Endocrine Control Chapter 26. Endocrine System Major Components Hypothalamus Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus gland.
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Endocrine Control
Chapter 26
Endocrine SystemMajor Components
• Hypothalamus• Pituitary gland• Pineal gland• Thyroid gland• Parathyroid glands• Thymus gland• Adrenal glands• Pancreatic islets• Ovaries• Testes
hypothalamus (part of the brain)
pituitary gland, anterior lobe
pituitary gland, posterior lobe
adrenal gland (one pair) cortex medulla
ovaries (one pair of female gonads)
testes (one pair of male gonads)
pineal gland
thyroid gland
parathyroid glands (four)
thymus gland
pancreatic islets
Fig. 26-1, p.449
Hormones
• Secreted by endocrine glands, endocrine cells, and hypothalmic neurons
• Travel through bloodstream to target cells
• Bind to receptors on target cells
Other Signaling Molecules
• Neurotransmitters– From axon endings of neurons
• Local signaling molecules– Prostaglandins– Nitric oxide (NO)
Three-Step Hormonal Action
• Activation of a receptor as it binds the hormone
• Transduction of signal into a molecular form that can work inside the cell
• Functional response of target cell
signal reception
signal transduction
cellular response
Responses to Hormones Vary
• Different hormones activate different responses in the same target cell
• Not all types of cells respond to a particular hormone
Main Hormone Types
Steroid hormones– Lipids derived from cholesterol
Peptide hormones– A few amino acids
Amine hormones– Modified amino acids
Protein hormones– Longer amino acid chains
Receptors
• Intracellular– Steroid hormones– Diffuse across plasma membrane
• Plasma membrane– Peptides and proteins– Too big or polar to diffuse– Second messengers (cAMP)
Steroid Hormones
receptor
hormone-receptor complex
gene product
hormone
• Most diffuse across the plasma membrane and bind to a receptor
• Hormone-receptor complex acts in nucleus to inhibit or enhance transcription
A steroid hormone molecule moves from the blood into interstitial fluid that bathes a target cell. Being a lipid-
soluable molecule, the steroid hormone diffuses across the target cell’s plasma membrane.
The mRNA transcript moves from the nucleus into the cytoplasm. There it becomes translated into a gene product that is required for the response to the hormone signal.
gene product
The hormone diffuses through the cytoplasm, then on through the nuclear envelope. Inside the nucleus, it will bind with a receptor molecule.
receptor
hormone-receptor complex
Now the hormone-receptor complex triggers transcription of gene regions in the DNA.
Fig. 26-2a, p.451
1
3
2
4
5
Peptide Hormone
• Hormone binds to a receptor at cell surface
• Binding triggers a change in activity of enzymes inside the cell
glucagon receptor
cyclic AMP + Pi
ATP
The cAMP activatesprotein kinase A.
glucagon
Protein kinase A converts phosphorylasekinase to active form and inhibits an enzyme required for glucagon synthesis.
ATP+Pi
The cAMP now activates protein kinase A.
A glucagon molecule diffuses from blood into the interstitial fluid that bathes the plasma membrane of a liver cell.
unoccupied glucagon receptor at target cell’s plasma membrane
Protein kinase A also inhibits an enzyme required for synthesis of glycogen.
Glucagon binds with the receptor, and the binding activates adenylate cyclase. This enzyme catalyzes the formation of cAMP inside the target cell.
Protein kinase A converts phosphorylase kinase to active form. This enzyme activates a different enzyme, which breaks down glycogen to its glucose monomers.
Fig. 26-2b, p.451
1
3
5
4
2
cyclic AMP
Hypothalamus and Pituitary
• Glands in brain– Structurally and functionally linked
• Master integrating center for endocrine and nervous systems
• Hypothalmic neurons produce– Neurotransmitters– Hormones
Pituitary Gland
• Pea-sized gland at base of hypothalamus• Two lobes– Posterior lobe stores and releases hormones
made in hypothalamus– Anterior lobe produces and secretes its own
hormones
Posterior PituitarySecretions
• Antidiuretic hormone (ADH)
• Oxytocin (OCT)
cell body in hypothalamus
axons
to the general circulation
Cell bodies in hypothalamus synthesize ADH or oxytocin
ADH, oxytocin move down axons, accumulate in axon endings
Small vessels carry hormones to general circulation
Action potentials cause release of hormones, which capillaries pick up
cell body
axon
capillaries
Stepped Art
Fig. 26-3, p.452
muscles in uterus wall
mammary glands
nephrons in kidneys
ADH
oxytocin
Cell bodies of secretory neurons in hypothalamus synthesize ADH or oxytocin.
The ADH or oxytocin moves downward inside the axons of the secretory neurons and accumulates in the axon endings.
Action potentials trigger the release of these hormones, which enter blood capillaries in the posterior lobe of the pituitary. Small blood vessels
deliver the hormone molecules to the general circulation.
