1 Homeostasis, Hormones and the Endocrine System
2 Homeostasis Animals can be regulators or conformers with regard to specific environmental variables Regulators – internal controls are used to maintain the body in the face of external fluctuations Conformers – internal conditions are allowed to conform to the external changes Animals can be regulators for some variables and conformers for others
3 Maintaining HomeostasisHomeostasis is maintained using negative feedback loops A specific variable is maintained at a set point (particular value) Anything above or below this set point is a stimulus which is detected by a sensor This sensor then triggers a response that will return the variable to the appropriate set point
4 Negative Feedback LoopsOccurs when the response reduces the stimulus Ex: Exercise causes an increase in temp which triggers sweating. Sweating decreases temp. Positive Feedback Loops Occurs when the response increases the stimulus Not usually associated with homeostasis Ex: during childbirth, pressure on the opening of the uterus causes contractions. This in turn leads to greater pressure and thus greater contractions until the baby is born.
5 What Are Hormones and How Do They Work?Hormones are molecules that are secreted into blood or hemolymph that communicate regulatory messages throughout the body. Hormones may reach a variety of cells, but they will only create a response in cells with the appropriate receptors.
6 Secreted Signaling MoleculesHormones are secreted by endocrine cells and travel to receptors via blood/hemolymph Variety of functions including homeostasis; response to environmental stimuli; growth, development and reproduction; response to stress, dehydration and low blood glucose
7 Secreted Signaling MoleculesLocal regulators are secreted molecules that act over short distances and reach their target cells via diffusion Function in blood pressure regulation; nervous system; reproduction Paracrine signaling acts on target cells that lie near the secreting cell Autocrine signaling acts on the secreting cell
8 Secreted Signaling MoleculesNeurotransmitters are used in nervous system function by diffusing short distances to target cells Neurohormones are hormones that are secreted by specialized neurons in the brain and then move to target cells via the bloodstream (such as ADH)
9 Secreted Signaling MoleculesPheromones are chemicals that are released into the environment Function in marking trails; defining territories; warning to predators; attraction of mates
10 Chemical Classes of HormonesThere are 3 groups of hormones: polypeptides (proteins and peptides), amines, and steroids These are organized according to chemical composition and can either be water-soluble or lipid-soluble This plays a role in movement and diffusion which will play a role in receptor location
11 Cellular Response PathwaysWater-soluble hormones cannot pass through the plasma membrane; therefore, they must bind to receptor proteins on the surface of the cell Causes signal transduction Lipid-soluble hormones penetrate the membrane and bind with receptor proteins in the cytoplasm or nucleus Receptor often directly triggers response Often a change in gene expression
12 Multiple Effects of HormonesMultiple effects by the same hormone can be brought about in several ways Target cells with the same receptor can elicit a different response if they have different signal transduction pathways and/or effector proteins Response of target cells may differ if they have different receptors for the hormone
13 Negative Feedback and the Endocrine SystemInsulin and glucagon work together to control blood glucose both using negative feedback Insulin stimulates nearly all body cells outside of the brain Glucagon targets cells in the liver Both of these hormones are made in clusters of cells known as islet of Langerhans found in the pancreas Alpha makes glucagon Beta makes insulin
14 Endocrine and Nervous System Coordination in InvertebratesEndocrine and nervous system are integrated in the control of reproduction and development
15 Endocrine and Nervous System Coordination in VertebratesSeveral glands play an integral role in regulating the bodies functions via the endocrine system Hypothalamus Pituitary gland Posterior and anterior Thyroid Parathyroid Pancreas Adrenal Gonads Pineal
16 Hypothalamus Leptin Secreted by adipose cells and targets the hypothalamus Related to the control of appetite As the number of adipose cells increases, the level of leptin in the blood increases, inhibiting appetite
17 Posterior Pituitary Releases hormones made in the hypothalamus both of which are neurohormones Oxytocin Regulates milk release during nursing which is stimulated by an infant suckling (positive feedback) Induces contractions during labor Mood and sexual arousal in males and females Antidiuretic Hormone (ADH) Regulates blood osmolarity by increasing water retention
18 Anterior Pituitary Secretes many hormones that are regulated by hormones produced by the hypothalamus Each is either a releasing hormone or an inhibiting hormone Every anterior pituitary hormone is controlled by at least one inhibiting hormone Sets of hormones from the hypothalamus, anterior pituitary, and the target endocrine gland often organize into a hormone cascade pathway Several steps lead to the eventual intended response
19 Tropic hormones regulate the functions of endocrine cells or glandsAnterior Pituitary Tropic hormones regulate the functions of endocrine cells or glands Thyroid-stimulating hormone (TSH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) FSH and LH stimulate male and female gonads Adrenocorticotropic hormone (ACTH) ACTH stimulates the production and secretion of steroid hormones by the adrenal cortex
