BIOLOGY 12 The Endocrine System

Introduction the nervous and endocrine systems are both regulatory mechanisms for the body the Endocrine System works more or less like a thermostat, where levels of hormones increase or decrease to maintain homeostasis

Definition endocrine system: the internal system of chemical communication involving hormones, the ductless glands that secrete hormones and the molecular receptors on or in target cells that respond to hormones

Two types of Glands: exocrine glands: excrete their product into tunnels or ducts that empty onto an epithelial surface ex. digestive system, sweat glands endocrine glands: ductless glands that secrete hormones directly into the bloodstream

Hypothalamus Pituitary Thyroid Thymus Adrenal glands Pancreas Testes / Ovaries

Endocrine Gland

Hormones hormone: one of many types of circulating chemical signals found in all multicellular organisms are formed in specialized cells travel in body fluids coordinate the various parts of the organism by interacting with target cells target tissue: tissue on which a hormone acts

Two types of Hormones 1. protein (ex. Insulin) attach themselves on receptors found on the target cells the receptors are very specific when the hormone attaches to the receptor, the receptor causes chemical reactions inside the cell indirect impact on cell

Two types of Hormones 2. lipid (ex. Steroids) unlike proteins, they enter the cell membrane once inside they link to internal receptors the steroid / receptor complex moves into the nucleus where it activates a gene the gene then creates a protein the protein formed is the response of the target cell to the hormone

Gland and Hormone pituitary gland prolactin (PRL) adrenal gland stimulates milk production from a females breasts after childbirth can affect sex hormones from the ovaries in women and the testes in men adrenal gland cortisol glucocortoid keeps blood glucose levels stable pancreas insulin decreases blood sugar concentrations affects the uptake of glucose by cells pineal gland melatonin important for maintaining Circadian rhythms (light and dark activity) reproductive glands (testes and ovaries) testosterone, progesterone, estrogen

Summary negative feedback: a primary mechanism of homeostasis, whereby a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation *works more or less like a thermostat*

Example

Example

Textbook Review Read Pages 372-377 Read Pages 384-387 Questions 1-3 Questions 3,4,5 and 6