AP Biology Animal Form and Function

1. AP Biology Animal Form and Function Endocrine System

2. Endocrine System • The Endocrine System produces hormones that help maintain homeostasis and regulate reproduction and development. • A hormone is a chemical messenger produced in one part of the body that affects target cells in another part of the body

3. Hormones • Transported throughout the body in the blood • Minute amounts of hormones can have significant influence on target cells • Hormones may be steroids, peptides, or modified amino acids

4. Brain and Hypothalamus • Through the senses, the brain and hypothalamus monitors the external environment and internal conditions of the body. • The brain may determine that some kind of response is necessary to maintain homeostasis.

5. Neurosecretory Cells • Actions needed to maintain homeostasis are initiated by special neurosecretory cells that link the hypothalamus and the pituitary gland. • Neurosecretory cells are structured like neurons, but instead of secreting neurotransmitters in the synapses, they secrete hormones into the blood

6. Pituitary Gland • The Pituitary Gland is the size of a pea and is divided into posterior and anterior sections. It is often called the Master Gland because it controls the actions of other glands. The Anterior Pituitary is connected to the hypothalamus, which controls the output of hormones by the Pituitary Gland.

7. Anterior Pituitary Gland • The Anterior Pituitary Gland is linked to the hypothalamus via the bloodstream. • When the concentration of a particular anterior pituitary hormone is too low, the hypothalamus will send releasing factors via the bloodstream that stimulate the production of the needed hormone. Anterior Pituitary produces 6 hormones: TSH, STH, ACTH, LH, FSH, and prolactin

8. Posterior Pituitary Gland • The posterior lobe of the pituitary gland is derived from neural tissue and its connection to the hypothalamus is neural. • Posterior Pituitary produces 2 hormones: ADH and oxytocin. These are produced by the nerve cell bodies that are located in the hypothalamus, where they are packaged into secretory granules and sent down the axons to be stored in the posterior pituitary.

9. Anterior Pituitary Hormones • FSH: Follicle-stimulating hormone. Stimulates activities of the ovaries and testes. In females, it stimulates the development of the ovarian follicle, which leads to the production and secretion of estrogen. • LH: Luteinizing hormone. Stimulates ovulation and formation of the corpus luteum. Stimulates synthesis of estrogen and progesterone

10. Anterior Pituitary Hormones • STH (or HGH): Somatotropic hormone (or Human Growth Hormone). Stimulates protein synthesis and general growth in the body.

11. Anterior Pituitary Hormones • TSH: Thyroid-stimulating hormone. • Works to stimulate the synthesis and secretion of thyroid hormones • Thyroid hormones regulate the rate of metabolism in the body.

12. Anterior Pituitary Hormones • ACTH: Stimulates the secretion of adrenal cortical hormones, which work to maintain electrolytic homeostasis in the body. • Prolactin: controls lactogenesis—production of milk by the breasts. Decreases the synthesis and release of GnRH, and thus inhibits ovulation.

13. Posterior Pituitary Hormones • ADH: Stimulates reabsorption of water by the collecting ducts of the nephron in the kidneys • Oxytocin: Stimulates uterine contraction and milk ejection for breastfeeding.

14. Hormones of the Adrenal Gland • The Adrenal Glands are located on top of the kidneys. • They produce 3 hormones: Cortisol, Aldosterone, and Epinephrine • Cortisol: a stress hormone released in response to physiological challenges • Aldosterone: Regulates sodium concentration of body • Epinephrine: Raises blood glucose level, increases metabolic activity—fight or flight hormone (aka: adrenaline)

15. Pancreatic Hormones • Insulin—Secreted in response to high blood glucose levels • When secreted, it promotes the conversion of glucose in the blood to glycogen and lowers blood sugar. • Glucagon—Stimulates the conversion of glycogen into glucose. • Raises blood sugar.

16. Sex Hormones • Progesterone: Regulates menstrual cycle and pregnancy • Estrogen: Stimulates development of sex characteristics in women. Secreted in ovaries. Induces the release of LH, including the LH surge of the menstrual cycle. With progesterone, it helps maintain the endometrium during pregnancy.

17. Sex Hormones • Testosterone—Stimulates sex characteristics in men. • Secreted in testes.

18. Thyroid Hormones and Parathyroid • Calcitonin: Lowers blood calcium. Works antagonistically to PTH • Thyroxine: Stimulates metabolic activities. • Parathyroid hormone (PTH); Increases serum concentration of Ca2+, assisting in the process of bone maintenance.

19. How is the Hormone Secretion Process Regulated? – and + Feedback • Negative Feedback-occurs when a hormone acts to inhibit further secretion of the hormone of interest. • Positive Feedback-occurs when a hormone acts to increase secretion of the hormone.

20. Negative Feedback Example: • Insulin is released by the pancreas. • When the blood glucose gets too high, the pancreas is stimulated to produce insulin. • This causes cells to use more glucose. As a result of this activity, the blood glucose levels decline, halting production of insulin.

21. Positive Feedback Example: • An example of positive feedback is the LH surge that occurs prior to ovulation in females. • Estrogen is released as a result of the action of FSH. It travels to the anterior pituitary to stimulate the release of even more LH, which acts on the ovaries to stimulate even more estrogen.

22. Hormones Can Work Antagonistically to Maintain Homeostasis • Insulin/Glucagon: Both are hormones of the pancreas and have opposing effects on blood glucose. • Suppose you just ate a sugary snack that pushes blood glucose above the desired level. This results in the release of insulin to stimulate the uptake of glucose from the blood to the liver to be stored as glycogen. • If you go a long time between meals, however, your blood glucose may go below the desired level. This causes glucagon to be released. Glucagon acts on the liver to stimulate the removal of glycogen from storage and produce glucose to pump into the bloodstream.