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Questions and Answers
What are the two main control systems of the body?
What are the two main control systems of the body?
The nervous system and the endocrine system
What do endocrine glands secrete?
What do endocrine glands secrete?
Hormones
Where do endocrine glands secrete hormones?
Where do endocrine glands secrete hormones?
Into the bloodstream
Hormones can only act on distant target cells.
Hormones can only act on distant target cells.
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Which of the following are examples of hormones made from modified amino acids?
Which of the following are examples of hormones made from modified amino acids?
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What are the three types of stimuli that can trigger hormone release?
What are the three types of stimuli that can trigger hormone release?
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What is the primary mechanism for regulating hormone release?
What is the primary mechanism for regulating hormone release?
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What does the pineal gland secrete?
What does the pineal gland secrete?
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What is the function of the hypothalamus?
What is the function of the hypothalamus?
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What are the two main lobes of the pituitary gland?
What are the two main lobes of the pituitary gland?
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What is the role of the anterior pituitary gland?
What is the role of the anterior pituitary gland?
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What hormone is secreted by the thyroid gland?
What hormone is secreted by the thyroid gland?
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What is the role of the parathyroid gland?
What is the role of the parathyroid gland?
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Which part of the adrenal gland is responsible for producing cortisol?
Which part of the adrenal gland is responsible for producing cortisol?
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What are the two main hormones secreted by the adrenal medulla?
What are the two main hormones secreted by the adrenal medulla?
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What are the two main hormones secreted by the pancreas?
What are the two main hormones secreted by the pancreas?
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Which of the following cells in the pancreas secrete insulin?
Which of the following cells in the pancreas secrete insulin?
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Which of the following cells in the pancreas secrete glucagon?
Which of the following cells in the pancreas secrete glucagon?
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Study Notes
Endocrine System Overview
- The endocrine system is one of the body's two main control systems, the other being the nervous system.
- It controls and integrates many bodily processes.
- Key processes include: reproduction, growth and development, electrolyte, water, and nutrient balance in the blood, cellular metabolism and energy balance, and mobilization of body defenses.
Endocrine Glands and Hormones
- Endocrine glands secrete hormones into the systemic circulation.
- Hormones are transported in the blood to tissues where they have a specific action.
- They are distinct from exocrine glands such as meibomian, lacrimal, and sweat glands.
What is a Hormone?
- Classically, a hormone is a chemical substance secreted by specialized endocrine cells directly into the blood to affect distant target cells.
- Target cells can sometimes be local, in which case the substances are referred to as paracrines or autocrines.
Hormone Composition
-
Amino acid based:
- Polypeptides: cannot pass through plasma membranes by diffusion but are water-soluble; these are the most prevalent type (e.g., TRH, TSH, GnRH, FSH, LH, insulin, glucagon)
- Modified amino acids: small, cannot pass through plasma membranes by diffusion but are water-soluble (e.g., thyroxine)
- Steroids: synthesized from cholesterol, small, fat-soluble, and can pass through plasma membranes (e.g., cortisol, estrogen, testosterone)
Stimuli for Hormone Release
- Humoral stimuli: Hormone release is triggered by altered levels of certain ions or nutrients in the blood (e.g., PTH release in response to low blood calcium).
- Neural stimuli: Hormone release is triggered by neural input (e.g., epinephrine and norepinephrine release from the adrenal medulla in response to stress).
- Hormonal stimuli: Hormone release is triggered by another hormone (e.g., hormones from the hypothalamus stimulating other endocrine glands).
Hormone Release Regulation
- Negative feedback: Hormone B inhibits secretion of gland A. Hormone A stimulates secretion of gland B. Hormone B has an action on target cells. This is a common mechanism to regulate hormone release.
Major Endocrine Glands
- Pineal: sleep-wake cycle
- Pituitary: growth, lactation, thyroid function
- Thyroid: metabolism
- Thymus: T cell maturation
- Adrenal: stress response
- Pancreas: glucose metabolism
- Ovaries: ovulation
- Testes: spermatogenesis
Pineal Gland
- Secretes melatonin, which peaks at night.
- Causes drowsiness and lowers body temperature.
- Regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus.
Hypothalamus
- Receives input from higher brain centers (limbic system - emotion) and visceral/somatic senses via the brain stem.
- Regulates hormone release from the pituitary gland.
- It is part of the CNS and links the CNS to the endocrine system.
Pituitary Gland
- Lies close to the optic nerves.
- Has two regions:
- Anterior lobe: secretes multiple hormones from various cell types
- Posterior lobe: secretes oxytocin and vasopressin
Anterior Pituitary Cells
- Secretes various hormones:
- Somatotrophs: growth hormone
- Lactotrophs: prolactin
- Corticotrophs: ACTH
- Thyrotrophs: TSH
- Gonadotrophs: FSH and LH
Anterior Pituitary Regulation
- Hypothalamic nuclei release neuroendocrine signals (e.g., TRH, GnRH, PIF) which travel down the portal vein.
- Signals act on specific cells in the anterior pituitary, stimulating the release of hormones into the hypophyseal vein.
Pituitary Hormones and their Relationship to Hypothalamus, Anterior Pituitary
- Neuroendocrine signals (e.g. TRH) from the hypothalamus stimulate release of specific hormones (e.g. TSH) from the anterior pituitary.
- Other signals have inhibitory effects.
- There is close coordination and regulation between the hypothalamus and the anterior pituitary.
Posterior Pituitary
- Secretes oxytocin and vasopressin (ADH).
- Hormones stored in the supraoptic and paraventricular nuclei before release.
- Release is regulated by neural signals from the hypothalamus.
FSH and LH in Females
- GnRH from the hypothalamus stimulates cyclical release of LH and FSH from the pituitary, regulating the menstrual cycle.
- LH triggers ovulation.
- FSH promotes ovarian follicle development and estrogen/progesterone secretion.
FSH and LH in Males
- GnRH, LH, and FSH are involved in similar ways to regulate male reproductive function as in females.
- LH stimulates testosterone production in the testes.
- FSH helps maintain spermatogenesis in the testes.
Growth Hormone
- Released by the pituitary gland.
- Stimulates growth through the liver and various other tissues.
- Important for skeletal muscle protein synthesis, bone growth and chondrocyte activity.
- Excessive secretion can lead to acromegaly.
Thyroid Gland
- Secretes thyroid hormones (thyroxine (T4) and triiodothyronine (T3)) into the bloodstream.
- Thyroid hormone release is regulated by negative feedback involving the hypothalamus and pituitary.
- Hormones affect growth, metabolism, body temperature regulation, and mood.
- Iodine is necessary for thyroid hormone production.
Parathyroid Glands
- Contain cells that secrete parathyroid hormone (PTH).
- PTH regulates blood calcium levels through effects on the kidneys ( increasing calcium reabsorption.
- PTH also has an impact on bone and the GI tract to regulate Calcium homeostasis levels.
Adrenal Glands
- Sit atop the kidneys.
- Have three regions (cortex and medulla):
- Cortex: secretes corticosteroids (aldosterone, cortisol, androgens) that are involved in electrolyte balance, blood pressure, metabolism, immune function and stress response. ACTH from the anterior pituitary regulates corticosteroid secretion.
- Medulla: secretes adrenaline and noradrenaline to help with emotional and physical stress response. Medulla hormones are controlled by sympathetic innervation.
Pancreas
- An endocrine and exocrine gland.
- Secretes insulin and glucagon for blood glucose regulation.
- Insulin lowers blood glucose.
- Glucagon raises blood glucose.
- Contains pancreatic islets with alpha (glucagon) and beta (insulin) cells.
Beta Cells and Diabetes
- Beta cells produce insulin.
- Type 1 diabetes is an autoimmune disease that damages beta cells preventing insulin secretion. This results in increased levels of blood glucose. Type 2 diabetes is characterized by decreased responsiveness to insulin.
- The pancreas also releases certain hormones like SOMATOSTATIN and GASTRIN as well as others.
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Description
Test your knowledge on the endocrine system and its functions. This quiz covers key processes, hormone classification, and the roles of various endocrine glands. Dive into the fascinating world of hormones and their impact on bodily functions.
