L10 The Endocrine System

- autocrine signaling

- cell releases signals to be received by self

paracrine signaling

- cell releases signals to extracellular liquid and reaches neighboring cells by diffusion

Hormones

-Chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body -Hormones reach all parts of the body, but only target cells have receptors for that hormone -Hormones are produced in endocrine cells

Endocrine glands vs exocrine glands

-Endocrine cells are often grouped in ductless organs called endocrine glands, such as the thyroid and parathyroid glands, testes, and ovaries -In contrast, exocrine glands, such as salivary glands, have ducts to carry secreted substances onto body surfaced or into body cavities •endocrine glands go through circulatory system- don't do shit with ducts -Endocrine glands make hormones, exo dont. Exocrine glands have ducts, endocrine don't

What is the endocrine system and what is its function?

-Endocrine system is a collection of glands and secretory tissues whose function is to regulate multiple organs within the body to 1) meet the growth and reproductive needs of the organism and 2) respond to fluctiations within the internal environment, including various types of stress, to maintain homeostasis (stable internal environment)

Adrenal medulla hormones

-Epinephrine and norepinephrine: raise blood glucose level; increase metabolic activities; constrict certain blood vessels

Anterior pituitary hormones:

-Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): Stimulate ovaries and testes -Thyroid-stimulating hormone (TSH): stimulates thyroid gland -Adrenocorticotropic hormone (ACTH): Stimulates adrenal cortex -Prolactin: Stimulates mammary gland cells -Growth hormone (GH): Stimulates growth and metabolic functions

Hypothalamus gland hormones

-Hormones released from posterior pituitary (oxytocin and vasopressin) -Releasing and inhibiting hormones: regulate anterior pituitary

Pancreas hormones

-Insulin: lowers blood glucose level -Glucagon: raises blood glucose level

Posterior pituitary hormones:

-Oxytocin: stimulates contraction of smooth muscle cells in uterus and mammary glands -Vasopressin: (also called antidiuretic hormone, ADH): promotes retention of water by kidneys; influences social behavior and bonding

Parathyroid glands hormone:

-Parathyroid hormone (PTH): raises blood calcium level

Invertebrates and growth control

-The endocrine pathway that controls the moulting of larva originates in the larval brain where neurosecretory cells produce PTTH -In the prothoracic gland, PTTH directs the release of ecdysteroid -Bursts of ecdysteroid trigger each successive moult as well as metamorphosis -Metamorphosis is not triggered until the level of another hormone, JH (juvenile hormone), drops

Thyroid gland hormones:

-Thyroid hormone (T3 and T4): stimulates and maintains metabolic processes -Calcitonin: Lowers blood calcium level

Difference in water-soluble and lipid-soluble mechanism

-Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors -Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells -They bind to receptors in the cytoplasm or nucleus of the target cells

Negative feedback and positive feedback

A negative feedback loop inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity -For example, the release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin -This causes target cells in the pancreas, a gland behind the stomach, to raise the pH in the duodenum Positive feedback (= rare) reinforces a stimulus to produce an even greater response -For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin

Endocrine system characteristics

Acts via hormones and blood stream Primarily controls activities requiring duration rather than speed Coordinates, integrates body functions in conjunction with nervous system -linked through hypothalamus Maintains internal environment (Homeostasis) -Regulates organic metabolism and H2O, electrolyte balance -Controls storage, utilization of energy substances -Regulates response of body to external stimuli -Induces adaptive changes to help cope with stressful situations Regulates smooth, sequential growth and development Controls reproduction

Testes hormones

Androgens: support sperm formation; promote development and maintenance of male secondary sex characteristics

Pituitary gland is made up of:

Anterior pituitary and Posterior pituitary

Female sex hormones

Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics In mammals, progestins, which include progesterone, are primarily involved in preparing and maintaining the uterus Synthesis of the sex hormones is controlled by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary

Ovaries hormones:

Estrogens: stimulate uterine lining growth; promote development and maintenance of female secondary sex characteristics Progestins: promote uterine lining growth

Adrenal cortex hormones:

Glucocoticoids: raise blood glucose level Mineralocorticoids: Promote reabsorption of Na+ and excretion of K+ in kidneys

Hormonal regulation of growth

Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic effects It promotes growth directly and has diverse metabolic effects It stimulates production of growth factors An excess of GH can cause gigantism, while a lack of GH can cause dwarfism

Anterior pituitary hormones

Hormone production in the anterior pituitary is controlled by releasing hormones and inhibiting hormones secreted by the hypothalamus For example, prolactin-releasing hormone from the hypothalamus stimulates the anterior pituitary to secrete prolactin (PRL), which has a role in milk production

Pineal gland hormone:

Melatonin: Participates in regulation of biological rhythms

Evolution of hormone function

Over the course of evolution the functions of particular hormones have diverged For example, thyroid hormone plays a role in metabolism across many lineages, but in frogs has taken on a unique function: stimulating the resorption of the tadpole tail during metamorphosis Prolactin also has a broad range of activities in vertebrates

What is attached to the hypothalamus in vertebrates?

Pituitary gland

tropic hormones

Sets of hormones from the hypothalamus, anterior pituitary, and a target endocrine gland are often organized into a hormone cascade pathway The anterior pituitary hormones in these pathways are called tropic hormones

What does the hypothalamus do in vertebrates?

The hypothalamus receives information from the nervous system and initiates responses through the endocrine system

Multiple effects of hormones

The same hormone may have different effects on target cells that have -Different receptors for the hormone -Different signal transduction pathways For example, the hormone epinephrine can increase blood flow to major skeletal muscles, but decrease blood flow to the digestive tract

Classes of hormones

a) hormones fall into three major classes: polypeptides, steroids, and amines b) Polypeptides are water-soluble whereas steroid hormones and lipid-soluble c) Amine hormones can be either water suluble (adrenaline/epinephrine) or lipid soluble (thyroxine)

Paracrine and autocrine signaling versus endocrine signaling

a) local regulators are molecules that act over short distances, reaching target cells solely by diffusion through extracellular fluids -in paracrine signaling, the target cells lie near the secreting cels -in autocrine signaling, the target cell is also the secreting cel b) hormones are chemical signals that are secreted into the circulatory system by endocrine cells and reach their targets via the bloodstream -in endocrine signaling, the target cells are too distant to be reaches

endocrine signaling

endocrine system acts via hormones and blood stream. This is termed endocrine signaling to distinguish from auto- and paracrine signaling

Endocrine system acts via:

hormones and blood stream

How is homeostitic endocrine control achieved

negative feedback circuits