Chapter 45: Hormones &The Endocrine System

Steph JonesAP Biology

Ms. Loughnane

Basics• Hormone: a chemical signal that is secreted into the

circulatory system (usually the blood) and communicates regulatory messages within a body

• Target cells are the cells that contain the specific receptor that only activates when that specific hormone is secreted

• Two main systems involved are: Nervous System & Endocrine System

Control Pathways

• Three major hormonal control pathways: Endocrine, Neurohormone, Neuroendocrine.

• Regulation by hormones:1) Receptor detects stimulus and sends info to control

center2) After comparing the desired set point, the control center

sends signal to an effector3) The effector responds and sends a changing signal into

the control pathways

Feedback• After the effector sends out a changing signal

into the pathways, it becomes either:

• Negative feedback, where the effector response reduces the initial stimulus, and eventually the response stops

OR

• Positive Feedback, which reinforces the stimulus and leads to a greater response

• Feedback regulates hormonal pathways used to maintain homeostasis

Classes of Hormones

• Proteins and Peptides - small polypeptide containing up to 30 amino acids (both are water-soluble)

• Amines that come from Amino Acids (water-soluble)

• Steroids (lipid-soluble)

Signaling

• Three Key Events:1. Reception – occurs when the signal molecule

binds to a specific receptor protein in or on target cell

2. Signal Transduction – events within target cell3. Response – a change in cell behavior as a

response to the stimulus and to maintain homeostasis

Cell-Surface Receptors for Water-Soluble Hormones

• Most peptide/protein hormones that come from amino acids bind to receptors that are located inside the plasma membrane

• Signal Transduction Pathway: a series of changes in cellular proteins that converts an extracellular chemical signal to specific intracellular response

Cell-Surface Receptors for Water-Soluble Hormones (cont’d)

• Binding causes a signal transduction pathway that leads to a response in cytoplasm or changes in gene expression

* Remember: the same hormone can have different effects on target cells that have:

- Different receptors- Different signal transduction pathways- Different effector proteins

Intracellular Receptors for Lipid-Soluble Hormones

• Intracellular receptors of steroid hormones transduce a signal within a target cell

• The chemical signal activates the receptor which leads to the cell’s response

Paracrine Signaling

• Paracrine Signaling: local regulators convey messages between neighboring cells

• Faster than the long-distance endocrine signaling

Paracrine Signaling (cont’d)

• Local regulators greatly help maintain homeostasis

ex: nitric oxide (NO) is released by by blood vessels when blood oxygen level falls. NO activates an enzyme that relaxes smooth muscle cells, which dilates vessels and improves blood flow to tissues

Hypothalamus

• Hypothalamus: a region of the lower brain that contains different sets of nuerosecretory cells

Pituitary Gland

• Pituitary Gland: At the base of the Hypothalamus; has two parts:

- Posterior Pituitary: stores and secretes 2 hormones that are made by neurosecretory cells located in the hypothalamus

- Anterior Pituitary: make and secrete at least 6 hormones into the blood

Tropic Hormones

• Regulate the function of endocrine organs, and coordinate endocrine signaling throughout the body

Posterior Pituitary Hormones

• Releases 2 hormones:

• ADH (antidiuretic hormone): kidney tubules

• Oxytocin: mammary glands, uterine muscles

Anterior Pituitary Hormones: Tropic Effects Only

• thyroid-stimulating hormone (TSH): Thyroid

• follicle-stimulating hormone (FSH): testes & ovaries

• luteinizing hormone (LH): testes & ovaries

• adrenocorticotropic hormone (ACTH): Adrenal cortex

Anterior Pituitary Hormones: Nontropic Effects Only

• Prolactin: mammary glands

• Endorphin: pain receptors in brain

• Melanocyte-stimulating hormone (MSH): melanocytes

Anterior Pituitary Hormones:Nontropic & Tropic Effects

• Growth hormone: Liver & bones

Nonpituitary Hormones

• Help regulate metabolism, homeostasis, development, and behavior

• There are 6 types: Thyroid, Parathyroid & Calcitonin, Insulin & Glucagon, Adrenal, Gonadal, Melatonin & Biorhythms

Thyroid Hormones• Thyroid Gland: two lobes on the ventral

surface of the trachea, produce 2 hormones produced by the amino acid tyrosine: Triiodothyronine (T3) and Thyroxine (T4).

• They stimulate metabolism, influence development and maturation

Parathyroid Hormone (PTH) & Calcitonin

• Play the major role in calcium (Ca2+) homeostasis, control blood calcium levels

• PTH raises blood Ca2+ levels when they drop and Calcitonin lowers Ca2+ levels when they rise

Insulin & Glucagon

• Help maintain glucose homeostasis, the pancreas synthesizes them

• Insulin lowers blood glucose levels and glucagon raises them

Adrenal Hormones: Adrenal Medulla• Secreted by the Adrenal glands, two glands,

adrenal cortex, outer portion and adrenal medulla, central portion

• Epinephrine and norepinephrine are releasedby nuerosecretory cells in the adrenal medulla in response to stress or danger.

Adrenal Medulla

Adrenal Hormones: Adrenal Cortex

• The adrenal cortex releases glucocorticoids (influence glucose metabolism & immune system), mineralocorticoids (salt and water balance), and small amounts of sex hormones

Adrenal Cortex

Gonadal Sex Hormones• There are three sex hormones: androgens (ex. Testosterone),

estrogens, and progestins

-Androgens stimulate development/maintenance of male reproductive system- Estrogen maintain female reproductive system and female secondary sex characteristics- Progestins prepare/maintain uterus

• Produced by the gonads, or testes and ovaries

• Produced in both males and females, just in different amounts

Melatonin and Biorhythms

• Pineal gland in the brain secretes melatonin• The secretion of Melatonin is regulated by

light/dark cycles and is related to biological rhythms with reproduction

Invertebrates

• They also contain endocrine system and nervous system interactions

• Varied hormones regulate many different aspects of homeostasis– Molting in insects includes 3 different hormones• Brain hormone• Ecdysone• Juvenile Hormone

Picture Citations(respectively)

• http://zaborina.i.ph• http://www.gynaeonline.com• http://www.clivir.com• http://www.thyroidinstitute.org• http://www.healingtherapies.info