20 Nontropic hormones target nonendocrine tissuesAnterior Pituitary Nontropic hormones target nonendocrine tissues Prolactin Stimulates mammary gland growth and milk synthesis in mammals Regulates fat metabolism and reproduction in birds Delays metamorphosis in amphibians Regulates salt and water balance in freshwater fish Melanocyte-stimulating hormone (MSH) In mammals, inhibits hunger In fish, reptiles and amphibians, regulates the activity of pigment containing cells
21 Anterior Pituitary Growth Hormone (GH) stimulates growth through tropic and nontropic effects Several disorders are related to GH being secreted at too small or too great an amount
22 Thyroid The thyroid gland consists of 2 lobes on the ventral surface of the trachea Thyroid hormone is actually 2 similar molecules Triiodothyronine (T3) – 3 iodine atoms Thyroxine (T4) – 4 iodine atoms Largely T4 is secreted, but target cells then convert it to T3 Functions in metabolism, development and maturation and helps to control body temperature
23 Parathyroid Parathyroid glands are a set of 4 small structures embedded in the posterior surface of the thyroid Parathyroid hormone raises the level of blood Ca2+ through a variety of means In bone, mineralized matrix is decomposed (the thyroid may release calcitonin to prevent this) In kidneys, Ca2+ is reabsorbed Stimulates vitamin D which then actively takes up Ca2+ from the intestines
24 Adrenal Gland Glands associated with the kidneysHave 2 parts: the adrenal cortex and the adrenal medulla Catecholamines (medulla) Epinephrine and norepinephrine are related to the “fight or flight” response and are secreted in times of stress (pleasure and danger) Increase available energy Increase heart rate and dilate the bronchioles for increased oxygen Alter blood flow: blood is shunted away from skin, digestive system and kidneys and towards heart, brain and skeletal muscle
25 Adrenal Gland Corticosteroids (Cortex) MineralocorticoidsGlucocorticoids Promote glucose synthesis from noncarbohydrate sources Can be used as an anti-inflammatory Mineralocorticoids Maintain salt and water balance
26 Pineal Glands Tissue near the center of the mammalian brain associated with biorhythms (circadian rhythms) Melatonin regulates functions associated to light and seasons related to changes in day length
27 Gonads Sex hormones are related to growth, development, reproductive cycles and sexual behavior. Androgens Male sex hormones secreted by the testes, largely testosterone Estrogens Female sex hormones secreted by the ovaries, largely estradiol Progestin A second hormone important to mammalian females (uterus maintenance), largely progesterone
28 Reproductive Organs Females Males Ovaries Oviducts and UterusVagina and Vulva Mammary Glands Males Testes Ducts Accessory Glands Penis
31 Vagina and Vulva The vagina is a thin-walled chamber that is the repository for sperm during copulation and serves as the birth canal The vagina opens to the outside at the vulva, which consists of the labia majora, labia minora, hymen, and clitoris The clitoris has a head called a glans covered by the prepuce The vagina, labia minora, and clitoris are rich with blood vessels; the clitoris also has many nerve endings
32 Testes Testes consist of highly coiled tubes surrounded by connective tissue Sperm form in these seminiferous tubules Leydig cells produce hormones and are scattered between the tubules Production of normal sperm cannot occur at the body temperatures of most mammals The testes of many mammals are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity
33 Ducts From the seminiferous tubules of a testis, sperm pass into the coiled tubules of the epididymis During ejaculation, sperm are propelled through the muscular vas deferens and the ejaculatory duct, and then exit the penis through the urethra
34 Accessory Glands Semen is composed of sperm plus secretions from three sets of accessory glands The two seminal vesicles contribute about 60% of the total volume of semen The prostate gland secretes its products directly into the urethra through several small ducts The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra
36 Hormones in Male ReproductionFollicle-stimulating hormone (FSH) promotes the activity of Sertoli cells, which nourish developing sperm and are located within the seminiferous tubules Luteinizing hormone (LH) regulates Leydig cells, which secrete testosterone and other androgen hormones, which in turn promote spermatogenesis Testosterone regulates the production of Gonadotropin-releasing hormone (GnRH), FSH, and LH through negative feedback mechanisms Sertoli cells secrete the hormone inhibin, which reduces FSH secretion from the anterior pituitary
37 Hormones in Female ReproductionIn females, the secretion of hormones and the reproductive events they regulate are cyclic Prior to ovulation, the endometrium thickens with blood vessels in preparation for embryo implantation If an embryo does not implant in the endometrium, the endometrium is shed in a process called menstruation Hormones closely link the two cycles of female reproduction: Changes in the uterus define the menstrual cycle (also called the uterine cycle) Changes in the ovaries define the ovarian cycle
38 The Ovarian Cycle The sequential release of GnRH then FSH and LH stimulates follicle growth Follicle growth and an increase in the hormone estradiol characterize the follicular phase of the ovarian cycle The follicular phase ends at ovulation, and the secondary oocyte is released Following ovulation, the follicular tissue left behind transforms into the corpus luteum; this is the luteal phase The corpus luteum disintegrates, and ovarian steroid hormones decrease
39 The Uterine Cycle Hormones coordinate the uterine cycle with the ovarian cycle Thickening of the endometrium during the proliferative phase coordinates with the follicular phase Secretion of nutrients during the secretory phase coordinates with the luteal phase Shedding of the endometrium during the menstrual flow phase coordinates with the growth of new ovarian follicles A new cycle begins if no embryo implants in the endometrium After about 500 cycles, human females undergo menopause, the cessation of ovulation and menstruation