Fig. 26-3, p.452
a
b
c
d
Anterior Pituitary
• Responds to hypothalmic signals• Releasers– Stimulate secretion of pituitary hormones
• Inhibitors– Inhibit release of pituitary hormones
Anterior PituitarySecretions
• Adrenocorticotropin (ACTH)• Thyroid stimulating hormone
(TSH)• Follicle-stimulating hormone
(FSH)• Luteinizing hormone (LH)• Prolactin (PRL)• Growth hormone (GH)
thyroidgland
ACTH TSH FSH LH PRL GH (STH)
testes in malesovaries in females
mammary glands
Hormones secreted from anterior lobe cells enter small blood vessels that lead to the general circulation.
Cell bodies of different secretory neurons in the hypothalamus secrete releasing and inhibiting hormones.
The hormones are picked up by a capillary bed at the base of the hypothalamus.
Bloodstream delivers hormones to a second capillary bed in anterior lobe of pituitary.
Molecules of the releasing or inhibiting hormone diffuse out of capillaries and act on endocrine cells in the anterior lobe.
most cells (growth-promoting effects)
Fig. 26-4, p.453
a
e
b
c
d
adrenalglands
Abnormal Pituitary Output
• Pituitary gigantism • Pituitary dwarfism • Acromegaly
Abnormal Pituitary Outputs
Thymus, Thyroid and Parathyroid
• Thymus– Immune function
• Thyroid– Development and metabolism– Regulated by feedback loops
• Parathyroid– Calcium levels
Hypothalamus
Anterior Pituitary
Thyroid Gland
ResponseStimulus
Blood level of thyroid hormone falls below a set point.
+TRH
TSH
Thyroid hormoneis secreted
Rise in the blood level of thyroid hormone inhibits secretion of TRH and TSH.
–
–
Negative Feedback and Thyroid Function
Thyroid Function
• Requires mineral iodine– Deficiency causes
goiter
Parathyroid and Calcium
• Parathyroid hormone (PTH)– regulates blood calcium– secreted when calcium levels drop– causes bone cells to release calcium from bone
tissue– stimulates calcium reabsorption by kidneys
Calcium and Vitamin D
• Without vitamin D, not enough calcium is absorbed
• Low blood calcium causes oversecretion of PTH– Breaks down existing bone– Causes rickets
Adrenal Glands and Stress
• Adrenal cortex secretes cortisol and aldosterone
• Negative feedback maintains blood cortisol levels
HypothalamusStimulusResponse
Anterior Pituitary
Adrenal Cortex
Cortisol is secreted, with these effects:
adrenal cortex
adrenal medulla
Blood level of cortisol falls below a set point
kidney
Both the hypothalamus and pituitary detect rise in blood level of cortisol and slow its further secretion.
CRH
ACTH
+
–
Cellular uptake of glucose from blood slows in many tissues, especially muscles (not the brain).
Proteins degraded in many tissues, especially in muscles. The free amino acids are converted to glucose and used in the assembly or repair of cell structures.
Fats in adipose tissue degraded to fatty acids that enter blood as an alternative energy source, indirectly conserving glucose for the brain.
–
ab
f
c
d
e
Negative Feedback Control of Adrenal Glands
Stress Response
• Stress can cause nervous system to override feedback loop
• Cortisol levels rise above normal, suppress inflammation
• Persistent high cortisol levels may harm health
The Pancreas and Glucose Homeostasis
stomach
pancreas
smallintestine
Pancreatic Hormones and Glucose Balance
• Glucagon– Secreted by alpha cells in islets– Raises blood glucose level
• Insulin– Secreted by beta cells in islets– Lowers blood glucose level
• Somatostatin– Secreted by delta cells– Blocks insulin and glucagon secretion
Fig. 26-9, p.456
Stimulus Stimulus
alpha cells
glucagon
LIVER
insulin
beta cells
Increase in blood glucose
+
PANCREAS
–
Decrease in blood glucose
alpha cells
glucagoninsulin
beta cells+ –
MUSCLE FAT CELLS Body cells, especially in muscle and adipose tissue, take up and use more glucose.Cells in skeletal muscle and liver store glucosein the form of glycogen.
ResponseDecrease in blood glucose
Cells in liver break down glycogen faster. The released glucose monomers enter blood.
Response Increase in blood glucose
a f
g h
i
je
b c
d
Diabetes Mellitus
Excess glucose accumulates Type 1
• Autoimmune disease
• Usually appears in childhood
• Insulin injections
Type 2
• Target cells don’t respond
• Usually appears in adults
• Diet, drugs
Table 26-2, p.457
Sex Hormones
• Testes and ovaries synthesize the same sex hormones in different amounts– Estrogens– Progesterone– Testosterone
• Influence sexual traits
The Pineal Gland• Photosensitive gland embedded in brain• In absence of light, secretes melatonin• Influences seasonal behaviors• Affects human biological clock– sleep-wake cycles– seasonal affective disorder
Deformed Frogs
• Something in water triggers deformities• Problem thyroid function?• Tadpoles from “hotspots” developed normally
when given extra thyroid hormones• UV, parasites also play a role
Effects of Pollution on Frogs
Table 26-3, p.459
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