Chemical Signals in Animals 9. c. Students know how

feedback loops in the nervous and endocrine systems regulate conditions in the body.

9. i.* Students know how hormones (including digestive, reproductive, osmoregulatory) provide internal feedback mechanisms for homeostasis at the cellular level and in whole organisms.

Hormone Dysfunction

Hormone Dysfunction

Feedback Loops

Feedback loops are how the nervous system uses the endocrine system to regulate body conditions.

The presence or absence of hormones in blood brought to the brain by the circulatory system will trigger an attempt to regulate conditions in the body.

Hormone Example The hormone leptin, which fat cells

produce as they become filled with storage reserves.

Leptin is carried by the blood to the brain, where it normally acts to stop hunger

An example of negative feedback. When fat reserves diminish, the concentration of leptin decreases, a phenomenon that in turn causes the appetite center in the brain to start the hunger stimulus and activate the urge to eat.

Hormones work with the Nervous System

For ex-ample, in the digestive system, where insulin released from the pancreas into the blood regulates the uptake of glucose by muscle cells.

The pituitary master gland produces growth hormone for controlling height.

Mode of Action: Chemical Signaling 1- Plasma membrane reception

• signal-transduction pathways (neurotransmitters, growth factors, most hormones)

2- Cell nucleus reception • steroid hormones, thyroid hormones, some local regulators

Vertebrate Endocrine System Tropic hormones ~

a hormone that has another endocrine gland as a target

Hypothalamus~pituitary Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus Adrenal glands Pancreas Gonads (ovary, testis)

The hypothalamus & pituitary, I Releasing and inhibiting hormones Anterior pituitary: Growth (GH)~bones

√gigantism/dwarfism √acromegaly

Prolactin (PRL)~mammary glands; milk production

Follicle-stimulating (FSH) & Luteinizing (LH)~ovaries/testes Thyroid-stimulating (TSH)~ thyroid Adrenocorticotropic (ACTH)~

adrenal cortex Melanocyte-stimulating (MSH)

Endorphins~natural ‘opiates’; brain

pain receptors

The pituitary, II

The posterior pituitary: Oxytocin~

uterine and mammary gland cell contraction

Antidiuretic (ADH)~ retention of water by

kidneys

Pituitary Hormones

Follicle-stimulating hormone [FSH] and luteinizing hormone [LH] control the gonads

Thyroid-stimulating hormone [TSH] controls the thyroid, and adrenocorticotropic hormone [ACTH] regulates the formation of glucocorticoids by the adrenal cortex).

This master gland is itself controlled by the hypothalamus of the brain.

The pineal, thyroid, & parathyroid Melatonin~ pineal gland;

biological rhythms

Thyroid hormones: Calcitonin~

lowers blood calcium Thyroxine~ metabolic processes

Parathyroid (PTH)~ raises blood calcium

The pancreas

Beta cells: •insulin~ lowers blood glucose levels

Type I diabetes mellitus (insulin-dependent; autoimmune disorder)

Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets)

The adrenal glands Adrenal medulla (catecholamines): •epinephrine &

norepinephrine~ increase basal metabolic rate (blood glucose and pressure)

Adrenal cortex (corticosteroids): •glucocorticoids (cortisol)~ raise blood glucose •mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+

The gonads

Ovaries estrogens

(estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin

progestins (progesterone)~uterine lining growth

Testes Steroid hormones:

precursor is cholesterol

androgens (testosterone)~ sperm formation; male secondary sex characteristics;

gonadotropin

Regulatory systems Hormone~ chemical signal

secreted into body fluids (blood) communicating regulatory messages

Target cells~ body cells that respond to hormones

Endocrine system/glands~ hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts

Neurosecretory cells~ actual cells that secrete hormones

Feedback mechanisms ~ negative and positive

Local regulators: cells adjacent to or near point of secretion

Growth factors ~ proteins for cell proliferation

Nitric oxide (NO) ~ neurotransmitter; cell destruction;

vessel dilation Prostaglandins ~

modified fatty acids secreted by placenta and immune system; also found in semen