Endocrine and Reproductive Systems

Endocrine System and Reproductive System

Endocrine System: Key Concepts

• The endocrine system produces chemical messenger molecules called hormones.

• Hormones are secreted into the blood by endocrine organs.

• Hormones act only on specific cells called target cells.

• Target Cells: Only target cells have specific receptors for hormone interaction (key and lock mechanism).

• Hormones are categorized into steroid and non-steroid hormones. Differing in mechanisms of action.

• Negative Feedback loops: Some hormones use these to maintain homeostasis.

• Other hormones regulate major life changes (growth, sexual maturation) without negative feedback loops.

• Pituitary Gland: A major gland, often called the master gland.

  • Secretes eight hormones that regulate production of many other hormones from other glands.

Endocrine Glands

• Hormones are secreted by endocrine glands.

• Endocrine glands are ductless organs secreting into interstitial fluid, lymph, and blood.

• Secreted hormones reach target cells via the circulatory system.

• Endocrine system control is slower than the nervous system (relies on passive diffusion).

Steroid Hormones

• Enter target cells due to lipid solubility.

• Structurally related to lipids or fat molecules

• Cell membranes are made of lipids.

• Diffuse through the cell membrane and bind to intracellular receptors.

• Forms a hormone-receptor complex within the cell (nucleus or cytoplasm).

• The complex attaches to DNA in the nucleus to activate specific genes.

• DNA is transcribed into RNA, then translated into a protein.

• The protein product carries out the cellular response.

• Slower-acting due to diffusion and intracellular processes.

• Hormone must diffuse to its intracellular receptor.

Non-Steroid Hormones

• Bind to receptors on the target cell membrane.

• Structurally related to proteins and lipid insoluble.

• Cannot cross the cell membrane.

• Binding to the receptor activates existing enzymes through intermediate mechanisms.

• Binding signals ATP conversion into a secondary messenger (cyclic AMP).

• Cyclic AMP activates enzyme cascades, leading to a final product that alters cell activity.

• Faster-acting because: Hormone has a localized space to find it's receptor, uses already generated proteins/enzymes , no nucleus involvement.

Negative Feedback Loops

• Endocrine glands serve as the control center in these loops.

• The brain can be a higher-level control center, signaling endocrine glands via the nervous system.

• Hormones are the pathway between the control center and effector cells.

• Target tissues/organs are the effectors.

• The loop reverses the initial change to maintain homeostasis.

• Example: Erythropoietin regulates red blood cell production.

Hypothalamus and Pituitary Gland

• Located in the forebrain and act as master regulators.

• Hypothalamus: Homeostatic control center, linking nervous and endocrine systems.

  • Receives neural input about internal body conditions.

  • Produces two hormones that signal other endocrine glands.

  • Monitors and controls pituitary gland secretions.

• Pituitary Gland: Located beneath the hypothalamus.

  • Secretes eight hormones regulating other endocrine organs.

  • Has two lobes: posterior and anterior.

Posterior Pituitary

• Stores ADH and oxytocin.

• Neuroendocrine cells function as both nerve and endocrine cells.

• Cell bodies in the hypothalamus produce hormones.

• Axons extend to the posterior pituitary where hormones are stored.

• Stimulation of the hypothalamus releases hormones.

• Neuroendocrine cells send impulses down the axon, secreting hormones into capillaries.

• ADH acts on the kidneys to regulate water balance.

• Oxytocin acts on mammary glands and uterus muscles.

• Neuroendocrine reflex: Nursing stimulates nerve receptors in nipples. Which leads to the release of oxytocin.

Anterior Pituitary

• Produces six key hormones.

• Each hormone secreted by a separate cell type.

• Connection with the hypothalamus is endocrine, not neural.

• Pituitary portal system: Special blood supply between hypothalamus and anterior pituitary.

• Releasing and inhibiting hormones control secretion of anterior pituitary hormones.

• Hormones Secreted

  • ACTH

  • Thyroid Stimulating Hormone

Pituitary Dwarfism

• Example of an endocrine disorder of the pituitary gland.

• Hypo secretion of growth hormone during childhood results in pituitary dwarfism.

• Can be prevented with early diagnosis and growth hormone treatment.

• Tumors can cause decreased hormonal output.

Pancreas

• Secretes glucagon, insulin, and somatostatin.

• Has both endocrine and exocrine functions.

• Pancreatic hormones regulate blood sugar (glucose) levels.

• Endocrine cells located in islets of Langerhans.

  • Alpha cells: Secrete glucagon, which raises blood sugar.

  • Beta cells: Secrete insulin, which lowers blood sugar.

  • Delta cells: Secrete somatostatin, which inhibits glucagon and insulin secretion.

