Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not
The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells
Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors
Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells
Fig. 45-5-1 NUCLEUS Signal receptor (a) (b) TARGET CELL Signal receptor Transport protein Water- soluble hormone Fat-soluble hormone
Fig. 45-5-2 Signal receptor TARGET CELL Signal receptor Transport protein Water- soluble hormone Fat-soluble hormone Gene regulation Cytoplasmic response Gene regulation Cytoplasmic response OR (a) NUCLEUS (b)
Multiple Effects of Hormones
The same hormone may have different effects on target cells that have
Different receptors for the hormone
Different signal transduction pathways
Different proteins for carrying out the response due to different transcription factors they activate
A hormone can also have different effects in different species
Fig. 45-8-1 Glycogen deposits receptor Vessel dilates. Epinephrine (a) Liver cell Epinephrine receptor Glycogen breaks down and glucose is released. (b) Skeletal muscle blood vessel Same receptors but different intracellular proteins (not shown)
Fig. 45-8-2 Glycogen deposits receptor Vessel dilates. Epinephrine (a) Liver cell Epinephrine receptor Glycogen breaks down and glucose is released. (b) Skeletal muscle blood vessel Same receptors but different intracellular proteins (not shown) Epinephrine receptor Different receptors Epinephrine receptor Vessel constricts. (c) Intestinal blood vessel
Negative feedback and antagonistic hormone pairs are common features of the endocrine system
Hormones are assembled into regulatory pathways
A negative feedback loop inhibits a response by reducing the initial stimulus
Negative feedback regulates many hormonal pathways involved in homeostasis
Fig. 45-11 Pathway Example Stimulus Low pH in duodenum S cells of duodenum secrete secretin ( ) Endocrine cell Blood vessel Pancreas Target cells Response Bicarbonate release Negative feedback –
Insulin and Glucagon: Control of Blood Glucose – an example of antagonistic hormone pairs
The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin
Insulin reduces blood glucose levels by
Promoting the cellular uptake of glucose
Slowing glycogen breakdown in the liver
Promoting fat storage
Glucagon increases blood glucose levels by
Stimulating conversion of glycogen to glucose in the liver
Stimulating breakdown of fat and protein into glucose
Remember: Glucagon – “Glucose ON!”
Fig. 45-12-2 Homeostasis: Blood glucose level (about 90 mg/100 mL) Insulin Beta cells of pancreas release insulin into the blood. STIMULUS: Blood glucose level rises. Liver takes up glucose and stores it as glycogen. Blood glucose level declines. Body cells take up more glucose.
The anterior pituitary gland secretes releasing hormones and inhibiting hormones.
TSH – thyroid stimulating
FSH and LH – stimulates gonads
ACTH - stimulates adrenal cortex
Prolactin – milk production
MSH – stimulates production of melanocytes (skin pigments)
GH – growth hormone
Fig. 45-17 Hypothalamic releasing and inhibiting hormones Neurosecretory cells of the hypothalamus HORMONE TARGET Posterior pituitary Portal vessels Endocrine cells of the anterior pituitary Pituitary hormones Tropic effects only: FSH LH TSH ACTH Nontropic effects only: Prolactin MSH Nontropic and tropic effects: GH Testes or ovaries Thyroid FSH and LH TSH Adrenal cortex Mammary glands ACTH Prolactin MSH GH Melanocytes Liver, bones, other tissues
A tropic hormone regulates the function of endocrine cells or glands
The four strictly tropic hormones are
Thyroid-stimulating hormone (TSH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Adrenocorticotropic hormone (ACTH)
T 3 and T 4 , regulates metabolism (needs dietary iodine to function properly – goiter)
Calcitonin – lowers calcium in blood – deposition in bones and secretion into kidney filtrate
PTH parathormone – raises calcium levels in blood – from bones and reuptake in kidneys
Fig. 45-20-2 PTH Parathyroid gland (behind thyroid) STIMULUS: Falling blood Ca 2+ level Homeostasis: Blood Ca 2+ level (about 10 mg/100 mL) Blood Ca 2+ level rises. Stimulates Ca 2+ uptake in kidneys Stimulates Ca 2+ release from bones Increases Ca 2+ uptake in intestines Active vitamin D
Epinephrine (adrenaline ) – raises metabolic rate, “fight or flight”
Glucocorticoids – glucose from noncarb sources, such as muscles
Mineralocorticoids (aldosterone ) – induces kidneys to reabsorb water and salts
Both of these deal with long-term stress
Fig. 45-21c (b) Long-term stress response Effects of mineralocorticoids: Effects of glucocorticoids: 1. Retention of sodium ions and water by kidneys 2. Increased blood volume and blood pressure 2. Possible suppression of immune system 1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose Adrenal gland Kidney Adrenal cortex
Androgens (testosterone) – gender, male secondary sex characteristics
Estrogen – maintenance of female reproductive system and development of secondary female characteristics
Progesterone – prepares uterus for child
Melatonin – biological clock
Hormonal pathways work with the hypothalamus and anterior pituitary to coordinate responses
Ex – in the gonads
GnRH (hypothalamus) affects FSH and LH (anterior pituitary) which affects estrogens and androgens (ovaries/testes)
Which endocrine gland?
Too little of my hormone and you will feel tired and sluggish and probably gain weight.
A malfunction in this gland can result in a giant.
This gland prepares me for an emergency situation by increasing my heartrate.
This gland is also used in the digestive system. It also comes into play when I eat lots of M and M’s!
This gland is called the “master gland” because it secretes nine hormones many of which control other endocrine glands by feedback control.
If this gland is not working properly, diabetes can result.
If this gland is not working properly, your nerves and muscles will not function properly either due to calcium deficiency.
These glands do not function properly in chromosomal mutations such as in Turner’s and Klinefelter’s syndrome.
This gland makes me wake up in the morning and ready to go!