1. BIOLOGY 12
The Endocrine System

2. 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

3. 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

4. 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

5. Hypothalamus
Pituitary
Thyroid
Thymus
Adrenal glands
Pancreas
Testes / Ovaries

6. Endocrine Gland

7. 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

8. 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

9. 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

10. 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

11. 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*

12. Example

13. Example

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