Overview of the endocrine system
- the endocrine system and the nervous system often do not function independently but in conjunction with each other
- both function to achieve and maintain stability of the internal environment
- both perform their regulatory functions by means of chemical messengers sent to specific cells
- the endocrine system secretes hormones into the bloodstream to signal specific target cells (target tissues/organs) throughout the body
Endocrine system
Collection of specialized cells, and tissues that secrete hormones
Endocrine glands
Ductless organs that secrete hormones into the blood, interstitial fluid, and lymph
Hormones
- chemical messengers secreted by endocrine glands
- circulate in the bloodstream
- act on specific cells in the body (target cells) that have the appropriate hormone receptor
Characteristics of the endocrine system
1) hormones have access to every cell
2) each hormone acts only on specific cells (target cells)
3) only specific cells have receptors for specific hormones
4) endocrine control is slower than the nervous system
5) endocrine and nervous systems interact
classification of steroid hormones
- molecules manufactures form cholesterol by the endocrine cells
Lipid - soluble, which allows them to easily pass through the phospholipid bilayer
Classification of non-steroidal hormones
- molecules synthesize primarily from amino acids
- protein hormones
- glycoprotein hormones
- peptide hormones
- amino acid derivative hormones
How steroid hormones work
- lipid - soluble, chemically derived from cholesterol
- enter target cells by diffusion across the cell membrane
- bind to intracellular receptor, forming a complex
- once in the nucleus, hormone-receptor complex attaches to DNA, activating specific genes
- mRNA is produced and then translated
- protein product carries out cellular response to hormone
- slower acting than no steroid hormones; takes minutes to hours
How non-steroid hormones work
- water soluble
- bind to receptors on target cell membranes
- work through intermediate mechanisms to active existing enzymes
- may involve “second messenger” within the cell, such as cyclic AMP (cAMP)
- faster actin than steroid hormones; takes seconds to minutes
How hormones participate in feedback loops
- many hormones participate in internal homeostasis control mechanisms
- Negative feedback loops involving hormones include the following:
- endocrine gland serves as the control center
- hormone is the pathway between the control center and the effectors
- target tissues or organs are the effectors
- Negative feedback loops involving hormones include the following:
Hypothalamus
- homeostatic control center of the brain
- links nervous system and endocrine system
- produces two hormones of its own
- monitors and controls hormone secretions of the pituitary gland
Pituitary gland
- “master” gland
- secreted eight different hormones that regulate other endocrine organs
- two lobes: posterior and anterior
Posterior pituitary gland
- the posterior pituitary is connected to the hypothalamus by neuroendocrine cells
- hormones (ADH and oxytocin) made in cell bodies in hypothalamus are transported down axons to axon ensigns in posterior pituitary for storage and release - Posterior pituitary hormones: non-steroidal
- Antidiuretic hormone (ADH)
Conserves water in kidneys
Regulates water balance in the body - oxytocin
Causes urine contraction during labor, and milk ejection through neuroendocrine reflex
- Antidiuretic hormone (ADH)
Anterior pituitary
- controlled by the hypothalamus
- releasing and inhibits hormones form hypothalamus travel to pituitary through pituitary portal system
- the release of each anterior pituitary hormone is controlled, at least partially, by the hypothalamus
The six key hormones of the pituitary gland
ACTH (Adrenocorticotropic hormone): stimulates adrenal cortex to release glucocorticoids (cortisol); promotes and maintains normal growth and development of the cortex of the adrenal gland
TSH (Thyroid-stimulating hormone): acts on thyroid gland, promotes release of thyroid hormones
FSH & LH (Gonadotrophs): stimulate growth, development, and function of ovaries and testes; not produced until about age 10-13 (puberty); increase in production initiates sexual maturation and development at puberty
Prolactin: stimulates development of mammary glands an milk production
Growth hormone: has widespread effects on the body; major effects on bone, muscle; most of its growth-promoting effects occur during childhood and adolescence
Pituitary disorders
Diabetes insipidus: hypo secretion of ADH results in inability to conserve water appropriately; causes excessive urinate, dehydration, thirst
Gigantism: hypersecretion of growth hormone in body
Acromegaly: excessive growth hormone over a long period in adults
Pituitary dwarfism: hyposecretion of growth hormone, treated by administration of GH throughout childhood
Pineal gland
- tiny structure resembling a pine nut, located on the dorsal aspect of the brains diencephalon
- it is a member of two body systems because it acts as a part of the nervous system and as a part of the endocrine system
- produced a number of different hormones, but the principle hormone is melatonin
- important aspect of the “biological clock”
Thyroid gland
- Secretion: mediated through hypothalamus-pituitary secretions
- steroidal hormones: thyroxine (T4) and triiodothyronine (T3); both regulate production of ATP from glucose and modify the metabolic rate
Calcitonin: Lowers blood calcium levels; decreases rate of bone reabsorption by inhibiting osteoclasts; stimulates uptake of calcium by bones
Parathyroid hormone (PTH):
- parathormone
- PTH is the main hormone for blood calcium homeostasis
- increasing the amount of osteoclasts activity and inhibiting osteoblast to release calcium into the bloodstream
Iodine deficiency can cause goiter
- iodine is quirked for production for active thyroid hormones
- inadequate dietary iodine leads to underproduction of thyroid hormones
- the feedback response to inadequate thyroid hormone is for the hypothalamus and pituitary t further stimulate the thyroid gland in a vicious cycle that causes hypertrophic of the thyroid (goiter)
Adrenal cortex
- Zona Glomoerulosa:
- mineralcorticoids
- Zona fasciculata:
- glucocorticoids
- Zona reticularis:
- glucocorticoids
- gonadcorticoids
- corticosteroids
Adrenal medulla
- epinephrine -> 80%
- norepinephrine -> 20%
Adrenal cortex is where
The adrenal cortex is in the outer layer of the adrenal gland
- glucocorticoids, such as cortisol
- mineralcorticoids, such as aldosterone
Adrenal medulla is where
The adrenal medulla is the inner layer of the adrenal gland
- epinephrine (adrenaline)
- norepinephrine (noradrenaline)
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Chapter 145
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Chapter 275
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Chapter 362
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Unit One Quizzes57
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Chapter 458
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Metabolism And Electrolytes33
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Chapter 549
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Body Systems And Cardiovascular Disease39
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Chapter 669
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Exam 153
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Chapter 751
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Chapter 945
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Unit 2 Quiz Questions39
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chapter 1042
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Chapter 1172
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Chapter 1257
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Exam 267
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Chapter 1353
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Unit 3 Quiz48
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Chapter 1448
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Chapter 1536
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Chapter 1637
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Exam 345
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Chapters 24 And 2562
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Final Exam88
