1. Ch 45 – Hormones & the Endocrine System
Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body
Hormones reach all parts of the body, but only target cells are equipped to respond

2. Two systems coordinate communication throughout the body
Endocrine system: secretes hormones that coordinate slow, long-acting responses (reproduction, development, energy metabolism, growth, and behavior)
(video 3:05)
Nervous system: conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells

3. Chemical signals bind to receptor proteins on target cells
45.1: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways
Chemical signals bind to receptor proteins on target cells
Only target cells respond to the signal
Secreted chemical signals include
-- Hormones -- Local regulators
-- Neurotransmitters -- Neurohormones
-- Pheromones

4. Hormones (a) mediate responses to environmental stimuli and regulate growth, development, and reproduction
Local regulators (b&c) travel over short distances by diffusion; they help regulate blood pressure, nervous system function, and reproduction; ex: nitric oxide, cytokines, growth factors, prostaglandins
Blood
vessel
Response
Endocrine signaling -- secrete hormones directly into
surrounding fluid
Response
(b) Paracrine signaling -- acts on cells near the secreting cell
Figure 45.2 Intercellular communication by secreted molecules
Response
(c) Autocrine signaling – acts on secreting cell itself

5. that diffuse a short distance and bind to receptors on target cell
Synapse
Neuron
Response
(d) Synaptic signaling – at synapses, neurons release neurotransmitters
that diffuse a short distance and bind to receptors on target cell
Neurosecretory
cell
Figure 45.2 Intercellular communication by secreted molecules
Blood
vessel
Response
(e) Neuroendocrine signaling – neurohormones are a class of hormones
that originate from neurons in brain and diffuse through bloodstream

6. Pheromones
Chemical signals used to communicate with other individuals in the species
Mark trails to food sources, warn of predators, and attract potential mates

7. Chemical Classes of Hormones
Three major classes of molecules function as hormones in vertebrates:
Polypeptides (proteins and peptides)
Amines derived from amino acids
Steroid hormones

8. Do not pass through cell membranes easily
Receptors on cell surface
Secreted by exocytosis
Travel freely in bloodstream
Pass through cell membranes easily
Receptors are inside cell
Travel in bloodstream bound to transport proteins
Water-soluble
Lipid-soluble
0.8 nm
Polypeptide:
Insulin
Steroid:
Cortisol
Figure 45.3 Hormones differ in form and solubility
Amine:
Epinephrine
Amine:
Thyroxine

9. Ex: steroids, thyroid hormones, hormonal form of vitamin D
Water-
soluble
hormone
Fat-soluble
hormone
Animation:
Lipid-Soluble
Hormone
Animation:
Water-Soluble
Hormone
Ex: epinephrine
Transport
protein
Ex: steroids, thyroid hormones, hormonal form of vitamin D
Signal receptor
TARGET
CELL OR
Signal
receptor
Figure 45.5 Receptor location varies with hormone type
Cytoplasmic
response
Gene
regulation
Cytoplasmic
response
Gene
regulation
(a)
NUCLEUS
(b)

10. 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
A hormone can also have different effects in different species

11. Same receptors but different intracellular proteins (not shown)
Fig
Same receptors but different
intracellular proteins (not shown)
Different receptors
Epinephrine
Epinephrine
Epinephrine
Epinephrine
 receptor
 receptor
 receptor
 receptor
Glycogen
deposits
Vessel
dilates.
Vessel
constricts.
Glycogen
breaks down
and glucose
is released.
Figure 45.8 One hormone, different effects
(a) Liver cell
(b) Skeletal muscle
blood vessel
(c) Intestinal blood
vessel

12. Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Organs containing
endocrine cells:
Thyroid gland
Thymus
Parathyroid glands
Heart
Liver
Adrenal
glands
Stomach
Figure Major human endocrine glands
Pancreas
Testes
Kidney
Kidney
Small
intestine
Ovaries

13. Pathway
Example
Negative feedback regulates many hormonal pathways involved in homeostasis
A negative feedback loop inhibits a response by reducing the initial stimulus –
Stimulus
Low pH in
duodenum
S cells of duodenum
secrete secretin ( )
Endocrine
cell
Negative feedback
Blood
vessel
Figure A simple endocrine pathway
Target
cells
Pancreas
Response
Bicarbonate release

14. Promotes cellular uptake of glucose Promotes fat storage
Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis
Insulin:
Made by beta cells
Promotes cellular uptake of glucose
Promotes fat storage
Slows glycogen breakdown in liver
Glucagon:
Made by alpha cells
Promotes conversion of glycogen to glucose in liver
Promotes breakdown of fat and protein into glucose
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level
rises.
Blood glucose
level declines.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Figure Maintenance of glucose homeostasis by insulin and glucagon
STIMULUS:
Blood glucose level
falls.
Blood glucose
level rises.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Glucagon

15. Diabetes Mellitus
Diabetes mellitus is perhaps the best-known endocrine disorder
Caused by a deficiency of insulin or a decreased response to insulin in target tissues
Results in elevated blood glucose levels

16. Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells
Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors
Clip

17. 45.3: The endocrine and nervous systems act individually and together in regulating animal physiology
Signals from the nervous system initiate and regulate endocrine signals

18. Clip Cerebrum Thalamus Pineal gland Hypothalamus Cerebellum Pituitary
Spinal cord
Hypothalamus receives information from the nervous system and initiates responses through the endocrine system
Posterior pituitary stores and secretes hormones that are made in the hypothalamus
Anterior pituitary makes and releases hormones under regulation of the hypothalamus
Hypothalamus
Figure Endocrine glands in the human brain
Posterior
pituitary
Anterior
pituitary
Clip

