 39-2Chapter 39The Reproductive SystemReproductionA life process necessary for the survival of a species, but not an individualThe Male Reproductive SystemThe testes produce the male sex cell sperm through the process of meiosis.Sperm are haploid (23 chromosomes).The testes also produce the hormone testosterone.Testosterone aids in sperm production and is responsible for the development of secondary sex characteristics.The Male Reproductive SystemSection 39-3

The Female Reproductive SystemThe ovaries produce the female sex cell eggs through the process of meiosis.Eggs are haploid (23 chromosomes).The ovaries also produce the hormones estrogen and progesterone.Estrogen aids in egg development and is responsible for the formation of secondary sex characteristics. Progesterone prepares the uterus for implantation by a fertilized egg.

The Female Reproductive SystemSection 39-3

The Menstrual CycleBeginning with puberty, the female reproductive system begins a periodic cycle of events regulated by hormones from the pituitary and ovaries.This is known as the menstrual cycle.This cycle prepares the uterus each month for the advent of pregnancy, when a fertilized egg will implant itself in the uterine wall.If this does not occur, the uterine lining is shed out the vagina. This is called menstruation.

The Menstrual CycleSection 39-3Fertilization and DevelopmentFertilization occurs in the Fallopian tube (oviduct).A sperm unites with the egg to produce a diploid zygote (46 chromosomes).The zygote undergoes a series of mitotic cell divisions without growth in size (cleavage) on its way to the uterus.Approximately 7 days later the hollow ball of cells (blastocyst) implants itself in the uterine wall.Development occurs in the uterus (womb).

Implantation of blastocystDay 7FertilizationDay 4Day 3Day 2Day 1Day 0Egg released by ovaryFertilization and ImplantationSection 39-4Uterine wallBlastocystMorula4 cells2 cellsZygote Ovary Fallopian tube DevelopmentAfter implantation the cells begin to differentiate.Tissue from both the mother and embryo form the placenta a temporary organ that will nourish the developing baby.Throughout the next nine months the developing baby obtains nutrients and gets rid of wastes through its connection to the placenta, the umbilical cord.Nutrients and wastes pass between the blood of the mother and baby by diffusion.

The PlacentaSection 39-4

BirthAt the end of nine months hormone changes produce a series of contractions in the uterus known as labor.The protective membrane surrounding the baby (amnion) ruptures releasing fluid (water breaks).Birth is imminent. Contractions stretch the cervix to a diameter of about 10 cm and the baby is delivered head first (usually).Contractions close off the umbilical cord near the baby. The cord is cut, and eventually falls off leaving a scar (belly button).Soon after, a second series of contractions force the placenta out of the womb (after birth).