• Between Meals: Glucagon is secreted as blood glucose levels decline.

  • Causes breakdown of glycogen to glucose in the liver.

• After a Meal: Insulin is secreted as blood glucose levels rise.

  • Promotes uptake of glucose by liver, muscle, and adipose tissue cells.

  • Stimulates conversion of glucose into glycogen in the liver.

  • Stimulates conversion of glucose into protein in liver/muscle and fat in adipose tissue.

• Physiological significance of somatostatin is not well understood.

Adrenal Glands

• Comprise the cortex and the medulla.

• Two small endocrine organs above the kidneys.

• Adrenal Cortex (outer layer)

  • Produces steroid hormones:

    • Glucocorticoids (cortisol): Maintains blood glucose levels by promoting utilization of fats and breakdown of proteins.

    • Mineralocorticoids (aldosterone): Regulates sodium and potassium minerals.

• Adrenal Medulla (inner layer)

  • Produces non-steroid hormones:

    • Epinephrine (adrenaline) and norepinephrine (noradrenaline): Enhance sympathetic nervous system functions (fight or flight response).

Thyroid and Parathyroid Glands

• Anatomically and functionally linked.

• Thyroid Gland: Located below the larynx, at the front of the trachea.

  • Produces thyroxin: Speeds up cellular metabolism.

  • Secretes calcitonin: Promotes bone growth and lowers blood calcium levels.

• Parathyroid Glands: Four small glands embedded in the back of the thyroid gland.

  • Produce parathyroid hormone (PTH): Regulates blood calcium levels.

Thyroxine

• Increases ATP from glucose in body cells.

• The basal rate is regulated by thyroid stimulating hormone.

• Fall in thyroxine concentrations increases thyroxine releasing hormone from the hypothalamus.

• Thyroxine stimulating hormone stimulates secretion of thyroxine by the thyroid gland.

• Conditions increasing energy requirements (cold temperatures) raise the steady state of hormone concentrations.

• Iodine Deficiency: results in the absence of thyroxine. It's required for its production

  • Thyroxine stimulating hormone levels will stimulate the thyroid gland to actually grow to an enormous size.

Parathyroid Hormone

• Secreted by parathyroid glands, controls blood calcium levels.

• Raised blood calcium levels signal the parathyroid gland to reduce parathyroid hormone secretion.

Calcitonin

• Secreted by the thyroid gland also participates in controlling blood calcium levels

• Increased blood calcium levels signal to the thyroid gland to increase calcitonin secretion.

• Tells bones to take up more calcium and lowers our blood calcium levels.

• Calcitonin works only in childhood. Parathyroid hormone takes over blood calcium level controls after that.

Testes

• The testes located in the scrotum is responsible for the production of sperm.

• Production of steroid sex hormones. - Testerone: Before birth, testosterone production via fetal testes is responsible for the development of the external male genitalia.

• Between birth and puberty, testosterone production actually declines to almost zero.

• Release of luteinizing hormone then stimulates resumes testosterone production.

• regulates development of a normal functioning of sperm, reproductive organs, and sex drive, and also the development of secondary male characteristics

Ovaries

• Located in the abdomen produce the female sex hormones estrogen and progesterone.

• During puberty, the anterior pituitary starts to release luteinizing hormone, as we saw in males for testosterone, and also follicular stimulating hormones, so LH and FSH.

  • stimulates to the ovaries to begin secreting estrogen and progesterone.

• Estrogen initiates the development of the female secondary sex characteristics so for example breast development and widening of the pelvis in preparation for birth.

• Menstrual cycle: regulated by both estrogen and progesterone. These are the monthly changes that occur in the tissues of the uterus that prepare the female body for pregnancy.

Pineal Gland

• Secrets Melatonin

• Cyclic manner, that is coupled to the daily cycle of light and dark that we are detecting through our eyes

• The rate of secretion of melatonin rises nearly tenfold at nighttime, or when we are detecting it, there is less light around.

• During the day when a person is exposed to strong light, nerve impulses from the retina inhibit the release of melatonin.

Diabetes Mellitus

• High flow of urine with a sweet taste. Disease of sugar regulation, or blood glucose regulation which we saw occurs in the pancreas.

• Inability to get glucose into cells where it can be used for cellular respiration to make ATP

• Result in an abnormally high glucose concentration in the blood (kidney's ability to reabsorb all that is filtered is overwhelmed)

• Body cells turn to the metabolism of fat and proteins to generate ATP.

Type 1

• Occurs in five percent to ten percent of all cases. Is caused by the failure of the pancreas to produce enough insulin.

• Insulin dependent diabetes: The person depends on daily injections of insulin to allow glucose to enter cells.