19. Table 45-1
Table 45.1

20. Table 45-1a
Table 45.1

21. Mammary glands, uterine muscles
Hypothalamus
Oxytocin induces uterine contractions and release of milk
Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys
Clip
Neurosecretory cells of the hypothalamus
Axon
Posterior
pituitary
Anterior
pituitary
Figure Production and release of posterior pituitary hormones
HORMONE
ADH
Oxytocin
TARGET
Kidney tubules
Mammary glands, uterine muscles

22. Pathway
Example
Stimulus
Suckling
Oxytocin
Suckling sends a message to the hypothalamus via the nervous system to release oxytocin, which further stimulates the milk glands
This is an example of positive feedback, where the stimulus leads to an even greater response +
Sensory neuron
Hypothalamus/ posterior pituitary
Neurosecretory cell
Posterior pituitary secretes oxytocin ( )
Positive feedback
Blood vessel
Figure A simple neurohormone pathway
Target cells
Smooth muscle in breasts
Response
Milk release

23. Liver, bones, other tissues
Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones from the hypothalamus
Tropic effects only: FSH LH TSH ACTH
Neurosecretory cells of the hypothalamus
Nontropic effects only: Prolactin MSH
Nontropic and tropic effects: GH
Hypothalamic releasing and inhibiting hormones
Portal vessels
Endocrine cells of the anterior pituitary
Posterior pituitary
Figure Production and release of anterior pituitary hormones
Pituitary hormones
HORMONE
FSH and LH
TSH
ACTH
Prolactin
MSH GH
TARGET
Testes or ovaries
Thyroid
Adrenal cortex
Mammary glands
Melanocytes
Liver, bones, other tissues

24. Hormone Cascade Pathways
A hormone can stimulate the release of a series of other hormones, the last of which activates a nonendocrine target cell; this is called a hormone cascade pathway
The release of thyroid hormone results from a hormone cascade pathway involving the hypothalamus, anterior pituitary, and thyroid gland
Hormone cascade pathways are usually regulated by negative feedback

25. A tropic hormone regulates the function of endocrine cells or glands
Tropic Hormones
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)

26. Nontropic hormones target nonendocrine tissues
Nontropic hormones produced by the anterior pituitary are
Prolactin (PRL): stimulates lactation in mammals but has diverse effects in different vertebrates
Melanocyte-stimulating hormone (MSH): influences skin pigmentation in some vertebrates and fat metabolism in mammals

27. Growth Hormone
Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic actions
It promotes growth directly and has diverse metabolic effects
It stimulates production of growth factors
An excess of GH can cause gigantism, while a lack of GH can cause dwarfism

28. 45.4: Endocrine glands respond to diverse stimuli in regulating metabolism, homeostasis, development, and behavior
Endocrine signaling regulates metabolism, homeostasis, development, and behavior

29. Thyroid Hormone: Control of Metabolism and Development
The thyroid gland consists of two lobes on the ventral surface of the trachea
It produces two iodine-containing hormones: triiodothyronine (T3) and thyroxine (T4)

30. Thyroid hormones stimulate metabolism and influence development and maturation
Hyperthyroidism, excessive secretion of thyroid hormones, causes high body temperature, weight loss, irritability, and high blood pressure
Graves’ disease is a form of hyperthyroidism in humans
Hypothyroidism, low secretion of thyroid hormones, causes weight gain, lethargy, and intolerance to cold

31. Parathyroid Hormone and Vitamin D: Control of Blood Calcium
Two antagonistic hormones regulate the homeostasis of calcium (Ca2+) in the blood of mammals
Parathyroid hormone (PTH) is released by the parathyroid glands
Calcitonin is released by the thyroid gland

32. Falling blood Ca2+ level Blood Ca2+ level (about 10 mg/100 mL)
Fig
Active vitamin D
Stimulates Ca2+ uptake in kidneys
Increases Ca2+ uptake in intestines
PTH
Parathyroid gland (behind thyroid)
Stimulates Ca2+ release from bones
Figure The roles of parathyroid hormone (PTH) in regulating blood calcium levels in mammals
STIMULUS:
Falling blood Ca2+ level
Blood Ca2+ level rises.
Homeostasis:
Blood Ca2+ level (about 10 mg/100 mL)

33. Adrenal Hormones: Response to Stress
The adrenal glands are adjacent to the kidneys
Each adrenal gland actually consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion)
The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)
The adrenal cortex releases a family of steroids called corticosteroids in response to stress

34. Clip Fig. 45-21 Figure 45.21 Stress and the adrenal gland Stress
Nerve signals
Hypothalamus
Spinal cord
Releasing hormone
Nerve cell
Anterior pituitary
Blood vessel
ACTH
Adrenal medulla
Adrenal cortex
Adrenal gland
Kidney
(a) Short-term stress response
Figure Stress and the adrenal gland
(b) Long-term stress response
Effects of epinephrine and norepinephrine:
Effects of mineralocorticoids:
Effects of glucocorticoids:
1. Glycogen broken down to glucose; increased blood glucose
2. Increased blood pressure 3. Increased breathing rate 4. Increased metabolic rate
1. Retention of sodium ions and water by kidneys
1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose
5. Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity
2. Increased blood volume and blood pressure
2. Possible suppression of immune system

35. Gonadal Sex Hormones
The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins
All three sex hormones are found in both males and females, but in different amounts
Clip

36. The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system
Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks

37. Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics
In mammals, progestins, which include progesterone, are primarily involved in preparing and maintaining the uterus
Synthesis of the sex hormones is controlled by FSH and LH from the anterior pituitary

38. Melatonin and Biorhythms
The pineal gland, located in the brain, secretes melatonin
Light/dark cycles control release of melatonin
Primary functions of melatonin appear to relate to biological rhythms associated with reproduction