• Autoimmune disorder: The person's own immune system attacks the insulin producing cells in the pancreas (genetic component).

Type 2

• * Occurs in ninety percent to ninety five percent of all cases (non insulin dependent diabetes).

• Insulin secretion still happens by the pancreas. But where the error occurs is that the cells of the person's body fail to respond adequately to the insulin that is being secreted, even when present. (resistant)

• * Lifestyle factors are thought to be the major determinant. Over time resistance of constant exposure of a cell to too much glucose cells causes insulin resistant which increases glucose and pancreas secretes more insulin eventually wearing out.

Male Reproductive System

Key Concept

• Can deliver over 100,000,000 sperm at once.

Organs

• Testes: Responsible for generating testosterone (endocrine) and sperm.

• Scrotum: Sack of skin and smooth muscle that holds the testes. Maintains the testes at a slightly lower temperature which helps sperm production.

• Seminiferous Tubules: Within the testes, where sperm production takes place.

• Epididymis and Ductus deferens: Sperm become motile. Transports sperm to where it joins the seminal vesicle, which becomes the ejaculatory duct where sperm is transported

• Ejaculatory Duct*: transports sperm.

Semen

• Accessory Glands: Help sperm survive. Semen is a mixture of sperm and secretions from these glands, the fluids help them survive.

  • Seminal Vesicles: Contributes seminal fluid to semen.

    • Contains Fructose: energy source for sperm to move.

    • Contains Prostaglandins: induce muscle contractions in the female reproductive tract to help sperm travel more effectively.

  • Prostate Gland: Contributes an alkaline fluid of semen.

  • Bulbourethral Glands: Secrete mucus into the urethra to wash away traces of acidic urine and lubrication to help that transportation.

The Sperm Cell

• Contains a head, a midpiece, and a tail.

• Head contains the DNA and is covered by an acrosome (cap with enzymes to penetrate the egg).

• Midpiece contains mitochondria that produce energy for tail movement.

• Sperm is propelled by tail which moves by whip like action.

• Testosterone controls growth and function of the male reproductive tissues stimulates sexual behavior, controls development of 2ndary sexual characteristics determines rate of sperm formation

Spermatogenesis

• Process of sequential cell division in sperm generation happening in testicular structures and walls.

• Sertolli Cells: Support spermatogenesis.

• The entire process of sperm formation and maturation takes about nine to ten weeks.

• Sertoli cells produce inhibin to help with the process.

Testestarone Hormone Feedback Loop

• Controls growth and function of the male reproductive tissues.

• Stimulates sexual behavior.

• Controls development of secondary sexual characteristics

  • Determines the rate of sperm formation within the testes.

Female Reproductive System

Key Concept

• Usually releases just one egg each month controlled by hormones

Organs

• Ovaries: Release immature eggs called oocytes. The eggs is then called an Ovi duct.

• Oviducts/Fallopian Tubes: Leads from the ovaries to the uterus.

• Fimbrae: Projections. Move the egg into the Ovi duct.

• Fertilization usually takes place in the upper third of the oviduct.

Uterus

• A hollow pear-shaped organ where the embryo grows. The walls of the uterus comprise two layers of tissue.

  • Endometrium (inner lining): Fertilized egg attaches in a process called implantation after implantation, the endometrium helps to form the placenta.

  • Myometrium(Outer layer): Composed of think layers of smooth muscles it stretches during pregnancy provides force to expel fetus during birth.

Cervix

• Narrow part of the uterus that extends slightly into the vagina. Permits sperm to enter the uterus and also allows the fetus to exit during birth.

Mammary Glands

• Altered sweet glands glands consist of hundreds of small producing loblues contractile cells. that allow milk to be released. and the ducts deliver it to the nipple

• Estrogen and progesterone: help prepare glands for lactation

• Prolactin: at birth stimulate lactation.

• Oxytocin: stimulates the contractions that release milk during birth.

Menstrual Cycle

• Pattern of changes occurring in both ovaries and the uterus, lasts about 28 day. Consists of an.

  • Ovarian Cycle: Oocytes matures and released from ovaries into the oviducts from immature to mature.

  • Uterine Cycles: prepares for the pregnancy.

  • Together, they release to egg maturation to prepare to implantation.

Ovarian Cycle

• Increasing (follicular stimulating hormone) causes follicles to mature (grow). As growing secrets estrogen.

• (Luteinizing hormone) stimulates (ruptures the follicle) the releases the egg. Which the follicle forms luteum (produces protrerone). if Fertilization and pregnancy this produces HCG (chrionic gonaotropin). It helps aids the uternine in the endometrial lining for the empbro

Uterine Cycle

• Prepares hormones by endometrial thickening.